JPS63143508A - Preform for fluoride glass fiber and its production - Google Patents

Abstract

PURPOSE:To suppress degradation of mechanical strength and generation of a scattering loss by infiltration of moisture into a glass rod contg. 15-25% NaF by coating said glass rod with Ge-Se glass contg. 10-20% Ge and removing the moisture on the rod surface by the plasma in a vacuum vessel. CONSTITUTION:A core part and clad part are constituted of the glass having the compsn. contg. ZrF4, BaF2, NaF, LaF3, and AlF3 and 15-25mol% NaF. Since this glass is drawn at 315-340 deg.C, the coating material is constituted of the Ge-Se glass contg. 10-20mol% Ge is order to maintain the viscosity of the coating material for the glass at 10<3>-10<6> Poise. Gaseous halogen 30 introduced into the vacuum vessel 25 is subjected to high-frequency heating 29 and the moisture sticking to the glass rod 26 surface is removed by the generated radicals so that the Ge-Se glass evaporated in a crucible 32 is uniformly deposited by evaporation on the rod 26 surface. The infiltration of the moisture to the glass rod is, therefore, completely prevented, by which the scattering loss at the time of drawing and the degradation in the mechanical strength and absorption loss of the fiber are suppressed.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention is directed to a fluoride glass fiber brifform that can transmit light in the wavelength range of 2 to 4 μm with low loss and can spin fibers with high mechanical strength. and its manufacturing method.

(Prior art and its problems) Fluoride glass fiber is attracting attention as a fiber for long-distance communication using light in the 2-4 μm band, and theoretically has an ultra-low resistance of about 0.01-0.001 dB/km. A loss value is expected. However, at present, even the smallest fiber loss is about 1 dB/km, which is about two to three orders of magnitude larger than the theoretical value. In addition, regarding mechanical strength, which is a practically important factor, the current level is 200 to 300 MPa.
The theoretical value is only about 1000. This increases the loss of current fluoride glass fibers and also
The biggest cause of a decrease in strength is the contamination of moisture when a core with a cladding and a coating applied to the outer periphery (hereinafter referred to as a "preform") is drawn into a fiber.

Conventional base material manufacturing methods include a method called a build-in casting method and a method called a rotational casting method.

FIG. 1 is a diagram for explaining the conventional build-in casting method. In the figure, 1 is a clad glass melt, 2 is a metal mold, 3 is a clad glass tube, and 4 is a core glass melt. In this method, first, as shown in FIG. 1(A), a clad glass melt 1 heated and melted in a crucible is poured into a metal mold 2 maintained at a temperature near the glass transition point. Next, as shown in (b), before the entire glass has cooled down, the metal mold 2 is tilted and the glass melt 1 inside is poured out. As a result, a cooled and solidified clad glass tube 3 is formed on the wall surface of the metal mold 2.

Next, as shown in (c), the core glass melt 4 is poured into the clad glass tube 3 and cooled and solidified to obtain a base material for fluoride glass fiber having a core clad structure as shown in (d). Hereinafter, it will be referred to as [fluoride glass rod]. Since these base material manufacturing processes are performed in a completely inert gas atmosphere, there is almost no contamination of moisture during the process.

Next, the surface of the rod is polished to be smooth, covered with a Teflon heat-shrinkable tube to form a preform, and drawn into a fiber using a drawing device. In the conventional technology,
It is unavoidable that moisture gets mixed into the process from polishing to wire drawing. For example, since rod polishing must be performed in the atmosphere, a considerable amount of moisture adheres to the surface of the rod after polishing. Generally, the glass surface has the property of easily adsorbing moisture, and once the moisture has been adsorbed,
Vacuum drying, which is a commonly thought drying method, or 250℃
It cannot be removed by heat drying as described below. Therefore, in the prior art, a Teflon heat shrink tube is coated with adsorbed water on the surface to form a preform, and the preform is subjected to wire drawing. Therefore, when the preform is heated to the drawing temperature (approximately 320°C), a chemical reaction occurs between the fluoride glass, which has become more chemically reactive due to the temperature rise, and the water adsorbed on the surface of the rod. Crystalline substances may be formed in the fiber, and moisture may be mixed into the fiber due to thermal diffusion.

