JP6170968B2 - Optical fiber preform manufacturing method and optical fiber manufacturing method - Google Patents

Description

  The present invention relates to an optical fiber preform manufacturing method, an optical fiber preform, and an optical fiber manufacturing method.

There is a technique for manufacturing an optical fiber preform (preform) by filling SiO ₂ particles in a container and vitrifying it by heating. For example, in Patent Document 1, SiO ₂ particles are packed in a quartz tube, and after removing impurities by gas treatment and heat treatment, the SiO ₂ particles are melted and vitrified by heat treatment. Moreover, in patent document 2, 3, clad glass is manufactured around the glass rod used as a core within a container using the said technique.

US Patent US8,720,230B2 (registered on May 13, 2014) Special table 2012-503590 (announced February 9, 2012) JP2014-84257 (released on May 12, 2014)

By the way, when a silica tube is filled with SiO ₂ particles to form a particle layer, a filter for passing a gas for removing impurities through the upper surface, the lower surface, or both of the particle layer and not passing through the SiO ₂ particles is used. Therefore, it is necessary to dispose a filter having heat resistance. As such a filter, it is possible to use a ceramic porous body, for example. However, when a hard material such as ceramic is disposed, the shape and size must be changed according to the size of the quartz tube to be manufactured and the size of the hole through which gas is conducted.

Furthermore, as shown in FIG. 5, when the lower surface of the particle layer 20 and a hard filter 30 such as ceramics are in contact, the boundary surface (lower surface of the particle layer) between the particle layer 20 and the hard filter 30 is SiO. The void 40 having a size of about ₂ particles or larger is likely to be generated. Such a gap 40 cannot be easily removed even if the quartz tube 10 is vibrated. Further, there is a possibility that the void 40 near the boundary surface of the particle layer 20 may move to the inside of the particle layer 20 due to, for example, movement of the quartz tube 10 filled with particles or vibration due to attachment to a heating device. There is. When the particle layer 20 is heated and integrated in the presence of the voids 40, bubbles are generated in the integrated glass or the glass diameter becomes non-uniform. Therefore, a low-quality optical fiber preform is manufactured, and thereby an unreliable optical fiber is completed.

Accordingly, the present invention has been made in view of the above problems, and its object is to suppress the generation of voids in the particle layer in the production of an optical fiber preform using SiO ₂ particles, and to produce a high-quality optical fiber. The object is to provide a manufacturing method for manufacturing a base material.

In order to solve the above-mentioned problems, a method of manufacturing an optical fiber preform according to the present invention includes a filter placement step of placing a filter in a quartz tube having both ends open, and SiO ₂ particles in contact with the filter in the quartz tube. A particle layer forming step of forming a particle layer containing, and (a) a vacuum processing step of evacuating the inside of the quartz tube, or (b) a dopant for removing impurities from the particle layer or introducing a dopant into the particle layer the gas for a gas treatment step of flowing the particle layer, comprising a gas treatment process, wherein the filter passes gas and does not pass through the SiO ₂ particles, flocculent made of SiO ₂ It is characterized by its body.

  According to the above method, the particle layer is formed in contact with the filter. Since this filter is a cotton-like body, it is deformed so as to fill a void that may be formed between the filter and the particle layer. Therefore, generation | occurrence | production of the space | gap between a filter and a particle layer can be suppressed.

Further, since the filter allows gas to pass therethrough, the gas treatment process can be reliably performed, and since the filter does not allow SiO ₂ particles to pass therethrough, the particle layer can be fixed in the quartz tube. Furthermore, since the filter is made of SiO ₂ , the optical fiber preform can be formed without bringing unnecessary impurities into the optical fiber preform, that is, without mixing the impurities.

  As can be seen from the above, according to the above method, generation of voids in the particle layer can be suppressed, and a high-quality optical fiber preform can be manufactured.

  In the method for manufacturing an optical fiber preform according to the present invention, the filter is preferably quartz wool.

