Method for manufacturing optical fiber, and drawing furnace used for drawing optical fiber

Abstract

This method for manufacturing an optical fiber comprises: a step for disposing a preform within a drawing furnace; and a step for heating and drawing the preform in the drawing furnace. The drawing furnace is provided with a furnace core tube in which the preform is accommodated, and a heating device that is disposed outside the furnace core tube and heats the furnace core tube. The heating device generates a heat zone in the furnace core tube. The maximum value of the form factor of the drawing furnace calculated using formulas (1) and (2) is less than 0.08, where r is the radius of the furnace core tube, and y is the distance from the longitudinal end of the furnace core tube to the longitudinal position of the heat zone. In the formulas, dA1 is the minute area of the heat zone on the surface of the furnace core tube heated by the heating device, and A2 is the cross-sectional area at the longitudinal end of the furnace core tube.

Description

Method for manufacturing optical fibers, and drawing furnace used for drawing optical fibers.

[0001] This disclosure relates to a method for manufacturing optical fibers and a drawing furnace used for drawing optical fibers. This application claims priority under Japanese application No. 2025-014157, filed on 30 January 2025, and incorporates all the provisions of the said Japanese application.

[0002] Patent documents 1, 2, 3, and 4 disclose a method for manufacturing optical fibers by heating and melting an optical fiber preform and drawing it into a wire.

[0003] Japanese Patent Publication No. 2004-224587, Japanese Patent Publication No. 2004-307250, Japanese Patent Publication No. 2009-234857, Japanese Patent Publication No. 2014-152082

[0004] A method for manufacturing an optical fiber according to one embodiment of the present disclosure comprises the steps of: placing an optical fiber preform in a drawing furnace; and heating the optical fiber preform in the drawing furnace and drawing a fiber. The drawing furnace comprises a furnace tube configured to house the optical fiber preform inside; and a heating device configured to be placed outside the furnace tube and to heat the furnace tube. The heating device generates a heat zone in the furnace tube. When the radius of the furnace tube is r and the distance from the longitudinal end of the furnace tube to the longitudinal position of the heat zone is y, the maximum value of the shape factor of the drawing furnace calculated by the following equations (1) and (2) is less than 0.08. Here, dA １ A is a minute area of ​​the heat zone on the surface of the core tube that is heated by the heating device, ２ This is the cross-sectional area at the longitudinal end of the reactor core tube.

[0005] Figure 1 is a schematic cross-sectional view of a drawing furnace used for drawing optical fibers. Figure 2 is a perspective view showing the elements used to calculate the shape factor in the drawing furnace. Figure 3 is a cross-sectional view showing an example of an optical fiber preform used for drawing optical fibers.

[0006] In the neckdown phase formed during optical fiber drawing, it is desirable to reduce the heating temperature (e.g., maximum temperature) required by the heating device to obtain the desired glass viscosity in order to reduce energy consumption. Furthermore, it is expected that lowering the maximum temperature will increase the viscosity of the entire molten portion of the preform, the so-called neckdown portion, thereby improving the controllability of the glass fiber structure.

[0007] The present disclosure aims to provide a method for manufacturing optical fibers and a drawing furnace used for drawing optical fibers, which can reduce the heating temperature during drawing and improve the controllability of the glass fiber structure.

[0008] According to this disclosure, the heating temperature when drawing optical fibers can be reduced.

[0009] First, the contents of embodiments of the present disclosure will be listed and described. [1] A method for manufacturing an optical fiber according to one embodiment comprises the steps of: placing an optical fiber preform in a drawing furnace; and heating the optical fiber preform in the drawing furnace and drawing it. The drawing furnace comprises a furnace tube configured to house the optical fiber preform inside; and a heating device configured to be placed outside the furnace tube and to heat the furnace tube. The heating device generates a heat zone in the furnace tube. When the radius of the furnace tube is r and the distance from the longitudinal end of the furnace tube to the longitudinal position of the heat zone is y, the maximum value of the shape factor of the drawing furnace calculated by the following equations (1) and (2) is less than 0.08. Here, dA １ A is a minute area of ​​the heat zone on the surface of the core tube that is heated by the heating device, ２ This is the cross-sectional area at the longitudinal end of the reactor core tube.

