Flattened comb generation using only phase modulators driven by fundamental frequency sinusoidal sources with small frequency offset

We propose and experimentally demonstrate a simple scheme to generate flattened optical subcarriers at low insertion loss using only phase modulators driven by fundamental frequency sinusoidal sources. A small frequency offset is introduced in the second stage to obtain phase-insensitive, stable, and flattened subcarriers. Theoretical and numerical analysis with experimental results are carried out on this scheme. Twenty-one stable comb tones with 25 GHz frequency spacing are obtained with power difference less than 3 dB. The good bit-error-ratio performance of 160.8 Gb/s polarization-division-multiplexing quadrature-phase-shift-keying signal carried by one selected subcarrier clearly demonstrates the feasibility of this comb generation scheme.