Abstract
A novel low-complexity coherent receiver solution is presented to improve
spectral efficiency in wavelength-division multiplexing (WDM) systems. It is based on
the receiver-side partial-response equalization and maximum-likelihood sequence
detection (MLSD) in prefiltered WDM systems. The partial-response equalization shapes
the channel into an intermediate state with a known partial response which is finally
recovered by MLSD without the need of channel estimation. In this scheme, the severe
intersymbol interference induced by the prefiltering can be shared between the
partial-response equalization and MLSD. Therefore, a tradeoff can be made between
complexity and performance. The feasibility of receiver-side partial-response shaping
relaxes the efforts and requirements on the transmitter-side prefiltering, which permits
the mature WDM components to implement prefiltering. In addition, the partial-response
equalization or shaping structure is also improved based on our prior art, which further
simplifies the overall scheme. For near-baudrate-spacing optically prefiltered WDM
systems, duobinary response is experimentally proved as a good intermediate response to
shape. Due to the short memory of the duobinary response, the complexity of the receiver
based on duobinary shaping has been reduced to a low level. As a whole, the proposed
scheme provides a good alternative to Nyquist-WDM at comparable spectral efficiencies.
With the proposed receiver-side duobinary shaping technique, three sets of experiments
have been carried out to verify the improved duobinary shaping scheme and meanwhile
demonstrate the main features, including 5 × 112-Gb/s polarization-multiplexed
quadrature phase-shift keying (PM-QPSK) WDM transmission over a 25-GHz grid,
single-channel 40-Gbaud PM-QPSK experiment, and 30-GHz-spaced 3 × 224-Gb/s PM
16-ary quadrature amplitude modulation transmission.
© 2012 IEEE
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