KR20050050143A - Method for manufacturing the preform of optical fiber, preform of optical fiber, optical fiber, apparatus for manufacturing the preform of optical fiber - Google Patents

Abstract

An optical fiber mother material producing method comprises the following steps: a pipe holding step for holding a pipe (23) in a suspended state, a rod holding step for holding a rod (27) inserted in the pipe (23), a heating step for progressively axially heating the held pipe (23) and rod (27) by an annular heating furnace (15), an integrating step for progressively axially welding the heated pipe (23) and rod (27) for integration, a detection step for detecting changes in the inclination of the pipe (23) accompanying the progress of integration of the pipe (23) and rod (27), and a correction step for correcting the inclination of the pipe (23) in such a manner as to cancel the detected change in inclination in the midst of integration of the pipe(23) and rod (27).

Description

TECHNICAL FOR MANUFACTURING THE PREFORM OF OPTICAL FIBER, PREFORM OF OPTICAL FIBER, OPTICAL FIBER, APPARATUS FOR MANUFACTURING THE PREFORM OF OPTICAL FIBER}

The present invention relates to a method for manufacturing an optical fiber base material by a so-called Rod-In Tube method, a manufacturing apparatus, and an optical fiber base material and an optical fiber manufactured by the method.

Optical fiber is widely used in various fields including communication. Such an optical fiber is manufactured by carrying out drawing processing to a columnar optical fiber base material. This optical fiber base material is, for example, Modified Chemical Vapor Deposition (MCVD), Outside Vapor-Phase Deposition (OVD), Vapor-phase Axial Deposition (VAD), and Rod. Manufactured by In Tube method.

Among these, the Rod-In Tube method is a method of manufacturing an optical fiber base material by integrating a quartz pipe and a quartz rod including a core part by using an annular heating furnace. Specifically, the rod is placed so as to be positioned at its center while keeping the pipe suspended by the pipe holding portion so that its axial direction is coaxial with the central axis of the heating furnace, and spaced from its inner circumferential surface within the pipe. Keep it with the holding part. Both the pipe holding portion and the rod holding portion are configured to be movable, and by moving these holding portions, the pipe and the rod are sequentially transferred into the annular heating furnace. In this way, the pipe and the rod are integrated in the axial direction by heat fusion, and as a result, an optical fiber base material is produced (see, for example, Japanese Patent Application Laid-Open No. 7-10580).

As described above, in manufacturing the optical fiber base material by the Rod-In Tube method, the pipe is axially deformed to eliminate the gap between the pipe and the rod and to integrate the pipe and the rod. For this reason, there exists a general problem that the core part of an optical fiber base material is easy to be eccentric.

In addition, in terms of the productivity of the optical fiber base material, the pipes and rods are enlarged. As a result, the core of the optical fiber base material is eccentric. In other words, as the pipe becomes larger, the pipe becomes very heavy. When the pipe holding portion holds such a heavy pipe, the pipe holding portion receives a load in a downward direction and causes warping. Furthermore, since the pipe holding portion is a moving structure rather than a fixed structure, the warpage becomes relatively large. Therefore, in the first stage of holding the pipe in the pipe holding part, the pipe position is adjusted so that the pipe shaft coincides with the furnace shaft while the pipe holding part is in the idle state.

However, as the integration of the pipe and the rod proceeds, the load on the pipe holding portion decreases, and the warpage generated in the pipe holding portion also decreases. The pipe shaft is then displaced from the furnace shaft and the rods are off the center of the pipe. As a result, when these are heat-sealed, they are integrated in order from the smallest gap between the pipe and the rod. In addition, as the pipe deviates from the central axis of the heating furnace, the heat applied to the pipe becomes nonuniform in the circumferential direction, and the pipe thickness becomes non-uniform before being integrated with the rod. As a result, the core part of the optical fiber base material is eccentric, and the optical fiber obtained by drawing out the optical fiber base material is also eccentric in the core.

1 is a perspective view showing an apparatus for manufacturing an optical fiber base material.

2 is a cross-sectional view showing an apparatus for manufacturing an optical fiber base material.

3 is a graph showing the relationship between the axial length of a rod, the amount of radial distortion, and the outer diameter variation.

4 is a graph showing the relationship between the axial length of the rod, the amount of radial distortion, and the outer diameter variation in a direction different from that of FIG.

Fig. 5 is a graph showing the relationship between the axial length and the combined distortion amount in three-dimensional coordinates.

6 is a view from the VI direction arrow of FIG.

FIG. 7 is a view from the arrow VII of FIG. 1; FIG.

8 is a perspective view showing a manufacturing apparatus for carrying out pipe holding using an iron weight;

9 is a perspective view showing a state in which the pipe is inclined with respect to the central axis of the heating furnace.

10 is a diagram showing a measurement result of a core eccentric shift of an optical fiber base material according to Example 1-1.

11 is a diagram showing a measurement result of a shift in the optical fiber base material core eccentricity according to Comparative Example 1-1.

12 is a diagram showing a measurement result of a shift in the optical fiber base material core eccentricity according to Comparative Example 1-2.

Fig. 13 is a diagram comparing core part eccentricity of optical fiber base materials according to Example 1-1 and Comparative Examples 1-1 and 1-2 in terms of core eccentricity of optical fiber.

14 is a diagram showing a measurement result of a shift in the optical fiber base material core eccentricity according to Comparative Example 2-1.

FIG. 15 is a diagram showing a measurement result of a shift in the optical fiber base material core eccentricity in Example 2-1. FIG.

Fig. 16 is a diagram comparing core part eccentricity of optical fiber base materials according to Example 2-1 and Comparative Example 2-1 in terms of core eccentricity of optical fiber.

This invention is made | formed in view of such a point, and the objective is to suppress the core part eccentricity of an optical fiber base material at the time of manufacturing an optical fiber base material by integrating a pipe and a rod.

The method of manufacturing an optical fiber base material of the present invention includes a pipe holding step of maintaining a quartz pipe in a suspended state, a rod holding step of holding a quartz rod including a core part in an inserted state of the pipe, and maintaining the pipe and the rod. A heating step of sequentially heating in the axial direction by an annular heating furnace having a central axis direction in the vertical direction, and an integration step of fusion and fusion of the heated pipe and the rod in the axial direction, and the pipe and the rod. And a detecting step of detecting a change in inclination of the pipe accompanying the progress of integration of the pipe, and a step of correcting the inclination of the pipe so as to cancel the change in the detected inclination while integrating the pipe and the rod.

As the integration of the pipe and the rod proceeds, the load on the pipe holding portion holding the pipe becomes small. As a result, the warpage generated in the pipe holding portion is reduced, and the pipe slope is changed.

When the pipe slope is changed, the pipe slope is corrected to offset the slope change. As a result, the pipe and the rod can be integrated while the pipe posture is kept constant.

In the pipe holding step, the position of the pipe may be determined such that the central axis of the retained pipe is coaxial with the central axis of the furnace.

By doing so, even if the warpage of the pipe holding portion decreases during the integration of the pipe and the rod, the pipe axis always coincides with the central axis of the furnace. As a result, the core eccentricity of the optical fiber base material is suppressed.

Positioning of the pipe may be carried out in a plurality of directions by using a thread ironed at the lower end, lowering the thread to the pipe side position, and adjusting the pipe axial direction in the direction in which the thread is continued in a plurality of directions. do.

Iron weights are generally used to determine the verticality of relatively large objects, such as the slope of building columns, and are known to be highly accurate. Therefore, by adjusting the position of the pipe using a weight, the axial direction of the pipe can be made the vertical direction with high precision.

