JP2005320197A - Apparatus for manufacturing optical fiber preform, and method of manufacturing optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for manufacturing an optical fiber preform and a method of manufacturing the optical fiber preform which can form an optional temperature distribution in a furnace core tube constituting a heating furnace in a dehydration process and a sintering process of a porous base material for an optical fiber by using the heating furnace. <P>SOLUTION: In the apparatus for manufacturing the optical fiber preform provided with the heating furnace 10 having the furnace core tube 12 housing the porous base material 11 for the optical fiber, the heating furnace 10 is equipped with a first heater 13A and a second heater 13B for heating the porous base material 11 for the optical fiber housed in the furnace core tube 12, the first heater 13A and the second heater 13B are arranged along the longitudinal direction of the furnace core tube 12 so as to surround the outer circumference of the furnace core tube 12, and the first heater 13A and the second heater 13B are made possible to control the temperature mutually independently. The porous base material 11 for the optical fiber housed in the furnace core tube 12, the first heater 13A, and the second heater 13B are made mutually movable. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber preform manufacturing apparatus for forming an optical fiber preform by dehydrating and sintering a porous preform for an optical fiber, and an optical fiber preform manufacturing method using the same. .

  As a manufacturing method of an optical fiber preform used for manufacturing an optical fiber, generally, a porous preform for optical fiber is formed, and this optical fiber preform is provided in an optical fiber preform manufacturing apparatus. In such a heating furnace, a method of dehydrating and sintering to form an optical fiber preform is used.

FIG. 2 is a schematic configuration diagram illustrating an example of a heating furnace provided in a conventional optical fiber preform manufacturing apparatus.
In the heating furnace 100 of this example, a cylindrical furnace core tube 102 made of quartz glass that contains a porous preform 101 for optical fibers, and a porous preform 101 for optical fibers accommodated in the furnace tube 102 are heated. Heater 103 for housing, housing 104 housing heater 103, inlet 105 for introducing inert gas into the core tube 102, and support rod 106 for supporting the optical fiber porous preform 101 It is roughly composed of

  In the heating furnace 100, a porous optical fiber preform 101 can move in the furnace core tube 102 (see, for example, Patent Document 1).

 When the optical fiber porous preform 101 is dehydrated by the heating furnace 100, the temperature is low enough that the optical fiber porous preform 101 does not become transparent glass and the dehydration reaction proceeds sufficiently. It needs to be set high.

 When the sintering is performed following the dehydration of the optical fiber porous preform 101, the temperature is sufficiently high so that the optical fiber porous preform 101 is vitrified and the optical fiber porous preform 101 is porous. It is necessary to set it low enough that the optical fiber preform formed by vitrifying the preform 101 does not extend due to its own weight.

However, the ideal temperature distribution in the core tube 102 differs between the dehydration process and the sintering process of the optical fiber porous preform 101. Therefore, as shown in FIG. 2, it is difficult to form an ideal temperature distribution in both processes with one heater 103 in the core tube 102, and particularly when the porous optical fiber base material 101 is enlarged, There was a problem that either the dehydration process or the sintering process, or both the dehydration process and the sintering process were not performed efficiently.
JP-A-5-339012

  The present invention has been made in view of the above circumstances, and in the dehydration process and sintering process of the optical fiber porous preform using the heating furnace, an arbitrary temperature distribution is formed in the furnace core tube forming the heating furnace. An object of the present invention is to provide an optical fiber preform manufacturing apparatus and a method of manufacturing an optical fiber preform.

  In order to solve the above-mentioned problems, the present invention is an optical fiber preform manufacturing apparatus including a heating furnace having a furnace core tube containing a porous preform for an optical fiber, wherein the heating furnace is provided in the furnace core tube. Two or more heaters for heat-treating the optical fiber porous preform accommodated in the optical fiber, and the heaters are arranged in parallel along the longitudinal direction of the core tube so as to surround the outer periphery of the core tube, The two or more heaters provide an optical fiber preform manufacturing apparatus that can be independently temperature controlled.

