Abstract: Methods for producing a semifinished part for the manufacture of an optical fiber are disclosed. The methods are optimized in terms of bending. The methods include the steps of providing a shell tube with a shell refractive index which is lower in relation to the light-conducting core. Then, at least one protective, intermediate and/or barrier layer is applied to a radially outermost and/or innermost tube surface of the respective shell tube, wherein a build-up of light-conducting layers is realized on the inner side and/or the outer side of the shell tube. Finally, the shell tubes are joined by collapsing so as to form the semifinished part.

Abstract: A method for manufacturing an optical fiber preform that includes preparing a glass cylinder with inner and outer surfaces forming at least part of a cladding portion are repeatedly polished, and a glass core rod that includes a core portion having a higher refractive index than the cladding portion; and inserting the core rod into the glass cylinder and heating the glass cylinder and core rod to form a single body. The repeated polishing of the inner surface of the glass cylinder includes passing pure water that does not contain a cutting fluid over the inner surface for at least the final polishing. The polishing is preferably performed using a polishing cloth to which are affixed diamond abrasive grains. The glass core rod and the glass cylinder are preferably formed of composite quartz glass.

Abstract: A method for manufacturing an optical fiber preform is described that includes detecting structural integrity of the tube during a collapsing phase utilizing a fluid flow that is fed to the tube. Also, a system for manufacturing optical fiber preforms is described that comprises a holder configured to hold a tube, a heater configured to heat at least part of the tube to a tube collapsing temperature, and a fluid supply system configured to supply a fluid to the tube held by the holder. The system comprises a tube integrity monitor configured to monitor structural integrity of the tube, during a collapsing phase, by monitoring the fluid.

Abstract: A method for producing an optical fiber preform according to the present invention includes a collapse step of collapsing a silica-based glass tube by heating with a heat source continuously traversed in the longitudinal direction of the glass tube to form a first glass rod to be formed into a core part or part of a core part of an optical fiber, the glass tube having an inner surface doped with an alkali metal, in which the glass tube has a maximum alkali metal concentration of 500 to 20,000 atomic ppm, a maximum chlorine concentration of 0 to 1000 atomic ppm, and a maximum fluorine concentration of 0 to 10,000 atomic ppm, and in which in the collapse step, the maximum temperature of the outer surface of the glass tube is 2000° C. to 2250° C., and the traverse speed of the heat source is 30 mm/min to 100 mm/min.

Abstract: A method for producing an optical fiber preform according to the present invention includes an etching step of heating a silica-based glass tube using a heat source continuously traversed in the longitudinal direction of the glass tube to etch the inner surface portion of the glass tube containing impurities while an etching gas is allowed to flow into the glass tube. The glass tube has a maximum alkali metal concentration of 500 to 20,000 atomic ppm, a maximum chlorine concentration of 0 to 1000 atomic ppm, and a maximum fluorine concentration of 0 to 10,000 atomic ppm. In the etching step, the maximum temperature of the outer surface of the glass tube is in the range of 1900° C. to 2250° C., and the heating time is set to a time equal to or less than a time (min) given by ( 7 - alkai ? ? metal ? ? concentration ? ? ppm 5000 ) .

Abstract: Disclosed is a method of heat treating quartz glass deposition tubes at between 900° C. and 1200° C. for at least 115 hours. The resulting deposition tubes are useful in forming optical preforms that can yield optical fibers having reduced added loss.

Abstract: Core rod sections useable for production of finished optical fiber preforms are fabricated by inserting one or more core body pieces axially end-to-end inside a glass cylinder, thereby defining joints between adjacent ones of the inserted pieces. The cylinder is mounted with the contained core body pieces in the region of a furnace. The glass cylinder and core body pieces are heated together in the furnace, thereby elongating the cylinder and the core body pieces contained in the cylinder, and the cylinder collapses to form a finished core rod. Core rod sections are cut from the finished core rod at positions that coincide with the joints between the core body pieces. One or more of the cut core rod sections are useable for the production of optical fiber preforms.

