Delay, linewidth and bandwidth limitations in optical phase-locked loop design

Maximum laser linewidth and loop gain in an optical phase-locked loop (OPLL) are calculated as a function of loop delay and filter bandwidth, using a cycle-slipping criterion. It is shown that a loop delay of less than 2 ns would permit the realisation of OPLLs using the recently reported submegahertz linewidth monolithic tunable semiconductor lasers.