WO2003018493A1

WO2003018493A1 - Method of producing optical fiber base material

Info

Publication number: WO2003018493A1
Application number: PCT/JP2002/008486
Authority: WO
Inventors: Hideaki Ito; Masataka Kon; Nobusada Nagae; Akihiko Fukuda; Tomonori Shimono; Keiji Miyashita
Original assignee: Mitsubishi Cable Industries, Ltd.
Priority date: 2001-08-22
Filing date: 2002-08-22
Publication date: 2003-03-06
Also published as: KR100964548B1; JP2003054973A; KR20040036716A; JP4450533B2; CN1545489A; CN1282618C

Abstract

An optical fiber base material (4) is produced by inserting a glass rod (2) for core or for core and clad into a glass pipe (1) for clad, decreasing the pressure in the glass pipe (1) while heating it by a heater (3), and performing simultaneous integration and stretching of the glass pipe (1) and glass rod (2). At this time, the integration of the glass pipe (1) and glass rod (2) is effected with a tension longitudinally imparted to the glass rod (2) as by setting the feed speed VR of the glass rod (2) at a value lower than the feed speed VP of the glass pipe (1).

Description

Itoda »Manufacturing method of optical fiber preform

Technical field

According to the present invention, a glass rod for a core or a glass opening for a core and a cladding is inserted into a glass pipe for a cladding, and the inside of the glass pipe is decompressed while heating both of the cores. The present invention relates to a method for manufacturing an optical fiber preform that simultaneously integrates with a glass head and extends the glass fiber. Background art

The main methods for manufacturing optical fiber preforms include the following three methods: OVD (Outside Vapor-phase Deposition), VAD (Vapor-phase Axial Deposition), and MCVD (Modified Chemical Vapor Deposition). Can be Here, in the VAD method and the MC VD method, from the viewpoint of productivity, a large part of the optical fiber preform is occupied after the core or the core and the glass opening for the clad are manufactured. A method of forming a clad on the outer periphery of the glass opening by a separate process is employed.

Specifically, as a method for forming the above-mentioned clad, a so-called external method is known in which glass fine particles called soot are deposited on the above-mentioned glass opening and heated to form a transparent glass. ing.

On the other hand, the core or the core and the glass opening for the clad are inserted into the glass pipe for the cladding manufactured in advance in a separate process, and the glass pipe and the glass rod are integrated into a so-called opening. The Addin tube method is known (for example, see Japanese Patent Publication No. 56-45867). In the rod inch-Eube method, for example, the glass pipe and the glass opening are heated by a Pana flame, and the glass pipe is heated to a core opening by the gas of the Pana flame. A method is known in which the two are integrated by pressing them against a pad. Also, in contrast to this, the glass pipe and the glass rod are sequentially heated from one end to the other end by a heating furnace or the like in a state where the pressure in the glass pipe is reduced, so that the inside and outside of the glass pipe are heated. A method is also known in which the two are sequentially integrated from one end to the other end by the pressure difference.

The optical fiber preform manufactured by the above-described manufacturing method is turned into an optical fiber by a drawing process. A method in which this drawing process is performed simultaneously with the manufacturing of the optical fiber preform by the above-mentioned open-din tube method. Is also known (for example, see Japanese Patent Application Laid-Open No. 50-85345).

By the way, in recent years, from the viewpoint of reduction of production cost, etc., it is required to increase the size and length of the optical fiber preform. Therefore, it is necessary to increase the diameter of the optical fiber preform. Is being done.

However, if such a large-diameter optical fiber preform is drawn as it is, it takes a long time to stabilize the optical fiber of the target diameter, and a large amount of the preform is consumed for initial stabilization. It will be lost. 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, which was originally intended for cost reduction, cannot achieve the purpose. There is an inconvenience of doing so.

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 optimal diameter that maximizes the yield before the drawing process. I am trying to do it. The process of stretching the optical fiber preform is performed at the same time as the production of the optical fiber preform by integrating the glass pipe and the glass opening to improve the productivity. A method is known (for example, see Japanese Patent Application Laid-Open No. 7-180580).

