Optical control of light in a waveguide by high-Q cavity modulation

High Q factor whispering gallery mode resonators with their ultrahigh selectivity for optical resonances are used to demonstrate switching of cw light with cw light. This switching can result in either higher or lower throughput of a light beam in a waveguide channel and has implications for optical computation and communications. The effect in the present letter is based on small index of refraction alterations induced by a thermo-optic effect. The sign of the effect can be controlled by the relative position of sphere to the waveguide. The geometry used in our demonstration, which has been able to detect an index of refraction alteration of 10^-7, is potentially capable of monitoring such changes as small as 10^-10 and can be generalized to other means of optical switching and modulation for optical device and computing applications.