JP5503453B2 - OPTICAL FIBER BASE MATERIAL MANUFACTURING METHOD, HOLE STRUCTURE OPTICAL FIBER MANUFACTURING METHOD, AND PRESSURE / PRESSURE CONNECTOR - Google Patents

Description

  The present invention relates to an optical fiber preform manufacturing method for manufacturing a hole-structured optical fiber, a method for manufacturing a hole-structure optical fiber, and a pressure-reducing connector used therefor.

  As a hole structure optical fiber having a hole structure, a so-called holey fiber (HF) or a photonic crystal fiber (PCF), a photonic bandgap fiber (PBGF), And hole assisted fiber (HAF).

  HF or PCF is a type of optical fiber that realizes the transmission of light using the principle of total reflection by lowering the average refractive index of the cladding part by regularly arranging holes in the cladding part around the core part. is there. In addition, PBGF forms photonic band gaps by arranging vacancies in the cladding part so as to form a photonic crystal, and introduces a core part as a crystal defect therein to realize light transmission. Type of optical fiber. In addition, as for PBGF, a core part may be formed of a void | hole. In addition, HAF further reduces the average refractive index of the clad part by providing holes in the clad part of a normal solid optical fiber consisting of a solid core part and a clad part, thereby improving the light confinement characteristics in the core part. An improved type of optical fiber.

  There are the following methods for manufacturing these hole-structured optical fibers. First, holes are formed in an optical fiber preform having a region to be a core portion with a drill device or the like (see Patent Document 1), or a glass material around a quartz glass tube (hole glass tube) that becomes a hole. (See Patent Document 2) to prepare an optical fiber preform having holes. The optical fiber preform is drawn while controlling the internal pressure of the hole or the glass tube for the hole, and the hole-structured optical fiber is made into a fiber while maintaining the desired hole so as not to be crushed. Manufactured (see Patent Document 3).

  However, when a hole is made in an optical fiber preform having a region to be a core portion as in Patent Document 1 with a drill device or the like, it is necessary to make many small-diameter holes in a clad portion relatively close to the core portion. Therefore, it is necessary to use a small-diameter drill blade. However, due to restrictions on the strength and length of the drill blade, it is the limit to open a hole with a length of about 400 mm. Difficult to do. As described above, if the length of the optical fiber preform is restricted, the length of the hole-structured optical fiber that can be drawn at a time is also restricted, which makes it difficult to reduce the manufacturing cost. In addition, when a glass tube for holes is used as in Patent Document 2, a large load is required for the procurement cost of the glass tube, the assembly work, or the cutting of the glass material that fills the periphery thereof. Cost reduction becomes difficult.

  Therefore, as a method of solving the problems such as the length of the holes, material procurement cost, manufacturing process load such as assembly work and cutting, first, a portion that becomes the core portion of the optical fiber and the periphery of the core portion A plurality of glass rods (hole forming glass rods) having at least one or more holes extending along the longitudinal axis are prepared, and the hole forming glass rods are long glass tubes made of the same material as the clad portion. (Clad forming glass tube) Insert a plurality of the glass tubes in series in the longitudinal direction of the long glass tube, and heat and melt these hole forming glass rods and the glass tube for clad formation. An optical fiber preform is manufactured. As described above, Patent Documents 4 and 5 disclose a method of elongating an optical fiber preform for a hole-structured optical fiber by using a so-called rod-in-tube method and overcoming the restriction on the length of the preform. ing.

JP 2002-145634 A JP 2003-342032 A JP 2004-307250 A JP 2005-022945 A JP 2005-053756 A

However, in order to lengthen the base material by the above-described method, the hole positions of the plurality of hole-forming glass rods must be matched, and fusion and integration with the long glass tube must be performed while maintaining the positions. In general, when the number of hole-forming glass rods to be inserted is increased to 3 or more, the difficulty of the manufacturing operation is extremely increased. Further, if the hole position is shifted, it becomes difficult to control the internal pressure in the drawing process, and it becomes impossible to obtain a hole-structured optical fiber. Further, additional work such as drilling for providing a shaft misalignment prevention means for adjusting the hole position and pin preparation occurs, which causes an increase in work load and cost. Accordingly, there remains a need to overcome these challenges in order to further reduce the manufacturing cost of holey structure optical fibers.
Furthermore, in order to melt and integrate the gap between the hole-forming glass rod and the long glass tube by reducing the gap between the hole-forming glass rod and the long glass tube by the rod-in-tube method while maintaining the desired hole shape, the hole portion is in a pressurized state. Although a means for simultaneously realizing the reduced pressure in the gap is required, there has been no connector for increasing and decreasing pressure that has a relatively simple structure and can withstand repeated use over a long period of time.

  The present invention has been made in view of the above, and it is possible to easily increase the size of an optical fiber preform for a hole-structured optical fiber, and to reduce the manufacturing cost. It is an object of the present invention to provide a method of manufacturing a structured optical fiber and a pressure-reducing connector used therefor.

  In order to solve the above-described problems and achieve the object, an optical fiber preform manufacturing method according to the present invention includes a core portion and a cavity portion formed on the outer periphery of the core portion and having a void. An optical fiber preform manufacturing method for manufacturing an optical fiber preform for manufacturing a hole-structured optical fiber, comprising preparing a hole-forming glass tube in which holes extending in the longitudinal direction are formed around the opening hole And a clad outer peripheral portion forming step for forming an outer peripheral portion of the clad portion on the outer periphery of the hole forming glass tube, and a core glass rod having a core portion inside the hole forming glass tube And an integration step of heating the hole forming glass tube into which the core glass rod is inserted to integrate the core glass rod and the hole forming glass tube. To do.

  Further, in the method of manufacturing an optical fiber preform according to the present invention, in the above invention, the hole forming glass tube preparation step includes a step of preparing a glass tube, and a step of providing the holes in the glass tube, And a stretching step of heating and stretching the glass tube provided with the holes so as to have desired inner and outer diameters.

  Moreover, in the manufacturing method of the optical fiber preform according to the present invention, in the above invention, the integration step depressurizes the space formed between the core glass rod and the hole forming glass tube. Integration is performed while pressurizing inside the pores of the pore-forming glass tube.

