Optical fiber ribbon core and optical cable

Abstract

An optical fiber ribbon core (10) comprises: a plurality of optical fibers (20) arranged in parallel; and a connection part (11) for connecting the plurality of optical fibers (20). In the optical fiber ribbon core (10), the elastic modulus of a tape-forming resin composition forming the connection part (11) is 50-300 MPa. When the optical fiber ribbon core is bent, a gap is generated between the tape-forming resin composition and each of the plurality of optical fibers (20).

Description

Optical fiber ribbon and optical cable

[0001] The present disclosure relates to an optical fiber ribbon and an optical cable.

[0002] Patent Documents 1 to 3 disclose optical fiber ribbons in which a plurality of optical fibers are arranged in parallel and integrated with a resin.

[0003] JP 2005-222080 A JP 2005-165363 A JP 2000-155248 A

[0004] The optical fiber ribbon according to an embodiment of the present disclosure includes a plurality of optical fibers arranged in parallel, and a connecting portion connecting the plurality of optical fibers. The connecting portion is formed of a tape-formed resin composition having an elastic modulus of 50 MPa or more and 300 MPa or less, and when bent, a gap is generated between each of the plurality of optical fibers and the tape-formed resin composition.

[0005] Fig. 1 is a cross-sectional view showing an optical cable according to an embodiment. Fig. 2 is a cross-sectional view showing an example of an optical fiber ribbon included in the optical cable shown in Fig. 1. Fig. 3 is a plan view showing an example of an optical fiber ribbon included in the optical cable shown in Fig. 1. Fig. 4 is a schematic diagram showing a bent optical fiber ribbon. Fig. 5 is a schematic diagram showing an enlarged view of the center of the optical fiber ribbon shown in Fig. 4.

[0006] [Problem to be Solved by the Present Disclosure] Optical cables that house a large number of optical fiber ribbons, each of which integrates multiple optical fibers, are being considered. In such optical cables, as the density increases, distortion such as bending occurs in each of the optical fibers built in, resulting in microvent loss. As a result, transmission loss in each optical fiber increases. Therefore, there is a demand for optical fiber ribbons and optical cables that can prevent the increase in transmission loss.

[0007] Effect of the Present Disclosure According to the present disclosure, it is possible to provide an optical fiber ribbon and an optical cable that prevent an increase in transmission loss in each optical fiber.

[0008] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. [1] An optical fiber ribbon according to one embodiment of the present disclosure includes a plurality of optical fibers arranged in parallel and a connecting portion connecting the plurality of optical fibers. The elastic modulus of the tape-formed resin composition forming the connecting portion is 50 MPa or more and 300 MPa or less, and when the tape-formed resin composition is bent, a gap is generated between each of the plurality of optical fibers and the tape-formed resin composition.

[0009] In the optical fiber ribbon described above in [1], the elastic modulus of the tape-formed resin composition forming the connecting portion connecting the multiple optical fibers is 50 MPa or more and 300 MPa or less, and gaps are formed between the optical fibers and the tape-formed resin composition when the ribbon is bent. In this case, since the connecting portion is formed from a material softer than conventional materials, gaps are formed between the optical fibers and the connecting portion when the ribbon is bent. Due to such gaps, even if the optical fiber ribbon is bent in the width direction when being cabled, the optical fibers move relative to the connecting portion, and fiber distortion due to bending is unlikely to occur. Therefore, this optical fiber ribbon can prevent an increase in transmission loss due to the occurrence of microvents. The "elastic modulus" referred to here means Young's modulus at 23°C (room temperature). Note that if the elastic modulus of the tape-formed resin composition is less than 50 MPa, the resin is easily deformed, which deteriorates the lateral pressure resistance of the optical fiber and increases loss.

