An optical waveguide structure is formed by embedding a core material within a
medium of lower refractive index, i.e. the cladding. The optical index of refraction
of amorphous silicon (a-Si) and polycrystalline silicon (p-Si), in the wavelength
range between about 1.2 and about 1.6 micrometers, differ by up to about 20%, with
the amorphous phase having the larger index. Spatially selective laser crystallization
of amorphous silicon provides a mechanism for controlling the spatial variation
of the refractive index and for surrounding the amorphous regions with crystalline
material. In cases where an amorphous silicon film is interposed between layers
of low refractive index, for example, a structure comprised of a SiO2
substrate, a Si film and an SiO2 film, the formation of guided wave
structures is particularly simple.