One of the reasons why the rod is covered with a Teflon heat shrink tube after polishing is that when the rod is drawn, the rod comes into contact with moisture in the atmosphere, which prevents the formation of crystalline substances and moisture loss as mentioned above. This is to prevent mixing into the fiber. Of course,
This objective has been achieved to some extent by coating Teflon heat shrink tubing. However, since Teflon has the property of transmitting a certain amount of moisture, it is not possible to completely prevent moisture from entering the fiber from the atmosphere. In addition, since Teflon itself contains a certain amount of water, Teflon itself also becomes a source of a small amount of water.

As explained above, when a conventional fluoride glass fiber preform is drawn into a fiber, water adsorbed on the surface of the glass rod, moisture in the atmosphere, moisture contained in the Teflon heat shrink tube, etc. are drawn into the fiber. It was not possible to prevent the contamination. Therefore, the water mixed into the fiber causes a chemical reaction with the fluoride glass, producing a crystalline substance, which significantly reduces the mechanical strength of the fiber and increases the loss due to scattering. Strong absorption occurs around the wavelength of 9 μm,
There was a problem in that the loss of the fiber increased significantly.

(Objective and Features of the Invention) The present invention has been made to solve the above-mentioned problems in the technical field. Since it is possible to prevent moisture from entering the fluoride glass fiber when drawing it, there is no decrease in the mechanical strength of the fiber and an increase in scattering loss caused by crystals generated by moisture, and there is no increase in absorption loss. An object of the present invention is to provide a preform for a fluoride glass fiber that can draw a fluoride glass fiber, and a method for manufacturing the same.

The feature of the preform for fluoride glass fiber according to the present invention is that both the core part and the cladding part whose refractive index is lower than that of the core part are ZrF, -BaFz-NaFLaF3.
Contains at least a component of A I F3, and contains Na
When the F content is expressed in mol%, 15≦NaF≦25
The fluoride glass rod is comprised of a fluoride glass rod having a fluoride glass rod in the range of 1 to 1, and a coating layer containing at least Se and 20 mol % or less of Ge for coating the rod.

In the method for manufacturing a preform for fluoride glass fiber according to the present invention, both the core portion and the cladding portion having a lower refractive index than the core portion are made of ZrF4-BaFz-NaF-La.
contains at least a component of F, -AlF2, and NaF
a first step of producing a fluoride glass rod in which the content of NaF is in the range of 15≦NaF≦25 when expressed in mol%; a plasma generating part that generates plasma of halogen gas; The rod is inserted into a vacuum vessel having a thin film manufacturing section for producing a coating layer containing at least % or less of Ge, and a reaction between the plasma generated in the plasma generating section and the rod causes the above-mentioned The present invention includes a second step of removing moisture adhering to the surface of the rod, and a third step of covering the rod with the coating layer produced by the thin film manufacturing section.

(Principle of the invention) The present invention will be explained in detail below.

As mentioned above, the reason why moisture gets mixed into the fiber when drawing a conventional preform into a fiber is that the Teflon heat shrink tube is coated with moisture attached to the surface of the glass rod. This is due to the fact that it allows water vapor to pass through to a certain extent and that Teflon itself contains a certain amount of water. Therefore, in order to prevent moisture from entering when drawing a preform, a fluoride glass rod consisting of a core portion with a high refractive index and a cladding portion with a low refractive index is first prepared, and then the surface of the glass rod is coated by some means. After removing the attached moisture, a special coating material having the following characteristics is coated on the surface of the glass rod by some means that does not allow moisture to be re-introduced to form a preform, and then the glass rod and coating layer are bonded together. I think it would be a good idea to draw the line at the same time. The properties necessary for the coating material are the following.

■ Can be drawn together with fluoride glass rod.

■ Made of highly water-resistant material that does not allow moisture to pass through.

■ The material itself does not contain moisture.

■Do not react with fluoride glass during drawing.

From the above viewpoint, the present inventors have developed a new coating material to replace the conventional Teflon heat-shrinkable tube, and a method for coating a glass rod with this coating material without re-deposition of moisture after removing moisture from the surface of the glass rod. We considered the following.

(Example 1) First, a preform for fluoride glass fiber will be described.

The materials that can be considered as coating materials for fluoride glass rods are almost limited to resins and glasses due to the restriction that the materials can be drawn. However, in conventional resins,
There was nothing that satisfied the above conditions. In the end, the materials that satisfy the above conditions are S, Se, and T.
It has been found that there is a chalcogenide glass containing elements such as e, Ge, and ^S.

