JP2009227548A - Method for producing preform for photonic crystal fiber, and method for producing photonic crystal fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a preform for a photonic crystal fiber in which the structure of air holes is stable, further, collapse and roughening at the inside of the holes are prevented, and satisfactory characteristics can be obtained, and to provide a method for producing a photonic crystal fiber. <P>SOLUTION: The method for producing the preform for the photonic crystal fiber comprises: a stage where a plurality of wire rods formed of a conductive material expanding in the radial direction by application of electric current are lined up with a prescribed arrangement at a space part of a molding die where a space of a columnar shape is formed; a stage where a silica raw material is introduced into the space part, and temporal curing is applied so as form a silica intermediate body; a stage where electric current is applied to the wire rods so as to be thermally expanded in a radial direction, thereafter, the application of the electric current is intercepted, and then, the wire rods are removed from the silica intermediate body; and a stage where the silica intermediate body is subjected to sintering treatment so as to be made into glass, in this order. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a base material for a photonic crystal fiber and a method for manufacturing a photonic crystal fiber. More specifically, a method for producing a base material for a photonic crystal fiber and a photonic crystal, in which the structure of the holes is stable, and the inside of the holes is prevented from being collapsed and roughened, and good characteristics can be obtained. The present invention relates to a fiber manufacturing method.

  A conventional optical fiber is composed of two layers of a core and a clad covering the core. Further, the constituent material of the core and the clad is based on silica (quartz), and the core has a composition in which an additive such as germanium is added to silica in order to make the refractive index higher than that of the clad. In the optical fiber having such a configuration, light incident on the optical fiber is confined inside the core due to the difference between the refractive index of the core and the refractive index of the cladding, and propagates in the optical fiber.

  On the other hand, as the optical signal processing and the speed of the optical communication network are increased, the capacity of the light incident on the optical fiber is increased, so that various nonlinear effect phenomena are likely to occur. In addition, when such a nonlinear effect phenomenon occurs, the transmission characteristics propagating in the optical fiber are also deteriorated. Therefore, the appearance of an optical fiber having a high capacity and a low loss has been desired.

  In recent years, a photonic crystal fiber (also called a photonic crystal fiber (PCF)) has been attracting attention as an optical fiber that has solved the problems of the conventional optical fibers described above. The photonic crystal fiber has a structure in which air holes (air holes) regularly arranged in the direction along the core are formed in the periphery of the core in the cladding, and the inside of the air holes is filled with gas. Adopted. By adopting such a structure, it is possible to transmit light in a wide wavelength range several times that of the prior art, and to realize a communication speed of 100 to 1000 times.

  In addition, the photonic crystal fiber is considered to improve the weakness of the optical fiber that is extremely weak to bending and to reduce bending loss, so that the degree of freedom of wiring can be greatly increased. The photonic crystal fiber can contribute to the spread of so-called FTTH (Fiber To The Home) as an ultimate use form of broadband. As a method for producing the photonic crystal fiber, for example, a base material for a photonic crystal optical fiber is formed by bundling a plurality of fine quartz tubes (capillaries) having the same diameter as the fine quartz rod around the fine quartz rod. (Preform), and the base material is drawn to produce a photonic crystal optical fiber (see, for example, Patent Document 1).

JP 2003-206148 A

  However, in the photonic crystal fiber in which the base material for the conventional photonic crystal optical fiber is drawn, the holes due to the small diameter quartz tube are crushed when the base material is drawn, and the diameter of the holes is not uniform, There was a problem that the structure of the pores was not stable, such as disordered arrangement. In addition, the state of the formed holes is important for photonic crystal fibers and the like. For example, if the inside of the hole is broken or the inside surface of the hole is in a rough state, good characteristics may not be obtained. The offer of was desired.

  The present invention has been made in view of the above problems, and is intended for a photonic crystal fiber that can stabilize the structure of the holes, prevent collapse and roughening of the inside of the holes, and obtain good characteristics. An object of the present invention is to provide a manufacturing method of a base material and a manufacturing method of a photonic crystal fiber.

