JP2502617Y2 - Reaction vessel for growing porous optical fiber preform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to improvement of a reaction vessel for growing an optical fiber preform.

(Prior Art) Conventionally, as a method for producing a porous base material of an optical fiber, for example, in the VAD method, SiCl ₄ is put into an oxyhydrogen flame 5 as shown in FIG. Fine SiO ₂
Particles are deposited in the longitudinal direction of the starting material to produce the porous base material 6. In this case, split the burner 4 and reacted with ejected combustion gas and SiCl ₄ to the multi-tube structure, making the GeO ₂ or the like at the same time is ejected reacting GeCl additive such as ₄ from a portion, SiO ₂ And GeO ₂ etc. have a predetermined radial spatial concentration distribution.

In addition, the external method is to supply the additives such as SiCl ₄ and GeCl ₄ into the oxyhydrogen flame to cause flame hydrolysis to generate SiO ₂ and Ge.
While depositing fine particles such as O _{2 on the} outer periphery of the glass rod core material as the starting material, the glass rod core material is moved in the axial direction of the core material,
This is a method of growing fine particles such as O ₂ and GeO ₂ in the axial direction.

Here, Ge is added as an additive to obtain a refractive index distribution.
Although Cl ₄ is mentioned, other additives may be used, and a method of mixing a plurality of additives is also known.

Furthermore, although an example in which an additive is added and reacted at the time of the flame reaction is shown here, a method of forming a pure SiO ₂ porous body and injecting the additive at the time of sintering is also known.

However, as described above, since HCl is generated as a by-product of the flame hydrolysis reaction, the material of the conventionally used reaction container for growing an optical fiber preform is mainly Pyrex glass. FIG. 3 shows a typical example of such a reaction container for growing an optical fiber preform by the VAD method.

In Fig. 3, source gases such as SiCl ₄ and GeCl ₄ are
It is sent to the burner 4 together with H ₂ and O ₂ gas. The raw material gas sent to the burner 4 reacts in the oxyhydrogen flame 5 to produce glass particles such as SiO ₂ and GeO ₂ .

Then, the generated glass fine particles adhere to the periphery of the support rod 7 pulled in the axial direction while rotating, and become the porous optical fiber preform 6.

These reactions are carried out in a reaction vessel 9 made of Pyrex glass, which is close to a cylinder. The entire reaction container 9 is exhausted through the exhaust pipe 8 to the exhaust system so that the internal pressure of the reaction container is higher than atmospheric pressure.
Exhaust is performed so that mmHg is lowered.

(Problems to be solved by the invention) However, although the material of the reaction container for growing a porous optical fiber preform described above was made of Pyrex glass,
The material of the reaction vessel for growing the optical fiber preform made of Pyrex glass is; easily cracked by the thermal strain of the oxyhydrogen flame.

 It is difficult to make a large one.

It is difficult to make a free-form and strong container, and there are restrictions in manufacturing the optical fiber preform.

Pyrex glass contains about 20% by weight of impurities other than SiO ₂ , which reacts with the generated HCl gas and aqueous solution and adheres to the generated porous optical fiber preform growth in the form of gas or fine particles. , Increase fiber loss.

 There is a problem such as.

Therefore, the present invention was made in order to eliminate the drawbacks of the conventional reaction container for growing an optical fiber preform, and the reaction container is made of a high-purity carbon material with a Si surface.
By using a material coated with a C film, it is possible to manufacture a reaction vessel with high strength in a free shape that is not easily cracked even by thermal strain due to an oxyhydrogen flame, and does not cause fiber loss due to the inclusion of impurities. A reaction container for growing a high quality optical fiber preform.

(Means for Solving the Problems) That is, the present invention is; In a porous optical fiber preform manufacturing apparatus configured to be housed, a reaction container for growing a porous optical fiber preform, wherein a material having a SiC film coated on a high-purity carbon material surface is used as the material of the reaction container. The present invention is also characterized in that the film thickness of the SiC film coated on the surface of the high-purity carbon material that constitutes the reaction vessel is 5 μm or more.

(Function) As a material of the reaction container for growing the porous optical fiber base material,
Since a high-purity carbon material coated with a SiC film is used, it has the following advantages.

(Note that the temperature of 500 ° C shown below is the maximum temperature under these operating conditions.) Good corrosion resistance.

That is, the SiC film used was 500
There is no change in weight at the boiling point in aqueous HCl (35%) at ℃.

On the other hand, Pyrex glass is an aqueous solution of HCl (5%, 90%
There is a weight change of about 0.03mg / cm ^{2 under} the condition of ℃, 24hr).

 Good thermal shock resistance.

