JP3963235B2 - Manufacturing method of optical fiber preform - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for manufacturing an optical fiber preform, and in particular, a method for manufacturing an optical fiber preform using a plasma sintering method in which raw material powder for an optical fiber is placed in a predetermined mold and subjected to pressure sintering. It is about.
[0002]
[Prior art]
For example, as a method for manufacturing an optical fiber preform, various methods such as the well-known CVD method and VAD method have been developed.
[0003]
[Problems to be solved by the invention]
However, in these methods, for example, (1) the number of steps required to obtain a preform is large, and the growth of the base material is slow, resulting in poor productivity. (2) The majority of SiO2 fume does not adhere to the target. It is inevitable that it is treated as industrial waste. (3) Equipment costs are high. (4) Location is limited in terms of transportation and storage of raw materials (eg, SiO2, oxygen, hydrogen, helium gas). Etc. are caused.
[0004]
Therefore, for example, as a preform for optical fiber manufacturing, a preformed raw material powder is put into a predetermined mold, and this is pressed and integrated at a high pressure. Has been proposed and studied.
However, in such a method, for example, when the size is large to some extent, there is a possibility that voids may be generated inside due to unevenness in temperature and particle size distribution only by pressurization and current heating, and there is a problem in moldability. . Therefore, it is conceivable to add a binder for improving the moldability to the raw material powder, but it is also conceivable that the optical characteristics are lowered.
[0005]
In view of the above circumstances, the present invention can manufacture a large number of high-quality products in a short time, has little risk of environmental pollution, has no restrictions on location conditions, and increases the equipment cost. It is an object of the present invention to provide a method for manufacturing a non-optical fiber preform.
[0006]
[Means for Solving the Problems]
That is, according to the first aspect of the present invention, a hollow cylindrical die is filled with a raw material powder that is a clad of an optical fiber, and a raw material powder that is a core of an optical fiber is filled inside the die. Electrodes are arranged on both sides of the die, and a high frequency pulse is applied while pressing the raw material powder with the electrodes to generate a plasma discharge between the raw material powders. The body is heated and sintered.
[0007]
Further, in the invention according to claim 2, in the invention according to claim 1, a jacket formed of an appropriate material which becomes a part of the core after sintering is set in a portion filled with the core in the die. It is something to keep.
[0008]
Further, in the invention according to claim 3, in the invention according to claim 1, the raw material powder to be the optical fiber core is solidified to an extent that does not collapse in advance and formed into a columnar shape.
Prior to filling the raw material powder to be clad into the die, it is set on the die.
[0009]
The invention according to claim 4 is the invention according to claim 1, wherein a container is mounted in the die, and after the raw material powder is inserted and filled inside and outside the container, the container is pulled out and then discharged and discharged. Sintering by energization is performed.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows an apparatus for manufacturing an optical fiber preform according to the first embodiment. Here, in order to make the explanation easy to understand, this apparatus will be described prior to a method for manufacturing an optical fiber preform.
[0011]
The optical fiber preform manufacturing apparatus of this embodiment is formed in a hollow cylindrical shape, an outer container (die) 1 and an inner container 2 arranged concentrically inside and outside, and a shape capable of closing upper and lower ends of these containers. The upper and lower electrodes 3 also serving as pressure dies, a plasma generating power source 4 for applying a high voltage to these electrodes 3, and a pressure cylinder (by air pressure or hydraulic pressure) 5 are provided. In the figure, reference numeral M1 denotes a core raw material powder, and M2 denotes a clad raw material powder.
[0012]
The outer container 1 is made of a material having a high electric resistance and having impact pressure resistance and heat resistance, such as cermet and graphite. The inner container 2 is withdrawn to the outside after the raw material powder M1 is filled. In particular, the inner container 2 has an excessive amount between the raw material powders at the boundary between the raw material powder M1 and the raw material powder M2. Use a member that is thin enough to prevent mixing. Further, the outer container 1 may have a structure that can be divided into, for example, two parts so that the inner sintered product can be easily taken out. Further, the inner container 2 can be attached to and detached from the lower electrode 31.
[0013]
Moreover, it is preferable that the sintered base material (preform) has a spindle shape corresponding to dehydration sintering and wire drawing in subsequent steps. The electrode 31 of this embodiment has a flat inner surface, but as shown in FIG. 2, the inside of a punch 31B (described later) fixed to the lower electrode 31 was previously formed into a spindle shape. The use of the curved punch 31C is advantageous because it does not require a step of processing and forming the spindle shape of the base material after sintering. Here, if the bottom shape is a conical shape with a sharpened tip, it is easier to draw out during drawing.
[0014]
In this embodiment, the lower electrode 31 of the electrode 3 and the pressure cylinder 5 are fixedly fixed to a stable support. In addition, punches 31A and 32A formed of a conductive and heat-resistant material such as tungsten, molybdenum or graphite are fixed to the upper and lower electrodes 31 and 32 so as to be detachably inserted into the outer container 1. Yes. The punch 31B is also formed of the same material. Moreover, pressurization can be performed simultaneously from the upper and lower sides as well as from the upper side.
