On the limits of digital back-propagation in the presence of transceiver noise

Abstract

This paper investigates the impact of transceiver noise on the performance of digital back-propagation (DBP). A generalized expression to estimate the signal-to-noise ratio (SNR) obtained using DBP in the presence of transceiver noise is described. This new expression correctly accounts for the nonlinear beating between the transceiver noise and the signal in the optical fiber transmission link. The transceiver noise-signal nonlinear beating has been identified as the main reason for the discrepancy between predicted and practical performance of DBP; which has not been previously suggested. This nonlinear beating has been included in the GN model, allowing DBP gains in practical systems to be predicted analytically. Experiments and split-step simulations with and without polarization-mode dispersion (PMD) in the transmission link have been performed. The results show that the impact of transceiver noise greatly outweighs that of PMD, and the analytical expressions are confirmed by the numerical simulations.

The Impact of Transceiver Noise on Digital Nonlinearity Compensation

“…For comparison, the gain in reach with respect to DBP (X = 0) is analyzed. The TRX noise accumulation factor for DBP is ξ TRX,DBP = κ R N 1+ [11]. Inserting ξ TRX,opt and ξ TRX,DBP in (4), forcing SNR opt = SNR DBP and solving for ∆N max = Nopt NDBP yields the reach increase of split NLC with respect to DBP.…”

“…Reach increases of around 100% (from 640 km to 1280 km) and 150% (from 1000 km to 2500 km) have been experimentally demonstrated, when NLC is applied jointly to all received channels [10], [11]. For shorter distances, even a threefold increase in transmission distance was experimentally achieved (233% from 300 km to 1000 km) [11]. Overcoming the relatively small bandwidths of digitalto-analog converters and the use of mutually coherent sources enabled the application of transmitter-side NLC, sometimes referred to as transmitter-side DBP or digital precompensation (DPC) [12].…”

“…Receiver-side NLC, also called digital back-propagation (DBP), has been proposed in numerous research papers to reduce the impact of fiber nonlinearities and achieve improved transmission performance [4]- [9]. Reach increases of around 100% (from 640 km to 1280 km) and 150% (from 1000 km to 2500 km) have been experimentally demonstrated, when NLC is applied jointly to all received channels [10], [11]. For shorter distances, even a threefold increase in transmission distance was experimentally achieved (233% from 300 km to 1000 km) [11].…”

“…This phenomenological quantity combines all noise contributions from transmitter and receiver such as quantization noise of analogue-to-digital (ADC) or digital-to-analogue (DAC) converters and noise from linear electrical amplifiers and optical components. We recently showed that resulting TRX noise-signal interactions (hereafter "TRX noise beating") arXiv:1710.00782v1 [eess.SP] 13 Sep 2017 significantly reduce the gains of (receiver-side) digital backpropagation [11]. Due to the adverse impact of transceiver noise-signal beating, the performance analysis of transmitterside, receiver-side and split NLC must be substantially revised for practical transmission systems with realistic transceiver sub-systems.…”

Perturbation-Based FEC-Assisted Iterative Nonlinearity Compensation for WDM Systems

“…Several variants of DBP based on the split-step Fourier method (SSFM) have been studied to compensate signal-signal distortions. In practice, the noise originated from the transceivers and the optical amplifiers will also impact the system producing stochastic NLI from signal-noise and noise-noise nonlinear interactions [5], [6]. Moreover, signal-signal distortions will also exhibit a Edson P. da degree of randomness due to random fluctuations in the phase or the frequency of the optical carriers [3], as well as due to stochastic time-varying effects of the fiber channel, such as polarization mode dispersion (PMD) [7].…”