However, the inventor of the present invention produced a large and long optical fiber preform using a large-diameter and long glass pipe and a correspondingly long glass port. At that time, the optical fiber preform had a large core eccentricity.

This increase in the core eccentricity is due to the fact that the heating furnace is large and has a large output (for example, the furnace has an outer diameter of 100 mm and an inner diameter of 22 It is considered that this was caused by the combination of the setting of 0 mm and output of 700 kVA) and the bending of the glass opening caused by the long glass rod. 'In other words, in such a large heating furnace, the heat easily escapes from the upper end opening of the heating furnace, so that the temperature of the outer surface of the glass pipe tends to decrease. If the temperature of the outer surface of the glass pipe decreases, the outer surface of the manufactured optical fiber preform becomes rough. Therefore, when using a large heating furnace, the output is set higher than the output required to integrate the glass pipe and the glass mouth, so that the outer surface of the glass pipe is kept at a high temperature. .

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, while the glass pipe is formed by a pure quartz, Garasuro' de is formed by quartz G e 0 ₂ or the like in a portion in the optical fiber becomes co § was added. For this reason, the softening temperature of the glass mouth is lower than the softening temperature of the glass pipe made of 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.

Even if the glass rod is easily deformed in this way, if the glass rod does not bend in the longitudinal direction and the bracket opening is inserted coaxially with the glass pipe, the optical fiber motherboard can be used. No eccentricity of the core in the material occurs. In other words, the diameter of the glass pipe is uniformly reduced in the circumferential direction when it is integrated, so if there is no bend in the glass slot, the glass pipe contacts the glass mouth evenly in the circumferential direction. I will be. For this reason, the two are integrated with the glass rod positioned at the center position of the glass pipe, and as a result, the eccentricity of the core in the optical fiber preform does not occur. However, since the auxiliary rod is abutted and joined to the end of the glass rod, bending occurs at the joint portion of the auxiliary rod (the auxiliary rod is gripped by gripping means. In addition, the holding means positions the glass opening 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 bending amount becomes large. When a glass rod having such a bend (a glass rod and a catching rod) is inserted into a glass pipe, the glass rod is inserted into the glass pipe even if the glass rod is coaxially inserted into the glass pipe. It becomes relatively inclined with respect to the pipe, and the size of the clearance (clearance) between the pipe glass pipe and the glass rod varies in the circumferential direction of the glass pipe, where the clearance is small. Can be done.

In this state, when the diameter of the glass pipe is reduced, a portion having a small clearance comes into contact with the glass rod earlier than other portions. At this time, if the glass rod has such a rigidity that the shape is maintained, the core eccentricity does not become so large. However, as described above, when the glass rod is in a state of being easily melted and deformed, the molten glass portion (the molten glass of the glass rod) is pulled toward the glass pipe by its surface tension. Will be able to Thus, 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 in the radial direction. If the relative positions of the glass pipe and the glass opening are shifted from each other, the displacement increases as the glass pipe and the glass rod are integrated.

When a large and long optical fiber preform is manufactured using a large-diameter and long glass pipe and a long glass port, it is considered that the eccentricity of the core becomes large. .

The present invention has been made in view of such circumstances, and has as its object. However, in the production of an optical fiber preform in which the glass pipe and the glass rod are simultaneously integrated and drawn, an object is to produce an optical fiber preform in which the eccentricity of the core is suppressed. Disclosure of the invention

In order to achieve the above object, the present invention provides a surface tension for pulling molten glass of a glass rod toward a glass pipe by applying tension in a longitudinal direction of the glass rod when the glass pipe and the glass rod are integrated. And tried to oppose it.

Specifically, in the present invention, a glass opening for a core or a glass opening for a core and a glass is inserted into a glass pipe for a cladding, and the glass pipe is heated while being heated by a heating furnace. The present invention is directed to a method for producing an optical fiber preform in which the inside is decompressed and the glass pipe and the glass port are simultaneously integrated and drawn.

In the present invention, the glass pipe and the glass rod are integrated with each other in a state where tension is applied in the longitudinal direction of the glass rod.

By doing so, when the glass pipe and the glass head are integrated, only a part of the glass pipe in the circumferential direction comes into contact with the glass head, and the molten glass in the glass head becomes molten. Even when the glass rod is pulled toward the glass pipe by the surface tension, 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 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 minimize the amount of eccentricity.

