JP7536670B2 - Optical fiber core wire manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing optical fiber core wire.

In optical fiber cores, a technique is known in which the primary layer and secondary layer covering the bare optical fiber are set to a desired Young's modulus using an ultraviolet-curable resin (Patent Documents 1 and 2). For example, the Young's modulus of the primary layer is set low, so that the primary layer can buffer the external force applied to the bare optical fiber and suppress the optical transmission loss (microbend loss) caused by minute deformation of the bare optical fiber. In addition, the Young's modulus of the secondary layer is set higher than that of the primary layer, so that the secondary layer protects the bare optical fiber and the primary layer from external forces.

JP 2018-177630 A Patent No. 6576995

After manufacturing, optical fiber cores may undergo a coloring process or a tape-making process involving irradiation with ultraviolet light. For this reason, the curing of the primary layer also progresses due to the ultraviolet light that has passed through the secondary layer, and the curing of the primary layer cannot be sufficiently suppressed, which can lead to the problem that microbend loss cannot be effectively avoided.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide a manufacturing method for optical fiber core wire that can sufficiently suppress hardening of the primary layer after manufacturing.

According to the present invention, there is provided a method for manufacturing an optical fiber core, comprising: a drawing process for drawing a bare optical fiber from a fiber preform; a first coating process for coating a first ultraviolet-curable resin around the bare optical fiber; a first irradiation process for irradiating the bare optical fiber with ultraviolet light in a first wavelength region in an atmosphere having a first oxygen concentration higher than 2% after the first coating process; a second coating process for coating a second ultraviolet-curable resin around the first ultraviolet-curable resin; a second irradiation process for irradiating the bare optical fiber with ultraviolet light in a second wavelength region different from the first wavelength region after the second coating process; and a third irradiation process for irradiating the bare optical fiber with ultraviolet light in the first wavelength region after the second irradiation process.

According to the present invention, when further ultraviolet light is irradiated after production, the curing of the primary layer can be sufficiently suppressed, and microbend loss can be effectively avoided.

1 is a cross-sectional view of a colored optical fiber manufactured by a manufacturing method according to a first embodiment. 1 is a cross-sectional view of an optical fiber ribbon manufactured by a manufacturing method according to a first embodiment. FIG. 2 is a schematic diagram of a manufacturing apparatus used in the manufacturing method according to the first embodiment. 2 is a schematic cross-sectional view showing a structure of a first irradiation device according to the first embodiment. FIG. 1 is a flowchart of a manufacturing method according to a first embodiment. FIG. 13 is a schematic diagram of a manufacturing apparatus used in a manufacturing method according to a second embodiment.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Elements having common functions throughout the drawings will be given the same reference numerals, and duplicate descriptions may be omitted or simplified.

[First embodiment]
1 and 2 show optical fiber core wires manufactured by the manufacturing method according to the first embodiment. FIG. 1 is a cross-sectional view of a colored optical fiber core wire manufactured by the manufacturing method according to the first embodiment. The optical fiber core wire 1 includes a bare optical fiber 2, a primary layer 3 coated on the outer periphery of the bare optical fiber 2, and a secondary layer 4 coated on the outer periphery of the primary layer 3. The colored optical fiber core wire further includes a colored layer 5 coated on the outer periphery of the optical fiber core wire 1. The colored optical fiber core wire is coated with three coating layers, the primary layer 3, the secondary layer 4, and the colored layer 5. FIG. 2 is a cross-sectional view of an optical fiber ribbon manufactured by the manufacturing method according to the first embodiment. The optical fiber ribbon is formed by bundling a plurality of optical fiber core wires 1 into a band shape via an adhesive layer 6.

The optical fiber bare wire 2 is formed of, for example, quartz glass, and transmits light. The primary layer 3, secondary layer 4, colored layer 5, and adhesive layer 6 are each formed by curing an ultraviolet-curable resin by ultraviolet irradiation. The ultraviolet-curable resin is not particularly limited as long as it is polymerizable by ultraviolet irradiation. The ultraviolet-curable resin is, for example, a resin that can be polymerized by photoradical polymerization. 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 by ultraviolet irradiation, such as urethane (meth)acrylate, epoxy (meth)acrylate, and polyester (meth)acrylate, such as polyether-based urethane (meth)acrylate and polyester-based urethane (meth)acrylate, and preferably has at least two polymerizable unsaturated groups. Examples of the polymerizable unsaturated group in the ultraviolet-curable resin include groups having an unsaturated double bond, such as a vinyl group, an allyl group, an acryloyl group, and a methacryloyl group, and groups having an unsaturated triple bond, such as a propargyl group. Among these, acryloyl and methacryloyl groups are preferred in terms of polymerizability. The UV-curable resin may be a monomer, oligomer, or polymer that initiates polymerization and hardens upon exposure to UV 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.

