JPH038735A - Preparation of fluoride glass optical fiber preform - Google Patents

Abstract

PURPOSE:To prepare the subject base material capable of suppressing the optical loss thereof caused by the interfacial irregularity and heterogeneous crystalliza tion between the core and clad of the optical fiber by pouring melted fluoride glass into an upstanding fluoride glass tube and cooling and solidifying the glass in a specific condition. CONSTITUTION:Melted fluoride glass for the core of an optical fiber is poured into a fluoride glass tube for the clad of the optical fiber and simultaneously maintained so as not to contact with the inner wall of the fluoride glass tube until the melted fluoride glass for the core reaches the dropping point thereof in the glass tube for the clad. The core melted fluoride glass which has reached the dropping point is cooled and solidified to provide the preform. The prepara tion method prevents that the fluoride glass tube for the clad is irregularly and heterogeneously again heated by the melted fluoride glass for the core so as to cause the irregularity, crystallization, etc., at an interface between the two kinds of the fluoride glass, thereby permitting to prepare the fluoride glass optical fiber preform having an excellent transmission characteristic in a good yield.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application The present invention relates to a method for manufacturing an optical fiber matrix made of fluoride glass.

2. Prior Art Fluoride glass optical fibers are known for infrared transmission.

Compared to silica glass optical fibers, fluoride glass optical fibers can transmit longer wavelength light and have lower Rayleigh scattering loss, so they can be used as optical fibers that transmit from visible light to infrared wavelengths in the 13gm band. Useful.

In addition to the double crucible method, glass casting methods such as the built-in casting method and the rotary casting method are generally employed as manufacturing techniques for the fluoride glass optical fiber base material.

"Problem to be Solved by the Invention J Unlike oxide glasses, fluoride glasses have low glass-forming ability, such as crystallization in the glass softening temperature range and sudden changes in viscosity due to temperature changes. The fiber base material is highly difficult to manufacture.

For example, in the case of the base material manufacturing method using the double crucible method, contamination of 0)II at the interface between the core and cladding and crystallization at the interface between the core and cladding are unlikely to occur, but the viscosity of fluoride glass fluctuates significantly with temperature. Due to its large size, it is difficult to control the viscosity and flow of molten fluoride glass having a core and cladding structure, that is, a waveguide structure.

Therefore, when using the double crucible method, it is not possible to deal with the irregular flowability of molten fluoride glass, and the scattering loss of the optical fiber increases, such as air bubbles entering from the crucible wall to the core and cladding interface. .

In addition, in the base material manufacturing method using the glass casting method, after pouring molten fluoride glass for the cladding into a mold and forming a tube (cooling and solidifying), a fluoride glass for the core is poured into the fluoride glass tube for the cladding. An optical fiber base material is produced by injecting molten fluoride glass. At the time of injecting the glass, the high temperature molten fluoride glass for the core flows along the inner wall of the fluoride glass tube for the cladding, which has been cooled and solidified. The inner wall of the glass tube is reheated irregularly and unevenly.

Therefore, even when using the glass casting method, interface irregularities and crystallization (causing scattering loss) between the core and cladding occur.

In view of such technical problems, the present invention seeks to provide a method for manufacturing a fluoride glass optical fiber preform that can suppress loss due to irregularities in the interface between the core and cladding and crystallization.

In order to achieve the intended purpose, the method for manufacturing a fluoride glass optical fiber preform according to the present invention is to produce a fluoride glass for the cladding by standing up a molten fluoride glass for the core. While injecting the molten fluoride glass into the tube, the molten fluoride glass for the core is kept in a non-contact state with the inner wall of the fluoride glass tube until it reaches the falling point in the glass tube for the cladding, and It is characterized by cooling and solidifying the core fluoride glass melt that has reached a certain point.

r Effect J The method of the present invention involves injecting molten fluoride glass for the core into an upright fluoride glass tube for the cladding, cooling and solidifying the molten fluoride glass for the core in the glass tube to form a fluoride glass optical fiber. The base material is prepared, but during glass injection, the molten fluoride glass for the core and the inner wall of the fluoride glass tube for the cladding are kept in a non-contact state, so that the fluoride glass tube for Fullerad is the same as the molten fluoride glass for the core. The glass does not reheat irregularly and unevenly.

