An optical fiber including: (1) a first outer cladding region including a no-slope portion establishing a 0% baseline (.sub.0); (2) a core region surrounded by the first outer cladding region, the core region including (i) an outer radius (r.sub.1) from 4.0 m to 6.5 m and (ii) a maximum relative refractive index (.sub.1max) from 0.3% to 0.6%, the core region exhibiting an value of 5 or greater; and (3) a depressed index cladding region surrounding the core region and surrounded by the first outer cladding region, the depressed index cladding region including (i) an outer radius (r.sub.3) from 14 m to 28 m, (ii) a relative refractive index (.sub.3) from 0.45% to 0.30%, and (iii) a trench volume (V.sub.T) from 65%-m.sup.2 to 140%-m.sup.2. The optical fiber exhibits lower LP01 bending loss than LP11 bending loss at operating wavelengths in the O- and C-bands.

An optical fiber comprising: (i) a core comprising silica and having a maximum relative refractive index delta .sub.1MAX; and LP01 effective area>100 m.sup.2 at 1550 nm;

(ii) an inner cladding surrounding the core and having a minimum relative refractive index delta .sub.2MIN and .sub.coreMAX>.sub.2MIN; (iii) an outer cladding surrounding the inner cladding and comprising a first outer cladding portion with a maximum refractive index .sub.3A such that .sub.3A>.sub.2MIN; and another outer cladding portion surrounding the first outer cladding portion with a maximum refractive index delta .sub.3B wherein with a maximum refractive index delta .sub.3B wherein .sub.3B>.sub.3A, said another portion being the outermost portion of the outer cladding; and (iv) a coating layer surrounding the outer cladding, and in contact with said another outer cladding portion, the coating layer having a relative refractive index delta .sub.C wherein .sub.C>.sub.3B.

Multimode beam combiners include at least one gradient-step index optical fiber in which a refractive index difference at a core/cladding interface is selected to provide a numerical aperture so as to provide stable, uniform beam output. One or more such fibers is formed into a tapered bundle than can be shaped to provide a selected illuminated aperture. The fibers in the bundle can be separated by respective tapered claddings so as to be optically coupled or uncoupled. Illumination systems can include a plurality of such fibers coupled to a plurality of laser diodes or other light sources.

In one embodiment, an optical fiber includes an inner core having a core refractive index delta and profile shape parameter in the range of 1.8 to 2.6, including endpoints, and a cladding layer surrounding the inner core. The cladding layer includes an inner cladding segment having an inner refractive index delta, a trench segment having a trench refractive index delta, and an outer cladding segment having an outer refractive index delta. The optical fiber further includes a coating layer surrounding the cladding layer and having a thickness of less than 30 m and a modulus greater than or equal to 0.5 GPa.