JPH08217482A - Fluoride optical fiber-producing apparatus and production of fluoride optical fiber - Google Patents

Abstract

PURPOSE: To obtain a fluoride optical fiber having high strength by connecting surface treating part for carrying out dry etching of fluoride optical fiber preform to heat melting drawing part in a state blocked from outside air. CONSTITUTION: Plasma is generated into an ion gun 8 and beam accelerating voltage is applied to an argon ion drawn from the plasma and the argon ion is neutralized by a new trizer and irradiated into fluoride optical fiber preform. At this time, the preform is rotated in circumferential direction by a device 3 for rotating a preform-supporting rod. In a furnace center pipe 12, the optical fiber preform is feed into a heater 13 for preform heating and softened and drawn in the lower direction to provide the objective fiber. At this time, high- purity Ar gas is fed from a gas inlet 11 into the furnace center pipe 12. Since problem of surface crystallization of optical fiber preform can be solved according to the method, fluoride optical fiber having high strength and low loss can be prepared. Consequently, fluoride fiber can be practiced for mounting of optical amplifier, etc., and reduction of cost and high performance of optical communication system is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluoride optical fiber used for long-distance transmission, infrared light transmission, and light amplification, and particularly to manufacture a high-strength fluoride optical fiber. Apparatus and method therefor.

[0002]

2. Description of the Related Art In recent years, a multi-component glass optical fiber having a core doped with a rare earth element, particularly a fluoride optical fiber, has been attracting attention as an active medium for lasers and optical fiber amplifiers. In particular, a fluoride optical fiber with Pr ³⁺ (praseodymium ion) added in its core has an optical amplifying action in the 1.3 μm band, which is an important wavelength band in optical communication, and is therefore studied as an optical fiber amplifier. Development is active (Oishi et al., Applied Physics, Volume 62, No. 1,
p. 36, 1993).

By the way, in order to put the optical fiber into practical use, mechanical strength is an important parameter. A quartz optical fiber has a high strength of about 5 to 6 GPa (gigapascal). On the other hand, in the case of a fluoride-based optical fiber, the intrinsic mechanical strength of the fluoride glass itself is as low as about one-third that of silica glass, and
Since the fluoride glass itself is easily crystallized, there is a disadvantage that a part of the glass is crystallized in the heating / drawing step or the drawing step of the base material during the production of the optical fiber. Therefore, at present, it is difficult to manufacture a high-strength fluoride optical fiber.

Therefore, the strength of the fluoride single-mode optical fiber used in the conventional optical fiber amplifier is 300.
It is about MPa, and it is the current situation that it has not yet reached a level that can withstand mounting.

A conventional method for manufacturing such a fluoride single-mode optical fiber is as follows: (i) A rod made of fluoride glass having a jacket tube with at least a portion having a higher refractive index than the jacket tube. To obtain a composite material, and heating and stretching the composite material to obtain a base material; and (ii) heating and drawing the base material, or inserting the base material into a jacket tube. Heating and drawing to obtain an optical fiber. In the above drawing step, the surface of the jacket tube is
After optical polishing using abrasive grains such as l ₂ O ₃ or CeO ₂ , surface treatment is performed by wet etching using an etching solution in which 0.4 mol of zirconium oxychloride is dissolved in 1N hydrochloric acid. Was going on. However, in this method, since easily soluble components such as BaF _{2 on the} surface of the jacket tube are selectively eluted by the etching solution, rough scratches such as polishing scratches can be removed, but the glass surface itself becomes rough. However, there is a problem that microscopic unevenness remains.
In addition, since water in the atmosphere is easily adsorbed to the micro unevenness, the adsorbed water causes a hydrolysis reaction during drawing, and microcrystals such as oxides are generated on the surface of the jacket tube.
Since the fine crystals serve as the starting point of breakage, the optical fiber strength is not improved.

On the other hand, according to the surface treatment method of the fluoride fiber base material disclosed in Japanese Patent Application No. 63-151641, the surface of the fluoride fiber base material is a highly reactive gas such as F ₂ or HF. The moisture adsorbed on the surface is removed by heat treatment by, so that the strength of the optical fiber is enhanced. However, in such a conventional method and device, since the dry etching device and the drawing device are not connected in series, the fluoride fiber preform after the surface treatment by dry etching is set in the drawing device. When performing the above, there was a problem that the surface of the fiber preform was exposed to the atmosphere and new moisture was adsorbed or dust or the like was attached.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for manufacturing a high-strength fluoride optical fiber, which solves the above-mentioned conventional problems.

