JPH06166529A - Preparation of jacket pipe - Google Patents

Abstract

PURPOSE:To prepare a jacket pipe composed of oxide glass of high purity with a high accuracy for preparing low-loss fiber having high strength and weather resistance. CONSTITUTION:A glass material melted in a melting furnace is poured into a mold and cooled to ambient temperature to prepare a glass rod, which is then subjected to perforation processing. The resultant glass rod is housed in an electric furnace 1 to polish the inner surface of the glass rod 3 with a flame from a burner 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low loss transmission medium for optical communication or a sensor, an amplification medium for an optical amplifier or a laser, or a fluoride glass optical fiber used as a high energy transmission medium for medical use. The present invention relates to a method of manufacturing a jacket tube which is an outer tube jacket of a clad of an optical fiber used for jacket stretching and jacket drawing of an optical fiber preform in order to improve its strength and weather resistance.

[0002]

2. Description of the Related Art As a method of controlling the core diameter of an optical fiber, a rod-in-tube method is used in which a core tube is coated with a jacket tube having the same composition as the clad, and a core tube having a core / clad structure is used. A jacket stretching method of coating and stretching (Japanese Patent Application No. 2-134018) and a jacket drawing method are used. Oxide glass tubes that are generally commercially available as a method for manufacturing the jacket tube used in the above method are mainly those in which the raw material is melted in the crucible and allowed to flow downward through the holes in the bottom of the crucible, and at the same time on the central axis of the crucible A hollow glass tube is obtained by the die provided in. On the other hand, for low-melting point multi-component glass, especially for fluoride fiber, a method of forming a hole in the center of a glass rod prepared by injecting a molten glass raw material into a hollow mold to form a pipe, or a glass melt. Is poured into a cylindrical hollow mold, and then the mold is rotated at a high speed while keeping the mold inclined or horizontal to produce a hollow cylindrical pipe by centrifugal force (Japanese Patent Application No. 4-23).
9413).

A fluoride optical fiber containing ZrF ₄ as a main component has excellent transmission characteristics in the infrared wavelength region,
It has attracted attention as a transmission medium for sensors or high-power lasers in the infrared region. Further, transmission to the infrared region means that the transmission window is provided in a region where Rayleigh scattering is low, and as a result, it is expected to realize a fiber having lower loss than quartz. Further, in recent years, it has been attracting attention as an optical fiber amplifier, particularly as an amplifying medium which can obtain a high gain in a 1.3 μm region in which Pr is an active ion. However, the fact that the fluoride glass has a transmission characteristic up to the infrared region means that the binding force of the components constituting the glass is weak. For this reason, the fluoride optical fiber has insufficient mechanical strength and is considered to be a serious obstacle to practical use of this fiber. Further, since it is composed of a fluoride, it has a drawback that it reacts with moisture in the air to cause hydrolysis, resulting in crystallization and consequently a decrease in strength. In order to solve these problems, a method has been proposed in which a jacket tube is made of glass composed of an oxide having a strong binding force as a constituent of the glass, and the jacket wire is drawn together with the fluoride glass (LJB Vachaet. Al. , Material Science Forum
Vols. 32-33 (1988) pp. 571-576). However, fluoride glass grows due to crystal growth due to heat treatment during drawing and drawing, which causes an increase in loss and a decrease in strength.Therefore, a die method that easily scratches the inner and outer wall surfaces and impurities such as abrasives on the inner wall. However, there was a problem in producing this oxide glass jacket tube by a drilling method that tends to remain. Further, the rotation casting method can make a jacket tube without causing scratches on the inner wall, but there is a limitation that this method cannot be used for highly viscous oxide glass.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a method for producing a jacket tube of high purity and high accuracy.

