Abstract: A method of drawing an optical fiber in which a glass optical fiber is drawn while fusing by heating and pulling by a pulling mechanism one end of an optical fiber preform made of glass, includes drawing the glass optical fiber from the one end of the optical fiber preform while controlling a drawing speed to make an external diameter of the glass optical fiber larger than an external diameter of a product-to-be glass-optical fiber to be used to manufacture a product. The method includes adjusting an external diameter of the glass optical fiber to an external diameter passable through a die for forming a coating. The method also includes arranging the die around the glass optical fiber having the external diameter passable through the die.

Abstract: In an optical fiber manufacturing method, the cooling device and the coating device are connected in an airtight manner and by preventing a cooling gas, flowing inside the cooling device, from flowing into the coating device by a meniscus of resin inside of the coating device, a flow of the cooling gas inside the cooling device is discharged to an outside of an upper end of the cooling device as an upward stream; helium gas as the cooling gas flows into a lower portion of the cooling device and carbon dioxide gas as the cooling gas which is separated from the helium gas flows into a side lower than a position where the helium gas flows in, during the forcible cooling; and a flow rate of the helium gas and a flow rate of the carbon dioxide gas are individually controlled.

Abstract: In an optical fiber drawing device of the present invention, as an operational parameters corresponding to the real drawing speed in the duration from the moment of starting the operation of the optical fiber drawing device till the moment of reaching the target drawing speed are extracted from operational parameters stored in a operational parameter storage unit and applied to the optical fiber drawing device. The operational parameters include a base preform feeding speed, a target variation of real drawing speed, a gain multiplied by the speed element related with the variation of the real drawing speed, an operation cycle, a drawing furnace temperature, a coating resin pressure to coat the optical fiber, and flow of cooling gaseous helium, etc.

Abstract: A glass base material elongating method of sequentially feeding rod-like glass base materials hung by a glass base material feeding mechanism into a heating furnace, and pulling a glass rod with a smaller diameter by a pulling chuck at a lower part of the heating furnace, includes: aligning, by an alignment guiding device that guides the glass rod, a guiding center of the alignment guiding device with an axis of the glass rod, the alignment guiding device guiding the glass rod between the heating furnace and the pulling chuck.

Abstract: Apparatus and methods for making an optical fiber preform at low cost avoiding the apparatus from being damaged are provided. Apparatus for making an optical fiber preform by depositing glass particles on the circumferential surface of a glass rod comprises: a chamber, a plasma torch, a glass particle supplying part, a composition modification gas supplying part, and an exhaust part. The chamber surrounds the heating portion of the glass rod heated by the plasma torch. The plasma torch heats the glass particles by a plasma flame. The glass particle supplying part introduces glass particles towards the heating portion of the glass rod in the chamber. The composition modification gas supplying part introduces composition modification gas into the chamber in order to modify the composition of the glass particles to be deposited on the heating portion of the glass rod in the chamber.

Abstract: Various embodiments of the present invention relate to glass fiber forming bushings, to methods of controlling the temperature of bushings having multiple segments, to systems of controlling the temperature of bushings having multiple segments, and to other systems and methods. In one embodiment, a method of controlling the temperature of a bushing having multiple segments comprises forming a plurality of filaments from a bushing comprising at least two segments, gathering the filaments into at least two ends, measuring the size of each of the at least two ends, comparing the measured size of the at least two ends to a desired end size, adjusting the amount of current passing through the at least two bushing segments in response to the end size comparisons.

Abstract: A glass base material, which is a base material of an optical fiber, comprising: a core; and a clad surrounding the core; wherein: a rate of change in a relative-refractive-index-difference between the core and the clad in a longitudinal direction of the glass base material is substantially 6% or less.

Abstract: A method of fabricating micro/nano optical wires is disclosed, which comprises: providing a micro/nano optical wire drawing device comprising a feeding wheel, a drawing wheel, and a heating unit; fastening one end of a micrometer-sized preform at the feeding wheel; making the other end of the preform pass through the heating unit and be fastened at the drawing wheel; and switching on the heating unit to heat the perform to a softening temperature of the preform and drawing the preform by the drawing wheel to form a micro/nano optical wire. A device of fabricating micro/nano optical wires is also disclosed.

Abstract: In some embodiments of the present invention, an electrical field is applied across a waveguide substrate so as to induce ion exchange process that affects the cross section of the waveguide. Shaped electrical field may, according to the invention, may control the size and shape of the waveguide along it.

