JP2009209016A - Drawing apparatus of optical fiber preform and manufacturing method of optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drawing apparatus of an optical fiber preform with which the optical fiber preform can be drawn without occurrence of bending and non-circle; and to provide a manufacturing method of the same. <P>SOLUTION: The drawing apparatus is used for drawing an optical fiber preform by heating and softening it. The drawing apparatus is equipped with: a cylindrical furnace core tube in which the optical fiber preform is arranged; a cylindrical heating body arranged so as to surround the furnace core tube; a heat insulating body arranged at the outer periphery of the furnace core tube and the heating body; and a furnace body for accommodating the furnace core tube, the heating body and the heat insulating body. The heat insulating body and the furnace body each has a through-hole which is formed at a position opposing across the central axis of the furnace core tube. At least one of the furnace core tube and the heating body is formed in such a manner that the length in the longitudinal direction at a part directly above the position where the through-hole is formed becomes longer than the length at a part directly above an orthogonal position forming an angle of 90° in the circumferential direction with the position where the through-hole is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a drawing apparatus for heating and softening an optical fiber preform, and a method for manufacturing the optical fiber preform.

  In recent years, the size of optical fiber preforms has been increasing for the purpose of improving the productivity of optical fibers and reducing costs. When manufacturing a large-sized optical fiber preform, first, a core preform including the core portion of the optical fiber is formed, and the core preform is heated and softened and stretched using a stretching apparatus equipped with a heating furnace. After reducing the diameter and lengthening the entire length, a portion to be a clad portion is formed on the outer periphery of the core preform, and an optical fiber preform is manufactured. Also, when drawing an optical fiber from a large optical fiber preform, the drawing is performed after the optical fiber preform is heated and softened and stretched using a stretching device to reduce its outer diameter and length. (See Patent Documents 1 to 3). Hereinafter, it is referred to as an optical fiber preform including the core preform.

  For example, in a stretching apparatus for stretching an optical fiber preform disclosed in Patent Document 1, in order to stretch the optical fiber preform to a predetermined outer diameter, the outer diameter of the stretched optical fiber preform is, for example, that of a laser system. While measuring using an outer diameter measuring device, feedback control is performed on the moving speed of the optical fiber preform and the temperature in the heating furnace so that the outer diameter is constant.

  Here, in patent document 1, in order to control an outer diameter correctly, the defect | deletion part is provided in the furnace body and the outer diameter of the taper part of the optical fiber preform, ie, the meniscus part, is measured in a defect | deletion part. And in order to prevent that the heat in a furnace flows out from the small window arrange | positioned in the location corresponding to the defect | deletion part of a furnace body, it has enabled it to arrange a heat insulation member in a small window.

Japanese Patent No. 3159116 JP-A-8-310827 Japanese Patent Laid-Open No. 3-146432

  However, when the defect part and the window are provided in the furnace body as described above, even if the heat insulating member is arranged, the outflow of heat in the furnace cannot be completely prevented, and the temperature in the furnace corresponds to the defect part. Since the temperature is lowered at the position, there is a problem that the temperature is uneven in the circumferential direction, and the stretched optical fiber preform may be bent or the cross section thereof may be non-circular.

  The present invention has been made in view of the above, and an object of the present invention is to provide an optical fiber preform stretching apparatus and an optical fiber preform manufacturing method capable of stretching an optical fiber preform without occurrence of bending or non-circularity. And

  In order to solve the above-described problems and achieve the object, an optical fiber preform stretching apparatus according to the present invention is a stretching apparatus that heats and softens an optical fiber preform and stretches the optical fiber preform. A cylindrical furnace core tube, a cylindrical heating body disposed so as to surround the core tube, a heat insulator disposed on the outer periphery of the core tube and the heating body, the core tube and the heating And a furnace body containing the heat insulator, each of the heat insulator and the furnace body having through holes formed at positions facing each other across a central axis of the core tube, At least one of the tube and the heating body has a length in a longitudinal direction immediately above the formation position of the through hole, and a length in a position immediately above the orthogonal position that forms 90 degrees in the circumferential direction with respect to the formation position of the through hole. It is also formed to be long The features.

