Crosstalk and prefiltering in a two-channel ASK heterodyne detection system without the effect of laser phase noise

This technical memorandum reports an experimental study on the crosstalk in a two-channel ASK heterodyne detection system where the effect of laser phase noise is negligible. The purpose of the study is to establish criteria for the channel separation in multichannel ASK heterodyne transmission systems. 

Four results are described: (1) the dependence of the crosstalk penalty on the radio of channel separation to bit rate and on the optical power level of the image band, (2) comparison of the measured crosstalk penalties with the ones obtained from a simple model, (3) the effect of electrical prefiltering on the crosstalk penalty, and (4) demonstration of simultaneous broadcasting of two video/audio channels operated at 45 Mb/s using AT&T VIVID(TM) teleconferencing systems. 

The main conclusions are: (1) the channel separation can be as low as four times the bit rate without incurring any crosstalk penalty as long as the optical power of the image band is comparable to the optical power of the signal band, and (2) electrical prefiltering of the transmitted signals significantly reduce the crosstalk penalty in multichannel ASK heterodyne systems where the effect of laser phase noise is negligible.