Abstract: Disclosed is a method of heat treating quartz glass deposition tubes at between 900° C. and 1200° C. for at least 115 hours. The resulting deposition tubes are useful in forming optical preforms that can yield optical fibers having reduced added loss.

Abstract: Disclosed is a method of heat treating quartz glass deposition tubes at between 900° C. and 1200° C. for at least 115 hours. The resulting deposition tubes are useful in forming optical preforms that can yield optical fibers having reduced added loss.

Abstract: A multi-functional method and apparatus are disclosed for producing a low hydroxyl ion-containing core rod from a tube suitable for the production of low-water optical fibers. The method and apparatus combine the use of process steps of (1) hermetically sealing a tubular quartz handle of a tubular porous core preform to a tube used to feed the porous preform into a sintering furnace, (2) dehydration and sintering, and (3) elongation of the sintered preform under vacuum, all without exposing the preform's central aperture surface to ambient atmosphere.

Abstract: An optical fiber preform is fabricated by inserting a number of core body pieces end-to-end inside a glass cylinder, wherein the pieces may have a cladding-to-core diameter (D/d) ratio within the range of one to four. The cylinder with the inserted core body pieces is mounted vertically on a furnace and heated so that the cylinder becomes elongated and its outside diameter collapses to form a core rod from which core rod sections with D/d ratios greater than five, can be cut. A soot overcladding is deposited on the circumference of a core rod section until the diameter of the deposited soot builds to a determined value. The core rod section with the deposited soot overcladding is consolidated to obtain a finished optical fiber preform. The preform preferably has a D/d ratio of about 15 or more, and an optical fiber may be drawn directly from the preform.

Abstract: A method of forming an optical fiber preform using, for example, an MCVD process, is modified to reduce the presence of hydrogen-induced transmission losses in an optical fiber drawn from the preform. A relatively porous, unsintered soot layer is first formed (similar to the initial soot layer commonly associated with the solution-doped process of the prior art) and then subjected to a flow of a metal halide (such as SiCl4) to reduce the presence of excess oxygen. It is imperative that the metal halide treatment occur in the absence of oxygen. Sintering of the treated layer, followed by a conventional collapsing process is then used to form the inventive preform. In accordance with the present invention, both the sintering and collapsing steps are performed in a non-oxygen based ambient. When the drawn fiber is then later exposed to hydrogen, the lack of oxygen thus eliminates the formation of Si—OH and the associated attenuation problems.

Abstract: A core rod is inserted into a cladding pipe, moisture in a space between the core rod and the cladding pipe is removed, and an optical fiber is drawn while the space is connected to a dry-gas atmosphere and/or being decompressed and while the core rod and the cladding pipe are being unified with each other. Alternatively, the core rod is inserted into the cladding pipe, and an optical fiber is drawn from one end while moisture on the surface of the core rod and the internal surface of the cladding pipe is being removed. Accordingly, a high quality optical fiber is manufactured with good productivity.

Abstract: Disclosed is a method of heat treating quartz glass deposition tubes at between 900° C. and 1200° C. for at least 115 hours. The resulting deposition tubes are useful in forming optical preforms that can yield optical fibers having reduced added loss.

Abstract: An optical fiber having a longitudinal direction and a cross-section perpendicular thereto, said fiber in a cross-section comprising: (a) a core region (11) having a refractive index profile with a highest refractive index nc, and (b) a cladding region comprising cladding features (10) having a center-to-center spacing, ?, and a diameter, d, of around 0.4? or larger, wherein nc, ? and d are adapted such that the fiber exhibits zero dispersion wavelength of a fundamental mode in the wavelength range from 1530 nm to 1640 nm; a method of producing such a fiber; and use of such an optical fiber in e.g. an optical communication system, in an optical fiber laser, in an optical fiber amplifier, in an optical fiber Raman amplifier, in a dispersion compensator, in a dispersion and/or dispersion slope compensator.