[0008]

In order to solve the above-mentioned problems, the apparatus for producing a fluoride optical fiber according to claim 1 of the present invention comprises a surface treatment section for surface-treating a fluoride optical fiber preform by dry etching. In a fluoride optical fiber manufacturing apparatus having at least a drawing part for drawing the fluoride optical fiber preform by heating and melting, the surface treatment part and the drawing part are connected and are shielded from the outside air. .

A fluoride optical fiber manufacturing apparatus according to a second aspect of the present invention is the manufacturing apparatus according to the first aspect, wherein a coating portion for resin-coating the drawn fluoride optical fiber is connected to the drawing portion. It is characterized by

According to a third aspect of the present invention, there is provided a fluoride optical fiber manufacturing apparatus, wherein:
A base material support rod for supporting the fluoride optical fiber base material,
It is characterized by having a base material support rod cover that shields the base material support rod from the atmosphere.

According to a fourth aspect of the present invention, there is provided the apparatus for producing a fluoride optical fiber according to any one of the first to third aspects, wherein the surface treatment section has an inlet and an outlet for an ion flow and a vacuum exhaust. It is characterized by having a mouth and a gas inlet.

A fluoride optical fiber manufacturing apparatus according to a fifth aspect of the present invention is characterized in that, in the manufacturing apparatus according to any one of the first to fourth aspects, the wire drawing portion has a gas introduction port.

A fluoride optical fiber manufacturing apparatus according to a sixth aspect of the present invention is characterized in that, in the manufacturing apparatus according to any one of the first to fifth aspects, there is provided means for rotating the base material support rod around an axis. To do.

According to a seventh aspect of the present invention, in the apparatus for producing a fluoride optical fiber according to any one of the second to sixth aspects, the coating section comprises a glove box having an atmosphere gas supply pipe and an exhaust pipe. It is characterized by

An apparatus for manufacturing a fluoride optical fiber according to claim 8 of the present invention is characterized in that, in the manufacturing apparatus according to any one of claims 2 to 7, a shutter is installed between the drawing portion and the coating portion. .

The method for producing a fluoride optical fiber according to claim 9 of the present invention comprises a surface treatment step of surface-treating the fluoride optical fiber preform by dry etching, and drawing the fluoride optical fiber preform by heating and melting. In the method for producing a fluoride optical fiber, the drawing step is performed in an atmosphere of an inert gas at atmospheric pressure, a fluorine-containing gas, or a mixed gas thereof.

According to a tenth aspect of the present invention, in the method for producing a fluoride optical fiber according to the ninth aspect, the fluorine-containing gas is NF ₃ , F ₂ , HF, SF ₆ , CF ₄ ,
It is characterized in that it is at least one gas selected from the group consisting of XeF ₂ .

A method for manufacturing a fluoride optical fiber according to a tenth aspect of the present invention is the method for manufacturing a fluoride optical fiber according to the ninth or tenth aspect, further comprising a coating step of resin-coating the drawn fluoride optical fiber after the drawing step. It is characterized by having.

A method for manufacturing a fluoride optical fiber according to a twelfth aspect of the present invention is the method for manufacturing a fluoride optical fiber according to any one of the ninth to eleventh aspects, wherein the surface treatment step accelerates ions generated by plasma. It is characterized in that it is a step of colliding with the surface of the compound optical fiber preform.

A method for manufacturing a fluoride optical fiber according to a thirteenth aspect of the present invention is the method for manufacturing a fluoride optical fiber according to any one of the ninth to twelfth aspects, wherein the surface treatment step is Ar, F ₂ , Cl.
₂ , Br ₂ , CF ₄ , C ₂ F ₆ , NF ₃ , SF ₆ , Xe
It is characterized in that it is performed using at least one gas selected from the group consisting of F ₂ .

