Abstract:
Optical transmission and directivity pattern of a tunable diffraction grating that is based on the X-cut lithium niobate electro-optical crystal are studied. It is demonstrated that the intensities in 0 and $\pm1$ diffraction orders decrease by 40% relative to the original level when a voltage of 792 V is applied to electrodes on the crystal. Diffraction orders at angels of $\pm\lambda/(2d)$ and $\pm3\lambda/(2d)$ are demonstrated. The changes of directivity pattern are caused by scattering phase diffraction grating that emerges in the crystal in the presence of the electric field of electrodes and vanishes in the absence of voltage. A hysteresis dependence of the intensity of the zero diffraction order on the voltage is related to the formation of needle-shaped domains with a length of up to 100 $\mu$m and a width of up to 10 $\mu$m that are oriented perpendicularly to the electrodes. In the vicinity of the domains, the electric field causes rotation of the crystal indicatrix and depolarization and scattering of the transmitted radiation. Under normal conditions, the lifetime of the domains is several weeks when the voltage is switched off and the electrodes are not short-circuited.
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