Digital equalisation at 10.7Gb/s using maximum likelihood sequence estimation- a present and future technology

Improvements in silicon processing speeds have resulted in integrated circuits that can sample and digitally process 10 Gbit/s data. Signal processing techniques that have radically altered radio communication can now be applied to optical communications to improve tolerance to impairments such as chromatic dispersion and polarisation mode dispersion, as well as transmitter/receiver imperfections. Whereas optical components tend to be expensive to produce, electronics lends itself to integration and mass production, leading to a reduction in network level cost. For low cost systems using direct detection at the receiver, maximum-likelihood sequence estimation (MLSE) is recognised as being the optimum receiver detection method. We present architecture & results from our first generation digital equaliser chip set (DECS). The equaliser requires no previous knowledge of the transmission channel, can adapt to channel changes, is robust against transient behaviour, and has been demonstrated in conjunction with NRZ. The MLSE algorithm may also be used in conjunction with other technologies such as duobinary or directly-modulated lasers to further increase the tolerance to signal distortion and therefore reduce the network cost. We discuss the challenges in a practical implementation of the MLSE