Extending the 3D scanning range of reflective dynamic focusing device-based laser scanners

Yi Liu, Yaqing Qiao, Yuhang Ding, Wangrong Lu, Tianting Chen, Haoran Ma, Jun Duan, Wei Xiong, and Leimin Deng

DOI: 10.1364/OL.509656 Received 18 Oct 2023; Accepted 21 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: Reflective dynamic focusing devices (RDFDs) have shown their potential in laser scanning as high-performance laser Z-direction focusing devices. However, the scanning range of RDFD-based scanners is limited by the aberrations during dynamic focusing. An aspheric symmetry correction (ASC) method was proposed to extend the effective scanning range. An aspheric lens was introduced to correct the optical path difference (OPD) and optimize aberrations. As a result, the scanning range in the three-dimensional (3D) space increased by 15.2%. The ASC method has been proven to extend the 3D scanning range of RDFD-based scanners and may have broad application prospects.

High-efficiency cladding-pumped Er/Yb co-doped alumino-phosphosilicate fiber for extended L-band amplification

Le He, Yang Chen, Xiaoke Yin, Zhimu Gu, Shaokun Liu, Wenzhen Li, Ying-bin Xing, Yingbo Chu, Nengli Dai, and Jinyan Li

DOI: 10.1364/OL.509954 Received 20 Oct 2023; Accepted 21 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: Extending the gain bandwidth of L-band optical fiber amplifier has provoked widespread interest. To date, achieving high-efficiency extended L-band amplification remains a challenge. Here, we report a cladding-pumped Er/Yb co-doped alumino-phosphosilicate fiber, prepared by the modified chemical vapor deposition process. We demonstrate high-efficiency of alumino-phosphosilicate glass for cladding-pumped Er/Yb co-doped fiber, with a gain per unit fiber length of 0.45 dB/m at 1625 nm and a gain ripple of ~9.4 dB. For 0.8 W pump power, the fiber exhibits a 20 dB gain-bandwidth covering 1575-1625 nm and 6.9 dB noise figure at 1625 nm. Additionally, the utilization of multi-mode laser diode enables further significant power savings and cost reduction. To the best of our knowledge, Er/Yb co-doped fiber in alumino-phosphosilicate glass is first proposed, with a cladding pumped scheme for enhancing extended L-band performance.

A versatile model for laser-induced birefringence enabling half-wave-plates inside silicon

Alperen Saltik and Onur Tokel

DOI: 10.1364/OL.504600 Received 29 Aug 2023; Accepted 21 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: Laser writing enables optical functionality without altering material surfaces. To achieve this goal, efforts generally focus on laser-written regions. It has also been shown that birefringence surrounding the modified regions can be exploited for fabricating optics. The effect has been used to fabricate wave-plates in glass, with significant potential for other materials and wavelengths. Here, we establish analogous stress control and birefringence engineering inside silicon. We first develop a robust analytical model enabling the prediction of virtually arbitrary stress patterns. Then, we tailor three-dimensional laser lithography to create the first polarization-control optics inside silicon.

Coupled air lasing gain and Mie scattering loss: aerosol effect in filament-induced plasma spectroscopy

Jiayun Xue, Zhi Zhang, Yuezheng Wang, bingpeng shang, jiewei guo, Shishi Tao, Zhang Nan, Lanjun Guo, Pengfei Qi, Lie Lin, and Weiwei Liu

DOI: 10.1364/OL.506003 Received 20 Sep 2023; Accepted 21 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: Femtosecond laser filament-induced plasma spectroscopy (FIPS) demonstrates great potential in remote sensing for identifying atmospheric pollutant molecules. Due to the widespread aerosols in the atmosphere, the remote detection based on FIPS would be affected from both the excitation and the propagation of fingerprint fluorescence, which still remain elusive. Here the physical model of filament-induced aerosol fluorescence is established to reveal the combined effect of Mie scattering and amplification spontaneous emission, which is subsequently proved by the experimental results, the dependence of the backward fluorescence on the interaction length between filament and aerosols. These findings provide an insight into the complicated aerosol effect in the overall physical process of FIPS including propagation, excitation, and emission, paving the way to its practical application in atmospheric remote sensing.

Submillimeter resolution and high precision φ-OFDR using a complex domain denoising method

Kaijun Liu, Guolu Yin, Zeheng Zhang, Zixuan Zhong, Huafeng Lu, Duidui Li, and Tao Zhu

DOI: 10.1364/OL.507753 Received 09 Oct 2023; Accepted 21 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: Phase noise is one of the main obstacles to achieve high spatial resolution, high precision, and large measurement range in φ-OFDR. Here, we proposed a complex domain denoising method to achieve unwrapping of phase signals. In this method, the wrapped phase was used to construct a complex signal, and then both real and imaginary parts are denoised by using the wavelet packet. The two sets of denoised signals are reconstructed into complex form, allowing obtain unwrapped phase. Additionally, the spatial position correction algorithm addresses the phase decoherence from strain accumulation. Finally, a high numerical aperture optical fiber is used to enhance the Rayleigh scattering intensity by 15 dB. The comprehensive approach yields remarkable results: a sensing resolution of 0.89 mm, a root means square error of 1.5 με and a maximum strain sensing capability of 2050 με.

Nano-displacement sensing by phase-diversity optical digital coherent detection utilizing alternating quadrature phase modulated reference light

Xiaoyan wang, Mitsuki Kondo, AYUMI Ito, and Masanori Hanawa

DOI: 10.1364/OL.509587 Received 18 Oct 2023; Accepted 20 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: We have introduced a nanometer-scale non-contact displacement sensing method that relies on phase-diversity optical digital coherent detection. In our prior work, we used a conventional setup involving a 90°optical Hybrid, two balanced amplified photodetectors (BAPs) , and a narrow-linewidth (NLW) laser, which is complex and costly. However, in this paper, we have streamlined the system configuration by employing alternating quadrature phase modulation (AQPM) reference light, implemented using a phase modulator and a BAP. Moreover, we’ve employed an economical Distributed Feedback (DFB) laser, enabling us to achieve displacement sensing at 1.6 nm with a resolution of 0.6 nm. It’s notable that there is some degradation in performance due to phase noise compared to the NLW laser, which achieves displacement sensing down to 0.6 nm with a 0.2 nm resolution. Nevertheless, the DFB-AQPM system holds significant potential for cost-effective, high-resolution nanometer-scale sensing applications.

Influence of neutron irradiation on electronic properties of hexagonal boron nitride measured by terahertz time-domain spectroscopy

Jing Zhang, Wen Xu, Hua Wen, Xingjia Cheng, Shun Zhou, Haowen Li, Zhu Wang, and Gaokui He

DOI: 10.1364/OL.507302 Received 29 Sep 2023; Accepted 20 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: Due to the low atomic number of B, hexagonal boron nitride (hBN) has a large neutron scattering cross section and, therefore, is an ideal material for realization of solid-state neutron detector. Here we apply the THz time-domain spectroscopy to study the effect of neutron irradiation on electronic properties of pyrolytic (PBN) and hot-pressed boron nitride (HBN). The key electronic parameters of these samples, such as the static dielectric constant εb, the effective carrier density N*, the carrier relaxation time τ, and the electronic localization factor c, are determined optically and their dependences upon the neutron irradiation fluence (NIF) are examined. We find that for both PBN and HBN samples, N* and εb decrease while τ and |c| increase with increasing NIF. These results can be used to further understand how the neutron irradiation affects the basic physical properties of hBN material with the help of our very recent results obtained from X-ray diffraction, Raman spectroscopy and photoluminescence measurements. We believe that the results obtained from this work can benefit to the design and application of hBN material for neutron detectors.

Nonlinear post-compression of a hybrid vortex mode in a gas-filled capillary

Mekha VIMAL, Michele Natile, Jean-François LUPI, Florent Guichard, Dominique Descamps, Marc Hanna, and Patrick Georges

DOI: 10.1364/OL.506009 Received 14 Sep 2023; Accepted 18 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: We demonstrate nonlinear temporal compression of avortex beam by propagation in a gas-filled capillary.Starting from an ytterbium-based laser delivering 700 μJ640 fs pulses at 100 kHz repetition rate, the vortex beamis generated using a spiral phase plate and coupled to acapillary where it excites a set of four modes that havean overlap integral of 97% with a Laguerre-Gauss LG10mode. Nonlinear propagation of this hybrid, orbitalangular momentum (OAM)-carrying mode results intemporal compression down to 74 fs at the output. Ex-tensive beam and pulse characterizations are carried outto determine the spatial profile and temporal durationof the compressed pulses. This result in multimodenonlinear optics paves the way towards the generationof OAM-carrying few-cycle pulses, isolated attosecondXUV pulses, and tunable UV pulses through resonantdispersive wave emission.

High transparent conductive Ga doped ZnO based multilayer thin films with embedded ultrathin TiN layer deposited in oxygen-containing atmosphere

Yang Liu, Huaqing Yu, Qingdong Zeng, and Qingyu Ruan

DOI: 10.1364/OL.509968 Received 20 Oct 2023; Accepted 17 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: To avoid metal layer oxidation during the deposition of transparent conductive oxide (TCO)/metal/TCO multilayer films in an oxygen containing atmosphere, ultra-thin (< 10 nm) titanium nitride (TiN) layer has been proposed to replace metal embedding in gallium doped zinc oxide (GZO) film for the development of indium free transparent electrodes. The effects of TiN thickness on the structure, morphology, electrical and optical properties of GZO/TiN/GZO multilayer thin films deposited in argon-oxygen mixtures on glass substrates by magnetron sputtering are investigated. The experimental results reveal that the multilayers with 8 nm-thick TiN layer have the optimal performance (figure of merit of 2.75 × 10-1 Ω-1): resistivity of 4.68 × 10-5 Ω cm, and optical transmittance of above 91% in the visible region, which is superior to the sandwich film with the metal embedded layer.

Analysis of High-Contrast All-Optical Dual WavelengthSwitching in Asymmetric Dual-Core Fibers

The Tai Le Xuan, Mattia Longobucco, Viet Hung Nguyen, Bartosz Paluba, Marek Trippenbach, Boris Malomed, Ignas Astrauskas, Audrius Pugzlys, Andrius Baltuska, Ryszard Buczynski, and Ignac Bugar

DOI: 10.1364/OL.500292 Received 13 Jul 2023; Accepted 17 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: We present systematically produced experimental and theoretical investigation of dual-wavelength switching of 1560 nm, 75 fs signal pulses (SPs) driven by 1030 nm, 270 fs control pulses (CPs) in a dual-core fiber (DCF). We demonstrate the switching contrast of 31.9 dB at the 14 mm fiber length by in-coupling temporally synchronized CP-SP pairs into the fast core of the DCF with a moderate inter-core asymmetry. A model based of three coupled propagation equations is used to identify the nonlinear compensation of the asymmetry as a physical mechanism behind the efficient switching performance.

Heat accumulation and phase transition induction in VO2 thin film by femtosecond pulse-periodic radiation

Zixin Wang, Ivan Kislyakov, Xun Cao, Ningning Dong, and Jun Wang

DOI: 10.1364/OL.507192 Received 29 Sep 2023; Accepted 17 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: The kinetics of optical switching due to the insulator-metal phase transition in VO2 thin film is studied experimentally at different laser pulse repetition frequencies (PRFs) in the NIR range and compared with temperature kinetics obtained through the thermal conductance calculations. Two switching processes have been found with characteristic times <2 ms and <15 ms depending on PRF, the former is explained by accumulation of a metallic domains remaining after a single-pulse phase transition, the latter is referred to the heat accumulation in the film. Consequently, the dynamics of the microscopic domains is leading in the initiation of phase transition under pulse-periodic conditions compared to the macroscopic heat transfer. The reverse transition at the radiation turn-off depends on PRF with a time coefficient of 17.5 μs/kHz, and is determined by the metallic domains decay in the film. The results are important for understanding the nature of the insulator-metal transition in thin films of VO2, as well as using them in all-optical switches of pulse-periodic laser radiation.

Orthogonal dual-slab Yb:KGd(WO₄)₂ regenerative amplifier for spectra shaping and high power output

Zhihua Tu, Jie Guo, Zebiao Gan, Zichen Gao, Yongxi Gao, yuguang huang, wenhao guo, and Xiaoyan Liang

DOI: 10.1364/OL.510381 Received 03 Nov 2023; Accepted 17 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: A high-power regenerative amplifier (RA) based on orthogonal dual-slab Yb:KGd(WO₄)₂ (Yb:KGW) was demonstrated, which provided a maximum average power of 33.7 W at repetition rate of 75-200 kHz before compression, corresponding to an optical-to-optical conversion efficiency of 51.4%. This is the highest average power from the Yb:KGW solid-state RA to the best of our knowledge. The compressed pulse duration of 205 fs was realized under the maximum output power. By adjusting the gain of the crystals respectively, the spectra shaping can be achieved. A combination spectrum with root-mean-square (RMS) bandwidth of 4.5 nm was generated at output power of 20 W with compressed pulse duration of 159 fs. Meanwhile, effective mitigation of thermal effects by dual-slab configuration guaranteed the nearly diffraction-limited beam quality: M_x^2 =1.17 and M_y^2=1.20. The amplifier can potentially boost average power to 50 W and serve as a front end for kilowatt and hundreds of kilohertz laser system.

Enhancing Microstructure and Device Performance of InGaN Quantum Dot Micro-LEDs through Substrate Off-cut Angle Modulation

Ying Gu, Yi Gong, Fan Zhang, Zhang Peng, Haowen Hua, Shan Jin, Wenxian Yang, jianjun Zhu, and Shulong Lu

DOI: 10.1364/OL.507707 Received 10 Oct 2023; Accepted 16 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: InGaN quantum dots (QDs) are regarded as a compelling candidate material for the fabrication of high-quality GaN-based Micro-LEDs. In this work, to study the impact of substrate structure on InGaN QDs and the performance of QDs-based micro-LEDs, GaN-on-Sapphire substrates with off-cut angles towards the a-axis of 0.2°, 0.4°, and 0.7° were utilized as templates for the fabrication of InGaN QDs and InGaN QDs-based micro-LEDs. Experimental results show that GaN template with 0.4° off-cut angle exhibits the narrowest terrace width and enables InGaN QDs to be higher and more uniform. The InGaN QDs sample grown on 0.4° substrate has a very small wavelength shift of 2.5 nm with temperature increasing and owns the longest PL luminescence peak wavelength implying the highest In content. Furthermore, electroluminescence (EL) spectra demonstrate that QDs-based micro-LED array has excellent wavelength stability under various injection current, and the stability can be improved further on GaN template with narrower terraces. The results indicate that altering the terrace width of GaN template is a feasible scheme for improving the properties of GaN-based micro-LEDs.

