JPS61163133A - Preparation of single polarization optical fiber - Google Patents

Abstract

PURPOSE:To prepare stressed single polarization optical fiber having higher quality with better dimensional precision than conventional product inexpensively by prepg. a parent material for optical fiber by the sol-gel method and drawing the parent material. CONSTITUTION:A wet gel contg. a section for constituting a clad section 3, core constituting section 1, and stressed section 2 in the optical fiber to be formed from the parent material by the sol-gel method is prepd. The wet gel is dried and sintered to prepare the titled single polarization optical fiber. The clad sol for constituting the afore-mentioned clad section is poured into a cylindrical vessel provided with a freely attachable and detachable mold fixed to a necessary position. The sol for constituting the core and for pit are poured into plural cavities formed after detaching the mold, and poured sol are gelled. Thus, the above-described wet gel is prepd. preferably.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a polarization-maintaining optical fiber used in coherent optical transmission systems, optical fiber sensors, and the like. More specifically, the present invention relates to a method of manufacturing a stress-applied polarization-maintaining optical fiber having side bits. (Fig. 1) [Conventional technology] Conventional stress-applying polarization-maintaining light with side bits 7
Since it is difficult to completely synthesize the base material for optical fiber using the vapor phase method, the core clad base material is sandwiched between stress-applying base materials on both sides, placed in a jacket tube, and the remaining space is filled with a filler base material. It was manufactured by drawing a buried assembly.

(Jacket method, Electric Corporation, JP-A-58-104 [Problems to be solved by the invention]) This method requires a great deal of labor and time, resulting in extremely high manufacturing costs.In addition, at the assembly stage, each base material must be manufactured with precision. However, it is extremely difficult to arrange them without any gaps, so
Another problem was that it was difficult to manufacture high-quality polarization-maintaining optical fibers with good dimensional accuracy such as the shape of the core.

The present invention solves the above problems, and its purpose is to:
By creating an optical fiber base material (preform) using the sol-gel method and drawing the optical fiber base material, we can produce high-quality side bits with better dimensional accuracy than that obtained with the conventional jacket method. It is an object of the present invention to provide a method for manufacturing a stress-applied polarization-maintaining optical fiber having the following characteristics at a lower cost than the conventional jacket method.

[Means for solving problems]

The method for manufacturing a polarization-maintaining optical fiber of the present invention uses a sol-gel method to separate a portion that will constitute a cladding portion when an optical fiber is made, a portion that will constitute a core portion when an optical fiber is made, and an optical fiber. The process includes the step of creating a wet gel that contains a part that forms a stress applying part when it is at an angle of 1° with the fiber, and drying and sintering the wet gel to create a base material for a polarization preserving optical fiber. shall be.

Further, in the manufacturing method of the present invention, the cladding portion.

In order to produce a high-purity wet gel that contains the core and bit parts with high positional accuracy, we created a sol solution (hereinafter referred to as cladding) whose main raw material is an alkyl silicate hydrolyzed solution, which constitutes the cladding part when used as an optical fiber. sol),
A removable mold is poured into a cylindrical container fixed at a required position to gel, and after the mold is removed, optical fibers are formed in the plurality of hollows or depressions that are formed to form a core part. A sol solution whose main raw material is an alkyl silicate hydrolyzed solution (hereinafter referred to as the sol for core), and a sol solution whose main raw material is an alkyl silicate hydrolyzed solution that constitutes the stress applying part when it is made into an optical fiber (hereinafter referred to as the sol for bits). Preferably, the wet gel is produced by pouring and gelling.

Alternatively, in the production method of the present invention, the following method may be used to produce a high purity wet gel that contains the cladding part, core part, and bit part with high positional accuracy.

That is, the sol for the cladding is poured into a cylindrical container with a removable mold fixed at the required position and allowed to gel, and after removing the mold, the sol is poured into the bit hole among the plurality of hollow parts or depressions that are formed. Pour the bit sol and let it gel, then pour the cladding sol into the core cladding hole at the center of the wet gel, then cover the cylindrical container, attach it to a rotating device, and rotate it preferably at a rotation speed of 200 rpm or more. In this method, the wet gel is produced by gelatinizing the sol while transferring the core sol into the resulting core pores and gelling the core sol.

Further, in the manufacturing method of the present invention, it is desirable to use a mold having a structure that allows expansion and contraction. This is because if a mold with a structure that allows expansion and contraction is not used, the sol for the cladding will gel and when the mold is removed (or rather, pulled out), the inner surface of the gel and the mold will remain in close contact with each other. This is because cracks such as cladding are likely to occur on the inner surface of the gel, making it difficult to obtain a high-quality optical fiber because holes with clean inner surfaces cannot be formed. On the other hand, when using the mold with the expandable structure of the present invention, when the cladding sol gels and the mold is removed, the inner surface of the gel can be removed without touching the mold, leaving an extremely clean inner surface. A hole is formed.

