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.

The present embodiment relates to an optical fiber having a W-type refractive index d profile or a trench-type refractive index profile and having reduced microbending loss in a wavelength band to be actually used. The optical fiber includes a center core, an inner cladding surrounding the center core, and an outer cladding surrounding the inner cladding. The inner cladding has a refractive index lower than a refractive index of at least the center core and the outer cladding has a refractive index lower than the refractive index of the center core and higher than the refractive index of the inner cladding. Wavelength dependency of microbending loss has a local maximal value and a shortest wavelength .sub.th where the microbending loss becomes 10% of the local maximal value is longer than 1560 nm.

An optical fiber with ultra-low attenuation and large effective-area includes a core layer and cladding layers. The cladding layers have an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary outer cladding layer. The core layer has a radius of 4.8-6.5 m, and a relative refractive index difference of 0.06% to 0.10%. The inner cladding layer has a radius of 9-15 m, and a relative refractive index difference of about 0.40% to 0.15%. The trench cladding layer has a radius of about 12-17 m, and a relative refractive index difference of about 0.8% to 0.3%. The auxiliary outer cladding layer has a radius of about 37-50 m, and a relative refractive index difference of about 0.6% to 0.25%. The outer cladding layer is a pure silicon-dioxide glass layer.

A distributed Brillouin sensor system comprising a pump laser, and a combined fiber assembly including at least a first optical fiber section and a second optical fiber section is described. The pump laser is arranged so as to send a pump signal into a first end of combined fiber assembly, and the detector system is arranged to detect Brillouin backscattering from the combined fiber assembly. The combined fiber assembly is characterized by the first section having a low Brillouin gain, and the second fiber section having a high Brillouin gain.

A manufacturing method of an optical fiber includes forming an optical fiber by forming a plurality of resin-coating layers around a glass fiber including a core part and a cladding part, and forming a marking on an outermost layer, which is a colored layer having pigment, of the plurality of resin-coating layers by melting or scorching a surface of the outermost layer with a laser.

The present invention relates to an optical fiber which can improve OSNR in an optical transmission system in which Raman amplification and an EDFA are combined. With respect to the optical fiber, a predetermined conditional formula is satisfied by an effective area Aeff.sub.1450 [m.sup.2] at a wavelength of 1450 nm, a transmission loss .sub.1450 [/km] at a wavelength of 1450 nm, and a transmission loss .sub.1550.sub._.sub.dB [dB/km] at a wavelength of 1550 nm. Further, with respect to the optical fiber, another predetermined conditional formula is satisfied by an effective area Aeff.sub.1550 [m.sup.2] at a wavelength of 1550 nm, and a transmission loss .sub.1550 [/km] at a wavelength of 1550 nm.

A single-mode fiber with an ultra-low attenuation and a large effective area includes a core layer having a radius of 4.8 to 6.5 and a relative refractive index difference n.sub.1 of 0.06% to 0.10%, and cladding layers. The cladding layers includes an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary cladding layer. The inner cladding layer has a radius of 9 to 15 m and a relative refractive index difference of 0.40% to 0.15%. The trench cladding layer has a radius of 12 to 17 m and a relative refractive index difference of 0.8% to 0.3%. The auxiliary outer cladding layer has a radius of 37 to 50 m and a relative refractive index difference of 0.6% to 0.25%. The outer cladding layer is a pure-silicon-dioxide glass layer.

An optical fiber comprising: (i) a core comprising silica and having a maximum relative refractive index delta .sub.1MAX; and LP01 effective area >100 m.sup.2 at 1550 nm; (ii) an inner cladding surrounding the core and having a minimum relative refractive index delta .sub.2MIN and .sub.coreMAX>.sub.2MIN; (iii) an outer cladding surrounding the inner cladding and comprising a first outer cladding portion with a maximum refractive index .sub.3A such that .sub.3A>.sub.2MIN; and another outer cladding portion surrounding the first outer cladding portion with a maximum refractive index delta .sub.3B wherein with a maximum refractive index delta .sub.3B wherein .sub.3B>.sub.3A, said another portion being the outermost portion of the outer cladding; and (iv) a coating layer surrounding the outer cladding, and in contact with said another outer cladding portion, the coating layer having a relative refractive index delta .sub.C wherein .sub.C>.sub.3B.

An optical fiber with large effective area, low bending loss and low attenuation. The optical fiber includes a core, an inner cladding region, and an outer cladding region. The core region includes a spatially uniform updopant to minimize low Rayleigh scattering and a relative refractive index and radius configured to provide large effective area. The inner cladding region features a large trench volume to minimize bending loss. The core may be doped with Cl and the inner cladding region may be doped with F.

An optical fiber 1A comprises an optical transmission member 10 including a core 12 and a clad 14, a primary resin layer 22, and a secondary resin layer 24. The effective area of the optical transmission member 10 is 130 m.sup.2 or larger. The transmission loss of the optical transmission member 10 at a wavelength of 1550 nm is 0.165 dB/km or smaller. The Young's modulus of the primary resin layer 22 is 0.7 MPa or lower, and the Young's modulus of the secondary resin layer 24 is 600 MPa or higher and 1500 MPa or lower. The difference between the transmission loss when the optical fiber 1A is wound at a tension of 80 g around a bobbin on which a metal mesh member having vertical wires of a 50-m diameter and horizontal wires of a 50-m diameter are wound and spaced at a pitch of 150 m, and the transmission loss of an optical fiber coil is 1.0 dB/km or smaller.