  In order to solve the above-mentioned problems, the method for manufacturing a preform for a photonic crystal fiber according to the present invention expands in a radial direction by applying an electric current to the space portion of a mold in which a cylindrical space portion is formed. A step of arranging a plurality of wires formed of a conductive material in a predetermined arrangement, a step of introducing a silica raw material into the space portion and pre-curing it to form a silica intermediate, and a diameter by applying an electric current to the wire A step of removing the wire from the silica intermediate after the thermal expansion in the direction, and then cutting off the application of current, and a step of sintering the silica intermediate to vitrify in order. And

  The method for producing a base material for a photonic crystal fiber according to the present invention comprises: producing a silica intermediate; removing a wire from the silica intermediate to form pores (air holes); It tries to become. Therefore, it is possible to provide a base material for a photonic crystal fiber in which the problems such as the collapse of holes due to the small diameter quartz tube at the time of drawing the base material and the uneven diameter of the holes are solved, and the structure of the holes is stable. Can do. In addition, when removing the wire from the silica intermediate, a current is applied to the wire to thermally expand in the radial direction, and then the wire is removed after the current application is cut off, and is formed in the silica intermediate. The holes are slightly widened with respect to the outer diameter of the wire. Therefore, when removing the wire, it is possible to prevent the pores from collapsing due to the friction between the inside of the pores and the surface of the wire, or to roughen the inside surface of the pores, and to obtain good characteristics. It is possible to provide a preform for a photonic crystal fiber that can be used.

In the method for producing a preform for a photonic crystal fiber according to the present invention, the silica raw material introduced into the space may be gel-like silica obtained by a sol-gel method.
Since the photonic crystal fiber base material manufacturing method uses gel-like silica obtained by a sol-gel method as a silica raw material, the gel-like silica is efficiently pre-cured and has a dense structure. A base material for silica intermediate or photonic crystal fiber can be obtained. In addition, the temperature of the sintering process in the subsequent step can be performed at a temperature lower than usual.

In the method for manufacturing a photonic crystal fiber preform according to the present invention, the silica raw material introduced into the space may be slurry silica.
In the photonic crystal fiber base material manufacturing method, slurry-like silica is used as a raw material, so that a silica intermediate having a dense structure or a photonic crystal fiber base material can be obtained by slurry casting.

In the method for producing a preform for a photonic crystal fiber according to the present invention, the wire is at least one selected from the group consisting of stainless steel, chromium, nickel, tungsten, iron (steel), molybdenum, cobalt, titanium, and an alloy thereof. It is a seed.
In the method of manufacturing the photonic crystal fiber base material, a specific metal material is selected as a conductive material that expands in the radial direction when an electric current is applied. Is easy to manufacture.

The method for manufacturing a preform for a photonic crystal fiber according to the present invention is characterized in that the wire is carbon.
In the method of manufacturing the photonic crystal fiber base material, carbon is selected as a conductive material that expands in the radial direction when an electric current is applied. Therefore, thermal expansion is efficiently performed by applying an electric current, and the hardness of the wire is increased. Also excellent.

The method for producing a photonic crystal fiber according to the present invention is characterized in that the photonic crystal fiber preform obtained by the above-described method for producing a photonic crystal fiber preform is drawn.
The photonic crystal fiber manufacturing method uses a photonic crystal fiber base material obtained by the above-described manufacturing method of the present invention, and draws the base material to form a photonic crystal fiber. Therefore, it is possible to manufacture a photonic crystal fiber that can stabilize the structure of the holes, prevent collapse and roughening of the inside of the holes, and implement good optical transmission by simple means.

  The photonic crystal fiber referred to in the present application includes both a structure having no holes in the core portion and a structure having holes.

  In the method for manufacturing a photonic crystal fiber preform according to the present invention, when removing a wire from a silica intermediate, a current is applied to the wire to cause thermal expansion in the radial direction, and then the current is cut off and then the wire is removed. I am doing so. Since the holes formed in the silica intermediate are slightly expanded with respect to the outer diameter of the wire, the holes may collapse due to friction between the inside of the holes and the surface of the wire when the wire is removed thereafter. Alternatively, it is possible to provide a base material for a photonic crystal fiber that can prevent the inner surface of the pores from being roughened and can obtain good characteristics.

