Integriert-optischer Sensor

An on-chip optical sensor (20) for the detection of the refractive index of gases has a substrate body (12) made of lithium niobate, in which a monomode waveguide (14) is provided, said waveguide stretching between two end faces (18, 19) of the substrate body (12) along its surface (24). Laser radiation (82) can be applied to an entrance face (16) and measurement light obtained by transmission from the exit facet (17) is applied to a light detector (69). The birefringent waveguide (14) stretches in the substrate body (12) along the X or Y kerf axis (54) of the sliced lithium niobate crystal (12). A thin layer (56) made of proton-exchanged lithium niobate, too thin to guide a mode, is provided in a lateral boundary surface (22) of the waveguide (14). The lateral boundary surface (22) is covered by a gas-sensitive coating (37) to which a measurement gas (58) can be applied. An electro-acoustic transducer (39) located at the entrance face (16) end is provided on the surface (24), said tra nsducer generates colinear acoustic surface waves in the lateral boundary surface (22) facing the waveguide (14). The laser radiation (82) applied to the entrance face (16) is linear polarized in the ordinary or extraordinary polarization direction (61), whereby the light detector (69) is twisted by 90 degrees in the direction of its polarization ...