4.6 kW linearly polarized and narrow-linewidth monolithic fiber amplifier based on a fiber oscillator laser seed

biao liao, tao luo, Runheng Xiao, chang shu, Junjie Cheng, zhilun zhang, Ying-bin Xing, Haiqing Li, Nengli Dai, and Jinyan Li

DOI: 10.1364/OL.507009 Received 02 Oct 2023; Accepted 16 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: In this work, a record output power of 4.6-kW linearly polarized and narrow-linewidth fiber amplifier based on an optimized fiber oscillator laser (FOL) seed was realized by employing a homemade polarization-maintaining Yb-doped fiber (PMYDF), corresponding to a slope efficiency of 79.5% and a 3 dB linewidth of 0.3452 nm. Through an effective strategy relying on decreasing the transmission fiber length from 200m to 120m and adding a chirped and tilted fiber Bragg grating (CTFBG), the stimulated Raman scattering (SRS) effects were well-suppressed. By applying the forward combiner with the interconnection between the pump arms into the MOPA system, the MI threshold is increased by more than 560 W and the slope efficiency of the upgraded MOPA system is boosted by 5%. During the experimental process of power amplification, the polarization extinction ratio (PER) remains higher than 15 dB and a near-diffraction-limited output beam at the laser power of 2980 W was measured with the M2x = 1.314 and M2y = 1.311.

5.3 ps Gain-Switched Pulse Generation from 30-GHz-modulation-bandwidth 1270 nm DFB Laser Diode

Masataka Kobayashi, Takahiro Nakamura, HIDEKAZU NAKAMAE, CHANGSU KIM, and Hidefumi Akiyama

DOI: 10.1364/OL.510237 Received 24 Oct 2023; Accepted 16 Nov 2023; Posted 16 Nov 2023  View: PDF

Abstract: We generated gain-switched pulses via electrical pulse excitations in a 1270 nm distributed feedback (DFB) laser diode (LD) with a direct-modulation bandwidth of 30 GHz. The measurements revealed short-pulse widths of 5.3 ps and 8.8 ps with and without chirp compensation, via a single-mode optical fiber. The 5.3 ps pulses exhibited a spectral width of 0.40 nm (spectral bandwidth of 71 GHz), yielding a time–bandwidth product of 0.38. Although the gain-switched pulses in DFB LDs inherently contain linear and nonlinear chirp, optimized pumping conditions enable generation of nearly transform-limited ps pulses after linear chirp compensation.

Determination of the refractive-index change in the excited state based on transient absorption microscopy

Tianyu Huo, Lihe Yan, Jinhai Si, Peipei Ma, Yanan Shen, and Xun Hou

DOI: 10.1364/OL.506090 Received 15 Sep 2023; Accepted 15 Nov 2023; Posted 16 Nov 2023  View: PDF

Abstract: Photo-induced excited-state carriers can affect both the absorption coefficient and refractive index of materials and influence the performance of photoelectric devices. Femtosecond time-resolved pump-probe transient absorption (TA) spectroscopy is usually used to detect carrier dynamics and excited-state absorption coefficients; however, measurements of transient refractive-index change are still difficult. We propose a method for determining the excited-state refractive-index change using TA microscopy. In the TA measurements, a Fabry-Pérot cavity formed by the front and back surfaces of the sample could lead to interference of the probe light. As the wavelength of the standing waves in the Fabry-Pérot cavity is closely related to the refractive index, the carrier-induced excited-state refractive-index change was obtained by comparing the transmission probe spectra between the ground and excited states. The proposed method was used to study the dynamics of excited-state refractive-index change in a perovskite film.

All-optically controlled holographic plasmonic vortex array for multiple metallic particles manipulation

Zhendong Ju, Haixiang Ma, Shuoshuo Zhang, xie xi, Changjun Min, Yuquan Zhang, and Xiaocong Yuan

DOI: 10.1364/OL.507098 Received 28 Sep 2023; Accepted 15 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: Due to sub-diffraction-limited size and giant field enhancement, plasmonic tweezers have natural advantage in trapping metallic particles. However, the strict excitation condition makes it difficult to generate arbitrary plasmonic field in a controllable manner, thus narrowing its practical applications. Here, we propose an all-optical plasmonic field shaping method based on a digital holographic algorithm, and generate plasmonic vortex arrays with controllable spots number, spatial location, and topological charge. Our experimental results demonstrate that multiple gold particles can be stably trapped and synchronously rotated in the vortex arrays, and the particles’ kinestate can be dynamically switched. The proposed holographic plasmonic vortex tweezers are suitable for a broadband particle trapping, and this method can be generalized to other surface electromagnetic waves like Bloch surface wave.

Improving the resolution of Fourier ptychographic imaging using a priori neural network

Junting Sha, Wenmao Qiu, Guannan He, Zhi Luo, and Bo Huang

DOI: 10.1364/OL.508134 Received 12 Oct 2023; Accepted 15 Nov 2023; Posted 15 Nov 2023  View: PDF

Abstract: In this paper, we propose a dual-structured prior neural network model to independently restore the amplitude and phase image using random latent code for Fourier Ptychography (FP). We demonstrate that the inherent prior information with the neural network can generate super-resolution images with a resolution that exceeds the combined numerical aperture of the FP system. This method doesn’t require a large labeled dataset. This is achieved by employing an appropriate forward physical model to guide the network's training process. The method is verified through both simulated and experimental data. The results suggest that integrating image prior information with system-collected data is a potentially effective approach for improving the resolution of FP systems.

Optical wavefront phase-tilt measurement using Si-photonic waveguide grating couplers

Siegfried Janz, Dan-Xia Xu, Yuri Grinberg, shurui wang, Martin Vachon, Pavel Cheben, Jens Schmid, and Daniele Melati

DOI: 10.1364/OL.506013 Received 14 Sep 2023; Accepted 14 Nov 2023; Posted 15 Nov 2023  View: PDF

Abstract: Silicon photonic wavefront phase-tilt sensors for wavefront monitoring using surface coupling grating arrays are demonstrated. The first design employs the intrinsic angle dependence of the grating coupling efficiency to determine local wavefront tilt, with a measured sensitivity of 7 dB/°. A second design connects four gratings in an interferometric waveguide circuit to determine incident wavefront phase variation across the sensor area. In this device, one fringe spacing corresponds to approximately 2° wavefront tilt change. These sensor elements can sample a wavefront incident on the chip surface without the use of bulk optic elements, fiber arrays, or imaging arrays. Both sensor elements are less than 60 m across, and can be combined into larger arrays to monitor wavefront tilt and distortion across an image or pupil plane in adaptive optics systems for free space optical communications, astronomy and beam pointing applications.

Multipartite entanglement encoded in the photon number basis by sequential excitation of a three-level system

Alan Santos, Christian Schneider, Romain Bachelard, Ana Predojevic, and Carlos Anton

DOI: 10.1364/OL.506403 Received 21 Sep 2023; Accepted 14 Nov 2023; Posted 15 Nov 2023  View: PDF

Abstract: We propose a general scheme to generate entanglement encoded in the photon number basis, via a sequential resonant two-photon excitation of a three-level system. We apply it to the specific case of a quantum dot three-level system, which can emit a photon pair through a biexciton-exciton cascade. The state generated in our scheme constitutes a tool for secure communication, as the multipartite correlations present in the produced state may provide an enhanced rate of secret communication with respect to a perfect GHZ state.

Sparse single-pixel imaging via optimization in non-uniform sampling sparsity

Rong Yan, Daoyu Li, xinrui Zhan, Xuyang Chang, Jun Yan, Pengyu Guo, and Liheng Bian

DOI: 10.1364/OL.509822 Received 20 Oct 2023; Accepted 14 Nov 2023; Posted 15 Nov 2023  View: PDF

Abstract: Reducing imaging time while maintaining reconstruction accuracy remains challenging for single-pixel imaging. One cost-effective approach is non-uniform sparse sampling. The existing methods lack intuitive and intrinsical analysis in sparsity. The limitation and lack impede our comprehension of the form's adjustable range and may potentially limit our ability to identify an optimal distribution form within a confined adjustable range, consequently impacting the method's overall performance. In this letter, we report a sparse sampling method with a wide adjustable range and define a sparsity metric to guide the selection of sampling forms. Through a comprehensive analysis and discussion, we select a sampling form that produces state-of-the-art high accuracy. These works will make up for the existing methods' lack of sparsity analysis, and help adjust methods to accommodate different situations and needs.

High-order exciton complexes induced by interlayer carrier transfer in 2D Van der Waals heterostructures

Yizhen Sui, Xiang'ai Cheng, Qirui Liu, Yuxiang Tang, Zhongjie Xu, and Ke We

DOI: 10.1364/OL.507084 Received 29 Sep 2023; Accepted 14 Nov 2023; Posted 16 Nov 2023  View: PDF

Abstract: High-order correlated excitonic states, such as biexciton, charged biexciton, polaron etc., hold a great promising platform in contemporary quantum and nonlinear optics due to their large Bohr radii and thus strong nonlinear interactions. The recently found 2D TMDs further give such excitonic states additional valley properties, with bound state of excitons in opposite valleys in momentum spaces. Despite great efforts that have been made on the emission properties of the excitonic states, their absorption features, especially the ultrafast absorption dynamics, are rarely reported. Here, we reported the enhanced optical absorption of the high-order charged-excitonic states in monolayer WS2, including singlet, triplet and semidark trions (3-particle state), and charged biexcitons (5-particle state), by utilizing the interlayer charge transfer-induced photo-doping effect in graphene-WS2 heterostructure. Depending on the recombination rates of the doping electrons, the absorption intensities of the charged complexes exhibit ultrafast decay dynamics, with lifetimes of several picoseconds. Due to many-body interaction, both increasing pump intensity and lattice temperature can broaden these fine excitonic absorption peaks and even reverse the shape of the transient absorption spectrum completely.

Precise Control of Optical Refractive Index in Nanolattices

Vijay Anirudh Premnath and Chih-Hao Chang

DOI: 10.1364/OL.507274 Received 03 Oct 2023; Accepted 14 Nov 2023; Posted 16 Nov 2023  View: PDF

Abstract: Recent developments in photonic devices, light field display, and wearable electronics have resulted from a competitive development towards new technologies to improve user experience in the field of optics. These advances can be attributed to the rise of nanophotonics and metasurfaces, which can be designed to manipulate light more efficiently. In these elements the performance scales are favorable to index contrast, making the use of low-index material important. In this research, we examine the precise control of refractive indices of low-index nanolattice material. This approach employs three-dimensional (3D) lithography and atomic layer deposition (ALD), allowing for precise control of the nanolattice geometry and its refractive index. The refractive indices of the fabricated nanolattices are characterized using spectroscopic ellipsometry and agrees well to models based on effective medium theory. By controlling the unit-cell geometry by the exposure conditions and the shell thickness by the ALD process, the effective index of the nanolattice film can be precisely controlled to as low as 5×10^(-4). The proposed index control technique opens a gamut of opportunities and enables better performance in nanophotonic elements used in displays and other integrated devices.

Highly efficient, high average power, narrowband, pump-tunable BWOPO

Kjell Mølster, Marie Guionie, Patrick Mutter, Antoine Zheng, Jean-Baptiste Dherbecourt, Jean-Michel Melkonian, Xavier Delen, Andrius Zukauskas, Fredrik Laurell, Patrick Georges, Myriam Raybaut, Antoine Godard, and Valdas Pasiskevicius

DOI: 10.1364/OL.506647 Received 26 Sep 2023; Accepted 14 Nov 2023; Posted 20 Nov 2023  View: PDF

Abstract: We demonstrate a continuously tunable mid-infrared source that produces narrowband radiation at 1981 nm and 2145 nm based on a tunable Yb-based hybrid MOPA pump and a backward-wave optical parametric oscillator (BWOPO). The BWOPO employs a PPRKTP crystal with 580 nm domain periodicity. The BWOPO has a record-low oscillation threshold of 19.2 MW/cm² and generates mJ-level output with an overall efficiency exceeding 70%, reaching an average power of 5.65W at the repetition rate of 5 KHz. The system is mechanically robust and optical cavity-free, making it suitable for spectroscopic systems on mobile platforms. The MIR signal frequency is tuned by pump tuning with a linear pump-to-signal frequency translation rate of 1-to-1.001 Hz/Hz.

Inter/intra-pulse dual-wavelength operated mid-infrared optical parametric oscillator

Tao Chen, Wenjie Yue, Wei Kong, Genghua Huang, Zhiping He, and Rong Shu

DOI: 10.1364/OL.512064 Received 10 Nov 2023; Accepted 13 Nov 2023; Posted 16 Nov 2023  View: PDF

Abstract: We demonstrate a pulsed mid-infrared (MIR) optical parametric oscillator (OPO) with both inter-pulse and intra-pulse dual-wavelength operation capability. A fiber master oscillator power amplifier incorporating an acousto-optic tunable filter (AOTF) was employed as the pump for the OPO. By finely adjusting the drive wave packets for the AOTF, dual-wavelength pump can be realized within each pulse or between two adjacent pulses. These special temporal-spectral behaviors of the pump can be transferred to MIR via an OPO. In the proof-of-principle experiments, two pump wavelengths at ~1065 nm and ~1076 nm were generated and amplified to ~31.2 W with equivalent spectral intensities for both pulsation modes. At the highest pump power, total idler power of ~3.5 W was achieved at ~3.45 μm and ~3.55 μm under both pulsation modes. To the best of our knowledge, this is the first demonstration of both inter-pulse and intra-pulse dual-wavelength operation via an OPO with an identical configuration. It is believed that our design may provide a promising solution to many practical applications including differential absorption lidar and tunable terahertz wave generation.