A method for producing a fluoride optical fiber according to a fourteenth aspect of the present invention is the method for producing a fluoride optical fiber according to any one of the ninth to thirteenth aspects, wherein the surface treatment step and the drawing step are performed.
It is characterized in that it is carried out under an atmospheric pressure atmosphere of an inert gas or nitrogen gas having a dew point of -60 ° C or lower.

Further, in the method for producing a fluoride optical fiber according to a fifteenth aspect of the present invention, in the method for producing a fluoride optical fiber according to the fourteenth aspect, the coating step is performed under an atmospheric pressure atmosphere of an inert gas or nitrogen gas having a dew point of -60 ° C or less. It is characterized by being performed below.

[0023]

According to the apparatus of the present invention as set forth in claim 1, the fiber drawing step following the fiber preform surface treatment step is performed in one step.
Since it can be performed with one device, the fiber preform surface treated by dry etching in the dry etching part of the device can be used as it is without contamination of the surface of the fiber preform. It becomes possible to process. Therefore, generation of surface crystals of the obtained optical fiber can be prevented, and a high-strength optical fiber can be manufactured.

According to the apparatus of the present invention described in claim 6, the fiber preform holding means has a means for rotating in the circumferential direction with respect to the preform supporting rod axis in the dry etching portion, so that the fiber preform holding means has a cylindrical shape. It becomes possible to perform the etching treatment uniformly over the circumference of the fluoride fiber base material.

According to the apparatus of the present invention as set forth in claim 7, since the coating portion is constituted by a glove box having an atmosphere gas supply pipe and an exhaust pipe, the inside of the glove box can be prevented from being contaminated and the resin can be prevented. It becomes possible to perform the steps up to the attachment.

According to the apparatus of the present invention as defined in claim 8, the fiber outlet provided in the lower part of the fiber base material heating part is partitioned from the coating part by the shutter which can be opened and closed, so that the fiber base material heating furnace upper part. The atmospheric gas introduced from the above becomes a stable laminar flow in the heating furnace, and the fiber diameter can be stably drawn.

Further, according to the method of the present invention as set forth in claim 9, after the surface of the fluoride optical fiber preform is dry-etched in the dry etching section, the inside of the container is exposed to an atmosphere of argon or nitrogen gas at atmospheric pressure. Then, by heating the fluoride optical fiber preform at a softening temperature or higher in the fiber preform heating unit provided below the container and drawing the fiber preform, the fiber preform surface subjected to the surface treatment by dry etching is drawn. The fiber can be processed as it is without being contaminated.

According to the method of the present invention as set forth in claim 12,
Dry etching is performed using Ar, F ₂ , Cl ₂ , Br ₂ , C
Ions generated by plasma using at least one gas selected from the group consisting of F ₄ , C ₂ F ₆ , NF ₃ , SF ₆ , and XeF ₂ are accelerated to cause the ions on the surface of the fluoride fiber preform. Made by colliding. Therefore, it is possible to uniformly etch the surface of the fiber preform for forcibly desorbing atoms from the surface regardless of the constituents of the fluoride glass.

Further, according to the method of the present invention as set forth in claim 14, the supporting rod cover, the dry etching portion, which are connected to each other,
By using an inert gas or N ₂ gas with a dew point of −60 ° C. or less as an atmospheric gas introduced into the fiber base material heating section and the coating section, the surface of the fluoride fiber base material surface-treated by dry etching is not contaminated. It becomes possible to keep.

[0030]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

FIG. 1 is a schematic view showing a preferred example of the fluoride optical fiber preform surface treatment wire drawing apparatus of the present invention.
In the figure, 1 is a fluoride optical fiber preform. The fiber base material 1 is held by a base material support rod 2. The base material support rod 2 can be moved in the vertical direction by the drive device 0, and is rotated about the axis by the rotating device (base material support rod rotating means) 3. Further, the base material support rod cover 4 having an airtight interior is provided on the outer periphery of the base material support rod 2.
The high-purity N ₂ gas having a dew point of −90 ° C. or lower is introduced into the base material support rod cover 4 through the gas introduction port 5, and the gas is discharged through the gas discharge port 6. There is.

