JPH0333703A - Optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical fiber with low loss, high strength, and particularly excellent tensile strength.

(Prior Art) In recent years, optical fibers have been widely used in various fields of public communications, and the field of use is expanding eastward. Along with this, requirements for characteristics such as optical loss and mechanical strength of optical fibers are becoming increasingly diverse and severe.

By the way, in a conventional high-strength optical fiber, a quartz cladding D is provided on the outside of the core C, as shown in FIGS. If there is a quartz clad optical fiber provided with layer E, the coefficient of linear expansion of the outer peripheral layer E is smaller than that of the quartz clad D, so the compressive stress of the outer peripheral layer E is applied to the +17i clad D. become. Therefore, dynamic fatigue strength and tensile strength are improved compared to ordinary optical fibers.

(Problem to be Solved by the Invention) However, the cladding D or the core C and the cladding D
In a fluorine-doped clad optical fiber that is doped with fluorine and has a refractive index distribution as shown in Figure 7, if an outer layer E containing titanium is provided outside the cladding D, dynamic fatigue will be reduced compared to an optical fiber without an outer layer. The strength will improve,
On the contrary, the tensile strength decreases. This is a dopant (
This is because adding fluorine, titanium, etc.) lowers the absolute value of the tensile strength, and at present there is no established method for increasing both the dynamic fatigue strength and tensile strength of the optical fiber. As described above, there is a contradictory problem in that an attempt to improve the dynamic fatigue strength of an optical fiber results in a decrease in tensile strength, and a solution to this problem is strongly desired.

(Objective of the Invention) An object of the present invention is to provide an optical fiber having excellent tensile strength and dynamic fatigue strength.

(Means for Solving the Problems) As shown in FIG. 1, the optical fiber of the present invention includes a core 1, an inner cladding 2 containing at least fluorine (fluorine-doped cladding), and an outer peripheral layer containing at least titanium (titanium-doped cladding) 2. The optical fiber is characterized in that a pure silica glass layer 4 is provided between the inner cladding 2 and the outer peripheral layer 3.

(Function) In the optical fiber of the present invention, the inner cladding (
Since a pure silica glass layer 4 with excellent tensile strength is provided on the outside of the fluorine-doped cladding 2, the initial tensile strength of the optical fiber produced by directly providing the titanium-doped cladding 3 on the outside of the fluorine-doped cladding 2 is Reduce the decline in

Moreover, in the outer measurement of the same glass layer 4, the outer peripheral layer containing titanium (
Since the titanium-doped cladding 3 is provided, the dynamic fatigue strength (dynamic fatigue coefficient) of the optical fiber is improved.

(Example) FIG. 1 shows an example of a fiber according to the present invention.

In the figure, l is a core, and 2 is an inner cladding formed on the outer surface of the core l. The core l and inner cladding 2 are doped with fluorine to lower their refractive index, as in the existing ones, and the refractive index of the core l and inner cladding 2 is lowered as shown in the refractive index distribution in FIG.
Its refractive index is also slightly smaller than that of pure silica glass.

3 in the figure is an outer peripheral layer provided as the outermost layer of the optical fiber A. This outer peripheral layer 3 is for improving the dynamic fatigue strength of the optical fiber, and is doped with titanium as in the conventional layer.

Reference numeral 4 shown in the figure is a pure silica glass layer formed between the inner cladding 2 and the outer peripheral layer 3. This pure silica glass layer 4 has excellent tensile strength and is intended to suppress a decrease in initial tensile strength caused by the fluorine-doped cladding 2 and titanium-doped cladding 3.

The optical fiber A of the present invention can be obtained, for example, as follows.

First, pure silica glass was doped with fluorine to obtain a fluorine-doped optical fiber base material having the refractive index distribution shown in FIG. This fluorine-doped optical fiber base material forms the core 1 and the inner cladding 2, and as shown in the figure, the relative refractive index difference of the core 1 with respect to pure silica glass is -0.02%,
The refractive index difference between the core 1 and the cladding 2 is -0.35%.

