Ultra-high speed optical wireless communications with gallium-nitride microLED

Abstract

This presentation describes recent activities on ultra-high speed Optical Wireless Communications (OWC) using Gallium-Nitride micro-LEDs designed and fabricated at CEA-Leti. Micro-LEDs are one of the most promising OWC optical sources due to their high illumination efficiency and their large modulation bandwidths. Pre-liminary work focused on the implementation of a 10-μm single blue micro-LED on sapphire wafer within an experimental OWC setup, mixing software generation of direct-current optical orthogonal frequency division multiplexing (DCO-OFDM) patterns and hardware optical components for light collection, high speed photo-detection and digital acquisitions. Intensity modulation conveys DCO-OFDM waveform and direct detection is used at reception. A high current density of 25.5 kA/cm² provided a modulation bandwidth of 1.8 GHz. Associated to bit and power loading with up to a 256-QAM subcarrier modulation, it enabled a new data rate of 7.7 Gb/s, compared to the previous record of 5.37 Gb/s reached with a blue 21-μm microLED in 2016. Towards a better understanding of the micro-LED design impact on OWC performance, next investigations will study the electrical modelling of such micro-LEDs in the high frequency regime. Future works will cover the use of large arrays of more than 10 thousands micro-LEDs. The first objective is to open the way to new digital-to-optical modulations by independently driving each pixel, to remove digital-to-analogue converter and target highly integrated system-on-chips for ultra-high speed OWC transmitters. Secondly, higher emitted optical power is expected to open such technology to indoor multiple access applications where light collection and emitter-receiver alignment may not be possible anymore.