The present disclosure relates to an optical fiber having a structure that has a low transmission loss and can be produced with high productivity. An optical fiber according to an embodiment includes a core and a cladding. The core is comprised of silica glass to which bromine is added, and the cladding has a refractive index lower than a maximum refractive index of the core. The core has compressive stress.

A single mode optical fiber having a core made from silica and less than or equal to about 11 weight % germania and having a maximum relative refractive index Δ.sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index Δ.sub.2MIN, a first outer cladding surrounding the inner cladding and a second outer cladding surrounding the first outer cladding. The viscosity at 1650° C. of the second outer cladding minus the viscosity at 1650° C. of the first outer cladding is greater than 0.1e.sup.7 Poise, and Δ.sub.1MAX>Δ.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The first outer cladding has a maximum relative refractive index Δ.sub.3MAX, and Δ.sub.3MAX>Δ.sub.2MIN.

A polarization maintaining fiber includes: a core; an inner cladding enclosing the core; two stress applying parts that sandwich the inner cladding therebetween; and an outer cladding enclosing the inner cladding and the two stress applying parts. Each of the two stress applying parts is depressed inward against the inner cladding, and the core has a flattened cross section having a long-axis that corresponds to a direction in which the two stress applying parts are aligned.

The core region of an optical fiber is doped with chlorine in a concentration that allows for the viscosity of the core region to be lowered, approaching the viscosity of the surrounding cladding. An annular interface region is disposed between the core and cladding and contains a concentration of fluorine dopant sufficient to match the viscosity of the core. By including this annular stress accommodation region, the cladding layer can be formed to include the relatively high concentration of fluorine required to provide the desired degree of optical signal confinement (i.e., forming a low loss optical fiber). The inclusion of the annular stress accommodation region allows for the formation of a large effective area optical fiber that exhibits low loss (i.e., <0.19 dB/km) in both the C-band and L-band transmission ranges.

An optical fiber preform of the present embodiment comprises a core portion and a cladding each comprised of silica glass. The core portion has a first dopant region including a central axis of the core portion and a second dopant region away from the central axis. The first dopant region contains a first dopant selected from among Na, K, and their compounds, and a concentration of the first dopant is 10 atomic ppm or more but 2,000 atomic ppm or less. The second dopant region contains a second dopant reducing viscosity of the silica glass. The second dopant has, as a characteristic at a temperature of 2,000 C. to 2,300 C., a diffusion coefficient of 110.sup.12 cm.sup.2/s or higher but lower than that of the first dopant, and a concentration of the second dopant region is 10 atomic ppm or more.

The present invention is generally directed to a photonic bad gap fiber and/or fiber preform with a central structured region comprising a first non-silica based glass and a jacket comprising a second non-silica based glass surrounding the central structured region, where the Littleton softening temperature of the second glass is at least one but no more than ten degrees Celsius lower than the Littleton softening temperature of the first glass, or where the base ten logarithm of the glass viscosity in poise of the second glass is at least 0.01 but no more than 2 lower than the base ten logarithm of the glass viscosity in poise of the first glass at a fiber draw temperature. Also disclosed is a method of making a photonic bad gap fiber and/or fiber preform.

A single mode optical fiber having a core made from silica and less than or equal to about 11 weight % germania and having a maximum relative refractive index .sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index .sub.2MIN, a first outer cladding surrounding the inner cladding and a second outer cladding surrounding the first outer cladding. The viscosity at 1650 C. of the second outer cladding minus the viscosity at 1650 C. of the first outer cladding is greater than 0.1e.sup.7 Poise, and .sub.1MAX>.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The first outer cladding has a maximum relative refractive index .sub.3MAX, and .sub.3MAX>.sub.2MIN.

A single mode optical fiber having a core made from silica and less than or equal to about 11 weight % germania and having a maximum relative refractive index .sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index .sub.2MIN, a first outer cladding surrounding the inner cladding and a second outer cladding surrounding the first outer cladding. The viscosity at 1650 C. of the second outer cladding minus the viscosity at 1650 C. of the first outer cladding is greater than 0.1e.sup.7 Poise, and .sub.1MAX>.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The first outer cladding has a maximum relative refractive index .sub.3MAX, and .sub.3MAX>.sub.2MIN.

The core region of an optical fiber is doped with chlorine in a concentration that allows for the viscosity of the core region to be lowered, approaching the viscosity of the surrounding cladding. An annular interface region is disposed between the core and cladding and contains a concentration of fluorine dopant sufficient to match the viscosity of the core. By including this annular stress accommodation region, the cladding layer can be formed to include the relatively high concentration of fluorine required to provide the desired degree of optical signal confinement (i.e., forming a low loss optical fiber).