Broadband on-chip photonic spin Hall element via inverse design
The device separates light with different spins, the left-handed component is coupled into the left waveguide, and the right-handed component is coupled into the right waveguide.
A photonic spin Hall (PSH) device sorts photons with different spin states and is a fundamental component of photonic information technologies. However, the PSH effect is rather weak for measurements using bulky and expensive equipment. The metasurface is a promising way to dramatically shrink an optical element to a size suitable for photonic spin devices. Using V-shaped nano-antennas, a metasurface device with a strong PSH effect is demonstrated with normal incidence. The emergence of a variety of Pancharatnam–Berry phase components has led to development of various photonic spin devices. However, most of these metasurface devices suffer from the low efficiency issues. On-chip photonic spin devices are also designed based on spin-orbital coupling by using micro-disks and nano-antennas, but the intrinsic resonance in this design limits the device's bandwidth and prevents the wide use.
The researchers from the Nanophotonics Research Center of Shenzhen University, Prof. Zhenwei Xie, Prof. Ting Lei and Prof. Xiaocong Yuan, proposed and demonstrated an integrated on-chip photon spin Hall device using inverse design. It has both high detection and emission efficiency, and a working bandwidth around 200 nm. Related research results are published on Photonics Research, Vol. 8, Issue 2, 2020 (Zhenwei Xie, Ting Lei, Haodong Qiu, Zecen Zhang, Hong Wang, Xiaocong Yuan. Broadband on-chip photonic spin Hall element via inverse design[J]. Photonics Research, 2020, 8(2): 02000121).
Prof. Xiaocong Yuan says that the photonic spin Hall element is fabricated on a silicon-on-insulator wafer compatible with a standard integrated photonic circuit, and its diameter is only 2.4 μm with 100 nm sized pixels. Therefore, it is expected to realize miniaturized and integrated photon spin devices. The spin light is detected and emitted with efficiencies of up to 22% and 35%, respectively.
This work may have applications for on-chip spin sorting, quantum computing, information processing, and optical communication.
In the future work, the researchers will investigate the phase change material based metasurface device using inverse design and develop controllable photon spin Hall effect devices.
基于逆向设计的宽带片上光子自旋霍尔效应元件
器件对具有不同自旋的光进行分离，左旋分量耦合到左侧波导，右旋分量耦合到右侧波导。
光子自旋霍尔效应（photonic spin Hall）器件可以区分具有不同自旋态的光子，是发展自旋光子信息技术的重要核心器件。但是一般情况下，微弱的光子自旋霍尔效应很难测量，其测量设备庞大且昂贵。超表面以其超薄超轻的特性，具有替代这些传统光学元件的潜力，因而在减小光子自旋霍尔效应器件的体积和尺寸方面具有很大的应用价值。
有研究人员使用超表面V形纳米天线，在垂直入射的情况下实现了超强的光子自旋霍尔效应。随着多种Pancharatnam - Berry相位（几何相位）超表面的出现，研究人员在此基础上设计了各种各样的光子自旋器件。然而，传统的超表面器件大多受限于损耗大、效率低等问题，无法得到实际应用。另外，也有研究人员基于自旋-轨道耦合并使用纳米微盘和纳米天线实现了片上光子自旋器件，但由于器件设计中的固有共振模式限制了其工作带宽，因而也无法广泛应用。
深圳大学纳米光子学研究中心的谢振威助理教授、雷霆副教授、袁小聪教授等研究人员基于逆向设计的原理，结合超表面技术，设计并验证了一种集成的片上光子自旋霍尔器件，它既具有高的检测和发射效率，又具有近200 nm的工作谱宽。相关研究结果发表于Photonics Research 2020年第8卷第2期上（Zhenwei Xie, Ting Lei, Haodong Qiu, Zecen Zhang, Hong Wang, Xiaocong Yuan. Broadband on-chip photonic spin Hall element via inverse design[J]. Photonics Research, 2020, 8(2): 02000121）。
袁小聪教授指出，该光子自旋霍尔器件是在与标准集成光子电路兼容的绝缘体硅片上制造的，它的直径仅为2.4 μm，由100 nm的单元构成，因而有望实现光子自旋器件的小型化和集成化。在1550 nm的工作波长下，该器件的检测效率可以达到22%；而作为自旋发射器时，其峰值效率可以达到35%。
展望未来，该器件有望用于片上光子自旋分类、量子计算、光信息处理和光通信等领域。在后续的工作中，将研究基于相变材料的逆向设计超表面结构，实现动态化可调控的光子自旋霍尔效应器件。