Influence of Time Delay on Pull-in Behaviour of Dither Optical Phase-Lock Loop

This paper analyses the impact of loop propagation delay on the pull-in behaviour of dither optical phase-lock loop (OPLL), neglecting the shot noise and phase noise of the loop. Analytical expressions of pull-in voltage, pull-in range, and acquisition time are presented in terms of all the parameters affecting the loop acquisition. Also, the influence of dither signal on the pull-in performance of dither OPLL is studied in the presence of loop propagation delay. It is found that the time delay associated with the filtering process within the loop gives rise to degradation in acquisition capability. In addition, dither signal allows pull-in from much larger frequency offset, decreases the acquisition time of the loop, and improves the acquisition characteristics of dither OPLL in terms of the pull-in voltage in the presence of loop delay. The tracking performance of dither OPLL regarding phase-error variance is investigated considering laser phase noise, photo-detector shot noise, and loop propagation delay. Simulation results are given in support of the analytical results.