JPS62187131A - Method for preparing base material for quartz optical fiber - Google Patents

Abstract

PURPOSE:To prepare a high-quality base material for quartz optical fiber by filling the sol liquid of metallic alkoxide in a hollow porous vessel consisting of the fine glass particles and hydrolyzing it to gelatinize it and thereafter dehydrating all parts and making these transparent. CONSTITUTION:A hollow porous base material 41 consisting of the fine glass particles is formed by a vapor phase synthetic method. An alkoxide sol liquid wherein metallic alkoxide, water and alcohol are made to an essential component is filled in the hollow part of the above-mentioned base material 41. As the above-mentioned metallic alkoxide, one or more kinds of Si(OR)4 (where R is alkyl group) and Ge(OR)4, Sn(OR)4, Pb(OR)2, Al(OR)3, Sb(OR)4, Ti(OR)4, Nd(OR)3, Er(OR)3 and Tb(OR)3 are suitably used. The above-mentioned alkoxide sol liquid is hydrolyzed to gelatinize it and thereafter dried. The porous base material 45 obtained thereby is introduced into a reactor core pipe 42 made of quartz and heated in the atmosphere mixed with He, Cl2 and O2, and all parts are dehydrated and made transparent. Thereby the base material for optical fiber contg. a dopant material such as Ge is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention combines the advantages of both the soot process and the sol-gel method to produce a high-quality silica-based optical fiber base material. It is about the method.

[Conventional technology] Conventionally, methods for producing high-quality silica-based optical fiber base materials include the external method (OVD method) and the vapor phase shaft method (VA method).
There are two methods: a gas phase synthesis method, typified by Method D), and a sol-gel method, in which glass is produced by hydrolyzing metal alkoxides.

In the external method, glass fine particles synthesized by flame hydrolysis are deposited around the starting rod, and then the porous body from which the starting rod is removed is vitrified.The hollow porous matrix is dehydrated and
When making it transparent, that is, making it transparent vitrification, dopants such as GeO2 added to the porous base material for refractive index control volatilize, resulting in a dip in the refractive index at the center of the core. be.

In the vapor phase axial growth method, since a porous base material is grown in the axial direction, it is difficult to precisely control the refractive index distribution, especially to form a complete step-type refractive index distribution.

Furthermore, as a common problem with these vapor phase synthesis methods,
Since the raw materials are supplied in a gas phase and glass fine particles with different compositions are deposited to form a core-clad structure through a flame hydrolysis reaction, the glass materials that can be manufactured are limited, and high melting point raw materials (NdCIL3, ErCj!3) are used. Such)
The disadvantage is that it cannot be used. Furthermore, as a glass material, SiOxNy (oxynitride glass, O<x<20<y<473) is difficult to synthesize using the above-mentioned external method or vapor phase method.

On the other hand, in the sol-gel method, a porous glass base material is produced through a hydrolysis reaction and a dehydration condensation reaction of metal alkoxides, so rare earth raw materials, which cannot be used in the gas phase synthesis method, can be used. This makes it possible to synthesize silica-based optical fibers containing a wide variety of dopant materials. In general, metal alkoxides such as S i (O
Using a mixture of CH3) 4 and Si (OChh CH3, S by treatment in N113 during vitrification
It has been reported that it is also possible to synthesize iOxNy (oxynitride glass).

t /I\ In addition, by controlling the sol composition (in particular, controlling 9H), it is possible to arbitrarily determine the fine fibers of glass particles and the deposition change in the drying process after gelation. Currently, optical fibers with a minimum transmission loss value of 2 dB/km have been developed by synthesizing a core made of pure silica glass using the sol-gel method, and forming an external cladding made of fluorine-doped silica glass using the sol-gel method. was realized.

However, on the other hand, the porous material is very soft immediately after gelling, and the gel material shrinks greatly during drying, which can cause cracks in the gel material at the core-clad interface.・It was difficult to simultaneously synthesize a base material with a clad structure using only the sol-gel method.

[Problems to be Solved by the Invention] Therefore, the purpose of the present invention is to exploit the advantages of the sol-gel method in that it is possible to produce a high-quality base material with high efficiency and to add a wide variety of dopant materials. In addition, by using a hollow porous base material produced by vapor phase synthesis as a structure to support the base material after gelation, and using it as a cladding part after vitrification, it is possible to overcome problems that would be difficult to achieve using the conventional sol-gel method. We have developed a base material for silica-based optical fibers that enables the integral formation of the core and cladding, which was previously difficult to achieve, as well as the formation of a complete step-like refractive index distribution and the addition of various dopant materials, which was difficult with vapor phase synthesis. The object of the present invention is to provide a manufacturing method.

