Optical fiber and optical connection assembly

Abstract

This optical fiber (2) comprises: a glass fiber (21) having a core (25), a cladding (26) surrounding the core, and at least one void (27) formed in the cladding and extending along the optical axis direction of the core; and a resin coating (22) covering the outer circumferential surface of the glass fiber. An exposed part (23) of the glass fiber exposed from the resin coating includes a bent section (51) that is bent with respect to the direction in which a coating part (24) of the glass fiber covered by the resin coating extends. The bent section (51) includes a bent segment that is maintained at a radius of curvature of 1.5 mm or less in a state in which bending stress does not remain. The at least one void (27) extends in the optical axis direction at least in the bending segment. Bending loss is 1.0 dB or less when bending having a radius of curvature of 1.5 mm or less is applied to the glass fiber (21) by 90 degrees.

Description

Optical Fiber and Optical Connection Assemblies

[0001] This application claims priority to Japanese Application No. 2024-085563, filed May 27, 2024, and incorporates by reference the entire contents of said Japanese application.

[0002] As optical modules become smaller, there is a demand for a lower profile for optical fibers used near the optical module (i.e., for an optical fiber whose one end is vertically connected to the optical module, the height from the substrate of the optical fiber must be kept low.) The lower profile of an optical fiber is generally achieved by forming a bent portion in a part of the optical fiber (see, for example, Patent Document 1).

[0003] International Publication No. 2017 / 022085

[0004] The optical fiber of the present disclosure comprises a glass fiber having a core, a cladding surrounding the core, and at least one hole formed in the cladding and extending along the optical axis direction of the core, and a resin coating covering the outer surface of the glass fiber. The exposed portion of the glass fiber exposed from the resin coating includes a bent portion bent with respect to the extension direction of the coating portion of the glass fiber covered with the resin coating. The bent portion includes a bent section maintained with a curvature radius of 1.5 mm or less in a state where no bending stress remains. The at least one hole extends along the optical axis direction at least in the bent section. When the glass fiber is bent 90 degrees with a curvature radius of 1.5 mm or less, the bending loss is 1.0 dB or less.

[0005] The optical fiber and optical connection assembly of the present disclosure can achieve an even lower height while improving optical properties.

[0006] FIG. 1A is a side view showing an optical connection assembly of the present disclosure. FIG. 1B is a cross-sectional view of the optical connection assembly taken along line A1-A1 in FIG. 1A. FIG. 2 is a perspective view showing multiple optical fibers of the optical connection assembly shown in FIG. 1A. FIG. 3 is a cross-sectional view showing a cross section of a glass fiber taken along a plane along the central axis of the optical fiber. FIG. 4A is a cross-sectional view showing an example of a cross section of a glass fiber taken along a plane intersecting the central axis of the optical fiber. FIG. 4B is a cross-sectional view showing an example of a cross section of a glass fiber taken along a plane intersecting the central axis of the optical fiber. FIG. 4C is a cross-sectional view showing an example of a cross section of a glass fiber taken along a plane intersecting the central axis of the optical fiber. FIG. 5A is a plan view showing an exposed portion of a glass fiber. FIG. 5B is a graph showing changes in the curvature of a bent portion included in the exposed portion. FIG. 6 is a diagram showing the relationship between the outer diameter of a glass fiber and the radius of curvature of the glass fiber. FIG. 7A is a diagram for explaining a method for manufacturing an optical fiber. FIG. 7B is a diagram for explaining a method for manufacturing an optical fiber.

[0007] [Problem to be Solved by the Present Disclosure] There is a demand for further reduction in height of optical fibers such as those described in Patent Document 1. However, the lower the height of an optical fiber, the greater the bending loss, which may result in deterioration of optical properties.

[0008] The present disclosure provides an optical fiber and an optical connection assembly that can be made even lower in height while improving optical properties.

[0009] Effect of the Present Disclosure The optical fiber and optical connection assembly of the present disclosure can achieve an even lower height while improving optical properties.

[0010] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0011] (1) An optical fiber according to one aspect of the present disclosure includes a glass fiber having a core, a cladding surrounding the core, and at least one hole formed in the cladding and extending along the optical axis direction of the core; and a resin coating covering the outer surface of the glass fiber. An exposed portion of the glass fiber exposed from the resin coating includes a bent portion bent with respect to the extension direction of the coating portion of the glass fiber covered with the resin coating. The bent portion includes a bent section maintained with a curvature radius of 1.5 mm or less in a state where no bending stress remains. The at least one hole extends along the optical axis direction at least in the bent section. When the glass fiber is bent 90 degrees with a curvature radius of 1.5 mm or less, the bending loss is 1.0 dB or less.

