Reaching 7.7 Gb/s in OWC with DCO-OFDM on a Single Blue 10-µm GaN Micro-LED

Luc Maret, Lam Ngoc Dinh, Alexandre Lagrange, Patrick Demars, Ludovic Dupré and Olivier Lartigue, CEA-Leti, France

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. Preliminary 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.

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The conference focuses on leading edge research on Optical Wireless Communication in its different forms and gathers experts from academia and industry to show their latest technical results and showcase their products and services. The application scope is broad and it ranges from Ultra-short range to Ultra-long range.

Conference topics cover visible light communication, infrared optical and ultraviolet communication. These different forms of OWC can potentially be employed in a diverse range of communication applications ranging from optical interconnects within integrated circuits through outdoor inter-building links to free-space satellite communications.

The following topics are being covered during the conference:

• Ultra-short range: for instance chip-to-chip communications in stacked and closely packed multi-chip packages
• Short range: For instance wireless personal area network (WPAN) applications under standard IEEE 802.15.7 and underwater communications.
• Medium range: indoor IR and visible light communications (VLC) for wireless local area networks (WLANs) and inter-vehicular and vehicle-to-infrastructure communications.
• Long range: inter-building connections, also called free-space optical communications (FSO).
• Ultra-long range: Laser communication in space especially for inter-satellite links and establishment of satellite constellations

This paper, Reaching 7.7 Gb/s in OWC with DCO-OFDM on a Single Blue 10-µm GaN Micro-LED, was presented during the conference which took place during the Photonics Applications Week.