[0005]

[Means for Solving the Problems] To achieve the above object, the present invention pours a molten glass material in a melting furnace into a mold, cools it to room temperature, and punches the glass rod. In the method for producing a jacket tube for polishing an inner surface by means of polishing, the method for producing a jacket tube is characterized in that the inner surface that has been subjected to the drilling process is polished with a flame. In other words, the method of manufacturing the jacket tube proposed by the present invention is characterized mainly in that the inner surface of the oxide glass tube having a low softening point is flame-polished.

[0006]

In the method for producing a jacket tube according to the present invention, since the glass tube is flame-polished, a highly precise and highly pure jacket tube can be easily produced, which results in low loss, high strength and weather resistance. High fibers can be made.

[0007]

EXAMPLES Next, examples of the present invention will be described. Figure 1
Shows a schematic sectional view of a flame polishing apparatus for a jacket tube according to the present invention, in which 1 is an electric furnace in which a heating wire is wound around a quartz tube, 2 is a jig for fixing a base material, 3 is a jacket tube, 4 is an oxyhydrogen burner. First, the jacket tube 3 having holes is fixed to the jig 2, and the entire jacket tube 3 is put into the electric furnace 1 and preheated while slowly rotating. Next, while maintaining rotation and heating, the oxyhydrogen burner 4 is slowly inserted into and pulled out from the inner surface of the jacket tube 3 to repeat flame polishing. Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 After melting, the composition was 60 P ₂ O _{5
-8ZnO-8PbO-10Li 2 O-} 10Na 2 O-
4V ₂ O ₅ (mol%), weighed so that the total amount becomes 60 g, put in a platinum crucible and heated in an Ar gas atmosphere at 400 ° C. for 2 hours to remove carbonates existing in the raw material in the form of CO _2. After that, it was held at 1000 ° C. for 2 hours to be melted. Next, the above melt was poured into a brass cylindrical hollow mold that had been heated to 200 ° C. in an electric furnace, and the mixture was cooled to room temperature. The obtained phosphate glass was punched with an electric drill, and then polished with an electric polishing machine until the inner diameter became 5 mmφ. Next, after dipping in a 20% hydrofluoric acid aqueous solution for 20 minutes for etching, the entire phosphoric acid glass tube has an inner diameter of 30 mm
Put it in an electric furnace 1 made by sprinkling platinum on a quartz tube with a diameter of 250 mm and heating it to 250 ° C while keeping it warm, while oxygen is added to a quartz tube with an outer diameter of 3 mmφ and a length of 200 mm with a hole of 1 mmφ at the tip. Then, the inner diameter of the glass tube 3 was flame-polished with the burner 4 which was burned at the tip and burned at the tip.

When the inner wall of this phosphoric acid glass tube was observed in detail, impurities such as scratches and dust were not found, and it was formed very smooth. Separately, the core composition is 49ZrF ₄ -25B
_{aF 2 -3.5LaF 3 ─2YF 3 -2.5AlF 3} -
18LiF (mol%), clad 47.5ZrF ₄ −
23.5BaF ₂ -2.5LaF ₃ ─2YF ₃ -4.5
A base material having an outer diameter of 5 mm and having a core / clad structure made of AlF ₃ -20 NaF (mol%)
It was produced by the casting method (Japanese Patent Laid-Open No. 63-11535). The surface of the base material was polished, further etched in a zirconium oxychloride / hydrochloric acid aqueous solution, sufficiently dried, and then inserted into the cylindrical oxide glass tube (jacket tube) described above. Then, while the pressure inside the jacket tube was reduced using a vacuum pump, the zone tube was softened by zone heating from the outside, and while stretching the base material and the jacket tube while changing the stretching speed, the core tube was stretched to have a constant core diameter. The outer diameter of the base material stretched in a tapered shape is 4.8.
It was polished to a constant mm, etched with an aqueous solution of hydrogen fluoride, and then sufficiently dried. This base material was inserted into another jacket tube of the same composition prepared in the same manner, and the outside of this jacket tube was covered with a Teflon FEP pipe. Zone heating was performed while decompressing the inside of the tube to perform jacket drawing. It was The resulting fiber has a length of 1k
m, the outer diameter was 125 μm, the core diameter was 10.5 mm, the relative refractive index difference was 0.61%, and the cutoff was 2.2 μm. When the cross section of this fiber was observed with a microscope, there was no generation or disorder of crystals at the interface between the fluoride glass and the oxide glass, and it was smooth. The minimum loss value of this fiber was 1.75 dB / km at a wavelength of 2.55 μm. Next, the tensile strength of this fiber was measured.
The measurement length is 20 m, the number of samples is 40, and the high-strength part is 7
00MPa, Teflon FE only for fluoride glass
This was a significant improvement from 400 MPa when the P pipe was coated.

