Analysis and application of scalable non-linear equalization in 112Gbit/s DP-64QAM coherent transmission over single mode fibers

We report on the performance comparison of all-optical and digital signal processing techniques to compensate fiber transmission impairments, i.e. chromatic dispersion (CD) and non-linear (NL) distortion caused by the Kerr effect. The methods are evaluated in coherent 112Gbit/s DP-64QAM system over 800km standard single mode fiber (SMF). The signals are transmitted over SMF with physical parameters of D=16 ps/nm-km, γ=1.3 (km^-1.W^-1) and α=0.2 dB/km. No in-line optical dispersion compensating fiber (DCF) is used to compensate the chromatic dispersion. The digital signal processing module is implemented by: (a) electronic dispersion compensation (EDC), through finite impulse response (FIR) filters and (b) split-step Fourier method based intra-channel non-linear equalizer, i.e. digital backward propagation (DBP). Furthermore, we numerically compare optical backward propagation (OBP) with optical phase conjugation (OPC) techniques, i.e. mid-link spectral inversion (MLSI), pre-dispersed spectral inversion (PD-SI) and optical phase conjugation with non-linearity module (OPC-NM). We also evaluate a self-phase modulation-based optical limiter with an appropriate pre-chirping to compensate for the intensity fluctuations, as a hybrid approach with OBP. The results depict improvement in system performance by a factor of ≈ 4dB of signal input power by all-optical signal processing methods, consequently improving the non-linear threshold point (NLT) and maximum transmission distance, which is comparative with ideal digital backward propagation (DBP) where the high complexity is the intrinsic impediment in the real-time implementation of the technique with coherent receivers. These numerical investigations will be helpful in deployment of scalable equalization of non-linearities in future optical networks.