JP2016011249A - Production method of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of an optical fiber preform which can suppress deformation and breakage of a rod-like member arranged in an outer part of a molding die by using the hydrostatic molding method.SOLUTION: A production method of an optical fiber preform includes a first step of putting rod-like members at positions, excluding the center of the cross section of a molding die vertical in the longitudinal direction, along the direction perpendicular to the cross section in the molding die of a specified shape, a step of filling the molding die with a powder material containing silica and a step of applying a hydrostatic pressure to the molding die, and the rod-like member is movable toward the center of the cross section of the molding die by a specified distance during application of the hydrostatic pressure.

Description

  The present invention relates to a method for manufacturing an optical fiber preform.

  As a manufacturing method of a multi-core fiber preform, a drill method, a stack & draw method, and the like are known. The drill method is a method in which holes are formed in a rod-shaped base material with a drill, and a core glass rod is inserted into the holes. The stack and draw method is a method in which a plurality of core glass rods and clad glass rods are inserted into a clad glass tube, and heated and stretched to integrate them.

  However, in the drill method, since holes are formed in the rod-shaped base material by a drill, there is a problem that the processing cost is high and the cost is high. Further, in the stack and draw method, since the core glass rod and the clad glass rod are inserted into the clad glass tube and heated and stretched, there is a problem that the position accuracy of the core is lowered.

  As a method for manufacturing an optical fiber preform, for example, as shown in Patent Documents 1 to 6, a hydrostatic pressure forming method has been devised.

  In the isostatic pressing method, a rod-shaped glass material for a core is installed in a mold having elasticity, and after filling glass powder around the core, hydrostatic pressure is applied to the mold from the outside, and the outer periphery of the rod-shaped glass material is applied. This is a method of compression-forming a porous glass body.

  The hydrostatic pressure molding method can achieve high molding accuracy and reliability, and at the same time has low production cost, and is excellent in mass productivity. Moreover, since it can form in a desired porous glass body shape easily by changing a shaping | molding die, there exists an advantage that the freedom degree of design is high.

JP-A-5-58656 Japanese Patent Laid-Open No. 5-254872 JP-A-5-254857 Japanese Patent Laid-Open No. 5-229839 Japanese Patent Laid-Open No. 6-51139 JP-A-9-71431

  However, it has been found that when a multi-core fiber is manufactured by applying the hydrostatic pressure forming method, deformation or breakage may occur in a rod-shaped glass material installed outside the center in the mold. This is because, as a result of the mold being elastically deformed by the application of hydrostatic pressure, stress is applied to the rod-shaped glass material disposed in the mold in the center direction of the mold.

  The present invention has been made in view of such problems, and in a method of manufacturing an optical fiber preform using an isostatic pressing method, it is possible to suppress deformation and breakage of a rod-shaped member arranged in a mold. The object is to provide a method of manufacturing an optical fiber preform.

  In order to achieve the above object, a method for manufacturing an optical fiber preform according to an aspect of the present invention removes the center of a cross section perpendicular to the longitudinal direction of a mold in a mold having a predetermined shape. A first step of installing a rod-shaped member at a position along a direction perpendicular to the cross section; a second step of filling a powder material containing silica into the mold; and a hydrostatic pressure applied to the mold. The rod-shaped member can be moved by a predetermined distance toward the center of the cross section of the mold during application of the hydrostatic pressure.

  In order to achieve the above object, an apparatus for manufacturing an optical fiber preform according to an aspect of the present invention is an apparatus including a forming cylinder, an upper lid body, and a lower lid body. The upper lid body and the lower lid body are provided with grooves for installing the upper and lower ends of the rod-shaped member in the molding cylinder, and the grooves are arranged in the radial direction of the cross section perpendicular to the longitudinal direction of the molding cylinder. It has a length obtained by adding a predetermined distance to the outer diameter.

  According to the present invention, in the method for manufacturing an optical fiber preform using the hydrostatic pressure molding method, there is an effect that deformation and breakage of the rod-shaped member arranged in the mold can be suppressed.

It is a cross-sectional view of a multi-core fiber preform according to an embodiment of the present invention. It is a schematic diagram of (a) center member arrange | positioned at the center part of the shaping | molding die concerning embodiment of this invention, and (b) the outer member arrange | positioned at the outer side part of a shaping | molding die. It is a schematic diagram which shows the structure of the shaping | molding die which concerns on 1st embodiment of this invention. It is a schematic diagram which shows (a) cross-sectional structure and (b) longitudinal cross-sectional structure of the upper lid body for shaping | molding which concerns on 1st embodiment of this invention. It is a schematic diagram which shows (a) cross-sectional structure and (b) longitudinal cross-sectional structure of the molding lower cover body which concerns on 1st embodiment of this invention. It is a flowchart which shows the manufacturing process of the optical fiber core preform which concerns on embodiment of this invention. It is a schematic diagram which shows arrangement | positioning of the center member to the lower cover body for shaping | molding of the shaping | molding die which concerns on embodiment of this invention. It is a schematic diagram which shows arrangement | positioning of the outer member to the lower cover body for shaping | molding of the shaping | molding die which concerns on embodiment of this invention. It is sectional drawing which shows arrangement | positioning of the outer member to the lower cover body for shaping | molding of the shaping | molding die which concerns on 1st embodiment of this invention. It is a schematic diagram which shows filling of the granulated powder in the cylinder for shaping | molding of the shaping | molding die concerning embodiment of this invention. It is a schematic diagram which shows fitting to the upper part of the shaping | molding die of the upper cover body for shaping | molding which concerns on embodiment of this invention. It is a schematic diagram which shows the application of the hydrostatic pressure to the shaping | molding die containing a center member, an outer side member, and granulated powder using the hydrostatic pressure shaping | molding apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the state of the shaping | molding die containing a center member, an outer side member, and granulated powder in the application of the isostatic pressure by the isostatic pressing apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the molded object shape | molded by the isostatic pressing apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the structure of the shaping | molding die concerning 2nd embodiment of this invention. It is a schematic diagram which shows (a) cross-sectional structure and (b) longitudinal cross-sectional structure of the top lid body for shaping | molding which concerns on 2nd embodiment of this invention. It is a schematic diagram which shows (a) cross-sectional structure and (b) longitudinal cross-sectional structure of the lower lid body for shaping | molding which concerns on 2nd embodiment of this invention. It is a schematic diagram which shows the cross-sectional structure of another glass forming mother body which concerns on 2nd embodiment of this invention. It is a schematic diagram which shows the cross-sectional structure of another upper cover body for shaping | molding which concerns on 2nd embodiment of this invention, and a lower cover body for shaping | molding. It is a figure which shows the graph of the measurement result of the outer diameter in one Example of this invention. It is a figure which shows the graph of the measurement result of the distance between core rods in one Example of this invention. It is a schematic diagram which shows the manufacturing method of the optical fiber preform which concerns on 3rd embodiment of this invention. It is a schematic diagram which shows the manufacturing method of the optical fiber preform which concerns on 3rd embodiment of this invention. It is a cross-sectional view of the molded object which concerns on 4th embodiment of this invention. It is the side view and cross-sectional view of the center member and outer member which concern on 5th embodiment of this invention. It is a figure which shows the graph of the result of having measured the distance between cores of the optical fiber which concerns on 5th embodiment of this invention. It is the longitudinal cross-sectional view and cross-sectional view of the molded object which concern on 6th embodiment of this invention. It is a cross-sectional view of the molded object which concerns on 6th embodiment of this invention. It is a cross-sectional view of the molded object which concerns on 7th embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

[First embodiment]
Hereinafter, an example of manufacturing a multi-core fiber preform that is an optical fiber preform will be described as a first embodiment of the present invention.

  As shown in FIG. 1, the multi-core fiber preform 10 includes a central core portion 1a provided on the central axis of the multi-core fiber preform 10 and a plurality (8 in FIG. 1) provided on the outer periphery of the central core portion 1a. The outer peripheral core portion 1b and the clad portion 3 formed on the outer periphery of the core portions 1a and 1b. The clad part 3 is made of, for example, pure quartz glass to which a dopant for adjusting the refractive index is not added. Each of the central core portion 1a and the outer peripheral core portion 1b includes a core 11 and a clad 13 provided on the outer periphery of the core 11.