Abstract: On the basis of a known process for the production of a preform for an optical fiber for optical data transmission technology, the productivity of the process for the production of complex refractive index profiles is to be improved by providing a quartz glass substrate tube which exhibits different doping in radial direction, introducing a core glass made of synthetic quartz glass into the substrate tube and covering the substrate tube with a jacket tube. A substrate tube suitable therefor is also being provided which tube requires less core glass material for the production of the preform, whether during the internal deposition or for the core glass rod in the rod-in-tube technique.

Abstract: A method of making an optical fibre including providing an increased diameter portion on a rod. The rod is assembled by positioning the rod in a tube such that an annular gap is defined between an outer surface of the rod and an inner surface of the tube, and such that the increased diameter portion of the rod engages the tube and supports the rod with respect to the tube, and supporting the rod and tube assembly by gripping the tube. At the lower end of the rod and tube assembly, portions of the tube are collapsed onto the rod such that the tube portions fuse to the rod forming collapsed portions of the rod and the tube assembly. The collapsed portions are drawn to form an optical fibre. The vertically oriented rod and tube assembly can also be collapsed to form an optical fibre preform.

Abstract: An object of the present invention is to provide an optical fiber manufacturing method and an optical fiber in which an increase in the transmission loss is suppressed by preventing hydroxyl group from entering near the core portion. This invention provides a method for manufacturing an optical fiber 10 including forming a glass pipe 16 by applying a ring portion 15 on the inner face of a starting pipe 14 as a starting material, inserting a glass rod 13 that becomes a central core portion 11 and a depressed portion 12 into the inside of the glass pipe 16, integrating the glass pipe 16 and the glass rod 13 by collapse to form a glass body 17, forming a preform 10a by providing a jacket portion 18 outside the glass body 17, and drawing the preform 10a, wherein the thickness of the starting pipe 14 is set in a range from 4 mm to 8 mm.

Abstract: A hybrid method of and apparatus for producing a structure capable of being drawn into an optical fiber. The method includes the steps of conducting vapor-phase reactants into an interior region of a glass tube, conducting aerosol form reactants into the interior of the glass tube. The tube is exposed to a heat, thereby causing a reaction among the vapor-phase and aerosol reactants. The reaction yields a product, in a solid form, within the tube. The apparatus includes a reaction tube, a vapor-phase reactant conduit, an aerosol-form conduit, and a heat source. The vapor-phase and aerosol-form reactant conduits facilitate introduction of vapor-phase and aerosol-form reactants into the reaction tube. The aerosol-form reactants are introduced proximate to a reaction zone created by the heat source. The aerosol-form reactants conduit and heat source travel the axial length of the reaction tube.

Abstract: An object of the present invention is to provide a method for manufacturing an optical fiber preform having a great diameter by reducing an eccentricity or a non-circularity of a core, an optical fiber preform having an small non-circularity and a complex refractive index profile, even with a great diameter, and an optical fiber that is applicable as a dispersion compensating fiber. The present invention involves a rod-in collapse process in which a glass rod is fixed within a glass pipe (or a dummy pipe attached to an end portion) via an aligning jig. The fixation via the aligning jig is made at one end or both ends, the aligning jig has a cylindrical shape with or without one or more reduced diameter portions. When fixed at one end, a heating and integrating process is preferably made from an opposite end. Employing the glass rod and the glass pipe having a refractive index distribution, a complex profile can be realized.

Abstract: An optical fiber structure having a holey fiber arranged in a holey outer support structure made up of holey tubes encased in a thin walled outer jacket. The holey fiber may have a solid core surrounded by a holey cladding having a plurality of rings of holes. With the invention it is possible to produce robust, coated and jacketed fibers with microstructured core features of micrometer size relatively easily using existing fiber fabrication technology. This improvement is a result of the outer holey structure which reduces the thermal mass of the supporting structure and makes it possible to reliably and controllably retain small hole features during the fiber fabrication process.

