JPS6221728A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To readily control the refractive index distribution and obtain readily the tiled base material having various refractive index distributions, by diffusing a specific alkoxide solution from the inner surface of a pipe of a tubular porous silica material of high purity, drying and sintering the resultant porous silica material. CONSTITUTION:An alkyl silicate is hydrolyzed under acidic, basic or neutral conditions to give a sol, which is ten put in a container, and a rod is inserted into the center thereof. After gelation, the rod is taken out or the sol is put in a rotatable cylindrical container and gelatinized while rotating the container on the axis thereof as a center and gelatinized to prepare and dry a tubular gel and give a porous tubular silica material of high purity which is a dry gel. An alkoxide (solution) of an element, expressed by formula I-IV (R is alkyl) and capable of increasing he refractive index is added to the interior of the tube and diffused into the above-mentioned porous material. The resultant material is slowly dried and heat-treated from room temperature to 300 deg.C to dehydrate the physically adsorbed water. The dehydrated material is then heated to 600 deg.C, heat-treated and decarbonized. Cl2 gas is passed through the material during the heat-treatment up to 900 deg.C to dehydroxylate the material and O2 gas is passed therethrough during heat treatment up to 1,000 deg.C to remove Cl2. Finally, the material if further heated to 1,500 deg.C, and He gas is passed therethrough the density and sinter the material.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing an optical fiber preform.

[Summary of the invention]

The present invention is a method for manufacturing an optical fiber base material, in which a solution containing an alkoxide of an element that increases the oil affixation rate of silica glass is diffused through the inner surface of a tubular porous silica tube to create an appropriate refractive index distribution. We have invented a new method for synthesizing optical fiber preforms by forming .

[Conventional technology]

Conventional methods for manufacturing optical fiber preforms are generally as follows.

1) MOVD method (filling is method) 2) OVPO method (external method is method) 5) VAII method (shaft is method) 1) MC!VIJ method is a method announced by Be1l Institute, and is Silicon tetrachloride, germanium tetrachloride as a dopant, and oxidation gas are fed into the tube, and when heated from the outside of the quartz tube with an oxyhydrogen flame, fine silica particles containing the dopant adhere.The dopant concentration is continuously adjusted in each adhered layer. It is possible to form an appropriate refractive index distribution by changing the target.If it is made solid, it can be used as a base material for optical fibers.On the other hand, 2) OVPO method
This is a method developed by Corning Incorporated, in which fine silica particles are formed on the surface of a quartz glass mandrel through a flame hydrolysis reaction, and then the mandrel is removed and heated to melt to form a transparent base material. The refractive index distribution is formed by controlling the composition of each material. Furthermore, 5) The VALI method is a method proposed by the Ibaraki Telecommunication Research Institute, in which fine silica particles generated in a flame are deposited on the tip of a starting material to form a porous base material, and then a transparent base material is formed in an electric furnace. The refractive index distribution is formed by utilizing the surface temperature distribution of the porous base material when forming the porous base material.

In addition to the above, fiber base materials can also be manufactured by the plasma CV1) method, but this method has not been put to practical use because the plasma flame is unstable.

The above five types of productivity have been put into practical use, and this is the most sophisticated method.

However, the above-mentioned method for manufacturing the five-piece rod has the following drawbacks. In other words, the production speed is slow for all methods, and the fastest VAI
Even with the J method, the maximum at the experimental level is 5t/■, and the M
In the CVLl method, (11f/zonal rate).Also, since the current original fiber price is one order of magnitude higher than the current telephone subscriber price, the Tonnan Corporation Vi optical fiber price is To achieve this goal, we increase the drawing speed and use an inexpensive polymer as the covering material, but in order to make it even cheaper, we use a transparent base material that is lower in cost than the conventional method. A method for creating a transparent matrix is needed.

As a method for creating a transparent base material that is different from conventional methods, an attempt was made to create a transparent base material for optical fibers for swimsuits using a sol-gel method using metal alkoxide as a raw material and heat-treating it in a chlorine atmosphere. (K, 5uSa, I
, Matsuyama, S 5atoh, T, Suga.
numa.