  Next, the manufacturing method of the multi-core fiber preform 10 and the manufacturing method of the multi-core fiber according to the first embodiment of the present invention will be described.

2 is a cross-sectional view of a rod-shaped member disposed in a mold according to an embodiment of the present invention, and FIG. 2A is a central member 1a that is a rod-shaped member disposed at the center of the mold, FIG. These are sectional drawings of the outside member 1b which is a rod-shaped member arrange | positioned outside with respect to the center part of a shaping | molding die. The central member 1a has an optical fiber core rod made of, for example, quartz, and an upper dummy rod 15 and a lower dummy rod 17 connected to the upper and lower sides of the core rod, respectively. Upper dummy rod 15 and the lower dummy rod 17 is made of, for example, quartz has a respective outer diameter _{d 15} and _{d 17.} The core rod has a core 11 and a clad 13 surrounding the core 11, and has a cylindrical shape extending in one direction. The core 11 is made of, for example, quartz glass having a high refractive index doped with germanium or the like, or quartz glass having a desired refractive index distribution formed by a plurality of dopants such as germanium and fluorine. The clad 13 is a quartz glass that constitutes a part of the central member 1a, and is made of, for example, pure quartz glass to which a dopant for adjusting the refractive index is not added.
The core rod can be manufactured using a known method such as VAD (Vapor Phase Axial Deposition), OVD (Outside Vapor Deposition), or MCVD (Modified Chemical Vapor Deposition).

The outer member 1 b is an optical fiber core rod made of, for example, quartz, and includes a core 11 and a clad 13. Cladding 13 has an outer diameter _{d 13.} The core 11 is made of, for example, quartz glass having a high refractive index doped with germanium or the like, or quartz glass having a desired refractive index distribution formed by a plurality of dopants such as germanium and fluorine. The clad 13 is a quartz glass that constitutes a part of the central member 1a, and is made of, for example, pure quartz glass to which a dopant for adjusting the refractive index is not added.
In this embodiment, a core rod having a core 11 and a clad 13 is used as the center member 1a and the outer member 1b. However, the present invention is not limited to this. Those having the role of a marker for identifying the mark may be used. Further, the cores 11 of the central member 1a and the outer member 1b may be all the same, or all or some of the cores may be different.

Outer diameter _{d 13} of the cladding 13, for example, it may be about 5 mm. Moreover, the length of the core rod used for the center member 1a and the outer member 1b can be about 500 mm, for example. The length of the core rod for use in the outer diameter d ₁₃ and central member 1a and the outer member 1b of the cladding 13, may be designed arbitrarily depending on the structure and the base material dimensions of the multi-core fiber to be manufactured to these numerical values It is not limited. As an alternative, the center member 1a and the outer member 1b can be made of metal, carbon, or ceramics.

  FIG. 3A is a perspective view showing the structure of the mold 2 according to the first embodiment of the present invention, and FIG. 3B is a front view showing the structure of the mold 2. The molding die 2 includes a molding cylinder 21, a molding upper lid body 23, and a molding lower lid body 25. The molding cylinder 21 is made of a material having elasticity and shrinkage. For example, a synthetic rubber material such as chloroprene rubber or a synthetic resin material such as polyurethane can be used. Moreover, the molding upper lid body 23 and the molding lower lid body 25 are made of metal or a material such as rubber or synthetic resin having the same degree of rigidity as that of metal, and for example, stainless steel can be used. In this embodiment, the mold 2 is illustratively a cylindrical structure, but the present invention is not limited to a cylindrical shape. In the isostatic pressing method, the shape of the molded body to be easily manufactured can be changed by changing the shape of the mold. For example, when it is desired to form a shape having a rectangular cross section, the present invention can be applied by preparing a mold that conforms to the shape. Moreover, the dimension of the shaping | molding die 2 can be about 45 mm in internal diameter and about 500 mm in length, for example. The dimensions of the mold can be arbitrarily designed according to the dimensions of the multi-core fiber preform, and are not limited to these numerical values.

4A is a cross-sectional structure taken along the line AA of the molding upper lid body 23 according to the first embodiment of the present invention, and FIG. 4B is a longitudinal section taken along the line BB of the molding upper lid body 23. It is a schematic diagram which shows a surface structure. As shown in the figure, the molding upper lid 23 has a center groove 233 for fitting the upper dummy rod 15 of the center member 1a at the center, and an outer groove for disposing the outer member 1b outside the center member 1a. 235. The central groove 233 is circular in cross section and has an inner diameter _d233 . The outer groove 235 is provided in an annular shape centering on the center of the molding upper lid, and has a groove width w ₂₃₅ .

Fig.5 (a) is a cross-sectional structure in CC line of the lower lid body 25 for shaping | molding which concerns on 1st embodiment of this invention, FIG.5 (b) is a schematic which shows the longitudinal cross-sectional structure in BB line. FIG. As shown in the figure, the molding lower lid 25 has a center groove 253 for fitting the lower dummy rod 17 of the center member 1a at the center and an outer member 1b for disposing the outer member 1b outside the center member 1a. It has a side groove 255. The central groove 253 is circular in cross section and has an inner diameter _d253 . The outer groove 255 is provided in an annular shape centering on the center of the molding upper lid, and has a groove width w ₂₅₅ .

The upper dummy bar 15 of the center member 1 a is fitted into the center groove 233 at the center of the molding upper lid body 23. Further, the lower dummy rod 17 of the center member 1 a is fitted into the center groove 253 in the center portion of the molding lower lid body 25. Therefore, the outside diameter _{d 15} of the upper dummy rod 15 is slightly smaller than the inner diameter _{d 233} of the central channel 233, the outside diameter _{d 17} of the lower dummy rod 17 is slightly smaller than the inner diameter _{d 253} of the central groove 253. Therefore, the center member 1a is fixed to the molding upper lid body 23 and the molding lower lid body 25 by fitting the upper dummy bar 15 and the lower dummy bar 17 into the central groove 233 and the central groove 253, respectively. In order to prevent a positional shift while fixing the central member 1a, the clearance between the dummy bar and the central groove is preferably 0 mm to the inner diameter of the mold 2 × 0.01 mm.

  Next, the manufacturing process of the optical fiber preform according to the present invention will be described with reference to FIGS. 6 and 7A to 7G.

  FIG. 6 is a flowchart showing the manufacturing process of the optical fiber preform according to the present invention.

  First, in step S301, as shown in FIG. 7A, the central member 1a is placed on the molding lower lid body 25 of the molding die 2. Specifically, the lower dummy rod 17 of the center member 1 a is fitted into the center groove 253 at the center of the molding lower lid body 25.

Next, in step S303, as shown in FIG. 7B, the outer member 1b is disposed on the molding lower lid body 25 of the molding die 2. Specifically, the lower end of the outer member 1 b is disposed at the initial position of the outer groove 255 of the molding lower lid body 25. As shown in FIG. 7C, in the outer groove 255, the outer member 1b is arranged in an arbitrary number of 1 or more (here, 8).
At this time, the outer member 1b is disposed, for example, such that the distance from the central member 1a is equal and the distance between adjacent outer members 1b is equal. At this time, the distance between the center member 1a and the outer member 1b is preferably determined in consideration of volume shrinkage in a sintering process described later.

  As described above, when the outer groove 255 is provided in an annular shape centering on the center portion of the molding lower lid body 25, an arbitrary plurality of outer members 1b can be disposed as shown in FIG. 7C. That is, a desired number of outer members 1b can be disposed at desired positions along the outer grooves 255. Therefore, it is possible to produce optical fibers with different designs using the same mold 2.

  Here, the initial position is a position in the outer groove 255 where the lower end of the outer member 1b should be disposed before application of hydrostatic pressure. For example, the lower end side surface of the outer member 1b and the outer side surface of the outer groove 255 are in contact with each other. Position. Thus, when the outer member 1b is arranged at the initial position, a gap is generated between the inner side surface of the outer groove 255 and the outer member 1b. This gap allows the outer member 1b to move toward the center of the mold 2 when applying hydrostatic pressure.

  Next, in step S305, as shown in FIG. 7D, the granulated powder 41, which is a powder material, is filled into the molding cylinder 21 of the molding die 2. At this time, from the viewpoint of uniformity of the powder filling density, it is desirable to place the molding die 2 on an electromagnetic vibration type sieving device and to fill the granulated powder 41 while applying vibration to the molding die 2.

