Manufacturing apparatus for optical fiber preforms, manufacturing method, optical fiber preforms, and optical fibers.

Abstract

To provide a device for manufacturing an optical fiber preform that can reduce irregularities at a surface of an optical fiber preform.SOLUTION: A device for manufacturing an optical fiber preform includes: a support part for rotating a core rod at a rotational speed r about a rotation axis of the core rod which extends in a longitudinal direction of the core rod; an N (N represents an integer of two or more) sets of burners and a raw material jetting ports installed at intervals of a distance d; and a burner array reciprocating at a speed v in the longitudinal direction around the core rod and forming a porous glass part in an outer periphery of the core rod. A rotation number (L+x) of the core rod when the burner array moves in the longitudinal direction by the distance d is expressed by rd / v=L+x, and when L represents any natural number and the offset x is larger than -0.5 and +0.5 or less, the absolute value of the rotation number x is larger than 2 / (2 N+1) and less than 3 / (3 N-1).SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] In recent years, in the process of manufacturing an optical fiber preform, a method for manufacturing an optical fiber preform has been proposed to reduce the unevenness on the surface of the optical fiber preform and improve the roundness of the optical fiber preform. The method for manufacturing an optical fiber preform described in Patent Document 1 includes a step of reducing the unevenness on the surface of the optical fiber preform by defining the ratio between the moving speed of a burner for depositing glass fine particles on a core rod, which is a starting material of the optical fiber preform, and the rotational speed of the core rod.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the method for manufacturing an optical fiber preform described in Patent Document 1 only defines the relationship between the moving speed of one burner and the rotational speed of the core rod. When a plurality of burners are used in the technique described in Patent Document 1, the flame trajectories of the plurality of burners overlap each other, and unevenness occurs on the surface of the optical fiber preform.

[0005] The present invention has been made in view of the above problems, and an object thereof is to reduce the unevenness on the surface of the optical fiber preform when a plurality of burners are used.

Means for Solving the Problems

[0006] According to one aspect of the present invention, a support portion rotates the core rod at a rotational speed r about a rotation axis of the core rod that extends in the longitudinal direction of the core rod, and a burner array comprising N sets (N is an integer of 2 or more) of burners and raw material nozzles provided at intervals of distance d, which reciprocates around the core rod at a speed v in the longitudinal direction and forms a porous glass portion on the outer circumference of the core rod, wherein the number of rotations of the core rod (L+x) when the burner array moves by the distance d in the longitudinal direction is

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[0007] According to the present invention, it is possible to provide a manufacturing apparatus for optical fiber preforms that can reduce surface irregularities of the optical fiber preform. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a side view of a deposition apparatus used for manufacturing optical fiber preforms in the first embodiment of the present invention. [Figure 2] Figure 2 is a block diagram of a control device for controlling a deposit apparatus in the first embodiment of the present invention. [Figure 3] Figure 3 is a side view of the burner array in the first embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram of the operation of the burner array in the first embodiment of the present invention. [Figure 5] Figure 5 shows the distance of the burner flame trajectory for the manufacturing conditions of the optical fiber preform in the first embodiment of the present invention. [Figure 6A]FIG. 6A is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 6B] FIG. 6B is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 6C] FIG. 6C is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 6D] FIG. 6D is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing the distance of the locus of the burner flame with respect to the manufacturing conditions of the optical fiber preform in the first embodiment of the present invention. [Figure 8A] FIG. 8A is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 8B] FIG. 8B is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 8C] FIG. 8C is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 8D] FIG. 8D is a developed view of the locus of the burner array formed on the side of the optical fiber preform in the first embodiment of the present invention. [Figure 9] FIG. 9 is a flowchart of the manufacturing method of the optical fiber preform and the optical fiber in the first embodiment of the present invention. [Figure 10A] FIG. 11A is a diagram showing the outer diameter variation of the optical fiber preform of Example 1 in the first embodiment of the present invention. [Figure 10B] FIG. 11B is a diagram showing the outer diameter variation of the optical fiber preform of Example 2 in the first embodiment of the present invention. [Figure 10C] FIG. 11C is a diagram showing the outer diameter variation of the optical fiber preform of the comparative example in the first embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described based on the drawings. The same reference numerals throughout the specification denote substantially identical components.

[0010] [First Embodiment]

[0011] FIG. 1 is a side view of a deposition apparatus used for manufacturing an optical fiber preform in the present embodiment. The core rod of the optical fiber preform 1 includes a core portion 11 and support portions 12A and 12B. The core portion 11 is a starting material of the optical fiber preform 1 and is formed of quartz glass or the like. The core portion 11 can be formed by heating and stretching a rod having a core and a cladding layer formed on the outer periphery of the core. The core portion 11 has a substantially cylindrical shape, and for example, can have a length of 4000 mm and a diameter of 60 mm. Glass fine particles are deposited on the outer periphery of the side portion of the core portion 11 in a deposition process described later, and the optical fiber preform 1 is formed.

[0012] The support portions 12A and 12B are support rods, and the support portions 12A and 12B are provided at both ends of the core portion 11, respectively. The support portions 12A and 12B are used for supporting the core portion 11 in a deposition process and a sintering process of glass fine particles. The support portions 12A and 12B are made of quartz or the like, similar to the core portion 11. The support portions 12A and 12B have a substantially cylindrical shape, and for example, can have a length of 1000 mm and a diameter of 90 mm. The lengths and diameters of the support portions 12A and 12B may be appropriately changed according to the length or diameter of the core portion 11, the thickness of the glass fine particles deposited, and the like.

[0013] The support portions 12A and 12B are joined to the core portion 11 so that the support axes of the support portions 12A and 12B and the core axis of the core portion 11 are located substantially on the same line. The support portions 12A and 12B are welded to the core portion 11 using an oxyhydrogen burner or the like. The method of welding is not limited to this, and welding may be performed using an electric furnace or the like.