Electronics Letters, 18,
12, 499-495 (1982)).

, this method uses an inexpensive metal alcohol P7 as a raw material,
Since the heat treatment temperature is different from that of the conventional method, there is a possibility that the low-cost transparent T can be used as a method for producing the material.

[Problems and objects to be solved by the invention] However, the above-mentioned prior art has the following drawbacks. In other words, 12 MOVD and 0VPOa have the problems of slow manufacturing speed and high cost as mentioned above, as well as the problems of raw material flow rate in order to create refractive index distributions such as step index, graded index, single mode, etc. There is a difficulty in having to control it to 1gi degree.

2) In the VAD method, Wl! of the oxyhydrogen burner is used to create a refractive index distribution in the same way. However, this method is also difficult to control and has a low yield of -11.

5) The sol-gel method has the problem that the refractive index distribution cannot be controlled using the conventional method.

In addition, as a method for controlling the refractive distribution, porous glass obtained by layering after phase separation of the glass was used.
:There is a molecular stuff ink method that involves diffusion, but the porous glass used in this method has poor purity and cannot be used as a base material for optical fibers, and the dopant is diffused as an aqueous solution, so water-insoluble dopants cannot be mixed in. There is a drawback that there is no

In other words, like Josui, all methods of manufacturing optical fiber preforms have the problem that there is no method for controlling a high refractive index distribution of f:IC on a single surface.

The present invention is intended to solve these problems, and its purpose is to provide a method for easily controlling the high refractive index distribution of treetops.

[Means for solving problems]

The method for manufacturing an optical fiber preform of the present invention includes the following steps:
It is characterized in that it is manufactured by diffusing a solution containing an alkoxide of an element that increases the refractive index of quartz glass, so that the internal refractive index is higher than the refractive index of many parts.

a) Step b of manufacturing a tubular high-purity silica porous body] Alkoxide of an element that increases the refractive index or its ff4
Step C of adding g into the tube of the high-purity porous silica material and diffusing it into the porous silica material] Step of drying the high-purity porous silica material after diffusion d) Sintering the dried high-purity porous silica material The high-purity silica porous material used in the present invention has alkyl 7
Dry gels obtained by a sol-gel method using silicate or finely powdered silica as raw materials, and porous gels made by heat-treating dry gels to increase their strength (hereinafter referred to as sintered gels) are suitable. Furthermore, Mcv, which is a common manufacturing method for optical fiber preforms,
IJ, ovpo.

A porous base material obtained by the VALI method or the like may be used.

The sol-gel method uses markyl-7 silicate as a raw material and hydrolyzes it with acid, base, or neutrality to form a sol, and the other method involves dispersing finely powdered silica in water to form a sol. 5-6 to the PI'11 of the sol after addition.
Alternatively, a basic hydrolysis sol of alkyl silicate is added to an acidic hydrolysis sol of alkyl silicate to adjust the pH to 5 to 6.

The high-purity porous silica used in the present invention may be any dry gel or sintered gel produced by the sol-gel method described above.

Next, as the element alkoxide that increases the refractive index of quartz glass, Ge(OR), , P(OR)s -Ti
(OR)4, A1<oRノ8. (R represents an alkyl group), and others include Ta, BQ, Zr
Alkoxides of elements such as , Nb, T1 are also possible.

When diffusing the above alkoxide from the inner surface of a tubular porous body with a small amount of force, if the alkoxide is a liquid, it can be diffused as it is, but the concentration in the quartz glass after diffusion becomes too high. Therefore, by diluting the alkoxide with an appropriate solvent, the degree of S in the quartz glass after diffusion can be appropriately controlled. The solvents are ethanol, methanol, and propanol.

Alcohols such as butanol and organic solvents such as benzene, acetone and chloroform are suitable.