Abstract: A fiber coating applicator includes a chamber and a cup positioned over the chamber. The cup is connected to the chamber by an entrance aperture. The chamber includes an exit aperture opposite the entrance aperture. The cup, entrance aperture, chamber, and exit aperture define a pathway for a fiber, such as an optical fiber, to be coated. The chamber further includes an input port for pumping a coating material into the chamber. The entrance aperture is dimensioned such that as a fiber travels along the pathway and coating material is pumped into the chamber, coating material travels upward through the entrance aperture around the fiber into the cup, the upward flow of coating material being restricted by the fiber and entrance aperture such that there is a hydrostatic pressure in the chamber. The exit aperture is dimensioned to shape coating material around a fiber traveling along the pathway.

Abstract: The specification describes a VAD method for dynamically controlling the growth rate of both the core soot and the cladding soot in response to separate growth monitors.

Abstract: Methods and apparatuses estimate and control optical fiber primary coating diameter for wet-on-wet optical fiber manufacturing. The primary coating diameter for a particular length of optical fiber is calculated based upon a measurement of the weight of primary and/or secondary coating material consumed during optical fiber manufacturing. Control of the primary coating diameter is effected by a coating controller which can increase or decrease the primary coating diameter through control of glass temperature, coating viscosity and/or other parameters during wet-on-wet fiber manufacture.

Abstract: The drawing method of the present invention uses a drawing furnace comprising a furnace muffle tube, a furnace body and a heater. According to the method, an optical fiber preform is inserted from the inlet of the furnace muffle tube, the optical fiber preform is melted by means of a heater, under a specified gas atmosphere, and is drawn toward the outlet of the furnace muffle tube by means of a specified drawing tension. The optical fiber preform and the drawing furnace used in this method both satisfy the condition of below-indicated formula (1): L/D?8??(1) wherein L indicates the length of the furnace body in the drawing direction and D indicates the diameter of the optical fiber preform.

Abstract: A method for manufacturing an optical fiber comprises setting a heating condition for heating a glass rod, which is a parent material of the optical fiber, and an elongating speed of the glass rod based on a prescribed numerical value which changes with a progress of elongation of the glass rod; heating and elongating the glass rod to generate a preform based on the heating condition and the elongating speed which are set by the setting; and drawing the preform to a filament-like form by further heating the preform to generate the optical fiber.

Abstract: When an optical fiber 3 is formed by drawing a preform 1, twisting is generated in the optical fiber 3. An outer diameter of the optical fiber 3 is continuously measured along a longitudinal direction of the optical fiber 3 from two different directions in a plane perpendicular to the advancing direction of the optical fiber 3 by a device for measuring twisting 4, thus twisting of the optical fiber 3 is measured.

Abstract: An apparatus and method for fabricating an optical fiber, an optical fiber preform, and an optical fiber core rod are disclosed herein. In particular, the process of fabricating an optical fiber preform involves, during a modified chemical vapor deposition process, collapsing the substrate tube into an optical fiber preform, and compressing the optical fiber preform in the longitudinal direction. An optical fiber preform that is shorter, but larger in diameter is thus formed. The optical fiber preforms therefore can be stacked during the optical fiber fabrication process, which is useful in drawing longer optical fibers with comparable outer diameter and core diameter to that used as the industry standard.

Abstract: A method capable of stably drawing an optical fiber with a gas-seal system and an apparatus for implementing the method. The method produces an optical fiber 40b by drawing the optical fiber preform 30 by heating and softening the leading-end portion of it while feeding it into a drawing furnace 20. The drawing furnace 20 allows a gas 15 to blow against the optical fiber preform 30. The inside of the drawing furnace 20 is sealed with a seal ring 14U and a shutter 14L located at the top and bottom portions of it, respectively. While the gas 15 is fed, the inner diameter of the seal ring 14U is adjusted according to the diameter of the optical fiber preform 30. Consequently, even when the preform diameter varies, the clearance between the seal ring 14U and the optical fiber preform 30 can be maintained constant, thereby enabling a stable drawing operation.

Abstract: Methods and apparatuses estimate and control optical fiber primary coating diameter for wet-on-wet optical fiber manufacturing. The primary coating diameter for a particular length of optical fiber is calculated based upon a measurement of the weight of primary and/or secondary coating material consumed during optical fiber manufacturing. Control of the primary coating diameter is effected by a coating controller which can increase or decrease the primary coating diameter through control of glass temperature, coating viscosity and/or other parameters during wet-on-wet fiber manufacture.

