JP2989957B2 - Forming method of preform for polarization-maintaining optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to coherent optical communication,
The present invention relates to a technique for manufacturing a stress imparting type constant polarization optical fiber used for an optical sensor or the like, and more particularly, to a technique for manufacturing a base material of the constant polarization optical fiber.

[0002]

BACKGROUND ART As is well known, the polarization maintaining optical fiber, E _x mode constituting the basic modes, the phase difference between E _y mode (orthogonal biaxial directions), and greater than the phase difference due to the disturbance,
A predetermined polarization plane is preserved.

As one type of constant polarization optical fiber, there is a stress applying type utilizing a birefringence phenomenon caused by stress. In the case of this constant polarization optical fiber, a polarization is preserved by applying a stress to a core. I'm sorry.

When a stress applying type constant polarization optical fiber is produced, two holes are formed in a predetermined portion of the cladding glass (a position sandwiching the core glass) in a preform stage, and a rod-like stress applying member is formed in each of the holes. Is generally attached to the lower end of the base material, and a weight for dropping is attached to the lower end of the base material.

[0005]

In the case of the above-mentioned constant polarization optical fiber preform, since it is a fragile quartz material, cracks often occur during perforation, and even after completion of this perforation, A highly difficult inner surface polishing, that is, a process for smoothly finishing the inner surface of each hole must be performed. Similarly, in the case of a stress-applying member made of a quartz material, a high-level processing technique is required since it is necessary to finish the heating-stretching, grinding, and polishing in correspondence with the holes of the base material precisely. Furthermore, even if the base material and the stress applying member can be satisfactorily finished, when the stress applying member is loaded into the base material, these inner and outer peripheral surfaces may be damaged. In addition, a complicated process such as attaching a quartz weight to the stretched end side of the base material is also required to perform the drawing process.

[0006] As described above, when the preform of the polarization-maintaining optical fiber is made through the existing means, there are many difficult processing steps, which tend to cause cracks and damage of the work. It is difficult to increase the yield and the productivity decreases.

SUMMARY OF THE INVENTION In view of the above technical problems, the present invention provides a method of forming a constant polarization optical fiber preform capable of reducing the processing difficulty in producing a preform, increasing the yield of non-defective products, and improving productivity. What you want to do.

[0008]

Means for Solving the Problems The method for forming a preform of a polarization-maintaining optical fiber according to the present invention is characterized by the following means in order to achieve the intended purpose. That is, in the molding space of the mold, a rod-shaped waveguide member for forming a waveguide of the constant polarization optical fiber, a rod-shaped stress applying member for forming a stress applying portion of the constant polarization optical fiber, After a molding material containing a powder for forming a porous glass body by filling the periphery of the waveguide member and the stress applying member, the molding die is pressurized from the outside, and the periphery of the waveguide member and the stress applying member. It is characterized in that a porous glass body formed by compression molding is produced.

[0009]

According to the method of the present invention, when a preform having a polarization-maintaining optical fiber is molded, a molding die containing a waveguide member, a stress applying member, a molding material and the like is externally pressurized to form a porous glass body in the molding space. Just make Thereafter, the porous glass body may be purified (removal of impurities and dehydration) and vitrified to form a transparent glass body.

In the case of the above-mentioned method of the present invention, the following points are technically advantageous for producing a preform of a polarization-maintaining optical fiber. Since it is not necessary to perform perforation processing and inner surface polishing on a ready-made base material, it does not involve highly difficult glass processing. Waveguide member,
Since the stress applying member is not loaded in the hole of the base material, each member is not limited in size and there is no need to precisely process the outer surfaces of these members. Furthermore, since the members are not fitted to each other, damage to the inside of the base material, which tends to occur in this type of fitting, does not occur. In addition, by filling an excess molding material in an upper portion and / or a lower portion in the molding space, a weight for drawing can be simultaneously molded at the extended end of the base material. Therefore, according to the method of the present invention, depending on such a molding means, it is possible to reduce the processing difficulty and reduce the number of processing steps when producing a constant polarization optical fiber preform. As a result, the yield of non-defective products And productivity is improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a molding method according to the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 11 denotes a molding cylinder, 12 and 13 denote a pair of molding lids, 14 denotes a pressure-resistant container,
Reference numeral 17 denotes a pressure medium.