  Further, in the method for manufacturing an optical fiber preform according to the present invention, in the above invention, in the integration step, a connecting member is fitted into the hole forming glass tube, and the connecting member is pressed from the outside. The pressure is reduced through the pressure reducing communication hole formed in the connecting member so as to communicate with the gap in a state where the gas flow between the gap and the hole is shielded, and communicated with the hole. As described above, pressurization is performed through a pressurizing communication hole formed in the connection member.

  The optical fiber preform manufacturing method according to the present invention is the process according to the above invention, wherein in the integration step, a hole extending in the longitudinal direction is formed in the hole forming glass tube around the opening hole. A decompression extension tube, an opening hole of the pressurization / decompression extension tube in an opening hole of the hole forming glass tube, and a hole of the pressurization / decompression extension tube in a hole of the hole formation glass tube are independent of each other. Then, the connection member is fitted to the end of the pressurizing / depressurizing extension pipe opposite to the end of the fusion connected, and the connection member is pressed from the outside to be locked. And formed in the connection member so as to communicate with the gap in a state where the flow of gas between the gap and the hole of the hole-forming glass tube is shielded via the pressure increasing / decreasing extension pipe. Holes in the hole-forming glass tube are pressure-reduced through the pressure-reducing communication holes Performing pressurization through is formed in the connecting member so as to communicate with the pressurizing passage, characterized in that.

  Moreover, in the manufacturing method of an optical fiber preform according to the present invention, in the above invention, in the integration step, the annular protrusion formed on the connection member is formed with an opening hole and a hole of the hole forming glass tube. The gas flow between the gap and the hole of the hole-forming glass tube is made airtight by closely adhering to the area between the hole and the area between the opening hole and the hole of the extension / decompression extension tube. It is characterized by shielding.

  The optical fiber preform manufacturing method according to the present invention is the method according to the above invention, wherein, in the integration step, the seal ring is a region between the opening holes of the hole forming glass tube or the pressure increasing / decreasing step. It is characterized in that the gas flow between the gap and the hole of the hole forming glass tube is shielded by tightly adhering to a region between the opening hole and the hole of the extension tube for use.

  Further, in the method for manufacturing an optical fiber preform according to the present invention, in the above invention, the cladding outer peripheral portion forming step includes porous glass fine particles formed on the outer peripheral surface of the hole forming glass tube by an external method. The method is characterized by depositing a layer and semi-sintering the porous glass fine particle layer using a semi-sintering method.

  Moreover, the manufacturing method of the optical fiber preform according to the present invention is characterized in that, in the above invention, the cladding outer peripheral portion forming step is performed prior to the integration step.

  Moreover, the manufacturing method of the optical fiber preform according to the present invention is characterized in that, in the above invention, the cladding outer peripheral portion forming step is performed after the integrating step.

  A method for producing a hole-structured optical fiber according to the present invention is a method for producing a hole-structured optical fiber comprising a core part and a cladding part formed on the outer periphery of the core part and having holes, A hole-forming glass tube preparation step for preparing a hole-forming glass tube in which holes extending in the longitudinal direction are formed around the opening hole, and a cladding outer periphery that becomes an outer peripheral region of the cladding part on the outer periphery of the hole-forming glass tube Clad outer peripheral portion forming step for forming a portion, insertion step for inserting a core glass rod having a region to become a core portion into the pore forming glass tube, and a pore forming glass tube having the core glass rod inserted therein And integrating the core glass rod and the hole-forming glass tube with each other, and the cladding outer peripheral portion forming step is performed before the insertion step and the integration step. Pipe outer peripheral surface The porous glass fine particle layer formed by the external method is deposited on the porous glass fine particle layer, and the porous glass fine particle layer is semi-sintered by using a semi-sintering method. The hole forming glass tube and the core glass rod formed with a hole are formed simultaneously with the drawing of the hole-structured optical fiber using a drawing heating furnace.

  Further, the pressure increasing / decreasing connector according to the present invention is a pressure increasing / decreasing connector used in the method for manufacturing an optical fiber preform of the above invention, and is fitted to the hole forming glass tube or the pressure increasing / decreasing extension tube. And a pressure reducing communication hole formed so as to communicate with the gap, and a hole of the hole forming glass tube or a hole of the pressure increasing / decreasing extension tube. The pressurizing communication hole and the hole forming glass tube or the region between the opening hole of the pressure increasing / decreasing extension tube and the hole between the gap and the hole of the hole forming glass tube It is characterized by comprising a connecting member having an annular protrusion for shielding gas flow, and a pressing member for pressing and locking the connecting member from the outside.

  Further, the pressure increasing / decreasing connector according to the present invention is a pressure increasing / decreasing connector used in the method for manufacturing an optical fiber preform of the above invention, and is fitted to the hole forming glass tube or the pressure increasing / decreasing extension tube. A connecting member having a fitting portion for pressure reduction, a communication hole for pressure reduction formed so as to communicate with the air gap, and a communication hole for pressurization formed so as to communicate with the air hole; A pressing member for pressing and locking, and closely contacting a region between the opening hole of the hole-forming glass tube and the hole of the hole-forming glass tube or the hole of the pressure increasing / decreasing extension tube And a seal ring for shielding the gas flow between the gap and the hole of the hole forming glass tube.

  In the pressure-intensifying connector according to the present invention as set forth in the invention described above, the connecting member has a spiral portion formed on the outer periphery and a tip portion having a wedge-shaped cross section, and the pressing member is the spiral A cap nut having a fitting portion that is screwed into a portion and that has a fitting portion that applies a stress that fits the tip portion against the hole-forming glass tube or the pressure-extension / decompression extension tube. And

  ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that the optical fiber preform for hole structure optical fibers can be enlarged easily, and manufacturing cost can be reduced.