Quartz wool can be easily placed in a quartz tube because it can be freely deformed. The density is easy to change. Therefore, when the density is low and the SiO ₂ particles are passed, the density can be increased so that the SiO ₂ particles do not pass. Quartz wool is easily available. Therefore, according to the above method, an optical fiber preform can be easily manufactured at low cost using quartz wool.

Further, in the method of manufacturing an optical fiber preform according to the present invention, another filter that sandwiches the particle layer between the filter and the filter is disposed in the quartz tube between the particle layer forming step and the gas treatment step. The other filter is preferably a cotton-like body made of SiO ₂ that allows gas to pass therethrough and does not pass the SiO ₂ particles.

  When no other filter is sandwiched between the filter and the particle layer, the rod for sealing the quartz tube is gradually buried in the quartz tube (in the particle layer). However, by arranging another filter by the above method, even if a rod for sealing the quartz tube is arranged, the rod can be prevented from being buried in the quartz tube by the other filter.

  The method for producing an optical fiber preform according to the present invention preferably includes a heating step of heating the particle layer to vitrify it.

  According to the above method, the particle layer can be heated to be vitrified, and an optical fiber preform in which the particle layer is vitrified and integrated can be manufactured. The particle layer may be melted and fiberized (drawn or spun) while heating without being vitrified. Thus, in this specification, even if the particle layer is not vitrified, what is in the stage before drawing for forming in an optical fiber is called an optical fiber preform.

  In the method of manufacturing an optical fiber preform according to the present invention, it is preferable that in the gas treatment step, the gas contains one or more of oxygen, chlorine, helium, and fluorine.

  According to the above method, impurities contained in the particle layer can be discharged as oxides by flowing oxygen. Further, by flowing chlorine, impurities and moisture contained in the particle layer can be discharged as chlorides. When flowing oxygen or chlorine, it is necessary to heat while flowing or after flowing.

  Moreover, an optical fiber preform to which fluorine is added as a dopant can be manufactured by flowing fluorine and vitrifying the particle layer with the particle layer filled with fluorine. The dopant can control the refractive index of the optical fiber. Note that it is not necessary to heat the particle layer at the stage of flowing fluorine into the particle layer.

  Further, when the particle layer is vitrified by heating in a state where helium is flown and the particle layer is filled with helium, it is vitrified in a state where no impurity gas is contained in the voids through a process of heating and defoaming. be able to. Therefore, glass with reduced impurities (when a glass rod is not placed in the quartz tube, a core material, and when a glass rod is placed in the center of the quartz tube and a particle layer is formed around it, a cladding material) Can be obtained. Note that it is not necessary to heat the particle layer at the stage of flowing helium into the particle layer.

  The optical fiber preform according to the present invention is manufactured by any one of the optical fiber preform manufacturing methods according to the present invention. Therefore, it is a high quality optical fiber preform. Therefore, a highly reliable optical fiber can be manufactured by using this optical fiber preform.

  An optical fiber manufacturing method according to the present invention includes a step of manufacturing an optical fiber preform using any one of the optical fiber preform manufacturing methods according to the present invention, and drawing the optical fiber preform by heating. And a drawing process.

  According to the above method, a highly reliable optical fiber can be manufactured.

According to the above method, in the production of an optical fiber preform using SiO ₂ particles, the generation of voids in the particle layer can be suppressed and a high-quality optical fiber preform can be produced.

It is a sectional view showing a state of being disposed quartz tube packed with SiO ₂ particles in a heating furnace. It is a figure which shows the quartz tube used for an optical fiber preform | base_material. It is a sectional view showing a state of being arranged another quartz tube packed with SiO ₂ particles in a heating furnace. It is a cross-sectional view showing a state in which was further disposed a separate quartz tube furnace filled with SiO ₂ particles. It is a figure which shows the space | gap which arises in a particle layer in manufacture of the conventional optical fiber preform.

