JPH04270133A - Production unit of porous optical fiber matrix - Google Patents

Abstract

PURPOSE:To obtain the title high-quality matrix by installing filters having mutually identical flow coefficient on the upstream and downstream parts of a reaction chamber to bring gas stream in a perfect laminar flow state. CONSTITUTION:Using a feed fan 8 equipped on the upstream side and an exhaust fan 9 onthe downstream side, air feeding and exhaustion are made at a constant gas flow. The upstream and downstream parts of a reaction chamber 7 having invariant sectional area and circular shape are respectively equipped with filters 5A and 5B with mutually identical flow coefficient, to accomplish dust removal and bringing gas stream to a laminar flow state by its speed set at 0.05-1.5m/s. The inside of the reaction chamber 7 is equipped with (A) a starting material 3 supported so as to be free in advance and retreat thereof across the gas flow route and also free in rotation thereof and (B) a burner 2, facing to said material 3, for allowing glass soot to be deposited thereon, thereby providing ensuring stable and fluctuation-free burning flame for glass material to be ensured the continuation, thus obtaining the objective high-quality matrix 1 with desired refractive index distribution.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for manufacturing a porous optical fiber preform, and more particularly to an apparatus for manufacturing a porous optical fiber preform that can accurately obtain a desired refractive index distribution.

0002

[Prior Art] There are widely known methods for manufacturing porous optical fiber preforms, including various CVD methods such as internal attachment, external attachment, and plasma, and the VAD method developed in Japan. In this way, silicon (Si), which is the main material of the optical fiber base material, and germanium (Ge), which is a dope material for changing the refractive index, are made into a gas phase and sprayed as a combustion flame onto the starting material using an oxyhydrogen flame burner. This is a method in which the material is deposited thereon in the form of soot. In this case, the desired refractive index distribution of the porous optical fiber base material is obtained by controlling the mixing ratio of the various materials mentioned above, and as a result, the flame blown out from the burner fluctuates or its direction changes. The continuation of a uniform and stable flame is an important condition for producing high-quality optical fiber preforms.

[0003] As a conventional technique clearly intended to ensure the above-mentioned manufacturing conditions, the one described in Japanese Patent Application Laid-Open No. 171939/1983 should be noted. In summary, as shown in FIG. 3, a filter 102 is provided on the inlet side of the gas flow, and a gas flow such as air or nitrogen is fed into the reaction chamber 101 with the outlet side facing the duct 103 in a "rectified state" as indicated by the arrow. The burner 2 is attached to the lower end of the starting material 3 rotating in the flow.
This is a technique for producing a porous optical fiber preform 1 by applying a glass soot to the porous optical fiber. The key point of the technology disclosed in this publication is, of course, that the gas flow flowing inside the reaction chamber 101 is in a "rectified state," and the publication emphasizes that this does not cause fluctuations in the flame emitted from the burner 2.

However, the term "rectification" does not exist in fluid mechanics, and the above publication does not give a specific definition, so its details are unclear, but Figure 1 of the same publication, which explains an example, As far as we can judge from (as shown in Figure 3),
It is recognized that the inventor's intention was not realized. This is because in this technology, the filter 10 is only placed on the inlet side of the gas flow.
2 is provided, and the outlet side is connected to the duct 103 with a narrower cross-sectional area, so the flow velocity of the gas flow increases toward the outlet side, and it is not always guaranteed that turbulence will not appear around the flame blown out from the burner 2. This is because it is thought that it will not be done.

[0005]

[Problems to be Solved by the Invention] As is obvious from the above, it is an object of the present invention to realize a completely laminar flow state of the gas flow in the reaction chamber that produces glass soot on the starting material, so that it is uniform and stable. An object of the present invention is to provide an apparatus for manufacturing a porous optical fiber preform that can continue a combustion flame of a glass material.

[0006]

[Means for Solving the Problems] This invention has been made to solve the above-mentioned problems, and includes an air supply fan that is provided on the upstream side and is set to supply a predetermined amount of gas supply air. and an exhaust fan provided on the downstream side and set to exhaust a gas volume equal to the gas supply volume, which has the same flow coefficient as the supply air filter. a reaction chamber partitioned by an exhaust side filter so that its cross-sectional area does not change in the direction of gas flow; and a starter that is rotatably supported in the reaction chamber so that it can move forward and backward in a direction across the gas flow path. The present invention is an apparatus for manufacturing a porous optical fiber preform, which has a burner that is provided to face the starting material and deposits glass soot thereon.

[0007] Furthermore, the present invention is characterized in that in the apparatus for manufacturing a porous optical fiber preform, the burner is disposed so that its axis is parallel to the direction of gas flow in the gas flow path. This is a manufacturing device for porous optical fiber preform.

