JP2012025625A - Method for producing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber which has a pore structure providing a favorable cross section when it is cut.SOLUTION: A plurality of hollow tubes 13 are arranged so as to surround the outer periphery of a core rod 11. Then, an inner clad layer is formed by integrally fusing the plurality of hollow tubes 13 to each other, and at the same time, the core rod 11 and the plurality of hollow tubes 13 are fused to each other. Thereafter, an outer clad layer 16 is formed to constitute a preform 17a.

Description

  The present invention relates to a method for manufacturing an optical fiber having a hole structure.

  With the expansion of optical communication to FTTH (Fiber To The Home), in-building wiring and equipment wiring with a small bending radius are required, and bending resistance is required for optical fibers.

  Therefore, attention has been paid to an optical fiber that has improved bending resistance by making the low refractive index layer adjacent to the core have a hole structure, and an optical fiber 61 as shown in FIG. 6 is an example.

  The optical fiber 61 includes a cladding layer 64 having a plurality of holes 63 arranged so as to surround the core 62 on the outer periphery of the core 62 that guides light waves. By reducing the refractive index and increasing the refractive index difference with the core 62, light waves are prevented from leaking to the outer periphery of the core 62 due to bending deformation or the like.

  In an optical fiber having this hole structure, in a conventional manufacturing method, a plurality of capillary tubes (capillaries) arranged and bundled around a core rod are further accommodated in a hollow jacket tube and an optical fiber preform ( An optical fiber having a hole structure is produced by forming a preform and drawing the preform (for example, Patent Document 1).

  Further, in order to precisely control the inner diameter of the holes and the distance between the holes, for example, a manufacturing method for controlling the internal pressure of the capillary tube, the temperature of the heating furnace for drawing, the drawing speed, etc. has been proposed (for example, Patent Document 2).

JP 2002-249335 A JP 2008-310034 A

  However, in the manufacturing method in which the drawing is performed with the preform in which the gap is formed between the capillary tubes as in the manufacturing method disclosed in Patent Document 2, gas (air) is discharged from the gap at the time of drawing. Since the gas discharge port is only on the preform end surface opposite to the drawing direction, the gas in the gap is easily left in the optical fiber after drawing, and the bubble portion 65 is formed inside the optical fiber 61 as shown in FIG. Is formed.

  This causes a problem that when the optical fiber 61 is cut, the appearance of the cross section becomes poor (the bubble portion 65 appears on the cut surface).

  An object of the present invention created in view of the above circumstances is to provide a method of manufacturing an optical fiber having a hole structure in which a bubble section is hard to be formed and a good cross section is obtained when cut. It is in.

  In order to achieve the above object, the present invention provides a hollow tube arranging step of arranging a plurality of hollow tubes so as to surround the outer periphery of the core rod, and the hollow tubes are fused together after the hollow tube arranging step. An inner cladding layer is formed by attaching and integrating, and an inner cladding layer forming step in which the core rod and the plurality of hollow tubes are fused, and an outer cladding layer is formed on the outer periphery of the inner cladding layer to perform a preform. A preform forming step for forming an optical fiber, and an optical fiber drawing step for manufacturing an optical fiber having a hole structure by drawing the preform after the preform forming step. Is the method.

  The hollow tube disposing step may be a step of disposing the hollow tube having a square cross section in a square lattice point centered on the core rod.

  The hollow tube arranging step may be a step in which one layer of the hollow tube is arranged on the outer periphery of the core rod.

  The preform forming step may be a step of forming the outer cladding layer by an external VAD method or an OVD method.

  A jacket tube preparation step of preparing a jacket tube having a hole portion formed in accordance with the outer peripheral shape of the inner cladding layer at a center portion thereof, wherein the preform formation step includes the hole of the jacket tube. The core rod and the inner clad layer may be inserted into a portion to form the outer clad layer made of the jacket tube.

  The hollow tube arranging step may be a step of arranging the hollow tube made of quartz.

