Optical fiber cable

Abstract

An optical fiber cable has: a jacket; and a core housed in the jacket and having an intermittently bonded ribbon core wire including a plurality of optical fibers and a plurality of bonding portions intermittently bonding the plurality of optical fibers in a long side direction. A concave portion and a convex portion are alternately arranged in a circumferential direction on an outer peripheral surface of the jacket, the concave portion has two connecting portions respectively connected to radially inner ends of two adjacent convex portions and a bottom surface between the two connecting portions.

Description

[0001] This application is a divisional application of Japanese Patent Application No. 201980047433.3, filed on October 9, 2019, entitled "Optical Fiber Cable". It claims priority from Japanese Patent Application No. JP2018-192706, with a priority date of October 11, 2018. Technical Field

[0002] This invention relates to optical fiber cables.

[0003] This application asserts priority based on Japanese Patent Application No. 2018-192706, filed on October 11, 2018, the contents of which are incorporated herein by reference. Background Technology

[0004] Previously, the optical fiber cable shown in Patent Document 1 was known. This optical fiber cable has a sheath and multiple optical fibers housed within the sheath. The outer circumferential surface of the sheath has alternating recesses and protrusions arranged circumferentially. In Patent Document 1, the multiple optical fibers are housed within a tube in a twisted state. Alternatively, the multiple optical fibers are co-coated with a UV-curable resin to form a cored wire.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: US Patent No. 6,963,686 Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] In the optical fiber cable of Patent Document 1, the recess is a V-shaped groove. Therefore, for example, when a circumferential force is applied to the protrusion, the stress tends to concentrate at the inner end of the groove, which can easily cause cracks in the sheath.

[0010] Furthermore, in structures where multiple optical fibers are simply twisted and housed within a tube, the fiber optic cable lacks sufficient rigidity, resulting in drawbacks in compression characteristics. On the other hand, in structures where multiple optical fibers are encased together in resin, the rigidity of the fiber optic cable can be achieved. However, encasing the fibers together in resin increases the core size, which is a drawback in terms of cable diameter reduction, and also increases the strain acting on the fiber, resulting in drawbacks in transmission loss.

[0011] The present invention was made in view of the following circumstances, and its object is to provide an optical fiber cable that improves the strength of the sheath and is advantageous in terms of compression characteristics, diameter reduction and transmission loss.

[0012] (II) Technical Solution

[0013] To address the aforementioned issues, the first aspect of the present invention relates to an optical fiber cable comprising: a sheath; and a core, which is housed within the sheath and has an intermittently bonded core wire, the intermittently bonded core wire comprising a plurality of optical fibers and a plurality of bonding portions intermittently bonding the plurality of optical fibers in the long side direction, wherein recesses and protrusions are formed on the outer peripheral surface of the sheath in an alternating circumferential arrangement, the recesses having two connecting portions respectively connected to the radially inner ends of two adjacent protrusions and a bottom surface located between the two connecting portions.

[0014] (III) Effects of the Invention

[0015] According to the above-described manner of the present invention, it is possible to provide an optical fiber cable that improves the strength of the sheath and is advantageous in terms of compression characteristics, diameter reduction, and transmission loss. Attached Figure Description

[0016] Figure 1A This is a cross-sectional view of the optical fiber cable according to this embodiment.

[0017] Figure 1B yes Figure 1A An enlarged view of part I.

[0018] Figure 2 This is a schematic diagram of an intermittently bonded cored wire.

[0019] Figure 3 This is a schematic diagram illustrating the air compression method.

[0020] Figure 4 This is a schematic diagram of the track used for air pressure testing.

[0021] Figure 5 This is a cross-sectional view of a deformed optical fiber cable.

[0022] Figure 6 This is an illustration of the cross-sectional area of ​​the concave portion.

[0023] Figure 7A This diagram illustrates the situation where the protrusion and the tensile body extend in a straight line.

[0024] Figure 7B This diagram illustrates the spiral twisting of the convex part and the tensile body.

[0025] Figure 8 This is a diagram illustrating the effect of the spiral torsion of the protrusions and tensile bodies on the bending stiffness of the optical fiber cable.

[0026] Figure 9 This is to explain as Figure 8 A graph showing the measurement angle X on the horizontal axis.

[0027] Figure 10It is a cross-sectional view of an optical fiber cable with multiple tensile strength elements arranged on the inner side of a protrusion.

[0028] Figure 11 This is a diagram illustrating the effect of the SZ-shaped torsion of the protrusion and tensile body on the bending stiffness of the optical fiber cable.

[0029] Figure 12A This is a cross-sectional view of an optical fiber cable with a low-friction material disposed on the top of the protrusion.

[0030] Figure 12B This is a cross-sectional view of an optical fiber cable in which a layer of low-friction material is disposed on the entire surface of the sheath.

[0031] Figure 12C This is a cross-sectional view of an optical fiber cable with protrusions formed by a low-friction material.

[0032] Figure 13A This is a cross-sectional view of an optical fiber cable with tear cords arranged inside some of the protrusions and tensile strength bodies arranged inside other protrusions.

[0033] Figure 13B This is a cross-sectional view of an optical fiber cable in which the protrusion with the tear cord embedded on the inside protrudes more than other protrusions.

[0034] Figure 13C This is a cross-sectional view of an optical fiber cable in which the width of the protrusion with the tear cord embedded on the inside is smaller than that of other protrusions.

[0035] Figure 13D It is a cross-sectional view of an optical fiber cable with tension elements arranged at equal intervals and tear cords arranged between the tension elements in the circumferential direction.

[0036] Figure 14A This is a cross-sectional view of an optical fiber cable, a variation of this embodiment.

[0037] Figure 14B This is a cross-sectional view of an optical fiber cable in another variation of this embodiment. Detailed Implementation

[0038] The optical fiber cable of this embodiment will now be described with reference to the accompanying drawings.

[0039] like Figure 1A As shown, the optical fiber cable 1 has a sheath 10, a core 20 housed in the sheath 10, and a plurality of tensile strength bodies 30 embedded in the sheath 10.

[0040] The core 20 has multiple optical fiber units 21 and a ferrule 22 that encloses these optical fiber units 21. Each optical fiber unit 21 has multiple optical fibers 21a and a binding member 21b for binding these optical fibers 21a.

