Optical fiber with low loss and nanoscale structurally homogeneous core

An optical fiber, comprising:

• a plurality of concentric fiber regions, including a core region and surrounding cladding regions that are doped with one or more index-modifying dopants in respective amounts and radial positions that are configured to create a selected index profile,
• wherein 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, and
• wherein 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,
• wherein the fiber regions are doped with one or more viscosity-reducing dopants in respective amounts and radial positions that are configured such that the drawn fiber has an attenuation of less than 0.17 dB/km at a transmission wavelength of 1550 nm.

An optical fiber, comprising:

• a plurality of concentric fiber regions, including a core region and surrounding cladding regions that are doped with one or more index-modifying dopants in respective amounts and radial positions that are configured to create a selected index profile,
• wherein 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, and
• wherein 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,
• wherein the fiber is doped with amounts of viscosity-reducing K dopant and Cl dopant,
• wherein the amount of K dopant is between 5 and 2,000 ppm, and
• wherein the amount of Cl dopant is between 100 and 15,000 ppm.

An optical fiber, comprising:

• a plurality of concentric fiber regions, including a core region and surrounding cladding regions that are doped with one or more index-modifying dopants in respective amounts and radial positions that are configured to create a selected index profile,
• wherein 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, and
• wherein 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,
• wherein the fiber is doped with amounts of viscosity-reducing Rb dopant, Cl dopant, and P dopant,
• wherein the amount of Rb dopant is between 5 and 2,000 ppm,
• wherein the amount of Cl dopant is between 100 and 15,000 ppm, and
• wherein the amount of P dopant is between 0% and 2%.

An optical fiber, comprising:

• a plurality of concentric fiber regions, including a core region and surrounding cladding regions that are doped with one or more index-modifying dopants in respective amounts and radial positions that are configured to create a selected index profile,
• wherein 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, and
• wherein 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,
• wherein the fiber is doped with amounts of viscosity-reducing Na and F dopant,
• wherein the amount of Na dopant is between 5 and 2,000 ppm, and
• wherein the amount of F dopant is between 100 and 150,000 ppm.