JPS63139028A - Production of optical fiber glass base material - Google Patents

Abstract

PURPOSE:To produce the title base material having an excellent transmission characteristic by dehydrating the SiO2 glass particles synthesized by a vapor- phase reaction, adding fluorine to the particles, sintering the particles, forming the particles into a tube, etching the inside of the tube, and depositing a synthetic glass film on the inner wall. CONSTITUTION:The soot 5 synthesized from the glass material introduced into the flame of a burner 4 is deposited on a starting material 7 being pulled up while rotating to obtain a pure SiO2 soot body 6. The soot body is heated in a heating furnace in the atmosphere contg. gaseous F or a vaporized fluoride and He, dehydrated, added with F, and sintered to obtain an F-SiO2 transparent glass body having <=1ppm residual OH. The glass body is formed into a tube, a vaporized fluoride is supplied into the tube, hence the tube is etched in the vapor phase. The glass contg. at least the glass material and a vaporized oxidizing agent is introduced into the tube to deposit a synthetic glass on the inner wall of the tube, and the tube is then heated to a high temp. to form a massive solid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a glass base material for an optical 7-eyeper, and in particular, the present invention relates to a method for manufacturing a glass base material for an optical 7-eyeper.
The present invention relates to a method of manufacturing an optical fiber in which the cladding 2 is made of pure 5102 and the cladding 2 is made of F~SiO2.

[Conventional technology]

Conventionally, a fiber structure in which the core is pure 5102 and the cladding is F-8-02 does not contain dopant h'l in the core, so it suffers from various drawbacks inherent to dopant-containing cores, such as increased scattering loss and radiation radiation. Since the increase in loss in the environment can be suppressed to a small level, it is expected that a fiber with good characteristics can be obtained.

However, manufacturing pure 5102 core/F-5102 cland fiber is relatively difficult, and the so-called Vk
D method (vapor phase shaft attachment method, see for example Japanese Patent Publication No. 56-55327), OVO method (external attachment method, for example U.S. Patent No. 5
, 775,075), etc.) alone, the diffusion rate of fluorine is high, and therefore the predetermined fluorine concentration distribution is Difficult to form. In addition, it is difficult to dehydrate the core/cland interface, so it is not easy to produce a fiber having this structure with good characteristics, especially a single mode fiber.

On the other hand, as an example of creating a fiber with this structure using the so-called MCVD method (the thickening method), a quartz glass tube is used as the starting material, and 5IC1!4,02 and SF6. By flowing a fluoride such as OF4, 5xF4 and heating from the outside, F -S 102
After forming a thick glass film on the inner wall of the tube, there is a method of further depositing SiO2 for the core [References 2R, Senshinso et al., In Technical Digest, Conference on Optical Fiber Communication (Optical Society of America), February 1984, 1), TUI3].

[Problem that the invention seeks to solve]

Conventionally, when producing an optical fiber having the structure shown in Fig. 1 using the UCVO method, there was a problem in that when vapor phase fluoride was used as a raw material, the deposition yield decreased, which slowed down the deposition rate of the glass film. Ta.

In addition, since quartz glass is used as the starting glass tube,
The refractive index distribution shape of the resulting fiber will have a so-called diplenite structure as shown in Figure 6. In this case, unless the cladding part 2 is made considerably larger than the core part IK, it will be susceptible to bending loss. There was also the problem of becoming. In the figure, 1 is pure 3102 core, 2 is F-SiO□clad, 3
is the 5102 quartz tube part. In the case of a single mode fiber for a wavelength of 1.3 μm, the diameter of this cladding layer is usually required to be at least 11 times the diameter of the core.

Therefore, when producing a fiber with a pure 5102 core/F-3102 clad structure by the MOVD method, it was necessary to form a synthetic glass layer, especially a cladding layer, very thick at a low synthesis rate.

In addition, after forming a synthetic glass layer to a predetermined thickness, it is further heated to a high temperature to collapse the hollow part using the surface tension of the glass (referred to as "collapse") to form a glass rod. Due to its high viscosity, this collapse operation requires a great deal of energy and time.

In addition, the fiber of the friend structure shown in FIG. 6 has an outermost layer of Si.
What is the expansion coefficient of O2 glass? -Since it is larger than that of SiO2 glass, residual stress in the tensile direction is applied to the outer peripheral portion of the fiber during the drawing process of this base material. This causes the problem that the fiber becomes vulnerable to scratches and strength deterioration is more likely to occur.