[0041] (Direction definition)

[0042] In this embodiment, the central axis of the optical fiber cable 1 is referred to as the central axis O. Furthermore, the long side direction of the optical fiber cable 1 (the long side direction of the optical fiber 21a) is simply referred to as the long side direction. The cross section orthogonal to the long side direction is called the cross section. When viewed from the cross section... Figure 1A In this context, the direction intersecting the central axis O is called the radial direction, and the direction of rotation around the central axis O is called the circumferential direction.

[0043] Furthermore, when viewed in cross-section, if the fiber optic cable 1 is non-circular, the central axis O is located at the centroid of the fiber optic cable 1.

[0044] like Figure 2 As shown, the fiber unit 21 in this embodiment is a so-called discontinuously bonded ribbon core wire. That is, the fiber unit 21 has a plurality of optical fibers 21a and a plurality of bonding portions 21c for bonding adjacent optical fibers 21a to each other. In the discontinuously bonded ribbon core wire, if the plurality of optical fibers 21a are stretched in a direction orthogonal to the long side direction, they expand in a mesh-like (spider web-like) pattern. In detail, a certain optical fiber 21a is bonded to the adjacent optical fibers 21a on both sides at different positions in the long side direction through the bonding portions 21c. Furthermore, the adjacent optical fibers 21a are spaced apart from each other in the long side direction and bonded to each other through the bonding portions 21c.

[0045] As the adhesive part 21c, thermosetting resin or UV-curing resin can be used.

[0046] Multiple fiber units 21 are twisted together around the central axis O. The twisting method can be helical or SZ-shaped.

[0047] A compression sleeve 22 encloses multiple optical fiber units 21 and is formed in a cylindrical shape. The two circumferential ends (the first end and the second end) of the compression sleeve 22 overlap each other to form an overlapping portion 22a. In the compression sleeve 22, the portion other than the overlapping portion 22a is referred to as the non-overlapping portion 22b. The non-overlapping portion 22b is located between the first end and the second end that form the overlapping portion 22a.

[0048] The material for the sheath 22 can be non-woven fabric or plastic tape components. When the sheath 22 is made of plastic, polyethylene terephthalate, polyester, etc., can be used as the material. Furthermore, absorbent tape that imparts water-absorbing properties to the aforementioned non-woven fabric or tape components can also be used as the sheath 22. In this case, the waterproof performance of the optical fiber cable 1 can be improved. When using plastic tape components as the sheath 22, water absorption can also be imparted by coating the surface of the tape component with absorbent powder.

[0049] Multiple tensile strength elements 30 are embedded in the sheath 10 at equal intervals along the circumference. Alternatively, the intervals between the embedded tensile strength elements 30 may not be equal. The number of tensile strength elements 30 can be varied appropriately. Materials for the tensile strength elements 30 can include, for example, metal wire (steel wire, etc.), tensile fibers (aramid fibers, etc.), and FRP (Fiber Reinforced Plastics). Specific examples of FRP include KFRP using Kera fibers and PBO-FRP using PBO (poly-paraphenylenebenzobisoxazole).

[0050] In addition to the tensile body 30, for example, a tear rope or the like can be embedded in the sheath 10.

[0051] The sheath 10 is formed into a cylindrical shape centered on the central axis O. The sheath 10 can be made of polyethylene (PE), polypropylene (PP), ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate copolymer (EVA), ethylene-propylene copolymer (EP), polyvinyl chloride (PVC), or other polyolefin (PO) resins.

[0052] A plurality of recesses 12 and protrusions 11 are formed on the outer peripheral surface of the sheath 10. The recesses 12 and protrusions 11 are arranged alternately in the circumferential direction. In this way, the outer peripheral surface of the sheath 10 has a concave-convex shape. The recesses 12 and protrusions 11 extend along the long side direction.

[0053] The protrusion 11 is positioned circumferentially at the same location as the tension-resistant body 30. In other words, when viewed in cross-section, the protrusion 11 lies on a straight line extending from the central axis O toward the center of the tension-resistant body 30. The recess 12 is positioned circumferentially at a different location than the tension-resistant body 30. In other words, when viewed in cross-section, the recess 12 does not lie on a straight line extending from the central axis O toward the center of the tension-resistant body 30.

[0054] The recess 12 has two connecting portions 12a and a bottom surface 12b. The connecting portions 12a are connected to the radially inner ends of adjacent protrusions 11 in the circumferential direction. The bottom surface 12b is located between the two connecting portions 12a. Figure 1B As shown, the connecting part 12a is formed as a curved surface that protrudes radially inward.

[0055] The bottom surface 12b is a curved surface centered on the central axis O, and when viewed in cross-section, it is an arc centered on the central axis O. However, the shape of the bottom surface 12b is not limited to a curved surface centered on the central axis O. For example, the bottom surface 12b can also be a shape that connects the two connecting parts 12a in a straight line.

[0056] As described above, the recess 12 has two connecting portions 12a and a bottom surface 12b located between these connecting portions 12a. Therefore, even if a circumferential force is applied to the protrusion 11, the stress is unlikely to concentrate in the recess 12. Thus, cracking and other defects in the recess 12 are suppressed, and the strength of the sheath 10 is improved.

[0057] Furthermore, the core 20 of this embodiment has an intermittently bonded core wire (fiber unit 21), which includes a plurality of optical fibers 21a and a plurality of adhesive portions 21c that intermittently bond the plurality of optical fibers 21a in the long side direction. Therefore, compared to the case where multiple unbonded optical fibers are simply stranded, the rigidity of the optical fiber cable 1 can be ensured, resulting in a structure that is beneficial for bending resistance and pressure delivery characteristics. Furthermore, compared to the case where multiple optical fibers are encapsulated together with resin, the diameter of the optical fiber cable 1 can be reduced, and the increase in transmission loss can be suppressed.

[0058] Furthermore, the connecting portion 12a is formed as a curved surface that protrudes radially inward. This allows for more reliable suppression of stress concentration at the connecting portion 12a and further enhances the strength of the sheath 10.

