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Hidden conditional random field-based equalizer for the 3D-CAP-64 transmission of OAM mode-division multiplexed
Optics Express
|September 15, 2023
Summary
A novel Hidden Conditional Random Field (HCRF) equalizer effectively mitigates nonlinear impairments in orbital angular momentum (OAM) mode-division multiplexing (MDM) optical communication systems. This method enhances receiver sensitivity and reduces computational complexity compared to existing techniques.
Area of Science:
- Optical Communications
- Signal Processing
- Nonlinear Optics
Background:
- Orbital Angular Momentum (OAM) mode-division multiplexing (MDM) is crucial for ultra-high capacity optical fiber communications.
- Nonlinear impairments, including modulation, square-law, and mode-coupling nonlinearities, severely affect OAM-MDM system performance.
- Existing equalization techniques face challenges in effectively mitigating these complex nonlinear distortions.
Purpose of the Study:
- To propose and evaluate a Hidden Conditional Random Field (HCRF) based equalizer for nonlinear mitigation in OAM-MDM systems.
- To enhance the performance of 20 GBaud three-dimensional carrierless amplitude and phase modulation-64 (3D-CAP-64) signals transmitted over OAM-MDM fiber channels.
- To compare the proposed HCRF equalizer's performance and computational complexity against Convolutional Neural Network (CNN) and Volterra Nonlinear Equalizer (VNE) approaches.
Main Methods:
- Developing an HCRF equalizer to estimate conditional probabilities of hidden variables, classifying constellation points, and mitigating nonlinearities.
- Utilizing statistical probability distributions of hidden variables within the HCRF equalizer for impairment correction.
- Conducting experiments with 20 GBaud 3D-CAP-64 signals across OAM modes l=+2 and l=+3.
Main Results:
- The HCRF equalizer improved receiver sensitivity by 2 dB (l=+2) and 1 dB (l=+3) at the 7% Forward Error Correction (FEC) threshold compared to CNN equalizers.
- Computational complexity was reduced by 30% versus VNE and 41% versus CNN equalizers.
- The proposed equalizer demonstrated superior Bit Error Ratio (BER) performance.
Conclusions:
- The HCRF equalizer is a highly effective method for mitigating nonlinear distortions in high-speed OAM-MDM fiber communication systems.
- The HCRF approach offers significant improvements in receiver sensitivity and substantial reductions in computational complexity.
- This technique shows great potential for advancing future optical communication systems requiring ultra-high capacity.
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