[0014] The porous glass portion 13 is a layer of glass microparticles deposited on the core portion 11. The porous glass portion 13 is deposited on the core portion 11 by the deposition apparatus 2. The deposition method for the porous glass portion 13 may be, for example, the VAD (Vapor phase Axial Deposition) method or the OVD (Outside Vapor Deposition) method. The OVD method is a method in which the core portion 11 is held at both ends and glass microparticles are deposited horizontally on the sides of the core portion 11. In this embodiment, a horizontal deposition apparatus is used and the porous glass portion 13 is deposited by the OVD method.

[0015] The porous glass portion 13 includes tapered portions 14A and 14B. The tapered portions 14A and 14B are formed to a predetermined length in the X direction. The predetermined length corresponds to the distance in the X direction from the burner at one end to the burner at the other end of the burner array, which will be described later.

[0016] The loading device 2 comprises a base 21, support parts 22A and 22B, gripping part 23, stress application part 24, control device 3, and burner array 4. The base 21 is a member that serves as the base of the loading device 2 and is substantially rectangular in shape. The base 21 is installed substantially horizontally with respect to the ground surface. The base 21 is provided with rails etc. that extend in the longitudinal direction of the base 21 and are located below the core part 11, and the support parts 22A and 22B and the burner array 4 are movable along these rails. In this embodiment, a configuration including one rail and one burner array 4 is described, but a configuration including multiple rails and multiple burner arrays 4 is also possible. In the case of a configuration including multiple rails and multiple burner arrays 4, it is preferable that the multiple rails are provided at a predetermined angle in the circumferential direction of the core part 11. For example, when three rails are provided, the three rails are provided at an angle of 120 degrees to each other in the circumferential direction, and a burner array 4 is installed on each rail. In a plan view, the longitudinal direction of the base 21 is defined as the X direction, the short direction of the base 21 as the Y direction, and the vertical direction of the base 21 as the Z direction.

[0017] The support sections 22A and 22B are columnar in shape, facing each other, and are provided on the upper part of the base 21. That is, support section 22A is provided at one end of the base 21, and support section 22B is provided at the other end of the base 21. At least one of the support sections 22A and 22B is movable on rails laid on the base 21. The support sections 22A and 22B are equipped with a rotary motor, a transmission, etc., that rotationally drives the core section 11 via the support sections 12A and 12B.

[0018] The gripping portion 23 and the stress-applying portion 24 constitute a chuck and are provided on the support portions 22A and 22B, respectively. The gripping portion 23 is made of a metal such as SUS (Steel Use Stainless) or a heat-resistant fluororesin, and has a plurality of jaws that can move closer to or further apart from each other. A gripping hole capable of gripping the support portions 12A and 12B is formed in the center of the plurality of jaws.

[0019] The stress-applying section 24 is provided around the gripping section 23, and is capable of applying stress to the gripping section 23. When the stress-applying section 24 applies stress to the gripping section 23, the multiple claws move closer to each other, and the diameter of the gripping hole decreases. As a result, the support sections 12A and 12B inserted into the gripping hole are gripped by the gripping section 23.

[0020] The control device 3 is connected to the deposition device 2 in a communicative manner and controls the operation of the deposition device 2 and the burner array 4. The control device 3 can control the rotation direction and rotation speed when the deposition device 2 rotates the core section 11, the magnitude of the stress in the stress application section 24, the movement direction, movement speed, and movement range in the X direction of the burner array 4.

[0021] The burner array 4 is equipped with multiple burners 41-4N and is installed on rails on a base 21. The burner array 4 moves along the rails in the X direction and can deposit glass microparticles on the core section 11 which rotates around the core axis. Burner 41 is a burner that blows glass microparticles onto the core section 11 and is a burner that uses, for example, a gas mainly composed of hydrocarbons (methane) and oxygen or oxyhydrogen as fuel. Burner 41 is equipped with a nozzle for supplying combustible gas, a nozzle for supplying combustion-supporting gas, a nozzle for supplying glass raw material (raw material nozzle), etc. For example, the combustible gas may be hydrogen or a gas mainly composed of hydrocarbons, and the combustion-supporting gas may be oxygen, etc. The glass raw material may be, for example, cyclic siloxane, SiCl4, etc. Burner 41 introduces glass raw material into the flame and generates glass microparticles through oxidation / thermal decomposition reactions, flame hydrolysis reactions, etc. Multiple burners 41-4N operate as a single unit. In this way, the porous glass portion 13 is deposited on the outer circumference of the core portion 11, forming the optical fiber base material 1.

[0022] Figure 2 is a block diagram of the control device for controlling the deposition apparatus in this embodiment. The control device 3 includes a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, a RAM (Random Access Memory) 303, a storage device 304, a display 305, a touch sensor 306, an input device 307, a communication interface 308, a sensor interface 309, and a bus 310. Each part is interconnected via the bus 310.

[0023] The CPU 301 controls the various parts of the deposition apparatus 2 and the burner array 4 using application programs. The ROM 302 consists of non-volatile memory and stores application programs for controlling the various parts of the deposition apparatus 2 and the burner array 4. The RAM 303 provides the memory area necessary for the operation of the CPU 301. The storage device 304 consists of a hard disk, semiconductor memory, etc.

[0024] The display 305 is composed of, for example, a liquid crystal display, an OLED (Organic Light Emitting Diode) display, an LED (Light Emitting Diode) display, etc. A touch sensor 306 is placed on the surface of the display 305. The touch sensor 306 is equipped with a capacitive or resistive detection circuit. The input device 307 is a user interface and may be, for example, a keyboard, a mouse, etc.