  An optical fiber preform stretching apparatus according to the present invention includes an outer diameter measuring instrument that is disposed outside the furnace body and that measures an outer diameter of the optical fiber preform from the through hole. It is characterized by that.

  In the optical fiber preform stretching apparatus according to the present invention, in the above invention, at least one of the heating body and the core tube has a length in the longitudinal direction directly above the formation position and directly above the orthogonal position. It is characterized by being formed so as to be continuously shorter toward the top.

  In the optical fiber preform stretching apparatus according to the present invention, in the above invention, the center of the through hole is located in a height region where a meniscus portion is formed when the optical fiber preform is stretched. It is characterized by.

  The optical fiber preform stretching apparatus according to the present invention is characterized in that, in the above invention, the center of the through hole is located 0 to 100 mm below the lower end of the meniscus portion.

  Further, in the method for manufacturing an optical fiber preform according to the present invention, an optical fiber preform is arranged in the furnace core tube of the drawing apparatus for an optical fiber preform according to any of the above inventions, and the arrangement is performed by the heating body. The optical fiber preform is heated, softened and stretched.

  According to the present invention, at least one of the core tube and the heating element has a length in the longitudinal direction directly above the position where the through hole is formed, and a position directly perpendicular to the position where the through hole is formed is 90 degrees in the circumferential direction. Since it is formed to be longer than the length at the top, even if heat flows out from the through hole, the temperature distribution in the core tube is maintained uniformly in the circumferential direction, so there is no occurrence of bending or non-circularity. There is an effect that the optical fiber preform can be drawn.

  Embodiments of an optical fiber preform stretching apparatus and an optical fiber preform manufacturing method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment)
First, an optical fiber preform stretching apparatus according to an embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view of an optical fiber preform stretching apparatus according to the present embodiment. As shown in FIG. 1, the stretching apparatus 10 includes a furnace core tube 1, a heater 2 that is a heating body, a heat insulating material 3, a furnace body 4, windows 5 and 5, and outer diameter measuring devices 6 and 6. Is provided.

  The core tube 1 has a cylindrical shape and is made of, for example, carbon. The heater 2 has a cylindrical shape and is disposed so as to surround the core tube 1. The heat insulator 3 is disposed on the outer periphery of the furnace core tube 1 and the heating body 2. The furnace body 4 has a cylindrical shape and houses the furnace core tube 1, the heater 2, and the heat insulator 3. Moreover, the furnace body 4 has openings 4a and 4b in the upper and lower lid portions, so that an optical fiber preform can be inserted.

  The heat insulator 3 and the furnace body 4 have through holes 3 a, 3 a, 4 c, and 4 c formed at positions facing each other across the central axis of the core tube 1. Transparent windows 5 and 5 are attached to the through holes 4c and 4c of the furnace body 4, respectively. Further, laser type outer diameter measuring devices 6 and 6 are provided outside the furnace body 4. One of the outer diameter measuring devices 6 and 6 outputs laser light, and the outputted laser light sequentially passes through the window 5, the through holes 4 c and 3 a, the lower part of the core tube 1, the through holes 3 a and 4 c, and the window 5. And arranged so as to reach the other.

  Here, in the core tube 1, the portion 1 a immediately above the formation position of the through holes 3 a, 3 a, 4 c, and 4 c is more rectangular than the portion 1 b immediately above the orthogonal position that forms 90 degrees in the circumferential direction with respect to this formation position. And extending downward. That is, the core tube 1 is formed such that the length in the longitudinal direction immediately above the formation position of the through holes 3a, 3a, 4c, and 4c is longer than the length directly above the orthogonal position. FIG. 2 is a schematic development view of the core tube 1 shown in FIG. The length L1 in which the part 1a shown in FIG. 2 extends from the part 1b is, for example, 10 to 50 mm. The length L1 is appropriately selected so that the difference between the maximum value and the minimum value in the vicinity of the core tube wall at the center height of the through holes 4c, 4c is 5 ° C. or less.