  The granulated powder 41 is a material for forming a porous glass body, and is mainly composed of primary particles of quartz glass powder (hereinafter simply referred to as glass powder). As this glass powder, for example, one having a high purity and usually having a particle size of about 0.01 μm to 100 μm is used. Although the smaller the particle size of the glass powder, the smaller the mass transfer distance during sintering, it is advantageous. However, when performing heat treatment (dehydration / purification) in an atmosphere containing chlorine gas, the particle size of the glass powder Is too small, chlorine gas cannot diffuse into the porous base material, and thus there is a possibility that the effect of the heat treatment cannot be obtained sufficiently. Therefore, it is desirable that the glass powder has a particle size that is large enough to form a pore size that allows chlorine gas to diffuse into the porous base material. Therefore, the particle size of the glass powder is preferably 8 μm to 12 μm from the viewpoint of diffusion of chlorine gas in the dehydration / purification process, strength of the molded body, and the like. Moreover, you may mix or add shaping | molding adjuvants, such as a binder and a plasticizer, to glass powder. As the binder, polyvinyl alcohol (PVA) can be used, and as the plasticizer, glycerin or the like can be used.

  The ratio of the glass powder, the binder, and the plasticizer is preferably 100: 1 to 10: 0 to 5 from the viewpoint of moldability, and can be, for example, about 100: 3: 1. Next, a solvent is added to the glass powder and stirred to make the glass powder into a mud. As the solvent, an aqueous system is preferable in consideration of the influence on the environment, and pure water is preferable from the viewpoint of purity. Next, the produced slurry-like glass is spray-dried to form a granulated powder (secondary particles) in which a plurality of primary particles are aggregated, and a granulated powder 41 having a particle size of 50 μm to 150 μm is generated. be able to. In addition, when the particle size of the granulated powder 41 is 50 μm to 150 μm, there is an advantage that the fluidity at the time of filling the mold is increased and the filling is facilitated while taking advantage of the primary particles.

  Next, in step S307, as shown in FIG. 7E, the molding upper lid body 23 is fitted to the upper part of the molding die 2 in order to seal the molding die 2. Specifically, the upper dummy rod 15 of the center member 1a is fitted into the center groove 233 at the center of the molding upper lid 23, and at the same time, the upper end of the outer member 1b is at the outer portion of the molding upper lid 23. It is installed at the initial position of the outer groove 235.

  The initial position here is a position in the outer groove 235 where the upper end of the outer member 1b should be arranged before application of the hydrostatic pressure, as in step S303, for example, the upper end side surface and the outer groove 235 of the outer member 1b. It is the position where the outer side surface of the contact. When the outer member 1b is thus arranged at the initial position, a gap is generated between the inner side surface, which is the other side surface of the outer groove 235, and the outer member 1b. This gap allows the outer member 1b to move toward the center of the mold 2 when applying hydrostatic pressure.

  The central member 1a is applied with hydrostatic pressure in a state where the upper and lower ends are fixed to the molding upper lid body 23 and the molding lower lid body 25, respectively. However, according to the hydrostatic pressure molding method, the pressure applied in the mold 2 is applied to the center of the mold 2 with a constant magnitude. For this reason, the pressure which causes the breakage and the deformation applied to the center member 1a arranged at the center of the mold 2 is small, for example, the pressure which bends the center member 1a to one side in the outer diameter direction.

  Next, in step S309, as shown in FIG. 7F, hydrostatic pressure is applied to the mold 2 including the center member 1a, the outer member 1b, and the granulated powder 41 using a hydrostatic pressure molding (CIP) device 43. . Specifically, the pressure medium 45 is introduced into the CIP device 43 in which the molding die 2 is installed, and the pressure in the CIP device 43 is increased to a predetermined pressure, for example, about 98 MPa (20 MPa to 294 MPa). This state is maintained for a predetermined time, for example, about 1 minute (0.5 to 10 minutes). In this manner, a silica molded body can be formed on the outer periphery of the center member 1a and the outer member 1b. In general, water or lubricating oil to which a corrosion inhibitor is added is used as the pressure medium 45, but other liquids may be used instead.

When a hydrostatic pressure is applied to the mold 2 in step S309, the molding cylinder 21 made of an elastic material is deformed toward the center of the mold 2 by the hydrostatic pressure, as shown in FIG. 7G.
If the outer member 1b is completely fixed, an event that the outer member 1b bends toward the center of the mold 2 due to the deformation of the molding cylinder 21 occurs, and the outer member 1b is deformed or damaged. Sometimes.

  However, in the molding die 2, between the inner side surface of the outer groove 235 of the molding upper lid body 23 and the outer member 1b, and between the inner side surface of the outer groove 255 of the molding lower lid body 25 and the outer member 1b. Has a gap, and the outer member 1b can move toward the center of the mold 2 when a hydrostatic pressure is applied. Therefore, it can suppress that the pressure which makes it bend in the center direction of the shaping | molding die 2 is applied to the outer member 1b.

  Next, in step S311, the pressure in the CIP device 43 is gradually reduced to take out the molding die 2 from the CIP device 43, and after taking out the molding as shown in FIG. 7H from the molding die 2, the molding is removed. Moisture and binder are removed and degreased by exposure to a predetermined temperature, for example, about 500 ° C. (400 ° C. to 800 ° C.) in a dry atmosphere for a predetermined time, for example, about 5 hours (1 hour to 10 hours). Finally, in step 313, dehydration, purification, and sintering processes are performed. As a result, the molded body becomes the multi-core fiber preform 10 shown in FIG. Specifically, the central member 1a of the molded body corresponds to the central core portion 1a of the multi-core fiber preform 10, and the outer member 1b of the molded body corresponds to the outer peripheral core portion 1b of the multi-core fiber preform 10. The granulated powder 41 corresponds to the clad portion 3 of the multi-core fiber preform 10. An optical fiber is manufactured by performing a drawing process on the multi-core fiber preform 10 (optical fiber preform) manufactured in this way.

  Hereinafter, the size of the gap between the inner side surface of the outer groove 235 of the upper lid body 23 for molding and the outer member 1b and the size of the gap between the inner side surface of the outer groove 255 of the lower lid body 25 for molding and the outer member 1b is preferable. The range will be described in more detail.

When the outer member 1b is disposed at a position where the upper and lower end side surfaces of the outer member 1b as the initial position are in contact with the outer groove 235 of the molding upper lid body 23 and the outer side surface of the outer groove 255 of the molding lower lid body 25. A gap is generated between the inner side surface of the outer groove 235 of the upper lid body 23 and the outer member 1b, and between the inner side surface of the outer groove 255 of the molding lower lid body 25 and the outer member 1b.
At this time, as described in FIG. 7B to FIG. 7E, the distance between the inner side surface of the outer groove 235 and the outer groove 255 and the outer member 1b is a distance α. That is, the groove width w ₂₃₅ of the outer groove 235 of the molding upper lid body 23 and the groove width w ₂₅₅ of the outer groove 255 of the molding lower lid body 25 are a distance α greater than the outer diameter d ₁₃ of the cladding 13 in the outer member 1b. Only big. In other words, the outer groove 235 and the outer groove 255 are arranged so that the outer diameter d ₁₃ (outer member 1b) of the outer member 1b extends in the center direction of the cross section of the mold 2 (that is, the radial direction of the cross section perpendicular to the longitudinal direction of the mold 2). When is not cylindrical, it has a length obtained by adding a distance α to the length along the center of the cross section.

The distance α is preferably substantially the same value as the maximum distance that the outer member 1b can move in the central direction along with the application of hydrostatic pressure, or a value that is larger than the maximum distance.
Thereby, when the outer member 1b is disposed at the initial position of the mold 2, the outer member 1b can move in the center direction of the mold 2 up to a distance α during application of the hydrostatic pressure.

