The transducer consists on a semiconductor device based on two stacked-i-n  heterostructures, that were designed to detect the emissions of the fluorescence resonance energy transfer between fluorophores in the cyan (470 nm) and yellow (588 nm) range of the spectrum. This research represents a preliminary study on the use of such wavelength sensitive devices as photodetectors for this kind of application. The device was characterized through optoelectronic measurements concerning spectral response measurements under different electrical and optical biasing conditions. To simulate the FRET pairs a chromatic time dependent combination of cyan and yellow wavelengths was applied to the device. The generated photocurrent was measured under reverse and forward bias to readout the output photocurrent signal. Different wavelength biasing light was also superimposed. Results show that under reverse bias the photocurrent signal presents four separate levels each one assigned to the different wavelength combinations of the FRET pairs. If a blue background is superimposed the yellow channel is enhanced and the cyan suppressed while under red irradiation the opposite behavior occurs. So under suitable biasing light the transducer is able to detect separately the cyan and yellow fluorescence pairs. An electrical model, supported by a numerical simulation supports the transduction mechanism of the device.

This work explores the integration of visible light communication technology with urban traffic management systems. Using RGBV LEDs, Visible Light Communication facilitates real-time data collection – such as vehicle position, speed, queue length, and waiting time – through transmitters embedded in streetlights, traffic signals, and vehicle headlights. These enable multiple communication modes: vehicle-to-vehicle vehicle-to-infrastructure), infrastructure-to-vehicle and lamp-to-vehicle. The system is simulated using the “Simulation of Urban Mobility traffic” simulator, replicating realistic vehicle dynamics and visible light communication-based data exchange. Communication channels operate using On-Off Keying modulation, transmitting 64-bit frames structured according to a defined visible light communication protocol. A key contribution of this work is the development of signal pre-processing and decoding algorithms at the receiver module. These algorithms demultiplex the composite optical signal received by the photodetector, enabling identification of the emitting sources and reliable data extraction. Signal processing techniques include baseline correction using asymmetric least squares smoothing, correction of capacitive effects, and transient noise filtering based on signal slope analysis. By integrating the traffic simulator outputs with the visible light communication system, the approach aims to enhance traffic monitoring, reduce congestion, and support the future integration of visible light communication into smart transportation infrastructure. This integration demonstrates the potential of combining advanced error correction techniques with traffic simulation data to improve urban communication infrastructures.

In this paper an integrated wavelength optical filter and photodetector for Visible Light Communication (VLC) is used. The proposed application uses indoor warm light lamps lighting using ultra-bright white LEDs pulsed at frequencies higher than the ones perceived by the human eye. The system was analyzed using two different types the white LEDs, namely, phosphor and trichromatic based LEDs. The signals were transmitted into free space and the generated photocurrent was measured by the pin-pin photodetector based on a-SiC:H/a-Si:H. This device operates in the visible spectrum, allowing thus the detection of the pulsed white light emitted by the LEDs. However, as it also works as a visible optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light, it is able to detect different wavelengths. This feature allows the detection of the individual components of the tri-chromatic white LED, which enlarges the amount of information transmitted by this type of white LED, when compared to the phosphor based LED. A capacitive optoelectronic model supports the experimental results and the physical operation of the device. A numerical simulation is presented.

Nowadays, Global Positioning Systems (GPS) are used everywhere for positioning and navigation. However, its use is not suitable in indoor environment, due to the strong attenuation inside buildings. Therefore, indoors navigation takes advantage of other technologies to infer position. Recently, several Visible Light Positioning (VLP) systems have been reported. Among these technologies, Visible Light Communication (VLC) is one of the most promising, as its operation is based on the use of Light Emitting Diode (LED) light, currently widely used in the illumination solutions of most buildings. In this paper, we propose an indoor navigation system based on VLC in an industrial application for automated warehouses, where the navigation of Autonomous Guided Vehicles (AGV) is supported by VLC. The proposed VLC system establishes bi-directional communication between the infrastructure and the guided vehicles. LED transmitters at the warehouse ceiling support downlink data transmission from the Infrastructure to Vehicle (I2V). This channel provides positioning and navigation of the vehicles, as well as transmission of dedicated messages related to the requested tasks of the management warehouse system to the AVGs. The uplink channel from the Vehicle to the Infrastructure (V2I) is used to acknowledge the requested tasks and transmit updates on the concluded tasks. Optical transmitters are tri-chromatic white LEDs with a wide angle beam. The characterization of the optical transmitter system is done through MatLab simulations for path loss and VLC channel gain prediction using the Lambertian model for the LED light distribution. Dedicated receivers based on a-SiC:H/a-Si:H photodiodes with selective spectral sensitivity are used to record the transmitted signal. The decoding strategy is based on accurate calibration of the output signal.

