JPH061631A - Method for synthesizing porous base material for optical fiber - Google Patents

Abstract

PURPOSE:To provide a method (device) for synthesizing porous base material for optical fiber improved in sticking ratio of a glass particulate to the porous glass body for optical fiber. CONSTITUTION:In the case of emitting the glass particulate 7 to be a clad part of the optical fiber from a burner 2 to a core rod 1 by introducing a raw material gas such as SiCl4 and GeCl4 and a combustion gas such as hydrogen and oxygen to the burner 2 to be stuck and deposited on the core rod 1, an electrode wire 3 is inserted into the burner 2 and by applying D.C. voltage of alternate positive and negative polarity to the electrode wire 3 with interposed 0 V, the glass particulate 7 is positively and negatively charged. The sticking ratio is improved by the attracting action of static electricity because the glass particulate 7 to be stuck to a target is different from the glass particulate 7 previously heaped on the target in polarity. Particularly by providing a period having no 0V charge, the target is provided with a period to be almost 0V and the sticking efficiency of the glass particulate 7 is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a porous preform for optical fibers.

[0002]

2. Description of the Related Art To manufacture an optical fiber preform,
A part of the core and the clad is manufactured as a porous glass base material by the VAD method, and after vitrification, the remaining clad portion is synthesized on the surface of the vitrified glass base material (target) by an external method. To do. The porous preform (preform) for optical fiber synthesized in this way is drawn to form a single mode optical fiber consisting of a core with a diameter of 10 μm and a clad with an outer diameter of 125 μm formed on the outer periphery of the core. To manufacture.

In any of the above processes for synthesizing a porous base material for an optical fiber, a raw material gas such as SiCl ₄ , GeCl _{4 is} generally used by using an oxyhydrogen burner.
Hydrolyzes the steam of oxyhydrogen flame into SiO ₂ , Ge
Fine particles of O ₂ are formed and attached to a rotating core rod or a target made of glass fine particles deposited on the core rod. The amount and distribution of the glass particles adhering to the target change due to various factors such as the shape of the burner flame and the temperature of the base metal surface.

Although stable production of a porous preform for optical fibers has been realized by studying the above-mentioned various factors up to now, from the viewpoint of reducing the production cost of the optical fiber, fine particles for the target are used. The adhering rate of is not yet sufficient, and only about 20 to 40% of the formed glass fine particles can be used. The glass particles that have not adhered to the target are discarded into the scrubber. The glass particles that did not adhere to the target are loss and at the same time
It has the double demerit of high processing cost in the scrubber. It is necessary to further improve the adhesion efficiency of glass particles on the target in order to reduce the cost of the porous base material for optical fibers, and eventually the optical fiber.

In response to such a demand, by using a direct current high voltage whose polarity does not change, the glass particles ejected from the burner are charged and effectively adhered to the target by electrostatic force, and the adhesion efficiency of the glass particles is improved. Attempts to improve have already been made. The method is to insert an electrode into the burner, apply a high voltage of a certain polarity to the electrode, charge the glass particles ejected from the burner to a certain polarity, and apply the electrostatic force to the charged glass particles. Is also used to attach to the target.

[0006]

In the above-mentioned method, when glass particles charged in the same polarity continuously are attached to the target, the electric charge is accumulated in the target and is attached later due to the potential. We have encountered the problem that the glass particles that repel are repelled, the adhesion efficiency is reduced, and cracks occur.

As a method for solving such a problem,
Prior to adhering the glass particles, static elimination ions are sprayed onto the target to lower the surface potential of the target. However, such ion spray on the target disturbs the shape of the flame from the burner,
There is a problem that the synthesis conditions of the porous preform for optical fibers are changed. In order to improve such a problem, the synthesizing device for the porous preform for optical fiber becomes complicated,
Eventually, the price of the optical fiber porous base material manufactured by using the optical fiber porous base material synthesizing apparatus was soared,
As a result, there is a problem of raising the price of optical fiber.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for synthesizing a porous preform for an optical fiber which solves the above-mentioned problems and further improves the adhesion efficiency of glass particles on a target. . Therefore, according to the present invention, in a method of hydrolyzing a vapor of a raw material gas in an oxyhydrogen flame to form glass fine particles, and adhering the glass fine particles to a target to synthesize a porous preform for an optical fiber, There is provided a method for synthesizing a porous preform for an optical fiber, characterized in that the glass particles charged positively or negatively are alternately made to reach the target.

