Highly flexible optical Nyquist pulses generation based on dual-parallel Mach–Zehnder modulator and intensity modulator

A new scheme for highly flexible optical Nyquist pulses generation is proposed by using a dual-parallel Mach–Zehnder modulator (DPMZM) and an intensity modulator (IM) without any external optical filter. The optical Nyquist pulses generator includes two stages. At the first stage, 2-, 3-, or 5-carrier light sources with two different frequency spacing are generated by utilizing a DPMZM. At the second stage, the light source used as seed light is then sent to IM, and two forms of optical frequency combs with spectral line flatness of less than 0.7 dB can be finally obtained by simply adjusting the DC bias and amplitude of radio frequency signal applied to IM. Ideal sinc-shaped Nyquist pulses are also generated in the time domain with bandwidth from 75 to 225 GHz and repetition rate from 40 to 80 ps. Simulation results show the high flexibility, effectiveness, and practicability of the proposed scheme, which can be applied to future high-capacity optical transmission systems.