Abstract: In an optical fiber drawing apparatus capable of drawing one piece of an optical fiber, the present invention provides an optical fiber drawing apparatus which is adapted to decrease a break of an optical fiber to be adjusted a curvature radius thereof by at least one or more moving rollers continuously installed after a fixing roller and to decrease a polarization mode dispersion (PMD) by a birefringence which is not desired in an optical fiber.

Abstract: In method of making an optical fiber and an apparatus, an optical fiber coated with UV curable resin is drawn at a drawing speed of 1000 m/min or more so that the optical fiber 5 has predetermined coating diameter from 235 &mgr;m to 265 &mgr;m. A transit time from an exit of a UV curing furnace to an entrance portion of a capstan for pulling the optical fiber downstream is set to be 0.5 seconds or more.

Abstract: A glass base material manufacturing apparatus for manufacturing a glass base material comprising: a plurality burners, arranged in a row at a predetermined intervals along the longitudinal direction of a starting base material of the glass base material, for forming a deposit, which is a base material of the glass base material by depositing glass soot on the starting base material while moving reciprocatory over a section of the entire length of the starting base material along the longitudinal direction of the starting base material; a plurality of flow rate regulators, at least one of which is connected to the plurality of burners, respectively, for regulating a flow rate of raw material gas of the glass soot, which is supplied to the plurality of burners; and a control unit connected to each of the plurality of flow rate regulators for controlling individually the plurality of flow rate regulators.

Abstract: A device draws an optical fiber from one end of a preform melted by a furnace, an optical sensor being disposed a the exit from the furnace to measure the diameter of the optical fiber for the purpose of adjusting the tension with which the optical fiber is drawn. The sensor is surrounded by a mask in two parts joined at two pairs of edges to form a dark chamber through which the optical fiber passes. The mask protects the optical sensor from radiation from ambient light sources, especially rays emitted by the furnace, which cause localized measurement artifacts. It improves the accuracy of measurement of the diameter of the optical fiber leading, by eliminating artifacts, to a reduction in the number of times the optical fiber is cut.

Abstract: A silica-based core rod is traversed by a heat source along its longitudinal axis, to provide heated, softened regions. During the traverse, compressive or tensile movements are provided along the rod's longitudinal axis, these movements inducing, respectively, increases or decreases in the core diameter at the softened regions. By providing selective core diameter increases and/or decreases across the entire length of the core rod, a desired core diameter profile is attained. It is possible to attain a substantially uniform core diameter, or a varying core diameter profile that provides particular properties, such as systematically varying dispersion. In addition, due to the ability to increase core diameter and core rod diameter in a controlled manner, it is possible to make larger core rods, and in turn larger fiber preforms, than presently possible.

Abstract: Disclosed herein is a dual-type system for producing optical fibers. According to this system, a draw tower is partitioned into a first spinning chamber and a second spinning chamber by a central partition frame. A preform feed unit, a furnace, a spinning nozzle and a diameter gauge are installed on each of the first and second spinning chambers in order to spin an optical fiber. Two coating units are installed at the lowest unit of the draw tower at positions corresponding to the first and second spinning chambers and used for coating the surfaces of the optical fibers spun and drawn through the first and second spinning chambers. Two ducts each having a filter are installed on a side of each unit of the draw tower at positions corresponding to the first and second spinning chambers for supplying fresh air to the optical fibers so as to prevent the optical fibers from absorbing foreign substances in addition to cooling the optical fibers.

Abstract: In a known method for the manufacture of a tube made of a vitreous material, especially of quartz glass, a hollow cylindrical semifinished product made of a vitreous material is carried essentially vertically to a heating zone, wherein it is heated and drawn off downwards—without the use of tools—to the tube by forming a transitional area from semifinished product to tube, while diameter and wall thickness of the tube are continuously measured, and the tube's measured geometrical data being used to generate a control signal with the aid of which a pressure difference is regulated between pressure P1 in the interior space of the semifinished product, the transitional area and the tube, as well as pressure P2 in the heating chamber which is regulated in the heating zone at least in the transitional area from semifinished product to tube and its adjacent tube area.

