JP4404214B2 - Manufacturing method of glass preform for optical fiber - Google Patents

Description

  The present invention relates to a method for producing a glass preform for optical fiber, which is produced by depositing glass particles.

An optical fiber widely used for communication and the like is mainly composed of a core and a clad, and is transparent by dehydrating and sintering a glass fine particle deposit (porous glass base material) obtained by depositing glass fine particles. After processing into a glass base material, the glass base material is manufactured by drawing. VAD and OVD methods are well known as methods for producing a glass particulate deposit. In this VAD method or OVD method, glass fine particles are generated in the flame of a burner, and the generated glass fine particles are deposited on a rod made of quartz or the like to form a cylindrical glass fine particle deposit in the axial or radial direction of the rod. It is a method of forming.
And as an example when manufacturing a glass preform for an optical fiber by this kind of method, a glass rod composed of a core part and a part of a clad part is formed in advance, and the remaining clad part is further formed on the outer peripheral side thereof. A step of depositing glass fine particles, so-called jacketing, is performed, and then the glass fine particle deposit is dehydrated and sintered.

By the way, if the ratio of the core part of the glass rod to the clad part that is pointed changes in the longitudinal direction, the characteristics of the glass preform for the optical fiber also change in the longitudinal direction, and an optical fiber with uniform characteristics is manufactured. become unable.
For this reason, the refractive index distribution of the glass base material before jacketing is measured at a plurality of positions different in the longitudinal direction, and the required amount of the remaining cladding is calculated from these measured values. A technique is known in which the glass base material is drawn into a glass rod so that the required amount of the remaining cladding portion is constant in the longitudinal direction (see, for example, Patent Document 1).

  In addition, the refractive index distribution of a glass rod having a core part and a part of a clad part is measured, and the variation in characteristics when the optical fiber is obtained from the measured value is within a desired range. Calculate the total thickness of the cladding of the base material, and after forming the approximate remaining cladding on the glass rod based on the calculated value, polish the cladding so that the refractive index distribution is uniform in the longitudinal direction. Or a technique for forming an additional clad portion is known (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 2003-300746 JP 2004-99408 A

  However, in the technique described in Patent Document 1, it is difficult to adjust the stretched diameter of the glass rod along the longitudinal direction, and complicated control is required. And when it does not become a desired extending | stretching diameter, the yield which manufactures the glass preform for optical fibers will deteriorate. Further, since the outer diameter of the stretched glass rod fluctuates in accordance with the change of the core diameter before stretching, the deposition rate of the glass fine particles is not uniform in the longitudinal direction when jacketing.

  In addition, in the technique described in Patent Document 2, since a complicated correction process of polishing or adding the clad portion after the formation of the optical fiber glass preform is added, the manufacturing cost of the optical fiber glass preform increases.

  The present invention provides a method for producing a glass preform for an optical fiber, which can produce a high-quality optical fiber preform with a high yield while suppressing the production cost as much as possible without performing a complicated correction process. It is aimed.

  The method for producing a glass preform for an optical fiber according to the present invention, which can solve the above-mentioned problems, includes a glass fine particle generated by a burner around a glass rod having a core part and a pre-attached clad part that becomes a part of the clad part. Is formed to form a glass fine particle deposit, and the glass fine particle deposit is sintered and transparentized to manufacture a glass base material for an optical fiber, the core portion of the glass rod and the tip of the glass rod The diameter ratio with the cladding portion is measured at a plurality of locations in the longitudinal direction, and based on the measurement results, the diameter ratio between the core portion and the cladding portion in the glass base material after transparency is uniformed in the longitudinal direction. The bulk density of the glass particulate deposit is set at a plurality of locations in the longitudinal direction, and the glass particulates are deposited so as to have the set bulk density.

  Moreover, in the method for producing a glass preform for an optical fiber of the present invention, while setting the bulk density of the glass particulate deposit at the measurement location where the diameter ratio between the core portion of the glass rod and the pre-clad portion is measured, It is preferable to set the bulk density between the measurement locations so as to continuously change.

  In the method for producing a glass preform for an optical fiber of the present invention, it is preferable to set the bulk density of the glass fine particle deposit to a value within ± 10% of the average value.

  In the method for manufacturing a glass preform for an optical fiber according to the present invention, it is preferable to deposit glass fine particles to be deposited on the glass rod at a set bulk density by adjusting a flow rate of combustion gas supplied to the burner. .