  According to the optical fiber manufacturing method of the present invention, there is provided an inner cladding layer forming step in which the core rod and the plurality of hollow tubes are heated under vacuum to melt and integrate the hollow tubes to form an inner cladding layer. Therefore, it is difficult to form a bubble portion in the inside, and a method for manufacturing an optical fiber having a good cross section when cut can be provided.

It is a perspective view which shows the structure of the preform which concerns on 1st embodiment of this invention. It is a perspective view which shows the structure of the preform which concerns on 2nd embodiment of this invention. It is a perspective view which shows the structure of the preform which concerns on 3rd embodiment of this invention. It is a perspective view which shows the structure of the preform which concerns on 4th embodiment of this invention. It is a perspective view which shows the structure of the preform which concerns on other embodiment of this invention. It is sectional drawing which shows the optical fiber which has the conventional hole structure.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1A, in the optical fiber manufacturing method according to the first embodiment, first, circular holes 12c communicating in the longitudinal direction are formed so as to surround the outer periphery of the core rod 11 made of pure quartz. A plurality of pure quartz circular hollow tubes 13c (cylindrical hollow tubes 13) are densely arranged on the honeycomb lattice points with the core rods 11 as the center (hollow tube arrangement step).

  Since the core rod 11 and the circular hollow tube 13c have a circular cross section, a gap portion 14 is formed between them.

  After disposing the hollow tube 13 on the outer periphery of the core rod 11 (after the hollow tube disposing step), as shown in FIG. 1B, these are heated in an evacuated electric furnace so that the hollow tube 13 An inner clad layer having a regular hexagonal cross section composed of a hollow tube assembly 15a, which is an aggregate of hollow tubes 13 that are fused and integrated with each other, is formed, and the core rod 11 and the hollow tube assembly 15a are fused. By attaching, the gas in the gap portion 14 is released (degassed), and the gap portion 14 formed between the core rod 11 and the hollow tube 13 and between the hollow tubes 13 disappears (inner Clad layer forming step).

  In addition, since the outer periphery of the hollow tube 13 is not sealed with a jacket tube or the like, defoaming can be efficiently performed from both ends and the outer peripheral side of the hollow tube 13.

  After forming the hollow tube aggregate 15a (inner cladding layer) on the core rod 11 (after the inner cladding layer forming step), as shown in FIG. 1 (c), an outer VAD method (Vaper phase Axial Deposition) The outer cladding layer 16 having a circular cross section is formed by a method (vapor phase axis method) or an OVD method (outside chemical vapor deposition method), and a preform 17a is formed (preform formation step). ).

  When the outer cladding layer 16 is formed by the VAD method or the OVD method, when the uneven portion due to the shape of the circular hollow tube 13c is formed on the outer peripheral surface of the inner cladding layer (hollow tube assembly 15a). However, since this uneven portion can be embedded, a void portion is not formed in the preform 17a, and it is efficient that a bubble portion is formed in an optical fiber having a hole structure manufactured by subsequent drawing. Can be prevented.

  After forming the outer cladding layer 16 (after the preform forming step), the preform 17a thus formed is drawn so as to have a predetermined fiber diameter, whereby an optical fiber having a hole structure is manufactured ( Optical fiber drawing process).

  Next, a second embodiment will be described.

  As shown in FIG. 2A, in the optical fiber manufacturing method according to the second embodiment, first, circular holes 12c communicating in the longitudinal direction are formed so as to surround the outer periphery of the core rod 11 made of pure quartz. A plurality of pure quartz-made square hollow tubes 13 s (square tube-shaped hollow tubes 13) are densely arranged on square lattice points with the core rod 11 as the center (hollow tube arrangement step).

  Here, since the square hollow tube 13s has a square cross section (square cross section), the square hollow tubes 13s can be brought into close contact with each other, and the generation of the void portion 14 can be suppressed.