[0010] In order to reduce the heating temperature (for example, the maximum heating temperature) by the heating device required to obtain a desired glass viscosity in the neck-down of the glass melt formed in the heating furnace during the fiber drawing of the optical fiber, the inventors focused on the radiant heat radiated from the longitudinal end of the core tube. This radiant heat can be calculated from the following formula (3) as the heat quantity Q. Here, A １ is the area of the heat zone on the surface of the core tube heated by the heating device, n is the number obtained by dividing the length in the longitudinal direction of the heat zone, σ is the Stefan-Boltzmann coefficient = 5.67×10 －８ [W / m ２ / K ４ [], T １ is the temperature of the heat zone, and T ２ is the temperature at the longitudinal end of the core tube. As is clear from formula (3), by reducing the maximum value of the form factor of the fiber drawing furnace, the radiant heat radiated from the longitudinal end of the core tube can be reduced, and the amount of heat Q radiated from the core tube can be reduced. That is, it is possible to reduce the amount of heat that is not directly used for melting the optical fiber preform, and it is also possible to reduce the energy used for heating (energy saving). Further, as in the above-described method for manufacturing an optical fiber, it is preferable to perform fiber drawing using a fiber drawing furnace in which the maximum value of the form factor is less than 0.08. According to this manufacturing method, the amount of heat Q radiated from the core tube can be reduced, and the heating temperature (for example, the maximum heating temperature) when drawing the optical fiber can be reduced.

[0011] [2] In the method for manufacturing an optical fiber according to [1] above, the maximum value of the form factor of the fiber drawing furnace may be less than 0.04. In this case, the amount of heat Q radiated from the core tube can be further reduced, and the heating temperature when drawing the optical fiber can be further reduced.

[0012] [3] In the method for manufacturing an optical fiber according to [1] or [2] above, in the fiber drawing step, the optical fiber preform may be heated by a heating device and drawn so that the amount of heat at the longitudinal end of the core tube, which is the amount of heat Q calculated by the following formula (3), is less than 5 kW. However, A １σ is the area of ​​the heat zone on the core tube surface heated by the heating device, n is the number of divisions of the longitudinal length of the heat zone, and σ is the Stefan-Boltzmann coefficient = 5.67 × 10⁻¹⁰ －８ [W / m ２ / K ４ ] and T １ This refers to the temperature of the heat zone, T ２ This is the temperature at the longitudinal end of the reactor core tube. In this case, the amount of heat Q radiated from the reactor core tube can be reliably reduced.

[0013] [4] In the optical fiber manufacturing method described in [3] above, the optical fiber preform may be heated with a heating device during the drawing process so that the heat quantity Q of the drawing furnace is less than 3 kW. In this case, the heat quantity Q radiated from the furnace tube can be reduced even more reliably.

[0014] [5] In any of the optical fiber manufacturing methods described in [1] to [4] above, the optical fiber preform may be a preform processed into a hollow core optical fiber. When drawing a hollow core optical fiber from an optical fiber preform, if there are areas with high heating temperatures, melting of thin parts (e.g., capillaries) within the preform corresponding to the hollow core may progress, causing distortion. However, as described above, by reducing the amount of heat dissipated and manufacturing in a heating furnace with a reduced heating temperature, even optical fibers with complex structures such as hollow core optical fibers can be manufactured by drawing while maintaining the desired structure with high precision.

