A highly effective technique for setting the power preemphasis in WDM optical systems

In wavelength-division-multiplexing (WDM) transmission systems, proper preemphasis of the input-channel powers is a key to optimizing the system performance. We present a novel technique for iteratively optimizing the preemphasis when many transmission effects can take place. The technique requires only the knowledge of the transmitted and received per-channel power values and of the uncorrected bit error rates taken from the forward-error-correction (FEC) chips. We first describe the procedure and test it using numerical simulations. We then demonstrate the technique in a realistic environment using a WDM 8 × 10-Gb/s laboratory test bed, where power preemphasis is automatically found by means of a common personal computer. Both numerical and experimental tests show that the proposed preemphasis is able to compensate for several impairments, including significant spread of receiver sensitivity, gain tilt of the optical amplifiers, significant third-order uncompensated dispersion, as well as single-channel nonlinear impairments.