How to Increase the Achievable Information Rate by Per-Channel Dispersion Compensation

TL;DR

The paper analyzes per-channel dispersion compensation (CDM) in long-haul WDM systems and demonstrates that CDM can yield higher AIR than nondispersion-managed (NDM) links when the detector mitigates XPM, while dispersion-managed (DM) links perform worst due to strong XPM. It extends the frequency-resolved logarithmic perturbation model to CDM, showing CDM increases the frequency coherence of XPM distortions across the channel bandwidth. AIR is computed under mismatched receivers using AWGN, AR(1), and HOAR auxiliary channels, revealing that exploiting XPM temporal correlation significantly boosts AIR for CDM. The results suggest CDM with FBG-based inline DC and XPM-aware receivers as a promising approach for future WDM networks, with extensions to polarization multiplexing identified as future work.

Abstract

Deploying periodic inline chromatic dispersion compensation enables reducing the complexity of the digital back propagation (DBP) algorithm. However, compared with nondispersion-managed (NDM) links, dispersion-managed (DM) ones suffer a stronger cross-phase modulation (XPM). Utilizing per-channel dispersion-managed (CDM) links (e.g., using fiber Bragg grating) allows for a complexity reduction of DBP, while abating XPM compared to DM links. In this paper, we show for the first time that CDM links enable also a more effective XPM compensation compared to NDM ones, allowing a higher achievable information rate (AIR). This is explained by resorting to the frequency-resolved logarithmic perturbation model and showing that per-channel dispersion compensation increases the frequency correlation of the distortions induced by XPM over the channel bandwidth, making them more similar to a conventional phase noise. We compare the performance (in terms of the AIR) of a DM, an NDM, and a CDM link, considering two types of mismatched receivers: one neglects the XPM phase distortion and the other compensates for it. With the former, the CDM link is inferior to the NDM one due to an increased in-band signal--noise interaction. However, with the latter, a higher AIR is obtained with the CDM link than with the NDM one owing to a higher XPM frequency correlation. The DM link has the lowest AIR for both receivers because of a stronger XPM.

Figures (7)

• Figure 1: Phase of the CD transfer function for a single span of $100$ km of SMF, and for the corresponding DCF and FBG as DC components.
• Figure 2: Correlation function (arbitrary unit) of the XPM phase distortion $\mathrm E[\theta(0,t)\theta^*(\Delta_f,t+\tau)]$ for NDM, DM, and CDM links with three WDM channels. The cross-sections of the three countour plots at $\tau=0$ and $\Delta_f=0$ are compared in parts (d) and (e), respectively.
• Figure 3: Normalized temporal correlation function of the XPM phase distortion link with five WDM channels.
• Figure 4: A schematic of the under studied WDM system model with three channels. Mod.: modulator; DC: dispersion compensator; MFS: matched filtering and sampling demodulator, EDFA: erbium-doped fiber amplifier.
• Figure 5: AIRs for a 50-GHz WDM grid. The ASE noise is injected (a) after each amplifier (b) at the transmitter. The capacity of the corresponding AWGN channel is shown (dotted line) for comparison.