[0015] [6] A drawing furnace according to one embodiment is a drawing furnace used for drawing optical fibers, comprising a furnace tube configured to house an optical fiber preform inside, and a heating device arranged outside the furnace tube and configured to heat the furnace tube. The heating device generates a heat zone in the furnace tube. When the radius of the furnace tube is r and the distance from the longitudinal end of the furnace tube to the longitudinal position of the heat zone is y, the maximum value of the shape factor calculated by the following equations (1) and (2) is less than 0.08. Here, dA １is a minute area of the heat zone on the surface of the core tube heated by a heating device, and A ２ is the cross-sectional area at the longitudinal end of the core tube.

[0016] As described above, the drawing furnace is a drawing furnace in which the maximum value of the shape factor is less than 0.08. Therefore, by using this drawing furnace, the amount of heat Q radiated from the core tube can be reduced, and the heating temperature when drawing the optical fiber with this drawing furnace can be reduced.

[0017] [Details of Embodiments of the Present Disclosure] Specific examples of a method for manufacturing an optical fiber and a drawing furnace used for drawing an optical fiber according to an embodiment of the present disclosure will be described below with reference to the drawings. In the following description, the same reference numerals will be used for the same elements or elements having the same function, and redundant descriptions will be omitted. The present invention is not limited to these examples, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0018] First, the drawing furnace used in the method for manufacturing an optical fiber according to the present embodiment will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view schematically showing a drawing furnace used for drawing an optical fiber. As shown in FIG. 1, the drawing furnace 1 includes a core tube 2, a heater 3 (heating device), an outer wall 4, and a heat insulating material 5.

[0019] The core tube 2 has a cylindrical shape and defines a heating space S inside. The core tube 2 houses a glass preform 10 (illustrated in FIG. 3) for an optical fiber inside the heating space S (inside). The core tube 2 is formed of, for example, a graphite material.

[0020] The heater 3 is a member for heating the core tube 2 to heat the optical fiber preform housed in the heating space S. The heater 3 may be a heater of a resistance heating method or a heater of an induction heating method. The heater 3 is disposed on the outer periphery of the core tube 2 and surrounds the heating space S. The heater 3 is formed of, for example, a graphite material. When the heater 3 heats the core tube 2, a heat zone T is generated in the core tube 2.

[0021] The outer wall 4 is a member that surrounds the heater 3. The outer wall 4 is formed of, for example, stainless steel or the like and is cooled by cooling water. The heat insulating material 5 is disposed between the heater 3 and the outer wall 4. The heat insulating material 5 is formed of, for example, a graphite material with a low bulk density. With such a structure, the heat insulating material 5 exhibits a heat insulating effect. The thickness of the heat insulating material 5 (in the case of the resistance heating method, the thickness between the heater 3 and the outer wall 4) may be, for example, 50 mm or more and 150 mm or less. Also, the inside of the wire drawing furnace 1 is filled with an inert gas such as nitrogen or argon.

[0022] In the neckdown formed during wire drawing using such a wire drawing furnace 1, in order to lower the maximum heating temperature of the heater 3 (heating element) necessary to obtain a desired glass viscosity, in the present embodiment, the radiant heat radiated from the longitudinal end 2a of the core tube 2 and the end opposite to 2a is reduced. Each radiant heat (heat quantity Q) can be calculated from a model formula using the form factor shown in FIG. 2 and the following formulas (1) to (3), where r is the radius of the core tube 2 and y is the distance from the longitudinal end 2a of the core tube 2 or the end opposite thereto to the longitudinal position of the heat zone T. Here, dA １ is the minute area of the heat zone T on the surface of the core tube heated by the heater 3, and A ２ is the cross-sectional area at the longitudinal end 2a of the core tube 2 (the area of the circular portion shown by the shaded portion in FIG. 2, including the space inside the core tube). The heat zone T is the portion of the core tube 2 heated by the heater 3 which is a heating device, and the length of the heat zone T is defined to be the same as that of the heater 3. However, A １ is the area of the heat zone T on the surface of the core tube heated by the heater 3, n is the number of divisions of the length in the length direction of the heat zone T, σ is the Stefan-Boltzmann coefficient = 5.67 × 10 －８ [W / m 7] ２ / K ４ ], T １ is the temperature of the heat zone T, and T ２ is the temperature of the longitudinal end 2a of the core tube 2.

