Optical fiber preform manufacturing method and optical fiber manufacturing method

Abstract

To provide a method for manufacturing an optical fiber preform, capable of preventing a support part from being damaged.SOLUTION: A method for manufacturing an optical fiber preform including: a seed rod including a core part and a support part bonded at one or both ends of the core part by heat fusion; and a porous glass part formed in the outer periphery of the core part comprises the steps of: holding the holding part of the support part and depositing porous glass on the seed rod to form a porous glass part; slowly cooling a boundary part between the core part and the support part and the vicinity area of the boundary part at a predetermined cooling rate in a predetermined temperature range; and heating and transparently vitrify the optical fiber preform.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an optical fiber preform and a method for manufacturing an optical fiber. [Background technology]

[0002] In recent years, as OVD (Outside Vapor Deposition) soot has become larger, the load on the support rod has increased. Meanwhile, a method for manufacturing an optical fiber preform that prevents cracks in the porous glass preform has been proposed. The method for manufacturing an optical fiber preform described in Patent Document 1 includes a step of gradually reducing the flow rate of fuel gas flowing into a burner and slowly cooling the surface temperature of the optical fiber porous preform while heating with the burner. The deposition apparatus described in Patent Document 2 is configured to prevent cracks in the glass particles at both ends of the optical fiber preform. Furthermore, in order to reduce the load associated with the larger size, a vertical OVD has been considered, and the deposition apparatus described in Patent Document 3 holds the optical fiber preform vertically within the apparatus and deposits glass particles in the vertical direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5163416 [Patent Document 2] Patent No. 6960728 [Patent Document 3] Patent Publication No. 2021-175695 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the manufacturing method of the optical fiber preform described in Patent Document 1 only involves slow cooling of glass particles deposited in the core portion. When the optical fiber preform is cooled, the support portion has a faster cooling rate because it lacks a porous layer or is thinner than the optical fiber preform portion on which the glass particles are deposited. This can lead to distortion and damage to the support portion. The configuration described in Patent Document 2 prevents the accumulation of glass particles on the support portion to prevent cracks in the porous preform, but does not prevent damage to the support portion. The deposition device described in Patent Document 3 reduces the load on the support portion due to the large size of the optical fiber preform, but does not mention distortion. Furthermore, it is necessary to control the updraft caused by the chimney effect, making the deposition device complex and expensive.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a method for manufacturing an optical fiber preform that can prevent damage to the support portion of the optical fiber preform. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a method for manufacturing an optical fiber preform having a seed rod having a core portion and support portions joined to both ends of the core portion by thermal fusion, and a porous glass portion formed on the outer periphery of the core portion, the method comprising: a step of holding a gripping portion of the support portion, depositing porous glass on the seed rod to form the porous glass portion; and a step of heating the optical fiber preform to vitrify it into a transparent glass, characterized in that after forming the porous glass portion in the seed rod, the method further comprises a step of using a flame of a burner to cool the boundary portion between the core portion and the support portion and the area near the boundary portion at a predetermined cooling rate. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for manufacturing an optical fiber preform that can prevent damage to the support portion. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a seed rod of an optical fiber preform according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of a portion II of the seed rod of the optical fiber preform shown in FIG. 1 according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a side view of a deposition apparatus used to manufacture an optical fiber preform according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of a sintering apparatus used to manufacture an optical fiber preform according to the first embodiment of the present invention. [Figure 5] FIG. 5 is a flowchart of the method for manufacturing a glass base material according to the first embodiment of the present invention. [Figure 6] FIG. 6 is a graph showing the temperature change in the annealing of the support portions of the examples and comparative examples according to the first embodiment of the present invention. [Figure 7] FIG. 7 is a table showing the presence or absence of cracks in the support portions of examples and comparative examples according to the first embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to the accompanying drawings. The same reference numerals throughout the specification refer to substantially the same components.

[0010] [First embodiment] FIG. 1 is a perspective view of a seed rod of an optical fiber preform in this embodiment, and FIG. 2 is a perspective view of a portion II of the seed rod of the optical fiber preform shown in FIG.