Tripling the spatial resolution of light field displays without losing angular resolution by computational subpixel realignment

Wenchao Yang, Yunfan Cheng, Guowei Zou, Bo-Ru Yang, and Zong Qin

DOI: 10.1364/OL.504215 Received 25 Aug 2023; Accepted 13 Nov 2023; Posted 13 Nov 2023  View: PDF

Abstract: Low spatial resolution is an urgent problem in integral imaging light field displays (LFDs). This study proposes a computational method to triple the spatial resolution without losing angular resolution. How rays reconstruct voxels through lenslets is changed so that every ray through a lenslet merely provides a subpixel. The three subpixels of a pixel no longer form one voxel but three independent voxels. We further demonstrate imperfect integration of subpixels, called sampling error, can be eliminated on specific image depths, including the central depth plane. By realigning subpixels in the above manner under no sampling error, the sampling rate of voxels is three times the conventional pixel-based LFDs. And the ray number of every voxel is preserved for an affected angular resolution. With unavoidable component alignment errors, resolution gains of 2.52 and 2.0 are verified in simulation and experiment by computationally updating the elemental image array. The proposed computational method further reveals that LFDs intrinsically have a tripled space-bandwidth product than presumed.

Inhibition of non-Hermitian topological phase transitions in sliding photonic quasicrystals

Stefano Longhi

DOI: 10.1364/OL.507937 Received 10 Oct 2023; Accepted 12 Nov 2023; Posted 13 Nov 2023  View: PDF

Abstract: Non-Hermitian (NH) quasicrystals have been a topic of increasing interest in current research, particularly in the context of NH topological physics and materials science. Recently, it has been suggested and experimentally demonstrated using synthetic photonic lattices that a class of NH quasicrystals can feature topological spectral phase transitions. Here we consider a NH quasicrystal with a uniformly-drifting (sliding) incommensurate potential and show that, owing to violation of Galilean invariance, the topological phase transition is washed out and the quasicrystal is always in the delocalized phase with an entirely real energy spectrum. The results are illustrated by considering quantum walks in synthetic photonic lattices.

A few-mode polymer waveguide amplifier with dual-layer coronal refractive index profile

Lizhan Gao, Fei Wang, cheng yu, Jiahui Shi, Changlong Li, Dan Zhao, and Meiling Zhang

DOI: 10.1364/OL.509244 Received 13 Oct 2023; Accepted 12 Nov 2023; Posted 13 Nov 2023  View: PDF

Abstract: A novel few-mode waveguide amplifier with dual-layer coronal core is first proposed. Reconfiguring the refractive index profile is adopted to equalize the modal gains pumped in a single mode. The polymer in terms of the prominent advantages of simple processing and the ease of adjusting refractive index is untilized. The waveguide supporting LP01, LP11a and LP11b is optimized by the genetic algorithm and fabricated by accurate alignment mask. The crosstalk effect and modal profiles are characterized. The modal gains with different signal power and pumping modes are revealed. The scheme in forward and backward pump are represented. An average gain of 11.84 dB per mode and an ultralow differential modal gain of 0.36 dB are obtained in a 0.3 cm waveguide at 1526 nm through backward pumping of the LP21b mode at 240 mW for an input signal power of 0.1mW.

Nonlinear optical properties and ultrafast carrier dynamics of ultrathin ReSe2

Yu Mao, Hongqiang Wang, Ivan Kislyakov, Zixin Wang, Ningning Dong, and Jun Wang

DOI: 10.1364/OL.510204 Received 23 Oct 2023; Accepted 12 Nov 2023; Posted 15 Nov 2023  View: PDF

Abstract: In recent years, rhenium diselenide (ReSe2) has shown great application potential in the field of ultrafast lasers and detectors due to the excellent optoelectronic properties. Here, we systematically studied the nonlinear optical absorption properties of mono- and bi-layer ReSe2 and the ultrafast carrier dynamics process from ultraviolet to near-infrared, which constitute the foundational groundwork essential for harnessing the potential of ultrathin ReSe2-based optoelectronic devices. We found that ReSe2 has huge nonlinear absorption performance and low saturation absorption intensity, which is better than many semiconductor materials. Meantime, pump-probe and transient absorption technology revealed the underlying dynamic mechanisms, including band gap renormalization and Auger recombination, et al. Such research endeavors promise to broaden the horizons of material science and propel the development of different applications.

Sub-diffraction optical beam lithography based on center-non-zero depletion laser

Chenyi Su, Chenliang Ding, Zhenyao Yang, Chun Cao, Yiwei Qiu, Dazhao Zhu, Cuifang Kuang, and Xu Liu

DOI: 10.1364/OL.504691 Received 05 Sep 2023; Accepted 12 Nov 2023; Posted 15 Nov 2023  View: PDF

Abstract: Photoinhibition mechanisms have been introduced in nanofabrication which allows breaking the diffraction limit by large factors. Donut-shaped laser is usually selected as a depletion beam to reduce linewidth, but the parasitic process has made the results of the experiment less than expected. As a result, the linewidth is difficult to achieve below 50 nm with 780 nm femtosecond and 532 nm continuous-wave lasers. Here, we propose a new method based on center-non-zero (CNZ) depletion laser to further reduce linewidth. By constructing a smaller zone of action under the condition of keeping the maximum depletion intensity constant, a minimum linewidth of 30 nm (λ/26) was achieved. Two ways to construct CNZ spots were discussed and experimented, and the results show the advantages of our method to reduce the parasitic process to further improve the writing resolution.

Adaptive feedback-driven probabilistic shaping for high-order modulation formats in fiber-THz seamless integration system at 320 GHz

Xiang Liu, Jiao Zhang, Min Zhu, Junhao Zhang, Weidong Tong, zhigang xin, Bingchang Hua, Yuancheng Cai, Mingzheng Lei, Bo Liu, and Jianjun Yu

DOI: 10.1364/OL.505468 Received 08 Sep 2023; Accepted 10 Nov 2023; Posted 13 Nov 2023  View: PDF

Abstract: In this letter, we propose a novel adaptive feedback-driven probabilistic constellation shaping (FBD-PCS) method based on the robustness evaluation criteria and employ variational autoencoder (VAE)-based equalizers to implement polarization demultiplexing and nonlinear equalization for the recovery of high-order PCS-QAM signals. We experimentally demonstrate the fiber-THz 2 × 2 MIMO system with a net rate of 366.4 Gbit/s using dual-polarization 40 Gbaud PCS-64QAM signal over a 20 km SSMF and 6 m wireless link. Specifically, the feedback mechanism drives the fiber-THz system to solve optimization problems, adaptively matching the optimal non-symmetric distribution of transmitted symbols that maximizes normalized generalized mutual information (NGMI). We also examine five scenarios to explore the nonlinear resistances of FBD-PCS symbols and the robustness of VAE-based equalizers. The results demonstrate the superiority of FBD-PCS over the Maxwell-Boltzmann (M-B) distributions in practical nonlinear-dominant systems. Additionally, the FBD-PCS signals can break limitations for ultra-high rate transmission with the help of advanced equalizers.

Sub-10-fs unipolar pulses of tailored waveshape from a multi-level resonant medium

Anton Pakhomov, Nikolay Rosanov, Mikhail Arkhipov, and Rostislav Arkhipov

DOI: 10.1364/OL.503802 Received 21 Aug 2023; Accepted 10 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: We theoretically demonstrate the possibility to tune the temporal waveform of unipolar pulses of femtosecond duration emitted from a multi-level resonant medium. This is achieved through the control of the medium response by a properly adjusted sequence of half-cycle unipolar or quasi-unipolar driving pulses and the spatial density profile of resonant centers along the medium layer. We show the producing of unipolar optical pulses of varying profile, like rectangular or triangular ones, from an extended layer of a multi-level medium.

Microsphere-assisted super-resolved hyperspectral microscopy

Mina Mollaei, Peyman Soltani, Majid Panahi, and Ali-Reza Moradi

DOI: 10.1364/OL.505058 Received 05 Sep 2023; Accepted 10 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Hyperspectral microscopy (HSM) combines conventional microscopy with basic hyperspectral imaging and results in 3D microscopic spatio-spectral information. The combination comes along with variety of applications, such as detection and classification of different material properties through spectral fingerprints, which otherwise cannot be detected with a color camera alone. However, similar to other microscopies, the resolution of HSM is limited by diffraction. In recent years microsphere (MS) assisted microscopy has attracted intensive attention for resolution enhancement. Here, we extend the MS idea into HSM. We show that MS-HSM reveals extra hyperspectral information about the specimen which are lost without it. Moreover, the insertion of MS results in super-resolved images. The resolution enhancement and obtaining the extra hyperspectral information can be tuned by the MS size.

Highly flexible and compact volumetric endoscope by integrating multiple micro-imaging devices

DEER SU, WEIDA GAO, Haoyu Li, Changliang Guo, and Weisong Zhao

DOI: 10.1364/OL.506261 Received 22 Sep 2023; Accepted 10 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Light-field endoscope can simultaneously capture the three-dimensional information of in situ lesions and enables single-shot quantitative depth perception with minimal invasion for improving surgical and diagnostic accuracy. However, due to oversized rigid probes, the clinical applications of current techniques are limited by their cumbersome devices. To minimize the size and enhance the flexibility, here we report a highly flexible and compact volumetric endoscope by employing precision-machined multiple micro-imaging devices (MIRD). To further protect the flexibility, the designed MIRD with a diameter and height of 5mm is packaged in pliable polyamide, using soft data cables for data transmission. It achieves the optimal lateral resolvability of 31 μm and axial resolvability of 255 µm, with an imaging volume over 2.3 × 2.3 × 10 mm3. Our technique allows easy access to the organism interior through the natural entrance, which has been verified through observational experiments of the stomach and rectum of a rabbit. Together, we expect this device can assist in the removal of tumors and polyps as well as the identification of certain early cancers of the digestive tract.

Involve Free Space Optics in Raman Distributed Temperature Sensing

Cheng-Kai Yao, Yibeltal Chanie Manie, Hung-Ming Chen, Wen-Yang Hsu, Tzu-Chiao Lin, and Peng-Chun Peng

DOI: 10.1364/OL.507460 Received 17 Oct 2023; Accepted 10 Nov 2023; Posted 16 Nov 2023  View: PDF

Abstract: This letter demonstrates the successful use of free-space optics (FSO) as a transition channel for an air segment in transmitting Raman backscattering signals for distributed temperature sensing (DTS). A barrier-free air segment link shaped by an FSO is part of the Raman-based DTS (RDTS) fiber optic transmission route. For this plan, the FSO enables delivery of the RDTS's pulse with the low-loss transmission over the air segment while also returning to the RDTS the varied Raman backscattered signals from the probing temperature variations for signal interpretation. The difference between the various temperatures sensed and the referential air temperature is nearly the same before and after passing the FSO. The viability of this technology provides a crucial base for tackling the high expense of installing and repairing DTS cables and the challenges associated with doing so owing to topographical restrictions.

Aluminum-based plasmonic metasurface for computational spectrometry with full coverage of visible light

Qingbin Fan, Weizhu Xu, Peicheng Lin, Yunfei Sun, Feng Yan, Xuemei Hu, Tao Yue, and Ting Xu

DOI: 10.1364/OL.503626 Received 18 Aug 2023; Accepted 09 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Reconstructive spectrometers/spectral cameras have immense potential for portable applications in various fields, including environmental monitoring, biomedical research and diagnostics, as well as agriculture and food safety. However, the performance of these spectrometers /spectral cameras are severely limited by the operational bandwidth, spectral diversity, and angle sensitivity of the spectral modulation devices. In this work, we propose a compact spectrometer based on plasmonic metasurfaces that operates across the entire visible wavelength range, covering wavelengths from 400 to 750 nm. We experimentally demonstrate the effective spectral reconstruction achieved by the designed metasurface spectrometer, exhibiting angle tolerance to the incident light within the range of ±12°. Our results highlight the potential for constructing broadband, large field-of-view hyperspectral cameras.

Immobilization of Photorefractive Solitons by Charge Anchoring on Conductive Walls

Hamed Tari, Alessandro Bile, Arif Nabizada, and Eugenio Fazio

DOI: 10.1364/OL.506249 Received 19 Sep 2023; Accepted 09 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Spatial solitons have shown great promise for various applications, but their limited stability in terms of beam movement has been a significant hindrance. This limitation is especially prominent in the conventional configuration where the bias electric field is oriented perpendicular to the soliton propagation direction, leading to instability caused by the drift-diffusion processes. To address this issue, we explore a novel approach where solitons are propagated from one bias plate to the other, with a tilted angle with respect to the field and to the optical axis of the photorefractive crystal. By directing the solitons towards the bias electrodes, we observe an intriguing anchoring effect that immobilizes the soliton beam, resulting in reduced self-bending. The charge distribution on the conductive walls is numerically investigated as a function of the crystallographic orientation of the c-axis. The immobilization of the soliton beams is a fundamental issue for their technological applications as waveguides in integrated photonic circuits, which would result in an addressable but perfectly stable waveguide over time.

Second harmonic generation in anisotropic lithium niobate metasurface governed by quasi-BICs.

Rongyu Liu and chaobiao zhou

DOI: 10.1364/OL.504379 Received 28 Aug 2023; Accepted 09 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Resonant metasurfaces can greatly trapped the light fields, so that they are widely used to enhance light-matter interactions at the nanoscale, such as promoting nonlinear effects of materials. Lithium niobate (LN) is an excellent non-linear optical material and is often employed to generate harmonic signals. In this work, we numerically study the second harmonic generation (SHG) characteristics of LN metasurface based on the quasi-bound states in the continuum. The designed BIC and excited quasi-BIC metasurfaces always hold C4v symmetry, the BIC is demonstrated to degenerates into two BICs due to the anisotropic characteristics of LN. Moreover, the excited two high Q-factor quasi-BICs can effectively enhance the SHG in LN, although the device maintains C4v symmetry, the SHG signal still shows polarization dependence. In addition, with the increase of Q-factor of quasi-BIC, the power and conversion efficiency η of SHG increase significantly, and the calculated η can reach 6.04×10-3, which can be further improved when the resonance mode is closer to BIC. These results have important implications for high quality nonlinear light sources based on LN materials.

