Gallium nitride micro-light-emitting diode structured light sources for multi-modal optical wireless communications systems

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

LED excitation of an on-chip imaging flow cytometer for bead-based immunoassay

A green LED is demonstrated to generate a uniform square illumination pattern for an on-chip imaging flow cytometer system. The proposed system is used to perform the detection of a bead-based immunoassay for a sepsis biomarker, procalcitonin

A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications

The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined

High speed spatial encoding enabled by CMOS-controlled micro-LED arrays

Arrays of GaN light-emitting diodes can be used for rapid display of pattern sequences or high speed parallel data transmission using different sites of the array. These operation modes can be combined with each other and are useful for light- fidelity networks with Gb/s capacity

Heterogeneous integration of gallium nitride light-emitting diodes on diamond and silica by transfer printing

We report the transfer printing of blue-emitting micron-scale light-emitting diodes (micro-LEDs) onto fused silica and diamond substrates without the use of intermediary adhesion layers. A consistent Van der Waals bond was achieved via liquid capillary action, despite curvature of the LED membranes following release from their native silicon growth substrates. The excellence of diamond as a heat-spreader allowed the printed membrane LEDs to achieve optical power output density of 10 W/cm2 when operated at a current density of 254 A/cm2. This high-currentdensity operation enabled optical data transmission from the LEDs at 400 Mbit/s

Spatially superposed pulse amplitude modulation using a chip-scale CMOS-integrated GaN LED array

We present a highly compact system capable of generating discrete optical wireless data signals from logic inputs, suitable for pulse amplitude modulation (PAM) transmission, in visible light communication (VLC)

Imprinted Networks as Chiral Pumps

We investigate the interaction between a chirally imprinted network and a solvent of chiral molecules. We find, a liquid crystalline polymer network is preferentially swollen by one component of a racemic solvent. This ability to separate is linked to the chiral order parameter of the network, and can be reversibly controlled via temperature or a mechanical deformation. It is maximal near the point at which the network loses its imprinted structure. One possible practical application of this effect would be a mechanical device for sorting mixed chiral molecules.Comment: 4 pages, 5 figure

Micro-LEDs for technological convergence between displays, optical communications, and sensing and imaging systems

Micro-LED displays are now emerging rapidly towards commercialization. This novel compound semiconductor display technology has the potential to interface very effectively to advanced electronics, in particular Si CMOS, to create new forms of display which also interrogate and communicate with their environment in sophisticated ways

Experimental demonstration of generalised space shift keying for visible light communication

A low complexity generalised space shift keying (GSSK) experimental set-up for visible light communication (VLC) is demonstrated. The GSSK encoder is implemented in a field programmable gate array (FPGA) board. No digitalto-analog converter (DAC) is required and up to 16 output channels are supported which greatly exceeds that of an arbitrary waveform generator (AWG). A 4 × 4 Gallium Nitride (GaN) micro-LED array is used as transmitter while 4 avalanche photo diode (APD) receiver boards are acting as receivers. GSSK exploits the natural differences between the multiple communication links. The bit error ratio (BER) performances are evaluated for different transmitter and receiver arrangements. It is also shown that how different receiver positions and increasing receiver number will affect the BER performance. The bit error performance greatly depends on the dissimilarity of the channel gains. A spectral efficiency of 16 bits/symbol is achieved by using all 16 micro-LEDs and 4 receivers. The implementation of the experiment is introduced in detail and experimental results are given

Fabrication, characterization and applications of flexible vertical InGaN micro-light emitting diode arrays

Flexible vertical InGaN micro-light emitting diode (micro-LED) arrays have been fabricated and characterized for potential applications in flexible micro-displays and visible light communication. The LED epitaxial layers were transferred from initial sapphire substrates to flexible AuSn substrates by metal bonding and laser lift off techniques. The current versus voltage characteristics of flexible micro-LEDs degraded after bending the devices, but the electroluminescence spectra show little shift even under a very small bending radius 3 mm. The high thermal conductivity of flexible metal substrates enables high thermal saturation current density and high light output power of the flexible micro-LEDs, benefiting the potential applications in flexible high-brightness micro-displays and high-speed visible light communication. We have achieved ~40 MHz modulation bandwidth and 120 Mbit/s data transmission speed for a typical flexible micro-LED