  After arranging the hollow tube 13 on the outer periphery of the core rod 11 (after the hollow tube arranging step), as shown in FIG. 2B, these are heated in a vacuumed electric furnace to form a square hollow tube. An inner clad layer having an octagonal cross section composed of a hollow tube aggregate 15b, which is an aggregate of hollow tubes 13 in which 13s are fused and integrated, is formed, and the core rod 11 and the hollow tube aggregate 15b are formed. By fusing, the gas in the void portion 14 is released (defoamed), and the void portion 14 formed between the core rod 11 and the hollow tube 13 disappears (inner clad layer forming step).

  After forming the hollow tube aggregate 15b (inner clad layer) on the core rod 11 (after the inner clad layer forming step), as shown in FIG. 2 (c), the outer periphery is externally attached by an external VAD method or OVD method. The clad layer 16 is formed, and a preform 17b is formed (preform formation step).

  After forming the outer cladding layer 16 (after the preform forming step), the preform 17b thus formed is drawn so as to have a predetermined fiber diameter, whereby an optical fiber having a hole structure is manufactured ( Optical fiber drawing process).

  Next, a third embodiment will be described.

  As shown in FIG. 3A, in the optical fiber manufacturing method according to the third embodiment, first, circular holes 12c communicating in the longitudinal direction are formed so as to surround the outer periphery of the core rod 11 made of pure quartz. A plurality of pure quartz circular hollow tubes 13 c (cylindrical hollow tubes 13) having one layer are arranged on a concentric circle with the core rod 11 as the center (hollow tube arranging step).

  Thereby, the number of the gaps 14 to be formed can be reduced, and the gaps 14 are easily lost in the subsequent process.

  After disposing the hollow tube 13 on the outer periphery of the core rod 11 (after the hollow tube disposing step), as shown in FIG. 3B, these are heated in an evacuated electric furnace so that the hollow tube 13 An inner clad layer having a regular hexagonal cross section composed of a hollow tube aggregate 15c, which is an aggregate of hollow tubes 13 that are fused and integrated together, is formed, and the core rod 11 and the hollow tube aggregate 15c are fused. By attaching, the voids 14 formed between the core rod 11 and the hollow tube 13 and between the hollow tubes 13 are eliminated (inner cladding layer forming step).

  After the hollow tube aggregate 15c (inner cladding layer) is formed on the core rod 11, as shown in FIG. 3C, the outer cladding layer 16 is formed on the outer periphery by the external VAD method or the OVD method. A reform 17c is formed (preform forming step).

  After forming the outer cladding layer 16 (after the preform forming step), the preform 17c thus formed is drawn so as to have a predetermined fiber diameter, whereby an optical fiber having a hole structure is manufactured. (Optical fiber drawing process).

  Next, a fourth embodiment will be described.

  As shown in FIG. 4A, in the optical fiber manufacturing method according to the fourth embodiment, first, rectangular holes 12r communicating in the longitudinal direction are formed so as to surround the outer periphery of the core rod 11 made of pure quartz. A plurality of pure quartz rectangular hollow tubes 13r (rectangular cylindrical hollow tubes 13) having a substantially circular shape are arranged on a concentric circle with the core rod 11 as the center (hollow tube arranging step). .

  After arranging the hollow tube 13 on the outer periphery of the core rod 11 (after the hollow tube arranging step), as shown in FIG. 4B, these are heated in a vacuumed electric furnace to form a rectangular hollow tube. By forming an inner cladding layer composed of a hollow tube assembly 15d that is an assembly of hollow tubes 13 in which 13r are fused and integrated, the core rod 11 and the hollow tube assembly 15d are fused. Then, the gas in the void portion 14 is released (defoamed), and the void portion 14 formed between the core rod 11 and the hollow tube 13 disappears (inner cladding layer forming step).

  Here, since the rectangular hollow tube 13r has a rectangular cross section, an uneven portion 18 resulting from the shape of the rectangular hollow tube 13r is formed on the outer peripheral surface of the hollow tube assembly 15d.

  After forming the hollow tube aggregate 15d (inner cladding layer) on the core rod 11 (after the inner cladding layer forming step), as shown in FIG. 4 (c), the outer periphery is externally attached by the external VAD method or OVD method. The clad layer 16 is formed, and a preform 17d is formed (preform formation step).

