Self-injection locking of the gain-switched laser diode

TL;DR

This paper demonstrates that gain-switched laser diodes can achieve self-injection locking with high-Q microresonators, significantly narrowing comb line linewidths and enabling tunable optical frequency combs with wide spacing ranges.

Contribution

It experimentally shows self-injection locking of gain-switched lasers to microresonators and characterizes the resulting ultra-narrow linewidth combs with tunable spacing.

Findings

Achieved sub-kHz Lorentzian linewidth of comb teeth.

Generated tunable optical frequency combs with line spacing from 10 kHz to 10 GHz.

Demonstrated dependence of comb characteristics on modulation and locking parameters.

Abstract

We experimentally observed self-injection locking regime of the gain-switched laser to high-Q optical microresonator. We revealed that comb generated by the gain-switched laser experiences a dramatic reduce of comb teeth linewidths in this regime. We demonstrated the Lorentzian linewidth of the comb teeth of sub-kHz scale as narrow as for non-switched self-injection locked laser. Such setup allows generation of high-contrast electrically-tunable optical frequency combs with tunable comb line spacing in a wide range from 10 kHz up to 10 GHz. The characteristics of the generated combs were studied for various modulation parameters - modulation frequency and amplitude, and for parameters, defining the efficiency of the self-injection locking - locking phase, coupling efficiency, pump frequency detuning.