Optical fiber ribbon

Abstract

An optical fiber ribbon (1A) comprises a plurality of optical fibers (11) arranged in parallel to a direction orthogonal to the longitudinal direction thereof. In at least a portion of the plurality of optical fibers (11), a plurality of connecting parts (21a) that connect the optical fibers (11) adjacent to each other are provided intermittently in the longitudinal direction. Each of the connecting parts (21a) is configured such that tear stress that occurs when being torn in the longitudinal direction exhibits a plurality of peaks. The tear stress exhibits a first peak (PA1) indicating the greatest tear stress, and a second peak (PA2) indicating a tear stress different from the greatest tear stress. The tear stress at the first peak (PA1) is at least 0.01 N, and the tear stress at the second peak (PA2) is at least 50% of the tear stress at the first peak (PA1).

Description

Optical fiber ribbon

[0001] This application claims priority to Japanese Patent Application No. 2022-078228, filed May 11, 2022, and incorporates by reference all of the contents of that application.

[0002] Patent Document 1 discloses an optical fiber ribbon in which connecting portions that connect two adjacent optical fibers are provided intermittently in both the longitudinal and width directions of the ribbon, and the tear strength of the connecting portions is 1.50 to 21.0 gf.

[0003] Patent Document 2 discloses an optical fiber ribbon comprising a plurality of optical fibers each having a colored layer and a plurality of connecting portions each connecting two adjacent optical fibers. The adhesive strength between the colored layer and the connecting portions is 0.38 N / mm. ２ 4.30N / mm or more ２ The tear strength at which the connecting portion is torn is 1.0 gf or more and 17.0 gf or less.

[0004] Japanese Patent Publication No. 2013-182157 Japanese Patent Publication No. 2019-168553

[0005] The optical fiber ribbon core wire of the present disclosure comprises a plurality of optical fiber core wires arranged in parallel in a direction perpendicular to the longitudinal direction, and in at least a portion of the plurality of optical fiber core wires, a plurality of connecting portions connecting adjacent optical fiber core wires are provided intermittently in the longitudinal direction, one of the plurality of connecting portions is configured so that the tearing stress when torn in the longitudinal direction has multiple peaks, the tearing stress has a first peak indicating the maximum tearing stress and a second peak indicating a tearing stress different from the maximum tearing stress, the tearing stress of the first peak is 0.01 N or more, and the tearing stress of the second peak is 50% or more of the tearing stress of the first peak.

[0006] FIG. 1 is a cross-sectional view of an optical fiber ribbon according to a first embodiment. FIG. 2 is a plan view of the optical fiber ribbon shown in FIG. 1. FIG. 3 is a graph showing the relationship between the tearing stress at a connection portion and the tearing length when the connection portion of the optical fiber ribbon shown in FIG. 1 is torn. FIG. 4 is a graph showing the relationship between the tearing stress at a connection portion and the tearing length when an optical fiber ribbon according to a comparative example is torn. FIG. 5 is a schematic diagram showing a method for measuring the tearing stress at a connection portion. FIG. 6 is a cross-sectional view of an optical fiber ribbon according to a second embodiment. FIG. 7 is a plan view of the optical fiber ribbon shown in FIG. 6. FIG. 8 is a graph showing the relationship between the tearing stress at a connection portion and the tearing length when the connection portion of the optical fiber ribbon shown in FIG. 6 is torn. FIG. 9 is a cross-sectional view of an optical fiber ribbon according to a modified example.

[0007] (Problem to be Solved by the Present Disclosure) When the strength of the joints of an optical fiber ribbon is weak, the joints may be torn when a bending force or other force is applied to the optical fiber ribbon or a cable in which the optical fiber ribbon is mounted. In this case, the individual optical fibers may easily come apart, making the optical fiber ribbon difficult to handle.

[0008] The present disclosure provides an optical fiber ribbon that can suppress deterioration in handleability.

