Optical fiber precursor wire manufacturing apparatus and optical fiber precursor wire manufacturing method

Abstract

To make uniform the thickness of a coating layer of an optical fiber precursor wire.SOLUTION: An optical fiber precursor wire manufacturing apparatus according to the present invention comprises a heating apparatus that draws an optical fiber bare wire from an optical fiber preform, a resin coating apparatus that applies an ultraviolet-curable resin to the optical fiber bare wire, and an ultraviolet irradiation apparatus that irradiates the ultraviolet-curable resin with ultraviolet rays to form a coating layer around the optical fiber bare wire, wherein the intensity of ultraviolet rays at an outlet of the resin coating apparatus is 0.1 mW / cm2 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] The optical fiber is manufactured by forming a coating layer around a bare optical fiber. The coating layer includes a primary layer that covers the bare optical fiber and a secondary layer that covers the primary layer. The coating layer is made of ultraviolet-curable resin and is formed by applying the ultraviolet-curable resin and curing it with ultraviolet light.

[0003] Since it is desirable that the thickness of the coating layer be uniform, techniques for achieving a uniform thickness of the coating layer are known. For example, the technique described in Patent Document 1 prevents air bubbles from being mixed into the ultraviolet-curable resin, thereby forming a uniform coating layer. Furthermore, the technique described in Patent Document 2 removes volatile components from the ultraviolet-curable resin, thereby forming a uniform coating layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2015-202969 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-81661 Summary of the Invention [Problem to be solved by the invention]

[0005] However, leakage light from the ultraviolet irradiation device may harden the resin adhering to the outlet of the resin applicator, which may cause the shape of the outlet of the resin applicator to change and result in an uneven thickness of the coating layer.

[0006] An object of the present invention is to make the thickness of the coating layer of an optical fiber uniform. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a heating device for drawing a bare optical fiber from an optical fiber preform, a resin applicator for applying an ultraviolet curable resin to the bare optical fiber, and an ultraviolet irradiation device for irradiating the ultraviolet curable resin with ultraviolet light to form a coating layer around the bare optical fiber, wherein the intensity of the ultraviolet light at the outlet of the resin applicator is 0.1 mW / cm 2 There is provided an optical fiber manufacturing apparatus characterized by the following:

[0008] According to another aspect of the present invention, there is provided a method for manufacturing an optical fiber strand, comprising the steps of: drawing a bare optical fiber from an optical fiber preform; applying an ultraviolet-curable resin to the bare optical fiber using a resin coating device; irradiating the ultraviolet-curable resin with ultraviolet light using an ultraviolet irradiation device to form a coating layer around the bare optical fiber; and reducing the intensity of the ultraviolet light at the outlet of the resin coating device. [Effects of the Invention]

[0009] According to the present invention, the thickness of the coating layer of the optical fiber can be made uniform. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of an optical fiber according to a first embodiment. [Figure 2] 1 is a schematic diagram of an optical fiber manufacturing apparatus according to a first embodiment. [Figure 3] 3 is a schematic diagram showing a method for measuring leakage light according to the first embodiment. FIG. [Figure 4] 3 is a flowchart of a method for manufacturing an optical fiber according to the first embodiment. [Figure 5] FIG. 10 is a schematic diagram of a primary layer coating apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Elements having common functions throughout the drawings will be designated by the same reference numerals, and duplicate descriptions may be omitted or simplified.

[0012] [First embodiment] 1 is a cross-sectional view of an optical fiber according to this embodiment. The optical fiber 1 includes a bare optical fiber 2, a primary layer 3 that coats the outer periphery of the bare optical fiber 2, and a secondary layer 4 that coats the outer periphery of the primary layer 3. The bare optical fiber 2 is coated with two coating layers, the primary layer 3 and the secondary layer 4.

[0013] The bare optical fiber 2 is made of, for example, silica-based glass and transmits light. The primary layer 3 is a soft layer and functions to buffer external forces applied to the bare optical fiber 2. The Young's modulus of the primary layer 3 is preferably 0.1 MPa or more and 2.0 MPa or less. The secondary layer 4 is a hard layer and functions to protect the bare optical fiber 2 and the primary layer 3 from external forces. The Young's modulus of the secondary layer 4 is preferably 500 MPa or more and 2000 MPa or less.

