JP2003327440A - Method for manufacturing preform for optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a preform for an optical fiber, by which the length of defective fiber generated for the time until the spinning operation is stabilized after the start of the spinning operation and the lost time for that time can be shortened when the preform is freshly set on a drawing device and the tip of the preform is melted and drawn so as to be spun into the fiber on the occasion of the manufacturing of the optical fiber. <P>SOLUTION: The method for manufacturing the preform for the optical fiber includes two processes comprising, after forming a glass body having a core, inserting the glass body into a glass tube and unifying them by heating and is characterized in that before heating and unifying, at least one end of the glass tube is ground into a tapered form similar to the meniscus form formed at the time of drawing. <P>COPYRIGHT: (C)2004,JPO

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, and more particularly to a method for manufacturing a communication optical fiber.

[0002]

2. Description of the Related Art An optical fiber uses quartz glass as a base material. Unlike ordinary glass materials, it is extremely difficult to melt while maintaining high purity.Therefore, a base material with a predetermined refractive index distribution was synthesized in advance, melted and softened in a heating furnace, and stretched into thin pieces. It is generally spun. As a base material synthesizing method, MCVD method, VAD method, OV
D method etc. are proposed. For example, as shown in FIG. 6 a), a central portion including a core is manufactured by these manufacturing methods (FIG. 6 shows the case of the VAD method) to form a VAD core rod 61,
A jacket tube 62 using a quartz tube as the cladding
To prepare. A method is known in which these are held by a VAD core rod support rod 64 and a jacket tube support tube 63, and heat-integrated to form a base material as shown in FIG. 6b). It is also known to carry out the integration simultaneously with the drawing. An electric furnace is usually used as the heating furnace of the wire drawing machine and the temperature is set to 2000 ° C. or higher.
The base material is inserted into this, the tip is melted by heating, and the fiber is spun by stretching. When spinning is in a steady state, the tip shape of the base material becomes stable by forming a meniscus that is determined by the outer diameter and viscosity of the base material, the temperature distribution by the heating furnace heater, the drawing speed, etc., and the fiber characteristics obtained are also stable. . However, immediately after the start of drawing, the tip shape of the base material is different from this, and spinning is not stable. In order to improve this, it has been proposed to pretreat the tip in advance (Japanese Patent Laid-Open No. 7-
330362, JP-A-8-310825). As a result, defects such as a change in fiber diameter and a change in characteristics immediately after the start are reduced, and work efficiency is achieved. However, although processing the tip into a conical shape is effective as described above, performing such a treatment after synthesizing the base material results in the following new problems and is still not sufficiently satisfactory. There wasn't. Performing the tip processing requires additional processing in addition to the conventional work, resulting in an unprecedented man-hour. If the processing method is inappropriate, the base material may be damaged during processing. Further, there is a risk of contaminating the base material due to processing, which may cause poor fiber strength. When the base material becomes large, the processing equipment itself becomes large, and not only the workability is poor, but also the cost for installing the equipment increases.

[0003]

Therefore, according to the present invention, when manufacturing an optical fiber, a spinning operation is started when a base material is newly set in a drawing device and a tip is melted and spun into a drawing fiber. An object of the present invention is to provide a manufacturing method of an optical fiber preform capable of shortening the length of a defective fiber and the loss time therebetween during the period from the completion to the stabilization.

