Patent ID: 7170671

Claim:
A method for forming an optical waveguide having a symmetric refractive index profile within a ferroelectric crystal comprising: providing a ferroelectric crystal substrate having at least one substantially planar surface; forming on said surface a dielectric layer having at least one strip-shaped channel formed therein, said channel having substantially parallel sides and said channel exposing a corresponding strip-shaped portion of said substrate surface; forming within said crystal and beneath said channel a waveguide region by a method further comprising: treating said substrate surface with a dilute proton exchange solution at a first temperature for a first time duration, producing, thereby, a waveguide region having a smoothly decreasing refractive index profile characterized by a highest H + ion concentration and highest index of refraction immediately beneath said substrate surface and a H + concentration and index of refraction diminishing smoothly therebelow; then treating said substrate with a reverse proton exchange solution at a second temperature for a second time duration, restoring, thereby, the original index of refraction of the crystal within a region immediately below said surface while leaving said substrate surface undamaged and leaving said waveguide region beneath said substrate surface with an unaltered crystalline phase and a normalized H + concentration below approximately 0.3.