  Hereinafter, one embodiment of the present invention will be described. The embodiment described below shows one embodiment of the present invention, and the present invention is not limited to the following embodiment, and includes the configuration of the present invention to achieve the object and effect. Needless to say, modifications and improvements within the scope of the present invention are included in the content of the present invention. Further, the specific structure, shape, and the like in carrying out the present invention are not problematic as other structures, shapes, and the like as long as the objects and effects of the present invention can be achieved.

(1) Configuration of photonic crystal fiber preform 1:
FIG. 1 is a schematic view of an embodiment of a photonic crystal fiber preform 1 (the photonic crystal fiber has the same configuration). A base material 1 for a photonic crystal fiber according to the present embodiment shown in FIG. 1 has a core portion 11 and a clad portion 12 surrounding the core portion 11, and a circular hole (air) around the core portion 11. A plurality of (holes) 13 are formed at predetermined intervals (six in FIG. 1).

  The cladding 12 forms a photonic crystal structure (photonic crystal structure) whose refractive index fluctuates two-dimensionally, and incident light is confined to the core 11 surrounded by the photonic crystal structure. Will be propagated.

(2) Configuration of photonic crystal fiber preform manufacturing equipment:
FIG. 2 is a schematic view showing an aspect of the manufacturing apparatus (base material manufacturing apparatus 5) of the base material 1 for the photonic crystal fiber.

  A base material manufacturing apparatus 5 shown in FIG. 2 includes a mold 51 in which a cylindrical space 52 is formed, and a wire 53 for forming a plurality of holes 13 arranged in a predetermined arrangement inside the space 52. And two wire rod fixing portions (an upper wire rod fixing portion 54 and a lower wire rod fixing portion 55) for determining the arrangement of the wire rod 53, a molding die 51, etc. Is provided as a basic configuration. Note that the wire 53 is electrically connected to a power application unit 58 for applying a current to the wire 53.

  The mold 51 placed on the pedestal 56 is a hollow cylinder having a cylindrical space 52 for introducing the raw material silica therein. Further, a slurry introducing portion 57 for introducing the raw material silica into the space portion 52 is formed at a predetermined position on the wall surface of the mold 51 so as to be connected to the space portion 52.

  An upper wire fixing portion 54 for closing the upper portion of the space portion 52 and a lower wire fixing portion 55 for closing the lower portion of the space portion 52 are disposed so as to be fitted into the molding die 51. Further, both the upper wire fixing part 54 and the lower wire fixing part 55 are formed with a plurality of through holes for positioning the wire 53. The arrangement of the through holes is the same in the upper wire fixing portion 54 and the lower wire fixing portion 55 and is formed to be the same with respect to the central axis (not shown) of the molding die 51. Therefore, the upper wire fixing part 54 and the lower wire fixing part 55 are positioned with respect to the central axis.

  A plurality of wire rods 53 arranged inside the space portion 52 are fixed at predetermined positions by two wire rod fixing portions 54 and 55. The wire 53 has a circular cross section and is formed of a conductive material that expands in the radial direction when a current is applied. As the conductive material constituting the wire 53, metal materials such as stainless steel, chromium, nickel, tungsten, iron (steel), molybdenum, cobalt, and titanium can be used. These metal materials may be used alone or as an alloy combining two or more. Note that the surface of the wire 53 may be coated with fluorine or the like. Further, as the wire 53, carbon may be used in addition to these metal materials.

  The wire 53 is electrically connected to the charging unit 58, and a current can be applied from the charging unit 58 to the wire 53. The application of current is performed after producing a silica intermediate (described later) obtained by temporarily curing slurry-like silica. The wire 53 to which a current is applied from the electrifying unit 58 is heated by the current application, thermally expands in the radial direction, and then, when the current application is interrupted, the wire contracts in the radial direction, and the state before the current application Return to. The charging unit 58 is connected to a power source (not shown). In the present embodiment, the application / cutoff of the current is adjusted by turning on / off the switch 59.

