Numerical evaluation of robust and spectrally efficient 112Gbit/s transmission employing digital backward propagation

We report on the complexity comparison of the digital signal processing (DSP) module to compensate chromatic dispersion and non-linearities, i.e. digital backward propagation (DBP) algorithm. The dual-polarization quadrature phase shift keying (DP-QPSK), dual-polarization quadrature duobinary (DP-QDB) and dual-polarization quadrature amplitude modulation (DP-16QAM) encoded signals at a bit-rate of 112Gbit/s for N-channels are transmitted over 1640km fiber link. The single channel (N=1) and multi-channel (N=10) DWDM transmission performances are compared in this paper. In case of multi-channel system, 10 transmitters are multiplexed with 25GHz channel spacing. The fiber link consists of Large Aeff Pure-Silica core fiber (LA-PSCF) with 20 spans of 82km each and has the physical parameters of: α=0.16dB, D=21ps(nm-km) and γ=0.6(km^-1.W^-1). No in-line optical dispersion compensator is employed in the link. Erbium-doped fiber amplifiers (EDFAs) are modelled with 13.12dB of gain and 4dB of noise figure. A phase-diversity homodyne coherent receiver is used to detect the signals. To simplify our numerical analysis, we neglect the effect of polarization mode dispersion (PMD) and laser line width. The system performances are evaluated by monitoring the bit-error-ratio (BER) and the forward error correction (FEC) limit corresponds to BER of 3.8×10^-3. The DBP algorithm is implemented after the coherent detection and is based on the logarithmic step-size based split-step Fourier method (L-DBP). The results depict that DP-QDB can be used to transmit 112Gbit/s signals with an spectral efficiency (SE) of 4-b/s/Hz, but at the same time has a higher tolerance to non-linear transmission impairments. By utilizing DP-QDB modulation, comparative system performance w.r.t DP-16QAM transmission can be achieved with 60% less computations and with a step-size of 205km.