[0059] Furthermore, since the compression sleeve 22 has an overlapping portion 22a, contact between the structural components inside the compression sleeve 22 and the sheath 10 can be suppressed. This prevents the optical fiber 21a from entering the softened sheath 10 during extrusion molding, thus preventing instability in the excess length of the optical fiber 21a. Additionally, it also prevents the optical fiber 21a from being sandwiched between the compression sleeve 22 and the sheath 10, thus preventing increased transmission loss.

[0060] Furthermore, the radius of curvature of the outer peripheral surface of the protrusion 11 can be smaller than the radius of the sheath 10 (the radius of the fiber optic cable 1). According to this structure, the contact area between the protrusion 11 and the microchannel (described in detail later) becomes smaller. Therefore, the operability of inserting the fiber optic cable 1 into the microchannel can be improved. In this embodiment, the "radius of the sheath 10" refers to the maximum value of the distance between the outer peripheral surface of the protrusion 11 and the central axis O. Since the maximum value varies depending on each protrusion 11, the average value of each maximum value is set as the "radius of the sheath 10".

[0061] Next, a specific embodiment of the optical fiber cable 1 of this embodiment will be described. However, the present invention is not limited to the following embodiments.

[0062] (Maximum compressive stress)

[0063] In this embodiment, as Figure 3As shown, the operability of inserting an optical fiber cable into a microduct D via air compression was studied. The microduct D refers to a pipe pre-installed underground, etc. In air compression, a seal S is installed at the end of the microduct D, and the optical fiber cable is inserted into the microduct D through the opening of the seal S. Furthermore, a pump P is connected to the seal S, allowing air to flow from the seal S into the microduct D. This creates an air layer between the optical fiber cable and the microduct D, thereby reducing friction.

[0064] Here, when laying fiber optic cables, sometimes the fiber optic cables are inserted into micro-ducts D over long distances, such as 2000m or more. When inserting fiber optic cables into micro-ducts D over such long distances, it is necessary to efficiently transmit force from the upstream side (-X side) to the downstream side (+X side) along the long side of the fiber optic cable.

[0065] The inventors of this application conducted in-depth research and found that, in order to properly transmit force from the upstream side to the downstream side of the optical fiber cable, it is preferable to keep the compressive strength (maximum compressive stress) of the optical fiber cable within a specified range.

[0066] The following describes the results of confirming the workability of air compression using several fiber optic cables with different compression strengths (Examples 1-1 to 1-7). Additionally, Example 1-8 is a loose-tube type fiber optic cable. Details of Example 1-8 will be described below.

[0067] Table 1

[0068]

[0069]

[0070] The results of the air pressure test for each fiber optic cable are shown in the "Air Pressure Test" column of Table 1. More specifically, each fiber optic cable was air pressure tested in a microduct D. A result of 2000m pressure test was considered good (OK), and a result of 2000m pressure test was considered insufficient (NG).

[0071] In addition, the micro-pipe D used in the air pressure test is Figure 4 The figure-eight shape shown. The inner width of the bend is 18.33m. Figure 4 The figure-eight shape shown has a total length of 125m for one lap. Although the illustration is omitted, by repeating this figure-eight shape 16 times consecutively, a track with a total length of 2000m is formed (illustration omitted). Pump P (refer to...) Figure 3 ) is positioned in the roughly straight section of the figure-eight shape, in Figure 4 In the direction indicated by arrow F, fiber optic cable is pressurized into the micro-channel D.

[0072] The “compressive strength” in Table 1 refers to the maximum compressive load (N) measured when a sample of length L' (mm) in Table 1 is compressed using a compression testing machine for each test example. This maximum compressive load is then divided by the cross-sectional area a (mm²). 2 The value is obtained from "). In addition, the calculation of compressive strength is carried out in accordance with JIS K7118:2011.

[0073] More specifically, a general-purpose universal testing machine was used as the compression testing machine. Each sample was mounted on the compression testing machine with both ends embedded in a metal cylinder. That is, the two ends of the sample were fixed as the boundary condition during the compression test. Each sample was compressed at a rate of 1 mm / min along its long side. The compressive load at which each sample was about to buckle was then measured as the "maximum compressive load."

[0074] In addition, the sample length L' of each sample is set to keep the value of d / L' constant (0.8).

[0075] As shown in Table 1, the compressive strength is 11.6 N / mm. 2 In the following test examples (1-1, 1-2), the compression test results were insufficient. This is because the compressive strength of the fiber optic cable was insufficient, causing buckling of the cable during its journey within the micro-duct D. If the fiber optic cable buckles within the micro-duct D, the force transmitted from the upstream to the downstream side of the cable is converted into a force pressing the cable against the inner surface of the micro-duct D at the buckled portion. As a result, the force is difficult to transmit to the downstream end of the cable, and its journey stops. Therefore, it is deemed impossible to perform a 2000m compression test.

[0076] In contrast, for a compressive strength of 12.8 N / mm 2 The above test examples (1-3 to 1-7) yielded good compression test results. This is because the compressive strength, i.e., the ease of deformation relative to the force along the central axis O of the optical fiber cable (long side direction), was above a specified amount, thus suppressing buckling of the optical fiber cable within the microduct D. Therefore, by suppressing buckling of the optical fiber cable, the force is reliably transmitted to the downstream end of the optical fiber cable, and it is considered that 2000m of compression can be performed.

[0077] Based on the above results, the optimal compressive strength of the optical fiber cable is 12.8 N / mm². 2 The above describes a structure that can suppress buckling of optical fiber cables within the microduct D, improving the ease of installation.

[0078] Furthermore, as shown in Test Examples 1-8 of Table 1, even for a compressive strength of 32.4 N / mm... 2The fiber optic cable also showed good results in the compression test. Therefore, it can be considered that setting the compression strength to 32.4 N / mm² is sufficient. 2 The following results were obtained from the pressure feeding test.

[0079] Based on the above, the preferred compressive strength of the optical fiber cable is 12.8 N / mm². 2 Above and 32.4 N / mm 2 the following.

[0080] (Overlap rate)

[0081] like Figure 1A As shown, in this embodiment, the pressure sleeve 22 has an overlapping portion 22a. The inventors of this application conducted research and discovered that if the ratio of the perimeter of the overlapping portion 22a to the total circumference of the pressure sleeve 22 is large, then... Figure 5 As shown, fiber optic cables are prone to deformation into a roughly elliptical shape. More specifically, they tend to become elliptical in the direction of the major axis of the overlapping portion 22a. If such deformation occurs, the following situation arises: the opening of the sealing portion S (refer to...) Figure 3 The sealing performance of the micro-channel D is reduced. In addition, the following situation also exists: the protrusion 11 located on the major axis of the ellipse is pressed forcefully against the inner circumferential surface of the micro-channel D, thereby increasing friction.

