JPH0557216B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for manufacturing an optical fiber preform.

[Conventional technology]

Optical fibers, especially those based on fused silica glass, are fully operational and are currently being used commercially throughout the world. Moreover, the demand for optical fibers is increasing year by year, and along with this, there is a need to supply high quality optical fibers in large quantities and at low cost. Conventionally, as shown in FIG. 3, a method for manufacturing a glass preform, which is the base material of this optical fiber, involves a target rod 1 made of a refractory mandrel or a glass rod prepared in advance.
A known method is to form a glass deposit layer 2 by traversing the oxyhydrogen burner 4 while rotating the target rod 1 and spraying transparent glass or glass fine particles onto the side surface of the target rod 1. In this case, silicon tetrachloride, which is a raw material for glass, is introduced into the oxygen/hydrogen flame of the oxyhydrogen burner 4, and the generated glass particles are deposited. Note that the raw material gas is not limited to silicon tetrachloride, and may be any gas that produces glass fine particles by oxidation. In this manufacturing method, it may be possible to deposit a large amount of glass by using an apparatus that generates a large amount of glass. However, the targets to be deposited, such as mandrels, glass rods, or glass fine particle deposition rods, are usually not very thick.
Using equipment that generates large amounts of glass does not increase the deposition yield. For example, if we consider introducing a metal halide such as silicon tetrachloride into an oxyhydrogen flame for oxidation, even if a burner with an oxyhydrogen flame diameter of about 50 mm is used on a mandrel with a diameter of about 5 mm, the It is known that the deposition yield is only a few percent at most. In other words, in order to ensure a reasonably high yield, the thickness of the flow of glass particles from the glass generator or the thickness of the flow of metal oxide vapor must not be too thin compared to the thickness of the target. is necessary, but increasing the thickness does not increase the deposition yield as described above. Therefore, another method is to deposit glass using a plurality of glass generators. For example, as shown in Figure 4, there are multiple
The burners 4 and 5 of the present invention are traversed parallel to the vertically arranged target rod 1, and a glass deposit layer 2 is formed on the rotating target rod 1. These burners 4 and 5 are oxyhydrogen burners similar to those shown in Fig. 3.
Metal halides such as silicon, germanium, aluminum, boron, and phosphorus are introduced into an oxyhydrogen flame to generate glass particles. When multiple burners are used in this way, the thickness of each burner does not need to be so large, and the overall glass deposition rate can be increased, increasing the overall deposition yield. . Furthermore, in addition to these oxyhydrogen burners 4 and 5, a plurality of high frequency induction plasma torches 9 and 10 as shown in FIG. 5 are used to form a glass deposit layer 2 on the side surface of the target rod 1. , attempts have also been made to increase the deposition rate.

[Problems to be solved by the invention]

However, while it is true that multiple glass generators can deposit larger amounts of glass in a shorter amount of time than a single glass generator, multiple glass generators are usually relatively Since the traverse is performed with a fixed positional relationship, only one glass generating device contributes to the deposition at both ends of the traverse, and as a result, the thickness of the glass deposited layer near both ends becomes thinner, and the thickness of the glass deposited layer near both ends becomes thinner. A sloped portion is formed. The formation of such an inclined portion means that the glass preform does not have the desired diameter in this portion, and only a glass preform with a short effective length can be obtained. That is, glass deposition on the sloped portions at both ends becomes wasteful, resulting in a low deposition yield. In order to reduce the length of this sloping portion, it is conceivable to shorten the distance between the plurality of glass generators, but since the flames of the burners interfere with each other, glass cannot be deposited stably. An object of the present invention is to provide a method for producing an optical fiber base material, which is suitable for mass production of optical fibers, and allows stable glass deposition with a high glass deposition rate and high deposition yield. shall be.

[Means to solve the problem]

According to this invention, a plurality of glass generators supplied with the same raw material are sequentially traversed in one direction parallel to the axis of the target rod, and when they reach the terminal end, they are returned to the starting end and traversed again. In the method for manufacturing an optical fiber base material, the glass generating devices are substantially deposited onto the target rod from each of the plurality of glass generating devices only during a period when the glass generating devices are traversed by the target rod. When one of these glass generators reaches the end of the range where glass is to be deposited, it is moved independently from the other glass generators and returned to the beginning of the range where glass is to be deposited, and then the glass generator is moved again. traverse in the same direction, and when the plurality of glass generators are traversing in the same direction, the distance between them is kept at a distance that prevents their operations from interfering with each other. It is characterized by the following.

