Addressing experimental self-generation of frequency combs in III-V/SiN hybrid integrated tunable lasers

We present experimental results featuring the self-generation of optical frequency combs in a III-V/SiN hybrid integrated laser with a frequency selective mirror. We model the laser through a set of time-delayed algebraic equations accounting for longitudinal mode competition, non-zero alpha factor and the narrowband SiN mirror. We are able to produce frequency combs matching the experimental case in terms of bandwidth, free-spectral range and optical frequency spectrum. Supported by our model, we demonstrate that the optical frequency combs occur when the laser becomes CW unstable due to the resonance between the relaxation oscillation frequency and the frequency separation between cavity modes, and efficient four-wave mixing allows for the locking mechanism between optical lines. The comb is characterized by both amplitude and frequency modulation.