[0012] In the above optical fiber, the bent portion includes a bent section in which a curvature radius is maintained at 1.5 mm or less when no bending stress remains. This enables the optical fiber to be made even thinner while avoiding breakage. The above optical fiber includes at least one hole extending along the optical axis direction of the core at least in the bent section. Furthermore, when the glass fiber is bent 90 degrees with a curvature radius of 1.5 mm or less, the bending loss is 1.0 dB or less. In this way, when holes having a refractive index lower than that of the cladding are formed in the cladding, the average refractive index of the cladding can be lowered, thereby sufficiently increasing the effective refractive index difference between the core and the cladding. In this case, the confinement effect of light guided through the core can be improved compared to when no holes are formed in the cladding. As a result, even when a sharp bend including a bent section with a curvature radius of 1.5 mm or less is formed in the optical fiber, a low connection loss of 1.0 dB or less can be maintained. Therefore, the above optical fiber enables the optical fiber to be made even thinner while improving its optical properties.

[0013] (2) In the optical fiber described in (1) above, the bent portion may include a first bent section that is a bent section maintained with a curvature radius of 1.5 mm or less, and a second bent section that is maintained with a curvature radius different from that of the first bent section. In this case, the change in the curvature radius in the bent portion can be made gradual. This can reduce the risk of breakage of the optical fiber when forming the bent portion in the optical fiber.

[0014] (3) In the optical fiber described in (1) or (2) above, the cladding may have an inner region located inside the bent portion relative to the core in a cross section of the bent portion taken along the optical axis, and an outer region located on the opposite side of the inner region across the core in the cross section. At least one hole may be formed in at least the outer region in the cross section. In this case, even if light propagating through the core cannot bend completely around the sharply bent section and some of the light leaks out into the outer region of the cladding, the hole formed in the outer region can keep the light within the optical fiber. In other words, the confinement effect of light guided through the core can be more effectively improved. This can more reliably improve the optical characteristics of the optical fiber.

[0015] (4) In the optical fiber according to any one of (1) to (3), the outer diameter of the glass fiber may be 75.0 μm or more and 150.0 μm or less. Even when an optical fiber having such an outer diameter is used, it is possible to further reduce the height while improving the optical characteristics.

[0016] (5) In the optical fiber described in any one of (1) to (4), at least one air hole may include an opening that opens at the tip end surface of the exposed portion. The opening may be sealed with a sealing member having a refractive index lower than that of the cladding. For example, if impurities enter the air holes through the opening at the tip end surface during use of the optical fiber, the refractive index difference between the core and the air holes may decrease, thereby reducing the confinement effect of light guided through the core. In contrast, in the above optical fiber, the opening at the tip end surface is sealed with a sealing member, which has a refractive index lower than that of the cladding. This prevents impurities from entering the air holes while maintaining a large effective refractive index difference between the core and the cladding. This reduces the risk of a decrease in the light confinement effect, thereby more reliably improving the optical characteristics of the optical fiber.

[0017] (6) An optical connection assembly according to one aspect of the present disclosure includes the optical fiber according to any one of (1) to (5) above, and an optical connection component to which the tip surface of the exposed portion is connected. The optical connection assembly includes the optical fiber according to any one of (1) to (5) above, and therefore exhibits the above-mentioned effects.

[0018] (7) The optical connection assembly described in (6) above may include a plurality of optical fibers arranged in a direction intersecting the optical axis direction. In this case, the plurality of optical fibers can be arranged at a higher density. [Details of the embodiment of the present disclosure]

[0019] Specific examples of the optical fiber and optical connection assembly of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. In the following description, the same elements in the description of the drawings will be given the same reference numerals, and duplicate descriptions will be omitted as appropriate.

[0020] 1A , the optical connection assembly 1 includes, for example, a plurality of optical fibers 2, a first optical connecting part 3, and a second optical connecting part 4. In the optical connection assembly 1, for example, the plurality of optical fibers 2 are optically connected to a plurality of optical ICs mounted on the main surface 10a of an optical IC substrate 10. The material of the optical IC substrate 10 is, for example, silicon, ceramic, or resin. The plurality of optical ICs are, for example, lined up in a row along the main surface 10a and exposed from the main surface 10a. In the following description, the direction in which the coatings 24 of the plurality of optical fibers 2 extend is defined as the X direction, the direction in which the plurality of optical fibers 2 are arranged is defined as the Y direction, and the direction intersecting the X direction and the Y direction is defined as the Z direction.

