All-fiber random Kerr optical frequency combs.

Optical frequency combs (OFCs) unite the electromagnetic spectrum coherently, and they can be realized in a number of different techniques, e.g., OFCs based on mode-locked lasers, electro-optic modulation of continuous-wave (CW) lasers, CW-pumped ring cavities such as micro-resonators, soliton formation and compression through modulation instability induced by dual-laser pumping, etc. Here, we introduce a different approach, achieving the first random Kerr OFC, the spectral-synthesized analog of a random laser. Based on modulation instability for simultaneous parametric amplification and temporal amplitude compression assisted by the distributed random feedback through Rayleigh scattering within a half-open cavity, trains of solitons are formed and further compressed leading to OFCs with spectral bandwidth over ~ 100 nm, wide comb spacing of ~ 1 nm, and minimum soliton duration of ~ 390 fs. The random Kerr OFC can operate continuously as a robust and flexible device, offering adjustable comb spacing, tunable soliton repetition rate, and tunable gate rate.