In the manner described above, the alkoxide of the element that increases the refractive index is diffused and the tubular silica porous body is dried. Since cracks are likely to form during this drying process, it is necessary to dry the product as slowly as possible.

The dried 7υ force porous body thus obtained after diffusion can be sintered by the following process.

a) Decarbonization process by heat treatment from mold temperature to 500℃ b) Decarbonization process by heat treatment from 500C to 600C C) Decarbonization process by passing chlorine gas during heat treatment from 600℃ to 1100℃ Hydroxyl group step (1) Dechlorination step by passing oxygen gas during heat treatment from 900°C to 1200°C e) Densification by passing helium gas or reducing pressure during heat treatment from 1000°C to 1500°C In the process, the transparent quartz glass having an appropriate refractive index distribution in the shape of a hollow tube, which can be manufactured by the above method, is solidified using a burner or the like to form a rod-shaped optical fiber base material.

〔Example〕

Example 1 Commercially available ethyl silicate 208F (1 mol) was mixed with 1N hydrochloric acid (18%) with vigorous stirring using WI1770 to hydrolyze the sol.
(inner diameter 10TBφ, length 100++w) m, t,
In the center of it is made of bopp propylene (outer diameter s x φ length 1
oom) Add the paste and let it gel in this state.

After gelation, the rod was pulled out to form a tubular gel and dried at 60 to 80°C mW to form a dry gel [outer diameter 6N, φ, inner diameter 18
A length of 60 fi] was obtained. Dry gel at 50℃/
Heat to 700℃ at a heating rate of hr to form a sintered gel.

An ethanol solution of 10 percent germanium impropoxide was added to the sintered gel tube and allowed to diffuse for 20 minutes. After drying at room temperature overnight, it was dried at 60° C. for 2 days. Place it in an electric furnace and heat it at 30℃/600℃ from room temperature.
The temperature was raised at a heating rate of hr, held at 600°C for 2 hours, and then chlorine gas was poured at a flow rate of 2j/-. Inkstone 50C/
Raise the temperature to 900℃ for hr and oxygen gas at CL5)/-5
0 minutes, heated to 950℃, and heated in helium atmosphere for 5 minutes.
It was held for 0 minutes and vitrified.

As a result of the above, the Ge in the central part is diffused and the G in the outer part and the outer circumference is
A tubular quartz glass having a double structure in which no tin was contained was obtained. If this is solidified and drawn, a step index type quartz fiber can be obtained. Transmission loss was 20 dB/Ax.

Example 2 Commercially available ethyl silicate 208f (1 mol) was added with PE1 (L
Add 72% of aqueous ammonia and 400% of ethanol and stir to make a sol. This sol was poured into a polypropylene cylindrical container (inner diameter 1011IIφ).

100 m), a polypropylene group 4 (outer diameter 3 φ, length 100 m) was inserted into the center, and gelation was performed in this state. After gelation, the rod is pulled out to form a tubular gel and dried at a temperature of 60 to 80C to form a dry gel (outer diameter 5
Hφ, inner diameter 1.5 φ, length 50-). The dry gel was heated to 900°C at 180°C/hr, held for 5 hours, and further heated to icl 000°C and held for 5 hours to obtain a v8M gel.

A 15 weight percent germanium ethoxide solution in acetone was added to the sintered gel tube and allowed to diffuse for 50 minutes.

Dry at room temperature overnight, then dry at 80°C for 1 day. 'Ft
Placed in an air furnace, heated from room temperature to 400°C and held for 5 hours for decarbonization, and while held at 900°C for 2 hours, chlorine gas was flowed in to perform the dehydration process. Flow the gas for 1 hour to perform the dechlorination process, then vacuum it for 15 minutes.
00tl: Hold it for 1 hour to make sure it becomes vitrified. As a result of the above, a double-structured tubular quartz glass (outer diameter 55 mm, inner diameter 111 mm, length 55 mm) has a central part where Ge is diffused and a peripheral part which does not contain any Go.
was gotten. When this was drawn, a step index type quartz fiber was obtained. Transmission loss is 90 tl
B/1rrtt and friend.

