Light-induced waveguide arrays in photorefractive crystals

Light-induced waveguide arrays pave a way to implement massive parallel and adaptive interconnection, and provide a fertile ground for investigating self-localized states, better known as discrete solitons. In this paper, creating planar and channel waveguide arrays by illuminations of two- or four-beam interference fields are investigated both theoretically and experimentally in LiNbO₃:Fe, SBN:Cr, and KNSBN:Ce crystals. The distributions of refractive index changes induced by multi-beam interference fields with different orientations in various photorefractive crystals are numerically simulated. Employing illuminations of two-beam interference fields, planar waveguide arrays are experimentally demonstrated in an open circuit LiNbO₃:Fe crystal and biased SBN:Cr and KNSBN:Ce crystals. An approach for fabricating channel waveguide arrays by employing illuminations of two-beam interference fields is presented. By fabricating a square and a rectangular channel waveguide arrays in a LiNbO₃:Fe crystal this approach is experimentally demonstrated. Creating channel waveguide arrays using four-beam interference fields with different orientations are also performed in the three kinds of crystals. The index profiles of the light-induced waveguide arrays are measured employing the intcrferometric method or the digital holography. The near field patterns, diffraction patterns and the guiding test results show that the waveguide arrays are successfully fabricated.