Corrugated focusing gratings for coupling radiation in and out of diffused LiNbO3 waveguides

A fabrication method is described and the results are given of an investigation of corrugated periodic and focusing gratings on the surfaces of diffused waveguides in LiNbO₃. The paraxial approximation is used to obtain analytic expressions for the optical parameters of a system employed to form focusing gratings designed to ensure the minimum dimensions of a focusing spot. In an experiment it was found that, for a focal length of 15 mm, radiation of the wavelength λ = 0.63 μ was focused by a corrugated surface of a waveguide of 1.5×3 mm dimensions into a spot of transverse size not exceeding 30×80 μ.