JP4450533B2 - Optical fiber preform manufacturing method - Google Patents

Description

【００６０】
つまり、ガラスパイプ１の送り速度Ｖ_Pは、実施例及び比較例とも１０ｍｍ／分とするのに対し、ガラスロッド２の送り速度Ｖ_Rは、実施例では９．６ｍｍ／分とする一方、比較例では１０ｍｍ／分とした。
【００６１】
また、実施例においては、ガラスロッド２の送り速度Ｖ_Rがガラスパイプ１の送り速度Ｖ_Pに比べて遅いことから、光ファイバ母材４におけるＣ／Ｃが所定の値となるように、ガラスロッド２の外径を、比較例におけるガラスロッド２の外径に比べて大きくしている（実施例５１ｍｍ、比較例５０ｍｍ）。また、実施例におけるガラスロッド２のコア径も、比較例におけるガラスロッド２のコア径に比べて大きくしている（実施例１３．０ｍｍ、比較例１２．５ｍｍ）。尚、ガラスパイプ１の内径及び外径は、実施例及び比較例ともにそれぞれ５４ｍｍ及び１８２ｍｍに設定されている。また、上記ガラスパイプ１とガラスロッド２とを一体化した光ファイバ母材４は、実施例及び比較例ともに、その外径が６０ｍｍとなるまで延伸されている。
【００６２】
表１より、比較例では光ファイバ母材４におけるコア偏心量が０．３ｍｍであるのに対し、ガラスロッド２の送り速度Ｖ_Rを遅くすることでこのガラスロッド２の長手方向に張力を付与した実施例では、光ファイバ母材４におけるコア偏心量が０．１ｍｍと極めて小さくなっている。つまり、上述したように、ガラスロッド２の長手方向に付与する張力によって、ガラスロッド２がガラスパイプ１の中心位置において位置付勢され、その結果、コアの偏心量が抑制されたものと考えられる。
【００６３】
以上の結果から、ガラスロッド２の長手方向に張力を付与してガラスパイプ１とガラスロッド２との一体化及び延伸を行う本発明に係る光ファイバ母材の製造方法は、コアの偏心量を低下して大型の光ファイバ母材を製造することができるといえる。
【図面の簡単な説明】
【図１】光ファイバ母材の製造中の状態を示す斜視説明図である。
【符号の説明】
１ ガラスパイプ
２ ガラスロッド
３ ヒータ（加熱炉）
４ 光ファイバ母材[0001]
BACKGROUND OF THE INVENTION
The present invention inserts a glass rod for a core or a glass rod for a core and a clad into a clad glass pipe, decompresses the glass pipe while heating both, and integrates the glass pipe and the glass rod. The present invention relates to a method for manufacturing an optical fiber preform that is simultaneously made and stretched.
[0002]
[Prior art]
There are three main methods of manufacturing an optical fiber preform: OVD (Outside Vapor-phase Deposition) method, VAD (Vapor-phase Axial Deposition) method, and MCVD (Modified Chemical Vapor Deposition) method. Here, in the VAD method and the MCVD method, from the viewpoint of productivity, after manufacturing the glass rod for the core or the core and the cladding, the cladding that occupies most of the optical fiber preform is used as the outer periphery of the glass rod. In addition, a method of forming by a separate process is employed.
[0003]
Specifically, as a method for forming the clad, a so-called external attachment method is known in which glass fine particles called soot are deposited on the glass rod and heated to form a transparent glass.
[0004]
On the other hand, the so-called rod-in-tube method is also known, in which the core or the core and the glass rod for cladding are inserted into a glass pipe for cladding manufactured in advance in a separate process, and the glass pipe and the glass rod are integrated. (See, for example, Japanese Patent Publication No. 56-45867). As the rod-in-tube method, for example, a method is known in which the glass pipe and the glass rod are heated by a burner flame, and the glass pipe is pressed against the core rod by the gas of the burner flame to integrate the two. In contrast, by heating the glass pipe and the glass rod in order from one end to the other end in a state where the pressure in the glass pipe is reduced, the inside and outside of the glass pipe are heated. There is also known a method in which both the above are sequentially integrated from one end to the other end due to the pressure difference.
