Integrated optical switches and gas sensors.

We have demonstrated new switching and gas-sensing effects in integrated optics using input and output grating couplers and Bragg reflector gratings with 1200 lines/mm on planar SiO(2)-TiO(2) waveguides. Switching is actuated by adsorption or desorption of water or other adsorbates on the waveguide surface through a change in the effective index of the guided modes under the grating. We derived theoretically the ultimate sensitivity limits of the grating devices employed either as switches or as gas sensors. Switching requires the adsorption and desorption, respectively, of less than one H(2)O monolayer. Sensors can detect variations in surface coverage of 1/100 of an H(2)O monolayer.