8.8 Gbps PAM-4 visible light communication link using an external modulator and a neural network equalizer

This Letter presents an experimental demonstration of a visible light communication system utilizing a LiNbO₃ external modulator to support the transmission of pulse amplitude modulation (PAM)-4 signals. To solve the problem of the low-frequency fluctuations and inter-symbol interference (ISI) introduced by the external modulator-based system, a neural network with a low-frequency signal as the second label (LFNN) is proposed. A data rate of 8.8 Gbps using PAM-4 is experimentally achieved under the 7% hard-decision forward error correction (HD-FEC) bit-error-ratio (BER) limit of 3.8 × 10^-3. To the best of our knowledge, this work represents the highest transmission data rate achieved thus far using external modulation in visible light communication systems.