Browsing by Author "Vieira, Manuel"
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- a-SiCH based devices as optical demultiplexersPublication . Louro, Paula; Vieira, Manuela; Costa, João; Vieira, Manuel; Fernandes, Miguel; Fantoni, Alessandro; Barata, ManuelIn this paper we present results on the use of a multilayered a-SiC:H heterostructure as a wavelength-division demultiplexing device (WDM) for the visible light spectrum. The WDM device is a glass/ITO/a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n)/ITO heterostructure in which the generated photocurrent at different values of the applied bias can be assigned to the different optical signals. The device was characterized through spectral response measurements, under different electrical bias. Demonstration of the device functionality for WDM applications was done with three different input channels covering wavelengths within the visible range. The recovery of the input channels is explained using the photocurrent spectral dependence on the applied voltage. The influence of the optical power density was also analysed. An electrical model, supported by a numerical simulation explains the device operation. Short range optical communications constitute the major application field, however other applications are also foreseen.
- Add/drop filters based on SiC technology for optical interconnectsPublication . Vieira, Manuela; Vieira, Manuel; Louro, Paula; Fantoni, Alessandro; Silva, VítorIn this paper we demonstrate an add/drop filter based on SiC technology. Tailoring of the channel bandwidth and wavelength is experimentally demonstrated. The concept is extended to implement a 1 by 4 wavelength division multiplexer with channel separation in the visible range. The device consists of a p-i'(a-SiC:H)-n/p-i(a-Si: H)-n heterostructure. Several monochromatic pulsed lights, separately or in a polychromatic mixture illuminated the device. Independent tuning of each channel is performed by steady state violet bias superimposed either from the front and back sides. Results show that, front background enhances the light-to-dark sensitivity of the long and medium wavelength channels and quench strongly the others. Back violet background has the opposite behaviour. This nonlinearity provides the possibility for selective removal or addition of wavelengths. An optoelectronic model is presented and explains the light filtering properties of the add/drop filter, under different optical bias conditions.
- An optical processor for data error detection and correction using a (9,5) binary code generator and the syndrome decoding processPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Silva, Vítor; Costa, JBased on a-SiC:H technology, we present an optical processor for data error detection and correction using a suitable (9,5) Hamming binary code generator and the syndrome decoding process. The optical processor consists of an a-SiC:H double p-i-n photodetector with two ultraviolet light biased gates. The relationship between the optical inputs (transmitted data) and the corresponding output levels (the received data) is established and decoded. Results show that under irradiation the device acts as an active filter. Under front irradiation the magnitude of the short wavelength is quenched and in the long wavelength range is enlarged, while the opposite happens under back lighting. Parity bits are generated and stored simultaneously with the data word. Parity logic operations are performed and checked for errors together. An all-optical processor for error detection and correction is presented to provide an experimental demonstration of this fault tolerant reversible system. Two original coloured string messages, having 4- and 5- bits, respectively, are analyzed and the transmitted 7- or 9- bit string, the parity matrix, the encoding and decoding processes, are explained. The design of SiC syndrome generators for error correction is tested.
- Bi-directional communication between infrastructures and vehicles through visible lightPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Vieira, PedroIn this paper a vehicular communication system that incorporates illumination, signaling, communications, and positioning functions is presented. The bidirectional communication between the infrastructures and the vehicles (I2V), between vehicles (V2V) and from the vehicles to the infrastructures (V2I) is performed through Visible Light Communication (VLC) using the street lamps and the traffic signaling LEDs to broadcast the information. As receivers and decoders, pin/pin SiC Wavelength Division Multiplex (WDM) photodetectors, with light filtering properties, are being used. White polychromatic-LEDs are used for lighting and to implement the WDM. This allows modulating separate data streams on four colors which together multiplex to white light. A traffic scenario is proposed, along with the transmitter to receiver setup. The performance of a cooperative driving system is evaluated. To achieve cooperative vehicular communications (I2V2V2I2V), streams of messages containing the ID physical address of the emitters are used, transmitting a codeword that is received and decoded by the receivers. As a proof of concept, a I2V2V2IV traffic scenario is presented, bidirectional communication between the infrastructures and the vehicles is established and tested. The experimental results confirm that the cooperative vehicular VLC architecture is a promising approach concerning communications between road infrastructures and cars, fulfilling data privacy.
- Bi-directional VLC LED-assisted navigation system for large indoor environmentsPublication . Vieira, Manuela; Vieira, Manuel; Louro, Paula; Fantoni, Alessandro; Vieira, PedroIn this paper, a LED-assisted positioning and navigation VLC system is proposed. A VLC scenario for large environments is stablished, the emitters and receivers are characterized and the communication protocol presented. Different layouts are analyzed. Square and hexagonal meshes are tested and a 2D localization design, demonstrated by a prototype implementation, is presented. The key differences between both topologies are discussed. For both, the transmitted information, indoor position, motion direction as well as bi-directional communication are determined. The results showed that the LED-aided VLC navigation system make possible to determine the position of a mobile target inside the network, to infer the travel direction along the time and to interact with information received.
