JPH0327492B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing an optical fiber base material capable of transmitting infrared rays in the wavelength range from visible light to 6 μm.

〓Prior art〓 One of the fibers for infrared transmission is one made of fluoride glass.For example, in the case of a fluoride glass optical fiber whose main component is zirconium fluoride, it simply transmits light in the infrared region. In addition, as a theoretically calculated transmission characteristic, 10 ^-2 ~
Excellent values below 10 ^-3 dB/Km can be expected.

For these reasons, fluoride glass is being considered for application as a next-generation communication medium, for example in the field of measurement using infrared light, and is attracting attention as a promising optical fiber material.

However, as a general trend of fluoride glass,
Due to its tendency to crystallize and low viscosity, it is difficult to produce the optical fiber by the well-known crucible melt spinning method.

As an alternative to this, a method has been adopted in which an optical fiber base material is once produced by a cast molding method, and then the optical fiber base material is heated and stretched to obtain an optical fiber. , Figure 3,
The method shown in FIG. 4 has been implemented.

In the case of FIG. 3, a precious metal crucible 51 containing fluoride glass is placed in an electric furnace (not shown), the fluoride glass is melted at 500 to 800°C, and then,
The crucible 51 is taken out from the electric furnace, the fluoride glass melt 52 in the crucible 51 is injected into the vertical mold 53, and after the fluoride glass melt 52 has cooled and solidified time has elapsed, the mold is released. As a result, an optical fiber base material, which is a fluoride glass molded product, is obtained.

In the case of FIG. 4 as well, an optical fiber preform is obtained in the same manner as described above, except that a horizontal split mold 55 having presser lids 54 on both sides is used.

〓Problems to be solved by the invention〓 In the case of the above-mentioned conventional example, regardless of whether it is vertical or horizontal,
The fluoride glass melt is injected into the mold manually.

In such manual operation, not only is the injection work including the injection speed of the fluoride glass melt generally not stable, but also the intake of outside air almost always occurs during the injection, resulting in air bubbles remaining in the base material.

Moreover, since the residual bubbles extend in the longitudinal direction of the base material, the yield of the base material deteriorates to about 50%.

On the other hand, the crucible is not kept warm after being removed from the electric furnace, and the fluoride glass melt inside the crucible is
Since it is cooled at a rate of 50 to 100°C/min, the viscosity of the melt increases over time.

Therefore, rapid injection of the melt is required, but rapid injection of the melt may cause the crystallization of the fluoride glass, such as generating large bubbles or slowing down the cooling rate of the melt. Become.

In addition, since the fluoride glass melt in the crucible is not kept warm, its viscosity changes over time. This causes continuous temperature changes and density fluctuations, which cause scattering at the optical fiber stage.

In view of the above-mentioned problems, the present invention has been devised to create a base material that does not cause defects such as residual bubbles or crystallization, and that allows a fluoride glass optical fiber with good characteristics to be obtained in a high yield and in a reasonable manner. The purpose is to provide a manufacturing method.

〓Means for Solving the Problems〓 The method for producing a fluoride glass optical fiber base material according to the present invention uses a heating furnace in which a base material mold and a crucible are movable relative to each other. Under the internal atmosphere control state, the fluoride glass contained in the crucible is melted and the temperature of the base material mold is adjusted, and then the crucible and the base material mold are brought close to each other to melt the fluoride glass contained in the crucible. The intended purpose is achieved by injecting a fluoride glass melt into a base material mold and cooling and solidifying the fluoride glass melt in the base material mold.

〓Operations〓 In the case of the method of the present invention, the fluoride glass in the crucible is melted, the temperature of the base material mold is adjusted, and the fluoride glass melt is poured into the base material mold in a heating furnace under controlled atmosphere. Since the fluoride glass melt poured into the base material mold is cooled and solidified, the inside of the heating furnace is not affected by outside air or temperature.

Therefore, when injecting the fluoride glass melt from the crucible into the base material mold, the injection speed can be freely controlled, preventing early viscosity changes of the fluoride glass melt, crystallization of the fluoride glass, etc. It can be avoided.