FIG. 1 is a schematic cross-sectional view of an example of an optical fiber preform manufactured by the manufacturing method according to the first embodiment. FIG. 2 is a flowchart of the method for manufacturing the optical fiber preform according to the first embodiment. FIG. 3 is a schematic view of a hole forming glass tube. FIG. 4 is a schematic view of a hole forming glass tube formed by connection. FIGS. 5-1 is explanatory drawing explaining the connection process of a support pipe | tube. 5-2 is explanatory drawing explaining the other aspect of the connection process of a support pipe | tube. FIG. 6 is an explanatory view for explaining the preliminary processing of the support tube. FIG. 7 is a schematic view of a hole-forming glass tube having a clad outer periphery. FIG. 8 is an explanatory diagram for explaining a support tube removing step. FIG. 9 is an explanatory view for explaining a core glass rod insertion step. FIG. 10 is a schematic cross-sectional view showing a state where the pressure increasing / decreasing connector according to the second embodiment is attached to the hole forming glass tube. FIG. 11 is a schematic cross-sectional view showing a pressure-increasing / decreasing connector according to Modification 1. FIG. 12 is a schematic cross-sectional view showing a pressure increasing / decreasing connector according to Modification 2. FIG. 13 is a schematic cross-sectional view showing a pressure increasing / decreasing connector according to Modification 3. FIG. 14 is a schematic cross-sectional view showing a pressure increasing / decreasing connector according to Modification 4. FIG. 15 is a schematic view showing a state in which an extension / decompression extension tube is connected to a hole forming glass tube. FIG. 16 is a schematic diagram showing a cross section along the front and longitudinal directions of the pressurizing / depressurizing extension pipe shown in FIG. 15. 17 is a schematic cross-sectional view showing a state where the pressure increasing / decreasing connector shown in FIG. 10 is attached to the pressure increasing / decreasing extension pipe shown in FIG.

  Embodiments of an optical fiber preform manufacturing method, a hole-structured optical fiber manufacturing method, and a pressure increasing / decreasing connector according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate.

(Embodiment 1)
First, the manufacturing method of the optical fiber preform according to the first embodiment of the present invention will be described. Hereinafter, the structure of the optical fiber preform manufactured by the manufacturing method according to the first embodiment will be described first, and then the manufacturing method according to the first embodiment will be described.

  FIG. 1 is a schematic cross-sectional view of an example of an optical fiber preform manufactured by the manufacturing method according to the first embodiment. As shown in FIG. 1, this optical fiber preform 1 is for manufacturing a hole assist fiber (HAF), and includes a core portion 1a and a cladding portion 1b formed on the outer periphery of the core portion 1a. Prepare.

  The core 1a is made of quartz glass to which a dopant for increasing the refractive index, such as germanium (Ge), is added. The clad part 1b is made of quartz glass having a lower refractive index than that of the core part 1a, for example, pure silica glass not containing a dopant for adjusting the refractive index. The clad portion 1b has six holes 1c formed so as to surround the core portion 1a and extending along the longitudinal direction.

  The clad portion 1b has an inner peripheral region 1ba and an outer peripheral region 1bb. The inner peripheral region 1ba has a hole 1c and is a region mainly formed from a hole-forming glass tube to be described later. The outer peripheral region 1bb is a region formed from a clad outer peripheral portion to be described later. The core portion 1a is formed by inserting a core glass rod, which will be described later, into a hole forming glass tube.

  By drawing the optical fiber preform 1, a HAF having a core portion formed from the core portion 1 a and a clad portion formed from the cladding portion 1 b and having holes formed from the holes 1 c is manufactured. can do. The ratio of the diameter of the core portion 1a to the outer diameter of the clad portion 1b is, for example, about 1:13 to 1:20 (approximately 6 to 6) so as to be the ratio of the core diameter and the clad diameter of the HAF to be manufactured. 10/125 μm).

  Next, a method for manufacturing the optical fiber preform according to the first embodiment for manufacturing the optical fiber preform 1 will be specifically described. FIG. 2 is a flowchart of the method for manufacturing the optical fiber preform according to the first embodiment. As shown in FIG. 2, the manufacturing method of the hole structure optical fiber according to the first embodiment includes a hole forming glass tube preparation step (step S101), a support tube connecting step (step S102), and a cladding. This includes an outer peripheral portion forming step (step S103), a core glass rod inserting step (step S104), a pressure increasing / decreasing connector mounting step (step S105), and an integrating step (step S106). However, the order of each process is not limited to this, and for example, the formation process of the outer periphery of the clad in step S103 may be performed after the integration process in step S106.

  In the manufacturing method of the optical fiber preform according to the first embodiment, the core glass rod is inserted into the opening hole of the hole forming glass tube in which the hole is formed, and the outer periphery of the clad is formed on the outer periphery of the hole forming glass tube. To form. For this reason, if a large diameter and thick glass tube is used as the hole forming glass tube, it is possible to provide a hole using a relatively large diameter drill blade. It becomes possible to avoid the restriction, and it is possible to manufacture the optical fiber preform 1 for a hole structure optical fiber longer than 400 mm. In addition, if the hole-forming glass tube is heated and stretched to a desired inner and outer diameter, it is possible to obtain a longer base material. Thus, a large-sized optical fiber base material for hole-structured optical fibers can be easily obtained. It can be. Or when performing the formation process of the said clad outer peripheral part after the said integration process, the optical fiber preform after the said integration process is heated and extended to a desired outer diameter, and a clad part is given to it. By doing so, the longer optical fiber preform 1 for a hole structure optical fiber can be manufactured.

Hereinafter, each step will be described. In addition, the numerical value shown in each process is an illustration, and this Embodiment 1 is not limited to this numerical value.
(Preparation process of hole forming glass tube)
First, the preparation process of the hole forming glass tube in step S101 will be described. First, a high-purity synthetic quartz glass tube having an inner diameter of about 20 mm, an outer diameter of about 40 mm, and a length of 400 mm is prepared. Six holes having an inner diameter of 5 mm along the longitudinal direction are perpendicular to the longitudinal axis using an ultrasonic drill. A hole-forming glass tube is formed by drilling so that the central angles in a simple cross section are equal.

  FIG. 3 is a schematic view of a hole forming glass tube. As shown in FIG. 3, the hole-forming glass tube 2 has holes 2 b formed so as to penetrate along the longitudinal direction around an opening hole 2 a that is a hollow portion of the glass tube.