Embodiment 1
Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is a cross-sectional view showing a state in which a quartz tube 1 packed with SiO ₂ particles 2 is placed in a heating furnace 8.

  The manufacturing method of the optical fiber preform of this embodiment is as follows.

  First, as shown in FIG. 2, a dummy rod 4 having a hollow center is connected to one end of a quartz tube 1 having both ends opened. As the quartz tube 1, a known tube can be used. For example, a tube having a diameter of 32 mm and a thickness of 2.5 mm can be used. As the dummy rod 4, a known one can be used, and it is made of, for example, quartz. For example, the dummy rod 4 having a diameter of 35 mm, a hollow diameter of 6 mm, and a length of 300 mm can be used. In addition, the numerical value of description is an illustration and is not limited to these.

  The quartz tube 1 and the dummy rod 4 may be connected by welding using a heating means such as a burner.

Next, the filter 3a is placed on the quartz tube 1 (filter placement step). The filter 3a is a cotton-like body made of SiO ₂ that allows gas to pass therethrough and does not pass the SiO ₂ particles. Thus, since the filter 3a is a cotton-like body, it deform | transforms so that the space | gap which may arise between the filter 3a and the particle layer 20 is filled. Therefore, generation | occurrence | production of the space | gap between the filter 3a and the particle layer 20 can be suppressed.

Moreover, since the filter 3a allows gas to pass therethrough, it is possible to reliably carry out a gas processing step described later. Furthermore, since the filter 3a does not pass the SiO ₂ particles, the particle layer 20 can be fixed in the quartz tube. Furthermore, since the filter 3a is made of SiO ₂ , the optical fiber preform can be formed without bringing unnecessary impurities into the optical fiber preform, that is, without mixing the impurities.

The filter 3a may be quartz wool, for example. However, it is not limited to this. Since quartz wool can be freely deformed, it can be easily placed in the quartz tube 1. Also, the density is easy to change. Therefore, when the density is low and passes through the SiO ₂ particles 2, the density can be increased so that the SiO ₂ particles 2 do not pass. Quartz wool is easily available. Therefore, an optical fiber preform can be easily manufactured at low cost by using quartz wool.

Next, the SiO ₂ particles 2 are packed in the quartz tube 1, and the particle layer 20 is formed in contact with the filter 3a (particle layer forming step). The SiO ₂ particles 2 may be derived from synthetic quartz or natural quartz.

Alternatively, the particle layer 20 may be formed by packing the quartz tube 1 so that the SiO ₂ particles 2 and the dopant solids have a desired concentration distribution. When the particle layer 20 is vitrified, the dopant solid is a molecule that exists as a molecule or a molecule that includes a dopant. When the particle layer 20 is vitrified, a dopant concentration distribution can be stably obtained in the longitudinal direction of the quartz tube 1. A plurality of dopant solids may be used.

In this embodiment, the SiO ₂ particles 2 are packed in the quartz tube 1 without using a binder. Therefore, there is no fear of impurity mixing by the binder. Further, since no binder is used, no pretreatment or calcining when using a binder is required.

Next, the filter 3b is disposed on the side of the particle layer 20 that is not in contact with the filter 3a, and the particle layer 20 is sandwiched between the filter 3a and the filter 3b (another filter arrangement step). Like the filter 3a, the filter 3b is a cotton-like body made of SiO ₂ that allows gas to pass therethrough and does not pass the SiO ₂ particles 2.

  Further, the quartz tube 1 is sealed with a glass rod 5 (sealing step). The glass rod 5 has two roles, a role of pressing the particle layer 20 and a role as a part of the lid. In the present embodiment, the gas treatment process and the heating process are performed with the quartz tube 1 arranged vertically as follows. Therefore, since the glass rod 5 on the filter 3b does not move so as to shift its position, the welding of the quartz tube 1 and the glass rod 5 is unnecessary. In this case, the gas 7 passes between the quartz tube 1 and the glass rod 5 in the gas processing step described later.

