JPH1160260A - Production of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject method capable of producing a high-quality optical fiber in a short time, apart from an environmental pollution, free from any restrictions on locational conditions, and inexpensive in equipment cost. SOLUTION: This method comprises; filling a powdery raw material M2 for a cladding of optical fiber into a hollow cylindrical external case 1, filling another powdery raw material M1 for a core of the optical fiber, arranging electrodes on both sides of the external case, applying a high-frequency pulse thereto while compressing the raw materials M1 and M2 to cause a plasma discharge between the raw materials M1 and M2, and concurrently therewith heating the section between the raw materials M1 and M2 by applying an electric current to both the electrodes so as to sinter the section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber preform, and more particularly, to a method using a plasma sintering method in which raw material powder for an optical fiber is put into a predetermined mold and sintered under pressure. The present invention relates to a method for manufacturing an optical fiber preform.

[0002]

2. Description of the Related Art For example, as a method of manufacturing an optical fiber preform, various methods such as a well-known CVD method and a VAD method have been developed.

[0003]

However, in these methods, for example, the number of steps until a preform is obtained is large, and the productivity is poor due to the slow growth of the base material. Without wearing
Being inevitable to be treated as industrial waste High equipment costs Due to the transportation and storage of raw materials (for example, SiO2, oxygen, hydrogen, helium gas), there are inconveniences such as location restrictions. I have.

Therefore, for example, as a preform for producing an optical fiber, a raw material powder formed in advance is put into a predetermined mold,
A mechanical shaping method in which this is pressurized to a high pressure to integrate it, or a method of sintering by heating with a mold or electric current have been proposed and studied. However, in such a method, for example, when the size becomes large to some extent, there is a possibility that voids may be generated in the inside due to irregularities in temperature and particle size distribution only by pressurization and electric heating, and there is a problem in moldability. . Therefore, it is conceivable to add a binder to the raw material powder for improving the moldability, but it is conceivable to cause a decrease in optical characteristics.

[0005] In view of the above circumstances, the present invention can mass-produce high-quality products in a short period of time, reduces the risk of environmental pollution, and does not limit the location conditions. It is an object of the present invention to provide a method for manufacturing an optical fiber preform that does not increase bulk.

[0006]

According to the first aspect of the present invention, a hollow cylindrical die is filled with a raw material powder to be a cladding of an optical fiber, and a core of the optical fiber is provided inside the die. The raw material powder to be filled, electrodes are arranged on both sides of the die, a high-frequency pulse is applied while pressing the raw material powder with the electrode, and a plasma discharge is generated between the raw material powders, The raw material powders are heated and sintered by electric heating between the electrodes.

According to a second aspect of the present invention, in the invention according to the first aspect, a jacket formed of an appropriate material which becomes a part of the core after sintering is formed in a portion of the die in which the core is filled. Is set.

According to a third aspect of the present invention, in the first aspect of the present invention, the raw material powder to be used as the optical fiber core is solidified in advance so as not to collapse and formed into a columnar shape, and the raw material powder to be the clad is formed. Is set on the die prior to filling the die.

According to a fourth aspect of the present invention, in the first aspect of the present invention, a container is mounted in a die.
After inserting and filling the raw material powder into and out of the container, the container is pulled out, and then sintering is performed by discharging and energizing.

[0010]

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 description easy to understand, the apparatus will be described prior to the method for manufacturing an optical fiber preform.

The optical fiber preform manufacturing apparatus of this embodiment has an outer container (die) 1 and an inner container 2 which are formed in a hollow cylindrical shape and are concentrically arranged inside and outside, and both upper and lower ends of these containers can be closed. Upper and lower electrodes 3 which are formed into a shape and also serve as pressure dies, a plasma generation power supply 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 drawing, reference numeral M1 denotes a raw material powder for a core, and M2 denotes a raw material powder for a clad.

The outer container 1 has a high electric resistance and a high impact pressure,
It is formed of a material having heat resistance, for example, cermet or graphite. Note that the inner container 2 is for extracting the raw material powder M1 to the outside after being filled. In particular, the inner container 2 has an excessive space between the raw material powders at the boundary between the raw material powders M1 and M2. Use a member that is thin enough to prevent mixing. Further, the outer container 1 may be configured to be, for example, divided into two so that the internal sintered product can be easily taken out. The inner container 2 is detachable from the lower electrode 31.

Also, a sintered base material (preform)
Is preferably a spindle shape in response to dehydration sintering and drawing in a later step. The electrode 31 of this embodiment has a flat inner surface. However, as shown in FIG. 2, the inside of a punch 31B fixed to the lower electrode 31 (described later) is formed in a spindle shape in advance. The use of the curved punch 31C is advantageous because it does not require a step of processing and forming a spindle shape of the base material after sintering. Here, if the bottom shape is a conical shape with a sharper tip, it is easier to draw out when drawing.

