A new type of all-silica optical fiber is described; a Structured Silica Clad Silica (SSCS) optical fiber, whose cladding is structured to provide mode mixing within the core; and/or to have an average effective refractive index. Its cross-section is essentially symmetrical, it can be used, among other objects, to provide flatter, more speckle-free outputs from fiber lasers, or other limited mode photonic sources. Building the new fiber structure around a rare earth doped laser core provides a better fiber laser/amplifier for cladding pumping. The structured silica cladding contains paired layers, in which a down doped silica layer is followed by a layer of pure, or lesser down-doped, or even up-dope silica, and die number of paired layers is, typically, from 5 to about 25, and, generally, within the paired layers the ratio of thickness of the higher RI layer of silicate the down-doped silica is very broad, lying between about 0.0625 to about 16, depending on the intended use of the SSCS fibers. In some versions, the main core material can be up-doped silica with pure silica or down-doped silica as the primary second component.

A radiation-resistant laser optical fiber preform core rod at least includes one type of activated ion (Yb.sup.3+, Er.sup.3+) and one or more types of co-doped ion (Al.sup.3+, P.sup.5+, Ge.sup.4+, Ce.sup.3+, F.sup.−), and —OD group of 16-118 ppm. Irradiation resistance of core rod glass can be effectively improved by sequentially performing pre-treatments, i.e. deuterium loading, pre-irradiation and thermal annealing on a preform core rod. Electron paramagnetic resonance test shows that, under the same radiation condition, the radiation induced color center concentration in a preform core rod treated by the method above is lower than in an untreated core rod by one or more orders of magnitude. The obtained core rod can be used for preparing a radiation-resistant rare earth-doped silica fiber, and has the advantages of high laser slope efficiency, low background loss, being able to be used stably in a vacuum environment for a long time, for example.

A multi-core fiber includes: a plurality of cores; and a cladding portion formed around outer peripheries of the cores. Further, the cores each have a propagation characteristic conforming to any one of a plurality of standards for optical propagation characteristics, and of the cores, cores that are closest to each other conform to standards different from each other.

The present disclosure provides a method for sintering of an optical fibre preform. The method includes manufacturing of the optical fibre preform. In addition, the method includes drying and sintering of the optical fibre preform. In addition, drying and sintering of the optical fibre preform results into a sintered optical fibre preform. Further, the method includes preparation of a glass rod from the sintered optical fibre preform. Furthermore, the method includes insertion of the glass rod into a centreline hole of the silica soot preform. The centreline hole is created by removing mandrel from the silica soot preform. Moreover, the method includes drying and sintering of the silica soot preform. Also, drying and sintering of the silica soot results into a sintered silica soot preform. Also, the method includes drawing of a rod from the sintered silica soot preform.

The production and new type of preforms are presented which yield, upon drawing, new, class of optical fibers, improved, speckle-free output optical fibers. Useful fibers, providing speckle-free, smooth output with flat top transmission of light from gaussian or few mode sources are produced from preforms introduced herein. The unique production of these improved preforms is also presented. The preforms, and thus the fibers produced in varying core dimensions from about 100 μm to above 1000 μm, are based on a structured silica section of mode mixing area adjacent to the inner core, or in the case of non-circular core, within the core. Plasma Vapor Deposition process is modified to achieve the structured sections in a well-controlled manner. The structured sections are composed of a number of pairs of layers, where a thin down-doped layer is alternated with a much thicker core material layer. The ratio of the thickness of the core layer to the thickness of the down-doped layer is about 3 to 25. The number of paired layers is typically between about 8 to 30-layer pairs. The effective NA of the structured section is dependent on the particulars of the structured silica section and of the individual down-doped layer. Both circular inner core examples and non-circular core examples are possible and are discussed, herein.

A method of making a multi-mode optical fiber that includes: depositing a porous germania-doped silica soot to form a germania-doped porous soot preform; depositing a porous silica layer over the porous soot preform; doping the porous soot preform and the porous silica layer with a fluorine dopant to form a co-doped soot preform having a core region and a fluorine-doped trench region; consolidating the co-doped soot preform to form a sintered glass, co-doped core preform having a refractive index alpha profile between 1.9 and 2.2 measured at 850 nm; depositing a cladding comprising silica over the sintered glass, co-doped preform to form a multi-mode optical fiber preform; drawing the optical fiber preform into a multi-mode optical fiber. Further, the step of doping the germania-doped soot preform and the porous silica layer is conducted according to a doping parameter (Φ) that is set between 20 and 300, and given by:

[00001]$\Phi =\frac{1\times {10}^{14}.Math.R_{\mathrm{prc}}^2.Math.\exp \left(-E/{\mathrm{RT}}_{\mathrm{dop}}\right).Math.T_{\mathrm{dop}}^{1/2}}{x^{3/4}}.$

Provided is an optical fiber glass preform in which a starting rod and a dummy glass are hardly separated from each other, and a method for manufacturing the glass preform. In the optical fiber glass preform, the dummy glass is fitted into one end of the starting rod, and a part of the dummy glass and the starting rod are surrounded by a clad glass. In the manufacturing method, at the time of connecting the starting rod and the dummy glass, a shape is adjusted in such a manner that an iron is brought into contact with a connection portion and is moved from a starting rod side toward a dummy glass side with appliance of a load.

An aspect of the present disclosure enables prediction of a refractive index profile of a transparent glass preform obtained in a production stage of a glass particulate deposit by a VAD method. The glass preform production apparatus includes a gas supply system, a burner, and a signal processing device. The signal processing device includes an imaging device that images a particle flow of glass fine particles, and a calculation unit. The calculation unit extracts, at any one or more time points during a period from the start of production to the end of production of the glass particulate deposit, image data representing a state of at least the flame or the particle flow from an image obtained by the imaging device, and regressively predicts a refractive index profile of the transparent glass preform serving as an objective variable from an explanatory variable including the image data.

An optical fiber includes a core and a cladding surrounding an outer periphery of the core and has a refractive index profile in which a relative refractive index difference with respect to a distance r from a center of the core is represented by Δ(r), where a value of A represented by

A=−∫.sub.0.sup.0.22MFD.sup.1.31(Δ(r)−Δ.sub.ref(r))dr+∫.sub.0.22MFD.sub.1.31.sup.0.44MFD.sup.1.31(Δ(r)−Δ.sub.ref(r))dr  (Formula 1)

is 0.3%.Math.μm or less, where a unit of r is μm, a unit of a relative refractive index difference Δ(r) is %, Δ.sub.ref(r)=−0.064r+0.494, and MFD.sub.1.31 is a mode field diameter at a wavelength of 1.31 μm.

A technique is described for fabricating one or more optical devices in a carbon-coated optical fiber. A photosensitive optical fiber is provided having a hermetic carbon coating. Further provided is a laser having a beam output that is configured to inscribe one or more refractive index modulations into the optical fiber through the hermetic carbon layer while leaving the hermetic carbon layer intact. The laser is used to inscribe one or more optical devices into the optical fiber through the hermetic carbon layer.