JP5644694B2 - Optical fiber manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing an optical fiber having a plurality of holes extending in the fiber axial direction.

  An optical fiber (HAF: Hole-Assisted Fiber) including a core made of glass having a high refractive index and a clad made of glass having a low refractive index and having a plurality of holes extending in the fiber axis direction is known (patent) Reference 1). This optical fiber includes a core region, a cladding region, and a jacket region, and a plurality of holes are arranged on the circumference of the cladding region in a cross section perpendicular to the fiber axis direction. Such an optical fiber can be manufactured by the methods disclosed in Patent Documents 2 to 5.

  In the optical fiber manufacturing method disclosed in Patent Document 2, a substantially cylindrical glass body having a core region, a cladding region, and a jacket region is perforated in the cladding region as an optical fiber preform. An optical fiber is manufactured by drawing a material. In the optical fiber manufacturing method disclosed in Patent Document 3, an optical fiber preform is formed by inserting a glass tube around a glass rod into a jacket tube and drawing the optical fiber preform. Manufacture optical fiber.

  In the optical fiber manufacturing method disclosed in Patent Document 4, an optical fiber preform is formed by performing jacket sooting on the outer peripheral surface of a perforated and stretched glass rod, and the optical fiber preform is drawn. To manufacture optical fiber. Alternatively, an optical fiber is manufactured by inserting a perforated and stretched glass rod into a jacket tube and performing rod-in drawing. In the latter case, the inner space of the jacket tube between the glass rod and the jacket tube is depressurized, and rod-in drawing is performed while adjusting the pressure of the inner space of the glass rod.

  In the optical fiber manufacturing method disclosed in Patent Document 5, a plurality of capillaries with one end sealed and one or more solid rods are packed into a support tube, and a capillary hole is formed at the opposite end of the sealed end. By integrating the gaps between the capillaries so as not to be crushed, the space inside the support tube and the space inside the capillary holes are divided into optical fiber preforms. Then, when drawing the optical fiber preform, the space inside the support tube is depressurized, and the space inside the capillary hole is set to atmospheric pressure to produce an optical fiber.

International Publication No. 2004/092793 JP 2002-145634 A Japanese Patent Laid-Open No. 2003-40637 JP 2003-81656 A Japanese Patent Laid-Open No. 2007-51024

  It is important that the optical fiber having a plurality of holes as described in Patent Document 1 has a uniform hole diameter along the axial direction in order for the characteristics to be constant along the axial direction. . For this purpose, it is important for the optical fiber preform to have a uniform hole diameter along the axial direction. However, these optical fiber manufacturing methods are not sufficient in terms of manufacturing yield and manufacturing cost. Specifically, it is as follows.

  Since the optical fiber manufacturing method disclosed in Patent Document 2 uses an optical fiber preform obtained by perforating a glass body, the processing cost is high. Moreover, since the accuracy of the drilling process for forming holes in the axial direction is deteriorated, a long optical fiber cannot be manufactured, and the productivity is poor.

  In the optical fiber manufacturing method disclosed in Patent Document 3, since a plurality of glass pipes are stacked around the glass rod, structural variations due to the arrangement collapse are likely to occur, and it is not easy to obtain desired optical characteristics. . In order to obtain desired optical characteristics, it is necessary to reliably stack the glass rod and the glass pipe with high dimensional accuracy, but this requires a lot of work. Since many glass surfaces are taken into the inside, foreign substances and bubbles are likely to be mixed therein, and disconnections and abnormal outer diameters are likely to occur in the drawing process. In addition, there is a problem that transmission loss is deteriorated due to mixing of OH groups and impurities.

  The optical fiber manufacturing method disclosed in Patent Document 4, that is, the method of inserting a perforated and stretched glass rod into a jacket tube to perform rod-in drawing can solve the above-described problems. However, as described in Patent Documents 4 and 5, in this manufacturing method, during drawing, the space in the jacket tube between the glass rod and the jacket tube is depressurized, while the space in the hole in the glass rod is reduced. Since it is necessary to pressurize and two types of pressure are used, the configuration of the drawing apparatus becomes complicated.