  In this embodiment, the gas 7 passes between the quartz tube 1 and the glass rod 5, but the gas 7 passes through the through-hole by using a glass rod 5 having a through-hole in the long axis direction. You may do it. In particular, when the quartz tube 1 is disposed horizontally as in Modification 2 described later, a glass rod 5 provided with a through hole is used in order to weld the quartz tube 1 and the glass rod 5.

  In the present embodiment, the filters 3a and 3b are arranged above and below the particle layer 20, but the filter 3b may not be arranged. That is, the glass rod 5 may be disposed in contact with the particle layer 20.

  Here, when the filter 3b is not disposed, the glass rod 5 is gradually buried in the quartz tube 1 (in the particle layer 20). However, it is possible to prevent the glass rod 5 from being buried in the quartz tube 1 by arranging the filter 3b.

  In addition, the process so far may be performed by arranging the quartz tube 1 vertically or horizontally. The subsequent processing is performed by arranging the quartz tubes 1 vertically as shown in FIG. A mode of performing the horizontal arrangement will be described in a second modification example.

  Then, the quartz tube 1 on which the particle layer 20 is formed as described above is installed in the heating furnace 8 as shown in FIG. As the heating furnace 8, a known one used for drawing an optical fiber preform can be used.

  Next, a connector 6 for removing gas from the particle layer 20 or flowing a gas 7 for introducing a dopant into the particle layer 20 is attached to the quartz tube 1, and the gas 7 is moved downward from above the particle layer 20. (Gas treatment process, gas treatment process). Conversely, if gas is flowed from below to above, the gas lifts up the particle layer 20 in the middle, and a relatively large void is formed in the particle layer 20 or the density of the particle layer 20 decreases. As described above, various problems occur in the particle layer 20. However, in this embodiment, since gas flows from the upper side to the lower side of the particle layer 20, the particle layer 20 always receives the force that presses downward in the direction of higher density. Can be prevented. Therefore, the malfunction which arises in the particle layer 20 in a gas treatment process can be suppressed, and a high quality optical fiber preform can be manufactured.

  Here, the gas 7 preferably contains one or more of oxygen, chlorine, helium, and fluorine.

  Impurities contained in the particle layer 20 can be discharged as oxides by flowing oxygen. Further, by flowing chlorine, impurities and moisture contained in the particle layer 20 can be discharged as chlorides. When flowing oxygen or chlorine, it is necessary to heat by the heating furnace 8 while flowing or after flowing.

  Moreover, fluorine can be added to the particle layer 20 as a dopant by flowing fluorine. The dopant can control the refractive index of the optical fiber. It is not necessary to heat the particle layer 20 at the stage of flowing fluorine into the particle layer 20.

  Further, when the particle layer 20 is vitrified by heating in a state where helium is flown and the particle layer 20 is filled with helium, the glass is formed in a state in which no impurity gas is contained in the voids through a process of heating and defoaming. Can be Therefore, glass with reduced impurities (in this embodiment, a core material, and in Embodiment 2, a clad material) can be obtained. Note that it is not necessary to heat the particle layer 20 at the stage of flowing helium into the particle layer 20.

  After the gas treatment, heating by the heating furnace 8 is performed to vitrify and integrate the particle layer 20 (heating step). When a gas for removing impurities is flowed in the gas treatment step, the heating step may be performed while evacuating. By evacuating and vitrifying the voids in the particle layer 20 in a vacuum state, bubbles can be prevented from remaining in the base material.

  Here, instead of the heating furnace 8, a burner (for example, an oxyhydrogen burner) may be used for the heating according to the necessity in the gas treatment process and the heating in the heating process. In the case of using a burner, in order to rotate the quartz tube 1, in the sealing step, the dummy rod 4 connected to the quartz tube 1 is fixed to one chuck of a lathe (not shown). Further, the glass rod 5 is fixed to the other chuck. Then, this glass rod 5 is inserted into the filter 3 b side in the quartz tube 1. Then, a gas treatment process and a heating process are performed.

