In the past several decades, the Finite-Difference Time-Domain (FDTD) method has become one of the most powerful numerical techniques in solving the Maxwell’s curl equations and has been widely applied to solve complex optical and photonic problems. This method divides space and time into a regular grid and simulates the time evolution of Maxwell’s equations. This paper reports some results, obtained by a set of FDTD simulations, about the characteristics of amorphous silicon waveguides embedded in a SiO2 cladding. Light absorption dependence on the material properties and waveguide curvature radius are analysed for wavelengths in the infrared spectrum. Wavelength transmission efficiency is determined analysing the decay of the light power along the waveguides and the obtained results show that total losses should remain within acceptable limits when considering curvature radius as small as 3 μm at its most.
In this work we correlate the dimension of the waveguide with small variations of the refractive index of the material
used for the waveguide core. We calculate the effective modal refractive index for different dimensions of the waveguide
and with slightly variation of the refractive index of the core material. These results are used as an input for a set of
Finite Difference Time Domain simulation, directed to study the characteristics of amorphous silicon waveguides
embedded in a SiO<sub>2</sub> cladding. The study considers simple linear waveguides with rectangular section for studying the
modal attenuation expected at different wavelengths. Transmission efficiency is determined analyzing the decay of the
light power along the waveguides. As far as near infrared wavelengths are considered, a-Si:H shows a behavior highly
dependent on the light wavelength and its extinction coefficient rapidly increases as operating frequency goes into visible
spectrum range. The simulation results show that amorphous silicon can be considered a good candidate for waveguide
material core whenever the waveguide length is as short as a few centimeters. The maximum transmission length is
highly affected by the a-Si:H defect density, the mid-gap density of states and by the waveguide section area. The
simulation results address a minimum requirement of 300nm×400nm waveguide section in order to keep attenuation
below 1 dB cm<sup>-1</sup>.