[0004]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems, and adjusted the tip of the base material to have a desired shape when the base materials are synthesized. It was found that it can be directly sent to the drawing step, and the present invention has been completed based on this finding. That is, in the present invention, (1) after forming a glass body including a core,
It consists of a two-step process of inserting this into a glass tube and heating and integrating it. Before heating and integrating, at least one end of the glass tube is ground into a tapered shape similar to the meniscus shape formed during drawing. (2) A glass body including a core is formed, and then the glass body is inserted into the glass tube, and then the tip portion is heat-integrated. It consists of a two-step process of simultaneously performing the drawing and drawing, and at least one end of the glass tube is ground to a taper shape similar to the meniscus shape formed during drawing before the heating and unifying. A method for manufacturing an optical fiber preform characterized by:
(3) The method for producing an optical fiber preform according to (1) or (2), characterized in that the tapered portion of the glass tube is mechanically ground and then the ground portion is washed. 4) The optical fiber according to the item (3), characterized in that after the glass tube is tapered by mechanical grinding, the ground portion is washed and further the surface of the ground portion is polished to be smooth. Base material manufacturing method,
(5) A portion of the glass body including the core, which corresponds to the tapered portion of the glass tube, is tapered at least a portion corresponding to a place where the tapering is started (1) or (2). (6) The method for producing a base material for an optical fiber described in (6), wherein the glass tube is melted by a heat source such as a flame or an electric furnace, stretched and thinned, and then the terminal is sealed (2). (7) Inserting a quartz rod with an outer diameter slightly smaller than the inner diameter of the tube and grinding the inside so that it approaches the tapered tip, 1. The method for producing an optical fiber preform according to (3) or (4), characterized in that the tip of is sealed by heating, and any one of (8), (1) to (7).
The present invention provides a method for producing an optical fiber, characterized in that, when an optical fiber preform produced by the method of the above item 1 is drawn, the one end processed portion is inserted into a drawing furnace and exposed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION According to the manufacturing method of the present invention, a base material is preliminarily manufactured to have an ideal tip shape at the time of synthesizing, rather than forming a wire drawing start end of the synthesized base material. Thus, it is possible to omit the work involved in the tip processing, and to suppress the inconveniences and costs associated therewith. The following description is based on the drawings as needed, but the drawings are examples of preferred embodiments of the present invention, and the present invention is not limited thereto.

[0006] Usually, the drawing device is vertically equipped with a furnace, a resin coater,
A resin curing device and a take-up capstan are arranged. The glass is melted in a furnace and continuously drawn by a capstan. Since the glass has to be pulled out at the beginning, the base material is put into a furnace to heat up and the tip end softens and catches falling by gravity. Therefore, as shown in FIG. 1, it is desirable that the starting end of the base material has a conical shape with a weight 14 attached to the tip. Further, it is advantageous that the tip shape 12 (conical shape) of the base material is similar to the meniscus 11 (also described for reference) formed at the time of drawing, and the taper shape grinding in the present invention is It is performed so as to resemble the meniscus shape.

As a feature of the method of manufacturing the base material in the present invention, a method of carrying out in two steps was selected. As a result, the glass body including the core portion and the glass body that is all the cladding portion are manufactured independently, so that even if terminal processing is performed in the cladding portion applying step, the refractive index profile can be appropriately adjusted during core synthesis to achieve good results. Obtaining fiber properties is performed independently and does not compromise productivity. Examples of the glass body that is the cladding portion include synthetic quartz. As a method of applying a layer made of a glass body that is all the clad portion to a glass body including a core portion,
A jacket method (1 below) in which a glass body including a core portion is inserted and integrated into a glass tube (for example, a quartz tube) and a method (2 below) in which the glass body is integrated at the same time as drawing can be used. With either method, the synthetic glass can be applied to the outside of the rod-shaped glass body.

1) Jacket Method Usually, a glass tube used for a jacket (hereinafter, also referred to as a jacket tube), for example, a quartz tube, is formed by forming a hollow ingot into a tubular shape and stretching it to obtain a desired length. It is obtained by cutting both ears with a cutter. Therefore, when a hollow ingot pipe or a stretched pipe is used, both ends thereof are usually cylindrical. A rod-shaped core glass is put in this, and it heats from the outside and is collapsed and integrated. As a result, the end of the effective part has a sharp cylindrical shape. If this is subjected to fire working in which it is stretched while being heated by a burner, or furnace working in which it is heated and stretched in an electric furnace, there arises a problem that the spinning is not stable immediately after the start of the above-mentioned drawing. In order to solve such a problem, in the present invention, the outside of the end of the pipe is tapered before the jacket. The taper is mechanically ground. Thereby, the taper can be formed efficiently. During mechanical grinding, abrasives and glass powder may adhere to the surface of the base material.If the fiber is made later, the outer diameter may change at this part and the strength may be insufficient. It is preferable. In addition, it is preferable that the surface of the processed portion is smooth, because the wire drawing is fast and stable when it is exposed, so that the loss reduction effect is high.

