Bromine doping of silica glass is demonstrated. Bromine doping can be achieved with SiBr.sub.4 as a precursor. Bromine doping can occur during heating, consolidation or sintering of a porous silica glass body. Doping concentrations of bromine increase with increasing pressure of the doping precursor and can be modeled with a power law equation in which doping concentration is proportional to the square root of the pressure of the doping precursor. Bromine is an updopant in silica and the relative refractive index of silica increases approximately linearly with doping concentration. Bromine can be used as a dopant for optical fibers and can be incorporated in the core and/or cladding regions. Core doping concentrations of bromine are sufficient to permit use of undoped silica as an inner cladding material in fibers having a trench in the refractive index profile. Co-doping of silica glass with bromine and chlorine is also demonstrated.

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.

Optical waveguide cores having refractive index profiles that vary angularly about a propagation axis of the core can provide single-mode operation with larger core diameters than conventional waveguides. In one representative embodiment, an optical waveguide comprises a core that extends along a propagation axis and has a refractive index profile that varies angularly about the propagation axis. The optical waveguide can also comprise a cladding disposed about the core and extending along the propagation axis. The refractive index profile of the core can vary angularly along a length of the propagation axis.

An object is to provide a beam propagating method capable of satisfying desired output power and a desired propagation distance and a required condition of beam quality and a method of designing an optical fiber designing the structure of an optical fiber. According to the present invention, an effective core cross-sectional area A.sub.eff is calculated based on desired specification values and, by appropriately adjusting the structure of an optical fiber satisfying the effective core cross-sectional area and the number of modes to be propagated, the structure of the optical fiber is determined. In this way, by controlling the excitation ratio of a high-order mode at the time of coupling laser light in the optical fiber designed as above, light of high-output laser can be propagated a long distance with the beam quality maintained.

The invention concerns a bending-loss single mode optical fibre having a Mode Field Diameter at 1310 nm greater than or equal to 9 microns and having a core and a cladding, the core refractive index profile having a trapezoid-like shape. According to an aspect of the invention, the cladding comprises a shallow trench with a refractive index difference Ant between 210.sup.3; and 0.910.sup.3, and: the trapezoid ratio r.sub.0/r.sub.1 of the core is between 0.1 and 0.6, preferably, between 0.2 and 0.5. more preferably between 0.25 and 0.45; the core surface integral Formula (I) is between 20.10 3 m and 24. 10.sup.3 m and the cladding surface integral Formula (II) is between 2510.sup.3 m and 910.sup.3 m, where n(r) is the refractive-index difference with respect to said outer cladding as a function of the radius r, and said single mode optical fibre fulfils the following criterion: 25.710.sup.3V.sub.010.2326V.sub.0226.810.sup.3.

An optical fiber according to an embodiment has a structure for enabling determination of improvement in transmission loss at a preform stage. The optical fiber includes: a core containing Cl and having an average refractive index lower than a refractive index of pure silica glass; a first cladding containing F; a second cladding; and a resin coating, in which an effective area at a wavelength of 1550 nm is 135 m.sup.2 or more and 170 m.sup.2 or less, a ratio of the effective area to a cutoff wavelength .sub.C is 85.0 m or more, a bending loss of an LP01 mode at a wavelength of 1550 nm and at a bending radius of R15 mm is less than 4.9 dB per 10 turns, and the resin coating includes a primary resin layer having a Young's modulus of 0.3 MPa or less.

Small-radius coated optical fibers having large mode field diameter and low bending losses. The coated fiber may have an outer radius of 110 m or less, while providing a mode field diameter of 9.0 m or greater and a bending loss when wrapped about a 15 mm mandrel of 0.5 dB/km or less at wavelength of 1550 nm. The coated fiber may have a mode field diameter of 9.2 m or greater and may have a bending loss at 1550 nm of 0.25 dB/km or less when wrapped about a 20 mm mandrel or a bending loss at 1550 nm of 0.02 dB/km or less when wrapped about a 30 mm mandrel.

An optical fiber includes a glass fiber and a coating resin covering an outer periphery of the glass fiber. The glass fiber includes a core, an inner cladding, a trench, and an outer cladding. An outer diameter of the glass fiber is 99 m or larger and 101 m or smaller. An outer diameter of the coating resin is 160 m or larger and 170 m or smaller. A mode field diameter for light having a wavelength of 1310 nm is 7.2 m or larger and 8.2 M or smaller. Bending loss at a wavelength of 1550 nm when wound in a ring shape having a radius of 10 mm is 0.1 dB/turn or less. Bending loss at the wavelength of 1550 nm when wound in the ring shape having the radius of 7.5 mm is 0.5 dB/turn or less.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

The present disclosure provides optical fibers with an impact-resistant coating system. The fibers feature low attenuation. The coating system includes a primary coating and a secondary coating. The primary coating and secondary coating have reduced thickness to provide low-diameter fibers without sacrificing protection. The primary coating has high tear strength and is resistant to damage caused by mechanical force. The secondary coating has high puncture resistance. The outer diameter of the optical fiber is less than or equal to 190 m.