JP4076111B2 - Optical fiber preform manufacturing method and manufacturing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a preform for optical fibers, in particular, to methods and apparatus for producing useful optical fiber preform in the manufacture of polarization maintaining fiber.
[0002]
[Prior art]
Conventionally, as a method of manufacturing an optical fiber, soot is formed by depositing silicon oxide fine particles generated by hydrolyzing a raw material gas such as silicon tetrachloride with an oxyhydrogen flame at the tip of a starting target material pulled up while rotating. VAD method (vapor phase shafting method) for producing a deposit, generated by hydrolyzing a raw material gas such as silicon tetrachloride with an oxyhydrogen flame by a rotating starting target material with a burner moving relative thereto An OVD method (external method) for depositing silicon oxide fine particles to produce a soot deposit, and a raw material gas is supplied into a cladding member such as a quartz tube, and the silicon oxide fine particles generated by the reaction are inner peripheral surfaces. An MCVD method for depositing and vitrifying the substrate is known.
[0003]
In a single mode optical fiber, light that propagates when stress is present in the core is divided into two polarization modes along the fast wave axis and the slow wave axis, and propagates in the core at different speeds. If the stress in the core does not change in the propagation direction, light propagates while maintaining this polarization mode . An optical fiber polarization-maintaining fiber used in some optical components has positively utilized this property. As a method of applying stress in the core, there is a method of inserting a stress applying member of a different material into a base material used for drawing an optical fiber, but the manufacturing process is complicated, and during these processes, There is a problem that many processes that cause quality deterioration such as drilling holes are included. In addition, as a polarization-maintaining fiber, an elliptical core having a cross-sectional shape has been proposed, but it is not easy to manufacture such a core.
[0004]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method and an apparatus for easily manufacturing an optical fiber preform useful for manufacturing a polarization-maintaining fiber.
[0005]
[Means for Solving the Problems]
In view of the above-described actual situation regarding the polarization-maintaining fiber, the present inventors have particularly made it for an optical fiber having an elliptical core region or a polygonal core region in the circumferential direction in a cross section perpendicular to the length direction. As a result of the trial production research on the soot deposit formation process, a practically desirable method has been found. The optical fiber preform obtained by the present invention is characterized by having an elliptical core region in the circumferential direction, and the ratio of the major axis to the minor axis of the core region is controlled.
The optical fiber preform obtained by the present invention has a polygonal core region in the circumferential direction, a line segment connecting the center and apex of the polygonal shape of the core region, and the center and the center The ratio of the line segment connecting the two is controlled.
[0006]
The optical fiber preform manufacturing method of the present invention is a method for manufacturing an optical fiber preform having an elliptical or polygonal core region in the circumferential direction, and is a method for producing a flame of glass raw material such as silicon tetrachloride. The soot deposit formed by depositing silicon oxide fine particles generated by the decomposition reaction on the starting target material is vibrated, and the vibration is due to the natural vibration of the system that vibrates including the soot deposit. There is a feature that the rotational speed and the vibration frequency of the soot deposit have an integer multiple relationship .
According to the optical fiber preform manufacturing method of the present invention, core regions having various shapes can be formed. For example, the triangular core region can be obtained by vibrating the soot deposit relative to the burner three times for one rotation of the soot deposit. Further, the quadrangular core region is obtained by vibrating four times, and the pentagonal core region is obtained by vibrating five times.
[0007]
An optical fiber preform manufacturing apparatus of the present invention is an optical fiber preform manufacturing apparatus having an elliptical or polygonal core region in the circumferential direction, a mechanism for rotating a starting target material, and tetrachloride A system comprising a burner for generating silicon oxide fine particles by flame hydrolysis of silicon or the like, and a mechanism for vibrating a soot deposit rotating with the starting target material , wherein the vibration vibrates including the soot deposit. the is due to the natural vibration is characterized by to relatively vibrating the distance between the deposition position and the burner of silicon oxide fine particles of the soot deposit body by a mechanism for vibrating the soot deposit body.
The apparatus for forming the soot deposit by the VAD method, the OVD method, or the MCVD method has a relative position between the deposition position of the silicon oxide fine particles of the soot deposit rotating with the starting target material and the burner for depositing the silicon oxide fine particles. A mechanism for detecting the vibration state and a mechanism for controlling the ratio between the frequency and the rotation number of the detected vibration state to be constant are provided.
In the case of an apparatus based on the MCVD method and the OVD method, relative vibration is performed only during the production of the core portion of the optical fiber preform, and the ratio between the frequency and the rotational speed is controlled to be constant.