As a method of charging the glass fine particles,
(1) Continuously in a cycle in which glass particles are charged positively for a first predetermined time, glass particles are not charged for a second predetermined time, and glass particles are negatively charged for a third predetermined time. A method of applying a voltage to an electrode inserted in a burner for injecting the glass particles so as to charge the glass particles, (2) a method of setting the second predetermined time to zero, that is, a non-charging time is provided. No way,
(3) Method of separately applying positive and negative DC voltages to respective electrode wires inserted in at least first and second burners arranged in relative reciprocal movement relative to the target (4) Positive and negative polarities are separately applied to the respective electrode wires inserted into each of at least the first and second burners arranged at a predetermined angle at a position where they rotate relative to the target. There is a method of applying a negative DC voltage.

[0010]

The electrode conductor is inserted inside the burner which forms the glass particles adhered to the target, and, for example, a direct high voltage of positive and negative polarities is alternately applied at regular intervals with 0V sandwiched (if necessary, this interval is (Although it may be zero), the positively charged and negatively charged fine particle streams are alternately sent to the target, and, for example, the positively charged target surface fine particles effectively attract the negatively charged fine particles by electrostatic force. . By providing a 0V voltage period during which high voltage of positive and negative polarity does not charge the glass particles, the surface potential of the target can be made to be near 0V, and the positive and negative charged state of the glass particles attached is improved. Therefore, the adhesion efficiency can be further improved. Any of the above-mentioned methods may be used as the method for charging the glass particles.

[0011]

EXAMPLE FIG. 1 shows a structural example of an apparatus for synthesizing an optical fiber porous preform for carrying out the method for synthesizing an optical fiber porous preform of the present invention. This apparatus for synthesizing a porous preform for optical fibers synthesizes a porous glass preform 8 by adhering glass particles 7 to a core rod 1 fixed to a shaft (not shown).
Therefore, the shaft that supports the core rod 1 (not shown)
Is reciprocally moved (traverse) in the left and right directions A and B while being rotated in the rotation direction R by a drive mechanism (not shown).
Flame 9 is ejected from the fixed water oxygen burner 2,
New glass particles 7 are further deposited on the core rod 1 and the glass particles 7 deposited on the core rod 1.

In this example, the burner 2 is constructed as a quadruple tube, Ar gas and SiCl ₄ are introduced into an inlet 21 connected to the burner inner tube 2a, and hydrogen gas (H) is introduced into an inlet 22 connected to the burner intermediate tube 2b. ₂ ) is introduced, and oxygen gas (O ₂ ) is introduced into the inlet 23 connected to the burner outer tube 2c, and is hydrolyzed in the oxyhydrogen flame, and the glass particles serving as the cladding of the optical fiber are injected as the flame 9. To be done. An electrode wire 3 is inserted in the burner 2, and a high voltage power source 6 is connected to the electrode wire 3 via an ammeter 5.

[0013]

[Embodiment 1] With reference to FIG. 1, an embodiment of a method of externally attaching a clad will be described. The axis that supports the core rod 1 is
Rotated at about 300 RPM and 500 mm
Traverse left and right at a speed of / min. A core rod 1 having an outer diameter of 20 mm and a length of 1 m is fixed to this shaft. Glass (SiO ₂ ) particles are attached to the outer periphery of the core rod 1 to an outer diameter of about 150 mm. Oxygen gas 30SL for burner 2
M, hydrogen gas 80 SLM, argon gas 20 SLM, S
iCl ₄ gas 10 SLM is introduced. In this embodiment, the electrode 3 made of tungsten and having an outer diameter of 1.6 mm was inserted into the center layer of the burner 2 up to a position 3 mm from the tip of the burner 2. A voltage having a waveform shown in FIG. 2 is applied to the electrode wire 3 from a DC high voltage power supply 6.