[0009] (Explanation of One Aspect of the Present Disclosure) First, embodiments of the present disclosure will be described below. (1) An optical fiber ribbon according to one aspect of the present disclosure comprises: a plurality of optical fibers arranged in parallel in a direction perpendicular to a longitudinal direction; at least some of the plurality of optical fibers have a plurality of connecting portions intermittently provided in the longitudinal direction for connecting adjacent optical fibers; one of the plurality of connecting portions is configured so that a tearing stress when torn in the longitudinal direction has a plurality of peaks; the tearing stress has a first peak indicating a maximum tearing stress and a second peak indicating a tearing stress different from the maximum tearing stress; the tearing stress of the first peak is 0.01 N or more; and the tearing stress of the second peak is 50% or more of the tearing stress of the first peak.

[0010] According to the present disclosure, the connecting portion has multiple peaks of stress that occur when it is torn apart. In other words, even if a tearing force acts on the connecting portion, the connecting portion is unlikely to tear completely in one go, but will tear little by little. Therefore, the optical fiber is unlikely to come apart, and deterioration in the handleability of the optical fiber ribbon can be suppressed.

[0011] According to the present disclosure, the first peak tear stress, which is the maximum tear stress, is equal to or greater than 0.01 N. Therefore, even if a slight force of less than 0.01 N acts on the connection portion, the connection portion will not tear. Therefore, deterioration in the handleability of the optical fiber ribbon can be suppressed.

[0012] According to the present disclosure, the second peak tear stress is 50% or more of the first peak tear stress. Even if a tear is formed in the connection portion against the first peak tear stress, the tear will not expand unless a relatively strong force of 50% or more of the first peak tear stress is applied, so the optical fiber is less likely to come apart, and deterioration in the handleability of the optical fiber ribbon can be suppressed.

[0013] (2) In the above (1), the elastic modulus of one of the connecting portions may be 1 GPa or more and 5 GPa or less. According to the present disclosure, since the elastic modulus of the connecting portion is 1 GPa or more, it is possible to prevent the connecting portion from being broken by a small external force. Furthermore, since the elastic modulus of the connecting portion is 5 GPa or less, it is possible to reduce transmission loss due to lateral pressure on the optical fiber ribbon at low temperatures.

[0014] (3) In the above (1) or (2), the tensile breaking strength of the one connecting portion may be 20 MPa or more. According to the present disclosure, since the tensile breaking strength of the connecting portion is 20 MPa or more, the optical fiber ribbon is less likely to come apart, and the handling of the optical fiber ribbon is improved.

[0015] (4) In any of the above (1) to (3), the first peak tear stress may be equal to or greater than 0.03 N. According to the present disclosure, since the first peak tear stress is equal to or greater than 0.03 N, the effect of making the connecting portion less likely to tear can be enhanced.

[0016] (5) In any of (1) to (3) above, a first length of the one connecting portion that is torn in the longitudinal direction when a force equivalent to the first peak tearing stress acts on the one connecting portion may be the same as a second length of the one connecting portion that is torn in the longitudinal direction when a force equivalent to the second peak tearing stress acts on the one connecting portion.

[0017] According to the present disclosure, a first length of the connection portion that is torn in the longitudinal direction when a force corresponding to the first peak tearing stress acts on the connection portion is the same as a second length of the connection portion that is torn in the longitudinal direction when a force corresponding to the second peak tearing stress acts on the connection portion, and the connection portion is torn at predetermined lengths. In other words, the entire connection portion is not torn at once, so the optical fiber is less likely to come apart, and deterioration in the handleability of the optical fiber ribbon can be suppressed.

[0018] Effect of the Present Disclosure According to the present disclosure, it is possible to provide an optical fiber ribbon that can suppress deterioration in handleability.

[0019] (Details of an embodiment of the present disclosure) Specific examples of an optical fiber ribbon according to an embodiment of the present disclosure will be described with reference to the drawings. Note that 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.

[0020] (First embodiment) Fig. 1 is a cross-sectional view showing an optical fiber ribbon 1A according to a first embodiment. Fig. 2 is a plan view of the optical fiber ribbon 1A. Fig. 1 is a cross-sectional view taken along line A-A of the optical fiber ribbon 1A shown in Fig. 2.