A polyether-based urethane (meth)acrylate is a compound having a polyether segment, a (meth)acrylate, and a urethane bond, such as a reaction product of a polyol having a polyether skeleton with an organic polyisocyanate compound and a hydroxyalkyl (meth)acrylate. A polyester-based urethane (meth)acrylate is a compound having a polyester segment, a (meth)acrylate, and a urethane bond, such as a reaction product of a polyol having a polyester skeleton with an organic polyisocyanate compound and a hydroxyalkyl (meth)acrylate.

Furthermore, the UV-curable resin may contain, in addition to the oligomer and the photopolymerization initiator, for example, a diluent monomer, a photosensitizer, a chain transfer agent, and various additives. As the diluent monomer, a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate is used. Here, the diluent monomer means a monomer for diluting the UV-curable resin.

In this embodiment, it is desirable that the photopolymerization initiators of the ultraviolet-curable resins in the primary layer 3 and the secondary layer 4 have sensitivity in different wavelength regions. For example, the photopolymerization initiator in the primary layer 3 may have sensitivity in the wavelength region of a UV LED lamp such as an ultraviolet light-emitting diode, and the photopolymerization initiator in the secondary layer 4 may have sensitivity in the wavelength region of a UV lamp such as a fluorescent tube.

The primary layer 3 is a soft layer having a Young's modulus of preferably 0.2 to 3 MPa, more preferably 0.2 to 1 MPa, and has the function of cushioning the external force applied to the bare optical fiber 2. The secondary layer 4 is a hard layer having a Young's modulus of preferably 500 to 2000 MPa, and has the function of protecting the bare optical fiber 2 and the primary layer 3 from external forces. The colored layer 5 is colored to identify the optical fiber core 1.

The optical fiber according to this embodiment is not limited to the configuration shown in Figs. 1 and 2. For example, the bare optical fiber 2 may be covered with four or more layers. Alternatively, the colored optical fiber core or the optical fiber ribbon may be housed in a sheath. The colored secondary layer 4 may be the outermost layer of the colored optical fiber core. When the secondary layer 4 is colored, the secondary layer 4 is colored by adding a coloring agent containing a pigment, a lubricant, etc. to the secondary layer 4. The content of the coloring agent in the colored secondary layer 4 may be appropriately determined depending on the content of the pigment contained in the coloring agent and the type of other components such as ultraviolet-curable resin.

The diameter of the bare optical fiber 2 may be 80 to 150 μm, and preferably 124 to 126 μm. The thickness of the primary layer 3 may be 10 to 60 μm. The thickness of the secondary layer 4 may be 10 to 60 μm. The thickness of the colored layer 5 may be about several μm.

Figure 3 is a schematic diagram of a manufacturing apparatus 10 used in the manufacturing method according to the first embodiment. The manufacturing apparatus 10 has a heater 11, a first coating device 12, a first irradiation device 13, a second coating device 14, a second irradiation device 15, a third irradiation device 16, a coating device 17, an irradiation device 18, a guide roller 19, and a winding device 20. The manufacturing apparatus 10 is an apparatus for manufacturing an optical fiber core 1 from a fiber preform 7. The fiber preform 7 is made of, for example, quartz-based glass, and is manufactured by a well-known method such as a VAD method, an OVD method, or an MCVD method. The heater 11 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 fiber preform 7 is heated and melted by the heater 11 arranged around the fiber preform 7, and is drawn to draw out the bare optical fiber 2. Hereinafter, the direction in which the drawn bare optical fiber 2 travels may be referred to simply as the "transport direction."

A first coating device 12 is provided below the heater 11. The first coating device 12 holds a coating material (also referred to as a first ultraviolet-curing resin) of the primary layer 3. The first coating device 12 coats the bare optical fiber 2 with the first ultraviolet-curing resin. A first irradiation device 13 is provided below the first coating device 12. The first irradiation device 13 has an ultraviolet light source including a UVLED lamp. The UVLED lamp is composed of a semiconductor element such as an ultraviolet light-emitting diode, and has the advantage of low power consumption. The bare optical fiber 2 coated with the first ultraviolet-curing resin enters the first irradiation device 13, and the first ultraviolet-curing resin is irradiated with ultraviolet light in an atmosphere with a first oxygen concentration higher than 2%. The ultraviolet light irradiated by the first irradiation device 13 is set to a first wavelength region that hardens the first ultraviolet-curing resin. As a result, the first ultraviolet-curing resin is hardened to form the primary layer 3.