Example 3 To commercially available methyl silicate 1s2f (1 mol), water 72i,
160 methanol was added and stirred to form a sol. This sol was added to a polypropylene cylindrical container (inner diameter 20wφ, length 150+w), and a polypropylene tube (outer diameter 54φ, length 1so+w) was inserted into the center of the container, and it was allowed to gel in this state. . After gelation, the rod is pulled out to form a tubular gel.
Dry the gel at a temperature of 60 to 80°C (outer diameter: 12 mm).

An inner diameter of 3 uφ and a length of 80 mm was obtained. 1 dry gel
The temperature was raised to 700'C at a rate of 00°C/hr to form a sintered gel.

A butanol solution of 50 weight percent germanium butoxide was diffused into the sintered gel tube for 5 minutes. 5 (After drying overnight in an IC, it was dried at 120°C for S days. It was placed in an electric furnace and heated from Tomi to 500°C.
Hold for 0 hours to perform a decarbonization process, flow chlorine gas at 700°C for 2 hours to perform a dehydration process, then flow oxygen gas for 1 hour at 800°C to perform a dechlorination process, and hold for 1000°C while flowing helium gas. It was heated to ℃ and vitrified. Due to the above, G
A double-structured tubular quartz glass (outer diameter 8 φ, inner diameter 2 w φ, length 60 m) having a central part where Ge is diffused and an outer part containing no Ge at all was obtained. When this is solidified and drawn, a step index type quartz fiber is obtained. Transmission loss was 10 dB/kM.

Example 4 Commercially available fine powder silica (Cabosil 200:0
Surface 1R200i/r (trade name) 602 manufactured by Abot Corporation was added to water 120-1 and thoroughly and uniformly dispersed to form a hydrosil. This sol was poured into a polypropylene cylindrical container (inner diameter 2
In addition to a polypropylene rod (outer diameter 5fiφ, length 200w) in the center.
The gel was subjected to gel comparison at 100C in this state. After molarization, the container and rod were removed to form a tubular gel. 1 of 60-80℃
dry gel (outer diameter 1611IIφ, inner diameter 4
A diameter of 160 m was obtained. 100 dry gel
The temperature was raised to 0C and held for 10 hours to form a sintered gel.

A 10 ffit percent ethyl phosphate solution in ethanol was added to the sintered gel tube and allowed to diffuse for 60 minutes. 50
After drying at ℃ for 5 hours, dry at 80℃ for 20 hours. Place it in an electric furnace and raise it from the lowest temperature to 600℃ (decarbonization process), then run chlorine gas at 1000℃ for 5 hours to perform the dehydration process, and then run oxygen gas at 1100℃ for 1 hour to dechlorinate it. Then, while flowing helium gas, the temperature is raised to 1400℃ to vitrify it. While the phosphorus was diffused due to the above,
U-shaped quartz glass with a double structure (outer diameter 10 mm) with a central subdivision and an outer part that does not contain any phosphorus.

An inner diameter of 2.5 fiφ and a length of 120 m) was obtained. When this is drawn with gold wire, a step index type quartz fiber 3 is obtained. The transmission loss was 150d13/7.3.

Example 5 Purified commercially available ethyl silicate 208F (1 mol) with 10
180 g of 2N hydrochloric acid was added, and the mixture was vigorously stirred for hydrolysis. Finely powdered silica (Aerosil 0X5) is added to this sol.
0: Product name of Aerosil's surface 4som','r product] 752? (1.22 mol) was added under stirring and made into a more uniform sol by ultrasonic waves or centrifugation. This sol was added to a polypropylene cylindrical container (inner diameter 2 (1 wφ, length 200 sm), Insert a polypropylene crack hole (external 1L5mmφ, depth 200mm) in the center,
It was gelled in this state. Next, remove the gelling container and rod and make it into a tubular gel. Dry gel at a temperature of 60 to 80°C (outer diameter 14 days φ, inner scratch A, 5IIImφ, length 14
0 wJ was obtained.

