Patent ID: 8849083

Claim:
An optical fiber for use with radiation of a wavelength, the optical fiber having a cross-sectional profile comprising a base glass material, the base glass material being silica optionally doped with one or more dopants; a first ring of first low refractive index glass features disposed in the base glass material, the first low refractive index glass features having refractive indices in the range of 0.0005 to about 0.0400 less than the refractive index of the base glass material in which they are disposed, the first low refractive index glass features having diameters in the range of about 10 μm to about 70 μm, the first ring having an inner diameter in the range of about 20 μm to about 180 μm; and a second ring of second low refractive index glass features disposed in the base glass material outside of and substantially concentric with the first ring of first low refractive index glass features, the second low refractive index glass features having refractive indices in the range of 0.0005 to about 0.0400 less than the refractive index of the base glass material in which they are disposed, the second low refractive index glass features having diameters in the range of about 10 μm to about 70 μm, the center-to-center spacing of the second low refractive index glass features being in the range of about 10 μm to about 90 μm, wherein the refractive index profile of the base glass material, and the refractive indices, sizes and spacings of the first and second low refractive index glass features provide a loss of less than about 0.7 dB/m for the fundamental mode and a loss greater than about 10 dB/m for all other modes in a coiled configuration having a coil diameter in the range of about 20 cm to about 200 cm, and wherein the effective area of the fundamental mode of the optical fiber is at least about 300 μm 2 .