  Narrow linewidth lasers and optical frequency combs generated with
mode-locked lasers revolutionized optical frequency metrology. The advent of
soliton Kerr frequency combs in compact crystalline or integrated ring optical
microresonators opens new horizons for applications. These combs, as was
naturally assumed, however, require narrow-linewidth single-frequency pump
lasers. We demonstrate that a regular multi-frequency Fabry-Perot laser diode
self-injection locked to an optical whispering gallery mode (WGM)
microresonator can be first efficiently transformed to a single-frequency
ultra-narrow-linewidth source and then to coherent soliton comb oscillator with
low power consumption and possibility of further integration.
