A optical fiber having core and cladding regions, a primary coating, and a secondary coating may be defined in part by a curve relating the microbend sensitivity to a ratio of the elastic modulus of the secondary coating to the elastic modulus of the primary coating (as plotted on respective y and x axes). The curve has a substantially peaked shape defined by a positive-slope region and a negative-slope region. The ratio of the elastic modulus of the secondary coating to the elastic modulus of the primary coating is within the positive-slope region.

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.

The present embodiment relates to an optical fiber line or the like configured by connecting a single-mode optical fiber with a cladding containing fluorine and a large A.sub.eff optical fiber by TEC connection, and a connection state between such two types of optical fibers is set such that a connection loss expressed in dB of a fundamental mode is equal to or less than 55% of an ideal butt loss expressed in dB at a wavelength of 1550 nm.

An optical fiber having an effective area that can be easily increased and bending loss characteristics that can be easily improved is provided. The optical fiber includes a glass fiber including a core and a cladding; a first resin coating layer that is in contact with the glass fiber and surrounds the glass fiber; and a second resin coating layer that surrounds the first resin coating layer and has a Young's modulus greater than a Young's modulus of the first resin coating layer. An effective area is greater than or equal to 110 m.sup.2 and less than or equal to 180 m.sup.2 at a wavelength of 1550 nm. A cable cut-off wavelength is less than or equal to 1530 nm. A uniformity of thickness of the first resin coating layer is greater than or equal to 60% and less than or equal to 80%.

A quasi-single-mode (QSM) optical fiber includes a core and a cladding surrounding the core. The core includes a centerline and an outer edge. The cladding includes an interior edge and an exterior edge. The cladding has a cladding outer diameter defined by the exterior edge of the cladding. The cladding outer diameter may be in the range of greater than 170 m to about 200 m. The QSM fiber has a cabled cutoff wavelength that is greater than about 1530 nm. The core and the cladding support a fundamental mode LP.sub.01 and a higher-order mode LP.sub.11. The fundamental mode LP.sub.01 has an effective area A.sub.eff>150 m.sup.2.

Provided is a few-mode optical fiber. The optical fiber includes: a core and a cladding enclosing the core. The cladding includes: a first inner cladding surrounding the core; a first high-refractive-index mode filter layer surrounding the first inner cladding; a second inner cladding surrounding the first high-refractive-index mode filter layer; a second high-refractive-index mode filter layer surrounding the second inner cladding; and an outer cladding surrounding the second high-refractive-index mode filter layer.

The present disclosure provides a few mode optical fiber. The few mode optical fiber includes a core region. A core region defined by a region around a central longitudinal axis of the few mode optical fiber. In addition, the core region has a first annular region extended from central longitudinal axis to radius r.sub.1, a second annular region extended from radius r.sub.1 to radius r.sub.2, a third annular region extended from radius r.sub.2 to radius r.sub.3, a fourth annular region extended from radius r.sub.3 to radius r.sub.4 and a fifth annular region extended from radius r.sub.4 to radius r.sub.5. Also, the few mode optical fiber has a cladding defined by the sixth annular region extended from radius r.sub.5 to radius r.sub.6.

A optical fiber having core and cladding regions, a primary coating, and a secondary coating may be defined in part by a curve relating the microbend sensitivity to a ratio of the elastic modulus of the secondary coating to the elastic modulus of the primary coating (as plotted on respective y and x axes). The curve has a substantially peaked shape defined by a positive-slope region and a negative-slope region. The ratio of the elastic modulus of the secondary coating to the elastic modulus of the primary coating is within the positive-slope region.

An optical fiber includes: a core; a cladding layer that is lower in refractive index than the core; and a depressed layer that lies between the core and the cladding layer and that is lower in refractive index than the cladding layer, wherein: the optical fiber has an effective core area Aeff that is equal to or greater than 100 ?m.sup.2 and equal to or less than 129 ?m.sup.2, the core has a radius r1 that is equal to or greater than 5.2 ?m and equal to or less than 7.4 ?m, the core has a refractive index volume Vcore that is equal to or greater than 8.5% ?m.sup.2 and equal to or less than 16.5% ?m.sup.2, the depressed layer has a refractive index volume Vdep that is equal to or greater than ?40% ?m.sup.2 and less than 0% ?m.sup.2.

An optical fiber comprises, from a center to a periphery, a fiber core of undoped silica; a cladding layer; and a coating of polyacrylate, wherein the fiber core has a radius of 5 to 7 m and an ellipticity of less than 1.5%, the cladding layer with an ellipticity of less than 0.4% comprises inner, intermediate, and outer cladding layers, the inner cladding layer being doped with fluorine of 5 to 12 m thickness, and refractive index difference to fiber core of 0.4 to 0.2%, the outer cladding layer being undoped quartz of 25 to 45 m thickness, and the coating comprises an inner coating of 25 to 40 m thickness, and an outer coating of 25 to 35 m thickness and an ellipticity of less than 2%. The optical fiber has high durability and large effective transmission area, a method and system for preparing such optical fiber are also disclosed.