[0023] As is clear from equation (3) above, the smaller the shape factor, the more the radiant heat radiated from the end 2a of the core tube 2 can be reduced, and the amount of heat Q released from the core tube 2 can be reduced. In the following experimental examples 1 to 14, the shape factor is changed by changing the radius r of the core tube 2 and the distance y from the longitudinal end 2a of the core tube 2 to the longitudinal position of the heat zone T, thereby reducing the amount of heat Q. Then, it is determined what shape factor provides good controllability during wire drawing by the wire drawing furnace 1. Controllability here refers to whether the capillary 12 has the desired structure when drawing wire using the glass preform 10 for hollow core optical fiber shown in Figure 3. Note that in Figure 1, y １ y is the longitudinal distance from the longitudinal end 2a of the core tube 2 to the end 3a of the heat zone T on the side closer to the end 2a, and y ｎ This indicates the longitudinal distance from the longitudinal end 2a of the reactor core tube 2 to the end 3a of the heat zone T on the side furthest from end 2a.

[0024] In these experimental examples 1 to 14, the reactor core tube 2 is considered as the model shown in Figure 2, and the amount of radiation from the heat zone radiating from the end 2a of the reactor core tube 2 is estimated using its shape factor. In each experimental example, the radius r of the reactor core tube 2 and the longitudinal distance y from the longitudinal end 2a of the reactor core tube 2 to the end 3a of the heat zone T on the side closer to the end 2a are used. １ The lengths of heater 3, core tube 2, etc., are as shown in Tables 1, 2, and 3 below. The heater temperature is set to 2000°C in each experimental example. This heater temperature corresponds to the temperature T in the heat zone T. １ This corresponds to the temperature T of the longitudinal end 2a of the core tube 2. ２ The temperature is set to 800°C in each experimental example. In each experimental example, a glass preform 10 for a hollow core optical fiber having the structure shown in Figure 3 is heated, and the results of drawing lines are shown. Line drawing result "A" indicates that the desired shape and structure are obtained, and the controllability is excellent. Line drawing result "B" indicates that some deformation is observed, but the shape and structure are within an acceptable range, and the controllability is good. Line drawing result "C" indicates that the desired shape and structure are not obtained, and the controllability is acceptable.

[0025]

[0026]

[0027]

[0028] As is clear from the above experimental example, by having a maximum value of the shape factor (calculated by equation (1)) in the drawing furnace 1 (core tube 2) of less than 0.08, the capillary 12 can be drawn into the desired structure when drawing with the glass preform 10 for hollow core optical fibers. That is, the maximum temperature of the heating element required to obtain the desired glass viscosity in the neck-down formed during drawing can be lowered, and it is confirmed that complex preforms such as glass preforms for hollow core optical fibers can be drawn into the desired glass structure with good controllability (corresponding to evaluations "A" and "B" of the drawing result). Furthermore, as is clear from the above experimental example, by having a maximum value of the shape factor in the drawing furnace 1 (core tube 2) of less than 0.04, the capillary 12 can be drawn into the desired structure more reliably when drawing with the glass preform 10 for hollow core optical fibers. In other words, it is possible to lower the maximum temperature of the heating element required to obtain the desired glass viscosity in the neck-down formed during wire drawing, and it is confirmed that complex preforms such as glass preforms for hollow core optical fibers can be drawn into the desired glass structure with greater controllability (corresponding to evaluation of wire drawing results [A]).

