Leidinger, MarkusMarkusLeidingerWerner, Christoph S.Christoph S.WernerYoshiki, WataruWataruYoshikiBuse, KarstenKarstenBuseBreunig, IngoIngoBreunig2022-03-052022-03-052016https://publica.fraunhofer.de/handle/publica/24571010.1364/OL.41.005474Whispering-gallery resonators made of undoped and MgO-doped congruently grown lithium niobate are used to study electro-optic refractive index changes. Hereby, we focus on the volume photovoltaic and the pyroelectric effect, both providing an electric field driving the electro-optic effect. Our findings indicate that the light-induced photorefractive effect, combining the photovoltaic and electro-optic effect, is present only in the non-MgO-doped lithium niobate for exposure with light having wavelengths of up to 850 nm. This leads to strong resonance frequency shifts of the whispering-gallery modes. No photorefractive effect was observed in the MgO-doped material. One has to be aware that surface charges induced by the pyroelectric effect result in a similar phenomenon and are present in both materials.enlithium niobatenonlinear optical materialsoptical resonatorsnonlinear optical devices621journal article