Coherent walk and lock in driven fast-gain frequency-combs

Abstract

Locking multiple modes into a frequency comb is key for multiple metrological applications, and a great effort has been therefore invested in this challenge over the last decade. The most common techniques are based on either nonlinearities or modulation of the cavity, while the latter is considered the more controllable method to produce frequency combs. The modulation couples cavity modes and creates a lattice in a synthetic dimension with coherent walk dynamics, but typically these dynamics are overthrown by the dissipative processes, leading to a spectrum that is narrow relatively to the full frequency ladder potential. Here we propose and demonstrate that by using fast-gain we preserve the full potential of the coherent walk and lock the frequency comb at its maximum possible bandwidth. Moreover, we find in our system a unique regime of dissipative fast-gain Bloch oscillations. We demonstrate these dynamics in RF-modulated quantum cascade laser ring devices.