  In the optical fiber preform manufacturing apparatus, it is preferable that the optical fiber porous preform housed in the furnace core tube and the two or more heaters are relatively movable.

  In the optical fiber preform manufacturing apparatus, it is preferable that the two or more heaters are movable along a longitudinal direction of the core tube.

  The present invention is also a method for manufacturing an optical fiber preform using the optical fiber preform manufacturing apparatus, wherein a glass preform is deposited on the outer periphery of a central glass rod to form a porous preform for an optical fiber. And a step B of housing the optical fiber porous preform in the furnace core tube, dehydrating and sintering, and in the step B, the two or more heaters, Provided is a method of manufacturing an optical fiber preform that forms a temperature distribution along the longitudinal direction of a porous preform for an optical fiber.

  In the step B, it is preferable to control the temperatures of the two or more heaters independently.

  In the step B, it is preferable to move the optical fiber porous preform housed in the furnace core tube relative to the two or more heaters.

  According to the present invention, since the temperature distribution in the furnace core tube can be set arbitrarily, it becomes easy to set the manufacturing conditions of the optical fiber preform. Moreover, the dehydration efficiency of the optical fiber porous preform can be improved, and elongation due to its own weight during sintering of the optical fiber porous preform can be reduced. Furthermore, the time required for dehydration and the time required for sintering of the optical fiber porous preform can be shortened.

  Hereinafter, an optical fiber preform manufacturing apparatus and an optical fiber preform manufacturing method embodying the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of an optical fiber preform manufacturing apparatus according to the present invention, and is a schematic configuration diagram showing a heating furnace provided in the optical fiber preform manufacturing apparatus.
The heating furnace 10 in this embodiment heats a cylindrical furnace core tube 12 made of quartz glass that houses the optical fiber porous preform 11 and the optical fiber porous preform 11 accommodated in the furnace core tube 12. A heater 13 for processing, a casing 14 housing the heater 13, an inlet 15 for introducing an inert gas into the core tube 12, and a support rod for supporting the optical fiber porous preform 11 16.

  The heating furnace 10 includes a first heater 13 </ b> A and a second heater 13 </ b> B arranged in parallel along the longitudinal direction of the core tube 12 so that the heater 13 surrounds the outer periphery of the core tube 12. .

  In this way, by arranging the first heater 13A and the second heater 13B in parallel along the longitudinal direction of the core tube 12, in the longitudinal direction of the optical fiber porous preform 11 in the core tube 12. Along with this, an arbitrary temperature distribution can be formed. Therefore, the temperature in the furnace core tube 12 is sufficiently high for the optical fiber porous preform 11 to be vitrified, and the optical fiber preform formed by vitrifying the optical fiber porous preform 11 is self-weighted. Can be set low enough not to stretch.

  In this embodiment, an example in which two heaters, the first heater 13A and the second heater 13B, are provided, but the optical fiber preform manufacturing apparatus of the present invention is not limited to this. In the optical fiber preform manufacturing apparatus of the present invention, three or more heaters may be provided in parallel along the longitudinal direction of the core tube. As described above, if three or more heaters are provided, temperature distributions of various patterns can be more precisely formed in the furnace core tube along the longitudinal direction of the optical fiber porous preform. Therefore, as the number of heaters is increased, the temperature in the furnace core tube is sufficiently high for the optical fiber porous preform to become transparent glass, and the optical fiber formed by vitrifying the optical fiber porous preform. It can be set so low that the base material does not stretch due to its own weight.

  When only one heater is provided as in the conventional optical fiber preform manufacturing apparatus, the temperature inside the core tube can be changed, but the longitudinal direction of the optical fiber porous preform within the core tube can be changed. A temperature distribution cannot be provided along. In the optical fiber preform manufacturing apparatus of the present invention, since two or more heaters are provided, various patterns of temperature distributions along the longitudinal direction of the optical fiber porous preform in the furnace core tube. Can be formed.