That is, the SiC film can be rapidly cooled from 500 ° C. to room temperature, but the Pyrex glass is cracked when it is rapidly cooled to 200 ° C. or higher.

 Good workability.

That is, when a reaction container is made of Pyrex glass, the dimensional tolerance after heat processing of the glass is, for example, about ± 1 to 2 mm with respect to the outer diameter of the container of about φ350, while SiC coating is applied. Carbon materials can have a tolerance of at least ± 0.2 mm or less.

 Can manufacture large containers.

That is, when a carbon substrate coated with SiC is used, it is possible to easily produce a reaction vessel having an outer diameter of φ500 or more, but it is difficult to produce Pyrex glass from the viewpoint of workability, time, cost, etc. is there.

 High-purity containers can be manufactured.

That is, the impurity content of Pyrex glass is about
20% by weight, whereas that of the SiC coated carbon material is below 20 ppm.

From the above, it can be seen that it is effective to use a high-purity carbon material coated with a SiC film as a material for a reaction container for growing a porous optical fiber preform.

(Example) Next, a typical example of the present invention will be described.

FIG. 1 shows a schematic structure of a reaction container for growing an optical fiber preform according to a typical embodiment of the present invention.

 FIG. 2 is an enlarged view of the X portion of FIG.

In FIGS. 1 and ₂ , raw material gases such as SiCl ₄ and GeCl ₄ are sent to the burner 4 together with H ₂ , O ₂ , Ar and the like.
Hydrolysis occurs in the oxyhydrogen flame 5 to produce fine glass particles such as SiO ₂ and GeO ₂ .

Then, the generated glass fine particles adhere to the periphery of the support rod 7 pulled in the axial direction while rotating, and become the porous optical fiber preform 6. The exhaust pipe 8 is provided inside the reaction vessel 9.
Is discharged to a waste gas treatment device (not shown).

At that time, the optical fiber preform 6 is axially manufactured in the reaction vessel 9.

The reaction vessel inner wall 1 and outer wall 3 are made of a SiC film. S
The iC film may have a thickness of 5 μm or more, preferably 30 to
200 μm is used, particularly preferably 50-150 μm.

In particular, if the thickness is less than 30 μm, pinholes are likely to occur in the film, and if it is greater than 200 μm, cracks are likely to occur due to thermal strain.

Further, the SiC film is coated on the surface of a heat-resistant high-purity carbon base material.

As described above, since the SiC film is coated on the heat-resistant carbon base material, there is an advantage that troubles such as peeling due to thermal strain do not occur.

Using the reaction vessel of this invention, the optical fiber preform 6 is actually used.
As a result of manufacturing for 6 months, it was confirmed that all the conventional problems can be solved and a high quality optical fiber can be manufactured stably.

In particular, regarding fiber loss, when an optical fiber was made using the glass base material obtained by using the reaction vessel of the present invention as a core, the transmission loss was 0.196 dB / km at the light wavelength of 1.55 μm compared to the conventional 0.196 dB / km. , 0.18 dB / km, which is extremely low, and a clear improvement in transmission characteristics was observed.

(Effects of the Invention) As described in detail above, the reaction container for growing an optical fiber preform of the present invention has no risk of cracking as compared with a conventional reaction container made of Pyrex glass.

 Large reaction vessels are easy to manufacture.

 Free-form can be manufactured.

It is possible to suppress the content of the impurity-containing material to a low level, and to minimize the fiber loss.

 And so on.

[Brief description of drawings]

FIG. 1 is a schematic view of a reaction container for growing an optical fiber preform according to the present invention. FIG. 2 is an enlarged view of part X in FIG. FIG. 3 is a schematic view of a reaction container for growing an optical fiber preform used in a conventional VAD method. 1: Reaction vessel inner wall 2: High-purity carbon base material 3: Reaction vessel outer wall 4: Burner (multi-tube) 5: Oxyhydrogen flame 6: Optical fiber base material 7: Support rod 8: Exhaust pipe 9: Reaction vessel (made by Pyrex )

Claims (2)

(57) [Scope of utility model registration request] 1. A target material for growing a porous optical fiber preform on the tip and an oxyhydrogen burner for producing fine particles,
In a manufacturing apparatus for a porous optical fiber preform, which is housed inside a reaction container for growing a porous optical fiber preform, as a material for the reaction container, SiC is used on the surface of a high-purity carbon material.
A reaction vessel for growing a porous optical fiber preform, characterized by using a material coated with a film. 2. The porous optical fiber preform according to claim 1, wherein the SiC film coated on the surface of the high-purity carbon material constituting the reaction vessel has a thickness of 5 μm or more. Growth reaction vessel.