  In the stretching apparatus 1 according to the present embodiment, since the core tube 1 is formed as described above, even if heat flows out from the through holes 3a, 3a, 4c, and 4c, the circumference in the core tube 1 is increased. Uniformity of temperature is maintained in the direction. This will be specifically described below.

  FIG. 3 is a diagram showing a cross section obtained by cutting the stretching apparatus 1 shown in FIG. 1 along the direction of the through holes 3a and 3a, and the relationship between the height direction position in the core tube 1 and the temperature distribution in this cross section. is there. In addition, in FIG. 3, description of the furnace body 4, the window 5, and the outer diameter measuring device 6 is abbreviate | omitted. As shown in FIG. 3, since the core tube 1 is long in the longitudinal direction in the portion 1a, the temperature distribution formed in the core tube 1 by the heater 2 has a shape extending downward as indicated by a curve C1 indicated by a broken line. However, since heat flows out from the through holes 3a and 3a formed in the heat insulator 3, the actual temperature distribution is such that the lower temperature distribution is the curve C1 as shown by the curve C2 indicated by the solid line. Narrower distribution shape.

  On the other hand, FIG. 4 shows a cross section of the stretching apparatus 1 shown in FIG. 1 cut along a direction orthogonal to the direction of the through holes 3a and 3a, and the height direction position and temperature distribution in the core tube 1 in this cross section. It is a figure which shows the relationship. As shown in FIG. 4, since the core tube 1 is short in the longitudinal direction in the portion 1b, the temperature distribution formed in the core tube 1 by the heater 2 is almost the same as the curve C2 shown in FIG. The distribution shape is similar. As a result, the temperature distribution in the core tube 1 is maintained uniformly in the circumferential direction.

  FIG. 5 is a view schematically showing a temperature distribution immediately below the core tube 1 in the cross section along the line AA shown in FIG. Arrows A1 and A2 indicate the direction in which the through holes 3a and 3a are formed, and the shade of color indicates the temperature. As shown in FIG. 5, in the stretching apparatus 1, the temperature distribution is maintained uniformly in the circumferential direction even immediately below the core tube 1.

  On the other hand, FIG. 6 is a diagram schematically showing the temperature distribution immediately below the core tube when the core tube having the same longitudinal length in the circumferential direction is used. Arrows A3 and A4 indicate the through hole formation direction. As shown in FIG. 6, when the same core tube is used in the circumferential direction in the longitudinal direction, the temperature decreases in the directions of arrows A3 and A4 due to the outflow of heat from the through holes. The temperature is high in the orthogonal direction.

  Next, a method for manufacturing an optical fiber preform using the stretching apparatus 10 will be described. FIG. 7 is an explanatory view for explaining a method of manufacturing an optical fiber preform using the stretching apparatus 10 shown in FIG. In addition, in FIG. 7, description of the furnace body 4 and the window 5 is abbreviate | omitted.

  First, for example, quartz glass support rods are welded to the upper and lower ends of an optical fiber preform 7 made of quartz glass, for example, and the upper and lower ends are arranged in the core tube 1 while being supported by chucks. Next, the inside of the core tube 1 is heated by the heater 2 so that the maximum temperature becomes 2000 ° C. or higher, and the vicinity of the lower end of the optical fiber preform 7 is heated and softened. Then, the outer diameter of the optical fiber preform 7 is gradually reduced to form the meniscus portion 7a, and the stretched optical fiber preform 8 is manufactured. Since the temperature distribution in the furnace core tube 1 is uniformly maintained in the circumferential direction, the drawing apparatus 10 can manufacture the optical fiber preform 8 that is free from bending and non-circularity.