Abstract: A method and an apparatus for producing a glass preform having a uniform J ratio by adjusting the weight of glass particles to be deposited on a starting glass rod. The method uses an OVD method by which glass particles are successively deposited on an external cylindrical surface of a starting glass rod to create a growing soot layer thereon and the soot layer is then vitrified into a transparent glassy body, wherein the glass particle deposition is conducted by adjusting an amount of glass particles to be deposited based on data of J ratio fluctuations (where the J ratio is a ratio of an outer diameter of a glass preform to an outer diameter of a starting glass rod) of a previously produced glass preform in its longitudinal direction so that the glass preform to be produced can attain a uniform J ratio in its longitudinal direction.

Abstract: The method includes axially modulating at least one plasma build-up pass in order to improve the opto-geometrical properties of the preform. The modulation preferably takes place during the final passes of plasma build-up and takes place by modulating the build-up grain flow rate. The diameter of the preform is evaluated (6), and a build-up control device (8) regulates grain flow rate (11, 5) in application of the above method.

Abstract: A method for manufacturing an optical fiber comprises setting a heating condition for heating a glass rod, which is a parent material of the optical fiber, and an elongating speed of the glass rod based on a prescribed numerical value which changes with a progress of elongation of the glass rod; heating and elongating the glass rod to generate a preform based on the heating condition and the elongating speed which are set by the setting; and drawing the preform to a filament-like form by further heating the preform to generate the optical fiber.

Abstract: In a elongating process, diameter gauges 20, 25 are provided at two locations of upstream measurement position P1 and downstream measurement position P2 which are in a taper portion 1b of an optical fiber preform 1, and fixed target diameters D10, D20 are set for the respective positions. Then a feed speed V1 of starting preform 1a is controlled based on a deviation (D1−D10) of measured diameter D1 at the measurement position P1, while a take-up speed V2 of elongated preform 1c is controlled based on a deviation (D2−D20) of measured diameter D2 at the measurement position P2. This decreases a time lag of control over the outside diameter of the elongated preform 1c and it thus becomes feasible to control the outside diameter in good response and with accuracy. Accordingly, an optical fiber preform elongating method and elongating apparatus are substantiated with improved elongating accuracy of the optical fiber preform and with improved productivity thereof.

Abstract: In a method of elongating a glass preform comprising the steps of holding both ends of the glass preform 1a with a first holding section 2 and a second holding section 3, respectively; moving the first holding section 2 and the second holding section 3 in a longitudinal direction of the glass preform 1a with the moving speed of the first holding section 2 faster than that of the second holding section 3 and, at the same time, heating and softening the glass preform 1a by a heating section 4 successively; and elongating the glass preform 1a by a tensile force applied thereto, so as to form an elongated body 1c; an electric furnace is employed in the heating section 4; and said method further comprising the steps of setting a reference value R1 with respect to an outside diameter at a specific position 1d in a tapered region 1b in the glass preform 1a in the process of elongating; acquiring an actually measured value R2 at the specific position 1d; and controlling the moving speed of the first holding section 2

Abstract: A method and apparatus for controlling the shape and position of a deformable object are described. At least a portion of an object is heated to a temperature sufficient to render the heated portion deformable by a force. An image profile of the heated portion of the object is obtained. A controller compares the image profile to a reference profile and produces an error image signal. Based on the error image signal, an instruction signal is generated. A force applicator responsive to the instruction signal applies a radial force to at least one distinct predetermined location on the heated portion of the object in response to the instruction signal to cause the heated portion of the object to conform to the reference profile. The invention is particularly useful in controlling the shape of an optical fiber preform.

Abstract: An apparatus for grinding a glass base material having a core and a clad comprising: a grinding wheel for grinding the clad; a measuring unit for measuring an eccentricity between a center position of the glass base material and a center position of the core at a plurality of positions along a longitudinal direction of the glass base material; a design unit for calculating target diameters substantially continuous throughout the longitudinal direction of the glass base material so that the eccentricity becomes substantially zero for each of the plurality of positions; and a control unit for controlling the grinding wheel to grind the clad so that a diameter of the glass base material to be the target diameter substantially continuous throughout the longitudinal direction of the glass base material based on the target diameters calculated by the design unit.

Abstract: Method for winding a fiber element onto a support. The fiber element having at least two longitudinal portions (Pi) with different characteristics. The method including the steps of supplying the fiber element to the support and associating with each longitudinal portion a respective value of the winding pitch (pi) which is different from the values associated with the portions adjacent thereto. The winding pitch associated with each portion being modulated in accordance with a periodic function.

