JP2007072251A - Optical fiber and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably manufacturing an optical fiber, having a cross-sectional structure in which many air holes and rod parts formed by collapsing the air holes of capillaries are combined to give high yield. <P>SOLUTION: In the manufacturing method, the capillaries leaving the air holes and having one sealed ends directed to one side, and the capillary collapsing the air holes and having one sealed ends directed to the other end are bundled and packed into a support tube 41. The support tube is heated and the inside of the tube is evacuated from the other side of the support tube; a differential pressure adjustment gas is supplied from one side; the matrix is integrated by a part of the capillaries 40A, 40B; the space inside the tube is divided into a space I on the other side and a space II on the one side; a heat zone is made to slowly migrate toward the other end sides of the capillaries, over the entire length in the longitudinal direction is subjected to integration; and the matrix having the cross-sectional structure, in which many air holes and the rod parts formed by having the air holes of the capillary collapsed are combined, is prepared. This matrix is spun, while the pressure in the air holes is controlled, and is made into a primary coated fiber to obtain the optical fiber having air holes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical fiber having holes in a cladding or a core, and more particularly to a method for manufacturing an optical fiber.

  Since the photonic crystal fiber has holes in the optical fiber, it is possible to realize characteristics that cannot be obtained with a conventional optical fiber having a core / clad structure. For this reason, photonic crystal fibers are expected to be used as various types of functional fibers and future transmission fibers, and are being studied. This photonic crystal fiber can be roughly classified into a refractive index guided fiber and a photonic bandgap fiber based on its guiding principle.

Refractive index guided fiber uses the low refractive index of holes to form an equivalent cladding with holes, and has a wideband single mode characteristic, ultra-low nonlinearity (large effective area) characteristic, super High nonlinear characteristics, polarization maintaining characteristics, ultra-high NA multimode characteristics, and the like can be obtained.
A photonic bandgap fiber is a fiber that confines light inside the fiber by forming a periodic structure in the cladding.

  As an example of the former, there is a hole assist type holey fiber that realizes a low bending loss. In this fiber, holes are placed around the conventional high-refractive-index core to form an equivalently large refractive index difference and achieve low bending loss without extremely reducing the mode field diameter (MFD). is doing. As such a fiber, for example, as shown in FIG. 1, a hole assist type holey comprising a core 2 and a clad 3 on the outer periphery thereof, and a plurality of holes 4A, 4B having different diameters are provided around the core 2. A fiber 1 has been reported (for example, see Non-Patent Document 1).

As another example of the refractive index guided fiber, there is a double clad fiber 5 as shown in FIG. 2 (see, for example, Non-Patent Document 2). The double clad fiber 5 includes a first clad 6 having a D-shaped cross section, an air hole layer 7 provided around the first clad 6, and a second clad 8 provided on the outer periphery of the air hole layer 7. It consists of and.
The double clad fiber 5 needs to have a high NA (Numerical Aperture) in order to reduce the area of the first clad 6 to increase the pumping light density and increase the incident efficiency of the pumping light. A structure having a large NA is provided by arranging holes around the first clad 6, and development for the purpose of increasing the output of optical amplifiers and fiber lasers is being promoted.

  In addition, the photonic bandgap fiber may have a structure in which the core is an air hole, and the light is confined depending on the size and period of the air hole in the clad portion. Has been reported. The photonic bandgap fiber 32 of FIG. 3 has a structure in which a core 33 formed of a central hole and a large number of holes 34 are provided in a cladding portion surrounding the core 33.

Furthermore, there are many photonic crystal fibers having structures and characteristics not exemplified here, and the hole position, hole size, and hole position are determined according to the characteristics. In the case of hole-assisted holey fibers with relatively few holes, in addition to the method of bundling capillaries and drawing, it is possible to make holes by making holes in the base material, but when the structure has a large number of holes, A method of manufacturing a fiber by bundling capillaries and spinning is common.
Patent Documents 1 to 7 disclose methods for manufacturing photonic crystal fibers by bundling capillaries in this way.
Kanning, et al. “Hall Assisted Holey Fiber for Low Bending Loss”, IEICE Technical Report, OFT 2004-7 (2004) Kazunori Fuchiguchi, et al. “Air-hole type Yb-doped double clad fiber”, 2003 IEICE General Conference, C-3-88 BJ Mangan, L. Farr, A. Langford, PJ Roberts, DP Williams, F. Couny, M. Lawman, M. Nason, S. Coupland, R. Flea and H. Sabert, “Low Loss (1.7dB / km) hollow core photonic bandgap fiber, ”OFC, RDP24, 2004 JP 2003-107255 A JP 2002-55242 A JP 2002-97034 A JP 2002-211941 A JP 2004-238246 A JP 2004-256374 A JP 2004-43286 A

  The problem when manufacturing optical fibers by bundling capillaries is that gaps between capillaries remain, resulting in deformation of holes in the drawing process. It is to end up. Furthermore, when the outer diameter of the capillary and the outer diameter of the rod are different at the time of manufacturing the base material, the gap becomes large, and it is easy to deviate from the target position when the capillaries or rods of the same diameter are packed closely. The designed characteristics cannot be obtained. Finally, characteristic deterioration (variation) due to variations in the hole diameter and position in the longitudinal direction of the fiber in the design and fiber state becomes a problem. Currently, various structures are disclosed as holey holey fibers, and several preforms and methods for manufacturing fibers are disclosed.