[0014] The diameter of the optical fiber 1 is 190 μm or more and 260 μm or less. The diameter of the bare optical fiber 2 is 80 μm or more and 150 μm or less, and preferably 124 μm or more and 126 μm or less. The thickness of the primary layer 3 is 5 μm or more and 60 μm or less. The thickness of the secondary layer 4 is 5 μm or more and 60 μm or less. Here, the diameter of the optical fiber 1 is determined by the sum of the diameter of the bare optical fiber 2, the thickness of the primary layer 3, and the thickness of the secondary layer 4. Therefore, the diameter of the bare optical fiber 2, the thickness of the primary layer 3, and the thickness of the secondary layer 4 are each selected so that the diameter of the optical fiber 1 is 190 μm or more and 260 μm or less.

[0015] When an external force is applied to the bare optical fiber 2, a light transmission loss (microbend loss) occurs due to minute deformation of the bare optical fiber 2. By setting the Young's modulus of the primary layer 3 low, the function of the primary layer 3 to buffer the external force is improved, and the microbend loss of the optical fiber strand 1 is suppressed.

[0016] The Young's modulus of the primary layer 3 is an ISM (In Situ Modulus), and the Young's modulus of the primary layer 3 can be measured by the following method.

[0017] First, a commercially available stripper is used to strip a few millimeters of the primary layer 3 and secondary layer 4 from the middle of a sample optical fiber. One end of the optical fiber with the coating layer formed thereon is then fixed to a glass slide with adhesive, and a load F is applied to the other end of the optical fiber with the coating layer formed thereon. In this state, the displacement δ of the primary layer 3 at the boundary between the stripped portion and the coated portion is measured using a microscope. The rate of change (slope) of the load F with respect to the displacement δ is then calculated by varying the load F to 10, 20, 30, 50, and 70 gf (i.e., 98, 196, 294, 490, and 686 mN, respectively). The primary modulus is calculated using the calculated slope and the following equation (1). The calculated primary modulus is the so-called ISM, and hereinafter, the primary modulus will be referred to as P-ISM. Note that when drawing the optical fiber, the drawing speed and UV irradiance are controlled to adjust the P-ISM. P-ISM=(3F / δ)*(1 / 2πl)*ln(DP / DG) ···(1)

[0018] The unit of P-ISM is [MPa]. On the right side of equation (1), F / δ is the rate (slope) of change in load (F) [gf] with respect to displacement (δ) [μm], l is the sample length (e.g., 10 mm), and DP / DG is the ratio of the outer diameter (DP) [μm] of the primary layer 3 to the outer diameter (DG) [μm] of the cladding of the optical fiber. Therefore, when calculating P-ISM using equation (1) from the F, δ, and l used, a predetermined unit conversion is required. The outer diameter of the primary layer 3 and the outer diameter of the cladding can be measured by observing the cross section of the optical fiber cut with a fiber cutter under a microscope.

[0019] Furthermore, the Young's modulus of the secondary layer 4 of the optical fiber is an ISM (In Situ Modulus), and the Young's modulus of the secondary layer 4 can be measured by the following method.

[0020] First, an optical fiber is immersed in liquid nitrogen and the coating layer is stripped off using a stripper, resulting in a hollow cylindrical sample with only the coating layer. The end of the sample is fixed to an aluminum plate using adhesive. The aluminum plate is chucked using a Tensilon universal tensile tester in an atmosphere of 23°C and 50% relative humidity. The sample is then stretched with a width of 6 mm, a gauge spacing of 25 mm, and a tensile speed of 1 mm / min. The force at 2.5% elongation is measured to calculate the S-ISM (2.5% secant modulus) of the secondary layer 4. The coating layer sample includes the primary layer 3 and the secondary layer 4. Because the S-ISM is sufficiently larger than the P-ISM, the effect of the P-ISM on the measured Young's modulus can be ignored, and the measured Young's modulus can be considered the S-ISM.

