Microdomain Patterns Recorded by an Electron Beam in He-Implanted Optical Waveguides on X-Cut LiNbO₃ Crystals

Abstract

We present the results of studies in planar optical waveguides fabricated by He-ion implantation with the energy of 500 keV in X-cut LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystals. The thickness of the formed waveguide layer confined by the depth D of the implanted layer is of about 1.06 μm. The refractive indices as well as differences in refractive indices were evaluated for wavelengths λ = 445, 626.5, and 650 nm. Domain gratings with the period λ = 4 μm were recorded in these samples by electron beam irradiation with acceleration voltages U in the range from 5 to 25 kV. Gratings characteristics measured by the PFM method were obtained for different domain thicknesses T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> determined by U. The optimum grating regularity is achieved when the domain growth occurs beyond the He-implanted damaged barrier, i.e., at T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ≤ D, which in the given case corresponds to U = 10 and 15 kV. Otherwise, (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> > D), the domain evolution is affected by the structurally damaged layer and the gratings become irregular.