In view of the current situation, the present invention was made with the aim of providing a method for easily and efficiently manufacturing a glass base material for an original fiber having a refractive index distribution as shown in FIG. It is something.

[Means for solving problems]

In the present invention, 5102 glass particles synthesized by a gas phase reaction are combined with fluorine gas or gas phase fluoride in a total heating furnace.
Heating in an atmosphere containing , the entire inner surface of the tube is subjected to vapor phase etching treatment, then glass containing at least a glass raw material and a vapor phase oxidizing agent is introduced into the tube to deposit a synthetic glass film on the inner wall of the tube, and then the tube is further heated to a high temperature. This is a method for manufacturing a glass base material for a fiber, which is characterized by heating to solidify the base material.

A preferred embodiment of the special VC of the present invention includes the above method in which the synthetic glass film is made of pure 5102 glass.

The present invention will be specifically described below, starting with various findings discovered by the present inventors during experiments and research, and how the present invention was arrived at based on these findings.

The present inventors have discovered that when further sintering 5lo2 glass fine particles (soot body) obtained by vapor phase synthesis such as VAD method or OVO method to make transparent glass, for example, F2
If gas or gas phase fluoride iHe such as SF6, CF4, 5IF4 etc. is introduced into the soot body in a heated atmosphere,
It has been found that the relative refractive index is 0 to 0.5% lower than that of quartz glass, and that a fluorine-doped molten glass body of 5102 having a uniform refractive index value can be easily exploded.

In addition, by obtaining F-3IO2 molten glass in this way, residual impurities can be reduced, and residual OH groups in the glass can also be +pp
It has been found that it is possible to obtain high quality products with a diameter of less than m.

Furthermore, it has been found that the viscosity of the F--SiO2 molten glass is considerably lower than that of quartz glass.

The present invention employs the F-S x O2 molten glass tube with high purity, low OH group concentration, and lower viscosity than quartz glass as the starting quartz tube for the above-mentioned so-called MOVD method, and uses this as a clamp to form a tube inside the tube. This is a method in which only the SiO2 core layer is deposited on the wall, and then the entire glass base material is collapsed and solidified.

In the present invention, high-purity F-3zO2 glass is synthesized in advance as a SiO2 soot body by a vapor phase synthesis method, and this is mixed with fF2 gas or SF6. IcF4゜5I
It is obtained by fluorine addition sintering by heating to a high temperature in an atmosphere containing a gas phase fluoride such as F4 and He. According to this method, the deposition rate of the SiO2 soot body is not limited by the addition of fluorine, and heating in an atmosphere of Ha and fluorine or vapor phase fluoride reduces the relative refractive index to ~0.5 compared to quartz glass. %F-SiO2 with low and uniform refractive index values
Since molten glass can be obtained, productivity is greatly improved.

Furthermore, the F-310□ molten glass obtained in this way has few residual impurities, and since the vapor-phase synthesized SiO2 soot can be easily dehydrated during sintering, the residual OH group is extremely low at 1 ppm or less. It is of high quality.

The production of pure SiO2 soot by vapor phase synthesis is the second step.
By the so-called VNO method as shown in the figure, soot 5 is synthesized from the glass raw material introduced into the flame of burner 4, and is deposited on starting material Z which is pulled upward while rotating.

Alternatively, as shown in FIG. 3, the soot 5 may be deposited on a rotating refractory starting material 8 such as alumina or zirconia using a burner 4 that moves relative to the starting material 8.

Next, if the F-SiO2 molten glass is in a tubular shape, it is made as is, or if it is in a rond shape, it is made into a tubular shape by drilling a hole using an ultrasonic drilling machine, etc., and this is used as a starting quartz tube for the so-called MCVD method. adopt. This eliminates the need for a process of synthesizing a large amount of cladding layer as in the conventional method, and it is only necessary to clean the inner metal wall of the tube by vapor phase etching, and then deposit only the SiO2 core layer on the inner wall of the tube. Therefore, the problems of low synthesis speed and long synthesis required when creating the F-3102 cladding layer using the conventional MC1VD method are solved, and only the thin core layer needs to be completely synthesized, so the synthetic film Since the shaping process can be completed in an extremely short time, there is no reduction in productivity in this process.