[0021] There are various possible methods for measuring microbend loss, and it can be measured using the following method. First, the transmission loss of an optical fiber wound on a bobbin wrapped with sandpaper is measured, and this transmission loss is defined as the transmission loss of the optical fiber in state A. Next, the transmission loss of an optical fiber wound on a bobbin not wrapped with sandpaper is measured, and this transmission loss is defined as the transmission loss of the optical fiber in state B. The difference between the transmission loss of the optical fiber in state A and the transmission loss of the optical fiber in state B is defined as the microbend loss of the optical fiber. Here, the transmission loss of the optical fiber in state B does not include transmission loss due to external forces and is considered to be the transmission loss inherent to the optical fiber. The grit size of the sandpaper is #1000, and the length of the optical fiber is 400 m or more. The optical fibers in states A and B are wound around the bobbin so that they do not overlap each other. In other words, the optical fibers in states A and B are wound around the bobbin in a single layer.

[0022] This measurement method is similar to the fixed diameter drum method defined in JIS C6823:2010. This measurement method is also called the sandpaper method. In addition, this measurement method measures transmission loss at a wavelength of 1550 nm, so the microbend loss in this embodiment is also a value at a wavelength of 1550 nm.

[0023] The effective core area (Aeff) can be used as an index to indicate the susceptibility of an optical fiber to microbend loss. The effective core area (Aeff) is expressed by the following formula (2). The effective core area (Aeff) is described, for example, in C-3-76 and C-3-77 of the 1999 Electronics Society Conference Proceedings of the Institute of Electronics, Information and Communication Engineers. Aeff=(πk / 4)*(MFD) 2 ···(2) Here, the effective core area Aeff is a value at a wavelength of 1550 nm, MFD is the mode field diameter (μm), and k is a constant. The effective core area Aeff represents the area of ​​a portion of a cross section perpendicular to the axis of the bare optical fiber 2 through which light of a given intensity passes. Generally, the larger the effective core area Aeff of the bare optical fiber 2, the weaker the optical confinement in the cross section of the bare optical fiber 2. In other words, when the effective core area Aeff of the bare optical fiber 2 is large, light within the bare optical fiber 2 is more likely to leak due to an external force applied to the bare optical fiber 2. Therefore, when the effective core area Aeff of the bare optical fiber 2 is large, microbending loss in the optical fiber strand 1 is more likely to occur.

[0024] On the other hand, by increasing the effective core area of ​​the bare optical fiber 2, it is possible to reduce the light intensity per unit area in the cross section of the bare optical fiber 2. This makes it possible to suppress the nonlinear optical effect of the bare optical fiber 2.

[0025] The optical fiber 1 according to this embodiment has a primary layer 3 that can effectively suppress microbending loss. That is, even when the effective core area of ​​the bare optical fiber 2 is large, the microbending loss of the optical fiber 1 can be effectively suppressed.

[0026] The effective core area Aeff of the bare optical fiber 2 is 80 μm 2 More than, for example, 130 μm 2 More than 150μm 2 It is preferable that the following condition is satisfied: This makes it possible to obtain the optical fiber 1 capable of suppressing the nonlinear optical effect of the bare optical fiber 2.

[0027] The primary layer 3 and the secondary layer 4 are formed by curing an ultraviolet curable resin by irradiating it with ultraviolet light. The ultraviolet curable resin will be described in detail below.

[0028] The ultraviolet curable resin is a resin that polymerizes and hardens when irradiated with ultraviolet light. The ultraviolet curable resin is not particularly limited as long as it can be polymerized when irradiated with ultraviolet light. The ultraviolet curable resin can be polymerized by, for example, photoradical polymerization.

[0029] The ultraviolet-curable resin is, for example, an ultraviolet-curable resin having a polymerizable unsaturated group such as an ethylenically unsaturated group that polymerizes and hardens when exposed to ultraviolet light, such as urethane (meth)acrylates such as polyether-based urethane (meth)acrylates and polyester-based urethane (meth)acrylates, epoxy (meth)acrylates, and polyester (meth)acrylates, and preferably has at least two polymerizable unsaturated groups.