  It is considered effective to draw the wire while pressurizing the space inside the hole after performing the jacket collapse on the perforated and stretched glass rod. However, in this case, there is a problem that the hole diameter variation in the axial direction is likely to occur in the collapse process. It is not impossible to eliminate axial hole diameter fluctuations at the base metal stage by pressurization control in the drawing process, but the drawing yield is reduced, or equipment costs are increased because a dedicated control system is provided. There are problems such as becoming higher.

  The present invention has been made to solve the above problems, and provides a method capable of manufacturing an optical fiber having a plurality of holes extending in the fiber axial direction at a high yield and at a low cost. Objective.

  An optical fiber manufacturing method according to the present invention includes a core region, a cladding region, and a jacket region, and has a plurality of holes that are arranged circumferentially in the cladding region and extend in the fiber axis direction in a cross section perpendicular to the fiber axis direction. A method of manufacturing an optical fiber, comprising: (1) a glass rod creating step in which a glass rod that is to be a core region and a cladding region is subjected to drilling in a portion that is to be a cladding region and heated and stretched to create a glass rod And (2) a glass rod is inserted into the jacket tube to be the jacket region, and the inner space of the jacket tube between the glass rod and the jacket tube is reduced in both the first end side and the second end side. Base material construction that welds the glass rod and jacket tube together and seals the inner space of the jacket tube in a decompressed state to create an optical fiber preform. And (3) a drawing step of manufacturing an optical fiber by drawing an optical fiber preform from the second end side while pressurizing the space in the hole of the glass rod from the first end side. Features.

  In the optical fiber manufacturing method of the present invention, the glass rod and the jacket tube are welded to each other on both the first end side and the second end side with the pressure in the space in the jacket tube and the space in the hole being reduced in the base material producing step. Then, the space inside the jacket tube may be sealed while the pressure is reduced, and the space inside the hole may be sealed, and then the space inside the hole may be opened to the atmospheric pressure on the first end side. At this time, in the base material creation step, on the first end side, the jacket pipe inner space is sealed but the hole inner space is not sealed, and the jacket pipe inner space is outside the first area. And a second region in which both of the space in the hole are sealed, and the space in the hole may be released to atmospheric pressure by cutting in the first region.

  Alternatively, in the optical fiber manufacturing method of the present invention, (1) one end side of the glass rod is sealed in the glass rod creating step, and (2) one end side of the glass rod is the second end side in the base material creating step. In the state where the glass rod is inserted into the jacket tube, the space in the jacket tube is sealed on the first end side in a state where the space in the hole is not crushed, and then the space in the jacket tube is decompressed on the second end side. It is good also as sealing.

  In the optical fiber manufacturing method of the present invention, it is preferable that the internal pressure of the space in the jacket tube is set to 1 kPa or less in the preform manufacturing step. In addition, when forming a plurality of holes in a portion to be a cladding region in a glass rod forming process, a radius Rc of a circumscribed circle of the plurality of holes arranged on the circumference and heat stretching It is preferable to form a plurality of holes so as to satisfy the relationship of 2Rc ≦ 0.9D with the outer diameter D of the previous glass rod.

  According to the present invention, an optical fiber having a plurality of holes extending in the fiber axial direction can be manufactured at a high yield and at a low cost.

It is a figure explaining a collapse process. It is a figure explaining a collapse process. 1 is a cross-sectional view of a glass rod 10. FIG. It is a figure explaining the preform | base_material production | generation process of the optical fiber manufacturing method of 1st Embodiment. It is a figure explaining the preform | base_material production | generation process of the optical fiber manufacturing method of 1st Embodiment. It is a figure explaining the preform | base_material preparation process of the optical fiber manufacturing method of 2nd Embodiment. It is a figure explaining the preform | base_material preparation process of the optical fiber manufacturing method of 2nd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

  The present invention is based on the following knowledge of the present inventors. An optical fiber preform is manufactured by performing a step of applying a jacket to a glass rod having a plurality of holes extending in the axial direction by a known rod in collapse method, and further manufacturing an optical fiber. In addition, the hole diameter variation in the axial direction may occur in the optical fiber. Upon further investigation of this phenomenon, it was found that the size of the hole diameter variation in the axial direction differs due to the following differences in the process of collapse.