A second application device 14 is provided below the first irradiation device 13. The second application device 14 holds the coating material (also called the second ultraviolet-curing resin) of the secondary layer 4. The second application device 14 applies the second ultraviolet-curing resin around the primary layer 3. A second application device 15 is provided below the second application device 14. The second application device 15 has an ultraviolet light source including a UV lamp. The UV lamp may be composed of, for example, a fluorescent tube such as a metal halide lamp or a mercury lamp. The bare optical fiber 2 coated with the second ultraviolet-curing resin enters the second irradiation device 15, and the second ultraviolet-curing resin is irradiated with ultraviolet light. The ultraviolet light irradiated by the second irradiation device 15 hardens the second ultraviolet-curing resin and is set to the second wavelength region. As a result, the second ultraviolet-curing resin is hardened to form the secondary layer 4. Note that the first wavelength region is a wavelength region different from the second wavelength region. This allows the first and second ultraviolet-curable resins coated around the bare optical fiber 2 to be selectively cured by irradiating them with ultraviolet light in the first or second wavelength range.

A third irradiation device 16 is provided below the second irradiation device 15. The third irradiation device 16 is configured similarly to the first irradiation device 13 and includes a UVLED lamp as an ultraviolet light source, but may include a UV lamp instead of the UVLED. The ultraviolet light irradiated by the third irradiation device 16 is set to a first wavelength region that hardens the first ultraviolet curing resin. The primary layer 3 and the secondary layer 4 are coated on the bare optical fiber 2 to form the optical fiber core 1. The optical fiber core 1 is guided by a guide roller 19 provided below the third irradiation device 16. The third irradiation device 16 may be further configured to irradiate ultraviolet light in the second wavelength region in addition to ultraviolet light in the first wavelength region. The ultraviolet light irradiation by the second irradiation device 15 and the third irradiation device 16 progresses the hardening of the secondary layer 4, and the secondary layer 4 becomes a hard layer having a sufficient Young's modulus compared to the primary layer 3. For example, after the optical fiber core is manufactured, it is desirable that the Young's modulus of the primary layer 3 is 0.2 to 3 MPa, and the Young's modulus of the secondary layer 4 is 500 to 2000 MPa.

The time from the end of ultraviolet irradiation by the second irradiation device 15 to the start of ultraviolet irradiation by the third irradiation device 16 is preferably as short as possible, for example, less than 0.05 seconds. As a result, after the temperature of the first ultraviolet curing resin rises due to the curing heat of the second ultraviolet curing resin, ultraviolet irradiation can be performed when the first ultraviolet curing resin is in a sufficiently high temperature state. This makes it possible to sufficiently suppress the progress of curing of the first ultraviolet curing resin. In this embodiment, the third irradiation device 16 is arranged so that the conveying direction in the third irradiation device 16 is the same as the drawing direction of the bare optical fiber 2. Therefore, the time from the end of ultraviolet irradiation by the second irradiation device 15 to the start of ultraviolet irradiation by the third irradiation device 16 can be particularly short, making it possible to further enhance the above-mentioned effects.

Below the third irradiation device 16, a coating device 17 is provided. The coating device 17 holds the coating material (also called the color layer material) of the color layer 5. The coating device 17 applies the color layer material around the optical fiber core 1. An irradiation device 18 is provided in the conveying direction of the coating device 17. The irradiation device 18 is configured in the same manner as the third irradiation device 16. The optical fiber core 1 enters the irradiation device 18, and the color layer material is irradiated with ultraviolet light. As a result, a color layer 5 containing ultraviolet curing resin as a main component is formed. The optical fiber core 1 is coated with the color layer 5, and the colored optical fiber core is formed. The colored optical fiber core is guided by the guide roller 19 and wound up by the winding device 20. The coating device 17 may hold the coating material of the adhesive layer 6 instead of the color layer material. The optical fiber core 1 may be wound up by the winding device 20 without applying the ultraviolet curing resin by the coating device 17 and irradiating it with ultraviolet light by the irradiation device 18. In this case, the optical fiber core 1 may be separately coated with a coloring layer 5 or an adhesive layer 6 by a coating device 17 and an irradiating device 18 after being wound.

It is preferable that the optical fiber core 1 be guided by the guide roller 19 after the secondary layer 4 has been completely cured. This prevents uncured ultraviolet-curable resin from adhering to the optical fiber core 1 when it comes into contact with the guide roller 19.

Figure 4 is a schematic cross-sectional view showing the structure of the first irradiation device 13. Figure 4 shows a cross-sectional view of the first irradiation device 13 in a plane parallel to the conveying direction of the bare optical fiber 2.

As shown in FIG. 4, the first irradiation device 13 has a housing 131, a quartz tube 132, an irradiation section 133, a UVLED lamp 134, a reflector 135, an upper cap 136, and a lower cap 137.

