On Mode-Spacing Division of a Frequency Comb by Temporal Phase Modulation

Abstract

Mode-spacing division of a phase-coherent optical frequency comb is numerically investigated using temporal phase modulation of a periodic optical pulse train. Different schemes, including Talbot and random phase modulations, are investigated and compared, i.e., concerning the tunability of mode-spacing division factors and the robustness to potential practical deviations on the modulation phase profiles. Talbot phase modulation provides a versatile technique for mode-spacing division of a frequency comb; however, the approach is found to be sensitive to phase deviations under certain design parameters. The results show the difficulty in obtaining experimentally the frequency shift by half mode spacing that is predicted by theory for odd division factors. In contrast, generalized random phase modulation methods, proposed here for the first time, utilize random 0-π or multilevel phase profiles to provide interesting alternative methods for implementation of mode-spacing division of a frequency comb. The use of random 0-π phase modulation simplifies the practical implementation of the scheme as it requires inducing only 0 and π phase shifts. The use of random multilevel phase modulation generalizes the approach by using multiple levels of random phase shifts. Both random phase modulation approaches enable successful mode-spacing division by any designed division factor, and they show a relatively lower sensitivity to phase deviations in the modulation functions.