  Since the outer cladding layer 16 is formed by the VAD method or the OVD method, as shown in FIG. 4B, unevenness caused by the shape of the rectangular hollow tube 13r is formed on the outer peripheral surface of the hollow tube assembly 15d. Even when the portion 18 is formed, since the uneven portion 18 can be embedded, a void portion is not formed in the preform 17d, and a bubble portion is formed in the optical fiber manufactured by subsequent drawing. This can be efficiently prevented.

  After forming the outer cladding layer 16 (after the preform forming step), the preform 17d thus formed is drawn so as to have a predetermined fiber diameter, whereby an optical fiber having a hole structure is manufactured ( Optical fiber drawing process).

  In short, the optical fiber manufacturing method according to the present invention includes a plurality of hollow tubes 13 (circular hollow tube 13a, square hollow tube 13s, or rectangular hollow tube 13r) so as to surround the outer periphery of the core rod 11. An inner clad layer forming step of forming the inner clad layers (hollow tube aggregates 15a, 15b, 15c, 15d) by heating the arranged ones under vacuum to fuse and integrate the hollow tubes together; Therefore, the gap 14 formed between the core rod 11 and the hollow tube 13 and / or between the hollow tubes 13 can be eliminated.

  Accordingly, since the gap portion 14 is not formed in the preforms 17a, 17b, 17c, and 17d to be formed, it is possible to efficiently prevent the bubble portion from being formed in the manufactured optical fiber. When the optical fiber is cut, it has a good cross section (no bubbles appear on the cut surface).

  Further, in the method for manufacturing an optical fiber according to the present invention, even if the concavo-convex portion 18 is formed on the outer periphery of the inner cladding layer made of the hollow tube aggregate 15d, the outer cladding formed by the external VAD method or the OVD method. The uneven portion 18 can be embedded with the layer 16.

  Accordingly, since the gap portion 14 is not formed in the preform 17d to be formed, it is possible to efficiently prevent the bubble portion from being formed in the manufactured optical fiber, and the optical fiber is cut. In this case, the cross section has a good cross section (no bubbles appear on the cut surface).

  In the embodiment described above, the outer cladding layer is formed by the external VAD method or the OVD method. However, as another embodiment, as shown in FIG. (Inner cladding layer) After producing the jacket tube 20 having the hole 19 formed so as to match the outer peripheral shape of the core 15a, the core rod 11 and the hollow tube aggregate 15a are assembled as shown in FIG. It is possible to form a preform 17e that is inserted into the jacket tube 20 and has the jacket tube 20 as an outer cladding layer.

  Even with this manufacturing method, no gap is formed between the core rod 11 and the hollow tube 13 and / or between the hollow tubes 13 or between the inner cladding layer (hollow tube assembly 15a) and the jacket tube 20. Therefore, it is possible to efficiently prevent the bubble portion from being formed in the manufactured optical fiber, and this optical fiber has a good cross section when cut (the bubble portion does not appear on the cut surface). It will be.

  Moreover, it is also possible to set it as the manufacturing method of the optical fiber which combined these embodiment.

  The present invention does not limit the material of the core rod, the inner cladding layer (that is, the hollow tube), and the outer cladding layer. For example, in order to increase the refractive index difference between the core rod and the inner cladding layer, an appropriate dopant is selected. It may be added to an empty tube.

  Hereinafter, examples of the present invention will be described in detail.

[Example 1]
First, as shown in FIG. 1A, a cylindrical hollow quartz tube (circular hollow tube 13c) of two layers is disposed around a quartz core rod (core rod 11), and then, as shown in FIG. As shown, these are heated and melted while degassing in a vacuum electric heating furnace, and the hollow quartz tubes are fused and integrated to form a hollow quartz tube assembly (hollow tube assembly 15a). An inner cladding layer was formed. The quartz core rod was made of pure silica, and the hollow quartz tube was made of fluorine-doped silica.