Add 5 weight percent germanium impropoxide in propanol to the dry gel tube and allow to diffuse for 10 minutes. After drying at room temperature for 2 days, it was dried at 80° C. for 5 days. Place it in an electric furnace and raise it from room temperature to 500℃ for the decarbonization process, then run chlorine gas at 950℃ to remove hydroxyl groups, then run oxygen gas at 1050℃ for 1 hour to perform the dechlorination process. The temperature is raised to 1,400℃ while flowing helium gas to vitrify it. As a result of the above, a tubular quartz glass with a double structure (outer diameter 10 wφ) has a central part where Ge is diffused and an outer part which does not contain any Ge.

An inner diameter of 2.5 wφ and a length of 1 oom was obtained. This ft
Upon drawing, a step index type quartz fiber was obtained. The transmission loss was '0 OdB/m.

Example row 6 Commercially available ethyl silicate 2080r (1 mmol) made from I#
Add 1800 d of Q.02 normal hydrochloric acid to the solution, stir vigorously and hydrolyze. Finely powdered silica (Aerosi) is added to this sol.
10Xso: A product name of 7529 (12.2 mol) manufactured by Aerosil Co., Ltd. with a surface area of 50 I/2 was mixed with a stirrer, and a homogeneous sol was made by ultrasonication or centrifugation. Add (11N) ammonia water dropwise to this sol to adjust the pH to 4.3.
A firefly. This sol 5j is placed in a cylindrical container (inner diameter 50φ
, length 2000fi), and gelled while rotating around its axis to form a tubular gel (outer diameter 50mmφ, inner diameter 200mm).
φ, length 2000 m). A tubular gel was placed in a suitable perforated container and dried at 10°C to obtain a dry gel (outer diameter 58 φ, inner diameter 1'5 mw φ, length 1500 µ).The dry gel was placed in an electric furnace and heated to 1000°C for 7 days. The product was kept for 10 hours to form a sintered gel.The inside of the tube of the sintered gel was VC5.
Add an ethanol solution of 0C50% manium ethoxide and diffuse for 100 minutes. After drying at room temperature for 1 hour, it was dried at 50°C for 2 days, and then at 80°C for 2 days. Place it in an electric furnace, raise it from room temperature to 4000°C to perform the decarbonization process, flow chlorine gas between 700°C and 1000°C to perform the dehydrogenation process, and then heat it to 1050°C for 1 hour using oxygen gas. Then, a dechlorination step was performed, and the temperature was raised to 1400° C. while flowing helium gas to vitrify the material.

As described above, a tubular quartz glass with a 2N structure (outer diameter 25 m + φ, inner diameter 10 mm) having a central portion where Ge is diffused and an outer portion containing no Ge at all.

A length of 1000 cm] was obtained. When this was drawn, a step index type quartz fiber was obtained. The transmission loss is 80dB/Ian.

Example 7 Purified Shishitomo commercially available ethyl silicate 4,4I and ethanol 6.
71. Add 1.5 j of water and 1 j of ammonia water, stir, and leave overnight. Concentrate with an evaporator. 2.5)
I made it. Hydrochloric acid was added dropwise to this to adjust the PI to 4.0. [This sol is referred to as A] Mayu purified and then added 002N hydrochloric acid [1L6] to 1.9J of commercially available ethyl silicate for hydrolysis. (This sol is B
The above A sol and B sol were mixed and stirred, and then aqueous ammonia was added dropwise to adjust the pH to 4.5. Float this sol 5j in a cylindrical volume 6 (inner diameter 50wφ, length 2000 mm), and gel it while rotating around its axis to form a tubular gel (outer diameter 5
0 φ, inner diameter 20 φ.

The length was 2000 wm). Place the tubular gel in a suitable perforated container and dry it at 60°C to form a dry gel
0 m1 Iφ, inner diameter 161 wφ, length 1600 m) was obtained. Place the dry gel in an electric furnace and raise the temperature to 1050°C.
It was held for a period of time to form a sintered gel.