[0005]
The optical fiber preform manufactured by the above-described manufacturing method becomes an optical fiber by a drawing process. A method of performing this drawing process simultaneously with the manufacturing of the optical fiber preform by the rod-in-tube method is also known. (See, for example, Japanese Patent Laid-Open No. 50-85345).
[0006]
Incidentally, in recent years, from the viewpoint of reducing production costs, etc., it has been demanded to increase the size and length of an optical fiber preform. For this reason, the optical fiber preform is made to have a large diameter. ing.
[0007]
However, if such a large-diameter optical fiber preform is drawn as it is, it takes a long time to stabilize the optical fiber with the target diameter, and a large amount of preform is consumed for initial stabilization. It becomes like this. As a result, the yield from the optical fiber preform to the optical fiber deteriorates, and the increase in the size of the optical fiber preform originally performed for the purpose of lowering the cost cannot be achieved. There is an inconvenience.
[0008]
Therefore, in order to eliminate such inconveniences, the optical fiber preform is usually stretched to reduce the diameter of the manufactured large-diameter optical fiber preform to an optimum diameter that maximizes the yield before the drawing process. Like to do. And as such an optical fiber preform drawing process, a method for improving the productivity by performing the optical fiber preform by integrating the glass pipe and the glass rod is known. (See, for example, JP-A-7-10580).
[0009]
[Problems to be solved by the invention]
However, when the inventor manufactured a large and long optical fiber preform using a large diameter and long glass pipe and a corresponding long glass rod, the optical fiber preform was The amount of eccentricity of the core has increased.
[0010]
The increase in the amount of eccentricity of the core is to make the heating furnace large and have a large output (for example, the furnace has an outer diameter of 1000 mm, an inner diameter of 220 mm, and an output of 700 kVA) in order to sufficiently melt the large-diameter glass pipe. This is considered to be caused by the combination of the fact that the glass rod is bent by making the glass rod long.
[0011]
That is, in such a large-sized heating furnace, heat easily escapes from the opening at the upper end of the heating furnace, so that the temperature of the outer surface of the glass pipe tends to decrease. When the temperature of the outer surface of the glass pipe is lowered, the outer surface of the manufactured optical fiber preform becomes rough. Therefore, when the large heating furnace is used, its output is set to be higher than that required for integrating the glass pipe and the glass rod so that the outer surface of the glass pipe is kept at a high temperature.
[0012]
However, when the output of the heating furnace is increased, a large amount of heat is given to the glass pipe and the glass rod. At this time, the glass pipe is made of pure quartz, whereas the glass rod is formed of GeO at the core of the optical fiber. ₂ It is formed of quartz to which etc. are added. For this reason, the softening temperature of a glass rod is lower than the softening temperature of the glass pipe which is pure quartz. As a result, by increasing the output of the heating furnace, the glass rod melts to a state where it is easily deformed.
[0013]
Even if the glass rod is easily deformed as described above, the core in the optical fiber preform is provided that the glass rod is not bent in the longitudinal direction and is inserted coaxially with the glass pipe. No eccentricity occurs. In other words, since the glass pipe is uniformly reduced in diameter in the circumferential direction when integrated, the glass pipe comes into contact with the glass rod uniformly in the circumferential direction unless the glass rod is bent. . For this reason, both will be integrated in the state in which the said glass rod was located in the center position of a glass pipe, As a result, eccentricity of the core in an optical fiber preform will not arise.
[0014]
However, since the auxiliary rod is joined to the end portion of the glass rod, bending occurs at the joined portion of the auxiliary rod (note that the auxiliary rod is gripped by the gripping means, The gripping means allows the glass rod to be positioned in the glass pipe and allows the glass rod to be introduced into the heating furnace). In particular, when the glass rod and the auxiliary rod are long, the amount of bending becomes large. When a glass rod (glass rod and auxiliary rod) with such a bend is inserted into the glass pipe, even if the glass rod is inserted coaxially with the glass pipe, the glass rod It will come to incline relatively, and the magnitude | size of the clearance gap (clearance) between a pipe glass pipe and a glass rod will vary with respect to the circumferential direction of a glass pipe, and the location where a clearance is small will be made.
