Fabrication of optical waveguides

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. The refractive index change due to this effect is proportional to the density and therefore resulted in a peak. The combined result of these two effects produces a 'W' shape refractive index profile.