As a result, a large-sized and high-power heating furnace is used, and for example, a large-diameter glass pipe with an outer diameter of 150 mm or more, and a large-diameter glass port with an outer diameter of 35 mm or more. Even when an optical fiber preform is manufactured using a head, an optical fiber preform can be manufactured while suppressing core eccentricity.

In order to suppress the eccentricity of the core by applying tension in the longitudinal direction of the glass opening, when the glass pipe and the glass rod are first integrated, in other words, when the glass pipe and the glass opening are integrated. At the end where the head and the head start to be integrated, it is important that the glass opening head is located at the center of the glass pipe. If the above-mentioned glass port is shifted from the center position of the glass pipe at the end where the glass pipe and the glass port start to be integrated, even if the glass rod is tensioned in the longitudinal direction of the glass rod, The rod is biased in a position that is not centered on the glass pipe. On the other hand, if the glass port is located at the center of the glass pipe at the end where the glass pipe and the glass port start to be integrated, the tension applied in the longitudinal direction of the glass rod causes However, this glass opening is biased at the center of the glass pipe, whereby the eccentricity of the core is suppressed.

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 lower than the feeding speed of the glass pipe.

In this way, the glass pipe and the glass mouth are integrated together. At the end, when the two are integrated, the glass rod feed speed is lower than the glass pipe feed speed. Is pulled in the longitudinal direction by the glass pipe. Thus, it is possible to apply tension in the longitudinal direction of the glass rod.

Here, the feed speed of the glass rod needs to be adjusted so that a tension that does not break the glass rod acts on the glass opening.従Tsu Te, feed speed V _R of the glass outlet head is the feed speed of the glass pipe to come to have a V _P, 0. To set so as to satisfy the _{_{9≤V R / V P <1.}} 0 preferable. The cross-sectional area of the above glass pipe and glass mouth is It is preferable to set a predetermined core / cladding ratio when the mouth and the head are integrated. Here, the core-to-cladding ratio (hereinafter also referred to as C / C) is a value obtained by dividing the cladding diameter in the optical fiber preform by the core diameter.

That is, when the feeding speed of the glass rod to the heating furnace is adjusted to a speed lower than the feeding speed of the glass pipe, compared to the case where the glass rod and the glass pipe are sent at the same speed, the speed per unit time is reduced. The feed rate of the glass mouth drops relatively to the feed rate of the glass pipe. Therefore, when the glass pipe and the glass head are integrated, the cross-sectional area of the glass head becomes relatively smaller than the cross-sectional area of the glass pipe, and C / C in the completed optical fiber preform is reduced. However, it does not become the predetermined c Z c. For this reason, by setting the cross-sectional areas of the glass pipe and the glass opening in advance in consideration of the decrease in the feeding amount of the glass rod, the feeding speed of the glass opening is made higher than the feeding speed of the glass pipe. Even if it is late, the glass pipe and the glass rod are integrated with the specified C / C. Specifically, the cross-sectional area of the glass rod may be set to be larger than when the feed speed of the glass pipe and the feed speed of the glass rod are the same.

The following inventions are inventions that enable production of a more precise optical fiber preform.

In other words, this is a problem particularly in the production of large and long optical fiber preforms.However, glass rods used in the production of such optical fiber preforms, for example, manufactured by the VAD method, etc. The diameter, the refractive index difference between the core and the clad, or the cZc of the glass rod may change in the longitudinal direction.

In this case, the glass rod is divided in the longitudinal direction so that the cutoff wavelength of the drawn optical fiber is set to a desired value. Then, the target CZC suitable for the structure of the divided glass rod is obtained, and the manufacturing process is individually adjusted for each divided glass opening so that the optical fiber preform is finished to the value. That is, a glass rod with a large core diameter or a glass rod with a small cZc If there is a part, if the glass pipe and the glass rod are integrated at the same feed rate, the C / C of the manufactured optical fiber preform reflects the structural variation of the glass port in the longitudinal direction. It will change in shape. For this reason, when there is a portion with a large core diameter in the glass rod, this portion was cut out and the cut out glass rod was modified to a smaller diameter for use. In addition, if there was a portion of the glass rod where the refractive index difference between the core and the clad was high, the portion was cut out and the target c Z c was set higher to form the base material.