[0029] Furthermore, from the above experimental examples, it can be confirmed that the glass preform 10 can be heated with the heater 3 and drawn in such a way that the heat quantity Q at the end 2a of the core tube 2, calculated by equation (3), is less than 5 kW. It can also be confirmed that the glass preform 10 can be heated with the heater 3 and drawn in such a way that this heat quantity Q is less than 3 kW. In other words, it can be confirmed that even if the radiant heat (heat quantity Q) from the end 2a of the core tube 2 is reduced to less than 5 kW or less than 3 kW, it is possible to draw in the desired structure and obtain energy-saving effects. It can also be confirmed that even for ordinary optical fibers that are not hollow core optical fibers, by setting the above conditions (maximum value of the shape factor (calculated by equation (1)) in the drawing furnace 1 (core tube 2) is less than 0.08, and the heat quantity Q calculated by equation (3) is less than 5 kW), it is possible to draw in the desired structure and obtain energy-saving effects.

[0030] Next, we will describe a method for manufacturing optical fibers by drawing a glass preform using the drawing furnace 1 described above.

[0031] First, a glass preform 10 for optical fibers having the cross-sectional structure shown in Figure 3 is prepared as the glass preform to be used in this manufacturing method. The glass preform 10 has a jacket tube 11 and a plurality of capillaries 12. The jacket tube 11 is made of, for example, silica glass (SiO ２ It is a hollow tube formed from ). Each of the multiple capillaries 12 is, for example, silica glass (SiO ２ The capillaries are hollow tubes formed from a material and have a smaller diameter than the jacket tube 11. In one example, the diameter of each capillary 12 is the same. The thickness of the capillaries 12 may be extremely thin compared to the thickness of the jacket tube 11. Each capillary 12 is fixed to the inner surface 11a of the jacket tube 11 at a contact point 13 inside the jacket tube 11 by heating with a flame or laser irradiation.

[0032] Next, the glass preform 10 is placed in the heating space S of the furnace tube 2 in the drawing furnace 1 shown in Figure 1. As described above, the drawing furnace 1 includes a furnace tube 2 configured to house the glass preform 10, a heater 3 positioned outside the furnace tube 2 and configured to heat the furnace tube 2, an outer wall 4 located on the outer circumference of the heater 3 and surrounding the heater 3, and an insulating material 5 positioned between the heater 3 and the outer wall 4. In this drawing furnace 1, when the radius of the furnace tube 2 is r and the distance from the longitudinal end 2a of the furnace tube 2 to the longitudinal position of the heat zone T is y, the maximum value of the shape factor of the drawing furnace 1 shown in equation (1) above is less than 0.08. Note that this maximum value of the shape factor may be less than 0.04.

[0033] Next, once the glass preform 10 is placed, the heater 3 is heated to a predetermined temperature. Due to the structure of the drawing furnace 1 described above, the heating temperature (maximum heating temperature) at this time can be lower than the heating temperature (maximum heating temperature) in conventional drawing methods. The lower end of the glass preform 10 is then heated and melted by the heater 3 of the drawing furnace 1 and drawn. The drawn optical fiber is then cooled, and a resin coating is applied to the outer circumference of the glass fiber. When drawing a hollow core optical fiber, internal pressure is applied to the hollow core portion 14 of the glass preform 10 and to each capillary 12. The drawing is then performed while adjusting the difference in this internal pressure. As a result, a hollow core optical fiber with the desired shape can be obtained.

[0034] In the optical fiber manufacturing method according to this embodiment, the optical fiber is drawn in the drawing furnace 1 (furnace tube 2) such that the maximum value of the shape factor in the drawing furnace 1 (furnace tube 2), calculated by formula (1), is less than 0.08. Therefore, this manufacturing method reduces the amount of heat Q radiated from the furnace tube 2 and reduces the heating temperature when drawing the optical fiber. In a conventional drawing furnace, the temperature distribution H shown in Figure 1 １ In contrast, in the wire drawing furnace 1 according to this embodiment, the temperature distribution H shown in Figure 1 ２As a result, the maximum heating temperature during wire drawing can be reduced. Furthermore, in the wire drawing furnace and the method for manufacturing optical fibers using the same according to this embodiment, since the heating temperature can be reduced, optical fibers with the desired glass shape and structure can be obtained even when wire drawing is performed using preforms with complex structures as described above.