  A plurality of hole-forming glass tubes shown in FIG. 3 may be produced, and these may be welded and connected in the longitudinal direction to form a long hole-forming glass tube. For the welding, two hole-forming glass tubes are selected, and the holes are set on both chucks of the horizontal machining lathe so that the positions of the holes are substantially coincided with each other. The opposite ends of the two pore-forming glass tubes are heated with a hydrogen flame burner and welded together. In addition, when a welding part swells in an outer diameter direction at the time of welding, it presses with a carbon-made iron and is made smooth. When the welded portion swells inward, the two hole-forming glass tubes may be moved relatively in the opposite directions while heating after welding, and the welded portion may be slightly stretched for adjustment. In this manner, a plurality of hole forming glass tubes are sequentially connected to prepare a hole forming glass tube having a desired length. FIG. 4 is a schematic view of the hole forming glass tube 4 formed by connection.

  These hole-forming glass tubes can be washed by immersing them in a hydrofluoric acid aqueous solution, thoroughly washed with pure water, etc., and dried to remove glass dust generated in the holes and remaining in the holes. desirable.

  The hole forming glass tube 2 having a large outer diameter may be heated and stretched to form a hole forming glass tube having a desired inner and outer diameter and length. In addition, if a glass tube having a large outer diameter (for example, 50 mm or more) and a thick wall (for example, 15 mm or more) is used, a drill blade having a larger diameter and a longer length may be used when forming a hole. it can. Therefore, even if the length of the glass tube is longer than 400 mm, it is possible to form a through-hole, so that a longer hole-forming glass tube 2 can be formed.

(Support pipe connection process)
Next, the connecting step of the support pipe in step S102 will be described. FIGS. 5-1 is explanatory drawing explaining the connection process of a support pipe | tube. In this connection step, a quartz glass support tube 5 is welded and connected to both ends of the hole forming glass tube 2. At this time, as shown in FIG. 5B, the air holes 2 b and the opening holes 2 a of the air hole forming glass tube 2 may be opened to the outside by the opening holes 5 a of the support tube 5. By doing so, the gas confined in the holes 2b expands with heating in the subsequent process, and as a result, the problem that the holes 2b expand is less likely to occur.
Further, it is desirable that the support tube 5 be processed in advance into a shape that can be attached to the apparatus in the subsequent formation process of the outer periphery of the clad, for example, as shown in FIG.

(Clad outer periphery forming process)
Next, the step of forming the outer periphery of the clad in step S103 will be described. FIG. 7 is a schematic view of a hole-forming glass tube having a clad outer periphery. In this forming step, a desired porous glass fine particle layer is deposited on the outer periphery of a portion excluding both ends of the hole forming glass tube 2 connected to the support tube 5 by a known external method. Next, this is heated and dehydrated in an atmosphere containing chlorine, and further heated at 1450 ° C. to advance the sintering to a density of about 95% of the density of transparent quartz glass (2.2 g / cm ³ ), A cloudy state containing closed cells is used. Thus, the semi-sintered clad outer peripheral portion 7 is formed. The outer diameter of the clad outer peripheral part 7 after semi-sintering is about 250 mm. In addition, a method of sintering the porous glass fine particle layer in a cloudy state in this way is called a semi-sintering method. According to this semi-sintering method, the heating temperature does not have to be as high as about 1500 to 1600 ° C. necessary for making the porous glass fine particle layer into a transparent glass state, thereby reducing power consumption during production. it can.

  Further, if a reduced pressure semi-sintering method in which the steps of heat dehydration to semi-sintering are performed under reduced pressure, it is possible to make the gas substantially free of closed cells.

  Next, the two support tubes 5 are cut and removed by the cutter C as shown in FIG. 8 from the hole forming glass tube 2 in which the clad outer peripheral portion 7 is formed in this way. At this time, the cutting site is slightly on the side of the hole forming glass tube 2 from the welded portion of the hole forming glass tube 2 and the support tube 5, and the support tube 5 does not remain on the cut surface of the hole forming glass tube 2 after cutting. Like that. Then, the inner surfaces of the opening hole 2a and the hole 2b are washed again with a hydrofluoric acid aqueous solution.

In the first embodiment, the outer peripheral portion of the cladding is formed using an external method and a semi-sintering method. The glass fine particle layer deposited by the external method has a density of 2.2 g as usual. You may completely vitrify so that it may become / cm < ³ >. Moreover, you may perform the formation process of a clad outer peripheral part using a rod-in-tube method.

(Core glass rod insertion process)
Next, the step of inserting the core glass rod in step S104 will be described. FIG. 9 is an explanatory view for explaining a core glass rod insertion step. As shown in FIG. 9, in this insertion step, a core glass rod 8 having a region to become the core portion 1a is prepared, washed with a hydrofluoric acid aqueous solution and dried, and then the pore-forming glass tube 2 Insert into the opening 2a. At this time, a gap is formed between the core glass rod 8 and the hole-forming glass tube 2, but the average width of the gap is preferably 5 mm or less from the viewpoint of ease of manufacture and prevention of eccentricity.

  The core glass rod 8 is prepared as follows. First, a porous base material made of quartz, for example, containing Ge is synthesized by, for example, a VAD (Vapor-phase Axial Deposition) method. Next, the porous base material is dehydrated and vitrified in a chlorine-containing atmosphere. As a result, a glass rod having a region to be the core portion 1a containing Ge in the whole or in the central portion is formed. Next, the glass rods are set on both chucks of the processing lathe, the chucks are rotated in the same cycle, and the glass rods are heated by the oxyhydrogen flame burner, while the chucks and the oxyhydrogen flame burner are relatively moved. And the glass rod is stretched to a diameter of about 16 mm to obtain a core glass rod 8 having a length of about 80 mm. The stretching of the glass rod is not limited to the oxyhydrogen flame burner, but may be a method by heating in an electric furnace or a plasma flame. In the present embodiment, the glass rod having a cross-sectional refractive index distribution shape of a substantially rectangular shape (step index) is used. However, a pseudo rectangle (pseudo step index) or a Gaussian distribution shape having a slight skirt shape in the peripheral region. (Graded index having a refractive index distribution coefficient α of approximately 2) may be used.

