Capacity and Cut-off Rate for Optical Communication Systems Using Photon-Counting Techniques

Numerical computation of the capacity of binary optical channel using photon-counting techniques have been performed. The results obtained show that the so-called two-photon coherent source (TCS) provides a better transmission of the optical information than ideal laser as already demonstrated by Yuen and Shapiro and also by Helstrom from the probability of error point of view. On the other hand rather than using capacity as the criterion, the R cut-off rate is taken as the practical measure of communication performance of the channel. This cut-off rate is calculated in different cases and for soft and hard decisions. A method of calculation to bound R is developed from the relationship between the channel reliability rate function and the probability generating function. This simple method is thus utilized to compare the performance of the channel with TCS and those obtained with ideal laser.