[0035] The optical fiber manufacturing method and the drawing furnace used in the manufacturing method according to the embodiments of this disclosure have been described in detail above. However, the present invention is not limited to the above embodiments and can be applied to various embodiments and modifications. For example, in the embodiments described above, the above method was used to manufacture a hollow core optical fiber, but the invention is not limited to this. That is, the optical fiber manufacturing method and drawing furnace described above may be applied to a manufacturing method using a normal optical fiber preform. Even in this case, the heating temperature for melting the optical fiber preform can be reduced while maintaining controllability of the drawing, and the energy required for heating can also be reduced.

[0036] 1…Fiber drawing furnace 2…Core tube 2a…End 3…Heater (heating device) 3a…End 4…Outer wall 5…Insulation material 10…Glass preform (optical fiber preform) 11…Jacket tube 11a…Inner surface 12…Capillary 13…Contact point 14…Hollow core section A ２ ...Cross-sectional area dA at the end of the core tube １ ...H (a small area of ​​the heat zone) １ , H ２ ...Temperature distribution S...Heating space T...Heat zone T １ ...heat zone temperature T ２ ...Temperature at the end of the reactor tube r...Radius of the reactor tube y...Longitudinal distance from the end of the reactor tube to the heat zone １ , y ｎ …distance

Claims

1. A method for manufacturing optical fibers, comprising the steps of: placing an optical fiber preform in a drawing furnace; and heating the optical fiber preform in the drawing furnace and drawing a fiber thereon, wherein the drawing furnace comprises a furnace tube configured to house the optical fiber preform inside, and a heating device positioned outside the furnace tube and configured to heat the furnace tube, wherein the heating device generates a heat zone in the furnace tube, and the maximum value of the shape factor of the drawing furnace, calculated by the following formulas (1) and (2), is less than 0.08, where r is the radius of the furnace tube and y is the distance from the longitudinal end of the furnace tube to the longitudinal position of the heat zone. Here, dA １ A is a minute area of ​​the heat zone on the surface of the furnace tube heated by the heating device, ２ This is the cross-sectional area at the longitudinal end of the reactor core tube.

2. The method for manufacturing an optical fiber according to claim 1, wherein the maximum value of the shape factor of the drawing furnace is less than 0.

04.

3. The method for manufacturing an optical fiber according to claim 1 or 2, wherein in the line drawing step, the optical fiber preform is heated with the heating device and line drawn such that the amount of heat Q at the longitudinal end of the furnace tube, calculated by the following formula (3), is less than 5 kW. However, A １ σ is the area of ​​the heat zone on the surface of the furnace tube heated by the heating device, n is the number of divisions of the longitudinal length of the heat zone, and σ is the Stefan-Boltzmann coefficient = 5.67 × 10 －８ [W / m ２ / K ４ ] and T １ The temperature of the heat zone, T ２ This is the temperature at the longitudinal end of the reactor core tube.

4. The method for manufacturing an optical fiber according to claim 3, wherein, in the line drawing step, the optical fiber preform is heated with the heating device and line drawn so that the heat quantity Q is less than 3 kW.

5. The method for manufacturing an optical fiber according to any one of claims 1 to 4, wherein the optical fiber preform is a preform that is processed into a hollow core optical fiber.

6. A drawing furnace used for drawing an optical fiber, comprising: a core tube configured to house an optical fiber preform therein; and a heating device disposed outside the core tube and configured to heat the core tube. The heating device generates a heat zone in the core tube. When the radius of the core tube is r and the distance from the longitudinal end of the core tube to the longitudinal position of the heat zone is y, the maximum value of the form factor calculated by the following formulas (1) and (2) is less than 0.

08. Drawing furnace. Here, dA １ is the minute area of the heat zone on the surface of the core tube heated by the heating device, and A ２ is the cross-sectional area of the longitudinal end of the core tube.

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