Hybrid integration of FEC and channel equalization for ultra-high bandwidth efficient coherent optical...

Area of Science:

• Optical Communications
• Signal Processing
• Information Theory

Background:

• Inter-symbol interference (ISI) is a major challenge in high-bandwidth optical systems, limiting efficiency.
• Existing methods often treat equalization and forward error correction (FEC) independently, leading to suboptimal performance.

Purpose of the Study:

• To propose and demonstrate a hybrid integrated forward error correction (FEC) equalization (IFE) scheme.
• To address severe ISI in ultra-high bandwidth efficiency (BE) applications within coherent optical interconnections.

Main Methods:

• An adaptive linear minimum mean square error (LMMSE) equalizer estimates channel response.
• Soft-input soft-output (SISO) a posteriori information from a low-density parity-check (LDPC) decoder assists ISI deduction.
• Experiments conducted on a 60 GBaud polarization division multiplexed 16 quadrature amplitude modulation system with a 5-GHz ultra-narrow bandwidth receiver.

Main Results:

• The IFE scheme achieved over 3-dB optical signal-to-noise ratio (OSNR) gain compared to serial equalizer/FEC structures at a bit error rate (BER) of 1x10^-2.
• Demonstrated superior ISI reduction ability compared to traditional soft-decision maximum likelihood sequence estimation (MLSE).

Conclusions:

• The proposed IFE scheme enables simultaneous accurate ISI deduction and reliable FEC decoding.
• The integrated approach offers greater robustness and performance gains in challenging optical communication scenarios.