JPH0881232A - Production of preform for eccentric core optical fiber - Google Patents

Abstract

PURPOSE: To obtain a preform for an eccentric core optical fiber having a core at a desired position and excellent optical characteristics by forming a channel on a glass rod along the longer direction of the glass rod forming a molded article containing a core material in the channel by power molding method and integrating the glass rod with the molded article. CONSTITUTION: A preform for an eccentric core optical fiber is produced by the following processes (a) to (c). (a) A groove 12 is formed on a glass rod 11 along the longer direction of the glass rod. (b) A molded article 16 containing a core material 14 is formed in the channel 12 by powder molding method and the glass rod 11 and the molded article 16 are integrated (15:granulated power). (c) The glass rod is purified and transparently vitrified to give a preform for an eccentric core optical fiber having the core material 14 at a desired position in the glass rod 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a preform of an eccentric core optical fiber used for an optical fiber type sensor or the like.

[0002]

2. Description of the Related Art As a conventional method for producing a preform for an eccentric core optical fiber, as shown in FIG.
Of the optical fiber preform having the core 42 at the center of the core by the vapor phase synthesis method, the outer periphery of the optical fiber preform is mechanically ground, and the core 42 is placed at an arbitrary position as shown in FIG.
There is a method of producing a preform for an eccentric core optical fiber.

Further, as a method for easily producing a base material for an eccentric core optical fiber, there is a method using a powder molding method such as a casting method and a pressure molding method. Specifically, a core rod is installed at an arbitrary position of a molding die, and a slurry containing silica powder or a granulated powder is arranged around the core rod to perform a casting molding method (JP-A-1-56331, Japanese Patent Application No. 4-331331). 1898
No. 51) and a pressure molding method (Japanese Patent Application No. 4-304418), and a transparent glass is formed into a preform for an eccentric core optical fiber.

[0004]

In the method of mechanically grinding the outer circumference of the optical fiber preform, it is necessary to grind a large amount of the optical fiber preform, so that the yield is very poor. In addition, it requires a high technique to grind the core rod so that the core rod is located at an appropriate position, and it is costly.

In the method utilizing the powder molding method, the strength of the obtained molded body is low and the handling thereof needs attention. Further, when the molded body is made into transparent glass, shrinkage occurs and the core rod moves, so that the position of the core rod may not be an appropriate position. In particular, when the pressure molding method is used as the powder molding method, a large shrinkage is accompanied during molding.

On the other hand, in the method of manufacturing a preform for a polarization maintaining fiber, there is a technique of forming a hole at a position displaced from the center of a glass rod, inserting a rod serving as a stress material, or filling silica powder. It is possible to apply this technique to make a hole for a core in an appropriate position of a glass rod and insert the core rod into this hole or fill the hole with silica powder. However, with this method, it takes time and effort to insert the core rod into the hole, and defects are likely to occur at the interface between the glass rod and the core rod. Further, when the silica powder is filled in the hole of the glass rod, the silica powder is filled and pressed along the axial direction of the glass rod, so that the packing density of the silica powder becomes nonuniform, and when this is vitrified, bubbles are generated. Will occur. As a result, the optical characteristics of the obtained eccentric core optical fiber deteriorate.

The present invention has been made in view of the above points, and has an eccentric core optical fiber which has a core at a desired position and can efficiently obtain a preform of an eccentric core optical fiber having excellent optical characteristics. An object of the present invention is to provide a manufacturing method of a fiber preform.

[0008]

According to the present invention, there is provided a step of forming a groove along a longitudinal direction of a glass rod, and a molded body containing a core material is formed in the groove by a powder molding method to form the glass rod. And a step of integrating the molded body,
A method for producing a preform for an eccentric core optical fiber, comprising the steps of subjecting this glass rod to a refining treatment and a transparent vitrification treatment.

Here, as the material of the glass rod, it is desirable to use silica glass produced by a vapor phase synthesis method and free from impurities and bubbles. The groove formed in the glass rod is preferably parallel to the axial direction along the longitudinal direction of the glass rod. That is, it is preferable that the groove is formed so that the glass rod has the same cross-sectional shape and dimension in the axial direction. The cross-sectional shape of the groove is not particularly limited as long as the molded body can be arranged. That is, the cross-sectional shape of the groove may be wedge-shaped or semi-circular. In addition, the groove formed in the glass rod,
It may be formed over the entire side surface of the glass rod or may be partially unformed. For example, by providing a region in which a groove is not formed near the end of the glass rod, it is possible to prevent the molded body in the groove from falling from the glass rod. In the present specification, the groove means that a region defined by the glass rod is formed when the glass rod is installed in the mold. Therefore, in this specification, a groove includes a cutout portion as shown in FIG. 3B in addition to a normal groove.