[0021] As shown in Fig. 2, a plurality of optical fibers 2 are arranged along the Y direction. Each optical fiber 2 is, for example, a single mode fiber (SMF). In this case, in an optical fiber 2 designed for a wavelength of 1310 nm, the cable cutoff wavelength is 1260 nm or less, and the mode field diameter for the wavelength of 1310 nm is 6.0 μm or more and 9.6 μm or less. In an optical fiber 2 designed for a wavelength of 1550 nm, the cable cutoff wavelength is 1480 nm or less, and the mode field diameter for the wavelength of 1550 nm is 6.0 μm or more and 10.8 μm or less.

[0022] Each optical fiber 2 includes a glass fiber 21 and a resin coating 22. For example, the outer diameter of the glass fiber 21 is 75.0 μm or more and 150.0 μm or less. The resin coating 22 is provided on the outer peripheral surface 21 a of the glass fiber 21 and covers the outer peripheral surface 21 a of the glass fiber 21. The resin coatings 22 of each optical fiber 2 are, for example, integrated with each other. The glass fiber 21 has an exposed portion 23 exposed from the resin coating 22 and a coated portion 24 coated with the resin coating 22. As shown in FIGS. 2 and 3 , the exposed portion 23 has a distal end portion 23 b including the distal end surface 23 a of the glass fiber 21. The coated portion 24 has a proximal end portion 24 b including the proximal end surface 24 a of the glass fiber 21. The proximal end surface 24 a is exposed from the resin coating 22.

[0023] The exposed portion 23 has a bent portion 51 that is bent with respect to the X direction in which the covered portion 24 extends. Details of the bent portion 51 will be described later. In addition to the bent portion 51, the exposed portion 23 has a first extending portion 52 and a second extending portion 53. The first extending portion 52 extends along the X direction between the covered portion 24 and the bent portion 51. The second extending portion 53 extends along the Z direction (strictly speaking, a direction slightly inclined from the Z direction) between the bent portion 51 and the tip surface 23 a.

[0024] 1A and 1B , the first optical connecting part 3 is, for example, an adapter to which the tip surfaces 23 a of the optical fibers 2 are connected. The first optical connecting part 3 is mounted on the main surface 10 a of the optical IC substrate 10, and optically connects the optical fibers 2 to the optical ICs on the main surface 10 a. The first optical connecting part 3 has, for example, a holding part 31, a cover part 32, and a protection part 33.

[0025] The holding portion 31 and the lid portion 32 hold the tip portions 23b of the exposed portions 23 of the multiple optical fibers 2. The holding portion 31 is, for example, a substrate on which multiple V-grooves 31b are formed. The holding portion 31 has a main surface 31a facing the lid portion 32. The main surface 31a of the holding portion 31 is formed with multiple V-grooves 31b extending in the direction in which the multiple optical fibers 2 extend. The multiple V-grooves 31b are aligned along the Y direction in which the multiple optical fibers 2 are arranged. The tip portions 23b of the multiple optical fibers 2 are placed in each of the multiple V-grooves 31b. The lid portion 32 covers the multiple V-grooves 31b and the tip portions 23b of the multiple optical fibers 2.

[0026] The protective portion 33 protects the exposed portion 23 of each optical fiber 2. The exposed portion 23 of each optical fiber 2, except for the tip portion 23b, is embedded inside the protective portion 33. The protective portion 33 is formed of, for example, polycarbonate, PPS (Poly Phenylene Sulfide) resin, or liquid crystal polymer.

[0027] The second optical connecting part 4 is, for example, a connector to which the base end faces 24a of the optical fibers 2 are connected. The second optical connecting part 4 is, for example, an FC connector or an MT connector. The second optical connecting part 4 has a ferrule 41 and a plurality of optical fibers 42. The ferrule 41 is attached to the base end parts 24b of the coating parts 24 of the optical fibers 2. Each base end part 24b is provided inside the ferrule 41.