FIG. 3 is a graph showing an increase in the amount of glass particles attached to the target according to the above-mentioned embodiment. The curve a in the figure shows an increase in the amount of the glass particles 7 adhering to the target when the voltage from the DC high voltage power supply 6 is not applied to the electrode wire 3 under the conditions of the raw material gas and the combustion gas introduced into the burner 2. It is a curve. A curve b is the amount of the glass particles 7 adhering to the target when a positive DC voltage of +10 KV is applied to the electrode wire 3 in the burner 2.
In this case, the application rate of the high voltage to the electrode wire 3 improves the deposition rate of the glass particles 7 as compared with the deposition amount shown by the curve a, but as the charge amount of the target increases,
The adhesion rate gradually decreased, and finally cracks occurred. Curve c is an increase curve of the amount of adhered glass particles 7 according to this embodiment. In this example, as shown in FIG. 2, 0 V is applied to the electrode wire 3 in the burner 2 from the DC high voltage power source 6.
Across the period T3 = 0.5 seconds, a DC voltage of positive and negative polarities, ± 10 KV, respectively, period T1 = 1 second, period T2
= 1 second, and continuously applied in a cycle of 3 seconds. In this case, no decrease in the adhesion rate of the glass particles 7 was observed, and the adhesion amount was larger than that of the curve a showing the adhesion amount of the glass particles 7 when the DC voltage was not applied to the electrode wire 3 over the entire synthesis time. Is about doubled.

A cycle of DC voltage application from the DC high voltage power supply 6 to the electrode wire 3 according to the present embodiment shown by the curve c, a ratio of voltage application times T1 and T2 of positive and negative polarities, a period T3 during which no voltage is applied, positive and negative The condition such as the amplitude of the voltage of the polarity is that the charged particles are desired to be attached on the target without being neutralized in the space between the burner 2 and the target. Therefore, the gas synthesized by the burner 2 and injected as the flame 9 is used. It is preferable that an appropriate value exists depending on the conditions, and as a result, the surface potential of the target is near 0 KV. If the cycle of voltage application from the DC high-voltage power supply 6 to the electrode wire 3 is too short, the particles are neutralized before reaching the target, and the effect of increasing the amount of adhesion is reduced. Therefore, there is a lower limit value that matches the flow velocity of the fine particles ejected from the burner 2. Although T3 = 0.5 seconds in this embodiment, almost the same effect can be expected even if T3 is set to 0.

[0016]

Second Embodiment In the second embodiment, as shown in FIG. 4, two burners 2A and 2B are used. Two burners 2A, 2B
Have electrode wires 3A and 3B inserted therein, and these electrode wires 3A and 3B are respectively supplied from the DC high-voltage power supply 6 to
A positive voltage and a negative voltage are applied. The polarity of the DC voltage applied to these electrode lines 3A and 3B is not changed. Therefore, the flame 9A injected from the burner 2A has a positive charge, and the flame 9B injected from the burner 2B has a negative charge. In the second embodiment, the configuration and conditions of the synthesizer of the optical fiber porous preform other than the burners 2A and 2B and the electrode wires 3A and 3B described above are the same as those in the first embodiment described above.

The core rod 1 is reciprocated while being rotated. When the core rod 1 moves in the direction A, the negative glass fine particles 7B due to the flame 9B ejected from the preceding burner 2B first adhere to the target, and the positive glass fine particles due to the flame 9A ejected from the burner 2A are adhered to the target. 7A is deposited. Or, conversely, when the core rod 1 moves in the direction B, the positive glass particles 7A due to the flame 9A ejected from the preceding burner 2A first adhere to the target, and then the flame 9B ejected from the burner 2B causes The negative glass particles 7B are adhered and deposited. In other words, the movement of the core rod 1 causes the glass particles 7A and 7B in the charged state having different polarities to be alternately attached to the target. Since the charging polarities are different, the glass particles 7A and 7B are efficiently attached to the target by the attractive force of static electricity. By adjusting the voltage value applied to the electrode lines 3A and 3B, the optimum adhesion condition can be obtained.

