Statistical Evaluation of the Error Rate of the Fiberguide Repeater Using Importance Sampling

Traditional computation of error rates of digital repeaters is often done by assuming that the noise is gaussian in nature. For a linear equalizer, the error rate at a given sampling time can then be easily computed if the signal and standard deviation of the noise are given.1 The fiberguide repeater has essentially three kinds of noise sources. Two noise sources are located in the detector, while the third is a thermal gaussian noise generated by the input stage of the preamplifier (see Fig. 1). The detector, which is an avalanche photodiode is governed by two intrinsic noise processes: the primary photo current, which is a Poisson process, and the avalanche multiplication process which produces the gain in the diode. Neither of these processes is gaussian. The probability density functions (PDF) for the output current of the diode were derived by Personick 23 and Mclntyre. 4 The expressions 745 AVALANCHE GAIN Fig. 1--Optical repeater.