JPS62246835A - Production of base material for quartz glass optical fiber - Google Patents

Abstract

PURPOSE:To pour the 2nd sol closely into the gelatinized matter of the 1st sol in a manner as to avoid generation of foam by pouring the 2nd sol under a reduced pressure into the 1st sol which gels to a tubular shape in a cylindrical vessel to gel the same. CONSTITUTION:The gelation is executed while the system for pouring the 2nd sol is maintained under a reduced pressure in a method for manufacturing a fiber made into two-layered structure having a refractive index distribution by gelatinizing the 2nd sol in the 1st sol which gels to the tubular shape in the cylindrical vessel. The wet gel of the form in which a hole is not bored in the central part is manufactured in the above-mentioned method particularly in the case of gelatinizing the 1st sol while rotating the same, then pouring the 2nd sol. The yield up to the final stage and the quality are remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a silica glass optical fiber by a sol-gel method.

[Conventional technology]

Transparent silica glass has excellent optical transparency in a wide wavelength range from ultraviolet to infrared, and is chemically stable.
It has attracted particular attention in the field of optical communications. Nowadays, when we talk about optical fiber, we generally refer to silica glass-based optical fibers. 15 MCVD and MAD methods are well-known methods for manufacturing silica glass-based optical fibers, but recently they have become cheaper. The sol-gel method is attracting attention as a means of manufacturing high-quality optical fibers.

In the sol-gel method of manufacturing silica glass optical fiber, *sg1 sol is adjusted for clad material. Gel it while rotating it in a tube shape, and then gel the second sol adjusted for the core inside it? There is a patent that allows (Head office organization review [Problems that the invention aims to solve]) However, with the conventional method, in order to increase the yield,
f, If the interval between the time when the sol of 1 is gelled and the time when the second sol is gelled is shortened, it is difficult to obtain a solid dry gel. Therefore, there was a drawback that it was necessary to pour a second sol during rotation to prepare a hollow fiber and dry it so as not to damage the hollow part. In addition, if fine air bubbles enter at the time of pouring the second sol, the air bubbles may remain even after vitrification, and it is necessary to perform a complete deaeration operation by reducing the pressure in advance. Problems like this? Is it something that is destined to be solved, and its purpose is the first sol? The second sol is poured into the gelled material without any gaps and without the generation of bubbles, etc. [Means for solving the problem] Production of the quartz glass-based optical fiber base material of the present invention to the method,
Will gel in a tubular shape, at least in a cylindrical container
In the method for producing a two-layer fiber with a refractive index distribution by gelling the second sol inside the sol, the system into which the second sol is poured is under reduced pressure. do.

〔Example〕

The present invention will be described in detail below based on Examples.

[Example 1] ■ Preparation of hydrolysis solution Add 0.0 to 576.6 tons of purified commercially available ethyl silicate
Add 199.5ff of 2N hydrochloric acid, stir vigorously and hydrolyze to obtain hydrolysis solution A.Purified commercially available ethyl silica) 134.11P and 17.4ff of 0.2N hydrochloric acid.
After adding fp and stirring vigorously while keeping the reaction solution below 5°C, the reaction solution turned into a homogeneous and transparent solution after about 30 minutes. Tetraethoxygermanium 1t65F while keeping this clear solution below 5℃? Add little by little and stir well to react. After reacting for 20 minutes, 32.5 t of water was added to the reaction solution while keeping the temperature below 5°C, and the reaction was carried out with thorough stirring to obtain a hydrolyzed solution B.

