Analysis of Gaussian Optical Receivers

We present some analytical methods for Gaussian optical receivers whose impulse responses of optical and electrical filters are Gaussian. We obtain the Gaussian optical receiver's eigenmodes exactly in frequency domain. Their eigenfunctions are Hermite functions multiplied by a common phase factor. Using these eigenmodes, we investigate the probability distribution functions of the electrical filter's output before the decision circuit. We derive a bit-error rate (BER) expression in a closed form using the lowest-order eigenmode. It is valid when the optical filter bandwidth is comparable to the modulation bandwidth as in conventional high capacity optical wavelength-division multiplexing transmission systems. The BER expression can be applied also to non-Gaussian optical receivers.