JP3106564B2 - Manufacturing method of optical fiber and silica-based optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates is related to the production of silica-based fiber-optic and its <br/>, and in particular the core of pure quartz glass
The present invention also relates to a method for reducing the residual stress in the core by applying the method to the production of an optical fiber having a fluorine-doped quartz glass clad .

[0002]

2. Description of the Related Art VAD (Vapor Phase Axial Deposition) is a general method for mass producing optical fiber preforms.
The law is known. In the VAD method, glass fine particles generated in an oxyhydrogen flame are deposited on a rotating starting member, for example, a glass rod, to form a cylindrical porous base material, and the porous base material is sintered to form a transparent light source. This is a method for producing a glass preform for fiber. In the VAD method, the porous base material is sintered,
To make the glass transparent, the base material is placed in an inert gas atmosphere for 1 hour.
It is necessary to heat to 600 ° C. or higher. In addition, since the loss characteristic in the communication wavelength region of the obtained optical fiber is impaired if water is mixed, the porous preform is usually dehydrated before or simultaneously with the transparency. As a dehydration treatment, a method is known in which a porous base material is heated at a high temperature in an inert gas atmosphere to which a chlorine-based gas is added.

[0003]

In recent years, single mode fibers using pure silica glass for the core and fluorine-doped silica glass for the cladding have been considered promising, particularly from the viewpoint of reducing the loss of the optical fiber. An optical fiber having pure silica as a core does not add GeO ₂ to the core, so that scattering loss can be reduced, which is extremely advantageous for reducing the loss. However, pure silica core - if the optical fiber made of a fluorine-added silica cladding, the viscosity of the small core portion of the cross-sectional area is larger than that of the clad portion, most of the tension at the time of drawing will be exerted on the core. As a result, during the vitrification, tensile stress remains in the core, causing various problems. That is, the refractive index of the core portion is reduced by the tensile stress (photoelastic effect), and the difference in the relative refractive index between the core and the clad is reduced. As a result, λc (cutoff wavelength) predicted at the preform stage, MFD (mold field) (Diameter) and λ ₀ (zero dispersion wavelength), and the residual tensile stress strongly depends on the manufacturing conditions (drawing conditions). Therefore, great care must be taken to stabilize the conditions. The present invention is more pure silica core such as - to solve the problems of fiber fluoridation cladding structure, providing a silica-based optical fibers that have been resolved methods and problems of fiber-optic can be prepared having a structure designed It is done for the purpose of.

[0004]

Means for Solving the Problems In view of the above, the present inventors have reduced the viscosity of pure silica glass serving as a core so that the difference between the viscosity of fluorine-doped silica glass serving as a clad and the viscosity thereof can be relatively reduced. We thought that this would reduce the stress concentration on the core during drawing, and as a result of various studies,
The inventors have found that the problem can be solved by adding a trace amount of halogen to pure quartz glass, and have reached the present invention. That is, the manufacturing method of the present invention that solves the above problem is a method of obtaining an optical fiber by drawing a porous preform containing quartz as a main component after dehydration and vitrification into a glass preform to obtain an optical fiber. In the dehydration step and / or the transparent vitrification step, heat treatment is performed in an atmosphere containing a halogen-based gas to reduce the halogen content in the quartz glass to 0.1%. 3 to 1
% By weight, and the obtained glass preform is used as a core of an optical fiber, and a fluorine-containing quartz glass is used as a clad. In the present invention, chlorine is particularly preferable as the halogen contained in the quartz glass. Further, the present invention has a core and a fluorine-containing quartz glass clad, and the core contains 0.1% of halogen containing chlorine. Provided is a silica-based optical fiber comprising silica glass containing 3 to 1% by weight.

[0005]