[0028] A plurality of optical fibers 42 are provided inside the ferrule 41. Each optical fiber 42 is, for example, a single-mode fiber. As shown in Fig. 3, the proximal end surface 24a of each coating 24 is fusion-spliced ​​to the distal end surface 42a of each optical fiber 42. Fig. 1A shows a fusion splicing point P, which is the portion where the distal end surface 42a and the proximal end surface 24a are fused together. In the second optical connecting part 4, the proximal end portion 24b of each optical fiber 2 and each optical fiber 42 are positioned by the ferrule 41.

[0029] The optical fiber 2 will be described in more detail below. Hereinafter, the direction in which the central axis C1 of the glass fiber 21 extends will be referred to as the "central axis direction."

[0030] As shown in Fig. 3, the glass fiber 21 is a holey fiber (HF) having a core 25, a cladding 26, and a plurality of air holes 27. As shown in Fig. 4A, the glass fiber 21 is a hole-assisted fiber (HAF) 21 having, for example, ten air holes 27. The glass fiber 21 may be a photonic crystal fiber 121 shown in Fig. 4B or a hollow-core photonic crystal fiber 221 shown in Fig. 4C. The photonic crystal fiber 121 includes a core 125, a cladding 126 surrounding the core 125, and a plurality of air holes 127 formed in the cladding 126. The plurality of air holes 127 includes a plurality of first air holes 127A arranged in a circumferential direction around the core 125, and a plurality of second air holes 127B surrounding the plurality of first air holes 127A and arranged in a circumferential direction around the core 125. For example, the plurality of air holes 127 are arranged in a lattice pattern so as to surround the core 125. The hollow-core photonic crystal fiber 221 includes a hollow core 225, a cladding 226 surrounding the hollow core 225, and a plurality of air holes 227 formed in the cladding 226. The hollow core 225 is a hollow region extending along the central axis of the hollow-core photonic crystal fiber 221. The plurality of air holes 227 include a plurality of first air holes 227A arranged in the circumferential direction centered on the hollow core 225, and a plurality of second air holes 227B surrounding the plurality of first air holes 227A and arranged in the circumferential direction centered on the hollow core 225. For example, the plurality of air holes 227 are arranged in a lattice pattern so as to surround the hollow core 225. The glass fiber 21 may be a polarization-maintaining optical fiber having at least one air hole 27 and having polarization-maintaining performance.

[0031] 3, the core 25 of the glass fiber 21 extends along the central axis direction of the glass fiber 21. The optical axis direction of the core 25 coincides with the central axis direction of the glass fiber 21. The core 25 is made of, for example, pure SiO ２ Glass or germanium dioxide (GeO ２ ) or SiO containing fluorine element ２The cladding 26 surrounds the core 25. The cladding 26 may be made of, for example, pure SiO. ２ Glass or SiO containing fluorine element ２ Includes glass.

[0032] The plurality of holes 27 are formed in the cladding 26. The plurality of holes 27 extend along the central axis direction of the glass fiber 21 (i.e., the optical axis direction of the core 25), and are formed at least in the bent portion 51 of the glass fiber 21. In this embodiment, the plurality of holes 27 are formed throughout the entire glass fiber 21, including the bent portion 51. In other words, the plurality of holes 27 extend continuously along the central axis direction from the distal end surface 23 a to the proximal end surface 24 a.

[0033] 4A, each air hole 27 is, for example, a circular hole having an inner diameter smaller than the outer diameter of the core 25, and is arranged at equal intervals in the circumferential direction centered on the core 25. In other words, each air hole 27 is arranged on an imaginary circle centered on the central axis C1 of the glass fiber 21. The inner diameter of each air hole 27 may be the same as or larger than the outer diameter of the core 25. The air layer present inside each air hole 27 has a refractive index lower than the refractive index of the cladding 26. In the glass fiber 21, the air hole occupancy rate S shown in the following formula (1) is, for example, 30% or more and 55% or less. S=Nπc ２ / (π(R+2c) ２ -πR ２ )...(1) Formula (1) will be explained with reference to FIG. 4A. In formula (1), "N" represents the number of holes 27 in a cross section intersecting the central axis direction of the glass fiber 21. "R" represents the radius of an imaginary circle L1 inscribed in the plurality of holes 27 in the cross section. "R+2c" represents the radius of an imaginary circle L2 circumscribed in the plurality of holes 27 in the cross section. In this case, "2c" represents the diameter d27 of the holes 27. "2R" represents the diameter d1 of the imaginary circle L1. "2R+4c" represents the diameter d2 of the imaginary circle L2.

