JP4252005B2 - Method for manufacturing glass base material for hole fiber, hole fiber and method for manufacturing the same - Google Patents

Description

  The present invention relates to a method for producing a glass preform for a holey fiber with improved purity of an optical fiber having a plurality of holes over its entire length (hereinafter simply referred to as a holey fiber), a holey fiber, and a method for manufacturing the holey fiber.

  In general, a widely used optical fiber has a solid structure in which a region having a high refractive index called a core is provided at the center of quartz glass or the like. On the other hand, optical fibers having pores inside such as photonic crystal fibers and holey fibers disclosed in Patent Document 1 are currently attracting attention. A photonic crystal fiber forms a photonic band gap by providing regularly arranged holes in the fiber, and guides light by adding defects to the photonic band gap.

A holey fiber has a hole in the cladding and lowers the effective refractive index of the cladding to give a difference in refractive index from the core. The waveguide principle is totally reflected like conventional optical fibers. Is used. In addition, a hole-added fiber having a shape in which a hole is formed around the core of a conventional optical fiber has been proposed.
All of these fibers have holes, and their shape, size, arrangement, etc. have a great influence on their transmission characteristics.

For the production of these fibers, a method of drawing a bundle of glass capillaries (capillary) as disclosed in Patent Document 2 (capillary method or stack and draw method) and disclosed in Patent Documents 3 and 4 There is a method (drilling method) in which a hole is formed in a glass rod as described above. Hereinafter, optical fibers having holes, such as photonic crystal fibers, holey fibers, and hole-added fibers, are collectively referred to as hole fibers.
As shown in FIG. 1, the perforating method synthesizes a porous glass base material and makes it transparent, and then performs perforation processing.

JP 2002-506533 A JP 2002-97034 A JP 2002-293562 A JP 2002-145634 A

  However, the capillary method has a problem that voids are likely to remain in the fiber or the shape of the hole tends to collapse when drawing. Further, since the capillary is used, there is a problem that OH group / impurity contamination is likely to occur on the outer surface, and it is difficult to reduce the loss.

  On the other hand, in the drilling method, it is difficult to make a fine deep hole in a very hard quartz glass, and a special method such as ultrasonic vibration grinding must be used. Furthermore, in order to manufacture a fiber having a large number of holes, the processing cost is extremely high and a long processing time is required. In addition, because quartz glass is a difficult-to-cut material, it is necessary to rotate the grinding tool at a high speed. There is a problem of disappearing.

  The present invention has been made in view of the above circumstances, and is suitable for manufacturing a holey fiber. For a holey fiber that enables low-cost manufacturing of a large-sized glass fiber for a holey fiber with less impurities. It aims at providing the manufacturing method of a glass base material, a hole fiber, and its manufacturing method.

  The method for producing a glass preform for a holey fiber according to the present invention is a method for producing a glass preform for an optical fiber having a plurality of holes in its entire length in the axial direction. A porous glass base material is formed, a plurality of holes are formed in the axial direction from the end of the porous glass base material, heat-treated in an atmosphere containing chlorine or fluorine, preferably 700 to 1200 ° C., and then porous. It is characterized by heating to a temperature at which the glass base material becomes transparent. Also, a porous glass base material is formed by depositing on the starting member rod, a plurality of holes are opened in the axial direction from the end of the porous glass base material, and the temperature becomes transparent after dehydration treatment with chlorine and fluorine treatment. You may heat to.

As the starting member rod, high-purity quartz glass or quartz glass containing a dopant is used, and glass fine particles generated by supplying the dopant raw material together with the glass raw material are deposited thereon.
The deposition of glass particulates may be axially from the tip of the starting member rod, axially along the side of the starting member rod, or perpendicular to the axis of the starting member rod on the side of the starting member rod. Although it is performed, it may be deposited in any direction.

Prior to the step of opening a plurality of holes, a step of heat treatment at 1100 to 1450 ° C. to adjust the density of the porous glass base material to 0.25 to 0.80 g / cm ³ may be provided. This density adjustment is preferably performed in an atmosphere containing chlorine or fluorine.
Furthermore, prior to the step of opening a plurality of holes, the end of the porous glass base material may be cut out, and the end surface may be processed into a plane perpendicular to the central axis before the holes are formed.

The transparent glass base material may be made transparent in an atmosphere containing a dopant. In addition, it is preferable that the inner surface of the hole of the transparent glass base material is mirror-polished.
A holey fiber can be obtained by heating and drawing the holey fiber glass preform thus manufactured.