A 50% germanium isopropoxide solution in ethanol was poured into the sintered gel tube and allowed to diffuse for 180 minutes. After drying at room temperature for 50 minutes at 7'C, drying at 40C for 5 hours and then drying at 90C for 5 days. Place it in an electric furnace and raise the temperature from room temperature to 300℃ for a decarbonization process.
At 900°C, chlorine gas was flown to perform the dehydration process, and the process was carried out for 10
The dechlorination process was carried out by flowing oxygen gas at 00°C for 1 hour, and the temperature was raised to 1500°C while flowing helium gas to vitrify it. As a result of the above, the central part where Ge is diffused and the outer G
Tubular quartz glass with a double structure (outer diameter 26II! lφ, inner diameter 10■φ, length 1
I hope I get 0106O. When this was drawn, a step index type quartz fiber was obtained. The transmission loss was 5 dB/y.

Example 8 Dry gel obtained in the same manner as Example 7 (outer diameter 40 m)
aφ, inner diameter 16 mm diameter, length 1600 mm] was placed in an electric furnace and heated to 1000° C. to form a sintered gel.

Add an ethanol solution of germanium ethoxide with a mold breakage percentage of 5 to the gel tube and let it diffuse for 5 hours.

5 hours at Etan, 10 hours at 40℃.

It was dried at 60°C for 1 day and allowed to mulch. Place in electric furnace and heat to 400℃
Step of dehydration #1tS at 1000C, 1
Dechlorination process at 100℃, vitrification in vacuum at 1450℃. As a result of the above, a tubular quartz glass (outer diameter 26 φ, inner diameter 10+w φ) in which the refractive index force gradually decreases by 1 from the inner surface to the outer surface of the glass tube.

A length of 1060 cm) was obtained. When this was solidified and evaporated, a graded index type quartz fiber was obtained. The transmission loss was 5 dB//ff. Example 9 A solution of germanium propoxide in benzene was added and diffused into a tube of a g-shaped porous base material obtained by the MCVLI method. It was dried at room temperature overnight and at 200°C for one day. Decarbonization process at 500℃ in electric furnace, 1000℃
Then, the glass was sintered in helium at 1,600°C, followed by a dechlorination process using oxygen gas pressure at 1,050°C. Through the above steps, a single-mode step-index type fiber base material was obtained.

Example 10 A propanol solution of aluminum inopropoxide was added and diffused into a tube-shaped porous base material obtained by the ovpo method and the VAD method. Dry at room temperature overnight and at 100°C for 2 days. Placed in an electric furnace, decarbonized at 400°C, dehydroxylated with chlorine gas at 950°C, 1050
Dequaternation step with oxygen gas at ℃, 1 step in helium gas
It was boiled to 600°C, 9!8 degrees solidified, and vitrified. A solid, step-index type fiber matrix was obtained in this glass tube.

As described above using the fire barrel example, it can be seen that step index, grade 7 index, and single mode fiber base materials can be easily manufactured using the method of the present invention. It is clear that the method of the present invention can be applied not only to such a fiber base material but also to the manufacture of various optical components such as Selfoc lenses.

〔Effect of the invention〕

As described above, according to the present invention, a molten alkoxide of an element that increases the refractive index of quartz glass is diffused from the inner surface of a tubular high-purity modified porous base material, and is dehydrated and calcined under appropriate conditions. In this way, quartz fiber base materials having various refractive index distributions can be manufactured.

