Generation of a flat optical frequency comb based on a cascaded polarization modulator and phase modulator

A scheme to generate a flat optical frequency comb (OFC) with a fixed phase relationship between the comb lines is proposed and experimentally demonstrated based on a cascaded polarization modulator (PolM) and phase modulator. Because the PolM introduces more controllable parameters compared with the conventional intensity modulator, 9, 11, and 13 comb lines can be generated with relatively low RF powers, or 15, 17, and 19 comb lines can be obtained if high RF powers are applied. The experimentally generated 9, 11, and 13 OFCs have a flatness of 1, 1.3, and 2.1 dB, respectively. The scheme requires no DC bias to the modulators, no optical filter, and no frequency divider or multiplier, which is simple and stable.