The study of the birefrigence modulator based on lithium niobate

This work investigates a lithium niobate X-cut birefringence modulator with a titanium diffusion channel waveguide. The wave voltage of the modulator depends on the growth and processing conditions of the lithium niobate crystal and on the technology of waveguide formation. The tolerance for determining the length of the electrodes and the gap between them exceeds 1 %. In this regard, the calculated values of the wave voltage can differ significantly, and an experimental measurement of the wave voltage is required for practical use. The authors present an experimental refinement for the value of the wave voltage of the modulator and perform a comparison of the value with the theoretical one. In the experiment, the wave voltage was determined using a scanning Michelson interferometer. It is shown that the experimentally measured value of the wave voltage diverges from the calculated one by more than 26 %. This difference is based on the assumption that the vector of the electric field inside the crystal is directed perpendicular to the axis of propagation of optical radiation, and the magnitude of the electric field does not change over the depth of the crystal. In this case, the overlap integrals of the ordinary and extraordinary waves are equal. In real modulators with a channel waveguide formed by titanium diffusion technology, these assumptions are not fulfilled. The refractive index of lithium niobate and the electro-optical coefficient may vary for different crystal samples, depending on the conditions of their growth, processing and waveguide formation technology. The results of the work can find application in the field of interferometric measuring devices, in which a birefringence modulator is used, since the value of the wave voltage is necessary for the design of control electronics.