  The chuck that supports the optical fiber preforms 7 and 8 is raised or lowered so as to apply tension to the optical fiber preforms 7 and 8. The chuck rising and lowering speed, the temperature of the heater 2 and the like are set so that the outer diameter of the optical fiber preform 8 measured by the outer diameter measuring device 6 through the through holes 3a and 3a of the heat insulating material 3 is constant. Feedback controlled.

  As described above, according to the stretching apparatus 10 according to the present embodiment, the optical fiber preform can be stretched without generation of bending or non-circle, and the optical fiber preform without bending or non-circle can be manufactured.

  In addition, it has the structure of the extending | stretching apparatus 10 which concerns on this Embodiment as an Example of this invention, the length of the parts 1a and 1b shown in FIG. 2 is 80 mm and 110 mm, respectively, and length L1 is 30 mm An optical fiber preform having an outer diameter of about 50 mm was manufactured from an optical fiber preform having an outer diameter of 90 mm using a stretching apparatus. On the other hand, as a comparative example of the present invention, an optical fiber preform similar to that of the example was manufactured using a stretching apparatus having the same structure as the stretching apparatus 10 but having a length L1 of 0 mm. In either case, the maximum temperature in the furnace core tube was 2000 ° C., and the position where the maximum temperature was reached was about 90 mm from the upper end of the through holes 4 c and 4 c formed in the furnace body 4.

  At this time, when the temperature in the core tube near the core tube wall was measured over the outer circumference at the center height of the through holes 4c and 4c, the difference between the maximum value and the minimum value was 10 ° C in the case of the comparative example. However, in the case of the example, it was 1 ° C. or lower. The temperature in the core tube near the core tube wall was measured as follows. First, the lower end of a quartz glass support rod is supported by a chuck, and a carbon disk having the same diameter as that of the optical fiber preform before stretching is formed on the upper end thereof, and its central axis coincides with the central axis of the support rod. Install as follows. In this state, a support rod with a disk was placed in the heating furnace so that the disk was positioned slightly above the through holes 4c and 4c, and the temperature in the core tube near the core tube wall was measured in this state.

  For the bending of the manufactured optical fiber preform, in the case of the comparative example, the radius of contact (the amount of deviation of the preform center axis from the rotation center axis when the preform is rotated about its longitudinal direction as the center axis) ) Was 5 mm, but in the example, it was 2 mm or less. Furthermore, the outer diameter of the manufactured optical fiber preform was 50 ± 0.3 mm at the maximum in the circumferential direction in the comparative example, and a large non-circular occurred, but in the circumferential direction in the example The maximum was 50 ± 0.1 mm, and the occurrence of non-circle was suppressed.

(Modification)
Next, a modification of the above embodiment will be described. In the stretching apparatus 20 according to this modification, the core tube is shorter than the stretching apparatus 10 according to the embodiment. Furthermore, the through holes formed in the furnace body and the heat insulating material are also located in the height region where the upper meniscus portion is formed.

  FIG. 8 is an explanatory diagram for explaining a configuration of a stretching apparatus according to a modification of the embodiment and a method for manufacturing an optical fiber preform using the stretching apparatus. As shown in FIG. 8, the stretching device 20 includes a furnace core tube 11, a heater 12, a heat insulating material 13, outer diameter measuring devices 6 and 6, and a furnace body and a window (not shown). The outer diameter measuring devices 6 and 6, the furnace body, and the window are the same as those of the stretching device 10. On the other hand, the core tube 11 and the heater 12 are shorter than those of the stretching device 10 in order to shorten the length of the meniscus portion 17a. Moreover, the heat insulating material 13 is located in the height area | region where the through-holes 13a and 13a are higher than the thing of the extending | stretching apparatus 10, and the meniscus part 17a is formed. Moreover, the outer diameter measuring devices 6 and 6 are also arranged at positions corresponding to the through holes 13a and 13a.