[0010] [2] In the optical fiber ribbon described in [1] above, the tape-formed resin composition may contain a lubricant. In this case, the tape-formed resin composition has low friction, and the adhesion between the surface of the optical fiber and the tape-formed resin composition of the joint portion is reduced. As a result, even if the optical fiber ribbon or each optical fiber is bent, a portion between the optical fiber and the joint portion will peel off, making it easier to release bending strain like a single-core cable. Therefore, this optical fiber ribbon further facilitates preventing an increase in transmission loss.

[0011] [3] In the optical fiber ribbon of [2] above, the lubricant content may be 0.5 wt % or more and 5 wt % or less. If the lubricant content is less than 0.5 wt %, gaps are less likely to form between the optical fiber and the tape-forming resin composition. On the other hand, if the lubricant content is greater than 5 wt %, the optical fiber core wire is more likely to peel from the tape-forming resin composition. In this way, by adjusting the lubricant content, peeling between the optical fiber and the connecting portion can be promoted depending on the degree of bending, and an increase in transmission loss can be more reliably prevented.

[0012] [4] In the optical fiber ribbon according to any one of [1] to [3] above, the connection portion may intermittently connect a plurality of optical fibers along the longitudinal direction of the optical fiber ribbon. According to the inventor's investigations, when the optical fiber ribbon is bent in the width direction (see, for example, FIGS. 4 and 5 ), bending strain is applied to each optical fiber, which may cause the optical fibers to have a meandering shape at the end of the optical fiber ribbon. However, as in the optical fiber ribbon according to this embodiment, intermittent connection can reduce bending strain in the longitudinal direction. Therefore, with this optical fiber ribbon, an increase in transmission loss can be prevented even when it is cabled.

[0013] [5] In the optical fiber ribbon according to any one of [1] to [4] above, the center-to-center pitch between adjacent optical fibers in the plurality of optical fibers may be larger than the fiber diameter of each of the plurality of optical fibers in a cross section perpendicular to the longitudinal direction of the optical fiber ribbon. In this case, a portion of the tape-formed resin composition will enter between adjacent optical fibers, making the optical fiber ribbon easier to bend. Therefore, with this optical fiber ribbon, an increase in transmission loss can be prevented even when the optical fiber ribbon is formed into a cable.

[0014] [6] In the optical fiber ribbon according to any one of [1] to [5] above, each of the plurality of optical fibers may have a plurality of cores and a cladding that is in contact with and surrounds the plurality of cores. In this case, in an optical fiber ribbon using a multicore fiber including a plurality of cores, an increase in transmission loss when cabled can be prevented. Furthermore, when fusion splicing the multicore fiber, each optical fiber can be easily moved even if it is coated with a connecting resin, making alignment easier.

[0015] [7] An optical cable according to an embodiment of the present disclosure includes a plurality of optical fiber ribbons according to any one of [1] to [6] above. In this case, as described above, an optical cable can be provided in which an increase in transmission loss of each optical fiber is prevented.

[0016] [8] In the optical cable of the above [7], ２ The core density, which indicates the number of optical fiber wirings per ２ In this case, it is possible to provide an optical cable in which optical fibers are packed at a high density.

[0017] [9] In the optical cable of [7] or [8], the transmission loss in each of the plurality of optical fibers when transmitting light with a wavelength of 1550 nm may be 0.22 dB / km or less. In this case, an increase in the transmission loss in each optical fiber can be prevented.

[0018]

[10] In the optical cable of any one of [7] to [9] above, the transmission loss in each of the plurality of optical fibers when transmitting light with a wavelength of 1625 nm may be 0.25 dB / km or less. In this case, the optical cable can be one in which an increase in the transmission loss in each optical fiber is prevented.