Abstract: The invention relates to a method for manufacture of a quartz glass preform for an optical fibre consisting of the following steps: preparation of a hollow cylinder made of porous quartz glass which exhibits an inner layer with a doping substance which increases the refractive index of quartz glass and an outer layer surrounding the inner layer, with a lower refractive index, and collapse of the hollow cylinder characterised by collapse of the porous hollow cylinder onto a quartz glass rod containing the doping substance.

Abstract: A microstructured fiber having a cladding comprising a number of elongated features that are arranged to provide concentric circular or polygonial regions surrounding the fiber core. The cladding comprises a plurality of concentric cladding regions, at least some of which comprising cladding features. Cladding regions comprising cladding features of a relatively low index type are arranged alternatingly with cladding regions of a relatively high index type. The cladding features are arranged in a non-periodic manner when viewed in a cross section of the fiber. The cladding enables waveguidance by photonic bandgap effects in the fiber core. An optical fiber of this type may be used for light guidance in hollow core fibers for high power transmission. The special cladding structure may also provide strong positive or negative dispersion of light guided through the fiber-making the fiber useful for telecommunication applications.

Abstract: The method of fabricating an optical waveguide fiber from a preform having a centerline aperture which includes reducing the pressure in the centerline aperture, then increasing the pressure in the centerline aperture to a pressure in order to improve uniformity, circularity, and/or symmetry around the centerline aperture region.

Abstract: The present invention provides a method of fabricating rare earth doped preforms and optical fibers by a combination of modified chemical vapor deposition (MCVD) process and solution doping technique said MCVD process is used to develop matched or depressed clad structure inside a silica glass substrate tube followed by deposition of porous silica soot layer containing GeO2, P2O5 or such refractive index modifiers by the backward deposition method for formation of the core and presintering the deposited particulate layer by backward pass with flow of GeCl4 and/or corresponding dopant halides, soaking the porous soot layer into an alcoholic/aqueous solution of RE-salts containing codopants such as AlCl3 in definite proportion, drying, oxidation, dehydration and sintering of the RE containing porous deposit and by collapsing at a high temperature to produce the preform followed by drawing the fibers by known technique to produce fibers with suitable core-clad dimensions and geometry.

Abstract: The present invention is a method of making a lithography photomask and photomask blank. The method of making the lithography photomask and photomask blank includes providing a silicon oxyfluoride glass tube having an OH content less than 50 ppm. The method further includes cutting the silicon oxyfluoride glass tube, flattening the silicon oxyfluoride glass tube, and forming the flattened cut silicon oxyfluoride glass tube into a photomask blank having a planar surface. The present invention includes a glass lithography mask preform. The glass lithography mask preform is a longitudinal silicon oxyfluoride glass tube that has an OH content ?10 ppm, a F wt. % concentration ?0.5 wt. %.

Abstract: A microstructured optical fiber is described. The microstructured optical fiber comprises an inner region and an outer region. The inner region includes an inner material and a plurality of holes formed in the inner material. The outer region surrounds the inner region, and includes an outer material. The softening point temperature of the inner material is greater than the softening point temperature of the outer material by at least about 50° C. Microstructured optical fiber preforms and methods for making the microstructured optical fibers are also described. The microstructured optical fiber may be made to have substantially undistorted holes in the inner region.

Abstract: An optical fiber preform having a low core noncircularity and eccentricity for producing an optical fiber having an improved polarization mode dispersion, a method for producing the preform, and an optical fiber produced from the preform. The optical fiber preform is produced by the following steps. Diameter-reduced portions 11a and 11b are formed in the vicinity of the ends of the glass pipe 11. A glass rod 12 is inserted into the glass pipe 11. The glass rod 12 is fixed to the glass pipe 11 at the diameter-reduced portion 11a. The glass pipe 11 and the glass rod 12 are heat-unified from the diameter-reduced portion 11b forward to the diameter-reduced portion 11a. The optical fiber preform has a core noncircularity of at most 1.5%. The optical fiber has a polarization mode dispersion of at most 0.15 ps/km1/2 at a wavelength of 1,550 nm.