■ Preparation of a solution containing ultrafine powdered silica (purified reprinted ethyl silica) 881. Q f,
Absolute ethanol 470817. Ammonia water (29%
) 282.4m and 504.8t of water were mixed, stirred vigorously for 2 hours, and allowed to stand overnight in a cool, dark place to synthesize ultrafine powdered silica.This solution was concentrated to about 6000R1f under reduced pressure.
After setting it to 00d, the pH was adjusted using 2N hydrochloric acid (['!-
After adjusting the temperature from approximately
I got RXL. This solution has an average particle size t of 0.14 μm.
Ultrafine powdered silica with 254.1? include. (
Calculated assuming a silica concentration of approximately 0.520t/rat and a yield of 100cm. )■) Preparation of sol solution and gelation hydrolysis 'Solution A and 4/5 of the solution containing ultrafine powdered silica? Mix and make sol solution A 7toSimilarly, mix 1/5 of the solution containing hydrolyzed solution B and ultrafine powder silica and make sol solution B 7to At this time, the volume of sol solution A is about 145%.
0WL1% PH value is about 5.62, the volume of sol solution B is about 360u/, the PH value is about 2.78, and 9◇ Next, use 0.2N ammonia water and water for sol solution A. to adjust the pH value to f4.71, and the volume to 1600 m
J? The first sol for cladding was prepared completely. Effective glass component: 0.2510 f/wtl, calculated value 1206-4111fs This sol was transferred to a cylindrical rotating container made of vinyl chloride (inner diameter: 4011Is, length: 10201Kg, internal volume: 1256.61tj), whose inner surface was coated with silicone. A cylindrical rotating container with a tight lid equipped with a device that evacuates the inside of the container and a ninth device that pours the solution into the tube during rotation? What is the O PH value you put on? After adjusting to 4.71, after 50 minutes, it started rotating at 750 rpm, and gelation occurred 10 minutes after starting rotation. So-called length 1000
Tubular wet gel tube with dimensions of mm tube. (The tubular wet gel is in a cylindrical rotating container.) In parallel, 0.2 cubic feet of ammonia water and water are added to the sol solution B to adjust the pH [? 4.12, and the volume Th400WLl
A second sol was prepared by adjusting the concentration to an effective glass fraction concentration of 0.
2355f/d.

The calculated value was poured into a rotary container 12 minutes after gelation, after the sol was completely rotated to create a vacuum of 10 mmHg, so that the tubular gel was completely filled with the second sol. P.H.
(ii? At 100 to after adjusting to t12, this solution also gelled, and a wet gel with a coaxial structure was obtained.
0O ■ 100 wet gels made using the same method as drying? It was aged in a cylindrical rotating container in a closed state at 50℃ for 2 days, and then the open area ratio was 0.4%. The wet gel was transferred to a polypropylene drying container and then placed in a dryer at 60°C to dry the wet gel.
Stable dry gel that does not crack even when left at room temperature (outer diameter 27
．． 0 'Im, length 675 dragon - average value) yield 100
100 pieces were obtained in % n0 ■ Sintering Next, this dry gel was placed in a quartz tubular sintering furnace and heated from 50°C to 200°C at a heating rate of 30°C/hr, and held at this temperature for 5 hours. , followed by a heating rate of 50℃/h
The sample was heated from 2.00° C. to 500° C. at this temperature and kept for 5 hours to perform desorption. Subsequently, it was heated from 300°C to 1100°C at a temperature increase rate of 30°C/br, and held at this temperature for 50 minutes to perform decarbonization, dechlorination ammonium treatment, and acceleration treatment of dehydration condensation reaction. Continued 7
When the temperature is lowered to 00℃, He 2 l/sin, CI, 0
．． Hold for 30 minutes while flowing a mixed gas of 21/sia, then only He? Temperature increase rate 60℃/h from sink
800'ct"t' heating at r1. to a a o ℃
He 21/win, CI.

0, 2. Hold the mixture for 1 hour while flowing a mixed gas of l/sin, and then increase the temperature to 60℃ without flowing only He.
/hr to 900℃ and fo900℃ to He21
/sin, clta, 2 J/■ia was kept flowing for 1 hour to remove OH groups.
Next, Ox rJ-4 for He 21 /mia
The temperature rise rate is 60℃/ without flowing the mixed gas of 1/sin.
The mixture was heated to 1050° C. for 1 hour and held at this temperature for 1 hour to perform dechlorination treatment. Subsequently, without flowing only He, it was heated to 1250° C. at a temperature increase rate of 30° C./hr, and held at this temperature for 30 minutes to perform a pore-closing treatment.

Next, the sample was transferred to a box furnace and heated at a rate of 6 from 1200℃.
Heat to 1350°C at 0°C/hr, and at this temperature 1
After holding for a period of time, the material became non-porous and a transparent preform for optical fiber was obtained. Also, there is no cracking during the sintering process, and the yield is H1oo%.
The size of this optical fiber base material was 18.
The diameter of the part corresponding to the core was 5.7cm. (Loss is less than 1-) When the OH groups contained in the optical fiber base material obtained in this example were quantified by measuring the absorption spectrum in the infrared region, no absorption peak at 2.7 μm was observed. It has been confirmed that it is below 1m)pm. A high-quality single-mode optical fiber was obtained without foaming even when the glass body was drawn by covering it with a quartz jacket tube and fusing it.

