Bit error evaluation of optically preamplified direct detection receivers with Fabry-Perot optical filters

The error performance of a preamplified, direct detection receiver with an optical filter of the Lorentzian type is studied. The analysis takes into account the influence of the optical intersymbol interference (ISI). A closed-form expression of the moment generating function (MGF) of the decision variable is derived. Error probabilities are evaluated from the MGF using a saddlepoint approximation. The Gaussian approximation is also examined. The detection sensitivity in terms of a quantum limit is calculated. The results show that there exists an optimum optical bandwidth, the reason being a tradeoff between the effect of ISI and the spontaneous emission noise. It is also shown that the Gaussian approximation gives a good estimate of the error probability, allowing to find in a simple manner the optimum parameters of optically preamplified, direct detection receiver.