[0082] In other words, it can be seen that the proportion of the overlapping portion 22a in the full circumference of the pressure sleeve 22 affects the workability of the air-pressed fiber optic cable.

[0083] Therefore, the following describes the results obtained from studying the proportion of the preferred overlapping portion 22a.

[0084] like Figure 1A As shown, the perimeter of the overlapping portion 22a as viewed in cross-section is set as W1. Furthermore, the perimeter of the non-overlapping portion 22b is W2 (not shown). In this case, the overlap ratio R is defined by the following formula (1).

[0085] R = W1 ÷ (W1 + W2) × 100 …(1)

[0086] The overlap ratio R represents the ratio of the perimeter of the overlapping portion 22a to the total circumference of the pressure sleeve 22.

[0087] In this embodiment, as shown in Table 2, multiple optical fiber cables with different overlap rates R are prepared (Examples 2-1 to 2-6).

[0088] Table 2, in the “Transmission Loss” column, shows the measurement results of the transmission loss for each fiber optic cable. More specifically, at a wavelength of 1550 nm, a transmission loss below 0.30 dB / km is considered good (OK), and a transmission loss greater than 0.30 dB / km is considered insufficient (NG).

[0089] The meaning of the "Air Pressure Test" column in Table 2 is the same as that in Table 1.

[0090] Table 2

[0091] Test case 2-1 2-2 2-3 2-4 2-5 2-6 Overlap rate R 27％ 20％ 13％ 9％ 5％ 3％ Transmission loss OK OK OK OK OK NG Air pressure test NG OK OK OK OK OK

[0092] As shown in Table 2, for test cases with an overlap ratio R of 5% or higher (2-1 to 2-5), the transmission loss results were good. In contrast, for test case with an overlap ratio R of 3% (2-6), the transmission loss results were insufficient. This is believed to be because, when the overlap ratio R is too small, the optical fiber protrudes from the overlap portion 22a to the outside of the pressure sleeve 22, applying localized bending to the optical fiber and increasing transmission loss.

[0093] Furthermore, for test cases with an overlap ratio R of 20% or less (2-2 to 2-6), the air pressure delivery test results were good. In contrast, for test case (2-1) with an overlap ratio R of 27%, the air pressure delivery test results were insufficient. The reason for this is that, as mentioned earlier, due to the excessively large overlap ratio R, the optical fiber cable deforms into an elliptical shape, thereby reducing the operability during air pressure delivery.

[0094] Based on the above results, the overlap ratio R is preferably 5% or more and 20% or less. This structure can suppress the increase in transmission loss caused by applying local bending to the optical fiber and improve the operability of air-pressurized conveying.

[0095] (Cross-sectional area of ​​the concave part)

[0096] When the optical fiber cable is inserted into the microchannel D via air compression, at least a portion of the air flows through the recess 12. Furthermore, a portion of the air flowing in the recess 12 flows between the protrusion 11 and the microchannel D, forming an air layer between them, thereby reducing friction. Based on the results of the inventors' research, it is preferable to set the cross-sectional area of ​​the recess 12, which serves as the air flow path, within a predetermined range in order to properly form the aforementioned air layer. The results of this research are explained below.

[0097] In this embodiment, a Figure 6The examples shown are multiple fiber optic cables with different concave cross-sectional areas A (Examples 3-1 to 3-6). The concave cross-sectional area A is the cross-sectional area of ​​the space defined by the closed curve L and all the concave portions 12 when a closed curve L tangent to the radial outer end of each protrusion 11 is drawn in cross-sectional view. In other words, the concave cross-sectional area A is the difference between the cross-sectional area of ​​the fiber optic cable in this embodiment and the cross-sectional area of ​​an imaginary fiber optic cable with the closed curve L as its outer peripheral surface.

[0098] In addition, the closed curve L is usually a circle centered on the central axis O. However, due to the deformation of the optical fiber cable, the closed curve L can also become elliptical.

[0099] Table 3

[0100] Test case 3-1 3-2 3-3 3-4 3-5 3-6 <![CDATA[Cross-sectional area A of the concave part (mm 2 )]]> 5.2 4.8 3.4 2.8 1.3 0.0 Air pressure test NG OK OK OK OK NG

[0101] As shown in Table 3, the cross-sectional area A of the concave portion is 5.2 mm. 2 In test example (3-1), the air pressure delivery test result was insufficient. This is because the cross-sectional area A of the recess was too large, reducing the seal between the seal S and the fiber optic cable, and easily causing backflow of air from the micro-channel D. If the amount of air flowing back from the micro-channel D is large, the amount of air between the inner surface of the micro-channel D and the fiber optic cable decreases, increasing friction. It is believed that due to this friction, force is difficult to transmit from the upstream side to the downstream side of the fiber optic cable, and the fiber optic cable stops moving.

[0102] In contrast, the cross-sectional area A of the concave portion is 1.3 mm. 2 Above and 4.8mm 2 In the following test examples (3-2 to 3-5), the air pressure delivery test results were good. This is because the concave cross-sectional area A is sufficiently small, the seal between the seal S and the fiber optic cable is good, and the backflow of air from the micro-channel D is suppressed. That is, it is assumed that by having sufficient air between the inner surface of the micro-channel D and the fiber optic cable, friction is reduced, and force can be transmitted from the upstream side to the downstream side of the fiber optic cable.

[0103] Furthermore, in test examples 3-6, since no uneven shape was formed on the sheath 10, the inner surface of the micro-channel D had greater friction with the optical fiber cable, causing the optical fiber cable to stop moving.

[0104] Based on the above results, the preferred cross-sectional area A of the concave portion is 1.3 mm. 2 Above and 4.8mm 2 Within the following range. This structure ensures the seal between the seal S and the fiber optic cable, improving the operability of air compression.

