The impact of finite intermediate frequency (IF) on the sensitivity of heterodyne ASK lightwave receivers is examined and quantified. It is shown that certain choices of IF (fIFT=αopt, 3αopt/2, 2αopt, etc.) yield the same performance as infinite fIF where αopt is the optimum IF filter bandwidth when fIF=. The approximate results presented in this paper are within 0.4dB of exact results.

This paper investigates the effect of crosstalk in multichannel coherent optical ASK systems. A closed-form signal-to-noise ratio (SNR) expression as a function of number of channels, channel separation, laser phase noise, intermediate frequency (IF) filter bandwidth expansion factor (α), system bit rate (Rb=1/T), and additive shot noise is presented. When the desired channel is between two channels in the electrical domain, the minimum permissible electrical domain channel spacing for a 1dB sensitivity penalty due to crosstalk is found to be 4.85Rb when α is optimum; and 8Rb when α=5 for νT=0.30 at BER=10-9. A fairly good agreement is found between the results of this work and those of a previous study.