[0015]
When there is a portion with such a small clearance, when the diameter of the glass pipe is reduced, only the portion with the small clearance comes into contact with the glass rod before the other portions. At this time, if the glass rod has rigidity enough to maintain its shape, the core eccentricity does not become so large, but as described above, when the glass rod is in a state of being easily melted and deformed, The molten glass of the glass rod is pulled toward the glass pipe by the surface tension. Thereby, in the vicinity where the glass pipe and the glass rod are integrated, the relative position between the glass pipe and the glass rod is shifted. Once the relative position between the glass pipe and the glass rod is shifted, the shift becomes larger as the glass pipe and the glass rod are integrated.
[0016]
Thus, when a large and long optical fiber preform is manufactured using a large diameter and long glass pipe and a long glass rod, it is considered that the amount of eccentricity of the core becomes large.
[0017]
The present invention has been made in view of such circumstances, and the purpose of the present invention is to produce an optical fiber preform in which the glass pipe and the glass rod are integrated and stretched at the same time. The object is to produce a suppressed optical fiber preform.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a surface tension that pulls the molten glass of the glass rod toward the glass pipe by applying tension in the longitudinal direction of the glass rod when the glass pipe and the glass rod are integrated. To counter.
[0019]
Specifically, the present invention inserts the glass rod for the core or the glass rod for the core and the clad into the clad glass pipe, and depressurizes the inside of the glass pipe while heating both by a heating furnace, Targeting a manufacturing method of an optical fiber preform in which the glass pipe and the glass rod are integrated and stretched at the same time, the glass pipe and the glass rod are integrated with each other by applying a tension in the longitudinal direction of the glass rod. , Thereby biasing the glass rod so that the glass rod is positioned at the center of the glass pipe. It is a specific matter to do in the state.
[0020]
Thus, when the glass pipe and the glass rod are integrated, only a part of the glass pipe in the circumferential direction comes into contact with the glass rod, and the molten glass of the glass rod is brought into contact with the glass pipe by its surface tension. Even when pulled to the side, the surface tension can be countered by the longitudinal tension acting on the glass rod. That is, the glass rod can be biased by the tension applied in the longitudinal direction of the glass rod so that the glass rod is positioned at the center position of the glass pipe. In this state, by integrating the glass pipe and the glass rod, it is possible to prevent the eccentricity of the core from increasing, and to suppress the eccentricity to a minimum.
[0021]
As a result, when using a large-sized and high-power heating furnace and manufacturing an optical fiber preform using, for example, a large-diameter glass pipe having an outer diameter of 150 mm or more and a large-diameter glass rod having an outer diameter of 35 mm or more. In addition, the core eccentricity is suppressed, and the optical fiber preform can be manufactured.
[0022]
In order to suppress the eccentricity of the core by applying tension in the longitudinal direction of the glass rod, when the glass pipe and the glass rod are first integrated, in other words, the glass pipe and the glass rod are integrated. It is important that the glass rod is located at the center position of the glass pipe at the end where the starting is started. If the glass rod is shifted from the center position of the glass pipe at the end where the glass pipe and the glass rod start to be integrated, the glass rod will be glass even if tension is applied in the longitudinal direction of the glass rod. The position is biased with the position shifted from the center position of the pipe. On the other hand, when the glass rod is located at the center position of the glass pipe at the end where the glass pipe and the glass rod start to be integrated, this glass rod is applied by the tension applied in the longitudinal direction of the glass rod. Is biased at the central position of the glass pipe, thereby suppressing the eccentricity of the core.
[0023]
Here, in order to apply tension in the longitudinal direction of the glass rod, for example, the feeding speed of the glass rod to the heating furnace may be adjusted to a speed slower than the feeding speed of the glass pipe.
[0024]
By doing so, when both of the glass pipe and the glass rod are integrated at the end where the glass pipe and the glass rod are integrated, the feed rate of the glass rod is slower than the feed rate of the glass pipe. To be pulled in the longitudinal direction. Thus, tension can be applied in the longitudinal direction of the glass rod.
