Wrinkling Labyrinth Patterns on Elastomeric Janus Particles

We describe a novel, low-cost and low-tech method for the fabrication of elastomeric Janus particles with diameters ranging from micrometers to millimeters. This consists of UV-irradiating soft urethane/urea elastomer spheres, which are then extracted in toluene and dried. The spheres are thus composed of a single material: no coating or film deposition steps are required. Furthermore, the whole procedure is carried out at ambient temperature and pressure. Long, labyrinthine corrugations ("wrinkles") appear on the irradiated portions of the particles' surfaces, the spatial periodicity of which can be controlled by varying the sizes of particles. The asymmetric morphology of the resulting Janus particles has been confirmed by scanning electron microscopy, atomic force microscopy, and optical microscopy. We have also established that the spheres behave elastically by performing bouncing tests with dried and swollen spheres. Results can be interpreted by assuming that each sphere consists of a thin, stiff surface layer ("skin") lying atop a thicker, softer substrate ("bulk"). The skin's higher stiffness is hypothesized to result from the more extensive cross-linking of the polymer chains located near the surface by the UV radiation. Textures then arise from competition between the effects of bending the skin and compressing the bulk, as the solvent evaporates and the sphere shrinks.

Photodetector with integrated optical thin film filters

This paper reports on optical filters based on a-SiC:H tandem pi'n/pin heterostructures. The spectral sensitivity is analyzed. Steady state optical bias with different wavelengths are applied from each front and back sides and the photocurrent is measured. Results show that it is possible to control the sensitivity of the device and to tune a specific wavelength range by combining radiations with complementary light penetration depths. The transfer characteristics effects due to changes in the front and back optical bias wavelength are discussed. 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.

Optical Filter Design Using Background Wavelength Processing Techniques

Amorphous SiC tandem heterostructures are used to filter a specific band, in the visible range. Experimental and simulated results are compared to validate the use of SiC multilayered structures in applications where gain compensation is needed or to attenuate unwanted wavelengths. Spectral response data acquired under different frequencies, optical wavelength control and side irradiations are analyzed. Transfer function characteristics are discussed. Color pulsed communication channels are transmitted together and the output signal analyzed under different background conditions. Results show that under controlled wavelength backgrounds, the device sensitivity is enhanced in a precise wavelength range and quenched in the others, tuning or suppressing a specific band. Depending on the background wavelength and irradiation side, the device acts either as a long-, a short-, or a band-rejection pass filter. An optoelectronic model supports the experimental results and gives insight on the physics of the device.

Theoretical Analysis of Multimodal Four-Wave Mixing in Optical Microwires

Optical fiber microwires (OFMs) are nonlinear optical waveguides that support several spatial modes. The multimodal generalized nonlinear Schrodinger equation (MM-GNLSE) is deduced taking into account the linear and nonlinear modal coupling. A detailed theoretical description of four-wave mixing (FWM) considering the modal coupling is developed. Both, the intramode and the intermode phase-matching conditions is calculated for an optical microwire in a strong guiding regime. Finally, the FWM dynamics is studied and the amplitude evolution of the pump beams, the signal and the idler are analyzed.

Reconfigurable SiC Embedded Photonic Structures with Self Optical Bias Control

Multilayered heterostructures based on embedded a-Si:H and a-SiC:H p-i-n filters are analyzed from differential voltage design perspective using short- and long-pass filters. The transfer functions characteristics are presented. A numerical simulation is presented to explain the filtering properties of the photonic devices. Several monochromatic pulsed lights, separately (input channels) or in a polychromatic mixture (multiplexed signal) at different bit rates, illuminated the device. Steady-state optical bias is superimposed from the front and the back side. Results show that depending on the wavelength of the external background and impinging side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. Particular attention is given to the amplification coefficient weights, which allow to take into account the wavelength background effects when a band or frequency needs to be filtered or the gate switch, in which optical active filter gates are used to select and filter input signals to specific output ports in wavelength division multiplexing (WDM) communication systems. This nonlinearity provides the possibility for selective removal or addition of wavelengths. A truth table of an encoder that performs 8-to-1 MUX function exemplifies the optoelectronic conversion.

