PERFORMANCE OF SMART LIGHTWAVE RECEIVERS WITH LINEAR EQUALIZATION

Signal processing techniques can be used to reduce linear and nonlinear distortion which occurs in high-speed lightwave systems due to fiber dispersion and nonideal responses of optoelectronic and electronic components. In this paper, the improvement in the performance of 2.5 and 10 Gb/s intensity modulation, direct detection systems is assessed for receivers which utilize an analog tapped delay line equalizer to compensate for signal distortion. Synchronous and fractionally spaced equalizers are evaluated. We consider smart receivers which jointly optimize the decision time, decision threshold and equalizer tap weights under a minimum bit error ratio criterion. This yields the optimum system performance and allows consideration of both reduced distortion and enhanced noise arising from the signal processing. The effectiveness of the equalization is determined as a function of several important system parameters. Three-tap and five-tap synchronous equalizers yield virtually the same improvement in receiver sensitivity. Depending on the system, a five-tap fractionally spaced equalizer with half-bit-period tap spacing may or may not be significantly more effective than a three-tap synchronous equalizer.