Patent ID: 7502540

Claim:
An optical fiber, comprising: a core region; and a cladding region, the cladding region including a first cladding region on outer circumference of the core region, the first cladding region including a main-medium region and a sub-medium region having a refractive index lower than a refractive index of the main-medium region, the sub-medium region includes inner sub-medium regions arranged at four folds rotationally symmetric centering on the core region, outer sub-medium regions arranged at four folds rotationally symmetric centering on the core region on outer side of the inner sub-medium regions, each of the four rotationally symmetric folds including a hole along a center axis of the core region, lateral cross sections of the inner sub-medium regions and lateral cross sections of the outer sub-medium regions are circular shaped having a substantially same diameter, the inner sub-medium regions and the outer sub-medium regions are formed with any one of a gaseous substance, a liquid, and a solid substance that fills inside of the hole, and wherein a mode field diameter at a wavelength of 1550 nanometers is equal to or larger than 6 micrometers and equal to or smaller than 11 micrometers. and a macro-bending loss with a curvature radius of 7.5 millimeters at the wavelength of 1550 nanometers is equal to or less than 0.1 dB/m.