  According to the present invention, since the hole is formed after adjusting the density of the porous glass base material to a density suitable for drilling, it is possible to easily open a deep hole as compared with the method of making a hole in a hard glass rod. In addition, it is possible to easily manufacture a large glass fiber for a holey fiber at a low cost. Furthermore, since the high purity treatment is performed after the perforating process is performed at the stage of the porous glass base material, the purity of the glass base material for the hole fiber can be improved.

The method for producing a glass preform for a holey fiber according to the present invention includes, for example, depositing glass fine particles generated by a flame hydrolysis reaction of a glass raw material to produce a porous glass preform, and the obtained porous glass preform. Is heated at 1100 to 1450 ° C. at the time of dehydration treatment or after dehydration treatment as necessary to shrink the porous glass base material, and its bulk density is 0.25 to 0.80 g / cm ³ suitable for drilling. After adjusting so that the porous glass base material is perforated in the axial direction, dehydration / purification treatment and clarification treatment are performed.

In the present invention, as shown in FIG. 2, a method for producing a glass preform for a holey fiber includes (1) a production process of a porous glass preform, (2) a density adjustment process, (3) a drilling process, It consists of five steps: (4) dehydration / purification step and (5) clarification step. In addition, (6) hole polishing process is added as needed. Thereafter, (7) a holey fiber is manufactured in a drawing process.
Hereinafter, these steps will be described in order.

  First, (1) the manufacturing process of the porous glass base material includes a conventionally known vapor-phase axial method (VAD method), external VAD method, external method (OVD method), etc. These methods are used to synthesize glass particles by flame hydrolysis of a glass raw material in a burner flame, and deposit these on a rotating starting member rod. .

  The VAD method is a method of depositing and growing from the tip of a starting member rod toward its axial direction. In the external VAD method, glass particles are deposited on the side surface of the starting member rod while moving the burner in one direction parallel to the axial end of the starting member rod, thereby forming the mother along the side surface of the starting member rod. Growing materials. In the OVD method, while the glass particles are deposited toward the side surface of the starting member rod, the burner is reciprocated in parallel with the axis of the starting member rod, and the base material is directed toward the side surface of the starting member rod in a direction perpendicular to the axis. Grow.

  Various properties such as refractive index and photosensitivity of glass can be changed by supplying dopant raw material together with glass raw material during deposition, or by using high purity quartz glass or quartz glass containing dopant for the starting member rod. Can do.

The porous glass base material thus obtained is heat-treated in a furnace heated to 1100 to 1450 ° C. in order to adjust to a density suitable for cutting prior to drilling, and 0.25 to 0 Adjusted to a density of 80 g / cm ³ . If the density is less than 0.25 g / cm ^3, it is too brittle and easily damaged during cutting. On the other hand, if it exceeds 0.80 g / cm ³ , it becomes too hard and cracks easily occur during cutting. Therefore, the density is adjusted to the above range. A particularly preferable range is around 0.4, because dehydration with chlorine can be performed efficiently and processability is also good.

  When adjusting the density of the porous glass base material, the glass fine particles are slightly melted and welded to each other, so that OH groups and impurities mainly present on the surface of the glass fine particles may be taken into the glass. In order to prevent this, OH groups and impurities can be removed by heating in an atmosphere containing chlorine or a fluorine compound in the density adjusting step. In addition, a density adjustment process can also be abbreviate | omitted by adjusting a density by the manufacturing process of a porous glass base material, and storing in the said range previously.

  Next, the porous glass base material adjusted to a density suitable for processing is punched by mechanical grinding. When drilling is performed for difficult-to-cut materials such as carbide drills and diamond drills, the tool life is long, so the blade replacement interval can be increased, and workability and processing accuracy are improved. The processing speed at this time varies depending on the hole diameter, depth, bulk density, etc., but can be 0.1 mm to several tens of mm / second or more, which is a much faster speed than the drilling of hard transparent glass. Can be drilled.

  Even if the porous glass base material is made by any of the VAD method, the external VAD method, and the OVD method, the end portion thereof is not a plane perpendicular to the axis. For this reason, the end of the porous glass base material is cut perpendicularly to the axis, and a flat surface is provided in the end in advance to facilitate subsequent drilling. Thereby, the depth of a hole can be equalized, the positional accuracy of the hole is improved, and the yield is improved.

