Hinkov, V.V.Hinkov2022-03-082022-03-081990https://publica.fraunhofer.de/handle/publica/302360An integrated optical sensor for simultaneously recording temperature and reflective index changes has a lithium niobate substrate (12) containing a monomode birefractive optical waveguide (14) extending between two end faces (18, 19) on the surface (24) of the substrate (12). A lateral limiting surface (22) of the optical waveguide (14) contacts a measuring fluid (58). The coupling surfaces (16, 17) of the optical waveguide (14) on the end faces (18, 19) are highly reflective. Laser radiation (82) can be applied to a coupling surface (16). The measuring signal obtained by the reflection or transmission of radiation from the coupling surface (16 or 17) can be applied to a primary light detector (69). The optical waveguide (14) in the substrate (12) extends along the X or Y axis of the cut lithium niobate crystal. On the side limiting surface (22) of the optical waveguide, there is a layer (56) of proton exchanged lithium niobate which is not thick enough to transmit a mode. The laser r adiation (82) which impinges on the coupling surface (16) is linear polarized, whereby its polarization direction (61) is predefined between the said axis (52) and the perpendicular cutting axes (54) of the lithium niobate crystal. The measuring signal obtained by reflection or transmission from the coupling surface (16 or 17) can be applied to a second light detector (70), whereby the ...de608621patent1989-3920840