The vacuum container 7 containing the fluoride fiber base material 1 has a base material support rod 2 penetrating the upper surface thereof through an O-ring seal, and irradiating the fiber base material 1 with an ion stream on the side surface thereof. There is an ion gun 8 for Also,
The lower surface of the vacuum vessel 7 can be separated from the core tube 12 located below by a gate valve (not shown). In addition, the inside of the vacuum container 7 is connected to the exhaust port 10 by a vacuum exhaust device (not shown),
It is possible to exhaust up to 10 ⁻⁶ Torr.

As described above, below the vacuum container 7,
A quartz core tube 12 is located. Inside the furnace tube 12, a dew point of -100 ° C for the atmosphere inside the furnace from the gas inlet 11
High purity Ar gas is introduced. A preform heating heater 13 is located on the outer periphery of the furnace core tube 12 and can heat the fiber preform 1 to a softening temperature.
Further, the shutter 14 is located below the core tube 12, and the glove box 1 located below the core tube 12
It is divided into 5.

A coating die 16 is located in the glove box 15 in which the glove G is provided. Further, in the glove box 15, N _{2 having a} dew point of −90 ° C. or less from the gas supply port 19 is provided. Gas is introduced.

An ultraviolet curing section 17 is located below the glove box 15, and the optical fiber coated with the resin here is wound by a winder 18.

In the above structure, the vacuum container 7 having the ion gun 8, the gas introduction port 9, the gas exhaust port 10 and the etching gas introduction port 20 constitutes a surface treatment section. Further, the furnace core tube 12 having the gas introduction port 11, the heater 13, and the shutter 14 constitutes a wire drawing portion. Further, the glove box 15 having the die 16 and the gas introduction port 19 constitutes a coating portion.

(Embodiment 1) In this embodiment, an inner diameter of 7
mm using a mold of 56.5 ZrF ₄ −
12BaF ₂ -17.5PbF ₂ -3.5LaF ₃ -2
It is composed of YF ₃ -2.5AlF ₃ -6LiF (mol%), and the cladding is 46.5ZrF ₄ -23.5BaF _2.
−2.5LaF ₃ −2.5YF ₃ −4.5AlF ₃ −2
Fluoride glass base material made of 0 NaF (mol%) (outer diameter 7.0 mm, length 150 mm, relative refractive index difference Δn = 4.
2%) was prepared by the suction casting method.

Also, using a mold having an inner diameter of 15 mm,
Fluoride jacket tube with the same composition as the clad glass of the base material (outer diameter 15 mm, inner diameter 7.0 mm, length 150 m
m) was produced by the rotation casting method. After polishing and etching the outer surfaces of the glass base material and the jacket tube, the surface water was removed by vacuum deaeration of both. The surface etching of the glass base material can be performed, for example, by housing the glass base material 1 in an etching bath 21 as shown in FIG.

Next, in the glove box 15 to which the N ₂ gas having a dew point of −90 ° C. or less is supplied, the base material is inserted into the jacket tube to produce a fluoride optical fiber base material, and subsequently, The fluoride optical fiber base material was held on the base material support rod 2 in the vacuum container 7, and the vacuum container 7 was evacuated to a vacuum degree of 10 ⁻⁶ Torr. Ar was used as the etching gas, and the Ar gas was supplied from the etching gas inlet 20 behind the ion gun 8 at a rate of 3 cc / min. At this time, the degree of vacuum in the vacuum container 7 is
It was 10 ⁻⁴ Torr.

Subsequently, plasma is generated in the ion gun 8 and the argon ions extracted from the plasma are heated to 40%.
A beam accelerating voltage of 0 V was applied to neutralize with a Neutrizer (not shown), and then the surface of the base material was irradiated. The irradiation time was 1 hour. At this time, the base material supporting rod rotating device 3 rotated the base material in the circumferential direction at a speed of 15 rotations per minute.

The base material thus surface-treated is evacuated again to 10 ^-6 Torr in the vacuum container 7,
The inside of the vacuum container 7 was returned to the atmospheric pressure by N ₂ gas having a dew point of −90 ° C. or less supplied from the gas inlet 9. Next, by opening a gate valve (not shown) and lowering the driving device 0, the fiber preform 1 is moved to the core tube 12
Moved to.

