JPH06273642A - Fluoride optical fiber - Google Patents

Abstract

PURPOSE:To provide the fluoride optical fiber having a high strength and high weatherability by coating the surface of the fluoride optical fiber with oxide glass essentially consisting of P2O5 and further coating the surface thereof with a UV curing resin layer. CONSTITUTION:This fluoride optical fiber is constituted by coating the surface of the fluoride optical fiber, which is formed by coating the surface of a core 1 consisting of the fluoride glass with a clad layer 2, with an oxide glass layer 3 essentially consisting of the P2O5 and coating the surface of this oxide glass layer 3 with the UV curing resin layer 4. The process for production of the fluoride optical fiber consists of inserting a fluoride glass preform having a core-clad structure into an oxide glass tube and integrally drawing the tube. The oxide glass tube is internally subjected to a dehydration treatment to suppress the reaction of the fluoride glass and the oxide glass at this time. The oxide glass has excellent water resistance and a high mechanical strength is easily obtainable therewith and, therefore, the optical fiber having the high strength and the high weatherability is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluoride optical fiber, and in particular, as a low loss transmission medium for optical communication or a sensor, an optical amplifier, an amplification medium for a laser, a high energy transmission medium used for medical treatment and the like. The present invention relates to a technique for improving the strength and weather resistance of a used fluoride glass optical fiber.

[0002]

2. Description of the Related Art Since 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 for high-power lasers in the infrared region. Further, transmission to the infrared region means that a transmission window is provided in a region where Rayleigh scattering is low, and as a result, it is expected to realize an optical fiber with lower loss than quartz. Furthermore, in recent years, fluoride optical fibers have been used in optical fiber amplifiers, especially P
It is attracting attention as an amplifying medium in which a high gain is obtained in the 1.3 μm region where r is an active ion.

[0003]

However, the fact that the fluoride glass has transmission characteristics 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 the realization of this optical fiber. Further, since it is composed of a fluoride, it reacts with moisture in the atmosphere to cause hydrolysis, which causes crystallization, resulting in a decrease in strength.

The conventional coating materials for fluoride optical fibers are:
FEP (fluor ethylene propylene copolymer: Teflon (trade name)) or ultraviolet rays (hereinafter referred to as UV)
It was one of the cured polyacrylates. At first glance, these resins seem to be effective as a coating material for moisture in the atmosphere, but they are capable of permeating water molecules as a molecular structure, and in the weather resistance test at high temperature, the moisture that penetrates through the coating material Erosion of the optical fiber due to. Therefore, there is a problem that sufficient reliability cannot be ensured for a long period of time.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a fluoride optical fiber having high strength and high weather resistance.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0007]

In order to achieve the above object, a fluoride optical fiber according to the present invention has an oxide containing P ₂ O ₅ as a main component on the surface of a fluoride optical fiber made of fluoride glass. The most main feature is that the glass is coated and the surface of the oxide glass is further coated with a UV curable resin layer.

In the method for producing a fluoride optical fiber of the present invention, a fluoride glass preform having a core-clad structure is inserted into an oxide glass tube and drawn as a unit. In particular, when drawing, the oxide glass tube is dehydrated to suppress the reaction between the fluoride glass and the oxide glass.

[0009]

According to the above-mentioned means, the coating material used conventionally is a resin and is permeable to moisture. On the other hand, oxide glass is excellent in water resistance and easily obtains high mechanical strength, so that the optical fiber can have high strength and high weather resistance.

Fluoride glass has a low glass transition temperature of about 300 ° C., and C at high temperature like quartz fiber.
Carbon coating by the VD method is impossible. In the present invention, considering the crystallization of glass and the microbending loss of the optical fiber, a material having the same drawing temperature and linear expansion coefficient of fluoride glass and oxide glass can be used as the coating material.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view showing the structure of Embodiment 1 of a fluoride optical fiber according to the present invention. As shown in FIG. 1, the fluoride optical fiber of Example 1 contains P ₂ O ₅ as a main component on the surface of a fluoride optical fiber obtained by coating the surface of a core 1 made of fluoride glass with a cladding layer 2. Is coated with the oxide glass layer 3 and the surface of the oxide glass layer 3 is coated with the UV curable resin layer 4.