  For cutting the end, if there is no transparent glass rod in the center, cut metal, wood, new building materials, glass, etc., such as gold saws, yarn saws, saws for woodwork, rotary cutting whetstones, wire saws, band saws, etc. What can be used can be used. When there is a transparent glass rod in the center, the transparent glass rod may be cut or excised after removing the porous portion using these cutting means.

The porous glass base material that has been subjected to perforation processing is heated to 700 to 1200 ° C. in an atmosphere containing chlorine or a fluorine compound as necessary to be dehydrated and purified. Thereafter, the glass is heated to a temperature at which it becomes transparent, whereby a transparent glass base material having pores is obtained.
The dehydration / purification treatment and the clarification step can be simultaneously performed in a heating furnace provided with a temperature gradient. Moreover, various characteristics, such as a refractive index of the glass obtained and photosensitivity, can be changed by setting it as the atmosphere containing a dopant in the case of transparency.

  Depending on the density of the porous glass base material before the perforating process and the processing method for perforating, the inner surface of the hole of the obtained transparent glass base material may be roughened. In such a case, the inner surface of the hole is mirror-polished using an abrasive, so that the light scattering of the glass base material can be suppressed and the transmission loss of the holey fiber obtained therefrom can be reduced. In order to mirror-polish the inner surface of the hole, for example, there can be mentioned a method of grinding / polishing using a material that can be used for grinding / polishing of normal glass such as powder of silicon carbide or cerium oxide.

  By using the glass preform for a hole fiber of the present invention, a hole fiber having high purity can be obtained at a low cost.

It is a process flow figure explaining the conventional drilling process. It is a process flow figure explaining the drilling process of this invention.

Claims (15)

In a manufacturing method of a glass preform for an optical fiber having a plurality of holes in the entire length in the axial direction, a porous glass preform is formed by depositing glass particles on a rotating starting member rod, and the porous glass preform A glass base material for a holey fiber, characterized in that a plurality of holes are made in the axial direction from the end, and after heat treatment in a chlorine or fluorine-containing atmosphere, the porous glass base material is heated to a temperature at which it becomes transparent. Production method. The method for producing a glass preform for holey fibers according to claim 1, wherein heat treatment is performed at 700 to 1200 ° C in a chlorine or fluorine-containing atmosphere prior to the transparent glass preform. The method for producing a glass preform for a holey fiber according to claim 1 or 2, wherein the starting member bar is high-purity quartz glass. The method for producing a glass preform for a holey fiber according to claim 1 or 2, wherein the starting member bar is quartz glass containing a dopant. The method for producing a glass preform for a holey fiber according to any one of claims 1 to 4, wherein the dopant raw material is supplied together with the glass raw material to produce glass fine particles. The method for producing a glass preform for a holey fiber according to any one of claims 1 to 5, wherein the glass fine particles are deposited in the axial direction from the tip of the starting member rod. The method for producing a glass preform for a holey fiber according to any one of claims 1 to 5, wherein the glass fine particles are deposited in an axial direction along a side surface of the starting member rod. The method for producing a glass preform for a holey fiber according to any one of claims 1 to 5, wherein the glass fine particles are deposited on a side surface of the starting member rod in a direction perpendicular to the axis of the starting member rod. The process of adjusting the density of a porous glass base material to 0.25-0.80 g / cm < ³ > by heat-processing at 1100-1450 degreeC prior to the process of opening a some hole. The manufacturing method of the glass preform | base_material for hole fibers in any one of these. The method for producing a glass preform for a holey fiber according to claim 9, wherein the step of adjusting the density is performed in an atmosphere containing chlorine or fluorine. The glass base for a holey fiber according to any one of claims 1 to 10, wherein an end of the porous glass base material is cut out prior to the step of forming a plurality of holes, and the end face is made a plane perpendicular to the central axis. A method of manufacturing the material. The method for producing a glass preform for a holey fiber according to any one of claims 1 to 11, wherein the transparent glass preform is made transparent in an atmosphere containing a dopant. The method for producing a glass preform for a holey fiber according to any one of claims 1 to 12, wherein the inner surface of the hole of the transparent glass preform is mirror-polished. A method for producing a holey fiber, wherein the glass preform for holey fiber manufactured using the method according to any one of claims 1 to 13 is heated and drawn. A holey fiber manufactured using the manufacturing method according to claim 14.

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