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- Light memory function in a double pin SiC devicePublication . Vaz da Silva, V; Vieira, Manuela; Vieira, Manuel; Louro, Paula; Barata, ManuelA double pi'npin heterostructure based on amorphous SiC has a non linear spectral gain which is a function of the signal wavelength that impinges on its front or back surface. An impulse of a configurable length and amplitude is applied to a 390 nm LED which illuminates one of the sensor surfaces, followed by a time period without any illumination after which an input signal with a different wavelength is impinged upon the front surface. Results show that the intensity and duration of the impulse illumination of the surfaces influences the sensor's response with different output for the same input signal. This paper studies this effect and proposes an application as a short term light memory. (C) 2015 Elsevier B.V. All rights reserved.
- SiC multilayer photonic structures with self optical bias amplificationPublication . Vieira, Manuela; Vieira, Manuel Augusto; Louro, Paula; Fantoni, Alessandro; Barata, Manuel; Vaz da Silva, VCharacteristics of tunable wavelength pi'n/pin filters based on a-SiC:H multilayered stacked cells are studied both experimental and theoretically. Results show that the device combines the demultiplexing operation with the simultaneous photodetection and self amplification of the signal. An algorithm to decode the multiplex signal is established. A capacitive active band-pass filter model is presented and supported by an electrical simulation of the state variable filter circuit. Experimental and simulated results show that the device acts as a state variable filter. It combines the properties of active high-pass and low-pass filter sections into a capacitive active band-pass filter using a changing photo capacitance to control the power delivered to the load.
- 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.
- Optoelectronic digital capture device based on Si/C multilayer heterostructuresPublication . Vaz da Silva, V; Vieira, Manuel Augusto; Louro, Paula; Vieira, Manuela; Barata, ManuelCombined tunable WDM converters based on SiC multilayer photonic active filters are analyzed. The operation combines the properties of active long-pass and short-pass wavelength filter sections into a capacitive active band-pass filter. The sensor element is a multilayered heterostructure produced by PE-CVD. The configuration includes two stacked SiC p-i-n structures sandwiched between two transparent contacts. Transfer function characteristics are studied both theoretically and experimentally. Results show that optical bias activated photonic device combines the demultiplexing operation with the simultaneous photodetection and self amplification of an optical signal acting the device as an integrated photonic filter in the visible range. Depending on the wavelength of the external background and irradiation side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. The output waveform presents a nonlinear amplitude-dependent response to the wavelengths of the input channels. A numerical simulation and two building-blocks active circuit is presented and gives insight into the physics of the device.
- Five channel WDM communication using a single a:SiC-H double pin photo devicePublication . Vaz da Silva, V; Barata, Manuel; Louro, Paula; Vieira, Manuel; Vieira, ManuelaAmorphous SiC heterostructures built as a double pin device has a non linear spectral gain which is a function of the signal wavelength that impinges on its front or back surface. Illuminating the device with several single wavelength data channels in the visible spectrum allows for Wavelength Division Multiplexing (WDM) digital communication. Using fixed ultra-violet illumination at the front or back surfaces enables the recovery of the multiplexed channels. Five channels, each using a single wavelength which is modulated by a Manchester coded signal at 12,000 bps, form a frame with 1024 bits with a preamble for signal intensity and synchronisation purposes. Results show that the clustering of the received signal enables the successful recovery of the five channel data using the front and back illumination of the surfaces of the double pin photo device. (C) 2015 Elsevier B.V. All rights reserved.
- Optoelectronic logic functions based on reconfigurable SiC multilayer devicesPublication . Vieira, Manuel Augusto; Vaz da Silva, V; Louro, Paula; Vieira, Manuela; Barata, ManuelWDM multilayered SiC/Si devices based on a-Si:H and a-SiC:H filter design are approached from a reconfigurable point of view. Results show that the devices, under appropriated optical bias, act as reconfigurable active filters that allow optical switching and optoelectronic logic functions development. Under front violet irradiation the magnitude of the red and green channels are amplified and the blue and violet reduced. Violet back irradiation cuts the red channel, slightly influences the magnitude of the green and blue ones and strongly amplifies de violet channel. This nonlinearity provides the possibility for selective removal of useless wavelengths. Particular attention is given to the amplification coefficient weights, which allow taking into account the wavelength background effects when a band needs to be filtered from a wider range of mixed signals, or when optical active filter gates are used to select and filter input signals to specific output ports in WDM communication systems. A truth table of an encoder that performs 8-to-1 multiplexer (MUX) function is presented.