[0105] (The twisted shape of the sheath)

[0106] The recess 12 serves as the airflow path during air-pressurized fiber optic cable delivery. For example, in the case where the recess 12 extends linearly along its long side (see reference...). Figure 7A And the case of spiral twisting along the long side (see reference). Figure 7B Under these conditions, the airflow pattern changes. Furthermore, it is believed that the different airflow patterns affect the workability of air-pressurized fiber optic cables.

[0107] Therefore, Table 4 is used to explain the results of the study on the relationship between the torsional shape of the sheath 10 and the workability of air-pressurized cables. Several fiber optic cables with different torsional angles θ were prepared (Examples 4-1 to 4-5). The torsional angle θ refers to the amount of torsion of the sheath 10 (protrusion 11) around the central axis O per 1m along the long side. For example, when θ = 90° / m, comparing portions 1m apart along the long side means that the positions of the protrusions 11 differ by 90° around the central axis O. Furthermore, in Examples 4-2 to 4-5, the tension body 30 was torn around the central axis O with the same torsional angle θ as the protrusion 11. Therefore, the cross-sectional shape of the fiber optic cables in Examples 4-2 to 4-5 is approximately the same at any position along the long side.

[0108] Table 4

[0109] Test case 4-1 4-2 4-3 4-4 4-5 Torsion angle (° / m) 0 5 10 120 180 Air pressure test NG NG OK OK OK

[0110] As shown in Table 4, for test cases (4-3 to 4-5) with a torsion angle of 10 ≤ θ (° / m) ≤ 180, the results of the air pressure test were good. This is believed to be because the pressure of the air flowing within the recess 12 can be effectively converted into a thrust that propels the optical fiber cable downstream. That is, the air flowing within the recess 12 exerts a vertical pressure on the side of the protrusion 11. Therefore, the larger the value of θ, the more inclined the side of the protrusion 11 is relative to the long side, and the more the air pressure is converted into a force in the long side direction.

[0111] In contrast, in test cases (4-1, 4-2) where the torsion angle θ was less than 5° / m, the results of the air pressure test were insufficient. This is believed to be because the pressure of the air flowing within the recess 12 could not be effectively used for the thrust of the optical fiber cable.

[0112] Based on the above, the torsion angle of the sheath 10 is preferably 10 ≤ θ (° / m) ≤ 180. This structure can effectively convert the pressure of the air flowing in the recess 12 into a force that propels the optical fiber cable downstream, thus improving the operability of air-pressurized cables.

[0113] Alternatively, when forming the sheath 10, a twisted shape can be actively provided on the sheath 10 so that 10≤θ(° / m)≤180. Or, the sheath 10 can be twisted by utilizing the force of the stranded helical fiber unit 21 to untwist.

[0114] Next, the results of the study on the influence of the torsional shape of the sheath 10 and the tensile body 30 on the bending stiffness of the optical fiber cable will be explained. In this embodiment, test examples 5-1 and 5-2 (refer to...) Figure 8 Two fiber optic cables. The fiber optic cable in Test Example 5-1 is the same as that in Test Example 4-1, such as... Figure 7A As shown, the sheath 10 and the tensile body 30 are free from torsion. The fiber optic cable of Test Example 5-2 is as follows... Figure 7B As shown, the sheath 10 and the tensile body 30 are spirally twisted, with a pitch of 700 mm along the long side. Test Examples 5-1 and 5-2 both employed a core 20 formed by twisting multiple fiber units 21 into an SZ shape. In Test Examples 5-1 and 5-2, the number of protrusions 11 and tensile bodies 30 were both 12.

[0115] Figure 8 This is a graph showing the bending stiffness value at each measured angle X for the fiber optic cables in test examples 5-1 and 5-2. Figure 9 As shown, the measurement angle X refers to the angle at which the force is applied when measuring bending stiffness. In this embodiment, a force is applied to the center of each of the 12 protrusions 11 and the 12 recesses 12, so the measurement angle X is 15° (=360°÷24).

[0116] like Figure 8 As shown, the optical fiber cable of Test Example 5-1 exhibits a large deviation in bending stiffness values ​​at each measured angle X. On the other hand, the optical fiber cable of Test Example 5-2 shows a smaller deviation in bending stiffness values ​​at each measured angle X compared to Test Example 5-1. This difference depends on whether the tensile body 30 is arranged in a helical torsional configuration. It can be assumed that in Test Example 5-2, the tensile body 30 is configured in a helical shape, thus homogenizing the bending stiffness in the circumferential direction.

[0117] As explained above, a tensile strength 30 is embedded inside the protrusion 11 of the sheath 10, and the protrusion 11 and the tensile strength 30 are twisted into a spiral shape centered on the central axis O, thereby enabling the bending stiffness of the optical fiber cable to be uniform in the circumferential direction. This provides an optical fiber cable that is easier to handle and easier to lay in microducts.

[0118] (Material of the tensile body)

[0119] Next, Tables 5 and 6 are used to explain the results of the study on the material of the tensile body 30. Table 5 shows test examples 6-1 to 6-3, which are fiber optic cables with 288 optical fibers. Table 6 shows test examples 7-1 and 7-2, which are fiber optic cables with 144 optical fibers.

[0120] Table 5

[0121]

[0122] Table 6

[0123]

[0124]

[0125] In Tables 5 and 6, "TM material," "tensile elastic modulus," "TM diameter," and "TM cross-sectional area" represent the material, tensile elastic modulus, diameter, and cross-sectional area of ​​the tensile body 30, respectively. "TM number" indicates the number of tensile bodies 30 in this test example. In addition, the same number of protrusions 11 as tensile bodies 30 are provided on the surface of the sheath 10 in each test example, and tensile bodies 30 are disposed inside each protrusion 11.

[0126] The "Tension Index" shown in Table 5 represents the tensile force required to achieve a specified elongation α (%) when a tensile force is applied along the long side of the optical fiber cables from Test Examples 6-1 to 6-3, using Test Example 6-1 as a reference. For example, the Tension Index of Test Example 6-2 is 1.25, therefore a tensile force 1.25 times that of Test Example 6-1 is required to achieve elongation α. ​​Except that the tensile force of Test Example 7-1 is used as a reference, the Tension Index shown in Table 6 is the same as that in Table 5.