In the core tube 12, the optical fiber preform was fed at a rate of 2 mm per minute to the preform heater 13 to be softened and pulled downward to obtain an optical fiber having an outer diameter of 125 μm. At this time, high-purity Ar gas having a dew point of −90 ° C. or less is introduced into the core tube 12 from the gas inlet 11 by 50
It was supplied at a rate of 0 cc / min.

The drawn optical fiber was coated with a resin for surface protection by a coating die 16, cured by an ultraviolet curing section 17, and then wound by a winder 18. After the drawing, the tensile strength of the optical fiber was measured by a tensile strength tester to find that it was 750MP.
The high strength of a was obtained. The surface of the fiber preform that had been surface-treated by dry etching remained in a transparent state, and no crystal or defect as a fracture starting point was observed by electron microscope observation of the fiber surface.

(Comparative Example 1) A fluoride glass base material having the same composition as in Example 1 and a jacket tube were produced, and the surface was polished and etched, and the high purity N having a dew point of -90 ° C or less was obtained. _The optical fiber preform was obtained by inserting the preform into the jacket tube in the glove box 15 to which ₂ gas was supplied.

The fiber base material is held by the base material support rod 2, and the fiber base material is fed into the base material heating heater 13 at a rate of 2 mm per minute in the furnace core tube 12 to be softened and pulled downward to the outside. An optical fiber having a diameter of 125 μm was obtained. The ultraviolet curable resin was applied to the surface of the drawn optical fiber in the same manner as in Example 1.

When the tensile strength of the optical fiber was measured, the tensile strength decreased to 300 MPa. The difference in optical fiber strength between this comparative example and Example 1 is due to the presence or absence of surface treatment by dry etching. That is, the optical fiber strength improved in Example 1 is that the jacket tube surface is crystallized by performing a surface treatment by dry etching on the surface of the jacket tube to remove residual scratches or roughness on the surface of the jacket tube. This is because the

Example 2 In this example, a fluoride glass base material and a jacket tube having the same composition as in Example 1 was used, the surface of which was polished and etched, and the dew point was −90 ° C. or lower. The optical fiber preform was prepared by inserting the preform into the jacket tube in the glove box to which the high-purity N ₂ gas was supplied.

The fluoride optical fiber preform is placed in a vacuum container 7
It was held by the base material support rod 2 inside, and the vacuum container 7 was evacuated to a vacuum degree of 10 ⁻⁶ Torr. NF ₃ was used as the etching gas, and was supplied from the etching gas inlet 20 behind the ion gun 8 at a rate of 3 cc / min. At this time, the degree of vacuum in the vacuum container 7 was 10 ⁻⁴ Torr.
Then, plasma is generated in the ion gun 8 to 400 V.
The ions extracted from the plasma were accelerated by applying the beam accelerating voltage of (1), neutralized by a neutralizer (not shown), and then irradiated on the surface of the base material. The irradiation time was 1 hour. At this time, by the base material support rod rotating device 3,
The base material was rotated circumferentially at a speed of 15 revolutions per minute. After the inside of the vacuum container 7 was evacuated to 10 ⁻⁶ Torr again, the inside of the container was returned to atmospheric pressure by N ₂ gas having a dew point of −90 ° C. or less supplied from the gas inlet 9, and a gate valve (not shown) was opened. The fiber base material was moved to the core tube 12 by lowering the driving device 0.

The optical fiber preform was fed into the preform heater 13 at a rate of 2 mm / min in the core tube 12 to be softened and pulled downward to obtain an optical fiber having an outer diameter of 125 μm. The surface of the drawn optical fiber was coated with a resin for surface protection by a coating die 16, cured by an ultraviolet curing section 17, and then wound by a winder 18.

When the tensile strength of the optical fiber was measured by a tensile strength tester, a high strength of 750 MPa was obtained.

The same effect as this is obtained by using an ECR type ion gun and using NF ₃ as an etching gas and F
₂ , Cl ₂ , Br ₂ , CF ₄ , C ₂ F ₆ , NF ₃ , SF
It was possible to confirm even when ₆ , XeF ₂ or the like was used.