[0034] In an optical fiber 2 (so-called holey fiber) in which such air holes 27 are formed in the cladding 26, the presence of the air layer reduces the average refractive index of the cladding 26, thereby enhancing the confinement effect of light guided through the core 25.

[0035] As shown in Fig. 3, in a cross section of the bent portion 51 taken on a plane along the central axis direction, the cladding 26 has an outer region R1 and an inner region R2. The inner region R2 is a region of the cladding 26 that is located more inward of the bent portion 51 than the core 25. More specifically, the inner region R2 is located between the core 25 and an inner circumferential surface 51e of the bent portion 51. The outer region R1 is a region of the cladding 26 that is located more outward of the bent portion 51 than the core 25. The outer region R1 is located on the opposite side of the core 25 from the inner region R2. More specifically, the outer region R1 is located between the core 25 and an outer circumferential surface 51d of the bent portion 51.

[0036] The plurality of holes 27 includes, for example, holes 27A formed in an outer region R1 located outside the bent portion 51 relative to the core 25, and holes 27B formed in an inner region R2 located inside the bent portion 51 relative to the core 25. The plurality of holes 27 may include other holes in addition to the holes 27A and 27B, or may include other holes instead of the holes 27A and 27B. Therefore, the arrangement of the plurality of holes 27 is not limited to the example in FIG. 3 and can be changed as appropriate according to the required specifications.

[0037] As shown in FIG. 3 , each air hole 27 includes a first opening 27 a that opens at the distal end surface 23 a of the glass fiber 21 and a second opening 27 b that opens at the proximal end surface 24 a of the glass fiber 21. The first openings 27 a are arranged to surround the core 25 at the distal end surface 23 a. The first openings 27 a are respectively blocked by a plurality of sealing members 28 having a refractive index lower than that of the cladding 26. For example, each sealing member 28 fills each first opening 27 a without gaps. The state in which the first openings 27 a are blocked by the sealing members 28 refers to a state in which the sealing members 28 are arranged without gaps inside the first openings 27 a as viewed along the central axis so that external impurities (e.g., water) cannot enter the first openings 27 a. Examples of materials for the sealing members 28 having a refractive index lower than that of the cladding 26 include resins such as fluorine-containing polymers. The second openings 27 b are arranged to surround the core 25 at the proximal end surface 24 a. The second openings 27b are closed by the distal end faces 42a of the optical fibers 42 to which the proximal end faces 24a of the glass fibers 21 are fusion-spliced.

[0038] The above-mentioned bent portion 51 will be described in more detail with reference to FIGS. 3, 5A and 5B.

[0039] The horizontal axis of Fig. 5B indicates the position in the central axis direction of the glass fiber 21. The vertical axis of Fig. 5B indicates the curvature of the glass fiber 21. In Figs. 5A and 5B, boundary B1 is the boundary between the bent portion 51 and the second extending portion 53. Boundary B2 is the boundary between the bent portion 51 and the first extending portion 52. As shown in Fig. 5B, the bent portion 51 has a first bent section 51a and second bent sections 51b and 51c. The first bent section 51a extends between the first extending portion 52 and the second extending portion 53. The second bent section 51b extends between the second extending portion 53 and the first bent section 51a. The second bent section 51c extends between the first bent section 51a and the first extending portion 52.

[0040] The first bent section 51a is a section in which a curvature of 0.67 (1 / mm) or more (i.e., a curvature radius of 1.5 mm or less) is maintained in a state in which no bending stress remains. A state in which no bending stress remains refers to a state in which strain generated when bending the exposed portion 23 of the glass fiber 21 is removed. For example, strain generated in the exposed portion 23 can be removed by bending the exposed portion 23 while heating the exposed portion 23. In this case, the bent shape of the bent portion 51 can be maintained without fixing both ends of the bent portion 51, so no bending stress remains in the bent portion 51. The curvature of the first bent section 51a ranges, for example, from 0.67 (1 / mm) to 1.0 (1 / mm). That is, the curvature radius of the first bent section 51a ranges from 1.0 mm to 1.5 mm. The first bent section 51a has a section in which the curvature is constant (e.g., 1.0 (1 / mm)) and a section in which the curvature changes.

