JPS5918329B2 - Crucible for manufacturing optical transmission bodies - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an improvement in a crucible for producing an optical transmission body used in the production of an optical transmission body using multiple crucibles.

(Prior Art and Problems) A method of manufacturing an optical transmission body using multiple crucibles is already known.

FIG. 1 is an explanatory view showing such a conventional method of manufacturing an optical transmission body and a crucible for manufacturing an optical transmission body used in the method. In FIG. 1a, reference numeral 1 denotes an internal ten crucible containing a core glass composition 2, and has a small hole 3 at the bottom. 4 is an external crucible containing a glass composition 5 for cladding, and has a small hole 6 at the bottom.

The internal crucible 1 is arranged inside the external crucible 4 so that the small holes 3 and 6 are concentric, and the entire crucible is placed in the electric furnace T1.
It is stored inside 5. The electric furnace 7 has a heating element 8 therein, and is capable of heating each crucible to a temperature sufficient to melt the glass composition contained therein. Note that a high frequency furnace may be used instead of the electric furnace 7 having a heating element. 20 The glass composition housed in each crucible is melted by heating to about 1400°C,
After further clarification (defoaming, homogenization), the molten material is concentrically drawn out from the small hole at the bottom of each crucible to form the optical transmission body 9 25 consisting of a multilayer core and cladding.

FIG. 1b shows a cross-sectional shape of the thus formed optical transmission body taken along the plane AA' in FIG. 1a, where 10 is a core portion and 11 is a cladding portion. The conventional crucible 3θ for manufacturing optical transmission bodies shown in FIG. 1 has the following problems.

(1) Under the influence of the temperature distribution of the electric furnace, temperature differences occur in the radial and height directions within the crucible during melting, refining, and drawing processing of the glass composition. In Figure 1, c
and d indicate the temperature distribution in the radial direction and height direction, respectively, in the electric furnace. (2) Such local temperature differences within the crucible inhibit the stirring effect of convection during the melting and fining processes, making it difficult to obtain optically homogeneous glass.

In particular, when the temperature near the outer wall of the internal crucible 1 is low, the viscosity of the molten glass for the cladding becomes high and convection becomes poor, which tends to cause the formation of crystal nuclei and devitrification phenomena. (3) During the drawing process of the optical transmission body, the molten glass may not flow smoothly and turbulence may occur due to variations in viscosity caused by temperature differences in various parts within the crucible.

For example, molten glass for tarac has a high viscosity near the outer wall of the internal crucible because the temperature is low, and a low viscosity near the inner wall of the external crucible because it is close to the heating element and has a high temperature. Turbulent flow occurs in the crucible based on this difference in viscosity, causing a thermochemical reaction between a part of the glass composition and a part of the crucible material, and the resulting substance is drawn out as an optical transmission body. This can cause the quality and performance of the optical transmission body to deteriorate, including its shape, dimensional accuracy, and characteristics. Particularly, in the case of an optical transmission body having a step index distribution, light is transmitted by utilizing the phenomenon of total reflection at the interface between the core portion and the cladding portion.

Therefore, when the above-mentioned thermal reaction products are involved in the interface and its vicinity, the shape and dimensions may partially change, scattering loss increases,
This causes a decline in quality performance such as a decline in mechanical strength. Therefore, it is necessary to make the flow speeds of the molten glass for the core and the molten glass for the clad approximately equal on the inner and outer walls of the internal crucible to avoid entrainment of thermochemical reaction products due to turbulent flow to produce a high-quality optical transmission body. Important in soil. (Object of the Invention) The present invention aims to eliminate the drawbacks of the prior art, and its purpose is to manufacture a high-quality glass optical transmission body that does not have the above-mentioned drawbacks and has low optical transmission loss. An object of the present invention is to provide a crucible for manufacturing an optical transmission body that can be used for manufacturing an optical transmission body using multiple crucibles.

(Embodiment of the Invention) FIG. 2 is a diagram showing an embodiment of a crucible for manufacturing an optical transmission body of the present invention.

The same figure shows a longitudinal cross-sectional view, and 12 is a core glass composition 13.
This is an internal crucible for melting, and two heating bodies 14 and 15 are provided within the crucible wall. The heating bodies 14 and 15 are electrically insulated from each other by having voids 16 and 17 between each heating body and between the heating body and the crucible wall, respectively, and have respective electrode terminals 18 and 2.
0 and 22 and 24 from an external power source (not shown) for heating.