[0008]
According to the present invention, the shaft of the rotating soot deposit is oscillated (vibrated) with the rotating chuck as a fulcrum so that the rotational frequency and the frequency of the soot deposit at the silicon oxide fine particle deposition position satisfy an integer multiple relationship. The vibration state is controlled, and a core region composed of a plurality of layers of deposited layers having different thicknesses in the major axis direction and the minor axis direction is continuously formed in the length direction of the optical fiber preform, There is a technical feature in forming a soot deposit having a cross-sectional shape and an elliptical core region or a polygonal core region.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The manufacturing method of the optical fiber preform of the present invention will be described in detail below.
FIG. 1 shows an optical fiber preform 3 comprising a core 1 and a clad 2, and the core 1 has an elliptical cross-sectional shape having a pair of major axis and minor axis. The core 1 may be a polygon such as a triangle or a quadrangle. If the manufacturing method of the optical fiber preform 3 of the present invention is used, an elliptical or polygonal core region can be formed.
[0010]
FIG. 2 shows a case where a glass raw material such as silicon tetrachloride is hydrolyzed with a flame from a burner 4, and the generated silicon oxide fine particles are deposited on a rotating starting target material to form a soot deposit 5. It shows how the optical fiber preform is manufactured. In order to form the elliptical core region in the optical fiber preform, it is necessary to vibrate the soot deposit body 5 relative to the burner 4 in the major axis direction of the ellipse, and FIG. On the other hand, the soot deposit 5 is vibrated, the rotation axis for rotating the starting target material is shifted from the direction of gravity, and the starting target material is swung (vibrated) with respect to the burner. The vibration of the body 5 is due to the natural vibration of this vibration system. The state of vibration is monitored by a camera and is fed back to the rotation mechanism as a predetermined number of revolutions, so that the number of revolutions is determined to be an integral number of the number of vibrations.
[0011]
FIG. 2B shows a case in which the burner 4 is vibrated, that is, reciprocated in the horizontal direction in the figure with respect to the soot deposit 5 . In either case, the vibration direction is the major axis direction of the core.
In the present invention, the relationship between the rotational frequency and the vibration frequency of the soot deposit is an integral multiple. This relationship is extremely important in making the vertical cross-sectional shape of the core elliptical. The ratio of the major axis to the minor axis of the core can be arbitrarily set by controlling the vibration width.
[0012]
FIG. 3 shows a state where an optical fiber preform having the configuration of the present invention is manufactured by the OVD method (external method), and the silicon oxide is rotated while the rod-like target material 6 is rotated and the burner 4 is relatively moved. The soot deposits 5 are formed by depositing fine particles thereon. In the example shown in FIG. 3, the rod-shaped target material 6 is rotated at a fixed position, and silicon oxide fine particles are deposited while the burner 4 approaches and separates from the rod-shaped target material 6. The relationship between the rotational speed of 5 and the reciprocating motion (frequency) of the burner 4 is controlled to an integral multiple.
[0013]
FIG. 4 shows how an optical fiber preform is manufactured by the MCVD method. The tubular target material 7 is rotated and the burner 4 is moved relative to the silicon oxide fine particles on the inner peripheral surface of the tubular target material 7. The base material is formed by depositing. In the example shown in FIG. 4, the tubular target material 7 is rotated at a fixed position, and silicon oxide fine particles are deposited while the burner 4 approaches and separates toward the tubular target material 7. And the reciprocating motion (frequency) of the burner 4 are controlled to an integral multiple.
[0014]
In the VAD method and the OVD method, the deposition efficiency of depositing the silicon oxide fine particles generated by the flame hydrolysis reaction on the rotating starting target material is sensitive to the manufacturing conditions, not only the flow rate of the gas forming the flame, It is also greatly affected by the distance from the flame.
[0015]
In the MCVD method, a combustion gas containing a glass raw material gas is supplied to a tubular target material into a tube and heated by a burner that moves relatively in parallel with the tubular target material. Vitrification and formation reaction of silicon oxide fine particles occur, and the silicon oxide fine particles generated earlier are deposited by a thermophoresis effect at a relatively low temperature part slightly away from the heating position. The amount of deposition at this time largely depends on the temperature of the deposition position.
[0016]
FIG. 5 is a diagram illustrating the positional relationship between the soot deposit and the burner. More specifically, the distance from the burner 4 at a certain position A on the circumference of the soot deposit 5 is d, the distance from the burner 4 at a position B rotated 90 degrees from the position A is d ′, and the position A When the distance from the burner 4 at the position A ′ rotated 180 degrees is d, the distance from the burner 4 at the position B ′ rotated 180 degrees from the position B is d ′, and d is larger than d ′, The soot deposition thickness on the AA ′ side is different from the soot deposition thickness on the BB ′ side, and an optical fiber preform having an elliptical core region is obtained.
