Johannes Herrnsdorf

High-Speed Integrated Visible Light Communication System: Device Constraints and Design Considerations

Visible light communications (VLC) has the potential to play a major part in future smart home and next generation communication networks. There is significant ongoing work to increase the achievable data rates using VLC, to standardize it and integrate it within existing network infrastructures. The future of VLC systems depends on the ability to fabricate low cost transceiver components and to realize the promise of high data rates. This paper reports the design and fabrication of integrated transmitter and receiver components. The transmitter uses a two dimensional individually addressable array of micro light emitting diodes (μLEDs) and the receiver uses an integrated photodiode array fabricated in a CMOS technology. A preliminary result of a MIMO system implementation operating at a data rate of 1 Gbps is demonstrated. This paper also highlights the challenges in achieving highly parallel data communication along with the possible bottlenecks in integrated approaches.

Active-Matrix GaN Micro Light-Emitting Diode Display With Unprecedented Brightness

Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of 106 cd/m2.

Temperature-dependent efficiency droop of blue InGaN micro-light emitting diodes

Temperature-dependent trends in radiative and Auger recombination coefficients have been determined at different injection carrier concentrations using InGaN micro-light emitting diodes 40 μm in diameter. The differential lifetime was obtained first from the measured modulation bandwidth and was then employed to calculate the carrier concentration in the quantum well active region. When the temperature increases, the carrier concentration increases, but both the radiative and Auger recombination coefficients decrease. In addition, the temperature dependence of radiative and Auger recombination coefficients is weaker at a higher injection carrier concentration, which is strongly related to phase space filling.

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.

A multigigabit per second integrated multiple-input multiple-output VLC demonstrator

In this paper, we report the performance of an imaging multiple-input multiple-output (MIMO) visible light communication (VLC) system. The VLC transmitter consists of a two-dimensional (2-D), individually addressable Gallium Nitride micro light-emitting diode (μLED) array. The receiver uses a 2-D avalanche photodiode array fabricated using complementary metal oxide semiconductor (CMOS). Using integrated CMOS-based LED drivers, a data rate greater than 1 Gb/s was obtained at a link distance of 1 m with the system field of view of 3.45° using four channels. At a reduced link distance of 0.5 m, a data rate of 7.48 Gb/s was obtained using a nine channel MIMO system. This demonstrates the feasibility of compact MIMO systems that offer substantial data rates.

Temporal Encoding to Reject Background Signals in a Low Complexity, Photon Counting Communication Link

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 system’s low power consumption and modest electronics requirements are demonstrated by employing it as a communications channel between two nano-satellite simulator systems.

CMOS-integrated GaN LED array for discrete power level stepping in visible light communications

We report a CMOS integrated micro-LED array capable of generating discrete optical output power levels. A 16 × 16 array of individually addressable pixels are on-off controlled through parallel logic signals. With carefully selected groups of LEDs driven together, signals suitable for discrete transmission schemes are produced. The linearity of the device is assessed, and data transmission using pulse amplitude modulation (PAM) and orthogonal frequency division multiplexing (OFDM) is performed. Error-free transmission at a symbol rate of 100 MSamples/s is demonstrated with 4-PAM, yielding a data rate of 200 Mb/s. For 8-PAM, encoding is required to overcome the baseline wander from the receiver, reducing the data rate to 150 Mb/s. We also present an experimental proof-of-concept demonstration of discrete-level OFDM, achieving a spectral efficiency of 3.96 bits/s/Hz.

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.

Design, Fabrication, and Application of GaN-Based Micro-LED Arrays With Individual Addressing by N-Electrodes

We demonstrate the development, performance, and application of a GaN-based micro-light emitting diode ( <inline-formula><tex-math notation=LaTeX>

Control of automated systems with a structured light illumination source

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