However, individually adjusting the manufacturing process in units of divided short glass rods would result in large-sized glass rods being made into a large number of optical fiber preforms with a small size, leading to a decrease in yield. And the management of the manufacturing process becomes complicated.

In order to solve this problem, the feed speed of the glass rod may be adjusted so that the glass pipe and the glass rod are integrated in the longitudinal direction at a desired core-cladding ratio. Here, "the glass pipe and the glass rod are integrated in the longitudinal direction at the desired core.cladding ratio" means that the core diameter of the glass rod or the difference in the refractive index between the core and the cladding is different. Even if there is variation in the longitudinal direction, the above-mentioned glass pipe and glass port are integrated so that these variations are canceled and the optical fiber preform with the target core-to-cladding ratio is produced in the longitudinal direction. Means.

In this case, even if the glass rod is such that the core diameter in the longitudinal direction, the refractive index difference between the core and the clad, or the cZc is changed, the glass pipe and the glass head can be formed as desired. It is integrated so that c Z c. For example, although the refractive index difference between the core and the cladding is uniform in the longitudinal direction, the czc increases from the end where the integration starts to the end where the integration ends. In the case of a glass slot, if the feed speed of the glass head is finely adjusted to increase as the integration progresses, an optical fiber with the desired czc in the longitudinal direction can be obtained. A base material is manufactured. Also, for example, although C / C is aligned in the longitudinal direction, the refractive index difference between the core and the cladding increases from the end where integration begins to the end where integration ends. In the case of a glass rod such as that described above, conversely, if the feed speed of this glass port is finely adjusted so as to reduce as the integration progresses, an optical fiber motherboard with the desired CZC in the longitudinal direction can be obtained. Wood is manufactured. Further, for example, in glass rods where both the refractive index difference between the core and the cladding and the C / C increase from the end where integration begins to the end where integration ends In such a case, calculate the target C / C for each minute section and increase or decrease the feed rate of the glass rod. As a result, a structure having a target czc corresponding to the core structure at each position can be continuously obtained, and an optical fiber preform having a desired cZc in the longitudinal direction is manufactured.

An optical fiber drawn from a large optical fiber preform that has been treated in this manner has a stable cutoff wavelength in the longitudinal direction, improving the yield of the optical fiber and reducing the cost. The production of optical fiber is realized.

Here, as the control of the feed speed of the glass rod, for example, before the two are integrated, the core diameter of the glass rod, the refractive index difference between the core and the clad, or the length of c Z c The amount of change in the direction may be measured or predicted, and the feed rate of the glass rod may be controlled by a control program based on this. If the difference in the refractive index between the core of the glass rod and the clad is uniform in the longitudinal direction, C / C is measured during the integration of the two, and the glass is measured based on the measured value. Feedback control for controlling the feed speed of the mouth may be performed. The feed speed of the glass pipe may be controlled instead of the glass rod.

Further, when the glass pipe and the glass rod are integrated while rotating one or both of the glass pipe and the glass rod around the longitudinal axis, the longitudinal central axis of the optical fiber preform can be obtained. Since the axial symmetry with respect to is improved, the amount of eccentricity of the core is further reduced. Also, this core eccentricity With further reduction, polarization dispersion characteristics are improved, and an optical fiber preform from which a more accurate optical fiber can be obtained is manufactured. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory perspective view showing a state in which an optical fiber preform is being manufactured. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Figure 1 shows the state of the optical fiber preform during manufacture, 1 is a glass pipe for cladding, 2 is a glass rod for core or core and cladding, 3 is the above glass pipe 1 and glass port 2 Is a heater for heating both. As the glass pipe 1, for example, a glass pipe manufactured by an OVD method or the like may be used. The above glass rod 2 is manufactured by sintering a glass fine particle deposit on which glass fine particles are deposited by the VAD method, and then stretching it, or forming a solid core by forming a core glass on the inner surface of the cladding pipe by the MCVD method. What should be done. Further, as the heating furnace provided with the heater 3, specifically, a carbon resistance heating furnace / a high-frequency induction heating furnace may be used.

