ADC bandwidth optimization in coherent optical polarization multiplexing quadrature phase-shift keying system

Numerical simulations were conducted to study the performance of a 112Gbit/s coherent polarization multiplexing (PolMux) quadrature phase-shift keying (QPSK) system. We addressed the bit resolution, bandwidth of analog-to-digital converters (ADC) in the presence of all chromatic dispersion, polarization-mode dispersion and imperfect laser frequency offset. Both return-to-zero (RZ) and non-return-to-zero (NRZ) QPSK waveforms are taken into account, while the filter type of ADC is assumed to have a Gaussian frequency response. An ADC with 6-bit resolution is found to be sufficient for 112Gbit/s PolMux QPSK transmission. And simulation results show that the ratio of optimum bandwidth of ADC to symbol rate is 0.5 for both RZ- and NRZ-QPSK formats when the 1^st-order Gaussian frequency response of ADCs is assumed.