[0041] The second bent sections 51b and 51c are sections having a curvature different from that of the first bent section 51a. The second bent sections 51b and 51c are sections in which the curvature is maintained, for example, less than 0.67 (1 / mm) (i.e., a radius of curvature greater than 1.5 mm). Therefore, the radius of curvature of the bent portion 51 is not constant at each position along the central axis. The radius of curvature of the bent portion 51 may be constant (e.g., a radius of curvature of 1.5 mm) at each position along the central axis. The bent portion 51 may not have the second bent sections 51b and 51c, and may have only the first bent section 51a. In other words, the bent portion 51 may have only a section in which the radius of curvature is maintained equal to or less than 1.5 mm. In FIG. 5B , the curve showing the change in curvature of the bent portion 51 may be a clothoid curve in which the curvature changes stepwise.

[0042] As described above, the glass fiber 21 having the plurality of holes 27 has an enhanced confinement effect of light guided through the core 25. Therefore, even if the glass fiber 21 has a bent portion 51 including a steep first bent section 51a with a curvature radius of 1.5 mm or less, a low bending loss can be maintained. In this embodiment, the bending loss of the glass fiber 21 when bent at a 90-degree angle with a curvature radius of 1.5 mm or less is maintained at 1.0 dB or less, or 0.5 dB or less. The bending loss is measured by a known method based on the ratio of the intensity of light incident on the optical fiber 2 to the intensity of light emitted from the optical fiber 2 (see, for example, ITU-T G.650.1 5.6 Test methods for the macro bend loss). According to this method, the bending loss is measured by calculating the difference between the transmitted light power when the optical fiber is not bent and the transmitted light power when the optical fiber is bent.

[0043] When measuring the curvature of the bent portion 51, first, a projection image of the optical fiber 2 projected onto a plane is obtained. Next, an image (profile) showing the outline of the optical fiber 2 is generated based on the projection image. Next, based on the image showing the outline of the optical fiber 2, the trajectory along which the optical fiber 2 extends is obtained as a set of coordinates in an XY coordinate system. Finally, the curvature of the bent portion 51 is calculated for each coordinate based on the trajectory along which the optical fiber 2 extends. This allows the curvature of the bent portion 51 for each coordinate to be obtained. Therefore, the curvature in the present disclosure may be the curvature at one coordinate included in the trajectory along which the optical fiber 2 extends.

[0044] The horizontal axis of Fig. 6 represents the outer diameter of the glass fiber. The vertical axis of Fig. 6 represents the minimum value of the radius of curvature of the glass fiber. As shown in the graph of Fig. 6, the smaller the outer diameter of the glass fiber, the smaller the radius of curvature that the glass fiber can tolerate, and the higher the possibility that the glass fiber will break when bent. For example, glass fibers having an outer diameter and a radius of curvature included in a region other than region R100 to the left of line L (i.e., region R11 to the right of line L) are more likely to break, and therefore, in conventional techniques, glass fibers having an outer diameter and a radius of curvature included in region R100 tend to be used.

[0045] In contrast, in the glass fiber 21 of this embodiment, as described above, the bent portion 51 is maintained in a state where no bending stress remains, thereby reducing the risk of breakage of the glass fiber 21. Therefore, even when using a glass fiber 21 having an outer diameter and a radius of curvature included in the region R11 to the right of the line L in Fig. 6 , breakage of the glass fiber 21 can be avoided. Within the region R11 in Fig. 6 , the use of a glass fiber 21 included in the region R12 having a radius of curvature of 1.5 mm or less and an outer diameter of 75.0 μm or more and 150.0 μm or less is required, and this embodiment can meet this requirement.

[0046] 7A and 7B , a method for manufacturing the optical fiber 2 will be described. The method for manufacturing the optical fiber 2 includes a step of preparing the optical fiber 2 and a step of forming the bent portion 51. In the step of forming the bent portion 51, the bent portion 51 is formed in the exposed portion 23 using, for example, a bend forming device 60.

[0047] The bending device 60 has two discharge electrodes 61, a power supply (not shown), a cooling chamber 63, an air inlet 64, and an exhaust port 65. The two discharge electrodes 61 are electrodes for heating the exposed portion 23 of the optical fiber 2. The power supply supplies power to the two discharge electrodes 61. In the cooling chamber 63, helium, which has high thermal conductivity, and an inert gas (e.g., nitrogen), which undergoes an endothermic reaction with oxygen in a high-temperature environment, are used as cooling media and are supplied through the air inlet 64 and exhausted through the exhaust port 65. This allows the high-temperature region heated by the arc discharge inside the cooling chamber 63 to be rapidly cooled.

