Self-pulsing in prism coupling into planar waveguides

Coupling argon-laser light into absorbing SiO(2)-TiO(2) waveguides, we observed at constant input power depending on the angle of incidence and the initial gap width, self-pulsing, bistability, or a special form of bistability with either a constant or a self-pulsing output. The system's dynamics is governed by two effects with different time constants, both caused by heating of the waveguide by the incoupled absorbed power: (1) thermal expansion of waveguide and prism, which reduces the coupling gap width and thus changes the incoupling efficiency, and (2) desorption of H(2)O molecules from the SiO(2)-TiO(2) layer, which changes the effective guide index.