1 and 2, reference numeral 21 denotes a rod holding member, 31 denotes a waveguide member, 32 denotes a stress applying member, 33 denotes a molding material, and 34 denotes a porous glass body.

In FIG. 1 and FIG. 3, reference numeral 35 denotes a constant polarization optical fiber preform having an opaque portion.
Denotes a constant polarization optical fiber preform that has been subjected to a transparent vitrification treatment.

The molding cylinder 11 is formed of a cylindrical body having both ends open, and is made of a material having elasticity such as rubber or synthetic resin, for example, silicone rubber or nitrile rubber.

The pair of molding lids 12 and 13 have a disk shape having a plurality of steps on the outer peripheral surface. The molding lids 12 and 13 are made of metal or rubber or synthetic resin having the same degree of rigidity as the metal. As an example, the molding lids 12 and 13 made of metal are employed. A suction hole (not shown) is formed in one or both of the molding lids 12 and 13 so as to penetrate the lid in the thickness direction to suck a molding space 27 described later. Sometimes.

The pressure vessel 14 has a pressure medium 1
It consists of a metal cylinder having seven entrances 15, 16. The pressure medium 1 is inserted into the entrances 15 and 16 of the pressure vessel 14.
7, a supply system and a discharge system (both not shown) are respectively connected.

The pressure medium 17 is supplied into a pressurizing space 19 which will be described later. In the case of the pressure medium 17, for example, it is made of water and another example is made of lubricating oil.

As shown in FIG. 2, the rod holder 21 includes a holding ring 23 for the waveguide member and a holding ring for the stress applying member, which are continuous from one side to the other side in the frame 22 having a ring shape. 24, and also has a gripping piece 25 that rises from the upper surface of the frame 22. As the material of the rod holder 21, an appropriate material is adopted from metal, rubber, synthetic resin and the like. In the rod holder 21, the inner shapes of the holding rings 23 and 24 correspond to the cross-sectional outer shapes of a waveguide member and a stress applying member described later.

A waveguide member 31 for forming an optical waveguide
Is a dehydrated and transparent vitrified quartz-based porous glass body formed by a method such as a gas phase reaction method, a casting slurry method, a sol-gel method, a slurry coating method, an extrusion molding method, or a powder molding method. Consists of The quartz-based waveguide member 31 manufactured in this manner is made of, for example, only a core glass, and has, as another example, a core glass and a part of the cladding glass on the outer periphery thereof. In any of these cases, the waveguide member 31 is of a single mode type with a predetermined refractive index distribution.

The stress applying member 32 is also made of, for example, a quartz-based transparent glass manufactured by the same means as the waveguide member 31. The stress applying members 32 include a tension type and a pressure type described below.

The molding material 33 for forming the porous glass body 34 is made of quartz-based glass powder. The glass powder is, for example, a quartz-based glass fine particle containing a dopant or a quartz-based glass containing a molding aid. And, as another example, pure silica fine particles containing no dopant. The glass powder particle size of the molding material 33 filled in the molding space 18 described later is usually 0.01 μm to 1 μm.
It is about 00 μm.

If the glass powder is remarkably refined and it is difficult to fill it into the molding space 18, a solvent such as pure water is used, or a molding aid and pure water are used to produce fine particles. The granulated powder may be granulated to a particle size of 50 μm to 100 μm, and the granulation enables uniform high-density filling of the glass powder. In this case, it is preferable that the proportion of powder having a particle size of 50 μm or more be 50% or more, and the proportion of powder having a particle size of 10 μm or less be less than 10%.

In some cases, a solvent such as pure water is mixed with the glass powder of the molding material 33 to form a sol. At this time, an organic material such as polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, methylcellulose, carboxymethylcellulose, ethylcellulose, hydroxypropylcellulose, and glycerin may be employed as a molding aid in the glass powder. The amount of the molding aid added to the glass powder is about 1 to 20% by weight, preferably 15% by weight or less, based on the glass powder.

