At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Ronald J Holmes

James Thomas Cargo

Michael C Hughes

Jeffrey B Bindell

Henry M O'Bryan, Jr

William James Minford

You S Kim

Oxides of tantalum and niobium are selectively etched using patterned silicon oxide deposited by a low-temperature chemical vapor deposition as a mask and a sulfate flux to selectively remove exposed portions of the tantalum or niobium oxide substrate.

Lithium niobate etchant

A proton-exchange method of forming optical waveguides within a lithium-based optical substrate is disclosed which utilizes sulfuric acid as the proton source. The substrate is masked to expose the areas desired to be transformed into waveguiding regions and immersed in a heated sulfuric acid bath for a period of time sufficient to provide the exchange between the protons in the acid and the lithium in the substrate. The presence of the protons in the substrate results in increasing the extraordinary refractive index .DELTA.n.sub.e in the unmasked area so that optical guiding may be accomplished. Upon removal of the substrate from the sulfuric acid bath, the substrate must be annealed so as to drive the protons to a depth sufficient to provide effective guiding.

Proton exchange method of forming waveguides in LiNbO.sub.3

A method of improving device performance of optical devices formed in optical substrates is disclosed. The method requires that the optical substrate material, for example, lithium niobate, be pre-annealed to form a surface layer with a known congruent composition before diffusing the waveguide material into the substrate. It has been determined that the composition of optical substrates can vary from boule-to-boule, or even along the length of a given boule. These variations affect the diffusion rate of the waveguide material and result in varying mode sizes (both width and depth of the mode). By pre-annealing all material, the diffusion rate will remain relatively constant, regardless of the particular boule. The pre-annealing can be accomplished either by pre-equilibrating the lithium niobate in a vapor-phase equilibrating crucible containing pre-reacted lithium niobate cullet with the desired composition, or pre-equilibrating the lithium niobate to the Li.sub.2 O-rich phase boundary in a two-phase (LiNbO.sub.3, Li.sub.3 NbO.sub.4) powder bed.

Method of improving waveguide uniformity in optical substrate and product

A process is described for producing optical integrated circuits on lithium niobate substrates in which the composition of the lithium niobate substrates is adjusted by a powder bed equilibration procedure. This procedure involved exposure of the lithium niobate crystals to a powder bed in a crucible during a heat treatment. A similar procedure is used during production of optical integrated circuits to maintain the desired Li/Nb composition in the substrate.

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Greenwich, PA, United States of America

Ronald J Holmes