Recirculating Frequency Shifting Based Wideband Optical Frequency Comb Generation by Phase Coherence Control

Recirculating frequency shifting (RFS) has attracted much attention for its advantages in flexible and high-quality optical frequency comb (OFC) generation. As the number of tones increases, the phase coherence of the tones plays a very important role in the stability of the generated OFC. It is found in this paper that by controlling the phase coherence of the tones, the peak-to-average power ratio (PAPR) of the generated OFC will decrease sharply. This will effectively relieve the distortion caused by fiber nonlinearity, which will enable the loop to support more tones under the condition of constant output power. Based on the phase coherence control method, a 100-tone OFC with 10-GHz frequency spacing and a single RFS loop is successfully realized.