Spectral Filtering Characteristics of a Quantum-Dash Fabry-Pérot Laser and Its Implications on 40 Gb/s XPM Based Optical Retiming Performance

The implications of filtering the emission from a quantum-dash Fabry-Pérot laser, which is actively mode locked by injection of a 40 Gb/s return-to-zero on-off-keyed signal, are investigated in the context of all-optical retiming based on cross-phase modulation in a highly nonlinear fiber. Using the measured complex optical spectrum, it is shown that a filtered clock signal with six laser modes exhibits the most suitable pulse shape for broadening the spectrum of a co-propagating data signal in the highly nonlinear fiber. It is also shown that for a filtered clock signal with six laser modes, simulated Brillouin scattering in the fiber is effectively suppressed. All-optical retiming using an appropriately filtered clock signal yields a root-mean-square timing jitter of 420 fs for an input signal with an optical signal-to-noise ratio of 22 dB (0.1 nm noise bandwidth).