Browsing by Author "Silva, V."
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- A five channels SiC MUX/DEMUX device with channel separation in the visible rangePublication . Vieira, Manuela; Silva, V.; Louro, Paula; Vieira, Manuel; Barata, ManuelIn this paper we present a tandem UV/VIS/ NIR wavelength selector based on a multilayer a-SiC:H optical filter that requires appropriate ultraviolet steady states optical switches to select the desired wavelengths in the ultraviolet/visible/infrared spectral ranges. Five ultra-light communication channels are transmitted together, each one with a specific bit sequence. Results show that the background side and intensity works as a selector in the infrared, visible and ultra violet light regions, shifting the sensor sensitivity. This nonlinearity allows the identification and decoding of the different input channels. This concept is extended to implement a 1 by 5 wavelength division multiplexer with channel separation in the visible range and a transmission capability of 30 Kbps. The relationship between the optical inputs and the output signal is established and an algorithm to decode the MUX signal presented.
- Majority logical function using a pi'npin a-SiC:H structurePublication . Silva, V.; Barata, Manuel; Louro, Paula; Vieira, Manuel; Vieira, ManuelaThe majority logic function has a true output value whenever more than half of the inputs have a true value. Majority logic, also known as majority voting, is used in many systems, for fault-tolerant design, in bioelectronics, and quantum dot cellular automata. The pi'npin heterostructure p-i'(a-SiC:H)-n/p-i(a-Si:H)-n can be illuminated from both back and front surfaces. Steady state illumination, optical bias, controls the light-to-dark sensitivity in the visible range. Several input data channels, each with a different wavelength, illuminate the front surface. Results show that a majority function of 3 and 5 inputs (MAJ-3, MAJ-5) is built with the pi'npin device projecting the way for a MAJ-n function.
- Optical signal processing for data error detection and correction using a-SiCH technologyPublication . Vieira, Manuel; Vieira, Manuela; Silva, V.; Louro, Paula; Costa, JoãoIn this paper, we explore the nonlinear properties of SiC multilayer devices under UV irradiation to design an optical processor for error detection and correction, that enables reliable delivery of spectral data of four-wave mixing over unreliable communication channels. The SiC optical processor for error detection and correction is realized by using a SiC pin/pin photodetector with UV biased optical gating elements. The relationship between the optical inputs and the corresponding digital output levels is established. Data shows that the optical bias act as a selector that picks one or more states by splitting portions of the input multi optical signals across the front and back photodiodes. Boolean operations are demonstrated optically, additional parity logic operations are performed and checked for errors together. As an example we describe an all-optical processor for error detection and correction and then, provide an experimental demonstration of this fault tolerant reversible system. An intuitive representation with a 4 bit original string coloured message and the transmitted 7 bit string, the parity matrix, the encoding and decoding processes and the design of SiC syndrome generators are presented.
- Optimized solid-state bipolar Marx modulador with resonant type droop compensationPublication . Canacsinh, Hiren; Silva, F. A.; Redondo, Luis; Rocha, L.; Silva, V.; Mendes, J.; Bermaki, H.; Semmak, A.In this paper a voltage droop compensation based on a resonant circuit is proposed for the optimized solid-state bipolar Marx modulator. Keeping the modularity characteristics and the circuit topology, one auxiliary resonant stage was added to the existing Marx stages. The compensation concept consists of adding the auxiliary voltage to the output positive or negative pulse for voltage droop compensation. Simulation results are presented for five stages Marx circuit, 10% voltage droop, using 800 V per stage, 100 ps pulse duration at 50Hz frequency.
- Transmission of signals using white LEDs for VLC applicationsPublication . Louro, Paula; Silva, V.; Rodrigues, I.; Vieira, Manuel; Vieira, ManuelaIn 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.
- VIS/NIR wavelength selector based on a multilayer pi'n/pin a-SiC:H optical filterPublication . Vieira, Manuela; Vieira, Manuel; Silva, V.; Louro, Paula; Rodrigues, I.; Fantoni, AlessandroIn this paper, we present a tandem visible/nearinfrared (VIS/NIR) wavelength selector based on a multilayer a-SiC:H optical filter that requires appropriate near-ultraviolet steady states optical switches to select the desired wavelengths in the VIS/NIR ranges. Spectral response measurements are presented and show the feasibility of tailoring the wavelength and bandwidth of a polychromatic mixture of different wavelengths. The selector filter is realized by using a two terminal double pi'n/pin a-SiC:H photodetector. Five visible/infrared communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analysed by reading out the photocurrent, under near-UV steady state background. Results show that the background side and intensity works as a selector in the infrared/visible regions, shifting the sensor sensitivity. This nonlinearity allows the identification and decoding of the different input channels in the visible/infrared ranges. This concept is extended to implement a 1 by 5 wavelength division multiplexer with channel separation in the VIS/NIR range and a transmission capability of 30 Kbps. The relationship between the optical inputs and the output signal is established and an algorithm to decode the Multiplexed (MUX) signal presented. An optoeletronic model gives insight on the system physics.