[0030] The polymerizable unsaturated group in the ultraviolet-curable resin may be, for example, a group having an unsaturated double bond such as a vinyl group, an allyl group, an acryloyl group, or a methacryloyl group, or a group having an unsaturated triple bond such as a propargyl group, etc. Among these, an acryloyl group or a methacryloyl group is preferred in terms of polymerizability.

[0031] The ultraviolet-curable resin may be a monomer, oligomer, or polymer that initiates polymerization and hardens upon irradiation with ultraviolet light, but is preferably an oligomer. An oligomer is a polymer with a degree of polymerization of 2 to 100. In this specification, "(meth)acrylate" refers to either or both of acrylate and methacrylate. The ultraviolet-curable resin contains any photopolymerization initiator (photoinitiator) that is sensitive in the ultraviolet region.

[0032] Polyether-based urethane (meth)acrylates are compounds having a polyether segment, a (meth)acrylate, and a urethane bond, such as the reaction product of a polyol having a polyether skeleton with an organic polyisocyanate compound and a hydroxyalkyl (meth)acrylate. Polyester-based urethane (meth)acrylates are compounds having a polyester segment, a (meth)acrylate, and a urethane bond, such as the reaction product of a polyol having a polyester skeleton with an organic polyisocyanate compound and a hydroxyalkyl (meth)acrylate.

[0033] The UV-curable resin of the primary layer 3 and the UV-curable resin of the secondary layer 4 may contain, in addition to the oligomer and photoinitiator, a diluent monomer, a photosensitizer, a UV absorber, an antioxidant, a chain transfer agent, a silane coupling agent, a lubricant such as silicone, and various additives. The diluent monomer may be a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate. Here, the diluent monomer refers to a monomer for diluting the UV-curable resin.

[0034] Next, a manufacturing apparatus used in the manufacturing method of the optical fiber wire according to this embodiment will be described. Fig. 2 is a schematic diagram showing a manufacturing apparatus 10 for the optical fiber wire 1 according to this embodiment. The manufacturing apparatus 10 includes a heating device 20, a primary layer coating device 30, a secondary layer coating device 40, a guide roller 50, and a winding device 60. The manufacturing apparatus 10 shown in Fig. 2 manufactures the optical fiber wire 1 from an optical fiber preform BM.

[0035] The optical fiber preform BM is made of, for example, silica-based glass and is manufactured by a well-known method such as the VAD method, the OVD method, or the MCVD method. The heating device 20 has a heater 21. The heater 21 can be any heat source such as a tape heater, a ribbon heater, a rubber heater, an oven heater, a ceramic heater, or a halogen heater. The end of the optical fiber preform BM is heated and melted by the heater 21 arranged around the optical fiber preform BM, and is then drawn to extract a bare optical fiber 2.

[0036] A primary layer coating device 30 is provided below the heating device 20. The primary layer coating device 30 has a resin applicator 31 and an ultraviolet ray irradiator 32. The resin applicator 31 holds an ultraviolet ray curable resin for the primary layer 3. The resin applicator 31 applies the ultraviolet ray curable resin for the primary layer 3 to the bare optical fiber 2 drawn out from the optical fiber preform BM.

[0037] An ultraviolet irradiation device 32 is provided below the resin application device 31. The ultraviolet irradiation device 32 is equipped with any ultraviolet light source such as a metal halide lamp, a mercury lamp, or a UV-LED. The resin application device 31 applies an ultraviolet-curable resin for the primary layer 3 to the bare optical fiber 2, and the bare optical fiber 2 then enters the ultraviolet irradiation device 32, where ultraviolet light is irradiated onto the ultraviolet-curable resin for the primary layer 3. As a result, the ultraviolet-curable resin for the primary layer 3 is cured, and the primary layer 3 is formed.

[0038] A secondary layer coating device 40 is provided below the primary layer coating device 30. The secondary layer coating device 40 has a resin coating device 41 and an ultraviolet ray irradiation device 42. The resin coating device 41 holds the ultraviolet ray curable resin of the secondary layer 4. The ultraviolet ray curable resin of the secondary layer 4 is applied to the primary layer 3 by the resin coating device 41.