However, in addition to ■■■, the covering material must also have the characteristics of ■. In other words, the property (2) requires that the coating material has a viscosity that allows drawing at the drawing temperature of the fluoride glass rod. The drawing temperature for fluoride glass rods depends on the glass composition and is usually between 300 and 40°C.
It varies in the range of about 00℃. Therefore, unless the composition of the fluoride glass is specified, the drawing temperature of the glass rod cannot be specified, nor can the coating material be specified.

In the present invention, the target fluoride glass rods include at least ZrF, BaFz, NaF,
It is composed of a glass containing LaF3°AlF3 and having a composition of 15≦NaF≦25 when the content of NaF is expressed in mol%. Here, the reason why the content of NaF is limited to 15 mol% or more and 25 mol% or less is as follows. In other words, this Na content is such that when the present inventors manufacture a glass rod using the current glass rod manufacturing technology in an environment without moisture contamination, a glass rod with almost no scattering due to crystallization is observed. This shows the composition range that can produce . Glass in this composition range has good thermal stability and is the most excellent material for ultra-low loss fibers in the 2-4 μm band. The drawing temperature for glasses in this composition range depends on the NaF content and is 315-340.
℃ range. Therefore, in order to draw with glass in this composition range, the viscosity of the coating material should be 315-340°C.
It must be about 103 to 10" Po1se. From this point of view, S, Se, Te, As, Ge
As a result of investigating the viscosity-temperature characteristics of chalcogen glasses of various compositions including
Ge-Se glass containing Ge with e≦20 or glass having the above composition range with S, Te, As, Sb, S
It has been found that a multi-component glass containing small amounts of i, P, etc. has such viscosity-temperature characteristics.

FIG. 2 is a characteristic diagram showing the viscosity-temperature characteristics of the Ge--Se glass according to the present invention. The vertical axis of the figure shows the viscosity of the glass, and the horizontal axis shows the temperature. Since the drawing temperature of the fluoride glass targeted in the present invention is 315 to 340°C,
The viscosity of the coating material is lO'3~10'P in this temperature range.
It is necessary to be within the range of o1se.

That is, a glass having a composition having a viscosity-temperature curve passing through the shaded area in FIG. 2 can be used as the coating material, and the range is Ge-Se glass with 10≦Ge≦20. For example, for fluoride glass with a drawing temperature of 340°C, 12≦Ge≦20. The drawing temperature is 315
For glass at ℃, Ge with a composition of lo≦Ge≦18
-Se glass can be used as a coating.

As described above, according to the present invention, a fluoride glass rod containing Ge of 10 mol% or more and 20 mol% or less
By coating with e-Se-based glass, a preform for a fluoride glass fiber containing almost no water can be produced.

(Example 2) Next, we will discuss a method for removing moisture adhering to the surface of a fluoride glass rod, and how to prevent moisture from re-attaching after removing moisture.
A method of coating a glass rod with Ge-5e glass will be described.

As mentioned above, glass has dangling bonds on its surface, so it has the property of easily adsorbing water, and normal methods such as vacuum drying or heat drying cannot completely remove the adsorbed water. difficult. In particular, in the case of fluoride glass, it cannot be heated above 250° C. due to its low softening point, and special means are required to remove adsorbed water.

Below, the method for manufacturing a preform of the present invention will be explained in detail.

(1) First step The first step is to produce a fluoride glass rod.In order to explain the manufacturing process in an easy-to-understand manner, the present inventors have already filed a patent application for "Fluoride Glass Rod". This will be explained using one example (Japanese Patent Application No. 155233/1983) of the "Fiber base material manufacturing apparatus".

FIG. 3 is a schematic diagram of manufacturing equipment for use in making fluoride glass rods according to the present invention. In the figure, 11 is an external crucible with a nozzle, 12 is glass for cladding, 13 is a crucible with nozzle, 14 is glass for core, 15 is a vertically moving rod, 16 is a jig for preventing glass melt from flowing out and for drawing out glass,
17 is a gas inlet, 18 is a closed container, 19 is a high frequency coil, 20 is a thermocouple, 21 is a control system, 22 is a high frequency power supply,
23 is a drive device for the vertically moving rod 15, and 24 is a gas discharge port. Although not shown, the closed container 18 has an openable/closable door on the front, which is opened when loading a glass material into the crucible 11, 13, and is sealed during operation.

