Optical waveguide fiber achromatic coupler

Claim 1

A 1×N achromatic coupler, wherein N is 2 or 3, said coupler comprising an elongated body of matrix glass, and three optical waveguide paths extending through said body, each of said paths comprising a core region surrounded by a cladding region of refractive index less than that of said core region, the lowest refractive index of said cladding regions being n 2 , a portion of said cladding regions disposed in contact with said body, said optical waveguide paths extending in sufficiently close proximity for a sufficiently long distance to form a coupling region where a portion of the optical power propagating in one of said paths couples to the other of said paths, said core regions being disposed in a triangular array in said coupling region when viewed in a plane perpendicular to the longitudinal axis of said body, the refractive index of at least that region of said body adjacent said paths being n 3 , where n 3 is lower than n 2 by such an amount that the value of Δ 2-3 is less than 0.125%, wherein Δ 2-3 equals (n 2 2 -n 3 2 )/2n 2 2 .

Claim 13

A method of making a 1×N fiber optic coupler, wherein N equals 2 or 3, said method comprising providing a glass tube having first and second opposite ends and a midregion, a longitudinal bore extending from a first end of said tube to a second end thereof, at least the inner portion of said tube adjacent said bore having a refractive index n 3 , disposing within said bore a portion of an input glass optical fiber and the end portions of two output glass optical fibers, each of said fibers having a core surrounded by a cladding of refractive index less than that of said core, a portion of said cladding of each of said fibers disposed in contact with said bore, the lowest refractive index of the claddings of said optical fibers being n 2 , wherein n 2 is greater than n 3 by such an amount that the value of Δ 2-3 is less than 0.125%, wherein Δ 2-3 equals (n 2 2 -n 3 2 )/2n 2 2 , a portion of said input fiber extending beyond the first end of said tube, a portion of said two output fibers extending beyond the second end of said tube, collapsing said tube midregion onto said fibers, and drawing the central portion of said midregion to reduce the diameter thereof and form a coupling region in which said input fiber and said two output fibers are disposed in a triangular array when viewed in a plane perpendicular to the longitudinal axis of said tube.

Claim 14

A method of making a 1×N fiber optic coupler, wherein N equals 2 or 3, said method comprising providing a glass tube having first and second opposite ends and a midregion, a longitudinal bore extending from a first end of said tube to a second end thereof, at least the inner portion of said tube adjacent said bore having a refractive index n 3 , disposing within said bore a portion of an input glass optical fiber and the end portions of two output glass optical fibers, each of said fibers having a core surrounded by a cladding of refractive index less than that of said core, a portion of said cladding of each of said fibers disposed in contact with said bore, the lowest refractive index of the claddings of said optical fibers being n 2 , wherein n 2 is greater than n 3 by such an amount that the value of Δ 2-3 is less than 0.125%, wherein Δ 2-3 equals (n 2 2 -n 3 2 )/2n 2 2 , a portion of said input fiber extending beyond the first end of said tube, a portion of said two output fibers extending beyond the second end of said tube, collapsing said tube midregion onto said fibers, and drawing the central portion of said midregion to reduce the diameter thereof and form a coupling region in which said input fiber and said two output fibers are disposed in a triangular array when viewed in a plane perpendicular to the longitudinal axis of said tube.