[0127] Furthermore, the elongation α is set within the range where the fiber optic cable elongates proportionally to the tensile force. Therefore, the tensile strength index of test examples 6-2, 6-3, and 7-2 is not affected by the value of the elongation α.

[0128] The "Outer Diameter Ratio" shown in Table 5 indicates the size of the outer diameter of the fiber optic cables in Test Examples 6-2 and 6-3 relative to the outer diameter of the fiber optic cable in Test Example 6-1. For example, the outer diameter of the fiber optic cable in Test Example 6-2 is 0.94 times that of the fiber optic cable in Test Example 6-1. Similarly, the "Outer Diameter Ratio" in Table 6 indicates the size of the outer diameter of the fiber optic cable in Test Example 7-2 relative to the outer diameter of the fiber optic cable in Test Example 7-1. Furthermore, the sheath 10 in each test example is designed to have the same minimum thickness; therefore, the smaller the diameter of the tensile body 30, the smaller the outer diameter ratio.

[0129] As shown in Table 5, the tensile strength indices of Test Examples 6-2 and 6-3 are 1.25 and 1.20, respectively. Compared with Test Example 6-1, they are less likely to extend along the long side, effectively protecting the optical fiber from tension. Furthermore, the TM diameters of Test Examples 6-2 and 6-3 are 0.25 mm and 0.30 mm, respectively, much smaller than those of Test Example 6-1. Therefore, the outer diameter of the optical fiber cables in Test Examples 6-2 and 6-3 is smaller than that in Test Example 6-1.

[0130] As shown in Table 6, the same results as in Table 5 were obtained for test examples 7-1 and 7-2 with 144 optical fibers.

[0131] As described above, by using PBO-FRP with a high tensile elastic modulus as the material of the tensile body 30, it is possible to provide an optical fiber cable that is difficult to stretch under tension relative to the long side direction and has a small outer diameter.

[0132] (Number of tensile elements relative to the protrusion)

[0133] The number of tensile strength members 30 disposed on the inner side of the protrusion 11 can be appropriately varied. For example, a structure with... Figure 10 The cross-sectional shape of the fiber optic cable is shown. Viewed in cross-section, Figure 10 The fiber optic cable shown has two tensile strength elements 30 embedded inside a protrusion 11. In this way, more than two tensile strength elements 30 can also be arranged inside a protrusion 11.

[0134] (Set the twist angle)

[0135] Next, Table 7 will be used to explain the effect of twisting multiple fiber units 21 into an SZ shape.

[0136] Table 7

[0137]

[0138] The fiber optic cables in Test Examples 9-1 to 9-4 have the following characteristics: Figure 1A The cross-sectional shape is shown. The number of protrusions 11 and tensile bodies 30 is 12. Discontinuously bonded cored wires are used as optical fiber units 21. The “Set Angle” in Table 7 indicates the set angle when multiple optical fiber units 21 are twisted together in an SZ shape. For example, when the set angle is ±350°, when the core 20 is housed in the sheath 10, the bundle of optical fiber units 21 is repeatedly rotated 350° in the CW direction and then 350° in the CCW direction. As a result, the bundle of optical fiber units 21 is housed in the sheath 10 in an SZ-shaped twisted state.

[0139] When the fiber unit 21 is stranded into an SZ shape, the bundle of fiber unit 21 is to be untwisted back to its original shape before stranding. Before untwisting occurs, the bundle of fiber unit 21 is wrapped with a compression sleeve 22 and a sheath 10, thereby maintaining the stranded state of the fiber unit 21 into an SZ shape inside the fiber cable.

[0140] Here, inside the optical fiber cable, the sheath 10 is subjected to a force from the fiber unit 21 via the compression sleeve 22, which aims to untwist it. The sheath 10 deforms due to this force, resulting in an SZ-shaped twist on its surface. In this case, the tensile strength 30 embedded in the sheath 10 also twists in an SZ shape. The angle of this SZ-shaped twist on the surface of the sheath 10 is represented by "Twist Angle of Sheath" in Table 7. For the optical fiber cable of Test Example 9-1, since the fiber unit 21 was not twisted in an SZ shape, no SZ-shaped twist appeared on the surface of the sheath 10. On the other hand, for the optical fiber cables of Test Examples 9-2 to 9-4, since the fiber unit 21 was twisted into an SZ shape, an SZ-shaped twist also appeared on the surface of the sheath 10.

[0141] The larger the set angle, the greater the force required for the fiber optic unit 21 to untwist. Therefore, as shown in Table 7, the larger the set angle, the greater the "torsion angle of the sheath".

[0142] The "Air Pressure Delivery Test" column in Table 7 shows the results of the air pressure delivery test performed on the fiber optic cables in Test Examples 9-1 to 9-4. The details of the air pressure delivery test are the same as those in Table 1. For example, in Test Example 9-1, the cable could be pressure delivered for 1500m in the air pressure delivery test, but further pressure delivery was difficult. In contrast, in Test Examples 9-2 to 9-4, the cable could be pressure delivered for more than 2000m in the air pressure delivery test. Furthermore, the details of "Transmission Loss" in Table 7 are the same as those in Table 2.

[0143] As shown in Table 7, the fiber optic units in Test Examples 9-2 to 9-4 achieved better results in the air pressure test than those in Test Example 9-1. This is because, by twisting the protrusion 11 and the recess 12 in an SZ shape, the pressure of the air flowing within the recess 12 can be effectively converted into a thrust that propels the fiber optic cable downstream. That is, the air flowing within the recess 12 exerts a vertical pressure on the side of the protrusion 11. Therefore, compared to Test Example 9-1 where the sheath 10 was not twisted, the air pressure was converted into a force along the long side, resulting in better air pressure test results. Furthermore, in Test Examples 9-2 to 9-4, by applying an SZ-shaped twist to the sheath 10, the tensile strength 30 embedded in the sheath 10 also twists in an SZ shape, and the bending stiffness of the fiber optic cable becomes more uniform in the circumferential direction. This is also considered a major reason for the better results in the air pressure test.

[0144] The bending stiffness values ​​of the fiber optic cables in Test Examples 9-1 and 9-2 at each measurement angle X are as follows: Figure 11 As shown. Furthermore, the method for measuring the bending stiffness value is the same as in test examples 5-1 and 5-2. According to... Figure 11 It can be seen that, compared with the optical fiber cable of Test Example 9-1, the optical fiber cable of Test Example 9-2 has a smaller deviation in the bending stiffness value at each measured angle X.