The upper end of each of the glass pipe 1 and the glass rod 2 is gripped by a gripping device (not shown) via an auxiliary pipe and an auxiliary rod (not shown). This gripping device is configured to rotate the glass rod 2 around its longitudinal axis. This makes it possible to integrate the glass rod 2 with the glass pipe 1 while rotating the glass rod 2 as necessary. Further, the gripping device is configured to move the glass pipe 1 and the glass rod 2 downward, respectively, and to send the glass pipe 1 and the glass rod 2 into the heater 3. Gripping device, the moving speed of the glass pipe 1 and Garasuro' de 2, i.e. the feed rate to the heater 3, the glass pipe 1 and the glass outlet head 2 in different velocity (V _P, V _R) to (See arrows in Figure 1). The feed speeds V _P and V _R of the glass pipe 1 and the glass mouth 2 are determined by the outer diameter of the glass rod 2 and the C / C of the glass rod 2 or the difference in the refractive index between the core and the clad. Control is performed by a control program that is set up based on the measured value of the change amount in the longitudinal direction.

The inside of the glass pipe 1 is connected to an exhaust device (not shown), and the inside of the glass pipe 1 is configured to be depressurized by operating the exhaust device. Further, the optical fiber preform 4 in which the glass pipe 1 and the glass rod 2 are integrated is configured to be taken up by a take-up device (not shown) provided below the preform. Thus, the optical fiber preform 4 is stretched (see the arrow in FIG. 1). In this way, the unification 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 simultaneously performed.

Next, a method of manufacturing the optical fiber preform 4 will be described in more detail step by step. First, the glass rod 2 is inserted into the glass pipe 1 with the catching pipe and the auxiliary rod joined to the upper ends of the glass pipe 1 and the glass rod 2 held by a holding device. Then, a lid that can be connected to the exhaust device is set above the glass pipe 1 (auxiliary pipe). Thus, the glass rod 2 is held coaxially with the glass pipe 1 so as to be slidable in a through hole provided in the center of the lid.

In this state, the glass pipe 1 and the glass rod 2 are respectively moved downward while depressurizing the inside of the glass pipe 1 by an exhaust device (see the arrow in FIG. 1). At this time, the feed speed V _R of Garasuro' de 2 is controlled to be slower than the feed speed V _P of the glass pipe 1. Further, when the CZC like of the glass slot de 2 is changed with respect to the longitudinal direction, by a control program set in advance, the feed speed V _R is finely adjusted, the glass Supaipu 1 and Garasuro' de 2 When they are integrated, they have a predetermined C / C. In this way, the lower ends of the glass pipe 1 and the glass opening 2 are introduced into the heater 3, whereby the lower ends of the two 1 and 2 are heated by the heater 3. . Then, the lower end of the glass pipe 1 is melted, and the diameter is reduced by a pressure difference between the inside and the outside, whereby the glass pipe 1 is integrated with the glass rod 2. The glass pipe 1 and the glass rod 2 that have started to be integrated are sent further downward, so that the glass pipe 1 and the glass rod 2 are sequentially heated in the longitudinal direction from the lower end to the upper end. Become. As a result, the glass pipe 1 and the glass rod 2 are sequentially integrated from the lower end to the upper end. The integrated optical fiber preform 4 is drawn by being pulled by a pulling device. In this way, the unification and extension of the glass pipe 1 and the glass mouth 2 are simultaneously performed, and the optical fiber preform 4 is manufactured.

In the method for manufacturing an optical fiber preform according to the present embodiment, when the glass pipe 1 and the glass rod 2 are integrated, the feeding speed V _R of the glass rod 2 is changed to the feeding speed of the glass pipe 1. Set later than V _P. As a result, when the glass pipe 1 and the glass rod 2 are integrated at the lower end, the glass opening 2 is pulled in the longitudinal direction by the glass pipe 1. As a result, the glass rod 2 is in a state where tension is applied in the longitudinal direction.

In this way, by integrating and extending the glass pipe 1 and the glass rod 2 while applying tension in the longitudinal direction of the glass rod 2, the eccentricity of the core is suppressed and the optical fiber preform 4 is formed. Can be manufactured.

