Provided is a coated optical fiber and an optical fiber cable capable of suppressing transmission loss (microbend loss) even in an optical fiber having high microbend sensitivity. In the present invention, the degree of freedom of a primary layer 11 represented by the equation (I) and the rigidity of a secondary layer 12 represented by the equation (II) are set in specific ranges, respectively. Thus, the present invention provides a coated optical fiber 1 capable of suppressing the transmission loss even when an optical fiber 10 having high microbend sensitivity such as a BI fiber having a large effective core cross-sectional area A.sub.eff of an optical fiber is used. The present invention can be widely used as a coated optical fiber 1 constituting a coated optical fiber ribbon or as a coated optical fiber 1 housed in an optical fiber cable. Further, an optical fiber cable including such coated optical fibers 1 enjoys the effect of the above-described coated optical fiber 1.
[Math. 1]
β.sub.P×P.sub.ISM≥600  (I)
(S/P)×(S.sub.ISM/P.sub.ISM)≤1,000  (II)

A single mode optical fiber including a core region doped with an alkali metal. The optical fiber has a total attenuation at 1550 nm of about 0.155 dB/km or less such that extrinsic absorption in the optical fiber contributes to 0.004 dB/km or less of the total attenuation

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 μm.sup.2 and less than or equal to 180 μm.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 coupled-core multicore optical fiber has a plurality of cores that are doped with alkali metals or chlorine to achieve low attenuation and a large effective area. The cores may be embedded in a common cladding region that may be fluorine doped. The cores may also be doped with chlorine, either with the alkali metals described above or without the alkali metals.

The optical fiber of the present invention includes a core, and a cladding that is provided on an outer periphery of the core and has a refractive index lower than a refractive index of the core region. In the optical fiber of the present invention, a V value representing a normalized frequency of an LP.sub.02 mode is greater than or equal to 4.8 and less than or equal to 6.4.

Provided is an optical fiber having identification mark, which includes an optical transmission medium (exemplified by glass fiber) including a core part and a cladding part, a primary resin layer coating the optical transmission medium, and a secondary resin layer coating the primary resin layer, in which identification marks for optical fiber identification (exemplified by continuous identification mark) are provided on a surface of the secondary resin layer at a predetermined interval along an axial direction of the optical transmission medium. An effective area of the optical transmission medium at a wavelength of 1550 nm is 90 μm.sup.2 or more, the predetermined interval is 100 mm or more and 500 mm or less, and a Young's modulus of the primary resin layer is 0.9 MPa or less.

A multicore optical fiber is provided that includes a first core with silica glass doped with chlorine and/or an alkali metal, a first inner cladding surrounding the first core, and a first outer cladding surrounding the first inner cladding and having a first trench region having a volume of about 30%Δ-micron.sup.2 or greater. The multicore optical fiber also includes a second core with silica glass doped with chlorine and/or an alkali metal, a second inner cladding surrounding the second core, and a second outer cladding surrounding the second inner cladding and having a second trench region having a volume of about 30%Δ-micron.sup.2 or greater. Additionally, a common cladding surrounds the first core and the second core, and the first core and the second core each have an effective area at 1550 nm of about 100 micron.sup.2 or less.

Provided is a coated optical fiber and an optical fiber cable capable of suppressing transmission loss (microbend loss) even in an optical fiber having high microbend sensitivity.

In the present invention, the degree of freedom of a primary layer 11 represented by the equation (I) and the rigidity of a secondary layer 12 represented by the equation (II) are set in specific ranges, respectively. Thus, the present invention provides a coated optical fiber 1 capable of suppressing the transmission loss even when an optical fiber 10 having high microbend sensitivity such as a BI fiber having a large effective core cross-sectional area A.sub.eff of an optical fiber is used. The present invention can be widely used as a coated optical fiber 1 constituting a coated optical fiber ribbon or as a coated optical fiber 1 housed in an optical fiber cable. Further, an optical fiber cable including such coated optical fibers 1 enjoys the effect of the above-described coated optical fiber 1.

[Math. 1]

β.sub.P×P.sub.ISM≥600   (I)

(S/P)×(S.sub.ISM/P.sub.ISM)≤1,000   (II)

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 μm to about 200 μm. 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 μm.sup.2.

The optical fiber has an effective area that is greater than or equal to 110 μm.sup.2 and less than or equal to 180 μm.sup.2 at a wavelength of 1550 nm and a cable cut-off wavelength of less than or equal to 1530 nm. An average value of a glass outer diameter in a longitudinal direction is 125±0.5 μm. When σ is a standard deviation of the glass outer diameter in the longitudinal direction, 3σ is greater than or equal to 0.1 μm and less than or equal to 0.5 μm.