Furthermore, since the inner wall of the F--SiO2 molten glass tube is etched, it is possible to synthesize the base material without impurities in the core/cladding interface.

In the present invention, common gas phase etching includes, for example, F
2 gas and SF6. HF, OF4. Co/2F
2. CClF3゜C(j/, F, NF3.SOF2
．． Various gas phase fluoride gases can be used, such as COF2.02F6. CI is also used as an etching gas for these! It is also possible to use a mixture of other gases such as 2,02, etc. CI! By mixing two gases, it is possible to prevent moisture from entering the glass or to perform etching while dehydrating the glass. 02 By mixing gas, etching can be performed while preventing the accumulation of reducing substances such as C and S.

5102 The synthetic glass film serving as the core layer is prepared using Sl compounds that do not contain H atoms, such as 5IC1!4, 5IBr4. Si, Ci/6, etc. are preferred, and SiO/4, which has a high vapor pressure, is particularly preferred. Further, examples of the gas phase oxidizing agent include o2,03 and the like.

Next, the tube with the core lv synthesized inside is heated to a higher temperature to make it solid, but since most of the glass to be collapsed is F-3102 molten glass, which has a low viscosity, the collapsing operation is very easy. Therefore, the heating energy and time required at this time can be significantly saved. The inventors have an outer diameter of 20n1 and an inner diameter of 5? III various quartz tubes, H2/10
A comparative experiment was conducted to heat and solidify using two burners, and the ratio of the required time was determined, and the results were as shown in Table 1.

Table 1 We also varied the OH concentration (ppm) contained in the F-8xO2 tubes, deposited core layers using these tubes, and fabricated single-mode fibers with these base material all-SiO2 cores/F-s process 02 cladding. The transmission loss value (ds/Km) at a wavelength of 1.3 .mu.m was measured and the results are shown in FIG. 4.

As is clear from FIG. 4, by controlling the OH concentration remaining in the F-3102 tube to 1 ppm or less, a fiber with a loss of t dB/Km or less over a length of 13 μm can be obtained. More preferably, the residual OH concentration to,s ppm or less is desired, and thereby a fiber with a practical loss of about 0.5 clB/Km can be obtained.

Furthermore, in the structure of the fiber obtained according to the present invention, compressive residual stress is applied to the outer periphery of the core, contrary to the structure of the fiber shown in FIG. This makes the fiber more resistant to scratches.

In the present invention, since F--SiO2 glass having a lower refractive index than 5102 is used as the cladding, a pure silica core fiber with low Rayleigh scattering loss and excellent environmental characteristics such as radiation resistance can be obtained.

In the above explanation, pure 51 is added to the F-SiO2 molten glass tube.
The example of depositing 02 was described, but instead of pure 5102, G
602. If the entire glass film containing additives such as P2O5 is deposited, the core becomes SiO2. The cladding is F-310
Fibers with a two-glass structure can similarly be obtained efficiently and with high quality.

Furthermore, during core deposition, for example, Goo/4. Additives that increase the refractive index such as POO/3, or 5IF4. By synthesizing a multilayer film by changing the ratio of other raw materials such as additives that lower the refractive index such as SF6, it is possible to manufacture a fiber with a refractive index distribution as shown in Figure 5 (IL). It is.

Furthermore, the method of the present invention is suitable for manufacturing fibers with a large refractive index difference between the core and the crand, such as dispersion-shifted fibers, which have a complicated refractive index distribution in the core portion as shown in FIG. is also suitable.

Although the above description has focused on single-mode fibers, multi-mode fibers can also be produced efficiently using the method of the present invention. In this case, since the refractive index value of the cladding is lower than that of SiO2, it is suitable for manufacturing a fiber base material with a large core-cland refractive index difference.

〔Example〕

Example 1 A soot body made of pure 5102 glass particles was prepared by introducing the gas phase raw materials shown in Table 2 into a burner using the VAD method whose schematic configuration is shown in FIG.

Table 2 By inserting and installing the obtained soot body in a tube furnace under the atmospheric conditions shown in Table 3, dehydration (first stage), fluoridation (second stage), and transparency (third stage) were carried out. ),
Made of transparent glass. When the OH value of these glass particles was measured using an infrared spectrometer, it was found to be 0, which is the detection limit of the measuring device.
It was found to be less than 5 ppm.

