Yangyang Fan

Complexity-reduced digital nonlinear compensation for coherent optical system

The high complexity of conventional intra-channel nonlinearity compensation algorithms, such as back-propagation, is considered as the major obstacle for the implementation. To reduce the complexity, perturbation analysis is applied because it considers multi-span transmission as one stage. In those perturbation based algorithms, such as perturbation back-propagation (PBP) and perturbation pre-distortion, the number of required compensation stage is much less than that of conventional back-propagation. To reduce the complexity further, the multi-tap finite impulse response filter (FIR) in PBP is replaced with one-tap infinite impulse response (IIR) filter. The number of required compensation stage of IIR PBP is only 15% of conventional back-propagation, whereas the complexity of each stage is almost same. In perturbation pre-distortion, the proposed perturbation combination reduces the number of terms from 19732 to 41, whereas no performance degradation is observed.

Digital nonlinear compensation for spectrally efficient superchannel transmission at 400Gbit/s and beyond

In order to push the nonlinear Shannon limit further within practical implementation constraints, we discuss various nonlinear compensation techniques for intra- and inter-subcarrier nonlinear effects. Experimental and numerical results prove the benefit is not just pre-FEC BER improvement.

Analytical Intrachannel Nonlinear Models to Predict the Nonlinear Noise Waveform

Intrachannel nonlinearity is considered as a major distortion in high capacity transmission systems. To better understand the nonlinear distortion, the nonlinearity modeling is an essential technology. Most of current nonlinear models focus on the statistical characteristics of nonlinear noise. In this paper, we investigate the analytical models that predict the time-varying nonlinear noise waveform. For the return-to-zero (RZ) pulse-shaped system, the “power weighted, additive-multiplicative model” is investigated under various system conditions for quadrature phase shift keying and 16 quadrature amplitude modulation formats, with dispersion managed and unmanaged link composed of standard single mode fiber or nonzero dispersion-shifted fiber. For the non-RZ and Nyquist pulses, the Nyquist nonlinear model is investigated. Both two models achieved 95% accuracy which is defined as the absolute value of the cross correlation between the noise waveform obtained by split step Fourier simulation and the waveform calculated by the model. Simulation also shows that the model functions well for the most optical power range of commercial communication systems.

LDPC SD-FEC Coding in the Nonlinear Domain

We describe behavior of soft decision (SD) forward error correction (FEC) with non-Gaussian noise which is observed in nonlinear transmission with higher order modulation format and digital nonlinear compensator with inadequate parameter.

Similarity and dissimilarity among different modulation formats under intra-channel nonlinearity in DCF-free link

We have examined intra-channel nonlinearity induced distortions in DCF-free coherent transmission system for different modulation formats in detail. Both similarity and dissimilarity of the noise characteristics have been observed and can be explained by the proposed new nonlinear model.