[0048] First, as shown in FIG. 7A, in the step of preparing the optical fiber 2, a predetermined length of the resin coating 22 is removed from the tip surface 23a to obtain the optical fiber 2 having the exposed portion 23 formed thereon.

[0049] Next, as shown in FIG. 7B , in the step of forming bent portion 51, bent portion 51 is formed by heating exposed portion 23 using bend forming device 60. In this embodiment, in the step of forming bent portion 51, first, exposed portion 23 is heated by two discharge electrodes 61. Next, a portion of heated exposed portion 23 is bent. Next, the bent portion of exposed portion 23 is cooled at a rate of decrease of 100°C / s or more until the surface temperature of the bent portion of exposed portion 23 drops from the maximum temperature during heating to 1000°C or less. This forms bent portion 51 in exposed portion 23. The portion of exposed portion 23 may be heated at the same time as bending the portion, or the portion of exposed portion 23 may be heated after bending the portion of exposed portion 23.

[0050] The effects obtained by the optical fiber 2 and optical connection assembly 1 of this embodiment described above will now be described. In this embodiment, the bent portion 51 includes a first bent section 51a whose curvature radius is maintained at 1.5 mm or less when no bending stress remains. This makes it possible to further reduce the height of the optical fiber 2 while avoiding breakage of the optical fiber 2. The optical fiber 2 of this embodiment includes at least one hole 27 extending along the central axis of the glass fiber 21 (i.e., the optical axis direction of the core 25) at least in the first bent section 51a. Furthermore, when the glass fiber 21 is bent 90 degrees with a curvature radius of 1.5 mm or less, the bending loss is 1.0 dB or less. In this way, when holes 27 having a lower refractive index than the cladding 26 are formed in the cladding 26, the average refractive index of the cladding 26 can be reduced, thereby sufficiently increasing the effective refractive index difference between the core 25 and the cladding 26. In this case, the confinement effect of light guided through the core 25 can be improved compared to when no holes 27 are formed in the cladding 26. As a result, a low connection loss of 1.0 dB or less can be maintained even when a sharp bend 51 including a first bend section 51a with a curvature radius of 1.5 mm or less is formed in the optical fiber 2. Therefore, the optical fiber 2 of this embodiment can be made even thinner while improving its optical characteristics.

[0051] As in the present embodiment, the bent portion 51 of the optical fiber 2 may include a first bent section 51a having a curvature radius of 1.5 mm or less and a second bent section 51b having a curvature radius different from that of the first bent section 51a. In this case, the change in the curvature radius can be made gradual in the bent portion 51. This reduces the risk of breakage of the optical fiber 2 when forming the bent portion 51 in the optical fiber 2.

[0052] As in the present embodiment, the cladding 26 may have an inner region R2 located more inward than the core 25 in the cross section of the bent portion 51, and an outer region R1 located on the opposite side of the inner region R2 across the core 25 in the cross section of the bent portion 51. At least one hole 27 may be formed in at least the outer region R1 in the cross section of the bent portion 51. In this case, even if light propagating through the core 25 cannot bend completely around the steep first bend section 51a and some of the light leaks into the outer region R1 of the cladding 26, the hole 27 formed in the outer region R1 can keep the light within the optical fiber 2. In other words, the confinement effect of light guided through the core 25 can be more effectively improved. This can more reliably improve the optical characteristics of the optical fiber 2.

[0053] As in the present embodiment, the outer diameter of the glass fiber 21 may be 75.0 μm or more and 150.0 μm or less. Even when using an optical fiber 2 having such an outer diameter, the optical characteristics can be improved and the height can be further reduced.

[0054] As in the present embodiment, at least one air hole 27 may include a first opening 27a that opens at the tip surface 23a of the exposed portion 23. The first opening 27a may be blocked by a sealing member 28 having a refractive index lower than that of the cladding 26. For example, if impurities enter the air hole 27 through the first opening 27a at the tip surface 23a during use of the optical fiber 2, the refractive index difference between the core 25 and the air hole 27 becomes smaller, which may reduce the confinement effect of light guided through the core 25. In contrast, in the optical fiber 2 of the present embodiment, the first opening 27a at the tip surface 23a is blocked by the sealing member 28, which has a refractive index lower than that of the cladding 26. This prevents impurities from entering the air hole 27 while maintaining a large effective refractive index difference between the core 25 and the cladding 26. This reduces the risk of a decrease in the light confinement effect, thereby more reliably improving the optical characteristics of the optical fiber 2.

