Comb generator for 100 Gbit/s OFDM and low-loss comb-line combiner using the optical inverse fourier transform (IFFT)

The generation of comb spectra is essential for optical OFDM transmitters. We describe a simple solution to this problem, feeding a dual drive Mach-Zehnder modulator with a 12.5 GHz sinusoidal at one arm and with a 25 GHz sinusoidal at the other arm separately. Up to eight optical subcarriers with 12.5 GHz spacing and a spectral flatness of <; 1 dB can be produced. Much lower drive voltage swings are required than with other techniques reported so far. The modulated optical subcarrier fields are multiplexed to a compound field employing a lossless optical inverse Fourier transform circuit. Further, this circuit strongly suppresses inter-subcarrier cross-talk.