  As can be seen from the above, when the method for manufacturing an optical fiber preform of the present embodiment is used, the generation of voids in the particle layer 20 is suppressed, and the problems occurring in the particle layer 20 in the gas treatment step are suppressed, A high-quality optical fiber preform can be manufactured.

  The optical fiber preform manufactured as described above is drawn (drawing step) to manufacture an optical fiber. By using the optical fiber preform manufacturing method of the embodiment, a high-quality optical fiber preform can be manufactured. Therefore, an optical fiber manufactured using this is highly reliable. In the present embodiment, the particle layer 20 is vitrified and integrated by the heating step, but an optical fiber may be manufactured by drawing while heating without being integrated. In the present embodiment, even if the particle layer 20 is not vitrified, what is in the stage before drawing to form an optical fiber is referred to as an optical fiber preform.

(Modification 1)
In the optical fiber preform manufacturing method described above, the gas processing step of flowing a gas through the particle layer 20 is performed, but vacuuming (decompression) may be performed instead of the gas processing step. In this case, an optical fiber preform is manufactured as follows using a glass rod 5 having no through hole.

  The filter 3a, the particle layer 20, the filter 3b, and the glass rod 5 are arranged in this order on the quartz tube 1 to which the dummy rod 4 is connected. And the glass rod 5 and the quartz tube 1 are welded using heating means, such as a burner, for example. Then, the dummy rod 4 is connected to a vacuum pump (not shown) using a connecting member such as a rotary joint, for example, and the inside of the quartz tube 1 is depressurized by the vacuum pump (vacuum processing step, gas processing step), and a heating furnace 8 to produce an optical fiber preform.

(Modification 2)
In the above description, the quartz tube 1 is arranged vertically to perform the gas treatment step or vacuum treatment step, and the heat treatment step. However, the quartz tube 1 is arranged horizontally and the gas treatment step or vacuum treatment step, and A heat treatment step may be performed. In the gas processing step or the vacuum processing step, the gas moves in the lateral direction.

  When arrange | positioning sideways, the quartz tube 1 and the glass rod 5 are welded at a sealing process so that the glass rod 5 may not slip | deviate. Then, since the passage of the gas 7 is eliminated, the glass rod 5 provided with a through hole in the major axis direction is used.

  When the heating furnace 8 is used for the heating according to the necessity in the gas treatment process and the heating in the heating process, the heating furnace 8 is configured so that the quartz tube 1 can be disposed horizontally. Even when the quartz tube 1 is disposed horizontally, it is preferable that both the filter 3a and the filter 3b are provided, but only the filter 3a may be provided.

  On the other hand, a horizontal lathe (not shown) is used when a burner is used for heating in the gas treatment step and heating in the heating step. In the sealing step, the glass rod 5 is inserted into the filter 3 b side in the quartz tube 1, and the quartz tube 1 is laid sideways while pressing the particle layer 20 with the glass rod 5. Then, the dummy rod 4 and the glass rod 5 connected to the quartz tube 1 are fixed to both chucks of the horizontal lathe, and the glass rod 5 and the quartz tube 1 are welded with a burner. Then, a gas treatment process and a heating process are performed.

  As described above, when the fiber preform is formed by arranging the quartz tube 1 horizontally and the particle layer 20 is drawn without being integrated, it is not necessary to close the through hole of the glass rod 5. When drawing the quartz tube 1 from the side connected to the dummy rod 4, the cavity of the dummy rod 4 is melted and closed. In this state, vacuuming is performed from the glass rod 5 side.

[Embodiment 2]
Another embodiment of the present invention will be described in detail with reference to FIG.

  In this embodiment, an optical fiber preform is manufactured by the following method.