[0021] As shown in Figures 1 and 2, the optical fiber ribbon 1A has multiple (12 in this example) optical fiber core wires 11 (11A to 11L in this example) arranged in parallel in a direction perpendicular to the longitudinal direction.

[0022] Each optical fiber 11 includes, for example, a glass fiber 12 consisting of a core and a cladding, and two coating layers 13 and 14 surrounding the glass fiber 12. The optical fiber 11 may also include a colored layer. The inner coating layer 13 of the two coating layers is formed of a cured product of a primary resin. The outer coating layer 14 of the two coating layers is formed of a cured product of a secondary resin.

[0023] The primary resin constituting the inner coating layer 13 in contact with the glass fiber 12 is a soft resin with a relatively low Young's modulus, serving as a buffer layer. The secondary resin constituting the outer coating layer 14 is a hard resin with a relatively high Young's modulus, serving as a protective layer. The Young's modulus of the cured secondary resin at room temperature (e.g., 23°C) is 900 MPa or more, preferably 1000 MPa or more, and more preferably 1500 MPa or more.

[0024] The secondary resin that will form the outer coating layer 14 is preferably an ultraviolet-curable resin composition containing a urethane acrylate oligomer, a monomer, and a photopolymerization initiator.

[0025] The outer diameter R of the optical fiber ribbon 11 (11A to 11L) is 180 μm or more and 250 μm or less. In the optical fiber ribbon 1A of this example, the outer diameter R is 200 μm.

[0026] In this example, the number of fibers in the optical fiber ribbon 1A is 12, but is not limited to this. The number of fibers in the optical fiber ribbon 1A may be, for example, 24, 48, or the like.

[0027] In the optical fiber ribbon 1A, 12 optical fibers 11A to 11L are arranged alternately in a state where they are spaced apart every N cores and in a state where they are in contact with each other. The optical fibers 11A to 11L in this example are arranged so that adjacent optical fibers 11A to 11L are alternately arranged in a state where they are spaced a certain distance from each other and in a state where they are in contact with each other every two cores. The 12 parallel-arranged optical fibers 11A to 11L are all connected together by a connecting resin 21.

[0028] As shown in Fig. 2, a plurality of connecting portions 21a are provided intermittently in the longitudinal direction of the plurality of optical fiber core wires 11. Similarly, a plurality of non-connecting portions 23 are formed intermittently in the longitudinal direction of the plurality of optical fiber core wires 11. The optical fiber ribbon 1A is an intermittently connected optical fiber ribbon in which connecting portions 21a and non-connecting portions 23 are provided intermittently in the longitudinal direction for every two optical fiber core wires. Note that the plan view of Fig. 2 shows a state in which the non-connecting portions 23 are opened in the parallel direction of the optical fiber core wires 11.

[0029] The connecting resin 21 of the optical fiber ribbon 1A is provided so as to cover the outer periphery of each optical fiber 11. The connecting resin 21 is provided with a plurality of connecting portions 21a that connect adjacent optical fibers 11 in at least a portion of the plurality of optical fibers 11. The connecting resin 21 further includes an outer covering portion 21b that covers the outer periphery of each optical fiber 11 (FIG. 1). The connecting portions 21a and the outer covering portion 21b are formed of the same resin. The optical fiber ribbon 1A also includes a plurality of non-connecting portions 23 where adjacent optical fibers are not connected.

[0030] In the optical fiber ribbon 1A of this example, in a cross section perpendicular to the longitudinal direction, the connecting portions 21a are provided between the optical fibers 11D and 11E, and between 11H and 11I. The non-connecting portions 23 are provided between the optical fibers 11B and 11C, between 11F and 11G, and between 11J and 11K. Meanwhile, the adjacent optical fibers 11A and 11B, 11C and 11D, 11E and 11F, 11G and 11H, 11I and 11J, and 11K and 11L are arranged so that there are no gaps between the optical fibers.

