FORMATION OF WAVE-GUIDES AND MODULATORS IN LINBO3 BY ION-IMPLANTATION

Ion implantation is an attractive method for writing optical circuits for use in integrated optics. In LiNbO3 it is shown that there are large changes produced in both refractive indices n0 and ne by the energy deposited in nuclear collisions between the implanted ions and the lattice. The process is insensitive to ion species and at 300 K a universal curve exists for the decrease of n0 as a function of deposited energy by nuclear collisions. Saturation changes of -6% occur at 300 ° K, and larger values are noted for 77 K implants. The saturation condition is reached after the deposition of ∼1022 keV cm-3 from the ion beams. Because the indices are reduced, ion beams have been used to write low index boundaries to define waveguiding regions. By using energetic light ions (e.g., 2-MeV He+) negligible change is produced in the surface layer where the energy loss is primarily electronic and thus the low index region is formed deep within the solid. The computed and measured mode characteristics are in good agreement. The guides show complex annealing characteristics but absorption losses are negligible after annealing at 200 ° C. Guiding action exists after heat treatments up to some 400 ° C. The surface layers retain crystallinity and electro-optic properties; as a demonstration of this we report results from three-dimensional modulators formed by helium-ion implantation.