For example, the distance α is preferably greater than or equal to the maximum value of the deformation amount of the molding cylinder 21 in the direction of the central axis of the molding cylinder 21 during application of hydrostatic pressure. However, in practice, the deformation amount of the molding cylinder 21 and the gap distance α are not necessarily equivalent. This is because, as the initial position of the outer member 1b is closer to the center of the molding cylinder 21, the amount of movement of the outer member 1b becomes smaller under general conditions. Therefore, the distance α can be designed to be shorter than the deformation amount of the molding cylinder 21 in consideration of the initial position of the outer member 1b.
The specific distance α is obtained by preliminary experiments or simulations based on, for example, the elastic deformation amount of the mold 2 and the characteristics of the granulated powder 41 (material used for molding the porous glass body).

  By setting the size of the gap to the distance α, the outer member 1b can move a distance α or less toward the center direction even during application of hydrostatic pressure. Thereby, even when the forming cylinder 21 is deformed by the hydrostatic pressure, the outer member 1b can be prevented from being bent by the applied pressure, and the outer member 1b can be prevented from being damaged or deformed by the hydrostatic pressure molding method. it can. Thereby, an optical fiber can be produced without causing deformation or breakage of the outer member 1b.

  In addition, when the moving distance of the outer member 1b assumed by application of hydrostatic pressure is less than the distance α, the side surface of the outer member 1b and the outer side surface of the outer groove 255 are not necessarily in contact with each other. That is, a desired position that can secure the assumed moving distance can be set as the initial position of the outer member 1b.

[Second Embodiment]
An example of producing a multi-core fiber preform that is an optical fiber preform will be described below as a second embodiment of the present invention.

  The second embodiment of the present invention is the same as the first embodiment of the present invention except for the shapes of the outer grooves of the upper lid body for molding and the lower lid body for molding. Therefore, the overlapping description is omitted here.

  FIG. 8A is a perspective view showing the structure of the mold 5 according to the embodiment of the present invention, and FIG. 8B is a front view showing the structure of the mold 5. The molding die 5 includes a molding cylinder 51, a molding upper lid body 53, and a molding lower lid body 55. The molding upper lid body 53 and the molding lower lid body 55 are made of a metal such as aluminum or a material such as rubber or synthetic resin having the same degree of rigidity as the metal. In the present embodiment, the mold 5 is illustratively a cylindrical structure, but the present invention is not limited to a cylindrical shape. As described above, in the isostatic pressing method, the shape of the molded body can be easily changed by changing the shape of the mold. For example, when it is desired to form a shape having a rectangular cross section, the present invention can be applied by preparing a mold that conforms to the shape. The dimensions of the mold 5 can be about 45 mm in inner diameter and about 500 mm in length. The dimensions of the mold can be arbitrarily designed according to the dimensions of the multi-core fiber preform, and are not limited to these numerical values.

FIG. 9A is a schematic cross-sectional structure taken along the line D-D of the molding upper lid 53 according to the second embodiment of the present invention, and FIG. 9B is a schematic view showing a vertical cross-sectional structure taken along the line EE. It is. As shown in the figure, the molding upper lid 53 has a center groove 533 for fitting the upper dummy rod 15 of the center member 1a at the center, and a plurality of (outside members 1b for arranging the outer member 1b outside the center member 1a). Here, the outer groove 535 of 8) is provided. The central groove 533 is circular in cross section and has an inner diameter d ₅₃₃ . Each of the outer grooves 535 has a length ₅₃₅ in the radial direction of the mold 5, a width in the circumferential direction of the outer side of the mold 5 is l ₅₃₅ , and the cross section thereof is at both ends in the radial direction of the mold 5. The part is semicircular and is an oval having a constant width in the circumferential direction.

Fig.10 (a) is a cross-sectional structure in the FF line of the shaping | molding lower cover body 55 which concerns on 2nd embodiment of this invention, and is a schematic which shows the longitudinal cross-sectional structure in FIG.10 (b) EE line FIG. As shown in the figure, the molding lower lid body 55 has a center groove 553 for fitting the lower dummy rod 17 of the center member 1a at the center and an outer member 1b for placing the outer member 1b outside the center member 1a. A side groove 555 is provided. The central groove 553 is circular in cross section and has an inner diameter _d553 . Each of the outer grooves 555 has a length of the mold 5 in the radial direction of w ₅₅₅ and a width of the mold 5 in the circumferential direction of 1 _555. It is a semicircle and is an oval with a constant width in the circumferential direction.
At this time, the outer groove 555 is disposed so that, for example, the distance from the center groove 553 is equal, and the distance between adjacent outer grooves 555 is equal. At this time, the distance between the center groove 553 and the outer groove 555 is preferably determined in consideration of volume shrinkage in a sintering process described later.
Although an example in which a plurality of outer grooves 535 and 555 are provided is shown here, one outer groove 535 and 555 may be provided.

Similar to the first embodiment of the present invention, the upper dummy bar 15 of the center member 1 a is fitted into the center groove 533 in the center of the molding upper lid 53. Further, the lower dummy rod 17 of the center member 1 a is fitted into the center groove 553 in the center portion of the molding lower lid body 55. Therefore, the outside diameter _{d 15} of the upper dummy rod 15 is slightly smaller than the inner diameter _{d 553} of the central channel 533, the outside diameter _{d 17} of the lower dummy rod 17 is slightly smaller than the inner diameter _{d 553} of the central groove 553. Therefore, the center member 1a is fixed to the molding upper lid 53 and the molding lower lid 55 by fitting the upper dummy bar 15 and the lower dummy bar 17 into the central groove 533 and the central groove 553, respectively.
In order to prevent a positional shift while fixing the central member 1a, the clearance between the dummy rod and the central groove is preferably 0 mm to the inner diameter of the mold 5 × 0.01 mm.

  The central member 1a is applied with hydrostatic pressure with the upper and lower ends fixed to the molding upper lid 53 and the molding lower lid 55, respectively. However, according to the isostatic pressing method, the pressure applied in the mold 5 is applied to the center of the mold 5 with a constant magnitude. For this reason, the pressure applied to the center member 1a disposed at the center of the mold 5 that causes damage or deformation, for example, the pressure that bends the center member 1a in one direction in the outer diameter direction is small.

In this embodiment, one outer member 1b is fitted in each of the outer grooves 535 and 555. The upper end of the outer member 1 b is disposed in the outer groove 535 in the outer portion of the molding upper lid 53. Further, the lower end of the outer member 1 b is disposed in the outer groove 555 in the outer portion of the molding lower lid body 55. Here, the circumferential width _{l 555} of width _{l 555} and outer grooves 555 in the circumferential direction of the outer groove 535 is slightly larger than the outer diameter _{d 13} of the outer member 1b. Therefore, by fitting the outer member 1b into the outer groove 535 and the outer groove 555, the movement of the outer member 1b in the circumferential direction of the mold 5 is restricted.
In addition, in order not to cause a circumferential position shift while fixing the outer member 1b, it is preferable that a clearance in the circumferential direction of the outer member 1b and the outer groove is 0 mm to an inner diameter of the mold 5 × 0.01 mm.

On the other hand, the radial length w ₅₃₅ of the molding upper lid 53 and the radial length w ₅₅₅ of the molding lower lid 55 are larger than the outer diameter d ₁₃ of the outer member 1b.
Accordingly, a gap is generated between the inner side surface of the outer groove 535 of the molding upper lid 53 and the outer member 1b, and between the inner side surface of the outer groove 555 of the molding lower lid 55 and the outer member 1b. By this gap, the outer member 1b can move toward the center of the mold 5 when the hydrostatic pressure is applied. Therefore, it can suppress that the pressure which makes the outer side member 1b bend to the center direction of the shaping | molding die 5 is applied.

As in the first embodiment, when the distance between the outer groove 535 and the inner side surface of the outer groove 555 and the outer member 1b is a distance α, the distance α is the center of the outer member 1b with the application of hydrostatic pressure. It is preferable that the value is substantially the same as the maximum distance that can be moved to or a value larger than the maximum distance.
As a result, when the outer member 1b is disposed at the initial position of the mold 5, the outer member 1b can move toward the center of the mold 5 up to a distance α during application of hydrostatic pressure.