[0145] Based on the above, by twisting multiple fiber units 21 in an SZ shape and applying an SZ-shaped torsion to the sheath 10 using a desired untwisting force, it is possible to provide an optical fiber cable with uniform bending stiffness in the circumferential direction, making it more suitable for air-pressurized delivery. Furthermore, in this embodiment, the fiber units 21 are twisted into an SZ shape. However, the same result can be obtained even if the multiple optical fibers 21a are not twisted into units but twisted into an SZ shape. In other words, the above-mentioned effects can be achieved simply by twisting multiple optical fibers 21a in an SZ shape and applying an SZ-shaped torsion to the sheath 10.

[0146] Furthermore, as shown in Table 7, for test examples 9-2, 9-3, and 9-4, it can be seen that the transmission loss is also good, in addition to the air pressure test. Therefore, by setting the SZ twist angle of the fiber optic unit 21 so that the twist angle of the sheath 10 is ±30° to ±70°, it is possible to provide an optical fiber cable with good transmission loss characteristics.

[0147] (Low-friction materials)

[0148] During air compression of the fiber optic cable, the sheath 10 and the miniature conduit D (refer to...) Figure 3 Since the contact between the microchannel and the sheath 10 is relatively simple, it is preferable to form the sheath 10 with a low coefficient of friction (hereinafter referred to as a low-friction material). On the other hand, if the entire sheath 10 is formed with a low-friction material, it is considered that the strength of the sheath 10 cannot be guaranteed, or it may lead to an increase in cost. Therefore, the portion of the sheath 10 that contacts the microchannel was formed with a low-friction material was investigated. Table 8 will be used to illustrate this below.

[0149] Table 8

[0150]

[0151]

[0152] As shown in Table 8, fiber optic cables for Test Examples 10-1 to 10-8 were prepared. In the fiber optic cables of Test Examples 10-1 and 10-2, the sheath 10 was formed from a single substrate B (with an average coefficient of kinetic friction of 0.27). Figure 12AAs shown, in the optical fiber cables of test examples 10-3 and 10-4, the top of the protrusion 11 is formed of a low-friction material M (with an average coefficient of kinetic friction of 0.20), and the remaining portion of the sheath 10 is formed of the aforementioned substrate B. That is, the low-friction material M is a material with a lower coefficient of friction than the substrate B. Furthermore, the average coefficient of kinetic friction was measured according to JIS K7125.

[0153] like Figure 12B As shown, in the optical fiber cables of test examples 10-5 and 10-6, a layer of low-friction material M is provided on the entire surface of the sheath 10 formed from substrate B. Figure 12C As shown, in the optical fiber cables of test examples 10-7 and 10-8, a protrusion 11 and a recess 12 are formed on the outer peripheral surface of the cylindrical substrate B using a low-friction material M.

[0154] The common feature of the fiber optic cables in Test Examples 10-3 to 10-8 is that the sheath 10 is formed of a substrate B and a low-friction material M, with the low-friction material M disposed at least on the top of the protrusion 11. Furthermore, in this specification, the "top" of the protrusion 11 refers to the portion that is bent in a manner that protrudes radially outward.

[0155] Air pressure feeding tests were conducted on the fiber optic cables of Test Examples 10-1 to 10-8. The pressure feeding speed (pressure feeding rate) of the fiber optic cables was approximately 60 m / min at the start of the test. For any of Test Examples 10-1 to 10-8, the pressure feeding rate decreased with increasing pressure feeding distance. For Test Example 10-1, the pressure feeding rate was almost zero at a pressure feeding distance of 2000 m. On the other hand, in Test Examples 10-2 to 10-8, the pressure feeding rate was 30 m / min or more at a pressure feeding distance of 2000 m, confirming that pressure feeding for distances exceeding 2000 m could be performed sufficiently. Therefore, the fiber optic cables of Test Examples 10-2 to 10-8 yielded better results than those of Test Example 10-1. In Test Examples 10-2 and 10-1, although the cross-sectional shape was the same, Test Example 10-1 had a larger outer diameter and a larger contact area with the micro-duct, thus increasing friction and resulting in decreased air pressure feeding performance compared to Test Example 10-2. In contrast, in test examples 10-3, 10-5, and 10-7, friction was reduced by using a low-friction material M to form the part in contact with the microchannel, which enabled good air delivery even for fiber optic cables with an outer diameter of 12 mm or more.

[0156] As explained above, by distributing the low-friction material M at least on the top of the protrusion 11, an optical fiber cable with good air pressure delivery characteristics can be provided. Furthermore, by forming the sheath 10 from the substrate B and the low-friction material M, compared to the case where the sheath 10 is formed entirely from the low-friction material M, it is possible to improve the strength of the sheath 10 and reduce costs.

[0157] However, given the air pressure delivery and cost required by the fiber optic cable 1, the entire sheath 10 can also be formed from a low-friction material M.

[0158] (Torn rope)

[0159] In fiber optic cable splicing or disassembly operations, it is necessary to remove the core 20 from the inside of the sheath 10. A tear cord configuration is proposed to facilitate the removal of the core 20. Figures 13A-13C The structure of.

[0160] exist Figure 13A In the fiber optic cable 1 shown, with Figure 1A In contrast, a portion of the tensile body 30 is replaced with tear cords 40. More specifically, two tear cords 40 are embedded inside the protrusions 11 of the sheath 10 and are configured to clamp the core 20 in the middle.

[0161] As the tear cord 40, a thread (yarn) made of twisted fibers such as PP (polypropylene) or polyester can be used. The tensile strength body 30 protects the optical fiber 21a from tension, while the tear cord 40 tears the sheath 10. Therefore, the tear cord 40 and the tensile strength body 30 are made of different materials. Specifically, the tensile strength body 30 has a higher tensile elastic modulus than the tear cord 40. Furthermore, the tear cord 40 is more flexible than the tensile strength body 30.