  In the method for producing a glass preform for an optical fiber according to the present invention, it is preferable that the outer diameter of the glass particulate deposit is made uniform in the longitudinal direction by adjusting a relative moving speed of the burner with respect to the glass rod. .

  According to the method for producing a glass preform for an optical fiber of the present invention, the bulk density of the glass fine particle deposit is set so that the diameter ratio between the core portion and the clad portion is uniform in the longitudinal direction, In order to deposit glass fine particles, the diameter ratio between the core portion and the cladding portion of the transparent optical fiber glass preform can be adjusted in the longitudinal direction without performing complicated correction processes such as polishing and addition of the cladding portion. It can be made uniform. Therefore, it is possible to manufacture a glass preform for an optical fiber with a high yield while suppressing the manufacturing cost as much as possible. An optical fiber having uniform characteristics in the longitudinal direction can be obtained from this glass preform for optical fiber.

Hereinafter, an example of an embodiment of a manufacturing method of an optical fiber glass preform according to the present invention will be described with reference to the drawings.
FIG. 1 shows an apparatus for producing a glass preform for an optical fiber according to the present embodiment, wherein (a) is a schematic front view, and (b) is a view seen from the bottom.
As shown in FIG. 1, this optical fiber glass preform manufacturing apparatus 10 has a reaction vessel 1, and an opening / closing plate 5 having an expandable / contractible opening 5 a is provided at the top of the reaction vessel 1. It has been. A suspending device 13 is installed on the outer upper side of the reaction vessel 1, and the seed bar 12 is suspended by the suspending device 13. A glass rod 11 is attached to the suspended seed rod 12, and the glass rod 11 is introduced into the reaction vessel 1 through the opening 5a.

The suspension device 13 allows the glass rod 11 attached to the seed rod 12 to be axially rotated and moved in the axial direction. Moreover, the suspending device 13 is configured so that the movement speed of the glass rod 11 in the axial direction can be changed.
When glass particles are deposited on the outer periphery of the glass rod 11, a glass particle deposit 19 having the glass rod 11 at the center can be produced.
Below the reaction vessel 1, a burner 7 that generates glass particles and an exhaust port 9 that discharges undeposited glass particles in the reaction vessel 1 are provided.

The burner 7 has a multiport structure in which the gas outlet has a plurality of ports. The burner 7 blows out a combustion gas or a glass raw material gas from each port, and in the flame generated by the combustion gas, Glass raw materials are produced by oxidizing or hydrolyzing a glass raw material. Here, the combustion gas supplied to the burner 7 mainly includes a combustion-supporting gas and a supplementary combustion gas, and examples of the combustion-supporting gas include hydrogen and examples of the combustion-supporting gas include oxygen. An example of the glass raw material gas is silicon tetrachloride (SiCl ₄ ).

  The burner 7 is connected to piping for supplying the combustion gas and the glass raw material gas, and gas flow controllers 15, 16, and 17 are attached to the middle of the piping, respectively. In addition, the glass raw material gas can be separately supplied to each port of the burner 7. The gas flow rate controller 16 for combustion gas is connected to the control device 4 via a line 23.

  In addition, a projector 2 is provided outside the reaction vessel 1 toward the bottom surface of the glass particulate deposit 19 formed by the burner 7, and receives light at a position where the light beam 18 from the projector 2 can be received. A container 3 is arranged (see FIG. 1B). The position of the deposition surface of the glass particulate deposit 19 is detected by the projector 2 and the light receiver 3. The light receiver 3 is connected to the control device 4 via a line 21. Further, the control device 4 is connected to the suspension device 13 via a line 25.

Next, a method for manufacturing a glass preform for an optical fiber using the manufacturing apparatus 10 will be described below.
In the glass rod 11 used in the present embodiment, a leading clad portion that is a part of the clad portion is formed around the core portion in advance. In the present embodiment, first, the diameter ratio between the core portion of the glass rod 11 on which the glass particles are deposited and the leading clad portion is measured at a plurality of locations along the longitudinal direction.

FIG. 2 shows the diameter ratio between the core portion and the leading clad portion along the longitudinal direction of the glass rod 11.
As shown in FIG. 2, the glass rod 11 may have a diameter ratio of the core portion to the leading clad portion that varies along the longitudinal direction in the manufacture. There is a variation of approximately ± 0.1 with respect to the target diameter ratio T = 4.6.

