JPS6120493B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for continuously manufacturing optical fiber preforms.

In recent years, research on optical fibers for communications has been actively conducted in various places, and a continuous manufacturing method for optical fiber base materials has even been established. A continuous manufacturing method for this base material is shown in FIG. Halides such as silicon germanium, phosphorus, and boron are oxidized using an oxyhydrogen burner 1, and each oxide powder is deposited and grown on a rotating shaft to produce a rod-shaped oxide object 2 with a diameter of 50 mm to 100 mm. Next, this oxide body is sequentially pulled up into a high-temperature furnace transparent vitrification furnace 3 to perform degassing and transparent vitrification, and the optical fiber base material 4 is continuously pulled up from the upper part of the high-temperature furnace.

In this process, transparent vitrification is performed at approximately 1600℃~
Since the temperature range is 1800°C, high-purity carbon, which can easily reach high temperatures, is used as the heating element. Carbon is significantly consumed when heated in the atmosphere, so when carbon is used as a heating element, the atmosphere in the furnace must be maintained in a completely reducing atmosphere. That is, in FIG. 1, the high temperature furnace 3
When the optical fiber preform 4 is pulled up from the high-temperature furnace 3, the furnace structure must be such as to prevent atmospheric air from entering the furnace from the upper outlet of the high-temperature furnace 3.

A method of completely sealing the inside and outside of the furnace in this way has conventionally been carried out using a manufacturing apparatus as shown in FIG. In this method, a heat insulating material 215 made of carbon felt or glass wool or the like is fixed between positioning fittings 213 and 214, and the heat insulating material 215 is brought into contact with the surface of the optical fiber base material 4 that is pulled up one after another. Seal the inside and outside of the furnace.

However, this sealing method had the following problems.

(1) Since physical force is applied to the optical fiber base material, the oxide growth surface on which the oxide powder adheres and grows fluctuates, making it impossible to obtain the desired refractive index distribution (optical properties deteriorate).

(2) It cannot respond to changes in the outer diameter of the optical fiber base material being manufactured.

(3) The surface of the optical fiber base material is contaminated by the insulation material.

In order to solve the above-mentioned problems, continuous production of the base material is carried out using a production apparatus shown in FIG.
That is, a cylindrical protection tube 211 is installed in the upper part of the high temperature furnace 3.
There is a method of providing a protective tube 211 and performing continuous manufacturing up to the length of the protective tube 211. Although this method solves the above-mentioned problems, the length of the base material to be manufactured is determined by the length of the protective tube, and the base material is not substantially continuously manufactured.

The present invention is characterized in that at the upper exit of a high-temperature furnace from which optical fiber base materials are sequentially pulled up, the atmosphere inside the furnace and the atmosphere outside the furnace are completely cut off without contacting the base materials for optical fibers. The purpose is to solve the conventional problems and provide stable continuous production of optical fiber preforms. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 4 shows an embodiment of the present invention, in which 30 is a high temperature furnace body (transparent vitrification furnace body), 210 is a heating element, and high purity carbon is used. Reference numeral 2 denotes the produced oxide object, which is pulled up at a predetermined speed and becomes a transparent optical fiber base material 4 by a heating element 210. 21 is a light source (for example, a YAG laser, etc.), 22 is an optical system composed of a combination of lenses, 23 is a light receiving section, 24 is a control circuit, 25 is a storage circuit, 26 is a motor, and 27 is a fiber.
Reference numeral 28 denotes a wringer which can obtain any inner diameter within the range of 15 mmφ to 45 mmφ, and its principle will be explained with reference to FIG.

Figure 5a is a front view of the wringer, and 31 is a spring for obtaining an arbitrary inner diameter, and 12 is not shown.
I used one. Pins 32 and 33 are provided at both ends of each spring, and the pin 32 is inserted into a concentric pin hole 35 of a fixed ring 34, and the spring 31 rotates about this pin as a fulcrum. FIG. 5b is a side view of the wringer, in which the rotating ring 36 is not shown in FIG. 5a, but it can be seen from FIG. 5b that the rotating ring 36 is provided on top of the spring 31. The pin 33 is supported by a rotating ring 36, and by rotating the rotating ring 36, the spring 31 rotates about the pin 32 as a fulcrum. As a result, an approximate circle is formed at the center of the wringer by the overlap of the 12 springs, and the diameter of the circle becomes larger or smaller depending on the rotation angle of the rotating ring 36.

