Control of automated systems with a structured light illumination source

Autonomous mobile devices can self-locate, navigate and receive control signals using structured illumination from a light-emitting diode array. We present a prototype system and discuss the properties of the optical wireless control

Positioning and data broadcasting using illumination pattern sequences displayed by LED arrays

Illumination of a scene with a time-sequence of spatial light patterns enables clients within the scene to navigate, receive broadcast wireless data, or make subsequent space-division multiple access connections to a high bandwidth wireless system. We have developed dedicated binary pattern sequences, for use with arrays of light-emitting diodes (LEDs), which are projected on the area of interest. The LED arrays can be in either active-matrix or matrix-addressable format. The properties of the different sequences are compared theoretically and experimentally, highlighting a trade-off between position update rate and resilience against pixel cross-talk and interference

Control of edge bulge evolution during photoresist reflow and it's application to diamond micro-lens fabrication

We present an empirical study of profile evolution of lithographically defined photoresist (PR) patterns during thermal reflow and apply the findings to diamond micro-lens fabrication. During PR reflow, a bulge forms at the edge of the PR pattern and propagates inwards as the temperature and PR thickness are increased. An empirical relationship for this propagation is derived. Furthermore, it was found that at a certain reflow temperature and a limited pattern size, there is a minimum initial thickness of the PR pattern for forming spherical lens profiles. Based on these findings, diamond micro-lenses with a diameter of 400 µm and a previously unachieved radius of curvature of over 13 mm were fabricated. This is underpinned by forming PR micro-lens patterns with a large radius of curvature and transferring the PR patterns through low-selectivity Ar/Cl2 inductively coupled plasma etching

Concept of a GaN-LED-based positioning system using structured illumination

Accurate self-orientation within a space can be achieved using only a simple photodetector and a remote Gallium Nitride micro-light-emitting diode array, emitting a time series of varying spatial illumination patterns onto the scene

Positioning and space-division multiple access enabled by structured illumination with light-emitting diodes

Self-location of devices in an illuminated area can be realized using light-emitting diode array luminaires with integrated electronic smart control. These smart lighting sources project a rapidly displayed time sequence of spatial illumination patterns onto the scene, which enables positioning on a millisecond timescale. We demonstrate a prototype system based on a CMOS-driven 16×16 array of GaN light-emitting diodes and its application to space-division multiple access in a Gb/s optical wireless network

High-Sensitivity Inter-Satellite Optical Communications using Chip-Scale LED and Single Photon Detector Hardware

Small satellites have challenging size weight and power requirements for communications modules, which we address here by using chip-scale light-emitting diode (LED) transmitters and single-photon avalanche diode receivers. Data rates of 100 Mb/s have been demonstrated at a sensitivity of -55.2 dBm, and simulations with supporting experimental work indicate ranges in excess of 1 km are feasible with a directional gain of up to 52 dBi and comparatively modest pointing requirements. A 750 m, 20 Mb/s link using a single micro-LED has been demonstrated experimentally. The low electrical power requirements and compact, semiconductor nature of these devices offer high data rate, high sensitivity communications for small satellite platforms

High sensitivity inter-satellite optical communications using LEDs and single photon receivers

High data rate communication links are difficult to perform with radio frequency technology under the strict size, mass and power (SMaP) constraints of small satellites. Transmitting data using the optical spectrum can permit higher data rates with more power efficient systems. Single photon avalanche diodes (SPADs) provide receivers with exceptional sensitivity levels, while light-emitting diodes (LEDs) bonded to electronic driver chips provide digitally controllable optical transmitters capable of high bandwidth spatial and temporal modulation. Data rates of 100 Mb/s have been demonstrated at a sensitivity of -55.2 dBm, and ray-tracing simulations indicate ranges in excess of 1 km are feasible with simple optical systems. Additionally, the divergent nature of LEDs can provide a level of spatial coverage, relaxing pointing and alignment requirements. The low electrical power requirements and compact, semiconductor nature of these devices may therefore bring high data rate, high sensitivity communications to small satellite platforms

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)

Poissonian communications : free space optical data transfer at the few-photon level

Communicating information at the few photon level typically requires some complexity in the transmitter or receiver in order to operate in the presence of noise. This in turn incurs expense in the necessary spatial volume and power consumption of the system. In this work we present a self-synchronised free-space optical communications system based on simple, compact and low power consumption semiconductor devices. A temporal encoding method, implemented using a gallium nitride micro-LED source and a silicon single photon avalanche photo-detector (SPAD) demonstrates data transmission at rates up to 100 kb/s for 8.25 pW received power, corresponding to 27 photons per bit. Furthermore, the signals can be decoded in the presence of both constant and modulated background noise at levels significantly exceeding the signal power. The systems low power consumption and modest electronics requirements are demonstrated employing it as a communications channel between two nano-satellite simulator systems

Efficient reconstruction of low photon count images from a high speed camera

Challenging imaging applications requiring ultra-short exposure times or imaging in photon-starved environments can acquire extremely low numbers of photons per pixel, (1 MHz) and low incident photon flux (<1 photon per pixel), image post processing can provide better grayscale information and spatial fidelity of reconstructed images than simple frame averaging, with improvements in SSIM up to a factor of 3. Various other image post-processing techniques are also explored and some of which result in a similar quality of image reconstruction to Bayesian retrodiction, with lower computational load. Image reconstructions using Bayesian Retrodiction or bilateral filtering are of comparable quality to frame averaging, as measured by the Structural Similarity Index Measure, when using less than 40% of the photon flux