In this paper we present results on the use of a semiconductor heterostructure based on a-SiC:H as a wavelength-division demultiplexer for the visible light spectrum. The proposed device is composed of two stacked p-i-n photodiodes with intrinsic absorber regions adjusted to short and long wavelength absorption and carrier collection. An optoelectronic characterisation of the device was performed in the visible spectrum. Demonstration of the device functionality for WDM applications was done with three different input channels covering the long, the medium and the short wavelengths in the visible range. The recovery of the input channels is explained using the photocurrent spectral dependence on the applied voltage. An electrical model of the WDM device is proposed and supported by the solution of the respective circuit equations. Short range optical communications constitute the major application field however other applications are foreseen. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this paper the viability of an integrated wavelength optical filter and photodetector for visible light communication (VLC) is discussed. The proposed application uses indoor warm light lamps lighting accomplished by ultra-bright light-emitting diodes (LEDs) pulsed at frequencies higher than the ones perceived by the human eye. The system was analyzed at two different wavelengths in the visible spectrum (430 nm and 626 nm) with variable optical intensities. The signals were transmitted into free space and measured using a multilayered photodetector based on a-SiC:H/a-Si:H. The detector works as an optical filter with controlled wavelength sensitivity through the use of optical bias. The output photocurrent was measured for different optical intensities of the transmitted optical signal and the extent of each signal was tested. The influence of environmental fluorescent lighting was also analysed in order to test the strength of the system. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Indoor navigation based on Visible Light communication (VLC) are attractive solutions for Indoor Positioning Systems, as Global Positioning Systems signals are strongly absorbed by the buildings and other wireless solutions need to be used. In this work it is proposed an indoor navigation system based on VLC technology for assisting warehouse management with autonomous vehicles. The system is designed to establish bidirectional communication between a static infrastructure and the mobile picking robot. Data transmission uses white tri-chromatic LEDs as optical emitters, a dedicated photodetector with selective spectral sensitivity and different coding schemes designed to ensure synchronization between frames, to shield the decoding process from errors and to minimize flickering effects.

A series of large area single layers and glass/ZnO:AVp(SixC1-x:H)/i(Si:H)/n(SixC1-x:H)/AI (0 < x < 1) heterojunction cells were produced by plasma-enhanced chemical vapour deposition (PE-CVD) at low temperature. Junction properties, carrier transport and photogeneration are investigated from dark and illuminated current-voltage (J-V) and capacitance-voltage (C-V) characteristics. For the heterojunction cells atypical J-V characteristics under different illumination conditions are observed leading to poor fill factors. High series resistances around 106 Q are also measured. These experimental results were used as a basis for the numerical simulation of the energy band diagram, and the electrical field distribution of the structures. Further comparison with the sensor performance gave satisfactory agreement. Results show that the conduction band offset is the most limiting parameter for the optimal collection of the photogenerated carriers. As the optical gap increases and the conductivity of the doped layers decreases, the transport mechanism changes from a drift to a diffusion-limited process.

Indoor navigation is hardly managed by the usual Global Positioning System (GPS) due to the strong attenuation of signals inside the buildings. Alternative based on RF optical, magnetic or acoustic signals can be used. Among the optical technologies, Visible Light Communication (VLC) provides good position accuracy. The proposed system uses commercial RGB white LEDs for the generation of the light, which is simultaneously coded and modulated to transmit information. The receiver includes a multilayered photodetector based on a-SiC:H operating in the visible spectrum. The positioning system includes multiple, identical navigation cells. Inside each cell, the optical pattern defined by the VLC transmitters establishes specific spatial regions assigned each to different optical excitations, which configures the footprint of the navigation cell. Demodulation and decoding procedures of the photocurrent signal measured by the photodetector are used to identify the input optical excitations and enable position recognition inside the cell. The footprint model is characterized using geometrical and optical assumptions, namely the Lambertian model for the LEDs and the evaluation of the channel gain of the VLC link. An algorithm to decode the information is established and the positioning accuracy is discussed. The experimental results confirmed that the proposed VLC architecture is suitable for the intended application.

Visible Light communication is a data transmission technology that uses the LED lighting infrastructure to simultaneously illuminate and communicate. The ubiquitous existence of LED lamps opened a new opportunity for addressing VLC communication in many indoor communication scenarios. The motivation for the application presented in this paper is the modern, efficient management of warehouses supported by autonomous navigation robots that grab goods and deliver the items at the packaging station. This functionality demands bi-directional communication among infrastructures and vehicles. In this paper we propose links for Infrastructure-To-Vehicle (I2V), Vehicle-ToInfrastructure (V2I) and Vehicle-To-Vehicle (V2V) to perform indoors, bi-directional communication for robot navigation in automated warehouses. In this work it is proposed a bidirectional communication system between a static infrastructure and a mobile robot (I2V). The LED lamps of the warehouse illumination system are used to lighten the space, and to transmit information about position and about racks content. The mobile robots communicate with the infrastructure (V2I) to transmit information on the items that are being removed and carried to the packaging station. The communication among the autonomous robots (V2V) provides information on the number of items intended to be collected when the vehicles are in the same lane, possibly with the purpose of collecting the same items. Different codification schemes are proposed to establish the V2I, I2V and V2V links. Tri-chromatic white LEDs with the red and blue chips modulated at different frequencies and a photodetector based on a-SiC:H/a-Si:H with selective spectral sensitivity are used at the emitter and receiver. Position information is provided by each LED lamp to the autonomous vehicle by adequate modulation of the RGB emitters. The decoding strategy is based on accurate calibration of the output signal. Different scenarios were designed and tested. Requirements related to synchronous transmission and flickering were addressed to enhance the system performance.