[0025] The communication interface 308 is a communication unit that transmits and receives data, and connects the control device 3 and the deposition device 2 in a communicative manner. Communication between the control device 3 and the deposition device 2 via the communication interface 308 may be either wired communication or wireless communication. The wireless communication method may be, for example, third-generation mobile communication, LTE (Long Term Evolution), fourth-generation mobile communication, fifth-generation mobile communication, short-range wireless communication such as Bluetooth®, or wireless LAN connection such as Wi-Fi.

[0026] The sensor I / F 309 acquires various data from the sensors provided by the deposition apparatus 2 and stores it in the storage device 304, etc. The various data may include, for example, the ambient temperature of the optical fiber base material 1, ambient humidity, mass of the optical fiber base material 1, surface temperature, surface roughness, rotation direction, rotation speed, acceleration, rotation angle, amount of porous glass portion 13 deposited, position of the burner array 4, and flame temperature of the burners 41-4N.

[0027] The control device 3 receives control parameters for the deposition apparatus 2 and the burner array 4 through operator input and controls the deposition apparatus 2 and the burner array 4. The control device 3 can also receive information from sensors (not shown) provided on the deposition apparatus 2 via the sensor I / F 309, calculate the rotation direction, rotation speed, rotation angle of the rotating optical fiber base material 1, the position of the burner array 4, etc., and reflect this information in the control of the deposition apparatus 2 and the burner array 4.

[0028] Figure 3 is a side view of the burner array in this embodiment. The burner array 4 comprises a burner base 401 and N burners 41 to 4N. Here, the number of burners N is an integer of 2 or more. The burner base 401 is movable in the X direction on rails of the base 21. The burners 41 to 4N are installed in a substantially linear manner on the upper part of the burner base 401. Burners 41 and 42 are installed with a distance d between them, and burners 41 and 43 are installed with a distance 2d between them. That is, the burners 41 to 4N are installed in a substantially linear manner on the upper part of the burner base 401, and a distance d is provided between adjacent burners. Therefore, the distance from burner 41 to burner 4N in the X direction is (N-1)d. The number of burners N and the distance d can be adjusted according to the length of the optical fiber base material 1, the desired amount of porous glass portion 13, the desired lengths of tapered portions 14A and 14B, etc. In the configuration where multiple rails and multiple burner arrays 4 are provided, the flame temperature in the burner array 4, the supply amount of combustible gas and combustion-supporting gas, the supply amount of glass raw material, the angle between the nozzle and the optical fiber base material 1, etc., can be controlled independently for each burner array 4.

[0029] Figure 4 is a schematic diagram of the operation of the burner array in this embodiment. Figures 4(A), (C), and (E) are side views of the optical fiber base material 1, and Figures 4(B), (D), and (F) are cross-sectional views of the optical fiber base material 1 along the I-I' line in Figures 4(A), (C), and (E), respectively. The optical fiber base material 1 rotates at a rotational speed r [rpm] around the core axis of the core portion 11. The number of burners N = 3, and the burner array 4 is equipped with three burners 41 to 43. The burner array 4 moves in the X direction at a moving speed v [mm / min], depositing the porous glass portion 13 on the optical fiber base material 1. When the optical fiber base material 1 rotates (L + x) while the burner array 4 moves a distance d [mm] in the X direction, the relationship between the rotational speed r of the optical fiber base material 1 and the moving speed v of the burner array 4 can be expressed as follows.

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[0030] The rotation speed L controls the period in the X direction of the flame trajectory of the burner 41. When the rotation speed L increases, the period in the X direction of the flame trajectory of the burner 41 decreases, and the density of glass microparticles deposited on the sides of the core portion 11 by the burners 41-4N increases. When the rotation speed L decreases, the period in the X direction of the flame trajectory of the burner 41 increases, and the density of glass microparticles deposited on the sides of the core portion 11 by the burners 41-4N decreases. The rotation speed L may be determined according to the number of burners N and the distance d between the burners, or it may be determined according to the deposition density of the porous glass portion 13 or the time required for the deposition process. Note that in the process of depositing glass microparticles, the rotation speed L does not necessarily have to be constant and can be changed as appropriate. For example, it may be determined according to the amount of deposition of the porous glass portion 13, the surface roughness, etc. However, it is desirable that the rotation speed L remains constant while the burner array 4 moves from one end to the other of the optical fiber base material 1 and deposits glass nanoparticles.

[0031] In Figures 4(A) and 4(B), the flame trajectory of burner 41 coincides with point P on the side of the optical fiber base material 1. Since burners 42 and 43 are located at distances d and 2d, respectively, from burner 41, the flame trajectories of burner 42 and burner 43 pass through positions at distances d and 2d, respectively, from point P in the X direction.

[0032] When offset x ≠ 0, in Figures 4(C) and 4(D), when the burner array 4 moves a distance d in the X direction, the optical fiber base material 1 rotates by (L+x), and the flame trajectory of burner 42 reaches the position of point P in the X direction. At this time, point P reaches a position rotated by offset x around the core axis from the position of point P in Figure 4(B), so the flame trajectory of burner 42 does not coincide with point P. In other words, the flame trajectory of burner 42 passes through a position where the flame trajectory of burner 41 has rotated by offset x around the core axis. Therefore, the flame trajectory of burner 42 does not coincide with the flame trajectory of burner 41.

[0033] In Figures 4(E) and 4(F), when the burner array 4 moves a further distance d in the X direction, the optical fiber base material 1 rotates further (L+x), and the flame trajectory of burner 43 reaches the position of point P in the X direction. At this time, point P reaches a position rotated by offset x around the core axis from the position of point P in Figure 4(D), so the flame trajectory of burner 43 does not coincide with point P. That is, the flame trajectory of burner 43 passes through a position rotated by offset x around the core axis from the flame trajectory of burner 42. Therefore, the flame trajectory of burner 43 does not coincide with the flame trajectories of burner 41 and burner 42.

