Two-dimensional photorefractive photonic lattices in lithium niobate

Abstract

Periodic structures of optical waveguides weakly coupled through evanescent fields suggest exciting possibilities for the switching and steering of light beams propagating within them due to effects of their nonlinear self-action. Some of similar effects have been observed and studied in the 1D waveguide arrays as well as in 1D and 2D photonic lattices optically induced in strontium-barium niobate crystals. This excellent electrooptic and photorefractive crystal has a disadvantage of its limited size which is typically less than 10-15 mm. One more perspective medium to optically form nonlinear photonic lattices is lithium niobate. We form two-dimensional photorefractive photonic lattices in Fe-doped and Cu-doped samples of lithium niobate using irradiation of either, He-Ne laser with a power of 1 mW or diode-pumped solid-state laser with frequency doubling that provides optical power up to 200 mW at wavelength of 532 nm. The recording procedure consists of two steps with formation of separate one-dimensional lattices at each step. The wave vectors of these lattices are adjusted under angles of the same value and opposite signs concerning the crystal optical axis. The ordinarily polarized light is used at the recording stage. The discrete diffraction and nonlinear self-action of extraordinarily polarized light beams within lattices formed is experimentally investigated at wavelength of 633 nm