[0031] The elastic modulus of the connecting resin 21 (connecting portion 21a and outer peripheral covering portion 21b) is 1 GPa or more and 5 GPa or less at room temperature (e.g., 23°C). In this example, the elastic modulus of the connecting portion 21a is 2.5 GPa or more and 2.8 GPa or less. The elastic modulus of the connecting resin 21 can be measured as the elastic modulus in the thickness direction of the cured adhesive resin using a nanoindenter (HYSITRON TI950 Tribolndenter manufactured by BRUKER) according to a test method based on ISO 14577. In this example, the indentation depth was 100 nm, and the elastic modulus of the connecting resin 21 was measured using a Berkovich indenter. The Young's modulus of the connecting portion 21a is, for example, 868 MPa at room temperature (e.g., 23°C). The tensile break strength of the connecting portion 21a is 20 MPa or more. The connecting portion 21a in this example has a tensile strength of 33 MPa and an elongation at break of 39%. The connecting resin 21 is, for example, an ultraviolet curable resin or a thermosetting resin.

[0032] It is preferable that the adhesive strength between the outermost layer of the optical fiber 11 and the linking resin 21 is strong. For example, the linking resin 21 may contain a ketone-based solvent. This increases the adhesive strength between the outermost layer of the optical fiber 11. This makes the linking resin 21 less likely to peel off from the optical fiber 11, and the optical fiber 11 less likely to fall apart.

[0033] An example of an index of adhesive strength is the tearing stress required to peel the connecting resin 21 from the outer peripheral surface of the optical fiber core 11 .

[0034] The tear stress of the connecting portion 21a is measured as follows: An incision is made with a knife or razor in the connecting portion 21a, which is formed at the center of one end of the optical fiber ribbon 1A in the width direction (the direction in which the optical fibers 11 are arranged side by side), and the end of the 12-fiber optical fiber ribbon 1A is separated into six fibers each. Each end of the outer coating portion 21b of the separated six fibers is grasped and pulled in the direction perpendicular to the longitudinal and width directions at a speed of 200 mm / min, and the tensile force at this time is measured as the tear stress.

[0035] FIG. 3 is a graph showing the relationship between the tearing stress of the connecting portion 21a and the tearing length when one connecting portion 21a of the optical fiber ribbon 1A is torn. As shown in FIG. 3, the connecting portion 21a of this example is configured so that the tearing stress has multiple peaks when torn in the longitudinal direction. In other words, when a force equivalent to the tearing stress acts on the connecting portion 21a, the connecting portion 21a is not completely torn by a single force, but is torn little by little through multiple peaks. The tearing stress of the connecting portion 21a has a first peak PA1, which indicates the maximum tearing stress, and a second peak PA2, which indicates a tearing stress different from the maximum tearing stress. The tearing stress of the first peak PA1, which is the maximum tearing stress, is 0.01 N or more. The tearing stress of the second peak PA2 is 50% or more of the tearing stress of the first peak PA1.

[0036] The tear stress of the connecting portion 21a further has a third peak PA3, a fourth peak PA4, and a fifth peak PA5 which are different from the tear stresses of the first peak PA1 and the second peak PA2. The second peak PA2, the third peak PA3, the fourth peak PA4, and the fifth peak PA5 are examples of second peaks which have tear stresses that are 50% or more of the tear stress of the first peak.

[0037] When a force equivalent to the tearing stress of the fifth peak PA5 acts on connecting portion 21a, a tear is formed in connecting portion 21a in the longitudinal direction. The length of connecting portion 21a torn at this time is designated as a fifth length LA5. If a force equivalent to the tearing stress of the fourth peak PA4 acts on connecting portion 21a after connecting portion 21a has been torn by the fifth length LA5, the tear formed at fifth peak PA5 expands, and connecting portion 21a is further torn in the longitudinal direction. The length of connecting portion 21a torn at this time is designated as a fourth length LA4. Subsequently, when a force equivalent to the tearing stress of the third peak PA3 acts on connecting portion 21a, connecting portion 21a is torn by the third length LA3; when a force equivalent to the tearing stress of the second peak PA2 acts on connecting portion 21a, connecting portion 21a is torn by the second length LA2; and when a force equivalent to the tearing stress of the first peak PA1 acts on connecting portion 21a, connecting portion 21a is torn by the first length LA1.