[Example 2] A first sol was prepared by performing the operations according to Example 1, and
After 7 rotations of gelation, the rotation device was stopped 12 minutes after gelation, and the second sol? Pour into a vertical wet gel tube and let it gel. The obtained wet gel was dried and sintered by the same operation 7 as in Example 1, and an optical fiber base material was produced with a yield of 90 cm.It was covered with a 0-mt quartz jacket tube and fused, and the glass When the body is drawn, 2% of it foams and ft-.

[Example 3] Perform all operations according to Example 1 to prepare the first sol,
12 minutes after the gelatinization, after the meal, while rotating, add the 20th sol. 20M pour,
Rotate it 11 times to create a tubular wet gel. So f'
When drying and sintering according to Lf Example 1, the yield was 1.
00% is the production rate of optical fiber base material. Another quartz jacketed tube? The glass body that is covered, fused, and solidified? It did not foam even after drawing the line, but when drying, the inner surface of the 20 pieces was scratched, increasing losses.

[Example 4] ■ Preparation of hydrolysis solution Purified commercially available ethyl silicate 549.1 F was added with 218 alf of absolute ethanol, stirred thoroughly, and then
．． 02 normal hydrochloric acid 190. Of? Add, stir vigorously to hydrolyze, and prepare hydrolyzed solution A.

Purified commercially available ethyl silica) 127.7F and absolute ethanol 55d? Add and stir well.
Regular hydrochloric acid 11. Of? Add and stir vigorously for 60 minutes.
o Add 11.1% tetraethoxygermanium to this reaction solution.
01F? Add it little by little and stir well. After vomiting for 20 minutes, add 56.5f'f of hydrochloric acid to this reaction solution.
A hydrolyzed solution B was obtained by adding f and reacting with thorough stirring.

■ Preparation of solution containing ultrafine powdered silica Purified and commercially available ethyl silica) 839. OIF.

Absolute ethanol 44841111. Ammonia water (29
h) 269. After mixing Od and water at 290.3 F and stirring vigorously for 2 hours, the mixture was kept in a cool and dark place overnight to synthesize ultrafine powdered silica. Approximately 5,700 of this solution was concentrated under reduced pressure to give 6
After adjusting the PHM to 40 d, the PHM was adjusted to about 8 d using 2N hydrochloric acid.
22 to 4.60, remove foreign substances etc. by rough centrifugation, and remove approximately 710 d of solution containing ultrafine powder silica. Obtained. This solution contained 242% of ultrafine powdered silica having an average particle size of 0.14 μm. (Value calculated assuming silica concentration of approximately 0.541flIll and yield of 100%) ■ Preparation of sol solution and gelation 4/5 of the solution containing hydrolyzed solution A and ultrafine powdered silica
? The mixture was mixed to obtain sol solution A. Similarly, 1/5 of the solution containing hydrolyzed solution B and ultrafine powdered silica? The mixture was mixed to obtain sol solution B. At this time, the volume of sol solution A is approximately 1550ml
%PHMn is about 4.54, and the volume of sol solution B is about 5
90m1. The pH value was approximately 4.57.Next, 0.2 cubic feet of ammonia water and water were added to the sol solution A to adjust the pH value to 5.32, and the volume was 1600m/
Prepare the first sol 1 by adjusting the ratio. (Effective glass component concentration 0.220 t/rttl, calculated value) 120 of this sol
6.4mj? % Cylindrical rotating container made of vinyl chloride with silicone coating on the inner surface (inner diameter 4011J length 102102
(inner volume: 1,256.6 m). Put a lid on this cylindrical rotating container, attach it to the rotating device, and check the pH value?
120 30 minutes after adjusting to 5.52
Started rotating with Orpm.

Gelation occurred 15 minutes after the start of rotation, but after 10 minutes of rotation, the outer diameter was 401111. Inner diameter 8, O
We obtained a tubular wet gel with dimensions of length 100C110. (The tubular wet gel is in a cylindrical rotating container) In parallel, sol solution B was prepared using 0.2N ammonia water and water to determine the pH value? 5.12 and the volume to 400 ml to prepare the next solution.Effective glass component concentration 0.22459/ml (calculated value), remove the water from the rotating device, and leave the cylinder standing still. After removing the lid of the rotary container and pouring this solution into the tubular wet gel after 12 minutes of gelation,
Vacuum was applied to rnHg. Ten minutes after adjusting the PI value to 5.12, this solution also gelled, and a wet gel with a coaxial structure was obtained.
1, length 1QOOWW1) ■Drying 20 wet gels prepared in the same way were aged in a cylindrical rotating container at 30°C for 2 days in a sealed state.
Of these, 100 were transferred to a polypropylene drying container with an opening ratio of 0.1 inch, and the remaining 10 were placed in a cylindrical rotating container with lids with an opening ratio of 0.1% on both ends. When the wet gel was dried in a dryer at 17°C, a stable dry gel (outer diameter 26.5 mm, length 663 fl - average value) that did not crack even when left at room temperature was obtained in 17 days. 'jo If the former method is selected as the drying method, the yield will be 90%, and if the latter method is selected, the yield will be 80%.

