Temporally controlled wideband optical frequency comb generation based on recirculating frequency shifting

In this paper, the temporal limitation factors of further broadening the bandwidth of the optical frequency comb (OFC) based on recirculating frequency shifting (RFS) is for the first investigated. It is found that the signal evolution in the RFS loop is not just simply the same as the straight-line transmission, but the resonance effect of the loop will dramatically affect the property of the generated OFC. Keeping the frequencies of tones away from the resonance frequencies of the loop as much as possible would avoid the phases of the tones synchronously locked, which could greatly decrease the temporal peak power of the generated OFC. This will relieve the influences caused by the instantaneous effect of erbium doped fiber amplifier (EDFA) and fiber nonlinearity, which, in return, would contribute to expand the spectral range of the OFC without much quality degradation. Finally, as an experimental verification, by adjusting the length of the RFS loop to minimize the resonance, a record 100-tone OFC with 10GHz frequency spacing by just single RFS loop is also successfully realized.