  Thin-film lithium niobate is an attractive integrated photonics platform due
to its low optical loss and favorable optical nonlinear and electro-optic
properties. However, in applications such as second harmonic generation,
frequency comb generation, and microwave-to-optics conversion, the device
performance is strongly impeded by the photorefractive effect inherent in
thin-films. In this paper, we show that the dielectric cladding on lithium
niobate microring resonator has a significant influence on the photorefractive
effect. By removing the dielectric cladding layer, the photorefractive effect
in lithium niobate ring resonators can be effectively mitigated. Our work
presents a reliable approach to control the photorefractive effect on thin-film
lithium niobate and will further advance the performance of integrated
classical and quantum photonic devices based on thin-film lithium niobate.