[0034] Thus, offset x controls the distance between the flame trajectories of burners 41 to 4N. For example, when offset x is 0, the flame trajectories of burners 41 to 4N overlap. When all the flame trajectories of burners 41 to 4N overlap, the surface irregularities of the optical fiber base material 1 can become large. Therefore, we consider an offset x value such that the flame trajectories of burners 41 to 4N are equally spaced and the surface irregularities of the optical fiber base material 1 are small.

[0035] When the flame trajectories of burner 41, burner 42, and burner 4N pass near point P, the distance in the X direction between point P and each flame trajectory can be determined. First, using the point when the flame trajectory of burner 41 coincides with point P as a reference, when the optical fiber base material 1 rotates once, the flame trajectory of burner 41 moves a distance d / (L+x) in the X direction from point P, as shown in equation (1). When the optical fiber base material 1 rotates L, the flame trajectory of burner 42 and point P are located approximately on the same straight line in the X direction. At this time, the distance in the X direction between the flame trajectory of burner 42 and point P is expressed by the following equation.

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[0036] Similarly, when the optical fiber base material 1 rotates by (N-1)L, the trajectory of the flame from the burner 4N and point P are located approximately on the same straight line in the X direction. At this time, the distance in the X direction between the trajectory of the flame from the burner 4N and point P is expressed by the following formula.

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[0037] In the vicinity of point P, the difference in distance in the X direction between the flame trajectory of burner 41 and the flame trajectory of burner 4N can be expressed as the difference between equation (1) and equation (3).

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[0038] Here, when the offset x = ±1 / (N-1), the value of equation (4) becomes 0, so the flame trajectory of burner 41 and the flame trajectory of burner 4N overlap.

[0039] Dividing equation (4) by equation (2) yields the distance between the flame trajectory of burner 41 and the flame trajectory of burner 42, and the ratio of the distance between the flame trajectory of burner 41 and the flame trajectory of burner 4N.

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[0040] Here, when offset x = ±1 / N, equation (5) becomes 1, so the distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 is equal to the distance between the flame trajectory of burner 41 and the flame trajectory of burner 4N. Since the intervals between the flame trajectories of burner 41 and burner 42, burner 42 and burner 43, ... burner 4(N-1) and burner 4N are always equal, all flame trajectories are equally spaced, and the surface irregularities of the optical fiber base material are minimized. Therefore, it is desirable that the value of offset x be a value other than 0, greater than -1 / (N-1) and less than +1 / (N-1), and more preferably set to ±1 / N.

[0041] Figure 5 is a diagram showing the distance of the burner flame trajectories for the manufacturing conditions of the optical fiber preform in this embodiment, with rotation speed L=5, number of burners N=4, distance between burners d=150 [mm], moving speed v [mm / min] of the burner array 4 when the rotation speed of the optical fiber preform 1 is r=30 [rpm], offset x, moving distance v / r of the burner array 4 in the X direction when the optical fiber preform 1 makes one rotation, and the values ​​of equation (2) (distance between the flame trajectory of burner 41 and the flame trajectory of burner 42), equation (4) (distance between the flame trajectory of burner 41 and the flame trajectory of burner 44), and equation (5). Figures 6A to 6D are unfolded diagrams of the flame trajectories of burners 41 to 44 formed on the side of the optical fiber preform 1 in this embodiment.

[0042] In Figure 5, when the offset x values ​​are 0.28 to 0.22 and -0.21 to -0.29, the travel speed v is 852 to 862 [mm / min] and 939 to 954 [mm / min], respectively. When the offset x values ​​are 0.28 to 0.22 and -0.21 to -0.29, the distance the burner array 4 moves in the X direction when the optical fiber base material 1 rotates once is 28.41 to 28.74 [mm] and 31.32 to 31.81 [mm], respectively.

[0043] Condition (k) in Figure 5 shows the values ​​of equations (2), (4), and (5) when offset x = -0.25, and Figure 6A shows the unfolded diagram of the flame trajectories of burners 41 to 44 when offset x = -0.25. In condition (k) in Figure 5, the values ​​of equation (2) and (4) are both 7.89, and the value of equation (5) is 1.00. Therefore, the distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 is equal to the distance between the flame trajectory of burner 41 and the flame trajectory of burner 44. In Figure 6A, the distance D2 between the flame trajectory of burner 41 and the flame trajectory of burner 42 is equal to the distance D4 between the flame trajectory of the adjacent burner 44 and the flame trajectory of burner 41, and all flame trajectories are equally spaced across the entire side of the optical fiber base material 1.

[0044] The conditions in Figure 5 (m) show the values ​​of equations (2), (4), and (5) when the offset x = -0.27, and Figure 6B shows the unfolded diagram of the flame trajectories of burners 41 to 44 when the offset x = -0.27. In the conditions in Figure 5 (m), the values ​​of equation (2) and equation (4) are 8.56 and 6.03, respectively, and the value of equation (5) is 0.70. Therefore, the distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 increases, and the distance between the flame trajectory of burner 41 and the flame trajectory of burner 44 decreases. In Figure 6B, distance D4 is smaller than distance D2.

[0045] Condition (n) in Figure 5 shows the values ​​of equations (2), (4), and (5) when offset x = -0.29, and Figure 6C shows the unfolded diagram of the flame trajectories of burners 41 to 44 when offset x = -0.29. In condition (n) in Figure 5, the values ​​of equation (2) and equation (4) are 9.07 and 4.61, respectively, and the value of equation (5) is 0.51. The distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 becomes even larger than in the case of condition (m) in Figure 5, and the distance between the flame trajectory of burner 41 and the flame trajectory of burner 44 becomes smaller. In Figure 6C, the distance D4 becomes even smaller than the distance D2, and the surface irregularities of the optical fiber base material 1 may become larger.

