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Majority logical function using a pi'npin a-SiC:H structure

Publication . Silva, V.; Barata, Manuel; Louro, Paula; Vieira, Manuel; Vieira, Manuela

The 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.

2016Conference object

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Local surface plasmon resonance of metallic nanoparticles embedded in amorphous silicon

Publication . Fantoni, Alessandro; Fernandes, Miguel; Vigranenko, Y.; Vieira, Manuela

This work reports a theoretical study aimed to identify the plasmonic resonance condition for a system formed by metallic nanoparticles embedded in an a-Si:H matrix. The study is based on a Tauc-Lorentz model for the electrical permittivity of a-Si:H and a Drude model for the metallic nanoparticles and the polarizability of an aluminium sphere shaped particle with radius of 10-20 nm. We also performed FDTD simulations of light propagation inside this structure reporting about the effects caused by a single nanosphere of aluminium, silver and, as a comparison, an ideally perfectly conductor. The simulation results show that it is possible to obtain a plasmonic resonance in the red part of the spectrum (600-650 nm) when 10-20 nm radius aluminium spheres are embedded into a-Si:H. (C) 2017 Portuguese Society of Materials (SPM). Published by Elsevier, S.L.U.

2017-04Journal article

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Optical signal processing for data error detection and correction using a-SiCH technology

Publication . Vieira, Manuel; Vieira, Manuela; Silva, V.; Louro, Paula; Costa, João

In 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.

2015-12Journal article

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VIS/NIR wavelength selector based on a multilayer pi'n/pin a-SiC:H optical filter

Publication . Vieira, Manuela; Vieira, Manuel; Silva, V.; Louro, Paula; Rodrigues, I.; Fantoni, Alessandro

In 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.

2015-12Journal article

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Seven channel wavelength demultiplexer using a tandem a:SiC-H/a:Si-H photo sensor

Publication . Silva, Vítor; Barata, Manuel; Vieira, Manuel; Louro, Paula; Vieira, Manuela

The pi'npin photo device is a tandem a: SiC-H / a: Si-H heterostructures. The device is electrically biased and can also be optically biased by ultra-violet illumination of the front or back surfaces. The front surface is also used for several pulsed single wavelength signals within the visible range. Experimental results show that the ultra-violet bias illumination at the front surface of the device enhances wavelengths longer than 500 nm while quenching the wavelengths shorter than 500 nm. The opposite happens when the bias is set at the back surface of the device; wavelengths shorter than 500 nm are enhanced while the ones above are quenched. Several digital applications have been built using the p'inpin device. This paper focuses on the use of the pi'npin device for seven channel Wavelength Division Multiplexing (WDM) digital communication using Manchester coded signals, with a single wavelength for each channel. The seven channels form a frame with 7*256 bits with a preamble for signal intensity and synchronization purposes. Results show that the clustering of the received signal enables the successful recovery of the seven channel data using the front and back illumination of the surfaces of the pi'npin photo device.

2016Conference object

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