In order to investigate the influence of the viscosity of the above-mentioned pure quartz glass, Cl is used as a representative halogen, and the amount of Cl in the quartz glass is analyzed by ion chromatography.
Quantitatively, a single mode fiber was manufactured using the quartz base material as a core, and the structure (λc, MFD),
The relative refractive index difference between the core and the clad was measured from the residual stress and the refractive index distribution of the fiber. It became clear that the residual stress in the fiber decreased as the Cl amount increased, and as a result, the relative refractive index difference between the core and the clad approached the value measured in the preform state (FIGS. 1 and 2). Further, the fiber structure (λc, MFD) almost coincided with the predicted value at the preform stage (FIG. 3). From the above, the viscosity of quartz glass can be reduced by increasing the amount of Cl in pure quartz glass, so that the fiber structure does not deviate from the predicted value at the preform stage, and Since the dependence is also reduced, it is very effective in producing a pure silica core single mode fiber. The amount of Cl in pure quartz glass is 0. 3 % by weight
It is preferably about 1% by weight. If the content is less than 0.3% by weight, the effect of Cl content is not exhibited, and it is not preferable because it largely deviates from the predicted value at the preform stage. Further, since the content of approximately 1% by weight substantially matches the predicted value of the preform, the content beyond this value is unnecessary. The same applies to the case of adding another halogen element having an effect of lowering the viscosity of quartz glass. Since fluorine also has a function of lowering the refractive index, when fluorine is added, it is necessary to add fluorine to the cladding in an amount equal to or more than the amount added to the core. In addition, iodine (I) and bromine (Br) are also effective, but it is advantageous to use a chlorine-based gas in that dehydration is the largest and there is no influence on the refractive index. Examples of the chlorine-based gas include Cl ₂ , CCl ₄ , SiCl ₄ , SOCl ₂ , and SCl ₂
And the like. However, for example, only dehydration treatment is performed using a chlorine-based gas, and another halogen-based gas is used in the transparency treatment, or another halogen-based gas is used in the dehydration treatment, and a chlorine-based gas is used in the transparency treatment. It is.

[0006] Actually, halogen is added to pure quartz glass in an amount of 0.1%.
In order to make the content within the range of 3 % by weight to 1% by weight, an appropriate one is selected from the halides,
In an atmosphere consisting of an inert gas such as e and a pressure of normal pressure to about 3 kg / cm ^2, it is heated at a temperature in the range of 1000 ° C. to 1700 ° C. to react with the porous base material to form a transparent glass. Specifically, the heat treatment of the porous base material in an atmosphere containing a halide gas includes the following steps: a) a step of dehydrating the porous base material, b) a transparent vitrification step of the porous base material, and c). It may be performed in any of a) to c) of the dehydration treatment step and the transparent vitrification treatment step, and particularly preferably a) or c). The addition amount can be controlled by adjusting the gas concentration, the processing temperature, and the like. However, in experiments performed by the present inventors, the width of the adjustment was at most about 1.5 times. Rather, the choice of the type of halide gas is more effective in adjusting the amount of addition. For example, when chlorine gas was used, the content was 0.2 to 0.4% by weight, but when SiCl ₄ gas was used, it was 0.5%. ~ 0.8% by weight
It became. That is, the content can be largely changed depending on the type of gas used. As the porous base material used in the present invention, those prepared by means known in the technical field of this type can be used.
And a porous base material obtained by a gas phase synthesis such as an OVD method. However, the present invention is not limited thereto. Although the bulk density of the porous base material is not particularly limited, it is generally about 0.2 to 0.4 g / cm ³ . In the above description, a porous body made of pure quartz is shown, but any porous body containing quartz as a main component may be used.

[0007]

EXAMPLE 1 First, as shown in FIG. 5, a burner 2 was opposed to a lower end of a starting member 3 vertically supported by the VAD method, and 1400 cc / min of SiCl ₄ was supplied into the burner 2. H
₂ 35 l / min, O ₂ 35 l / min, Ar10
At a rate of 1 liter / minute, the SiO ₂ glass fine particles (porous base material) 1 were deposited on the lower end of the starting member 3. The obtained porous preform 1 had a diameter of 125 mmφ and a length of 500 mm. The porous preform 1 was prepared by using a furnace tube 5 and a heater 4 shown in FIG.
Was inserted into a sintering furnace having The porous preform 1 inserted into the closed system is placed in a furnace maintained at 1200 ° C. as He 10 liter / min. As a halide gas (chlorine-based gas).
Dehydration treatment was performed by supplying 200 cc / min of iCl ₄ . Subsequently, the furnace temperature was raised to 1600 ° C., and He 10 liter /
Then, 200 cc / min of SiCl ₄ was supplied to obtain a transparent glass rod for core (core rod) . When the Cl content of this base material was analyzed by ion chromatography, it was 0.8% by weight. Next, this base material ( core rod ) is 5 mm in diameter.
After that, SiO ₂ glass fine particles were deposited to a thickness of 140 mm therearound by an external method. The obtained base material
(Composite of core rod and glass particle deposit) 135
Inserted in a furnace maintained at 0 ° C., He 10 liters /
After supplying 300 cc / min of SiF _{4 and} adding fluorine, the furnace temperature was increased to 1550 ° C. in the same atmosphere to form a transparent glass. The base material (preform) having the core-cladding thus obtained was made into a fiber having an outer diameter of 125 μm, and the characteristics were examined. FIG. 4 shows the refractive index distribution of the obtained fiber.