The method for manufacturing the fluoride optical fiber of the first embodiment will be described below. After melting, the composition is 58P ₂ O ₅ -5Zn
_{O-5PbO-15Li 2 O-} 15Na 2 O-2V 2 O 5 ( mol%) were weighed so as to obtain a total amount of 60 g, 2 hour hold to the raw material at 400 ° C. in an Ar gas atmosphere and put in a platinum crucible After removing the carbonates present in the form of CO ₂ ,
It was held at 00 ° C for 2 hours to be melted.

Next, the melt was poured into a brass cylindrical hollow mold that had been heated to 220 ° C. in an electric furnace, and was gradually cooled to room temperature. After making holes in the obtained phosphate glass with an electric drill, it was polished with an electric polishing machine until the inner diameter became 5 mmφ. Next, after being immersed in a hydrofluoric acid aqueous solution having a concentration of 20% for 20 minutes for etching, the inner diameter was flame-polished by a flame polishing method.

The flame polishing method is a method of polishing the inner wall of the jacket tube with a flame such as a burner. A specific example of this flame polishing method is described in, for example, Japanese Patent Application No. 4-343126 filed previously by the applicant of the present application, and therefore detailed description thereof will be omitted here.

The inner wall of this phosphoric acid glass tube was observed in detail, but impurities such as scratches and dust were not seen, and it was formed very smooth.

Separately, the core composition is 49ZrF ₄ -25BaF _2-.
3.5LaF ₃ -2YF ₃ -2.5AlF ₃ -18LiF (mol%), clad composition 47.5ZrF ₄ -23.5BaF ₂ -2.5
A base material having an outer diameter of 5 mm and having a core-clad structure made of LaF ₃ -2YF ₃ -4.5AlF ₃ -20NaF (mol%) was manufactured by the suction casting method. As this suction casting method, for example, Japanese Patent Laid-Open No.
The method described in JP-A-3-11535 is used.

After polishing the surface of this base material to a water-resistant abrasive paper No. 4000, it was etched with a hydrochloric acid aqueous solution of ZrOCl ₂ and sufficiently dried, and then the inside of the cylindrical oxide glass tube (jacket tube) described above was used. Inserted in. Then, while the pressure inside the jacket tube was reduced using a vacuum pump, the material was zone-heated from the outside to be softened, and while stretching the base material and the jacket tube while changing the stretching speed, stretching was performed so that the core diameter became constant.

The base material having a tapered outer diameter was polished so that the outer diameter was constant at 4.8 mmφ, 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 jacket was drawn by zone heating while reducing the pressure inside the tube.

The drawn optical fiber was immediately coated with UV cure coat by online coating.
The resulting optical fiber has a length of 400 m and a cladding outer diameter of 1
25 μm, oxide glass layer 3 thickness 70 μm, UV cure coat thickness 60 μm, core diameter 10.5 μm, relative refractive index difference 0.61%, cut-off 2.2 μm single mode optical fiber. It was When the cross section of this optical 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 layer 3, and it was smooth.

The loss value of this optical fiber has a wavelength of 2.55.
It was 1.75 dB / km in μm. Next, the tensile strength of this optical fiber was measured. The measurement length is 50 cm, the number of samples is 50, and the strength is 900 MPa. 400 MPa when only the fluoride glass is coated with the FEP pipe.
Greater improvement.

(Example 2) The composition of the oxide glass layer 3 used for coating was 55P ₂ O ₅ -5ZnO-5PbO-10K ₂ O-.
The oxide glass layer 3 was formed on the outside of the fluoride glass by the same method as in Example 1 except that 10Li ₂ O-10Na ₂ O-5Al ₂ O ₃ (mol%) was used, and UV cure coating was applied. A fluoride optical fiber was produced.

The obtained optical fiber has a length of 350 m, a cladding outer diameter of 125 μm, and an oxide glass layer 3 having a thickness of 80 μm.
m, and the thickness of the UV cure coat was 70 μm. The tensile strength of the produced optical fiber was measured by the same method as in Example 1 to obtain 1 GPa as the average value of the strength.

Next, in order to examine the weather resistance of the optical fiber, the optical fiber was left in a high temperature / high humidity container having a temperature of 80 ° C. and a humidity of 70%, and the tensile strength of the optical fiber sampled periodically was measured. did. The measurement result is shown in FIG.

As shown in FIG. 2, in an optical fiber coated with a conventional UV-curable acrylate resin that does not cover the oxide glass layer 3, crystallization proceeds due to hydrolysis from the surface due to moisture in the atmosphere. Although the strength of the optical fiber drastically decreases, it can be seen that the strength of the optical fiber coated with the oxide glass layer 3 is hardly recognized even after standing for 100 days or more, and the weather resistance is greatly improved. .