Positioning of the pipe uses a plurality of laser displacement meters arranged in a vertical direction apart from each other in the pipe side position, irradiates a laser beam from the respective laser displacement meters to the pipes, and up to the pipes measured by the respective laser displacement meters. The position adjustment which makes the distance of a mutually match mutually may be performed in several directions.

The laser displacement meter is composed of a laser light source for irradiating the laser light obliquely to the surface of the material under measurement, and a light receiving portion to which reflected light from the surface of the material under measurement is incident. If the position of the surface of the substance under test changes, the optical axis of the reflected light moves in parallel, so that the amount of surface displacement is found by detecting the position of the incident point of the light receiver.

By measuring the pipe displacement using a laser displacement meter, pipe positioning is possible mechanically. Higher precision positioning can be expected than in the case of manually measuring displacement.

In the Rod-In Tube method, in order to increase the yield of the optical fiber base material, a pipe composed of a pipe effective portion and upper and lower dummy pipes joined to the upper and lower ends thereof, respectively, is used. Moreover, the rod effective part and the rod which consists of the upper and lower dummy bars joined to the upper part and the lower part respectively are used. And in the integrated cargo which integrated the said pipe and the rod, what cut | disconnected the part corresponding to each said effective part is made into an optical fiber base material.

In the manufacture of the optical fiber base material, the pipe is maintained in a suspended state by the upper dummy pipe being held by the pipe holding portion.

When the pipe effective portion and the upper dummy pipe are correctly bonded in a straight line, the center of gravity of the pipe is on the central axis of the dummy pipe. In this case, even if the pipe is held in any direction (circumferential direction), the center of gravity position of the pipe moves on one plane as the pipe and the rod are integrated. As a result, the return direction of the bending of the pipe holding portion becomes a constant direction.

However, the pipe effective portion and the dummy pipe are usually joined by welding in a state where they are joined to each other. As a result, bending may occur between them. When bending occurs between the pipe effective portion and the upper dummy pipe, the pipe center of gravity shifts on the central axis of the upper dummy pipe. At this time, the plane passing through two axes between the central axis of the pipe effective portion and the upper dummy pipe central axis, and the direction in which the pipe effective portion tilts from the vertical direction due to the bending of the pipe holding portion holding the pipe, hold the pipe in another direction. Assume that you do. In this case, the returning direction of the pipe holding portion deflection due to the progress of the integration does not become a constant direction. That is, since the direction of the pipe (effective portion) inclination change does not become a certain direction, it becomes difficult to correct the inclination change of the pipe in the calibration step. As a result, as the inclination of the pipe changes, the central axis and the axes of the heating furnace and the rod are shifted from each other, which tends to cause the core portion of the optical fiber base material to be eccentric.

Therefore, the manufacturing method may further include a pipe determination step of determining the degree of bending of the pipe effective portion and the upper dummy pipe. And the pipe holding step includes a plane including two axes of the pipe effective part central axis and the upper dummy pipe central axis based on the determination result of the pipe determination step, and the bending of the pipe holding part holding the pipe. The pipe may be held so that the effective portion is inclined with respect to the vertical direction.

When the bending occurs between the pipe effective portion and the upper dummy pipe, the upper dummy pipe so that the plane passing over each central axis and the pipe holding portion are inclined in parallel due to the bending of the pipe holding portion. Is maintained by the pipe holding portion. That is, the bending direction of the pipe coincides with the bending direction of the pipe holding portion. As a result, the moving range of the center of gravity position of the pipe along the progress of integration is maintained on almost one plane, and the direction in which the deflection of the pipe retaining portion is returned becomes a constant direction. As a result, the pipe tilt correction in the calibration step becomes easy, and the core eccentricity of the optical fiber base material is suppressed.

However, the inventors have repeatedly studied, and as one of the causes of the eccentricity of the core portion of the optical fiber base material, it was found that the nonuniformity of the circumferential temperature distribution is affected in the annular heating furnace for heating the pipe and the rod. In other words, in the Rod-In Tube method, a carbon resistance heating furnace or a high frequency induction heating furnace is used as a heating furnace. For example, due to structural factors such as heater assembly state of the heating furnace, or over time due to uneven deterioration of the heater, The circumferential temperature distribution in the furnace may be uneven.

The nonuniformity of the circumferential temperature distribution in this heating furnace makes the molten state of a pipe nonuniform in the circumferential direction. As a result, the axial diameter deformation of the pipe is uneven in the circumferential direction and the core of the optical fiber base material is eccentric. Specifically, the core portion is eccentric in the direction of the position where the temperature is highest with respect to the central axis of the heating furnace.

Thus, the manufacturing method may further include a measuring step of measuring a circumferential temperature distribution in the heating furnace. The rod holding step may include maintaining the rod substantially in a coaxial state with a central axis of the heating furnace, and the pipe holding step may include the pipe based on the measurement result of the measuring step. It is good also as a step of keeping it in the state which inclined in the direction of the position where the temperature in the said heating furnace is highest with respect to the central axis of the.

By measuring the temperature distribution in the circumferential direction in the furnace, the circumferential position where the temperature is highest in the furnace is specified.

If the circumferential position with the highest temperature is specified in the furnace, the pipe is held in an inclined position in the direction of the position with the highest temperature with respect to the central axis of the furnace. In contrast, the rod is held in a position that is substantially coaxial with the central axis of the heating furnace. By doing so, the distance between the pipe inner circumferential surface and the rod circumferential surface becomes relatively wider at the circumferential position where the temperature is highest in the heating furnace.

The pipe and the rod held in this posture are heated by a heating furnace, whereby the pipe and the rod are integrated to produce an optical fiber base material.

As described above, the core portion of the optical fiber base material tends to be eccentric in the direction of the position where the temperature is highest with respect to the central axis of the heating furnace. Here, at the circumferential position where the temperature is the highest, the distance between the inner circumferential surface of the pipe and the rod circumferential surface is widened. As a result, when the pipe and the rod are integrated, the core portion included in the rod is suppressed from being eccentric to the circumferential position having the highest temperature. As a result, the core eccentricity of the optical fiber base material is suppressed.

The rod holding step is to hold the (first) rod substantially coaxially with respect to the central axis of the heating furnace, and the pipe holding step includes the (first) pipe as the central axis of the heating furnace. It is set to remain substantially coaxial with respect to. In this case, the manufacturing method includes a measuring step of measuring an eccentric direction of the core portion with respect to the central axis of the furnace in the integrated product in which the first pipe and the first rod are integrated after the integration step; A second rod holding step of holding a second rod different from the rod substantially coaxially with respect to the central axis of the furnace; and a second pipe different from the first pipe based on the measurement result of the measuring step. A second pipe holding step of holding the inclined core portion eccentrically with respect to the shaft; a second heating step of heating the held second pipe and the second rod with the heating furnace; A second integration step of integrating the second pipe and the second rod may further be included.

The 1st pipe and the 1st bar are integrated, and in the integrated goods, the eccentric direction of the core part with respect to the central axis of a furnace is measured. Thereby, the core part eccentricity tendency when the pipe and the rod are integrated in the heating furnace is grasped | ascertained. This is equivalent to indirectly confirming the temperature distribution in the furnace.

The temperature distribution nonuniformity in a heating furnace by time-dependent factors does not change rapidly. Moreover, the temperature distribution nonuniformity in a heating furnace by structural factors does not change with the same heating furnace. Thereby, the core part eccentricity tendency when the 1st pipe and the 1st rod are integrated, and the core part eccentricity tendency when the 2nd pipe and the 2nd rod are integrated are mutually the same. Here, "the same heating furnace" is not the same heating furnace, for example, before and after heater exchange. This is because the nonuniformity of the temperature distribution occurs depending on the assembly state of the heater.

