ASK coherent optical communications systems: simplified analysis

Presents a simple approximate analysis of ASK coherent optical communications systems and obtain, for the first time, a closed-form estimate of the bit error rate. The inaccuracy introduced by the approximation analysis is about 0.4 dB. The main application of the presented theory is expected to be in the analysis of practical imperfections (such as a finite IF filter bandwidth and a nonzero laser linewidth) on the system performance.