FIG. 5 is a partial view for explaining the third embodiment of the present invention, which utilizes the rotational movement of the target. In this embodiment, the burners 2C and 2D are arranged at different angular positions with respect to the target, and the electrode wires 3C and 3D are inserted into the burners 2C and 2D, respectively. Electrode wire 3C, 3
As in the second embodiment, a voltage having a constant polarity is applied to D. Therefore, from the burners 2C and 2D, flames 9C and 9D charged with positive polarity and negative polarity are ejected toward the target, respectively. With respect to the rotation of the target, the adhered state of the glass fine particles 7C and 7D that are ejected from the burners 2C and 2D and adhere to the target is the same as in the second embodiment. Therefore, according to this third embodiment as well,
Adhesion of high glass particles equivalent to that of the second example was realized.

Although the above embodiments have been described with respect to the external attachment method, it is needless to say that the present invention can be applied to the VAD method in the same manner as above.

[0020]

According to the present invention, positively and negatively charged fine particle streams are alternately sent to the target, and the positively charged particles on the surface of the target attract the negatively charged particles by electrostatic force, or vice versa. Therefore, by attracting the negatively charged fine particles on the target surface with the positively charged fine particles by the electrostatic force, it is possible to significantly improve the adhesion efficiency of the glass fine particles to the target. Synthesis of porous matrix,
As a result, the optical fiber can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of an apparatus for synthesizing an optical fiber porous preform for carrying out a method for synthesizing an optical fiber porous preform of the present invention.

FIG. 2 is a waveform diagram of a voltage applied to the electrode wires shown in FIG.

FIG. 3 is a graph showing an adhesion amount of glass particles adhered to a target according to the first embodiment shown in FIG. 1 and an adhesion amount of glass particles by a conventional method.

FIG. 4 is a diagram showing a schematic configuration of a second embodiment of the apparatus for synthesizing an optical fiber porous preform for carrying out the method for synthesizing an optical fiber porous preform of the present invention.

FIG. 5 is a diagram showing a schematic configuration of a third embodiment of the apparatus for synthesizing an optical fiber porous preform for carrying out the method for synthesizing an optical fiber porous preform of the present invention.

[Explanation of symbols]

 1 ... Core rod 2, 2A, 2B, 2C, 2D ... Burner 3, 3A, 3B, 3C, 3D ... Electrode wire 5 ... Ammeter 6 ... DC high voltage power supply 7, 7A, 7B, 7C, 7D.・ Glass fine particles 8 ・ ・ Porous glass base material 9, 9A, 9B, 9C, 9D ・ ・ Flame

Claims (5)

[Claims] 1. A method of synthesizing a porous preform for an optical fiber by hydrolyzing a vapor of a raw material gas in an oxyhydrogen flame to form glass fine particles, and adhering the glass fine particles to a target. A method for synthesizing a porous preform for an optical fiber, characterized in that the finely charged glass particles are alternately allowed to reach the target. 2. The glass fine particles are charged to a positive polarity for a first predetermined time, the glass fine particles are not charged for a second predetermined time, and the negative glass is charged for a third predetermined time. The porous preform for an optical fiber according to claim 1, wherein a direct current voltage is applied to an electrode inserted in a burner for injecting the glass particles so that the glass particles are continuously charged in a cycle for charging the particles. Method of synthesis. 3. The glass particles are continuously charged in a cycle in which the glass particles are charged positively for a first predetermined time and the glass particles are negatively charged for a second predetermined time. The method for synthesizing a porous preform for an optical fiber according to claim 1, wherein a direct current voltage is applied to an electrode inserted in a burner for injecting the glass particles so as to be charged. 4. The positive and negative charges of the glass fine particles are separately applied to respective electrode wires inserted in at least first and second burners arranged in a relative reciprocating movement relative to the target. The method for synthesizing a porous preform for an optical fiber according to claim 1, which is performed by applying a negative DC voltage. 5. The charging of the glass fine particles is inserted into each of at least first and second burners arranged at a predetermined angle at a position where they are relatively rotated with respect to the target. The method for synthesizing a porous preform for an optical fiber according to claim 1, which is performed by separately applying positive and negative DC voltages to the electrode wires.