  However, considering the manufacturing cost and the like, practically, the number of heaters is preferably two. Even if the number of heaters is two, the heat treatment of the large-sized porous optical fiber preform can be performed efficiently without increasing the time required for the heat treatment.

  The first heater 13A and the second heater 13B can be controlled independently. However, in the heat treatment of the optical fiber porous preform 11, in order to form an arbitrary temperature distribution along the longitudinal direction of the optical fiber porous preform 11 in the core tube 12, each is independently It is preferable that the temperature can be controlled.

  Furthermore, in order to form an arbitrary temperature distribution along the longitudinal direction of the optical fiber porous preform 11, the optical fiber porous preform 11 accommodated in the core tube 12 and the heater 13 are relative to each other. May be movable.

As a configuration in which the optical fiber porous base material 11 and the heater 13 are relatively movable, the optical fiber porous base material 11 itself supported by the support rod 16 is arranged along the longitudinal direction of the core tube 12. A configuration that enables reciprocal movement, a configuration that enables the heater 13 to reciprocate along the longitudinal direction of the core tube 12 together with the housing 14 that accommodates the heater 13, a first heater 13A that is accommodated in the housing 14, A configuration is provided in which each of the second heaters 13 </ b> B can reciprocate along the longitudinal direction of the core tube 12 (configuration that can move in the arrow direction in FIG. 1).
In addition, when the structure which can move the porous preform | base_material 12 for optical fibers and the heater 13 relatively is not provided, the length of the heater 13 is equal to or more than the length of the porous preform | base_material 12 for optical fibers. Set to.

  In particular, if the first heater 13A and the second heater 13B can move independently along the longitudinal direction of the core tube 12, the distance between the heaters can be arbitrarily set. Thereby, arbitrary temperature distribution can be formed in the core tube 12 along the longitudinal direction of the optical fiber porous preform 11.

  Next, an embodiment of a method for manufacturing an optical fiber preform according to the present invention will be described with reference to FIG.

  In the optical fiber preform manufacturing method of this embodiment, first, a porous preform 11 for an optical fiber is formed by a known method such as a VAD (Vapor Phase Axial Deposition) method or an OVD (Outside Vapor Deposition) method ( Step A).

  Next, the porous preform 11 for optical fiber is accommodated in the core tube 12 having a predetermined temperature distribution along the longitudinal direction by the first heater 13A and the second heater 13B, and chlorine gas is contained. It is passed through a helium atmosphere containing, dehydrated and sintered to obtain an optical fiber preform (step B).

  In this embodiment, in the process B, by independently controlling the temperature of the first heater 13A and the second heater 13B, in the furnace core tube 12 along the longitudinal direction of the optical fiber porous preform 11. Form a temperature distribution.

  In this step B, the optical fiber porous preform 11 accommodated in the core tube 12, the first heater 13A, and the second heater 13B are relatively moved.

Here, a specific example of the process B is shown.
In this step B, first, the porous preform 11 for optical fiber is dehydrated, and then the porous preform 11 for optical fiber is sintered.

In order to perform dehydration of the optical fiber porous preform 11, the inside of the core tube 12 is moved along the longitudinal direction while changing the temperature distribution in the core tube 12.
Here, the case where dehydration is performed by moving the optical fiber porous preform 11 from above to below will be described.
At the start of dehydration, the temperature of the second heater 13B is set higher than the temperature of the first heater 13A, and the temperature distribution in the core tube 12, particularly along the longitudinal direction of the casing 14 housing the heater 13 is set. The temperature distribution is set so that the upper side of the housing 14 is lower and becomes higher as it goes downward. That is, here, the temperature distribution in the furnace core tube 12 is set so as to increase from the front to the back along the traveling direction of the optical fiber porous preform 11.

  More specifically, at the start of dehydration, the temperature of the first heater 13A is set to 1200 to 1300 ° C, and the temperature of the second heater 13B is set to 1250 to 1400 ° C.