Thus, the second pipe is held in an inclined position in the eccentric direction of the core portion of the integrated product with respect to the central axis of the furnace. In contrast, the second rod is held in a position that is substantially coaxial with respect to the central axis of the heating furnace. By doing so, the distance between the inner circumferential surface of the pipe and the outer circumferential surface of the rod becomes relatively wider at the core portion eccentric position of the integrated cargo.

The second pipe and the second rod held in this posture are heated with a heating furnace, whereby the second pipe and the second rod are integrated to produce an optical fiber base material. In the optical fiber base material thus produced, when the first pipe and the first rod are integrated, the core part is suppressed from being eccentric in the direction in which the core part is eccentric. As a result, the core eccentricity of the optical fiber base material is suppressed.

What is necessary is just to set suitably the inclination amount at the time of inclining a 2nd pipe with respect to the central axis of a heating furnace according to the eccentricity of the core part of the integrated goods which integrated the 1st pipe and the 1st rod.

When the rod effective portion and the upper and / or lower dummy rods are fused in a large bent state, when the rod is inserted into the pipe, the rod touches or sweeps the inner wall of the pipe, causing a defect. This flaw forms the bright spot of the optical fiber base material (the bright spot of the optical fiber base material causes the loss of optical fiber). In addition, if the rod is bent largely, the rod cannot be coaxially positioned with the pipe, resulting in core eccentricity of the optical fiber base material.

Therefore, the manufacturing method may further include a bar determination step of determining whether the bar bending amount is equal to or less than a predetermined bending amount before the rod holding step.

By determining whether the bending amount of the bar is equal to or less than the predetermined bending amount, the bar that satisfies the condition is selected. By using a rod that satisfies the condition, when the rod is inserted into the pipe, the rod is prevented from contacting or sweeping the inner wall of the pipe and causing scratches. Moreover, the core part eccentricity of an optical fiber base material is suppressed. Here, the "bending amount" means the amount of distortion of the bar center per unit length with respect to the straight line connecting the centers of both ends of the bar. The predetermined amount of bending may be 1 mm / m.

The manufacturing method is based on the determination result of the bar determination step, when the bending amount of the rod is larger than the predetermined bending amount, the rod and the upper dummy bar so that the bending amount is less than the predetermined bending amount; And / or a modification step of correcting the fusion state of the lower dummy rod.

Discarding a rod larger than a predetermined amount of curvature leads to inconsistency, but by modifying the rod to a rod that satisfies the conditions, the material is usefully used.

It is preferable that the rod, the upper dummy bar and / or the lower dummy bar are fusion-bonded with these axes almost horizontal.

In the case of fusion-integrating the rod effective portion and the dummy rods in a standing state, even if these bends are actually large, they increase due to their own weight, and apparently, the bends are perceived to be small. In this case, during the integration of the rod and the pipe, the bending state is remarkable when lightened due to the consumption of the rod. That is, the amount of bending of the rod increases. As the bending state becomes remarkable, the rod is displaced from the center of the pipe and the core eccentricity of the optical fiber base material increases.

Therefore, fusion of the rod effective portion and the dummy rods is performed with these rod axes almost horizontal. In this case, it is possible to grasp the exact bending amount of the rod which fused the rod effective part and each dummy bar only by considering the influence of the bending in advance. In addition, the precise bending state of the rod can be identified, so the rod can be inserted into the pipe optimally. For example, it is possible to insert a rod into the pipe in a direction in which the eccentricity becomes smaller in relation to the bent state of the pipe.

The optical fiber base material of this invention created by said manufacturing method has a small core part eccentricity.

Moreover, since the core part eccentricity of the optical fiber base material is small, the optical fiber which took out the optical fiber base material created by the said manufacturing method has a small core eccentricity.

The optical fiber base material manufacturing apparatus of this invention is an apparatus which heats a quartz pipe and a quartz rod and integrates it by fusion | melting.

The manufacturing apparatus includes a pipe holding portion for holding the pipe and moving the held pipe in the axial direction, and an annular heating furnace for sequentially heating the pipe moved by the pipe holding portion in the axial direction. And detecting means for detecting a change in inclination of the pipe moved by the pipe holding part.

Since the detection means detects the inclination of the pipe, it is possible to correct the pipe inclination manually or mechanically based on the detection result.

The detecting means may directly detect the change in the inclination of the pipe. In addition, the inclination change of the pipe may be indirectly detected by detecting the displacement of the pipe holding portion. For example, as a detection means, the level sensor provided in the pipe holding | maintenance part, the laser displacement meter which detects the distance change to the target installed in the pipe holding | maintenance part, the angle detector which detects the inclination of a pipe holding part, etc. are mentioned.

Although the change of the pipe inclination can be objectively detected by the detecting means, the manual correction of the inclination of the pipe includes human factors, so that accurate correction is difficult.

Therefore, the manufacturing apparatus may further include displacement means for correcting the inclination of the pipe held in the pipe holding part so as to cancel the change in the inclination of the pipe based on the detection result of the detection means.

(Manufacturing device)

1 and 2 show an apparatus 10 for manufacturing an optical fiber base material. This manufacturing apparatus 10 is an apparatus which manufactures the optical fiber base material 30 by the Rod-In Tube method. Specifically, it is an apparatus for manufacturing the optical fiber base material 30 by integrating the pipe 23 to be clad in the optical fiber and the rod 27 to be the core in the optical fiber or to be the core and the clad.

The manufacturing apparatus 10 includes a support 11 extending in the Z direction (up and down directions in FIGS. 1 and 2), a pipe holding part 12 provided on the support 11, and the pipe holding part 12. In the upper position of, the rod holding portion 14 provided on the support 11 is provided.

The pipe holding part 12 holds the pipe 23 in a suspended state, as will be described later. This pipe holding part 12 is provided in the said support | pillar 11 via the pipe position adjustment part 13. The pipe holding part 12 is movable along the vertical position 11a of the support 11 together with the pipe position adjusting part 13 in the Z direction.

The pipe 23 is composed of a pipe valid portion 22, an upper dummy pipe 20 fused to an upper end of the pipe effective portion 22, and a lower dummy pipe 21 fused to a lower end thereof. Grooves 20a are formed on the outer circumferential surface of the upper dummy pipe 20 over its entire circumference. The total weight of the pipe 23 including the pipe effective portion 22 and the upper and lower dummy pipes 20 and 21 is 100 to 200 kg.

The pipe holding portion 12 is formed in an almost fork shape composed of a pair of binding stoppers extending in a direction orthogonal to the vertical wall 11a of the strut 11. A groove 20a formed in the upper dummy pipe 20 is sandwiched and fixed between the pair of binding stoppers. In this way, the pipe 23 is kept suspended in the Z direction. Thus, the pipe holding part 12 is in a cantilever state when holding the pipe 23. As mentioned above, since the pipe 23 is a heavy object, the pipe holding part 12 is bent under the load in the state where the pipe 23 is held.

The pipe positioning unit 13 moves the position of the pipe 23 in the X direction (direction toward the right in front of the left side of the ground in Fig. 1) and Y direction (direction toward the right front in the left side of the ground in FIG. 1). It is possible. In addition, the pipe position adjusting unit 13 is configured to be capable of adjusting the tilt θ of the pipe 23 in the Z direction.

The rod holding portion 14 is a holding portion 14a whose proximal end is provided on the vertical wall 11a of the support 11, and at the same time, its holding portion 14b holds the upper end of the rod 27. Becomes The rod 27 includes a rod effective portion 26, an upper dummy rod 24 fused to an upper end of the rod effective portion 26, and a lower dummy rod 25 fused to a lower end thereof.

The rod 27 is held in the suspended state inside the pipe 23 by the gripping portion 14b gripping the upper dummy bar 24.

