Delayed Single-Tap Frequency-Domain Chromatic-Dispersion Compensation

A long-haul transmission of 100 Gb/s without optical chromatic-dispersion (CD) compensation provides a range of benefits regarding cost effectiveness, power budget, and nonlinearity tolerance. The channel memory is largely dominated by CD in this case with an intersymbol-interference spread of more than 100 symbol durations. An efficient implementation of digital CD compensation is feasible by frequency-domain (FD) filtering. Still the large size of the Fourier transform requires a high gate-count and a large chip size. We propose a new FD filtering on the basis of a nonmaximally decimated discrete Fourier transform filter bank with a trivial prototype filter and a delayed single-tap equalizer per sub-band. This method, which can be regarded as an extension to the popular overlap-save method, allows us to increase the CD tolerance drastically. At the same time, the implementation complexity is not altered apart from adding simple memory elements realizing sub-band delays. With this technique, the uncompensated trans-Pacific transmission becomes feasible with the digital CD compensation.