For example, the distance α is preferably greater than or equal to the maximum value of the deformation amount of the molding cylinder 51 in the direction of the central axis of the molding cylinder 21 during application of hydrostatic pressure. However, in practice, the deformation amount of the forming cylinder 51 and the gap distance α are not necessarily equivalent. This is because, as the initial position of the outer member 1b is closer to the center of the molding cylinder 51, the amount of movement of the outer member 1b becomes smaller under general conditions. Therefore, the distance α can be designed to be shorter than the deformation amount of the molding cylinder 51 in consideration of the initial position of the outer member 1b.
The specific distance α is obtained by preliminary experiments or simulations based on, for example, the elastic deformation amount of the mold 5 and the characteristics of the material used for molding the porous glass body.

By setting the size of the gap to the distance α, the outer member 1b can move a distance α or less toward the center direction even during application of hydrostatic pressure. Thereby, even when the forming cylinder 51 is deformed by the hydrostatic pressure, the outer member 1b can be prevented from being bent by the applied pressure, and the outer member 1b can be prevented from being damaged or deformed by the hydrostatic pressure molding method. it can. Thereby, an optical fiber can be produced without causing deformation or breakage of the outer member 1b.
In addition, when the moving distance of the outer member 1b assumed by application of hydrostatic pressure is less than the distance α, the side surface of the outer member 1b and the outer side surface of the outer groove 555 are not necessarily in contact with each other. That is, a desired position that can secure the assumed moving distance can be set as the initial position of the outer member 1b.

In the present embodiment, the distance α can be different for each outer groove 535 and outer groove 555. For example, in the present embodiment, the molding upper lid body 53 and the molding lower lid body 55 each have eight outer grooves 535 and outer grooves 555. The vector amount of the hydrostatic pressure applied to the outer member 1b installed in these eight outer grooves varies depending on the shape of the mold 5 and the initial position of the outer member 1b. Therefore, based on the shape of the mold and the initial position of the outer member 1b, the distance between the outer grooves is a distance α ₁ to α _n (where n is the number of outer grooves. In this embodiment, n = 8). ) Can be designed separately.

The outer groove 535 and the outer groove 555 of the second embodiment of the present invention are not formed over the outer peripheral shape of the mold 5, and alternatively, a plurality of grooves having predetermined widths l ₅₃₅ and l _555. Is formed.

  By configuring the outer groove in this way, it is possible to suppress the outer member 1b from moving in the circumferential direction of the mold 5 due to application of hydrostatic pressure. Therefore, the positioning of the outer member 1b is facilitated, and the positional accuracy is improved. The configuration of the outer groove shown in the second embodiment is particularly effective when the hydrostatic pressure is not applied isotropically, for example, when the mold is not cylindrical.

As an example, when the multi-core fiber preform 9 having a substantially rectangular cross-sectional shape as shown in FIG. 11 is formed, the cross-sectional shape of the mold is not circular, and the hydrostatic pressure applied to each of the plurality of outer members 1b is , Each having a different vector quantity. However, as shown in FIG. 12, outer grooves 701 to 708 having gap distances α _{1 to} α ₈ each having different values in the center direction of the mold 7 are provided in the upper lid body for molding and the lower lid body for molding. Thus, the outer member 1b can be prevented from being damaged or deformed in the same manner as the cylindrical mold.

According to the method for manufacturing an optical fiber preform of the present invention, deformation and breakage of a rod-shaped member such as a core rod can be suppressed, and an optical fiber preform can be manufactured with high accuracy and low cost by a hydrostatic pressure molding method.
In addition, although the example which manufactures the multi-core fiber base material which is an optical fiber base material was demonstrated as embodiment of this invention, this invention is not limited to this. For example, the present invention can also be applied to a case where an eccentric core fiber is manufactured by installing one rod-like member at a position excluding the center of the cross section of the mold.

[Example]
A multi-core fiber preform (molded body) was produced using the method for producing an optical fiber preform of the first embodiment. In the first embodiment, an example in which the number of the outer members 1b is eight is shown, but in this example, the number of the outer members 1b is six. Using a core rod having an outer diameter of 5 mm and a length of 250 mm as the center member 1a and the outer member 1b, a molded body as shown in FIG. 7H was formed. And the outer diameter was measured about two orthogonal directions (X, Y) of the obtained molded object, and the average of the outer diameter and the outer diameter non-circularity were obtained. The outer diameter non-circularity is defined by (outer diameter in X direction) / (outer diameter in Y direction).

  The measurement results are shown in FIG. The horizontal axis in FIG. 13 represents the position in the length direction of the molded body, the left vertical axis represents the outer diameter, and the right vertical axis represents the outer diameter non-circularity. Table 1 shows the average value, the maximum value, and the minimum value, respectively, in the range of 30 mm to 230 mm excluding the full length or both ends from the measurement result of the outer diameter.

  As shown in FIG. 13, in the range of 30 to 230 mm (length: 200 mm) excluding both ends, the accuracy of the outer diameter of the base material (outer diameter non-circularity) is about 1%. When this portion is used as an effective portion of the multi-core fiber preform and a multi-core fiber is manufactured by drawing from the multi-core fiber preform, assuming that the outer diameter of the multi-core fiber is 180 μm, the expected optical fiber length is about 5 km. . Moreover, the outer diameter fluctuation of the multi-core fiber estimated from the outer diameter fluctuation of the multi-core fiber preform is about ± 1 μm with respect to the outer diameter of 180 μm, and sufficient accuracy can be obtained.

  Furthermore, the core rod was extracted from the manufactured molded body, the molded body from which the core rod was extracted was cut into three rings, and the core position was measured from the hole where the core rod was located. As the core position, the distance from the center of the hole with the outer core (outer member 1b) was measured on the cross-sectional image based on the center of the hole with the central core (center member 1a). This distance (distance between core rods) was measured for each of the six outer peripheral cores in each cross section. In addition, about the ring cutting position of three places, it measured as cross-section A, B, C in order from the one end of a molded object, and also measured in cross-section B 'facing the cross-section B in cross-section B. That is, when the molded product is cut into rounds, two cross-sections facing each other are generated at each position, and one of the two cross-sections is measured for the cross-sections A and C, and both of the two cross-sections are measured for the cross-sections B and B ′. . The measurement results are shown in FIG. The horizontal axis in FIG. 14 represents each cross section of the ring cut, and the vertical axis represents the distance between the center of the central core and the center of the outer core (distance between core rods).

  When the variation in the distance between the core rods (the amount obtained by dividing the deviation of the actual position with respect to the set position of the core rod by the outer diameter) was calculated from the measurement results shown in FIG. 7%, ± 1.1% in section B ′, and ± 0.7% in section C.

  Since a measurement error of about ± 0.4% is included due to the difference between the cross-sections B and B ′ facing each other, a fluctuation of about 2.6% may occur as the worst value. This is within the accuracy range required for multi-core fibers.

  When the core interval of the multi-core fiber is 50 μm, if the section B has a variation of ± 0.7%, the core position deviation is ± 0.4 μm or less, and good results are obtained.

[Third embodiment]
In the first and second embodiments described above, since the groove for enabling the rod-shaped member to move is provided in the lid of the mold, the rod-shaped member can move toward the center of the cross section of the mold during pressurization. . On the other hand, in the present embodiment, the rod-shaped member is restrained by the granulated powder instead of the lid of the mold, thereby enabling the rod-shaped member to move toward the center of the cross section of the mold during pressing. Therefore, also in this embodiment, the effect which suppresses the deformation | transformation or damage of the rod-shaped member by pressurization similarly to 1st and 2nd embodiment can be show | played.

  FIG. 15 is a schematic diagram showing the first half of the optical fiber preform manufacturing method according to the present embodiment. In the present embodiment, the center member 1a and the outer member 1b, which are rod-shaped members, are arranged using the upper fixing jig 61 and the lower fixing jig 63. The upper fixing jig 61 and the lower fixing jig 63 are made of a material such as metal, synthetic rubber, or synthetic resin, and for example, aluminum can be used. In the present embodiment, the upper fixing jig 61 and the lower fixing jig 63 are exemplified as cylindrical structures, but the present invention is not limited to this and may have any shape. The dimensions of the upper fixing jig 61 and the lower fixing jig 63 can be arbitrarily designed according to the dimensions of the multi-core fiber preform to be manufactured.