  As described above, since the diameter of the core glass rod 8 is about 16 mm and the outer diameter of the hole forming glass tube 2 is about 40 mm, the ratio is about 1: 2, and the optical fiber preform 1 described above is used. The ratio is smaller than 1:13 to 1:20, which is the ratio of the diameter of the core portion 1a to the outer diameter of the cladding portion 1b. However, in the first embodiment, the difference in the ratio is eliminated by further forming the cladding outer peripheral portion 7 in the hole forming glass tube 2. Therefore, since the size of the optical fiber preform 1 is not limited by the size of the hole forming glass tube 2, the optical fiber preform 1 to be finally manufactured can be made large.

(Integration process)
Next, the integration process of step S106 will be described. In this integration step, the hole forming glass tube 2 in which the core glass rod 8 is inserted and the clad outer peripheral portion 7 is formed is heated, and the gap between the core glass rod 8 and the hole forming glass tube 2 is collapsed. Thus, the closed cells contained in the outer peripheral region 1bb formed from the outer peripheral portion 7 of the clad formed by using the semi-sintering method are extinguished while melting and integrating the two. As a heat source in this case, a heat source capable of supplying a sufficient amount of heat to eliminate closed cells, for example, an oxyhydrogen flame burner, a plasma flame burner, or an electric furnace can be used. Or the method of performing this integration process simultaneously with drawing can also be used. Thus, the optical fiber preform 1 shown in FIG. 1 or an optical fiber having the same cross-sectional structure is manufactured. At this time, the core glass rod 8 forms the core portion 1a, the hole forming glass tube 2 forms the inner peripheral region 1ba of the clad portion 1b, and the clad outer peripheral portion 7 forms the outer peripheral region 1bb.

  In addition, when the reduced pressure semi-sintering method is used as the semi-sintering method, since the gas is not substantially present in the closed cells, the closed cells can be more easily extinguished.

  Alternatively, the insertion step and the integration step of the core glass rod 8 may be performed on the hole forming glass tube 2 before the cladding outer peripheral portion 7 forming step, and then the cladding outer peripheral portion 7 forming step may be performed. . If necessary, after the integration step, the core glass rod 8 is integrated, but the cladding outer peripheral portion 7 is formed by heating and stretching the non-formed hole forming glass tube 2 to have a desired outer diameter. A clad outer peripheral portion 7 may be provided.

  Moreover, you may form the clad outer peripheral part 7 using a rod-in-tube method. In this case, for example, a cladding glass tube having the same material as the hole-forming glass tube 2 is prepared, and the hole-forming glass tube 2 after being integrated with the core glass rod is inserted therein, and the rod-in-tube method is used. To be integrated by heating and melting. Alternatively, in the same manner as in the integration step, when the hole-forming glass tube 2 and the core glass rod are integrated, the formation of the cladding outer peripheral portion 7 using the rod-in-tube method is simultaneously performed to form a hole structure. The optical fiber preform 1 for the optical fiber may be obtained, or the rod-in-tube method is used when the hole forming glass tube 2 and the core glass rod are integrated as in the integration step. The formation of the cladding outer peripheral portion 7 may be performed simultaneously with drawing to obtain a hole-structured optical fiber.

  It should be noted that the void forming glass tube 2 and the core glass rod 8 or the void formed between the hole forming glass tube 2 and the cladding glass tube in the drawing process as described above is depressurized and the hole is formed. Integration is performed while pressurizing the inside of the holes of the glass tube 2. Thereby, it is possible to prevent the gas such as the atmosphere existing in the gap from remaining as bubbles in the optical fiber while maintaining the shape of the holes. As a result, the manufactured optical fiber has no air bubbles at the boundary surface between the inner peripheral region and outer peripheral region of the cladding part or the boundary surface between the inner region of the cladding part and the core part, and therefore has high long-term reliability. It becomes.

(Connector for pressure increase / decrease)
Next, as a second embodiment of the present invention, a pressure increasing / decreasing connector for performing pressurization and depressurization in an integration step will be described.

  FIG. 10 is a schematic cross-sectional view showing a state where the pressure increasing / decreasing connector 10 according to the second embodiment is attached to the hole forming glass tube 2. As shown in FIG. 10, the hole forming glass tube 2 has an opening hole 2a and a hole 2b. A core glass rod 8 is inserted into the opening hole 2 a, and a gap G is formed between the core glass rod 8 and the opening hole 2 a of the hole forming glass tube 2. Further, the pressure increasing / decreasing connector 10 includes a connection member 11 and a cap nut 12 as a pressing member.

  The connection member 11 includes a fitting portion 11a for fitting the hole forming glass tube 2, a spiral portion 11b for screwing the cap nut 12, and a gas flow between the gap G and the hole 2b. Are formed in the annular projection 11c, the pressure communication holes 11d and 11f formed so as to communicate with the hole 2b, and the annular projection 11c, and communicate with the gap G. And a pressure-reducing communication hole 11h formed at the bottom. The pressurizing communication hole 11d is annular and communicates with all the holes 2b. Further, a part of the pressurizing communication hole 11f is formed by the supply pipe 11e, and a part of the pressure reducing communication hole 11h is formed by the intake pipe 11g. Further, the connection member 11 has a tip portion 11i having a wedge-shaped cross section.

  The connecting member 11 is preferably made of a material having an appropriate hardness so as to be elastically deformed by a force applied from the outside, for example, a plastic material containing Teflon (registered trademark). In addition, the connection member 11 may become a high temperature due to radiation heat or heat conduction from a collapse heating furnace, a drawing furnace, or a hole-forming glass tube, and thus a material having high heat resistance such as Viton (registered trademark) is used. More preferably, it is made of a polymer compound material.

  The cap nut 12 has the fitting part 12a formed so that it might fit with the front-end | tip part 11i by screwing. The cap nut 12 is preferably made of a relatively hard material because it is necessary to press the distal end portion 11i from the outside and bring the fitting portion 11a into close contact with the hole-forming glass tube. Since it may become high temperature by the radiant heat and heat conduction from a hole formation glass tube, what consists of a material with high heat resistance is preferable.

  The pressure increasing / decreasing connector 10 is used as follows. First, the connecting member 11 is fitted to the hole forming glass tube 2 by the fitting portion 11a. Next, the cap nut 12 is screwed into the spiral portion 11 b of the connection member 11 to be pressed from the outside of the connection member 11, and the connection member 11 is locked to the hole forming glass tube 2. Here, when the tip portion 11i having a wedge-shaped cross section is fitted into the fitting portion 12a of the cap nut 12, the tip portion 11i is pressed from the fitting portion 12a in a direction to be pressed against the hole forming glass tube 2. Receive. As a result, the airtightness between the connecting member 11 and the outer periphery of the hole forming glass tube 2 is further increased.