[0162] like Figure 13A As shown, by embedding a tear cord 40 inside the protrusion 11 of the sheath 10, it is possible to both prevent the wall thickness of the sheath 10 from becoming thinner and to provide the tear cord 40. When removing the core 20 from the inside of the sheath 10, a portion of the protrusion 11 is cut open, the tear cord 40 is removed, and the tear cord 40 is stretched along the long side of the optical fiber cable. As a result, the sheath 10 is torn open, thereby allowing the core 20 to be removed.

[0163] like Figure 13A As shown, after fabricating an optical fiber cable with a pair of tear cords 40 arranged in such a way that the core 20 is sandwiched in the middle, the operation of removing the core 20 can be performed smoothly. Furthermore, the optical fiber cable may have one tear cord 40 or more.

[0164] As explained above, when viewed in cross-section, the tear cord 40 is positioned inside a portion of the protrusions 11, and the tension-resistant body 30 is positioned inside the other protrusions 11, thereby protecting the optical fiber 21a from tension and making it easier to remove the core 20 from the optical fiber cable.

[0165] Additionally, to identify the location where the tear cord 40 is embedded, a marking portion (coloring, etc.) can be provided on the protrusion 11 where the tear cord 40 is embedded. Alternatively, as... Figure 13B ,13C As shown in Figure 13D, the shape of the protrusion 11 with the tear rope 40 embedded on its inner side can also be different from the shape of other protrusions 11. Figure 13B In the example, the protrusion 11 with the tear rope 40 embedded on its inner side protrudes radially outward significantly more than other protrusions 11. Figure 13C In the example, the circumferential width of the protrusion 11 with the tear rope 40 embedded on the inside is smaller than that of the other protrusions 11.

[0166] exist Figure 13D In this example, the tear cord 40 is configured to contact the core 20. Furthermore, the tension members 30 are arranged at equal intervals in the circumferential direction, with the tear cord 40 positioned circumferentially between adjacent tension members 30. Additionally, the two tension members 30 that sandwich the tear cord 40 are located inside a protrusion 11.

[0167] By adopting Figure 13B , Figure 13C , Figure 13D This method allows the position of the tear cord 40 to be easily determined from the outside of the fiber optic cable.

[0168] Furthermore, the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0169] For example, such as Figure 14A As shown, the inner surface of the recess 12 can also be a curved surface that bulges inward toward the radial direction.

[0170] In addition, such as Figure 14B As shown, the number of protrusions 11 and tensile bodies 30 can also be inconsistent. Furthermore, as... Figure 14B As shown, the tensile body 30 can also be positioned closer to the inner circumferential surface than the outer circumferential surface of the sheath 10.

[0171] Furthermore, without departing from the spirit of the present invention, the structural elements in the above embodiments can be appropriately replaced with known constituent elements, and the above embodiments or variations can also be appropriately combined.

[0172] Explanation of reference numerals in the attached figures

[0173] 1-Fiber optic cable; 10-Sheath; 11-Protrusion; 12-Recess; 12a-Connector; 12b-Bottom; 20-Core; 21-Fiber optic unit (intermittently bonded cored wire); 21a-Fiber optic; 21c-Bonded part; 22-Compression sleeve; 22a-Overlapping part; 22b-Non-overlapping part; 30-Tension body; 40-Tear cord; B-Base material; M-Low friction material.

Claims

1. An optical fiber cable, comprising: Sheath; and The core, housed within the sheath, has an intermittently bonded core wire comprising a plurality of optical fibers and a plurality of adhesive portions intermittently bonding the plurality of optical fibers along their long sides. The outer circumferential surface of the sheath has recesses and protrusions arranged alternately in the circumferential direction. The recess has two connecting portions that are respectively connected to the radially inner ends of the two adjacent protrusions, and a bottom surface located between the two connecting portions. The compressive strength is 12.8 N / mm². 2 Above and 32.4 N / mm 2 the following, The compressive strength is a value obtained by dividing the compressive load of the fiber optic cable by the cross-sectional area of ​​the fiber optic cable.

2. The optical fiber cable according to claim 1, characterized in that, The connecting portion is formed as a curved surface that bulges inward toward the radial direction.

3. The optical fiber cable according to claim 1 or 2, characterized in that, The core has a pressure sleeve that wraps around the discontinuously bonded core wire.

4. The optical fiber cable according to claim 3, characterized in that, The pressure sleeve has a first end and a second end that overlap to form an overlapping portion, and a non-overlapping portion located between the first end and the second end.

5. The optical fiber cable according to claim 4, characterized in that, When the circumferential length of the overlapping portion is set as W1 and the circumferential length of the non-overlapping portion is set as W2, the overlap rate R calculated by R = W1 ÷ (W1 + W2) × 100 is in the range of 5% or more and 20% or less.

6. The optical fiber cable according to claim 1 or 2, characterized in that, When the torsion angle of the sheath for every 1m along the long side of the optical fiber cable is set to θ (° / m), 10≤θ≤180.

7. The optical fiber cable according to claim 1 or 2, characterized in that, The radius of curvature of the outer peripheral surface of the protrusion is smaller than the radius of the sheath.

8. The optical fiber cable according to claim 1 or 2, characterized in that, It also includes a tensile-resistant body embedded inside the protrusion of the sheath. The protrusion and the tensile body are twisted into a spiral shape centered on the central axis of the optical fiber cable.

9. The optical fiber cable according to claim 1 or 2, characterized in that, It also includes a tensile-resistant body embedded inside the protrusion of the sheath. The tensile body is formed from PBO-FRP.

10. The optical fiber cable according to claim 1 or 2, characterized in that, It also has multiple tensile strength elements embedded in the sheath. When viewed in cross-section, the plurality of tensile bodies are located inside one of the protrusions of the sheath.

11. The optical fiber cable according to claim 1 or 2, characterized in that, It has multiple discontinuously bonded core wires. An SZ-shaped torsion is applied to the sheath by twisting multiple of the discontinuous adhesive core wires in an SZ shape.

12. The optical fiber cable according to claim 1 or 2, characterized in that, The sheath is formed of a base material and a low-friction material with a coefficient of friction lower than that of the base material. The low-friction material is disposed at least on the top of the protrusion.

13. The optical fiber cable according to claim 1 or 2, characterized in that, It also includes a tensile strength element and a tear cord embedded in the sheath. In cross-sectional view, the tear cord is located inside a portion of the protrusions, and the tension body is located inside the other protrusions.

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