Exact laser line-width requirements evaluation for optical PSK homodyne communication systems with Dither loop

The laser line-width required in PSK homodyne communication systems with Dither phase-locked loop receivers are exactly evaluated. It is shown that second-order phase-locked loops require at least 0.2 pW of signal power per every Hz of laser line-width (this number refers to the system with the detector responsivity 0.94 A/W, damping ratio 0.707, and the phase error standard deviation 10 degrees). This signal power is used for phase locking, and is, therefore lost from the data receiver. This study for the first time shows the imperfect-phase-recovery-induced power penalty as a function of laser line-width. It can be estimated from the theoretical result that an optimal dither phase locked-loop receiver requires the laser line-width as Delta upsilon <= 3.14 x 10(-5) x R-b, where R-b is the system bit rate. This number refers to the system with power penalty of 1 dB at BER = 10(-10). (C) 2013 Elsevier GmbH. All rights reserved.