  Next, as shown in FIG. 1 (c), an outer cladding layer is formed on the outer circumferential surface of the inner cladding layer (hollow quartz tube aggregate) by using an external VAD method, and an optical fiber preform (pump) is formed. Reform) was formed. The refractive index of the outer cladding layer and that of the hollow quartz tube are the same (that is, the outer cladding layer is also made of fluorine-doped silica like the hollow quartz tube).

  The preform was drawn while adjusting the preform to have a desired diameter, and an optical fiber was produced.

[Example 2]
First, as shown in FIG. 2 (a), a rectangular hollow quartz tube (square hollow tube 13s) of two layers is arranged around the quartz core rod (core rod 11), and then, as shown in FIG. 2 (b). As shown, these are heated and melted while degassing in a vacuum electric heating furnace, and the hollow quartz tubes are fused and integrated to form a hollow quartz tube assembly (hollow tube assembly 15b). An inner cladding layer was formed. The quartz core rod was made of pure silica, and the hollow quartz tube was made of fluorine-doped silica.

  Next, as shown in FIG. 2 (c), an outer cladding layer was formed on the outer peripheral surface of the inner cladding layer (hollow quartz tube aggregate) by using an external VAD method to form a preform. The refractive index of the outer cladding layer and that of the hollow quartz tube are the same.

  The preform was drawn while adjusting the preform to have a desired diameter, and an optical fiber was produced.

[Example 3]
First, as shown in FIG. 3 (a), a cylindrical hollow quartz tube (circular hollow tube 13c) for one layer is arranged around the quartz core rod (core rod 11), and then, as shown in FIG. 3 (b). As shown, these were heated and melted while defoaming in a vacuum electric heating furnace, and the hollow quartz tubes were fused and integrated to form a hollow quartz tube assembly (hollow tube assembly 15c). An inner cladding layer was formed. The quartz core rod was made of pure silica, and the hollow quartz tube was made of fluorine-doped silica.

  Next, as shown in FIG. 3 (c), an outer cladding layer was formed on the outer peripheral surface of the inner cladding layer (hollow quartz tube aggregate) by using an external VAD method to form a preform. The refractive index of the outer cladding layer and that of the hollow quartz tube are the same.

  The preform was drawn while adjusting the preform to have a desired diameter, and an optical fiber was produced.

[Example 4]
First, as shown in FIG. 4 (a), a rectangular hollow quartz tube (rectangular hollow tube 13r) for one layer is disposed around the quartz core rod (core rod 11), and then, FIG. As shown, these are heated and melted while degassing in a vacuum electric heating furnace, and the hollow quartz tubes are fused and integrated to form a hollow quartz tube assembly (hollow tube assembly 15d). An inner cladding layer was formed. The quartz core rod was made of pure silica, and the hollow quartz tube was made of fluorine-doped silica.

  Next, as shown in FIG. 4 (c), the outer cladding layer (hollow quartz) is formed using the external VAD method while embedding the uneven portions formed on the outer peripheral surface of the hollow quartz tube assembly. Tube preform) to form a preform. The refractive index of the outer cladding layer and that of the hollow quartz tube are the same.

  The preform was drawn while adjusting the preform to have a desired diameter, and an optical fiber was produced.

[Example 5]
First, as shown in FIG. 1A, as in Example 1, two cylindrical hollow quartz tubes (circular hollow tubes 13c) are arranged around a quartz core rod (core rod 11). The inner clad layer made of the hollow quartz tube assembly (hollow tube assembly 15a) was formed by fusing and integrating the hollow quartz tubes with degassing in a vacuum electric heating furnace. . The quartz core rod was made of pure silica, and the hollow quartz tube was made of fluorine-doped silica.

  Next, as shown in FIG. 5 (a), after preparing a hollow jacket tube (jacket tube 20) having holes matched to the outer peripheral shape of the inner cladding layer (hollow quartz tube aggregate), FIG. As shown in b), a quartz core rod and an inner cladding layer (hollow quartz tube aggregate) were inserted into the hole to form a preform having a hollow jacket tube as an outer cladding layer. Note that the outer cladding layer (jacket tube) and the hollow quartz tube have the same refractive index.