[0038] In this example, the tear stress of the fifth peak PA5 is, for example, 0.016 N, and the fifth length LA5 is, for example, torn by about 13 mm. The tear stress of the fourth peak PA4 is, for example, 0.016 N, and the fourth length LA4 is, for example, torn by about 13 mm. The tear stress of the third peak PA3 is, for example, 0.016 N, and the third length LA3 is, for example, torn by about 10 mm. The tear stress of the second peak PA2 is, for example, 0.016 N, and the second length LA2 is, for example, torn by about 10 mm. The tear stress of the first peak PA1 is, for example, 0.018 N, and the first length LA1 is, for example, about 10 mm.

[0039] Thus, the tear stress of the second peak PA2 is the same as the tear stress of the first peak PA1 (90% of the tear stress of the first peak PA1). Furthermore, the first length LA1 is the same as the second length LA2, the third length LA3, the fourth length LA4, or the fifth length LA5. In this example, "the same length" does not mean that the two lengths are completely identical, but rather that one length is within ±30% of the other length.

[0040] The length of the torn connecting portion 21a may vary depending on the adhesion between the optical fiber 11 and the connecting portion 21a (connecting resin 21) in addition to the tearing stress. In other words, when a force equivalent to the tearing stress acts on the connecting portion 21a, the connecting portion 21a may break, forming a crack between adjacent optical fibers. Furthermore, when the connecting resin 21 forming the connecting portion 21a is peeled off from the optical fiber 11, forming a crack between adjacent optical fibers.

[0041] 4 is a graph showing the relationship between the tear stress of the connecting portion 21a and the tear length of the connecting portion 21a of the optical fiber ribbon 1Z as a comparative example. The elastic modulus of the connecting resin 21 (the connecting portion 21a and the outer covering portion 21b) of the optical fiber ribbon 1Z is 1.5 GPa at room temperature (e.g., 23°C). In the optical fiber ribbon 1Z, the Young's modulus of the connecting portion 21a is 115 MPa at room temperature (e.g., 23°C), the tensile strength of the connecting portion 21a is, for example, 16 MPa, and the elongation at break of the connecting portion 21a is 38%. When the peeling strength of the optical fiber ribbon 1A according to the first embodiment is set to 1 as a reference, the peeling strength of the optical fiber ribbon 1Z according to the comparative example is 0.2 or more and 0.3 or less. Except for the difference in the physical properties of the connecting resin 21, the configuration of the optical fiber ribbon 1Z is similar to that of the optical fiber ribbon 1A, and therefore a description thereof will be omitted.

[0042] As shown in FIG. 4 , the joint portion 21a of the optical fiber ribbon 1Z according to the comparative example is configured so that the tear stress has multiple peaks when torn in the longitudinal direction. However, it differs from the optical fiber ribbon 1A according to the present example in that the tear stress of the second peak PZ2 is not 50% or more of the tear stress of the first peak PZ1. In the optical fiber ribbon 1Z according to the comparative example, the tear stress of the first peak PZ1 is, for example, 0.02 N, and the tear stress of the second peak PZ2 is, for example, 0.009 N. That is, the tear stress of the second peak PZ2 is approximately 45% of the tear stress of the first peak PZ1. The tear stress of the third peak PZ3 and the tear stress of the fourth peak PZ4 are both approximately 0.005 N, which is approximately 25% of the tear stress of the first peak PZ1.

[0043] In the optical fiber ribbon 1Z according to the comparative example, a force equivalent to the tear stress of the first peak PZ1 acts on the connecting portion 21a, forming a tear of a first length LZ1. The first length LZ1 is, for example, 20 mm. Furthermore, in the optical fiber ribbon 1Z, after this tear is formed, if a relatively weak force, such as the tear stress of the fourth peak PZ4, the third peak PZ3, or the second peak PZ2, i.e., less than 50% of the tear stress of the first peak PZ1, acts on the connecting portion 21a, the tear expands. If the tear expands due to a relatively weak force, the optical fiber 11 is likely to fall apart, which may reduce the handleability of the optical fiber ribbon 1Z.

