An optical frequency comb generator using a modified single-sideband recirculating frequency shifter scheme adopting a linear IQ modulator as the kernel device (SSB-RFS-LIQM) is proposed. The optical comb lines generated by the proposed scheme possess good features such as extreme flatness and high optical signal-to-noise ratio (OSNR), compared to the quality we can obtain when we use a conventional IQ modulator in the SSB-RFS structure (called SSB-RFS-CIQM scheme). The mechanism of how the SSB-RFS-LIQM works is carefully analyzed with analytical and numerical methods. With the capability of strong suppression of high-order crosstalk and less demand of the gain of erbium-doped fiber amplifiers (and hence less amplified spontaneous noise induced) in the loop, 5.5 dB OSNR improvement can be achieved when 100 extreme flat comb lines are generated using the SSB-RFS-LIQM scheme compared to using the SSB-RFS-CIQM scheme.
A comprehensive investigation is done on a high-quality frequency comb or multicarrier generation using a single-sideband modulation based recirculating frequency shifter (SSB-RFS), which has shown a good capability to provide a large number of frequency-locked carriers for terabits transmission. The dominant factors, such as I/Q modulator, direct current-bias, radio-frequency signal, and band pass filter, are analyzed theoretically and experimentally in terms of the metrics such as flatness, signal-to-noise ratio, and stability. The achieved 69 flat tones by noise suppressed SSB-RFS are presented. An example of SSB-RFS based 2.56 Tb/s PDM-RZ-16QAM 792 km transmission is illustrated, which is enabled by the 20 high-quality carrier tones generated with the optimally operated SSB-RFS source.