The internal crucible 12 has a nozzle section 26 at its bottom for flowing out the molten core glass. electrode terminal 18,
20, 22, and 24 are insulated from the crucible in a suitable manner. 28 is an external crucible for melting the glass composition 29 for cladding, and a heating element 30 is provided within the wall of the crucible.

The heating body 30 has a gap 32 between it and the crucible wall and is electrically insulated, and can be heated by passing a current from an external power source (not shown) through a pair of electrode terminals 34 and 36. . The external crucible 28 has a nozzle section 38 at its bottom for flowing out the molten crucible glass. The material of the internal crucible 12 and the external crucible 28 is usually platinum, but quartz glass or ceramic (
High purity alumina, etc.) can also be used.

Inert gas is sealed or circulated in the gaps 16, 17, and 32. 40 is an upper furnace body, 42 is a lower furnace body, which are configured to be able to house the external crucible 28, each having heating bodies 44 and 46 inside,
It also has a lid 48 on the top.

These furnaces may be of any type, such as an electric furnace (resistance furnace) or a high-frequency heating furnace, as long as they can effectively heat the crucible housed therein. The respective glass compositions housed in the internal crucible 12 and the external crucible 28 are melted by heating in the furnace and the heating element in each crucible. The respective nozzle portions 26 and 38 are arranged concentrically so that the outflow of the molten glass produces a concentrically combined light transmitting body and is drawn downward. At this time, the glass compositions housed in each crucible are heated by heating elements in the walls of each crucible to correct inappropriate temperature distribution and melt at the optimal temperature commensurate with each glass composition. and can be clarified (defoamed). To heat the heating element within the crucible wall, electricity can be applied from each electrode terminal to generate heat as described above. In this case, the heating body can be made by molding, for example, high-purity graphite. FIG. 3 is a diagram showing an example of such a heating element made of graphite. In the figure, 50 is a resistance element made of graphite, which is manufactured to match the shape of the crucible so that it can be accommodated within the crucible wall, and is made to have a suitable resistance value by inserting a slit 51. Furthermore, it has electrode terminals 52 and 53 for supplying electricity from an external power source. It goes without saying that the resistance element 50 is not limited to graphite, and may also be a metal resistance wire. By selecting the inner thickness and shape and dimensions of the resistance element 50, the temperature distribution within the crucible can be optimized. Further, instead of using such a resistance heating method, it is also possible to perform heating using a high frequency induction method. In this case, it is also possible to selectively heat each heating element by considering the frequency used and the material of the crucible. Of course, it is also possible to use a combination of these various heating methods. Note that in the case of the high frequency induction method, the slits and electrode terminals shown in FIG. 3 are not necessarily required. In this way, in the crucible for producing an optical transmission body of the present invention, the heating method is not limited in any way. Any heating method may be used as long as it can maintain each crucible wall at a temperature that can provide each molten glass with optimal temperature conditions commensurate with its respective composition. It should be noted that heating by such a heating element in the crucible wall is sufficient as long as it can correct the above-mentioned inappropriate temperature distribution caused by the electric furnace used together, and usually does not require a large amount of electric power.

In FIG. 2, the atmosphere 54 inside the furnace surrounded by the furnace bodies 40, 42 and the lid 48 is filled with an inert gas such as nitrogen or argon so as to have a positive pressure with respect to the outside air. It is maintained.

55 is an inert gas introduction pipe for creating such an inert atmosphere.

Further, in FIG. 2, 56 is a pipe for introducing oxygen gas;
7 is a nozzle for blowing out oxygen gas.

In the melting and clarification process, the glass composition housed in the multi-crucible is further heated with oxygen gas preheated to 100°C or higher at the bottom of the crucible at the temperature inside the furnace.
Bubbling is performed by ejecting the liquid into the internal crucible and external crucible through a large number of small holes 58 provided in the nozzle 57. That is, the oxygen gas introducing pipe 56 and the oxygen gas blowing nozzle 57 are installed only during the melting and fining process, and are removed during the photoconductor drawing process.