[0019] [Details of the embodiments of the present disclosure] Specific examples of optical fiber ribbons and optical cables according to the embodiments of the present disclosure will be described below with reference to the drawings. In the following description, the same elements or elements having the same functions will be designated by the same reference numerals, and duplicated explanations will be omitted. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0020] An optical cable according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing an optical cable according to one embodiment. As shown in Fig. 1, the optical cable 1 includes a water-absorbing tape 2, a cable jacket 3, a tensile strength member 4, a tear cord 5, and a plurality of optical fiber ribbons 10. The optical cable 1 is a so-called slotless optical cable, and, for example, a plurality of optical fiber ribbons 10 are SZ-twisted in the longitudinal direction. The number of optical fiber ribbons 10 housed in the optical cable 1 (cable jacket 3) is not particularly limited, but may be, for example, 24 or 36, and they are arranged at high density. As an example, the optical cable 1 may have a 1 mm ２ The core density, which indicates the number of optical fibers in the optical fiber ribbon 10, is 5 cores / mm ２ That's all.

[0021] The water-absorbing tape 2 is wound, for example, vertically or horizontally, around the entire circumference of the plurality of optical fiber ribbons 10. The water-absorbing tape 2 is made of, for example, a base fabric made of polyester or the like to which water-absorbing powder is attached. This gives the water-absorbing tape 2 water-absorbing properties.

[0022] The cable jacket 3 is provided so as to cover the water absorption tape 2 (the plurality of optical fiber ribbons 10). The cable jacket 3 is made of a resin such as polyvinyl chloride (PVC) or polyethylene (PE). The cable jacket 3 is formed by extrusion molding the resin onto the plurality of optical fiber ribbons 10 around which the water absorption tape 2 is wound.

[0023] The strength members 4 are embedded inside the cable jacket 3. The strength members 4 are made of fiber-reinforced plastic (FRP), such as aramid FRP, glass FRP, or carbon FRP. The strength members 4 may also be made of a liquid crystal polymer. In the example shown in FIG. 1 , a pair of strength members 4, each having a circular cross section, are provided inside the cable jacket 3.

[0024] The tear cords 5 are used to tear the cable jacket 3 and are embedded in the cable jacket 3 along the longitudinal direction of the optical cable 1. In the example shown in Fig. 1, a pair of tear cords 5 are provided. Each tear cord 5 is provided facing each other at approximately the middle position of a pair of tensile members 4. By pulling out the tear cords 5, the cable jacket 3 can be torn in the longitudinal direction, and each optical fiber ribbon 10 can be taken out. The tear cords 5 are made of, for example, a tensile-resistant plastic material (e.g., polyester).

[0025] FIG. 2 shows a state in which the central axes C of the optical fibers 20 included in the optical fiber ribbon 10 are spread out along the ribbon width direction L1. That is, FIG. 2 shows the optical fiber ribbon 10 in a flat state along the ribbon width direction L1. When the optical fiber ribbon 10 is housed in the optical cable 1 as shown in FIG. 1 , it is bent (see, for example, FIGS. 4 and 5 ). FIG. 3 is a plan view of the optical fiber ribbon 10 along the longitudinal direction L2. As shown in FIGS. 2 and 3 , the optical fiber ribbon 10 includes a plurality of optical fibers 20 arranged in parallel in the ribbon width direction L1 (horizontal direction). The plurality of optical fibers 20 are connected to each other and held together by connecting portions 11 formed from a tape-formed resin composition. In the optical fiber ribbon 10, the center pitch P (the distance between the central axes C) between adjacent optical fibers 20 may be greater than the fiber diameter D (outer diameter), e.g., 200 μm, of each optical fiber 20 in a cross section ( FIG. 2 ) perpendicular to the longitudinal direction L2 of the optical fiber ribbon 10. 2, the number of optical fibers 20 included in one optical fiber ribbon 10 is 12, but is not limited to this and may be, for example, 8 or 16. The optical fiber ribbon 10 extends along a longitudinal direction L2 as shown in FIG.

