Direct chip-scale optical frequency divider via regenerative harmonic injection locking

A novel optical frequency division technique, called regenerative harmonic injection locking, is used to transfer the timing stability of an optical frequency comb with a repetition rate in the millimeter wave range (∼300GHz) to a chip-scale mode-locked laser with a ∼10GHz repetition rate. By doing so, the 300 GHz optical frequency comb is optically divided by a factor of 30× to 10 GHz. The stability of the mode-locked laser after regenerative harmonic injection locking is ∼10^-12 at 1 s with a 1/τ trend. To facilitate optical frequency division, a coupled opto-electronic oscillator is implemented to assist the injection locking process. This technique is exceptionally power efficient, as it uses less than 100µW of optical power to achieve stable locking.