1 and 2 are diagrams for explaining the collapse process. Each figure (a) is a figure which shows the cross section of the glass rod 10 and the jacket 20 in the certain time in the middle of a collapse process. Each figure (b) is a figure which shows the temperature distribution of the longitudinal direction in the same time. The jacket tube space 21 between the glass rod 10 and the jacket tube 20 is depressurized to a pressure P _1, while pressurizing the space within the pores 11 of the glass rod 10 to the pressure P _2, the left heat source from the right in the figures Let's move to and perform collapse. According to experiments conducted by the present inventor, as shown in FIG. 1, when the glass rod 10 is exposed to a high temperature before the jacket tube 20 is collapsed, the hole diameter in the axial direction of the optical fiber preform is determined. The fluctuation was great. Conversely, as shown in FIG. 2, when the glass rod 10 is exposed to a high temperature after the jacket tube 20 is collapsed, the variation in the axial hole diameter in the optical fiber preform was small.

According to various experiments conducted by the present inventors, in order to suppress the hole diameter variation in the axial direction in the optical fiber preform to be small, (a) the pressure P ₁ in the jacket tube inner space 21 is changed to the pressure in the space in the hole 11. with sufficiently smaller than P _2, to the same extent as the pressure outside of the pressure P ₂ of the jacket tube 20 of the space within the pores 11, the outer diameter of the inner diameter of the glass rod 10 (b) the jacket tube 20 (C) The radial position of the holes provided in the glass rod 10 is moved away from the collapse interface, (d) The moving speed of the heat source is reduced, and (e) the heat source It has been found that lowering the temperature is effective.

  However, among the above, slowing the moving speed of the heat source causes a decrease in productivity, and lowering the temperature of the heat source tends to leave bubbles at the collapse interface, both of which have problems. The present invention has been made on the basis of the above knowledge and consideration of the present inventors. Hereinafter, embodiments of the optical fiber manufacturing method of the present invention will be described.

  (First embodiment)

  The optical fiber manufacturing method according to the first embodiment includes a core region, a cladding region, and a jacket region, and a plurality of holes that are arranged on the circumference of the cladding region in a cross section perpendicular to the fiber axis direction and extend in the fiber axis direction Is a method of manufacturing an optical fiber having The optical fiber manufacturing method of the first embodiment includes a glass rod creating step for creating the glass rod 10, a preform creating step for creating an optical fiber preform by inserting the glass rod 10 into the jacket tube 20, and an optical fiber preform. A drawing step of drawing an optical fiber by drawing a material.

In the glass rod creation step, a glass rod is created as follows. A glass body including a quartz glass core to which GeO ₂ is added (a portion to be a core region of an optical fiber) and an optical cladding of quartz glass to which no GeO ₂ is added (a portion to be a cladding region of an optical fiber) Is made by sintering and vitrifying using a known VAD method or the like. Next, the glass body is stretched or peripherally ground to obtain a glass rod having an appropriate shape, and the glass rod is perforated. For example, the outer diameter of the glass rod is 50 mmΦ, and the length of the glass rod is 300 mm. The radius of the core region is 5 mm, and the relative refractive index difference between the core and the optical cladding is 0.35%.

  Next, the glass rod is perforated. FIG. 3 shows a cross-sectional view of the glass rod 10 after drilling. d is the hole diameter, a is the core radius, R is the inscribed circle radius of the hole, and D is the glass rod diameter. In the drilling process, d and R are obtained from a cross-sectional structure design of an optical fiber for realizing desired optical characteristics. For example, ITU-T Recommendation G. In order to realize an optical fiber that satisfies all of the optical characteristics of 657A1, A2, B2, and B3, the relative refractive index difference of the core region 2 with respect to the cladding region 3 is 0.35%, and d = 3. It is sufficient to design with 6 μm, a = 3.6 μm, and R = 10.4 μm. Therefore, in the drilling process of this embodiment, d = 5 mm and R = 14.5 mm.