[0046] The conditions in Figure 5 (h) show the values ​​of equations (2), (4), and (5) when offset x = -0.21, and Figure 6D shows the unfolded diagram of the flame trajectories of burners 41 to 44 when offset x = -0.21. In the conditions in Figure 5 (h), the values ​​of equation (2) and equation (4) are 6.58 and 11.59, respectively, and the value of equation (5) is 1.76. The distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 is small, and the distance between the flame trajectory of burner 41 and the flame trajectory of burner 44 is large. In Figure 6D, distance D4 is larger than distance D2, and the surface irregularities of the optical fiber base material 1 may become larger.

[0047] Thus, when the number of burners N=4, it is desirable that the value of offset x be ±1 / N=±0.25, that is, that the value of equation (5) is 1.00. The value of equation (5) may also be in the range of 3 / 4 to 4 / 3 (0.75 to 1.33), and even if it is in the range of 2 / 3 to 3 / 2 (0.67 to 1.50), the surface irregularities of the optical fiber base material 1 may be within an acceptable range. Therefore, when the value of equation (5) is in the range of 3 / 4 to 4 / 3 (0.75 to 1.33),

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[0048] Figure 7 is a diagram showing the distance of the burner flame trajectories for the manufacturing conditions of the optical fiber preform in this embodiment, and is a diagram showing the moving speed of the burner array 4 v [mm / min] when the rotation speed L=3, the number of burners N=3, the distance between burners d=120 [mm], the rotation speed of the optical fiber preform 1 r=20 [rpm], the offset x, the moving distance of the burner array 4 in the X direction v / r when the optical fiber preform 1 rotates once, and the values ​​of equation (2) (distance between the flame trajectory of burner 41 and the flame trajectory of burner 42), equation (4) (distance between the flame trajectory of burner 41 and the flame trajectory of burner 43), and equation (5). Figures 8A to 8D are unfolded diagrams of the flame trajectories of burners 41 to 43 formed on the side of the optical fiber preform 1 in this embodiment.

[0049] In Figure 7, when the offset x values ​​are 0.39 to 0.26 and -0.28 to -0.38, the travel speed v is 708 to 736 [mm / min] and 882 to 916 [mm / min], respectively. When the offset x values ​​are 0.39 to 0.26 and -0.28 to -0.38, the distance the burner array 4 moves in the X direction when the optical fiber base material 1 rotates once is 35.40 to 36.81 [mm] and 44.12 to 45.80 [mm], respectively.

[0050] Condition (d) in Figure 7 shows the values ​​of equations (2), (4), and (5) when offset x = 0.33, and Figure 8A shows the unfolded diagram of the flame trajectories of burners 41 to 43 when offset x = 0.33. In condition (d) in Figure 7, the values ​​of equation (2) and equation (4) are 11.89 and 12.25, respectively, and the value of equation (5) is 1.03. Therefore, the distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 is approximately equal to the distance between the flame trajectory of burner 41 and the flame trajectory of burner 43. In Figure 8A, the distance D2 between the flame trajectory of burner 41 and the flame trajectory of burner 42 is approximately equal to the distance D3 between the flame trajectory of the adjacent burner 43 and the flame trajectory of burner 41, and all flame trajectories are approximately equally spaced across the entire side of the optical fiber base material 1.

[0051] Condition (f) in Figure 7 shows the values ​​of equations (2), (4), and (5) when offset x = 0.29, and Figure 8B shows the unfolded diagram of the flame trajectories of burners 41-43 when offset x = 0.29. In condition (f) in Figure 7, the values ​​of equation (2) and equation (4) are 10.58 and 15.32, respectively, and the value of equation (5) is 1.45. Therefore, the distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 becomes larger, and the distance between the flame trajectory of burner 41 and the flame trajectory of burner 43 becomes smaller. In Figure 8B, distance D2 is slightly smaller than distance D3.

[0052] Condition (a) in Figure 7 shows the values ​​of equations (2), (4), and (5) when offset x = 0.39, and Figure 8C shows the unfolded diagram of the flame trajectories of burners 41-43 when offset x = 0.39. In condition (a) in Figure 7, the values ​​of equation (2) and (4) are 13.81 and 7.79, respectively, and the value of equation (5) is 0.56. The distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 becomes larger than in the case of condition (f) in Figure 7, and the distance between the flame trajectory of burner 41 and the flame trajectory of burner 43 becomes smaller. In Figure 8C, distance D3 becomes smaller than distance D2, and the surface irregularities of the optical fiber base material 1 may become larger.

[0053] Condition (g) in Figure 7 shows the values ​​of equations (2), (4), and (5) when offset x = 0.26, and Figure 8D shows the unfolded diagram of the flame trajectories of burners 41-43 when offset x = 0.26. In condition (g) in Figure 7, the values ​​of equation (2) and (4) are 9.57 and 17.67, respectively, and the value of equation (5) is 1.85. The distance between the flame trajectory of burner 41 and the flame trajectory of burner 42 is small, and the distance between the flame trajectory of burner 41 and the flame trajectory of burner 43 is large. In Figure 8D, distance D3 is larger than distance D2, and the surface irregularities of the optical fiber base material 1 may become larger.