In the case of the above-described molding apparatus, the components of the apparatus have the following relative relationships. As shown, the pair of molding lids 12 and 13 having a step on the outer peripheral surface have a large diameter portion, a medium diameter portion, and a small diameter portion, respectively. In this case, the large diameter portions of both the molding lids 12 and 13 are
4 and can be closely matched with each other,
13 has the same diameter as the outer diameter of the molding cylinder 11;
The small diameter portions of both the molding lids 12 and 13 can be closely fitted to the molding cylinder 11. Accordingly, when the pressure-resistant container 14 is used as an outer shell, and the molding cylinder 11 and the two molding lids 12 and 13 are assembled as shown in FIG.
The space enclosed by the molding cylinder 11 and the molding lids 12 and 13 is a molding space 18, and the space enclosed by the molding cylinder 11, the molding lids 12 and 13 and the pressure vessel 14. Becomes the pressurized space 19.

In the above description, both the molding lids 12, 13,
The rod holder 21 and the like are coated with, for example, a fluorine-based resin (trade name: Teflon) or glass in order to prevent contamination of the porous glass body 34. In particular, in the case of the rod holder 21, the fluorine-based resin coating is effective in increasing the surface smoothness and reducing the frictional resistance between the waveguide member 31 and the stress applying member 32. In addition, since the pressure-resistant container 14 does not directly participate in the molding space 18, they do not require a coating for preventing contamination. In addition, in assembling the members to be described later, a seal member is interposed, as necessary, at a contact point between the members requiring high airtightness and liquid tightness.

The above-described waveguide member 31, stress applying member 3
2. The transparent vitrified material of the porous glass body 34 satisfies the following relationship with respect to these refractive indices. That is, the core glass refractive index of the waveguide member 31 is N ₁ , the cladding glass refractive index of the waveguide member 31 is N ₂ , the stress applying member 32 is N ₃ , and the refractive index of the transparent vitrified material of the porous glass body 34. Are N ₄ , N ₁ > N ₂ = N ₄ ≧
N ₃ Alternatively, N ₁ > N ₄ > N ₂ ≧ N ₃ I am satisfied with the relationship. Note that when the waveguide member 31 is made of only the core glass, the above relationship is expressed as N ₁ > N ₄ ≧ N ₃ become that way.

Using the molding means described above, the waveguide member 3
1. When forming the constant polarization optical fiber preform 35 including the stress applying member 32 and the porous glass body 34, that is, the constant polarization optical fiber preform 35 having the opaque portion (the porous glass body 34), as follows. become.

At the time of molding, first, as shown in FIG. 1, a molding cylinder 11 and a pressure-resistant container 14 are placed on a molding lid 13.
The assembling in any order, the molding lid body 13 by an unillustrated jig after fixing the pressure vessel 14 to each other, turning on the molding material 33 to near the level L ₁ in the molding space 18.

Next, the rod holder 21 is moved to the molding space 18.
And each of the stress applying members 32 is inserted into the two holding rings 24 on both sides,
The waveguide member 31 is inserted into the central holding ring 23. In such a case, the waveguide member 31 is held on the axis in the molding space 18, and each stress applying member 32 is held on both sides of the waveguide member 31.

Thereafter, the rod holder 21 is moved to the molding space 18.
While pulling the inner, the same molded material 33 was charged into the molding space 18, and takes out the rod holder 21 from the molding space inside 18 when the input amount of the molding material 33 reaches the vicinity of the level L ₂ . At this time, the waveguide member 31 and the stress applying member 32 embedded in the molding material 33 stand at a predetermined position and stand alone. Subsequently, the molding material 33
Was charged to a level L ₃ of the molding space 18, wave guide 3
1. The stress applying member 32 is completely filled with the molding material 33.

After a predetermined amount of the molding material 33 is filled in the molding space 18, the molding lid 12 is assembled on the molding cylinder 11 and the pressure-resistant container 14, and the molding lid 12 is fixed by a jig (not shown). The body 12 and the pressure-resistant container 14 are fixed to each other and brought into the state shown in FIG. Further, this is charged into a high-pressure application device (not shown).

