Patent ID: 7190869

Claim:
A two-mode highly briefringent photonic crystal fiber, comprising: a core of a substantially transparent core material, having a core refractive index and a length, and has a core diameter; and a cladding region surrounding the length of core material, wherein the cladding region includes a first substantially transparent cladding material, having a first refractive index, and wherein the first substantially transparent cladding material has embedded along its length a substantially periodic array of holes having a second refractive index which is less than the first refractive index, wherein the array of holes has at least two larger holes having a diameter, d 2 , and being arranged substantially symmetrical about a center axis of the photonic crystal fiber; and a plurality of smaller holes having a diameter, d 1 , and being spaced apart by a pitch, Λ, wherein d 1 is smaller than d 2 , and wherein the dimensions of the smaller hole diameter, d 1 , the larger hole diameter d 2 , and the pitch, Λ, co-operate to give two modes propagation within the photonic crystal fiber independent of input radiation wavelength over an appropriate wavelength range, for a substantially fixed d 1 /Λ ratio within a range of approximately 0.5–0.65.