Therefore, in the case of the optical fiber base material manufactured by the method of the present invention, there is almost no interfacial irregularity or crystallization between the fluoride glass for the core and the fluoride glass for the cladding.

Therefore, a fluoride glass optical fiber without scattering loss can be obtained from such an optical fiber preform.

Embodiment A method for manufacturing a fluoride glass optical fiber preform according to the present invention will be described based on illustrated embodiments.

In FIG. 1, the base 11 consists of a plate-shaped horizontal part 12 and a vertical part 13 that are assembled together.

On the horizontal section 12, there is an X-axis (left/right) movement function and a Z-axis (left/right) movement function.
A known or well-known moving stage 14 having a movement function (back and forth), a well-known or well-known clamp 15 supported so as to be movable back and forth and left and right via the moving stage 14, and a vertically mounted stage via the clamp 15. The mold 16 is equipped with a mold 16.

The mold 16 - for example, consists of a bottomed cylindrical container made of a heat-resistant material such as glassy carbon.

As shown in FIG. 2, the vertical part 13 includes a lifting mechanism 17 for the Y axis (up and down), a funnel holder 18 supported so as to be able to rise and fall freely via the lifting mechanism 17, and the funnel holder 18.
The funnel 13 held by the funnel holder 18 on the mold 16 is equipped with a funnel 19 attached to the mold 16.
It consists of a mortar-shaped taper tube 20 and a thin tube 21 projecting downward from the bottom of the taper tube 20.

The elevating mechanism 17 is, for example, one equipped with a drive screw shaft,
The funnel holder 18 is equipped with a hydraulic and pneumatic cylinder.
For example, is made of a material that has heat retention and heat resistance (
(with a built-in heater in some cases), the funnel 19 is, for example,
It is made of precious metal such as u.

Furthermore, a heater 22 made of a cylindrical electric furnace is arranged to cover the outer periphery of the mold 18 and is fixed to the vertical part 13 via a fixture that does not connect in FIG.

In FIG. 2, a converter-type crucible 23 for melting fluoride glass is made of a heat-resistant metal material such as PT, and the crucible 23 is equipped with a traveling means (not shown) and is mounted on a funnel 19. It is located.

In the illustrated example described above, when manufacturing the fluoride glass optical fiber preform, the process is as follows.

On the base 11 of FIG. 1, the mold 16 is vertically attached to the moving stage 14 via the clamp 15.
It has a fluoride glass tube 24 for cladding inside.

The fluoride glass tube 24 for cladding is connected to the heater 2
The temperature is maintained at approximately 260°C through the

Incidentally, the fluoride glass tube 24 for the cladding is molded by the rotational casting method, and the tube 24, which is removed together with the mold 16 from the molding apparatus at that time, is placed on the moving stage 14 as described above. It will be installed.

When using the above rotational casting method, the raw materials for the fluoride glass tube 24 include ZrFa,
BaF2. LaF3. HfF4. NaF, AlF3,
Its composition ratio is 42Z rFa-23BaF2-4LaF
:+ -14HfF4-15NaF-3,8+oo l
Weigh out $A HF3, and add the fluoride raw material (
50g) to which NHF4.HF (18g) was added.

When heating and melting such a raw material, for example, it is heated at 860° C. for 30 minutes in an inert gas atmosphere consisting of N2, and then the molten fluoride glass is rapidly cooled.

In FIG. 1 and FIG. 1, a molten fluoride glass 25 for a core, which has been melted through a crucible 23, is injected into a fluoride glass tube 24 for a cladding.