[0044] In contrast, in the optical fiber ribbon 1A of this example, the tear stress of the first peak PA1, which is the maximum tear stress, is 0.01 N or more, so even if a small force of less than 0.01 N acts on the connecting portion 21a, the connecting portion 21a will not tear. Furthermore, because the tear stress of the second peak PA2 is 50% or more of the tear stress of the first peak PA1, even if a relatively large tear force is applied to the connecting portion 21a and a tear is formed in part of the connecting portion 21a, the tear in the connecting portion 21a will not expand unless a relatively large tear force is applied again. Therefore, the optical fiber 11 is less likely to come apart, and the optical fiber ribbon 1A is easy to handle, making it easier to fusion-splice the optical fiber ribbon 1A all at once.

[0045] The elastic modulus of the connecting portion 21a in this example is 1 GPa or more. This prevents the connecting portion 21a from being broken by a small external force. Furthermore, the elastic modulus of the connecting portion 21a is 5 GPa or less. This reduces transmission loss due to lateral pressure on the optical fiber ribbon 1A at low temperatures.

[0046] The tensile breaking strength of the connecting portion 21a in this example is 20 MPa or more. Since the connecting portion 21a will not break even with a small force, the optical fiber 11 is less likely to come apart, improving the handleability of the optical fiber ribbon 1A.

[0047] In the optical fiber ribbon 1A of this example, a first length LA1 of the connecting portion 21a torn in the longitudinal direction when a force equivalent to the tearing stress of the first peak PA1 acts on the connecting portion 21a is the same as a second length LA2 of the connecting portion 21a torn in the longitudinal direction when a force equivalent to the tearing stress of the second peak PA2 acts on the connecting portion 21a. In other words, the connecting portion 21a of the optical fiber ribbon 1A is torn at any desired length. In other words, the connecting portion 21a is not torn in its entirety at once, so the optical fiber 11 is less likely to come apart, and deterioration in the handleability of the optical fiber ribbon 1A can be suppressed.

[0048] The tear stress of the connecting portion 21a is measured as follows. Fig. 5 is a schematic diagram showing a method for measuring the tear stress of the connecting portion 21a. As shown in Fig. 5, of the optical fiber ribbon 1A, the outer coating portions 21b of six optical fibers 11A to 11F are held by a first holding portion G1, and the outer coating portions 21b of six optical fibers 11G to 11L are held by a second holding portion G2. In the up-down direction perpendicular to the longitudinal direction and the width direction, the first holding portion G1 is disposed above the optical fiber ribbon 1A, and the second holding portion G2 is disposed below the optical fiber ribbon 1A.

[0049] A connecting portion 21a is formed between the optical fiber 11F and the optical fiber 11G. The length La of the connecting portion 21a in the longitudinal direction is approximately 40 mm to 90 mm. In the initial state, the first gripping portion G1 and the second gripping portion G2 are positioned apart from each other in the vertical direction so that one end of the connecting portion 21a is positioned at the position where the optical fiber 11F begins to bend upward by the first gripping portion G1 and the position where the optical fiber 11G begins to bend downward by the second gripping portion G2. In other words, in the initial state, the connecting portion 21a connects the optical fiber 11F and the optical fiber 11G over their entire length. The initial distance D between the first gripping portion G1 and the second gripping portion G2 in the vertical direction is 70 mm. The measured length of the optical fiber ribbon 1A in the longitudinal direction is 150 mm.

