Patent ID: 7636505

Claim:
A microstructured optical fiber comprising: an optical fiber axis; a core extending along said axis, the core being made of a first, undoped material having a first refractive index; and a cladding coextensive with and surrounding the core, wherein the cladding comprises a background matrix made of said first material, and has a plurality of holes formed in said background matrix, said holes extending parallel to the fiber axis, being arranged around the core in substantially concentric rings, and being filled with a second material having a second refractive index lower than the first refractive index, the number of said rings of holes being two or three; the average distance between the holes being at least about 6 μm; the ratio between an effective radius of the core and the average distance between the holes being at most about 1; and the ratio between an average dimension of the holes and the average distance between the holes being at least about 0.5, and wherein: when the number of said rings is two, the average dimension of the holes ranges from about 3 μm to about 9 μm, and when the number of said rings is three, the average dimension of the holes ranges from about 3 μm to about 6.6 μm.