Thereafter, lubricating oil as a pressure medium 17 is injected into a pressurizing space 19 from a supply system (not shown) connected to the inlet / outlet 15 of the pressure-resistant container 14, and the molding cylinder 11 is pressurized from the outside.

Thus, in the molding space 18, the molding material 3
3, a porous glass body 34 having a uniform bulk density and no cracks or cracks is formed.

The following describes the entrances 15 and 16 of the pressure vessel 14.
While gradually discharging the pressure medium 17 in the pressurized space 19 to the outside from a discharge system (not shown) connected to the molding cylinder 11.
Is restored, and after the molding cylinder 11 is restored, it is taken out from the high-pressure applying device. Next, one of the molding lids 12 and 13 is removed from the end of the pressure-resistant container 14, and the porous glass body 34 is taken out of the molding space 18 together with the waveguide member 31 and the stress applying member 32.

The constant polarization optical fiber preform 35 thus formed has a porous glass body 34 as an opaque portion, as clearly shown in FIG. Accordingly, the porous glass body 34 hot the He, Cl ₂ Purification (removal of impurities and dehydration) in an atmosphere, and vitrification in a He atmosphere at about 1600 ° C. to finish a transparent glass body, obtain a transparent constant polarization optical fiber preform 36 shown in FIG. The constant polarization optical fiber preform 36 includes a waveguide section formed by the waveguide member 31, a stress applying section formed by the stress applying member 32, a clad section 39 formed by the transparent vitrified porous glass body 34, and a weight section 40 for drawing. , 41.

At the time of the above-mentioned transparent vitrification treatment, a birefringence phenomenon occurs in the waveguide member 31 due to stress, and the polarization plane is preserved.

As a well-known dopant for controlling the refractive index of SiO ₂ , trivalent B ₂ O ₃ , Al ₂
O ₃ , tetravalent GeO ₂ , TiO ₂ , ZrO ₂ , and
There are pentavalent P ₂ O ₅ and AsO ₅ , and F is also effective. These are the double component dopant for SiO _2, by combining various, with is the refractive index of SiO ₂ Koue or decrease, Koue or lowering the softening temperature of the SiO _2. As an example of the constant polarization optical fiber preform 36, the composition of the core glass (waveguide portion 37) is SiO ₂ —GeO ₂ , and the composition of the stress applying portion 38 is S.
iO ₂ -B ₂ O ₅ , and the composition of the cladding glass (the rest) other than these was pure SiO ₂ .

The cross section of the stress applying member 32 may be an ellipse, a polygon having more than a triangle, or the like.

A specific example of the molding method according to the present invention will be described below. As the waveguide member 31, one having an outer diameter of about 3.1 mmφ and a length of about 100 mm manufactured based on the VAD method was used. The waveguide member 31 has a core glass of SiO.
_2- GeO ₂ , the cladding glass is made of SiO ₂ ,
Core / cladding outer diameter ratio is 1/3, relative refractive index difference is 1.2
%. As the stress applying member 32, an outer diameter of about 7 mmφ and a length of about 100 mm manufactured based on the VAD method was used. In the case of this waveguide member 31, about 19 wt% B ₂ O ₃
- and the balance SiO _2. As the molding material 33, a commercially available silica powder was used. In the case of this molding material 33, the average particle diameter before granulation is about 1 μm, and the average particle diameter after granulation is about 30 μm.
m.

The molding cylinder 11 has an outer diameter of 80 mm.
A member made of silicone rubber having a diameter φ of 70 mm and a length of 250 mm was used. The pressure vessel 14 has an outer diameter of 1
An aluminum plate having a diameter of 10 mm, an inner diameter of 90 mm, and a length of 300 mm was used. Both molding lids 12 and 13
The one having dimensions corresponding to the molding cylinder 11 and the pressure-resistant container 14 was used.

