JPH04305024A - Method for heating and working fluoride glass - Google Patents

Abstract

PURPOSE:To heat and work a fluoride glass preform 4 without causing local crystallization on its surface. CONSTITUTION:A dry inert gas 9 is introduced into an applicator 3 to cover a fluoride glass preform 4 with the inert gas, a microwave is emitted from a microwave oscillator 1, and the part of the preform 4 to be worked is heated in the atmosphere. The heated preform 4 is drawn to obtain a fiber 8.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating fluoride glass, which is necessary in the manufacturing process of fluoride optical fibers.

0002

[Prior Art] A fluoride optical fiber containing ZrF4 as a main component has a power efficiency of 0.01 dB/k, which is higher than a silica optical fiber.
Its development is progressing with the expectation that it will have a low loss property of m. Normally, this type of fluoride optical fiber is made by heating and melting a glass raw material mixture prepared to have a predetermined glass composition in a crucible, pouring it into a suitable metal mold, and rapidly cooling it to vitrify it to form a base material. It is obtained by heating and stretching this base material.

[0003] In the manufacturing process of such fluoride optical fibers, various heating processes are indispensable in the process from forming the base material to producing the optical fiber.

However, the surface of fluoride glass easily crystallizes during the heating process due to the presence of moisture adsorbed on the surface or moisture in the atmosphere.

[0005] In order to prevent this, the heating atmosphere is generally a dry inert gas atmosphere or an atmosphere containing a fluorine compound gas.

Tubular furnaces and the like are used for heat processing such as surface treatment and stretching of the base material, but when an atmosphere containing fluorine compound gas is used as the heating atmosphere, strong Materials that can withstand corrosive fluorine compound gases must be used. As the material, aluminum, nickel, Monel alloy, etc. are used.

[0007]

[Problems to be Solved by the Invention] However, the normal processing temperature for fluoride glass is 300 to 400°C;
Since the temperature that aluminum can withstand is 400°C, it is in a very severe condition. Nickel and Monel alloys can withstand temperatures up to about 600°C, but unlike aluminum, there is a risk of loss if they are contaminated with glass.

[0008] Furthermore, in order to make the heating atmosphere a dry atmosphere, it is necessary to introduce a large amount of drying gas, and in order to perform stable and highly accurate heating using a tube furnace under such conditions, it is necessary to increase the heating length. The temperature gradient in the longitudinal direction of the tube furnace must be made as small as possible by enlarging the tube furnace. Therefore, it is very inconvenient in cases where local heating is required, such as jacketing or stretching of the base material, or wire drawing.
Increasing the size of the furnace is also unavoidable.

Furthermore, the viscosity of fluoride glass changes rapidly with changes in temperature. Therefore, in order to perform accurate processing, a highly accurate heat source that can locally heat the material is required.

0010

[Means for Solving the Problems] In view of the above-mentioned technical situation, the present invention aims to enable highly accurate local heating necessary for heating processing of fluoride glass, and at the same time achieve prevention of surface crystallization. The structure is such that the atmosphere in the processing area of the fluoride glass is a dry inert gas atmosphere or a dry inert gas atmosphere containing a fluorine compound,
It is also characterized by supplying microwaves to the processing area to heat it and perform processing.

[0011]

[Operation] In the above method, heating is performed locally on the processing area using microwaves. Further, since the surrounding area is a dry inert gas atmosphere, crystallization is also prevented.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows an embodiment of the method for heating fluoride glass according to the present invention. This example is
This is applied to drawing fluoride fiber.

1 is a microwave oscillator, 2 is a waveguide connected to the oscillator 1 and guides the microwave, 3 is an applicator coupled to the waveguide 2, and on the top thereof is a fluoride glass base material. 4 is installed or supplied. An atmospheric gas inlet 5 is provided on the lower side of the applicator 3, and an atmospheric gas exhaust port 6 is provided on the upper side of the applicator 3. Note that 7 in the figure is a tuner connected to the waveguide 2.

To carry out this method, first the fluoride glass matrix 4 is introduced into the upper part of the applicator 3. Next, an inert gas or a dry inert gas 9 containing a fluorine compound is introduced into the applicator 3 through the atmospheric gas inlet 5 and discharged through the atmospheric gas outlet 6 to a predetermined area around the fluoride glass base material 4. form an atmosphere.

Next, microwaves (2.45 GHZ are used in this embodiment) are supplied from the oscillator 1 to heat the fluoride glass base material 4. Oscillator 1 depending on the heating condition etc.
Since the reflected power in the direction changes, the tuner 7 is adjusted to minimize this. The viscosity of the base material 4 decreases as the temperature rises, and the base material 4 eventually becomes constricted and the tip falls off. The fiber 8 is drawn by drawing the fiber at a predetermined speed and continuously supplying the base material 4.

<Example 1> According to the above method, ZrF4-Ba with an outer diameter of 15 mm was actually prepared as a fluoride glass base material.
F2 -LaF3 -YF3 -AlF3 -LIF(
or NaF) type glass (Kanamori and
Sakaguchi, Japanese Jour
nal of Applied Physics, V
ol. 25, No. 6, 1986, ppL468-
L470), this was drawn at a drawing speed of 15 m/min to produce a fiber with an outer diameter of 125 μm. As the atmospheric gas, NF3 was mixed with dry gas extracted from liquefied argon, and the mixture was introduced. The flow rate ratio is 95
:5. At this time, the dew point inside the applicator (NF3 was not introduced during measurement) was -72°C. Also,
The required power was 374W.

The obtained fiber had an outer diameter variation of 125μ.
It was ±1 μm with respect to m. In the online measurement chart of the outer diameter, there were no pulse-like diameter fluctuations caused by surface crystallization, and the take-up speed was stable at about ±1.5 m/min. Further, no traces of crystallization were visually observed on the surface of the base material. The applicator was made of aluminum and was kept at a temperature of about 200° C., but no damage such as corrosion was observed.

<Example 2> By the method described above, a base material made of the same material as above was stretched into a base material having a diameter of 7 mm. The power required is 3
It was 65W. The atmosphere was the same as above. No crystallization was visually observed on the surface of the base material after stretching.

<Example 3> A sintered body of glass raw material powder prepared to have the same composition as the base material (outer diameter 20 mm, sintering temperature 4
The above heating method was applied to the zone melting surface at 60° C. for 2 hours. The required power was 512W. The melting surface was extremely horizontal, clearly indicating that internal heating was localized and extremely effective.

[0020]

[Effects of the Invention] According to the heating processing method for fluoride glass according to the present invention, the pressurized area can be heated extremely stably by directly heating the glass itself internally and locally using microwave heating. At the same time, since heating is performed in a dry inert gas atmosphere, crystallization of the glass surface can be prevented.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment.

[Explanation of symbols]

1 Microwave oscillator 2 Waveguide 3 Applicator 4 Fluoride glass base material 5 Atmosphere gas inlet 6 Atmosphere gas exhaust port 7 Tuner 8 Fiber

Claims (1)

[Claims] Claim 1: A feature of the present invention is that the atmosphere of the processing area of the fluoride glass is a dry inert gas atmosphere or a dry inert gas atmosphere containing a fluorine compound, and the processing is performed by supplying macro waves to the processing area and heating it. A heating processing method for fluoride glass.