Abstract: An optical fiber includes an optical fiber axis; a core extending along the axis, the core being made of a first, undoped material having a first refractive index; and a cladding coextensive to and surrounding the core. The cladding includes a background matrix made of the first material and has a plurality of holes formed in the background matrix extending parallel to the fiber axis arranged around the core in substantially concentric rings, and filled with a second material having a second refractive index lower than the first refractive index. The number of the rings of holes is two or three, an average distance between the holes is at least about 6 ?m, a ratio between an effective radius of the core and the average distance between the holes is at most about 1, and a ratio between an average dimension of the holes and the average distance between the holes is at least about 0.5.

Abstract: An optical fiber includes an optical fiber axis; a core extending along the axis, the core being made of a first, undoped material having a first refractive index; and a cladding coextensive to and surrounding the core. The cladding includes a background matrix made of the first material and has a plurality of holes formed in the background matrix extending parallel to the fiber axis arranged around the core in substantially concentric rings, and filled with a second material having a second refractive index lower than the first refractive index. The number of the rings of holes is two or three, an average distance between the holes is at least about 6 ?m, a ratio between an effective radius of the core and the average distance between the holes is at most about 1, and a ratio between an average dimension of the holes and the average distance between the holes is at least about 0.5.

Abstract: A microstructured optical fiber has a core region with a material having a refractive index nco and a microstructured region surrounding the core region with a background material having a refractive index nm which is lower than the refractive index nco. The microstructured region has a plurality of microstructures having a refractive index different from the refractive index nm, wherein the distance ?? between the centers of any couple of adjacent microstructures is at least equal to about ?p and not higher than about 1.5?p, wherein ?p is the spatial variation length of the electric field intensity in the microstructured region.