2) Simultaneous integration method during drawing Usually, the jacket tube used in the simultaneous integration method during drawing also has a sharp cylinder at both ends as described above, and has the same problem as above. In the simultaneous integration method at the time of drawing, the tip of the tube needs to be sealed in advance for the purpose of reducing the pressure inside. Using the method of heat shrinking and welding the tube after inserting the core material inside the jacket tube,
It is difficult to taper the tip efficiently. As a solution, in the present invention, the outer side of the pipe end is tapered by mechanical grinding before the core rod is inserted into the jacket pipe. Thereby, the taper can be formed efficiently. It is also preferable to clean the grinding part. Further, a rod is inserted inside the tip and the tip is heated and sealed from the outside. At this time, it is preferable to hollow the inside of the rod like a taper tip. This allows the tapered portion to be closer to the target shape.

As another method, it is also effective to heat and stretch the tube to give contraction and taper elongation so that the sealing operation and the taper processing are simultaneously performed. Particularly, a method of heating the central portion of a long tube and gradually stretching it is preferable because two tubes can be processed at one time and it is efficient.

3) Core taper processing In any case, it is preferable to process the core portion corresponding to the taper so that the core portion becomes thinner toward the tip, because the wire diameter is stabilized more quickly than in the case of no processing. This is an effect that the ratio of the core and the clad becomes close to the value at the parallel portion. Ideally, it should be constant in all the meniscus processed parts, but it is also preferable to grind the core rod into a conical shape so as to approximate it. In particular, it is effective to strengthen the approximation in the vicinity of the start of tapering, and the reason for this is that the fiber is substantially obtained at the exit portion from this vicinity.

[0012]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto. Here, a case will be described in which a single-mode optical fiber is manufactured by manufacturing a core preform including a part of the clad by the VAD method and further adding a clad portion using a tube. Even if the refractive index profile is of another type, the core portion may be manufactured by another manufacturing method.

As shown in FIG. 2, in the VAD method, the vaporized silicon tetrachloride, germanium tetrachloride, oxygen, and hydrogen gas were sent together to a core burner 21 having a multi-tube structure, and generated by ignition. A synthetic glass fine particle is obtained by hydrolyzing in a flame and sprayed on a seed rod 24 to form a porous core preform 23. In order to stabilize the characteristics, a similar clad burner 22 is arranged above the core burner 21, and silicon tetrachloride and oxygen / hydrogen are similarly reacted to provide a clad portion on the outer periphery of the core soot. This is 1500
Heat to about 1600 ° C. to obtain transparent glass. In a single mode optical fiber, the dimensional ratio of core to cladding is 1: 1
It is about 3, but it is difficult to give a thick cladding in the VAD process, and the finished VAD glass is 1: 4.5.
Met. Thus, a glass body including the core was produced. This is stretched and adjusted to an outer diameter of 30 mm, then, as shown below, a separately prepared outer diameter of 90 mm x inner diameter of 33 mm
It was inserted into the quartz tube of No. 3, and the ratio was adjusted to a predetermined value.

[Embodiment 1] As a tip grinding method, as shown in FIG. 3, a grinding wheel 32 having a cutting blade formed of diamond powder is pressed while rotating to bring the tip of the jacket tube 31 into the wheel 32. The shape was adjusted. It was carried out while sprinkling cooling water 33 to prevent heating of the processed part. Tube 3 vertically
1 was installed and the whetstone 32 was gradually pushed up from the bottom. At this time, if you make a hole in the center of the grindstone 32,
The shavings and the cooling water 33 flowed out well, which had the effect of keeping the contamination of the pipe at a minimum level. A cone-shaped grindstone was prepared for piercing the inside of the rod, and the same procedure was performed. As shown in FIG. 4, a support tube 42 is welded to the opposite end of the jacket tube 41 having the processed tip so that the processing lathe can grasp the same.
The lathe chuck 45 gripped the chuck at this portion. The support pipe 42 side was connected to a vacuum pump so that the inside could be sucked and depressurized. VAD that has been processed into a predetermined size and shape in advance
Similarly, a support rod 44 is attached to the pulling start side of the core rod 43 and set on a lathe by a lathe chuck 47,
I inserted it inside. After rotating the lathe and roasting the tip with oxygen and hydrogen flames to weld the pipe 41 and the core rod 43,
The pump was turned on to reduce the pressure inside. If the suction is started when the terminal is not completely closed, foreign matter will be sucked inside and bubbles will be generated, so be careful. After that, the burner was driven and solidified over the entire length. That is, the pre-integrated base material and the jacket tube as shown in FIG. 7a) are integrated as shown in FIG. 7b).

