Almost Zero-Jitter Optical Clock Recovery Using All-Optical Kerr Shutter Switching Techniques

In this paper, a new all optical phase-locked loop (OPLL) is proposed and analyzed. The scheme relies on using two optical Kerr shutters to reveal the OPLL´s error signal. The set of optical Kerr shutters and the subsequent low-speed photodetectors realize two nonlinear cross-correlations between the local clock pulse stream (called pump in Kerr shutter notations) and the time-shifted replicas of the incoming received data signal (called probe). The outputs of the cross-correlators are subtracted to form the error signal of the OPLL. We characterize the mathematical structure of the proposed OPLL and identify its two intrinsic sources of phase noise, namely, randomness of the received optical data pulses and the photo-detectors´ shot noises. The effects of the noise sources on the proposed OPLL performance are investigated, using the power spectral densities (PSDs) of the signals involved in the OPLL. Finally, PSDs are used to obtain a mathematical expression for the timing jitter. The analytical results show that only the shot noises due to photodetectors affect the OPLL performance, whereas the randomness nature of the incoming data signal has no effect on timing jitter of the proposed OPLL. The numerical results exhibit a sub-femtosecond timing jitter, which is considered to be extremely low and negligible in comparison to the extrinsic noises to OPLL usually originated from the electronic devices.