[0039] An ultraviolet irradiation device 42 is provided below the resin coating device 41. The ultraviolet irradiation device 42 may be configured similarly to the ultraviolet irradiation device 32. The bare optical fiber 2, in which the ultraviolet-curable resin of the secondary layer 4 is coated around the primary layer 3, enters the ultraviolet irradiation device 42, and ultraviolet light is irradiated onto the ultraviolet-curable resin of the secondary layer 4. As a result, the ultraviolet-curable resin of the secondary layer 4 is cured, and the secondary layer 4 is formed. The bare optical fiber 2 is coated with the primary layer 3 and the secondary layer 4, thereby forming the optical fiber 1.

[0040] The resin applicator 31 may be configured to separately hold the UV-curable resin for the primary layer 3 and the UV-curable resin for the secondary layer 4. In this case, the resin applicator 31 applies the UV-curable resin for the primary layer 3 to the bare optical fiber 2, and then applies the UV-curable resin for the secondary layer 4 around the UV-curable resin for the primary layer 3. Furthermore, in this case, the UV irradiation device 32 irradiates the UV-curable resin for the primary layer 3 and the UV-curable resin for the secondary layer 4 that have been applied to the bare optical fiber 2 with UV light. This forms the primary layer 3 and the secondary layer 4. In this case, the manufacturing apparatus 10 does not necessarily need to include the secondary layer coating device 40.

[0041] A guide roller 50 and a winding device 60 are provided below the secondary layer coating device 40. The manufactured optical fiber 1 is guided by the guide roller 50 and wound around the winding device 60.

[0042] In this embodiment, the distance between the resin application device 31 and the ultraviolet irradiation device 32 can be determined based on the intensity of the leakage light from the ultraviolet irradiation device 32. Figure 3 is a diagram showing a method for measuring leakage light according to this embodiment. Figures 3(a) and 3(b) show steps in the method for measuring leakage light.

[0043] First, as shown in FIG. 3(a), a resin coating device 31, an ultraviolet irradiation device 32, and a stage 33 are prepared. The stage 33 has an entrance 331 and an exit 332. The stage 33 is provided on the underside of the resin coating device 31 and supports the resin coating device 31. The entrance 331 is connected to the exit of the resin coating device 31. The ultraviolet irradiation device 32 is provided below the stage 33. The ultraviolet irradiation device 32 has an entrance 321 and an exit 322. The exit of the resin coating device 31 and the entrance 321 are separated by a distance d.

[0044] The bare optical fiber 2 passing through the outlet of the resin coating device 31 passes through the stage 33 via the entrance 331 and the exit 332. Thereafter, the bare optical fiber 2 passes through the ultraviolet irradiation device 32 via the entrance 321 and the exit 322.

[0045] 3(b), ultraviolet irradiation by the ultraviolet irradiation device 32 is started, and the intensity of the ultraviolet light at the inlet 331 is measured by the measuring device 34. The measuring device 34 may be configured integrally with the resin coating device 31, or may be configured separately from the resin coating device 31.

[0046] When ultraviolet irradiation by the ultraviolet irradiation device 32 starts, leakage light L enters the inlet 331 from the inlet 321. The measuring device 34 measures the intensity of the leakage light L at the inlet 331. Since the inlet 331 is connected to the outlet of the resin coating device 31, the intensity of the leakage light L at the inlet 331 is equal to the intensity of the ultraviolet light at the outlet of the resin coating device 31. Then, when the intensity of the leakage light L is 0.1 mW / cm 2 The distance d can be adjusted as follows: For example, by increasing the distance d, the intensity of the leaked light L at the outlet of the resin applying device 31 can be reduced.

[0047] 4 is a flowchart of the method for manufacturing an optical fiber according to this embodiment. First, the intensity of the leaked light L at the outlet of the resin coating device 31 is set to 0.1 mW / cm. 2 The leakage light L is reduced as follows (step S101). The step of reducing the leakage light L (step S101) includes a step of measuring the intensity of the leakage light L at the entrance 331 and a step of adjusting the distance d. Next, the optical fiber preform BM is placed in the manufacturing apparatus 10 (step S102).

[0048] Next, the heater 21 provided in the heating device 20 heats the optical fiber preform BM, and starts drawing the bare optical fiber 2 (step S103).

