JPH03215332A - Production of metal-coated fluoride glass optical fiber - Google Patents

Abstract

PURPOSE:To easily obtain the title optical fiber with both high weatherability and water resistance by continuously applying a metal (alloy) melt of a specified melting point on the surface of a fluoride optical fiber after drawing. CONSTITUTION:Firstly, a metal (alloy) with a melting point lower than the glass transition temperature of a fluoride glass is melted. The melt is then continuously applied on the surface of an optical fiber made of the fluoride glass after drawing, thus obtaining the objective optical fiber without causing the melting of the fluoride glass.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a fluoride glass optical fiber useful for medical purposes, sensors, communications, and the like.

(Prior Art) Fluoride glass optical fibers can transmit infrared rays with low loss, so they are useful for medical purposes, sensors, communications, and the like. This fluoride glass optical fiber is described in, for example, Japanese Patent Publication No. 60-47213. As described above, a rod-shaped core base material and a tubular clad base material are manufactured by melting a fluoride glass raw material in a metal crucible and pouring the melt into a metal mold. However, as is known as the so-called rod-in-tube method, it is manufactured by inserting a core base material into a clad base material and then drawing it in a resistance furnace to reduce the diameter.

By the way, fluoride glass has very high reactivity with water compared to other glasses such as oxide glass.
It easily reacts with water in the atmosphere, producing oxide crystals on the surface, as shown in the reaction formula below, for example.

ZrF2 +20H-+ZrO■+2HF When such a reaction occurs in a fluoride optical fiber, (1) surface scratches are generated and the mechanical strength is reduced.

(2) Absorption loss increases due to the intrusion of OH groups.

A problem arises.

Therefore, even if a fluoride optical fiber is coated with a resin through which gas easily passes, such as urethane acrylate, as is the case with ordinary optical fibers, the above-mentioned problems will occur, so it is not appropriate. In order to obtain a fluoride optical fiber with high strength and low loss, it is essential to coat it with a film having low transmittance for OH groups, such as ceramics or metals.

However, fluoride glasses have a glass transition temperature of about 3
Since the melting point is as low as 00°C, for example, carbon coats such as those used in quartz optical fibers with a melting point of approximately 2000°C, or metal coats such as those described in JP-A-57-200239 are applied. I can't.

Sputtering using high vacuum and vacuum evaporation are also conceivable, but there are problems in terms of productivity because the equipment becomes large and the deposition rate is extremely slow.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems, and by coating a fluoride optical fiber with a metal film with low transmittance of OH groups, it becomes waterproof. It is an object of the present invention to provide a method for manufacturing a metal-coated fluoride glass optical fiber with excellent properties.

(Means for Solving the Problems) The present invention provides a method for manufacturing a metal-coated fluoride glass optical fiber, in which a metal or an alloy having a melting point lower than the glass transition temperature of the fluoride glass in the fluoride glass optical fiber is melted. It is characterized in that it is continuously applied to the surface of a fluoride glass optical fiber after being drawn.

As the metal material to be coated, a metal element such as In, Sn, Pb, or Bi, or an alloy containing at least one thereof can be selected.

The oxygen concentration in the atmosphere during metal coating is desirably 10% or less.

The linear speed of the optical fiber during metal coating is desirably 1 m/min or more.

The melting temperature of the metal or alloy at the time of metal application is desirably a temperature equal to or lower than the melting point of the metal or alloy plus 50°C.

The hole diameter of the die used during metal coating is desirably at least the sum of the outer diameter of the optical fiber plus 50 μm and at most four times the outer diameter of the optical fiber.

(Function) According to the present invention, a metal or an alloy having a melting point lower than the glass transition temperature of the fluoride glass in a fluoride glass optical fiber is applied in a melt state, so that the fluoride glass is not melted. A metal coated fluoride glass optical fiber can be obtained.

(Example) FIG. 1 is a schematic diagram partially cut away to illustrate an apparatus applied to a manufacturing method of an example of the metal-coated fluoride glass optical fiber of the present invention. In the figure, 1 is a fluoride glass base material, 2 is a heater, 3 is a spun optical fiber, 4 is a laser outer diameter measuring device, 5 is a die, 6 is an inert gas supply port, 7 is a forced cooling device, 8 is the winder. The fluoride glass preform 1 is softened by heating with a heater 2 and is spun into an optical fiber 3. The outer diameter of the spun optical fiber 3 is measured by a laser outer diameter measuring device 4, and then guided to a die 5. The laser outer diameter measuring device 4 is used to control the spinning state and the outer diameter of the optical fiber using its measurement output. The die 5 is filled with the metal material to be coated in a molten state.

The metal material selected has a melting point lower than the glass transition temperature of the fluoride glass of the optical fiber. The thermal expansion coefficient of the metal material is preferably 10-4 to 10-' [1/°C].