That is, for example, when the glass rod 2 is bent, when the diameter of the glass pipe 1 is reduced, only a part of the glass pipe 1 in the circumferential direction comes into contact with the glass rod 2, and the glass rod 2 comes into contact. The molten glass of the rod 2 is pulled toward the glass pipe by its surface tension. However, since the glass rod 2 is given a tension in its longitudinal direction, Can resist surface tension. As a result, the glass rod 2 is biased to be positioned at the center 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 minimized.

According to this method, a large-sized and high-power heating furnace is used, for example, by 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 the optical fiber preform 4 is manufactured, the optical fiber preform 4 can be manufactured while suppressing the eccentricity of the core.

In addition, in order to suppress the eccentricity of the core by applying tension in the longitudinal direction of the glass rod 2, the above-mentioned glass port 2 is required at the end where the glass pipe 1 and the glass rod 2 start to be integrated. It is important that is located in the center of the glass pipe 1.

That is, if the glass opening 2 is radially displaced 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 If the core is eccentric when the glass rod 2 is first integrated with the glass rod 2, the glass rod 2 moves to the center of the glass pipe 1 even if tension is applied in the longitudinal direction of the glass opening 2. There is nothing to do. That is, the glass rod 2 is biased at a position shifted from the center position of the glass pipe 1. For this reason, the eccentricity of the core can be prevented from further increasing as the integration of the glass pipe 1 and the glass mouth 2 progresses, but when the glass pipe 1 and the glass rod 2 are first integrated, The resulting eccentricity of the core cannot be reduced.

Therefore, by positioning the glass rod 2 at the center of the glass pipe 1 at the end where the glass pipe 1 and the glass opening 2 start to be integrated, the amount of eccentricity of the core is reduced. It is important in making

In addition, the feed speed V _R of the glass rod 2 needs to be adjusted so that a tension that does not break the glass rod 2 acts on the glass rod 2. It is preferable to set, for example, 0.9≤V _R ZV _P <1.0.

Furthermore, when the feed rate V _R of Garasuro' de 2 also slow Ri by feeding speed V _P of the glass pipe 1, the feed amount of Garasuro' de 2 per unit time is relatively lowered with respect to the feed amount of Garasupai flop 1 I do. Therefore, when the glass pipe 1 and the glass rod 2 are integrated, the cross-sectional area of the glass rod 2 becomes relatively smaller than the cross-sectional area of the glass pipe 1. As a result, the C / C in the completed optical fiber preform 4 may not be the 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 a reduction in the feed amount of the glass rod 2. In this way, the feed speed V _R of Garasuro' de 2 be slower than the feed velocity V _P of the glass pipe 1, at a predetermined CZC, can Rukoto are integrated with the glass pipe 1 and Garasuro' de 2 .

Further, the glass rod 2 CZC, or when the refractive index difference between core and clad and has changed to the long side direction, by the control to Gensa slightly the feed velocity V _R of this Garasuro' de 2, the desired The optical fiber preform 4 that has become the CZC can be manufactured.

Furthermore, by integrating the glass opening 2 with the glass pipe 1 while rotating the glass opening 2 around the axis, the axial symmetry of the optical fiber preform 4 with respect to the central axis in the longitudinal direction is improved, and the optical fiber preform 4 is improved. Core eccentricity can be further reduced.

It should be noted that the present invention is not limited to the above-described embodiment, but includes various other embodiments. That is, in the above embodiment, as the control of the feed speed V _R of Garasuro' de 2, sets the advance control program, but as Gosuru by connexion system to, not limited to this, for example, a glass pipe 1 during the integration of the glass outlet head 2 by measuring the core diameter, it may perform feedback control for controlling the velocity V _R feed based on the core diameter was the measurement. Further, in the above-described embodiment, the glass opening 2 is rotated. However, the present invention is not limited to this. For example, the glass pipe 1 may be rotated. Even in this case, the axial symmetry with respect to the longitudinal central axis of the optical fiber preform 4 is improved, and the amount of eccentricity of the core of the optical fiber preform 4 can be further reduced. . Incidentally, both the glass pipe 1 and the glass rod 2 may be rotated.