When this is transferred to a wire drawing apparatus and heated in an electric furnace to soften the tip, it extends by the weight, so this is taken out and stretched by a capstan to 125 μm, and an ultraviolet curable resin is applied to coat the fiber. And It takes time to adjust the outer diameter to 125 μm without the tip processing, and after that, the dimensional ratio of the core and the clad did not reach a predetermined value, and it took time to stabilize, but it is defined in the present invention. This time was drastically shortened when the tip processing was applied. Although it depends on the size of the base material, in the base material used in this example, it takes about 2 to 3 hours from the start of drawing until the meniscus shape is stabilized, according to the present invention.
It was reduced to about time. It should be noted that although the fiber obtained by processing by the above method sometimes broke, the broken portion was analyzed and metal powder was detected. It is thought that this is because the whetstone pieces adhered during grinding, so we added a step of cleaning with a 5% hydrofluoric acid solution after grinding, rinsing with pure water, and then drying, and the occurrence of wire breakage during wire drawing was suppressed. Was done. Therefore, it is a preferred embodiment to carry out such a washing step in the present invention. However, if the surface is roughened by pickling, the wire diameter may fluctuate during the process of drawing it into a small diameter, and the coating die may be clogged. When the tip was mechanically polished for the purpose of preventing this, such a defect was improved. Therefore, it is a preferred embodiment to carry out such polishing in the present invention.

[Embodiment 2] As shown in FIG. 8a), in the same manner as in Embodiment 1, a support pipe 83 is welded to the opposite end of the jacket pipe 82 whose front end is processed so as to be gripped by a processing lathe. It was chucked at. Similarly, a support rod 84 was attached to the pulling start side of the VAD core rod 81 which was previously processed into a predetermined size and shape, set on a lathe, and inserted into the pipe 82. Rotate the lathe in the same manner as in Example 1,
The tube 82 and the core rod 8 were broiled at the tip with oxygen and hydrogen flames.
1 was welded. As a result, as shown in FIG. 8b), it is possible to combine the core rod and the tube with only the tip portion solidified. This was transferred to a wire drawing device and the tip was heated in an electric furnace. At the same time, the support tube 83 side was connected to a vacuum pump, and the pump was turned on to reduce the pressure inside. By doing this, solidification and stretching can be done at the same time. Even in this method, the same excellent effect of tip processing as in Example 1 was recognized.

[Embodiment 3] As shown in FIG.
When the core rod 81 and the jacket tube 82 are welded together at the end on the drawing start side by the method described in (1), the inner diameter of the tube 82 is straight, but the tip of the VAD rod 81 is thin, so that the clearance is Sometimes it became too big to weld well. Therefore, as shown in FIG. 9, an optical fiber preform was produced in the same manner as in Example 2 except that a rod whose inside was tapered was used as the jacket tube sealing rod 95 for sealing the tip. FIG. 5 shows an enlarged view in cross section showing the tip sealed state. As a result, the clearance was improved, and the tip shape shown in FIG. 9b) was produced when the tip portion completed welding in a short time (about 10 to 20 minutes) after the wire drawing was started. Even in this method, the same excellent effect of tip processing as in Example 1 was recognized.

[Embodiment 4] As shown in FIG. 10, in the same manner as in Embodiment 1, the jacket tube 102 having the processed tip is set on a glass lathe and heated with an oxygen / hydrogen flame.
The tube 102 was gradually extended to both sides. This creates a meniscus shape which also thins the tube. Finally, by burning off with a flame, the tip could be sealed as shown in FIG. 10b). Next, the tip of the VAD rod is also heated by a flame and then pulled down to form a taper. The rod 101 was inserted into the tube 102, and the support tube 103 was attached to the opposite side of the tube 102. This was set in the drawing device. When gradually inserting into the furnace and reducing the pressure in the interior with a vacuum device attached to the support tube, welding of the tip portion occurs, and further this portion extends and wire drawing can be started.
It was possible to manufacture a drawn optical fiber 105 as shown in c). Then, as with ordinary drawing, when the glass body is pushed into the furnace while the fiber is being taken out, solidification and fiberization proceed at the same time. Even in this method, the same excellent effect of tip processing as in Example 1 was recognized.