[Means for Solving the Problems] In order to achieve such an object, the present invention uses a hollow porous base material produced by a vapor phase synthesis method in the cladding part, and a hollow porous base material produced by a sol-gel synthesis method in the hollow part. A core part is prepared by.

That is, the present invention forms a hollow porous container made of glass fine particles, and fills the hollow part of the porous container with an alkoxide containing metal alkoxide, water, and alcohol as main components.
After filling the sol solution, the filled sol solution is gelled by a hydrolysis reaction, and the gelled whole is dehydrated and made transparent.

Here, the metal alkoxides include Si(OR)4 (wherein R represents an alkyl group) and (Ge(OR)
4, Sn(OR)4, Pb(OR)2, AJZ
(OR)3.

5b(OR)4, Ti(OR)z, Nd(OR
)3. It is preferable that at least one kind of alkoxide compound consisting of Er(OR)3°Tb(OR)3 is included. The alkoxide compound shown here is
It is a substance that becomes a dopant to increase the refractive index when gelatinized and dehydrated to become transparent.

The alkoxide sol can also contain Si3N4 fine particles.

Furthermore, as a metal alkoxide, 5t(OR)4
It is also suitable to use a mixture of Si(OR)3R and Si(OR)3R, fill a hollow porous matrix with an alkoxide sol solution, gel it, and then vitrify it in an atmosphere containing NH3.

In the second embodiment of the present invention, a hollow porous container made of glass particles is formed, and the main components are metal alkoxide, water, and alcohol, and the metal alkoxide is S 1 (OR
) 4 and prepared so that the specific surface area after gelation is larger than the specific surface area of the hollow porous base material, in other words, the bulk density of the gel body at various processing temperatures during vitrification treatment. A sol solution adjusted so that the bulk density is larger than the bulk density of the hollow porous base material is filled into the hollow part of the hollow porous base material, and alkoxide
The sol solution is gelled, and the gelled whole is dehydrated and made transparent in an atmosphere containing fluorine.

[Operation] The present invention differs from conventional techniques in that the core and cladding synthesis methods are separated.

The hollow porous base material used in the present invention can be prepared by drilling a hole in a porous base material with a bulk density of 0.5 to 1.5 g/cm3 using a method such as carbon or quartz. It can be produced by attaching glass particles around a rod on the outside by a method, or by attaching glass particles around a gas phase shaft by a method, etc., and then pulling out the rod at the center.

On the other hand, by using the hollow porous base material described above as a container for injecting the alkoxide sol and controlling the composition of the alkoxide sol, the particle size after gelation was reduced to 0.1μ.
■By setting the degree of the glass particles to the same level as that of glass fine particles produced by vapor phase synthesis, it is possible to minimize the formation of structural irregularities due to the shrinkage of the gel body during drying and the difference in the shrinkage rate between the core and cladding during vitrification. , it is possible to prevent peeling from the inner wall of the container due to shrinkage during gel drying, and since the outer porous base material also shrinks during vitrification, it can be used as a cladding part without causing irregularities at the interface with the gel body. It can be used.

Regarding the reasons why the gel body does not peel off during gelation and drying,
It is conceivable that after the sol solution is injected, it slightly penetrates into the inner wall of the hollow porous matrix and gels, thereby strengthening the bond between the core and the cladding.

According to the present invention, since the core part and the cladding part are made separately, and the core part is produced by the sol-gel method, it is possible to achieve a complete step-like refractive index distribution, which is difficult with conventional vapor phase synthesis methods. . Furthermore, the present invention can also have the advantage that a wide range of dopant materials can be used, which is a feature of the sol-gel method itself. In particular, as dopant materials, in addition to Ge and N shown in the examples, A
In addition to materials conventionally used in vapor phase synthesis methods such as JZ, Pb, and Sb, rare earth elements such as Nd and Er may also be used.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a diagram illustrating a first embodiment of the present invention,
Here, 41 is a hollow porous base material prepared by a vapor phase synthesis method, 42 is a quartz furnace core tube, 43 is a heater, 44 is a stand that supports the base material, and 45 is a hollow part of the hollow porous base material 41. This is a porous base material made by injecting a sol solution into a part and allowing it to gel.

First, the overall bulk density was 1.0 g/c using the vapor phase synthesis method.
A hollow porous base material 41 having a size of m3 was synthesized. In the hollow part, 5t(0(:83
)4 alkoxide compound Ge (OR) G as 4
e(OCH3)4. (Molar ratio of tuna to St(OCH3)t).

A sol solution consisting of H20, CH30H and NH4OH was injected. Next, the mixture was gelatinized at 70° C. and then sufficiently dried. Next, the base material is placed in the soaking section of the electric furnace, and He
(5J2/min) and Cj22 (70cc/min) at a heating rate of 50°C/hour to 1500°C, held at 1500°C for 1 hour, and then heated to 100°C/hour.
Cooled at a rate of 100 hrs.