The rod holding portion 14 is movable in the Z direction along the vertical wall 11a of the strut 11. Moreover, the rod holding part 14 is comprised so that the movement in the XY plane of the hold | maintained rod 27, and the inclination (theta) of the rod 27 with respect to the Z axis | shaft are possible.

The pipe 23 and the rod 27 are held in a predetermined posture by the pipe holding portion 12 and the rod holding portion 14. In addition, the pipe holding portion 12 and the rod holding portion 14 move downward in the Z direction, so that the pipe 23 and the rod 27 move downward, respectively. At this time, the moving speeds of the pipe and rod holders 12 and 14 can be changed, respectively. Thereby, the moving speed of the said pipe 23 and the rod 27 (feeding speed to the heating furnace 15 mentioned later) can be adjusted. In addition, it is also possible to set the moving speed of the pipe holding part 12 and the moving speed of the bar holding part 14 to different speeds. As a result, the pipe 23 and the rod 27 may be different from each other.

The manufacturing apparatus 10 further includes a heating furnace 15. The heating furnace 15 is disposed below the pipe holding part 12. The heating furnace 15 is substantially cylindrical and has an insertion hole 15a through which the pipe 23 and the rod 27 pass. The heating furnace 15 is equipped with the heater not shown in figure which heats the pipe 23 and the rod 27. As shown in FIG. This heating furnace 15 may be constituted by, for example, a carbon resistance heating furnace or a high frequency induction heating furnace.

When the pipe 23 and the rod 27 are moved downward by the pipe and rod holders 12 and 14, the pipe 23 and the rod 27 are axially directed from the bottom to the top thereof. It passes through the inside of the heating furnace 15 and the insertion hole 15a sequentially. In this way, the pipe 23 and the rod 27 are sequentially heated from the bottom to the top.

As shown in FIG. 1, four temperature sensors 18, 18, ... are disposed in the heating furnace 15 at substantially equal intervals in the circumferential direction thereof. The temperature in the heating furnace 15 is measured by each temperature sensor 18. Based on the measurement result of each temperature sensor 18, the temperature distribution of the circumferential direction in the heating furnace 15 is measured. Here, more than four temperature sensors 18 may be disposed as necessary. Also in this case, it is preferable to arrange | position the temperature sensor 18 at substantially equal intervals in a heating furnace circumferential direction.

As shown in FIG. 2, the manufacturing apparatus 10 includes rollers 16, 16,... Arranged at a lower position of the heating furnace 15. These rollers 16, 16, ... are disposed at each of two positions along the central axis of the heating furnace 15, respectively. Each of these rollers 16 is configured to be rotatable with the Y axis as the rotation center. The integrated product (optical fiber base material 30) of the pipe 23 and the rod 27 integrated by passing through the heating furnace 15 is interposed between the four rollers 16 and guided downward. The rotational speed of each of these rollers 16 can be changed, and thereby the induction speed of the optical fiber base material 30 from the heating furnace 15 can be adjusted. By adjusting the induction velocity from the heating furnace 15 of the optical fiber base material 30, the outer diameter of the optical fiber base material 30 is made into a predetermined diameter (target outer diameter).

The manufacturing apparatus 10 is provided with a vacuum pump (not shown). This vacuum pump is connected to the waste cap 29 (see FIG. 2). The waste cap 29 is provided on the upper end of the upper dummy pipe 20 so as to close the upper end opening. At the time of manufacture of the optical fiber base material 30, the inside of the said pipe 23 is pressure-reduced by driving this vacuum pump.

As shown in FIG. 1, the manufacturing apparatus 10 includes four laser displacement meters 17 in total. Two of the laser displacement meters 17 are disposed at positions corresponding to the upper positions of the pipes 23 (pipe valid portions 22) held by the pipe holding portions 12, and the other two are disposed on the pipe effective portions ( It is arranged at a position corresponding to the lower position of 22). Of the two laser displacement meters 17 and 17 disposed at the upper position or the lower position, one laser displacement gauge 17 is in a lateral position in the X direction with respect to the pipe effective portion 22, and the other laser displacement gauge 17 is It is arrange | positioned in the lateral position of the Y direction with respect to the pipe effective part 22, respectively. Each laser displacement meter 17 detects the distance to the outer peripheral surface of the pipe effective portion 22. The detection result of each laser displacement meter 17 is used when the pipe 23 is held by the pipe holding portion 12 as described later.

Moreover, the said manufacturing apparatus 10 is equipped with the other laser displacement meter 19. Moreover, as shown in FIG. This laser displacement meter 19 is provided in the pipe position adjustment unit 13. The target 12a is installed in the front end of the pipe holding part 12. The laser displacement meter 19 detects the distance L to the target 12a while moving in the Z direction integrally with the pipe holding part 12. According to this detection result, the inclination (bending) of the pipe holding part 12 is detected. The inclination of the pipe holding portion 12 corresponds to the inclination of the pipe 23 (effective portion 22) held by the pipe holding portion 12. The inclination of the pipe holding part 12 can also be detected by providing the said laser displacement gauge 19 to the pipe holding part 12, and detecting the distance to the vertical wall 11a.

Although the pipe position adjusting unit 13 will be described later in detail, the pipe holding unit 13 compensates for the inclination change of the pipe 23 detected by the laser displacement gauge 19 during the integration of the pipe 23 and the rod 27. The slope of the pipe 23 held in the portion 12 is corrected.

(Manufacturing method of optical fiber base material)

The manufacturing method of the optical fiber base material is broadly divided into four steps: 1) correcting the axial distortion of the rod, 2) determining the bending of the pipe, 3) holding the pipe and the rod, and 4) integrating the pipe and the rod. Each process is demonstrated below.

(Fix axis distortion)

As the rod 27 (rod effective portion 26), a glass particle deposit obtained by sintering glass fine particles deposited by the VAD method is sintered and stretched, or a core glass is formed and enriched on the inner surface of the cladding pipe by MCVD. do. The bar effective portion 26 may have a diameter of about 45 to 50 mm and a length of about 2500 mm.

As described above, the rod 27 includes a rod effective portion 26 and upper and lower dummy bars 24 and 25 joined to the rod effective portion 26. Creation of this bar 27 is concretely carried out as follows. That is, in the state where the rod effective portion 26 and the lower dummy rod 25 are laid in the horizontal direction, respectively, the lower end of the rod effective portion 26 and the upper end of the lower dummy rod 25 are bonded to each other. In this state, the joined portion is heated with a heating source to fuse the rod effective portion 26 and the lower dummy rod 25 together. Similarly, the rod effective portion 26 and the upper dummy bar 24 are fused together. When the bar 27 is created in this way, the amount of bending of the bar 27 is detected. That is, the start point I is set at one end of the bar 27, the end point E is set at the other end, and the following reference axis setting and distortion amount detection are performed in this state.

In the reference axis setting, the reference axis required for the distortion amount detection is set. The reference axis is a line connecting the center points of the start point I and the end point E in the width direction in one direction in the radial direction of the bar 27.

In the distortion amount detection, the width direction center point of the bar 27 is measured at predetermined intervals from the start point I to the end point E. FIG. Thereby, the center curve Cx of FIG. 3 which has the reference axis as the horizontal axis and the distortion amount Dx as the vertical axis is obtained. By this curve Cx, it is possible to visually and quantitatively grasp the tendency and the degree of misalignment of the center point with respect to the reference axis when the rod 27 is viewed from one direction in the radial direction, that is, the tendency of bending and the amount of bending. have. Here, in FIG. 3, the upper curve shows the trend along the outer position longitudinal direction of one bar 27 width direction, and the lower curve shows the transition along the outer position longitudinal direction of the other one bar 27 width direction. That is, the center curve Cx of FIG. 3 is the center locus of the upper curve and the lower curve.