- Cooperative vehicular communication systems based on visible light communicationPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Vieira, PedroThe use of visible light communication (VLC) in vehicular communication systems for vehicle safety applications is proposed. The system aims to ensure the communication between a LED-based VLC emitter and an on-vehicle VLC receiver. A traffic scenario is established. Vehicle-to-vehicle (V2V) and infrastructure-to-vehicle (12V) communications are analyzed. For the V2V communication study, the emitter was developed based on the vehicle headlights, whereas for the study of 12V communication system, the emitter was built based on streetlights. The VLC receiver is based on amorphous SiC technology and enhances the conditioning of the signal enabling to decode the transmitted information. Receivers are located at the rooftop of the vehicle, for 12V communications, and at the tails for V2V reception. Clusters of emitters, in a square topology, are used in the 12V transmission. The information and the ID code of each emitter in the network are sent simultaneously by modulating the individual chips of the trichromatic white LED. Free space is the transmission medium. An on-off code is used to transmit data. An algorithm to decode the information at the receivers is set. The proposed system was tested. The experimental results confirmed that the proposed cooperative VLC architecture is suitable for the intended applications.
- Design of a transmission system for indoors navigation based on VLCPublication . Louro, Paula; Rodrigues, F.; Costa, João; Vieira, Manuel; Vieira, ManuelaIn this research we present a system based on Visible Light Communication (VLC) with the dual purpose of indoor positioning and data transmission. We propose a system based on RGB white LEDs and a pinpin phototetector based on a-SiC:H/a-Si:H to detect the optical signals transmitted y the modulated emitters of the LEDs. A unit navigation cell is defined and characterized by a unique identifier, and the concept is enlarged to adjacent cells. Within each cell, each spatial region is assigned by the optical pattern of the correspondent emitters. Besides, the positioning and navigation functionality, additional data transmission is also demonstrated using four different channels in each navigation cell. A specific codification scheme and decoding algorithm are proposed and discussed. Error control methodology is also presented to enhance the decoding process. In this research we present a system based on Visible Light Communication (VLC) with the dual purpose of indoor positioning and data transmission. We propose a system based on RGB white LEDs and a pinpin phototetector based on a-SiC:H/a-Si:H to detect the optical signals transmitted y the modulated emitters of the LEDs. A unit navigation cell is defined and characterized by a unique identifier, and the concept is enlarged to adjacent cells. Within each cell, each spatial region is assigned by the optical pattern of the correspondent emitters. Besides, the positioning and navigation functionality, additional data transmission is also demonstrated using four different channels in each navigation cell. A specific codification scheme and decoding algorithm are proposed and discussed. Error control methodology is also presented to enhance the decoding process.
- Direct Color Sensor, Optical Amplifier and Demux Device Integrated on a Single Monolithic SiC PhotodetectorPublication . Vieira, Manuela; Louro, Paula; Vieira, Manuel; Costa, João; Fernandes, MiguelA pi'n/pin a-SiC:H voltage and optical bias controlled device is presented and its behavior as image and color sensor, optical amplifier and demux device is discussed. The design and the light source properties are correlated with the sensor output characteristics. Different readout techniques are used. When a low power monochromatic scanner readout the generated carriers the transducer recognizes a color pattern projected on it acting as a direct color and image sensor. Scan speeds up to 10(4) lines per second are achieved without degradation in the resolution. If the photocurrent generated by different monochromatic pulsed channels is readout directly, the information is demultiplexed. Results show that it is possible to decode the information from three simultaneous color channels without bit errors at bit rates per channel higher than 4000 bps. Finally, when triggered by light of appropriated wavelength, it can amplify or suppress the generated photocurrent working as an optical amplifier (C) 2009 Published by Elsevier Ltd.
- Error control on spectral data of four-wave mixing based on a-SiC technologyPublication . Vieira, Manuel; Vieira, Manuela; Vaz da Silva, V; Louro, Paula; Barata, ManuelIn this paper we exploit the nonlinear property of the SiC multilayer devices to design an optical processor for error detection that enables reliable delivery of spectral data of four-wave mixing over unreliable communication channels. The SiC optical processor is realized by using double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Visible pulsed signals are transmitted together at different bit sequences. The combined optical signal is analyzed. Data show that the background acts as selector that picks one or more states by splitting portions of the input multi optical signals across the front and back photodiodes. Boolean operations such as EXOR and three bit addition are demonstrated optically, showing that when one or all of the inputs are present, the system will behave as an XOR gate representing the SUM. When two or three inputs are on, the system acts as AND gate indicating the present of the CARRY bit. Additional parity logic operations are performed using four incoming pulsed communication channels that are transmitted and checked for errors together. As a simple example of this approach, we describe an all-optical processor for error detection and then provide an experimental demonstration of this idea. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- Estrutura financeira das concessões: análise comparativa entre concessões públicas e concessões privadas entre 2010 e 2014Publication . Vieira, Manuel; Breia, Arménio FernandesO objetivo deste estudo é analisar um setor primordial para o nosso País e para a população em geral – o setor das Águas. A estrutura de gastos, o endividamento, a diferenciação entre a gestão privada e a gestão pública das concessões e a influência nos seus resultados são temas de extrema importância para o futuro, não apenas para a sustentabilidade do próprio setor, como também para todos os consumidores. Esta investigação tem como base uma revisão bibliográfica, fundamentalmente sobre a origem das concessões no nosso País, a sua comparação com outro método de gestão em voga – as parcerias público-privadas. A revisão bibliográfica incide igualmente na análise utilizada para a comparação das empresas em estudo face às suas diferenças. Foi realizado um estudo de caso a três concessões sob a gestão publica e três sob a gestão privada, tentando-se identificar as principais diferenças. A resposta a perguntas tais como “O setor das Águas em Portugal é sustentável?” ou “Qual dos modelos analisados (Concessão privada ou concessão pública) obtem melhores resultados?” foram o principal foco. No final deste trabalho verificámos que o setor das Águas pode ser auto sustentável. Não se podendo afirmar inequivocamente qual das concessões é o melhor tipo de gestão, mas podendo-se verificar que a complementariedade das duas seria o melhor dos dois mundos.