In addition, in order to remove organic substances such as unreacted alkyl groups and carbon in the gel body, 02 was further mixed with the above-mentioned mixed gas at a rate of H2/min while the temperature was rising from 0 to 1000°C.

In the base material after transparentization, no interface irregularities were observed between the core and cladding, and a relative refractive index difference of 0.27% was achieved.

Embodiment 2 FIGS. 2, 3, and 4 are diagrams for explaining a second embodiment of the present invention, in which 50 is a base material support;
1 is a hollow porous base material produced by a vapor phase synthesis method, 52
53 is a heater, 53 is a furnace core tube, and 54 is a porous body in which a sol solution is injected into the inside of the hollow porous base material 51 and then gelled and dried.

Figure 3 shows the temperature program during the vitrification process, where the temperature is 0 to 800°C (50°C/50°C) during time 55.
During time 56, the atmosphere was He and NH3 at 800°C for 5 hours; during time 57, the heating rate was 50°C/hour from 800°C to 1000°C; , NH3, CAL 2 mixed atmosphere, time 58
Heating rate: 50°C/hour from 1000°C to 1500°C, He, 02 mixed atmosphere, 1500°C during time 59
, 1 hour, He atmosphere, time 60 shows a cooling process at a temperature decreasing rate of 100° C./hour.

FIG. 4 shows the distribution of the relative refractive index difference measured by a preform analyzer in the range of the core portion and the cladding portion.

First, a metal alkoxide S
5t(QC)Is)t, (SL(QCH3h)C as a mixture of i(OR)4 and Si(OR)3R)
1 (mole ratio of 3(St(OCH3) 4040%) and CH30H, H20, CH40H, then the whole was heated to 70°C
After gelatinization was performed by maintaining the temperature at 110° C., the temperature was gradually raised to 110° C. to dry it.

Next, it was set in the soaking section of an electric furnace and vitrified using the temperature program shown in FIG. In particular, He
2Jl/min, NH32IL/min, 800℃~1000
Up to ℃ He2fL/min, NH3211/min, c12
By processing in an atmosphere of 50 cc/min, N was added only to the core portion according to the following reaction.

In the base material after Si vitrification, no interface irregularity was observed between the core and cladding, and the relative refractive index difference was approximately 0.35 as shown in Figure 4.
%Met.

Example 3 FIG. 5 is a diagram showing the third example of the present invention, in which 71 is a bulk density 0.8 g/g produced by vapor phase synthesis method.
cm3 hollow porous base material; 72 is a porous base material gelled and dried after injecting a sol solution; 73 is a furnace core tube; 74 is a heater; 75 is a base material support stand.

As explained above, 5L (
OCH3)4, C1130H, H20, NH4OH
A sol solution consisting of This sol solution was adjusted to have a bulk density of approximately 1.3 g/cm 3 after drying. The porous base material thus obtained was 11e51/
1000 min in an electric furnace under a mixed atmosphere of 02 11/min
Raise the temperature to ℃ (temperature increase rate 50℃/hour), Question) II
It was heated under a mixed atmosphere of e5u/min and SF6200cc/min.

It has been known that the amount of fluorine added changes depending on the difference in the bulk density of the base material, but in this example, the ratio is also determined according to the difference in bulk density between the outer porous part and the central core part. A refractive index difference of 0.2% was obtained.

Example 4 As explained above, 5t (O
CH3)4, C)130H, H20, NH4 Kano.

A mixed sol solution containing Ge (OCH3) 4 and Nd (OCH3) 3 as an alkoxide compound containing a rare earth element was injected. However, the molar fraction of Ge(OCH3)4 to 5t(OCh3)4 is 3 units51(OCH3)
The mole fraction of Nd (QC) 13) 3 relative to 4 is 0.
003 zero (Nd concentration is 30 ppb). Using a sol solution having such a composition, gelation, drying, and vitrification were performed according to the procedures shown in Example 1.

The core of the resulting base material is slightly colored with Nd, and the relative refractive index difference between the core and cladding is 0.
27! It was. Using the outer base material thus obtained, it was drawn into a single mode optical fiber, and the loss wavelength characteristics were measured. The results are shown in FIG. Due to absorption by Nd2O3, a very large loss value was obtained at a short wavelength of 0.9 μm or less, but on the other hand, a low loss value was obtained at a wavelength of 1 μm×1.4 μm.

Example 5 A sol solution having the following composition was used as a sol solution to be injected into a hollow porous base material.

