锗/硅基外延InAs/GaAs量子点激光器的光学噪声特性研究

High-speed photonic integrated circuits on silicon are of high demand for applications in data centers, supercomputers, on-chip LiDAR and optical communication networks. Among the large variety of optical components, the most challenging one is to integrate laser sources on silicon. This is usually achieved by flip-chip bonding or wafer bonding of III-V semiconductor lasers on the silicon substrate. An alternative approach is to epitaxially grow semiconductor lasers on silicon, which is of low cost and high yield. Since 2010, InAs/GaAs quantum dot (Qdot) lasers epitaxially grown on germanium (Ge), on germanium-on-silicon (Ge-Si), and on silicon (Si) are successfully demonstrated. .In comparison with GaAs-based Qdot lasers, it has been extensively shown that the static performances of Ge or Si (Ge/Si)-based Qdot lasers degrade, due to the epitaxial growth defects including threading dislocations and antiphase domain boundaries. On the other hand, there are few reports on the dynamic performances, which are of prime importance for developing applications. In this project, we propose to investigate the relative intensity noise (RIN) and frequency noise (FN) characteristics of InAs/GaAs Qdot lasers epitaxially grown on Ge/Si. The optical noises in semiconductor lasers originate from quantum noises including spontaneous emission noise and random carrier generation and recombination, and from flicker noises including current source noises and thermal fluctuations. .The investigation includes the following contents: (1) The RIN and the FN at different bias currents and at different temperatures; (2) The resonance frequency and the damping factor extracted from the RIN spectrum; (3) The linewidth broadening factor extracted from the FN, which will be compared with that obtained from the FM/AM method; (4) The impacts of residual optical feedback on the RIN and on the FN, and the critical feedback level; (5) The reduction of the FN and the spectral linewidth using the optoelectronic feedback method..The aims of the investigation are: (1) Unveiling impacts of the Ge/Si substrate and the epitaxial defects on the RIN, the FN, the resonance frequency, the damping factor, and the linewidth enhancement factor; (2) Pointing out the critical feedback level of Ge/Si-based Qdot lasers for different pump currents and for different operation temperature; (3) Narrowing the spectral linewidth of Ge/Si-based Qdot lasers by at least two orders of magnitude..The RIN and the FN characteristics of Ge/Si-based Qdot lasers will be firstly simulated by developing a set of coupled rate equations, which includes Langevin noise sources of all the carriers, the photon and the phase of the electric field. Then, experiments will be performed correspondingly, including measurements of the RIN, the FN, the linewidth broadening factor, and the optical noise behavior with external optical feedback. Finally, the phase noise will be suppressed using the optoelectronic feedback method, through manipulating the feedback strength and the feedback delay time..This proposal is of prime importance both for improving the optical noise properties of Ge/Si-based Qdot lasers, and for designing photonic integrated circuits on silicon.

锗或硅（锗/硅）基集成激光光源的开发是硅基集成光路发展的重点和难点，其中激光器光学噪声性能的研究对于其在光通信、光谱检测和激光雷达等领域的应用有十分重要的意义。本申请项目拟研究锗/硅基外延InAs/GaAs量子点激光器的相对强度噪声和相位噪声特性。研究的主要内容包括锗/硅量子点激光器的相对强度噪声、相位噪声、共振频率、阻尼因子和线宽增加因子特性，激光器光学噪声随残留光反馈的变化行为，以及光电反馈对相位噪声的抑制作用。本项目将首先通过速率方程对锗/硅基量子点激光器的光学噪声特性进行理论模拟，然后通过实验测量表征其光学噪声行为。研究的目标是揭示锗/硅基量子点激光器的光学噪声特性和影响其性能的物理机制，阐明使得激光器失稳的残留光反馈的临界反馈比，并通过光电反馈的方法压缩激光器的光谱线宽。本项目的开展对于理解和改善锗/硅基量子点激光器的光学噪声特性以及硅基集成光路的设计有重要的指导意义。

锗/硅基量子点激光器为硅基光子集成电路提供了可靠的激光源，在激光通信、激光雷达和光计算等领域有重要的应用价值。然而直接外延生长的量子点激光器不可避免的会出现高密度的生长缺陷。因此，本项目主要研究了生长缺陷对锗/硅基量子点激光器光学噪声的影响，包括相对强度噪声和相位噪声。研究发现，生长缺陷通过缩短载流子的寿命增大激光器的相对强度噪声，但是对相位噪声影响不大。此外，生长缺陷会降低激光器的调制带宽并增加其阻尼因子。因此，锗/硅基量子点激光器对传输光路中的残留光反馈更加不敏感，这意味着硅基光子集成电路中不需要集成光隔离器。另外，p型掺杂有利于改善量子点激光器相对强度噪声的温度稳定性。同时，量子点中非激射能态中的载流子会增加激光器的线宽增宽因子和相对强度噪声，但是对相位噪声影响不大。而量子点激光器激发态激射对基态激射的光学噪声和线宽增宽因子有较大影响。此外，研究发现量子点激光器对于未来开发全片上储备池光计算系统有重要的应用价值。

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