  After the drilling process, impurities adhering during the process are removed by HF cleaning or the like, and the glass rod is heated and stretched to a predetermined outer diameter. Here, the stretched size of the glass rod has an outer diameter of 17 mmΦ and a length of 600 mm. In this stretching step, it is important that the pore diameter does not vary in the longitudinal direction. As a condition for this, it is preferable that the thickness of the region surrounded by the outer peripheral surface of the glass rod 10 and the circumscribed circle of the ten holes 11 is larger. Specifically, it is desirable to satisfy the relationship of 2Rc ≦ 0.9D between the radius Rc of the circumscribed circle of the 10 holes 11 and the outer diameter D of the glass rod before heating and stretching. Thereby, the longitudinal fluctuation of the hole diameter in the glass rod 10 after stretching can be suppressed to 3% or less.

  In the base material creation process following the glass rod creation process, the glass rod 10 is inserted into the jacket tube 20 to create an optical fiber preform as follows. FIG. 4 and FIG. 5 are diagrams for explaining a base material creation step of the optical fiber manufacturing method according to the first embodiment.

A jacket tube 20 having a predetermined outer diameter / inner diameter / length (for example, an outer diameter of 60 mmΦ, an inner diameter of 18 mmΦ, and a length of 500 mm) is prepared. The jacket tube 20 is to be the jacket region of the optical fiber. A quartz glass dummy pipe 31 is connected to the end of the jacket tube 20 on the first end side 41, and a quartz glass dummy pipe 32 is connected to the end of the jacket tube 20 on the second end side 42. Thereafter, the inner surface of the jacket 20 is subjected to gas phase etching to remove the impurity adhesion layer. This vapor phase etching is performed by heating from the outside to 1800 ° C. or higher while flowing SF ₆ gas into the jacket tube 20. It is also possible to remove impurities by flowing a gas containing chlorine into the jacket tube 20 at the same time. For example, in a state where SF ₆ gas (100 sccm) and Cl ₂ gas (50 sccm) are allowed to flow in the jacket tube 20, a heat source having a temperature of 2000 ° C. is traversed, and the inner surface of the jacket tube 20 is etched by about 1 mm in thickness.

The holes 11 are opened at both ends of the glass rod 10 after stretching, and the impurity layers on the surface of the glass rod 10 and the inner surface of the holes 11 are removed by etching with an HF aqueous solution. 20 (FIG. 4A). Next, while flowing a gas containing chlorine in the space 21 in the jacket tube and the space in the hole 11, the impurities attached to the inner surface of the hole and the surface layer of the jacket interface are heated to 1000 ° C. or more from the outside. Is further removed. For example, a heat source having a temperature of 1900 ° C. is traversed in a state where Cl ₂ gas (500 sccm) is allowed to flow through the jacket tube 20.

  Next, welding sealing is performed on the first end side 41 (FIG. 4B). At this time, the space inside the jacket tube 21 and the space inside the hole 11 are reduced to less than atmospheric pressure, and the first end side 41 is heated by the heat sources 61 and 62 from the outside, whereby the space inside the jacket tube space 21 and the glass rod 10 is emptied. Both holes 11 are crushed and sealed. At the time of sealing at the first end side 41, a first region 51 in which the jacket tube inner space 21 is sealed but the space in the air holes 11 is not sealed, and outside the first region 51 A second region 52 in which both the space in the jacket tube 21 and the space in the hole 11 are sealed is provided. Such processing is possible by utilizing the fact that the welding of the jacket interface proceeds because the glass is heated from the outside. Moreover, it can carry out more easily by using an oxyhydrogen burner as a heat source.

  Subsequently, welding and sealing are similarly performed on the second end side 42 (FIG. 4C). At this time, by reducing the pressure with a vacuum pump or the like, the space in the jacket tube 21 and the hole 11 after sealing on both the first end side 41 and the second end side 42 is set to 1 kPa or less.

  Next, the dummy pipes 31 and 32 are removed (FIG. 5A). At this time, the first end side 41 is cut at the first region 51 in which the space in the jacket tube 21 is sealed but the space in the hole 11 is not sealed. As a result, the space in the hole 11 is opened to the atmospheric pressure on the first end side 41. On the other hand, the holes 11 are sealed on the second end side 42. The jacket tube inner space 21 is sealed at both ends, and the internal pressure is 1 kPa or less.