[0054] When the number of burners N=3, it is desirable that the value of offset x be ±1 / N=±0.33, that is, that the value of equation (5) is approximately 1.00. Furthermore, the value of equation (5) may be in the range of 3 / 4 to 4 / 3 (0.75 to 1.33), and even if it is in the range of 2 / 3 to 3 / 2 (0.67 to 1.50), the surface irregularities of the optical fiber base material 1 may still be within an acceptable range. Therefore, when equation (5) is in the range of 3 / 4 to 4 / 3 (0.75 to 1.33),

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[0055] When the absolute value of offset x is greater than ±1 / N, the distance between the flame trajectories of burner 41 and burner 42 (distance D2 in Figures 6A-6D and 8A-8D) increases, and the distance between the flame trajectories of burner 41 and burner 4N (distance D4 in Figures 6A-6D and 8A-8D) decreases. On the other hand, when the absolute value of offset is less than ±1 / N, the distance between the flame trajectories of burner 41 and burner 42 (distance D2 in Figures 6A-6D and 8A-8D) decreases, and the distance between the flame trajectories of burner 41 and burner 4N (distance D4 in Figures 6A-6D and 8A-8D) increases. Therefore, by setting an appropriate offset x value according to the number of burners N, it becomes possible to manufacture optical fiber preforms with small surface irregularities.

[0056] Figure 9 is a flowchart of the manufacturing method for the optical fiber preform and optical fiber in the embodiment. First, the support parts 12A and 12B are joined to both ends of the core part 11 (step S101). The support parts 12A and 12B are melt-joined to the core part 11 using an oxyhydrogen burner or the like so that the virtual support axes of the support parts 12A and 12B and the virtual core axis of the core part 11 are positioned substantially on the same line.

[0057] Next, the core portion 11 (optical fiber base material 1) to which the support portions 12A and 12B are joined is placed in the deposition apparatus 2 (step S103). The support portions 12A and 12B are each gripped by the gripping portion 23 of the deposition apparatus 2.

[0058] When the operator inputs setting parameters such as rotation speed L, number of burners N, distance between burners d, rotation speed r of the optical fiber base material 1, and offset x to the control device 3 via the input device 307 (step S105), the CPU 301 substitutes the setting parameters into equation (1) to calculate the moving speed v of the burner array 4 and transmits the setting parameters and moving speed v to the deposition device 2. For example, when the operator inputs rotation speed L=5, number of burners N=4, distance between burners d=150 [mm], rotation speed r of the optical fiber base material 1=30 [rpm], and offset x=0.25 (in the case of the parameters in Figure 5(d)), the CPU 301 calculates the moving speed v of the burner array 4 = 857 [mm / min] and transmits the input setting parameters and moving speed v to the deposition device 2. Note that the offset x may be automatically set to an appropriate value according to the number of burners N. The rotation speed L may be automatically set to an appropriate value depending on the number of burners N and the distance d between burners, or it may be determined depending on the deposition density of the porous glass section 13 or the time required for the deposition process. In S105, the operator sets the rotation speed r and the CPU 301 calculates the travel speed v, but the operator may set the travel speed v and the CPU 301 calculates the rotation speed r.

[0059] Based on the setting parameters and the moving speed v input in S105, the deposition apparatus 2 rotates the optical fiber base material 1 at a rotational speed r, and glass raw material, flammable gas, and combustion-supporting gas are supplied to the burner array 4, causing glass nanoparticles to be deposited on the side of the core portion 11 by the burner array 4 (step S107). The burner array 4 reciprocates in the X direction at a moving speed v between the joint between the support portion 12A and the core portion 11 and the joint between the support portion 12B and the core portion 11. Burners 41-4N feed glass raw material into the flame, and the generated glass nanoparticles are deposited on the side of the core portion 11 at intervals based on the setting parameters.

[0060] Until a predetermined amount of glass nanoparticles is deposited on the side of the core portion 11 (NO in step S109), the burner array 4 reciprocates in the X direction at a moving speed v below the core portion 11, and the glass nanoparticles are deposited on the side of the core portion 11. When a predetermined amount of glass nanoparticles is deposited on the side of the core portion 11 (YES in step S109), the supply of glass raw material, flammable gas, and combustion-supporting gas to the burner array 4 is stopped, and the burner array 4 is extinguished. The deposition of a predetermined amount of glass nanoparticles may be determined, for example, by the thickness of the porous glass portion 13 in the Y direction or Z direction, or by the difference in mass of the optical fiber base material 1 before and after deposition.

[0061] When the temperature of the optical fiber base material 1 is lowered to a predetermined temperature by natural cooling, the support parts 12A and 12B are removed from the gripping part 23, and the optical fiber base material 1 is removed from the deposition apparatus 2 (step S111).

[0062] A support section 12A is vertically supported at the top of the sintering apparatus, and the optical fiber preform 1 is placed in the sintering apparatus. The optical fiber preform 1 is heated and sintered by the sintering apparatus (step S115). First, chlorine (Cl2) or the like is introduced into the furnace tube of the sintering apparatus from the gas introduction section. Next, the optical fiber preform 1 is heated by a heater while rotating in the furnace tube. This removes impurities contained in the optical fiber preform 1. Furthermore, chlorine is discharged to the outside of the furnace tube, and a mixed gas of chlorine and an inert gas is introduced into the furnace tube as an atmospheric gas. The optical fiber preform 1 is heated to a predetermined temperature by a heater while rotating in the furnace tube. The predetermined temperature may be, for example, 1500°C. When the sintering of the optical fiber preform 1 is complete, helium is discharged to the outside of the furnace tube, and the transparent vitrified optical fiber preform 1 is removed from the furnace tube. In the subsequent process, the transparent vitrified optical fiber preform 1 is heated and drawn. For example, the optical fiber base material 1 is heated to a heating temperature of 2000 to 2300°C. In this way, an optical fiber is formed.

[0063] As described above, according to this embodiment, by defining the relationship between the moving speed of the burner array equipped with multiple burners and the rotation speed of the core rod, it is possible to achieve better deposition efficiency than deposition of glass nanoparticles by a single burner and reduce surface irregularities of the optical fiber preform.