5t(OCH3)4, CH30H, H20, NH4
OH and i3N4 However, Si3N4 has an average particle size of 0.2 μm and a specific surface area of 1.0 m2/g, and Si (0(:H3)
0.0014 mol of Si3N4 was added to 41 mol, and mixed thoroughly and uniformly.

Using a sol solution having such a composition, gelation, drying, and vitrification were performed in the same manner as in Example 1.

FIG. 7 shows the refractive index distribution of the base material after vitrification. As is clear from FIG. 7, a relative refractive index difference of about 0.2% was obtained.

[Effects of the Invention] As explained above, according to the present invention, the core part and the cladding part are made separately, and the core part is produced by the sol-gel method, which is difficult to achieve with conventional gas phase synthesis methods. A completely stepped refractive index distribution can be achieved. Furthermore, the present invention can also have the advantage that a wide range of dopant materials can be used, which is a feature of the sol-gel method itself. In particular, as dopant materials, in addition to Ge and H shown in the examples, rare earth elements such as Nd and Er are used in addition to materials conventionally used in vapor phase synthesis such as L, Pb, and Sb. May be used.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the first embodiment of the present invention, Fig. 2 is a diagram showing the second embodiment of the invention, Fig. 3 is a temperature program diagram thereof, and Fig. 4 is a relative refractive index difference. Distribution diagram, FIG. 5 is a diagram showing the third embodiment of the present invention, FIG. 6 is a loss wavelength characteristic diagram of the fourth embodiment of the present invention, and FIG. 7 is a diagram of the fifth embodiment of the present invention. It is a relative refractive index difference distribution map. DESCRIPTION OF SYMBOLS 1... Starting rod, 2... Porous base material having a core and cladding, 3...
Synthesis torch, 4... Porous base material 2 from which the starting rod has been removed, 5... Heater, 6... Furnace core tube, 7... Seed rod, 21... Starting seed rod, 22 ... Porous base material with core cladding, 23.
...Torch for cladding synthesis, 24...Torch for core synthesis 25...Heater, 26...Furnace core tube, 31...Teflon container, 32...Sol liquid, 33...32 Porous base material after gelling and drying, 34
...Furnace core tube, 35...Heater, 36...Rod obtained by vitrifying 33, 41...Hollow porous base material produced by vapor phase synthesis method, 42...Furnace core tube, 43 ...Heater, 44...Base that supports the base material, 45...Base material gelled and dried after injecting the sol solution inside, 50...Base that supports 54, 51...Air Hollow porous base material made by phase synthesis method,
52... Heater, 53... Hearth tube, 54... Base material gelled and dried after injecting the sol solution into the inside of 51, 55-60... Temperature program, 61... Refractive index distribution 62... Core part, 63... Clad part, 71... Hollow porous base material, 72... Base material gelled and dried after injecting the sol solution into the hollow part, 73. ...Furnace core tube, 74...Heater, 75...Base that supports base material.

Claims (1)

[Claims] 1) A hollow porous container made of glass particles is formed, and a metal alkoxide, water,
A quartz-based optical fiber motherboard characterized by filling an alkoxide sol solution containing alcohol as a main component, gelling the alkoxide sol solution through a hydrolysis reaction, and dehydrating and making the gelled entire body transparent. How to make the material. 2) As the metal alkoxide, Si(OR)_4(
However, R represents an alkyl group), and (Ge(OR
)_4, Sn(OR)_4, Pb(OR)_2, Al(
OR)_3, Sb(OR)_4, Ti(OR)_4, N
d(OR)_3, Er(OR)_3, Tb(OR)_3
2. The method for producing a preform for a quartz-based optical fiber according to claim 1, wherein the preform contains at least one kind of alkoxide compounds consisting of the following. 3) The method for producing a base material for a silica-based optical fiber according to claim 1, wherein the alkoxide sol liquid contains Si_3N_4 fine particles. 4) A mixture of Si(OR)_4 and Si(OR)_3R is used as the metal alkoxide, the alkoxide sol solution is filled into the hollow part of the hollow porous container, and then gelled, and then containing NH_3. 2. A method for producing a preform for a quartz-based optical fiber according to claim 1, wherein the preform is vitrified in an atmosphere. 5) forming a hollow porous container made of glass fine particles, containing metal alkoxide, water, and alcohol as main components, and containing only Si(OR)_4 as the metal alkoxide;
A sol solution prepared so that the specific surface area after gelation is larger than the specific surface area of the hollow porous container is filled into the hollow part of the hollow porous container, and the alkoxide sol solution is heated by a hydrolysis reaction. gel, and dehydrate and dehydrate the entire gel in an atmosphere containing fluorine.
A method for producing a base material for a silica-based optical fiber, which is characterized by being transparent.