Next, after drawing the fluorine-doped optical fiber base material to a diameter of 30 mm, 5iCj24 was applied to the same base material at a rate of 0.15ff/
S obtained by introducing rnin into an oxygen-hydrogen flame
i Ox fine particles (soot) were coaxially deposited on the same optical fiber base material to a thickness of 3III, and SICQ a was applied to the east at O, 15 ff/min, and TiC ffn was applied at 0.38 ff/min.
The 5iOa-TiO2 fine particles (soot) obtained by introducing the Si
A sooted optical fiber preform was obtained by coaxially depositing it to a thickness of 2 mm on the Oa stack. In addition, this suit part is Tie
, contained 3 moff%.

Next, set He to 30 (ff/m1n) and CQ 2 to 0.
．． 3 (I2/min) in a vitrification furnace with a maximum temperature of 1610°C, and then vitrified at 120 m/min in a drawing furnace. After drawing the fiber, immediately apply ultraviolet curable resin to it to make the optical fiber with an outer diameter of 125μ.
An optical fiber core A having a coating outer diameter of 250 μm was obtained. The refractive index distribution profile of this optical fiber core A is as shown in Figure 1, and it is confirmed that a pure silica glass layer 4 is formed between the cladding 2 and the outer peripheral layer 4. .

For comparison of this optical fiber A, pure silica glass layer 4
Optical fiber B, which does not have the following properties, was obtained as follows.

First, the fluorine-doped optical fiber base material was prepared with a diameter of 30 mm.
After stretching, only the S i Oz -T i 02 fine particles (soot) (1) were coaxially deposited on the outer periphery to a thickness of 5 mm in the same manner as above, and transparent glass was formed in a vitrification furnace under the same conditions as above. This was drawn under the same conditions as above to obtain an optical fiber with an outer diameter of 125 μmφ and an outer diameter of the coating of 250 μm.
An optical fiber core B having a diameter of φ was obtained. The presence of a silica glass layer was not recognized in the refractive index distribution of this optical fiber core wire B.

The results of dynamic fatigue testing of the optical fibers A and B obtained as described above were as shown in FIG. In addition, in the same figure, the horizontal axis shows the stress velocity,
The vertical axis represents the logarithm of the median value α of the breaking strength, and the relationship between the two is 12oga = (1+nl-'I2og6 + (1
+nl-'I2ogk ■Here, n is the dynamic fatigue coefficient,
k is expressed as a constant, and the smaller the slope of the straight line in the figure, the greater the dynamic fatigue coefficient F
The larger in and the larger the 5-dynamic fatigue coefficient n, the less deterioration of strength against stress.

As is clear from FIG. 3 and the @ equation, the dynamic fatigue coefficient n values of both optical fibers A and B remain unchanged.

On the other hand, when a tensile test was conducted separately from the dynamic fatigue test, the initial tensile strength of optical fiber A was 5.6 kg/optical fiber, and that of optical fiber B was 5.2 kg/optical fiber.

In addition, the conventional # without titanium-doped cladding shown in the same figure
! The dynamic fatigue coefficient n of the quaternary fluorine-doped clad optical fiber C is about 2゛2, and the dynamic fatigue coefficient n of the optical fiber core A of the present invention is about 30, which is a higher value than the conventional one. I can see that

(Effect of the invention) The optical fiber of the present invention has the following effects.

■Since the pure silica glass layer 3 is provided between the inner cladding 2 and the outer peripheral layer 4, it is possible to suppress a decrease in the initial tensile strength of the optical fiber. Therefore, the dynamic fatigue coefficient n can be improved as in the conventional case.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the optical fiber of the present invention, Figure 2 is a refractive index distribution diagram of the same optical fiber, Figure 3 is a dynamic fatigue characteristic diagram of the same optical fiber and a conventional optical fiber, and Figure 4 is a diagram of the optical fiber of the present invention. The refractive index distribution diagram of the base material used in the tip fiber shown in the figure, Figure 5 is a cross-sectional view of a conventional quartz clad optical fiber, Figure 6 is a refractive index distribution diagram of the same quartz clad optical fiber, and Figure 7 is a conventional quartz clad optical fiber. FIG. 2 is a refractive index distribution diagram of a fluorine-doped clad optical fiber. l is the core 2, the inner cladding 3, the outer peripheral layer 4, the pure silica glass layer stress 4pIfmln/m1ni -〇-A --X=-8 -・--10

Claims (1)

[Claims] a core 1; an inner cladding 2 containing at least fluorine;
An optical fiber having an outer circumferential layer 3 containing at least titanium, characterized in that a pure silica glass layer 4 is provided between the inner cladding 2 and the outer circumferential layer 3.