An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

One embodiment of the disclosure relates to a method of making an optical fiber comprising the steps of: (i) exposing a silica based preform with at least one porous glass region having soot density of to a gas mixture comprising SiCl.sub.4 having SiCl.sub.4 mole fraction y.sub.SiCl4 at a doping temperature T.sub.dop such that parameter X is larger than 0.03 to form the chlorine treated preform, wherein $X=\frac{1}{1+\left[\left(\frac{}{{}_s-}\right)\frac{0.209748T_{\mathrm{dop}}\mathrm{Exp}\left[-5435.33/T_{\mathrm{dop}}\right]}{y_{\mathrm{SiCl}4}^{3/4}}\right]}$
and .sub.s is the density of the fully densified soot layer; and (ii) exposing the chlorine treated preform to temperatures above 1400 C. to completely sinter the preform to produce sintered optical fiber preform with a chlorine doped region; and (iii) drawing an optical fiber from the sintered optical preform.

An optical fiber with large effective area, low bending loss and low attenuation. The optical fiber includes a core, an inner cladding region, and an outer cladding region. The core region includes a spatially uniform updopant to minimize low Rayleigh scattering and a relative refractive index and radius configured to provide large effective area. The inner cladding region features a large trench volume to minimize bending loss. The core may be doped with Cl and the inner cladding region may be doped with F.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

An optical fiber with large effective area, low bending loss and low attenuation. The optical fiber includes a core, an inner cladding region, and an outer cladding region. The core region includes a spatially uniform updopant to minimize low Rayleigh scattering and a relative refractive index and radius configured to provide large effective area. The inner cladding region features a large trench volume to minimize bending loss. The core may be doped with Cl and the inner cladding region may be doped with F.

An optical fiber with large effective area, low bending loss and low attenuation. The optical fiber includes a core, an inner cladding region, and an outer cladding region. The core region includes a spatially uniform updopant to minimize low Rayleigh scattering and a relative refractive index and radius configured to provide large effective area. The inner cladding region features a large trench volume to minimize bending loss. The core may be doped with Cl and the inner cladding region may be doped with F.

An optical fiber has a core region that is doped with one or more viscosity-reducing dopants in respective amounts that are configured, such that, in a Raman spectrum with a frequency shift of approximately 600 cm.sup., the fiber has a nanoscale structure having an integrated D2 line defect intensity of less than 0.025. Alternatively, the core region is doped with one or more viscosity-reducing dopants in respective amounts that are configured such that the fiber has a residual axial compressive stress with a stress magnitude of more than 20 MPa and a stress radial extent between 2 and 7 times the core radius.

According to another aspect of the invention a majority of the optical propagation through the fiber is supported by an identified group of fiber regions comprising the core region and one or more adjacent cladding regions. The fiber regions are doped with one or more viscosity-reducing dopants in respective amounts and radial positions that are configured to achieve viscosity matching among the fiber regions in the identified group.

An optical fiber with large effective area, low bending loss and low attenuation. The optical fiber includes a core, an inner cladding region, and an outer cladding region. The core region includes a spatially uniform updopant to minimize low Rayleigh scattering and a relative refractive index and radius configured to provide large effective area. The inner cladding region features a large trench volume to minimize bending loss. The core may be doped with Cl and the inner cladding region may be doped with F.

A method of manufacturing a hollow core optical fiber including a vapor deposition step comprising vapor depositing a silica soot coating from one or more source materials over an outer surface of a cladding substrate tube of a workpiece that further includes capillary tubes disposed within a cavity of the cladding substrate tube. The compositions of the capillary tubes, the cladding substrate tube, and the silica soot coating can be manipulated with one or more viscosity-raising dopants or one or more viscosity-lowering dopants, or neither, to achieve a desired compositional profile of a hollow core optical fiber preform with a cladding consolidated from the silica soot coating of the workpiece. The desired composition profile results in a viscosity profile that prevents the capillary tubes from contacting each other during a drawing step performed upon the hollow core optical fiber preform.

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.