ErF3 microcrystals controllably deposited in perfluoride glass for up-conversion red emission

Liu Ruite, Hu Linjia, Wang Zaiyang, Wenkai Zhao, Longfei Zhang, Yigunag Jiang, and Long Zhang

DOI: 10.1364/OL.504575 Received 31 Aug 2023; Accepted 09 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: This paper first reports ErF3 microcrystals controllably deposited in perfluoride glass using phase-separation engineering techniques. The sample exhibited strong up-conversion red-light emission owing to the small distance between Er3+ ions and low phonon energy. The sample has a red/green ratio of up to 18.6, which, to our knowledge, is the highest reported value in Er3+-doped glass ceramics. Furthermore, the sample has a long fluorescence lifetime (3.18 ms @660-nm) and good color saturation (0.6255,0.3707). Therefore, this sample has the potential for application across multiple fields, such as color display, visible laser, and lighting.

Electro-optic properties of liquid crystal cells with nanowall electrodes

Yu-Chih Chiang, Risti Suryantari, Shih-Hung Lin, HARRY SILALAHI, Wei-Fan Chiang, Yi-Hong Shih, Wing-Kit Choi, and Chia-Yi Huang

DOI: 10.1364/OL.505221 Received 05 Sep 2023; Accepted 09 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: This work fabricates a nanowall electrode for achieving advanced liquid crystal (LC) devices and improving LC displays. The nanowall electrode consists of indium-tin-oxide (ITO) sheets stacked with nanowalls, and the nanowalls have a height and thickness of 4 µm and 500 nm, respectively. The high aspect ratio (8.0) of the nanowalls sets the nanowall electrode apart from previous electrodes. A flat electrode that comprises only ITO sheets is used to evaluate the nanowall electrode. The LC cell with the nanowall electrode exhibits better electro-optic properties than the LC cell with the flat electrode due to the strong transverse electric field and small subelectrode gap of the nanowall electrode. Especially, the operating voltage (3.7 V) of the nanowall cell is 36 % smaller than that (5.8 V) of the flat cell. Therefore, nanowall electrodes have potential in LC lenses, LC antennas, metaverse displays and digital optics.

Ultraviolet sensing based on an in-fiber ZnO microwire constructed Mach-Zehnder interferometer

Chen Chen, Ying Wang, Han Liu, Yubin Deng, Xun Wu, Changrui Liao, xiaoyu weng, Liwei Liu, Junle Qu, and Yiping Wang

DOI: 10.1364/OL.506796 Received 28 Sep 2023; Accepted 09 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: We propose a Mach-Zehnder interferometer based on an in-fiber ZnO microwire structure for ultraviolet sensing. The device undergoes femtosecond laser micromachining and chemical etching on a single-mode optical fiber initially, creating a microgroove that extends to half of the fiber core's depth, into which a single ZnO microwire is transferred. The ZnO microwire and the remaining fiber core are used as the sensing arm and the reference arm, respectively, forming a Mach-Zehnder interferometer. To enhance the stability and the sensitivity, ZnO nanoparticles are filled into the microgroove after the ZnO microwire is transferred. The fabricated device exhibits a sensitivity of 0.86 nm/(W·cm-2) for ultraviolet sensing, along with a response time of 115 ns (rise-time) and 133 µs (decay-time), respectively. The proposed sensor exhibits good ultraviolet sensitivity, offering a novel approach for ultraviolet sensing technology.

Electroluminescence and temperature-dependent time-resolved photoluminescence of monolithically integrated triple-wavelength InGaN-based LED

Xiaoyu Zhao and Shengjun Zhou

DOI: 10.1364/OL.508143 Received 12 Oct 2023; Accepted 09 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: Here, we propose a monolithically integrated triple-wavelength multiple quantum wells (MQWs) LED structure and conduct comprehensive research on its emission dynamics under electrical and optical excita-tion. Through experimental and numerical analysis, carrier transport and recombination process can be manipulated in bandgap-engineered MQWs, thus real-izing the manipulation of emission properties. A ra-tional triple-wavelength LED structure is heteroepitax-ially grown, which shows excellent color stability ver-sus injected currents. Furthermore, utilizing the tem-perature-dependent time-resolved photoluminescence (TRPL), triple wavelength peaks display different TRPL decay behaviors. Especially, an anomalous three-stage decay phenomenon is found for low-energy peak measured at 10 K, accompanied by a decay profile transition with the increasing temperature. The under-lying mechanisms are revealed and correlated with the carrier localization, interaction between different QWs as well as the competition between radiative and non-radiative recombination.

Simple high-resolution 3D microscopy by a dielectric microsphere: proof of concept

Vahid Abbasian, Arash Darafsheh, and Ali-Reza Moradi

DOI: 10.1364/OL.502599 Received 08 Aug 2023; Accepted 09 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: We present a simple high-resolution approach for 3D and quantitative phase imaging (QPI). Our method makes the most of a glass microsphere (MS) for microscopy and a glass plate for lateral shearing self-referencing interferometry. The single MS serves all the functions of a microscope objective (MO) in a digital holographic microscopy (DHM) setup, while offering the advantages of compactness, lightness, and affordability. A proof-of-concept experiment is performed on a standard diffraction grating and various effective parameters on the imaging performance are investigated. The results are validated by atomic force microscopy and Mirau-DHM, and 3D morphometric information of the sample under inspection is obtained. It is shown that even a relatively large MS (550 µm diameter) can be capable of a 40× MO with a 0.65 numerical aperture in conventional DHM arrangements. Furthermore, our technique is applied for 3D quantitative measurement and visualization of a human red blood cell, proving the principle of our easy-to-implement and vibration-immune arrangement for high-contrast label-free QPI of biological samples, and its utility in cell morphology, identification, and classification.

Design and fabrication of microcoil metamaterial absorber for the sub-terahertz region

Verdad Agulto, Ziqi Ling, Zixi Zhao, Shiyu Feng, Kosaku Kato, Motoharu Haga, Valynn Katrine Mag-usara, Masashi Yoshimura, and Makoto Nakajima

DOI: 10.1364/OL.502614 Received 10 Aug 2023; Accepted 09 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: The development of electromagnetic wave absorbers operating in the sub-terahertz (sub-THz) region is necessary in 6G communications. We designed and fabricated a sub-THz metamaterial absorber based on metal microcoils embedded and periodically arranged in a dielectric substrate. The microcoil parameters were optimized by calculating the electromagnetic response of the metamaterial using finite element analysis. An actual metamaterial was then fabricated based on the optimized parameters and characterized using THz time-domain spectroscopy. Our microcoil absorber exhibits an absorptance of > 80 % and a high shielding performance at about 250 GHz. The resonance frequency is widely tunable by controlling the microcoil array dimensions.

Skin solitons

Ioannis Komis, Ziad Musslimani, and Konstantinos Makris

DOI: 10.1364/OL.504192 Received 24 Aug 2023; Accepted 08 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: Recently, the concept of skin effect has gained considerable attention in the context of non-Hermitian photonics. The experimental realization of Hatano-Nelson systems in optical coupled cavities has provided the opportunity to consider the effect of optical nonlinearity. In this work, we probe the interplay between Kerr nonlinearity and non-Hermiticity in a Hatano-Nelson lattice. In particular, we examine the relation between self-focusing and the skin effect under single-channel excitation. Moreover, we numerically identify skin soliton solutions, which exhibit power threshold and spatial asymmetry.

Mode-locking of a Tm,Ho:CALYGO laser delivering 50 fs pulses at 2.08 µm: supplemental document

Heng Ding, Jian Liu, Yinyin Wang, Ning Zhang, Zhanxin Wang, Yongguang Zhao, Xiaodong Xu, Yanyan Xue, Jun Xu, Uwe Griebner, and Valentin Petrov

DOI: 10.1364/OL.510740 Received 31 Oct 2023; Accepted 08 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: We study the polarization dependent laser performance of a novel “mixed” Tm,Ho:CaYGdAlO4 crystal in the continuous wave (CW) and mode-locked regimes. Both in terms of the CW tunability range (261 nm) and the minimum pulse duration (50 fs at 2078 nm, spectral width of 95 nm) in the mode-locked regime, σ-polarization is superior. With extended inhomogeneous spectral broadening due to structural and compositional disorder, Tm,Ho: CaYGdAlO4 is promising for few-optical-cycle pulse generation around 2 µm.

Fan-in/fan-out for heterogeneous 19-core fibers based on metasurfaces with nonuniform phase plates

Yang Wang, Xutao Wang, Chunshu Li, Yichen He, Zhanhua Huang, Yaping Liu, Zhiqun Yang, and Lin Zhang

DOI: 10.1364/OL.507445 Received 06 Oct 2023; Accepted 08 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: In space-division-multiplexed transmission systems, it is essential to realize fan-in/fan-out devices that connect the cores between a multi-core fiber and single-mode fibers. In this letter, we propose a metasurface-based fan-in/fan-out device with nonuniform phase plates for heterogeneous 19-core fibers across the full C-band. Our results show that an average insertion loss of 0.85 dB and a maximum crosstalk of -25.5 dB can be achieved at 1550 nm. Across the C-band, the insertion loss and crosstalk are better than 2.78 dB and -19.96 dB, respectively. The proposed concept can flexibly handle various fiber configurations without additional complexity.

All-fiber amplification of highly-chirped dissipative solitons around 1.3 micron using stimulated Ramanscattering

Ekaterina Evmenova, Aleksandr Antropov, and Denis Kharenko

DOI: 10.1364/OL.505933 Received 14 Sep 2023; Accepted 08 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: An all-fiber amplification of highly-chirped dissipative solitons (DSs) by stimulated Raman scattering in a standard passive fiber with continuous-wave pumping is demonstrated for the first time. DSs with a duration of20 ps and a repetition rate of 15.6 MHz at the wavelength of 1275 nm are amplified by the pump wave at 1205 nm. On-off Raman gain dependence on the amplifier length and pump power, as well as pumping configuration are experimentally studied. The uniform amplification has been achieved with a net gain of 10 dB resulting in a pulse energy of 13 nJ at the backward pumping. Further Raman amplification is limited by emerging the next Stokes component. Output pulses are compressed bythe factor of 50 down to duration of 400 fs. As a result, the peak power reached the level of 9 kW. The demonstrated scheme can be a simple and robust alternative to the widely used parametric amplification of chirped pulses outside the dopant amplification band, and theresulting pulses can be used in multiphoton microscopy and other applications.

Development of all-solid-state air-cooled high power blue diode laser for metal processing.

Jayant Devara, Sandeep Jakhar, Yateendra Sihag, Biswajit Panda, Ananth Venkatesan, and Kamal Singh

DOI: 10.1364/OL.502493 Received 04 Aug 2023; Accepted 08 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: We present the design and development of an all-solid-state (fluid/refrigerant-free) 100 W scale blue laser system and show its applications in precision copper works. We combine powerful laser diode arrays with Peltier chips on a compact laser head to achieve stable thermal and optical performance. Good agreement between the thermal simulation of the 3D laser head and experiments validates stable thermal performance. The laser system emits 40-100 W continuous wave at $\lambda=452.2\pm2.5$~nm with 98\% power stability and $\sim 24$\% wall-plug efficiency inside a portable enclosure.This is the first all-solid-state air-cooled laser with 100 W class output. We achieve kW/cm$^2$ intensity level on mm-size focus with this source and demonstrate cutting, bending, and soldering copper on a battery pack. Furthermore, the copper-solder joints have nano-scale adhesion without cracks. Additionally, we unveil that 0.5-4 kW/cm$^2$ intensity laser annealing scan makes copper strips mechanically resilient to withstand extreme loading cycles without nano-scale cracks.

Addressing Data Scarcity in Optical Matrix Multiplier Modeling Using Transfer Learning

Ali Cem, Ognjen Jovanovic, Siqi Yan, Yunhong Ding, Darko Zibar, and Francesco Da Ros

DOI: 10.1364/OL.502517 Received 03 Aug 2023; Accepted 08 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: We present and experimentally evaluate using transfer learning to address experimental data scarcity when training neural network (NN) models for Mach-Zehnder interferometer mesh-based optical matrix multipliers. Our approach involves pre-training the model using synthetic data generated from a less accurate analytical model and fine-tuning with experimental data. Our investigation demonstrates that this method yields significant reductions in modeling errors compared to using an analytical model, or a standalone NN model when training data is limited. Utilizing regularization techniques and ensemble averaging, we achieve <1 dB root-mean-square error on the matrix weights implemented by a photonic chip while using only 25% of the available data.

Femtosecond-resolution optical pulse interleaving time error detector

Minji Hyun, Changmin Ahn, Youngseok Bae, Junhyung Cho, and Jungwon Kim

DOI: 10.1364/OL.504910 Received 08 Sep 2023; Accepted 08 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Pulse repetition rate multiplier (PRRM) is an essential component of microwave photonics systems, designed not only to alleviate photodiode saturation but also to provide more frequent pulses. However, the presence of interleaving time errors is known to compromise the advantages of PRRM. In this study, we present a high-sensitivity detection method for identifying these time errors using an electro-optic sampling-based timing detector (EOS-TD). We utilize two EOS-TDs: one for generating precise timing ruler signals and the other as a high-precision timing detector. In comparison to the conventional power ratio comparison method, our approach demonstrates sensitivity improvement by two orders of magnitude. This enhancement facilitates the measurement of femtosecond-level time errors. By enabling higher pulse rates while maintaining the ultra-low jitter, this method can be useful for building higher-speed photonic systems.

Adaptive-optics-based turbulence mitigation in a 400-Git/s free-space optical link by multiplexing Laguerre–Gaussian modes varying both radial and azimuthal spatial indices

Xinzhou Su, Zile Jiang, Yuxiang Duan, Huibin Zhou, Hao Song, Kai Pang, Cong Liu, Kaiheng Zou, Runzhou Zhang, Haoqian Song, Nanzhe Hu, Moshe Tur, and Alan Willner

DOI: 10.1364/OL.506270 Received 22 Sep 2023; Accepted 07 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: In general, atmospheric turbulence can degrade the performance of free-space optical (FSO) communication systems by coupling light from one spatial mode to other modes. In this paper, we experimentally demonstrate a 400-Gbit/s quadrature-phase-shift-keyed (QPSK) FSO mode-division-multiplexing (MDM) coherent communication link through emulated turbulence using four Laguerre Gaussian (LG) modes with different radial and azimuthal indices (LG10, LG11, LG-10, and LG-1-1). To mitigate turbulence-induced channel crosstalk and power loss, we implement an adaptive optics (AO) system at the receiver end. A Gaussian beam at a slightly different wavelength is co-propagated with the data beams as the probe beam. We use a wavefront sensor (WFS) to measure the wavefront distortion of this probe beam, and this information is used to tune a spatial light modulator (SLM) to adaptively correct the 4 distorted data-beam wavefronts. Using this adaptive-optics approach, the power loss and crosstalk are reduced by ~10 and ~18 dB, respectively.