However, the conventional techniques described in Patent Documents 1 to 7 have the following problems.
・ Depending on the design, capillaries and solid bars with different outer diameters may be packed, but in such a case, the gaps are larger than when packing capillaries or solid bars of the same diameter close together, and the positions of the caps are displaced. Cheap.
-As a method of filling the gap cleanly, it is very expensive to process the outer shape of the capillary and the inner surface of the support tube into a polygon such as a hexagon. There is a need for a method of filling the gap using a readily available circular capillary or support tube.
A method has been proposed in which both ends of the capillary are sealed and the gap is reduced to fill the gap, but the sealing pressure is determined by the capillary length, hole diameter, furnace heat zone length, temperature, etc. Must be sealed in consideration of Furthermore, it is difficult to seal all the capillaries to the same pressure. Further, the pressure in the capillary changes in the longitudinal direction at the time of integration, and the hole diameter and characteristics are not stable. Therefore, a method of producing a base material neatly in the longitudinal direction and adjusting the pressure to perform spinning is desirable.

  In Patent Document 1, as shown in FIGS. 4 and 5, the hollow core portions 36A and 36B, the lattice portions 37A and 37B provided so as to surround the core portions 36A and 36B, and the lattice portion 37A and 37B are connected to each other. Photonic bandgap fibers 35A and 35B comprising inter-coupling portions 38A and 38B and jackets 39A and 39B surrounding them are proposed. In the embodiment, as shown in FIGS. 6 and 7, a core portion is formed at the center. It is disclosed that a capillary 36C for use, a surrounding capillary 38C, and a rod 37C having a diameter smaller than that are combined and packed in a jacket tube 39C to produce a base material and a fiber. However, in the combination of capillaries and rods having different outer diameters as shown in FIGS. 6 and 7, the positions of the rods are easily displaced, and it is difficult to obtain an optical fiber with a clean arrangement. Furthermore, since the rod is packed in the gap between the capillaries, the rod diameter has an upper limit, and the degree of freedom in design is low.

As methods for filling the gaps between capillaries, for example, two methods described in Patent Document 2 and Patent Document 3 have been proposed.
In Patent Document 2, a cylindrical support tube is filled with a large number of capillaries in parallel with the center axis of the support tube, and a core member serving as a solid core is disposed on the center axis of the support tube. In the photonic crystal fiber manufacturing method in which a preform is manufactured and the preform is thinned by drawing, the cross-sectional shape of the outer periphery of the capillary 9 is a hexagonal shape as shown in FIG. A method is disclosed which forms the capillary layer 10 without gaps by fusing.
However, producing such a capillary 9 having a hexagonal cross-sectional shape on the outer periphery requires a further work as compared with a normal circular tube (circular cross-sectional shape on the outer periphery). Finally, there is a problem that the preform manufacturing cost increases.

Patent Document 3 includes a core that extends in the longitudinal direction in the center of the fiber and that is solid or hollow, and a porous portion that is provided so as to surround the core and has a large number of pores extending along the core. In the photonic crystal fiber manufacturing method provided, a cylindrical support tube is filled with a number of capillaries parallel to the central axis of the support tube, and a core rod that is a solid core is disposed on the central axis of the support tube. A method of manufacturing a preform and reducing the diameter of the preform by drawing is disclosed. Specifically, as shown in FIG. 9, a support tube 12 having a hexagonal cross section on the inner wall was used, and the support tube 12 was filled with a core rod 13 and a large number of capillaries 14. A preform 11 is illustrated. By combining this method with the method described in Patent Document 2, a preform having no gap between capillaries can be produced.
However, in the prior art described in Patent Document 3, as in the method of Patent Document 2, it is possible to produce a support tube having a hexagonal cross section on the inner wall by using a normal circular tube ( Compared with the production of a support tube having a circular inner wall cross-sectional shape), there is a problem that the manufacturing cost is finally increased because further processing work is required.

In Patent Document 4, in order to suppress the formation of a hydroxyl group (OH group) at the time of drawing, a preform 17 in which both ends of each capillary 15 are sealed is prepared and drawn as shown in FIG. A method of manufacturing a photonic crystal fiber is disclosed. In FIG. 10, reference numeral 15 is a capillary, 15a is a capillary sealing part, 16 is a support pipe, 16a is a support pipe sealing part, 17 is a preform, 17a is an auxiliary pipe, and 18 is a drawing furnace.
The presence of the hydroxyl group absorbs light having a wavelength of 1.38 μm, and is therefore undesirable because it causes deterioration in transmission loss as an optical fiber. Although the method described in Patent Document 4 seems to be effective in suppressing the formation of hydroxyl groups during the drawing process, the present inventors have examined that the pore diameter changes in the longitudinal direction in the drawing process, and is stable. There is a possibility that the photonic crystal fiber having the structure described above cannot be manufactured. This is probably because the pressure inside the capillary 15 sealed at both ends gradually changes as the drawing progresses. Moreover, in the drawing process after sealing both ends, since the pressure at the time of sealing is maintained, there is a problem that the hole diameter cannot be adjusted during the drawing process and the yield is deteriorated.
Furthermore, a phenomenon that a part of the capillary 15 is deformed in the drawing process also occurred. This is presumably because when the both ends of the capillaries 15 are sealed, there is a slight difference in internal pressure between the capillaries 15 and, as a result, the hole size varies in the drawing process. To prevent this, it is necessary to accurately control the internal pressure at the time of sealing, and there is a problem in stably producing photonic crystal fibers.

