Method for making metal halide optical fiber

Claim 1

In a method for making an optical fiber preform which comprises the vapor deposition of layers of metal halide glass or glass-forming constituents on the inside surface of a silicate glass substrate tube in the presence of a fluorine-containing reactant capable of attacking and releasing silicon compounds from the inside surface of the substrate tube, the improvement comprising, prior to vapor deposition, (a) providing a slurry coating of a sinterable, particulate, fluoride-resistant material on the inside surface of the tube, the slurry consisting essentially of the sinterable, particulate material and a volatilizable organic vehicle for the material; (b) removing the volatilizable organic vehicle to leave a dry deposit of the particulate sinterable material; and (c) heating the deposit to sinter the particulate material into a fluoride-resistant protective coating fused to the inside surface of the tube, whereby the fused protective coating acts as a passivation layer to retard the release of silicon compounds from the inside surface of the tube.

Claim 6

A method for making a metal halide optical fiber which comprises the steps of: (a) selecting a glass tube composed of a silicate glass exhibiting surface etching in the presence of HF; (b) coating the inside wall of the glass tube with a flowable slurry, the flowable slurry consisting essentially of a liquid vehicle and a particulate solid, the particulates solid consisting essentially of a sinterable composition for a fluorine-resistant glass; (c) heating the coated tube to evaporate the liquid vehicle and sinter the particulate solid to a non-porous glass film; (d) vapor-depositing a first metal halide layer on the glass film to form a metal halide cladding layer; (e) vapor depositing a second metal halide layer on the first metal halide layer to form a metal halide core layer; and (f) collapsing and drawing the tube, film, and metal halide layers into a metal halide optical fiber.

Claim 7

A method for making a metal halide optical fiber which comprises the steps of: (a) selecting a glass tube composed of a silicate glass exhibiting surface etching in the presence of HF; (b) coating the inside wall of the glass tube with a flowable slurry, the flowable slurry consisting essentially of a liquid vehicle and a particulate solid, the particulates solid consisting essentially of a sinterable composition for a fluorine-resistant glass; (c) heating the coated tube to evaporate the liquid vehicle and sinter the particulate solid to a non-porous glass film; (d) vapor-depositing a first metal halide layer on the glass film to form a metal halide cladding layer; (e) vapor depositing a second metal halide layer on the first metal halide layer to form a metal halide core layer; and (f) collapsing and drawing the tube, film, and metal halide layers into a metal halide optical fiber.