In this work, a method to generate a pulse train based on the strictly negative nonlinear phase shift during the amplification of a dynamic signal in a semiconductor optical amplifier (SOA) in association with frequency filtering is proposed. A 40 ps width pulse train with a huge continuous tunability repetition frequency ranging from 1 MHz to 5 GHz was experimentally demonstrated. The pulse train properties were characterized by methods such as duty cycle tailoring, and SOA injection current variation.
The optical transfer function of a pulsed local oscillator coherent receiver is derived. We point out that the transfer function is the amplitude of the spectral envelope of the locked optical modes of the pulsed local oscillator source. Using quantum theory of homodyne detection, and assuming an additive Gaussian circular optical noise, with a spectral density hν/2, at each optical input port of the optical mixer, a general discussion on the fundamental limit of the Signal-to-Noise Ratio of a pulsed coherent receiver is provided. It includes the influence of the time jitter of the sampling pulses. Results are numerically discussed in the context of time equivalent under sampling technique, but may be obviously extended to any real time sampling of optical signals.