Performance of electrical equalizers in optically amplified OOK and DPSK systems

We study the performance of feed-forward equalizers (FFEs) and decision-feedback equalizers (DFEs) in compensating chromatic dispersion and first-order polarization-mode dispersion (PMD) in optically amplified nonreturn-to-zero on-off keying (NRZ-OOK) and NRZ differential phase-shift-keying (DPSK) systems at 10 Gb/s. We use Monte Carlo simulation of the least-mean-square algorithm to estimate equalizer tap weights. Once stationary tap weights are obtained, we compute the bit-error ratio using an analytical method whose accuracy has been verified by simulation. We find that FFE and DFE offer the greatest improvement when combating first-order PMD with NRZ-OOK, reducing power penalties by about 45%. With NRZ-DPSK, the equalizers offer quite limited improvement.