[0011] The seed rod for the optical fiber preform includes a core 11 and support portions 12A and 12B. The core 11 is the starting material for the optical fiber preform and is made of silica glass or the like. The core 11 can be formed by heating and drawing a rod having a core and a cladding layer formed around the core. The core 11 is approximately cylindrical and includes side portions 111 and end portions 112 and 113. The side portion 111 has a predetermined length, and the end portions 112 and 113 have predetermined diameters. For example, the length can be 4000 mm and the diameter can be 70 mm. Glass particles are deposited on the outer periphery of the side portion 111 in a deposition process described below to form the optical fiber preform. In FIG. 1, the direction in which a virtual core axis 114 of the core 11 extends is called the X direction, the direction perpendicular to the X direction is called the Y direction, and the direction perpendicular to the X direction and the Y direction is called the Z direction.

[0012] The support portions 12A and 12B are support rods, and are provided at both ends of the core portion 11. The support portions 12A and 12B are used to support the core portion 11 during the glass particle deposition and sintering processes. The support portions 12A and 12B are made of quartz or the like, just like the core portion 11. The support portions 12A and 12B are approximately cylindrical, and each has side portions 121A and 121B and end portions 122A, 122B, 123A, and 123B. The side portions 121A and 121B have a predetermined length, and the end portions 122A, 122B, 123A, and 123B have a predetermined diameter. For example, the length may be 1000 mm and the diameter may be 65 mm. The length of side portions 121A and 121B and the diameter of end portions 122A, 122B, 123A and 123B may be changed as appropriate depending on the length of side portion 111 of core portion 11 or the diameter of end portions 112 and 113, the thickness of deposited glass particles, and the like.

[0013] Support parts 12A and 12B are joined to core part 11 so that virtual support axes 124A and 124B of support parts 12A and 12B and core axis 114 are positioned substantially on the same line, end part 122A is in contact with end part 112, and end part 122B is in contact with end part 113. End parts 122A and end part 112, and end parts 122B and end part 113 are welded together using an oxyhydrogen burner or the like. The welding method is not limited to this, and welding may also be performed using an electric furnace or the like. Here, the joint between end part 122A and end part 112 and its surrounding area are referred to as boundary part 115A (the boundary between end part 122A and end part 112 and the hatched area with diagonal lines in FIG. 2), and a predetermined length of side part 121 from end part 122A is referred to as nearby area 125A (the hatched area with dotted lines in FIG. 2). For example, the vicinity region 125A may be a region of the side portion 121A extending up to 800 mm in the direction from the end portion 122A toward the end portion 123A. The same applies to the boundary portion 115B and the vicinity region 125B of the support portion 12B. The vicinity regions 125A and 125B may be changed as appropriate depending on the length of the side portion 111, the diameter of the ends 112 and 113, the thickness of the deposited glass particles, etc.

[0014] The support portions 12A and 12B can be joined to one end or both ends of the core portion 11 depending on the deposition apparatus used in the glass particle deposition step described below. For example, when glass particles are deposited by a horizontal deposition apparatus, the support portions 12A and 12B are joined to both ends of the core portion 11. In this embodiment, the case where glass particles are deposited by a horizontal deposition apparatus will be described.

[0015] 3 is a side view of a deposition apparatus used to manufacture an optical fiber preform in this embodiment. The porous glass portion 13 is a layer of glass particles deposited on the core portion 11. The porous glass portion 13 is deposited on the core portion 11 by a deposition apparatus. The method for depositing the porous glass portion 13 may be, for example, a VAD (Vapor Phase Axial Deposition) method or an OVD (Outside Vapor Deposition) method. The VAD method is a method in which the core portion 11 is held vertically and glass particles are deposited vertically from the lower end to the upper end of the core portion 11. The OVD method is a method in which the core portion 11 is held at both ends and glass particles are deposited horizontally on the sides of the core portion 11. In this embodiment, a horizontal deposition apparatus is used as described above, and the porous glass portion 13 is deposited by the OVD method.

[0016] The deposition device 3 includes a base 31, support portions 32A and 32B, a gripping portion 33, a stress applying portion 34, a burner 38, and burners 39A and 39B. The base 31 is a member that serves as the foundation of the deposition device 3 and is formed in a substantially rectangular parallelepiped shape. The base 31 is placed substantially horizontally relative to the ground surface. The base 31 includes rails and the like that extend in the longitudinal direction of the base 31 and are provided below the core portion 11, and the support portions 32A and 32B and the burner 38 are movable along the rails. In a plan view, the longitudinal direction of the base 31 is the X direction, the lateral direction of the base 31 is the Y direction, and the vertical direction of the base 31 is the Z direction.