Next, based on the measurement results, the bulk density of the glass particulate deposit 19 that is deposited on the outer periphery of the glass rod 11 and becomes the remaining clad portion (called a jacket portion) is set at a plurality of locations in the longitudinal direction.
As a setting method, based on the measured diameter ratio, with respect to the target diameter ratio T, the diameter ratio between the core portion and the cladding portion in the optical fiber glass preform after the transparency is made uniform in the longitudinal direction. A portion where the diameter ratio of the tip clad portion to the core portion of the glass rod 11 is small increases the bulk density, and a portion where the diameter ratio is large decreases the bulk density.

  FIG. 3 shows an example in which the target bulk density of the glass particulate deposit 19 formed on the glass rod 11 having the diameter ratio shown in FIG. 2 is set. Here, the diameter ratio is measured at a plurality of locations in the longitudinal direction of the glass rod 11 to set the bulk density of the glass particulate deposit 19 formed at that location, and the target bulk density to be set between these measured locations. Is continuously changing. In addition, in the setting of this bulk density, you may set intermittently as a fixed bulk density from any measurement location to the adjacent measurement location, without changing continuously between measurement locations.

If the bulk density for depositing the glass particulates is too low, the glass particulate deposit 19 may be broken during the deposition of the glass particulates. If the bulk density is too high, it is difficult to make transparent by subsequent sintering. Become. In addition, if the difference in bulk density in the glass fine particle deposit 19 is large, the timing of transparency during sintering becomes non-uniform due to the difference in bulk density, and other parts are attracted to the place where it first becomes transparent. There is a possibility that the shape of the transparent glass preform for optical fiber is deformed. Therefore, the bulk density in the glass particulate deposit 19 is within ± 10% of the average value of the bulk density in the glass particulate deposit 19 (about 0.31 g / cm ^{3 in} the example of FIG. ³ ) (FIG. 3). In this example, it is desirable to set it within about ± 0.031 g / cm ³ .

When the bulk density of the glass particulate deposit 19 is set in this manner, the glass particulates are deposited as follows so as to achieve the set bulk density.
First, the glass rod 11 is attached to the tip of the seed rod 12, and the seed rod 12 is suspended from the suspension device 13. Then, the suspension device 13 is operated, and the glass rod 11 is lowered so that the distance between the glass particle 11 deposition start point of the glass rod 11 and the outlet of the burner 7 becomes a desired distance.
On the other hand, oxygen, hydrogen, and glass raw material gas are supplied to the burner 7 by the gas flow controllers 15, 16, and 17.

  The glass rod 11 is rotated about its axis, and an oxyhydrogen flame is emitted from the burner 7 toward the glass rod 11. In this oxyhydrogen flame, glass fine particles are generated by an oxidation reaction or hydrolysis reaction of the glass raw material gas. The glass rod 11 is pulled up at a predetermined speed while adhering the generated glass particles to the outer periphery of the glass rod 11, and the glass particle deposit 19 is gradually formed and grown.

At this time, the controller 4 sends a signal to the gas flow controller 16 for supplying hydrogen to control the flow rate of the hydrogen gas supplied to the burner 7 in order to deposit glass particles on the glass rod 11 with a preset bulk density. To do.
Here, when the bulk density of the deposited glass particles is increased, the combustion temperature is increased by increasing the flow rate of hydrogen gas, and when the bulk density is decreased, the flow rate of hydrogen gas is decreased. Reduce combustion temperature.

  At this time, the position of the deposition surface of the glass particulate deposit 19 is detected by the projector 2 and the light receiver 3. Data on the amount of received light detected by the light receiver 3 is sent to the control device 4, and the pulling speed of the glass rod 11 relative to the suspension device 13 (relative movement speed with respect to the burner) is controlled so that the amount of received light is constant. I do.

  In this way, by adjusting the pulling speed of the glass rod 11, the outer diameter of the glass fine particle deposit 19 deposited on the glass rod 11 is deposited so as to be uniform over the longitudinal direction.

As described above, after the glass fine particles are deposited at a preset bulk density and subjected to jacketing, the glass fine particle deposit 19 is then dehydrated and sintered to make it transparent, and thereby the glass base material for an optical fiber. To do.
And according to the glass base material for optical fibers obtained in this way, the fluctuation of the diameter ratio between the core portion of the glass rod 11 and the leading clad portion is corrected by the glass particles deposited thereafter, and the core portion And the diameter ratio of the clad portion are made uniform.