Example 2 In the same manner as in Example 1, a pure silica glass rod (core rod) was prepared using Cl ₂ as a chlorine-based gas. The atmosphere in the furnace at the time of the dehydration treatment and the transparency treatment is He 10
Liter / minute, Cl ₂ 200 cc / minute. This base material
The Cl content of the (core rod) was 0.3% by weight. Next, after stretching this base material (core rod) to a diameter of 5 mm,
Around this, 14 fine particles of SiO ₂ glass were
Deposited 0 mm thick. The obtained base material (core rod and
(Composite of lath particulates) was inserted into a furnace maintained at 1350 ° C., and He 10 L / min, SiF ₄ 300
After supplying cc / min and adding fluorine, the furnace temperature was raised to 1550 ° C. in the same atmosphere to form a vitrified transparent glass. The thus obtained base material having a core-clad (preform
Was made into a fiber having an outer diameter of 125 μm, and the characteristics were examined.

Comparative Example 1 In the same manner as in Example 1, CCl ₄ was used as a chlorine-based gas.
Was used to produce a pure quartz glass rod (core rod) . The atmosphere in the furnace at the time of dehydration treatment and clarification is He 10 liter / min, CCl ₄ 20 cc / min, and O ₂ 60 cc / min. The Cl content of this base material (core rod) was 0.05% by weight. Next, this base material ( core rod ) is
m, and then SiO ₂ is stretched around it by an external method.
Glass particles were deposited to a thickness of 140 mm. The obtained base material (composite of core rod and glass fine particle deposit) was added to 13
Inserted in a furnace maintained at 50 ° C., He 10 liters /
After supplying 300 cc / min of SiF _{4 and} adding fluorine, the furnace temperature was increased to 1550 ° C. in the same atmosphere to form a transparent glass. The base material (preform) having the core-cladding thus obtained was made into a fiber having an outer diameter of 125 μm, and the characteristics were examined.

Comparison of Fiber Characteristics Made from Examples 1 and 2 and Comparative Example 1 Regarding the three fibers having different Cl contents obtained as described above, the residual stress, the relative refractive index difference, and the fiber structure (λ
c, MFD) are shown in comparison with FIGS. As can be seen from FIG. 1, the greater the Cl content in the pure quartz glass, the smaller the residual stress after drawing. That is, Cl
It is estimated that the viscosity of the quartz glass decreases as the amount of the base material increases. As a result of reducing the residual stress in the fiber, FIG.
As shown in the figure, the relative refractive index difference between the core and the clad increases as the Cl content increases, and is close to the measured value of the preform. FIG. 3 shows λc, M of each fiber having a different Cl amount.
9 shows FD measurement results. As is clear from FIG. 3, since the relative refractive index difference is closer to the measured value at the preform stage for a fiber having a larger Cl content, λc, MFD
Is close to the predicted value and the fluctuation range is small.

[0011]

As described above, according to the present invention, the viscosity of the core portion of a pure quartz core -fluorine-doped quartz clad single mode fiber can be reduced by increasing the amount of halogen, particularly Cl, in pure quartz glass. As a result, the residual stress generated at the time of drawing can be reduced. Therefore, the core-clad relative refractive index difference after drawing almost matches the actual measurement value at the preform stage, and the λc and MFD characteristics can almost match the predicted values, which is extremely effective.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of Cl during vitrification of pure silica and the residual stress of a fiber.

FIG. 2 is a graph showing the relationship between the Cl content during vitrification of pure silica and the relative refractive index difference between a core and a clad of a fiber.

FIG. 3: Cl content during vitrification of pure silica and λ of fiber
It is a figure which shows the relationship with c, MFD.

FIG. 4 is a diagram showing a refractive index distribution of a pure quartz core-fluorine-doped quartz clad fiber.

FIG. 5 is a schematic view showing a method for producing a glass particle body.

FIG. 6 is a schematic view showing a step of sintering a porous preform.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass particulate body (porous base material) 2 Burner 3 Starting member 4 Heater 5 Core tube

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C03B 37/00-37/16 C03C 1/00-14/00

Claims (3)

(57) [Claims] 1. A method for obtaining an optical fiber by dehydrating a transparent preform containing quartz as a main component and vitrifying the porous preform to obtain a glass preform, wherein the dehydrating step and / or the transparent vitrification are performed. In the process, halogen is added to quartz glass by heat treatment in an atmosphere containing a halogen-based gas. A method for producing an optical fiber, comprising 3 to 1% by weight, using the glass preform obtained as a core of the optical fiber, and using a fluorine-doped quartz glass as a clad. 2. The method according to claim 1, wherein said halogen is chlorine. 3. A core and a fluorine-doped quartz glass clad, wherein the core contains chlorine-containing halogen in an amount of 0.1 to 1 mm.
A quartz-based optical fiber comprising quartz glass containing 3 to 1% by weight.