Photon point process for traveling-wave laser amplifiers

The authors determine the evolution of the photon point process of a light beam as it passes through a traveling-wave laser amplifier (TWA). In particular, when coherent light is presented to the input of the amplifier, the output photon statistics are characterized by a marked-Poisson (MP) point process, which has a noncentral-negative-binomial (NNB) output photon-number distribution (PND). Using this distribution we calculate the probability of error (PE) for an ON-OFF keying (OOK) direct-detection photon-counting communication system, and show that the results differ somewhat from those obtained when the Gaussian-PND approximation is used. It is shown that receiver performance is optimized by filtering the amplifier output. Analysis of the point process is of interest because it permits the time response of the amplifier to be determined; this, in turn, allows the effects of intersymbol interference to be calculated