[0050] In this measurement method, the second gripping portion G2 is fixed, and the first gripping portion G1 is moved upward so as to move away from the second gripping portion G2. The moving speed of the first gripping portion G1 is 200 mm / min. As the first gripping portion G1 moves upward, the optical fiber 11F held by the first gripping portion G1 moves away from the optical fiber 11G held by the second gripping portion G2. Thus, the connecting portion 21a connecting the optical fiber 11F and the optical fiber 11G begins to tear. A detector (not shown) installed directly or indirectly on the first gripping portion G1 measures the force applied to the first gripping portion G1 when the connecting portion 21a is torn as the tearing stress of the connecting portion 21a. At the same time, the length of the torn connecting portion 21a is measured. In this measurement method, the second gripping portion G2 is fixed and the first gripping portion G1 is moved, but the first gripping portion G1 may be fixed and the second gripping portion G2 may be moved.

[0051] Second Embodiment Next, an optical fiber ribbon 1B according to a second embodiment will be described with reference to Fig. 6 to Fig. 8. Note that the same components as those of the optical fiber ribbon 1A according to the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted.

[0052] 6 shows a cross-sectional view of the optical fiber ribbon 1B. The optical fiber ribbon 1B differs from the optical fiber ribbon 1A according to the first embodiment in that adjacent optical fibers are alternately arranged one fiber at a time between being spaced apart by a fixed distance and being connected to each other.

[0053] In the optical fiber ribbon 1B of this example, the connecting portions 21a are provided between the optical fiber core wires 11A and 11B, between 11C and 11D, between 11E and 11F, between 11G and 11H, between 11I and 11J, and between 11K and 11L. The non-connecting portions 23 are provided between the optical fiber core wires 11B and 11C, between 11D and 11E, between 11F and 11G, between 11H and 11I, and between 11J and 11K. The elastic modulus of the connecting portions 21a of this example is, for example, 2.6 GPa.

[0054] FIG. 7 is a plan view of the optical fiber ribbon 1B. As shown in FIG. 7, a plurality of connecting portions 21a are provided intermittently in the longitudinal direction of the plurality of optical fiber core wires 11. Similarly, a plurality of non-connecting portions 23 are also formed intermittently in the longitudinal direction of the plurality of optical fiber core wires 11. The optical fiber ribbon 1B is an intermittently connected optical fiber ribbon in which connecting portions 21a and non-connecting portions 23 are provided intermittently in the longitudinal direction for each optical fiber core wire. The other configurations are the same as those of the optical fiber ribbon 1A. Note that the plan view of FIG. 7 shows a state in which the non-connecting portions 23 are opened in the parallel direction of the optical fiber core wires 11. FIG. 6 is a cross-sectional view taken along the line B-B of the optical fiber ribbon 1B shown in FIG. 7.

[0055] 8 is a graph showing the relationship between the tearing stress of the connecting portion 21a of the optical fiber ribbon 1B and the tearing length when the connecting portion 21a is torn. As shown in FIG. 8, the connecting portion 21a of this example is also configured so that the tearing stress has multiple peaks when torn in the longitudinal direction. The tearing stress of the connecting portion 21a has a first peak PB1 indicating the maximum tearing stress and a second peak PB2 indicating a tearing stress different from the maximum tearing stress.

[0056] The first peak PB1 has two peaks PB11 and PB12, but these are considered to be one peak here. More specifically, if the tear stress of the second peak PB12, which is located close to the first peak PB11, is within ±20% of the tear stress of the first peak PB11, the two peaks PB11 and PB12 are considered to be one peak PB1, and the tear stress of the first peak PB11 is considered to be the tear stress of the first peak PB1.

[0057] The tear stress of the first peak PB1, which is the maximum tear stress, is 0.03 N or more. In this example, the tear stress of the first peak PB1 is, for example, 0.062 N. The tear stress of the second peak PB2 is 50% or more of the tear stress of the first peak PB1. In this example, the tear stress of the second peak PB2 is, for example, 0.051 N, which is 83% of the tear stress of the first peak PB1.

[0058] In this way, in this example, the tear stress of the first peak PB1 is 0.03 N or more, which enhances the effect of making the connecting portion 21a less likely to tear.