At the time of molding based on the above, first, the molding material 33 was charged into the molding space 18 whose upper end is open. At this time, the injection amount of the molding material 33 is about 50 mm in height (with reference to the inner surface of the molding lid 13). Next, the waveguide member 31 and the stress applying member 32 are formed in the molding space 18.
After setting, the molding space 18 was additionally filled with about 860 g of the molding material 33, and the upper end of the molding space 18 was closed by the molding lid 12. In the material filling at this time, the rod holder 21 was used halfway. 100 mm above the filling material 33 in the molding space 18 (the molding lid 1
2 (based on the inner surface of 2) corresponds to the weight portion 40 for drawing. As an example, these are called CIP (Cold Isostatic Pres
sing). Thereafter, a pressure medium (lubricating oil) 17 was injected into the pressure space 19, and the molding cylinder 11 was pressed at a pressure of 500 kgf / cm ² for about 1 minute. Thus, in the molding space 18, a porous glass body 34 having a uniform bulk density and no cracks or cracks was molded with a molding material 33 having an outer diameter of about 70 mmφ and a length of about 230 mm.

Thereafter, over a period of about 30 minutes, the pressure medium 17 in the pressurized space 19 is gradually discharged to the outside, and the molding cylinder 11 is restored. It was taken out of the high-pressure application device. Subsequently, the molding lid 12 is removed from the molding cylinder 11, and the constant polarization optical fiber preform 35 (the waveguide member 31, the stress applying member 32, and the porous glass body 34) is taken out from the molding space 18. Was.

Thereafter, the porous glass body 34 is
Purification (removal and dehydration of impurities) in an atmosphere of Cl ₂ and He at 210 ° C., and vitrification in a He atmosphere of 1620 ° C. to form a transparent glass body, with a waveguide member 31 and a stress applying member 32 provided inside A transparent constant polarization optical fiber preform 36 was obtained.

In the following, the base material was drawn by a known heating drawing method to form a constant polarization optical fiber having a core diameter of 5 μmφ, and a coating layer made of an ultraviolet curable resin was applied to the outer periphery of the optical fiber immediately after the drawing. . Constant polarization optical fiber in this embodiment the cut-off wavelength is 0.84 .mu.m, crosstalk length per 100 m - 25 dB, the beat length is 2.2mm
This is comparable to the currently used constant polarization optical fiber.

[0045]

According to the method of the present invention, after the waveguide member, the stress applying member and the molding material are put in the molding space of the molding die, the molding die is pressurized from the outside to apply the waveguide member and the stress applying member. Since a porous glass body is formed around the member by compression molding, it is possible to alleviate the processing difficulty and reduce the number of processing steps when manufacturing a constant polarization optical fiber preform. As a result, the constant polarization optical fiber preform ( Yield) and productivity is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the method of the present invention.

FIG. 2 is a perspective view showing an example of a rod holder used in the method of the present invention.

FIG. 3 is a perspective view of a constant polarization optical fiber preform having a porous glass body formed by the method of the present invention.

FIG. 4 is a perspective view of the constant polarization optical fiber preform after the above-mentioned porous glass body is formed into a transparent glass.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Molding cylinder type 12 Molding lid 13 Molding lid 14 Pressure-resistant container 15 Pressure medium inlet / outlet 16 Pressure medium inlet / outlet 17 Pressure medium 18 Molding space 19 Pressurized space 21 Rod holder 31 Guide member 32 Stress applying member Reference Signs List 33 molding material 34 porous glass body 35 constant polarization optical fiber preform with opaque part 36 constant polarization optical fiber preform without opaque part

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C03B 37/00-37/16 C03B 20/00

Claims (1)

(57) [Claims] 1. A rod-shaped waveguide member for forming a waveguide of a constant polarization optical fiber in a molding space of a molding die, and a rod-shaped stress applying member for forming a stress applying portion of the constant polarization optical fiber. And, after introducing a molding material containing powder for forming a porous glass body by filling the periphery of these waveguide members and stress applying members, and then pressing the molding die from the outside, the waveguide member,
A method of forming a base material of a polarization-maintaining optical fiber, comprising forming a porous glass body formed by compression around a stress applying member.