[0017] The support portions 32A and 32B are columnar, face each other, and are provided on the upper part of the base 31. That is, the support portion 32A is provided at one end of the base 31, and the support portion 32B is provided at the other end of the base 31. At least one of the support portions 32A and 32B is movable on rails laid on the base 31. The support portions 32A and 32B are equipped with a rotary motor, a transmission, etc. that rotate the core portion 11 via the support portions 12A and 12B.

[0018] The gripping portion 33 and the stress applying portion 34 constitute a chuck and are provided on the support portions 32A and 32B, respectively. The gripping portion 33 is made of a metal such as SUS (Steel Use Stainless) or a heat-resistant fluororesin, and has a plurality of claws that can move close to or apart from each other. A gripping hole is formed in the center of the plurality of claws so that the support portions 12A and 12B can be gripped.

[0019] The stress applying portion 34 is provided around the gripping portion 33 and is capable of applying stress to the gripping portion 33. When the stress applying portion 34 applies stress to the gripping portion 33, the multiple claws move closer to each other and the diameter of the gripping hole becomes smaller. As a result, the support portions 12A and 12B inserted into the gripping holes are gripped by the gripping portion 33.

[0020] The burner 38 is a burner that sprays glass particles onto the core region 11, and is, for example, a burner that uses oxyhydrogen as fuel. The burner 38 is installed on a rail on the base 31. The burner 38 moves on the rail and can deposit glass particles onto the core region 11 that rotates around the core axis 114. The burner 38 includes a nozzle for supplying a flammable gas, a nozzle for supplying a combustion support gas, and a nozzle for supplying glass raw material. For example, the flammable gas can be hydrogen or the like, and the combustion support gas can be oxygen or the like. The glass raw material can be SiCl4 or the like. The burner 38 injects glass raw material into the flame and generates glass particles by a flame hydrolysis reaction. The burner 38 can adjust the position of the nozzle in the vertical direction of the core axis 114 depending on the thickness of the glass particles deposited on the side region 111. In this way, a porous glass region 13 is deposited on the outer periphery of the core region 11, and the optical fiber preform 1 is formed.

[0021] Burner 39A is an oxyhydrogen burner that sinters the porous glass adhering to boundary 115A and the adjacent region 125A, and burner 39B is an oxyhydrogen burner that sinters the porous glass adhering to boundary 115B and the adjacent region 125B. Burners 39A and 39B are also called auxiliary sintering burners or side burners and are equipped with nozzles for supplying flammable gas and combustion-supporting gas. Burners 39A and 39B are installed so as not to come into contact with burner 38. Burners 39A and 39B can heat predetermined regions of support members 12A and 12B that rotate around support shafts 124A and 124B. Burners 39A and 39B may heat not only boundary 115A and 115B and the adjacent regions 125A and 125B, but also predetermined regions extending from boundary 115A and 115B toward optical fiber preform 1. For example, the peripheries of both ends of the optical fiber preform 1, where the amount of glass particles deposited is smaller than that of the central periphery in the X direction of the optical fiber preform 1, may be heated.

[0022] Burners 39A and 39B may be installed on the rail on which burner 38 is installed, or may be installed on a rail that is separate from the rail on which burner 38 is installed. In this case, burners 39A and 39B can move on the rail and heat support parts 12A and 12B.

[0023] Burners 39A and 39B gradually lower the flame temperature, thereby slowly cooling support members 12A and 12B. When the required amount of deposition by burner 38 is reached and deposition is terminated, the deposition support members 12A and 12B have no porous layer or a thinner porous layer than the porous glass portion 13, resulting in a faster cooling rate of the glass surface. Furthermore, as the deposition amount of the porous glass portion 13 increases, the load on support members 12A and 12B increases. This increases the likelihood of distortion in support members 12A and 12B, leading to cracks and breakage. After the glass particle deposition process, slowly cooling support members 12A and 12B within a predetermined temperature range and at a predetermined cooling rate can suppress distortion of support members 12A and 12B.

[0024] 4 is a cross-sectional view of an apparatus used in a sintering process for manufacturing an optical fiber preform according to an embodiment. The sintering apparatus 5 includes a furnace tube 51, an intake hole 52, an exhaust hole 53, a heater 54, an upper cover 55, and a support 56.