Next, the operation of the present invention will be explained with reference to FIG.

A light beam emitted from the light source 22 is guided to the optical system 22 by a fiber 27 (quartz fiber, multicomponent fiber, plastic fiber, etc.). The optical system 2 is configured such that the light beam emitted from the optical system 22 is cut off by the optical fiber base material 4.
Adjust 2. The light beam emitted from the optical system 22 is received by the light receiving section 23, where it is converted into an electric signal, and the control device 24 extracts an electric signal corresponding to the outer diameter variation of the optical fiber base material. The electrical signal is stored in the memory circuit 25. After delaying the electric signal by the time corresponding to the distance from the outer diameter variation measurement position of the optical fiber base material 4 to the wringer 28 by the memory circuit 25, the electric signal is sent to the motor 26, and this electric signal is Therefore, the motor 26 is operated to vary the inner diameter of the diaphragm 28 by an amount corresponding to the outer diameter of the optical fiber preform 4 that is continuously pulled up.

In addition, the same electric signal is delayed by a time corresponding to the distance from the outer diameter variation measuring position to the wringer 28'.
Motor 26' is operated to change the inner diameter of restrictor 28' in the same manner as described above.

Note that there is a gas introduction section 29 between the restrictors 28 and 28'.
The gas flow rate is set so that the pressure between the two constrictors is higher than the pressure inside the furnace and the outside pressure, and the space between the optical fiber base material to be manufactured and the constrictor is gas-sealed.

As mentioned above, with this gas seal, even if the outer diameter of the optical fiber base material that is successively pulled up changes due to the operation of cutting off the atmosphere inside and outside the furnace, it will not contact the base material. Moreover, the atmosphere inside the furnace and the atmosphere outside the furnace can be completely separated.

Experimental examples using the apparatus of the present invention will be described below.

The optical fiber base material 4 was pulled up at a speed of 60 mm/hour, and the outer diameter of the optical fiber base material 4 was measured using an outer diameter measuring device. The distance from the outer diameter measurement position to the wringer 28 is 30 mm, and the distance to the wringer 28' is 50 mm.
were installed respectively. In other words, since the pulling speed of the optical fiber base material is 60 mm/hour, it takes 30 minutes for the part whose outer diameter is measured to reach the wringer 28.
Similarly, the time to reach the wringer 28' is 50 minutes.

After delaying the electrical signal corresponding to the outer diameter variation of the optical fiber base material by this amount of time, the memory circuit 25 was adjusted so as to send the electrical signal to the motors 26, 26' linked to both the diaphragms. Both restrictors are opened 2 mm larger than the measured outer diameter of the base material, and Ar gas is divided into 5 parts from the gas introduction part between both restrictors to make the pressure in both restrictors lower than the pressure inside the furnace and the outside air pressure. The temperature was also raised to completely separate the atmosphere inside the furnace and the atmosphere outside the furnace.

FIG. 6 shows changes in the outer diameter of the base material and changes in the inner diameter of the wringer 28, 28' over time. A is a change in the outer diameter of the base material measured at the base material outer diameter measurement position, B is a change in the inner diameter of the wringer 28, and C is a change in the inner diameter of the wringer 28'.

As can be seen from FIG. 6, even if the outer diameter of the base material changes with the apparatus of the present invention, the inner diameters of the two squeezers change in accordance with the change in the outer diameter of the base material.
In this experiment, the base material was manufactured continuously for 26 hours.
The carbon heating element showed no wear and tear, and the atmosphere inside and outside the furnace was completely separated. Manufactured outer diameter
Among the base materials for optical fibers with a diameter of 21 mm and a length of 140 cm,
Three locations, one at both ends and one at the center, were made into fibers, and the variation in loss characteristics in the longitudinal direction was investigated. As a result, the wavelength
The loss at 0.85 μm is 2.3 for all three optical fibers.
The loss was ~2.4 dB/Km, and no loss variation in the longitudinal direction was observed. In addition, the band characteristics of optical fibers, which vary depending on the refractive index distribution of the optical fiber base material, are
As a result of measurements on optical fiber, 600MHz/
A value greater than Km was obtained, and there was no longitudinal variation in the refractive index distribution.