  According to the stretching device 20, the outer diameter of the meniscus portion 17a of the optical fiber preform 17 can be measured, and feedback control can be performed based on the outer diameter. Since the meniscus portion 17a has a low viscosity, the degree of change in the outer diameter when the raising / lowering speed of the optical fiber preform 17 is changed is large. Therefore, by performing feedback control based on the outer diameter of the meniscus portion 17a, feedback control with higher control responsiveness can be performed, and the stretched optical fiber preform 18 is made to have a desired outer diameter with higher accuracy. be able to. Furthermore, in this drawing apparatus 20, since the length of the core tube 11 and the heater 12 is shortened and the length of the meniscus portion 17a is shortened, the control response is further enhanced.

  In addition, in order to make control responsiveness high, the height of the outer diameter measurement is preferably 0 to 100 mm from the lower end of the heater 12, and more preferably 0 to 50 mm. Therefore, it is preferable that the positions of the through holes 13a and 13a have the same height.

Hereinafter, the optimum outer diameter measurement position will be described more specifically. The control responsiveness is higher when the outer diameter measurement position is closer to the heater 12. Here, as described in Patent Document 3, the optimum position for outer diameter measurement depends on the inclination of the meniscus portion 17a. That is, when the gradient of the meniscus portion 17a at a certain position is A [mm / mm] and the outer diameter is D [mm], the outer diameter is A / D ≧ 0.2 × 10 ⁻² [mm ⁻¹ ]. Measuring the diameter is preferable in order to increase the controllability of the outer diameter.

However, as described in Patent Document 3, if the outer diameter measurement position is too far from the lower end of the meniscus portion 17a, the meniscus portion 17a is reduced in diameter even downstream of the outer diameter measurement position. The difference between the value and the final outer diameter increases. Further, when the moving speed of the lower chuck is changed by feedback control, the tension applied to the optical fiber preform 8 is changed. For this reason, the final fluctuation of the outer diameter may be larger than the fluctuation of the measured value, which is not preferable. Therefore, when the lower end portion of the meniscus portion 17a is defined as a position where A / D is 0.5 × 10 ⁻³ [mm ⁻¹ ], the outer diameter measurement position is preferably within 100 mm from the lower end portion of the meniscus portion 17a. More preferably, it is within 50 mm. In order to bring the lower end portion of the meniscus portion 17a closer to the position of the outer diameter measurement, the meniscus portion 17a may be increased in gradient to shorten the length of the meniscus portion 17a.

In order to realize the position of the outer diameter measurement that satisfies the A / D ≧ 0.2 × 10 ⁻² [mm ⁻¹ ], which is a preferable range from the lower end portion of the meniscus portion 17a as described above, The position where the temperature in the core tube 11 is 85% of the maximum temperature is preferably within 120 mm from the maximum temperature position, and more preferably within 70 mm.

(Other variations)
In the above-described embodiment and its modification, the length of the core tube in the longitudinal direction varies depending on the position of the core tube extending in a rectangular shape immediately above the position where the through hole is formed. However, the present invention is not limited to this. FIG. 9 is a schematic development view of a core tube provided in a stretching apparatus according to another modification of the embodiment of the present invention. As shown in FIG. 9, the core tube 31 in this modification is formed in a sine wave length in the longitudinal direction, and continuously shortens from the portion 31a to the portion 31b at a position orthogonal to the portion 31a. ing. By disposing the core tube 31 in the stretching apparatus so that the portion 31a is positioned immediately above the formation position of the through hole, the temperature distribution in the core tube can be maintained more uniformly in the circumferential direction.

  Furthermore, in the said embodiment and its modification, it formed so that the length of the longitudinal direction of a core tube might differ with the position, However, The length of the longitudinal direction of a heater may differ with the position. FIG. 10 is a schematic development view of a core tube provided in a stretching apparatus according to still another modification of the embodiment of the present invention. As shown in FIG. 10, the heater 42 in this modification is formed such that a portion 42 a disposed immediately above the formation position of the through hole extends in a rectangular shape with respect to a portion 42 b at a position orthogonal to the position. . The length L2 that the portion 42a shown in FIG. 10 extends from the portion 42b is 10 to 50 mm. As a result, the temperature distribution in the core tube can be maintained uniformly in the circumferential direction, as in the above-described embodiment and modifications thereof. As a further modification, the length of the heater in the longitudinal direction may be formed in a sine wave shape as shown in FIG. Further, the lengths of both the core tube and the heater in the longitudinal direction may be formed so as to differ depending on their positions.

