Preform for an optical waveguide containing a core with a non-circular geometry and at least one cladding layer, in which the dopand concentration of the cladding layer is increased compared to the dopand concentration of a preform with circular core geometry and identical NA. A method for the production of a preform for an optical fiber is provided. An optical waveguide with a nominal dopand concentration of c(eff)Fc(nom) in at least one cladding layer is also provided.

A control device which is used in a manufacturing apparatus of an optical fiber, the manufacturing apparatus including a drawing unit and a coating unit. The control device includes: one or a plurality of non-contact holding portions which hold the bare optical fiber at any position between the drawing unit and the coating unit; a position detection unit; and a control unit which controls a flow rate of a fluid introduced into the non-contact holding portion on the basis of the floating position detected by the position detection unit. The non-contact holding portion comprises a guide groove. The control unit detects the floating position of the bare optical fiber at at least one of the non-contact holding portions, compares the detected floating position with a predetermined reference floating position, and controls a flow rate of the fluid introduced into the non-contact holding portions.

Optical fibers having low fictive temperature and methods of making such fibers are described. Management of the cooling rate of an optical fiber during fiber draw permits control over the fictive temperature of the fiber. Non-monotonic cooling rates are shown to promote reductions in fiber fictive temperature. The non-monotonic cooling includes slower cooling rates in upstream portions of the process pathway and faster cooling rates in downstream portions of the process pathway. Reduction in fiber fictive temperature is achieved by controlling the ambient temperature of the fiber to slow the cooling rate of the fiber in upstream portions of the process pathway that correspond to the fiber temperature regime in which the fiber viscosity is sufficiently low to permit efficient structural relaxation. Increases in cooling rate in downstream portions of the process pathway permit adjustment of fiber temperature as needed to meet entrance temperature requirements of downstream processing units. Lower fiber fictive temperature and lower fiber attenuation are achieved at faster draw speeds through non-monotonic cooling of fiber temperature.

According to some embodiments a method of processing an optical fiber comprises the steps of: (i) drawing the fiber at a drawing rate of at least 30 m/sec; and (ii) cooling the drawn fiber in a gas at an average cooling rate less than 5000 C./s, such that said cooling reduces the temperature of the fiber from an entering temperature in the range between 1500 C. and 1700 C. to another temperature in the range between 1200 C. and 1400 C., the gas being at a temperature between 800 C. and 1500 C.; and the thermal conductivity of the gas being not greater than 1.510.sup.4 cal/cm-s-K for at least one temperature within a range of 800 C. to 1500 C. at one atm (atmosphere) pressure absolute.

A manufacturing method of an optical fiber includes drawing an optical fiber preform and forming a bare optical fiber, coating an outer circumference of the bare optical fiber with a coating layer including a resin, and holding the bare optical fiber using one or a plurality of non-contact holding portions at any position between a position where the bare optical fiber is formed and a position where the coating is performed. The non-contact holding portion includes a guide groove which guides the bare optical fiber, and an internal space portion into which a fluid is introduced from an outside, in the guide groove, and an outlet through which the fluid in the internal space portion is blown to float the bare optical fiber in the guide groove is formed.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

The core region of an optical fiber is doped with chlorine in a concentration that allows for the viscosity of the core region to be lowered, approaching the viscosity of the surrounding cladding. An annular interface region is disposed between the core and cladding and contains a concentration of fluorine dopant sufficient to match the viscosity of the core. By including this annular stress accommodation region, the cladding layer can be formed to include the relatively high concentration of fluorine required to provide the desired degree of optical signal confinement (i.e., forming a low loss optical fiber).

A method of producing an optical fiber is provided that includes the steps of flowing a first gas into an optical fiber draw furnace. The first gas is passed through a heated section configured to contain and heat a glass source from which the optical fiber is drawn, passing the first gas through a muffle which defines a capture chamber. A portion of the first gas is removed through at least one reclaim port operatively coupled to the capture chamber. A second gas flows into a gas screen at a rate configured to substantially recover a pressure drop associated with removing the portion of the first gas.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

A quartz glass fibre includes a fibre core of quartz glass produced by modified chemical vapor deposition (MCVD). A fluorine-doped radial layer is provided on the fibre core. A cladding layer of quartz glass contains chlorine and covers the fluorine-doped radial layer to define a hydrogen barrier around the fibre core in response to being irradiated by defect-generating ultra-violet (UV) radiation. The cladding layer has at least one of a combination of E defects and non-bridging oxygen hole center (NBOHC) defects and a combination of SiOH and SiH compounds.