[0015]
The plasma generating power source 4 performs high-frequency pulses and sintering energization, and the generated high-frequency pulses are applied between the electrodes 31 and 32 to generate plasma between the pressed raw material powders M1 and M2. . Thus, when the particle interface is activated, the raw material powders M1 and M2 are energized and sintered by Joule heat. Further, it is possible to sinter by gradually increasing the direct current component of the high frequency pulse without dividing the operating time of the high frequency pulse and the direct current energization clearly. In the above process, the press pressure between the electrodes 31 and 32 is constant or changed according to time. Further, the frequency of the high frequency pulse and the energized power are appropriately changed depending on the classification of the raw material powder and the size of the product.
In addition, plasma sintering here is a method of sintering powder particles by high frequency plasma discharge generally. Normally, silicon dioxide powder particles, which are raw material powders, have high interface resistance, so current does not flow at low voltages. However, when a pulse of several thousand volts is applied, the particle interface breaks down and ionizes, causing plasma discharge. Will occur. The gas ions and electrons generated by this plasma discharge act on the powder particle interface to remove the oxide film and adsorbed gas to activate the particle surface, promote adhesion between particles, and facilitate sintering. . The plasma generation time and the sintering time are variables that are appropriately determined depending on the kind of powder, the material, and the size of the product.
[0016]
Next, an optical fiber preform manufacturing method using the optical fiber preform manufacturing apparatus of the first embodiment will be described.
First, the inner electrode 2 is disposed concentrically with the outer container 1 by raising and opening the upper electrode 32. Next, the raw material powder M1 serving as a core is filled inside the inner container 2, and the raw material powder M2 serving as a clad is filled outside. For example, in order to make a step index type SM optical fiber, the raw material powder M1 is a raw material powder for a core obtained by mixing and classifying powders of silicon dioxide and a dopant (eg, germanium). The clad raw material powder M2 is obtained by classifying silicon dioxide powder to which no dopant is added.
[0017]
After the filling of the raw material powders M1 and M2, the inner container 2 is pulled out from the outer container 1. Although the raw material powders M1 and M2 are not solidified and show some fluidity in the outer container 1, as described above, the wall thickness of the inner container 2 is so thin that the inner container 2 is pulled out. The raw material powders M1 and M2 are not excessively mixed at the boundary between the inner and outer layers.
After removing the inner container 2, the cylinder 5 is operated, the upper electrode 32 is lowered, the outer container 1 is closed and a predetermined pressure is applied to press the raw material powder. At the same time, the power supply 4 is operated to energize the upper and lower electrodes 31 and 32 for an appropriate time. The high frequency current for generating plasma is, for example, 3,000 to 5,000 amperes, and the frequency is about several GHz.
[0018]
As described above, the method of manufacturing the step index type optical fiber has been described. When the index distribution is changed (for example, a graded index type optical fiber), a plurality of inner containers 2 having different diameters are prepared, and Are arranged concentrically in the outer container 1. And after filling raw material powders with different dopant concentrations between the inner containers, each inner container 2 is pulled out and sintered in the same procedure as described above.
According to this manufacturing method, since the dopant concentration in the section partitioned by each inner container is different, it is possible to change the index distribution of the optical fiber preform.
In addition, according to the said manufacturing method, although some raw material powder can mix in the boundary surface of a filling body, there is no practical problem in the optical fiber after dehydration sintering by dehydration sintering.
In addition to the manufacturing method of this embodiment, for example, prior to pulling out the inner container 2, the inner and outer raw material powders M1 and M2 have a certain degree of hardness (hardness that allows the inner container 2 to be pulled out relatively easily). And then pulling out the inner container 2, and again the raw material powder M1 and M2 generated by the thickness of the inner container 2 in the gap between the core or the clad (or a raw material giving an intermediate index between them) The raw material powder M1 and M2 may be pressed again after the raw material powder (which may be powder) is charged and filled. In the case of this manufacturing method, the inner container 2 is easier to put into the gap if it has a certain thickness.
[0019]
In this embodiment, a single-core optical fiber preform is manufactured. Of course, however, a double-core panda fiber (polarization plane preserving fiber) in which two inner containers are arranged can be manufactured. In addition, the present invention can be applied to various modes such as a boater fiber and an elliptical jacket fiber.
[0020]
Next, an optical fiber preform manufacturing method using another optical fiber preform manufacturing apparatus according to the present invention will be described.
