A Broadband, Rectangular, and Self-Sustained Optical Frequency Comb Generation Employing Recirculation Frequency Shifter

To generate a self-sustained rectangular optical frequency comb (OFC) with tunable spacing and bandwidth, we propose and experimentally demonstrate a novel scheme by using an optoelectronic oscillator employing recirculation frequency shifter (RFS) loop. In this scheme, the oscillating signal is separated to drive the Mach–Zehnder modulator (MZM) in the oscillation loop and the inphase/quadrature modulator in the RFS loop separately. Then more than 50-tone OFCs, which have a rectangular spectral profile and the flatness better than 6 dB, are obtained with 8-GHz spacing and 10-GHz spacing by tuning the center frequency of the microwave filter respectively. Besides, the phase noise of the driving signals are both lower than
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110 dBc/Hz at 10 kHz offset frequency.