Phase noise reduction of a 2 μm passively mode-locked laser through hybrid III-V/silicon integration

• Main Authors: Li, Xiang, Sia, Brian Jia Xu, Wang, Wanjun, Qiao, Zhongliang, Guo, Xin, Ng, Geok Ing, Zhang, Yu, Niu, Zhichuan, Tong, Cunzhu, Wang, Hong, Liu, Chongyang
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2022
• Subjects: Engineering::Electrical and electronic engineering; Quantum-Dot Lasers; Transmission
• Online Access: https://hdl.handle.net/10356/159840
• Institution: Nanyang Technological University

Passively mode-locked semiconductor lasers are promising for a wide variety of chip-scale high-speed and high-capacity applications.However, the phase noise/timing jitter of such light sources are normally high, which restricts their applications. A simple and low-cost chip-scale solution to address this issue is highly desired. In this work, a two-section GaSb-based passively mode-locked laser (MLL) emitting in the 2 m wavelength band with a fundamental repetition frequency of 13.35 GHzis presented.Dramatic phase noise reduction is achieved through its hybrid integration with a silicon photonic circuit which provides chip-scale optical feedback to the MLL.Under a fixed laser bias condition, more than 50 improvement of radio frequency linewidth to sub-kilohertz level is realized by carefully adjusting the feedback strength (via a p-i-n junction-based variable optical attenuator) and optical length of the feedback loop (via integrated heater on the silicon waveguide). The phase noise reaches 113 dBc=Hz at 1 MHz offset with integrated timing jitters of 274 fs (100 kHz to 100 MHz) and 123 fs (4 to 80 MHz). At the same time, the pulse-To-pulse jitter reaches as low as 7.8 fs/cycle. These values are record low for 2 m passively mode-locked semiconductor lasers. Our results prove the feasibility of MLL noise reduction with the chip-scale hybrid III-V/silicon integration method, bringing low-noise light sources to the silicon platform. Moreover, this work also suggests the potential miniaturization of various other functional setups with the same method.