[0059] (Modification) Although the optical fiber ribbons 1A and 1B each include a connecting resin 21 that coats the outer periphery of the optical fiber 11, the optical fiber ribbon 1C does not necessarily have to include a connecting resin 21 that coats the outer periphery. An optical fiber ribbon 1C according to a modification will be described with reference to Fig. 9. Note that the same components as those in the optical fiber ribbons 1A and 1B according to the first embodiment are designated by the same reference numerals, and description thereof will be omitted.

[0060] 9 shows a cross-sectional view of the optical fiber ribbon 1C. The optical fiber ribbon 1C differs from the optical fiber ribbon 1A in that adjacent optical fibers are alternately arranged, one fiber at a time, with a fixed distance between them and the other fiber connected to them. The optical fiber ribbon 1C also differs from the optical fiber ribbons 1A and 1B in that it does not have an outer coating 21b that covers the outer periphery of each optical fiber 11. Some adjacent optical fibers are connected to each other by a connecting portion 21a.

[0061] In the optical fiber ribbon 1C of this example, the connecting portions 21a are provided between the optical fiber core wires 11A and 11B, between 11C and 11D, between 11E and 11F, between 11G and 11H, between 11I and 11J, and between 11K and 11L. The connecting portions 21a are formed so that there are no gaps between any two adjacent optical fiber core wires. Furthermore, the non-connecting portions 23 are provided between the optical fiber core wires 11B and 11C, between 11D and 11E, between 11F and 11G, between 11H and 11I, and between 11J and 11K.

[0062] Such an optical fiber ribbon 1C has the same effects as the optical fiber ribbons 1A and 1B. In particular, the joint portion 21a of the optical fiber ribbon 1C is also configured so that the tear stress has multiple peaks when torn in the longitudinal direction, and the optical fiber ribbon 1C can suppress deterioration in its handleability.

[0063] Although the present disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present disclosure.

[0064] In the optical fiber ribbon of this example, the connecting portion 21 a and the non-connecting portion 23 are formed by providing the connecting resin 21 in a portion in the longitudinal direction, but the forming method is not limited to this. The non-connecting portion 23 may also be formed by providing a tape coating that integrally covers each optical fiber 11 and cutting a portion in the longitudinal direction between the optical fiber 11.

[0065] 1A, 1B, 1C, 1Z: optical fiber ribbon 11, 11A, 11B, 11C, 11D, 11E, 11F, 11G, 11H, 11I, 11J, 11K, 11L: optical fiber core 12: glass fiber 13: inner coating layer 14: outer coating layer 21: connecting resin 21a: connecting portion 21b: outer coating portion 23: non-connecting portion D: initial distance LA1, LZ1: first length LA2: second length LA3: third length LA4: fourth length LA5: fifth length PA1, PB1, PZ1: first peak PA2, PB2, PZ2: second peak PA3: third peak PA4: fourth peak PA5: fifth peak PB11, PB12: peak R: outer diameter

Claims

1. A plurality of optical fiber cores arranged in parallel in a direction perpendicular to the longitudinal direction, In at least a portion of the optical fiber cores, a plurality of connecting portions for connecting adjacent optical fiber cores are intermittently provided in the longitudinal direction, One of the plurality of connecting portions is configured such that a tear stress when torn in the longitudinal direction has a plurality of peaks, The tear stress has a first peak indicating a maximum tear stress and a second peak indicating a tear stress different from the maximum tear stress, The first peak tear stress is 0.01 N or more; The second peak tear stress is 50% or more of the first peak tear stress.

2. 2. The optical fiber ribbon according to claim 1, wherein the elastic modulus of the one connecting portion is equal to or greater than 1 GPa and equal to or less than 5 GPa.

3. 2. The optical fiber ribbon according to claim 1, wherein the tensile strength of the one joint portion is 20 MPa or more.

4. 2. The optical fiber ribbon according to claim 1, wherein the first peak tear stress is 0.03 N or more.

5. 2. The optical fiber ribbon according to claim 1, wherein a first length of the one connection portion that is torn in the longitudinal direction when a force equivalent to the first peak tearing stress acts on the one connection portion is the same as a second length of the one connection portion that is torn in the longitudinal direction when a force equivalent to the second peak tearing stress acts on the one connection portion.