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.

A few mode optical fiber that includes an optical core and an optical cladding surrounding the optical core. The FMF has a step-index profile. The optical core has a core outer radius R.sub.17.5 m and a core refractive index difference n.sub.1 such that 14.510.sup.3<n.sub.1<2410.sup.3. The optical cladding comprises: an index ring with: a ring inner radius R.sub.r1 between 12 m and 19 m; a ring refractive index difference n.sub.r such that n.sub.1/n.sub.r is between 2 and 4; a ring volume V.sub.ring=n.sub.r(Rr.sub.2.sup.2Rr.sub.1.sup.2) between 1.8 m.sup.2 and 4.1 m.sup.2 where R.sub.r2 is the ring outer radius; an inner cladding between the optical core and the index ring, with an inner cladding inner radius R.sub.i1 and an inner cladding outer radius R.sub.i2, the inner cladding having an inner cladding refractive index difference .sub.clad1 between 1.010.sup.3 and 1.010.sup.3.

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.

Described herein are coated optical fibers including an optical fiber portion, wherein the optical fiber portion includes a glass core and cladding section that is configured to possesses certain mode-field diameters and effective areas, and a coating portion including a primary and secondary coating, wherein the primary coating is the cured product of a composition that possesses specified liquid glass transition temperatures, such as below 82 C., and/or a viscosity ratios, such as between 25 C. and 85 C., of less than 13.9. Also described are radiation curable coating compositions possessing reduced thermal sensitivity, methods of coating such radiation curable coating compositions to form coated optical fibers, and optical fiber cables comprising the coated optical fibers and/or radiation curable coating compositions elsewhere described.

A multicore fiber for communication 10 which allows propagation of an optical signal includes: a clad 12; a core 11a which is arranged in a center of the clad 12; and seven to ten cores 11b which are arranged at equal intervals surrounding the core 11a, and the cladding diameter is 230 m, distances between centers of the mutually neighboring cores 11a and 11b are 30 m or more, distances between the centers of the cores 11b and an outer peripheral surface of the clad 12 are 35 m or more and a mode field diameter of light propagating in the cores 11a and 11b is 9 m to 13 m.

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.

The present disclosure provides a few mode optical fiber (100). The few mode optical fiber (100) includes a core region (102). A core region (102) defined by a region around a central longitudinal axis (116) of the few mode optical fiber (100). In addition, the core region (102) has a first annular region (106) extended from central longitudinal axis (116) to radius r.sub.1, a second annular region (108) extended from radius r.sub.1 to radius r.sub.2, a third annular region (110) extended from radius r.sub.2 to radius r.sub.3, a fourth annular region (112) extended from radius r.sub.3 to radius r.sub.4 and a fifth annular region (114) extended from radius r.sub.4 to radius r.sub.5. Also, the few mode optical fiber (100) has a cladding defined by the sixth annular region (104) extended from radius r.sub.5 to radius r.sub.6.

The disclosed subject matter relates to a polarization-maintaining very large mode area (PM VLMA) Erbium-doped fiber and a polarization maintaining, Er-doped VLMA amplifier.

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.