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Several authors characterized the photo-induced absorption (PA) in a-Si:H by performing suitable physical models describing the optical modifications of the illuminated material. Usual investigation techniques study the phenomenon by analysing transmitted or reflected probe light directed on the film surface. Alternatively, we report an in-guide analysis performed through properly designed planar a-Si:H/SiO2 waveguides, fabricated on a c-Si substrate by plasma enhanced chemical vapour deposition (PECVD). The technique allows a wider interaction region between the probe and the pump beams, then the experimental setup sensitivity improves highly. As probe, we used a coherent beam emitting at 1550 nm wavelength and different pump lights in the visible spectrum. We observed the amplitude modulation induced over the probe radiation traveling through the waveguide when an intermittent visible pump was shone over it. LEDs emitting at 644, 612 and 590 nm wavelengths, at intensities up to 0.85 mW/cm(2), were alternatively used. The PA effect shows a linear increasing on the pump intensity and is stronger for longer wavelength pumps. A numerical analysis of the optical propagation was performed to evaluate the absorption variation: at the highest pump intensity the maxima values for Deltaalpha(1550) were 2.15, 1.7 and 0.88 cm(-1), respectively, for pump emitting at 590, 612 and 644 nm.

A novel rib waveguide-integrated switch is proposed and theoretically discussed. The device is based on the total internal reflection phenomenon (TIR) and the thermo-optic effect (TOE) in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). It takes advantage of a bandgap-engineered a-Si:H layer to explore the properties of an optical interface between materials showing similar refractive indexes but different thermo-optic coefficients. In particular, thanks to modern plasma-enhanced chemical vapor deposition techniques, the refractive index of the amorphous film can be properly tailored to match that of c-Si at a given temperature. TIR may be achieved, however, at the interface by acting on the temperature, because the two materials have different thermo-optic coefficients. The switch is integrated in a 4-mum-wide and 3-mum-thick single-mode rib waveguide. The substrate is a silicon-on-insulator (SOI) wafer with an oxide thickness of 500 nm. The active middle region optimal length is 282 mum. The device performance is analyzed at a wavelength of 1.55 mum. It is shown that the output crosstalk and insertion loss are less than -26 and 3.5 dB, respectively.

Credit risk has always been an important issue for banks and other financial intermediaries. A reliable and consistent computing system is necessary to simplify the decision making process in uncertain domains such as the assessment of credit risk. In recent years fuzzy logic techniques have been in their wide-ranging use in modeling of uncertainties, vagueness, impreciseness and the human thought process. Therefore in this paper we present a fuzzy logic based intelligent system for the assessment of credit risk. It aims at efficiently and intelligently managing the process, handling its complexity, and monitoring large amounts of dynamic information in a distributed way, by using a society of intelligent agents, each carrying out a different function autonomously. The system, developed through the PRACTIONIST framework, helps users to perform both quantitative and qualitative assessment of customers' reliability