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

A two-layer structure in LiNbO₃ fabricated by Ti-indiffusion and proton exchange has been developed and studied. This structure is especially suitable for constructing refractive-index sensors with a large measurement range. Besides its high sensitivity this structure offers some additional advantages, including the possibility of optimizing the sensitivity for a given measurand and the elimination of the necessity for buffer layers. The largely different sensitivities of the fundamental TE₀- and TM₀-modes achieved allows the measurement and the reference channel to be incorporated in the same waveguide. This allows a new type of polarization interferometry that increases the flexibility of the refractive-index sensor design