  Further, by screwing the cap nut 12, the annular protrusion 11 c of the connection member 11 is brought into close contact with the region between the opening hole 2 a and the hole 2 b of the hole forming glass tube 2. The region between the opening hole 2a and the hole 2b can be hermetically sealed, and the gas flow between the gap G and the hole 2b can be shielded. And the inside of the space | gap G can be pressure-reduced by suck | inhaling the gas in the space | gap G from the intake pipe 11g connected to the vacuum pump through the communication hole 11h for pressure reduction. At the same time, the inside of the hole 2b can be pressurized by supplying gas into the hole 2b from the supply pipe 11e connected to the gas supply pipe through the pressurizing communication holes 11d and 11f.

Note that the gas supplied to the pores 2b from the supply pipe 11e, it is possible to use for example air or Ar, an inert gas such as N _2. Further, the pressure-intensifying / depressurizing connector 10 can be attached and detached at every integration step and used many times.

Next, modified examples 1 to 4 of the connector for pressure increase / decrease will be described.
(Modification 1)
FIG. 11 is a schematic cross-sectional view showing a pressure-increasing / decreasing connector according to Modification 1. The pressurizing / decompressing connector 20 according to this modification 1 is different from the pressurizing / depressurizing connector 10 shown in FIG. 10 in that the connecting member 11 is replaced with a connecting member 21 and a seal ring 23 is provided. The point will be described.

  As with the connection member 11 shown in FIG. 10, the connection member 21 includes a fitting portion 21a, a spiral portion 21b, pressurizing communication holes 21d and 21f, a decompression communication hole 21h, a supply pipe 21e, and an intake pipe. Although it has 21g and the front-end | tip part 21i, it does not have a thing corresponding to the cyclic | annular protrusion part 11c of the connection member 11. FIG. The pressure increasing / decreasing connector 20 includes a flat seal ring 23 having substantially the same shape as that of the annular protrusion 11c. The decompression communication hole 21 h communicates with the gap G through the opening hole of the seal ring 23.

  A preferable material of the connection member 21 is the same as that of the connection member 11. It is desirable that the seal ring 23 has a material hardness that can cause necessary elastic deformation and plastic deformation in order to ensure airtightness. Moreover, it is preferable that it is a material with high heat resistance. As materials that can realize these, plastic materials including Teflon (registered trademark), polymer compound materials such as Viton (registered trademark), or relatively soft metal materials such as aluminum are applicable.

  The pressure increasing / decreasing connector 20 can be used in the same manner as the pressure increasing / decreasing connector 10. When the connecting member 21 is fitted to the hole forming glass tube 2, the seal ring 23 is disposed between the connecting member 21 and the hole forming glass tube 2. Next, by screwing the cap nut 12 into the spiral portion 21b of the connection member 21, the seal ring 23 is pressed between the opening hole 2a and the hole 2b of the hole forming glass tube 2 by being pressed by the connection member 21. Since it is in close contact with the region, the connection member 21 and the region between the opening hole 2a and the hole 2b of the hole forming glass tube 2 are hermetically sealed, and the gas flow between the gap G and the hole 2b is shielded. can do.

  In addition, when the connector 20 for pressure increase / decrease is attached / detached at every integration step, the seal ring 23 is deformed by pressing and releasing, so that shape deformation, material deterioration, scratches and the like are likely to occur. There is a possibility that airtightness cannot be maintained sufficiently. However, since the seal ring 23 can be easily replaced, it may be replaced when it deteriorates.

(Modification 2)
FIG. 12 is a schematic cross-sectional view showing a pressure increasing / decreasing connector according to Modification 2. The pressure increasing / decreasing connector 30 according to the second modification is different from the pressure increasing / decreasing connector 20 according to the first modification shown in FIG. 11 in that the seal ring 23 is replaced with a seal ring 33. The seal ring 33 is formed with a protruding portion that projects into the opening hole 2 a of the hole forming glass tube 2. As a result, the seal ring 33 is preferable because it has good fit to the hole-forming glass tube 2 and is less likely to cause unnecessary displacement.

(Modification 3)
FIG. 13 is a schematic cross-sectional view showing a pressure increasing / decreasing connector according to Modification 3. The pressure increasing / decreasing connector 40 according to Modification 3 is different from the pressure increasing / decreasing connector 30 according to Modification 2 shown in FIG. 12 in that the seal ring 33 is replaced with a seal ring 43. Since the seal ring 43 has a trapezoidal cross section and has a shape in which the outer diameter decreases downward, the seal ring 43 protrudes into the opening hole 2a of the hole forming glass tube 2. As a result, like the seal ring 33, the seal ring 43 has good fitability to the hole forming glass tube 2 and is preferably less likely to cause unnecessary displacement.

(Modification 4)
FIG. 14 is a schematic cross-sectional view showing a pressure increasing / decreasing connector according to Modification 4. The pressurizing / decompressing connector 50 according to Modification 4 includes a connecting member 51, a cap nut 52, and the same seal ring 23 as shown in FIG.

  As with the connecting member 21 shown in FIG. 11, the connecting member 51 includes a fitting portion 51a, a spiral portion 51b, pressurizing communication holes 51d and 51f, a pressure reducing communication hole 51h, a supply pipe 51e, and an intake pipe. 51g and a replaceable tip 51i having an annular shape with a wedge-shaped cross section. Further, the portion other than the tip 51i of the connection member 51 is made of, for example, a corrosion resistant metal (SUS304 or the like). On the other hand, the preferred material of the tip 51 i is the same as that of the seal ring 23. The tip 51i may be bonded to or separated from the connection member 51 as long as it is replaceable.

  The cap nut 52 has a fitting portion 52a formed so as to be engaged with the tip portion 51i by screwing. The cap nut 52 is made of a corrosion-resistant metal, for example.