The oxygen gas jetting nozzle 57 is the nozzle part 26 of the multiple crucible.
A plurality of small holes 58 are provided so as to be able to engage with the tips of the crucibles and 38, and in this state to blow out oxygen gas from the bottoms of both the internal crucible and the external crucible at an appropriate ratio. As mentioned above, the nozzle parts 26 and 38 of the multiple crucibles are inserted into the upper and lower furnace bodies and the inner and outer crucibles so that the temperature of these parts is 700°C or less. By predetermining the temperature distribution created by the heating element, it is possible to increase the viscosity of the molten glass in these parts, thereby preventing the molten glass from flowing out during the melting and fining steps.

In the drawing process of the optical transmission body, the nozzle heating element 60 is heated by an arbitrary method to raise the temperature of the nozzle parts 26 and 38 by about 200°C, thereby reducing the viscosity of each molten glass. After lowering the oxygen gas, the oxygen gas introduction pipe 56 and the oxygen gas jetting nozzle 57 are removed downward, thereby drawing out the optical transmission body downward.
FIG. 4 is a diagram showing the structure of a second embodiment of a crucible for manufacturing an optical transmission body according to the present invention.

In this figure, only the internal crucible 62 is shown in a longitudinal cross-sectional view. Reference numeral 64 denotes a heating element, which has the same structure as that explained with reference to FIG. 2, but unlike the case of FIG. 2, only one heating element is provided.

The heating element 64 is electrically insulated from the outer wall of the crucible 62 by a slight gap 66, and is embedded in the crucible. The void 66 is filled with or circulated with an inert gas. The heating element 62 is made of a suitable resistor such as high-purity graphite, and is connected to an external power source (not shown) through electrode terminals 68 and 70.
It can be heated by applying electricity. Electrode terminals 68, 7
0 is insulated from the crucible in a suitable manner. Note that the heating method for the heating element does not depend on the electrical heating method as described above.
A high-frequency heating method may be used in which high-frequency heating is performed using a suitable high-frequency coil (not shown). The internal crucible 62 shown in FIG. 4 can be used in place of the internal crucible 12 in the apparatus shown in FIG. In this case, by appropriately selecting the ratio between the inner wall thickness t1 and the outer wall thickness T2 of the crucible to change the heat transfer state, the inner crucible 12 provided with the two heating elements shown in FIG. The same effect can be obtained as in the case of . FIG. 5 is a diagram showing filling of an inert gas in a crucible for manufacturing an optical transmission body according to the present invention.

In the figure, a longitudinal cross-sectional view is shown for either an internal or external crucible. The crucible 71 has a heating element 72 inside its side wall, and a gap 74 is provided between the heating element 72 and the crucible wall to keep the heating element in an insulated state. Reference numerals 76 and 78 are electrode terminals for supplying electricity to the heating element.

Electrode terminals 76, 78 are insulated from crucible 71 in a suitable manner. The electrode terminals 76 and 78 are made of pipes, and the electrode terminals 76 and 78 are made of pipes, and the electrode terminals 76 and 78 are connected to each other through a small hole provided near the connection part of the heating element in the crucible.
After the cavity 74 is reduced in pressure to vacuum, an inert gas is filled in at low pressure. As an example, the air gap 74 has a pressure of 5 x 10-3 mmHg.
After exhausting the crucible to the following temperature, beta-out the entire crucible at approximately 300℃ for 10 hours, and then pumping low-pressure argon gas to approximately 130m.
Fill with mHg and seal the pipe at the electrode terminal. By doing so, it is possible to prevent the internal inert gas pressure from exceeding 1 atm even at the maximum temperature of the crucible, thereby preventing damage and deformation of the crucible during heating. Note that the electrode terminal 76,
Needless to say, it may be circulated through the internal pipes of 78. FIG. 6 is a diagram showing the structure of an electrode terminal portion in the crucible for producing an optical transmission body shown in FIG. 5.

In the figure, a indicates a case where one heating element 72 is provided in the crucible 71. An electrode terminal 76 made of a pipe communicates with a cavity 74 in the crucible wall through a small hole 80.
The cavity 74 is evacuated and filled with inert gas through this part. Further, b shows a case in which two heating bodies 72 and 77 are provided in the crucible 71. In this case as well, the cavity 74 is evacuated and filled with inert gas by the electrode terminals 76, 7C made of pipes and the respective small holes 80.
It is done through. By filling the void 74 with inert gas in this way, evaporation of the heating element embedded in the crucible is suppressed when the heating element is heated for a long time.