(2) Sintering When all 17 dry gels were sintered using the same method as in Example 1, an optical fiber base material was obtained with a yield of 90%. The size of this optical fiber base material is 18.5m1t in diameter.
, the length is 465 mm, of which the diameter of the portion corresponding to the core is 765.7 m, and the absorption spectrum of the OH groups contained in the optical fiber base material obtained on the real side is measured in the infrared region. When quantified by
No absorption peak was observed at all, and it was confirmed that the absorption peak was less than %lppm. Mat#j! A high-quality optical fiber was obtained without foaming even when it was pulled.

As shown in this example, using alcohol when preparing a hydrolysis solution saves the effort of cooling and is more practical than when alcohol is not used. 1 liter, mixed with a hydrolysis solution or a solution containing ultrafine powdered silica.
The viscosity of the sol solution is also lower, making it easier to work with.

[Example 5] After gelling the first sol in the same manner as in Example 4,
After preparing and pouring the second sol, it was covered with a lid and allowed to gel, and then dried and sintered according to Example 3. An optical fiber preform was manufactured with a yield of 85%. OH
It was confirmed that the amount was 1 ppm or less when determined from the infrared absorption of the base, and foaming occurred at a rate of 1.5 cm when drawn.

As shown in the examples above, after gelling the first sol,
Inside the system when pouring the second sol? By reducing the pressure, the yield up to the final process and the fiber quality can be improved. Foaming during line drawing can be prevented. This method is effective in all manufacturing methods in which the fiber is manufactured by completely gelling the first sol and gelling the second sol inside the first sol.

〔Effect of the invention〕

As described above, according to the present invention, wc2
In the method of manufacturing a two-layer fiber with a refractive index distribution by completely gelling the sol, the system into which the second sol is poured is under reduced pressure, which improves the yield and quality in the final process cabinet. be able to. Especially w41
When the second sol is gelled while rotating, it is possible to create a wet gel without a hole in the center, which significantly improves the yield and quality up to the final process. be able to.

that's all

Claims (6)

[Claims] (1) A method for producing a two-layered fiber having a refractive index distribution by gelling a second sol inside a first sol gelling into a tubular shape at least in a cylindrical container. 2. A method for producing a base material for a silica glass optical fiber, characterized in that the system into which the sol is poured is under reduced pressure. (2) The first and second sols are alkyl silicate, acidic aqueous solution, alcohol solution, and have an average particle size of 0.0.
The silica glass-based light according to claim 1, which is a solution containing, if necessary, silica fine particles or a dispersion thereof having a particle diameter of 1 to 1/μm, and a dopant for adjusting the refractive index. Method for manufacturing fiber base material. (3) The method for producing a base material for a silica glass optical fiber according to any one of claims 1 to 2, wherein the acidic catalyst is hydrochloric acid or hydrogen chloride gas. (4) As the silica fine particles, white carbon obtained by hydrolyzing SiCl_4 with an oxyhydrogen flame burner, ultrafine powder silica obtained by a wet method using sodium silicate as a raw material, or alkyl silicate hydrated with aqueous ammonia. 4. A method for producing a preform for a silica glass optical fiber according to any one of claims 1 to 3, characterized in that any one of ultrafine powdered silica obtained by decomposition is used. (5) As the dispersion solution of the silica fine particles, the amount of silica contained in the aqueous solution containing the silica fine particles described in the previous section and 0% or more of alcohol with respect to the solvent is 0.01 to 1.0 g/c.
m^2, or a solution containing ultrafine powder silica obtained by hydrolyzing an alkyl silicate with aqueous ammonia containing 0% or more alcohol. Amount is 0.01-1.0g
5. A method for producing a preform for a silica glass optical fiber according to any one of claims 1 to 4, characterized in that the preform is concentrated to a concentration of /cm^2. (6) The additive element is Ge, Ti, P, B, Al, Z
6. The method for manufacturing a preform for a silica glass optical fiber according to any one of claims 1 to 5, characterized in that the preform is r, Sb, Ta, or Nb.