For comparison, the base material was continuously manufactured by the method using the conventional equipment shown in Figures 2 and 3. The insulation material that comes into contact with the base material gradually wears out, and 6 hours after the start of continuous production,
A gap of 2 mm or more was created between the optical fiber base material and the heat insulating material, and continuous production could only be carried out for 10 hours. After completing the production of the base material, we examined the carbon heating element and found that it was worn out, and its initial resistance had increased from 0.06Ω to 0.18Ω after completion.

A heat insulating material is attached to the surface of the manufactured base material, and as a result of drawing this base material and manufacturing a 10 km optical fiber, the loss characteristic is 2.6 dB/2 at a wavelength of 0.85 μm.
Km to 4.2dB/Km, and the band characteristic is 85M
There were "variations" from Hz/Km to 230MHz/Km, and there were large fluctuations in both characteristics.

In the method using the conventional device shown in Fig. 3,
Although good results were obtained in both loss characteristics and band characteristics, continuous production of the base material could only be carried out for 8 hours.

As explained above, the optical fiber preform continuous production apparatus of the present invention is equipped with two diaphragms capable of obtaining an arbitrary diameter, and the space between them is sealed with gas, thereby producing a transparent optical fiber preform. The outer diameter of the fiber is optically measured, and the aperture diameter of the two diaphragms is changed according to the measured diameter, making it possible to completely disconnect the inside and outside of the furnace without contacting the transparent optical fiber base material. There are advantages that can be achieved. Therefore, it is possible to obtain the optical fiber to be manufactured with extremely little variation in both the loss characteristics and the band characteristics in the longitudinal direction. Furthermore, since the carbon heating element is not consumed, continuous production can be carried out over a long period of time. Further, the present invention is effective as a device for maintaining the atmosphere in a commercially available resistance furnace using carbon as a heating element, when samples are continuously inserted into the furnace.

[Brief explanation of the drawing]

1, 2, and 3 are schematic configuration diagrams of a conventional optical fiber base material manufacturing apparatus, FIG. 4 is an embodiment of the apparatus of the present invention, and FIGS. 5a and 5b are A front view and a side view of the diaphragm used in the present invention, and FIG. 6 are diagrams showing changes in the outer diameter of the optical fiber base material and changes in the inner diameter of the diaphragm. 1... Glass particle synthesis torch (oxyhydrogen burner), 2... Oxide object, 3... High temperature furnace (transparent vitrification furnace), 4... Base material for optical fiber (glass base material), 5... Rotary pulling Device, 21...Light source,
22...Optical system, 23...Light receiving unit, 24...Control device, 25...Storage circuit, 26, 26'...Motor, 27...Optical fiber, 28, 28'...Aperture device, 29... Gas inlet, 30...High temperature furnace body (transparent vitrification furnace body), 31...Blade, 32, 33
... Pin, 34 ... Fixed ring, 35 ... Pin hole, 36 ... Rotating ring, 210 ... Heating element, 2
11... Protection tube, 212... Starting rod, 213,2
14...Positioning metal fittings, 215...Insulating material.

Claims (1)

[Claims] 1. In an apparatus for producing an optical fiber preform, which produces a porous sintered preform for an optical fiber by flame hydrolysis and continuously produces a transparent preform for an optical fiber in a transparent vitrification furnace, the transparent At the upper end of the vitrification furnace, there are two diaphragms that can select any diameter, a gas seal that seals between these two diaphragms, and a device for measuring the outer diameter of the glass base material. The method is characterized in that the optical fiber base material is manufactured continuously by interlocking the device and the outer diameter measuring device, and by completely cutting off the atmosphere inside and outside the furnace without contacting the glass base material with the gas seal. Optical fiber base material continuous manufacturing equipment.