(3) Production of base material 1 for photonic crystal fiber:
Hereinafter, an example of a method for manufacturing the photonic crystal fiber base material 1 using the base material manufacturing apparatus 5 of FIG. 2 will be described. FIG. 3 is a flowchart showing an example of a procedure for carrying out the method for manufacturing the photonic crystal fiber preform 1 of the present invention. In the flowchart of FIG. 3, “step” described below is simplified as “S”.

(A) Preparation of silica raw material (step 1):
As silica (quartz glass) used as a raw material of the base material 1 for photonic crystal fibers, known materials generally applied to optical fibers and the like, such as powdered silica, can be used. By using a slurry cast method in which slurry silica is a raw material, or by using a sol-gel method in which gel silica is a raw material, a dense silica intermediate or photonic crystal fiber base material 1 is manufactured. can do.

  In the preparation of the silica raw material, when manufacturing the photonic crystal fiber preform 1 by the slurry cast method, it is preferable to use slurry silica as the silica raw material. Slurry silica is easily prepared by mixing and pulverizing powdered silica, water, alcohol such as ethanol, a dispersant such as tetramethylammonium hydroxide, a binder and the like until a slurry is obtained.

  On the other hand, when the sol-gel method is adopted for the production of the base material for the photonic crystal fiber, it is preferable to use gel-like silica as the silica raw material. Here, the sol-gel method is a method of obtaining solid glass or ceramics from a metal alkoxide solution through a sol state or a gel state. Specifically, starting from a solution state raw material, a jelly-like gel is prepared through a chemical reaction such as hydrolysis and condensation polymerization, and then the solvent left inside is removed by heat treatment to further promote densification. This is a method for producing glass and ceramics. In the present invention, by using the sol-gel method, a silica intermediate having a dense structure or a base material for a photonic crystal fiber can be obtained. Can be implemented.

  By mixing and stirring silica powder, which is a starting material, and alcohol (ethanol, methanol, etc.) and the like as a mixed solution and then allowing to stand, polycondensation of the starting material occurs and a sol solution is prepared.

  By subjecting the sol solution to heat treatment, condensation polymerization of silica powder and alcohol further proceeds, and the solvent is removed to form gel-like silica. The gel-like silica thus obtained is used as a silica raw material.

(B) Arrangement of wires in the space of the mold (Step 2):
A plurality of wires 53 are arranged in a predetermined arrangement in the space 52 formed in the forming die 51 constituting the base material manufacturing apparatus 5 having the configuration shown in FIG. In the present embodiment, the plurality of wire rods 53 pass through through holes formed at predetermined positions of the upper wire rod fixing portion 54 and the lower wire rod fixing portion 55, and the upper wire rod fixing portion 54 and the lower wire rod fixing portion 55. Is inserted into the upper and lower sides of the mold 51 to adjust the position, whereby the wire 53 is positioned and fixed in a state of being arranged in a predetermined arrangement.

  In addition, manufacture of the silica raw material shown to (a), and arrangement | positioning of the wire 53 to the space part 52 shown to (b) do not ask | require in particular order, The space part 52 previously shown to (b) is shown. After the arrangement of the wire 53, the silica raw material shown in (a) may be manufactured, and there is no problem even if both are performed simultaneously.

(C) Introduction of raw material silica into the space 52 (step 3):
The slurry-like or gel-like silica raw material prepared in (a) is introduced from the silica introduction part into the space part 52 of the mold 51 in which the wire 53 is arranged at a predetermined position, and the silica is introduced into the space part 52. Fill with raw materials.

(D) Production of silica intermediate (preliminary curing of raw silica) (Step 4):
The silica raw material introduced into the space 52 is subjected to a heat treatment to remove moisture and the like inside, and becomes a temporarily cured silica intermediate. The heat treatment may be performed at a temperature at which the silica raw material is not sintered. In addition, it is preferable to dry at about 20-50 degreeC before heat processing, and to remove the water | moisture content inside a silica raw material to some extent.