[0026] As shown in FIG. 2 , each of the optical fibers 20 includes a glass fiber 21 and a resin coating layer 25 that contacts and surrounds the glass fiber 21. The optical fiber 20 has a central axis C and extends along the central axis C. The glass fiber 21 includes a plurality of cores 22 and a cladding 23 that contacts and surrounds the plurality of cores 22 and has a refractive index lower than that of the plurality of cores 22. Both the cores 22 and the cladding 23 are formed of glass. In the example shown in FIG. 2 , the glass fiber 21 includes four cores 22, but the number of cores 22 is not limited to this. The number of cores 22 included in the glass fiber 21 may be one or more and may be more than four. The outer diameter of the glass fiber 21 is, for example, 125 μm, and the core diameter D (outer diameter) of the optical fiber 20 may be, for example, 165 μm, 180 μm, 200 μm, 220 μm, or 250 μm. The glass fiber 21 is protected from the external environment (for example, lateral pressure) by the resin coating layer 25 .

[0027] The resin coating layer 25 includes a primary resin layer and a secondary resin layer that contacts and surrounds the primary resin layer. The primary resin layer is formed by curing an ultraviolet-curable resin composition containing a photopolymerizable compound, a photopolymerization initiator, and a silane coupling agent with ultraviolet light. Examples of the photopolymerizable compound include urethane (meth)acrylate and epoxy (meth)acrylate. The primary resin layer has a lower modulus of elasticity (Young's modulus) than the secondary resin layer and is softer than the secondary resin layer. For example, the Young's modulus of the primary resin layer at 23°C is 0.1 MPa or more and 5 MPa or less. This provides the optical fiber 20 with lateral pressure resistance, thereby suppressing an increase in transmission loss in the optical fiber 20 even when lateral pressure is applied.

[0028] The secondary resin layer is formed by curing a resin composition containing urethane (meth)acrylate, a monomer, and a photopolymerization initiator with ultraviolet light. The secondary resin layer has a higher elasticity (Young's modulus) than the primary resin layer, and is harder than the primary resin layer. For example, the Young's modulus of the secondary resin layer at 23°C is 1200 MPa or more and 2800 MPa or less. The thickness of each of the primary resin layer and the secondary resin layer is, for example, 5 μm or more and 50 μm or less.

[0029] In the optical fiber ribbon 10, the material of the resin composition forming the connecting portion 11 connecting the plurality of optical fibers 20 to each other is adjusted so that the Young's modulus (elastic modulus) at 23°C is 300 MPa or less. Specifically, a tape-forming resin with a low Young's modulus is used as the main component to reduce the Young's modulus of the connecting portion 11. The Young's modulus at 23°C of the resin composition forming the connecting portion 11 may be 250 MPa or less, 240 MPa or less, 200 MPa or less, 150 MPa or less, or 125 MPa or less. The Young's modulus at 23°C of the resin composition forming the connecting portion 11 may be 50 MPa or more, 75 MPa or more, or 100 MPa or more. For example, a urethane acrylate resin or the like can be used as the tape-forming resin having such a Young's modulus. Note that, when the tape-forming resin is a curable resin, the Young's modulus of the connecting portion 11 is the value after curing by UV or the like.

[0030] The Young's modulus at 23°C of the resin composition forming the coupling portion 11 may be lower than that of the secondary resin layer of the resin coating layer 25 of the optical fiber 20, or may be softer than the secondary resin layer. On the other hand, the Young's modulus at 23°C of the resin composition forming the coupling portion 11 may be higher than that of the primary resin layer of the resin coating layer 25 of the optical fiber 20, or may be harder than the primary resin layer. The coupling portion 11 is formed so as to cover the secondary resin layer of the resin coating layer 25.

[0031] The tensile strength of the resin composition forming the connecting portion 11 may be 30 MPa or less, or may be 20 MPa or less. The breaking elongation of the resin composition forming the connecting portion 11 may be 20% or more, or may be 40% or more.

[0032] A lubricant may be added to the resin composition forming the connecting portion 11. For example, a silicon-based lubricant may be used as the added lubricant. The content of the lubricant in the resin composition forming the connecting portion 11 may be 0.5 wt % or more and 5 wt % or less.