Abstract: This invention relates to a method of preparing an optical fiber preform with the preform having a uniform refractive index profile for the deposited oxide material that ultimately forms the optical fiber core. One embodiment of the invention relates to a process for preparing an optical fiber preform comprising the steps of etching a substrate a first time to remove a portion of a deposited oxide material from the preform by using a gas comprising an etchant gas containing fluorine at a sufficient temperature and gas concentration to create a fluorine contamination layer in the remaining deposited oxide material; and etching the preform a second time using a gas comprising an etchant gas containing fluorine at a sufficient temperature and gas concentration to remove the fluorine contamination layer without any substantial further fluorine contamination of the remaining deposited oxide material. Further embodiments relate to similar processes.

Abstract: A micro-structured optical fiber precursor 1 is made by size reducing a multiple core optical fiber having solid multiple cores or a multiple core optical fiber preform O having multiple solid core preforms C. A fiber fuse is induced in at least one of the cores 2 of the precursor 1. The effect of the fiber fuse is to consume the core 2 along the whole length of the fiber or to consume periodically spaced lengths of core 2 along the whole length of the fiber.

Abstract: A method of producing with the collapsing process an optical fiber preform capable of forming an optical fiber in which an increment in transmission loss due to OH absorption is reduced, and an optical fiber preform and an optical fiber produced with the method. The method comprises reducing the amount of hydrogen atom-containing substances in a glass pipe, sealing one end of the glass pipe, and collapsing the glass pipe to obtain a solid body. One aspect of the method comprises heating the glass pipe at 550° C. or below, sealing one end of the glass pipe, and collapsing the glass pipe to obtain a solid body. The preform produced with the method has a feature in that its portion formed by the interface portion at the time of the collapsing contains OH groups at a concentration of 100 wt. ppb or below. The optical fiber produced by drawing the preform has a feature in that its OH-originated loss is less than 0.5 dB/km at a wavelength of 1.38 &mgr;m.

Abstract: The invention relates to a dispersion flattened fiber (DFF) with high negative dispersion and a manufacturing method thereof. The dispersion flattened fiber comprises a central core; ring-type cores and low refractive regions alternately formed outside the central core; a cladding surrounding outside the ring-type cores and low refractive regions; and a coating outside the cladding. Since the dispersion flattened fiber has the dispersion of −20 to −60, it has a wide range of application and can be used for various purposes in the field of optical telecommunication.

Abstract: A method of forming a holey waveguide, the method comprising the steps of forming a guiding region of a preform, forming a cladding region of the preform, wherein at least a portion of the cladding region of the preform is formed from a plurality of cladding tubes of at least two different diameters, choosing at least one of the diameters of the cladding tubes in a manner such as to reduce a total number of cladding tubes required to build up said portion of the cladding region when compared with utilising cladding tubes of the same diameter for said portion, and drawing the waveguide from the preform.

Abstract: The present invention provides a method of preparing preforms for optical fibers. The invention allows one to remove or significantly reduce undesirable refractive index variations in the central portion of the optical fibers. The method of preparing the preform having a central duct includes the steps of a first collapsing step, an etching step and a second collapsing step. The first collapsing step reduces the size of the central duct without closing the central duct by heating the preform at a first preform collapsing temperature. A portion of the last deposited layer of the core glass layers is etched by flowing an etchant gas through the central duct at a lower temperature than the preform collapsing temperature. The preform is finally collapsed at a second collapsing temperature to close the central duct of the preform and form a solid rod.