[Example 2] A jacket tube was produced by the same composition and method as in Example 1, a base material of fluoride glass was inserted, and jacket stretching was performed. The base material is the same as in Example 1.
After etching and drying, a wire was drawn while covering with a UV curable resin. The transmission loss characteristics of this fiber were almost the same as in Example 1. Further, the tensile strength was measured by the same method as in Example 1. Maximum measurement result is 900M
It has reached Pa, which is much higher than the maximum value of 550 MPa of the fiber UV-coated only on the fluoride glass. Next, both fibers were kept in a high temperature and high humidity tank having a temperature of 70 ° C. and a humidity of 80% for one week, and then the tensile strength was measured in the same manner. The strength of the fiber UV-coated only on the fluoride glass was significantly weakened to 200 MPa or less, whereas the fiber coated with the oxide glass and UV-coated had an average strength of 800 MPa, and almost no deterioration was observed. .

[Example 3] When a jacket tube was made by the same composition and method as in Example 1, the inner diameter of the tube was flame-polished in the same manner as the outer diameter, and then the fluoride glass was used. The base material was inserted and the jacket was stretched. After that, Teflon FRP and UV cure coat were used together as a coating material and drawn. The tensile strength was significantly improved, and an average strength of 950 MPa was obtained. The maximum strength for a similar coating on a fluoride glass jacketed fiber was 600 MPa.

FIG. 2 shows the oxide jacket fiber and the fluoride jacket fiber obtained in Example 3 at a temperature of 60.
Wavelength 1.3 when put in a high temperature and high humidity chamber at ℃ and 70% humidity
It is the time change of the transmission loss of the fiber in μm. In FIG. 2, the horizontal axis represents the number of days and the vertical axis represents the transmission loss. In the figure, a broken line indicates that light does not pass. As is clear from this figure, the oxide glass jacketed fiber has a significantly smaller change in transmission characteristics than the fluoride glass jacketed fiber.

[0013]

As described in the above embodiments, by using the method of the present invention, a highly accurate and highly pure oxide glass tube can be obtained, so that a fiber with low loss, high strength and high weather resistance can be obtained. Can be made. Therefore, there is an advantage that the reliability problem, which has been an obstacle to the practical use of the conventional fiber made of fluoride glass, can be overcome.

[Brief description of drawings]

FIG. 1 shows a schematic cross-sectional view of a specific example of a jacket tube flame polishing apparatus according to the present invention.

FIG. 2 shows transmission characteristics of a fluoride glass jacket fiber and an oxide glass jacket fiber.

[Explanation of symbols]

 1 Electric furnace 2 Jig 3 Jacket tube 4 Oxygen burner

Claims (3)

[Claims] 1. A method of producing a jacket tube, comprising pouring a glass material melted in a melting furnace into a mold, cooling the glass material to room temperature, and making a hole in the glass rod to polish the inner surface. A method for producing a jacket tube, which comprises polishing the inner surface subjected to heat treatment with a flame. 2. The method for producing a jacket tube according to claim 1, wherein when flame-polishing, the glass rod subjected to the perforating process is housed in an electric furnace and heated in the method for producing the jacket tube. . 3. The method for producing a jacket tube according to claim 1, wherein the inner surface of the holed glass rod is washed with a liquid for etching the glass prior to flame polishing. Manufacturing method.