On the performance of electrical equalization in optical fiber transmission systems

A variety of equalizers have been proposed to improve the bit-error rate (BER) of optical fiber communications by reducing the effects of chromatic dispersion (CD), polarization-mode dispersion (PMD), and other fiber impairments. Therefore, it is of interest to establish the ultimate performance of electrical equalizers under different conditions. The results presented here are based on the fact that maximum-likelihood sequence detection (MLSD) obtains the lowest BER of all possible detectors, under mild conditions. Thus, the MLSD performance is a lower bound on the BER of any electrical equalizer. We consider linear channels with PMD (all orders), CD, and the nonlinear effect of the photodetector.