When forming a groove in the glass rod, methods such as mechanical grinding and etching using a reagent such as hydrofluoric acid are adopted. Since this mechanical grinding only forms a groove, the yield is better than the method of forming a hole along the longitudinal direction in the glass rod or the method of grinding the outer circumference of the optical fiber preform into a circular shape.

The core material in the molded article means not only a rod having no clad but only a core, and a rod having a part of the clad outside the core. It is advantageous to use a rod having a part of the cladding from the viewpoint of transmission loss.

Silica-based powder or the like is used as the material of the molded body. In particular, since the glass rod and the molded body are integrally formed, the material of the molded body preferably has the same composition as that of the material of the glass rod. In addition, a molding aid such as polyvinyl alcohol may be added to the above material in order to improve the mechanical strength of the molded body. In this case, it is necessary to perform a degreasing treatment to remove the molding aid before subjecting the molded body to the refining treatment and the transparent vitrification treatment.

Examples of the powder molding method include a pressure molding method, a casting molding method and an extrusion molding method. Particularly, as the powder molding method, it is desirable to use a hydrostatic pressure method using a rubber molding die made of urethane rubber or the like. The refining treatment and the transparent vitrification treatment are performed under the same conditions as those used in the ordinary manufacturing process of optical fiber preforms.

[0014]

The method for producing a preform for an eccentric core optical fiber according to the present invention comprises forming a groove in a glass rod along its longitudinal direction,
It is characterized in that a molded body containing a core material is formed in the groove by a powder molding method to integrate the glass rod and the molded body.

According to the present invention, since only the groove is formed in the glass rod, the processing applied to the glass rod is simple and the yield is very good. Further, the molded body formed in the groove as in the present invention has better uniformity than the molded body formed by forming a hole in the glass rod and filling the silica-based powder.

Further, since the molded body is formed only in the groove formed in the glass rod, the handling in the manufacturing process becomes easy. Further, since the molded body region is small, the movement of the core rod due to shrinkage during molding is small. further,
Since the positioning of the core rod can be performed when the core rod is installed in the molding die, the position of the core rod can be changed at that time. Therefore, the flexibility of the position of the core rod is wide, and the core rod can be easily installed. Therefore, it is possible to obtain an eccentric core optical fiber having a high core position accuracy.

[0017]

Embodiments of the present invention will be specifically described below with reference to the drawings. (Example 1) First, as shown in FIG. 1 (A), a part of the side surface of a glass rod 11 having an outer diameter of 32 mmφ and a length of 250 mm produced by a vapor phase synthesis method was cut with a diamond cutter, and the glass rod 11 was cut. A continuous groove 12 was formed along the longitudinal direction. Then, the inner surface of the groove 12 was polished with a grindstone to make it smooth, and then etched with hydrofluoric acid.

Next, as shown in FIG. 1 (B), a glass rod 11 is placed in a molding rubber mold 13, and core: clad = 1: 2, Δ = 0.3%, outer diameter 4.1 mmφ, length. 25
A core rod 14 manufactured by the VAD method of 0 mmφ was installed at a substantially central portion of a region defined by the molding rubber mold 13 and the groove 12. The core rod 14 is installed at an appropriate position when it becomes the final base material in consideration of the shrinkage of the silica-based powder to be used and the transparent vitrification treatment.

Next, the average particle size 8 produced by the vapor phase synthesis method
66 parts by weight of pure water, 1.6 parts by weight of PVA (polyvinyl alcohol), and 1.0 parts by weight of glycerin were mixed with 100 parts by weight of silica powder, and the slurry was stirred to form a slurry. The obtained slurry was granulated with a spray dryer to obtain granulated powder having an average particle size of 100 μm. The granulated powder 15 is applied to the molding rubber mold 13 and the groove 1.
2 and a region defined by the core rod 14
Filled outside the.

Next, this mold was placed in a hydrostatic pressure device and the mold was hydrostatically pressurized at a pressure of 1000 kgf / cm ² . After the pressure molding, the mold was taken out from the hydrostatic pressure device, and the glass rod was taken out from the mold. In this glass rod, as shown in FIG. 1C, the glass rod 11 and the molded body 16 were integrally molded without the molded body 16 coming off from the glass rod 11.

This glass rod was heated at 500 ° C. for 5 hours in a nitrogen atmosphere containing oxygen to degrease it, and then refined at 1200 ° C. in a He atmosphere containing chlorine (chlorine concentration 1%). Then, add it to He under an atmosphere of 1600
A transparent vitrification treatment at ℃ was performed to produce a preform for an eccentric core optical fiber. The eccentric core optical fiber preform after the transparent vitrification treatment has a cross-sectional shape shown in FIG.
No bubbles were observed at the boundary between the glass rod 11 and the core rod 14.