For example, when the void is not filled with inert gas, 14
After a total of about 64 hours of use at 00° C., a considerable amount of heating material (graphite) evaporated and adhered to the surface of the cavity in the crucible made of dielectric (silica glass). From this, a large amount of heating element material evaporates when used for a long time, and when used for an even longer time, the heating element material thermally diffuses into the dielectric and finally diffuses into the molten glass. It is expected that this will increase the optical transmission loss of the optical transmission body and deteriorate the quality characteristics. When the cavity is filled with an inert gas as described above, even after heating at 1400°C for about 70 hours, there is very little vapor deposition of the heating body material on the surface of the crucible cavity surrounding the heating body. It is thought that it can withstand long-term use.

By filling the cavity in the crucible wall with inert gas in this way, it is possible to extend the life of the heating element and improve the quality of the molten glass, and also to equalize the temperature of the crucible wall through convection of the filled gas. It can be carried out.

(Effects of the Invention) As explained above, according to the method for manufacturing an optical transmission body and the crucible for manufacturing an optical transmission body of the present invention, the temperature distribution in the electric furnace can be controlled by the heating bodies provided in the internal crucible and the external crucible. By heating and correcting, it is possible to melt and clarify the glass for the core and the cladding at the optimal temperature according to each glass composition, and furthermore prevents turbulent flow of the molten glass in the crucible. This can prevent thermal reaction products between the glass composition and the crucible material from being drawn into the molten glass.

Furthermore, by filling the void inside the crucible wall with an inert gas, it is possible to extend the life of the heating element and improve the quality of the molten glass, as well as to equalize the temperature of the crucible wall through convection of the filled gas. can. As described above, according to the crucible for manufacturing an optical transmission body of the present invention, the various drawbacks seen in the prior art are significantly improved, and it is possible to manufacture a high-quality glass optical transmission body that is optically extremely homogeneous and has low loss. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional method for manufacturing an optical transmission body and a crucible for manufacturing an optical transmission body, FIG. 2 is a diagram showing an embodiment of the crucible for manufacturing an optical transmission body of the present invention, and FIG. 3 is a graph. FIG. 4 is a diagram showing an example of a heating body made of Aite, FIG. 4 is a diagram showing a second embodiment of the crucible for manufacturing an optical transmission body of the present invention, and FIG. FIG. 6 is a diagram showing the structure of the electrode terminal portion in the crucible for producing an optical transmission body of FIG. 5. 1...Internal crucible, 2...Glass composition for core, 3...Small hole, 4...External crucible, 5... Glass composition for cladding, 6...
...Small hole, 7...Electric furnace, 8...
Heating body, 9... Optical transmission body, 10... Core part, 11... Clad part, 12...
Internal crucible, 13...Glass composition for core, 1
4, 15... Heating body, 16, 17...
Air gap, 18, 20, 22, 24... Electrode terminal,
26... Nozzle part, 28... External crucible, 29... Glass composition for cladding, 30...
... Heating body, 32 ... Gap, 34, 36
... Electrode terminal, 38 ... Nozzle part, 4
0... Upper furnace body, 42... Lower furnace body,
44, 46... Heating body, 48... Lid,
50... Resistance element, 51... Slit, 52, 53... Electrode terminal, 54...
Furnace atmosphere, 55... Inert gas introduction pipe, 56... Oxygen gas introduction pipe, 57...
...Oxygen gas jetting nozzle, 58...Small hole,
60...Nozzle part heating body, 62...Internal crucible, 64...Heating body, 66...
Gap, 68, 70... Electrode terminal, 71...
... Crucible, 72, 72' ... Heating body, 74.
...Gap, 76,7fI,78...Electrode terminal, 80...Small hole.

Claims (1)

[Scope of Claims] 1. In a crucible having a small hole at the bottom, the crucible wall is formed hollow, a heating element is provided in the hollow part and placed across a gap from the wall body, and an inert gas is provided in the hollow part. 1. A crucible for manufacturing an optical transmitter, characterized in that a plurality of crucibles each containing or circulating the same are arranged so that the small holes are concentric. 2. The crucible for manufacturing an optical transmission body according to claim 1, characterized in that the crucible includes two heating bodies, each of which is configured to be able to heat independently. 3. The crucible for manufacturing an optical transmission body according to claim 1, wherein the crucible wall that covers the heating body in the crucible has different heat transfer conditions between the inside and the outside.