In the manufacturing method of the second embodiment shown in FIG. 3, the same manufacturing apparatus as in the previous embodiment can be used. However, instead of the raw material powder M <b> 1 serving as a core after sintering loaded in the inner container 2, A cylindrical core solid powder P1 is prepared in which the raw material powder M1 is hardened so as not to collapse during handling until it is set in the manufacturing apparatus. Then, this solid core powder P1 is inserted and kept upright in the middle of a hole (not shown) for setting the punch 31D provided in the lower electrode 31.
[0021]
Therefore, if the outer container 1 is subsequently fitted to the punch 31D, the raw material powder for cladding is charged and loaded into a portion other than the core solid powder P1 in the outer container 1.
Thereafter, as in the previous embodiment, if the plasma power source is used for sintering while pressing, the inner container 2 is not used, so the preform need only be taken out from the outer container 1. In addition, instead of the core solid powder P1, a clad solid powder that has been hardened to some extent in a cylindrical column shape (the center portion is hollowed out) is prepared, and after setting this in the outer container 1, The raw material powder for the core may be charged and charged.
[0022]
Next, an optical fiber preform manufacturing method using still another optical fiber preform manufacturing apparatus according to the present invention will be described.
In the manufacturing method of the third embodiment shown in FIG. 4, a manufacturing apparatus similar to that of the first embodiment can be used. However, the jacket J becomes a part of the core (or may be clad) after sintering. In addition, those formed of the same raw material as the core raw material powder are used. The dopant is adjusted so as to be different from the core or the clad as required.
[0023]
Therefore, according to this method, since discharge and energization are performed between the raw material powders together with the pressurization, it is easy to remove the outer container 1 after sintering. In other words, the jacket J is sintered as it is. Since it becomes part of the core, there is no need to pull it out. In addition, although the said process has demonstrated the manufacturing method of the porous preform | base_material (preform), the dehydration sintering process can also be completed by carrying out electric current sintering for a long time. In this case, it becomes possible to manufacture an optical fiber preform that can be shifted to a drawing process.
In the above method, powder is used for the core. However, as shown in FIG. 5, the core is preliminarily used as a sintered material M1 ′, and the surrounding is filled with the powder material M2 ′ of the clad and sintered. It is also possible. This method facilitates the molding of the base material shape at the bottom end (particularly the conical tip of the core).
[0024]
【The invention's effect】
As described above, according to the present invention, the hollow cylindrical die is filled with the raw material powder that becomes the cladding of the optical fiber, and the inner side is filled with the raw material powder that becomes the core of the optical fiber. Electrodes are arranged on both sides of the die, and a high frequency pulse is applied while pressing the raw material powder with this electrode to generate a plasma discharge between the raw material powders. Since the space is heated and sintered, an optical fiber preform can be manufactured in a short time, and unlike the conventional mechanical shape method, a binder is not required, so that a high-quality one can be provided.
[0025]
In addition, according to the present invention, if the raw material powder is produced in advance in a special place with high airtightness and the raw material powder is transported from there, there is little risk of environmental pollution, in particular. It is possible to provide a method of manufacturing an optical fiber preform having a number of excellent features such as no restrictions on the location conditions and the fact that equipment costs are not increased.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an optical fiber preform manufacturing apparatus according to the present invention.
FIG. 2 is a schematic sectional view showing a modification of the apparatus.
FIG. 3 is a schematic perspective view showing another optical fiber preform manufacturing apparatus.
FIG. 4 is a schematic perspective view showing still another optical fiber preform manufacturing apparatus.
FIG. 5 is an explanatory view showing a modification of the present invention.
[Explanation of symbols]
1 External container 2 Internal container 3 Electrode 4 Plasma power supply 5 Cylinder J Jacket M1 Raw material powder (for core)
M2 raw material powder (for clad)
P1 core solid powder

Claims (4)

The hollow cylindrical die (1) is filled with the raw material powder (M2) serving as the clad of the optical fiber, and the raw material powder (M1) serving as the core of the optical fiber is filled inside the die (1). 1) Place electrodes (3) on both sides of
A high frequency pulse is applied while pressurizing the raw material powder (M1 · M2) with this electrode (3) to generate plasma discharge between the raw material powder (M1 · M2), and between the electrodes (3). A method for producing an optical fiber preform, wherein the raw material powders (M1 and M2) are heated and sintered by energization heating. The jacket (2 ') formed of an appropriate material that becomes a part of the core after sintering is set in a portion filled with the core in the die (1). Manufacturing method of optical fiber preform. The raw material powder that becomes the optical fiber core is solidified to the extent that it does not collapse in advance and formed into a columnar shape,
2. The method of manufacturing an optical fiber preform according to claim 1, wherein the raw material powder (M1) to be clad is set on the die (1) prior to filling the die (1). The container (2) is mounted in the die (1), the raw material powder (M1 and M2) is inserted and filled in and out of the container (2), and then the container (2) is pulled out and then discharged and discharged by energization. The method for manufacturing an optical fiber preform according to claim 1, wherein the optical fiber preform is bonded.

Images