(Embodiment 3) In this embodiment, an inner diameter of 7
by using a mold of mm, core, 35InF ₃ -20
_{ZnF 2 -22BaF 2 -10SrF 2 -5YF 3} -3
It is made of PbF ₂ -5NaF (mol%), and the cladding is 35InF ₃ -20ZnF ₂ -20BaF ₂ -10.
SrF ₂ -5YF ₃ -5AlF ₃ -5NaF (mol
%) Indium fluoride glass base material (outer diameter 7.0 mm, length 150 mm, relative refractive index difference Δn = 1.2)
%) Was produced by the suction casting method. In addition, using a mold having an inner diameter of 15 mm, a fluoride jacket tube (outer diameter 1
5 mm, inner diameter 7.0 mm, length 150 mm) were manufactured by the rotational casting method.

After the outer surfaces of the glass base material and the jacket tube were polished, the both surfaces were vacuum deaerated to remove the water content on the surface. Next, the fiber preform was produced by inserting the preform into the jacket tube in the glove box 15 to which N ₂ gas having a dew point of −90 ° C. or less was supplied.

The fiber base material is held on the base material support rod 2 in the vacuum container 7, and the vacuum container 7 is evacuated to 10 ^-6 Torr.
It was evacuated to r. Ar was used as the etching gas, and 3c was introduced from the etching gas inlet behind the ion gun 8.
It was supplied at a rate of c / min. At this time, the degree of vacuum in the vacuum container 7 was 10 ⁻⁴ Torr. Subsequently, plasma was generated in the ion gun, a beam acceleration voltage of 500 V was applied to the argon ions extracted from the plasma, and the surface of the base material was irradiated with neutralization by a neutralizer (not shown). The irradiation time was 1 hour. At this time, the base material supporting rod rotating device 3 rotated the base material in the circumferential direction at a speed of 15 rotations per minute. The inside of the vacuum vessel 7 is again 10 ⁻⁶ To
After evacuation to rr, the inside of the vacuum container 7 was returned to atmospheric pressure by N ₂ gas having a dew point of −90 ° C. or lower supplied from the gas inlet 9. Then, a gate valve (not shown) was opened, and the drive unit 0 was lowered to move the fiber preform to the core tube 12.

In the core tube 12, the fiber preform is fed into the preform heater 13 at a rate of 2 mm / min.
It was softened and pulled downward to obtain an optical fiber having an outer diameter of 125 μm. The tensile strength of the drawn optical fiber was measured by a tensile strength tester, and a high strength of 850 MPa was obtained.

In addition to the aluminum-based fluoride glass and the lead-based fluoride glass, the same method can be applied to a glass system such as a fluoride glass and a chloride glass doped with chlorine ions, which easily generate surface crystals. It was possible to fabricate a high-strength optical fiber in which the generation of surface crystals was suppressed.

Example 4 Using a mold having an inner diameter of 5 mm, 56ZrF ₄ -14BaF ₂ -15PbF ₂ -3.5LaF
_{3 -2YF 3 -2.5AlF 3 -7LiF (mol} %)
Glass rod for core with a composition of (outer diameter 5.0 m
m, length 50 mm). The glass tube for the clad is 46.5 ZrF using a mold with an inner diameter of 20 mm.
₄ -23.5BaF ₂ -2.5LaF ₃ -2.5YF ₃
To produce a glass rod -4.5AlF ₃ -20NaF (mol%) composition, a hole having an inner diameter of 0.5mm by ultrasonic machining. After polishing and etching the outer surface of the glass rod for core, the surface water was removed by vacuum degassing, and the glass rod was held by the base material support rod 2 in the vacuum container 7. After evacuating the vacuum container 7 to a vacuum degree of 10 ⁻⁶ Torr, surface treatment was performed under the same conditions as in Example 1.

The glass rod for core, which has been surface-treated as described above, is evacuated again to 10 ^-6 Torr in the vacuum vessel 7, and then the dew point -90 supplied from the gas introduction port 9 is set.
The temperature was returned to atmospheric pressure by N ₂ gas at a temperature of not higher than 0 ° C., a gate valve (not shown) was opened, and the drive unit 0 was lowered to move to the core tube 12.

In the furnace tube 12, the glass rod for core was fed into the heater 13 for heating the base material at a rate of 2 mm / min, was softened, and was pulled downward to be drawn to an outer diameter of 0.5 mm.