  In this way, when the dehydration of the optical fiber porous preform 11 is started, the dehydration reaction on the lower end side is promoted, so that it is possible to solve the problem that dehydration is difficult to be performed locally.

  In the middle of the dehydration (when the optical fiber porous preform 11 is between the first heater 13A and the second heater 13B), the first heater 13A and the second heater 13A are used to accelerate the dehydration reaction. A temperature distribution is formed such that the temperatures of the heaters 13B are substantially equal.

  More specifically, when the temperature of the first heater 13A and the second heater 13B at the start of dehydration is in the above range, the temperature of the first heater 13A is set to 1200 to 1300 ° C. and the first The temperature of the second heater 13B is set to 1200 to 1300 ° C.

  In this way, the dehydration reaction can be carried out at a suitable temperature in a wide range of the optical fiber porous preform 11, so that the dehydration reaction can be efficiently promoted.

  At the end of dehydration (when the upper taper portion of the optical fiber porous preform 11 is applied to the first heater 13A), the temperature of the first heater 13A is set higher than the temperature of the second heater 13B. The temperature distribution in the core tube 12 is set high, and in particular, the temperature distribution along the longitudinal direction of the casing 14 housing the heater 13 is set so that the upper side of the casing 14 is higher and lower as it goes downward. To do. That is, here, the temperature distribution in the core tube 12 is set so as to decrease from the front to the back along the traveling direction of the optical fiber porous preform 11.

  More specifically, at the end of dehydration, the temperature of the first heater 13A is set to 1200 to 1400 ° C., and the temperature of the second heater 13B is set to 1200 to 1300 ° C.

  In this way, at the end of the dehydration of the optical fiber porous preform 11, the vicinity of the upper tapered portion of the optical fiber porous preform 11 is difficult to be heated, thereby preventing the problem that the dehydration reaction is not accelerated. And the dehydration reaction is performed efficiently.

Subsequently, in order to sinter the porous preform 11 for optical fibers, the temperature distribution in the core tube 12 is changed while moving vertically in the core tube 12 along its longitudinal direction.
In the sintering of the optical fiber porous preform 11, one of the first heater 13A and the second heater 13B is set higher than the other, and the temperature distribution in the core tube 12, particularly the heater 13, is accommodated. The temperature distribution along the longitudinal direction of the housing 14 is set so that the upper side of the housing 14 is lower and goes higher, or the upper side of the housing 14 is higher and goes downward. Set to lower. That is, the temperature distribution in the core tube 12 is set so as to increase toward the front in the traveling direction of the optical fiber porous preform 11, or in the traveling direction of the optical fiber porous preform 11. Set to go lower as you go forward.

  More specifically, at the time of sintering, for example, the temperature of the first heater 13A is set to 1300 to 1400 ° C., and the temperature of the second heater 13B is set to 1500 to 1600 ° C.

  In this way, the temperature distribution in the furnace tube 12 is set so that one of the heaters is higher when the high temperature region is excessively widened in the sintering of the optical fiber porous preform 11. This is because unnecessary gas in the base material 11 cannot be sufficiently removed, or deformation of the optical fiber base material obtained by sintering the porous base material 11 for optical fibers becomes too large.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

(Example)
The optical fiber preform was manufactured by dehydrating and sintering the porous preform for the optical fiber by using the optical fiber preform manufacturing apparatus as shown in FIG.
In the dehydration of the optical fiber porous preform 11, the temperature of the first heater 13A at the start of dehydration was set to 1350 ° C., and the temperature of the second heater 13B was set to 1250 ° C.
The temperature of the first heater 13A in the middle of dehydration was set to 1250 ° C., and the temperature of the second heater 13B was set to 1250 ° C.
At the end of dehydration, the temperature of the first heater 13A was set to 1250 ° C., and the temperature of the second heater 13B was set to 1350 ° C.
The dehydration time from the start to the end of the dehydration was 4 hours.
Further, the temperature of the first heater 13A during sintering was set to 1350 ° C., and the temperature of the second heater 13B was set to 1550 ° C.
The sintering time was 8 hours.
By repeating the above series of steps, 100 optical fiber preforms were produced.