The housing 131 is box-shaped with side walls and two bottom walls. The housing 131 may be made of a sturdy metal, but the material of the housing 131 is not limited to a specific material. The quartz tube 132 is provided so as to penetrate the two bottom walls of the housing 131. The quartz tube 132 is made of, for example, silica-based glass, and transmits ultraviolet light. The bare optical fiber 2 passes through the first irradiation device 13 by passing through the quartz tube 132.

The irradiation unit 133 is accommodated inside the housing 131 and is arranged to surround the quartz tube 132. The UVLED lamp 134 is provided in the irradiation unit 133. The ultraviolet light irradiated from the UVLED lamp 134 passes through the quartz tube 132 and is absorbed by the first ultraviolet curing resin applied to the bare optical fiber 2. The reflector 135 is accommodated inside the housing 131 and is arranged to surround the quartz tube 132 and the irradiation unit 133. A part of the ultraviolet light irradiated from the UVLED lamp 134 is reflected by the reflector 135. The ultraviolet light reflected by the reflector 135 also passes through the quartz tube 132 and is absorbed by the first ultraviolet curing resin applied to the bare optical fiber 2. By providing the reflector 135, the ultraviolet light irradiated from the UVLED lamp 134 can be efficiently absorbed by the first ultraviolet curing resin.

The number and arrangement of the irradiation units 133, UVLED lamps 134, and reflectors 135 are not limited to those shown in FIG. 4. The irradiation units 133, UVLED lamps 134, and reflectors 135 are preferably arranged so that the entire surface of the bare optical fiber 2 is irradiated with ultraviolet light. For example, it is preferable that a plurality of UVLED lamps 134 are arranged on a circumference centered on the axis of the bare optical fiber 2 in a plane perpendicular to the axis of the bare optical fiber 2. The entire surface of the bare optical fiber 2 does not need to be irradiated with direct light from the UVLED lamps 134, and a portion of the surface may be irradiated with only reflected light from the reflector 135.

The housing 131 is provided with an air inlet 131a and an exhaust port 131b. The air inlet 131a supplies cooling gas into the housing 131, and the exhaust port 131b exhausts the cooling gas to the outside of the housing 131. The UVLED lamp 134 housed in the housing 131 is cooled by the cooling gas. The UVLED lamp 134 may deteriorate due to heat generated by irradiation with ultraviolet rays. By providing the air inlet 131a and the exhaust port 131b, the cooling gas can be easily circulated within the housing 131, which cools the UVLED lamp 134 and effectively suppresses deterioration of the UVLED lamp 134.

The upper cap 136 is provided on the upper bottom wall of the housing 131 and houses the quartz tube 132 that penetrates the upper bottom wall. The lower cap 137 is provided on the lower bottom wall of the housing 131 and houses the quartz tube 132 that penetrates the lower bottom wall. The upper cap 136 is provided with an air inlet 136a, and the lower cap 137 is provided with an exhaust port 137a. Oxygen gas is supplied into the housing 131 through the air inlet 136a, and the oxygen gas is exhausted to the outside of the housing 131 through the exhaust port 137a. As described later, the oxygen gas preferably has an oxygen concentration higher than 2% in order to suppress hardening of the primary layer 3. The oxygen concentration of the oxygen gas is not particularly limited as long as it is 2% or more, but may be set to an oxygen concentration of 2 to 20%, preferably 3 to 10%. Alternatively, air may be used as the oxygen gas. The oxygen gas may contain inert gases such as nitrogen, argon, and helium as other components. The inside of the upper cap 136, the quartz tube 132, and the lower cap 137 are filled with oxygen gas. This allows ultraviolet light to be irradiated onto the bare optical fiber 2 in an atmosphere with a predetermined oxygen concentration. Note that oxygen gas may be supplied into the housing 131 via the air supply port 137a of the lower cap 137, and the oxygen gas may be exhausted to the outside of the housing 131 via the exhaust port 136a of the upper cap 136.

