Relative stability of first-order and second-order optical phase-locked loop considering non-negligible propagation delay

The effect of loop delay on the relative stability of first- and second-order optical phase-lock loop (OPLL) is analyzed. The gain margin and phase margin for OPLL with modified first-order loop filter and active low-pass loop filter are demonstrated considering all the parameters affecting the loop stability. The tracking performance of OPLL in terms of phase-error variance is highlighted considering shot noise, white frequency induced phase noise and loop propagation delay in stable operating condition, too.