Next, the distortion amount Dy is measured similarly to the above in the case where the rod 27 is viewed from the other direction in the radial direction perpendicular to the one direction. Thereby, as shown by the curve Cy in the center of FIG. 4, it is possible to visually and quantitatively grasp the tendency and the degree of the center point position distortion with respect to the reference axis when the bar 27 is viewed from the other direction in the radial direction. have.

After measuring the distortion amounts Dx and Dy, the synthesized distortion amount Q is calculated in the following equation based on these distortion amounts Dx and Dy.

Q = {(Dx) ² + (Dy) ² } ^1/2

As shown in FIG. 5, three-dimensional coordinates are set in which the axial length L of the rod 27 is the Z axis, the distortion amount Dx is the X axis, and the distortion amount Dy is the Y axis. . Then, by plotting the combined distortion amount Qi (i is the measured position) at each measurement position on the three-dimensional coordinates, a synthesis curve Cp connecting these curves is obtained. Here, in FIG. 5, a square (represented by a dotted line in FIG. 5) composed of the distortion amount Dx and the distortion amount Dy, together with the composite curve Cp, and the X coordinate surface passing through the angle of the rectangle, are shown. The curve Cx and the curve Cy of the Y coordinate surface are displayed.

According to the synthesis curve Cp, the curve Cx, and the curve Cy, the occurrence state of the bending of the rod 27, its tendency (direction), and the amount thereof can be grasped accurately in three dimensions. When the amount of distortion per unit length of the rod 27, that is, the amount of bending, is greater than 1 mm / m, the rod effective portion 26, the upper dummy rod 24, and / or the lower dummy rod 25 of the rod 27 are used. Re-heat the fused portion with) to correct the bending of the rod 27 so that the bending amount is 1 mm / m or less.

(Pipe bending judgment)

As the pipe 23 (pipe effective portion 22), one manufactured by the OVD method or the like is used. The pipe effective portion 22 may have an outer diameter of about 180 mm, an inner diameter of about 50 mm, and a length of about 2000 mm.

As described above, the pipe 23 is constituted by a pipe valid portion 22 and upper and lower dummy pipes 20 and 21 joined to the pipe effective portion 22. Since the pipe effective portion 22 and the upper dummy pipe 20 are bonded to each other by fusion of end faces, as shown in FIGS. 6 and 7, bending occurs between the pipe effective portion 22 and the upper dummy pipe 20. There is a case. Here, in FIG. 6, the bending between the pipe effective portion 22 and the upper dummy pipe 20 is exaggerated for clarity. The bending caused between the pipe effective portion 22 and the upper dummy pipe 20 causes the core portion of the optical fiber base material 30 to be eccentric. In addition, the bending between the pipe effective portion 22 and the lower dummy pipe 21 does not affect the core eccentricity of the optical fiber base material 30.

In order to suppress the core portion eccentricity, the pipe effective portion 22 is fused to the upper and lower dummy pipes 20 and 21 to form a pipe 23, and then the bending of the pipe 23 is measured. The method of measuring bending may be any method. As an example, although not shown in detail, the pipe 23 is placed so that the pipe effective portion 22 is horizontal, and the pipe 23 is rotated by 90 degrees while supporting the lower portion of the pipe effective portion 22 with a roller. Then, the displacement of the upper dummy pipe 20 is measured by a dial gauge (four points). The bending direction between the pipe effective part 22 and the upper dummy pipe 20 can be determined according to the displacement of the four points.

From the determination result, the bending direction between the pipe effective portion 22 and the upper dummy pipe 20, that is, two of the central axis C1 of the pipe effective portion 22 and the central axis C2 of the upper dummy pipe 20, is determined. When the plane A (refer FIG. 6, 7) containing a center axis | shaft is found out, the graduation mark 28 which shows the plane A is set in the upper surface of the upper dummy pipe 20 (refer FIG. 1). Here, when the central axis C1 of the pipe effective portion 22 and the central axis C2 of the upper dummy pipe 20 are completely coincident with each other, the scale mark 28 is set at an arbitrary position on the upper surface of the upper dummy pipe 20. do.

(Keep of pipes and rods)

The preparation of each of the pipe 23 and the rod 27 is completed as mentioned above. In the next step, the pipe 23 and the rod 27 are held in the manufacturing apparatus 10, respectively.

First, the groove 20a of the upper dummy pipe 20 is inserted into the pipe holding portion 12 to put the pipe 23 in a suspended state. At this time, since the pipe 23 is a heavy object, the pipe holding part 12 receives a load downward and warp occurs in the Y direction. Subsequently, using the graduation marks 28 set on the upper dummy pipe 20, the direction of the pipe 23 is adjusted so that the plane A is parallel to the bending direction (Y direction) of the pipe holding part 12. Set it.

Next, using the laser displacement meter 17, the distance to the outer peripheral surface of the pipe effective part 22 is measured in upper and lower two points in the X direction, upper and lower two points in the Y direction, and four points in total. . And the inclination of the pipe 23 is adjusted with the pipe position adjustment part 13 so that the difference of the measured value may be minimum. That is, the inclination of the pipe 23 is adjusted so that the axial direction of the pipe effective part 22 may become a vertical direction. After making the axial direction of the pipe effective part 22 into a vertical direction, the position adjustment of the pipe 23 in the X direction and a Y direction is performed. As a result, the central axis of the pipe effective portion 22 coincides with the central axis of the heating furnace 15. In this way, the maintenance of the pipe 23 is completed.

Next, the upper end portion of the upper dummy bar 24 is gripped by the rod holding portion 14, and the rod holding portion 14 causes the rod 27 to be substantially coaxial with the central axis of the heating furnace 15. The positions of the rods 27 in the X and Y directions and their inclinations are adjusted. The rod 27 is then inserted into the pipe 23. In this way, the holding of the rod 27 is completed.

Here, the laser displacement meter 17 is used when the pipe 23 is held, but is not limited thereto. For example, an ironing weight may be used instead of the laser displacement meter 17. That is, as shown in FIG. 8, the thread 32 which cut off the iron weight 31 at one end along the longitudinal direction of the pipe 23 is lined up, and the direction in which the thread 32 continues the axial direction of the pipe effective part 22 is shown. Matches Specifically, the distance between the pipe effective part 22 and the seal 32 is measured by two points, the upper and lower parts in the X direction, and the upper and lower two points and the four points in the Y direction. In this way, the inclination of the pipe effective part 22 is adjusted by the pipe position adjustment part 13 so that the measured value may be mutually equal to each other. Even in this way, the axial direction of the pipe effective portion 22 can be matched with the axial direction of the heating furnace 15.

In addition, the pipe 23 may be positioned vertically by using the laser displacement meter 17 and the iron weight together. For example, after positioning the pipe effective portion 22 vertically using the laser displacement meter 17, it is checked whether the pipe effective portion 22 is vertically positioned using the ironing weight. At this time, the inclination of the pipe effective part 22 is finely adjusted as needed. By doing in this way, the position adjustment of the pipe 23 can be performed more accurately.

(Integration of pipes and rods)

As described above, each of the pipe 23 and the rod 27 is retained. In the next step, the pipe 23 and the rod 27 are integrated.

First, the upper opening of the upper dummy pipe 20 is closed with a waste cap 29, and the pressure inside the pipe 23 is reduced with a vacuum pump. In this state, the pipe holding part 12 and the rod holding part 14 are respectively moved downward at a predetermined speed.