[0025]
Here, it is necessary to adjust the feeding speed of the glass rod so that a tension that does not break the glass rod acts on the glass rod. Therefore, the feed speed V of the glass rod _R Is the glass pipe feed speed V _P 0.9 ≦ V _R / V _P It is preferable to set so as to satisfy <1.0.
[0026]
The cross-sectional areas of the glass pipe and the glass rod are preferably set so as to have a predetermined core / cladding ratio when the glass pipe and the glass rod are integrated. Here, the core / cladding ratio (hereinafter also referred to as C / C) refers to a value obtained by dividing the clad diameter by the core diameter.
[0027]
That is, when the feeding speed of the glass rod to the heating furnace is adjusted to a speed slower than the feeding speed of the glass pipe, the glass rod per unit time is compared with the case where the glass rod and the glass pipe are fed at the same speed. The feed amount of the glass pipe decreases relative to the feed amount of the glass pipe. For this reason, when the glass pipe and the glass rod are integrated, the cross-sectional area of the glass rod becomes relatively smaller than the cross-sectional area of the glass pipe, and the C / C in the completed optical fiber preform is a predetermined C / C will not become. For this reason, considering the amount of decrease in the feed amount of the glass rod, by setting the cross-sectional area of the glass pipe and the glass rod in advance, specifically, the cross-sectional area of the glass rod is determined as the feed speed of the glass pipe. Even if the feeding speed of the glass rod is set slower than the feeding speed of the glass pipe by setting the feeding speed of the glass rod to be the same as that of the glass rod, the glass pipe and the glass rod have a predetermined C / C. Integrate with.
[0028]
The invention according to claim 4 or claim 5 is an invention in which a highly accurate optical fiber preform can be manufactured.
[0029]
That is, it is a problem particularly in the production of a large and long optical fiber preform. A glass rod used for the production of such an optical fiber preform, for example, manufactured by the VAD method or the like, has its core. The diameter, the refractive index difference between the core and the clad, or the C / C of the glass rod may change in the longitudinal direction.
[0030]
In this case, after dividing the glass rod in the longitudinal direction so that the cut-off wavelength of the drawn optical fiber is finished to a desired value, a target C / C suitable for the structure of the divided glass rod is obtained, and the value is obtained. It is necessary to individually adjust the manufacturing process for each glass rod divided so that the optical fiber preform is finished. That is, when there is a glass rod portion with a larger core diameter or a glass rod portion with a smaller C / C, if the glass pipe and the glass rod are integrated at the same feed rate, the manufactured optical fiber preform C / C changes in the longitudinal direction in a manner reflecting the structural variation of the glass rod. For this reason, the glass rod part with a large core diameter cut out this part, and corrected and used this cut-out glass rod more narrowly. Further, the glass rod portion having a high refractive index difference between the core and the clad has been made into a base material by cutting the glass rod portion and setting the target C / C higher.
[0031]
However, adjusting the manufacturing process individually for each divided short glass rod results in finishing the glass rod manufactured in a large size into a small number of optical fiber preforms, resulting in a decrease in yield. And there are many problems such as complicated manufacturing process management.
[0032]
In order to solve this problem, as described in claim 4, the feeding speed of the glass rod may be adjusted so that the glass pipe and the glass rod are integrated at a desired core / cladding ratio in the longitudinal direction. . Here, “the glass pipe and the glass rod are integrated in the longitudinal direction with a desired core / cladding ratio” means that the core diameter of the glass rod or the refractive index difference between the core and the cladding is in the longitudinal direction. Even if there is variation, this means that the glass pipe and the glass rod are integrated so as to become an optical fiber preform having a target core / cladding ratio in which these variations are canceled.
