Semiconductor laser mode locking stabilization with optical feedback from a silicon PIC

TL;DR

This paper demonstrates stabilization of semiconductor mode-locked lasers using optical feedback from a silicon photonic integrated circuit, significantly reducing RF linewidth and enhancing coherence despite back-reflections.

Contribution

It introduces a method to stabilize mode-locked lasers with integrated optical feedback, improving linewidth and coherence without the need for downstream isolators.

Findings

RF linewidth reduced from 15.01 kHz to 2.77 kHz

Linewidth reductions achieved despite back-reflections

Enhanced laser coherence demonstrated

Abstract

Semiconductor mode-locked lasers can be used in a variety of applications ranging from multi-carrier sources for WDM communication systems to time base references for metrology. Their packaging in compact chip- or module-level systems remains however burdened by their strong sensitivity to back-reflections, quickly destroying the coherence of the mode-locking. Here, we investigate the stabilization of mode-locked lasers directly edge coupled to a silicon photonic integrated circuit, with the objective of moving isolators downstream to the output of the photonic circuit. A 2.77 kHz 3 dB RF linewidth, substantially improved compared to the 15.01 kHz of the free running laser, is obtained in the best case. Even in presence of detrimental reflections from the photonic circuit, substantial linewidth reductions from 20 kHz to 8.82 kHz, from 572 kHz to 14.8 kHz, and from 1.5 MHz to 40 kHz are realized.