Generation of Flat Optical Frequency Comb Based on a DP-QPSK Modulator

An approach to generate flat optical frequency comb (OFC) is proposed and experimentally demonstrated using a single integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. By adjusting six dc bias points and two modulation indices of the modulator, the OFC with adjustable comb number and exactly the same intensity can be theoretically generated according to the equations derived from the DP-QPSK modulation model. Experimental results show that the proposed OFC generator can produce 7, 9, 11, and 13 lines with a spectral flatness of 0.96, 1.13, 2.01, and 1.17 dB, respectively. The unwanted-mode suppression ratio of the generated 7, 9, 11, and 13 lines OFCs are 10.33, 9.54, 6.79, and 10.45 dB, respectively. In addition, the generated OFC exhibits good frequency tunability. The nine-lines OFCs with frequency spacing of 6.02, 7.02, 8.02, and 9.02 GHz are experimentally generated.