[0008]

[Operation] The reaction chamber, which has an unchanged cross-sectional area and is partitioned by filters on both sides of the air supply and exhaust sides, is combined with flow rate control of the gas flow, which is adjusted so that the predetermined air supply and exhaust volumes are equal. This achieves a completely laminar state of gas flow inside the glass material, thereby ensuring stable continuation of the glass material flame without fluctuations.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. Air supply fan 8 supplying gas such as air or nitrogen
On the other hand, on the downstream side, an exhaust fan 9 is provided which is set to have an exhaust amount equal to the air supply amount of the air supply fan 8, and one gas flow path is provided between the air supply fan 8 and the exhaust fan 9. is formed. At an appropriate interval in the middle of this gas flow path,
A supply side filter 5A and an exhaust side filter 5B capable of removing harmful dust mixed in the gas are arranged, and a reaction chamber 7 is defined between these two filters 5A and 5B. In the gas flow path, the space from the air supply fan 8 to the air supply side filter 5A will be called an air supply chamber 6A, and the space from the exhaust side filter 5B to the exhaust fan 9 will be called an exhaust chamber 6B.

The amount of air supplied by the air supply fan 8 is set to be large enough to realize a laminar flow of gas within the reaction chamber 7. Of course, this varies depending on the size of the cross-sectional area of the reaction chamber 7, but the approximate gas flow velocity v0 in the reaction chamber 7 is approximately 0.05 to 1.
It is 5m/s.

The reaction chamber 7 is required to have a cross-sectional area that does not change in the direction of gas flow. However, it is preferable that the shape is a hollow cylinder whose axis is in the direction of gas flow, that is, its cross-sectional shape is circular. This is because, together with the fact that the air supply chamber 6A and the exhaust chamber 6B form a truncated cone shape with a small diameter toward the reaction chamber 7, this makes it possible to increase the Reynolds number of the gas flow in the reaction chamber 7. By raising
In other words, this is because even if the flow velocity v0 of the gas flow increases, it helps to ensure a laminar flow state within the reaction chamber 7.

In the reaction chamber 7, of course, a starting material 3 is disposed so as to be able to move forward and backward in a direction transverse to the gas flow and to be rotatable, and an oxyhydrogen flame burner 2 that supplies a glass material in a vapor phase is also provided. This burner 2 may be arranged at an angle with respect to the direction of the gas flow as in the prior art, as shown by the broken line, but it is also possible to arrange it parallel to the gas flow because it disturbs the laminar flow state around the burner 2. It is effective because it is not.

The gas flow path of the present invention is equivalent to the model shown in FIG. 2 if it is shown diagrammatically for easy understanding. In other words,
Naturally, the flow path becomes narrower in the air supply side and exhaust side filters 5A, 5B, and becomes wider in the reaction chamber 7. Therefore, if a completely laminar flow is realized in the reaction chamber 7 as originally planned in this invention, the law of continuity in fluid flow (the flow rate at each cross section of the flow, that is, the product of the cross-sectional area and the flow velocity is constant) is established, and the air supply side and exhaust side filters 5A,
The flow velocity v0 in the portion 5B is higher than the flow velocity v0 in the reaction chamber 7. Just in case, if you add an extra, both filters 5A
, 5B, the flow rate of gas in the numerous narrow passages inside each filter 5A, 5B should be considered. If this is the case, it will be understood that the gas flow rate is naturally faster in the flow path with the smaller cross-sectional area.

[0014]

[Effects of the Invention] According to the present invention, the hydrolysis reaction for producing glass soot is carried out in a reaction chamber with an unchanged cross-sectional area, which is partitioned by filters on both sides of the air supply side and the exhaust side, respectively. By adjusting the supply air volume and exhaust volume of the reaction chamber to be equal, and by controlling the flow rate of a clean gas flow from which dust has been removed, it is possible to achieve a completely laminar state of gas flow inside the reaction chamber. As a result, stable continuation of the combustion flame of the glass material without fluctuation is ensured, which has the effect of producing high-quality porous optical fibers.

Further, in an embodiment in which the burner is arranged parallel to the direction of the gas flow, there is an advantage that a laminar flow state of the gas flow inside the reaction chamber can be realized more reliably.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing one embodiment of the invention.

FIG. 2 is a simplified cross-sectional view schematically showing a gas flow path of the present invention.

FIG. 3 is a side sectional view showing a typical prior art.

[Explanation of symbols]

1 Porous optical fiber base material 2 Burner 3 Starting material 4 Rotary chucks 5A, 5B Air supply side and exhaust side filters 8 Air supply fan 9 Exhaust fan

Claims (2)

[Claims] 1. An air supply fan (8) provided on the upstream side and set to supply a predetermined amount of gas supply air, and an air supply fan (8) provided on the downstream side with an amount of gas exhaust equal to the gas supply amount. In the gas flow path between the exhaust fan (9), which is set to exhaust air, the direction of gas flow is controlled by the supply side filter (5A) and the exhaust side filter (5B), which has the same flow coefficient. a reaction chamber (7) which is partitioned so that its cross-sectional area does not change; and a starting material (3) which is rotatably supported in the reaction chamber (7) so as to be able to move forward and backward in a direction across the gas flow path. ), and a burner (2) provided opposite the starting material (3) and depositing glass soot thereon.
An apparatus for manufacturing a porous optical fiber preform, comprising: 2. The porous optical fiber preform according to claim 1, wherein the burner (2) is arranged so that its axis is parallel to the direction of gas flow in the gas flow path. manufacturing equipment.