In Patent Document 5, a support tube is filled with a core rod that is a solid core and a plurality of capillaries that are cladding portions, or a plurality of capillaries that are core forming spaces that are hollow cores and that are cladding portions. A method of manufacturing a photonic crystal fiber is disclosed that includes a preform manufacturing process for manufacturing a preform and a drawing process for heating and stretching the preform to draw it into a fiber shape. Further, in Patent Document 5, as a drawing process, as shown in FIG. 11, a preform in which a capillary 19 is arranged on a support tube 20 with its rear end protruding is provided as a capillary external pressure control chamber 21 and a capillary internal pressure control. The target photonic crystal fiber is attached to a drawing apparatus provided with a chamber 22 for controlling the external pressure of the plurality of capillaries 19 and / or the internal pressure of the plurality of capillaries in the support tube 20 during the drawing process. It has gained.
However, such pressure adjustment has a problem in that the preform processing of the portion connected to the pressure control unit is complicated, and the pressure control system is also complicated, so that the production cost of the fiber is increased.

  In the case of producing a preform 28 in which a core tube 29 and a large number of capillaries 30 are filled in a support tube 31 having a hexagonal hole in cross-sectional shape of the inner wall as shown in FIG. As shown in the figure, the capillary 30 can be lengthened and the pressure can be controlled by controlling the pressure in the gap and inside the capillary. However, the capillary 30 is very thin, so it is easy to break when an excessive force is applied, and it can be processed stably. It was difficult to do.

  Patent Document 6 points out that there is a problem in Patent Document 4 that the fiber swells and breaks during spinning when the capillary is thin. It is disclosed that both ends are sealed and spun to suppress swelling. However, when the inventors conducted a production test of the same method, it is difficult to adjust the pressure when sealing the capillary at both ends, and it must be adjusted each time according to the size and length of the base material, The versatility was poor.

  Patent Document 7 discloses a method in which both ends of a capillary are sealed, a gap is decompressed to produce a base material, and the base material is drawn. In this case as well, when the inventors conducted a production test of the same method, it was difficult to set the pressure when sealing the capillary, and the internal pressure of the capillary changed when integrated, which was stable in the longitudinal direction. The base material could not be produced.

  The present invention has been made in view of the above circumstances, and is a method capable of stably producing an optical fiber having a cross-sectional structure in which a large number of holes and a rod portion formed by collapsing the holes of a capillary are combined with high yield. For the purpose of provision.

In order to achieve the above object, the present invention provides:
(1) sealing one end of the capillary;
(2) A plurality of capillaries with one end sealed or a plurality of capillaries and a solid rod, a capillary that leaves a hole is directed toward one side, and a capillary that crushes a hole is sealed Bundling one end toward the other side and packing them into a support tube,
(3) Next, connecting the connector connected to the vacuum exhaust device to the one side of the support tube and connecting the connector connected to the differential pressure adjusting gas supply device to the other side,
(4) Next, the step of heating the vicinity of one end of the capillary to a temperature at which the capillary is softened and deformed with a heater,
(5) In the state of step (4), the inside of the tube is evacuated from the one side of the support tube by the vacuum evacuation device, and the differential pressure adjusting gas is supplied into the tube from the other side of the support tube. Integrating the base material at the section and dividing the space in the pipe into the space I on the one side and the space II on the other side;
(6) Next, the process of reducing the pressure of the space I and controlling the space II to be almost atmospheric pressure,
(7) Next, the heat zone is moved slowly along the longitudinal direction of the capillary, and integration is performed over the entire length of the capillary to combine a large number of holes and a rod portion formed by collapsing the holes of the capillary. Producing a base material having a cross-sectional structure,
(8) Next, the step of spinning the base material while controlling the pressure inside the hole, forming a strand to obtain an optical fiber having a hole,
An optical fiber manufacturing method is provided.

  In the manufacturing method of the optical fiber of this invention, it is preferable that the heating temperature of the said process (4) is the range of 1700 degreeC-2100 degreeC.

  In the method for producing an optical fiber of the present invention, it is preferable that the differential pressure with respect to the atmospheric pressure in the space I in the step (6) is in the range of −0.50 kPa to −101 kPa.

  In the method for producing an optical fiber of the present invention, it is preferable that the differential pressure with respect to the atmospheric pressure in the space II in the step (6) is in the range of −0.50 kPa to +10 kPa.

  In the optical fiber manufacturing method of the present invention, it is preferable that the holes belonging to both the space I and the space II are not sealed in the step (7), and the holes are opened and stretched.

  Moreover, this invention provides the optical fiber manufactured by the manufacturing method of the optical fiber which concerns on this invention mentioned above.

