Theoretical and experimental study on improved frequency-locked multicarrier generation by using recirculating loop based on multifrequency shifting single-sideband modulation

We propose and experimentally demonstrate a novel scheme to generate optical frequency-locked multicarrier by using a recirculation frequency shifter (RFS) loop based on multifrequency shifting single-sideband (MFS-SSB) modulation with improved tone-to-noise ratio (TNR) performance. Theoretical study shows that we can generate N subcarriers for each round trip without interference by using MFS-SSB, and the recirculation times are reduced to 1/N of the regular scheme based on single-frequency shifting single-sideband (SFS-SSB) modulation. Finally, the double-frequency shifting SSB modulation is carried out for demonstration in our experiments with a double-carrier source from double ECLs and single ECL with carrier suppression. Using this scheme, we successfully generate more than 95 frequency-locked subcarriers with 15-GHz frequency spacing and TNR larger than 25.3 dB and 23.3 dB, respectively. Compared with the results of a regular SFS-SSB scheme, more subcarriers with improved TNR (10 dB and 8 dB for the 95th subcarrier) are obtained.