The drawn glass rod for core was inserted into the above glass tube for cladding to obtain an optical fiber preform. The base material was surface-treated again in the vacuum container 7 under the same conditions as in Example 1. After the inside of the vacuum container 7 is evacuated to 10 ⁻⁶ Torr again, the dew point supplied from the gas inlet 9 −
The base material was moved to the core tube 12 by returning to atmospheric pressure with N ₂ gas at 90 ° C. or lower, opening a gate valve (not shown), and lowering the drive unit 0.

The optical fiber preform was fed into the core tube 12 at a rate of 2 mm / min into the heater 13 for heating the preform, softened and pulled downward to obtain an optical fiber having an outer diameter of 125 μm.

The obtained optical fiber is a single mode optical fiber having a length of 500 m, a core diameter of 1.7 μm and a cutoff wavelength of 0.95 μm, and a loss value of 1.3 μm is 0.2 dB / m was a low loss. The obtained optical fiber had a high tensile strength of 750 MPa.

Example 5 Using a mold having an inner diameter of 5 mm, the core was 56 Zr doped with Pr ³⁺ of 500 ppm.
_{F 4 -14BaF 2 -15PbF 2 -3.5LaF 3} -
2YF ₃ −2.5AlF ₃ −7LiF (mol%), and the cladding was 46.5ZrF ₄ −23.5BaF.
₂ -2.5LaF ₃ -2.5YF ₃ -4.5AlF ₃ -
Fluoride glass base material made of 20 NaF (mol%) (outer diameter 5.0 mm, length 150 mm, relative refractive index difference Δn =
4.2%) was prepared by the suction casting method. Further, using a mold having an inner diameter of 15 mm, a fluoride jacket tube having the same composition as the clad glass of the base material (outer diameter 15 mm, inner diameter 5.0 mm, length 150 mm).
Was produced by the rotation casting method.

The surface of the base material was polished and etched, and vacuum deaeration was performed to remove water on the surface, and then the base material supporting rod 2 in the vacuum container 7 was held. After evacuating the vacuum container 7 to a vacuum degree of 10 ⁻⁶ Torr, surface treatment was performed under the same conditions as in Example 1. The base material subjected to the surface treatment is evacuated again to 10 ^-6 Torr in the vacuum container 7, and then returned to the atmospheric pressure by the N ₂ gas having a dew point of -90 ° C or less supplied from the gas inlet 9 to drive the driving device. The base material was moved to the glove box 15 by lowering 0.

The surface-treated preform in the glove box 15 is inserted into the jacket tube to obtain an optical fiber preform, and the preform is held on the preform supporting rod 2 again.
The surface treatment was performed in the vacuum container 7 under the same conditions as in Example 1. After that, the inside of the vacuum container 7 is evacuated to 10 ⁻⁶ Torr again, and returned to atmospheric pressure by N ₂ gas having a dew point of −90 ° C. or lower supplied from the gas inlet 9, and a gate valve (not shown) is opened to drive it. The optical fiber preform was moved to the core tube 12 by lowering the apparatus 0.

In the core tube 12, the optical fiber preform was fed at a rate of 2 mm per minute into the preform heater 13 to be softened and pulled downward to obtain an optical fiber having an outer diameter of 125 μm.

The obtained optical fiber is a single mode optical fiber having a length of 500 m, a core diameter of 1.7 μm and a cutoff wavelength of 0.95 μm, and as shown in FIG.
The loss value at 1.3 μm was 0.2 dB / m, which was a low loss.

In FIG. 3, the large peak is Pr.
It is absorption caused by ³⁺ . Further, the obtained optical fiber had a high tensile strength of 750 MPa.

Using the optical fiber obtained in this example,
When a signal light amplifier with a wavelength of 1.31 μm was constructed by optical pumping with a wavelength of 1.017 μm, a gain coefficient of 0.2 dB / mW was obtained.

[0070]

As shown in the above embodiments, according to the present invention, the problem of surface crystallization of the optical fiber preform can be solved, so that a fluoride optical fiber with high strength and low loss can be manufactured. Therefore, there is an advantage that the fluoride fiber can be put to practical use for mounting an optical amplifier or the like, and the cost and performance of the optical communication system can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing one embodiment of a fluoride optical fiber manufacturing apparatus of the present invention.

