Loading...
21 results
Search Results
Now showing 1 - 10 of 21
- 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.
- Non-selective optical wavelength-division multiplexing devices based on a-SiC:H multilayer heterostucturesPublication . Vieira, Manuela; Fernandes, Miguel; Louro, Paula; Vieira, Manuel; Barata, Manuel; Fantoni, AlessandroIn this paper we present results on the optimization of multilayered a-SiC:H heterostructures for wavelength-division (de) multiplexing applications. The non selective WDM device is a double heterostructure in a glass/ITO/a-SiC:H (p-i-n) /a-SiC:H(-p) /a-Si:H(-i')/a-SiC:H (-n')/ITO configuration. The single or the multiple modulated wavelength channels are passed through the device, and absorbed accordingly to its wavelength, giving rise to a time dependent wavelength electrical field modulation across it. The effect of single or multiple input signals is converted to an electrical signal to regain the information (wavelength, intensity and frequency) of the incoming photogenerated carriers. Here, the (de) multiplexing of the channels is accomplished electronically, not optically. This approach offers advantages in terms of cost since several channels share the same optical components; and the electrical components are typically less expensive than the optical ones. An electrical model gives insight into the device operation.
- 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.
- Seven channel wavelength demultiplexer using a tandem a:SiC-H/a:Si-H photo sensorPublication . Silva, Vítor; Barata, Manuel; Vieira, Manuel; Louro, Paula; Vieira, ManuelaThe 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.
- New stacked photodevices for signal multiplexing and demultiplexing applications in the visible spectrumPublication . Vieira, Manuela; Louro, Paula; Fantoni, Alessandro; Fernandes, Miguel; Vieira, Manuel Augusto; Barata, ManuelResults on the use of a double a-SiC:H p-i-n heterostructure for signal multiplexing and demultiplexing applications in the visible range are presented. Pulsed monochromatic beams together (multiplexing mode), or a single polychromatic beam (demultiplexing mode) impinge on the device and are absorbed, accordingly to their wavelength. Red, green and blue pulsed input channels are transmitted together, each one with a specific transmission rate. The combined optical signal is analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that in the multiplexing mode the output signal is balanced by the wavelength and transmission rate of each input channel, keeping the memory of the incoming optical carriers. In the demultiplexing mode the photocurrent is controlled by the applied voltage allowing regaining the transmitted information. A physical model supported by a numerical simulation gives insight into the device operation.
- 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.
- Optical processing devices based on a-SiCH multilayer architecturesPublication . Vieira, Manuela; Louro, Paula; Vieira, Manuel; Fernandes, Miguel; Costa, João; Fantoni, Alessandro; Barata, ManuelRed, green and blue optical signals were directed to an a-SiC:H multilayered device, each one with a specific transmission rate. The combined optical signal was analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that when a chromatic time dependent wavelength combination with different transmission rates irradiates the multilayered structure, the device operates as a tunable wavelength filter and can be used in wavelength division multiplexing systems for short range communications. An application to fluorescent proteins detection is presented. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- 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.
- «
- 1 (current)
- 2
- 3
- »