[0049] The primary layer coating device 30 applies an ultraviolet curable resin for the primary layer 3 to the periphery of the drawn bare optical fiber 2, and irradiates the ultraviolet curable resin for the primary layer 3 with ultraviolet light to form the primary layer 3 (step S104).

[0050] Next, the secondary layer coating device 40 applies an ultraviolet curable resin for the secondary layer 4 around the primary layer 3, and irradiates the ultraviolet curable resin for the secondary layer 4 with ultraviolet light to form the secondary layer 4 (step S105). This results in the optical fiber 1. The manufactured optical fiber 1 is taken up by the take-up device 60.

[0051] It is not necessary to irradiate the primary layer 3 with ultraviolet light in the step of forming the primary layer 3 (step S104). In this case, the primary layer 3 is cured in the step of forming the secondary layer 4 (step S105).

[0052] If an abnormality occurs in the resin applicator 31, the ultraviolet-curable resin of the primary layer 3 leaks out of the outlet of the resin applicator 31 and is cured by ultraviolet light L leaking from the ultraviolet irradiation device 32. The cured resin adheres to the outlet of the resin applicator 31, causing the shape of the outlet of the resin applicator 31 to change, making the thickness of the primary layer 3 non-uniform and potentially causing microbending loss in the optical fiber strand 1.

[0053] In this embodiment, the intensity of the ultraviolet light at the outlet of the resin application device 31 is 0.1 mW / cm 2 The distance d between the outlet and inlet 321 of the resin applicator 31 is adjusted as follows: This suppresses ultraviolet curing of the ultraviolet curable resin at the outlet of the resin applicator 31, making it possible to make the coating layer of the optical fiber 1 uniform.

[0054] In this embodiment, the distance d from the outlet of the resin applying device 31 to the inlet 321 is 35 cm or more and 150 cm or less. By adjusting the distance d to 35 cm or more, the intensity of the leaked light L at the outlet of the resin applying device 31 can be reduced to 0.1 mW / cm 2 If the distance d is greater than 150 cm, the time from application of the ultraviolet-curable resin to irradiation with ultraviolet light becomes too long, making it easier for foreign matter to adhere to the primary layer 3.

[0055] Alternatively, the intensity of leakage light from the ultraviolet irradiation device 42 in the resin coating device 41 may be measured, and the distance between the resin coating device 41 and the ultraviolet irradiation device 42 may be determined in the same manner. This makes it possible to suppress the generation of hardened resin at the outlet of the resin coating device 41 and make the thickness of the secondary layer 4 uniform.

[0056] [Second embodiment] Next, an optical fiber manufacturing apparatus according to a second embodiment will be described. The optical fiber manufacturing apparatus according to this embodiment differs from the first embodiment in that it includes a light shielding plate 35. The following description will focus on the configurations that differ from the first embodiment.

[0057] 5 is a schematic diagram of a primary layer coating apparatus 30 according to the second embodiment. The primary layer coating apparatus 30 further includes a light-shielding plate 35. The light-shielding plate 35 may contain an ultraviolet absorbing material such as zinc oxide or indium tin oxide. The light-shielding plate 35 is provided between the stage 33 and the ultraviolet irradiation device 32. The light-shielding plate 35 has an entrance 351 and an exit 352. The light-shielding plate 35 is provided in the step of reducing leak light (step S101).

[0058] After passing through the stage 33, the bare optical fiber 2 passes through the light shielding plate 35 via the entrance 351 and the exit 352. Thereafter, the bare optical fiber 2 passes through the ultraviolet irradiation device 32 via the entrance 321 and the exit 322.

[0059] In this embodiment, the light shielding plate 35 blocks the leaking light L, so that the intensity of the ultraviolet light at the outlet of the resin coating device 31 is 0.1 mW / cm 2 This allows the coating layer of the optical fiber 1 to be made uniform. Furthermore, in this embodiment, even when the distance from the outlet to the inlet 321 of the resin applicator 31 is short, the intensity of the ultraviolet light at the outlet of the resin applicator 31 can be reduced. This allows the manufacturing time of the optical fiber 1 to be shortened.

