High-bandwidth GaN-based mini-LEDs on the c-sapphire substrate are promising candidates for underwater optical wireless communication (UOWC) systems due to their compatibility with the mature LED fabrication process. Here we fabricate and characterize mini-LEDs based on a single-layer InGaN active region with a peak emission wavelength around 484 nm for high-speed UOWC links. Since the LED diameter affects the trade-off between the modulation bandwidth and the optical modulation amplitude, mini-LEDs with varying mesa diameters from 100 µm to 175 µm are fabricated for the measurement. The 150 µm mini-LED with a 3-dB optical bandwidth of 906 MHz performs the best and enables the transmission of a net 4 Gb/s PAM-4 signal over 2 m of underwater distance using only linear equalization. This UOWC system has achieved, to the best of our knowledge, the highest net data rate and the highest data-rate-distance product based on a single-pixel mini-LED.
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