[0033]
In this case, even if the glass rod is such that the core diameter, the refractive index difference between the core and the clad, or the C / C changes in the longitudinal direction, the glass pipe and the glass rod have the desired C / C. It is integrated in the state. For example, although the refractive index difference between the core and the clad is aligned in the longitudinal direction, C / C is increased from the end where integration is started toward the end where integration is completed In the case of a rod, if the feed rate of the glass rod is finely adjusted to increase as integration proceeds, an optical fiber preform having a desired C / C in the longitudinal direction is manufactured. For example, although C / C is aligned in the longitudinal direction, the refractive index difference between the core and the clad seems to increase from the end where integration is started toward the end where integration is completed. In the case of a simple glass rod, the optical fiber preform having a desired C / C in the longitudinal direction can be obtained by finely adjusting the feed rate of the glass rod to decelerate as integration progresses. Manufactured. Further, for example, in the case of a glass rod in which both the refractive index difference between the core and the clad and C / C are increasing from the end where integration is started toward the end where integration is completed First, the target C / C for each minute section is obtained, and the feed rate of the glass rod is adjusted to increase or decrease. As a result, a target C / C structure corresponding to the core structure at each position can be continuously obtained, and an optical fiber preform having a desired C / C in the longitudinal direction is manufactured.
[0034]
An optical fiber drawn from a large optical fiber preform subjected to such a process has a stable cutoff wavelength in the longitudinal direction, which improves the yield of the optical fiber and reduces the cost of the optical fiber. Manufacturing is realized.
[0035]
Here, as control of the feeding speed of the glass rod, for example, before integrating the two, the core diameter of the glass rod, the refractive index difference between the core and the clad, or the amount of change in the longitudinal direction of C / C May be measured or predicted, and the feed rate of the glass rod may be controlled by a control program built based on this. Further, when the refractive index difference between the core and the clad of the glass rod is aligned in the longitudinal direction, C / C is measured during the integration of the two, and the glass rod is based on the measured value. Feedback control for controlling the feed speed of the head may be performed. In addition, you may make it control the feed rate of a glass pipe instead of a glass rod.
[0036]
Further, as described in claim 5, when the integration of the glass pipe and the glass rod is performed while rotating one or both of the glass pipe and the glass rod around the longitudinal axis thereof, the optical fiber mother Since the axial symmetry with respect to the longitudinal center axis of the material is improved, the amount of core eccentricity is further reduced. In addition, with further reduction in the amount of core eccentricity, the polarization dispersion characteristic is improved, and an optical fiber preform is manufactured from which a more accurate optical fiber can be obtained.
[0037]
【The invention's effect】
As described above, according to the method for manufacturing an optical fiber preform in the present invention, the glass pipe and the glass rod are integrated and stretched in a state where tension is applied in the longitudinal direction of the glass rod. An optical fiber preform that suppresses the eccentricity of can be manufactured.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0039]
FIG. 1 shows a state in which an optical fiber preform is being manufactured, where 1 is a glass pipe for cladding, 2 is for a core, or a glass rod for core and cladding, and 3 is for heating both the glass pipe 1 and the glass rod 2. It is a heater. What is necessary is just to use what was manufactured by the OVD method etc. as the said glass pipe 1, for example. In addition, the glass rod 2 is produced by sintering a glass fine particle deposited body in which glass fine particles are deposited by the VAD method and then stretching or forming a core glass on the inner surface of the clad pipe by the MCVD method. What should I do? Furthermore, as the heating furnace provided with the heater 3, specifically, a carbon resistance heating furnace or a high frequency induction heating furnace may be used.
[0040]
The upper ends of the glass pipe 1 and the glass rod 2 are held by a holding device (not shown) via an auxiliary pipe and an auxiliary rod (not shown). The gripping device is configured to rotate the glass rod 2 around its longitudinal axis, thereby enabling the glass rod 2 to be integrated with the glass pipe 1 while rotating as necessary. Has been. The gripping device is configured to move the glass pipe 1 and the glass rod 2 downward to send both 1 and 2 into the heater 3. The speed is different between the glass pipe 1 and the glass rod 2 (V _P , V _R ) (See arrows in FIG. 1). Feed speed V of this glass pipe 1 and glass rod 2 _P , V _R Is controlled by a control program built on the basis of the measured values of the outside diameter of the glass rod 2 and the C / C of the glass rod 2 or the change in the refractive index difference between the core and the cladding with respect to the longitudinal direction. I have to.