As a result, the pipe 23 and the rod 27 pass through the insertion hole 15a of the heating furnace 15 in the axial direction, and the pipe 23 and the rod 27 are connected to the heating furnace 15. Thereby sequentially heating from the bottom to the top. The pipe 23 and the rod 27 are sequentially melted from the lower end toward the upper end, but the molten pipe 23 is reduced by the pressure difference between the inside and the outside by depressurizing the inside of the pipe 23. As a result, the pipe 23 and the rod 27 are sequentially fused and integrated in the axial direction thereof.

When the integration of the pipe 23 and the rod 27 proceeds here, the load to the pipe holding portion 12 is lowered, and the bending of the pipe holding portion 12 is also reduced. This changes the amount of inclination of the pipe 23 with respect to the central axis of the furnace 15.

Therefore, during manufacture of the optical fiber base material 30, the position change of the pipe 23 is detected by the laser displacement meter 19. As shown in FIG. And the pipe position adjustment part 13 corrects the attitude | position of the pipe 23 so that the change of attitude | position of the detected pipe 23 may be canceled.

At this time, as mentioned above, the bending direction (Y direction) of the said plane A and the pipe holding part 12 becomes parallel. As a result, the center of gravity of the pipe 23 moves on the plane A as the integration progresses. That is, the pipe 23 changes the inclination only in the Y direction. Therefore, the pipe position adjusting unit 13 only needs to correct the inclination of the pipe 23 in the Y direction.

In this way, during the integration of the pipe 23 and the rod 27, the central axis of the pipe 23 always coincides with the central axis of the furnace 15.

In addition, although the attitude | position change of the pipe 23 in the integration of the pipe 23 and the rod 27 is measured by the laser displacement meter 19, it is not limited to this. For example, the level holding part may be provided in the pipe holding part 12 to measure the change in posture of the pipe 23. In addition, you may measure the attitude | position change of the pipe 23 by detecting the inclination of the pipe holding | maintenance part 12 with an angle detector.

The integrated product in which the pipe 23 and the rod 27 are integrated is guided by the roller 16. As a result, the integrated product is stretched until it reaches a predetermined outer diameter. In this way, the optical fiber base material 30 is completed. The optical fiber base material 30 is predrawn with a drawing device, not shown, to become an optical fiber.

As described above, according to the method for manufacturing the optical fiber base material, the slope change of the pipe 23 is detected by the laser displacement gauge 17 during the integration of the pipe 23 and the rod 27 and based on the detected value. Thus, the pipe 23 is displaced so that the central axis of the pipe 23 coincides with the axis of the heating furnace. Therefore, the optical fiber base material 30 with a small amount of eccentricity of a core part can be manufactured.

Further, by holding the pipe 23 so that the plane A and the pipe effective portion 22 are inclined from the vertical direction in parallel, the direction in which the inclination of the pipe 23 changes during integration is a constant direction. The pipe positioning unit 13 can position the pipe 23 coaxially with the heating furnace 15 only by correcting the inclination in one direction.

In addition, the bending amount of the bar 27 is measured, and when the bending amount is large, the fusion state of the rod effective portion 26, the upper dummy bar 24 and / or the lower dummy bar 25 is corrected in advance. Thus, when the rod 27 is inserted into the pipe 23, the rod 27 is prevented from coming in contact with the inner wall of the pipe 23 or being swept away from being scratched. In addition, the core part eccentricity of the optical fiber base material 30 is suppressed. Moreover, even if the bending amount of the rod 27 is large, the rod 27 is modified and used, so that the material can be effectively utilized.

The rod bending portion 26, the upper dummy bar 24, and the lower dummy bar 25 are fused together with these bar axes almost horizontal to determine the exact amount of bending. As a result, the bending amount of the rod 27 does not increase during the integration of the pipe 23 and the rod 27. Also in this respect, the core part eccentricity of the optical fiber base material 30 is suppressed.

(Keep the pipe in consideration of the temperature distribution of the furnace)

-first-

When the optical fiber base material 30 is manufactured by the manufacturing method mentioned above, the eccentricity of the core part is normally suppressed. However, depending on the conditions, the eccentricity of the core portion may be relatively large. This is one of the reasons for the nonuniformity of the circumferential temperature distribution of the heating furnace (15). In other words, the temperature distribution in the circumferential direction in the heating furnace 15 becomes uneven, so that the molten state of the pipe 23 becomes uneven in the circumferential direction, and as a result, in the direction of the position where the temperature is highest with respect to the central axis of the heating furnace 15. The core is eccentric. Therefore, when the nonuniformity of temperature distribution is comparatively large, the optical fiber base material 30 is manufactured as follows. This makes it possible to reduce the eccentricity of the core portion.

That is, the pipe 23 and the rod 27 are maintained in the state which each center axis becomes coaxial with the center axis of a heating furnace according to the above-mentioned procedure. Then, the temperature in the heating furnace 15 is measured by each temperature sensor 18 provided in the heating furnace 15, and the temperature distribution of the circumferential direction in the heating furnace 15 is measured from the measurement result. And the pipe 23 is made into the attitude | position which inclined the said pipe 23 to the position direction with the highest temperature in this heating furnace 15 with respect to the central axis of the said heating furnace 15 by the pipe position adjustment part 13. As a result, as shown in FIG. 9, the central axis Z1 of the rod 27 is substantially coaxial with the central axis of the heating furnace 15, while the central axis C1 of the pipe 23 (effective portion 22) is provided. Is inclined with respect to the central axis of the furnace 15 (in the drawing example, the direction of the position where the temperature in the furnace 15 is highest is assumed to be the positive side in the X direction, so that the central axis C1 of the pipe 23 is ) Is inclined to the positive direction in the X direction with respect to the central axis of the furnace (15). As a result, the clearance between the inner peripheral surface of the pipe 23 and the circumferential surface of the rod 27 becomes relatively wider at the + side of the X direction. Here, in the drawing example, the inclination of the pipe 23 is shown to be exaggerated rather than actual for clarity.

In this state, the pipe 23 and the rod 27 are integrated. During this integration, the inclination change of the pipe 23 is detected by the laser displacement meter 19, and the inclination of the pipe 23 is corrected so as to cancel the change. As a result, the pipe 23 maintains its original posture. In this case, the central axis of the pipe 23 and the central axis of the heating furnace 15 do not necessarily coincide.

According to this manufacturing method, the integration of the pipe 23 and the rod 27 is performed in the state where the clearance between the pipe 23 and the rod 27 is increased at the circumferential position where the temperature is high in the heating furnace 15. Is carried out. Although the core part tends to be eccentric in the direction of the highest temperature in the heating furnace 15, the clearance between the pipe 23 and the rod 27 is large in this position. Therefore, the eccentricity of the core portion is suppressed.

In addition, as the integration of the pipe 23 and the rod 27 proceeds, the bending of the pipe holding portion 12 decreases, and thus the attitude of the pipe 23 changes, but the pipe 23 with the laser displacement gauge 19. The change of the inclination amount of) is measured, and accordingly, the posture of the pipe 23 is maintained in the original posture. Thereby, the eccentricity of a core part can be suppressed over the whole axial direction of the optical fiber base material 30.

-second-

The manufacturing method which concerns on "second" is a manufacturing method which paid the attention that the eccentricity of the core part resulting from the temperature distribution nonuniformity in the heating furnace 15 has reproducibility. This is because the temperature distribution nonuniformity in the heating furnace 15 due to time-dependent factors does not change rapidly, and the temperature distribution nonuniformity in the heating furnace 15 due to structural factors does not change if the same heating furnace 15 is used. . That is, in the manufacturing method of the "second", the pipe 23 and the rod 27 are integrated, the optical fiber base material 30 is manufactured, and the core part eccentric direction and the eccentricity of the optical fiber base material 30 are measured. Then, when the optical fiber base material 30 is manufactured, the pipe 23 is held in an inclined position with respect to the central axis of the heating furnace 15 according to the measurement result. Hereinafter, the manufacturing method regarding "second" is explained concretely.

