Abstract: In an over-sampled maximum-likelihood sequence estimation (MLSE) receiver system, the optimal sample spacing is determined for a variety of conditions. In an illustrative implementation, the system includes an optical filter for tightly filtering an incoming optical data signal with an on-off-keying (OOK) non-return-to-zero (NRZ) format, followed by an optical-to-electrical converter, an electrical filter, a sampler, and a MLSE receiver. The sampler samples the filtered electrical data signal twice each bit period with unequal sample spacings. For wide optical filtering bandwidths, the optimal sample spacing occurs at less than 50% of a bit period. For narrow bandwidths, the optimal sample instances occur closer to the maximum eye opening.

Abstract: Severe inter-symbol interference (ISI), introduced by narrow-band optical filtering in high spectral efficiency wavelength-division multiplexed (WDM) systems to avoid coherent WDM crosstalk, can be substantially mitigated by the use of maximum-likelihood sequence estimation (MLSE) reception. Compared to conventional threshold detection, the use of an MLSE receiver allows, for example, a 22% reduction in optical receive filter bandwidth. For tight optical filtering, the MLSE receiver benefits from taking into account noise correlation. MLSE receivers with one and with two samples per bit are described and it is shown that while oversampling is beneficial for wide-band optical filters, the benefit goes away for narrow-band optical filtering, thereby facilitating MLSE design for rates beyond 10 Gb/s.

Abstract: In an over-sampled maximum-likelihood sequence estimation (MLSE) receiver system, the optimal sample spacing is determined for a variety of conditions. In an illustrative implementation, the system includes an optical filter for tightly filtering an incoming optical data signal with an on-off-keying (OOK) non-return-to-zero (NRZ) format, followed by an optical-to-electrical converter, an electrical filter, a sampler, and a MLSE receiver. The sampler samples the filtered electrical data signal twice each bit period with unequal sample spacings. For wide optical filtering bandwidths, the optimal sample spacing occurs at less than 50% of a bit period. For narrow bandwidths, the optimal sample instances occur closer to the maximum eye opening.