  Next, the dummy pipe 33 quoted by the pressure line is connected to the first end side 41 (FIG. 5B). At this time, the dummy pipe 33 is connected so that the hole 11 is not blocked. Furthermore, the surface is cleaned by flame polishing or the like. In the step of reheating the optical fiber preform by flame polishing or the like, it is desirable to gradually heat in order to avoid the occurrence of cracks starting from the collapse of the jacket interface. For example, it is possible to avoid cracking by means such as gradually increasing the thermal power of the oxyhydrogen burner to the required condition over 5 minutes or more. In this way, an optical fiber preform is created.

  Finally, in the drawing process, the optical fiber preform is drawn from the second end side 42 while pressurizing the space in the hole 11 of the glass rod 10 from the first end side 41 through the dummy pipe 33, and the optical fiber preform is drawn. Manufacture fiber.

  According to the optical fiber manufacturing method of the present embodiment, the pressure in the jacket tube inner space 21 is 1 kPa or less, while the pressure in the drawing furnace is at the atmospheric pressure level (−101.3 kPa). Integration proceeds automatically by heating. Further, the feeding speed of the optical fiber preform into the furnace in the drawing process is set to 5 mm / min or less. Therefore, collapse at a sufficiently slow speed can be realized, but even if such a low feed speed is used in the drawing process, productivity does not decrease. Further, in the drawing process, a neck-down portion exists, and the collapse occurs while the outer diameter of the jacket tube 20 is reduced. Can be narrower than the process. On the other hand, since the space in the hole 11 is pressurized, an optical fiber having a desired hole diameter can be obtained by adjusting the pressure.

  Actually, when the optical fiber was manufactured by drawing the optical fiber preform by pressurizing the space in the hole 11 at a constant value under the conditions exemplified above, the longitudinal variation of the hole diameter of the optical fiber was 0. It was 3 μm or less. This is equivalent to the fluctuation level due to the stretching before the collapse, and the result is that the excessive fluctuation hardly occurs in the jacket collapse process performed at the time of drawing. Further, the longitudinal variation of the optical characteristics due to this variation in the hole diameter has no problem with respect to the target property standard.

  The optical fiber manufacturing method of the present embodiment can realize a reduction in cost as compared with a method of directly drilling an optical fiber preform. The optical fiber manufacturing method of the present embodiment has less structural variation and less impurity contamination than the stack method. Compared with the method of depressurizing the space in the jacket tube while pressurizing the space in the hole while drawing, the optical fiber manufacturing method of the present embodiment only needs to pressurize the space in the hole at the time of drawing. It can be simplified and equipment costs can be reduced. Moreover, the optical fiber manufacturing method of this embodiment can omit the collapse of an effective part at the time of base material manufacture, and since there are few heating processes, it is excellent in stability of the hole diameter of a longitudinal direction. Another advantage of the optical fiber manufacturing method of the present embodiment is that the high-temperature chlorine air baking treatment for the inner surface of the holes is performed simultaneously with the jacket application process. As a result, impurities on the inner surface of the hole can be efficiently removed, so that productivity is excellent.

  (Second Embodiment)

  The optical fiber manufacturing method of the second embodiment also includes a core region, a cladding region, and a jacket region, and has a plurality of holes that are arranged on the circumference of the cladding region in a cross section perpendicular to the fiber axis direction and extend in the fiber axis direction. Is a method of manufacturing an optical fiber having The optical fiber manufacturing method of the second embodiment also includes a glass rod creating step for creating the glass rod 10, a preform creating step for creating the optical fiber preform by inserting the glass rod 10 into the jacket tube 20, and an optical fiber preform. A drawing step of drawing an optical fiber by drawing a material.

  The glass rod creation step in the second embodiment is similar to the glass rod creation step in the first embodiment, but differs in that one end side of the glass rod 10 is sealed.