According to the manufacturing method of the present invention, a capillary having the same outer diameter as a capillary for hole formation is used, and the hole is crushed to form a solid rod portion, and a large number of holes and capillary holes are crushed. Since the base material having a cross-sectional structure in which the formed rod portion is combined is produced, the gap between the hole and the rod portion can be prevented.
Further, by adjusting the cross-sectional area (inner diameter) of the capillary for forming the rod part, the diameter of the rod part formed by crushing the capillary can be adjusted.
In addition, since the capillary for hole formation seals one end and keeps the pressure in the capillary leaving the void during integration, the hole diameter is stable in the longitudinal direction of the base material. And an optical fiber having stable optical characteristics over the entire length of the capillary can be manufactured.
Further, it is not necessary to adjust the pressure according to the design and size of the base material, compared to the case where the capillary is sealed at both ends, and any shape base material can be easily manufactured.
Further, by integrating at the base material stage, it is only necessary to control the pressure in the air holes during spinning, and it is not necessary to create a complicated spinning pressure system, and the spinning device can be simplified.
Also, during the integration, the two pressures are finally controlled, but the space can be divided between the upper and lower parts of the base material by the step (5). The integration process can be performed without a simple structure, and the integration apparatus can be simplified.
According to the manufacturing method of the present invention, a base material having a cross-sectional structure in which a large number of holes and a rod portion formed by collapsing the holes of a capillary can be manufactured with a yield of almost 100%, In addition, the optical fiber can be manufactured with a high yield by spinning the base material.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 13 is a cross-sectional view for explaining the basic principle of the optical fiber manufacturing method according to the present invention. In this example, a capillary 40A for forming a hole, a capillary 40B for crushing the hole to form a rod portion, and a solid bar 42 for forming a core region are centered on the solid bar 42. Are combined so as to be surrounded by a plurality of capillaries 40A and 40B and inserted into the support tube 41. The capillaries 40A and 40B and the solid bar 42 have the same outer diameter.

  The combination of the capillaries 40A and 40B and the solid rod 42 is not limited to the example shown in FIG. 13, and various changes can be made. In the manufacturing method of the present invention, it is only necessary to have a capillary 40A for forming a hole and a capillary 40B for forming a rod part by crushing the hole, and an optical fiber having a hole core (air core) is manufactured. Instead of the solid rod 42 in FIG. 13, another capillary can be used. Further, the number and arrangement of the capillaries 40A and 40B, the outer diameter of the solid rod 42, and the like are not limited to this example, and can be set as appropriate. Further, the wall thickness of the capillary 40B can be set as appropriate according to the outer diameter of the solid rod portion in the optical fiber to be manufactured. To reduce the outer diameter of the rod portion, a thin capillary is used. When the outer diameter of the rod portion is increased, a thick capillary can be used.

  The capillaries 40A, 40B, the solid rod 42, and the support tube 41 may all be made of the same material (for example, pure quartz glass), or a part of, for example, quartz glass in the core region and other parts of quartz glass. May be different. A rare earth element such as Er or Yb can be added to the solid rod 42 for forming the core region. In particular, by adding the rare earth element to the core of a core rod having a core / cladding structure, a double clad fiber having high output amplification characteristics can be obtained. Furthermore, Al, P, etc. can be co-added to the core together with the rare earth element, and conversion efficiency can be improved by co-adding Al, P, etc. It is also possible to produce a fiber grating by adding Ge to the core.

  In the manufacturing method of the present invention, as shown in FIG. 13, the capillaries 40A and 40B and the solid rod 42 are packed into a support tube 41, and these are integrated into a base material, and this base material is further drawn. An optical fiber is produced. In this integration process, in the prior art, a rod having a small diameter may be packed between capillaries. However, when rods having different diameters are packed, as shown in FIG. 6 and FIG. 7, the gap increases, the upper limit is generated in the diameter, or the arrangement relationship shifts.

  As means for solving this, in the present invention, the capillary 40B having the same outer diameter as that of the other members (capillary 40A and solid rod 42) and the same rod portion as the cross-sectional area to be designed is packed, and the capillary 40B is integrated in the integration process. The rod portion is crushed to form a rod portion. By this method, the position of the rod portion can be integrated without being deviated from the design position. Moreover, the freedom degree of the diameter of a rod part can be made very large. Moreover, by producing the base material by this method, it is possible to obtain a base material and a strand having a stable pore structure in the longitudinal direction.

14-17 is a figure explaining the integration process in one Embodiment of this invention.
In the integration step of this embodiment, first, as shown in FIG. 14, one end sealing portion 45 is formed in capillaries 40A and 40B (step (1)). The one-end sealing portion 45 only needs to be able to completely prevent gas flow between the internal space inside the capillaries 40A and 40B and the outside of the one-end sealing portion 45. Usually, one of the capillaries 40A and 40B is heated and melted. Is done. If the one-end sealing portion 45 is too long, an extra length is required for the support tube 41. Therefore, it is desirable to form the one-end sealing portion 45 as short as possible.

  Next, as shown in FIG. 14, among the plurality of capillaries in which the one-end sealing portion 45 is formed, the capillary 40A that leaves a hole is directed toward the top, and the capillary 40B that crushes the hole is sealed. The solid rod 42 is arranged and bundled with the one end directed downward and packed in the support tube 41 (step (2)).

An upper connector 46 and a lower connector 47 are attached to both ends of the support pipe 41 (step (3)). The upper connector 46 is provided with an exhaust port 46A connected to a vacuum exhaust device such as a vacuum pump (not shown). The lower connector 47 is provided with a gas supply port 47A connected to a supply device for a differential pressure adjusting gas 49 (not shown). As the differential pressure adjusting gas 49 supplied into the pipe from the lower part of the support pipe 41, a high-purity gas not containing impurities such as H ₂ O that increases the loss of the produced base material, for example, Ar gas, He gas, etc. N ₂ gas or the like is desirable. Further, as a supply device for supplying the differential pressure adjusting gas 49 into the support pipe 41 via the lower connector 47, the supply amount of the differential pressure adjusting gas 49 can be precisely adjusted according to the internal pressure of the support pipe 41. It is desirable to have such functions. In the present embodiment, the longitudinal direction of the support tube 41 is arranged in the vertical direction, the exhaust is exhausted from the upper end side of the support tube 41, and the differential pressure adjusting gas 49 is supplied from the lower end side. The direction of the support pipe 41 and the direction of exhaust / gas supply are not limited to this example, and various changes can be made.