Abstract: A method and apparatus for controlling the shape and position of a deformable object are described. At least a portion of an object is heated to a temperature sufficient to render the heated portion deformable by a force. An image profile of the heated portion of the object is obtained. A controller compares the image profile to a reference profile and produces an error image signal. Based on the error image signal, an instruction signal is generated. A force applicator responsive to the instruction signal applies a radial force to at least one distinct predetermined location on the heated portion of the object in response to the instruction signal to cause the heated portion of the object to conform to the reference profile. The invention is particularly useful in controlling the shape of an optical fiber preform.

Abstract: A method for drawing a glass ingot comprises holding a vertically suspended glass ingot 5 at an upper end thereof, passing the ingot through a heating furnace 10 having upper and lower openings, and drawing the glass ingot while moving one end or both ends thereof, wherein a plurality of heating means 1 are provided along vertical directions in the heating furnace 10, and the temperatures of the respective heating means 1 are individually control to control a temperature distribution within the heating furnace 10.

Abstract: In the manufacturing of optical fiber preform with excellent accuracy of outer diameter made of the rod as drawn from synthetic quartz ingot, the outer diameter measuring devices 67 and 68 measure the outer diameters of the cone 2 and rod 3 drawn from the ingot 1, and the drawing speed is controlled based on the measured outer diameters. The optical fiber preform manufacturing apparatus that finishes the rod into truly round form without any curve has a rotary holding means 13 and 14 that hold the rod 3 resulting from the heating and drawing of the ingot 1 rotating it in synchronization with the rotation of the ingot 1, a comparison device 18 that outputs a signal after comparing the outer diameter of the cone 2 as measured by the outer diameter measuring device 11 with that of the referential circle, a control device 19 that controls the rotational amount of the rotating device 10, and a control device 20 that controls the rotational amount of the rotary holding device 13 and 14.

Abstract: A glass blank is sent to a heating zone where it is softened region by region and drawn continuously in a controlled manner as a drawing bulb is formed. Estimates of at least one controlled variable are predicted free of dead time; in addition, at least one geometric variable of the component which can be correlated with the controlled variable is measured continuously, and the measurement values thus obtained are used to adjust the predicted estimates. On the basis of the predicted estimates thus adjusted, the nominal-actual deviation of the controlled variable is determined and converted to a change in a controlling variable. To ensure the production of a component with especially high dimensional accuracy, a geometric variable is measured at a first measurement site in the area of the drawing bulb for the prediction of the estimate, and the temperature of the drawing bulb be measured and used as a controlled variable.

Abstract: A method for making an optical fiber preform comprises depositing fine particles of glass serving as a dad on the surfaces of a rod-shaped core over a given length of the rod-shaped core by use of a plurality of oxyhydrogen flame burner units, detecting an amount of the resultant deposit to check uniformity in the amount of the deposit along the lengthwise direction of the rod-shaped core during the course of the deposition, and further depositing fine particles of glass on any surface portion of the rod-shaped core within the given length from at least one burner unit other than the plurality of burner units to correct the amount of the deposit over the given length based on the results of the detection. The resultant deposit is dehydrated and fired by a usual manner to obtain a preform. An apparatus for carrying out the method is also described.

Abstract: An apparatus for fabricating an optical fiber coated with metal, constructed with a crucible for melting the optical fiber preform to draw an uncoated optical fiber, a diameter measuring device for measuring the diameter of the uncoated optical fiber to regulate it, a metal coater for coating the uncoated optical fiber with metal to prevent penetration of moisture, a temperature controller for controlling the inside temperature of the metal coater, a post-cooler for cooling the metaled optical fiber from a high temperature, a capstan for drawing the optical fiber from the optical fiber preform by applying a rotational force against a portion of the metaled optical fiber, and a spool for winding the metaled optical fiber. The metaled optical fiber includes a core for transmitting light, a cladding on the core having lower refractive index than the core, and a metal coating formed on the cladding for preventing penetration of moisture.

