JPS593039A - Manufacture of fluoride glass for optical fiber - Google Patents

Abstract

PURPOSE:To manufacture the titled glass having a very low concn. of OH groups, by pretreating finely powdered starting materials for fluoride glass with HF, F3, BF3, CF4, Cl2, CCl4 or SOCl2 and by melting the pretreated materials with an electric furnace. CONSTITUTION:Finely powdered starting materials 10 for fluoride glass are charged into a platinum crucible 2, and the crucible 2 is mounted on a stage 8. A cover 3 is put on the crucible 2, and a pipe attached to the cover 3 is connected to an exhaust system. A platinum crucible 6 is mounted on a crucible stand 7 below an electric furnace 1, and the stand 7 is moved upward to insert the crucible 6 into the crucible 2. After heating the materials 10 with the furnace 1, a gas for an OH group removing reaction is introduced from a pipe 4 to cause said reaction. HF, F2, BF3, CF4, Cl2, CCl4 or SOCl2 is used as the gas. After finishing the reaction, the materials 10 freed of OH groups are melted by heating with the furnace 1 and allowed to flow in the crucible 6 through holes 11. The resulting molten glass is cast in a casting mold, annealed in the mold, and slowly cooled to manufacture a fluoride glass preform.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a glass for a fluoride optical fiber, which is used for producing an infrared-transmitting fluoride optical fiber, and has a reduced concentration of OH groups, which are a factor of impurity absorption loss.

Conventional fluoride optical fiber glass is produced by simply mixing a predetermined amount of fluoride raw materials with an appropriate amount of NH4F-HF, and then simply placing the mixture in an inert gas atmosphere.
A platinum crucible or metal crucible is melted in or H
After sintering and melting in an active gas atmosphere such as F or Cal, the melt was cast into a mold. Mixed NH, F・1 (the amount of F is limited,
In addition, since the glass raw material is sintered at a temperature above 289.5°C, which is the boiling point of Nl(,F -) IF, its scattering is rapid, so the OH removal effect is small, and the OH groups in the raw material are extremely small. Only some of them are removed.

Furthermore, in the method of simply melting in an active gas, heating the raw material causes intense vaporization of the raw material, so that the atmospheric gas does not penetrate smoothly into the raw material, and the OH removal effect cannot be improved. Further, after the raw material is melted, the reaction between the atmospheric gas and the OH groups occurs only on the surface of the melt, and the efficiency of the OH removal system is extremely low. For this reason, there are many OH groups remaining in the glass melt, so impurities are absorbed by the OH groups in the optical fiber produced by drawing the preform produced by annealing the obtained fluoride optical fiber glass. The amount of loss has increased, and the transmission loss characteristics have become significantly worse.

In the present invention, HF#F, , OF, , HF8.
Ol, .

The method is characterized by removing OH groups by reacting OOl or 5 ozs, and its purpose is to produce a fluoride optical fiber glass having an extremely low OH group concentration.

The glass raw materials used in the present invention include Li and Na.

Be, Mg, Oa, Sr, Ba,
AI, Sn, Pb, Sb.

Bi, Zn, Y, Ga, La, G
These are fluorides such as a, Lu, Th, Zr, and Hf.

There is a mixed gas diluted with a gas. The crucible used for the vitrification reaction is made of platinum or gold, and the crucible for raw material pretreatment has holes on a part or the entire bottom of the crucible and a pipe for guiding the gas to the raw material, and the crucible is made of platinum or gold. It consists of a melting crucible that collects the glass melt that flows down from the hole at the bottom of the pretreatment crucible. The vitrification reaction and casting into a mold for producing optical fiber preforms are carried out in a dry box purged with nitrogen, etc. and whose inner wall is protected by a material that is not easily attacked by fluorine, such as fluororesin. It is desirable that the reaction be carried out while preventing water and oxygen from entering the reaction system.

In the production method according to the present invention, a fluoride glass raw material is placed in a pretreatment crucible, placed on a melting crucible, placed in an electric furnace, and heated with HF, etc. at 800°C to 550°C for 0.6 to 5 hours. By guiding the gas through a pipe installed in the pretreatment crucible, ejecting it below the bottom of the pretreatment crucible, and diffusing it into the glass raw material through a hole drilled in the bottom of the crucible,
When the reaction between the OH groups in the glass raw material and gases such as IF is promoted, and then the temperature of the electric furnace is raised to 800°C-1000°C, the glass raw material begins to melt and is released from the hole at the bottom of the crucible for pretreatment. It is dropped into a melting crucible placed under the crucible and stored, and after being melted at the above temperature for 1 to 8 hours, it is heated at 200°C to 800°C in the same dry atmosphere to prepare an optical fiber preform. The preform is cast into a mold that has been preheated to a temperature of 100 mL, and then slowly cooled to room temperature to form a preform.

The present invention will be explained in detail below based on implementation, but the present invention is not limited thereby.