  When the cap nut 52 is screwed together, the pressure-intensifying connector 50 can bring the outer peripheral surface of the hole-forming glass tube 2 into close contact with the connecting member 51 by the tip 51i, thereby realizing airtightness. ing.

  In addition, the connecting member 51 and the cap nut 52 are made of a material such as a corrosion-resistant metal that does not cause shape deterioration, and airtightness is realized by the tip 51i. When the tip 51i is attached / detached at each integration step, the tip 51i is subjected to deformation due to pressing and releasing, so that shape deformation, material deterioration, scratches and the like are likely to occur, and the airtightness cannot be sufficiently maintained as it is used. there is a possibility. However, since the tip 51i is replaceable, it is more economical because it is not necessary to replace other parts of the connector 50 for pressure increase / decrease even if deterioration or the like occurs.

  By the way, by using an extension / decompression extension tube as described below, if the compression / decompression connector is separated from the upper end of the hole-forming glass tube, by the radiant heat generated during heating in the integration step, It is possible to prevent or reduce deterioration of the pressure increasing / decreasing connector.

  FIG. 15 is a schematic view showing a state in which the pressure increasing / decreasing extension tube 60 is connected to the hole forming glass tube 2 constituting the hole forming glass tube 4. FIG. 16 is a schematic diagram showing a cross section along the front surface and the longitudinal direction of the pressurizing / depressurizing extension tube 60 shown in FIG. 15. Further, FIG. 17 is a schematic cross-sectional view showing a state where the pressure increasing / decreasing connector 10 shown in FIG. 10 is attached to the pressure increasing / decreasing extension pipe 60 shown in FIG.

  As shown in FIGS. 15 to 17, this pressurizing / depressurizing extension tube 60 includes an opening hole 60 a that communicates with the opening hole 2 a of the hole forming glass tube 2, and one piece that extends in the longitudinal direction and communicates with the hole 2 b. A through hole 60b and an annular annular recess 60c formed at one end and communicating with the through hole 60b are provided. Since the annular recess 60c is annular, the through hole 60b communicates with all the holes 2b.

  When using this pressure / decompression extension tube 60, as shown in FIG. 17, one end of this pressure / reduction extension tube 60 is welded and connected to the hole-forming glass tube 2, and the other end. The connector 10 for pressure increase / decrease is attached to. As a result, the pressurizing / depressurizing connector 10 can be separated from the hole-forming glass tube 2. Then, in this separated state, the inside of the opening hole 2a is decompressed by the intake pipe 11g from the decompression communication hole 11h of the pressurizing / decompressing connector 10 through the opening hole 60a, and for pressurization through the through hole 60b. The inside of the air hole 2b can be pressurized from the communication hole 11f by the supply pipe 11e. Note that the gas flow between the opening hole 2a and the hole 2b causes the annular protrusion formed between the annular recess 60c and the through hole 60b to be in close contact with the region between the opening hole 2a and the hole 2b. It is shielded by.

  Further, a dummy tube having the same hole structure as that of the hole forming glass tube 2 may be further connected to the side of the pressurizing / depressurizing extension tube 60 where the annular recess 60c is formed. In the case of using the pressure-extension / decompression extension tube 60 with the dummy tube, the dummy tube portion is cut after the use, and the pressure-reduction extension tube 60 is removed from the hole forming glass tube 2. If it does in this way, the structure where the annular recessed part 60c and the dummy pipe | tube of the extension pipe 60 for pressure increase / decrease were connected will remain in the extension pipe 60 side for pressure increase / decrease. Therefore, the pressure-increasing / depressurizing extension tube 60 with the dummy tube can be used again without re-forming a complicated structure such as the annular recess 60c in the pressure-increasing / depressurizing extension tube 60.

  Further, this pressure-intensifying extension pipe 60 may be used instead of the support pipe 5 shown in FIG. That is, in the connection step of the support tube, the support tube 5 is welded and connected to one end of both ends of the hole forming glass tube 2, and the pressurizing / depressurizing extension tube 60 is welded and connected to the other end. At this time, the hole 2b and the opening 2a of the hole-forming glass tube 2 are opened to the outside by the opening 60a of the pressure increasing / decreasing extension tube 60. Further, when the pressurizing / depressurizing extension pipe 60 is used instead of the support pipe 5, the pressurizing / depressurizing extension pipe 60 is used as it is without excising the pressurizing / depressurizing extension pipe 60, and the pressurizing / depressurizing in the integration process is performed. Also good.

  In the above embodiment, the case where the optical fiber preform and hole structure optical fiber to be manufactured are HAF has been described. However, the present invention is also applicable to the manufacture of other hole structure optical fibers and optical fiber preforms. It can be done.

  The present invention is not limited to the above embodiment. What combined suitably the component of said each embodiment and its modification is also contained in this invention.

DESCRIPTION OF SYMBOLS 1 Optical fiber base material 1a Core part 1b Clad part 1ba Inner circumference area 1bb Outer circumference area 1c Hole 2, 4 Hole formation glass tube 2a, 5a, 60a Open hole 2b Hole 5 Support pipe 7 Clad outer part 8 Core glass rod 10, 20, 30, 40, 50 Connector for pressure increase / decrease 11, 21, 51 Connection member 11a, 12a, 21a, 51a, 52a Fitting part 11b, 21b, 51b Spiral part 11c Annular projection part 11d, 11f, 21d, 51d Pressure communication hole 11e, 21e, 51e Supply pipe 11g, 21g, 51g, 51h Air intake pipe 11h, 21h Pressure reduction communication hole 11i, 21i, 51i Tip part 12, 52 Cap nut 23, 33, 43 Seal ring 60 For pressure reduction Extension tube 60b Through hole 60c Annular recess C Cutter G Gap S101 to S106 Steps

Claims (14)

