Ramar Corporation

S Anantha Narayanan

Amaresh Mahapatra

A method for diffusing titanium into a single-crystal lithium niobate substrate and guided wave devices produced therefrom provide improved mode match with coupled fibers. Preferably, the titanium diffusion occurs at a diffusion temperature for a time between about 8 hours and about 18 hours. Outdiffusion of lithium oxide is allowed to occur during titanium diffusion. The outdiffused region, typically at least about 25 .mu.m, is much deeper than the titanium diffusion depth, typically about 5-10 .mu.m.

Guided wave device and method of fabrication thereof

A method for co-diffusing titanium and aluminum into a single-crystal lithium niobate substrate and guided wave devices produced therefrom are provided. Titanium diffused into the substrate forms a light guiding region. A layer of aluminum deposited over the light guiding region and diffused into the substrate buries the light guiding region below the substrate surface. In an alternate embodiment, a layer of aluminum forms a mode shaping region which surrounds the light guiding region on two sides. The mode shaping region has ordinary and extraordinary indices of refraction less than the substrate such that mode mismatch between a device fabricated thereby and an externally coupled fiber is reduced. The aluminum can be diffused into LiNbO.sub.3 at a much lower temperature without affecting diffused titanium guides. Preferably, the titanium diffusion occurs at about 1000.degree. to about 1100.degree. C. while further aluminum diffusion occurs at a lower temperature in the range of about 900.degree. to 950.degree. C.

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Lowell, MA, United States of America

S Anantha Narayanan