Photorefractive properties of ion-implanted waveguides in strontium barium niobate crystals

Abstract

Planar optical waveguides were formed in cerium-doped strontium barium niobate single crystals (Sr0.61Ba0.39 Nb2O6, SBN61), either by proton or helium ion implantation. Proton-implanted samples show a large increase of dark conductivity that reduces or even prevents the recording of refractive index gratings, For waveguides formed by helium implantation this effect is absent, and they can be used for efficient holographic recording. Photorefractive properties of the waveguides are investigated by two-beam coupling. After implantation with 2.0 MeV He+ and doses of (0.5 - 5) x 10(15) cm(-2), the samples have to be polarized again, because heating or charge effects at the crystals surface during the implantation process decreases or even reverses the effective electrooptic coefficients in the waveguiding layer. For repoled samples, we find logarithmic gain coefficients of up to 45 cm(-1) with time constants for the build-up of the purely pi/2-shifted refractive index grating of the order of 1 ms for the blue lines of an Ar+ laser. Photoconductivity depends nonlinearly on light intensity with an exponent x approximate to 0.55. With increasing implanted helium dose, both electronic and nuclear damage of the waveguiding layer grows, and the photorefractive properties of the waveguides are considerably degraded.