Figure 6. Frequency and time-domain representation of the generated sinc-shaped Nyquist pulses.

Pulse duration and repetition rate can be easily modified by adjusting the bias voltage of the modulators as well as the frequency and amplitude of modulating signals. Frequency combs with different bandwidth and number of spectral components have been experimentally generated. (a) Measured spectrum and (b) measured time-domain waveform of a comb generated with N=9 spectral components separated by Δf=10 GHz, and expanding over a bandwidth of 90 GHz. (c) Spectrum and (d) time-domain waveform of a comb generated with N=10, Δf=10 GHz, and bandwidth of 100 GHz. (e) Spectrum and (f) time-domain waveform of a comb generated with N=15, Δf=6 GHz, and bandwidth of 90 GHz. (g) Spectrum and (h) time-domain waveform of a comb with N=6, Δf=26 GHz, and an extended bandwidth of 156 GHz. The comb has been spectrally broadened using the second-order sidebands of the first MZM. A power difference among spectral components lower than 0.2 dB is obtained in all cases. The shaded boxes in a,c,e and g represent the theoretical Nyquist bandwidth of the generated sinc pulses. Spectral measurements are obtained with a resolution of 0.01 nm, temporal waveforms acquired with a 500-GHz optical oscilloscope using a sampling interval of 0.2 ps and two time-averaged traces. Only the waveform in h is measured with eight times averaging.