Fluoride glass has a glass transition temperature of about 270°C and a crystallization temperature of about 360°C, so if a metal with a melting point of 270°C or higher is used, the surface of the optical fiber will melt during the coating process. Crystallized by heat from the liquid,
This can significantly reduce the initial strength of the optical fiber and, at higher temperatures, may cause the optical fiber to melt. Furthermore, if a metal material with a large coefficient of thermal expansion is selected, stress will be generated at the interface between the optical fiber and the metal coating due to cooling after coating, resulting in deterioration of initial strength and increase in transmission loss. The metal material used is I, which is known as a low melting point metal.
A metal element of n s S ny P b y B i or an alloy containing at least one thereof is preferable.

In order to prevent oxidation during coating, the surface atmosphere of the die 5 filled with the metal melt is preferably replaced with an inert gas such as N2 or He supplied from an inert gas supply port, and the atmosphere on the surface is replaced with oxygen. The concentration is preferably 10% or less.

The diameter of the hole in the die 5 is preferably greater than or equal to the outer diameter of the optical fiber plus 50 μm and less than four times the outer diameter of the optical fiber. The reason for this is that if the hole diameter is smaller than this range, the optical fiber may become clogged due to fluctuations in the outer diameter of the spun optical fiber, or the initial strength may deteriorate due to contact with the die. This is because if the diameter is large, an excessive amount of melt is supplied onto the optical fiber, and bumps are likely to occur in the coating.

The melting temperature of the metal or alloy at the time of metal application is desirably a temperature equal to or lower than the melting point of the metal or alloy plus 50°C. If coating is carried out at a temperature higher than this range,
The viscosity of the melt is too low, making it difficult to apply it to a stable thickness in the longitudinal direction.

The linear speed of the optical fiber during metal coating is desirably 1 m/min or more. If the linear velocity is slower than this, the self-centering force in the die 5 will be weak, resulting in uneven thickness of the coating and a decrease in initial strength due to contact between the optical fiber and the die.

The optical fiber that has passed through the coating die 5 is cooled by a forced cooling device 7 to prevent the applied uncured metal from sagging due to gravity and causing bumps immediately after coating. Metal-coated optical fiber is
The metal fluoride optical fiber is wound by the winder 8 and is highly water resistant.

A specific example in which a fluoride glass optical fiber having a waveguide structure and having a Zr-Ba-La-AI-Na-F composition is coated with metal by the method of the present invention will be described. A glass base material having an outer diameter of 7.2 mm and a length of 120 mm was used, and this base material was heated to about 330° C. with a heater to soften it and spin. The spun optical fiber passes through a die and is wound on a winder, with an outer diameter of 200 μm and a linear speed of 3 m.
A line was drawn under the condition of /min.

The conditions for metal coating were as follows: metallic indium with an In purity of 99.99% was supplied to the die which was heated to 200°C and replaced with N2 gas. The hole diameter of the die was 350 μm. He gas was supplied to the forced cooling device at a flow rate of 51/min to cool the coated optical fiber.

FIG. 2 is a cross-sectional view of the optical fiber obtained through the above steps. 11 is core, 12 is clad, 13 is in
It is a covering layer. The thickness of the In coating layer is 40 μm,
The adhesion between the metal and the fluoride glass was also good, and no holes were observed. This optical fiber is heated to 90% humidity.
Although it was left in an atmosphere at a temperature of 20"C for 10 days, the initial strength was maintained. Also, in terms of loss wavelength characteristics,
No increase in loss of 2.9 μm due to the influence of OH groups was observed.

In the above-mentioned optical fiber without metal coating, the initial strength was reduced by 50% in an environmental test under the same conditions.

(Effects of the Invention) As is clear from the above description, according to the present invention, a metal or an alloy having a melting point lower than the glass transition temperature of the fluoride glass in a fluoride glass optical fiber is melted in a die. By applying it in a liquid state, it is possible to coat metal without melting the fluoride glass or deteriorating its initial strength, making it easy to create metal-coated fluoride glass optical fibers with excellent weather resistance and water resistance. Moreover, there is an effect that good productivity can be obtained.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway schematic diagram illustrating an apparatus applied to a manufacturing method of an embodiment of the metal-coated fluoride glass optical fiber of the present invention, and FIG. 2 is a cross-sectional view of the manufactured optical fiber. It is a diagram. 1...Fluoride glass base material, 2...Heater, 3.
...Spun optical fiber, 4...Laser outer diameter measuring device, 5...Dice, 6...Inert gas supply port, 7
... Forced cooling device, 8... Winding machine.

Claims (1)

[Claims] A metal characterized in that a metal or alloy having a melting point lower than the glass transition temperature of the fluoride glass in the fluoride glass optical fiber is continuously applied in a melt state to the surface of the fluoride glass optical fiber after drawing. A method of manufacturing a coated fluoride glass optical fiber.