Hybrid reservoir-feed-forward equalization for enhanced PAM-4 transmission

In this work, we propose a novel hybrid reservoir-feed-forward (RFF) equalizer that employs a single microring resonator for 25-GBaud PAM-4 transmission. The proposed architecture synergistically combines the nonlinear dynamics and short-term memory effects of the microring resonator with a ridge regression-optimized linear readout layer, enabling high-efficiency signal equalization. Experimental results demonstrate that the RFF equalizer outperforms the conventional feed-forward equalization (FFE) at matched tap counts. At the BER threshold of 2.7 × 10^-2, the RFF exhibits a 1.5-dB enhancement in receiver sensitivity compared to the FFE.