Next, the manufacturing method will be explained.

■ Put the cladding glass 12 into the outer crucible 11 with the nozzle,
Further, the core glasses 14 are respectively loaded into the inner crucibles 13 with nozzles. The tip of the nozzle is closed by contacting with a jig 16 for preventing outflow of the glass melt and for drawing out the glass, which is attached to the upper end of the vertically moving rod 15. Note that the cladding glass 12 includes, for example, 33ZrF4-2011fF,
-17BaFz-23NaF -4LaFi -3AJ
F3, 53ZrF* 20Ba for core glass 14
Although a glass having a composition of Pz-2ONaF-4LaF3-3A IFs is used, the composition ratio is not limited to this.

(2) A fluorine-based gas is introduced from the gas inlet 17 to create a fluorine-based gas atmosphere inside the sealed container 18, and the crucible 11.13 is heated by the high-frequency coil 19 to heat the glass 12.
14 is melted for a certain period of time. The melting temperature at this time is set as high as possible within a range where the components of glasses 12 and 14 do not evaporate significantly.

■ Lower the temperature of the glass melt 12.14 to as low a temperature as possible without precipitation of the crystalline phase from the glass melt 12.14, and after holding it for a certain period of time, lower the temperature of the glass to a temperature at which the viscosity of the glass can be drawn out. After that, the vertical moving rod 15 is moved downward to simultaneously pull out the core glass 12 and the thalassod glass 14 from the tip of the nozzle, and the core glass 12 and the thalassod glass 14 are cooled and solidified to obtain a base material for fluoride glass fiber, that is, a fluoride glass rod. .

The temperature control in this process is performed by directly detecting the temperature of the glass 14 with a thermocouple 20, and by adjusting the output of the high frequency power supply 22 with the control system 21, and the control system controls the drawing speed of the glass 12.14. 21 electrically controls the drive device 23 for the vertically moving rod 15.

The above has been explained using an apparatus that can produce a long fluoride glass loft with low loss. Other manufacturing methods may also be used.

(2) Second Step FIG. 4 is a schematic diagram of an apparatus for manufacturing a preform for fluoride glass fiber of the present invention, and the following procedure will be explained using this preform manufacturing apparatus.

In the figure, 25 is a vacuum container containing a plasma generation section and a thin film manufacturing section which will be described later, 26 is a fluoride glass rod produced in the first step described above, and 27 is a vacuum vessel for supporting the fluoride glass rod 26. Support rod, 28 is support rod 2
7, a movement control unit that controls the rotation and movement of 7; 29, a high-frequency coil for generating plasma of halogen gas;
0 is a high-frequency power supply for applying voltage to the high-frequency coil 29; 31 is a Ge-Se-based coating material source; 32 is a heating crucible for vapor deposition that accommodates the coating material source 31; 33 is a heating crucible for heating the heating crucible 32; For example, a heater such as a heater (
(The power supply is omitted in the figure), 34 is NF3, CF4, B
F: An inlet for introducing a halogen gas such as l, C1z, CC1a, etc. which generates highly reactive halogen radicals when turned into plasma, and 35 an exhaust port for discharging reaction gas and reaction products. In the following description, the high-frequency coil 29°, the high-frequency power source 30, and the halogen-based gas inlet 34 are collectively referred to as a plasma generation section, a coating material source 31. The heating crucible 32 for vapor deposition and the heater 33 are collectively referred to as a thin film manufacturing department.

(2) Support the fluoride glass rod 26 produced in the first step with the support rod 27 and place it in the vacuum container 25.

(2) A halogen-based gas at a gas pressure of about 10-1 to 10-'' Torr is introduced from the inlet 34, and a high voltage is applied to the high-frequency coil 29 from the high-frequency power supply 30 to generate halogen radicals in the plasma generation section. The generated halogen radicals react with moisture adhering to the surface of the fluoride glass rod 26, and the moisture is decomposed and removed.This step is one of the features of the present invention.
Moisture adhering to the surface is completely removed.

(2) Next, the inside of the vacuum container 25 is brought to a high vacuum of about 10 4, and the reaction gas and reaction products are exhausted from the exhaust port 35.

(3) Third step ■ The heating crucible 32 for vapor deposition is heated by the heater 33.