In this embodiment, the lower electrode 31 of the electrodes 3 and the pressure cylinder 5 are fixedly mounted on a stable support. The upper and lower electrodes 3
In order to removably fit into the external container 1, 1 and 32,
Punches 31A and 32A formed of a conductive and heat-resistant material, for example, tungsten, molybdenum, or graphite are fixed. The punch 31B is also formed of the same material. Pressurization can be performed not only from the upper side but also from the upper and lower sides simultaneously.

The plasma generating power supply 4 is for performing high-frequency pulses and sintering energization. The generated high-frequency pulses are applied between the electrodes 31 and 32, and the pressed raw material powder M is applied.
1. Generate plasma between M2 particles. Thereby, if the particle interface is activated, the raw material powders M1, M
2 and sinter by Joule heat. In addition, sintering can be performed by gradually increasing the DC component of the high-frequency pulse without clearly dividing the operation time of the high-frequency pulse and the direct current application. In the above process, the pressing pressure between the electrodes 31 and 32 is constant or changed according to time. In addition, the frequency of the high-frequency pulse and the electric power are appropriately changed according to the classification of the raw material powder and the size of the product. Here, the plasma sintering is generally a method of sintering powder particles by high frequency plasma discharge. Normally, powder particles of silicon dioxide, which is a raw material powder, do not flow at low voltage due to high interface resistance, but when a pulse of several thousand volts is applied, the particle interface is broken down and ionized,
Plasma discharge occurs. Gas ions and electrons generated by this plasma discharge act on the interface of the powder particles to remove the oxide film and the adsorbed gas, activate the particle surface, promote the adhesion between the particles, and facilitate sintering. . The plasma generation time and the sintering time are variables appropriately determined depending on the type, material, and size of the product.

Next, a method for manufacturing an optical fiber preform using the apparatus for manufacturing an optical fiber preform of the first embodiment will be described. First, the upper electrode 32 is raised and opened, and the outer container 1 is opened.
And the inner container 2 is arranged concentrically. Then, the inner container 2
The inside is filled with the raw material powder M1 serving as a core, and the outside is filled with the raw material powder M2 serving as a clad. For example, to produce a step index type SM optical fiber, the raw material powder M1 is a core raw material powder obtained by mixing and classifying silicon dioxide and a powder of a dopant (for example, germanium). As the cladding raw material powder M2, a material obtained by classifying silicon dioxide powder to which no dopant is added is used.

After the filling of the raw material powders M1 and M2 is completed, the inner container 2 is pulled out of the outer container 1. This raw material powder M1,
M2 is not solidified and shows some fluidity in the outer container 1. However, as described above, since the inner container 2 has a very small wall thickness, after the inner container 2 is pulled out, the inner and outer layers are separated. Therefore, the raw material powders M1 and M2 do not excessively enter and mix. 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 supply electricity between the upper and lower electrodes 31 and 32 for an appropriate time. The high frequency current for plasma generation is, for example, 3,000 to 5,000 amperes, and the frequency is about several GHz.

The method of manufacturing the step-index optical fiber has been described above. In the case where the index distribution is changed (for example, a graded-index optical fiber), a plurality of inner containers 2 having different diameters are prepared. These are arranged concentrically in the outer container 1. Then, after filling the raw material powders having different dopant concentrations between the internal containers, each internal container 2 is pulled out and sintered in the same procedure as described above. According to this manufacturing method, the index distribution of the optical fiber preform can be changed because the concentration of the dopant in the section partitioned by each internal container is different. In addition, according to the above-mentioned manufacturing method, although a small amount of raw material powder can be mixed and mixed at the boundary surface of the filling body, the optical fiber after dehydration sintering has no practical problem by dehydration sintering. In addition to the manufacturing method of this embodiment, for example, prior to extracting the inner container 2, the inner and outer raw material powders M1 and M2 are hardened to a certain degree (hardness such that the inner container 2 can be pulled out relatively easily). Press
Thereafter, the inner container 2 is pulled out, and the gap between the raw material powders M1 and M2 generated by the thickness of the inner container 2 is again used for core or clad (or a raw material powder giving an intermediate index between them). After charging and charging the raw material powders, the entire raw material powders M1 and M2 may be pressed again. In the case of this manufacturing method, the inner container 2
It is easier to insert into the gap if there is a certain thickness.