First, the pipe 23 is held by the pipe holder 12, and the rod 27 is held by the rod holder 14, so that each of the pipe 23 and the rod 27 is heated by the heating furnace 15. Position it to be nearly coaxial with respect to the central axis. This point is the same as the manufacturing method mentioned above.

In this state, the pipe 23 and the rod 27 are integrated. During the integration of the pipe 23 and the rod 27, the pipe position adjusting unit 13 corrects the pipe 23 attitude so as to maintain a coaxial state between the pipe 23 and the central axis of the heating furnace 15. In this way, the optical fiber base material 30 (1st optical fiber base material) which integrated the pipe 23 and the rod 27 is completed.

And the core part eccentric state of this completed 1st optical fiber base material 30 is measured. Specifically, the eccentric direction with respect to the central axis of the core part heating furnace 15 and the amount of eccentricity are measured.

Next, while maintaining the separate pipe 23 as the pipe holding portion 12, and maintaining a separate bar 27 as the rod holding portion (14). The pipes 23 and the rods 27 are connected to the pipe positioning portion 13 and the rod holding portion 14 such that the pipes 23 and the rods 27 are substantially coaxial with respect to the central axis of the furnace 15. Adjust your posture individually.

The pipe 23 is inclined in the eccentric direction with respect to the central axis of the heating furnace 15 along the eccentric direction measured by the first optical fiber base material 30 (see FIG. 9). At this time, the inclination amount of the pipe 23 may be appropriately adjusted according to the amount of eccentricity of the core portion of the first optical fiber base material 30. For example, if the amount of eccentricity of the core part is 0.1 mm order, what is necessary is just to set the inclination amount of the pipe 23 to 0.1 mm / m (the inclination amount per 1 m pipes) order.

In this state, the pipe 23 and the rod 27 are integrated to manufacture the optical fiber base material 30. During the integration of the pipe 23 and the rod 27, the pipe in which the pipe positioning portion 13 is held by the pipe holding portion 12 so as to cancel the change in the attitude of the pipe 23 detected by the laser displacement meter 19 ( 23) Correct the posture.

As described above, according to the second manufacturing method, the optical fiber base material 30 is manufactured by keeping the pipe 23 and the rod 27 substantially coaxial with respect to the central axis of the heating furnace 15, thereby producing the heating furnace ( 15), the tendency of the core part eccentricity can be grasped | ascertained when the pipe 23 and the rod 27 are integrated.

Next, the optical fiber base material 30 is manufactured by holding the pipe 23 in the inclined attitude with respect to the central axis of the heating furnace 15 so that the eccentricity tendency of the core part is suppressed. As a result, the newly manufactured optical fiber base material 30 is suppressed from the core part eccentricity.

For example, before and after replacing the heater of the heating furnace 15, the temperature distribution in the heating furnace 15 changes. Therefore, the eccentric tendency of the core part is grasped | ascertained by the optical fiber base material 30 manufactured immediately after replacing a heater, and the optical fiber base material 30 may be manufactured by maintaining the pipe 23 in the inclined posture correspondingly to the eccentric tendency from then on.

Moreover, the temperature distribution of the heating furnace 15 changes with time by deterioration of a heater. For this reason, it is preferable to fine-adjust the inclination direction and the inclination amount of the pipe 23 at the time of next manufacture, in the state which confirmed the core part eccentricity tendency of the optical fiber base material 30 manufactured just before.

The apparatus used for the manufacturing method of the optical fiber base material which concerns on the "second" here is substantially the same as the manufacturing apparatus 10 shown to FIG. However, since it is necessary to measure the temperature distribution in the heating furnace 15, the temperature sensor 18 should just be equipped with at least 1 as monitoring the temperature in the heating furnace 15. As shown in FIG.

(Example)

Next, the Example concretely implemented is demonstrated.

First Embodiment

With regard to the bending of the pipe, an embodiment actually carried out will be described.

First, as Example 1-1, the optical fiber base material 30 is manufactured using the manufacturing apparatus 10 mentioned above. The pipe 23 used at this time is an outer diameter of 179.4 mm and an inner diameter of 54.1 mm, and the rod 27 is an outer diameter of 51.4 mm. The average clearance between the inner circumferential surface of the pipe 23 and the circumferential surface of the rod 27 is 1.35 mm. In addition, as a manufacturing condition, both the feed rate of the pipe 23 and the feed rate of the rod 27 are 14.4 m / min.

In Example 1-1, while the scale 28 is kept in the pipe holding portion 12 in the pipe holding direction 12 so as to coincide with the bending direction of the pipe holding portion 12, the pipe 23 and The pipe 23 tilts during the integration of the rod 27.

As the comparative example 1-1, the optical fiber base material 30 is manufactured using the pipe 23 and the rod 27 of the same shape using the said manufacturing apparatus 10. FIG. The manufacturing conditions are the same as in the case of Example 1-1, but in Comparative Example 1-1, the pipe 23 is connected to the pipe holding portion so that the scale 28 does not coincide with the bending direction of the pipe holding portion 12. 12). In addition, during the integration, the inclination of the pipe 23 is not corrected.

In addition, as the comparative example 1-2, the optical fiber base material 30 is manufactured using the pipe 23 and the rod 27 of the same shape using the said manufacturing apparatus 10. FIG. The manufacturing conditions are the same as in the case of Example 1-1, but in Comparative Example 1-2, the pipe 23 is connected to the pipe holding part so that the scale 28 does not coincide with the bending direction of the pipe holding part 12. 12). In addition, the slope of the pipe 23 is corrected during integration.

10-12, the cross section of the optical fiber base material 30 manufactured in Example 1-1, Comparative Example 1-1, and 1-2 respectively shows the variation of the core part eccentricity from manufacture start to finish.

As shown in FIG. 11, when the pipe 23 is held without considering the bending of the pipe 23 and the inclination of the pipe 23 is not corrected during integration, the core portion is greatly eccentric in the X and Y directions. do.

As shown in FIG. 12, although the pipe 23 is held without considering the bending of the pipe 23, when the inclination of the pipe 23 is corrected during integration, the core portion is in one direction (Y direction). Although eccentricity is suppressed, it is largely eccentric in the other direction (X direction).

On the other hand, as shown in FIG. 10, when the pipe 23 is held in consideration of the bending of the pipe 23 and the slope of the pipe 23 is corrected during integration, the core eccentricity is suppressed. have.

FIG. 13 is a graph comparing the results of converting the core portion eccentricity of the optical fiber base materials 30 manufactured in Example 1-1 and Comparative Examples 1-1 and 1-2 into the core eccentricity of the optical fiber. According to this, the amount of core eccentricity of Example 1-1 was significantly smaller than the amount of core eccentricity of each comparative example.

Therefore, by maintaining the pipe 23 in consideration of the bending and correcting the inclination of the pipe 23 during integration, it is possible to suppress the eccentricity of the core portion.

Example 2-

The Example actually performed about the temperature distribution of a heating furnace is demonstrated. First, as the comparative example 2-1, the optical fiber base material 30 is manufactured using the said manufacturing apparatus 10. FIG. The pipe 23 used at this time has an outer diameter of 180 mm and an inner diameter of 54 mm, and the rod 27 has an outer diameter of 50 mm. The average clearance between the inner circumferential surface of the pipe 23 and the circumferential surface of the rod 27 is 2.32 mm. Moreover, as manufacturing conditions, glass processing amount (total glass amount of the pipe 23 and the rod 27 integrated per unit time) shall be 360 ml / min. Here, the glass processing amount is adjusted by adjusting the conveyance speed of the pipe 23 and the rod 27 to the heating furnace 15. Moreover, the speed ratio which is the ratio of the feed speed of the pipe 23 and the feed speed of the rod 27 is set to 0.90.