[0025] The core tube 51 is a cylindrical reaction vessel capable of storing the optical fiber preform 1 and may be made of transparent quartz glass or the like. The intake hole 52 is provided at the bottom of the core tube 51 and introduces a dehydration gas, an inert gas, or the like into the interior 511 of the core tube 51. For example, the dehydration gas may be chlorine or thionyl chloride, and the inert gas may be argon or helium. The exhaust hole 53 is provided at the upper side of the core tube 51 and exhausts the dehydration gas, the inert gas, or the like filled in the core tube 51 as needed. The heater 54 is provided around the core tube 51 and heats the optical fiber preform 1. The top cover 55 is provided at the top of the core tube 51 and seals the top of the core tube 51 after the optical fiber preform 1 is stored in the core tube 51. The top cover 55 has an opening 551 through which the support part 12A can be inserted.

[0026] The support part 56 is provided on the upper part of the furnace tube 51, and holds the support part 12A to suspend and support the optical fiber preform 1. The support part 56 is configured to be rotatable by a driving mechanism (not shown). As the support part 56 rotates, the optical fiber preform 1 rotates in the interior 511 of the furnace tube 51 and is heated by the heater 54. As a result, the core portion 11 and the porous glass portion 13 of the optical fiber preform 1 are sintered and vitrified.

[0027] 5 is a flowchart of a method for manufacturing a glass base material according to this embodiment. First, the support portions 12A and 12B are joined to both ends of the core portion 11 (step S101). The support portions 12A and 12B are fusion-joined to the core portion 11 using an oxyhydrogen burner or the like so that the core axis 114, the support axis 124A, and the support axis 124B are positioned on approximately the same line.

[0028] Next, the core 11 (optical fiber preform) to which the support portions 12A and 12B are joined is placed in the deposition apparatus 3 (step S102). The support portions 12A and 12B are each held by a holding portion 33 of the deposition apparatus 3. Here, it is desirable that the holding portion 33 holds the support portions 12A and 12B so as not to prevent the burners 39A and 39B from heating the nearby regions 125A and 125B.

[0029] The deposition device 3 rotates the support members 12A and 12B and the core member 11, and the burner 38 deposits glass particles on the side member 111 (step S103). The burner 38 reciprocates in the X direction, for example, below the core member 11, and throws glass raw material into the flame, and the generated glass particles are deposited on the side member 111. While the porous glass member 13 is being deposited on the side member 111, the burners 39A and 39B may heat the porous glass member 13 deposited on both ends of the core member 11. Because low-density porous glass bodies are deposited on both ends of the core member 11, cracks and the like are more likely to occur. For this reason, by using the burners 39A and 39B to heat the porous glass member 13 deposited on both ends of the core member 11, respectively, it is possible to prevent cracks and the like from occurring in the porous glass member 13 in the areas with a low deposition amount.

[0030] When the porous glass portion 13 is sufficiently deposited in the core portion 11, the supply of glass raw material, flammable gas, and combustion supporting gas to the burner 38 is stopped, and the burner 38 is extinguished. Then, the support portions 12A and 12B are gradually cooled to the target temperature by the burners 39A and 39B (step S104). The method for gradually cooling the support portions 12A and 12B will be described in detail below. While gradually lowering the temperature of the flames of the burners 39A and 39B, the flames of the burners 39A and 39B are blown onto the boundary portions 115A and 115B and the adjacent regions 125A and 125B. This gradually lowers the temperature of the boundary portions 115A and 115B and the adjacent regions 125A and 125B from a predetermined temperature to the target temperature. That is, the boundary portions 115A and 115B and the adjacent regions 125A and 125B are gradually cooled at a predetermined cooling rate within the temperature range from the predetermined temperature to the target temperature. The predetermined temperature and the target temperature may be, for example, 1150°C and 1050°C, respectively. The temperature range from the predetermined temperature to the target temperature preferably includes temperatures around the strain point of quartz, more preferably including, for example, 1090°C, and the temperature range may be from 1100°C to 1050°C. The predetermined cooling rate may be, for example, 5°C / min, 10°C / min, 20°C / min, 30°C / min, etc. When the temperatures of boundary portions 115A, 115B and nearby regions 125A, 125B are lowered to the target temperature, burners 39A, 39B are extinguished, and boundary portions 115A, 115B and nearby regions 125A, 125B are naturally cooled (step S105).

