A two-stage optical frequency comb generator based on polarization modulators and a Mach–Zehnder interferometer

A two-stage optical frequency comb (OFC) generator is proposed based on two polarization modulators (PolMs) and a Mach–Zehnder interferometer (MZI). In the first-stage OFC generator, a group of even-order sidebands and a group of odd-order sidebands are generated with similar powers, respectively, based on a single PolM. By tuning the power difference between the two sideband groups using an MZI, a flat OFC with increased comb-lines can be generated. In the experiment, OFCs with up to 11 comb-lines are generated with good flatness, which is better than most of the previous scheme based on a single modulator. To further increase the comb-line number, a second-stage OFC generator is followed using another PolM, which could increase the comb-line number by a factor of up to 5 theoretically. Performance of the proposed two-stage OFC generator is investigated through simulations and experiments. The results can verify the feasibility of the proposed OFC generator, which is a cost-effective way to generate flat OFCs with a large number of comb-lines.