[0017]
In the case of the OVD method, it is sufficient to apply vibration only when the core portion is formed. In the VAD method, the formation of the core portion is more sensitive to the change in the distance between the burner and the soot deposition portion than the formation of the cladding portion, and therefore, only the core portion is conveniently elliptical.
[0018]
Also in the MCVD method, by regularly changing the distance between the soot deposit and the burner, the soot deposition thickness on the AA ′ side and B as shown in FIG. 5 in the VAD method and the OVD method. The soot deposition thickness on the −B ′ side is different, and an optical fiber preform having an elliptical core region is obtained.
[0019]
In order to regularly change the distance between the soot deposit and the burner, in the VAD method, the burner is fixed and the soot deposit is shaken and vibrated. In the OVD method, the burner is moved closer to or away from the burner. Can be done conveniently.
[0020]
In the present invention, the number of vibrations per rotation of the soot deposit is an integral multiple, and the soot deposit and the burner are relatively moved closer to and away from each other during one revolution of the soot deposit. A polygonal core region can be formed by giving an integer number of times and forming a plurality of thick deposition layers in the length direction of the soot deposit.
In the present invention, the means for detecting the positional relationship between the soot deposit and the burner is arbitrary. For example, the deposition position of the silicon oxide fine particles in the soot deposit is detected by processing an image captured from a camera. Can
[0021]
【Example】
Example 1
Soot deposition by using a device that forms soot deposits by the VAD method, hydrolyzing glass raw materials such as silicon tetrachloride with a flame from a burner, and depositing silicon oxide fine particles generated by the reaction on the starting target material Formed body. The apparatus used was a mechanism in which the rotation axis for rotating the starting target material was shifted from the direction of gravity, and the starting target material was swung (vibrated) with respect to the burner (the mode shown in FIG. 2A). This frequency is the natural frequency of the system including the soot deposit. Since the weight of this vibration system changes as deposition progresses, a mechanism that detects the vibration of the soot deposit is attached to the device, and the change in the frequency is monitored and fed back to the rotation speed. An optical fiber preform having an elliptical core region was produced by controlling the halves to be exactly ½.
In addition, although the example which manufactures the preform | base_material for optical fibers which has an elliptical core area | region was demonstrated, according to this invention, an elliptical core area | region or the number of sides is arbitrary by changing the relationship between a rotation speed and a frequency. An optical fiber preform having a polygonal core region can be manufactured.
[0022]
【The invention's effect】
According to the present invention, an optical fiber preform having an elliptical or polygonal core region can be easily manufactured by improving the conventional apparatus for manufacturing a circular core in cross section. It was also very desirable.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an optical fiber preform of the present invention.
FIG. 2 (a) is a schematic explanatory view showing a state in which the optical fiber preform of the present invention is manufactured, showing a mode in which a soot deposit is vibrated and a burner is fixed, and (b) is a soot deposit. An example is shown in which the body is fixed and the burner is vibrated .
FIG. 3 is a schematic explanatory view showing a state in which an optical fiber preform is manufactured by an OVD method.
FIG. 4 is a schematic explanatory view showing a state in which an optical fiber preform is manufactured by an MCVD method.
FIG. 5 is a schematic diagram for explaining the positional relationship between a soot deposit and a burner.
[Explanation of symbols]
1 Core 2 Clad 3 Optical Fiber Base Material 4 Burner 5 Soot Deposit 6 Bar Target Material 7 Tubular Target Material

Claims (3)

  A method of manufacturing a preform for an optical fiber having an elliptical or polygonal core region in a circumferential direction, and starting from silicon oxide fine particles generated by a flame hydrolysis reaction of a glass raw material such as silicon tetrachloride The soot deposit formed by depositing on the material is vibrated, and the vibration is caused by the natural vibration of the system that includes the soot deposit and vibrates. A method for producing a preform for optical fiber, wherein the relationship is an integral multiple. An optical fiber preform manufacturing apparatus having an elliptical or polygonal core region in the circumferential direction, and a mechanism for rotating a starting target material and silicon oxide fine particles by flame hydrolysis of silicon tetrachloride and the like And a mechanism for vibrating the soot deposit that rotates with the starting target material , wherein the vibration is due to the natural vibrations of the system that vibrates including the soot deposit, An optical fiber preform manufacturing apparatus characterized by relatively vibrating the deposition position of silicon oxide fine particles in the soot deposit and the burner by a mechanism for vibrating.   A mechanism for detecting a relative vibration state between the deposition position of the silicon oxide fine particles in the soot deposit and a burner for depositing the silicon oxide fine particles, and a ratio between the frequency and the rotation number of the detected vibration state are made constant. The optical fiber preform manufacturing apparatus according to claim 2, further comprising a control mechanism.

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