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Gas Line Absorption Mitigation in Hollow-Core Fibre using Spectral Pre-Equalisation

Eric Sillekens, Ronit Sohanpal

TL;DR

This work addresses CO2 gas-line absorption (GLA) in hollow-core fibre transmissions, which induces sharp spectral notches that degrade the channel Q-factor. It introduces a frequency-domain spectral pre-equalisation scheme that estimates a pre-compensated transfer function via $H_{\mathrm{preEQ}}(f)=\exp\left(L(f)+j\mathcal{H}\{L(f)\}\right)$, where $L(f)=-\tfrac12\ln(P_{\mathrm{Welch}}(f))$, and applies a MMSE regulariser $W_{\mathrm{mmse}}(f)=\frac{|H_{\mathrm{preEQ}}(f)|^2}{|H_{\mathrm{preEQ}}(f)|^2+\lambda}$ with $\lambda=10^{-\mathrm{SNR_{est}}/10}$. The method, combined with a short adaptive equaliser, yields a total Q-factor penalty reduction of $5.5$ dB while using only $3$ taps, outperforming a $383$-taps RLS-equaliser by $1.3$ dB and significantly reducing computational complexity. Modeling uses a Lorentzian notched GLA response $H_{\mathrm{GLA}}(f)$ and a 300 km HCF link with a $140$ GBd $1024$-QAM channel, demonstrating substantial DSP-based mitigation potential for practical high-bandwidth HCF systems. This approach can be integrated with existing CD compensation and processed in block-wise fashion for real-time deployment.

Abstract

We study the impact of CO 2 absorption on hollow-core fibre transmission. Using spectral pre-equalisation, we digitally post-compensate gas-line absorption and show a 5.5 dB reduction in Q-factor penalty, outperforming a 383-tap equaliser by 1.3 dB.

Gas Line Absorption Mitigation in Hollow-Core Fibre using Spectral Pre-Equalisation

TL;DR

This work addresses CO2 gas-line absorption (GLA) in hollow-core fibre transmissions, which induces sharp spectral notches that degrade the channel Q-factor. It introduces a frequency-domain spectral pre-equalisation scheme that estimates a pre-compensated transfer function via , where , and applies a MMSE regulariser with . The method, combined with a short adaptive equaliser, yields a total Q-factor penalty reduction of dB while using only taps, outperforming a -taps RLS-equaliser by dB and significantly reducing computational complexity. Modeling uses a Lorentzian notched GLA response and a 300 km HCF link with a GBd -QAM channel, demonstrating substantial DSP-based mitigation potential for practical high-bandwidth HCF systems. This approach can be integrated with existing CD compensation and processed in block-wise fashion for real-time deployment.

Abstract

We study the impact of CO 2 absorption on hollow-core fibre transmission. Using spectral pre-equalisation, we digitally post-compensate gas-line absorption and show a 5.5 dB reduction in Q-factor penalty, outperforming a 383-tap equaliser by 1.3 dB.
Paper Structure (5 sections, 4 equations, 2 figures)

This paper contains 5 sections, 4 equations, 2 figures.

Table of Contents

  1. Introduction
  2. HCF transmission simulation including GLA modelling
  3. Spectral pre-equalisation scheme.
  4. Results and discussion
  5. Conclusion

Figures (2)

  • Figure 1: (a) CO2 gas line absorption from the HiTRAN database, (b) Bode plot of a simulated Lorentzian absorption peak, (c) HCF transmission simulation scheme.
  • Figure 2: (a) Q factor vs. tap length with/without the spectral pre-equaliser for 140 GBd 1024 QAM transmission system, (b) the PSD of the received signal before and after spectral pre-equalisation, and (c) the Bode plot $H_\text{preEQ}(f)$.