  The preform was drawn while adjusting the preform to have a desired diameter, and an optical fiber was produced.

[Comparative Example 1]
Two layers of cylindrical hollow quartz tubes were arranged around the quartz core rod, and these were further inserted into a hollow jacket tube to form a preform (manufacturing method disclosed in Patent Document 2). The quartz core rod was made of pure silica, and the hollow quartz tube and the jacket tube were made of fluorine-doped silica.

  Each of the optical fibers manufactured according to Examples 1 to 5 and Comparative Example 1 was cut vertically at 1000 points with respect to the longitudinal direction (that is, the cut surfaces were 2000 points), and each cut surface was observed with an optical microscope. The presence or absence of the bubble part was checked. The number of bubble portions generated in 2000 locations on the cut surface was counted to evaluate the bubble generation frequency (percentage).

  The results are shown in Table 1.

  As shown in Table 1, from the results of Example 1 and Comparative Example 1, after disposing the hollow tube around the core rod as in the present invention, the hollow tube is fused and integrated with each other. It has been found that the frequency of occurrence can be reduced.

  From the results of Example 2, compared to the results of Example 1, by making the hollow quartz tubes into a quadrangular shape, the hollow quartz tubes can be brought into close contact with each other. It can be seen that the occurrence frequency can be reduced.

  From the results of Example 3 and Example 4, the number of voids formed is reduced by arranging the hollow quartz tube for one layer, and the voids are arranged in the vicinity of the outer peripheral surface. Therefore, it turns out that a void | hole part lose | disappears easily and the generation frequency of a bubble part can further be reduced.

  From the results of Example 5, the outer clad layer was formed by the external VAD method even when the hollow quartz tube aggregate (inner clad layer) was inserted into the hollow jacket tube and the preform having the hollow jacket tube as the outer clad layer was constructed. It was confirmed that the occurrence frequency of the bubble part can be reduced as in the case of forming.

  In Examples 1 and 2, the hollow quartz tubes for two layers were fused and integrated at a time, but the first layer was first arranged and fused and then the second layer was further integrated. When the fusing is performed and fusion integration is performed, defoaming can be performed more effectively, and the occurrence frequency of the bubble portion can be further reduced.

  It goes without saying that the embodiments of the present invention are not limited to the above-described embodiments, and various other embodiments are envisaged.

11 Core rod 13 Hollow tube 15a Hollow tube assembly (inner cladding layer)
16 Outer cladding layer 17a Preform

Claims (6)

A hollow tube arranging step of arranging a plurality of hollow tubes so as to surround the outer periphery of the core rod;
After the hollow tube placement step, the plurality of hollow tubes are fused and integrated to form an inner cladding layer, and an inner cladding layer forming step is performed to fuse the core rod and the plurality of hollow tubes. ,
Forming a preform by forming an outer cladding layer on the outer periphery of the inner cladding layer; and
After the preform formation step, an optical fiber drawing step for drawing an optical fiber having a hole structure by drawing the preform;
An optical fiber manufacturing method characterized by comprising:   2. The method of manufacturing an optical fiber according to claim 1, wherein the hollow tube arranging step is a step of arranging the hollow tubes having a square cross section in a square lattice point shape centered on the core rod.   The optical fiber manufacturing method according to claim 1, wherein the hollow tube arranging step is a step in which one layer of the hollow tube is arranged on an outer periphery of the core rod.   The optical fiber manufacturing method according to claim 1, wherein the preform forming step is a step of forming the outer cladding layer by an external VAD method or an OVD method. A jacket tube preparation step of preparing a jacket tube having a hole formed in accordance with the outer peripheral shape of the inner cladding layer at the center thereof, and
The preform forming step is a step of inserting the core rod and the inner cladding layer into the hole of the jacket tube to form the outer cladding layer made of the jacket tube. Optical fiber manufacturing method.   The optical fiber manufacturing method according to claim 1, wherein the hollow tube arranging step is a step of arranging the hollow tube made of quartz.

Images