(2) A coating material 31 of Ge--Se glass that has been heated and vaporized is deposited on the fluoride glass rod 26. At this time, the coating material can be uniformly applied to the surface of the fluoride glass rod 26 by moving the support rod 27 back and forth or rotating it using the movement control unit 28 . What is important in this step is to remove moisture adhering to the surface of the fluoride glass rod 26 and then attach the coating material of the present invention to produce a preform.

In addition, in FIG. 4, a vacuum evaporation method is used for the thin film manufacturing section, but the method is not limited to this, and a sputtering method or the like may be used. For example, when a sputtering method is used in the thin film manufacturing section, an electrode and a Ge-5e'Jd
Prepare a target and place 10-2 in the vacuum container 25.
If the gauge gas is introduced at a pressure of ~10-3 Torr,
Similarly to the vacuum evaporation method, a preform to which a Ge-Se glass coating is attached can be produced.

As mentioned above, according to the invention, the fluoride glass rod 2
6, and then completely remove the moisture adhering to the surface of the rod 26 with halogen gas plasma.
By producing a preform for fluoride glass fiber with e-Se glass coating material attached to the surface of the wand 26, it is possible to create a fluoride glass fiber that does not contain any moisture even when the preform is drawn in the atmosphere. can be provided.

(Effects of the Invention) As explained in detail above, the present invention provides that both the core portion and the cladding portion having a lower refractive index than the core portion are made of ZrFa, -B.
Ge-Se on the surface of a fluoride glass rod containing at least the components aF, -NaF-LaFs-^IF,
By producing a preform for fluoride glass fiber coated with glass, no moisture is mixed in when drawing the preform, which reduces scattering loss, decrease in fiber mechanical strength, and absorption loss that occur during fiber drawing. Can be suppressed. Therefore, long-path Mi1!1 reliable fluoride glass fibers in the 2 to 4 μm band, which are expected in the future, can be produced with low loss and high strength, so the effect is extremely large.

[Brief explanation of the drawing]

Figure 1 (a), (b), (c), and (d) are schematic diagrams for explaining the manufacturing process diagram of a conventional fluoride glass rod, and Figure 2 is a side view of the viscosity-temperature characteristics of the Ge-Se glass according to the present invention. 3 is a schematic side view of the manufacturing apparatus used for manufacturing the fluoride glass rod used in the present invention, and FIG. 4 is a schematic diagram of the apparatus for manufacturing the preform for fluoride glass fiber according to the present invention. . 1.12... Thalassod glass melt (glass for cladding), 2... Metal mold, 3... Clad glass tube,
4.14...Core glass melt (glass for core), 11
... Crucible with nozzle, 13... Inner crucible with nozzle,
15... Moving rod, 16... Glass drawer jig,
17, 34...Gas inlet, 18...Airtight container, 1
9, 29...High frequency coil, 20...Thermocouple, 21
...Control system, 22.30...High frequency power supply, 23...
- Drive device, 24, 35... Exhaust port, 25... Vacuum container, 26... Fluoride glass rod, 27... Support rod, 28... Movement control unit, 31... Covering material Source, 32... Heating crucible for vapor deposition, 33... Heater.

Claims (2)

[Claims] (1) Both the core part and the cladding part whose refractive index is smaller than the core part are ZrF_4-BaF_2-NaF-LaF_
Contains at least a component of 3-AlF_3 and contains NaF
A fluoride glass rod whose content, expressed in mol%, is in the range of 15≦NaF≦25, and Se for coating the surface of the fluoride glass rod, which is 10 mol% or more and 20 mol% or less. Ge-S containing at least Ge of
A preform for a fluoride glass fiber comprising a coating layer made of e-type glass. (2) Both the core part and the cladding part whose refractive index is smaller than the core part are ZrF_4-BaF_2-NaF-LaF_
Contains at least a component of 3-AlF_3 and contains NaF
A first step of producing a fluoride glass rod in which the content of NaF is in the range of 15≦NaF≦25 when expressed in mol%, a plasma generation part that generates plasma of halogen gas, and Se and 20 mol%. The fluoride glass rod is inserted into a vacuum container having a thin film production section for producing a coating layer containing at least Ge as described below, and the plasma generated in the plasma generation section and the fluoride glass rod are a second step of reacting to remove moisture adhering to the surface of the rod; and a third step of covering the surface of the fluoride glass rod with the coating layer produced in the thin film manufacturing department A method of manufacturing a preform for a fluoride glass fiber comprising: