Patent ID: 7606452

Claim:
A device for providing an expanded mode field from a single mode optical waveguide, comprising: a length of single mode fiber having a core with a refractive index n co and a cladding with a refractive index n cl , wherein n cl<n co and wherein the cladding has an outer diameter 2ρ; a length of fiber rod absent a cladding wherein the refractive index of the fiber rod is substantially the same as the cladding index n cl of the single mode optical fiber, wherein the outer diameter of the length of fiber rod is 2ρ, substantially the same as the cladding diameter of the single mode fiber; wherein an end of the length of single mode fiber and an end of the length of rod are fused together forming a fusion splice; and, wherein a region including the fusion splice and a portion of the fiber rod and a portion of the single mode fiber about the fusion splice are adiabatically tapered.