The obtained base material for eccentric core optical fiber was processed by a flame burner and then drawn to obtain an eccentric core optical fiber. This eccentric core optical fiber had the cross-sectional shape shown in FIG. This eccentric core optical fiber had a core at a position as designed, and had optical characteristics equivalent to those of an eccentric core optical fiber manufactured by a usual method. (Example 2) The glass rod 11 having the groove 12 formed therein was placed in a casting mold (made of resin) 21 in the same manner as in Example 1. Further, as shown in FIG. 2, the core rod 14 was installed in the substantially central portion of the region defined by the casting mold 21 and the groove 12 in the same manner as in Example 1. The core rod 14 is installed at an appropriate position when it becomes the final base material in consideration of the shrinkage of the silica-based powder to be used and the transparent vitrification treatment.

Next, the average particle size 8 produced by the vapor phase synthesis method
Solid content of 77% using pure water as a solvent for silica powder of μm
The slurry 22 of was prepared. Add this slurry 22 to the funnel 2
3 was used to inject into the region defined by the casting mold 21 and the groove 12, that is, outside the core rod 14, and left in this state for 6 hours.

Then, the glass rod was taken out from the molding die. This glass rod, as shown in FIG.
The glass rod 11 and the molded body 16 were integrally molded without the molded body 16 coming off the glass rod 11. Next, this glass rod was placed in a dryer at 100 ° C. and heated for 12 hours to remove water.

This glass rod was heat-treated at 500 ° C. for 5 hours in a nitrogen atmosphere containing oxygen to degrease it, and then refined at 1200 ° C. in a He atmosphere containing chlorine (chlorine concentration 1%). Then, add it to He under an atmosphere of 1600
A transparent vitrification treatment at ℃ was performed to produce a preform for an eccentric core optical fiber. The eccentric core optical fiber preform after the transparent vitrification treatment has a cross-sectional shape shown in FIG.
No bubbles were observed at the boundary between the glass rod 11 and the core rod 14.

The obtained base material for eccentric core optical fiber was processed by a flame burner and then drawn to obtain an eccentric core optical fiber. This eccentric core optical fiber had the cross-sectional shape shown in FIG. This eccentric core optical fiber has a core at a position as designed, and has optical characteristics equivalent to those of an eccentric core optical fiber manufactured by a usual method. Example 3 An eccentric core optical fiber similar to Example 1 except that a glass rod 31 having a semicircular groove 32 having a cross-sectional shape as shown in FIG. 3A is used. Got This eccentric core optical fiber is shown in FIG.
It had a sectional shape shown in FIG. This eccentric core optical fiber has a core at a position as designed, and has optical characteristics equivalent to those of an eccentric core optical fiber manufactured by a usual method. (Example 4) An eccentric core optical fiber was obtained in the same manner as in Example 1 except that the glass rod 33 having the cutout 34 formed to have the cross-sectional shape as shown in FIG. 3B was used. . This eccentric core optical fiber is shown in FIG.
It had a sectional shape shown in FIG. This eccentric core optical fiber has a core at a position as designed, and has optical characteristics equivalent to those of an eccentric core optical fiber manufactured by a usual method.

[0027]

As described above, according to the method for producing a preform for an eccentric core optical fiber of the present invention, a groove is formed in a glass rod along its longitudinal direction, and a molded body containing the core material is powdered in the groove. Formed by a molding method to integrate the glass rod and the molded body, and subjecting the glass rod to a refining treatment and a transparent vitrification treatment, the handling is easy, and the core material does not move due to shrinkage of the molded body. A base material of an eccentric core optical fiber having a core at a desired position and having excellent optical characteristics can be efficiently obtained at low cost.

[Brief description of drawings]

1A to 1E are views for explaining a method for manufacturing a preform for an eccentric core optical fiber of the present invention.

FIG. 2 is a cross-sectional view showing another example of a glass rod used in the method for producing a preform for an eccentric core optical fiber of the present invention.

FIG. 3 is a cross-sectional view showing another example of a glass rod used in the method for producing a preform for an eccentric core optical fiber of the present invention.

4A and 4B are views for explaining a conventional method of manufacturing a preform for an eccentric core optical fiber.

[Explanation of symbols]

11, 31, 33 ... Glass rod, 12, 32 ... Groove, 1
3 ... Molded rubber mold, 14 ... Core rod, 15 ... Granulated powder,
21 ... Casting mold, 22 ... Slurry, 23 ... Funnel, 3
4 ... Cutout part.

Claims (1)

[Claims] 1. A step of forming a groove in a glass rod along a longitudinal direction thereof, and a molded body containing a core material is formed in the groove by a powder molding method to integrate the glass rod and the molded body. A method for producing a preform for an eccentric core optical fiber, comprising: a step; and a step of subjecting this glass rod to a refining treatment and a transparent vitrification treatment.