JPH0416524A - Production of fluoride optical fiber - Google Patents

Abstract

PURPOSE:To improve the strength of the optical fiber by heat-treating a part or the whole of the fluoride glass preform, fluoride glass rod and fluoride glass pipe in an F-contg. gas and then drawing the preform. CONSTITUTION:A fluoride glass rod having a core composition obtained by casting a molten glass and a fluoride glass tube having a clad composition are etched in a hydrochloric acid soln. of ZrOCl2, washed with water and then vacuum-dried. The glass rod and tube are heat-treated at 0-400 deg.C in the atmosphere of a gaseous mixture of one or >=2 kinds among HF, CF4, NF3, SF6, BF3, F2, etc. The atmosphere is then replaced by gaseous Ar, and the rod and tube are cooled to room temp. to obtain a preform. The preform is inserted into a glass tube in an N2 atmosphere, 'Teflon FEP(R)' is used as the coating material, and the preform is drawn to obtain a fluoride optical fiber having a low loss and high strength.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a fluoride optical fiber, and more particularly to a method of manufacturing a fluoride optical fiber with low loss and high strength.

(Conventional technology) Fluoride optical fiber has a 1O-2 dB/km performance that exceeds that of quartz fiber.
The following transmission loss is expected, and it is seen as a promising transmission medium capable of long-distance non-relaying.

However, fluoride glass reacts with moisture in the air, easily producing OH groups on its surface that cause absorption loss, and oxide crystals that cause scattering loss due to dehydration and condensation of OH groups during heating during drawing. This has the disadvantage that the transmission characteristics are deteriorated due to the generation of Furthermore, there was also the disadvantage that the strength of the fiber was significantly reduced due to the formation of oxide crystals.

Up until now, the surface treatment methods for the base material include chemical etching the surface of the base material after polishing in a hydrochloric acid solution of zirconium oxychloride, and then drying it in an inert gas, or using a fluorine-containing gas as a discharge gas after drying. A method of surface treatment in plasma was used.

(Problems to be Solved by the Invention) However, drying in an inert gas cannot efficiently remove surface OH groups, and oxygen impurities remain due to dehydration condensation. It was not possible to suppress the production.

On the other hand, plasma treatment exposes the glass surface to high-energy particles, which causes problems such as sputtering of the surface by ions, which causes surface roughness, and defects that cause absorption loss.

(Object of the Invention) An object of the present invention is to provide a method for manufacturing a fluoride optical fiber with low loss and high strength, which solves the above-mentioned drawbacks.

(Means for Solving the Problems) In order to solve the above problems, the method for producing a fluoride optical fiber according to the present invention includes a step of drawing a fluoride glass base material to produce a fluoride optical fiber; In the process of producing a fluoride optical fiber by inserting a fluoride glass rod having a fluoride glass base material or core composition into a fluoride glass or Teflon FEP pipe and drawing it, the fluoride glass base material, the The method is characterized in that a part or all of the fluoride glass rod and the fluoride glass pipe are heated in a fluorine-containing gas and then drawn.

That is, it is characterized in that the surface of the base material or glass tube, which has been chemically etched and dried in an inert gas or under reduced pressure, is heat-treated in a fluorine-containing gas.

The present invention will be explained in more detail.

According to the present invention, as described above, a fluoride glass base material,
A part or all of the fluoride glass rod or fluoride glass pipe is heat-treated with fluoride gas, and in the present invention, as long as the fluoride gas is a fluoride gas that can remove surface OH groups, Basically, it is not limited.

For example, if the fluorine-containing gas is fluorine, hydrogen, carbon,
The gas is a compound of fluorine and at least one of boron, nitrogen, chlorine, bromine, iodine, and sulfur, and any one of the fluorine-containing gases can be a mixed gas of two or more.

Specific examples include HF, CF4, NF3, SF
b, BF3, F2, and the like.

Furthermore, the treatment temperature with fluoride-containing gas is 0 to 400°C.
If the temperature is less than 0°C, the fluoride-containing gas may not be activated because the temperature is too low;
If the fluoride glass is exceeded, there is a risk that the fluoride glass to be treated may crystallize.6 (Example) The present invention will be explained in detail below with reference to Examples, but the present invention is not limited thereto in any way.

(Example 1) Core composition (49 mol% ZrF4-2) produced by casting a glass melt into a cylindrical mold and rapidly cooling it
5 mol% BaF2-3.5 mol%LaF3-2 mol%Y
A glass rod (diameter 6 mm, 150 mm length) with F3-2.5 mol% AlF3-18 mol% LiF) and a rotary silanal casting method (D, C, Tran
et, at.

Electron, Lett vol 1g, P,
59. (1982)) cladding composition (
47.5 mol% ZrF4-23.5 mol% BaF2-2
．． 5 mol%LaF3-2 mol%YF3-4.5 mol%A
A glass tube (outer diameter 12 mm, inner diameter 6 mm, length 150 mm) containing IF-20 mol % LiF) was etched with a hydrochloric acid solution of zirconium oxychloride, washed with water, and then dried under reduced pressure. These rods and glass tubes were heated in HF (
50vo 1%) He (50vo 1%) atmosphere (11/m1n) was heated to 200° C. and held for 10 hours. Thereafter, the atmosphere was replaced with Ar gas and the furnace was cooled to room temperature. The base material treated in this manner was inserted into a glass tube under a nitrogen atmosphere, and was drawn using Teflon FEP as a coating material to obtain a 700 m fluoride optical fiber. Figure 1 shows the measurement results of the transmission loss characteristics of the obtained fiber. For comparison, the loss characteristics of a fluoride optical fiber produced in the same manner as in this example except that no HF gas treatment was performed are also shown. As is clear from this figure, the fiber produced by the conventional method has a large absorption peak due to OH groups near 2.9 μm, and also has significant wavelength-independent scattering loss.

