ИСТИНА

Optical frequency combs revolutionized metrology and experimental physics and were marked by Nobel Prize in 2005 (J.Hall, T.Hänch). The advent of microresonator based Kerr combs [1] opens a path to novel applications where traditional combs requiring bulky apparatus cannot be used. In this case, frequency comb is formed spontaneously in optical ring-type or whispering gallery microresonator in four-wave mixing cascaded processes. Though initial expectations were somewhat mitigated by intrinsic chaotic character of first generation combs [2], it was shown than coherent mode-locked combs associated with solitons are still possible without significant additional efforts on different platforms [3, 4]. Key advantages of microresonator based frequency combs are their compact form factor, high power per comb line, and ability to access microwave repetition rates, relevant for many application including high capacity telecommunications or microwave photonics. It was also revealed that coherent Kerr combs are possible not only for anomalous group velocity dispersion necessary for bright optical solitons but also in normal dispersion systems using the so-called “platicons” – solitonic like flat-toped waveforms [5]. This opens the ability to generate coherent combs in the UV or mid IR spectral range with the gain bandwidth limited only by the transparency window. Dynamical probing of soliton states allows for controlled switching and locking of multiple soliton states down to single soliton per roundtrip mostly convenient for applications [8]. Moreover, slow frequency tuning of the pump laser augmented with phase or amplitude modulation corresponding to the free spectral range of the microresonator provides reliable convergence of initially excited chaotic comb to mode locked single-soliton state.