Self-stabilization of an optical frequency comb using a short-path-length interferometer.

We stabilized the repetition rate of an optical frequency comb using a self-referenced phase-locked loop. The phase-locked loop generated its error signal with a fiber-optic delay-line interferometer that had a path-length difference of 8 m. We used the stabilized repetition rate to generate a 10 GHz signal with a single-sideband phase noise that was limited by environmental noise to -120  dBc/Hz at an offset frequency of 1 kHz. Modeling results indicate that thermoconductive noise sets a fundamental phase noise limit for an 8 m interferometer of -152  dBc/Hz at a 1 kHz offset frequency. The short length of the interferometer indicates that it could be realized as a photonic integrated circuit, which may lead to a chip-scale stabilized optical frequency comb with an ultralow-phase-noise repetition rate.