  A ring-shaped heater 48 is provided on the outer periphery of the support tube 41. One or both of the heater 48 and the support tube 41 are provided with a moving means (not shown) for gently moving the heater 48 along the longitudinal direction of the support tube 41.

  Next, an upper portion of 20 mm or more from one end of the capillary 40A that is not sealed is heated to a temperature at which quartz is softened and deformed by the heater 48 (step (4)). The heating temperature of the base material by the heater 48 is preferably in the range of 1700 ° C to 2100 ° C.

  Next, the inside of the pipe is evacuated from the upper part of the support pipe 41 by the vacuum exhaust device, the differential pressure adjusting gas 49 is supplied into the pipe from the lower part of the support pipe 41, and the base material is integrated by a part of the capillaries 40A and 40B. As shown in FIG. 15, an integrated region 50 is formed in a part of the base material (step (5)). By forming this integrated region 50, the space in the support tube 41 communicates with the internal space of the capillary 40B and the space I communicating with the gap between the tube and the rod, and the internal space of the capillary 40A. It is divided into space II.

  When an airflow state as shown in FIG. 14 is created, gas flows between the capillaries 40A and 40B or between the capillaries 40A and 40B and the support tube 41. Conversely, gas does not flow inside the capillary 40A because one end is sealed. In this state, according to Bernoulli's theorem, the place where the gas flows is reduced to the place where the gas does not flow. If this is realized in a state where the glass is softened, the gap is selectively crushed, and an integrated region 50 is formed, resulting in a state as shown in FIG. 15, the capillaries 40A and 40B or between the capillaries 40A and 40B and the support tube 41 are divided into a space I and an internal space II of the capillary 40A, and the spaces are adjusted to a reduced pressure state and an atmospheric pressure, respectively. When the member is traversed while being heated, the entire length of the base material is integrated. Furthermore, the capillary 40B that wants to selectively crush the holes can be crushed by reducing the pressure of the space I through the communication of the holes I with the holes I (step (6)).

  In the present embodiment, the space I on the upper side of the integrated region 50 is depressurized by a vacuum pump or the like, and the differential pressure adjusting gas 49 is supplied to the space II on the lower side of the integrated region 50 so that the pressure is almost atmospheric pressure. adjust. The pressure in the space I and the space II is not limited to this example, and the differential pressure with respect to the atmospheric pressure in the space I is set to a range of −0.50 kPa to −101 kPa, and the differential pressure with respect to the atmospheric pressure in the space II is − It is preferable to be in the range of 0.50 kPa to +10 kPa (however, the pressure is space I <space II).

  As shown in FIG. 16, after the space I is in a reduced pressure state and the space II is almost at atmospheric pressure, the heating material by the heater 48 is traversed along the longitudinal direction to integrate the base material, for example, FIG. As shown in FIG. 4, the base material 51 having a structure in which the core region 60 is surrounded by a large number of holes 52 over the entire length is obtained (step (7)). In the method for producing an optical fiber of the present invention, it is preferable that the hole portion of the base material is not sealed in the step (7), and the hole is opened and stretched.

  The base material 51 is spun while controlling the pressure in the pores, and is coated with a coating material such as an ultraviolet curable resin to form a strand to obtain an optical fiber (step (8)).

In the fiber manufacturing method of the present embodiment, a capillary having the same outer diameter as the hole forming capillary is used, and the hole is crushed to form a solid rod portion made of quartz glass. Since the base material having the cross-sectional structure in which the rod portion formed by collapsing the holes is combined is produced, the gap between the holes and the rod portion can be prevented.
Further, by adjusting the cross-sectional area (inner diameter) of the capillary for forming the rod part, the diameter of the rod part formed by crushing the capillary can be adjusted.
In addition, since the capillary for hole formation seals one end and keeps the pressure in the capillary leaving the void during integration, the hole diameter is stable in the longitudinal direction of the base material. And an optical fiber having stable optical characteristics over the entire length of the capillary can be manufactured.
Further, it is not necessary to adjust the pressure according to the design and size of the base material, compared to the case where the capillary is sealed at both ends, and any shape base material can be easily manufactured.
Further, by integrating at the base material stage, it is only necessary to control the pressure in the air holes during spinning, and it is not necessary to create a complicated spinning pressure system, and the spinning device can be simplified.
Also, during the integration, the two pressures are finally controlled, but the space can be divided between the upper and lower parts of the base material by the step (5). Integration processing can be performed without taking a simple structure, and the integration apparatus can be simplified.
According to the manufacturing method of the present invention, a base material having a cross-sectional structure in which a large number of holes and a rod portion formed by collapsing the holes of a capillary can be manufactured with a yield of almost 100%, In addition, the optical fiber can be manufactured with a high yield by spinning the base material.
Hereinafter, the effects of the present invention will be demonstrated by examples.