Although a single-core optical fiber preform is manufactured in this embodiment, a double-core panda fiber (polarization preserving fiber) in which, for example, two internal containers are arranged can also be manufactured. In addition, the present invention can be applied to various aspects such as a boat fiber and an elliptical jacket fiber.

Next, a method for manufacturing an optical fiber preform using another apparatus for manufacturing an optical fiber preform 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, but the inner container 2
Instead of the raw material powder M1 serving as a core after sintering and charged into the inside, a cylindrical core solidified in advance so that the raw material powder M1 is not broken down during handling before setting in a manufacturing apparatus. Powder P1 is prepared. Then, a punch 3 provided with the core solid powder P1 on the lower electrode 31 is provided.
Insert and stand upright in the middle of the 1D setting hole (not shown).

Therefore, after that, the outer container 1 is
D, the core solid powder P in the outer container 1
Raw material powder for cladding is charged and charged into portions other than 1. Thereafter, as in the previous embodiment, if sintering is performed by a plasma power supply while pressurizing, the preform only needs to be taken out of the outer container 1 because the inner container 2 is not used. Instead of the core solid powder P1, a clad solid powder having a cylindrical columnar shape (the center portion is hollowed out) which has been solidified to some extent is prepared, and after setting this in the external container 1, the center portion is formed. Raw material powder for the core may be charged and loaded.

Next, a method of manufacturing an optical fiber preform using another apparatus for manufacturing an optical fiber preform according to the present invention will be described. In the manufacturing method of the third embodiment shown in FIG. 4, the same manufacturing apparatus as that of the first embodiment can be used.
The jacket J is formed of the same material as the raw material powder of the core so that it becomes a part of the core (or may be a clad) after sintering. The dopant is adjusted to be different from the core or cladding as needed.

Therefore, according to this method, by performing discharge and energization between the raw material powders while applying pressure, a simple operation of simply removing the outer container 1 after sintering is sufficient.
In other words, since the jacket J is sintered as it is and becomes a part of the core, there is no need to pull it out. In addition, although the above-mentioned process describes the manufacturing method of the porous base material (preform), by performing the electric sintering for a long time,
The dehydration sintering step can be completed. In this case, it becomes possible to manufacture an optical fiber preform that can be shifted to the drawing step. In the above method, powder is used for the core. However, as shown in FIG. 5, the core is previously used as the sintered material M1 ', and the surrounding material is filled with the powder material M2' of the clad and sintered. It is also possible. According to this method, the base material at the bottom end (particularly, the conical tip of the core) can be easily formed.

[0024]

As described above, according to the present invention, a hollow cylindrical die is filled with a raw material powder to be a cladding of an optical fiber, and a raw material to be a core of an optical fiber is filled inside the die. The powder is filled, 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 and simultaneously conduct electricity between the electrodes. Heating and sintering between raw material powders by heating makes it possible to manufacture optical fiber preforms in a short time and, unlike the conventional mechanical shape method, does not require a binder, providing high quality products it can.

Further, according to the present invention, if the raw material powder is manufactured in advance in a dedicated place having a high airtightness and the raw material powder is transported from there, there is a possibility of environmental pollution. It is possible to provide a method for manufacturing an optical fiber preform having a number of excellent features such as a small number, no restriction on location conditions, and no increase in equipment cost.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an apparatus for manufacturing an optical fiber preform 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 apparatus for manufacturing an optical fiber preform.

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]

 Reference Signs List 1 outer container 2 inner 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)

[Claims] 1. A hollow cylindrical die (1) is filled with a raw material powder (M2) serving as a cladding of an optical fiber, and a material powder (M2) serving as a core of the optical fiber is filled inside the die.
1), electrodes (3) are arranged on both sides of the die (1), and a high-frequency pulse is applied while the raw material powder (M1 · M2) is pressed by the electrode (3), thereby obtaining the raw material powder. Body (M1
M2), a plasma discharge is generated, and the raw material powder (M1 · M
2) A method for producing an optical fiber preform, wherein the space is heated and sintered. 2. A jacket (2 ') made of an appropriate material that becomes a part of the core after sintering is set in a portion of the die (1) where the core is filled. Item 2. The method for producing an optical fiber preform according to Item 1. 3. A raw material powder to be an optical fiber core is solidified in advance so as not to collapse and formed into a column shape, and a die (1) is filled with the raw material powder (M1) to be a clad before filling the die (1). The method for producing an optical fiber preform according to claim 1, wherein the optical fiber preform is set in the optical fiber preform. 4. A container (2) is mounted in a die (1),
The light according to claim 1, wherein after the raw material powders (M1 and M2) are inserted and filled into and from the container (2), the container (2) is extracted, and then sintering is performed by discharging and energizing. Manufacturing method of fiber preform.