[0033] As shown in FIG. 3 , the optical fiber ribbon 10 may have connection regions 15, in which adjacent optical fibers 20 are connected, and non-connection regions 16, in which adjacent optical fibers 20 are not connected, intermittently provided along the longitudinal direction L2. In the connection regions 15, the optical fibers 20 are connected to each other using an adhesive or the like. In the example shown in FIG. 3 , a pair of optical fibers 20 are connected to each other in the connection regions 15, and are not connected to each other (i.e., are separated) in the non-connection regions 16. Such an optical fiber ribbon 10 is a so-called intermittently bonded fiber ribbon. By forming the optical fiber ribbon 10 as an intermittently bonded fiber ribbon, the optical fiber ribbon 10 can be easily deformed (e.g., rolled up) when housed within the cable jacket 3 as shown in FIG. 1 . Furthermore, when fusion splicing the optical fibers 20 of the optical cable 1, each optical fiber 20 can be easily separated.

[0034] [Experimental Example] Here, the increase in transmission loss when optical fiber ribbons 10 having the above-described structure are tape-assembled into an optical cable 1 is compared and evaluated for the cases where the Young's modulus of the connecting portion 11 is changed and where a lubricant is added to the connecting portion 11. In this experiment, four samples, Experimental Example 1, Experimental Example 2, Experimental Example 3, and Experimental Example 4, were prepared. The transmission loss when light having a wavelength of 1550 nm (1.55 μm) is passed through the optical fiber was measured as the cabling loss and compared for each Experimental Example. In Experimental Example 1 and Experimental Example 2, the connecting portion 11 was formed using a resin composition having a Young's modulus of 910 MPa at 23°C. In Experimental Example 3, the connecting portion 11 was formed using a resin composition having a Young's modulus of 240 MPa. In Experimental Example 4, the connecting portion 11 was formed using a resin composition having a Young's modulus of 127 MPa. Furthermore, in Experimental Examples 2 to 4, a lubricant was added to the resin composition forming the connecting portion 11. The lubricant added was silicone. The amount of lubricant added was 2 wt %.

[0035] The test conditions were as follows: - Wire diameter of the optical fiber 20 (outer diameter of the optical fiber): 250 μm - Shape of the optical fiber ribbon 10: intermittently bonded fiber ribbon - Number of optical fibers 20 included in the optical fiber ribbon 10: 12 (12 cores) - Number of optical fibers included in the optical cable 1: 432 (432 cores) - Outer diameter of the optical cable 1: 14.5 mm - Inner diameter of the optical cable 1 (cable jacket 3): 9 mm

[0036] Table 1 below shows a summary of the test conditions and test results.

[0037] As shown in Table 1, by setting the Young's modulus at 23°C of the resin composition used in the connecting portion 11 to 300 MPa or less, the cable loss at a wavelength of 1.55 μm can be set to 0.21 dB / km or less, and it was confirmed that an increase in transmission loss can be prevented. Furthermore, a comparison between Experimental Examples 3 and 4 confirmed that an increase in transmission loss can be further prevented by lowering the Young's modulus of the resin composition used in the connecting portion 11 (for example, to 200 MPa or less or 150 MPa or less). Furthermore, a comparison between Experimental Examples 1 and 2 confirmed that the use of a lubricant can prevent an increase in transmission loss.

[0038] 4 and 5, it was confirmed that when the optical fiber ribbon 10 of Experimental Example 3 or 4 was bent, a portion of the area between the optical fiber 20 and the connecting portion 11 was peeled off, forming a gap S. It was considered that the presence of such a gap S reduced the bending loss of the optical fiber 20.

[0039] As described above, in the optical cable 1 and optical fiber ribbon 10 according to the present embodiment, the elastic modulus of the tape-formed resin composition forming the connecting portion 11 connecting the plurality of optical fibers 20 is 50 MPa or more and 300 MPa or less, and when bent, a gap S is formed between each of the plurality of optical fibers 20 and the tape-formed resin composition. Because the connecting portion 11 is formed from a material softer than conventional materials, a gap S is formed between the optical fibers 20 and the connecting portion 11 when the optical fiber ribbon 10 is bent during cabling. Due to this gap S, even if the optical fiber ribbon 10 is bent in the width direction during cabling, for example, the optical fibers 20 move relative to the connecting portion 11, making it difficult for the fibers to be distorted by bending. Therefore, the optical cable 1 and optical fiber ribbon 10 can prevent an increase in transmission loss due to the occurrence of microvents. Note that if the elastic modulus of the tape-formed resin composition is less than 50 MPa, the resin is more likely to deform, which deteriorates the lateral pressure resistance of the optical fiber and increases loss. However, the optical cable 1 and optical fiber ribbon 10 according to the present embodiment can also prevent such an increase in loss.