[0055] As in this embodiment, the optical connection assembly 1 may include a plurality of optical fibers 2 arranged in the Y direction that intersects with the central axis direction of the glass fiber 21. In this case, the plurality of optical fibers 2 can be arranged at a higher density.

[0056] The present disclosure is not limited to the above-described embodiment, and various other modifications are possible. In the above-described embodiment, the optical fiber 2 includes the sealing member 28 that closes the first opening 27a. The optical fiber 2 may not include the sealing member 28. In this case, the first optical connecting part 3 may include an optical fiber connected to the front end surface 23a where the first opening 27a is formed. The front end surface 23a may be fusion-spliced ​​to the optical fiber, and the optical fiber may be optically connected to the optical IC of the optical IC substrate 10 using the optical fiber. The exposed portion 23 of the optical fiber 2 may not include the first extending portion 52 and the second extending portion 53, and may include only the bent portion 51.

[0057] In the above-described embodiment, the exposed portion 23 of the glass fiber 21 is heated by arc discharge, but may be heated by a burner, a CO laser, or a heater, for example. The exposed portion 23 is cooled using the cooling chamber 63, but may be cooled by directly blowing an inert gas thereon, for example.

[0058] 1...optical connection assembly 2...optical fiber 3...first optical connecting part 4...second optical connecting part 10...optical IC substrate 10a...main surface 21...glass fiber 21a...outer circumferential surface 22...resin coating 23...exposed portion 23a...tip surface 23b...tip portion 24...coating portion 24a...base end surface 24b...base end portion 25...core 26...clad 27, 27A, 27B...hole 27a...first opening 27b...second opening 28...sealing member 31...holding portion 31a...main surface 31b...V-groove 32...lid portion 33...protective portion 41...ferrule 42...optical fiber 42a...tip surface 51...bent portion 51a...first bent section 51b, 51c...second bent section 51d...outer circumferential surface 51e...inner circumferential surface 52...first extension portion 53...Second extension portion 60...Bending device 61...Discharge electrode 63...Cooling chamber 64...Air intake port 65...Exhaust port 121...Photonic crystal fiber 125...Core 126...Cladding 127...Hole 127A...First hole 127B...Second hole 221...Hollow-core photonic crystal fiber 225...Hollow core 226...Cladding 227...Hole 227A...First hole 227B...Second hole B1...Boundary B2...Boundary C1...Central axis L...Straight line P...Fusion splicing point R1...Outer region R2...Inner region R11...Region R12...Region R100...Region

Claims

1. An optical fiber comprising: a glass fiber having a core, a cladding surrounding the core, and at least one hole formed in the cladding and extending along the optical axis direction of the core; and a resin coating covering the outer surface of the glass fiber, wherein an exposed portion of the glass fiber exposed from the resin coating includes a bent portion bent in the direction in which the coated portion of the glass fiber covered with the resin coating extends, and the bent portion includes a bent section maintained with a curvature radius of 1.5 mm or less in a state in which no bending stress remains, and the at least one hole extends along the optical axis direction in at least the bent section, and wherein the bending loss when the glass fiber is bent 90 degrees with a curvature radius of 1.5 mm or less is 1.0 dB or less.

2. The optical fiber according to claim 1, wherein the bent portion includes a first bent section, which is the bent section maintained at a radius of curvature of 1.5 mm or less, and a second bent section maintained at a radius of curvature different from that of the first bent section.

3. An optical fiber according to claim 1 or claim 2, wherein the cladding has an inner region located inside the bent portion relative to the core in a cross section of the bent portion taken along a plane along the optical axis direction, and an outer region located on the opposite side of the inner region across the core in the cross section, and the at least one air hole is formed in at least the outer region in the cross section.

4. An optical fiber according to any one of claims 1 to 3, wherein the outer diameter of the glass fiber is 75.0 μm or more and 150.0 μm or less.

5. An optical fiber according to any one of claims 1 to 4, wherein the at least one air hole includes an opening that opens at the tip face of the exposed portion, and the opening is sealed with a sealing member having a refractive index lower than that of the cladding.

6. An optical connection assembly comprising: the optical fiber according to any one of claims 1 to 5; and an optical connection part to which the tip end face of the exposed portion is connected.

7. The optical connection assembly according to claim 6, comprising a plurality of said optical fibers arranged in a direction intersecting said optical axis direction.

Images