  6 and 7 are diagrams for explaining a base material creating step of the optical fiber manufacturing method according to the second embodiment. The base material creation step in the second embodiment is substantially the same as the base material creation step in the first embodiment, but the inside of the jacket tube 20 so that the sealed one end side of the glass rod 10 becomes the second end side 42. The point in which the glass rod 10 is inserted into the space (FIG. 6 (a)) is different, and the space 21 in the air hole 11 is not crushed on the first end side 41 (FIG. 6 (b)). )). When sealing the second end side 42 thereafter, the air holes 11 of the glass rod 10 are already sealed, and only the space 21 in the jacket tube is sealed in a decompressed state (FIG. 6C). Thereby, the optical fiber preform | base_material sealed in the state which pressure-reduced the jacket pipe inner space 21 can be produced easily.

  The subsequent steps (FIGS. 7A and 7B) are the same as those in the first embodiment. For the drawing process, it is possible to perform flame polishing and drawing without changing the pressurization drawing to the dummy pipe 33 without changing the configuration shown in FIG. Alternatively, if necessary, the glass rod 10 is temporarily opened on the second end side 42 in the configuration shown in FIG. 7A, and the inner surface of the hole 11 is cleaned (HF cleaning of the inner surface of the hole 11). It is also possible to draw the thermal research and drawing after adding a heat treatment with flowing gas containing chlorine and chlorine.

DESCRIPTION OF SYMBOLS 10 ... Glass rod, 11 ... Hole, 12 ... Core, 13 ... Optical clad, 20 ... Jacket pipe, 21 ... Space in jacket pipe, 31, 32, 33 ... Dummy pipe, 41 ... First end side, 42 ... Second End side, 51 ... 1st area | region, 52 ... 2nd area | region, 61.62 ... Heat source.

Claims (6)

A method of manufacturing an optical fiber having a core region, a cladding region, and a jacket region, and having a plurality of holes arranged in a circle in the cladding region and extending in the fiber axis direction in a cross section perpendicular to the fiber axis direction. And
A glass rod creating step for creating a glass rod by performing a drilling process on a portion to be the cladding region with respect to the glass body to be the core region and the cladding region, and heating and stretching;
The glass rod is inserted into the jacket tube to be the jacket region, and the space in the jacket tube between the glass rod and the jacket tube is reduced in pressure on both the first end side and the second end side. A base material creation step of welding the glass rod and the jacket tube to each other, sealing the jacket tube space in a decompressed state, and creating an optical fiber preform;
A drawing step of producing an optical fiber by drawing the optical fiber preform from the second end side while pressurizing the void space of the glass rod from the first end side;
An optical fiber manufacturing method comprising:   In the base material creating step, the glass rod and the jacket tube are welded to each other on both the first end side and the second end side in a state in which the space in the jacket tube and the space in the hole are decompressed. The space inside the jacket tube is sealed in a decompressed state, and the space inside the hole is also sealed, and thereafter, the space inside the hole is opened to the atmospheric pressure on the first end side. An optical fiber manufacturing method as described in 1.   In the base material creating step, on the first end side, the jacket pipe inner space is sealed, but the hole inner space is not sealed, and the jacket outside the first area. 2. A second region in which both the space in the pipe and the space in the hole are sealed is provided, and the space in the hole is opened to atmospheric pressure by cutting in the first region. 2. An optical fiber manufacturing method according to 2. In the glass rod creating step, one end side of the glass rod is sealed,
In the base material creation step, the glass rod is inserted into the jacket tube so that the one end side of the glass rod is the second end side, and the void space is not crushed on the first end side. Sealing the jacket tube space in a state, and then sealing the jacket tube space in a depressurized state on the second end side,
The optical fiber manufacturing method according to claim 1.   The optical fiber manufacturing method according to any one of claims 1 to 4, wherein an inner pressure of the inner space of the jacket tube is set to 1 kPa or less in the base material creating step. In the glass rod manufacturing step, when forming a plurality of holes by drilling a portion to be the cladding region, a radius Rc of a circumscribed circle of the plurality of holes arranged on the circumference and heating The plurality of holes are formed so as to satisfy a relationship of 2Rc ≦ 0.9D with the outer diameter D of the glass rod before stretching. The optical fiber manufacturing method as described.

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