  The lower fixing jig 63 has a groove (may be a through hole) for fitting the center member 1a and the outer member 1b. The upper fixing jig 61 has a groove (may be a through hole) for fitting the center member 1a and the outer member 1b. The grooves of the upper fixing jig 61 and the lower fixing jig 63 are provided at positions corresponding to the initial positions of the center member 1a and the outer member 1b. Furthermore, the upper fixing jig 61 has a large number of through holes through which the granulated powder 41 can pass.

  First, as shown in FIG. 15A, a central member 1a, outer members 1b (six in this embodiment), and a forming cylinder 71 are arranged between a lower fixing jig 63 and an upper fixing jig 61. Specifically, the upper dummy rod 15 of the central member 1a and one end of each outer member 1b are fitted into grooves (or through holes) provided in the upper fixing jig 61 and the lower fixing jig 63, and for molding. The cylinder 71 is disposed between the upper fixing jig 61 and the lower fixing jig 63 so as to surround the center member 1a and the outer member 1b. In addition, since the upper and lower sides of the molded body are inverted in a later process, the central member 1a, the outer member 1b, and the molding cylinder 71 are disposed upside down at this stage.

  Next, as shown in FIG. 15 (b), through a through hole (not shown) provided in the upper fixing jig 61, the space surrounded by the upper fixing jig 61, the lower fixing jig 63 and the molding cylinder 71. Is filled with the granulated powder 41. When the granulated powder 41 is filled, vibration is applied to the upper fixing jig 61, the lower fixing jig 63, and the forming cylinder 71 while suppressing the center member 1a and the outer member 1b from above so as not to float.

  After the filling of the granulated powder 41 is completed, the upper fixing jig 61 is removed as shown in FIG.

  FIG. 16 is a schematic diagram showing the latter half of the method for manufacturing an optical fiber preform according to this embodiment. As shown in FIG. 16A, after the upper fixing jig 61 is removed, a molding lower lid body 75 is attached to the upper side of the molding cylinder 71 and is surrounded by the molding lower lid body 75 and the molding cylinder 71. The granulated powder 41 is further filled in the space to be stored. A part of the center of the molding lower lid body 75 is configured to be removable. After the part is removed, the granulated powder 41 is filled, and then the part is attached again. On the granulated powder 41 side of the molding lower lid body 75, a tapered portion having an inclination is provided so that the thickness of the molding lower lid body 75 gradually decreases from the peripheral portion toward the central portion. The molding lower lid 75 has a central groove 253 similar to the molding lower lid 25 shown in FIG. 5, but does not have an outer groove 255. That is, in the state where the molding lower lid body 75 is attached to the upper side of the molding cylinder 71, the center member 1a is fitted into the center groove 253 of the molding lower lid body 75, but the outer member 1b is the molding lower lid body. 75 is not supported.

  Next, as shown in FIG. 16B, the lower fixing jig 63, the central member 1a, the outer member 1b, the molding cylinder 71, the granulated powder 41, and the molding lower lid 75 are integrally turned upside down. Let As a result, the lower fixing jig 63 is positioned on the upper side, and the molding lower lid body 75 is positioned on the lower side. Then, the lower fixing jig 63 is removed.

  Next, as shown in FIG. 16 (c), after the lower fixing jig 63 is removed, a molding upper lid body 73 is attached to the upper side of the molding cylinder 71 and is surrounded by the molding upper lid body 73 and the molding cylinder 71. The granulated powder 41 is further filled in the space to be stored. A part of the center of the molding upper lid 73 is configured to be removable. After the part is removed, the granulated powder 41 is filled, and then the part is attached again. On the granulated powder 41 side of the molding upper lid 73, a tapered portion is provided with an inclination so that the thickness of the molding upper lid 73 gradually decreases from the peripheral portion toward the central portion. The molding upper lid 73 has a central groove 233 similar to the molding upper lid 23 shown in FIG. 4, but does not have an outer groove 235. That is, in the state where the molding upper lid body 73 is attached to the upper side of the molding cylinder 71, the center member 1a is fitted into the central groove 233 of the molding upper lid body 73, but the outer member 1b is supported by the molding upper lid body 73. Not.

  Then, an optical fiber preform | base_material is obtained by performing the application of a hydrostatic pressure, dehydration, refinement | purification, and a sintering process similarly to FIG.

  In the state shown in FIG. 16C, the outer member 1b is not supported by the molding upper lid body 73 and the molding lower lid body 75, and is applied by the granulated powder 41, which is a powder material, to the initial position (that is, the application of hydrostatic pressure). It is constrained to a position to be placed before. Since the granulated powder 41 has fluidity, the outer member 1b restrained by the granulated powder 41 is movable when an application of hydrostatic pressure is applied. Therefore, according to the method for manufacturing an optical fiber preform according to the present embodiment, an effect of suppressing deformation or breakage of the rod-shaped member due to pressurization can be achieved as in the first and second embodiments.

When the manufacturing process of the optical fiber preform according to this embodiment was tested and a hydrostatic pressure of 1 ton / cm ² was applied for 1 minute, neither deformation nor breakage was observed in either the central member 1a or the outer member 1b. It was.

[Fourth embodiment]
In 3rd embodiment, the cross-sectional shape of a shaping | molding die (molding cylinder 71) is circular. FIG. 17A is a cross-sectional view of the molded body before and after sintering when the cross-sectional shape of the mold is circular. In the state before sintering in FIG. 17A, the radius R1 of the molded body in the region where the outer member 1b does not exist is equal to the radius R2 of the molded body in the region where the outer member 1b exists. The radius R1 is the radius of the portion of the cross section of the molded body that does not pass through the center of the cross section and does not pass through the outer member 1b, and the radius R2 is the radius of the outer member 1b that passes through the center of the cross section of the molded body. This is the radius of the passing part.

  When the sintered body is sintered, the granulated powder 41 contracts greatly, whereas the outer member 1b, which is a core rod, hardly contracts. Therefore, the change in volume differs between the portion where the outer member 1b is present and the portion where the outer member 1b is not present in the molded body. As a result, as for the cross-sectional shape of the sintered compact (optical fiber preform), six vertices are arranged in the region where the outer member 1b exists as in the state after sintering in FIG. There are cases in which the shape is substantially hexagonal. Furthermore, since the stress applied to the outer member 1b becomes non-uniform, the cross-sectional shape of the outer member 1b may be slightly extended and deformed in the circumferential direction.

  On the other hand, in this embodiment, the cross-sectional shape of the molded body (optical fiber preform) after sintering can be made substantially circular by adjusting the cross-sectional shape of the molded body before sintering.

  FIG. 17B is a cross-sectional view of the molded body before and after sintering according to the present embodiment. In the state before sintering in FIG. 17B, the radius R1 of the molded body in the region where the outer member 1b does not exist is larger than the radius R2 of the molded body in the region where the outer member 1b exists (that is, R1> R2). ). As a result, the cross-sectional shape of the green body before sintering becomes a substantially hexagonal shape in which six vertices are arranged in a region where the outer member 1b does not exist, as in the state before sintering in FIG.

  When the molded body having such a configuration is sintered, the radius R1 of the region where the outer member 1b does not exist is greatly reduced than the radius R2 of the region where the outer member 1b exists. As a result, the cross-sectional shape of the sintered body after sintering is substantially circular. Moreover, since the stress applied to the outer member 1b is made uniform, deformation of the outer member 1b can be suppressed.

  Specific values (or ratios) of the radii R1 and R2 can be appropriately determined in consideration of the arrangement of the outer member 1b, the density of the granulated powder 41, and the like.

[Fifth embodiment]
In the third embodiment, the application of the hydrostatic pressure after FIG. 16C is performed in a state in which a molding die is attached to the molded body. Therefore, the shrinkage amount of the molded body in the vicinity of the molding upper lid body 73 and the molding lower lid body 75 is smaller than the shrinkage amount of the molded body in the central portion. As a result, in the molded body after pressurization, as shown in FIG. 7H, both end portions are thicker than the central portion. In an exemplary molded body after pressurization, the outer diameter of the central portion is about 41 mm, and the outer diameter of both ends is about 44 mm.

  When such a molded body is sintered to form an optical fiber preform, and the optical fiber preform is drawn to produce an optical fiber, a central core located at the center of the optical fiber and an outer periphery of the optical fiber are located. The distance between the outer peripheral cores (hereinafter referred to as the inter-core distance) is smaller at both ends than at the center. This is because, since the outer diameter of the optical fiber is substantially constant, the thick end portions are large in the state of the optical fiber preform, and the distance between the center member 1a and the outer member 1b is relatively reduced. Because. Since the permissible range of the inter-core distance is determined by the standard, the yield deteriorates particularly when the portions where the inter-core distance is smaller than the permissible range increase at both ends.