Figure 5 is a flowchart of the manufacturing method according to the first embodiment. First, a drawing process is performed to draw the bare optical fiber 2 from the fiber preform 7. Next, in the first coating process, the first coating device 12 applies a first ultraviolet-curing resin around the drawn bare optical fiber 2 (step S101). Next, in the first irradiation process, the first irradiation device 13 irradiates the bare optical fiber 2 with ultraviolet light in a first wavelength region in an atmosphere with a first oxygen concentration higher than 2% to form a primary layer 3 (step S102). Next, in the second coating process, the second coating device 14 applies a second ultraviolet-curing resin around the primary layer 3 (step S103). After that, in the second irradiation process, the second irradiation device 15 irradiates the bare optical fiber 2 with ultraviolet light in a second wavelength region different from the first wavelength region to form a secondary layer 4 (step S104). Then, in the third irradiation step, the third irradiation device 16 irradiates the bare optical fiber 2 with ultraviolet light in the first wavelength region, causing a curing reaction in the first ultraviolet-curable resin of the primary layer 3 (step S105). After that, the coating device 17 applies a colored layer material around the optical fiber core 1 (step S106), and irradiates ultraviolet light to form the colored layer 5 (step S107). As a result, the optical fiber core 1 coated with the colored layer 5 is obtained. Note that the application of the ultraviolet-curable resin by the coating device 17 (step S106) and the irradiation of ultraviolet light by the irradiation device 18 (step S107) may be performed separately after the optical fiber core 1 is wound by the winding device 20.

In the manufacturing process of the optical fiber core, after the optical fiber core 1 is formed, the primary layer 3 may be cured by ultraviolet irradiation when forming the colored layer 5 (step S107). More specifically, if the secondary layer 4, the colored layer 5, and the secondary layer 4 are colored, the ultraviolet light that passes through the colored secondary layer 4 is absorbed by the primary layer 3, and the curing of the primary layer 3 may proceed further. If the ultraviolet-curable resin cures too much, the Young's modulus of the primary layer 3 becomes high, and it may become difficult for the primary layer 3 to adequately buffer the external force applied to the bare optical fiber 2. As a result, microbend loss may occur.

According to this embodiment, in the first irradiation step (step S102), the curing of the first ultraviolet curable resin proceeds in an atmosphere with an oxygen concentration higher than 2%. At this time, a reaction occurs between oxygen and the photopolymerization initiator and between oxygen and the growing polymer radical, suppressing the progress of the curing of the first ultraviolet curable resin.

In the second irradiation step (step S104), polymerization reactions occur repeatedly in the process of forming the secondary layer 4, which has a high Young's modulus, generating a large amount of curing heat. At this time, the temperature of the first ultraviolet-curable resin of the primary layer 3 rises due to the curing heat of the secondary layer 4, etc. In the subsequent third irradiation step (step S105), the ultraviolet light in the first wavelength region causes a curing reaction in the first ultraviolet-curable resin of the primary layer 3, but the first ultraviolet-curable resin is at a high temperature, so the progress of curing is suppressed.

Therefore, according to this embodiment, even if further ultraviolet light is irradiated after the optical fiber core 1 is manufactured, the hardening of the primary layer 3 is sufficiently suppressed, making it possible to effectively avoid microbend loss.

In this embodiment, the application of the second ultraviolet-curable resin may be performed when the first ultraviolet-curable resin is cured, or when the first ultraviolet-curable resin is not sufficiently cured. That is, the manufacturing method of this embodiment can be used for both the wet-on-dry method and the wet-on-wet method. When the wet-on-dry method is adopted, only the first ultraviolet-curable resin is held in the first application device 12, and the second ultraviolet-curable resin is held in the second application device 14. At this time, the application of the first ultraviolet-curable resin in the first application step (step S101), the formation of the primary layer 3 in the first irradiation step (step S102), and the application of the second ultraviolet-curable resin in the second application step (step S103) are each performed as separate steps. On the other hand, when the wet-on-wet method is adopted, the first application device 12 holds the first ultraviolet-curable resin and the second ultraviolet-curable resin separately. In this case, the manufacturing apparatus 10 does not necessarily have to have the second coating device 14. In this case, in the first coating step (step S101), the first ultraviolet curing resin is coated and the second ultraviolet curing resin is coated, and the second coating step (step S103) can be omitted.

[Second embodiment]
Next, a manufacturing method according to the second embodiment will be described with reference to Fig. 6. This embodiment differs from the first embodiment in that an additional fourth irradiation step is performed between the second application step of the secondary layer 4 and the second irradiation step.

Figure 6 is a schematic diagram of a manufacturing apparatus 10 used in the manufacturing method according to the second embodiment. A fourth irradiation device 21 for performing the fourth irradiation step is provided below the second coating device 14 and above the second irradiation device 15. The fourth irradiation device 21 is equipped with an ultraviolet light source that cures the second ultraviolet curing resin of the secondary layer 4. The ultraviolet light source of the fourth irradiation device 21 may be a UVLED lamp or a UV lamp, but it is preferable that it is capable of irradiating ultraviolet light in the second wavelength region. The fourth irradiation device 21 cures the second ultraviolet curing resin by irradiating ultraviolet light toward the bare optical fiber 2 in an atmosphere of a second oxygen concentration, similar to the second irradiation device 15. Here, the second oxygen concentration can be set appropriately, but as described later, it is preferable that the average oxygen concentration of the first oxygen concentration and the second oxygen concentration exceeds 2%.

