Abstract
Gallium nitride-based light-emitting diodes (LEDs) have revolutionized the lighting industry with their efficient generation of blue and green light. While broad-area (square millimetre) devices have become the dominant LED lighting technology, fabricating LEDs into micro-scale pixels (micro-LEDs) yields further advantages for optical wireless communications (OWC), and for the development of smart-lighting applications such as tracking and imaging. The smaller active areas of micro-LEDs result in high current density operation, providing high modulation bandwidths and increased optical power density. Fabricating micro-LEDs in array formats allows device layouts to be tailored for target applications and provides additional degrees of freedom for OWC systems. Temporal and spatial control is crucial to use the full potential of these micro-scale sources, and is achieved by bonding arrays to pitch-matched complementary metal-oxide-semiconductor control electronics. These compact, integrated chips operate as digital-to-light converters, providing optical signals from digital inputs. Applying the devices as projection systems allows structured light patterns to be used for tracking and self-location, while simultaneously providing space-division multiple access communication links. The high-speed nature of micro-LED array devices, combined with spatial and temporal control, allows many modes of operation for OWC providing complex functionality with chip-scale devices.This article is part of the theme issue ‘Optical wireless communication’.
Highlights
The wireless transmission of data is ubiquitous in the modern world, with both the number of devices and volume of data transfer ever increasing to support a wirelessly connected Internet of Things (IoT)
These digital control signals in turn are supplied through application-specific integrated circuits (ASICs), micro-controllers, or through field-programmable gate arrays (FPGAs). All of these provide a low footprint in terms of size, weight and power (SWaP), retaining this important property of micro-light-emitting diode (LED), and they can connect to standard computer interfaces such as universal serial bus
A detailed discussion of modulation schemes, multiplexing techniques, and hardware that underpin Gb s−1 Optical wireless communications (OWC) is given by Rajbhandari et al [4], which provides an extensive review of visible light communications using Gallium nitride (GaN) devices, including micro-LEDs, up to 2016
Summary
The wireless transmission of data is ubiquitous in the modern world, with both the number of devices and volume of data transfer ever increasing to support a wirelessly connected Internet of Things (IoT). Using such on/off switching, micro-LED pixels can (when required) be driven by extremely short electrical pulses, with frequency components beyond the modulation bandwidth of the device This has produced optical pulses as short as 300 ps with an output power density of ≈10 W cm−2 [16]. These digital control signals in turn are supplied through application-specific integrated circuits (ASICs), micro-controllers, or through field-programmable gate arrays (FPGAs) All of these provide a low footprint in terms of size, weight and power (SWaP), retaining this important property of micro-LEDs, and they can connect to standard computer interfaces such as universal serial bus. The integrated nature of a micro-LED array bonded to bespoke CMOS control electronics, combined with digital control through FPGA devices, provides a compact optical transmitter system capable of high-speed spatial and temporal modulation of optical signals. This allows the multi-functional OWC systems described in this paper to be implemented in application areas with SWaP limitations, such as small satellites, drones, IoT devices and wearable technology
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