Two-layer waveguiding structure in LiNbO3 with birefringence reversal for refractive-index sensors with large measurement range

We have developed and investigated a novel two-layer structure in LiNbO3 fabricated with Ti-indiffusion and proton exchange. This structure is especially suitable for constructing refractive-index sensors with a large, up to 2.2, measurement range. Next to its high sensitivity this structure offers also some additional advantages like the possibility to optimize the sensitivity for a given measurand, the elimination of the necessity of buffer layers etc. The largely different sensitivities of the two fundamental TE0- and TM0-modes achieved allows the measurement and the reference channel to be incorporated in the same waveguide. In this way, a new type polarization interferometry can be introduced increasing the flexibility of the refractive-index sensors design.