(E) Application and interruption of current to the wire 53 (step 5):
In the silica intermediate obtained by temporarily curing the slurry-like silica, there are a plurality of wires 53 so as to penetrate in the longitudinal direction inside the space portion 52 of the mold 51, but in the present invention, Then, an electric current is applied to the wire 53 from the charging unit 58 to thermally expand in the radial direction, and then the wire 53 is removed from the silica intermediate after the application of the current is cut off. Thus, by applying an electric current to thermally expand the wire 53 in the radial direction, the holes (air holes) 13 formed in the silica intermediate due to the presence of the wire 53 become the outer diameter of the wire 53. On the other hand, when the wire 53 is removed, the holes 13 are collapsed due to friction between the inside of the holes 13 and the surface of the wire 53 or the inner surface of the holes 13 is roughened. Can be prevented.

  The application of the current is sufficient if the wire 53 is heated to such an extent that the constituent material of the wire 53 is thermally expanded. Note that the application of the current may be performed once or may be repeated twice or more.

(F) Removal of the wire 53 from the silica intermediate (step 6):
When the current is interrupted, the wire 53 is removed from the silica intermediate. When a current is applied to the silica intermediate and the wire 53 is thermally expanded in the radial direction, the holes (air holes) 13 formed in the silica intermediate are slightly expanded with respect to the outer diameter of the wire 53. Therefore, the removal of the wire 53 is also performed smoothly.

(G) Sintering treatment of silica intermediate (step 7):
The silica intermediate is removed from the mold 51 and vitrified by a sintering process to become the photonic crystal fiber preform 1.

(4) Production of photonic crystal fiber 1a:
The photonic crystal fiber base material 1 obtained by the manufacturing method described above is drawn into a photonic crystal fiber 1a (step 8). FIG. 4 is a schematic view showing an aspect of a manufacturing apparatus (drawing apparatus 6) for the photonic crystal fiber 1a.

  A drawing apparatus 6 shown in FIG. 4 includes a fixing unit 61 that holds and fixes the photonic crystal fiber preform 1, a heating unit 62 that heats the photonic crystal fiber preform 1, and a drawn photonic crystal. An application portion 63 for applying a coating agent for protecting the fiber 1a and a winding portion 64 for winding the photonic crystal fiber 1a are provided.

  The lower end portion of the photonic crystal fiber base material 1 held and fixed to the fixing portion 61 is introduced into the heating portion 62, and the lower end portion of the photonic crystal fiber base material 1 is heated to near the melting point to draw a fiber. To do. The photonic crystal fiber 1a drawn in a semi-molten state from the base material 1 for the photonic crystal fiber is coated with a coating agent serving as a protective agent at the coating unit 63 and wound up at the winding unit 64 in a cured state. Will be.

  In this way, the core part 11 formed to extend in the center axis direction at the center of the photonic crystal fiber 1a, the clad 12 surrounding the core part 11 around the core part 11, and a predetermined arrangement. A photonic crystal fiber 1a in which a plurality of air holes (air holes) 13 are formed is manufactured.

(5) Effects of the present invention:
As described above, in the method for manufacturing the photonic crystal fiber preform 1 according to the present invention, a silica intermediate is manufactured, and the wire 53 is removed from the silica intermediate to form holes (air holes) 13. Then, it is made to vitrify by sintering treatment. Therefore, the problems such as the collapse of the holes 13 caused by the fine-diameter quartz tube and the uneven diameter of the holes 13 at the time of drawing the preform 1 for the photonic crystal fiber, which has been a concern in the conventional manufacturing method, are solved. The base material 1 for a photonic crystal fiber having a stable structure 13 can be provided.

  In addition, when removing the wire 53 from the silica intermediate, a current is applied to the wire 53 to cause thermal expansion in the radial direction, and then the wire 53 is removed after the current application is cut off. The formed holes (air holes) 13 are slightly expanded with respect to the outer diameter of the wire 53. Therefore, when removing the wire 53, it is possible to prevent the void from collapsing due to friction between the inside of the hole 13 and the surface of the wire 53, or the inner surface of the hole 13 from being roughened. It is possible to provide the photonic crystal fiber base material 1 capable of performing good optical transmission.