[Effect]

A plurality of glass generators are configured to be movable independently of each other, and they are traversed in one direction.
When one glass generating device reaches the end of the range where glass is to be deposited, it is returned to the starting end of the range where glass is to be deposited independently of the other glass generating devices and is traversed again in the same direction as above, and in this one direction. Since glass is substantially deposited on the target rod only during the traversal period, multiple glass generators are used to deposit glass at any position on the target rod one after another. The speed will be very fast. In addition, since each glass generator performs glass deposition during the entire process from the beginning to the end of the range where glass is to be deposited, multiple glass generators perform deposition one after another even near both ends. Therefore, long slope parts are not formed near both ends of the deposited layer, and the length of the part deposited to a uniform thickness can be increased, improving the deposition yield. Furthermore, when glass deposition is actually performed by traversing multiple glass generators in one direction, these glass generators are spaced apart by a predetermined distance, so their operations do not interfere with each other. can be avoided and stable glass deposition can be achieved.

【Example】

In Figure 1, a mandrel, a transparent glass rod,
Target rod 1 consisting of a glass fine particle deposition rod, etc.
The glass lathe 3 is gripped at both ends by chucks 32 so that it can be mounted on the glass lathe 3 and rotated by a motor 33.
One target rod 1 attached in this way
In contrast, in this embodiment, two oxyhydrogen burners 4 and 5 are used. These burners 4 and 5 are supplied with combustible gas such as hydrogen or natural gas and oxidizing gas such as oxygen from a gas supply device 8 to generate a combustion flame. A metal halide such as silicon tetrachloride is introduced from the device 8, and glass is produced by an oxidation reaction. This glass adheres to the side surface of the target rod 1 in the form of fine particles or transparent glass to form a glass deposit layer 2. In addition, although the oxyhydrogen burners 4 and 5 are used here as mentioned above,
It is of course possible to use other glass generating devices such as high frequency induction plasma torches. These burners 4 and 5 can be independently traversed by traverse devices 6 and 7, respectively. That is, burners 4 and 5
are fixed to moving blocks 63 and 73,
These moving blocks 63, 73 move around the frame 6.
Screw shaft 6 attached to 1,62
2 and 72, respectively, and these screw shafts 62 and 72 are rotated by motors 64 and 74 to move in a direction parallel to the axis of the target rod 1. As a result, both the burners 4 and 5 are allowed to traverse the same range of glass deposition from left to right in the figure. These burners 4, 5 produce substantial glass deposition when traversing in one direction (to the right in the figure in this example) and substantially no glass deposition when traversing in the opposite direction (to the left). is configured so that no glass deposition is performed. Therefore, the supply of raw material gas may be stopped during the period of leftward movement, and if the leftward movement speed is high, there is no need to stop the raw material gas. Then, the rightward movement is made at the same speed for burners 4 and 5,
The distance between them is maintained to such an extent that they do not interfere with each other. Here, saying that they do not interfere with each other does not mean that the glass deposits are not affected by each other at all, but rather that there is no substantial obstacle to forming the glass deposited layer 2. The return stroke to the left should be at a sufficiently high speed in proportion to the speed of movement in the right direction. And burners 4 and 5
The direction of glass blowing is 10° to 45° to each other.
Make a certain angle. Next, the glass deposition process using these burners 4 and 5 will be explained with reference to FIG. First, as shown in FIG. 2A, the burner 4 starts moving rightward from the starting end of the area where glass is to be deposited, and the glass generated during this movement is deposited on the side surface of the target rod 1 to form the glass deposited layer 2. Form. The other burners 5 may be placed in any position, but it is ensured that no substantial deposition takes place in some of the burners 5. When the preceding burner 4 reaches a certain distance from the starting end, the burner 5 is started to traverse from the starting end as shown in FIG. 2B, and glass deposition by the burner 5 is started. Then, at each position of the target rod 1, glass is deposited by the preceding burner, and then glass is deposited by the burner 5 that moves immediately after, so the glass deposition rate is twice that of a single burner. Deposition rate. When the preceding burner 4 reaches the end of the area to be deposited glass, it reverses and begins to return to the starting point, as shown in FIG. 2C. This return speed is made faster than the rightward traverse speed. The burner 5 moves to the right at a constant speed, completely independent of the movement of the burner 4, and performs glass deposition. When the preceding burner 4 returns to the starting point, traverse to the right and glass deposition are started again. When the burner 5 that is moving later reaches the terminal end as shown in FIG. 2D, it is reversed and moved leftward at high speed and returned to the starting end. Burner 4 is burner 5
Glass deposition is carried out at a constant rate regardless of this movement of the glass. In this way, since the two burners 4 and 5 are caused to traverse the same area and deposit glass, it is possible to avoid the formation of sloped portions at both ends of the glass deposited layer 2, and to deposit a portion of uniform thickness. It can be made longer. In addition, although two burners were used above for convenience of explanation, it is of course possible to use three or more burners. Next, I specifically manufactured a glass base material using this manufacturing method, and also tried making an optical fiber.
This will be explained. First, a transparent glass rod containing 30% by weight of germanium oxide was prepared in advance. Its outer diameter was 10 mm and length was 700 mm. Pure silica glass rods of the same thickness were fused to both ends of this transparent glass rod to form a target rod. Glass was deposited using two oxyhydrogen burners as described above, with the portion of the glass rod containing germanium oxide as the portion to be glass-deposited. The traverse range was 700 mm, the traverse speed in one direction during glass deposition was 150 mm/min, and the return traverse speed in the opposite direction was approximately 2000 mm/min. The burner interval during glass deposition was set to be at least 300 mm. During glass deposition, gas was supplied to the two burners at flow rates of hydrogen 200/min, oxygen 20/min, argon 1/min, and silicon tetrachloride 1/min, and the glass deposition was carried out at approximately 6/min.
After some time, it was possible to obtain a glass fine particle deposited layer with an outer diameter of 140 mm and a length of 650 mm at the outer diameter portion. This layer of glass fine particles is heated to approximately 1650°C.
By heating in a heating furnace, the glass rod was turned into transparent glass and the entire glass rod was made of transparent glass. This glass rod is a so-called optical fiber preform, and when this preform was drawn into a fine fiber in a heating furnace with a maximum temperature of approximately 2100°C, the transmission loss at a wavelength of 0.85 μm was observed.
A practical optical fiber of 3.5dB/Km was obtained.