In this embodiment, too, a method for manufacturing an optical fiber core 1 is provided that has the same effect as the first embodiment, due to the high temperature curing of the first ultraviolet curing resin and the inhibition of curing by oxygen. Furthermore, in this embodiment, the second irradiation process and the fourth irradiation process allow the curing of the second ultraviolet curing resin of the secondary layer 4 to be performed stepwise under different ultraviolet irradiation conditions.

The irradiation conditions such as the ultraviolet light source and oxygen concentration in the second and fourth irradiation steps can be changed as appropriate. For example, when a UV lamp is used as the ultraviolet light source, a sufficient amount of ultraviolet light can be irradiated, which increases the Young's modulus of the secondary layer 4 and allows the surface to be sufficiently cured. This makes it possible to suppress scraping when the secondary layer 4 comes into contact with the guide roller 19. On the other hand, when a UV LED lamp is used as the ultraviolet light source, the power consumption associated with ultraviolet light irradiation can be reduced. For example, in the fourth irradiation step, the amount of light required for surface curing can be sufficiently obtained with a low-power UV LED lamp. In addition, in the subsequent second irradiation step, the inside of the secondary layer 4 can be sufficiently cured using a UV lamp that can ensure a sufficient amount of light. Furthermore, when the second oxygen concentration in the fourth irradiation step is lower than the first oxygen concentration, the curing of the surface of the secondary layer 4 is less likely to be hindered, and the surface curing of the secondary layer 4 can be sufficiently performed.

As described above, according to this embodiment, the secondary layer 4 is hardened in multiple irradiation steps, making it possible to manufacture a low-cost, high-quality optical fiber.

The following describes the experimental results of the optical fiber core wire manufacturing method according to the first and second embodiments of the present invention.

Table 1 shows the evaluation of microbend loss in the examples and comparative examples of the optical fiber core manufacturing method in the first embodiment. That is, Table 1 shows the irradiation conditions and microbend loss evaluation for ultraviolet irradiation in the first irradiation step in the first irradiation device 13, the second irradiation step in the second irradiation device 15, and the third irradiation step in the third irradiation device 16 in Examples 1 to 4 and Comparative Examples 1 and 2.

"UVLED" in Table 1 indicates that ultraviolet irradiation was performed using a UVLED as a light source. "UV" in Table 1 indicates that ultraviolet irradiation was performed using a UV lamp as a light source. "More than 2%" in Table 1 indicates that ultraviolet irradiation was performed in an atmosphere with an oxygen concentration higher than 2%. "2% or less" in Table 1 indicates that ultraviolet irradiation was performed in an atmosphere with an oxygen concentration of 2% or less. "Air atmosphere" in Table 1 indicates that ultraviolet irradiation was performed in an air atmosphere. "Reflector" in Table 1 indicates that ultraviolet irradiation was performed so that a part of the surface of the bare optical fiber 2 was irradiated only with reflected light from the reflector 135. "Vertical direction" in Table 1 indicates that the conveying direction of the optical fiber core 1 passing through the third irradiation device 16 is the same as the drawing direction of the bare optical fiber 2. "Horizontal direction" in Table 1 indicates that the conveying direction of the optical fiber core 1 passing through the third irradiation device 16 is changed from the vertical direction by the guide roller 19.

"Evaluation" in Table 1 indicates whether the microbend loss in the optical fiber core 1 after additional irradiation with ultraviolet light meets the standard (1.0 dB/km or less). If the microbend loss meets the standard, the evaluation is judged as good (OK), and if the microbend loss does not meet the standard, the evaluation is judged as poor (NG).

There are various methods for measuring microbend loss. In this specification, the difference between the transmission loss of the optical fiber to be measured in state A, in which an optical fiber of 400 m or more in length is wound in a single layer without overlapping with a tension of 100 gf around a large bobbin wrapped with sandpaper of #1000, and the transmission loss of the optical fiber in state B, in which the optical fiber is wound around the same bobbin as state A with the same tension and length as state A but without sandpaper, is defined as the value of microbend loss. Here, the transmission loss of the optical fiber in state B does not include microbend loss, and is considered to be a transmission loss inherent to the optical fiber itself. This measurement method is similar to the fixed diameter drum method specified in JIS C6823:2010. This measurement method is also called the sandpaper method. In this measurement method, the transmission loss is measured at a wavelength of 1550 nm, so the microbend loss below is also a value at a wavelength of 1550 nm.