<Reference Example 1>
A quartz glass support tube 41 having an outer diameter of 40 mm and an inner diameter of 33 mm is packed with a large number of quartz glass capillaries 40A, air core forming capillaries 44 and quartz glass solid rods 43 as shown in FIG. The materials were integrated to produce a base material 51A having a cross-sectional shape as shown in FIG.
Here, the hole forming capillary 40A and the air core forming capillary 44 were sealed at one end and arranged with the sealing side facing upward in FIG. For the hole forming capillary 40A, a quartz glass circular tube having an outer diameter of 1.5 mm, an inner diameter of 1.3 mm, and a length of 400 mm was used. As the solid rod 43, a quartz glass rod having an outer diameter of 1.5 mm and a length of 400 mm was used. As the capillary 44 for the air core at the center, a circular tube made of quartz glass having an outer diameter of 3.9 mm, an inner diameter of 3.5 mm, and a length of 400 mm was used.
Next, the base material is set in a stretching machine, set so that the center of the heat zone is located 40 mm above the lower end of the capillary 40A, heated at 1900 ° C., and supplied with Ar gas from the bottom with a vacuum pump from the top. As shown in FIG. 15, a part of the base material was integrated.
After that, the space I shown in FIG. 16 is depressurized by a vacuum pump and adjusted so that the differential pressure from the atmospheric pressure becomes −90 kPa, and the differential pressure from the atmospheric pressure in the space II is in the range of +0.5 kPa. As shown in FIG. 17, the entire length of the base material was integrated by stretching to an outer diameter of 30 mm while moving the heat zone at 1870 ° C. As a result, as shown in FIG. 19, it has a core region 53 consisting of a hole core (air core) at the center, and hexagonal holes 52 and solid rod portions are regularly arranged around the core region 53. A base material 51A having a structure was obtained.
The cross section of the obtained base material 51A had almost the same hole diameter in the upper part and the lower part of the base material.

<Example 1>
As shown in FIG. 20, a support tube 41 made of quartz glass having an outer diameter of 40 mm and an inner diameter of 33 mm, an air core forming capillary 44, a large number of holes forming capillaries 40A, and a large number of rod portion forming capillaries 40B. A base material 51B having a cross-sectional shape as shown in FIG.
Here, the hole forming capillary 40A and the air core forming capillary 44 were sealed at one end and arranged with the sealing side facing upward in FIG. Capillary 40B that crushes the air holes to form the rod portion was sealed at one end and placed with the sealing side facing downward in FIG. For the hole forming capillary 40A, a quartz glass circular tube having an outer diameter of 1.5 mm, an inner diameter of 1.3 mm, and a length of 400 mm was used. As the rod portion forming capillary 40B, a quartz glass circular tube having an outer diameter of 1.5 mm, an inner diameter of 0.7 mm, and a length of 400 mm was used. As the central air core forming capillary 44, a quartz glass circular tube having an outer diameter of 3.9 mm, an inner diameter of 3.5 mm, and a length of 400 mm was used.
Next, the base material is set in a stretching machine, set so that the center of the heat zone is located 40 mm above the lower end of the capillary 40A, heated at 1900 ° C., and supplied with Ar gas from the bottom with a vacuum pump from the top. As shown in FIG. 15, a part of the base material was integrated.
After that, the space I shown in FIG. 16 is depressurized by a vacuum pump and adjusted so that the differential pressure from the atmospheric pressure becomes −90 kPa, and the differential pressure from the atmospheric pressure in the space II is in the range of +0.5 kPa. As shown in FIG. 17, the entire length of the base material was integrated by stretching to an outer diameter of 30 mm while moving the heat zone at 1870 ° C. As a result, as shown in FIG. 21, it has a core region 53 consisting of a substantially hexagonal hole core (air core) at the center, and a large number of triangular holes 52 and small hexagonal rod portions 54 around it. A base material 51B having a structure in which thin partition walls 55 that connect these rod portions 54 are regularly arranged is obtained.
The obtained cross section of the base material had almost the same pore diameter at the top and bottom of the base material.

<Example 2>
FIG. 22 shows a support tube 41 made of quartz glass having an outer diameter of 39 mm and an inner diameter of 33 mm, an air core forming capillary 44, a large number of holes forming capillaries 40A, and a large number of rod portion forming capillaries 40B. A base material 51C having a cross-sectional shape as shown in FIG.
Here, the hole forming capillary 40A and the air core forming capillary 44 were sealed at one end and arranged with the sealing side facing upward in FIG. Capillary 40B that crushes the air holes to form the rod portion was sealed at one end and placed with the sealing side facing downward in FIG. For the hole forming capillary 40A, a quartz glass circular tube having an outer diameter of 1.5 mm, an inner diameter of 1.3 mm, and a length of 400 mm was used. As the rod portion forming capillary 40B, a quartz glass circular tube having an outer diameter of 1.5 mm, an inner diameter of 0.7 mm, and a length of 400 mm was used. As the central air core forming capillary 44, a quartz glass circular tube having an outer diameter of 6.5 mm, an inner diameter of 5.8 mm, and a length of 400 mm was used.
Next, the base material is set in a stretching machine, set so that the center of the heat zone is located 40 mm above the lower end of the capillary 40A, heated at 1850 ° C., and supplied with Ar gas from the bottom with a vacuum pump from the top. As shown in FIG. 15, a part of the base material was integrated.
After that, the space I shown in FIG. 16 is depressurized by a vacuum pump and adjusted so that the differential pressure from the atmospheric pressure becomes −90 kPa, and the differential pressure from the atmospheric pressure in the space II is in the range of +0.02 kPa. As shown in FIG. 17, the entire length of the base material was integrated by stretching to an outer diameter of 30 mm while moving the heat zone at 1830 ° C. As a result, as shown in FIG. 23, it has a core region 53 consisting of a substantially hexagonal hole core (air core) at the center, and a large number of triangular holes 52 and small hexagonal rod portions 54 around it. A base material 51C having a structure in which the thin partition walls 55 that connect the rod portions 54 are regularly arranged is obtained.
It can be seen that the base material 51C shown in FIG. 23 has a smaller diameter of the rod portion 54 than the base material 51B of the first embodiment. Moreover, it could be produced without any disturbance of the arrangement.