- Logic functions based on optical bias controlled SIC Tandem devicesPublication . Vaz da Silva, V; Vieira, Manuel; Vieira, Manuela; Louro, Paula; Fantoni, Alessandro; Barata, ManuelThe purpose of this paper is the design of an optoelectronic circuit based on a-SiC technology, able to act simultaneously as a 4-bit binary encoder or a binary decoder in a 4-to-16 line configurations and show multiplexer-based logical functions. The device consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n multilayered structure produced by PECVD. To analyze it under information-modulated wave (color channels) and uniform irradiation (background) four monochromatic pulsed lights (input channels): red, green, blue and violet shine on the device. Steady state optical bias was superimposed separately from the front and the back sides, and the generated photocurrent was measured. Results show that the devices, under appropriate optical bias, act as reconfigurable active filters that allow optical switching and optoelectronic logic functions development providing the possibility for selective removal of useless wavelengths. The logic functions needed to construct any other complex logic functions are the NOT, and both or either an AND or an OR. Any other complex logic function that might be found can also be used as building blocks to achieve the functions needed for the retrieval of channels within the WDM communication link. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- Logical functions in a tandem SiC devicePublication . Vaz da Silva, V; Vieira, Manuel; Louro, Paula; Barata, Manuel; Vieira, ManuelaThis study demonstrates logical functions based on SiC technology. The device consists of a p-i’(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure with low conductivity doped layers. Experimental optoelectronic characterization of the fabricated device is presented and shows the feasibility of tailoring channel bandwidth and wavelength by optical bias through illumination in the back and front sides with violet light. Two digital light signals are applied to the front side of the device while violet light steadily shines either at the back or front sides. Each digital light signal is composed by two wavelengths, one from the long and the other from the short visible wavelength range. One digital signal is the Red–Blue pair and the other the Green–Violet. The NOT logical function is shown with the Red–Blue pair likewise with the Green–Violet pair. The background biasing either at front or at the back side allows for an inverted signal or non inverted signal. Experimental results show and explain the interaction of two digital signal pairs and the identification of the logical AND, OR and XOR operations by the selection of the violet biasing illumination side.
- Reconfigurable photonic logic architecture: an overviewPublication . Vaz da Silva, V; Barata, Manuel; Vieira, ManuelaThe photosensor studied in this document, is an amorphous silicon structure deposited on transparent glass allowing illumination on both sides. It responds to wavelengths from near infrared range to the ultra-violet. The front illumination surface is used for inputting light signal. The dynamic characteristics of the photosensor are altered by using optical bias on either surface of the sensor, thus the same input results in different outputs. Experimental studies made with the photosensor evaluate its applicability as a multiplexer, demultiplexer and logical operations device. A memory effect was observed. A programmable pattern emission system, and a validation and recovery system were built to illuminate the sensor with input light signals and to analyze the resulting output.
- Light memory operation based on a double pin SiC devicePublication . Vaz da Silva, V; Barata, Manuel; Vieira, Manuel; Louro, Paula; Vieira, ManuelaExperimental optoelectronic characterization of a p-i'(a-SiC:H)-n/pi(a-Si:H)-n heterostructure with low conductivity doped layers shows the feasibility of tailoring channel bandwidth and wavelength by optical bias through back and front side illumination. Front background enhances light-to-dark sensitivity of the long and medium wavelength range, and strongly quenches the others. Back violet background enhances the magnitude in short wavelength range and reduces the others. Experiments have three distinct programmed time slots: control, hibernation and data. Throughout the control time slot steady light wavelengths illuminate either or both sides of the device, followed by the hibernation without any background illumination. The third time slot allows a programmable sequence of different wavelengths with an impulse frequency of 6000Hz to shine upon the sensor. Results show that the control time slot illumination has an influence on the data time slot which is used as a volatile memory with the set, reset logical functions. © IFIP International Federation for Information Processing 2015.