Abstract

Blue LEDs are cost-effective optical sources suitable for underwater optical wireless communication (UOWC) systems. However, the nonlinearity and the low-pass response of LEDs alongside the limited sensitivity of photodetectors constrain the capacity and reach of UOWC systems. Here we address these issues by means of a combined DSP scheme consisting of partial pre-emphasis and nonlinear pre-distortion. Partial pre-emphasis pre-compensates for the low-pass response of the system while relaxing the power reduction induced by a high peak-to-average power ratio, whereas nonlinear pre-distortion can effectively alleviate the LED nonlinearity with only marginal impact on the signal power. Further, it is found that the signal power and the signal SNR at the receiver can be improved by setting a low current bias for the mini-LED because of less saturated radiative recombination. The effectiveness of this combined DSP scheme and device conditioning approach is experimentally validated and enables the transmission of a net 5.75 Gb/s PAM-8 signal over 2 m of distance underwater, which, to our knowledge, is the highest net data rate achieved for single-pixel LED-based UOWC systems.

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