Low-Noise 1.3 µm InAs/GaAs Quantum Dot Laser Monolithically Grown on Silicon
Schematic of monolithic QD laser on Si.
Silicon (Si) photonics is one of the most buoyant technologies in the world today and is set to revolutionize optical communications and interconnects. However, the lack of a practical Si-based laser has become a severe limitation. This is because that Si is an inefficient emitter. Much effort has been directed toward monolithic integration of III-V lasers with Si with a view to achieving low-cost, large-scale integration of photonics circuits. Recently, monolithic integration of III-V lasers on Si has shown substantial advances by utilizing self-assembled quantum dots (QDs) as the active region. Their unique properties, in particular, the enhanced tolerance to defects, have allowed rapid development in 1.3 μm III-V QD lasers grown directly on Si substrates, including low threshold current, high output power, high operation temperature, and extremely long lifetime. Other than that, the relative intensity noise (RIN), is the key figure of merit to investigate the laser performance in fibre-optic communication networks, since the RIN leads to a limited signal-to-noise ratio (SNR), and thus an increased bit-error rate (BER) restricts the data transmission rate and distance. Unfortunately, monolithic III-V QD laser on Si with a low RIN level has not yet been reported.
Very recently, researchers from Prof Huiyun Liu's MBE Group of University College London (UCL) have demonstrated a high-performance and low-noise electrically pumped continuous-wave (CW) 1.3 μm single transverse mode InAs/GaAs QD lasers grown directly on Si with threshold current as low as 12.5 mA at room temperature (RT), a maximum lasing operation temperature up to 90°C, and an ultra-low RIN measured to be in the level between -150 and -160 dB/Hz. Attributing to this low RIN feature, 25.6 Gb/s data transmission supporting standard 100 Gb/s solution over 13.5 km single mode fibre has been demonstrated by this Si-based QD laser. The experimental results indicate that the monolithically integrated InAs/GaAs QD laser on Si is suitable for future low-cost data transmission in hyper/inter-data centres and metropolitan data links. Related results are published in Photonics Research, Vol. 6, Issue 11, 2018 (M. Liao et al., Low-Noise 1.3 µm InAs/GaAs Quantum Dot Laser Monolithically Grown on Silicon).
Dr Siming Chen, Royal Academy of Engineering Research Fellow hosted by UCL, the principal investigator of this project, believes that this work has significance for high-performance practical on-chip Si-based laser. The further work will focus on the integration of on-chip lasers with other Si-based photonic components, both actively and passively, to develop end-to-end Si photonics integrated photonics circuits by the monolithic method.
低噪声1.3 μm硅基外延量子点激光器
硅基单片量子点激光器
近年来在光通信、光互连的巨大需求推动下，硅基光电子集成技术蓬勃发展。但由于硅的发光效率极低，硅基光源这一核心器件成为制约其发展的瓶颈。将发光特性优良的III-V族化合物半导体材料直接外延生长到硅衬底上，并制作高性能硅基半导体激光器一直被视为实现大规模、低成本、高性能硅基光源和光电集成芯片的关键技术。近年来，人们利用自组装量子点独特的缺陷免疫能力，在1300 nm通信波段的硅基光源方面取得了丰硕的成果，包括低阈值、高功率、高温以及超长使用寿命在内的重要激光性能都已经实现。除此之外，在实际的通信应用中，激光器光源的强度噪声一直是一个至关重要的指标，过高的强度噪声会导致低信噪比和高误码率，从而限制信息传输的带宽和距离。可遗憾的是近年来一直没有硅基低噪声量子点激光器的报道。
最近，来自英国伦敦大学学院刘会赟教授分子束外延课题组的研究人员，实现了高性能与低噪声的硅基外延InAs/GaAs量子点单横模激光器。该激光器的波长在1300 nm通信波段，其阈值电流仅有12.5 mA，最高工作温度可达90 ℃，相对强度噪声水平低至-150~-160 dB/Hz。得益于优秀的低噪声性能，该激光器还实现了在25.6 Gb/s 的传输速率下13.5 km的单模光纤数据传输。该传输速率可为100 G太比特以太网的实现提供解决方案。这项研究成果将硅基外延激光器的性能推进到了接近高速光通信实用器件的水平，为未来的大规模光电集成奠定了基础。相关结果发表在Photonics Research 2018年第6卷第11期上 (M. Liao et al., Low-Noise 1.3 µm InAs/GaAs Quantum Dot Laser Monolithically Grown on Silicon) 。
英国皇家工程院研究员、该项目的负责人陈思铭博士表示，这项工作对实现高性能、可实用硅基光源有着重要的意义。在未来的研究中，该团队将致力于将这些高性能硅基激光器与其他有源以及无源硅基器件进行单片集成，从而实现高性能、低成本的硅基外延片上集成芯片。