In particular, if the fluoride glass melt is injected into the base mold at a constant flow rate, air bubbles will not be trapped in the melt, and at this time, the injected fluoride glass melt will solidify continuously. It is also possible to control the glass temperature by controlling the so-called melt injection speed, so the fluidity due to thermal diffusion of the melt injected into the base mold is suppressed, and density fluctuations do not occur. Also from this point of view, crystallization of the fluoride glass can be prevented.

In this way, the fluoride glass cooled and solidified in the base material mold becomes a fluoride glass optical fiber base material with excellent properties and quality.

〓Example〓 Hereinafter, an example of the method of the present invention will be described with reference to the drawings.

In FIG. 1, a machine base 1 is equipped with a rotating body 2 made of, for example, an aluminum plate.

The rotating body 2 has a shaft 3 at the center of its front and rear surfaces,
A gear (worm wheel) 4 is attached to the shaft 3 on the front side, and is supported on the machine base 1 via a bearing 5 so as to be rotatable in horizontal to vertical directions.

As a means for rotating the rotating body 2, the machine base 1 is equipped with a motor 6, and a small gear (worm gear) 7 attached to the motor shaft is meshed with the gear 4.

Handles 8A and 8B are provided on both sides of the upper surface of the rotating body 2.
Vacuum flange 10 having moving axes 9A and 9B with attached
A and 10B are attached, respectively, and the heating furnace 11 is supported at both ends via these vacuum flanges 10A and 10B.

The heating furnace 11 is mainly composed of a core tube 12 made of quartz and electric heaters 13 and 14 in the form of a coil or a band. (left end and right end).

Inside the furnace core tube 12 of the heating furnace 11, a heat sink member 15 is installed corresponding to one heater 13, and a quartz boat 16 is installed inside the furnace core tube 12 corresponding to the other heater 14. A mold 17 is fixed to the boat 16, and a crucible 18 made of precious metal such as gold or platinum is attached to the boat 16.

Furthermore, a heat sink member 15, a boat 16
are connected to the vacuum flanges 10A, 10B via joints 19A, 19B, respectively.

In the figure, 20 is a gas inlet communicating with the inside of the reactor core tube 12;
21 is a gas outlet communicating with the inside of the furnace tube 12.

When carrying out the method of the present invention using the apparatus shown in FIG.
After maintaining the inside of the furnace core tube 12 of the heating furnace 11 in a clean atmosphere using an inert gas or the like, the fluoride glass in the crucible 18 is heated and melted by the heater 14, and in order to adjust the temperature of the mold 17, the fluoride glass is heated and melted. It is heated by the heater 13 and kept warm.

After the fluoride glass in the crucible 18 is melted as described above, the temperature of the fluoride glass melt is lowered to the injection temperature, and then the handle 8
The vacuum flanges 10A and 10B are operated by the respective moving shafts 9A and 9B with A and 8B to move the base material mold 17 and the crucible 18 closer to each other in the direction in which they butt together. 1
8.

Thereafter, the motor 6 is driven, and the rotation at this time is transmitted to the shaft 3 through a gear transmission system such as a pinion 7 and a gear 4, thereby causing the rotating body 2 to rotate at a constant speed counterclockwise in the figure.

Due to this rotation, the rotating body 2 in the horizontal state is rotationally displaced so that the base material molding die 17 is at the bottom and the crucible 18 is at the top, so that the fluoride glass melt in the crucible 18 flows into the base material molding die 17 at a constant flow rate. injected with

After finishing injecting the melt into the base material mold 17,
By operating the vacuum flange 10A using each moving shaft 9A with a handle 8A, returning the base material mold 17 containing the fluoride glass melt to the heater 13 side, and lowering the temperature of the heater 13 at a constant rate,
The fluoride glass melt in the mold is cooled and solidified.

Thus, an optical fiber matrix made of fluoride glass is obtained.

FIG. 2A shows the optical fiber base material 30 for the core obtained as described above, and the surface of the optical fiber base material 30 is polished, and as shown by the imaginary line in the figure, the optical fiber base material 30 is made of plastic. Clad pipe 3
After jacketing 1, it is drawn (heated and drawn) in a known spinning furnace equipped with a ring heater to obtain a plastic-clad fluoride glass optical fiber.