As a result, it becomes possible to manufacture an optical fiber base material having a refractive index distribution using the sol-gel method, which contributes to the cost reduction of optical fibers. Furthermore, it has the effect that the method for controlling the refractive index distribution in the conventional manufacturing method of optical fiber base material can be simplified.

that's all

Claims (12)

[Claims] (1) A method for manufacturing an optical fiber base material, which is characterized by comprising the following steps. a) Step of manufacturing a tubular high-purity porous silica body b) Adding an alkoxide of an element that increases the refractive index or a solution thereof into the tube of the high-purity porous silica body and diffusing it into the high-purity porous silica body. Step c) Drying the high-purity silica porous body after diffusion d) Sintering the high-purity silica porous body after drying (2) The method for manufacturing an optical fiber preform according to claim 1, wherein the step of manufacturing the tubular high-purity silica porous body comprises the following method. a) Process of hydrolyzing alkyl silicate in acidic, basic or neutral conditions to form a sol b) Adding the sol to a cylindrical container and inserting a rod into the center,
After gelation, the rod is removed to create a tubular gel and dried to form a dry gel, or the sol is added to a cylindrical container and gelled while rotating around its axis to create a tubular gel and dried. Dry gel process (3) The dry gel, which is a high-purity silica porous material obtained by the step b), is heat-treated to an appropriate temperature of 60°C to 1400°C.
A method for producing an optical fiber base material as described in . (4) The method for manufacturing an optical fiber preform according to claim 1, wherein the step of manufacturing the tubular high-purity porous silica body comprises the following steps. a) Step of adding and dispersing finely powdered silica to water or acidic hydrolyzed sol of alkyl silicate to form a silica sol b) Adding silica sol to a cylindrical container, inserting a rod into the center of the container, and pulling out the rod after gelation. The process of creating a tubular gel and drying it to make a dry gel, or the process of adding silica sol to a cylindrical container and gelling it while rotating around its axis to create a tubular gel and drying it to make a dry gel. (5) The dry gel, which is a high-purity silica porous material obtained in step b), is heat-treated to an appropriate temperature of 60 to 1500°C.
A method for producing an optical fiber base material as described in . (6) For the optical fiber according to claim 4 or 5, wherein ammonia water is added dropwise to the silica sol obtained in step a) to adjust the pH value to 3 to 6. Method of manufacturing base material. (7) The method for manufacturing an optical fiber preform according to claim 1, wherein the step of manufacturing the tubular high-purity silica porous body comprises the following steps. a) A first solution containing silica fine particles obtained by hydrolyzing an alkyl silicate with a basic reagent and a second solution obtained by hydrolyzing an alkyl silicate with an acidic reagent at a predetermined ratio. Step b) Add a basic reagent to the sol solution obtained by mixing and adjust the pH value to 3 to 6 to make a sol. b) Add the sol to a cylindrical container and insert a rod into the center.
After gelation, the rod is pulled out to create a tubular gel and dried to form a dry gel, or the sol is added to a cylindrical container and gelled while rotating around its axis to create a tubular gel and dried. Dry gel process (8) Claim 7, characterized in that the dry gel, which is a high-purity silica porous material obtained in step b) above, is heat-treated to an appropriate temperature of 60 to 1500°C.
A method for producing an optical fiber base material as described in . (9) The alkoxide of the element that increases the refractive index is Ge
(OR)_4, P(OR)_3, Ti(OR)_4, A
l(OR)_3, (R represents an alkyl group), the method for manufacturing an optical fiber preform according to any one of claims 1 to 8. (10) Any one of claims 1 to 8, wherein the solvent for the alkoxide of the element that increases the refractive index is an organic solvent such as ethanol, methanol, acetone, benzene, propanol, or butanol. A method for manufacturing an optical fiber base material according to claim 1. (11) The method for manufacturing an optical fiber preform according to claim 1, wherein the step of sintering the dried high-purity porous silica body comprises the following step. a) Decarbonization process by heat treatment from room temperature to 300°C b) Decarbonization process by heat treatment from 300°C to 600°C c) By passing chlorine gas during heat treatment from 600°C to 1100°C Dehydroxylation step d) 900°C to 1
Dechlorination step by passing oxygen gas during heat treatment up to 200°C e) Densification step by passing helium gas or reduced pressure during heat treatment from 1000°C to 1500°C (12) A rod-shaped optical fiber preform is obtained by solidifying a tubular optical fiber preform. A method of manufacturing a base material for optical fiber.