Coherent Lightwave Communications

Abstract

The chief objective of this paper is to develop a fundamental understanding of the effects of laser phase noise on the performance of coherent lightwave communication systems. A comprehensive treatment applicable to a wide variety of coherent receiver designs under a broad range of conditions is provided. Our models and analytical tools are developed in sufficient detail to encompass a broad range of applications. Formulas are derived for the bit error rate in homodyne and heterodyne Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK), Frequency Shift Keying (FSK) and on‐off keying. Estimates are provided of the penalties accrued due to phase noise. Based on detailed mathematical analysis and estimates, we made several findings. Near quantum‐limited receiver sensitivity can be achieved with PSK using homodyne detection only at signaling rates 3000 times greater than the laser linewidth. A receiver sensitivity 3 to 6 decibels poorer than the quantum limit can be achieved with heterodyne rather than homodyne detection. DPSK, for example, can operate at rates only 300 times greater than the laser linewidth. At lower rates, FSK is an attractive candidate. It can be designed to be extremely tolerant of phase noise by using wide frequency deviations.

Phase Noise Countermeasures for Coherent Optical Phase Shift Keying

“…Fig. 1: Conventional coherent homodyne PSK receiver laser phase noise, there is a minimum bit rate below which the required error probability can never be achieved, regardless of what the received signal strength is [1,2]. However, the degradation in system performance due to laser phase noise can be reduced by operating the transmission system at high bit rates.…”

“…In this paper, we examine the possibility of using a conventional binary phase shift keying (PSK) modulation. Previous studies developed understanding of the effects of laser phase noise on the performance of coherent lightwave transmission systems using various modulations [1][2][3][4][5][6]. Mazo [7] considered high rate redundancy provided by repetition or by more complex coding techniques to counter the deleterious effects of laser phase noise.…”

A comparison of sensitivity degradations for optical homodyne versus direct detection of on-off keyed signals

“…In this analysis we obtain a sensitivity corresponding to Peo = Pe I' This represents an upper bound, since it may be possible to obtain a better sensitivity by optimizing Peo and Pel sep arately to produce an average error probability below 10-9 . For direct detection eL = 0 and, in the case of no noise sources other than shot noise, the integrator output No is identically zero (without fluctuations) when a binary "0" is received. Thus the threshold C may be set such that any detected signal will be counted as a "1" , as shown in and (9) or (10) The threshold C can be numerically evaluated from (9) and substituted in (10) to yield the required value of NI from which e� can be found.…”

FDM Transmission with ASK Modulation and Optical Multiport Receiver

“…The phase noise is supposed to be a Wiener process [12,13] and the filter bandwidth W is assumed equal to z(R + kB L ), where B L is the sum of the transmitting and local laser linewidths, z = 1 for homodyne detection, z=(l + ω, Ρ /2πΚ) for intradyne detection and z=2 for heterodyne detection, k is an enhancement coefficient that can be chosen equal to 8 [13,14]. The double summation in (15) and (16) represents the intermodulation term.…”