An optical fiber according to an embodiment comprises, as a structure suitable for large capacity transmission over a long haul, a core, a cladding having an outer diameter of 80 m or more and 130 m or less, a primary coating, and a secondary coating having elasticity higher than that of the primary coating and an outer diameter of 210 m or less. The optical fiber having the structure as described above has an MFD of 10 m or more at a wavelength of 1550 nm, a cable cutoff wavelength longer than 1260 nm, and a microbending loss of 0.6 dB/km or less at a wavelength of 1550 nm.

It is an object of the present invention to provide a multicore optical fiber, a design method for the multicore optical fiber and an optical transmission method using the multicore optical fiber including four cores having a standard cladding diameter of 125?1 ?m for an existing single mode optical fiber covering several thousands of kilometers of transmission. The multicore optical fiber according to the present invention disposes two-stage claddings with different refractive indices around each core, and designates as a predetermined range, a core radius a1, a radius a2 of a first cladding region surrounding each core, specific refractive index ?1 relative to the core of the first cladding region and a specific refractive index ?2 relative to the core of a second cladding region including four cores and the first cladding region.

An optical fiber is provided that includes a core region and a cladding region. The core region is formed of silica glass doped with chlorine and/or an alkali metal. The cladding region surrounds the core region and includes an inner cladding directly adjacent to the core region, an outer cladding surrounding the inner cladding, and a trench region disposed between the inner cladding and the outer cladding in a radial direction. The trench region has a volume of about 30% -micron.sup.2 or greater. Additionally, the optical fiber has an effective area at 1550 nm of about 100 micron.sup.2 or less.

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 an inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

The present disclosure provides an optical fiber (100). The optical fiber (100) includes a core region (102). The core region (102) is defined by a region around central longitudinal axis (112) of the optical fiber (100). In addition, the core region (100) has a first annular region (106). The first annular region (106) is defined from the central longitudinal axis (112) to a first radius from the central longitudinal axis. Moreover, the core region (102) has a second annular region (108). The second annular region (108) is defined from the first radius to a second radius. Further, the core region (102) has a third annular region (110). The third annular region (110) is defined from the second radius to a third radius. Also, the optical fiber (100) includes a cladding (104). The cladding region (104) has a fourth radius.

It is an object of the present invention to provide a multicore optical fiber, a design method for the multicore optical fiber and an optical transmission method using the multicore optical fiber including four cores having a standard cladding diameter of 125?1 ?m for an existing single mode optical fiber covering several thousands of kilometers of transmission. The multicore optical fiber according to the present invention disposes two-stage claddings with different refractive indices around each core, and designates as a predetermined range, a core radius a1, a radius a2 of a first cladding region surrounding each core, specific refractive index ?1 relative to the core of the first cladding region and a specific refractive index ?2 relative to the core of a second cladding region including four cores and the first cladding 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 a CMCF including a structure to achieve more efficient reduction in transmission loss by suppressing decrease in concentration of alkali metal due to diffusion of alkali metal. In the CMCF including a plurality of cores, a power coupling coefficient h between adjacent cores is set to 110.sup.3/m or more, to maintain an optical coupling state between the adjacent cores. In addition, alkali metal contributing to reduction in transmission loss is added to each of the cores such that a stress maximum value _.sub.max between adjacent cores has a negative value.

The present disclosure provides an optical fiber. The optical fiber includes a core region. The core region is defined by a region around central longitudinal axis of the optical fiber. In addition, the core region has a first annular region. The first annular region is defined from the central longitudinal axis to a first radius r.sub.1 from the central longitudinal axis. Moreover, the core region has a second annular region. The second annular region is defined from the first radius r.sub.1 to a second radius r.sub.2. Further, the core region has a third annular region. The third annular region is defined from the second radius r.sub.2 to a third radius r.sub.3. Also, the optical fiber includes a cladding. The cladding region has a fourth radius r.sub.4.

The present disclosure provides an optical fiber. The optical fiber includes a core region. The core region is defined by a region around central longitudinal axis of the optical fiber. In addition, the core region has a first annular region. The first annular region is defined from the central longitudinal axis to a first radius r.sub.1 from the central longitudinal axis. Moreover, the core region has a second annular region. The second annular region is defined from the first radius r.sub.1 to a second radius r.sub.2. Further, the core region has a third annular region. The third annular region is defined from the second radius r.sub.2 to a third radius r.sub.3. Also, the optical fiber includes a cladding. The cladding region has a fourth radius r.sub.4.