【Effect of the invention】

According to the method for producing a glass base material of the present invention, a large amount of glass can be deposited in a very short time, the deposition operation can be performed stably, and the length of the portion of the deposited layer with uniform thickness can be reduced. It can be lengthened to reduce slopes and improve deposition yield.

[Brief explanation of drawings]

FIG. 1 is a perspective view of one embodiment of the present invention, FIGS. 2A, B, C, and D are schematic diagrams showing each state for explaining the operation, and FIGS. 3, 4, and 5 are Each is a schematic diagram of a conventional example. 1...Target rod, 2...Glass deposit layer, 3
...Glass lathe, 4,5...Oxyhydrogen burner, 6,
7... Traverse device, 8... Gas supply device,
9,10...High frequency induction plasma torch.

Claims (1)

[Claims] 1 Multiple glass generators supplied with the same raw material are sequentially traversed in one direction parallel to the axis of the target rod, and when they reach the terminal end, they are returned to the starting end and traversed again. In the method for manufacturing an optical fiber base material, the plurality of glass generators are movable independently of each other, in which glass is deposited substantially on the target rod from each of the plurality of glass generators only during a period of time during which the glass generators are used. When one of these glass generators reaches the end of the range where glass is to be deposited, it is moved independently of the other glass generators and returned to the beginning of the range where glass is to be deposited and again in the same direction as above. In addition, when the plurality of glass generators are traversing in the same direction, the distance between them is maintained at a distance that does not interfere with each other's operations. Characteristic method for manufacturing optical fiber base material.