Generation of flat optical frequency comb based on cascaded modulators and sawtooth wave signal

A novel approach for generating optical frequency combs (OFCs) using cascaded modulators is proposed. Here, the sawtooth wave signal is used to drive a dual-driven Mach–Zehnder modulator (DDMZM) to generate optical frequency comb, and the cascaded phase modulator (PM) is used to flatten the obtained optical frequency comb further. Compared with the traditional schemes, the tunable frequency spacing can be achieved by adjusting the sawtooth wave signal's period, and the high driving voltage is also not required. To generate many comb lines with high flatness, the amplitude and rise time ratio of the sawtooth wave signal are studied in detail. Our results reveal that an optical frequency comb with high flatness is achieved when the amplitude and rise time ratio of the sawtooth wave signal is 2 V and 0.99, respectively. The optical frequency comb with high flatness and tunability will have application in elastic optical networks.