In the manufacturing method of the present invention, it is desirable that the cladding sol, core sol, and bit sol contain at least a hydrolyzed solution containing an alkyl silicate as a raw material and a fine powder mainly consisting of ultrafine silica powder. . This is because, as described in Japanese Patent Application No. 58-237577, a practical size can be obtained by mixing a hydrolyzed solution containing a metal alkoxide as a raw material and ultrafine powder in an appropriate ratio in a raw sol. This is because a quartz glass body having a high yield can be obtained with high yield.

This will be explained in detail below using examples.

[Example 1] Table 1 Using the raw materials shown in Table 1, an acidic hydrolyzed solution used for the sol for cladding, an acidic hydrolyzed solution used for the sol for the core, and an acidic hydrolyzed solution used for the sol for bits. made. In parallel, ultrafine powder silica was synthesized using the raw materials shown in Table 1, and after a vacuum method, neutralization was performed using dilute hydrochloric acid (ultrafine powder with an average particle size of L14 μm) was synthesized using dilute hydrochloric acid. Prepare a solution containing silica, mix these according to Table 1, and then use dilute ammonia water and water to adjust the PIl value and effective glass component concentration to create a cladding sol 250.
0d, core sol 200sj, and bit sol 200- were made. This sol for two pours was transferred to a cylindrical container shown in FIG. 2, and gelatinized in 50 minutes. Ten minutes after the cladding sol gelatinized, the mold was separated from the inner surface of the gel by reducing the internal pressure of the mold from 5 atm to 1 atm or less, and was removed without touching the gel. Next, the core sol was transferred to the center hole, and the bit sol was transferred to the holes on both sides.Both the core sol and the bit sol gelled in about 15 minutes, and the cladding part and the core Department,
A cylindrical wet gel containing the bit part inside was obtained. The obtained wet gel has a diameter of 60 m and a length of 80 m.
The diameter corresponding to the core part is 508m.
m, the diameter corresponding to the bit part was 1 ZOmm, and the interval between them was IA7M. (Figure 3) Hold this wet gel in a sealed cylindrical container at 30°
After aging at C for 2 days, it was transferred to a drying container with an opening ratio of 4% (L). Next, this drying container was placed in a dryer at 60°C to dry the wet gel.
Stable dry gel that does not crack even when left at room temperature (diameter 39
．． 6 trtm, length 528 m+n) was obtained. Next, this dry gel was placed in a quartz tubular furnace and heated to 1000°C. Thereafter, the temperature was lowered to 700°C, and then the temperature was raised to 900°C while flowing chlorine gas to perform OH group removal treatment. Thereafter, the temperature was raised to 950° C. while flowing oxygen gas to perform a dechlorination treatment, and then the temperature was raised to 1250° C. while flowing only helium sludge to perform a pore-closing treatment. Thereafter, the sample was placed in a vertical tube furnace, heated to 1,350°C, and held at 1,350°C for 1 hour to become non-porous, yielding a transparent glass body. The size of this glass body, that is, the base material for a polarization maintaining optical fiber, was 278 mm in diameter and 371 mm in length.

When the OH groups contained in the polarization-maintaining light 7 Eyeper base material obtained in this example were fixed by measuring the absorption spectrum in the infrared region, no absorption peak was observed at 47 μm, and the absorption peak at 1 ppm or less was observed. It was confirmed that there is. Furthermore, when the base material is drawn into an optical fiber with an outer diameter of 125 μm, the diameter of the core portion is approximately &3 μm, which is 1°311
rn (7), -f Single mode waveguiding power for light;
confirmed to occur. In addition, the bit part (stress applying part) with a diameter of 25 μm is correctly arranged in an axially symmetrical position with respect to the central axis of the core part, and the distance between the central axis of the bit part and the central axis of the core part is both 2a5 μm. It was confirmed that the polarization maintaining optical fiber of this example was manufactured with good positional accuracy.

[Example 2] A clad sol, a core sol, and a bit sol were made in the same manner as in Example 1. Of these, the sol for cladding was transferred to the cylindrical container shown in Figure 4, and
Gelified in minutes. Ten minutes after the cladding sol gelled, the mold was pulled out, but the surface of the mold dragged the gel, making it impossible to obtain holes with clean inner surfaces.

[Example 3] The sol for cladding (pure silica, non-doped), the sol for core (doped with Ge5mo1%), and the sol for bit (doped with B15mo1%) having the same composition as shown in Example 1 were mixed into ultrafine powder. It was made using only an acidic hydrolysis solution as a raw material, without using silica.