(Comparative example)
The optical fiber preform was dehydrated and sintered using the optical fiber preform production apparatus as shown in FIG. 2 to produce an optical fiber preform.
In the dehydration of the optical fiber porous preform 101, the temperature of the heater 103 at the start of dehydration was set to 1300 ° C.
The temperature of the heater 103 in the middle of dehydration was set to 1250 ° C.
The temperature of the heater 103 at the end of dehydration was set to 1300 ° C.
The dehydration time from the start to the end of the dehydration was 5 hours.
The temperature of the heater 103 during sintering was set to 1550 ° C.
The sintering time was 8 hours.
By repeating the above series of steps, 100 optical fiber preforms were produced.

Table 1 shows the number of times heating of the optical fiber porous preform was interrupted due to elongation during sintering of the optical fiber porous preform in the examples and comparative examples.
Moreover, the optical fiber was manufactured using the optical fiber preform | base_material obtained by the Example and the comparative example, and the loss in wavelength 1380nm was measured. A loss exceeding 0.310 dB / km was regarded as defective, and the yield of the optical fiber preform was calculated. The results are shown in Table 1.

From the results of Table 1, it was found that according to the example, the time required for dehydration and sintering of the optical fiber porous preform is shorter than that of the comparative example.
It was also confirmed that an optical fiber preform capable of manufacturing an optical fiber with a small loss at a wavelength of 1380 nm can be manufactured.

  The optical fiber preform manufacturing apparatus and the optical fiber preform manufacturing method of the present invention can also be applied to the manufacture of quartz glass used for applications other than the optical fiber preform.

It is a schematic block diagram which shows one Embodiment of the manufacturing apparatus of the optical fiber preform which concerns on this invention, and is a schematic block diagram which shows the heating furnace with which this optical fiber preform manufacturing apparatus was equipped. It is a schematic block diagram which shows an example of the heating furnace with which the manufacturing apparatus of the conventional optical fiber preform was equipped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Heating furnace, 11 ... Porous preform | base_material for optical fibers, 12 ... Furnace core tube, 13 ... Heater, 13A ... 1st heater, 13B ... 2nd heater, 14 ... casing, 15 ... introduction port, 16 ... support rod.

Claims (6)

An apparatus for producing an optical fiber preform comprising a heating furnace having a furnace core tube containing a porous preform for an optical fiber,
The heating furnace includes two or more heaters that heat-treat the optical fiber porous base material accommodated in the furnace core tube, and the heaters extend in the longitudinal direction of the furnace core tube so as to surround the outer periphery of the furnace core tube. An apparatus for producing an optical fiber preform, wherein the two or more heaters can be independently controlled in temperature.   2. The optical fiber preform manufacturing apparatus according to claim 1, wherein the optical fiber porous preform accommodated in the furnace core tube and the two or more heaters are relatively movable.   3. The optical fiber preform manufacturing apparatus according to claim 1, wherein the two or more heaters are movable along a longitudinal direction of the core tube. 4. An optical fiber preform manufacturing method using the optical fiber preform manufacturing apparatus according to any one of claims 1 to 3,
Step A for depositing glass fine particles on the outer periphery of the central glass rod to form a porous preform for optical fiber, and Step B for storing the porous preform for optical fiber in the furnace core tube, dehydrating and sintering In the step B, the temperature distribution is formed in the furnace core tube along the longitudinal direction of the porous optical fiber preform by the two or more heaters in the step B. Production method.   5. The method of manufacturing an optical fiber preform according to claim 4, wherein in the step B, the temperatures of the two or more heaters are independently controlled. The optical fiber according to claim 4 or 5, wherein, in the step B, the optical fiber porous preform housed in the furnace core tube is moved relative to the two or more heaters. A manufacturing method of a base material.

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