At this time, the mold 16 is finely adjusted in the X-axis direction and the Z-axis direction by the moving stage 14 so that the vertical axis of the fluoride glass tube 24 for cladding and the vertical axis of the funnel 19 are aligned with each other, and The funnel holder 18, which was waiting in the raised position, is lowered by the lifting mechanism 17, and the funnel 19
The thin tube 21 is inserted into the fluoride glass tube 24 for cladding to near the bottom, and then the molten fluoride glass 25 for the core in the crucible 23 is poured into the tapered tube 20 of the funnel 19.

The molten fluoride glass 25 for the core inside the tapered tube 20 flows into the fluoride glass tube 24 for the cladding through the thin tube 21, and as the amount of the inflow increases,
The molten glass liquid level inside the fluoride glass tube 24 for cladding rises.

In response to this rise in the liquid level, the funnel 18 is moved up and down by the lifting mechanism 17.
While raising the thin tube 21 from inside the fluoride glass tube 24 for cladding, the tube 24 is filled with a predetermined amount of molten fluoride glass 2 for core.
Fill with 5.

Furthermore, the core molten fluoride glass 25 in the cladding fluoride glass tube 24 is rapidly cooled to obtain an optical fiber base material 26 in which both of these fluoride glasses are integrated.

By the way, the raw materials for the fluoride glass 25 for the core are:
ZrFa, BaF2, PbF2, LaF3. Na
F, AlF3 with a composition ratio of 58ZrFa-21Ba
F? -2PbF2-4LaF3-15NaF-3,8+
The fluoride raw material (30 g) was weighed so as to have 1% AlF3, and NHF4.HF (11 g) was added thereto.

These conditions such as heating, melting, and cooling of the raw materials are the same as described above, and the base material manufacturing means illustrated in FIGS. 1 and 2 is installed, for example, in a glove box purged with N2 gas. Ru.

In the embodiments described above, the base material outer diameter (cladding diameter) I
A fluoride glass optical fiber base material with Oamφ, core diameter e++mφ, and length 200II1 m was prepared and inspected, and no microbubbles or crystallization were observed at the interface between the core and the cladding.

Furthermore, the above-mentioned base material was drawn by a well-known melt spinning method to obtain a fluoride glass optical fiber having a fiber diameter of 150 gmφ and a length of 1 km.

The transmission characteristic of this optical fiber was 1 dB/lv at a wavelength of 2.35 gra.

"Effect of the Invention 1 As explained above, the method of the present invention allows the molten fluoride glass for the core to reach the falling point in the glass tube for the cladding during glass injection during the production of the base material. Since the fluoride glass tube and the inner wall of the fluoride glass tube are kept in a non-contact state, the fluoride glass tube for the cladding is not irregularly and non-uniformly reheated by the molten fluoride glass for the core. No interface irregularities or crystallization occur.

Therefore, when using the method of the present invention, a base material of a fluoride glass optical fiber having excellent transmission characteristics can be manufactured with a high yield.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing an example of the method for manufacturing a fluoride glass optical fiber preform according to the present invention, and FIG. 2 is an enlarged view of the same essential parts. 11...Base 12...Horizontal part of the base 13...Vertical part of the base 14...Movement stage 15...Clamp 16...Mold 17...Elevating mechanism 18...Funnel holder 19...Funnel 20...Funnel taper tube 21... ... Funnel thin tube 22 ... Heater 23 ... Crucible 24 ... Fluoride glass for cladding 25 ...
...Fluoride glass 2B for core...Optical fiber base material

Claims (1)

[Claims] The molten fluoride glass for the core is injected into the upright fluoride glass tube for the cladding, and the molten fluoride glass and the fluoride glass for the core reach the falling point in the cladding glass tube. A method for producing a fluoride glass optical fiber preform, characterized by maintaining the inner wall of a fluoride glass tube in a non-contact state, and cooling and solidifying the molten fluoride glass for the core that has reached a falling point.