370 research outputs found

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

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    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

    Handover - Enabling Learning in Communication for Safety (HELiCS): a report on achievements at two hospital sites

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    The provision of health care is becoming increasingly complex and fragmented.1,2 As a result, to ensure continuity of care, the handover of clinical tasks is becoming more frequent and important. However, the general lack of clinical handover planning and training in handover communication creates unacceptable risks for patients.1 Not surprisingly, clinical handover has been identified as a major international policy and research priority

    Embedding Fiber Bragg Grating Sensors in Carbon Composite Structures for Accurate Strain Measurement

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    Fiber Bragg grating (FBG) sensors written by femtosecond laser pulses in polyamide-coated low bending loss optical fibers are successfully embedded in carbon composite structures, following laminating and light resin molding processes which optimize the size of each ply to address esthetic, drapability, and structural requirements of the final components. The sensors are interrogated by a tunable laser operating at around 1.55 μm, and their response to temperature and strain variations is characterized in a thermally controlled chamber and by bending tests using suspended calibrated loads and a laser scanning system. Experimental results are in good agreement with simulations, confirming that the embedding process effectively overcomes potential issues related to FBG spectral distortion, birefringence, and losses. In particular, the effects of the composite material nonhomogeneity and FBG birefringence are investigated to evaluate their impact on the monitoring capabilities. A bimaterial mechanical beam model is proposed to characterize the orthotropic laminates, pointing out better accuracy in estimating the applied load with respect to the classical homogeneous beam model. A comparative analysis, performed on different instrumented carbon composite samples and supported by theory, points out the repeatability of the FBG sensors' embedding process and the effectiveness of the technology for real-time accurate strain measurement. Based on such measurements, damages and/or changes in local stiffness can be effectively detected, allowing for structural health monitoring (SHM) of composite structures for applications in specific industrial fields such as automotive and aerospace

    Neural Network-Based Joint Spatial and Temporal Equalization for MIMO-VLC System

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    The limited bandwidth of white light-emitting diode (LED) limits the achievable data rate in a visible light communication (VLC) system. A number of techniques, including multiple-input-multiple-output (MIMO) system, are investigated to increase the data rate. The high-speed optical MIMO system suffers from both spatial and temporal cross talks. The spatial cross-talk is often compensated by the MIMO decoding algorithm, while the temporal cross talk is mitigated using an equalizer. However, the LEDs have a non-linear transfer function and the performance of linear equalizers are limited. In this letter, we propose a joint spatial and temporal equalization using an artificial neural network (ANN) for an MIMO-VLC system. We demonstrate using a practical imaging/non-imaging optical MIMO link that the ANN-based joint equalization outperforms the joint equalization using a traditional decision feedback as ANN is able to compensate the non-linear transfer function as well as cross talk

    MIMO Visible Light Communications Using a Wide Field-of-View Fluorescent Concentrator

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    This letter reports a demonstration of a 2 x 2 multiple-input multiple-output (MIMO) indoor visible-light communication (VLC) system using a novel fluorescent optical concentrator-based receiver. This potentially allows a high degree of spatial multiplexing to be achieved using a simple receiver structure that can have a wide field-of-view. Details of a two-channel MIMO VLC system that operates at 32 Mb/s with a receiver acceptance angle of ±22.5° are given, and future directions are discussed.PostprintPeer reviewe

    Novel fast color-converter for visible light communication using a blend of conjugated polymers

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    The authors thank EPSRC for financial support from UP-VLC Project Grant (EP/K00042X/1).Visible Light Communications (VLC) is a promising new technology which could offer higher data transmission rates than existing broadband RF/microwave wireless technologies. In this paper, we show that a blend of semiconducting polymers can be used to make a broadband, balanced color converter with a very high modulation bandwidth to replace commercial phosphors in hybrid LEDs for visible light communications. The resulting color converter exploits partial Förster energy transfer in a blend of the highly fluorescent green emitter BBEHP-PPV and orange-red emitting MEH-PPV. We quantify the efficiency of the photoinduced energy transfer from BBEHP-PPV to MEH-PPV, and demonstrate modulation bandwidths (electrical-electrical) of ∼200 MHz, which are 40 times higher than commercially available phosphor LEDs. Furthermore, the VLC data rate achieved with this blend using On-Off Keying (OOK) is many times (∼35) higher than that measured with a commercially available phosphor color converter.PostprintPeer reviewe

    Visible Light Communication Using a Blue GaN μLED and Fluorescent Polymer Color Converter

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    This letter presents a novel technique to achieve high-speed visible light communication (VLC) using white light generated by a blue GaN mu LED and a yellow fluorescent copolymer. We generated white light suitable for room illumination by optimizing the ratio between the blue electroluminescence of the mu LED and yellow photoluminescence of the copolymer color converter. Taking advantage of the components' high bandwidth, we demonstrated 1.68 Gb/s at a distance of 3 cm (at 240 lx illumination). To the best of our knowledge, this is the fastest white light VLC results using a single blue LED/color converter combination.PostprintPeer reviewe

    Colloidal Quantum Dot Color Converters for Visible Light Communications

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    The properties and performance of CdSSe/ZnS colloidal quantum dot composite materials for use as InGaN LED color converters in visible light communications applications is reported. 500Mb/s optical wireless transmission is demonstrated
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