[0019]

According to the method for producing a base material for an optical fiber of the present invention, the tip of the base material is adjusted to have a desired shape at the time of synthesizing the base materials, so that the finished base material is directly drawn. Therefore, it is possible to suppress the inconveniences and costs associated with the work of processing the base material tip after synthesis. Furthermore, by using the optical fiber preform manufactured according to the present invention, it is possible to reduce the length of a defective fiber and the time loss that occur between the start of the spinning operation and the stabilization during the drawing of the optical fiber. The optical fiber can be manufactured efficiently.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a cross section of a drawing taper shape and a tip shape in the present invention.

FIG. 2 is an explanatory diagram showing a method of manufacturing core soot by the VAD method.

FIG. 3 is an explanatory view showing a cross-sectional view of a tip external cutting process in the present invention.

FIG. 4 is an explanatory view showing a sectional view of a jacket process in the present invention.

FIG. 5 is an explanatory view showing the insertion of a cone-shaped grinding sealing rod in the present invention in a sectional view.

FIG. 6 is an explanatory diagram showing, in a cross-sectional view, a) a state before welding of a core rod and a jacket tube, and b) a shape example after the base material and the jacket tube are integrated with each other in the related art.

7A and 7B are explanatory views showing changes in shape of a jacket pipe and a base material in a cross-sectional view in Example 1, FIG. 7A) shows a base material and a jacket pipe before integration, and FIG. 7B) shows a base material and a jacket. An example of the shape after the tubes are integrated is shown.

8 is an explanatory view showing, in a sectional view, changes in the shapes of the core rod and the jacket tube before and after performing Example 2. FIG.
a) shows a state before welding of the core rod and the jacket tube, and FIG. 8 b) shows a shape of the base material after welding.

9 is an explanatory view showing a change in shape of the core rod and the jacket tube before and after performing Example 3 in a sectional view.
9A shows the state before welding of the core rod and the jacket tube, and FIG. 9B shows the shape of the base material after welding.

FIG. 10 is an explanatory view showing changes in shape of the core rod and the jacket pipe before and after carrying out Example 4, in a sectional view, FIG. 10a) shows a state before welding the core rod and the jacket pipe, and FIG. The shape of the jacket tube after welding is shown, and Fig. 10c) shows the state at the time of drawing.

[Explanation of symbols]

71 VAD core rod 72 Jacket tube 73 Jacket tube support tube 74 VAD core rod support rod

Claims (8)

[Claims] 1. A two-step process of forming a glass body including a core and then inserting the glass body into a glass tube to heat and integrate the glass body. Before the heat integration, at least one end of the glass tube is lined. A method for manufacturing an optical fiber preform characterized by grinding a taper shape similar to the meniscus shape formed during drawing. 2. A two-step process of forming a glass body including a core, inserting the glass body into a glass tube, heating and integrating the tip portion, and simultaneously performing heating integration and drawing while depressurizing the inside. Before the heating and unifying, at least one end of the glass tube is ground to have a tapered shape similar to a meniscus shape formed during drawing, and a method for manufacturing an optical fiber preform. 3. The method for producing an optical fiber preform according to claim 1, wherein the grinding process is performed after mechanically grinding the tapered shape of the glass tube. 4. The taper-shaped grinding of the glass tube is performed by mechanical grinding, the ground portion is washed, and further the surface of the ground portion is polished to be smooth. Manufacturing method of optical fiber preform. 5. A glass body including the core, wherein a portion corresponding to a tapered portion of the glass tube is tapered at least at a portion corresponding to a place where the tapering is started. Manufacturing method of optical fiber preform. 6. The method for producing an optical fiber preform according to claim 2, wherein the glass tube is heated and melted, stretched and thinned, and then the terminal is sealed. 7. A quartz rod, the outer diameter of which is slightly smaller than the inner diameter of the tube and whose inside is ground so as to approach the tapered tip, is inserted into the inside of the tip-processed tube, and the tip of the tube is heated and sealed. The method for manufacturing an optical fiber preform according to claim 3 or 4, wherein 8. When drawing the optical fiber preform manufactured by the method according to any one of claims 1 to 7, the optical fiber preform is inserted into a drawing furnace from the portion processed at one end thereof and exposed. Optical fiber manufacturing method.