Deconvolution Stimulated Raman Scattering Microscopy Enhanced by Quantum Light

Li Gong, Shulang Lin, and Zhiwei Huang

DOI: 10.1364/OL.509616 Received 19 Oct 2023; Accepted 07 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: Stimulated Raman scattering (SRS) microscopy is a powerful tool for label-free chemical contrast bio-imaging. However, its spatial resolution is limited by diffraction; its noise level is also fundamentally limited by the shot noise due to the quantum nature of light. In this work, we apply the squeezed light technique associated with the deconvolution method to achieve quantum-enhanced super-resolution SRS microscopy. To generate squeezed pump light, we design a unique cascaded scheme by using two nonlinear crystals, in which the second harmonic generation (SHG) from the first crystal is used to boost the SHG of the second crystal sequentially. Such a cascaded light squeezed scheme suppresses the shot noise down to 89.7% (1dB), which can be readily applied to the existing conventional SRS microscopy. We combine the squeezed light-controlled SRS with the Richardson-Lucy deconvolution method to break the diffraction limit by improving the spatial resolution of ~2.2-fold compared to conventional SRS imaging. We realize the quantum-enhanced super-resolution SRS imaging in a variety of samples (e.g., oleic acid, porcine muscle tissue), suggesting the potential of squeezed light SRS with deconvolution for label-free super-resolution chemical imaging in biological and biomedical systems.

Mobile recognition and positioning for multiple visible light communication cells using convolutional neural network

Xiaoxiao Du, Yan-Yu Zhang, Chao Wang, Fan Peng-hui, and Zhu Yi-Jun

DOI: 10.1364/OL.503007 Received 14 Aug 2023; Accepted 07 Nov 2023; Posted 08 Nov 2023  View: PDF

Abstract: The industrial Internet of Things (IIoT) environment involves multiple production items, such as robots, automated guided vehicles (AGVs), etc. The actual industrial scenario requires communication of production items while also considering mobile recognition and positioning. Hence the perception approach requires not only combining communications but also realizing the recognition and positioning of multiple communication cells.This letter proposes a multi-optical cell recognition and positioning framework based on LED image features. The LED images are obtained by a CMOS image sensor. This framework utilizes convolutional neural networks (CNN) to train LED images for recognition between multiple optical cells and locates precise positions through region recognition within the optical cells. The experimental results show that the mean recognition accuracy of the trained optimal CNN model for two LED cells is above 99\%. The mean accuracy of region recognition within the optical cell is as high as 100\%, which is significantly better than other traditional recognition algorithms. Therefore, the proposed framework can provide location-aware services for visible light communication and has a wide application prospect in IIoT.

Study of optical and electrical characteristics of perovskite solar cells incorporating MoO3 as an active layer

Himanshu Gehlot, Manu Faujdar, Sumit Pokhriyal, Narendra Khatri, and Awanish Sharma

DOI: 10.1364/OL.506477 Received 21 Sep 2023; Accepted 06 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: Perovskite-based solar cell technologies have sparked much interest in recent decades. A solar cell's efficiency is an essential factor in developing a highly efficient device. The power conversion efficiency (PCE) of Perovskite-based solar cells can be enhanced by adding new material to the photon absorbing layer and altering the electron and hole transport layers. Titanium dioxide (TiO2) is commonly used in electron transport layers (ETLs), but it has been shown that replacing TiO2 with Molybdenum trioxide (MoO3) improves PCE. We use the OghmaNano software to simulate a perovskite-based solar cell and investigate the PCE for TiO2 and MoO3 ETL layers by altering their thickness. The influence of electron and hole drift-diffusion, carrier continuity equations in position space to describe charge flow within the device, Poisson's equation, and charge carrier recombination have all been investigated in the context of solar cell simulation. It was observed that by substituting the ETL layer of TiO2 with MoO3 in the device, the PCE significantly increases.

Integrating Key Generation and Distribution with Quantum Noise Stream Cipher System without Compromising Transmission Performance

yuang Li, yajie li, kongni zhu, Shuang Wei, mingrui zhang, Yongli Zhao, and jie zhang

DOI: 10.1364/OL.503743 Received 23 Aug 2023; Accepted 06 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: We propose and experimentally demonstrate a secure quantum noise stream cipher transmission system that integrates key generation and distribution. At the stage of carrier phase recovery, the estimated phase noise is used to generate the randomness keys without additional equipment. Based on direct sequence spread spectrum technology, we integrate the distributed keys with quantum noise stream cipher signals. The key distribution and encryption transmission can be completed simultaneously without occupying additional bandwidth or time slots. By changing the position of distributed keys in the encryption base, the BER performance of QAM/QNSC signals cannot be affected by the keys. Experimental results demonstrate that the 54.5 Mbps key distribution and 31 Gbps encryption transmission without OSNR penalty can achieved simultaneously over 120 km standard single-mode fiber.

Enhanced performances of photonic reservoir computing using a semiconductor laser with random distributed optical feedback

DeYu Cai, YU HUANG, Yigong Yang, Pei Zhou, and Nianqiang Li

DOI: 10.1364/OL.506633 Received 26 Sep 2023; Accepted 05 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: We propose and experimentally demonstrate a photonic time-delay reservoir computing (TDRC) system with random distributed optical feedback under optical injection. To evaluate the performance, we calculate the memory ability and perform two benchmark tasks, i.e., chaotic time series prediction and nonlinear channel equalization task. Our numerical results show that the proposed TDRC has a superior performance compared with the case with conventional single optical feedback. This is attributed to the fact that the random distributed optical feedback offers multiple external cavity modes, which enhance the nonlinearity of the reservoir laser. Additionally, the experimental result also shows that our proposed TDRC scheme outperforms the computer with single optical feedback in the chaotic time series prediction task. Our work offers a novel path to improve the performance of TDRC by introducing random distributed optical feedback.

Integrated photonic molecule Brillouin laser with high power sub-100-mHz fundamental linewidth

KAIKAI LIU, Jiawei Wang, Nitesh Chauhan, Mark Harrington, Karl Nelson, and Daniel Blumenthal

DOI: 10.1364/OL.503126 Received 17 Aug 2023; Accepted 05 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Photonic integrated lasers with ultra-low fundamental linewidth and high output power are important for precision atomic and quantum applications as well as high-capacity communications and fiber sensing, yet wafer-scale solutions have remained elusive. Here we report an integrated stimulated Brillouin laser (SBL), based on a photonic molecule coupled resonator design, that achieves sub-100 mHz fundamental linewidth with greater than 10 mW output power in the C-band, fabricated a 200-mm wafer-scale, silicon nitride (Si3N4) CMOS-foundry compatible platform. The photonic molecule design is used to suppress the second order Stokes emission, allowing the primary lasing mode photon population to increase with pump power without phase noise feedback from higher Stokes orders. The nested waveguide resonators have a measured 184 million intrinsic Q and 92 million loaded, over an order of magnitude improvement over prior photonic molecules, enabling precision resonance splitting of 198 MHz at the second order Stokes (S2) frequency offset. We demonstrate S2-suppressed single-mode Brillouin lasing with a minimum fundamental linewidth of 71 mHz, corresponding to a mHz²/Hz white-frequency-noise floor, over an order of magnitude lower than prior integrated SBLs, with an ~11 mW output power and 2.3 mW threshold power. The frequency noise reaches the resonator-intrinsic thermo-refractive noise limited floor over the range of 2 kHz to 1 MHz and the laser phase noise reaches -155 dBc/Hz at a 10 MHz offset from carrier. The performance of this chip-scale SBL shows promise not only to improve the reliability and reduce size and cost, but also to enable new precision experiments that require the high-speed manipulation, control and interrogation of atoms and qubits. Realization in the silicon nitride ultra-low loss platform is adaptable to a wide range of wavelengths from the visible to infrared and enables integration with other components for systems-on-chip solutions for a wide range of precision scientific and engineering applications including quantum sensing, gravitometers, atom interferometers, precision metrology, optical atomic clocks, and ultra-low noise microwave generation.

Watt-level 815 nm lasing from Tm3+-doped fluorotellurite glass fibers

Junjie Wang, Zhixu Jia, Yingshuai Ren, Chuanze Zhang, Yasutake Ohishi, Weiping Qin, and Guanshi Qin

DOI: 10.1364/OL.505703 Received 11 Sep 2023; Accepted 05 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: Tm3+-doped fluorotellurite fibers based on TeO2-BaF2-Y2O3(TBY) glasses were fabricated by using a rod-in-tube method. By using an 81 cm-long Tm3+-doped fluorotellurite fiber as the gain medium and a 1400/1570 nm dual-wavelength pump technique, lasing at 815 nm was obtained for a threshold pump power of 629 mW at 1400 nm and a fixed pump power of 960 mW at 1570 nm. As the 1400 nm pump power is increased to 1803 mW, the obtained maximum output power was about 1616 mW. The corresponding optical-to-optical conversion efficiency was about 58.5%. Our results show that Tm3+-doped fluorotellurite fibers are promising gain media for constructing 815 nm fiber lasers.

Post-FEC Performance Evaluation of Optical SDM Systems with Mode-dependent Loss

Luis Díez, Francisco Cañete, and Torres Luis

DOI: 10.1364/OL.502544 Received 04 Aug 2023; Accepted 05 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: This work is focused on the bit error rate (BER) performance of spatial division multiplexing (SDM) systems over an optical channel with mode-dependent loss or gain (collectively referred to in this paper as MDL). When this latter is non-negligible, the BER has a random nature that introduces the outage probability as an important performance metric for the system design, and also impacts on the selection of a forward-error correction (FEC) scheme. The pre-FEC BER has been characterized as a random variable, and its probability density function (PDF) and the system coding gain depend on the signal-to-noise ratio (SNR) at the receiver input [1]. Hence, the common and simple approach of adding a coding gain factor to the pre-FEC BER to obtain the post-FEC BER is no longer valid for such kind of optical systems. We analyze the resulting performance taking into account all the particularities of the SDM system with MDL applied to an optimal linear multiple input multiple output (MIMO) receiver followed by a low-density parity check (LDPC) FEC algorithm. The post-FEC BER analysis includes both a comparison between simplifications in the log-likelihood ratio (LLR) computations, and a comparison of BER performance between the use of a single LDPC decoder shared among all SDM modes and the classical approach of one independent LDPC decoder per received mode.

Optical frequency comb generation using cascaded injection of semiconductor lasers

Hsu-Ting Tang and Yu-Han Hung

DOI: 10.1364/OL.504685 Received 01 Sep 2023; Accepted 05 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: We study optical frequency comb (OFC) generation using cascaded injection of semiconductor lasers in this work. The OFC generation system is operated in two cascaded optical injection stages. When a master laser optically injects into the first stage with proper injection power and frequency, period-one (P1) dynamics are invoked in an optically injected semiconductor laser of the first stage. Another semiconductor laser in the second stage is then optically injected by the P1 dynamics. With proper injection power adjusted in the second stage, the P1 dynamics are regenerated, and the semiconductor laser relaxation oscillations (ROs) become undamped so that subharmonic oscillations appear. Because a subharmonic oscillation frequency is half of an oscillation frequency of the P1 dynamics, extra optical frequency components appear in the middle of the adjacent optical frequency components of the P1 dynamics, thus signaling OFC generation. The OFC signals exhibit at least 15 comb lines, resulting in a bandwidth greater than 140 GHz. Microwave comb signals are obtained after photodetection, although the microwave linewidth is on the order of a few megahertz because of the semiconductor laser noise. Thus, we propose a cascaded injection-locking scheme to stabilize the P1 dynamics and OFC signals. We have demonstrated pure microwave generations with a linewidth of less than 3 Hz and low phase noise.

Demonstration of an 800G CDM-SDM coherent PON utilizing weakly-coupled multicore fibers with CDM tributaries manipulation

Lin Sun, Luxiao Zhang, Meng Mao, Bin Chen, Junjie Xiong, Lin Ma, Jun Li, Gordon Liu, Yi Cai, Zhaohui Li, and Gangxiang Shen

DOI: 10.1364/OL.505923 Received 20 Sep 2023; Accepted 04 Nov 2023; Posted 06 Nov 2023  View: PDF

Abstract: In this letter, we present an experimental demonstration of downstream signaling in a 16×50 Gbit/s coherent passive optical network (CPON) using the code and space division multiplexing (CDM-SDM) approach. We realize optical SDM through the utilization of a 4-core weakly-coupled multicore fiber (WC-MCF), enhancing the total available optical launch power at the optical line terminal (OLT). This enhancement significantly improves the power budget for CPONs that connect with a large number of optical network units (ONUs). At the second stage of the CPON, four CDM-assigned ONUs are connected to individual cores of the WC-MCF, thereby supporting the connectivity of up to 16 ONUs. Through experiments, we have noted substantial disparities in the downstream signaling performance among individual CDM-assigned ONUs, particularly as the capacity is increased to 800 Gbit/s. To address this issue, we have employed an innovative approach by leveraging space-time coding techniques to manipulate the CDM tributaries, to achieve a balanced reception performance for all ONUs within the CPON. We believe that the proposed CDM-SDM CPON scheme, complemented by the advanced DSP flowchart, holds significant promise for future PON systems characterized by substantial capacity and extensive connectivity.

Highly efficient nonlinear vortex beam generation by using compact nonlinear fork grating

Yangfeifei Yang, Hao Li, Haigang Liu, and Xianfeng Chen

DOI: 10.1364/OL.506901 Received 28 Sep 2023; Accepted 04 Nov 2023; Posted 10 Nov 2023  View: PDF

Abstract: Vortex beams with orbital angular momentum (OAM) are extremely important in optical trapping, optical micromachining, high-capacity optical communications, and quantum optics. Nonlinear generation of such vortex beam enables vortex beams to be obtained at new wavelengths, which opens up new possibilities for all-optical switching and manipulation of vortex beams. However, previous nonlinear vortex beams generation suffer from either low efficiency or low-level integration. Here, we use the technique of ultraviolet photolithography assisted inductively coupled plasma (ICP) etching to realize a compact nonlinear fork grating for high efficiency nonlinear vortex beam generation. In our experiment, the depth of such compact nonlinear fork grating structure can be precisely controlled by etching time. The vortex beams with topological charge of l=±1,±2,±3 can be generated in the far field and the normalized nonlinear conversion efficiency of such nonlinear vortex beam is 189%W¯¹cm¯² . Our method not only provides an efficient and compact method for nonlinear vortex beam manipulation, but also suits for timesaving and large-area nonlinear functional device fabrication.

