Provided is an optical fiber having W-shaped refractive-index distribution and in which a micro-bend loss in an actual usage waveband is reduced. The optical fiber includes a core, inner cladding that surrounds the core and has a refractive index smaller than a refractive index of the core, and outer cladding that surrounds the inner cladding and has a refractive index smaller than the refractive index of the core and larger than the refractive index of the inner cladding. When a coupling coefficient between a fundamental mode and a cladding mode is denoted by C.sub.01-CL, a coupling coefficient between the fundamental mode and a higher-order mode is denoted by C.sub.01-11, and a coupling coefficient between the higher-order mode and the cladding mode is denoted by C.sub.11-CL, C.sub.total defined as C.sub.total=C.sub.01-CL+C.sub.01-11C.sub.11-CL has a minimum value at a wavelength ranging between 1520 nm and 1630 nm.

Methods for producing an optical fiber by elongating a silica glass blank or a coaxial group of silica glass components, on the basis of which a fiber is obtained that comprises a core zone, an inner jacket zone enclosing the core zone and a ring zone surrounding the inner jacket zone, are known. In order to provide, proceeding from this, a method, a tubular semi-finished product and a group of coaxial components for the cost-effective production of an optical fiber, which is characterized by a high quality of the boundary between the core and jacket and by low bending sensitivity, according to the invention, the silica glass of the ring zone is provided in the form of a ring zone tube made of silica glass having a mean fluorine content of at least 6000 weight ppm and the tube has an inner tube surface and an outer tube surface, wherein via the wall of the ring zone tube, a radial fluorine concentration profile is adjusted which has an inner fluorine depletion layer with a layer thickness of at least 1 m and no more than 10 m, in which the fluorine content decreases toward the inner tube surface and is no more than 3000 weight ppm in a region close to the surface which has a thickness of 1 m.

A method of manufacturing a glass core preform for optical fibres including providing a porous soot core preform having a central longitudinal hole extending axially therethrough and an a/b ratio of from 0.20 to 0.40; simultaneously dehydrating and doping with fluorine the soot core preform at a temperature of from 1000 C. to 1350 C. by exposing it to an atmosphere containing a chlorine-containing gas and a fluorine-containing gas, the content of the fluorine-containing gas in the atmosphere being of from 0.01% to 0.50% by volume, and simultaneously consolidating the soot core preform and closing the central longitudinal hole by exposing the soot core preform to an atmosphere substantially devoid of fluorine and of chlorine at a consolidation temperature of from 1500 C. to 1650 C., while reducing the pressure down the central hole, thereby forming a glass core preform.

The present invention provides a large-effective-mode-area low-loss optical fiber with optimized cladding components, which comprises a core layer and a cladding comprising, from the inside to the outside, a first sinking layer, a second sinking layer, an optional third sinking layer, and an outer cladding. In the present invention, phosphorus and aluminum are co-doped in the optical fiber cladding, to form a tetrahedron [AlPO.sub.4] in glass, thus optimizing the viscosity of the cladding while effectively reducing the refractive index of the cladding, without causing increased hydrogen loss. The process is simple, and highly repeatable.

A method for producing a depressed-cladding core rod of an ultra-low water peak optical fiber, the method including 1) producing a core rod component; 2) producing an inner cladding casing component; 3) disposing the core rod hollow shaft and the casing hollow shaft respectively in the glass lathe; 4) cutting off connections among a pressure controlling pipe, a scrubber, and a vacuum pump; 5) connecting the inner cladding casing to the core rod hollow shaft hermetically; 6) turning on the glass lathe; 7) transporting a first mixture gas to the core rod hollow shaft; 8) moving a high temperature heat source; 9) transporting a second mixture gas to the core rod hollow shaft; 10) transporting the first mixture gas to the core rod hollow shaft; 11) transporting the first mixture gas under certain conditions; and 12) controlling relevant parameters to fuse the inner cladding casing with the core layer rod.

The present invention provides a process for fabrication of ytterbium (Yb) doped optical fiber through vapor phase doping technique. The method comprises deposition of Al2O3 and Yb2O3 in vapor phase simultaneously in combination with silica during formation of sintered core layer. This is followed by collapsing at a high temperature in stepwise manner to produce the preform and drawing of fibers of appropriate dimension. The process parameters have been optimized in such a way that Al and Yb-chelate compounds can be transported to the reaction zone without decomposition and condensation of precursor materials. Thus variations of dopants concentration along the length of the preform have been minimized to <1% and good repeatability of the process has also been achieved. The resulting fibers also have smooth core-clad boundary devoid of any star-like defect. The process can be reliably adopted for fabrication of large core Yb doped optical fibers. The fibers also show low loss, negligible center dip and good optical properties suitable for their application as fiber lasers.

A bend-resistant mini optical fiber and manufacturing method thereof, first, preparing a preform via a modified chemical vapor deposition process, and manufacturing an optical fiber via drawing at a certain temperature. The advantageous of the present invention are as following, the bend-resistant mini optical fiber is primarily formed by a core layer, a platform layer, a depression layer, an outer cladding layer and a coating layer, and the relative refractive index and radius of each of the layers is reasonably controlled; and a cutoff wavelength is effectively controlled by employing an automatic temperature and tension monitoring procedure during the drawing process, such that the cutoff wavelength and a mode field diameter are maintained in a relatively stable range, and the cutoff wavelength is adjusted upward while the mode field diameter remains stable, thus facilitating a decrease of bend loss of the optical fiber.

An optical fiber containing alkali metal elements or the like in which Rayleigh scattering loss can be reduced is provided. An optical fiber includes a core composed of silica glass and a cladding which surrounds the core, has a refractive index lower than a refractive index of the core, and is composed of silica glass containing fluorine. The core contains a first group of dopants and a second group of dopants having a diffusion coefficient lower than a diffusion coefficient of the first group of dopants. The difference between the maximum value and the minimum value of residual stress in the optical fiber is 150 MPa or less.

A method of making an optical fiber preform comprising in order: (i) manufacturing a glass preform with at least one porous layer; (ii) exposing the glass preform with at least one porous layer to a fluorine precursor at temperature below 1295 C. to make a fluorine treated preform, and (iii) exposing the fluorine treated glass preform with at least one porous silica based layer the temperatures above 1400 C. to completely sinter the preform. Preferably, the porous silica based layer of the glass preform exposed to fluorine precursor has average density of at least 0.7 g/cm.sup.3 but less than 1.9 g/cm.sup.3.

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.