In Comparative Example 2-1, the pipe 23 and the rod 27 are held so as to be substantially coaxial with respect to the central axis of the heating furnace 15, thereby integrating both. During the integration, the attitude of the pipe 23 is corrected so that the coaxial state between the pipe 23 and the central axis of the heating furnace 15 is maintained.

FIG. 14: shows the variation of the core part eccentricity from manufacture start to the end in the cross section of the optical fiber base material 30 manufactured by the comparative example. According to FIG. 14, it can be seen that in the comparative example, the core part tends to be eccentric toward the negative (-) side in the X direction.

Next, as Example 2-1, the optical fiber base material 30 is manufactured using the pipe 23 and the rod 27 of the same shape using the same manufacturing apparatus 10 as the case of the said comparative example. Since the manufacturing apparatus 10 is the same, the temperature distribution in the heating furnace 15 at the time of manufacturing the thing of an Example is the same as when manufacturing the thing of the comparative example 2-1.

 In Example 2-1, the pipe 23 is 0.3 mm in the negative direction in the X direction with respect to the central axis of the heating furnace 15 in the optical fiber base material 30 of Comparative Example 2-1, based on the core eccentric state. Keep in a tilted position with a slope of / m. The rod 27 is maintained in the attitude | position which becomes substantially coaxial with the center axis of the heating furnace 15 here. In this state, the pipe 23 and the rod 27 are integrated to manufacture the optical fiber base material 30. And the attitude | position of the pipe 23 is correct | amended during integration so that the attitude | position of the pipe 23 may maintain the attitude | position which was originally maintained.

FIG. 15 shows a variation in core portion eccentricity from the start of manufacture to the end in the cross section of the optical fiber base material 30 manufactured in Example 2-1. According to FIG. 15, in the comparative example 2-1, the core part tended to be eccentric toward the negative direction of the X direction, but in Example 2-1, the tendency was suppressed and the amount of core part eccentricity became small.

Next, FIG. 16 is a graph which compares the result which converted the core part eccentricity of the optical fiber base material 30 manufactured by Example 2-1 and the comparative example 2-1 into the optical fiber core eccentricity. As shown in FIG. 16, the amount of core eccentricity of Example 2-1 was significantly smaller than the amount of core eccentricity of Comparative Example 2-1.

Therefore, the core part eccentricity by the temperature distribution nonuniformity in the heating furnace 15 can be eliminated by maintaining the pipe 23 in the attitude | position inclined suitably with respect to the central axis of the heating furnace 15. FIG.

The present invention relates to a method for manufacturing an optical fiber base material by a so-called Rod-In Tube method, a manufacturing apparatus, and an optical fiber base material and an optical fiber manufactured by the method.

Claims (15)

A pipe holding step of keeping the quartz pipe suspended; A rod holding step of maintaining the quartz rod including the core portion inserted into the pipe; A heating step of sequentially heating the retained pipes and rods in an axial direction thereof by an annular heating furnace having a central axis direction perpendicular thereto; An integration step of integrating the heated pipes and rods sequentially by fusion in the axial direction thereof; A detecting step of detecting a change in inclination of the pipe accompanying the integration of the pipe and the rod; And a calibrating step of calibrating the pipe inclination to cancel the change in the detected inclination during the integration of the pipe and the rod. The method of claim 1, In the pipe holding step, the position of the pipe is determined so that the central axis of the maintained pipe is coaxial with the central axis of the furnace. The method of claim 2, Positioning of the pipe is performed by lowering the thread to the side of the pipe using a thread ironed at a lower end, and performing a position adjustment in a plurality of directions to match the pipe axial direction to the direction in which the thread continues. A method for producing an optical fiber base material. The method of claim 2, Positioning of the pipe uses a plurality of laser displacement meters arranged in a vertical direction apart from each other in the pipe side position, irradiates a laser beam from the respective laser displacement meters to the pipes, and up to the pipes measured by the respective laser displacement meters. A method for manufacturing an optical fiber base material, which is performed by performing a position adjustment in a plurality of directions so as to coincide with each other. The method of claim 1, The pipe is composed of an effective part and a dummy pipe joined to an upper end of the effective part, and the pipe is held in a suspended state by the dummy pipe being held by the pipe holding part. Further comprising a pipe determination step of determining the degree of bending of the effective portion and the dummy pipe, The pipe holding step includes a plane including two axes of the effective part central axis and the dummy pipe central axis based on the determination result of the pipe determining step, and the effective part being vertically oriented by the bending of the pipe holding part holding the pipe. And holding the pipe so that the tilting direction is parallel to each other. The method of claim 1, Further comprising a temperature measuring step of measuring the temperature distribution in the circumferential direction in the heating furnace, The rod holding step is to maintain the rod in a state substantially coaxial with the central axis of the heating furnace, The pipe holding step is a step of maintaining the pipe in a state in which the pipe is inclined in the direction of the position where the temperature in the heating furnace is the highest with respect to the central axis of the heating furnace based on the measurement result of the measuring step. Manufacturing method. The method of claim 1, The rod holding step is to maintain the rod in a state substantially coaxial with respect to the central axis of the heating furnace, The pipe holding step is to maintain the pipe substantially coaxial with respect to the central axis of the furnace, A measuring step of measuring an eccentric direction of the core portion with respect to the central axis of the heating furnace in the integrated package in which the pipe and the rod are integrated after the integration step; A second rod holding step of holding the second rod substantially coaxial with respect to the central axis of the furnace; A second pipe holding step of holding the second pipe in an inclined state in an eccentric direction of the core part of the integrated cargo with respect to the central axis of the heating furnace, based on the measurement result of the measuring step; A second heating step of heating the retained second pipe and the second rod with the heating furnace, And a second integration step of integrating the heated second pipe and the second rod. The method of claim 1, The rod is composed of an effective portion, an upper dummy rod fusion-bonded to the upper end of the effective portion, and a lower dummy rod fusion-bonded to the lower end of the effective portion, Before the rod holding step, further comprising a bar determination step of determining whether the bending amount of the bar is less than a predetermined bending amount, the manufacturing method of the optical fiber base material. The method of claim 8, The predetermined amount of bending is 1mm / m, the manufacturing method of the optical fiber base material. The method of claim 8, Based on the determination result of the bar determination step, when the bending amount of the rod is larger than the predetermined bending amount, the rod and the upper dummy bar and / or the lower dummy so that the bending amount is less than or equal to the predetermined bending amount. Further comprising a modification step of correcting the fusion state of the rod, the optical fiber base material manufacturing method. The method of claim 8, The rod, the upper dummy bar and / or the lower dummy bar are fusion bonded together with their axes substantially horizontal. The optical fiber base material created by the manufacturing method of Claim 1. The optical fiber which extracted the optical fiber base material created by the manufacturing method of Claim 1. In the optical fiber base material manufacturing apparatus which heats a quartz pipe and a quartz rod and integrates it by fusion | melting, A pipe holding portion which holds the pipe and moves the pipe in the axial direction; An annular heating furnace that sequentially heats the pipe moved by the pipe holding unit in the axial direction thereof; Apparatus for manufacturing an optical fiber base material having a detecting means for detecting a change in inclination of a pipe moved by the pipe holding part. The method of claim 14, And a displacement means for correcting the inclination of the pipe held in the pipe holding portion so as to cancel the change in the inclination of the pipe on the basis of the detection result of the detection means.