Hybrid 3D-Printed Fiber-Solid State Laser

Simon Angstenberger, Pavel Ruchka, Mario Hentschel, Tobias Steinle, and Harald Giessen

DOI: 10.1364/OL.504940 Received 19 Sep 2023; Accepted 04 Nov 2023; Posted 21 Nov 2023  View: PDF

Abstract: Microscale 3D-printing has revolutionized micro-optical applications ranging from endoscopy, imaging, to quantum technologies. In all these applications miniaturization is key, and in combination with the nearly unlimited design space it is opening novel avenues. Here, we push the limits of miniaturization and durability by realizing the first fiber laser system with intra-cavity on-fiber 3D-printed optics. We demonstrate stable laser operation at over 20 mW output power at 1063.4 nm with a full width half maximum (FWHM) bandwidth of 0.11 nm and a maximum output power of 37 mW. Furthermore, we investigate the power stability and degradation of 3D-printed optics at Watt power levels. The intriguing possibilities afforded by free-form microscale 3D-printed optics allow us to combine gain in a solid-state crystal with fiber guidance in a hybrid laser concept. Therefore, our novel ansatz enables the compact integration of bulk active media in fiber platforms at substantial power levels.

Self-powered solar-blind detector array based on ε-Ga2O3 Schottky photodiodes for dual-mode binary UV communication

Kanglong Xia, Z. Liu, Shulin Sha, Zhaoying Xi, Jiahan Zhang, Mingming Jiang, Yufeng Guo, and Weihua Tang

DOI: 10.1364/OL.506189 Received 19 Sep 2023; Accepted 03 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: In this work, a solar-blind UV metal-semiconductor Schottky photodiode array is constructed by using metalorganic chemical vapor deposition grown ε-Ga2O3 thin film, possessing high-performance and self-powered characteristics, towards dual-mode (self-powered and biased modes) binary light communication. For the array unit, the responsivity, specific detectivity and external quantum efficiency are 30.8 A/W/63.3 mA/W, 1.51×104%/30.9%, 1.28×1014/5.4×1012 Jones for biased/self-powered operation. The rise and decay time are 0.19 ms and 7.96 ms, respectively; suggesting an ability to trace fast light signal. As an array, the deviation of photocurrent is only 4.3%, importance of accurate information communication. Through certain definition of “1/0” binary digital information, the “NY” and “IC” characters are communicated to illustrate the self-powered and biased modes by right of ASCII codes, based on the prepared ε-Ga2O3 solar-blind UV Schottky photodiode array. This work made dual-mode binary deep-UV light communication come true, and may well guide the development of UV optoelectronics.

Space-time coupling by soliton self-mode conversion technique in optical fibers

Ru Li, Manlin Liu, Weiyi Hong, and Aiping Luo

DOI: 10.1364/OL.505184 Received 06 Sep 2023; Accepted 03 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: Soliton self-mode conversion is a versatile technique that allows for both wavelength changes and mode transformations. This process can be controlled by adjusting the input power, with higher power resulting in a stronger nonlinear effect that facilitates soliton self-mode conversion. Our research has demonstrated that soliton self-mode conversion is a viable method for achieving spatiotemporal coupling. This technique can be applied in optical fibers to link two pulses, resulting in distinct spatial distributions that can be controlled by adjusting the initial time intervals.

Anti-phase pulsation of counter-propagating dissipative solitons in a bidirectional fiber laser

Kai Yang, Zi rui Luo, Zexian Zhang, Ze-Yu Zhan, Daixuan Wu, Meng Liu, Aiping Luo, Wen-Cheng Xu, and Zhi-Chao Luo

DOI: 10.1364/OL.502534 Received 03 Aug 2023; Accepted 03 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: Due to its unique geometric structure, the bidirectional ultrafast fiber laser is an excellent light source for dual-comb applications. However, sharing the same gain between the counter-propagating solitons also gives rise to complex dynamics. Herein, we report the anti-phase pulsation of counter-propagating dissipative solitons in a bidirectional fiber laser. The in-phase and anti-phase soliton pulsation can be manipulated by adjusting the intracavity birefringence. The periodic modulation of polarization-dependent gain (PDG) caused by polarization hole burning (PHB) in the gain fiber can be responsible for anti-phase pulsation of bidirectional dissipative solitons. These findings offer new insights into the complex dynamics of solitons in dissipative optical systems and performance improvement of bidirectional ultrafast fiber lasers.

Control of vortex orientation of ultrashort optical pulsesusing spatial chirp

Miguel Porras and Spencer Jolly

DOI: 10.1364/OL.506253 Received 19 Sep 2023; Accepted 03 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: Introducing a spatial chirp into a pulse with a longitudinalvortex, such as a standard pulsed Laguerre-Gaussbeam, results in a vortex pulse with an arbitrary orientationof the phase line singularity between longitudinal and transverse,depending on the amount of chirp. Analytical expressionsare given for such pulses with arbitrary topologicalcharge valid at any propagation distance.

Dispersion engineering in Brillouin fiber laser cavity forKerr frequency comb formation

Moise Deroh, Erwan Lucas, and Bertrand Kibler

DOI: 10.1364/OL.506610 Received 22 Sep 2023; Accepted 03 Nov 2023; Posted 07 Nov 2023  View: PDF

Abstract: We conduct numerical and experimental investigations on Kerr combs generation in a nonlinear and nonreciprocal fiber cavity by leveraging both stimulated Brillouin backscattering and cascaded four-wave mixing. By engineering the net cavity dispersion to be either normalor anomalous, we enable the formation of diverse patterns and localized structures in the cavity field. The comb’s properties depend crucially on the mismatch between the frequency spacing of the bi-chromatic pump and the free spectral range of the Brillouin laser cavityin both cases. Particularly, in the anomalous regime, adjusting this parameter yields coherent, stable frequency combs in the modulation instability regime. This allows control and expansion of the spectral bandwidth up to 2 THz in normal dispersion and to 6 THz under anomalous net dispersion. This versatile and easily reconfigurablemethod holds potential for applications in high-speed communications and microwave synthesis.

532 nm laser beam steering using power-efficient focal plane array

Zhaoyang Wu, Yanfeng Zhang, Shihao Zeng, Shuqing Lin, and Siyuan Yu

DOI: 10.1364/OL.504268 Received 30 Aug 2023; Accepted 02 Nov 2023; Posted 06 Nov 2023  View: PDF

Abstract: Laser beam steering is important for classical and quantum information processing. On-chip beam steering is a major motivation for developing large-scale photonic integrated circuits such as optical phased arrays. A major challenge for such arrays is to simultaneously control a large number of on-chip phase shifters, which requires complicated analog control algorithm and rapidly increasing power consumption. We report a green light (532 nm) 1x16 focal plane array photonic integrated circuit with simple control and low power consumption. Fabricated on a silicon nitride platform, the focal plane array achieves angular beam steering over a 10° field of view, with ultra-low electrical power consumption (4×3.1 mW).

High-precision wavelength measurement using virtual Fizeau cavity

yixuan liu, Shibang Ma, kun yang, Lingqiang Meng, zong yi, and Jianxin Li

DOI: 10.1364/OL.504076 Received 23 Aug 2023; Accepted 02 Nov 2023; Posted 06 Nov 2023  View: PDF

Abstract: Fizeau wavelength measurement plays an important role in the fields of optical communication, optical metrology, and optical testing technology. The accuracy of the traditional multistage Fizeau wavemeter is limited owing to the degradation of the stripe symmetry and finesse caused by the variations in cavity length. Herein, we propose a virtual Fizeau cavity (VFC) based on the principle of phase difference to address this issue. The principle analysis and simulation of this measurement system are presented, along with experiments that verified the feasibility and performance of the VFC method. The wavelength measurement accuracy of this system is superior to 60 MHz in the 350–1100 nm wavelength range. The design concept of “virtual–real combined” cavities first proposed in this paper introduces possibilities for the development of high-accuracy Fizeau wavelength measurements.

On-chip coherent beam combination of waveguide amplifiers on Er3+-doped thin film lithium niobate

Zhiwei Fang, Rui Bao, LvBin Song, Jinming Chen, Zhe Wang, jian Liu, LANG GAO, zhaoxiang liu, Zhihao Zhang, Min Wang, Haisu Zhang, and Ya Cheng

DOI: 10.1364/OL.504540 Received 29 Aug 2023; Accepted 02 Nov 2023; Posted 02 Nov 2023  View: PDF

Abstract: We demonstrate on-chip coherent beam combination of two waveguide amplifiers on Er3+-doped thin film lithium niobate (Er: TFLN) platform. Our device is built based on an electro-optic modulator fabricated on Er: TFLN. The output power of the coherently combined amplifiers is measured as high as 12.9 mW, surpassing that of previous single waveguide amplifiers based on Er3+-doped thin film lithium niobate platform.

Low threshold Lasing from Bound States in the Continuum with Dielectric Metasurfaces

Huiwen Xue, shengqiong chen, Jiebin Niu, Shengjie Zhao, chen lu, Longjie Li, Feng Jin, Changqing Xie, and Lina Shi

DOI: 10.1364/OL.505704 Received 12 Sep 2023; Accepted 02 Nov 2023; Posted 02 Nov 2023  View: PDF

Abstract: Bound states in the continuum (BICs) with extremely large quality factors (Q-factors) can enhance the light-matter interacting, and thus achieve low-threshold lasing. Here, we theoretically propose and experimentally demonstrate the low-threshold lasing at room-temperature based on BICs. A threshold of approximately μW/cm2 peak intensity under 10-ns-pulsed optical excitation is presented in an all-dielectric metasurface system consisting of titanium dioxide (TiO2) nano-pillars with a dye film. Also, the multi-mode lasing can be excited by the higher pumping. Our results may find exciting applications in on-chip coherent light sources, filtering and sensing.

An SNR-enhanced signal delivery scheme with delta-sigma modulation in a 4-mode fiber system

Jianyu Long, Chen Wang, Bohan Sang, Junjie Ding, KAIHUI WANG, Bowen Zhu, Tianqi Zheng, Wen Zhou, Bing Ye, Weizhang Chen, Bo Liu, Lei Shen, and Jianjun Yu

DOI: 10.1364/OL.505986 Received 14 Sep 2023; Accepted 02 Nov 2023; Posted 02 Nov 2023  View: PDF

Abstract: This Letter proposes a novel scheme for optimizing the SNR of signal to improve the system performance by 1-bit delta-sigma modulation (DSM) in a four-mode MDM system for mobile fronthaul. 1-bit digitalized signal with an SNR of 60 dB from transmitter digital signal processing (Tx DSP) can be achieved. Based on this system, an experimental demonstration of the ultra-high-order 1048576-QAM signal transmission over a 50-km strong-coupling few-mode fiber (FMF) is successfully realized. With DSP, the bit error rate (BER) of received 1048576-QAM signals over four modes transmission is below the 20% soft-decision forward error correction (20% SD-FEC) threshold of 2.4×10-2. To the best of our knowledge, this is the first time that the combination of DSM technology and strong-coupling MDM system is achieved, and that the highest-modulation order with DSM reported in MDM system is reached. This experimental demonstration of the proposed novel scheme in MDM system can provide an effective solution for ultra-large-capacity mobile fronthaul in the future.

X-ray-based overlay metrology using reciprocal space slicing analysis

Jiahao Zhang, Xiuguo Chen, Tianjuan Yang, and Shiyuan Liu

DOI: 10.1364/OL.505346 Received 07 Sep 2023; Accepted 02 Nov 2023; Posted 03 Nov 2023  View: PDF

Abstract: Overlay serves as the pivotal performance indicator for lithography tools, and its prompt and precise measurement significantly underpins process yield control. At present, diffraction-based overlay metrology employing optical wavelengths encounter constraints in terms of measurement sensitivity. When transitioning to X-ray wavelengths, the critical dimension small-angle X-ray scattering (CDSAXS) method for nanostructure characterization necessitates reciprocal space mapping (RSM) and inverse problem solving, resulting in substantial throughput constraints. In this work, we propose an X-ray-based overlay metrology using reciprocal space slicing analysis (RSS), yielding high-precision overlay measurement at one single angle of incidence (AOI). Moreover, we examine the robustness of the proposed method against errors stemming from overlay target grating fabrication and measurement processes, substantiating its efficacy as a novel X-ray-based overlay metrology and unveiling the potential application of X-ray-based techniques within the realm of integrated circuit metrology.

Pump-probe-alternating photothermal interferometry for two-component gas sensing

Linhao Guo, Pengcheng Zhao, HOI LUT HO, Shoulin Jiang, Haihong BAO, Shoufei Gao, Yingying Wang, and Wei Jin

DOI: 10.1364/OL.505462 Received 12 Sep 2023; Accepted 02 Nov 2023; Posted 03 Nov 2023  View: PDF

Abstract: We demonstrate a high-sensitivity acetylene/methane gas sensor based on hollow-core fiber photothermal interferometry (PTI) with a pump-probe-alternating technique. This technique utilizes two distributed feedback lasers as pump and probe beams alternatively for two gas components to facilitate photothermal phase modulation and detection through time-division multiplexing. With a 2.5-cm-long hollow-core conjoint-tube fiber, noise-equivalent concentration of 370 parts per billion (ppb) and 130 ppb are demonstrated for methane and acetylene, respectively. Noise characteristics of the PTI system are analyzed and experimentally tested. The proposed technique eliminates the need for an additional laser in the traditional PTI setup, enabling the construction of a sensitive yet more compact and cost-effective multi-gas component detection system.