An optical fiber preform manufacturing method for manufacturing a hole-structured optical fiber including a core portion and a cladding portion formed on an outer periphery of the core portion and having holes,
A hole forming glass tube preparation step of preparing a hole forming glass tube in which holes extending in the longitudinal direction are formed around the opening hole;
A clad outer peripheral portion forming step for forming a clad outer peripheral portion to be an outer peripheral region of the clad portion on the outer periphery of the hole forming glass tube;
An insertion step of inserting a core glass rod having a region to be a core portion into the pore-forming glass tube;
An integration step of heating the hole forming glass tube into which the core glass rod is inserted to integrate the core glass rod and the hole forming glass tube;
An optical fiber preform manufacturing method comprising:   The hole forming glass tube preparation step includes a step of preparing a glass tube, a step of providing the holes in the glass tube, and heating the glass tube provided with the holes to have a desired inner diameter and outer diameter. The method for producing an optical fiber preform according to claim 1, further comprising a drawing step of drawing.   The integration step is to perform integration while reducing the pressure in the gap formed between the core glass rod and the hole forming glass tube and pressurizing the hole in the hole forming glass tube. The method of manufacturing an optical fiber preform according to claim 1 or 2.   In the integration step, a connection member is fitted into the hole forming glass tube, the connection member is pressed and locked from the outside, and a gas flow between the gap and the hole is shielded. The pressure is reduced through the pressure reducing communication hole formed in the connection member so as to communicate with the gap and the pressure is applied through the pressure communication hole formed in the connection member so as to communicate with the hole. The method for manufacturing an optical fiber preform according to claim 3.   In the integration step, an extension / decompression extension tube in which a hole extending in the longitudinal direction is formed around the opening hole is formed in the hole forming glass tube. The opening hole of the extension tube is melt-connected so that the holes of the pressurizing / depressurizing extension tube communicate with the holes of the hole-forming glass tube independently of each other, and the melting connection of the pressurizing / depressurizing extension tube The connection member is fitted to the end opposite to the end, and the connection member is pressed and locked from the outside, and the gap and the hole-forming glass tube are interposed via the pressure-increasing / decreasing extension tube. In a state where the flow of gas between the holes is shielded, the pressure is reduced through a pressure reducing communication hole formed in the connecting member so as to communicate with the gap, and the hole forming glass tube communicates with the hole. So that pressure is applied through the pressurizing communication hole formed in the connecting member. Nau, method for manufacturing an optical fiber preform according to claim 3, characterized in that.   In the integration step, the annular protrusion formed on the connection member is formed between the opening hole and the hole of the hole forming glass tube or between the opening hole and the hole of the pressure increasing / decreasing extension tube. 6. The optical fiber preform according to claim 4, wherein a gas flow between the gap and the hole of the hole-forming glass tube is shielded by tightly adhering to the region. Production method.   In the integration step, the seal ring is brought into tight contact with an area between the opening hole and the hole of the hole forming glass tube or an area between the opening hole and the hole of the pressure increasing / decreasing extension tube to be airtight. 6. The method for manufacturing an optical fiber preform according to claim 4, wherein gas flow between the gap and the hole of the hole-forming glass tube is shielded.   In the cladding outer peripheral portion forming step, a porous glass fine particle layer formed by an external method is deposited on the outer peripheral surface of the hole forming glass tube, and the porous glass fine particle layer is semi-sintered using a semi-sintering method. The method for manufacturing an optical fiber preform according to any one of claims 1 to 7, wherein the method is performed.   The method for manufacturing an optical fiber preform according to any one of claims 1 to 8, wherein the cladding outer peripheral portion forming step is performed prior to the integration step.   The method for manufacturing an optical fiber preform according to any one of claims 1 to 8, wherein the cladding outer periphery forming step is performed after the integration step. A method of manufacturing a hole-structured optical fiber comprising a core part and a cladding part formed on the outer periphery of the core part and having holes,
A hole forming glass tube preparation step of preparing a hole forming glass tube in which holes extending in the longitudinal direction are formed around the opening hole;
A clad outer peripheral portion forming step for forming a clad outer peripheral portion to be an outer peripheral region of the clad portion on the outer periphery of the hole forming glass tube;
An insertion step of inserting a core glass rod having a region to be a core portion into the pore-forming glass tube;
An integration step of heating the hole forming glass tube into which the core glass rod is inserted to integrate the core glass rod and the hole forming glass tube;
Prior to the insertion step and the integration step, the cladding outer peripheral portion forming step deposits a porous glass fine particle layer formed by an external method on the outer peripheral surface of the hole forming glass tube, and the porous glass fine particles By semi-sintering the layer using a semi-sintering method,
The integration step is performed simultaneously with the drawing of the hole-structured optical fiber by using the drawing furnace and the hole-forming glass tube formed with the semi-sintered clad outer peripheral portion and the core glass rod. A method for manufacturing a hole-structured optical fiber, which is characterized. A connector for pressure increase / decrease used in the method for manufacturing an optical fiber preform according to any one of claims 3 to 11,
A fitting portion for fitting into the hole forming glass tube or the pressure increasing / decreasing extension tube, a pressure reducing communication hole formed to communicate with the gap, and a hole in the hole forming glass tube or The pressurizing communication hole formed so as to communicate with the hole of the pressurizing / depressurizing extension pipe, and the region between the hole forming glass pipe or the opening hole of the pressurizing / depressurizing extension pipe and the hole An annular protrusion for shielding the gas flow between the gap and the hole of the hole-forming glass tube, and a connecting member,
A pressing member for pressing and locking the connecting member from the outside;
A connector for pressurizing and depressurizing, comprising: A connector for pressure increase / decrease used in the method for manufacturing an optical fiber preform according to any one of claims 3 to 11,
A fitting portion for fitting into the hole forming glass tube or the pressure increasing / decreasing extension tube, a pressure reducing communication hole formed so as to communicate with the gap, and a hole communicating with the hole. A connecting member having a communication hole for pressurization,
A pressing member for pressing and locking the connecting member from the outside;
The gap and the void-forming glass tube are made in close contact with a region between the opening hole of the hole-forming glass tube and the hole of the hole-forming glass tube or the hole of the extension / decompression extension tube. A seal ring for shielding the flow of gas between the holes;
A connector for pressurizing and depressurizing, comprising:   The connection member has a spiral portion formed on an outer periphery and a tip portion having a wedge shape in cross section, and the pressing member is screwed into the spiral portion, and the tip portion is fitted into the tip portion. The connector for pressure increasing / decreasing according to claim 12 or 13, wherein the connector is a cap nut having a fitting portion for applying a stress to press the portion against the hole forming glass tube or the pressure increasing / decreasing extension tube.

Images