Abstract: The present invention provides methods for fabricating optical fiber preforms and optical fibers. According to one embodiment of the invention, a method for making an optical fiber preform includes the steps of providing at least one sacrificial rod having an outside surface; forming a material on the outside surface of each sacrificial rod to yield a structured body, the structured body including a structured material in substantial contact with the at least one sacrificial rod; removing each sacrificial rod from the structured body; and including the structured body in the optical fiber preform. The preform may be drawn into an optical fiber. The methods of the present invention are especially useful in the fabrication of microstructured optical fibers.

Abstract: The present invention relates to a method of manufacturing a solid preform by moving a heat source parallel to the longitudinal axis of a substrate tube, whose inner surface is coated with one or more doped or undoped glass layers, so as to collapse the substrate tube into the solid preform in a number of passes, with an etchant being supplied to the interior of the substrate tube after a number of passes of the heat source.

Abstract: In a known method for the manufacture of a solid quartz glass cylinder (18) by drawing from a hollow quartz glass cylinder (5) in a vertical drawing process, the hollow cylinder (5) is passed to a heating zone (4), softened therein in one area after the other and the solid cylinder (18) is drawn off from the softened area (15) with a reduced inside pressure (P1) being maintained in the inside bore (19) of the hollow cylinder (5) versus an outside pressure (P2) applied on the outside thereof.

Abstract: The present invention relates to a method for collapsing a hollow substrate tube into a rod-like preform while heating by reciprocating a heating element along the length of the substrate tube. The present invention is characterized in that a constant electric power is supplied to the heating element during collapsing.

Abstract: This invention relates to a method of preparing an optical fiber preform with the preform having a uniform refractive index profile for the deposited oxide material that ultimately forms the optical fiber core. One embodiment of the invention relates to a process for preparing an optical fiber preform comprising the steps of etching a substrate a first time to remove a portion of a deposited oxide material from the preform by using a gas comprising an etchant gas containing fluorine at a sufficient temperature and gas concentration to create a fluorine contamination layer in the remaining deposited oxide material; and etching the preform a second time using a gas comprising an etchant gas containing fluorine at a sufficient temperature and gas concentration to remove the fluorine contamination layer without any substantial further fluorine contamination of the remaining deposited oxide material. Further embodiments relate to similar processes.

Abstract: An active optical fiber (20) having: a silica glass cladding (4), and a glass core (2), doped with a rare earth, comprising a quantity of SiO2 of at least 50% in weight, and a quantity of an oxide XO not exceeding 40% in weight, wherein the element X is selected from the group comprising Ca, Sr, Ba and Zn.

Abstract: A method for manufacturing optical fiber preform and fiber. According to the method, a core cane segment is formed with a refractive index delta preferably between 0.2% and 3% that is most preferably formed by an OVD method. A sleeve is formed including at least one down-doped moat preferably having a refractive index delta between −0.1% and −1.2% and at least one up-doped ring preferably having a refractive index delta between 0.1% and 1.2%. The sleeve is formed by introducing glass precursor and dopant compounds into a cavity of a preferably silica glass tube (e.g., one of an MCVD and PCVD method). The core cane segment is inserted into the sleeve and the sleeve is collapsed onto the core cane segment to form a core-sleeve assembly. The core-sleeve assembly is again drawn into a cane and additional cladding is preferably formed thereon. Optical fiber may be drawn from the preform in a conventional draw apparatus.

Abstract: An object of the present invention is to provide a method for manufacturing an optical fiber preform having a great diameter by reducing an eccentricity or a non-circularity of a core, an optical fiber preform having an small non-circularity and a complex refractive index profile, even with a great diameter, and an optical fiber that is applicable as a dispersion compensating fiber.

Abstract: The present invention concerns a preform for an optical fiber, an optical fiber so obtained and methods for making the same. The fiber is characterized in that porous glass doped with at least one dopant is used. Resulting fibers can be used to make high attenuation fibers.