  On the other hand, in this embodiment, by adjusting the arrangement of the outer member 1b in the molded body, the distance between the cores in the optical fiber manufactured from the molded body can be improved.

  FIG. 18A is a side view of the center member 1a and the outer member 1b according to the present embodiment. FIG. 18A shows the central member 1a and the outer member 1b inside the molded body before sintering, and the granulated powder 41 is omitted for visibility. In the present embodiment, when the molded body is manufactured, the outer member 1b is twisted with respect to the central member 1a (the central axis of the molded body), that is, inclined to the circumferential direction of the cross section of the molded body. Specifically, at the stage of FIG. 15A, the upper end portion of the outer member 1b is rotated by 20 ° relative to the lower end portion of the outer member 1b with respect to the center normal of the cross section of the mold. The outer member 1b is disposed between the upper fixing jig 61 and the lower fixing jig 63 so as to be positioned. As a result, the longitudinal direction of the outer member 1b is inclined with respect to the longitudinal direction of the central member 1a. Further, the distance between the central member 1a and the outer member 1b at the upper end and the lower end is increased by 0.5% compared to the third embodiment. Note that the direction and angle of rotation may be arbitrarily designed by performing experiments and simulations.

  18B is a cross-sectional view taken along the line GG in FIG. 18A, and FIG. 18C is a cross-sectional view taken along the line H-H in FIG. (D) is sectional drawing cut | disconnected by the JJ line | wire of Fig.18 (a). 18 (b) to 18 (c), the broken line indicates the outer diameter of the granulated powder 41. In the upper end portion shown in FIG. 18 (b) and the lower end portion shown in FIG. 18 (d), the distance R3 between the center member 1a and the outer member 1b is the same, and the outer member 1b is the center member 1a (of the molded body). It is in a state of being rotated by 20 ° relative to the central axis). On the other hand, in the central portion shown in FIG. 18C, the distance R4 between the central member 1a and the outer member 1b is smaller than the distance R3 at the upper end portion and the lower end portion (that is, R3> R4). In other words, when the outer member 1b is twisted with respect to the center member 1a, the distance between the center member 1a and the outer member 1b is the same at the upper end and the lower end, but the distance is reduced at the center.

FIG. 19 is a graph showing a result of estimating the inter-core distance of the optical fiber. Specifically, first, the position of the glass rod in the molded body is measured by X-ray CT imaging of both ends and a space between the both ends of the molded body having a total length of 250 mm. Next, the molded body is made into transparent glass, and the core interval when the outer diameter is drawn to 180 μm is determined. The density in the cross section of the molded body was 1.45 g / cm ^{3 and} was constant. Further, the horizontal axis in FIG. 19 is a measurement position set at equal intervals from one end of the molded body to the other end, and the vertical axis is an estimated value of the inter-core distance (μm). FIG. 19 shows the distance between the cores of the optical fiber manufactured from the molded body according to the case of no rotation (third embodiment) and the optical fiber manufactured from the molded body according to the case of 20 ° rotation (this embodiment). Has been.

  In the exemplary standard, the inter-core distance is 50 ± 0.5 μm. As can be seen from FIG. 19, the optical fiber according to the present embodiment has a larger range within the standard than the optical fiber according to the third embodiment. That is, in the optical fiber according to the present embodiment, it is possible to reduce the nonstandard range at both ends. Specifically, in the graph of FIG. 19, the yield of the present embodiment is improved by 3% compared to the third embodiment.

  This embodiment is not limited to the third embodiment, and can also be applied to the case where the outer member 1b is supported by upper and lower lids as in the first and second embodiments. In this case, by rotating the upper lid bodies 23 and 53 for molding and the lower lid bodies 25 and 55 for molding in the first and second embodiments relatively (for example, 20 °), FIG. Similarly, the outer member 1b can be twisted with respect to the central member 1a, and the same effect can be realized.

  According to the present embodiment, the outer member 1b and the central member 1a are arranged by twisting the outer member 1b with respect to the central member 1a in the molded body, that is, by tilting the outer member 1b in the circumferential direction of the cross section of the molded body. The distance between them can be made longer at both ends than at the center. As a result, the distance between the cores of the optical fiber manufactured from the molded body can be improved, and the yield of the optical fiber can be improved.

[Sixth embodiment]
In 3rd embodiment, the outer side member 1b is restrained by the granulated powder 41 which is a powder material in a molded object. Since the outer member 1b restrained by the powder material is likely to be displaced before application of hydrostatic pressure, the accuracy of the position of the outer member 1b is maintained particularly when an optical fiber preform including a large number of outer members 1b is manufactured. Difficult to do.

  On the other hand, in this embodiment, an optical fiber preform including a larger number of outer members 1b can be manufactured with high accuracy by producing a molded body in a plurality of times.

  20A is a longitudinal sectional view of the inner molded body 81, and FIG. 20B is a longitudinal sectional view of the inner molded body 81 and the outer molded body 83. FIG. FIG.20 (c) is sectional drawing cut | disconnected by the KK line | wire of FIG.20 (b). In the present embodiment, first, after forming the inner molded body 81, the outer molded body 83 is manufactured outside the inner molded body 81, and the inner molded body 81 and the outer molded body 83 are used as an integral molded body.

  Specifically, first, after each member is arranged according to the steps of FIGS. 15A to 15C and FIGS. 16A to 16C, the inner molded body 81 is applied by applying a hydrostatic pressure. Is made. As shown in FIG. 20A, in the inner molded body 81, six outer members 1b are arranged at equal intervals on a circumference centered on the central member 1a. The number and arrangement of the central member 1a and the outer member 1b in the inner molded body 81 are not limited to this configuration, and may be arbitrarily designed.

  Next, using the inner molded body 81 instead of the central member 1a, each member is arranged according to the steps of FIGS. 15 (a) to 15 (c) and FIGS. 16 (a) to 16 (c), and then the hydrostatic pressure is changed. By performing the application, the outer molded body 83 is produced outside the inner molded body 81. As shown in FIGS. 20 (b) and 20 (c), in the outer molded body 83, twelve outer members 1b are equally spaced on the circumference centered on the central member 1a outside the inner molded body 81. Placed in. The number and arrangement of the outer members 1b in the outer molded body 83 are not limited to this configuration, and may be arbitrarily designed.

  The upper fixing jig 61, the lower fixing jig 63, the molding upper lid 73, the molding lower lid 75, and the molding cylinder having different sizes are used for producing the inner molded body 81 and the outer molded body 83. Two sets of 71 are prepared. The upper dummy bar 15 and the lower dummy bar 17 are thickened in two stages so as to correspond to two types of molds, that is, the inner molded body 81 and the outer molded body 83.

  In the present embodiment, the molded body is manufactured twice, but may be divided into three or more times. In that case, a plurality of sets of upper fixing jig 61, lower fixing jig 63, upper molding body 73, lower molding body 75, and molding cylinder 71 having different sizes are prepared, as shown in FIG. The steps of ~ 15 (c) and FIGS. 16 (a) to 16 (c) and the application of hydrostatic pressure may be repeated.

  This embodiment is not limited to the third embodiment, and can also be applied to the case where the outer member 1b is supported by upper and lower lids as in the first and second embodiments. In this case, a plurality of sets of molding cylinders 21 and 51, molding upper lid bodies 23 and 53, and molding lower lid bodies 25 and 55 having different sizes are prepared, and the steps of FIGS. That's fine.

  According to this embodiment, the arrangement and pressurization of the outer member 1b, which is a rod-shaped member, are performed in a plurality of times, so the number of outer members 1b restrained by the powder material before pressurization can be reduced. Thereby, the position shift of the outer member 1b can be reduced, and an optical fiber preform including a large number of rod members in the outer member 1b can be manufactured with high accuracy.

