Angularly homogenizing gradient index optical fiber having a refractive index profile that is non-quadratic to a degree sufficient to enhance precession of light as it is propagated through the fiber. Deviation from the quadratic may be limited to avoid profoundly changing the radial boundary within the fiber. Beam asymmetry, for example, associated with small aperture sources launched into a fiber off axis, may be made more symmetric as the beam is propagated through the homogenizing gradient index optical fiber. A refractive index profile may be manufactured to avoid a pure quadratic profile, or a fiber having a refractive index profile that is quadratic in only some orientations about the fiber axis may be twisted during draw to induce a refractive index profile path that enhances propagation precession.

The present invention relates to an optical fiber with improved bend performance and manufacturing method thereof. The optical fiber (100) comprises a core region (108) defined by a core refractive index profile (200) and a cladding region (106) surrounding the core region defined by a cladding refractive index profile (400). Particularly, the core region has a first core (102) defined by a first core refractive index (RI) profile (202) and a first core RI max (peak) and a second core (104) defined by a second core RI profile (204) and a second core RI max (core). Moreover, the cladding region further comprises a first cladding (106) and a third cladding (110) composed of pure silica and a second cladding (108) composed of a down-doped silica, where the down-dopant is fluorine.

A single mode optical fiber is provided that includes a core region having an outer radius r.sub.1 and a maximum relative refractive index .sub.1max. The single mode optical fiber further includes a cladding region surrounding the core region, the cladding region includes a depressed-index cladding region, a relative refractive index .sub.3 of the depressed-index cladding region increasing with increased radial position. The single mode optical fiber has a bend loss at 1550 nm for a 15 mm diameter mandrel of less than about 0.75 dB/turn, a bend loss at 1550 nm for a 20 mm diameter mandrel of less than about 0.2 dB/turn, and a bend loss at 1550 nm for a 30 mm diameter mandrel of less than 0.005 dB/turn. Additionally, the single mode optical fiber has a mode field diameter of 9.0 microns or greater at 1310 nm wavelength.

An optical fiber and a method for preparing an optical fiber is described. A refractive index difference between at least two points in a cross section of the optical fiber is greater than or equal to 0.01, at least five groups of points in the cross section meet a preset condition, a k.sup.th group of points in the at least five groups of points include a point x.sub.k and a point y.sub.k, the point x.sub.k and the point y.sub.k are any point in the cross section, the preset condition includes nx.sub.kny.sub.k0.001 and rx.sub.kry.sub.k<0, nx.sub.k is a refractive index of the point x.sub.k, ny.sub.k is a refractive index of the point y.sub.k, rx.sub.k is a distance from the point x.sub.k to a center of the cross section, ry.sub.k is a distance from the point y.sub.k to the center of the cross section, and k is a positive integer greater than or equal to 1.