It is typical sectional drawing of the extending | stretching apparatus of the optical fiber preform which concerns on embodiment. FIG. 2 is a schematic development view of the core tube shown in FIG. 1. It is a figure which shows the relationship between the cross section which cut | disconnected the extending | stretching apparatus shown in FIG. 1 along the direction of a through-hole, and the height direction position in a core tube in this cross section, and temperature distribution. It is a figure which shows the relationship between the cross section which cut | disconnected the extending | stretching apparatus shown in FIG. 1 along the direction orthogonal to the direction of a through-hole, and the height direction position in a core tube in this cross section, and temperature distribution. It is the figure which showed typically the temperature distribution just under the core tube in the AA cross section shown in FIG. It is the figure which showed typically the temperature distribution just under a core tube when the length of a longitudinal direction uses the same core tube in the circumferential direction. It is explanatory drawing explaining the method to manufacture an optical fiber preform using the extending | stretching apparatus shown in FIG. It is explanatory drawing explaining the structure of the extending | stretching apparatus which concerns on the modification of embodiment, and the method of manufacturing an optical fiber preform | base_material using this extending | stretching apparatus. It is a typical expanded view of the core tube provided in the extending | stretching apparatus which concerns on another modification of embodiment. It is a typical expanded view of the heater with which the extending | stretching apparatus which concerns on another modification of embodiment was equipped.

Explanation of symbols

1, 11, 31 Core tube 1a, 1b, 31a, 31b, 42a, 42b Portion 2, 12, 42 Heater 3, 13 Heat insulating material 3a, 4c, 13a Through hole 4 Furnace body 4a, 4b Opening 5 Window 6 Outer diameter Measuring device 7, 8, 17, 18 Optical fiber preform 7a, 17a Meniscus part 10, 20 Stretching device

Claims (6)

A drawing device that heats, softens and stretches an optical fiber preform,
A cylindrical core tube in which the optical fiber preform is disposed;
A cylindrical heating element disposed so as to surround the furnace core tube;
A heat insulator disposed on the outer periphery of the furnace tube and the heating body;
A furnace body containing the furnace tube, the heating body, and the heat insulator;
The heat insulator and the furnace body each have through holes formed at positions facing each other across the central axis of the core tube, and at least one of the core tube and the heating body is the through hole The length in the longitudinal direction immediately above the formation position is formed so as to be longer than the length immediately above the orthogonal position that forms 90 degrees in the circumferential direction with respect to the formation position of the through hole. An optical fiber preform stretching device.   The apparatus for stretching an optical fiber preform according to claim 1, further comprising an outer diameter measuring device that is disposed outside the furnace body and measures an outer diameter of the optical fiber preform from the through hole.   The at least one of the heating body and the furnace core tube is formed so that a length in a longitudinal direction is continuously shortened from an immediately upper portion of the forming position to an immediately upper portion of the orthogonal position. 3. An apparatus for stretching an optical fiber preform according to 1 or 2.   4. The optical fiber preform according to claim 1, wherein the center of the through hole is located in a height region where a meniscus portion is formed when the optical fiber preform is stretched. Material stretching device.   5. The optical fiber preform stretching apparatus according to claim 4, wherein the center of the through hole is located 0 to 100 mm below the lower end of the meniscus portion.   An optical fiber preform is disposed in the core tube of the optical fiber preform stretching apparatus according to any one of claims 1 to 5, and the disposed optical fiber preform is heated and softened by the heating body. A method of manufacturing an optical fiber preform characterized by stretching.

Images