Registration free 3D Super-Resolution Generative Deep-learning Network for Fluorescence Microscopy Imaging

Hang Zhou, yuxin li, Bolun Chen, Hao Yang, Maoyang Zou, Wu Wen, Yayu Ma, and Min Chen

DOI: 10.1364/OL.503238 Received 15 Aug 2023; Accepted 02 Nov 2023; Posted 09 Nov 2023  View: PDF

Abstract: 3D optical imaging microscopy provides an important data foundation for studying brain structures. However, limited by the imaging capability of existing optical systems, it is difficult to achieve large-scale high-resolution imaging. Image super-resolution methods provide an effective way to enhance the resolution of large-scale images, but they rely on pixel-level registered high and low-resolution image samples, which are challenging to obtain. To address these issues, we propose a 3D image super-resolution method that performs super-resolution (SR) training and prediction on unregistered low and high-resolution neuronal images. The network is built on the CycleGAN framework, the 3D attention mechanism UNet network. We tested our method on high and low-resolution neuronal images with 20×/1.0-NA and 5×/0.16-NA, respectively. Compared to other non-registered super-resolution methods, our approach achieves the best reconstruction results. Our method holds promise for advancing research in the field of large-scale neuronal imaging at a low cost.

Mid-infrared dual-comb spectroscopy for rapid temperature distribution characterization

Xing Zou, MengLin Zhang, Chenyu Liu, Zhong Zuo, Yuanfeng Di, Siying He, Siyi Wang, Daping Luo, CHENGLIN Gu, and Wenxue Li

DOI: 10.1364/OL.506609 Received 28 Sep 2023; Accepted 31 Oct 2023; Posted 03 Nov 2023  View: PDF

Abstract: Due to the influence of chemical reactions, phase change, and other phenomena, the combustion system is a complicated high-temperature environment. Therefore, the spatio-temporally resolved monitoring of the temperature field is crucial for gaining a comprehensive understanding of the intricate combustion environment. In this study, we proposed a fast and high-precision temperature measurement technique based on mid-infrared (MIR) dual-comb spectroscopy with a high spectral resolution and fast refresh rate. Based on this technique, the spatio-temporally resolved measurement of a non-uniform temperature field was achieved along the laser path. To verify the capability of DCS for temperature measurement, the band-head ro-vibrational lines of the CO₂ molecule were acquired, and the 1-σ uncertainty of the retrieved temperature was 3.2 °C at 800 °C within 100-ms. The results demonstrate the potential of our fast and high-precision laser diagnostic technique which can be further applied to combustion kinetics.

Observation of higher-order topological corner states in photonic two-dimensional trimer lattices

Weizhao Cheng, Weijie Liu, Wenchao Yan, Bin Zhang, and Feng Chen

DOI: 10.1364/OL.506765 Received 26 Sep 2023; Accepted 31 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: We demonstrate the first experimental observation of higher-order topological corner states in the photonic two-dimensional (2D) trimer lattices. Using femtosecond laser direct writing technology, we experimentally fabricate a series of 2D trimer lattices with different open boundary conditions, and thereby observe two kinds of 0D topological boundary states, i.e., topological corner states and topological defect corner states. Interestingly, these corner states and defect corner states can not only exist in the band gap, but also coexist with the bulk states, and show obvious localization properties. This work provides fresh perspectives on higher-order topology in artificial microstructures.

Orange surface waveguide laser in Pr:LiYF4 produced by femtosecond laser writing

Amandine Baillard, Pavel Loiko, Carolina Romero, Víctor Arroyo, Javier Vazquez de Aldana, Michael Fromager, Abdelmjid Benayad, Alain BRAUD, Patrice Camy, and Xavier Mateos

DOI: 10.1364/OL.507073 Received 02 Oct 2023; Accepted 31 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: Depressed-cladding surface channel waveguides were inscribed in a 0.5 at.% Pr:LiYF4 crystal by femtosecond Direct Laser Writing. The waveguides consisted of a half-ring cladding (inner diameter: 17 μm) and side structures (“ears”) improving the mode confinement. The waveguide propagation loss was as low as 0.14±0.05 dB/cm. The orange waveguide laser operating in the fundamental mode delivered 274 mW at 604.3 nm with 28.4% slope efficiency, a laser threshold of only 29 mW and linear polarization (π), representing record-high performance for orange Pr waveguide lasers.

3D Quantitative Phase Imaging in Off-axis Digital Holographic Microscopy: Synergistic Reconstruction Framework

Raul Castaneda, Carlos Trujillo, and Ana Doblas

DOI: 10.1364/OL.506400 Received 20 Sep 2023; Accepted 31 Oct 2023; Posted 31 Oct 2023  View: PDF

Abstract: Digital Holographic Microscopy (DHM) enables the three-dimensional (3D) reconstruction of quantitative phase distributions from a defocused hologram. Traditional computational algorithms follow a sequential approach in which one first reconstructs the complex amplitude distribution and later applies focusing algorithms to provide an in-focus phase map. In this work, we have developed a synergistic computational framework to compensate for the linear tilt introduced in off-axis DHM systems and autofocus the defocused holograms by minimizing a cost function, providing in-focus reconstructed phase images without phase distortions. The proposed computational tool has been validated in defocused holograms of human red blood cells and three-dimensional images of dynamic sperm cells.

Improved stability second harmonic conversion of a diode-pumped Yb:YAG laser at the 0.5 kW-level

DANIELLE CLARKE, Paul Phillips, Martin Divoky, Jan Pilar, Petr Navratil, Martin Hanus, Patricie Severova, Ondrej Denk, Tomas Paliesek, Martin Smrž, Paul Mason, Thomas Butcher, Chris Edwards, John Collier, and Tomáš Mocek

DOI: 10.1364/OL.497181 Received 08 Jun 2023; Accepted 31 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: We report on efficient and stable, type-I phase matched second harmonic conversion of a nanosecond high-energy, diode-pumped, Yb:YAG laser. With a frequency doubling crystal in an enclosed, temperature-controller with optical windows, 0.5% energy stability was achieved for approximately half an hour. This resulted in 48.9 J pulses at 10 Hz (489 W) and a conversion efficiency of 73.8%. These results are particularly important for stable and reliable operation of high-energy, frequency-doubled lasers.

An efficient continuous-wave Nd:YVO4/KGW intracavity Raman laser

Jingni Geng, Quan Sheng, Shijie Fu, Wei Shi, and Jian-Quan Yao

DOI: 10.1364/OL.503201 Received 14 Aug 2023; Accepted 31 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: We demonstrate an efficient Nd:YVO4/KGW intracavity Raman laser in continuous-wave (CW) scheme. With a V-shaped fundamental laser cavity and a short Stokes cavity in it, the oscillating beam sizes are designed to alleviate the thermal effect and to enhance the Raman gain for efficient CW operation. The output power of CW Stokes wave at 1177 nm reached 9.33 W under an incident laser diode pump power of 36.65 W, with corresponding optical efficiency being 25.5%. To the best of our knowledge, these are the highest Stokes output power and conversion efficiency of CW intracavity Raman lasers.

Multi-derivative method for phase extraction without knowing carrier frequencies in off-axis digital holography

Zhong Zhi, Diyao Song, lei liu, Viorel Nastasa, Bin Liu, and Shan Mingguang

DOI: 10.1364/OL.503902 Received 22 Aug 2023; Accepted 31 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: We propose a multi-derivative method to reconstruct the phase in off-axis digital holography (DH). By numerically computing first-, second- and third-order derivatives of the hologram, we demonstrate that one can extract the quantitative phase information in a straightforward way, without prior knowledge of the carrier frequencies or Fourier transform. In contrast to existing advanced derivative methods, our approach markedly streamlines the alignment and retrieval processes, all without requiring any special prerequisites. This enhancement seamlessly translates into improved reconstruction quality. Furthermore, when compared to cutting-edge Fourier-division-based methods, our technique distinctly accelerates the phase retrieval speed. We verified our method using white light diffraction phase microscopy and laser off-axis DH, and the results indicate that our method can allow fast, high-quality retrieval with frame rates up to 40 fps for one- megapixel holograms on a regular computer.

Increasing the Q-factor of Fabry-Perot etalons using focused Bessel beam illumination.

Dylan Marques, Oliver Sheppard, James Guggenheim, and Peter Munro

DOI: 10.1364/OL.505390 Received 14 Sep 2023; Accepted 31 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: Sensing and filtering applications often require Fabry-Perot (FP) etalons with an Interferometer Transfer Function (ITF) having high visibility, narrow Full Width at Half Maximum (FWHM), and high sensitivity. For the ITF to have these characteristics, the illumination beam mustmatch the modes of the FP cavity. This is challenging when a small illumination element size is needed as traditional focused beams do not match the FP cavity modes. Bessel beams are a potential alternative as their structure resembles the FP cavity modes whilst possessing a focused core. To study the feasibility of using Bessel beam illumination, in this paper, ITFs of an FP etalon were measured using Bessel and Gaussian beams. A Bessel beam with core size of 29 μm provided an ITF with visibility 3.0 times higher, a FWHM 0.3 times narrower, and a sensitivity 2.2 times higher than a Gaussian beam with waist 30 μm. Thus, the results show that Bessel beam illumination can provide similar ITFs to collimated beam illumination while also having with a focused core.

Semi-spontaneous temporal evolution of relief/fluorescence hybrid gratings for holographic encryption

Yuxin Tao, Hongfang Liu, Xiuli Wang, Zhong Liu, Xin Li, Jingying Miao, Shencheng Fu, and Xintong Zhang

DOI: 10.1364/OL.505557 Received 11 Sep 2023; Accepted 30 Oct 2023; Posted 31 Oct 2023  View: PDF

Abstract: Holographic systems can reconstruct the entire wavefront of light which are developed as an excellent platform of information encryption. Although holography has utilized multiple modulation dimensions, little attention is given to its combination with fluorescence emitting. Herein, we propose a semi-spontaneous time-dependent encryption strategy of hybrid holographic fringes with surface relief and fluorescent emission mediated by a plasmonic polymer doped with fluorescent dyes. It is found that the two kinds of optical characteristic regions exhibit unique temporal evolution from overlapped mode to staggered one. The mode switching is closely related to the strong quenching effect of gold ions and nanoparticles which are dominant at early and later recording stage, respectively. Thus, the real and deceptive information are recorded at different holographic writing periods. High-secret information of text or images is constructed by the array of different sets of holographic fringes, and identified by comparing the dual channel results of Confocal Laser Scanning Microscopes. This work puts a bright way to dynamic holographic encryption.

Frequency noise measurements using coherent self-heterodyne detection

Simon Thomsen, Mónica Far Brusatori, Niklas Arent, Rakesh Ranjan Kumar, and Nicolas Volet

DOI: 10.1364/OL.505960 Received 20 Sep 2023; Accepted 30 Oct 2023; Posted 31 Oct 2023  View: PDF

Abstract: We present a refined way to extract the frequency noise (FN) power spectral density (PSD) of lasers by tailoring the delay in a conventional delayed self-heterodyne setup to sub-coherence lengths. The method achieves direct proportionality between electrical spectrum analyzer traces and FN PSDs which provide the intrinsic linewidth of the lasers. This proposed method is validated by comparing the FN PSD with that obtained from a commercial frequency noise analyzer. The method provides a cost-effective alternative for FN measurements, which also requires minimal post processing as compared to state-of-the-art.

Inverse designed light nanorouter for spatially multiplexed optical filter

Yuqi Peng, Hai Peng Lu, Dasen Zhang, Licheng Wang, Zhanying Ma, and Jun Jun Xiao

DOI: 10.1364/OL.505205 Received 08 Sep 2023; Accepted 30 Oct 2023; Posted 30 Oct 2023  View: PDF

Abstract: It is attractive to use optical nanorouter by artificial nanostructures to substitute the traditional Bayer filter for an image arraysensor, which, however, poses great challenges in balancing the design strategy and the ease of fabrication. Here we implementand compare two inverse design schemes for rapid optimization of RGGB Bayer-type optical nanorouter. One is based on themultiple Mie scattering theory and the adjoint gradient that is applicable to arrays of nanospheres with varying sizes, and the otheris based on the rigorous coupled wave analysis and the genetic algorithm. In both cases, we study layered nanostructures that canbe efficiently modeled respectively which greatly accelerates the inverse design. It is shown that the color-dependent peakcollection efficiencies of nanotouters designed in the two methods for red, green, and blue wavelengths reach 37%, 44%, 45%, and48%, 49%, 58%, respectively. We further demonstrate color nanorouters that provide light focusing to four quadrants working inboth the visible and infrared bands, which promises multispectral imaging applications

Shaping the angular spectrum of a Bessel beam to enhance light transfer through dynamic strongly-scattering media

Dennis Scheidt, Alejandro Arzola, and Pedro Quinto-Su

DOI: 10.1364/OL.502579 Received 10 Aug 2023; Accepted 30 Oct 2023; Posted 31 Oct 2023  View: PDF

Abstract: We prepare a quasi-non-diffracting Bessel beam defined within an annular angular spectrum with a spatial light modulator. The beam propagates though a strongly scattering media and the transmitted speckle pattern is measured at one point with a Hadamard Walsh basis that divides the ring into $N$ segments ($N=16,64,256, 1024$). The phase of the transmitted beam is reconstructed with 3 step interferometry and the intensity of the transmitted beam is optimized by projecting the conjugate phase at the SLM. We find that the optimum intensity is attained for the condition that the transverse wave vector $k_\perp$ (of the Bessel beam) matches the spatial azimuthal frequencies of the segmented ring $k_\phi$. Furthermore, compared with beams defined on a 2d grid (i.e. Gaussian) a reasonable enhancement is achieved for all the $k_\perp$ sampled with only 64 elements. Finally, the measurements can be done while the scatterer is moving as long as the total displacement during the measurement is smaller than the speckle correlation distance.

Switchable rotation of metal nanostructures in an intensity chirality-invariant focus field

Yixuan Chen, jiakang zhou, xie xi, Haixiang Ma, Shuoshuo Zhang, Zhenwei Xie, Changjun Min, Yuquan Zhang, and xiaocong yuan

DOI: 10.1364/OL.503217 Received 14 Aug 2023; Accepted 30 Oct 2023; Posted 31 Oct 2023  View: PDF

Abstract: Light-induced rotation is a fundamental motion form that is of great significance for flexible and multifunctional manipulation modes. However, current optical rotation by a single optical field is mostly unidirectional, where switchable rotation manipulation is still challenging. To address this issue, we demonstrate a switchable rotation of non-spherical nanostructures within a single optical focus field. Interestingly, the intensity of the focus field is chiral invariant. The rotation switch is a result of the energy flux reversal in front and behind the focal plane. We quantitatively analyze the optical force exerted on a metal nanorod at different planes, as well as the surrounding energy flux. Our experimental results indicate that the direct switchover of rotational motion is achievable by adjusting the relative position of the nanostructure to the focal plane. This result enriches the basic motion mode of micro-manipulation and is expected to create potential opportunities in many application fields, such as biological cytology and optical micromachining.