  And by drawing the preform | base_material 1 for photonic crystal fibers obtained with the manufacturing method of this invention, the structure of the void | hole 13 which enjoyed the said effect is stabilized. In addition, the photonic crystal fiber 1a capable of preventing collapse and roughening of the inside of the hole 13 and performing good optical transmission can be manufactured by a simple means.

(6) Modification of the embodiment:
In the above-described embodiment, the mode in which the six holes (air holes) 13 shown in FIG. 1 are formed as the photonic crystal fiber base material 1 or the photonic crystal fiber 1a is shown. The configuration of the fiber preform 1 and the like is not limited to this, and the number and arrangement of the formed holes 13 may be determined according to the required characteristics. FIG. 5 is a front view showing another embodiment of the photonic crystal fiber preform 1 and shows an embodiment in which 18 holes 13 are formed. In FIG. 5, the core portion has no holes, but the photonic crystal fiber referred to in the present application includes both a structure having no holes and a structure having holes in the core portion.

  In addition, the specific structure, shape, and the like in the implementation of the present invention may be other structures as long as the object of the present invention can be achieved.

  INDUSTRIAL APPLICABILITY The present invention can provide a photonic crystal fiber that performs good optical transmission and a base material for the photonic crystal fiber, and can be advantageously used in the optical communication industry.

It is the schematic which showed the one aspect | mode of the preform | base_material for photonic crystal fibers. It is the schematic which showed the one aspect | mode of the manufacturing apparatus (base material manufacturing apparatus) of the preform | base_material for photonic crystal fibers. It is the flowchart which showed an example of the procedure which enforces the manufacturing method of the preform | base_material for photonic crystal fibers of this invention. It is the schematic which showed the one aspect | mode of the manufacturing apparatus (drawing apparatus) of a photonic crystal fiber. It is the front view which showed the other aspect of the preform | base_material for photonic crystal fibers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material for photonic crystal fibers 1a Photonic crystal fiber 11 Core part 12 Cladding part 13 Hole (air hole)
5 Base Material Manufacturing Device 51 Mold 52 Space Part 53 Wire Material 54 Upper Wire Material Fixing Unit (Wire Material Fixing Unit)
55 Lower wire fixing part (wire fixing part)
56 Pedestal 57 Slurry introduction part 58 Power application part 59 Switch 6 Drawing device 61 Fixing part 62 Heating part 63 Application part 64 Winding part

Claims (6)

A step of arranging a plurality of wires formed of a conductive material that expands in a radial direction by application of current in a predetermined arrangement in the space of the mold in which a cylindrical space is formed;
A step of introducing a silica raw material into the space portion and pre-curing it into a silica intermediate;
Applying a current to the wire to thermally expand in the radial direction, and then removing the wire from the silica intermediate after blocking the application of the current;
A method for producing a base material for a photonic crystal fiber, comprising: a step of sintering the silica intermediate to vitrify in order.   The method for producing a base material for a photonic crystal fiber according to claim 1, wherein the silica material introduced into the space is gel-like silica obtained by a sol-gel method.   The method for producing a base material for a photonic crystal fiber according to claim 1, wherein the silica raw material introduced into the space portion is slurry silica.   4. The wire according to claim 1, wherein the wire is at least one selected from the group consisting of a simple substance of stainless steel, chromium, nickel, tungsten, iron (steel), molybdenum, cobalt, titanium, and an alloy thereof. The manufacturing method of the preform | base_material for photonic crystal fibers in any one.   The method for manufacturing a photonic crystal fiber preform according to any one of claims 1 to 3, wherein the wire is carbon.   The photonic crystal fiber base material obtained by the method for manufacturing a photonic crystal fiber base material according to any one of claims 1 to 5, further comprising a step of drawing the photonic crystal fiber base material. Crystal fiber manufacturing method.

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