In Example 1, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in an atmosphere with an oxygen concentration higher than 2%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source. The irradiation conditions for the third irradiation step were vertical ultraviolet irradiation using a UVLED as a light source. In Example 1, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

In Example 2, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in an atmosphere with an oxygen concentration higher than 2%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source in an air atmosphere. The irradiation conditions for the third irradiation step were ultraviolet irradiation in the vertical direction using a UVLED as a light source. In Example 2, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

In Example 3, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in an atmosphere with an oxygen concentration higher than 2%. At this time, ultraviolet irradiation was performed so that a portion of the surface of the bare optical fiber 2 was irradiated only with reflected light from the reflector 135. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source. The irradiation conditions for the third irradiation step were vertical ultraviolet irradiation using a UVLED as a light source. In Example 3, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

In Example 4, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in an atmosphere with an oxygen concentration higher than 2%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source. The irradiation conditions for the third irradiation step were horizontal ultraviolet irradiation using a UVLED as a light source. In Example 4, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

In Comparative Example 1, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in an atmosphere with an oxygen concentration of 2% or less. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source in an air atmosphere. The irradiation conditions for the third irradiation step were vertical ultraviolet irradiation using a UVLED as a light source. In Comparative Example 1, the microbend loss after additional ultraviolet irradiation exceeded 1.0 dB/km, and the evaluation was poor (NG).

In Comparative Example 2, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in an atmosphere with an oxygen concentration higher than 2%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source. Thereafter, ultraviolet irradiation in the third irradiation step was not performed. In Comparative Example 2, the microbend loss after additional ultraviolet irradiation exceeded 1.0 dB/km, and the evaluation was poor (NG).

As shown in Table 1, when the first irradiation step is performed in an atmosphere with an oxygen concentration higher than 2%, and then the second and third irradiation steps are performed, it has been confirmed that the microbend loss during additional irradiation of ultraviolet rays is 1.0 dB/km or less. Therefore, it is preferable to perform the first irradiation step in an atmosphere with an oxygen concentration higher than 2%.

As described above, according to this embodiment, when further ultraviolet light is irradiated after production, the hardening of the primary layer can be sufficiently suppressed and microbend loss can be effectively avoided.

Table 2 shows the evaluation of microbend loss in the examples and comparative examples of the optical fiber core wire manufacturing method in the second embodiment. That is, Table 2 shows the irradiation conditions and microbend loss evaluation for ultraviolet irradiation in each of the first irradiation step in the first irradiation device 13, the fourth irradiation step in the fourth irradiation device 21, the second irradiation step in the second irradiation device 15, and the third irradiation step in the third irradiation device 16 in Examples 5 to 8.

In Table 2, "3-10%" indicates that ultraviolet irradiation was performed in an atmosphere with an oxygen concentration of 3-10%. Also, in Table 2, "1-10%" indicates that ultraviolet irradiation was performed in an atmosphere with an oxygen concentration of 1-10%. Also, in Table 2, "less than 2%" indicates that ultraviolet irradiation was performed in an atmosphere with an oxygen concentration of less than 2%. The other notations in Table 2 have the same meanings as in Table 1.

In Example 5, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in a first oxygen concentration atmosphere of 3 to 10%. The irradiation conditions for the fourth irradiation step were ultraviolet irradiation using a UV lamp as a light source in a second oxygen concentration atmosphere of 1 to 10%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UVLED as a light source. The irradiation conditions for the third irradiation step were ultraviolet irradiation using a UVLED as a light source. The average oxygen concentration between the first oxygen concentration under the irradiation conditions for the first irradiation step and the second oxygen concentration under the irradiation conditions for the fourth irradiation step was more than 2%. In Example 5, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

In Example 6, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in a first oxygen concentration atmosphere of 3 to 10%. The irradiation conditions for the fourth irradiation step were ultraviolet irradiation using a UV lamp as a light source in a second oxygen concentration atmosphere of 1 to 10%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source in an air atmosphere. The irradiation conditions for the third irradiation step were vertical ultraviolet irradiation using a UVLED as a light source. The average oxygen concentration between the first oxygen concentration under the irradiation conditions for the first irradiation step and the second oxygen concentration under the irradiation conditions for the fourth irradiation step was more than 2%. In Example 6, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

In Example 7, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in a first oxygen concentration atmosphere of 3 to 10%. The irradiation conditions for the fourth irradiation step were ultraviolet irradiation using a UVLED as a light source in a second oxygen concentration atmosphere of less than 2%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source in an air atmosphere. The irradiation conditions for the third irradiation step were vertical ultraviolet irradiation using a UVLED as a light source. The average oxygen concentration between the first oxygen concentration under the irradiation conditions for the first irradiation step and the second oxygen concentration under the irradiation conditions for the fourth irradiation step was more than 2%. In Example 7, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

