JP6205394B2 - Optical fiber preform manufacturing method, optical fiber preform, 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, Patent Document 1 discloses that a quartz tube is filled with SiO ₂ particles, and after removing impurities by gas treatment and heat treatment, the SiO ₂ particles are melted and vitrified by heat treatment. Further, for example, Patent Documents 2 and 3 disclose that clad glass is manufactured using the above technique around a glass rod serving as a core in a container.

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, in the conventional optical fiber preform manufacturing method, in the gas treatment process in which a silica tube is filled with SiO ₂ particles to form a particle layer and a gas for removing impurities is flowed, the gas is flowed from the bottom to the top of the particle layer. ing. At this time, when the gas flow rate is increased (the gas flow rate per unit time is increased), macroscopic voids (voids having a size sufficiently larger than the size of SiO ₂ particles) are often formed in the particle layer. May be.

The reason why macro voids are formed in the particle layer is as follows. That is, each SiO ₂ particles constituting the particle layer, until starting gas flow, the frictional force received from the SiO ₂ particles adjacent to the gravity acting on the SiO ₂ particles is stationary in a position to balance. When the gas starts to flow from the bottom to the top, the SiO ₂ particles receive upward force (force opposite to gravity) from the gas. (Because the SiO ₂ particles are not packed most closely, there are always SiO ₂ particles with a gap in the vicinity). When a SiO ₂ particles move, you are possible to other SiO ₂ particles move to a new gap caused by movement of the SiO ₂ particles. Therefore, when the movement of a SiO ₂ particles occurs, the movement of the SiO ₂ particles present in the periphery of the SiO ₂ particles are chained to occur, as a result, macro voids are formed. Such voids are more likely to occur as the gas flow rate increases.

  When macro voids are formed in the particle layer, bubbles remain in the completed optical fiber preform. Such bubbles may cause disconnection when drawing the optical fiber preform or cause deterioration of optical characteristics of the completed optical fiber. For this reason, in the conventional optical fiber preform manufacturing method, it is necessary to keep the gas flow rate low in the gas processing step, which is an impediment to hindering the reduction of manufacturing time (that is, reduction of manufacturing cost). It was.

  In addition, when a gas that is lighter than the atmosphere is flowed, if the gas is introduced from below the particle layer, it passes through only the portion where the gas easily flows, and the gas layer is allowed to pass through the entire particle layer. Can not. This causes a secondary problem that an optical fiber preform with low homogeneity is completed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical fiber preform manufacturing method and the like that can manufacture an optical fiber preform in a shorter time than conventional ones. .

An optical fiber preform manufacturing method according to the present invention includes a particle layer forming step of forming a particle layer containing SiO ₂ particles in a quartz tube, and a dopant is introduced to remove impurities from the particle layer or into the particle layer. And a gas processing step of flowing a gas for performing downward from above the particle layer.

According to the above method, a gas for removing impurities from the particle layer or for introducing a dopant into the particle layer flows from above to below the particle layer. When gas flows from above to below, the force that the SiO ₂ particles receive from the gas is a downward force, that is, a force in the same direction as gravity. Therefore, even when the gas flow rate is increased, the macroscopic movement in the particle layer is caused by the chain movement of SiO ₂ that has lost the constraint due to the frictional force, as in the case where the gas is flowed from the lower side to the upper side in the gas treatment process. No voids are formed. For this reason, the flow rate of gas can be made higher than before, and the manufacturing time can be reduced as compared with the conventional method.

  Moreover, it is preferable that the manufacturing method of the optical fiber preform which concerns on this invention includes the heating process which heats the said particle layer and vitrifies in addition to the said method.

  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 addition to the above method, the method for manufacturing an optical fiber preform according to the present invention includes a rod arranging step of arranging a rod at the center in the quartz tube, and the particle layer forming step arranges at the center in the quartz tube. Preferably, the particle layer is formed around the formed rod.

  According to the above method, since the rod is arranged at the center in the quartz tube and the particle layer is formed around the rod, an optical fiber preform in which the rod is used as the core and the particle layer is used as the clad can be manufactured.

  In the optical fiber preform manufacturing method according to the present invention, in addition to the above method, the gas preferably 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 manufactured in a short time. Therefore, by using this optical fiber preform, a highly reliable optical fiber can be manufactured at low cost.

  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 at low cost.

  According to the above method, the optical fiber preform can be manufactured in a shorter time than conventional.

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.

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, when a gas is flowed from the bottom to the top, the gas lifts the particle layer 20 on the way, and so on, so that macroscopic voids in the particle layer 20 (voids having a size sufficiently larger than the size of the SiO ₂ particles 2). Various problems occur in the particle layer 20 such that the particle layer 20 can be formed or the density of the particle layer 20 decreases. However, in this embodiment, since the 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.

  Furthermore, since a macro void can be prevented from being generated in the particle layer 20 by flowing the gas from the upper side to the lower side of the particle layer 20, a large flow rate of gas can be flowed. Therefore, the time of the gas treatment process can be shortened, and as a result, the optical fiber preform and the optical fiber can be manufactured at low cost. Further, as the particle layer 20 becomes larger, macroscopic voids are more likely to be generated. However, since the voids can be prevented from flowing by flowing gas from above the particle layer 20, the size of the base material is increased. Is also advantageous.

  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 evacuation, the voids in the particle layer 20 are vitrified in a vacuum state, so that no bubbles can be left 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)
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.

[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 modifications, and various modifications are possible within the scope of the claims, and technical means disclosed in the embodiments or modifications 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

Claims (8)

A particle layer forming step of forming a particle layer containing SiO ₂ particles in the quartz tube ;
Manufacturing method of the preceding SL gas for introducing a dopant into the particle layer, the optical fiber preform which comprises a gas treatment step of flowing downward from the top of the particle layer. A particle layer forming step of forming a particle layer containing SiO ₂ particles in the quartz tube;
The gas for removing impurities from the particle layer, seen including a gas treatment step of flowing downward from above the particle layer,
A method for producing an optical fiber preform, wherein impurities are removed from the particle layer without flowing a gas from below to above the particle layer . Method for manufacturing an optical fiber preform according to claim 1 or 2 wherein the particle layer is heated to include a heating step for vitrification, it is characterized. A rod placement step of placing a rod in the center of the quartz tube;
In the particle layer forming step, the optical fiber preform according to any one of claims 1 to 3, characterized in that to form the particle layer around the rod arranged in the center of the quartz tube Production method. The gas production method of an optical fiber preform according to claim 1, characterized in that the full Tsu elements. The gas, oxygen, chlorine, and at least one or more helium, method for manufacturing an optical fiber preform according to claim 2, characterized in that.   A rod placement step of placing the rod in the center of the quartz tube;
  SiO in the quartz tube ₂ A particle layer forming step for forming a particle layer containing particles, wherein SiO is formed around the rod arranged at the center of the quartz tube. ₂ A particle layer forming step of forming a particle layer containing particles;
  A gas treatment step of flowing a gas for removing impurities from the particle layer or introducing a dopant into the particle layer from above to below the particle layer. Production method. A step of manufacturing an optical fiber preform using the method of manufacturing an optical fiber preform according to any one of claims 1 to 7 ,
And a drawing step of drawing the optical fiber preform by heating.

Images