<Reference Example 2>
A quartz glass support tube 41 having an outer diameter of 35 mm and an inner diameter of 22 mm is packed with a large number of quartz glass capillaries 40A and a solid rod 42 made of quartz glass for forming a core region as shown in FIG. Integration was performed to produce a base material 51D having a cross-sectional shape as shown in FIG.
Here, the capillary 40A for hole formation was sealed at one end and arranged with the sealing side facing upward in FIG. As the hole forming capillary 40A, a quartz glass circular tube having an outer diameter of 2.1 mm, an inner diameter of 1.88 mm, and a length of 500 mm was used. As the solid rod 42 for forming the core region, a quartz glass rod having an outer diameter of 2.1 mm and a length of 400 mm was used.
Next, the base material is set in a stretching machine, set so that the center of the heat zone is located 40 mm above the lower end of the capillary 40A, heated at 1980 ° C., and supplied with Ar gas from the bottom with a vacuum pump from the top. As shown in FIG. 15, a part of the base material was integrated.
Thereafter, the space I shown in FIG. 16 is depressurized by a vacuum pump and adjusted so that the differential pressure from the atmospheric pressure is −98 kPa, and the differential pressure from the atmospheric pressure is +1.0 kPa in the space II. As shown in FIG. 17, the entire length of the base material was integrated by stretching to an outer diameter of 25 mm while moving the heat zone at 2000 ° C. As a result, as shown in FIG. 25, the structure has a solid core region 53 with a hexagonal cross section at the center, and hexagonal holes 52 regularly arranged through thin partition walls 55 around the core region 53. The base material 51D having was obtained.
The cross section of the obtained base material 51C had almost the same hole diameter at the top and bottom of the base material.

<Example 3>
A quartz glass support tube 41 having an outer diameter of 35 mm and an inner diameter of 22 mm is filled with a large number of quartz glass capillaries 40A and 40B as shown in FIG. 26, and the base material is integrated, as shown in FIG. A base material 51E having a cross-sectional shape was produced.
Here, the capillary 40A for hole formation was sealed at one end and arranged with the sealing side facing upward in FIG. The solid core capillary 40B was sealed at one end and arranged with the sealing side facing downward in FIG. For both the hole forming capillary 40A and the solid core capillary 40B, quartz glass circular tubes having an outer diameter of 2.1 mm, an inner diameter of 1.88 mm, and a length of 500 mm were used.
Next, the base material is set in a stretching machine, set so that the center of the heat zone is located 40 mm above the lower end of the capillary 40A, heated at 1980 ° C., and supplied with He gas from the bottom with a vacuum pump from the top. As shown in FIG. 15, a part of the base material was integrated.
Thereafter, the space I shown in FIG. 16 is depressurized by a vacuum pump and adjusted so that the differential pressure from the atmospheric pressure is −98 kPa, and the differential pressure from the atmospheric pressure is +1.0 kPa in the space II. As shown in FIG. 17, the entire length of the base material was integrated by stretching to an outer diameter of 25 mm while moving the heat zone at 2000 ° C. As a result, as shown in FIG. 27, a structure having a small core region 53 with a hexagonal cross section at the center and hexagonal holes 52 regularly arranged through thin partition walls 55 therearound. A base material 51E having the following was obtained.
Since the core region 53 of the base material 51E was formed by crushing the pores of the capillary 40B, the cross-sectional area could be made smaller than that of the core region 53 of the base material 51D of Reference Example 2.

<Comparative Example 1>
According to the description in Patent Document 1, as shown in FIGS. 6 and 7, an attempt was made to produce a photonic bandgap fiber using a capillary and a rod having a smaller outer diameter than that. However, when the rod is thin and assembled. The position of the rod moved and the base material could not be produced successfully.

<Comparative example 2>
Based on the description of Examples 1 and 2 of Patent Document 7, pure quartz was used as the glass material, and the temperature and pressure conditions were changed to conditions suitable for pure quartz, and fiber production was attempted. However, while the gap in the glass capillary is heated under reduced pressure, the pores in the capillary are sealed at both ends, so the condition for sealing both ends is difficult as in Comparative Example 1, and the base material is heated and integrated. During this time, the pressure in the hole changes, and the hole diameter is not stable in the longitudinal direction of the base material. As shown in Patent Document 7, the cross section with the base material has no clear gap, but the pore diameter could not be stabilized in the longitudinal direction. Therefore, even if the obtained base material was spun, the optical characteristics changed in the longitudinal direction, and the yield was very poor.

<Comparison of base material yield>
In Examples 1 to 3 and Reference Examples 1 and 2, the yield of the base material was approximately 100%, and the yield was about 85% including the stability in the longitudinal direction of the holes at the time of stranding.
On the other hand, in Comparative Examples 1 and 2, the yield of the base material was about 40%, and the yield at the time of forming the strand was about 10% including the stability in the longitudinal direction of the holes.