In Example 8, the irradiation conditions for the first irradiation step were ultraviolet irradiation using a UVLED as a light source in an air atmosphere. The irradiation conditions for the fourth irradiation step were ultraviolet irradiation using a UVLED as a light source in a second oxygen concentration atmosphere of less than 2%. The irradiation conditions for the second irradiation step were ultraviolet irradiation using a UV lamp as a light source in an air atmosphere. The irradiation conditions for the third irradiation step were vertical ultraviolet irradiation using a UVLED as a light source. The average oxygen concentration between the first oxygen concentration under the irradiation conditions for the first irradiation step and the second oxygen concentration under the irradiation conditions for the fourth irradiation step was more than 2%. In Example 8, the microbend loss after additional ultraviolet irradiation was 1.0 dB/km or less, and the evaluation was good (OK).

As shown in Table 2, when the first irradiation step is performed in an atmosphere with an oxygen concentration higher than 2%, and then the fourth, second, and third irradiation steps are performed, it has been confirmed that the microbend loss during additional irradiation of ultraviolet light is 1.0 dB/km or less. Therefore, it is preferable to perform ultraviolet light irradiation by the first irradiation device 13 in an atmosphere with an oxygen concentration higher than 2%.

Furthermore, according to the second embodiment, it is preferable that the average oxygen concentration between the first oxygen concentration under the irradiation conditions of the first irradiation step and the second oxygen concentration under the irradiation conditions of the fourth irradiation step is greater than 2%.

As described above, according to this embodiment, when further ultraviolet light is irradiated after production, the hardening of the primary layer can be sufficiently suppressed and microbend loss can be effectively avoided.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, an example in which part of the configuration of one of the embodiments is added to another embodiment, or an example in which part of the configuration of another embodiment is replaced with another embodiment, is also an embodiment of the present invention. Furthermore, with regard 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.

1 Optical fiber core 2 Bare optical fiber 3 Primary layer 4 Secondary layer 5 Colored layer

Claims (11)

a drawing process of drawing a bare optical fiber from a fiber preform;
a first coating step of coating a first ultraviolet curing resin around the bare optical fiber;
a first irradiation step of irradiating the bare optical fiber with ultraviolet light in a first wavelength region in an atmosphere having a first oxygen concentration higher than 2% after the first coating step;
a second coating step of coating a second ultraviolet curable resin around the first ultraviolet curable resin;
a second irradiation step of irradiating the bare optical fiber with ultraviolet light in a second wavelength range different from the first wavelength range after the second coating step;
A method for manufacturing an optical fiber core, comprising: a third irradiation step of irradiating the bare optical fiber with ultraviolet light in the first wavelength region after the second irradiation step. a fourth irradiation step of irradiating the bare optical fiber with ultraviolet light in the second wavelength region in an atmosphere having a second oxygen concentration after the second coating step and before the second irradiation step,
2. The method for producing an optical fiber according to claim 1, wherein an average oxygen concentration of the first oxygen concentration and the second oxygen concentration is higher than 2%. The method for manufacturing an optical fiber core wire according to claim 1 or 2, characterized in that the second coating process is performed after the first irradiation process. The method for manufacturing an optical fiber core wire according to claim 1 or 2, characterized in that the second coating process is performed after the first coating process and before the first irradiation process. The method for manufacturing an optical fiber core wire according to any one of claims 1 to 4, characterized in that the second irradiation step is carried out in an air atmosphere. The method for manufacturing an optical fiber core wire according to any one of claims 1 to 5, characterized in that the first oxygen concentration is 2 to 20%. The method for manufacturing an optical fiber core wire according to any one of claims 1 to 6, characterized in that the first oxygen concentration is 3 to 10%. The method for manufacturing an optical fiber core wire according to any one of claims 1 to 7, characterized in that the conveying direction of the bare optical fiber in the third irradiation process is the same as the drawing direction of the bare optical fiber. The method for manufacturing an optical fiber core wire according to any one of claims 1 to 8, characterized in that in the first irradiation step, ultraviolet light in the first wavelength region is irradiated from a plurality of light sources arranged on a circumference centered on the axis in a plane perpendicular to the axis of the bare optical fiber. The method for manufacturing an optical fiber core wire according to any one of claims 1 to 9, characterized in that the ultraviolet light in the first wavelength region is emitted from a semiconductor element, and the ultraviolet light in the second wavelength region is emitted from a fluorescent tube. The method for manufacturing an optical fiber core wire according to any one of claims 1 to 10, characterized in that after manufacturing the optical fiber core wire, the Young's modulus of the first ultraviolet curing resin is 0.2 to 3 MPa, and the Young's modulus of the second ultraviolet curing resin is 500 to 2000 MPa.

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