[0031] Compared to the areas where a large amount of glass particles is deposited, the cooling rate is faster around the ends 112 and 113 because the amount of deposited glass particles is smaller there. Similarly, the cooling rate is also faster in the support portions 12A and 12B where no glass particles are deposited. Furthermore, the load on the support portions 12A and 12B increases depending on the amount of deposition of the porous glass portion 13. This makes the support portions 12A and 12B more likely to be distorted, which may result in damage to the support portions 12A and 12B. After the glass particle deposition process, the boundary between the core portion and the support portion and the surrounding area are slowly cooled to a target temperature at a predetermined cooling rate, thereby suppressing the occurrence of distortion in the support portion. This makes it possible to prevent damage to the support portion.

[0032] When the temperatures of the support parts 12A and 12B are lowered to a predetermined temperature by natural cooling, the support parts 12A and 12B are detached from the holder 33, and the optical fiber preform 1 is removed from the deposition device 3 (step S106). Furthermore, the joint between the support part 12B and the core part 11 may be melted by a burner or an electric furnace, and the support part 12B may be separated and removed from the optical fiber preform 1 (step S107).

[0033] The support part 12A is supported by the support part 56, and the optical fiber preform 1 is placed vertically in the interior 511 of the furnace tube 51 (step S108). The optical fiber preform 1 is heated and sintered by the sintering device 5 (step S109). First, chlorine (Cl2) or the like is introduced into the interior 511 through the intake hole 52. Next, the optical fiber preform 1 is heated by the heater 54 while rotating in the interior 511. This removes impurities and the like contained in the optical fiber preform 1. Furthermore, chlorine is exhausted to the outside of the furnace tube 51 through the exhaust hole 53, and helium (He) is introduced into the interior 511 through the intake hole 52 as an atmospheric gas. The optical fiber preform 1 is heated to a predetermined temperature by the heater 54 while rotating in the interior 511. The predetermined temperature may be, for example, 1500°C. When the sintering of the optical fiber preform 1 is completed, the helium is discharged from the furnace tube 51 through the exhaust hole 53, and the transparent vitrified optical fiber preform 1 is removed from the furnace tube 51. In the subsequent steps, the transparent vitrified optical fiber preform 1 is heated and drawn. In this manner, an optical fiber is formed.

[0034] As described above, according to this embodiment, damage to the support portion can be prevented by slowly cooling the boundary portion between the core portion and the support portion and the surrounding area within a predetermined temperature range and at a predetermined cooling rate.

[0035] [Example] Fig. 6 is a graph showing the temperature change during the annealing of the support portions of the examples and comparative examples of this embodiment, and Fig. 7 is a table showing the presence or absence of cracks in the support portions of the examples and comparative examples of this embodiment. As described above, after the deposition process of the porous glass portion 13, the support portions 12A and 12B were annealed at a predetermined cooling rate, and the presence or absence of cracks in the support portions 12A and 12B was examined. The weight of the optical fiber preform 1 after the deposition process used in the examples was 180 kg, and the diameter of the support portions 12A and 12B made of quartz was 63 mm. After the deposition process, the burner 38 was extinguished, and then the flames of the burners 39A and 39B were blown onto the boundary portions 115A and 115B and the neighboring regions 125A and 125B, and the support portions 12A and 12B were annealed.

[0036] The temperature change of the support portions 12A and 12B when they are slowly cooled from 1150°C to 1050°C at a cooling rate of 5°C / min is shown by a solid line in Fig. 6, and the weight of the optical fiber preform, the diameter of the support portions, and the presence or absence of cracks in the support portions are shown in the first row of Fig. 7 (Example 1). The temperature change of the support portions 12A and 12B when they are slowly cooled from 1150°C to 1050°C at a cooling rate of 10°C / min is shown by a dashed line in Fig. 6, and the weight of the optical fiber preform, the diameter of the support portions, and the presence or absence of cracks in the support portions are shown in the second row of Fig. 7 (Example 2). The temperature change of the support parts 12A and 12B when the support parts 12A and 12B were slowly cooled at a cooling rate of 20°C / min from 1150°C to 1050°C is shown by the dashed line in Figure 6, and the weight of the optical fiber preform, the diameter of the support parts, and the presence or absence of cracks in the support parts are shown in the third row of Figure 7 (Example 3). When the temperatures of the support parts 12A and 12B reached the target temperature, the burners 39A and 39B were extinguished, and the support parts 12A and 12B were allowed to cool naturally. In Example 1-3, no cracks were generated in the support parts 12A and 12B, and the support parts 12A and 12B were not damaged when the optical fiber preform 1 was removed from the deposition device 3.

