JPH061634A - Surface treatment of fluoride glass base material - Google Patents

Abstract

PURPOSE:To improve the tensile strength of glass fiber by applying liquid phase etching to the most exterior layer clad part of a cylindrical fluoride glass base material to provide the specified surface roughness. CONSTITUTION:The relationship between the surface roughness and the tensile strength in material compositions of the most exterior layer clad part of a cylindrical fluoride glass parent material is measured to determine the surface roughness meeting the allowable tensile strength. The surface roughness is defined as the average of the absolute values of the differences between the measured distance values from points on one generating line outside the cylindrical glass base material to the central axis of the cylinder and the average radius value. The surface roughness is preferably <=0.05mum. The relationship between the solute concentration and etching time of etching solution (example: hydrochloric acid solution of zirconium oxychloride) and the surface roughness is measured to determine the solute concentration and the etching time meeting the desired tensile strength, permitting liquid phase etching to be performed. According to this method, since the surface corrosion of the base material glass is restrained while controlling the surface roughness of the base material glass, fiber of high tensile strength is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment of a preform, which is one of the manufacturing steps of a fluoride glass fiber.

[0002]

2. Description of the Related Art As a fiber that transmits light in the infrared region and is used as an optical transmission medium for optical communication, a fluoride fiber using a fluoride glass, which has a small transmission loss in the light in this wavelength region, has been receiving attention. . This fluoride fiber is used as a long-distance transmission medium that takes advantage of low loss, and as a constituent element of a fluoride optical fiber amplifier that can amplify infrared light instead of the conventional OE / EO conversion. Fluoride single-mode optical fibers with mechanical properties are expected.

In the case of a single mode / fluoride fiber that guides infrared light, the core diameter is usually set to 1 from the condition for establishing a single mode.
It is necessary to finish the fiber diameter to 0 μm or less in accordance with the international standard (CCITT standard) to about 125 μm. Conventionally, in order to achieve a desired core diameter and clad thickness, a process of inserting a cylindrical core preform or a cylindrical core / clad preform into a cylindrical clad preform and heating and drawing the desired core is performed. A method is adopted in which the fiber is manufactured by repeating the heating-integrated drawing by the rod-in-tube method until the diameter-to-clad diameter ratio is reached.

Each base material formed in each step is subjected to surface polishing and surface treatment such as liquid phase etching for removing surface dirt and impurities and smoothing the surface. In particular, the core base material and the innermost layer clad base material are subjected to surface contamination and impurities removal for optical waveguide characteristics, and the outermost layer clad base material is subjected to liquid phase etching for surface smoothing. Be implemented.

[0005]

It is known that when the above-mentioned outermost layer cladding base material is subjected to liquid phase etching to smooth the surface, the tensile strength of the finished fluoride glass fiber is increased. Known liquid-phase etching solutions include zirconium oxychloride (ZrOCl ₂ ) hydrochloric acid solution, boric acid (H ₃ BO ₃ ) hydrochloric acid solution, and ammonium nitrate (NH ₄ NO ₃ ) nitric acid solution.

However, there have been no examples of systematically examining the solute concentration and etching time of the above liquid phase etching solution, the smoothing of the surface of the base material, and the influence on the fiber strength. There are only reports of improved fiber strength at specific etching times (Electronics Letters 22).
(1986) p949-950, J. Mat. Sci.
Lett. 6 (1987) p1440-1442, J.
Mat. Sci. 26 (1991) p5149-515
4). Therefore, since the fiber was produced without optimizing the liquid phase etching method, the solute concentration was unnecessarily increased to increase the surface roughness and the fiber strength was impaired. (Note that the fiber strength reduction by unnecessarily lowering the solute concentration and promoting surface crystallization was investigated by liquid phase etching of the core base material and the innermost clad base material to maintain the waveguide characteristics. The lower limit of the concentration of non-crystallizing solute is known.) The present invention has been made to solve the above problems, and an object thereof is to provide a fluoride glass fiber having high mechanical strength. .

[0007]

The surface treatment method for a fluoride glass base material of the present invention measures the relationship between the surface roughness and the tensile strength in the material composition of the outermost clad portion of a cylindrical fluoride glass base material. Then, the first step of determining the surface roughness that satisfies the allowable tensile strength, and the relationship between the solute concentration of the etching solution and the etching time and the surface roughness are measured, and the solute concentration range that satisfies the allowable tensile strength and the etching. The second step of determining the time range is characterized in that the fluoride glass base material is subjected to liquid phase etching within the solute concentration range and the etching time range.

In the above surface treatment method, the surface roughness is defined as the absolute value of the difference between the measured distance value from the center axis of the cylinder and the average radius value at each point on one generatrix outside the cylinder type fluoride glass base material. It is characterized in that it is defined by an averaged value. The surface roughness is set to 0.05 μm or less.