It is sectional drawing which illustrates the conventional hole assist type | mold holey fiber. It is sectional drawing which illustrates the conventional double clad fiber. It is sectional drawing which illustrates the conventional photonic band gap fiber. 2 is a cross-sectional view showing an optical fiber structure exemplified in FIG. 1 of Patent Document 1. FIG. 3 is a cross-sectional view showing an optical fiber structure illustrated in FIG. 2 of Patent Document 1. FIG. 6 is a cross-sectional view showing a combination of a capillary and a rod exemplified in FIG. 5 of Patent Document 1. FIG. FIG. 7 is a cross-sectional view showing a combination of a capillary and a rod exemplified in FIG. 6 of Patent Document 1. 2 is a cross-sectional view of the capillary shown in FIG. 1 of Patent Document 2. FIG. 2 is a cross-sectional view of the preform shown in FIG. 1 of Patent Document 3. FIG. FIG. 5 is a configuration diagram of a drawing apparatus shown in FIG. 4 of Patent Document 4. It is a block diagram of the drawing apparatus shown by FIG. 2 of patent document 5. FIG. It is sectional drawing which illustrates another preform | base_material for fiber manufacture. It is the schematic explaining pressure control in a support pipe in patent documents 5. It is a block diagram which shows process (1)-process (3) of this manufacturing method. It is a block diagram which shows the process (4) and process (5) of this manufacturing method. It is a block diagram which shows the process (6) of this manufacturing method. It is a block diagram which shows the process (7) of this manufacturing method. It is sectional drawing of the preform | base_material before integration which showed the preform | base_material manufactured by the reference example 1, and packed the capillary and the solid rod in the support pipe | tube. 6 is a cross-sectional view of a base material manufactured in Reference Example 1. FIG. 1 is a cross-sectional view of a base material before integration in which a capillary is packed in a support pipe, showing Example 1 of the base material manufactured according to the present invention. 1 is a cross-sectional view of a base material manufactured in Example 1. FIG. It is Example 2 of the preform | base_material manufactured by this invention, and is sectional drawing of the preform | base_material before integration which packed the capillary in the support pipe | tube. 6 is a cross-sectional view of a base material manufactured in Example 2. FIG. It is sectional drawing of the preform | base_material before integration which showed the preform | base_material manufactured by the reference example 2, and packed the capillary and the solid rod in the support pipe | tube. 6 is a cross-sectional view of a base material manufactured in Reference Example 2. FIG. It is Example 3 of the base material manufactured by this invention, and is sectional drawing of the base material before integration which packed the capillary in the support pipe | tube. 6 is a cross-sectional view of a base material manufactured in Example 3. FIG.

Explanation of symbols

40A, 40B ... Capillary, 41 ... Support tube, 42, 43 ... Solid rod, 44 ... Capillary for air core formation, 45 ... One end sealing part, 46 ... Upper connector, 46A ... Exhaust port, 47 ... Lower connector, 47A DESCRIPTION OF SYMBOLS ... Gas supply port, 48 ... Heater, 49 ... Differential pressure adjusting gas, 50 ... Integrated region, 51, 51A to 51E ... Base material, 52 ... Hole, 53 ... Core region, 54 ... Rod part, 55 ... Partition .

Claims (6)

(1) sealing one end of the capillary;
(2) A plurality of capillaries with one end sealed or a plurality of capillaries and a solid rod, a capillary that leaves a hole is directed toward one side, and a capillary that crushes a hole is sealed Bundling one end toward the other side and packing them into a support tube,
(3) Next, connecting the connector connected to the vacuum exhaust device to the one side of the support tube and connecting the connector connected to the differential pressure adjusting gas supply device to the other side,
(4) Next, the step of heating the vicinity of one end of the capillary to a temperature at which the capillary is softened and deformed with a heater,
(5) In the state of step (4), the inside of the tube is evacuated from the one side of the support tube by the vacuum evacuation device, and the differential pressure adjusting gas is supplied into the tube from the other side of the support tube. Integrating the base material at the section and dividing the space in the pipe into the space I on the one side and the space II on the other side;
(6) Next, the process of reducing the pressure of the space I and controlling the space II to be almost atmospheric pressure,
(7) Next, the heat zone is moved slowly along the longitudinal direction of the capillary, and integration is performed over the entire length of the capillary to combine a large number of holes and a rod portion formed by collapsing the holes of the capillary. Producing a base material having a cross-sectional structure,
(8) Next, the step of spinning the base material while controlling the pressure inside the hole, forming a strand to obtain an optical fiber having a hole,
An optical fiber manufacturing method comprising:   The method for manufacturing an optical fiber according to claim 1, wherein the heating temperature in the step (4) is in the range of 1700 ° C to 2100 ° C.   3. The method of manufacturing an optical fiber according to claim 1, wherein a differential pressure from the atmospheric pressure in the space I is set to a range of −0.50 kPa to −101 kPa in the step (6).   The method for producing an optical fiber according to any one of claims 1 to 3, wherein a differential pressure from the atmospheric pressure in the space II is set in a range of -0.50 kPa to +10 kPa in the step (6).   The optical fiber according to any one of claims 1 to 4, wherein in the step (7), the holes belonging to both the space I and the space II are not sealed, and the holes are opened and stretched. Production method. An optical fiber manufactured by the method according to claim 1.

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