(Example 3) The composition of the oxide glass layer 3 used for coating was 50P ₂ O ₅ -5B ₂ O ₃ -5ZnO-5PbO-1.
The oxide glass layer 3 was formed on the outside of the fluoride glass in the same manner as in Example 1 except that 0K ₂ O-10Li ₂ O-10Na ₂ O-5Al ₂ O ₃ (mol%) was used, and UV cure was performed. A coated fluoride optical fiber was produced.

The obtained optical fiber has a length of 300 m, a cladding outer diameter of 125 μm, and an oxide glass layer 3 having a thickness of 90 μm.
m, and the thickness of the UV cure coat was 65 μm. The tensile strength of the produced optical fiber was measured by the same method as in Example 1 to obtain 1.1 GPa as the average value of the strength.

Next, the obtained optical fiber coated with the oxide glass layer 3 and the conventional optical fiber coated only with a UV-curable acrylate resin were put in a high temperature and high humidity container having a temperature of 80 ° C. and a humidity of 70%. Figure 3 shows the change over time in the transmission loss of the optical fiber at a wavelength of 1.3 µm. The horizontal axis is the number of days, and the vertical axis is the transmission loss. In FIG. 3, a broken line indicates that light does not pass. As is clear from this figure, the optical fiber coated with the oxide glass layer 3 has
It can be seen that the change in transmission characteristics is significantly smaller than that of the uncoated optical fiber.

(Example 4) Example 1 except that the composition of the oxide glass layer 3 used for coating was selected from Table 1.
The oxide glass layer 3 was formed on the outer side of the fluoride glass in the same manner as in (1), and a UV optical coat-provided fluoride optical fiber was produced.

The obtained optical fiber had a length of 310 m, an outer diameter of the cladding of 125 μm, and a thickness of the oxide glass layer 3 of 95 μ.
m, and the thickness of the UV cure coat was 75 μm. The tensile strength of the produced optical fiber was measured in the same manner as in Example 1 to obtain 1.2 GPa as the average value of the strength.

Next, the optical fiber coated with the obtained oxide glass layer 3 was placed in a closed container and a conventional U
FIG. 4 shows the change over time in the transmission loss of the optical fiber at a wavelength of 1.3 μm when the optical fiber coated with only the V-curable acrylate resin was placed in a high temperature and high humidity container having a temperature of 80 ° C. and a humidity of 70%. The horizontal axis is the number of days, and the vertical axis is the transmission loss. In FIG. 4, a broken line indicates that light does not pass.

Regarding the technique of putting the optical fiber in a closed container, Japanese Patent Application No. 4-2, which is a prior application of the present applicant.
The technique described in 01103 was used.

As is apparent from FIG. 4, the change in transmission characteristics of the optical fiber coated with the oxide glass layer 3 is much smaller than that of the optical fiber not covered by being placed in a closed container.

[0033]

[Table 1]

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Absent.

[0035]

As described above, by using the oxide glass composition of the present invention, it is possible to obtain a fluoride optical fiber having high strength and high weather resistance. As a result, it is possible to overcome the problem of reliability, which has been an obstacle to practical use of conventional optical fibers using fluoride glass as a basic element.

[Brief description of drawings]

FIG. 1 is a first embodiment of a fluoride optical fiber according to the present invention.
Sectional view showing the configuration of

FIG. 2 is a second embodiment of a fluoride optical fiber according to the present invention.
Tensile strength characteristic chart showing the weather resistance test results of the oxide glass-coated fiber and the optical fiber having only UV cure coat,

FIG. 3 is a third embodiment of a fluoride optical fiber according to the present invention.
Of the transmission characteristics of the oxide glass-coated fiber and the optical fiber only of UV cure coat,

FIG. 4 is a fourth embodiment of a fluoride optical fiber according to the present invention.
The figure which shows the transmission characteristic only of what put the oxide glass coating fiber of above into a closed container, and UV cure coat fiber only.

[Explanation of symbols]

1 ... Core made of fluoride glass, 2 ... Clad layer, 3
... an oxide glass layer containing P ₂ O ₅ as a main component, 4 ... a UV curable resin layer.

Claims (1)

[Claims] 1. The surface of a fluoride optical fiber made of fluoride glass is coated with an oxide glass containing P ₂ O ₅ as a main component, and the surface of the oxide glass is further coated with an ultraviolet curable resin layer. A fluoride optical fiber, characterized in that