Abstract: The present invention is an improvement to the method of growing silicon films on a substrate by bringing the substrate in contact with molten silicon. The improved growth technique may be classified as an asymmetric mode of growth of silicon on the substrate and is characterized by the substrate being maintained at a lower temperature than the solidification of silicon in the area of the substrate where the silicon layer growth is taking place, that is in the area of the liquid-solid interface. The lower temperature of the substrate, say 5.degree.-10.degree. C. below the freezing temperature of silicon, causes the liquid-solid interface to be tilted to be nearly parallel to the substrate surface but inclined at a reentrant angle, so that the leading edge of the crystallization front is on the substrate. This provides an advantage of increased growth speed.

Abstract: Optical waveguides are fabricated by heating a region of a body of flat filter glass with an energy beam such as a scanning focused laser beam. The region is locally heated to a temperature at which softening occurs. Upon cooling two differing effects occur, the two effects causing a "W" shaped index of refraction profile. The first effect is the photoelastic effect due to the residual stress introduced as the heated material cools and contracts. The residual tensile stress is constant in the softened region, but decreases as the distance from the center of the heating increases. Since the density and therefore the refractive index of this region is inversely proportional to the residual stress, this effect resulted in a local refractive index minimum. The other effect is the material density change in the softened region. As the cooling rate is small in the center and large in the edge of this softened region, a density change occurs with the center attaining the highest value and decrease towards the edge.