Example 1 FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus used in the manufacturing method of the present invention.

In FIG. 1, 1 is a platinum electric furnace, 2 is a platinum crucible for pretreatment, 8 is a lid with an exhaust hole for the platinum crucible for pretreatment, 4 is a platinum pipe, 5 is a supporter that holds down the platinum pipe 4,
6 is a platinum crucible for melting, 7 is a vertically movable crucible stand on which the platinum crucible 6 is placed, 8 is a stage on which the platinum crucible 2 is placed,
Reference numeral 9 indicates an electric furnace stand, 10 indicates a raw material, and 11 indicates a hole at the bottom of the platinum crucible 2. In FIG. 2, 12 is a quartz glass mold annealing cylinder, 18 is a three-split brass mold with a diameter of 9 mm and an inner diameter of 150 fins, and 14 is an electric furnace for annealing.

A glass melting furnace and a mold annealing furnace shown in FIG. 1 and FIG. 2 described later are installed in a glove box, and the inside of the glove box is replaced with nitrogen to create a dry atmosphere. Fluoride glass raw materials ZrF, , BaF, .

Put G, dF, and AIF into platinum crucible 2, and place 2 on stage 8. Next, supporter 6 and Nozuib 4
While pressing down, place the lid 8 on top of the platinum crucible 2,
Connect the pipe of lid 8 to the exhaust system. Platinum crucible 6 is placed on crucible stand 7 lowered below the electric furnace, crucible stand 1 is lifted into the electric furnace, and platinum crucible 6 is inserted into platinum crucible 2. Therefore, the platinum electric furnace 1 was set at 450°C, and while flowing HF gas through the supporter 4 for 0.5//min,
A time-removal treatment of OH groups was performed. After 8 hours, the platinum electric furnace 1 was heated to 900°C and melted for 1 hour. During this time, all of the raw material flowed out into the platinum crucible 6 through the hole 11 made at the bottom of the platinum crucible 2.

FIG. 2 is a schematic diagram showing an example of the configuration of an annealing apparatus used for producing an optical fiber preform, in which a mold 13 is placed in a mold annealing tube 12 and an O-61/m
The annealing electric furnace 14 was heated at 260° C. while flowing nitrogen at
The tube 12 was preheated at a temperature of .degree. After 2 hours, the HF flow was stopped, the crucible stand 7 was lowered, the platinum crucible 6 was taken out, the glass melt was cast into a preheated mold 18, and the glass melt was heated at 260°C in the cylinder 12. After annealing for 20 hours, it was slowly cooled to room temperature, and the outer diameter was 9mm x length 14mm.
A fluoride glass preform was obtained.

Application Example The preform obtained in Example 1 was drawn by the method shown in FIG. The transparent fluoride optical fiber preform 15 is inserted into the fluororesin tube 16, and the electric furnace stand 17 is
The small electric furnace 18 placed on the was raised at a rate of 0.1 cm/min, and the fluoride light 7 eyelid 20 was wound onto the winding bobbin 19. A fluororesin-coated graded index optical fiber (outer diameter 500 μm, cladding diameter 200 μm) was obtained from the base material of Example 1. This optical fiber is 2
．． 100 (iB/- or less window in 5μ island zone, OH
The absorption loss due to the group is 800 (IB/-
It was an optical fiber capable of transmitting infrared rays, which was reduced to below.

The absorption loss due to OH group is No. 000 d in the conventional method.
However, by the method of the present invention, the conventional 1
We were able to reduce this to less than 1/0.

As explained above, according to the present invention, HF can be efficiently diffused into the fluoride glass raw material.1 Furthermore, since the glass melting and casting are performed in a dry atmosphere, fluoride light with very little contamination of OH groups is possible. It has the advantage of being able to produce fiber preforms.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus used in the manufacturing method of the present invention, FIG. 2 is a schematic diagram showing an example of the configuration of an annealing apparatus used for manufacturing an optical fiber preform, The figure is a schematic drawing of the base material obtained in Example 1 of the present invention. 1... Platinum electric furnace 2... Platinum crucible for pretreatment 8... Lid with exhaust pipe for the platinum crucible for pretreatment 4... Platinum vibrator 5... Supporter 6...
Platinum crucible for melting 7... Crucible stand 8... Stage 9... Electric furnace stand 10... Raw material
11... Hole 12... Quartz glass mold annealing tube, 18... Brass mold 14... Electric furnace for annealing 11... Preform 16... Fluorine resin tube 17... Electricity Hearth stand 1B...
Small electric furnace 19... Winding ribbin 20... Fluoride optical fiber patent applicant Nippon Telegraph and Telephone Public Corporation Figure 3

Claims (1)

[Claims] L A fluoride glass raw material is prepared in a fine powder state without sintering, as HF, F, , HF8. OF, ,
07. . 001 or 5 oz, and then melted in an electric furnace and the glass melt is poured out to synthesize a glass with an extremely small amount of OH groups mixed in. Fabrication method.