Abstract: A furnace body for a glass preform elongating apparatus which makes an elongated body by passing the glass preform through the furnace body and elongating the glass preform while heating the glass preform, the furnace body comprising a furnace core tube shaped like a cylinder through which the glass preform passes and having so adequate length in an axial direction that the elongated body may not bend or distort its form, a heating member disposed at an outer peripheral portion of the furnace core tube, a thermal insulator enveloping the furnace core tube and the heating member from outside in circumferential and axial directions thereof, and a furnace body outer shell holding the thermal insulator therein, wherein a through hole is disposed near the heating member downstream thereof in an advancing direction of the glass preform so as to penetrate through the furnace core tube, thermal insulator, and furnace body outer shell in the direction orthogonal to the furnace core tube.

Abstract: The specification describes a process and apparatus for monitoring and controlling the ellipticity of preform tubes during Modified Chemical Vapor Deposition. In response to computer generated signals from the monitoring device, the tube collapse rate is adjusted dynamically by locally changing the temperature of the glass tube, or by changing the physical force acting to collapse the tube.

Abstract: A method for delivering a coated glass stream having a first inner layer and a second outer layer wherein the method includes providing a vertical orifice, delivering molten glass from a first source through the orifice, providing a gap about the orifice intermediate its upper and lower ends, delivering glass from a second source about the gap such that the glass from the second source flows through the gap to provide an outer layer about the glass from the first source as it flows through the orifice, and controlling the size and shape of the gap parallel to the flow and the size of the gap perpendicular to the flow such that the gap provides sufficient flow resistance and the gap is of sufficient size and shape to prevent clogging.

Abstract: An apparatus for monitoring a moving filamentary product having a device for monitoring the centering of the filamentary product relative to the coating, and a device for monitoring the quality of the coating. The centering monitoring device includes two light sources positioned at 90.degree. to each other in a plane perpendicular to the filamentary product. The coating quality monitoring device includes an optical receiver disposed between the two light sources in the same plane, and at 45.degree. to each of them, to receive the light beams reflected by the coating.

Abstract: An apparatus for accurately inspecting an electroconductive film using an eddy current and an apparatus for production of an optical fiber which measures on-line the electrical resistance, which shows the state of formation of the electroconductive hermetic coating of the optical fiber by an electroconductive film inspection method and reflects back the measurement results to the hermetic coating forming conditions. Optical fiber is made up of a core, a cladding, amorphous carbon film or other electroconductive hermetic coating formed on the outer surface of the cladding, and a protective coating. The electrical resistance of the hermetic coating generates an eddy current at the coating, the eddy current generated is detected, and the phase angle of the complex impedance is detected to enable calculation.

Abstract: An apparatus and method for measuring preform diameter and runout during manufacture of the preform. A Keyence LB1201 displacement gauge is used to determine distance between a sensing unit and the surface of an optical waveguide preform. It was found that the gauge produced an alternating signal imposed on a constant signal. By dividing the signal into its constant and alternating components, preform diameter and runout can be measured. A water cooled band pass filter and housing are used to protect the sensing unit.The preform surface can be mapped using a pair of sensing units, capable of moving parallel to the preform axis of rotation, located in diametric opposition about the preform.

Abstract: A method and apparatus for continuously producing an endless thermoplastic material, such as yarn or tape, and winding the material into a package. A physical parameter of the package, such as its diameter or weight, is monitored, and a control signal is generated which is a function of the monitored physical parameter. The control signal is then compared to a predetermined reference signal, and an output signal is generated when the difference between the control signal and the reference signal exceeds a predetermined deviation. The output signal thus represents the quality of the material in the package, and it may be used to permit classification of the final product or to control the operating conditions of the apparatus so as to maintain a desired quality level.

Abstract: A method and apparatus are provided for detecting irregular portions of an optical fiber which arise due to microscopic bubbles, bruises, and the like during an optical fiber drawing process. The present invention operates by varying the pulling rate of a pulling capstan based on feeding back measurements of the external diameter of the optical fiber to the pulling capstan. The ratio of a given pulling rate variation to a predetermined time period is then computed. The computed ratio is then compared to a previously specified value.

Abstract: A system for controlling the drawing of a hermetically-coated optical waveguide fiber from a preform is provided in which two measurements of fiber diameter are made and combined into an overall control signal. The first measurement is made on bare fiber in the region of the preform's root using an interference technique. The second measurement is made after the hermetic coating has been applied using a shadow technique. The first measurement provides high speed, high accuracy data needed for process control and defect detection. It is, however, subject to error due to fluctuations in the root with tractor speed. The second measurement reduces the effects of such error on the overall control signal.