Using this sol (the effective glass component concentration is slightly lower than the sol shown in Example 1), a wet gel of the same size as in Example 1 was made in the same manner as shown in Example 1.

However, when we tried to make 10 bottles of this wet gel, age it under various conditions, and dry it to make a dry gel that would not break even when left at room temperature, all 10 bottles broke or cracked during the drying process. did.

[Example 4] Sol for cladding (pure silica, non-doped) with the same composition as shown in Example 1, sol for core (Ge5!+101%)
dope), bit sol (B 15 mob% dope)
An optical fiber was manufactured in the same manner as in Example 1, except that ultrafine powder silica obtained by a vapor phase method using SiO2° as a raw material was used as the ultrafine powder silica. A high-quality polarization-maintaining optical fiber with good dimensional accuracy was obtained.

[Example 5] In the same manner as shown in Example 1, a sol for cladding,
A core sol and a bit sol were prepared, and a wet gel shown in FIG. 5 was prepared using a method similar to that of Example 1. (Diameter: 60 m, length: 800 mm) This wet gel was dried and sintered in the same manner as in Example 1 to obtain a transparent glass similar to that shown in FIG. 5, that is, a base material for a polarization-maintaining optical fiber. (Diameter 2 z8 rta w length 571
(Scream) The base material of CD.

When the fiber was placed in a quartz jacketed tube with an outer diameter of 44 mm and an inner diameter of 29 rpm and drawn, a high-quality polarization-maintaining optical fiber with good dimensional accuracy was obtained as in Example 1. [Example 6] As shown in Example 1. Sol for cladding,
A core sol and a bit sol were prepared, and a wet gel shown in FIG. 6 was prepared using a method similar to Example 1. (Diameter 60 fMn, length 800 rm) When this wet gel was dried and sintered in the same manner as in Example 1, a transparent glass similar to that shown in Fig. 6, that is, a base material for a polarization preserving optical fiber was obtained. . (Diameter 278mm, length 37mm
1 m) When this base material was placed in a quartz jacketed tube with an outer diameter of 44mm and an inner diameter of 29rrrm and drawn, a high quality polarization maintaining optical fiber with good dimensional accuracy was obtained as in Example 1 [Example 7] In the same manner as shown in Example 1, a sol for cladding,
A core sol and a bit sol were prepared, and a wet gel shown in FIG. 7(A) was prepared using a method similar to Example 1. Next, transfer the bit sol into the bit hole of this wet gel and let it gel, then pour the separately prepared clad sol into the center core clad hole, then put 7 taps into the cylindrical container and rotate it. Attach to the device 1
Gelify while rotating at 200 rpm. Figure 7 (B)
We made the wet gel shown in . Finally, the core sol was transferred into the core hole of this wet gel and gelled to produce a wet gel in which the cylindrical cladding and core bit were integrated. (Diameter 60 mm, length a o ttat)
When this wet gel was dried and sintered in the same manner as in Example 1, a transparent glass similar to that shown in FIG. 3, that is, a base material for a polarization-maintaining optical fiber, was obtained. (Diameter 27.8F1
1311. When this base material was drawn, a high-quality polarization-maintaining optical fiber with good dimensional accuracy was obtained as in Example 1.

[Example 8] Cladding sol (pure silica, non-doped) and core sol (G.

5rn01% doped), bit sol (B15m.

1% dope), a hydrolyzed solution of ethyl silicate and finely powdered silica, a hydrolyzed solution of ethyl silicate and finely powdered silica to which germanium oxide fine powder was added, and a hydrolyzed solution of ethyl silicate and fine boron oxide powder added. Example 5 except that the finely powdered silica was used as the raw material.
When an optical fiber was manufactured in the same manner as in Example 5, a high-quality polarization-maintaining optical fiber with good dimensional accuracy was obtained.

〔Effect of the invention〕

As described above, according to the present invention, an optical fiber preform is produced using the sol-gel method, and by drawing the optical fiber preform, it can be obtained using the conventional jacket method. A stress-applied polarization-maintaining optical fiber with high-quality side bits with better dimensional accuracy than
It can be manufactured at a lower cost than the conventional jacket method. Therefore, it becomes possible to supply large quantities of polarization maintaining optical fibers at low cost to applied fields such as coherent optical transmission systems and optical fiber sensors, and we are confident that the present invention will make an extremely large contribution to this field.

