Multiple-frequency-spaced flat optical comb generation using a multiple-parallel phase modulator

We propose multiple-frequency-spaced flat optical comb generation using an electro-optic (EO) multiple-parallel phase modulator. We formulate and clarify the operating conditions in which we can generate optical combs adding the two important functionalities of spectral shaping: (1) multiplication of frequency spacing and (2) spectral flattening. The frequency spacing of the generated comb is enhanced much higher than the EO modulation bandwidth. The spectral shaping is achieved fully through the EO modulation process without relying on any optical filters. This filter-less configuration is advantageous for flexible tuning of wavelength and frequency spacing of the generated combs. The concept is numerically verified, focusing on N×25-GHz-spaced comb generation.