[0064] [Second Embodiment] In this embodiment, the initial phase of the rotation angle of the core rod is controlled when the burner array repeatedly moves back and forth. The following description of this embodiment will focus on the configurations that differ from the first embodiment. Components similar to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted or simplified.

[0065] In step S107 of Figure 9, the burner array 4 moves in the X direction from one end to the other of the optical fiber preform 1, depositing glass nanoparticles on the side of the core portion 11. The control device 3 stores the initial phase θ1 of the rotation angle of the optical fiber preform 1 when the burner array 4 starts moving from one end. This series of steps is called the first forward deposition step.

[0066] After the burner array 4 moves to the other end of the optical fiber base material 1, the burner array 4 moves from the other end of the optical fiber base material 1 back to the first end, depositing glass nanoparticles on the side of the core portion 11. The control device 3 stores the initial phase θ2 of the rotation angle of the optical fiber base material 1 when the burner array 4 starts moving from the other end. This series of steps is called the first return path deposition step.

[0067] When the burner array 4 moves to one end of the optical fiber base material 1, the burner array 4 begins moving from that end. At this time, the control device 3 controls the initial phase θ3 of the rotation angle of the optical fiber base material 1 to a value different from the initial phase θ1. For example, the difference between the initial phases θ1 and θ3 may be less than the absolute value of the offset x greater than 0. That is, the initial phase θ3 may be set so that the flame trajectory of burner 41 in the current deposition process is formed between the flame trajectory of burner 41 formed in the first forward deposition process and the flame trajectory of burner 42 formed in the first forward deposition process. Based on the initial phase θ3, when the burner array 4 moves to the other end of the optical fiber base material 1, the burner array 4 temporarily stops depositing glass nanoparticles. This series of processes is called the second forward deposition process.

[0068] When the burner array 4 moves to the other end of the optical fiber base material 1, the burner array 4 begins moving from the other end of the optical fiber base material 1. At this time, the control device 3 controls the initial phase θ4 of the rotation angle of the optical fiber base material 1 to a value different from the initial phase θ2. For example, the difference between the initial phases θ2 and θ4 may be less than the absolute value of the offset x greater than 0. That is, the initial phase θ4 may be set such that the flame trajectory of burner 4N in the current deposition process is formed between the flame trajectory of burner 4N formed in the first return deposition process and the flame trajectory of burner 4(N-1) formed in the first return deposition process. Based on the initial phase θ4, when the burner array 4 moves to one end of the optical fiber base material 1, the burner array 4 temporarily stops depositing glass nanoparticles. This series of processes is called the second return deposition process.

[0069] Similar to the second forward deposition process, when the burner array 4 moves to one end of the optical fiber base material 1, the burner array 4 begins moving from that end. At this time, the control device 3 controls the initial phase θ5 of the rotation angle of the optical fiber base material 1 to a value different from the initial phase θ3. For example, the difference between the initial phases θ3 and θ5 can be greater than 0 and less than the absolute value of the offset x. That is, the initial phase θ5 can be set so that the flame trajectory of the burner 41 in the current deposition process is formed between the flame trajectory of the burner 41 formed in the second forward deposition process and the flame trajectory of the burner 42 formed in the first forward deposition process. Based on the initial phase θ5, when the burner array 4 moves to the other end of the optical fiber base material 1, the burner array 4 temporarily stops depositing glass nanoparticles. This series of processes is called the third forward deposition process.

[0070] A predetermined angle is added to the initial phase at one end and the other end with each deposition process, and by repeating the above deposition process, glass nanoparticles are deposited by the burner array 4, forming the optical fiber preform 1. In this embodiment, the initial phase of the burner array 4 is set for each deposition process, and the burner array 4 deposits glass nanoparticles on the side of the core portion 11. The predetermined angle may be calculated based on the number of deposition processes required to obtain a predetermined deposition amount in S109, or it may be determined based on the distribution of the amount of glass nanoparticles deposited by the burners 41 to 4N. The predetermined angle added to the initial phase at one end of the optical fiber preform 1 may be the same as the predetermined angle added to the initial phase at the other end, or different predetermined angles may be added to the initial phase at each end.

[0071] In the process of depositing glass microparticles from one end to the other end of the optical fiber preform 1 (forward path), the initial phases are set so that the flame trajectories of the burners 41-4N for the first forward path, second forward path, third forward path, etc., do not overlap with each other. In the process of depositing glass microparticles from the other end to the other end of the optical fiber preform 1 (return path), the initial phases are set so that the flame trajectories of the burners 41-4N for the first return path, second return path, third return path, etc., do not overlap with each other. On the other hand, in the deposit process for the forward path and the deposit process for the return path, the flame trajectories for the forward path and the flame trajectories for the return path intersect with each other, so it is not always necessary to consider their respective initial phases.

[0072] As described above, according to this embodiment, by defining the relationship between the moving speed of the burner array equipped with multiple burners and the rotation speed of the core rod, and further setting the initial phase of the flame trajectory of the burner array for each deposition process, deposition efficiency is improved compared to deposition of glass nanoparticles with a single burner, and surface irregularities of the optical fiber preform are reduced.

[0073] [Example 1] With a rotation speed L=5, burner count N=4, burner distance d=150 [mm], rotation speed r=30 [rpm] of the optical fiber preform 1, and offset x=-0.25 (for condition (k) in Figure 5), the optical fiber preform 1 was manufactured by the manufacturing method of the first embodiment, and the variation in outer diameter of a portion of the optical fiber preform 1 in the portion where the side of the optical fiber preform 1 is approximately cylindrical (excluding the tapered portions 14A and 14B) was investigated. Figure 10A shows the variation in outer diameter of the optical fiber preform 1 in this embodiment. The average thickness of the deposited porous glass portion 13 was approximately 200 mm. As shown in Figure 10A, the variation in outer diameter was -0.04 to 0.04 mm or less, and it was possible to manufacture an optical fiber preform 1 with small surface irregularities. The standard deviation of the variation in outer diameter in Figure 10A is 1.26 × 10⁻⁶. -2 It was [mm].