This OH group is the result of residual OH groups adsorbed on the core rod surface and the inner surface of the glass tube, and the wavelength-independent scattering loss is due to oxide crystals generated by dehydration and condensation of some of these OH groups. In the fiber produced in this example, the absorption peak due to OH groups is significantly reduced, and the wavelength-independent scattering loss is also reduced. It can be seen that oxygen impurities such as water and OH groups can be removed. Furthermore, the obtained fiber was given a gauge length of 1 m,
A tensile test was conducted at a tensile speed of 59 m, m/min, and 50 samples. The average value of tensile strength is 1.0
The GPa was significantly improved compared to the 400 MPa of the fiber produced using the conventional method.

In this method, CF4, NF3 is used instead of HF gas.
, SF6, and BF3 also produced similar effects to those of HF gas.

(Example 2) Having a core/clad structure (core composition = 49 mol% Z
rF4-25 mol% BaF2-3.5 mol% LaF3-
2 mol% YF3-2.5 mol% AlF3-18 mol%L
iF, cladding composition = 47.5 mol% ZrF4-23.
5 mol%Ba, F2-2.5 mol%LaF3-2 mol%
Using a base material with a diameter of 6 mm and a length of 150 mm, F2 gas (F2 (50 VO 1%) diluted with Ar as a fluorine-containing gas) was used.
A fluoride optical fiber was fabricated in the same manner as in Example 1, except that the treatment temperature was 0°C by cooling. The transmission loss characteristics of the fabricated fiber are shown in Figure 2. The fabricated fiber shown below has a minimum loss of 0.
7 dB/km, indicating that oxygen impurities can be removed by fluorine treatment. The average value obtained by the tensile test was 1. IGPa, and a high-strength fiber was obtained by this method.

(Example 3) 53 mol% ZrF4-20 mol%BaF2-4 mol%L
aF3-3 mol% AIF-20 mol% NaF glass rod with a diameter of 8 mm was used as the core, Teflon FEP was used as the cladding, and HF (50vo 1%) was used as the fluorine-containing gas.
) F2 (50vo1%), 100 as processing temperature
300 m in the same manner as in Example 1 except that the temperature was
Figure 3 shows the transmission loss characteristics of the fabricated fluoride optical fiber.As is clear from this figure, the absorption of OH groups around 2.9 μm was significantly reduced. Furthermore, by mixing HF and F2, oxygen impurities could be removed more efficiently even at lower temperatures than when treating with a single gas.

In this method, absorption loss due to OH groups, scattering loss due to oxides, and strength reduction were able to be significantly reduced even when the core glass was a fluoride glass mainly composed of HfF4-BaF2, as in the above example.

(Example 4) Composition 22 mol% BaF2 - 22 mol% CaF2 - 16 mol% YF3 - 40 mol% AlF3 glass rod with a diameter of 8 mm was used as the core, Teflon FEP was used as the cladding, SF6 was used as the fluorine-containing gas, and the processing temperature was 400°C. A fluoride optical fiber was produced in the same manner as in Example 1 except that the temperature was changed to .degree. Figure 4 shows the transmission characteristics of the fabricated fiber. As is clear from this figure, absorption by OH groups near 2.9 μm can be significantly reduced, and scattering loss independent of wavelength is also reduced. The tensile strength of this fiber was 1.0 GPa, and a low-loss, high-strength fluoride optical fiber was obtained by the method of this example.

(Effects of the Invention) As shown in the above examples, by using the method of the present invention, oxygen impurities adsorbed on the surface of the base material and the surface of the glass tube used as a jacket can be removed, which is difficult to do in the past. This method has the advantage of being able to produce a fluoride optical fiber with low loss and high strength.

[Brief explanation of the drawing]

Figure 1 shows the transmission loss characteristics of the fluoride optical fiber manufactured in Example 1, Figure 2 shows the transmission loss characteristics of the fluoride optical fiber manufactured in Example 2, and Figure 3 shows the transmission loss characteristics of the fluoride optical fiber manufactured in Example 3. Transmission Loss Characteristics of Fluoride Optical Fiber FIG. 4 shows the transmission loss characteristics of the fluoride optical fiber produced in Example 4.

Claims (3)

[Claims] (1) Step of drawing a fluoride glass base material to produce a fluoride optical fiber, and inserting a fluoride glass base material or a fluoride glass rod having a core composition into a fluoride glass or Teflon FEP pipe and drawing it. In the step of producing a fluoride optical fiber, a part or all of the fluoride glass base material, the fluoride glass rod, and the fluoride glass pipe are heated in a fluorine-containing gas and then drawn. A method for manufacturing a fluoride optical fiber. (2) The fluorine-containing gas is fluorine or a gas of a compound of fluorine and at least one of hydrogen, carbon, boron, nitrogen, chlorine, bromine, iodine, and sulfur, and any one of the fluorine-containing gases or The method for manufacturing a fluoride optical fiber according to claim 1, characterized in that the mixed gas is a mixture of two or more gases. (3) The method for manufacturing a fluoride optical fiber according to claim 1 or 2, wherein the heat treatment temperature is in the range of 0°C to 400°C.