Single-shot observation of nonlinear pulse splitting in a Kerr medium

Yen-Yu Chang, Jeremy Gulley, Zhengyan Li, James Welch, Rafal Zgadzaj, Aaron Bernstein, and Michael Downer

DOI: 10.1364/OL.503170 Received 01 Sep 2023; Accepted 29 Oct 2023; Posted 30 Oct 2023  View: PDF

Abstract: We report single-shot, time-resolved observation of self-steepening and temporal splitting of near-infrared, 30 fs, micro-joule pulses propagating nonlinearly in flint (SF11) glass. A coherent, smooth-profiled, 60-nm-bandwidth probe pulse that propagated obliquely to the main pulse through the Kerr medium recorded a time sequence of longitudinal projections of the main pulse’s induced refractive index profile in the form of a phase shift “streak”, which frequency-domain interferometry recovered with ~ 10 fs temporal resolution. A three-dimensional simulation based on a unidirectional pulse propagation equation reproduced observed pulse profiles.

High-power narrow spectral width 975nm semiconductor laser with high process compatibility achieved by high-order gratings

ZhenWu Liu, Li ZHONG, Wei Li, suping Liu, and ma yu

DOI: 10.1364/OL.505825 Received 15 Sep 2023; Accepted 28 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: We present a broad-area laser diode with a 101st-order high-order distributed Bragg reflection (HO-DBR) structure, fabricated with the conventional UV lithography techniques. Based on the Finite-Difference Time-Domain (FDTD) algorithm ,a maximum output power of 10.5 W, emitting around 975nm with the spectral width of less than 0.5 nm FWHM has been achieved. This method provides insights for reducing the manufacturing costs of the high-power narrow spectral width DBR lasers.

6 W diode-pumped Tm:GdVO4 laser at 2.29 μm

Xiaoxu Yu, Kirill Eremeev, Zhongben Pan, Pavel Loiko, Hongwei Chu, Han Pan, Shengzhi Zhao, Alain BRAUD, Patrice Camy, and Dechun Li

DOI: 10.1364/OL.505131 Received 14 Sep 2023; Accepted 28 Oct 2023; Posted 06 Nov 2023  View: PDF

Abstract: A compact 1.5 at.% Tm:GdVO4 laser pumped by a 794 nm laser diode generated 6.09 W at 2.29 μm (the 3H4 → 3H5 Tm3+ transition) with a high slope efficiency of 30.8% and linear laser polarization (π), representing a record-high output for any 2.3 μm Thulium laser. The polarized spectroscopic properties of Tm3+ ions in GdVO4 were also revised. The peak stimulated-emission cross-section of Tm3+ ions is 2.97 × 10-20 cm2 at 2280 nm corresponding to an emission bandwidth of 42 nm for π-polarized light.

Unified framework for terahertz radiation from a single- or two-color plasma filament

Feifan Zhu, Jiayu Zhao, Li Lao, Yan Peng, and Yiming Zhu

DOI: 10.1364/OL.498603 Received 21 Jun 2023; Accepted 27 Oct 2023; Posted 09 Nov 2023  View: PDF

Abstract: The plasma filament induced by photo-ionization in transparent media (e.g., air) is a competitive terahertz (THz) source, whose mechanism has been widely studied in two separate schemes, i.e., the one- or two-color femtosecond laser filamentation. However, the physical commonality of these two schemes is less explored currently, and a common theory is in urgent need. Here, we proposed the traveling-wave antenna (TWA) model applicable to both single- and dual-color laser fields, which successfully reproduced the reported far-field THz angular distribution/dispersion from different filament lengths with either a constant or a varied plasma density. This work paves the way towards a deeper understanding of the important laser-filament-based THz sources within the same theoretical framework.

High-Q Adiabatic Micro-resonators on a Wafer-Scale Ion-Sliced 4H-Silicon-Carbide-on-Insulator Platform

Liping Zhou, Ailun Yi, Yongquan Su, Bingcheng Yang, Yifan Zhu, Jiachen Cai, Chengli Wang, Zhenyu Wu, sannian song, Jiaxiang Zhang, and Xin Ou

DOI: 10.1364/OL.505777 Received 14 Sep 2023; Accepted 26 Oct 2023; Posted 31 Oct 2023  View: PDF

Abstract: 4H-silicon-on-insulator (4H-SiCOI) has emerged as a prominent material contender for integrated photonics owing to its outstanding material properties such as CMOS compatibility, high refractive index, and high second- and third-order nonlinearities. Although various micro-resonators have been realized on the 4H-SiCOI platform, enabling numerous applications including frequency conversion, electro-optical modulators, they may suffer from a challenge associated with spatial mode interactions, primarily due to the widespread use of multimode waveguides. We study the suppression of spatial mode interaction in the adiabatic micro-resonators built up with adiabatic bends, and demonstrate micro-resonators with improved Q values above 1×105 on ion-sliced 4H-SiCOI platform with a SiC thickness nonuniformity less than 1%. The spatial-mode-interaction-free micro-resonators reported on the CMOS-compatible wafer-scale 4H-SiCOI platform would constitute an important ingredient for the envisaged large-scale integrated nonlinear photonic circuits.

Stable few-cycle out-of-phase solitons in rectangular multi-core fiber

Alexey Balakin, Sergey Skobelev, and A Litvak

DOI: 10.1364/OL.503453 Received 15 Aug 2023; Accepted 26 Oct 2023; Posted 27 Oct 2023  View: PDF

Abstract: Stable out-of-phase soliton-like distributions of the wave field with few-cycle durations are found in fibers consisting of a rectangular lattice of weakly coupled cores. The stability of found distributions for durations larger than the critical value is shown analytically and numerically. Numerical simulation shows that the radiation of linear dispersive waves rather quickly transforms shorter pulses to the found solution with critical duration.

Highly sensitive magnetic field sensor based on Fe2O3 nanorods grown on the surface of tapered few mode fiber

Li Li, Chao Jiang, Yuanyuan Han, Chuanju Hu, Longfeng Deng, Jiawei Gao, Wenbo Jiang, Fulin Chen, Haidong Tan, Jian Wen, and Hong Li

DOI: 10.1364/OL.506207 Received 19 Sep 2023; Accepted 26 Oct 2023; Posted 27 Oct 2023  View: PDF

Abstract: A magnetic field (MF) sensor with stable structure and high sensitivity has been proposed and experimentally verified. We used the water bath method to produce a layer of Fe2O3 nanorods on a tapered few mode fiber (FMF) surface to form a Mach-Zehnder interferometer (MZI). The experiment found that the nanostructure produced on the surface of FMF were particularly stable and firm. Under the action of external MF, the magnetic permeability of Fe2O3 nanorod will change, leading to a change in its refractive index, resulting in a linear shift in the resonance wavelength of MZI. The experimental results showed that the MF sensitivity of MZI reached -0.5348 nm/mT in 10 mT ～ 80 mT. In addition, MZI has a certain sensitivity to environmental humidity and temperature. To eliminate crosstalk, a long-period fiber grating and a fiber Bragg grating are cascaded with MZI to achieve simultaneous measurement of three quantities and eliminate their cross-sensitivity.

Free-space quasi-phase matching

Nazar Kovalenko, Victor Hariton, Kilian Fritsch, and Oleg Pronin

DOI: 10.1364/OL.502825 Received 10 Aug 2023; Accepted 24 Oct 2023; Posted 24 Oct 2023  View: PDF

Abstract: We report a new approach to phase-matching of nonlinear materials based on the free-space multipass cells. This technique is applicable to noncentrosymmetric nonlinear crystals, including crystals, that cannot be birefringent phase-matched or quasi-phase matched by periodic poling. Notably, by using this approach, the crystalline quartz is quasi-phase matched with the demonstrated increase of the second harmonic generation efficiency by a factor of 40. The method can be extended toward UV and THz ranges. This promises to revolutionize experimental nonlinear optics and all applications by increasing the number of available crystals for quasi-phase-matching by at least one order of magnitude and brings fresh motivation for developing novel nonlinear materials.

THz Photodiode Integration with Multi-Octave-Bandwidth Dielectric Rod Waveguide Probe

Shuya Iwamatsu, Muhsin Ali, José Luis Fernández Estévez, Marcel Grzeslo, Sumer Makhlouf, Alejandro Rivera, Guillermo Carpintero, and Andreas Stohr

DOI: 10.1364/OL.504354 Received 08 Sep 2023; Accepted 24 Oct 2023; Posted 25 Oct 2023  View: PDF

Abstract: Photonic integrated circuits play a vital role in enabling THz applications that require multi-octave bandwidth. Prior research has been limited in bandwidth due to rectangular waveguide (WRs) interconnects, which can only support single octave at low loss. To overcome this fundamental limitation, we exploit ultra-wideband (UWB) near-field coupling between planar waveguides and silicon (Si)-based subwavelength dielectric rod waveguides (DRWs) to interconnect THz bandwidth uni-traveling-carrier photodiodes (UTC-PDs) at 0.08–1.03 THz. In a proof-of-concept experiment, the on-chip integrated UTC-PDs demonstrate a UWB operation from 0.1 THz to 0.4 THz. Furthermore, by employing Si DRWs as probes, multi-octave device-under-test characterization of UTC-PDs integrated with UWB transition is enabled with only one DRW probe. The proposed UWB interconnect technology is distinct from previously used WR-based ground-signal-ground probes or quasi-optical free-space coupling since it can provide multi-octave bandwidth and enable on-chip THz circuit integration.

Near-infrared Radiation Induced Attenuation in Nested Anti-resonant Hollow-core Fibres

Sacha Medaer, Tom Bradley, DIEGO DI FRANCESCA, Qiang Fu, Gregory Jasion, Jochen Kuhnhenn, Stefano Meroli, Francesco Poletti, Bernhard Schmauss, Austin TARANTA, Konstantin Vidiajev, Udo Weinand, Natalie Wheeler, Raphael Wolf, and Daniel Ricci

DOI: 10.1364/OL.504167 Received 24 Aug 2023; Accepted 23 Oct 2023; Posted 30 Oct 2023  View: PDF

Abstract: This Letter reports the first spectral radiation induced attenuation (RIA) measurements of nested anti-resonant nodeless hollow-core fibres (NANF). A 5-tube NANF, alongside a solid-core single-mode radiation resistant fibre (SM-RRF), were irradiated under $\gamma$-ray up to 101 kGy ($SiO_2$) and under $X$-ray up to 241 kGy ($SiO_2$). No RIA was observed in the NANF in the second half of the O-band, the S-band, the C-band, and the L-band. The NANF showed a reduction of absorption bands associated with water and $HCl$ under irradiation. Three new attenuation peaks were radiolytically induced and are attributed to the creation of $HNO_3$. These peaks are centered respectively at 1441 nm, 1532 nm, and 1628 nm, with a full width at half maximum (FWHM) of respectively 10 nm, 12 nm, and 12 nm. These results demonstrate that the wide bandwidth range of NANFs is essentially unaffected by radiation, but the internal gas contents of the NANF must be managed to avoid producing undesirable spectral features through radiolytic reactions. Wide spectral regions almost unaffected by the ionizing radiation could open new possibilities for the use of NANF in harsh radiation environments.

Synchrotron-based X-ray Fluorescence Ghost Imaging

Mathieu Manni, Adi Ben Yehuda, Yishay Klein, Bratislav Lukic, Andrew Kingston, Alexander Rack, Sharon Shwartz, and Nicola Viganò

DOI: 10.1364/OL.499046 Received 27 Jun 2023; Accepted 21 Oct 2023; Posted 23 Oct 2023  View: PDF

Abstract: X-ray Fluorescence Ghost Imaging (XRF-GI) was recently demonstrated for x-ray lab sources. It has the potential to reduce acquisition time and deposited dose by choosing their trade-off with spatial resolution, while alleviating the focusing constraints of the probing beam. Here, we demonstrate the realization of synchrotron-based XRF-GI: We present both an adapted experimental setup and its corresponding required computational technique to process the data. This not only extends the above-mentioned advantages to synchrotron XRF imaging, but it also presents new possibilities for developing strategies to improve precision in nano-scale imaging measurements.

Broadband optical properties of Ti3C2 MXene revisited

Daria Panova, Gleb Tselikov, Georgy Ermolaev, Alexander Syuy, Dmitrii Zimbovskii, Olesya Kapitanova, Dmitry Yakubovsky, Arslan Mazitov, Ivan Kruglov, Andrey Vyshnevyy, Aleksey Arsenin, and Valentyn Volkov

DOI: 10.1364/OL.503636 Received 07 Sep 2023; Accepted 13 Oct 2023; Posted 01 Nov 2023  View: PDF

Abstract: The exceptional optical, electrical, and mechanical capabilities of layered transition metal carbides, nitrides, and carbonitrides, called MXenes, revolutionized materials science. Among them, Ti₃C₂ received the most attention owing to the developed synthesis and processing methods, high conductivity, and pronounced plasmonic response. The latter, however, remains controversial with the open question of whether the peak around 800 nm has plasmonic or interband transition origin. To address this issue, we combine spectroscopic ellipsometry and transmittance results with first-principle computations. Their combination reveals that although Ti₃C₂ is a metal, its optical response becomes plasmonic (Re ε < 0) above 1415 nm, in contrast to the previous understanding. In addition to fundamental significance, this dual dielectric/plasmonic optical response opens a path for theranostic applications, as we demonstrated on the example of Ti₃C₂ nanospheres. Thus, our study revisits broadband (300 – 3300 nm) optical constants of Ti₃C₂ and broadens its application scope in photonics.

Wide field time of flight measurements of highly scattering media

André Stefanov, Pascal Tijkorte, Gijs Hannink, Lynn Roth, and Martin Frenz

DOI: 10.1364/OL.498659 Received 23 Jun 2023; Accepted 07 Oct 2023; Posted 30 Oct 2023  View: PDF

Abstract: We present a setup that makes use of a time-resolved single-photon camera to determine the scattering parameters of media. The measurement is realized in a non-contact way, both for the illumination laser and for the detection. By fitting the time-of-flight acquired distributions at different spatial positions with the diffusion equation, we retrieve the scattering coefficients of a highly diffusive isotropic reference media for wavelengths in the range from 540 to 840 nm.