[0040] In the optical cable 1 and optical fiber ribbon 10 according to this embodiment, the tape-formed resin composition forming the connecting portion 11 contains a lubricant. This reduces the friction of the tape-formed resin composition, thereby reducing the adhesion between the surface of the optical fiber 20 and the tape-formed resin composition of the connecting portion 11. As a result, even if the optical fiber ribbon 10 or each optical fiber 20 is bent, a portion of the optical fiber 20 separates from the connecting portion 11, making it easier to release bending strain like a single-core cable. Therefore, the optical cable 1 and the optical fiber ribbon 10 make it even easier to prevent an increase in transmission loss.

[0041] In the optical cable 1 according to the present embodiment, by using the optical fiber ribbon 10 having the above-described shape, the transmission loss when transmitting light having a wavelength of 1550 nm in each of the plurality of optical fibers 20 is 0.22 dB / km or less. Similarly, in this optical cable 1, the transmission loss when transmitting light having a wavelength of 1625 nm in each of the plurality of optical fibers 20 is 0.25 dB / km or less.

[0042] DESCRIPTION OF SYMBOLS 1...Optical cable 2...Water absorption tape 3...Cable jacket 4...Tensile strength member 5...Tear cord 10...Optical fiber ribbon 11...Connection portion 15...Connection region 16...Non-connection region 20...Optical fiber 21...Glass fiber 22...Core 23...Cladding 25...Resin coating layer C...Central axis D...Core diameter L1...Tape width direction L2...Longitudinal direction P...Central pitch S...Gap

Claims

1. An optical fiber ribbon comprising: a plurality of optical fibers arranged in parallel; and a connecting portion connecting the plurality of optical fibers; wherein the elastic modulus of the tape-formed resin composition forming the connecting portion is 50 MPa or more and 300 MPa or less; and when bent, a gap is generated between each of the plurality of optical fibers and the tape-formed resin composition.

2. The optical fiber ribbon according to claim 1, wherein the tape-forming resin composition contains a lubricant.

3. The optical fiber ribbon according to claim 2, wherein the content of the lubricant is 0.5 wt % or more and 5 wt % or less.

4. An optical fiber ribbon according to any one of claims 1 to 3, wherein the connecting portion intermittently connects the plurality of optical fibers along the longitudinal direction of the optical fiber ribbon.

5. An optical fiber ribbon according to any one of claims 1 to 4, wherein the center pitch between adjacent optical fibers in the plurality of optical fibers is greater than the fiber diameter of each of the plurality of optical fibers in a cross section perpendicular to the longitudinal direction of the optical fiber ribbon.

6. An optical fiber ribbon according to any one of claims 1 to 5, wherein each of the plurality of optical fibers has a plurality of cores and a cladding that contacts and surrounds the plurality of cores.

7. An optical cable comprising a plurality of optical fiber ribbons according to any one of claims 1 to 6.

8. 1 mm ２ The core density, which indicates the number of optical fibers per unit area, is 5 cores / mm. ２ The optical cable according to claim 7 , wherein:

9. An optical cable according to claim 7 or 8, wherein the transmission loss in each of said plurality of optical fibers when transmitting light with a wavelength of 1550 nm is 0.22 dB / km or less.

10. An optical cable according to any one of claims 7 to 9, wherein the transmission loss in each of the plurality of optical fibers when transmitting light with a wavelength of 1625 nm is 0.25 dB / km or less.

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