JPS6045133B2 - Method for manufacturing base material for optical glass fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a preform for optical glass fibers, which is highly pure and free of impurities.

1. The method for manufacturing a base material for optical glass fiber includes forming glass layers with different refractive indexes on the inner wall surface of quartz glass, and then
The method described in JP-A No. 50-120352 (internal attachment method) for solidifying the central space, and the method described in JP-A-49 for forming a layer of glass fine particles on the outer surface of a cylindrical seed rod by fire hydrolysis. The method described in No. 100551 (external attachment method) is known.

In the former method, a glass layer through which light propagates is formed on the inner wall surface of the glass tube, and the glass tube and the formed glass layer are integrated into an optical glass fiber base material, so the purity, shape, and quality of the glass tube itself are improved. Directly affects the properties of optical glass fiber base material.

Moreover, since the glass tube is heated from the outside surface of the glass tube with a heating source such as an oxyhydrogen flame, and the inside of the glass tube is heated by heat conduction, fluctuations in the wall thickness of the glass tube and non-uniformity such as ellipse can occur. If there is, the temperature distribution inside the tube will be uneven,
This causes variations in the thickness of the glass film that is formed, causing non-uniformity in the roundness of the resulting base material and in its properties depending on location. Moreover, since heating is performed through a glass tube, if the tube diameter is increased beyond a certain level, the temperature inside the tube will become lower near the central axis, which will deteriorate the reaction efficiency of the raw materials, so there are restrictions on the thickness of the quartz tube. For this reason, the size of a single base material is also limited, and it is difficult to produce a long fiber base material. In the latter method, halides, which are raw materials for glass, such as silicon tetrachloride and germanium tetrachloride, are hydrolyzed with moisture generated by an oxyhydrogen flame, so the resulting base material inevitably contains one of the impurities. The 0H group will be included.

The OH group contained in glass has a fundamental absorption band at a wavelength of 2.73 μm and harmonic absorption bands at wavelengths such as 1.37 μm and 0.95 μm. Moreover, the absorption band combined with the glass constituent SiO2 has a wavelength of 1.24 μMlO. They occur at 88 μm, and these absorption bands have relatively wide tails, so
This causes deterioration of the loss characteristics of the optical fiber. ．． In particular, the absorption peak of OH groups at 1.37 μm reaches as high as 60 dB/Km due to the presence of 1 ppm of OH groups, which is an impurity that poses a major obstacle to reducing loss in long wavelength bands. The present invention solves the drawbacks of the above-mentioned conventional methods! In order to prevent the contamination of impurities from the outside, the quality of the quartz tube does not affect the characteristics of the optical fiber.The glass is deposited in a closed tube, and all the materials used to make the optical fiber are synthetic. It is characterized by being made of glass, and its purpose is to obtain a high quality optical fiber base material that is free from any impurities.

The present invention will be explained in detail below with reference to the drawings. Example 1 1st
The figure is a schematic diagram of an embodiment of the present invention, in which 10 is an oxygen gas supply port, 11 is a flow rate controller that controls the flow rate of oxygen gas introduced from the supply port 10, and 12 is a main component of SiCl4.
a flow controller that controls the flow rate of the carrier gas carrying the vapor;
13 is a flow rate controller that controls the flow rate of a carrier gas that carries raw material GeCl4 vapor for controlling the refractive index, and 14 is a carrier gas that carries raw material PCl3 or BBr3 vapor for controlling the refractive index and lowering the glass melting temperature. 21 is a flow rate controller for controlling the flow rate of the main component raw material SlCl.
22 is a container storing raw material GeCl4 for controlling the refractive index, 23 is a raw material PCl3 or BB for controlling the refractive index and lowering the glass melting temperature.
A container 24 in which R3 is stored is a container in which the carrier gas containing each raw material vapor and oxygen gas are combined; the mixed gas with a desired mixing ratio of raw material vapor and oxygen gas is introduced into the reaction container. 25 is an exhaust port for discharging unreacted gas and surplus gas, 31 is a reaction container for sealing the reaction part,
32 is a starting carbon rod to be heated by high frequency induction; 33 and 34 are fixing jigs for fixing and rotating the starting carbon rod; 35 is a glass sintered body deposited on the surface of the starting carbon rod; 36 is a starting carbon rod. This is a high-frequency induction coil for inducing high-frequency waves.

To operate this, the starting carbon rod 32 is fixed in the reaction vessel 31 with rotating fixing jigs 33 and 34, and a high frequency induction coil 36 is connected to the frequency. Flows high frequency power of Hz.

