Gain-through-filtering enables tuneable frequency comb generation in passive optical resonators

International audienceOptical frequency combs (OFCs), consisting of a set of phase locked equally spaced laser frequency lines, have led to a great leap in precision spectroscopy and metrology since seminal works of Hänsch et al. at the beginning of 21-st century. Nowadays, OFCs are cornerstones of a wealth of applications ranging from chemistry and biology to astrophysics including ultra-precise metrology, spectroscopy, molecular fingerprinting, new generation of LIDARs and others. Driven passive optical resonators constitute the ideal platform for OFC generation in terms of compactness and low energy footprint. We propose here a new technique for generation of OFCs with tuneable repetition rate in externally driven optical resonators based on the gain-through-filtering process, a simple and elegant passive method, due to an asymmetric spectral filtering on one side of the pump wave. We demonstrate a proof-of-concept experimental result in a fibre resonator, pioneering a new technique that does not require specific engineering of the dispersion to generate frequency agile frequency combs