A 2.4GHz axial optical comb from a Fabry-Perot laser self-injection locked to a SNAP microresonator

This work investigates a new operating regime of a Fabry–Pérot (FP) laser diode coupled to a high-Q fiber microresonator based on Surface Nanoscale Axial Photonics (SNAP) platform. Due to a precisely engineered parabolic profile of the effective radius variation in the SNAP resonator, a high density of axial modes with a small free spectral range (FSR) is achieved. We demonstrate stable frequency locking of the laser simultaneously to multiple axial modes, leading to the formation of an equidistant optical frequency comb with a repetition rate of ~2.4 GHz. Transient states with periodic envelope modulation of the spectrum, characteristic of soliton molecule formation, are also observed. The influence of the fiber length between the FP diode and the SNAP microresonator on the spectral purity of generation is discussed.