[0041]
Further, the inside of the glass pipe 1 is connected to an exhaust device (not shown). By operating the exhaust device, the inside of the glass pipe 1 is decompressed. Further, the optical fiber preform 4 in which the glass pipe 1 and the glass rod 2 are integrated is constructed so as to be taken up by a take-off device (not shown) provided below the optical fiber preform 4, thereby the optical fiber preform. The material 4 is drawn (see the arrow in FIG. 1). Thus, the integration of the glass pipe 1 and the glass rod 2 and the stretching of the optical fiber preform 4 in which the glass pipe 1 and the glass rod 2 are integrated are performed simultaneously.
Next, the manufacturing method of the optical fiber preform 4 will be described in more detail in order. First, the auxiliary pipe and auxiliary rod joined to the upper ends of the glass pipe 1 and the glass rod 2 are held by the holding device. Then, the glass rod 2 is inserted into the glass pipe 1. And the lid | cover which can be connected to an exhaust apparatus is set to the upper part of the said glass pipe 1 (auxiliary pipe). Thereby, the said glass rod 2 is hold | gripped coaxially with the said glass pipe 1 in the state which can slide within the through-hole provided in the center part of this lid | cover.
[0042]
In this state, the glass pipe 1 and the glass rod 2 are respectively moved downward while the inside of the glass pipe 1 is depressurized by an exhaust device (see the arrow in FIG. 1). At this time, the feed speed V of the glass rod 2 _R Is the feed speed V of the glass pipe 1 _P It is controlled to be a slower speed. Further, when the C / C or the like of the glass rod 2 is changed with respect to the longitudinal direction, the feed speed V is set by a preset control program. _R Is finely adjusted so that when the glass pipe 1 and the glass rod 2 are integrated, a predetermined C / C is obtained.
[0043]
Thus, the lower end portions of the glass pipe 1 and the glass rod 2 are introduced into the heater 3, whereby the lower end portions of the both 1 and 2 are heated by the heater 3. And while the lower end part of the said glass pipe 1 fuse | melts, it will integrate with the said glass rod 2 by reducing in diameter by the pressure difference inside and outside. Since the glass pipe 1 and the glass rod 2 that have started the integration are sent further downward, the glass pipe 1 and the glass rod 2 are sequentially heated in the longitudinal direction from the lower end to the upper end, Thereby, the said glass pipe 1 and the glass rod 2 come to integrate sequentially from the lower end toward an upper end. The integrated optical fiber preform 4 is drawn by being drawn by a drawing device. In this way, the glass pipe 1 and the glass rod 2 are integrated and stretched simultaneously, and the optical fiber preform 4 is manufactured.
[0044]
And in the manufacturing method of the optical fiber preform which concerns on this embodiment, when integrating the glass pipe 1 and the glass rod 2, the feeding speed V of this glass rod 2 _R The feed speed V of the glass pipe 1 _P Depending on the setting. Thereby, when the glass pipe 1 and the glass rod 2 are integrated at the lower end portion thereof, the glass rod 2 is pulled by the glass pipe 1 in the longitudinal direction. As a result, the glass rod 2 is in a state in which tension is applied in the longitudinal direction.
[0045]
Thus, by integrating and stretching the glass pipe 1 and the glass rod 2 in a state where tension is applied in the longitudinal direction of the glass rod 2, the eccentricity of the core is suppressed and the optical fiber preform 4 is manufactured. be able to.
[0046]
That is, since the glass rod 2 is bent, when the glass pipe 1 is reduced in diameter, only a part of the glass pipe 1 in the circumferential direction is in contact with the glass rod 2, and the glass Even when the molten glass of the rod 2 is pulled to the glass pipe side by its surface tension, the glass rod 2 is given the tension in the longitudinal direction, so that it can counter the surface tension. Accordingly, the glass rod 2 is biased so as to be positioned at the center position of the glass pipe 1. In this state, since the glass pipe 1 and the glass rod 2 are integrated, the amount of eccentricity of the core in the optical fiber 4 is suppressed to the minimum.