  By applying this embodiment, as shown in FIGS. 21A and 21B, a transparent glass body (optical fiber preform) is formed in which a central member 1a and an outer member 1b are arranged in a grid pattern (lattice shape). It is possible. FIG. 21A is a cross-sectional view of the molded body before application of hydrostatic pressure, and FIG. 21B is a cross-sectional view of the molded body after application of hydrostatic pressure. 21 (a) and 21 (b), a dummy member 1c, which is a rod-shaped member made of quartz glass having no core, is disposed instead of the center member 1a. In the molded body before application of the hydrostatic pressure in FIG. 21A, four outer members 1b are arranged on each vertex of a rectangle centering on the dummy member 1c in the inner molded body 81, and the outer molded body 83 is disposed. Inside, eight outer members 1b (two on each side) are arranged on a rectangular side centered on the dummy member 1c outside the inner molded body 81, and the dummy member 1c is further centered on the outer side. Four outer members 1b are arranged on each vertex of the rectangle. An optical fiber preform having 16 cores arranged in a grid pattern as shown in FIG. 21 (b) is manufactured by sintering after applying hydrostatic pressure to the molded body having such a configuration. Can do. The shape of each molded body and the arrangement of the rod-shaped member on the mold before molding take into account the shrinkage of the granulated powder 41 during hydrostatic pressure and the shrinkage of the granulated powder 41 during sintering. Thus, a desired arrangement is selected after sintering. As shown in FIG. 21 (a), the outer member 1b located particularly at the apex of the outer rectangle has a large moving distance due to the application and sintering of the hydrostatic pressure, so that it is shifted to the outside before the hydrostatic pressure is applied. It is desirable that

[Seventh embodiment]
In an optical fiber, it is known that crosstalk can be reduced by providing a hole between cores. In the present embodiment, an optical fiber preform serving as a base of an optical fiber having holes is manufactured by disposing a rod-shaped member having holes in the molded body.

  FIG. 22A is a cross-sectional view of a molded body according to this embodiment. The molded body according to the present embodiment is produced by any one of the first to sixth embodiments. In the present embodiment, a hole member 1d is used in addition to the center member 1a and the outer member 1b. The hole member 1 d has a pipe shape extending in one direction, and has a hole extending along the longitudinal direction at the center instead of the core 11. The hole member 1 is made of, for example, quartz and may be made of the same material as that of the clad 13. The diameter of the hole in the hole member 1 may be arbitrarily designed according to the optical fiber to be manufactured.

  In the cross section of the molded body shown in FIG. 22 (a), a central member 1a is arranged at the center, and six holes are formed on each vertex of a first regular hexagon (indicated by a broken line) centered on the central member 1a. A member 1d is arranged. Furthermore, six hole members 1d are arranged on each vertex of a second regular hexagon (indicated by a broken line) centered on a central member 1a larger than the first regular hexagon, and the second Six outer members 1b are arranged on the midpoint of each side of the regular hexagon. By sintering the molded body having such a configuration, an optical fiber preform having holes between cores as shown in FIG. 22B can be manufactured.

  In the form shown in FIG. 22 (a), a molded body is produced by applying a hydrostatic pressure after disposing a hole member 1d in advance in a mold. On the other hand, it is also possible to embed the hole member 1d in the molded body after application of hydrostatic pressure. FIG.22 (c) is a cross-sectional view of the molded object of the previous stage which produces the molded object of Fig.22 (a). In FIG.22 (c), the temporary member 1e which is a rod-shaped member is arrange | positioned in the position which arrange | positions the hole member 1d. The temporary member 1e has the same diameter and length as the hole member 1d and is made of any material such as metal or quartz.

  The temporary member 1e is removed from the molded body of FIG. 22C by mechanical processing or the like, and the hole member 1d is inserted into the space where the temporary member 1e was present. Thereby, the molded object which has the same structure as Fig.22 (a) is producible.

  The shape of each molded body and the arrangement of the rod-shaped member on the mold before molding take into account the shrinkage of the granulated powder 41 during hydrostatic pressure and the shrinkage of the granulated powder 41 during sintering. Thus, the desired arrangement after sintering is determined. As shown in FIGS. 22 (a) and 22 (c), the outer member 1b located on each side of the outer regular hexagon has a large moving distance due to the application and sintering of the hydrostatic pressure. In this case, it is desirable to displace them outward.

1a Center member
1b Outer member 2, 5, 7 Mold
3 Clad part 9, 10 Multi-core fiber preform
11 core
13 clad
15 Upper dummy stick
17 Lower dummy rod 21, 51, 71 Molding cylinder 23, 53, 73 Molding upper lid 25, 55, 75 Molding lower lid
41 Granulated powder
43 Hydrostatic pressing (CIP) equipment
45 Pressure medium
61 Upper fixing jig
63 Lower fixing jig 233, 253 Central groove 235, 255 Outer groove 535, 555 Outer groove 701 Outer groove

Claims (15)

A first step of installing a rod-shaped member along a direction perpendicular to the cross section at a position excluding the center of the cross section perpendicular to the longitudinal direction of the mold in the mold having a predetermined shape;
A second step of filling the mold with a powder material comprising silica;
A third step of applying hydrostatic pressure to the mold;
Including
The method of manufacturing an optical fiber preform, wherein the rod-shaped member is movable by a predetermined distance toward the center of the cross section of the mold during application of the hydrostatic pressure. The mold includes a groove for installing the rod-like member in the upper and lower parts;
The method for manufacturing an optical fiber preform according to claim 1, wherein the groove has a length obtained by adding the predetermined distance to the outer diameter of the rod-shaped member in the radial direction of the cross section.   The method for manufacturing an optical fiber preform according to claim 2, wherein the groove is formed in an annular shape having a predetermined width centered on the center of the cross section. The method for manufacturing an optical fiber preform according to claim 2, wherein one groove is formed per one rod-shaped member. The method for manufacturing an optical fiber preform according to any one of claims 1 to 4, wherein the predetermined distance is larger than a maximum value of a deformation amount of the mold during application of the hydrostatic pressure. 2. The optical fiber preform according to claim 1, wherein in the third step, the hydrostatic pressure is applied to the mold in a state where the rod-shaped member is not in contact with the mold and is restrained by the powder material. Production method. By installing the rod-shaped member using a jig in the first step and removing the jig in the second step, the rod-shaped member is restrained by the powder material without contacting the mold. The method of manufacturing an optical fiber preform according to claim 6, wherein The method for manufacturing an optical fiber preform according to any one of claims 1 to 7, wherein the cross section of the mold is non-circular. The radius of the part which does not pass the said rod-shaped member through the center of the said cross section in the said cross section of the said shaping | molding die is larger than the radius of the part which passes the said rod-shaped member through the center of the said cross section. Manufacturing method of optical fiber preform. The rod-shaped member is arranged in a state in which an upper end portion of the rod-shaped member is rotated relative to a lower end portion of the rod-shaped member with respect to a central normal line of the cross section of the mold. The manufacturing method of the optical fiber preform as described in any one of these. A fourth step of removing the molded body from the mold after the third step, and a fifth step of arranging the molded body in a second mold larger than the mold after the fourth step. And the steps
After the fifth step, a sixth step of executing the third step from the first step using the second mold instead of the mold;
The method for manufacturing an optical fiber preform according to any one of claims 1 to 10, further comprising: The optical fiber preform according to any one of claims 1 to 11, wherein the rod-shaped member is a core rod for an optical fiber having different refractive indexes at the center of the cross section perpendicular to the longitudinal direction of the rod-shaped member and the outer layer. Manufacturing method. The method of manufacturing an optical fiber preform according to any one of claims 1 to 11, wherein the rod-shaped member has a hole extending along a longitudinal direction. A seventh step of removing the rod-shaped member after the third step;
After the seventh step, an eighth step of disposing a second rod-shaped member having a hole extending along the longitudinal direction in a space formed by removing the rod-shaped member;
The method for manufacturing an optical fiber preform according to any one of claims 1 to 11, further comprising: A molding cylinder;
An upper lid,
A lower lid,
A device comprising:
The upper lid body and the lower lid body are provided with grooves for installing the upper end and the lower end of a rod-shaped member in the molding cylinder,
An apparatus for manufacturing an optical fiber preform, wherein the groove has a length obtained by adding a predetermined distance to the outer diameter of the rod-shaped member in a radial direction of a cross section perpendicular to the longitudinal direction of the forming cylinder.

Images