Stable Fabry-Perot Optical Frequency Comb Generation Using Differential Phase Detection

We present a stable optical frequency comb (OFC) with a Fabry-Perot (F-P) phase modulator. By measuring the phase variation difference of upper and lower sidebands of the OFC signal, the state variation of the OFC is first precisely detected and then compensated by controlling its bias voltage through a homodyne phase-locked loop. Thanks to the precise differential phase detection, the bias drift induced by the fiber delay variation has been fully eliminated as common-mode noise, and the OFC can remain long-term stable without any additional reference signal. The deviation of the phase difference is merely 0.056 degrees over 3800 s. Moreover, the experiment shows that the OFC can still keep stable under a drastic temperature change, further validating the performance of the proposed stabilization method.