[0074] [Example 2] With a rotation speed L=5, burner count N=4, burner distance d=150 [mm], rotation speed r=30 [rpm] of the optical fiber preform 1, and offset x=-0.27 (for the conditions (m) in Figure 5), the optical fiber preform 1 was manufactured by the manufacturing method of the first embodiment, and the variation in outer diameter of a portion of the part of the optical fiber preform 1 where the side is approximately cylindrical was investigated. Figure 10B shows the variation in outer diameter of the optical fiber preform 1 in this embodiment. The average thickness of the deposited porous glass portion 13 was approximately 200 mm. As shown in Figure 10B, the variation in outer diameter was -0.07 to 0.07 mm or less, and it was possible to manufacture an optical fiber preform 1 with small surface irregularities. In this embodiment, the value of equation (5) was 0.70, and if the value of equation (5) was within the range of 2 / 3 to 3 / 2 (0.67 to 1.50), the surface irregularities of the optical fiber preform 1 were within an acceptable range. Note that the standard deviation of the outer diameter variation in Figure 10B is 2.53 × 10⁻⁶. -2 It was [mm].

[0075] [Comparative Example] On the other hand, as a comparative example, with a rotation speed L=5, number of burners N=4, distance between burners d=150 [mm], rotation speed r=30 [rpm] of the optical fiber base material 1, and offset x=-0.29 (condition (n) in Figure 5), the optical fiber base material 1 was manufactured by the manufacturing method of the first embodiment, and the variation in outer diameter of a portion of the part of the optical fiber base material 1 where the side is approximately cylindrical was investigated. Figure 10C shows the variation in outer diameter of the optical fiber base material 1 in this embodiment. The average thickness of the deposited porous glass portion 13 was approximately 200 mm. As shown in Figure 10C, the variation in outer diameter was -0.17 to 0.17 mm or less, with some variations exceeding 0.1 mm. In this comparative example, the value of equation (5) was 0.51, and when the value of equation (5) was outside the range of 2 / 3 to 3 / 2 (0.67 to 1.50), the surface irregularities of the optical fiber base material 1 became larger. The standard deviation of the outer diameter variation in Figure 10C is 6.22 × 10⁻⁶. -2 It was [mm].

[0076] In Examples 1 and 2, it was found that if the value of equation (5) was within the range of 2 / 3 to 3 / 2 (0.67 to 1.50), the variation in the outer diameter of the optical fiber base material 1 could be suppressed to 0.05% or less. On the other hand, in the comparative example, it was found that if the value of equation (5) was outside the range of 2 / 3 to 3 / 2 (0.67 to 1.50), the variation in the outer diameter of the optical fiber base material 1 became larger than 0.05%. [Explanation of symbols]

[0077] 1: Optical fiber base material 2: Deposition device 3: Control device 4: Burner Array

Claims

1. A support portion that rotates the core rod at a rotational speed r around the axis of rotation of the core rod, which extends in the longitudinal direction of the core rod, The device comprises at least one burner array comprising N sets (N is an integer of 2 or more) of burners and raw material nozzles arranged at intervals of distance d, moving around the core rod at a velocity v in the longitudinal direction, and forming a porous glass portion on the outer circumference of the core rod, The rotational speed (L+x) of the core rod when the burner array moves by the distance d in the longitudinal direction is 【Number 1】 When expressed as such, where L is any natural number, and the offset x is greater than -0.5 and less than or equal to +0.5, the absolute value of the offset x is [Math 2] A manufacturing apparatus for optical fiber preforms, characterized by the following:

2. Furthermore, the absolute value of the offset x is [Math 3] The apparatus for manufacturing optical fiber preforms according to claim 1, characterized in that it is the same as described in claim 1.

3. Furthermore, the offset x is [Math 4] The apparatus for manufacturing optical fiber preforms according to claim 1, characterized in that it is the same as described in claim 1.

4. The optical fiber preform manufacturing apparatus according to claim 1, characterized in that determining either the speed v or the rotation speed r determines the other.

5. The burner array is capable of repeatedly moving from one end of the core rod to the other end, The optical fiber preform manufacturing apparatus according to claim 1, characterized in that the first initial phase of the rotation angle of the core rod when the first movement is initiated and the second initial phase of the rotation angle of the core rod when the second movement following the first movement is initiated are different from each other.

6. The optical fiber preform manufacturing apparatus according to claim 5, characterized in that the difference between the first initial phase and the second initial phase is greater than 0 and less than the absolute value of the offset x.

7. The process includes a step in which at least one burner array forms a porous glass portion on the outer circumference of a core rod, The core rod rotates at a rotational speed r about the axis of rotation of the core rod which extends in the longitudinal direction of the core rod. The burner array comprises N sets of burners (where N is an integer of 2 or more) and raw material nozzles arranged at intervals of distance d, and moves around the core rod at a velocity v in the longitudinal direction. The rotational speed (L+x) of the core rod when the burner array moves by the distance d in the longitudinal direction is [Math 5] When expressed as such, where L is any natural number, and the offset x is greater than -0.5 and less than or equal to +0.5, the absolute value of the offset x is [Math 6] A method for manufacturing an optical fiber preform, characterized by the following:

8. An optical fiber preform manufactured by the optical fiber preform manufacturing apparatus described in claim 1.

9. An optical fiber manufactured by drawing the optical fiber preform described in claim 8 at a high temperature.

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