Optical Front-End for Soft-Decision LDPC Codes in Optical Communication Systems

A low-complexity soft-decision 12.5 Gb/s optical receiver for decoding low-density parity-check codes reusing conventional hard-decision receivers is investigated. The simulated and experimental results show that the proposed optical receiver exhibits coding gains of 2.75 and 6.73 dB for post-forward-error-correction bit error rates of 10-4 and 10-9, respectively, over a hard-decision uncoded system for a 60 km single-mode optical fiber transmission. The soft-decision circuitry consumes approximately 5 W and is optimized to provide two confidence levels, one above and one below the hard-decision levels.