Thus, according to the method for manufacturing a glass preform for an optical fiber of the present embodiment, the diameter ratio between the core portion and the cladding portion is improved without performing a complicated correction process and with a high yield while suppressing the manufacturing cost as much as possible. Is uniform in the longitudinal direction (within a range of ± 5% with respect to the target outer diameter), an optical fiber glass preform can be obtained.
And by adjusting the pulling-up speed of the glass rod 11, the outer diameter of the glass fine particle deposit 19 can be made uniform, so that the subsequent transparency can be performed uniformly in the longitudinal direction, and a high outer diameter. It can be smoothly introduced into a heating furnace where accuracy is required, and the transparency process by sintering can be facilitated.

  When the optical fiber glass preform manufactured as described above is drawn to obtain an optical fiber, an optical fiber having a uniform refractive index distribution in the longitudinal direction can be obtained.

  For example, as shown in FIG. 3, the glass rod 11 having a variation of ± 10% with respect to the target diameter ratio T = 4.6 as shown in FIG. 3 is jacketed by adjusting the bulk density as shown in FIG. In this case, the expected cutoff wavelength in the total length when the refractive index distribution in the longitudinal direction of the glass base material after transparency is measured by a preform analyzer to form an optical fiber is 1250 for a single mode optical fiber (SMF). It falls within the range of ˜1270 nm.

  On the other hand, when the control of the present embodiment is not performed and the flow rate of hydrogen gas is constant and jacketing is performed with a constant bulk density in the longitudinal direction, an estimated cutoff wavelength in the entire length when an optical fiber is used. Becomes 1230 to 1290 nm, and changes greatly in the longitudinal direction.

In the above embodiment, the VAD method in which the glass particles 11 are deposited in the axial direction of the glass rod 11 while pulling up the glass rod 11 has been described as an example. However, the glass particles are deposited in a layered manner in the radial direction on the glass rod 11. It can also be applied to the OVD method. In the case of this OVD method, the bulk density of the layer of the glass fine particle deposit to be formed may be adjusted in the longitudinal direction for each layer.
The present invention is not limited to the production of a glass preform for a single mode optical fiber, but can also be applied to the production of a glass preform for a multimode optical fiber.

The glass base material manufacturing apparatus which concerns on this embodiment is shown, (a) is a schematic front view, (b) is the figure seen from the bottom face. It is a graph showing the diameter ratio of the core part and tip clad part along the longitudinal direction of a glass rod. It is a graph which shows the example of the setting of the bulk density with respect to the glass rod which has the diameter ratio shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 7 Burner 4 Control apparatus 10 Manufacturing apparatus of glass preform for optical fiber 11 Glass rod 13 Suspension apparatus 16 Gas flow controller 19 Glass particulate deposit

Claims (5)

A glass fine particle deposit is formed by depositing glass fine particles generated by a burner around a glass rod having a pre-clad portion that becomes a part of a core portion and a clad portion, and the glass fine particle deposit is sintered to be transparent. A method for producing a glass preform for an optical fiber by
The diameter ratio between the core portion of the glass rod and the pre-clad portion is measured at a plurality of locations in the longitudinal direction, and based on the measurement result, the diameter ratio between the core portion and the cladding portion in the glass base material after transparency is A glass base material for an optical fiber, wherein the bulk density of the glass particulate deposit is set at a plurality of locations in the longitudinal direction so as to be uniform in the longitudinal direction, and the glass particulates are deposited so as to have the set bulk density Manufacturing method.   Set the bulk density of the glass particulate deposit at the measurement location where the diameter ratio between the core portion of the glass rod and the pre-clad portion is measured, and set the bulk density between the measurement locations to change continuously. The method for producing a glass preform for an optical fiber according to claim 1.   The method for producing a glass preform for an optical fiber according to claim 1 or 2, wherein the bulk density of the glass particulate deposit is set to a value within ± 10% of the average value.   The light according to any one of claims 1 to 3, wherein the fine glass particles to be deposited on the glass rod are deposited at a set bulk density by adjusting a flow rate of the combustion gas supplied to the burner. Manufacturing method of glass base material for fiber.   5. The optical fiber glass preform according to claim 4, wherein an outer diameter of the glass fine particle deposit is made uniform in a longitudinal direction by adjusting a relative moving speed of the burner with respect to the glass rod. Method.

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