[Paper Review] A Joint Technique for Nonlinearity Compensation in CO-OFDM Superchannel Systems

O. S. Sunish Kumar, Abdelkerim Amari+3 more|arXiv (Cornell University)|Jun 27, 2021

Optical Network Technologies5 references3 citations

TL;DR

This paper proposes a joint single-channel digital back-propagation and phase-conjugated twin-wave (SC-DBP-PCTW) technique to mitigate fiber nonlinearity in CO-OFDM superchannel systems. By combining intra-channel compensation via SC-DBP with inter- and intra-channel nonlinear distortion cancellation via PCTW, the scheme achieves performance comparable to multi-channel DBP with 16 steps/span while offering a 28% reach gain over PCTW and over double the reach of linear dispersion compensation, at significantly lower computational complexity.

ABSTRACT

We propose a technique combining the singlechannel digital-back-propagation (SC-DBP) with phaseconjugated-twin-wave (PCTW) to compensate nonlinearities in CO-OFDM superchannel systems. This exhibits a similar performance as multi-channel DBP while providing increased transmission reach compared to SC-DBP, PCTW, and linear dispersion compensation (LDC).

Motivation & Objective

• To address the performance limitations of single-channel digital back-propagation (SC-DBP) and phase-conjugated twin-wave (PCTW) techniques in mitigating fiber nonlinearity in CO-OFDM superchannel systems.
• To overcome the high computational complexity and impracticality of multi-channel DBP (MC-DBP) in dynamic optical networks.
• To develop a low-complexity, high-performance alternative that combines the strengths of SC-DBP and PCTW for improved nonlinearity compensation.
• To evaluate the transmission reach, Q-factor gain, and computational complexity of the joint technique relative to existing methods such as LDC, SC-DBP, PCTW, and MC-DBP.

Proposed method

• The joint SC-DBP-PCTW technique applies single-channel digital back-propagation (SC-DBP) with 1 step/span to compensate for deterministic intra-channel nonlinear distortions.
• After SC-DBP, the phase-conjugated twin-wave (PCTW) technique is applied via coherent superposition of the two orthogonal polarization states to cancel first-order inter- and intra-channel nonlinear distortions.
• The method leverages the complementary strengths of SC-DBP (intra-channel compensation) and PCTW (inter- and intra-channel compensation) in a two-stage processing chain at the receiver.
• The simulation setup uses a 401.33 Gbps 16-QAM CO-OFDM superchannel with four 37.5 GHz-spaced channels, 3300 data subcarriers, and 3% cyclic prefix over 25×80 km SSMF spans with EDFA amplification.
• Receiver processing includes polarization diversity detection, carrier phase recovery, channel equalization, SC-DBP, and PCTW coherent superposition before symbol demapping.
• Computational complexity is evaluated in terms of real multiplications per subcarrier and CPU running time, comparing SC-DBP-PCTW against LDC, SC-DBP, PCTW, and MC-DBP with 16 steps/span.

Experimental results

Research questions

• RQ1 Can a joint SC-DBP-PCTW technique achieve performance comparable to MC-DBP with 16 steps/span in a 401.33 Gbps CO-OFDM superchannel system?
• RQ2 Does the joint technique provide a significant increase in transmission reach compared to individual SC-DBP, PCTW, and linear dispersion compensation (LDC) schemes?
• RQ3 What is the computational complexity trade-off of the SC-DBP-PCTW technique relative to MC-DBP and the individual components?
• RQ4 How does the spectral efficiency of the PCTW-based scheme compare to other techniques, and what is the performance cost of this trade-off?
• RQ5 Can the joint technique achieve a favorable performance-complexity trade-off for practical deployment in dynamic optical networks?

Key findings

• The SC-DBP-PCTW scheme achieves a 3 dB Q-factor gain over linear dispersion compensation (LDC) at 2000 km transmission distance.
• The scheme provides a 2.3 dB Q-factor gain over SC-DBP and a 0.5 dB gain over PCTW at the same distance, demonstrating superior nonlinear compensation.
• The maximum transmission reach of the SC-DBP-PCTW scheme reaches 5600 km at the 20% overhead soft-decision FEC limit, which is 28% higher than PCTW and over double that of LDC (2380 km).
• The SC-DBP-PCTW technique achieves performance similar to MC-DBP with 16 steps/span, indicating effective mitigation of both intra- and inter-channel nonlinearities.
• The computational complexity of SC-DBP-PCTW is an order of magnitude lower than MC-DBP and less than the sum of individual SC-DBP and PCTW complexities, confirming its efficiency.
• Despite a spectral efficiency loss due to PCTW, the joint scheme delivers substantial reach and performance gains, making it a strong candidate for high-capacity, long-haul optical transmission.