Frequency stability of a 10 GHz optical frequency comb from a semiconductor-based mode-locked laser with an intracavity 10,000 finesse etalon.

An optical frequency comb is constructed using a semiconductor gain medium with a fiber-coupled external cavity and stabilized to an intracavity 10,000 finesse etalon, which is temperature stabilized and held in a vacuum chamber at 10(-6)  Torr. Optical frequency stability measurements show that the comb has a reduced sensitivity to environmental fluctuations. An upper limit on the optical frequency variation of 100 kHz over >12  min of continuous operation is measured using a real-time spectrum analyzer. This measurement is limited by the linewidth of the reference source, and further measurements with a frequency counter show a fractional deviation of 2×10(-11) at 50 ms. Furthermore, out-of-band ASE rejection is shown to be >36  dB, a tenfold improvement over that of a laser with a 1000 finesse FPE.