Optical demultiplexer based on an a-SiC:H voltage controlled device

In this paper we present results on the use of a semiconductor heterostructure based on a-SiC:H as a wavelength-division demultiplexer for the visible light spectrum. The proposed device is composed of two stacked p-i-n photodiodes with intrinsic absorber regions adjusted to short and long wavelength absorption and carrier collection. An optoelectronic characterisation of the device was performed in the visible spectrum. Demonstration of the device functionality for WDM applications was done with three different input channels covering the long, the medium and the short wavelengths in the visible range. The recovery of the input channels is explained using the photocurrent spectral dependence on the applied voltage. An electrical model of the WDM device is proposed and supported by the solution of the respective circuit equations. Short range optical communications constitute the major application field however other applications are foreseen. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optical processing devices based on a-SiCH multilayer architectures

Red, 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

a-SiCH Based Devices as Optical Demultiplexers

In 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.

Direct Color Sensor, Optical Amplifier and Demux Device Integrated on a Single Monolithic SiC Photodetector

A 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.

Hélices e Espirais em Micro e Nanofibras Celulósicas

A celulose é o polímero renovável mais abundante do mundo. É conhecido pela sua excelente biocompatibilidade, propriedades térmicas e mecânicas. A celulose assim como os polipéptideos e o ADN, pertence a uma família de moléculas orgânicas que dão origem à formação de fases líquidas cristalinas (LCs) colestéricas. A Passiflora Edulis, tal como outras plantas trepadeiras, possui longas e flexíveis gavinhas que permitem à planta encontrar um suporte para se fixar. As gavinhas podem assumir a forma de espirais ou de hélices consoante sejam sustentadas por apenas uma ou por ambas as extremidades. As hélices apresentam muitas vezes duas porções helicoidais, uma esquerda e outra direita, separadas por um segmento recto denominado perversão. Este comportamento é consequência da curvatura intrínseca das gavinhas produzidas pela planta trepadeira. O mesmo comportamento pode ser observado em micro e nanofibras celulósicas fabricadas a partir de soluções líquido-cristalinas, numa escala três a quatro ordens de grandeza inferior à das gavinhas. Este facto sugere que o modelo físico utilizado tenha invariância de escala. Neste trabalho é feito o estudo de fibras e jactos que imitam as estruturas helicoidais apresentadas pelas gavinhas das plantas trepadeiras. As fibras e jactos são produzidos a partir de soluções líquidas cristalinas celulósicas. De modo a determinar as características morfológicas e estruturais, que contribuem para a curvatura das fibras, foram utilizadas técnicas de imagem por ressonância magnética (MRI), microscopia óptica com luz polarisada (MOP), microscopia electrónica de varrimento (SEM) e microscopia de força atómica (AFM) . A variação da forma das estruturas helicoidais com a temperatura parece ser relevante para o fabrico de membranas não tecidas para aplicação em sensores termo-mecânicos.

Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue

Agência Financiadora - Fundação para a Ciência e Tecnologia - PTDC/CTM NAN/113021/2009

Ensaios avançados com fibras ópticas = advanced characterization of optical fibers

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia de Electrónica e Telecomunicações

Add/drop filters based on SiC technology for optical interconnects

In 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.

Logic functions based on optical bias controlled SIC Tandem devices

The 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

Tunnig optical A-Sic/A-Si active filters by UV bias light in the visible and infrared spectral ranges

Visible range to telecom band spectral translation is accomplished using an amorphous SiC pi'n/pin wavelength selector under appropriate front and back optical light bias. Results show that background intensity works as selectors in the infrared region, shifting the sensor sensitivity. Low intensities select the near-infrared range while high intensities select the visible part according to its wavelength. Here, the optical gain is very high in the infrared/red range, decreases in the green range, stays close to one in the blue region and strongly decreases in the near-UV range. The transfer characteristics effects due to changes in steady state light intensity and wavelength backgrounds are presented. The relationship between the optical inputs and the output signal is established. A capacitive optoelectronic model is presented and tested using the experimental results. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.