[0047]
According to this method, a large-sized and high-power heating furnace is used, and the optical fiber preform 4 is formed by, for example, a large-diameter glass pipe 1 having an outer diameter of 150 mm or more and a large-diameter glass rod 2 having an outer diameter of 35 mm or more. Even when manufacturing, the optical fiber preform 4 can be manufactured while suppressing the eccentricity of the core.
[0048]
In order to suppress the eccentricity of the core by applying tension in the longitudinal direction of the glass rod 2, the glass rod 2 is made of glass at the end where the glass pipe 1 and the glass rod 2 start to be integrated. It is important that the pipe 1 is located at the center position.
[0049]
That is, when the glass rod 2 is shifted from the center position of the glass pipe 1 at the end where the glass pipe 1 and the glass rod 2 start to be integrated, in other words, the glass pipe 1 and the glass rod 2 are the first. When the core is eccentric when integrated into the glass rod 2, even if tension is applied in the longitudinal direction of the glass rod 2, the glass rod 2 does not move to the center position of the glass pipe 1. Is biased at a position shifted from the center position of the glass pipe 1. For this reason, although the eccentricity of the core can be prevented from further increasing as the integration of the glass pipe 1 and the glass rod 2 proceeds, the core generated when the glass pipe 1 and the glass rod 2 are first integrated is prevented. The eccentricity cannot be reduced.
[0050]
Therefore, in order to reduce the amount of eccentricity of the core, it is important to keep the glass rod 2 at the center of the glass pipe 1 at the end where the glass pipe 1 and the glass rod 2 start to be integrated. Become.
[0051]
Further, the feeding speed V of the glass rod 2 _R Needs to be adjusted so that a tension that does not break the glass rod 2 acts on the glass rod 2. For example, 0.9 ≦ V _R / V _P It is preferable to set so as to satisfy <1.0.
[0052]
Furthermore, the feed speed V of the glass rod 2 _R The feed speed V of the glass pipe 1 _P If the speed is slower than that, the feed amount of the glass rod 2 per unit time is relatively decreased with respect to the feed amount of the glass pipe 1, so that the glass rod 2 is integrated when the glass pipe 1 and the glass rod 2 are integrated. Is relatively small with respect to the cross-sectional area of the glass pipe 1. For this reason, C / C in the completed optical fiber preform 4 may not become a predetermined C / C. Therefore, it is preferable to set the cross-sectional areas of the glass pipe 1 and the glass rod 2 in advance in consideration of the amount by which the feed amount of the glass rod 2 decreases. In this way, the feed speed V of the glass rod 2 _R The feed speed V of the glass pipe 1 _P Even later, the glass pipe 1 and the glass rod 2 can be integrated at a predetermined C / C.
[0053]
When the C / C of the glass rod 2 or the difference in refractive index between the core and the clad changes in the longitudinal direction, the feeding speed V of the glass rod 2 _R By controlling to slightly increase / decrease, the optical fiber preform 4 having a desired C / C can be manufactured.
[0054]
Further, by integrating the glass rod 2 with the glass pipe 1 while rotating the glass rod 2 around the axis, the axial symmetry with respect to the longitudinal central axis of the optical fiber preform 4 is improved, and the core of the optical fiber preform 4 is improved. The amount of eccentricity can be further reduced.
[0055]
<Other embodiments>
In addition, this invention is not limited to the said embodiment, Other various embodiment is included. That is, in the above embodiment, the feed speed V of the glass rod 2 _R As a control, a control program is set in advance and controlled by this. However, the present invention is not limited to this. For example, the core diameter is measured during the integration of the glass pipe 1 and the glass rod 2, and this measurement is performed. Feed speed V based on the measured core diameter _R You may make it perform the feedback control which controls.
[0056]
Moreover, in the said embodiment, although the glass rod 2 is rotated, you may make it rotate not only this but the glass pipe 1, for example. Even in this case, the axial symmetry of the optical fiber preform 4 with respect to the central axis in the longitudinal direction is improved, and the core eccentricity of the optical fiber preform 4 can be further reduced. Note that both the glass pipe 1 and the glass rod 2 may be rotated.