[0009]

According to the surface treatment method of the present invention, in order to prevent excessive erosion of the surface of the cylindrical fluoride glass base material by liquid phase etching, the etching solution based on the surface roughness defined by the present inventor. Since the solute concentration and the etching time are controlled, the surface can be smoothed without impairing the mechanical strength of the finished fiber.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. As the material for the outermost clad portion, a glass having the following composition which is commonly used is selected. Glass composition: 53ZrF ₄ -20BaF ₂ -4LaF ₃
-3AlF ₃ -20NaF First, only consisting of this material, creating a large number of cylindrical glass having the same diameter finish fluoride glass preform. Zirconium oxychloride (ZrOCl
Liquid phase etching was carried out for 30 minutes with various solute concentration solutions of hydrochloric acid solution of ₂ ), hydrochloric acid solution of boric acid (H ₃ BO ₃ ) and nitric acid solution of ammonium nitrate (NH ₄ NO ₃ ). The relationship of the defined surface roughness Ra is measured.

[0011]

[Equation 1]

The results of this measurement are shown in the graph of FIG. In Fig. 1 (a), the solute is zirconium oxychloride (ZrOCl).
₂ ) in the case of the hydrochloric acid solution, FIG. 1B shows the case of the hydrochloric acid solution in which the solute is boric acid (H ₃ BO ₃ ), and FIG.
(C) is a case of a nitric acid solution whose solute is ammonium nitrate (NH ₄ NO ₃ ). The vertical axis of the graph is the surface roughness R
a, the horizontal axis represents the solute concentration.

Next, each post-etched cylindrical glass is heated and drawn to form a fiber having a diameter of 125 μm. A tensile rupture test is performed on these fibers to measure the relationship between the surface roughness Ra and the tensile rupture force. The measurement result is shown in FIG. FIG. 2A is a graph showing the breaking probability of the fiber with respect to the tensile strength for each surface roughness, the horizontal axis shows the tensile strength, and the vertical axis shows the breaking probability. From this graph, as a value representative of the tensile breaking force corresponding to each surface roughness, the tensile strength with a breaking probability of 50% is obtained and graphed to obtain FIG. 2 (b). As is clear from the graph of FIG. 2B, the fiber strength decreases as the surface roughness Ra increases, but the surface roughness Ra is 0.05 μm.
If it is suppressed to m or less, the tensile strength in the case of an almost ideal surface can be obtained without further reducing the surface roughness.
From the above, the surface roughness Ra of the base material after etching was set to 0.
It is set as a management target to be less than or equal to 05 μm.

Subsequently, the etching solution which achieves this control target is determined from the graph of FIG. As a result, the appropriate solution and etching time to be used in the base material liquid phase etching process in the manufacturing process of the fluoride glass fiber using the material for the outermost layer clad are as follows.

(1) Zirconium oxynate concentration is 0.1
Liquid phase etching is performed for 30 minutes with a hydrochloric acid solution of ˜0.3 mol / l.

(2) Boric acid concentration is 0.05 to 0.2 mo
Liquid phase etching is carried out for 30 minutes with a 1 / l hydrochloric acid solution.

(3) Ammonium nitrate concentration is 0.2 to
Liquid phase etching is performed for 30 minutes with a 0.4 mol / l nitric acid solution.

By applying these liquid phase etching methods to the fluoride glass base material used for the outermost layer clad portion by the liquid phase etching method, proper surface smoothing can be realized and fluoride having high tensile strength can be realized. Glass fibers can be manufactured.

The present invention is not limited to the above embodiment, and when the material of the outermost clad portion or the etching solution type is changed, the liquid phase etching method may be determined by the same procedure as in the embodiment.

[0020]

As described above in detail, according to the surface treatment method for a fluoride glass preform of the present invention, the tensile strength of the finished fiber is not lowered by using the surface roughness of the preform glass as a control parameter. The surface erosion of the matrix glass due to the liquid phase etching of the matrix glass is suppressed to a certain extent, so that there is an effect that a fluoride glass fiber having high tensile strength can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the solute concentration of an etching solution and the surface roughness after etching.

FIG. 2 is a diagram showing the relationship between the surface roughness of the outermost cladding base material and the fiber tensile strength.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Nishimura, 1st Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Koji Nakazato 1st, Taya-cho, Sakae-ku, Yokohama, Kanagawa Sumitomo Electric Ki Industry Co., Ltd. Yokohama Works

Claims (3)

[Claims] 1. The relationship between the surface roughness and the tensile strength in the material composition of the outermost clad portion of the cylindrical fluoride glass base material is measured to determine the surface roughness satisfying the allowable tensile strength. A first step, and a second step in which the relationship between the solute concentration and etching time of the etching solution and the surface roughness is measured, and the solute concentration range and the etching time range satisfying the allowable tensile strength are determined. A method for surface treatment of a fluoride glass base material, comprising a pre-process, and subjecting the fluoride glass base material to liquid phase etching within the solute concentration range and the etching time range. 2. A value obtained by averaging the surface roughness degrees with an absolute value of a difference between a measured distance value from the center axis of the cylinder and a mean radius value at each point on one generatrix outside the cylinder type fluoride glass base material. The method for surface treatment of a fluoride glass base material according to claim 1, wherein 3. The surface treatment method for a fluoride glass base material according to claim 2, wherein the surface roughness is 0.05 μm or less.