Optical Sinc-Shaped Nyquist Pulses Generation From Frequency-Quadrupled Rectangular Frequency Comb

Frequency-quadrupled rectangular optical frequency comb (OFC) generation with Nyquist temporal waveforms using a dual-parallel Mach-Zehnder modulator (DP-MZM) and a remodulation structure is proposed. The remodulation structure is formed by a coupler, a photodiode, and an intensity modulator. Its function is similar to optical carrier suppression (OCS) modulation index amplifier, which can achieve the modulation index improve of approximately 77.9% in the OCS modulation. This result in no special modulation index is needed in the proposed scheme. By using a 4 GHz sinusoid signal, a 4-tones frequency-quadrupled OFC with sideband spacing of 16 GHz and flatness within 0.5 dB is experimentally generated. The temporal waveform is sinc-shaped Nyquist pulse with duty cycle 23% and the repetition rate is quadrupling that of the local oscillator frequency, which shows great potential in generating a cost-effective pulses. Moreover, being benefited from the filter-free structure, the high flexibility of the generated Nyquist pulse has also been demonstrated.