[0060] The light shielding plate 35 may be provided in the secondary layer coating device 40. In this case, the light shielding plate 35 is provided between the resin applying device 41 and the ultraviolet irradiating device 42. This allows the secondary layer 4 to be formed uniformly.

[0061] The following describes the results of an experiment on the optical fiber manufacturing apparatus according to the embodiment of the present invention. When the distance from the outlet of the resin applicator 31 to the inlet 321 is 35 cm, the intensity of the ultraviolet light at the outlet of the resin applicator 31 is 0.1 mW / cm. 2 At this time, no hardened resin was produced at the outlet of the resin coating device 31. On the other hand, when the distance from the outlet of the resin coating device 31 to the inlet 321 was 10 cm, the intensity of the ultraviolet light at the outlet of the resin coating device 31 was 0.9 mW / cm 2 At this time, hardened resin was produced at the outlet of the resin application device 31.

[0062] As described above, according to the present invention, the thickness of the coating layer of the optical fiber can be made uniform.

[0063] The distance from the outlet of the resin applying device 31 to the inlet 321 can be 35 cm or more and 150 cm or less. By adjusting the distance to 35 cm or more, the leakage light L at the outlet of the resin applying device 31 can be reduced to 0.1 mW / cm. 2 If the distance is greater than 150 cm, the time from application of the UV-curable resin to irradiation with UV rays becomes too long, making it easier for foreign matter to adhere to the primary layer 3.

[0064] The present invention is not limited to the above-described embodiments and can be modified in various ways. For example, an example in which a part of the configuration of one embodiment is added to another embodiment, or an example in which a part of the configuration of another embodiment is replaced with another embodiment, is also an embodiment of the present invention. Furthermore, with respect to parts not specifically explained or illustrated in the embodiments, well-known or publicly known techniques in the relevant technical field can be applied as appropriate. [Explanation of symbols]

[0065] 1. Optical fiber strand 2 Bare optical fiber 20 Heating device 21 Heater 30 Primary layer coating device 31 Resin application device 32 Ultraviolet irradiation device 40 Secondary layer coating device 41 Resin application device 42 Ultraviolet irradiation device 50 Guide roller 60 Winding device BM Optical Fiber Preform

Claims

1. a heating device for drawing a bare optical fiber from an optical fiber preform; a resin applicator that applies an ultraviolet curable resin to the bare optical fiber; an ultraviolet irradiation device that irradiates the ultraviolet curing resin with ultraviolet light to form a coating layer around the bare optical fiber, The intensity of the ultraviolet light at the outlet of the resin coating device is 0.1 mW / cm ２ An optical fiber manufacturing apparatus characterized by the following:

2. 2. The optical fiber manufacturing apparatus according to claim 1, wherein the distance from the outlet of said resin applying device to the inlet of said ultraviolet ray irradiation device is 35 cm or more.

3. 2. The optical fiber manufacturing apparatus according to claim 1, further comprising a measuring device for measuring the intensity of ultraviolet light at the outlet of the resin applying device.

4. 2. The optical fiber manufacturing apparatus according to claim 1, further comprising a light shielding plate between the resin applying device and the ultraviolet ray irradiating device.

5. A step of drawing a bare optical fiber from an optical fiber preform; applying an ultraviolet curing resin to the bare optical fiber by a resin application device; a step of irradiating the ultraviolet curing resin with ultraviolet light by an ultraviolet irradiation device to form a coating layer around the bare optical fiber; and reducing the intensity of ultraviolet light at the outlet of the resin coating device.

6. 6. The method for manufacturing an optical fiber according to claim 5, further comprising the step of measuring the intensity of the ultraviolet light at the outlet of the resin coating device.

7. 6. The method for manufacturing an optical fiber according to claim 5, wherein the reducing step includes a step of adjusting a distance between the resin applying device and the ultraviolet ray irradiation device.

8. 6. The method for manufacturing an optical fiber according to claim 5, wherein the reducing step includes a step of providing a light shielding plate between the resin applying device and the ultraviolet ray irradiating device.

9. The intensity of the ultraviolet light at the outlet of the resin coating device is 0.1 mW / cm ２ 9. The method for manufacturing an optical fiber according to claim 5, wherein the following is true:

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