Analysis of OSNR margin improvement in beyond 100Gb/s PDM-DQPSK systems due to FEC

The OSNR margin improvements due to FEC limit elevation in 112Gb/s PDM-DQPSK systems under two different receiver schemes, direct detection and coherent detection with digital signal processing (DSP), are analyzed. FEC limit elevation provides more benefit to the direct detection scheme than to the coherent detection scheme in 112Gb/s PDM-RZ-DQPSK system. For the cases of non-ideal receivers employment and long haul fiber link transmission, FEC performance improvement is more profitable than that for the ideal BtB case.