Abstract: The present invention provides a method for manufacturing a photonic crystal fiber that has a core portion in which a fiber core extends in a lengthwise direction and is formed as a solid or a void, and a porous clad portion provided around the core portion and having numerous pores extending along the core portion. A preform is fabricated by packing numerous capillaries into a cylindrical support pipe such that they are parallel to the central axis of the support pipe and disposing a core rod to serve as the solid core portion at the central axis portion of the support pipe. The preform is drawn to make it small in diameter.

Abstract: A method and apparatus are disclosed for the manufacture of an optical fiber preform having incorporated therein a comparatively high concentration of rare earth dopant material, and which thus can be drawn and processed into an optical fiber having low numerical aperture, low core attenuation, and high pumping power absorption. The high concentrations of rare earth dopant material are accomplished through either the “hybrid vapor processing” (HVP) method or a “hybrid liquid processing” (HLP) method, each capable of being practiced in combination or independently of one another. The HVP method involves the vaporization of a rare earth halogen by the exposure thereof to a sufficiently elevated temperature, independently, or contemporaneously with the transport of the resultant rare earth halogen laden vapor, into a glass forming oxidation reaction zone on a flowing stream of essentially an unreactive inert gas, such as helium.

Abstract: There is provided a dispersion-managed fiber preform and a fabricating method thereof preform by modified chemical vapor deposition (MCVD). A core and a clad having the refractive index distribution of an optical fiber with a positive dispersion value are uniformly deposited in a glass tube. The preform with the positive dispersion value is heated at every predetermined period with a torch and the heated preform portions are etched to have a negative dispersion value. Then, the preform alternately having positions with the positive dispersion value and positions with the negative dispersion value along the length direction is collapsed.

Abstract: Disclosed is an apparatus for fabricating an optical fiber, which comprises a furnace for melting a sealed preform assembly to draw an uncoated optical fiber, a coater for coating the uncoated optical fiber, a capstan for drawing the optical fiber from the optical fiber preform by applying a drawing force, an adjoiner for holding a primary optical fiber preform inserted centrally into an overcladding tube with an equidistant space between the outer surface of the primary optical fiber preform and the inner surface of the overcladding tube, and a preform positioner for supporting the sealed preform assembly in a specified position with respect to the furnace.

Abstract: A tube-encased fiber grating includes an optical fiber 10 having at least one Bragg grating 12 impressed therein which is embedded within a glass capillary tube 20. Light 14 is incident on the grating 12 and light 16 is reflected at a reflection wavelength &lgr;1. The shape of the tube 20 may be other geometries (e.g., a “dogbone” shape) and/or more than one concentric tube may be used or more than one grating or pair of gratings may be used. The fiber 10 may be doped at least between a pair of gratings 150,152, encased in the tube 20 to form a tube-encased compression-tuned fiber laser or the grating 12 or gratings 150,152 may be constructed as a tunable DFB fiber laser encased in the tube 20. Also, the tube 20 may have an inner region 22 which is tapered away from the fiber 10 to provide strain relief for the fiber 10, or the tube 20 may have tapered (or fluted) sections 27 which have an outer geometry that decreases down to the fiber 10 and provides added fiber pull strength.

Abstract: The method of fabricating an optical waveguide fiber from a preform having a centerline aperture which includes reducing the pressure in the centerline aperture, then increasing the pressure in the centerline aperture to a pressure in order to improve uniformity, circularity, and/or symmetry around the centerline aperture region.

Abstract: Disclosed is an apparatus and method for sintering an over-jacketing tube in the zone sintering phase of an optical fiber preform fabrication process using a sol-gel process. The sintering apparatus includes: a processing tube; a gel tube assembly connected to a top rotation cap positioned at the top opening of the processing tube and being rotated at a predetermined rate, a ceramic pin extending downwardly from the center axis of the rotation cap, and a gel tube suspended from the bottom of the ceramic pin and suspended along the same axle of the processing tube; and a movable furnace initially positioned at the bottom of the processing tube and translating in a vertical direction along the processing tube for thermally treating the gel tube.