Next, an experiment performed on the method of manufacturing the optical fiber preform 4 according to the present invention will be described.

o

Table 1 shows an example in which the optical fiber preform 4 was manufactured by setting the feed rate V _R of the glass rod 2 (VAD rod) for the core and the clad to be lower than the feed rate V _P of the glass pipe 1 (pipe). (example) in an example of manufacturing an optical fiber preform 4 the feed speed V _R of Garasuro' de 2 equal to the feed speed V _P of the glass pipe 1 (Comparative example), the core of the optical fiber preform 4 The experimental results evaluated for the amount of eccentricity are shown.

Example Comparative example

V A D rod outer diameter 51mm 50mm

Core diameter 13.0mm 12.5mm

V A D Rod feed rate 9.6mm / min 10mm / min Pipe inner diameter 54mm 54mm Pipe outer diameter 182mm 182mm Pipe feed rate 10mm / rain lOmmZ min

Feeding speed ratio 0.96: 1.00 1.00: 1.00 Stretched base material outer diameter 60rara 60mm

Base material core eccentricity 0.3 ram That is, the feeding speed V _P of the glass pipe 1, for both the embodiments and the comparative examples with respect to the 1 Om m / min, feed speed V _R of Garasuro' de 2, in the embodiment and 9. 6 mm / min On the other hand, in the comparative example, it was 10 mm / min.

In the embodiment, since the feed speed V _R of Garasuro' de 2 is slower than the feeding speed V _P of the glass pipe 1, as C / C in the optical fiber preform 4 is a predetermined value, Garasuro' the outer diameter of the de-2, is increased to have (example 5 1 mm, Comparative example 5 0 mm) than the outer diameter of the glass rod de 2 in Comparative example ₀ also the core diameter of the Garasuro' de 2 in example The diameter is larger than the core diameter of the glass port 2 in the comparative example (Example 13.0 mm, Comparative Example 12.5 mm). Note that the inner and outer diameters of the glass pipe 1 are set to 54 mm and 182 mm, respectively, in the example and the comparative example. 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 of the optical fiber preform 4 becomes 60 mm in both the working example and the comparative example (stretched preform outer diameter). . According to Table 1, the core eccentricity of the optical fiber preform 4 was 0.3 mm in the comparative example, whereas the core eccentricity of the optical fiber preform 4 was 0.1 mm in the example. I have. That is, in the embodiment in which the tension is applied in the longitudinal direction of the glass rod 2 by reducing the feed speed V _R of the glass rod 2, the glass rod 2 is moved by the tension applied in the longitudinal direction of the glass rod 2. It is considered that the position was biased at the center position of the pipe 1, and as a result, the eccentricity of the core was suppressed.

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 tension in the longitudinal direction of the glass rod 2, the eccentricity of the core is reduced. It can be said that it is possible to manufacture a large-sized optical fiber preform with a decrease.

Claims

The scope of the claims

1. Insert a glass rod for core or glass opening for core and cladding into the glass pipe for cladding, and depressurize the above glass pipe while heating both with a heating furnace. A method for manufacturing an optical fiber preform in which a glass pipe and a glass rod are simultaneously integrated and drawn, and

A method for producing an optical fiber preform, wherein the glass pipe and the glass head are integrated with each other while tension is applied in a longitudinal direction of the glass head.

2. The method for producing an optical fiber preform according to claim 1, wherein the feeding speed of the glass rod to the heating furnace is adjusted to a speed lower than the feeding speed of the glass pipe.

3.The cross-sectional area of the glass pipe and the glass rod is set so as to have a predetermined core-to-cladding ratio when the glass pipe and the glass port are integrated. A method for producing the optical fiber preform according to the above.

4. The light according to claim 2, wherein the feeding speed of the glass rod to the heating furnace is adjusted such that the glass pipe and the glass rod are integrated in a longitudinal direction at a desired core-to-cladding ratio. Manufacturing method of fiber base material.

5. The method according to claim 1, wherein the glass pipe and the glass rod are integrated while rotating one or both of the glass pipe and the glass mouth around its longitudinal axis. A method for manufacturing an optical fiber preform.