[0057]
【Example】
An experiment conducted on the method for manufacturing the optical fiber preform 4 according to the present invention will be described.
[0058]
Table 1 shows the feed speed V of the glass rod 2 (VAD rod) for the core and cladding. _R Feed rate V of glass pipe 1 (pipe) _P Example (Example) in which the optical fiber preform 4 was manufactured at a later time and the feed speed V of the glass rod 2 _R The feed speed V of the glass pipe 1 _P The experiment result evaluated about the amount of core eccentricity in optical fiber base material 4 in the example (comparative example) which manufactured optical fiber base material 4 in the same way is shown.
[0059]
[Table 1]

[0060]
That is, the feed speed V of the glass pipe 1 _P Is 10 mm / min for both the example and the comparative example, whereas the feed speed V of the glass rod 2 is _R Was 9.6 mm / min in the example, while 10 mm / min in the comparative example.
[0061]
In the embodiment, the feeding speed V of the glass rod 2 _R Is the feed speed V of the glass pipe 1 _P Therefore, the outer diameter of the glass rod 2 is made larger than the outer diameter of the glass rod 2 in the comparative example so that C / C in the optical fiber preform 4 becomes a predetermined value ( Example 51 mm, comparative example 50 mm). Moreover, the core diameter of the glass rod 2 in an Example is also larger than the core diameter of the glass rod 2 in a comparative example (Example 13.0 mm, Comparative example 12.5 mm). The inner diameter and outer diameter of the glass pipe 1 are set to 54 mm and 182 mm in both the examples and the comparative examples, respectively. Further, the optical fiber preform 4 in which the glass pipe 1 and the glass rod 2 are integrated is stretched until the outer diameter becomes 60 mm in both the examples and the comparative examples.
[0062]
From Table 1, in the comparative example, the core eccentric amount in the optical fiber preform 4 is 0.3 mm, whereas the feed speed V of the glass rod 2 is _R In the embodiment in which tension is applied in the longitudinal direction of the glass rod 2 by slowing down the core, the core eccentricity in the optical fiber preform 4 is as small as 0.1 mm. That is, as described above, the glass rod 2 is biased at the center position of the glass pipe 1 by the tension applied in the longitudinal direction of the glass rod 2, and as a result, the eccentric amount of the core is considered to be suppressed. .
[0063]
From the above results, the manufacturing method of the optical fiber preform according to the present invention in which the glass pipe 1 and the glass rod 2 are integrated and stretched by applying a tension in the longitudinal direction of the glass rod 2 has the eccentricity of the core. It can be said that a large-sized optical fiber preform can be manufactured by lowering.
[Brief description of the drawings]
FIG. 1 is an explanatory perspective view showing a state in which an optical fiber preform is being manufactured.
[Explanation of symbols]
1 Glass pipe
2 Glass rod
3 Heater (heating furnace)
4 Optical fiber preform

Claims (4)

Insert the glass rod for the core or the glass rod for the core and the clad into the clad glass pipe, and decompress the inside of the glass pipe while heating both with a heating furnace, so that the glass pipe and the glass rod are integrated. A method for manufacturing an optical fiber preform that simultaneously performs crystallization and stretching,
Tension is applied in the longitudinal direction of the glass rod by adjusting the glass rod and glass rod integration to the heating furnace at a speed slower than that of the glass pipe. The method of manufacturing an optical fiber preform, wherein the glass rod is positioned and biased so that the glass rod is positioned at the center of the glass pipe. In claim 1 ,
A method of manufacturing an optical fiber preform, wherein the cross-sectional areas of a glass pipe and a glass rod are set so as to have a predetermined core / cladding ratio when the glass pipe and the glass rod are integrated. In claim 1 ,
A method for producing an optical fiber preform, wherein a feed rate of a glass rod to a heating furnace is adjusted so that the glass pipe and the glass rod are integrated in a longitudinal direction at a desired core / cladding ratio. In claim 1 ,
A method for producing an optical fiber preform, wherein the glass pipe and the glass rod are integrated while rotating either one or both of the glass pipe and the glass rod about the longitudinal axis thereof.

Images