[0037] [Comparative Example] On the other hand, as a comparative example, when the weight of the optical fiber preform 1 after the deposition process was 180 kg, the diameter of the support portions 12A and 12B was 63 mm, and the support portions 12A and 12B were slowly cooled at a cooling rate of 30°C / min from 1150°C to 1050°C, the temperature change of the support portions 12A and 12B is shown by the two-dot chain line in Fig. 6, and the weight of the optical fiber preform, the diameter of the support portions, and the presence or absence of cracks in the support portions are shown in the fourth row of Fig. 7 (Comparative Example 1). Furthermore, as another comparative example, when the weight of the optical fiber preform 1 after the deposition process was 300 kg, the diameter of the support portions 12A and 12B was 63 mm, and the cooling rate from 1150°C to 1050°C was 20°C / min, the presence or absence of cracks in the support portions 12A and 12B was investigated (Comparative Example 2). In the cases of Comparative Examples 1 and 2, cracks occurred in the support parts 12A and 12B, and the support parts 12A and 12B were damaged before the optical fiber preform 1 was removed from the deposition device 3. As described above, it was confirmed that the support parts 12A and 12B are easily damaged when the cooling rate is high within a predetermined temperature range. [Explanation of symbols]

[0038] 1: Optical fiber base material 11: Core part 115: Boundary 12: Support Department 125: Nearby area 13: Porous glass part 3: Deposition equipment 38: Burner 39: Burner 5: Sintering equipment

Claims

1. a seed rod having a core portion and support portions joined to both ends of the core portion by thermal fusion; a porous glass portion formed on the outer periphery of the core portion, a step of holding the gripping portion of the support portion and depositing porous glass on the seed rod to form the porous glass portion; and heating the optical fiber preform to vitrify it into a transparent glass. the method further comprises a step of cooling, after forming the porous glass portion in the seed rod, the boundary portion between the core portion and the support portion and a region in the vicinity of the boundary portion using a flame of a burner in a temperature range of 1050°C to 1150°C at a cooling rate of 20°C / min or less, 2. A method for manufacturing an optical fiber preform, wherein the burner is an auxiliary burner for annealing.

2. 2. The method for manufacturing an optical fiber preform according to claim 1, wherein the cooling step cools the boundary portion and the adjacent region by lowering the temperature of the flame of the burner.

3. 3. The method for manufacturing an optical fiber preform according to claim 1, wherein the cooling rate is 5° C. / min or more and 20° C. / min or less.

4. 4. The method for manufacturing an optical fiber preform according to claim 1, wherein the cooling step is carried out within a temperature range including 1090°C.

5. 5. The method for manufacturing an optical fiber preform according to claim 4, wherein the cooling step is carried out at a temperature in the range of at least 1080° C. to 1100° C.

6. 6. The method for manufacturing an optical fiber preform according to claim 4, wherein the cooling step is carried out at a temperature in the range of at least 1050° C. to 1150° C.

7. The weight of the optical fiber preform is 180 kg or more, 7. The method for manufacturing an optical fiber preform according to claim 1, wherein the support portion is substantially cylindrical and has a diameter of 63 mm or more.

8. 8. The method for manufacturing an optical fiber preform according to claim 1, wherein the optical fiber preform is a horizontal type.

9. 9. The method for manufacturing an optical fiber preform according to claim 1, wherein the adjacent region includes a part of the support portion.

10. 10. The method for manufacturing an optical fiber preform according to claim 9, wherein the vicinity region further includes an end portion of the porous glass portion.

11. 11. The method for manufacturing an optical fiber preform according to claim 9, wherein the part of the support portion is an area having a length of 800 mm or less from the boundary portion in the longitudinal direction of the support portion.

12. 12. A method for manufacturing an optical fiber, comprising drawing, at a high temperature, an optical fiber preform manufactured by the method for manufacturing an optical fiber preform according to claim 1.

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