Optimum filtering for optically preamplified direct detection: the influence of photon-count statistics

The quantum limited bit error rate for optical communications systems is calculated in case of intensity modulation and optically preamplified direct-detection. The impact of optical and electrical filtering onto the effective photon-count statistics is accounted for, in correspondence to different combinations of optical and electrical filters. The optimum values of the optical and electrical bandwidths, which minimize the receiver sensitivity, are calculated and compared with the values obtained by means of the commonly used Gaussian approximation.