  First, as shown in FIG. 3, after the filter 3a is arranged on the quartz tube 1 to which the dummy rod 4 is connected, the glass rod 5A is arranged at the center of the quartz tube 1 as in the first embodiment (rod arranging step). . A known glass rod 5A can be used.

Next, the particle layer 20 is formed by packing SiO ₂ particles around the glass rod 5A. Thereafter, the filter 3b is arranged. In the present embodiment, unlike the first embodiment, the glass rod 5 is not disposed, but may be disposed. When the glass rod 5 provided with a through hole is disposed, the through hole is provided so as to correspond to the particle layer 20, that is, at a position where gas can flow through the particle layer 20.

  Thereafter, as in the first embodiment, gas treatment or vacuum treatment and heat treatment are performed to manufacture an optical fiber preform.

  In the present embodiment, the glass rod 5A becomes the core of the optical fiber, the particle layer 20 becomes the first cladding, and the quartz tube 1 becomes the second cladding.

(Modification)
A modification of the second embodiment will be described with reference to FIG. As shown in FIG. 4, a filter 3 a is arranged on the quartz tube 1 to which the dummy rod 4 is connected. Here, the filter 3a is formed in a shape with a recessed center so that the arrangement position of the glass rod 5A is fixed to some extent.

  Next, the glass rod 5A is arranged at the center of the quartz tube 1 (rod arranging step). Here, the glass rod 5 </ b> A has a length that fits into the hole of the connector 6 and is thinner than the hole of the connector 6.

Next, the particle layer 20 is formed by packing SiO ₂ particles around the glass rod 5A. Thereafter, the filter 3b is arranged. Here, the filter 3b is formed in a shape having a hole in the center so as to surround the glass rod 5A.

  Next, the glass rod 5 </ b> A is fixed with the rod fixing jig 9. The rod fixing jig 9 has a shape in which a hole is opened at the center so as to surround the glass A, and a hole in which a gas 7 can pass is used.

  Thereafter, the connector 6 is attached, gas treatment or vacuum treatment, and heat treatment are performed to manufacture an optical fiber preform.

  Note that the present invention is not limited to the above-described embodiments and examples, and various modifications can be made within the scope shown in the claims, and technical means disclosed in the embodiments or examples are appropriately used. Embodiments obtained in combination are also included in the technical scope of the present invention.

1 quartz tube 2 SiO ₂ particles 3a, 3b filter 4 dummy rod 5 glass rod 5A glass rod 6 Connector 7 Gas 8 furnace 20 particulate layer 40 gap

Claims (6)

A filter placement step of placing the filter in a quartz tube having both ends open;
A particle layer forming step of forming a particle layer containing SiO ₂ particles in contact with the filter in the quartz tube;
(A) A vacuum processing step of evacuating the quartz tube, or (b) a gas processing step of flowing a gas for removing impurities from the particle layer or introducing a dopant into the particle layer into the particle layer. A gas treatment step,
The method for manufacturing an optical fiber preform, wherein the filter is a cotton-like body made of SiO ₂ that allows gas to pass therethrough and does not pass the SiO ₂ particles.   The method for manufacturing an optical fiber preform according to claim 1, wherein the filter is quartz wool. Further comprising another filter placement step of placing another filter that sandwiches the particle layer with the filter between the particle layer formation step and the gas treatment step in the quartz tube,
3. The optical fiber preform according to claim 1, wherein the other filter is a cotton-like body made of SiO ₂ that allows gas to pass and does not pass the SiO ₂ particles. 4. Method.   The method for producing an optical fiber preform according to any one of claims 1 to 3, further comprising a heating step of heating the particle layer to vitrify the particle layer.   The optical fiber preform according to any one of claims 1 to 4, wherein in the gas treatment step, the gas contains one or more of oxygen, chlorine, helium, and fluorine. Method.   Producing an optical fiber preform using the method of producing an optical fiber preform according to any one of claims 1 to 5,
  And a drawing step of drawing the optical fiber preform by heating.

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