As a result, high frequency power is induced in the starting carbon rod 32 by electromagnetic induction, and the reaction vessel 31 is heated. The heating temperature can be changed by changing the electric power flowing through the coil.
A power of about 10 KW was required to reach a temperature of about 0.05°C. At this time, when the high-frequency induction coil 36 and the starting carbon rod 32 are moved relative to each other, the area of the heated carbon rod moves as the high-frequency induction coil 36 moves. Movement speed is 5~25c! I went with n/Min.
Raw material vapor SiCl4: 100cc/Mi from the inlet 24
n, C; ECl4:50cc/Min9PCl,:5c
c/Min and oxygen gas at a total of 1.5 e/Min, and at the same time, the high frequency induction coil 36 induces high frequency power to the starting carbon rod 32 to generate a power of 1200 to 1600.
When heated to .degree. C., the introduced raw material gas and oxygen gas form a glass sintered body on the carbon rod through a chemical reaction. By performing the reciprocating motion of the high-frequency induction coil 36 many times, the formed glass sintered body grows in layers one after another. The reciprocating motion of the high-frequency induction coil was repeated 100 times, and the obtained glass sintered body had an outer diameter of 40Tf0nφ and a length of 40''. Next, as shown in Figure 2, the supply of raw materials is stopped and the power supplied to the high frequency induction coil 36 is reduced to 20KW.
The carbon rod 32 is heated to 18000C, and the glass sintered body 3 formed on the heated carbon rod
5 becomes a transparent glass body 37. 2 high frequency induction coils
When moving at a speed of ~10Tf1m/Min, the glass sintered body gradually becomes a transparent glass body. Example 2 Glass sintered body 3 obtained by the method described in Example 1
The carbon rod 32 was pulled out from the support rod 41 (there are no particular restrictions on this as long as it is made of a material such as a quartz glass rod or a carbon rod that can withstand temperatures of about 1800°C). The glass sintered body 35 is attached with pins 42 and heated in a heating furnace 44 having a cylindrical heater 43 to form a transparent glass body 45.

If the glass body is sequentially moved downward at a speed of 2 to 10 orders/min, the entire glass sintered body becomes a transparent glass body. Example 3 In the method described in Example 1, glass sintered body layers were produced by changing the mixing ratio of raw material vapor so that the refractive index of the glass sintered body decreased sequentially from the layer closer to the surface of the carbon rod. By doing so, a glass sintered body with a distribution in which the refractive index gradually decreases from the center toward the outer periphery can be obtained.

The obtained glass sintered body is made into a transparent glass body by the method shown in Example 1 or Example 2. Example 4 SiO instead of the container 23 storing glass raw material PCl3
A transparent glass body can also be obtained based on the method according to Examples 1 to 3 by replacing the container storing the raw material BBr3 that lowers the refractive index of 2.

As explained above, in the method for manufacturing a glass fiber base material of the present invention, the process of producing a glass sintered body is performed in a closed container without moisture or other transition metal impurities being mixed. A transparent glass body of high purity can be obtained, and since all the obtained transparent glass bodies are synthesized by chemical reactions and no quartz tube is used as a starting material, there are advantages such as being independent of the shape and quality of the quartz tube. There is.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of an embodiment of the present invention, Figure 2 is a diagram showing the process of making a transparent glass body from a glass sintered body obtained by the method of the present invention, and Figure 3 is a diagram showing the process of making a transparent glass body by the method of the present invention. It is a figure which shows the other process of making the obtained glass sintered compact into a transparent glass body. 10...Oxygen gas supply port, 11, 12, 13
, 14...Flow rate controller, 21...Si
Raw material container storing Cl4, 22... Raw material container storing GeCl4, 24... Inlet for introducing mixed gas into the reaction container, 25... Exhaust port, 31...・・・
・Reaction container, 32...Starting force - Bon rod, 33,
34... Fixing jig, 35... Glass sintered body, 36... Induction coil, 37...
Transparent glass body, 41...Support rod, 42...
... Zen, 43... Heater, 44...
Heating furnace, 45...transparent glass body.

Claims (1)

[Claims] 1. In a method for manufacturing an optical fiber base material consisting of a core and a coating layer having different refractive indexes, an electrically conductive material such as graphite or platinum is added along the central axis of a glass tube. A raw material gas that becomes glass fine particles or transparent glass through thermal oxidation is introduced into a glass tube that surrounds the center rod, and a raw material gas that becomes glass particles or transparent glass through thermal oxidation is introduced together with oxygen gas. By inducing high-frequency power to heat the center rod and repeatedly moving the positions of the center rod and the high-frequency induction coil from side to side or up and down, a glass fine particle deposit layer or a transparent glass layer is formed on the outer periphery of the heated center rod. A method for producing a base material for optical glass fiber, characterized in that: 2. In the method for manufacturing a preform for optical glass fiber according to claim 1, components of the raw material gas to be flowed into the glass tube are controlled by relative movement of the high-frequency coil and the center rod in the right and left or up and down directions. A method for manufacturing an optical fiber preform, characterized in that the refractive index of the deposited glass fine particles or the transparent glass layer is changed from directly on the outer surface of the center rod toward the outer peripheral surface of the deposited layer by gradually changing the refractive index according to the refractive index of the deposited glass particles or the transparent glass layer. 3. Remove the center rod from a glass preform obtained by the method for manufacturing an optical glass fiber preform according to claim 1 or 2, and then remove the space formed by removing the center rod from the outside. Heating with a more suitable heating source,
A method for producing a base material for optical glass fiber, which is characterized by gradually reducing the size and forming a completely solid body.