FIG. 2 is a diagram showing a method for etching a glass base material used in the method for producing a fluoride optical fiber of the present invention.

FIG. 3 is a characteristic diagram showing a loss characteristic of an optical fiber obtained by another embodiment of the optical fiber manufacturing method of the present invention.

[Explanation of symbols]

 0 drive device 1 fluoride optical fiber base material 2 base material support rod 3 base material support rod rotating device 4 base material support rod cover 5, 9, 11, 19 gas inlet 6 gas outlet 7 vacuum container 8 ion gun 10 Exhaust port 12 Core tube 13 Heater 14 Shutter 15 Glove box 16 Die 17 Ultraviolet curing part 18 Winding machine G Glove box glove

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C03C 13/04 C03C 13/04 25/02 25/02 C // G02B 6/00 356 G02B 6 / 00 356A (72) Inventor Shoichi Sudo 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (15)

[Claims] 1. A fluoride optical fiber manufacturing apparatus comprising at least a surface treatment unit for surface-treating a fluoride optical fiber preform by dry etching, and a drawing unit for drawing the fluoride optical fiber preform by heating and melting. An apparatus for producing a fluoride optical fiber, wherein the surface treatment section and the drawing section are connected to each other and shielded from the outside air. 2. The fluoride optical fiber manufacturing apparatus according to claim 1, wherein a coating part for resin-coating the drawn fluoride optical fiber is connected to the drawing part. 3. A base material support rod that supports the fluoride optical fiber base material, and a base material support rod cover that shields the base material support rod from the atmosphere.
The fluoride optical fiber manufacturing apparatus according to. 4. The fluoride according to claim 1, wherein the surface treatment unit has an inlet and an outlet for an ion flow, a vacuum outlet, and a gas inlet. Optical fiber manufacturing equipment. 5. The fluoride optical fiber manufacturing apparatus according to claim 1, wherein the drawing portion has a gas introduction port. 6. The fluoride optical fiber manufacturing apparatus according to claim 1, further comprising means for rotating the base material support rod around an axis. 7. The fluoride optical fiber manufacturing apparatus according to claim 2, wherein the coating portion is a glove box having an atmosphere gas supply pipe and an exhaust pipe. 8. A shutter is installed between the drawing portion and the coating portion.
5. The fluoride optical fiber manufacturing apparatus according to any one of 1. 9. A method for manufacturing a fluoride optical fiber, which comprises at least a surface treatment step of surface-treating a fluoride optical fiber base material by dry etching and a drawing step of drawing the fluoride optical fiber base material by heating and melting. The method for producing a fluoride optical fiber, wherein the drawing step is performed in an atmosphere of an inert gas at an atmospheric pressure, a fluorine-containing gas, or a mixed gas thereof. 10. The fluorine-containing gas is NF ₃ , F ₂ ,
The method for producing a fluoride optical fiber according to claim 9, wherein the fluoride optical fiber is at least one gas selected from the group consisting of HF, SF ₆ , CF ₄ , and XeF ₂ . 11. A coating step of resin-coating the drawn fluoride optical fiber, following the drawing step.
The method for producing a fluoride optical fiber according to. 12. The surface treatment step is a step of accelerating ions generated by plasma to collide with the surface of the fluoride optical fiber preform. A method for producing a fluoride optical fiber as described above. 13. The surface treatment step comprises Ar, F ₂ , C
l ₂ , Br ₂ , CF ₄ , C ₂ F ₆ , NF ₃ , SF ₆ , X
13. The method for producing a fluoride optical fiber according to claim 9, wherein the method is performed using at least one gas selected from the group consisting of eF ₂ . 14. The surface treatment step and the drawing step are performed under an atmospheric pressure atmosphere of an inert gas or nitrogen gas having a dew point of −60 ° C. or less, according to claim 9. Fluoride optical fiber manufacturing method. 15. The coating process comprises a dew point of −60.
The method for producing a fluoride optical fiber according to claim 14, wherein the method is performed in an atmospheric pressure atmosphere of an inert gas or nitrogen gas at a temperature of not higher than 0 ° C.