Table 3 The outer periphery of the obtained rod with an outer diameter of 58s + 100mm was ground to an outer diameter of 55F111, and a hole with an inner diameter of 10mm was drilled in the center of the rod using an ultrasonic drilling machine to form a tubular shape. This pipe was ultrasonically cleaned with pure water, and the outside diameter was 2
It was extended to 2 hours. This F-8: Hold the IO2 tube on a glass platen, and heat the wire tube from the outside with a H2)02 burner to approximately +
While heating to 650C, SF was added to the tube at 300C.
CZ min, O2 was flowed at a flow rate of 12/min, and the burner was traversed from side to side four times. Next, after making the burner reciprocate once with only SF6 stopped, add 5 s 1c/4 into the pipe.
The tube was heated at a flow rate of 0 cc/min and O2 flow rate of 200 cc/min, and the flame was adjusted so that the tube became transparent at the high temperature point, and the burner was moved once.

After this, by further increasing the amount of H2)02 supplied to the burner, the temperature of the wire tube was raised to approximately +800C and heated.
The tube was solidified. The moving speed of the burner at this time is 4 m/
minutes, and the blue gold could be completely shaped into a rondo with one traverse.

The obtained base material was drawn into a fiber with an outer diameter of 125 μm, and its transmission characteristics were evaluated, and it was found to be 1.3 μm.
The transmission loss at m wavelength is 0.38 dB/Km,
At a wavelength of 158 μm, it had excellent characteristics of s ds / xm.

〔Effect of the invention〕

As explained above, the method for producing a glass base material for an original fiber of the present invention involves dehydrating, fluoridating, and sintering a 5102 soot body synthesized in a vapor phase, and then melting F-SiO2 with very little residual impurities and residual 0H3L. Using a tube made of glass as the crund layer, using this as the starting tube, the inside of the tube is vapor-phase etched, and then only the core layer is completely formed using the MCVD method, reducing both time and energy consumption, and creating a motherboard of high quality and good transmission characteristics. Materials can be manufactured efficiently.

Furthermore, since the bottom diameter of the core layer type is made solid, the amount of low-viscosity F--SiO2 glass is large, so the collumps operation is easy and the energy cost can be reduced. As described above, the fiber according to the present invention is inexpensive to produce and exhibits very good transmission characteristics, and because the crand is F-SIO2 glass, it has less Rayleigh scattering than a fiber with a pure SiO2 crand. It also has excellent environmental properties, and is excellent in that there is no bending loss that is seen when the outer layer of the land is made of quartz tube, which is the sixth factor, and there is no cause of decrease in fiber strength due to residual stress. be. The present invention is suitable for single mode fibers with a large refractive index difference between the core and the crand, especially 1.5
Although it is advantageous for the production of so-called dispersion-shifted fibers whose dispersion wavelength is in the μm wavelength, it is also effective when used for the production of multimode fibers.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the refractive index distribution of the fiber according to the present invention, Figures 2 and 3 are diagrams showing the refractive index distribution of the fiber according to the present invention.
An explanatory diagram of the process of synthesizing the 102 soot body. The fourth factor is the residual OH@ concentration (ppm) in the F-3102 cland glass and the pure S 102 core/F-
A graph showing the relationship between the transmission loss value (aa7'Km) at a wavelength of 1.3 μm for a fiber with a 3102 cladding. Fig. 6 is a diagram showing the refractive index distribution t- of a pure SiO2 core type single mode fiber by a conventional method (ucvo method).

Claims (2)

[Claims] (1) SiO_2 glass microparticles synthesized by gas phase reaction are heated in a heating furnace in an atmosphere containing fluorine gas or gas phase fluoride and He to perform dehydration and fluorine addition sintering,
F-S with a residual OH amount of 1 ppm or less
The iO_2 transparent glass body is processed into a tube shape, the inner surface of the tube is subjected to vapor phase etching treatment while the tube is heated from the outside, and subsequently a gas containing at least a glass raw material and a vapor phase oxidizing agent is introduced into the tube. 1. A method for producing a glass preform for an optical fiber, comprising: depositing a synthetic glass film on the inner wall of the tube; and then heating the tube to a higher temperature to make it solid. (2) The method for manufacturing a glass preform for optical fibers according to claim (1), wherein the synthetic glass film is made of pure SiO_2 glass.