[Brief explanation of drawings]

FIG. 1 shows a cross-sectional view of a stress-applied polarization-maintaining optical fiber having side bits, of which (A) and (B) are one type. 1... Core part 2... Bit part 5... Clad part FIG. 2 is a diagram for explaining the cylindrical container used in Example 1 of the present invention. (A) is a cross-sectional view of the cladding sol during gelation, and (B) is a cross-sectional view of a mold having an expandable structure. 4... Cylindrical container 5... Phthalo... Mold 7 for core hole... Mold 8 for bit hole... Pressure 11 Adjuster 9 ... Hole 10 ... Sol for cladding 11 ... Silicon-coated hard rubber mold 12 ...
- Expandable tube 15...gas FIG. 3 is a cross-sectional view of the wet gel obtained in Example 1 of the present invention. 14... Cross-sectional view of the wet gel 15... Part that will become the core part 16... Part that will become the bit part 17... Part that will become the rim 2 Rad part Figure 4 is used in the present invention, Example 2 It is a figure explaining the cylindrical container which was used. (A) is a cross-sectional view during gelation of the cladding sol, and (B) is a diagram illustrating the mold used here. 18 Mold for core hole 19 Mold for bit hole 20 Mold made of Teflon FIG. 5 is a sectional view of the wet gel obtained in Example 5 of the present invention. 21... Cross-sectional view of wet gel 22... Part that will become the core part 23... Part that will become the bit part 24... Part that will become the cladding part Figure 6 was obtained in Example 6 of the present invention. FIG. 3 is a cross-sectional view of a wet gel. 25... Cross-sectional view of wet gel 26... Part that will become the core part 27... Part that will become the bit part 2... Part that will become the cladding part Figure 7 shows the present invention, implementation, and example 7. This figure explains the manufacturing process. (A) is a cross section of the wet gel immediately after removing the mold; (B) is a cross-section of the wet gel immediately after removing the mold; (B) is a cross-section of the wet gel after the bit sol is transferred into the bit hole in (A) and gelled; FIG. 2 is a cross-sectional view of a wet gel obtained by pouring a sol for cladding into a cylindrical container, then capping the cylindrical container, attaching the container to a rotating device, and gelling the container while rotating the container. 29...Cross-sectional view of wet gel 30...Core clad hole Sl...Bit hole 32...Clad part 53...Cross-sectional view of wet gel 34...Core hole 35... Part 36 that will become the cladding part... Above the part that will become the bit part

Claims (5)

[Claims] (1) Using the sol-gel method, a part that constitutes the cladding part when made into an optical fiber, a part which constitutes the core part when made into an optical fiber, and a stress applying part when made into an optical fiber are formed. 1. A method for manufacturing a polarization-maintaining optical fiber, comprising the steps of: preparing a wet gel containing a portion therein, and drying and sintering the wet gel to produce a base material for a polarization-maintaining optical fiber. (2) In the manufacturing method according to claim 1,
A sol solution (hereinafter referred to as cladding sol) whose main raw material is an alkyl silicate hydrolyzed solution, which will constitute the cladding part when it is made into an optical fiber, is poured into a cylindrical container with a removable mold fixed at the required position and gelled. After removing the mold, a sol solution (hereinafter referred to as core sol) containing an alkyl silicate hydrolyzed solution as the main raw material and an optical When made into a fiber, it constitutes a stress applying part,
Claim 1, characterized in that the wet gel is made by pouring a sol solution (hereinafter referred to as bit sol) containing an alkyl silicate hydrolyzed solution as a main raw material and gelling it.
A method for manufacturing a polarization-maintaining optical fiber as described in . (3) In the manufacturing method according to claim 1,
A sol solution (hereinafter referred to as cladding sol) whose main raw material is an alkyl silicate hydrolyzed solution, which will constitute the cladding part when it is made into an optical fiber, is poured into a cylindrical container with a removable mold fixed at the required position and gelled. , After removing the mold, a sol solution (hereinafter referred to as a sol solution containing an alkyl silicate hydrolyzed solution as the main raw material) which will constitute the bit part when an optical fiber is made into the bit hole among the plurality of hollow parts or depressions that are formed is inserted into the bit hole. After that, pour the sol for the cladding into the center hole for the core cladding, put a lid on the cylindrical container, attach it to a rotating device, and gel it while rotating at a rotation speed of preferably 200 rpm or more. 2. The method for manufacturing a polarization-maintaining optical fiber according to claim 1, characterized in that the wet gel is produced by transferring the core sol into the resulting core hole and gelling it. (4) In the manufacturing method according to claims 2 and 3, a mold having at least an expandable structure is used as the mold. 3. A method for manufacturing a polarization-maintaining optical fiber according to item 3. (5) The cladding sol, the core sol, and the bit sol contain at least a hydrolyzed solution containing an alkyl silicate as a raw material and an ultrafine powder mainly consisting of ultrafine silica powder. A method for manufacturing a polarization-maintaining optical fiber according to claims 2 to 4.