By the way, the optical fiber obtained in this way has a transmission loss of 3 dB/Km in the 2 μm wavelength band, which is about 1/30th of the conventional value.

In addition, the above-mentioned plastic clad pipe 31
Instead, a tube made of fluoride glass having a refractive index lower than that of the optical fiber base material 30, for example, a tube made of fluoride glass molded by a mold rotation method, is used, and the cladding tube and the optical fiber base material 30 are If this is spun using the rod incubation method, an optical fiber in which both the core and the cladding are made of fluoride glass can be obtained.

Next, other embodiments of the method of the present invention will be described.

When producing an optical fiber base material using the apparatus shown in FIG. 1, a tube for the cladding made of fluoride glass is preformed by a separate means, for example, by the above-mentioned mold rotation method, and such a tube is used as the base material. The material is set in the mold 17.

Thereafter, in the same manner as described above, the fluoride glass in the crucible 18 is melted, the temperature of the base material mold 17 is adjusted (heat-retained), and the base material is formed in the furnace tube 12 of the heating furnace 11 in an atmosphere-controlled state. The fluoride glass melt is injected into the mold 17, and the fluoride glass melt is cooled and solidified within the base molding mold 17.

FIG. 2B shows the optical fiber preform 40 obtained as described above, and the optical fiber preform 40 is composed of a fluoride glass 41 for the core and a fluoride glass 42 for the cladding.

This optical fiber base material 40 is also free from bubbles, crystallization, fluctuations in refractive index, etc.
A low-loss fluoride glass optical fiber can be obtained by spinning it using a known heated drawing means.

= Effect of the invention = As explained above, when the method of the present invention is used,
In a controlled atmosphere inside the heating furnace, the fluoride glass contained in the crucible is melted and the temperature of the base material mold is adjusted, and then the crucible and the base material mold are brought close to each other to The fluoride glass melt is injected into the base material mold, and the fluoride glass melt in the base material mold is cooled and solidified, thereby producing a base material from which fluoride glass optical fibers with good transmission characteristics can be obtained at a high yield. can do.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing one embodiment of the method of the present invention, FIGS. 2A and B are explanatory diagrams showing each example of the optical fiber base material obtained by the method of the present invention, and FIGS. FIG. 4 is an explanatory diagram of the conventional method. 11...Heating furnace, 12...Heating furnace core tube, 13...
Heater, 14... Heater, 17... Base material mold, 18
... Crucible, 30 ... Optical fiber base material (for core), 4
0... Optical fiber base material, 41... Fluoride glass for core, 42... Fluoride glass for cladding.

Claims (1)

[Claims] 1. Using a heating furnace in which a base material mold and a crucible are installed so that they can move relatively close to each other, fluoride glass contained in the crucible is heated under a controlled atmosphere inside the heating furnace. After melting and adjusting the temperature of the base material mold, the crucible and the base material mold are brought close to each other, and the fluoride glass melt in the crucible is injected into the base material mold to mold the base material. A method for producing a fluoride glass optical fiber base material, comprising cooling and solidifying a fluoride glass melt in a mold. 2. The method for producing a fluoride glass optical fiber base material according to claim 1, which comprises placing a fluoride glass for the core in a crucible and melting it, and injecting the fluoride glass melt into a base material mold. . 3 Set a fluoride glass tube for the cladding in advance in the base material mold, place the fluoride glass for the core in the crucible and melt it.
A method for producing a fluoride glass optical fiber preform according to claim 1, wherein the fluoride glass melt is injected into a fluoride glass tube in a preform mold. 4. The method for producing a fluoride glass optical fiber preform according to claim 1, wherein the heating means of the crucible and the heating means of the preform mold are independent of each other. 5. Claims 1 to 3, in which the heating furnace is rotated so that when the fluoride glass melt in the crucible is injected into the base material mold, the crucible is at the top and the base material mold is at the bottom. A method for producing a fluoride glass optical fiber base material according to any one of the above. 6. The method for producing a fluoride glass optical fiber base material according to claim 5, wherein the heating furnace is rotated at a constant speed.