Bending application device and bending test device for measuring bending loss

Abstract

Provided is a bend-imparting device 30 having at least three mandrels (exemplified by a fixed mandrel 55 and a moving mandrel 65), the bend-imparting device 30 imparting a bend to a delivered optical fiber F by winding the optical fiber onto the mandrels. The diameter of the optical fiber is D, the radius of the mandrels is r, the direction linking the upstream contact point T1 where the optical fiber begins to contact a mandrel and the downstream contact point T2 where the optical fiber begins to separate from the mandrel is a first direction (exemplified by the horizontal direction), the interval between adjacent mandrels in the first direction is 2r+d, a direction orthogonal to the first direction is a second direction (exemplified by the vertical direction), and the interval between adjacent mandrels in the second direction is s. The angle θ formed by the second direction and the common internal tangent of the adjacent mandrel as seen from the center position of the optical fiber is 0-45 degrees (inclusive) and satisfies numerical expression 3.

Description

Technical Field

[0001] The present disclosure relates to a bending application device for measuring bending loss and a bending test device.

[0002] This application claims priority based on Japanese Application No. 2020-102572 filed on June 12, 2020, and incorporates all the descriptions described in the above Japanese application.

Background Art

[0003] Bending loss characteristics are one of the basic characteristics of optical fibers. In the recommendation G.652 of the international standard ITU-T (International Telecommunication Union - Telecommunication Standardization sector), the characteristics of general-purpose single-mode optical fibers (SMF: Single Mode Fiber) are described, and in the recommendation G.657, the characteristics of low-bending-loss single-mode optical fibers are described. Bending loss is determined by the attenuation of light with respect to the bent optical fiber. For example, Patent Document 1 discloses a structure for obtaining bending loss by providing a plurality of side surfaces with different curvatures on a single cylinder.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] A bending device for measuring the bending loss of an optical fiber according to an aspect of the present disclosure is a bending device having at least three mandrels, and applying bending to the optical fiber by winding the fed optical fiber around the mandrels. The mandrels are arranged alternately at a predetermined interval such that the outer circumferences of adjacent mandrels in the longitudinal direction of the optical fiber face each other without contact. Let the diameter of the optical fiber be D and the radius of the mandrel be r. In a plane orthogonal to the rotation axis of the mandrel, taking the first direction as the direction connecting the upstream contact point where the optical fiber wound around the central mandrel among three mandrels of the same diameter arranged continuously along the longitudinal direction of the optical fiber begins to contact the central mandrel and the downstream contact point where the optical fiber wound around the central mandrel begins to leave the central mandrel, the interval between adjacent mandrels as seen in the first direction is 2r + d, taking the second direction as the direction orthogonal to the first direction in a plane orthogonal to the rotation axis of the mandrel, the interval between adjacent mandrels as seen in the second direction is s, and the angle θ formed by the second direction and the common internal tangent of adjacent mandrels as seen at the center position of the optical fiber is 0 degrees or more and 45 degrees or less. wherein each of the adjacent mandrels includes a fixed mandrel that does not move and a movable mandrel configured to be movable between a reference position where no bending is applied to the optical fiber and a forward position where bending is applied to the optical fiber with respect to the fixed mandrel, and among the plurality of movable mandrels, the movable mandrel located on the downstream side when viewed in the longitudinal direction of the optical fiber is moved prior to the movable mandrel located on the upstream side to apply bending to the optical fiber . Here, the angle θ satisfies the following equation (3).

Brief Description of the Drawings

[0006]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 2D

Figure 3

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Figure 6

Figure 7

Figure 8

DETAILED DESCRIPTION OF THE INVENTION

[0007] [PROBLEMS TO BE SOLVED BY THE PRESENT DISCLOSURE] In the structure described in Patent Document 1 above, since the number of winding turns of the optical fiber is small, it is difficult to obtain the bending loss for a low bending loss single mode optical fiber. On the other hand, simply increasing the number of winding turns of the optical fiber deteriorates the efficiency, and since the optical fiber is wound in a spiral shape and the winding angle of the optical fiber tends to be small, accurate bending loss may not be obtained. Furthermore, even when a thin-diameter (for example, about φ200 μm) optical fiber is wound, the winding angle of the optical fiber tends to be small, so that accurate bending loss may not be obtained.

[0008] The present disclosure has been made in view of the above circumstances, even if the number of winding turns of the optical fiber is increased, without reducing the winding angle of the optical fiber around the mandrel and an object thereof is to provide a bending application device and a bending test device for measuring bending loss that can be obtained efficiently and accurately.

[0009] [EFFECTS OF THE PRESENT DISCLOSURE] According to the above, it becomes possible to efficiently and accurately obtain the bending loss.

[0010] [DESCRIPTION OF EMBODIMENTS OF THE PRESENT DISCLOSURE] First, the contents of the embodiments of the present disclosure will be listed and described. The bending device for measuring bending loss according to the present disclosure is a bending device that (1) has at least three mandrels and bends the fed optical fiber by winding it around the mandrels. The mandrels are arranged alternately at a predetermined interval such that the outer circumferences of adjacent mandrels are non-contact and face each other in the longitudinal direction of the optical fiber. Let the diameter of the optical fiber be D and the radius of the mandrel be r. In a plane perpendicular to the rotation axis of the mandrel, taking the first direction as the direction connecting the upstream contact point where the optical fiber wound around the central mandrel among three mandrels of the same diameter continuously arranged along the longitudinal direction of the optical fiber starts to contact the central mandrel and the downstream contact point where the optical fiber wound around the central mandrel starts to leave the central mandrel, the interval between adjacent mandrels in the first direction is 2r + d, taking the second direction as the direction perpendicular to the first direction in a plane perpendicular to the rotation axis of the mandrel, the interval between adjacent mandrels in the second direction is s, and the angle θ formed by the second direction and the common internal tangent of adjacent mandrels seen at the center position of the optical fiber is 0 degrees or more and 45 degrees or less. wherein each of the adjacent mandrels includes a fixed mandrel that does not move and a movable mandrel configured to be movable between a reference position where no bending is applied to the optical fiber and a forward position where bending is applied to the optical fiber with respect to the fixed mandrel, and among the plurality of movable mandrels, the movable mandrel located on the downstream side when viewed in the longitudinal direction of the optical fiber is moved prior to the movable mandrel located on the upstream side to apply bending to the optical fiber . Here, the angle θ satisfies the following formula (3). If the interval "2r + d" in the first direction and the interval "s" in the second direction that satisfy the formula (3) for the angle θ are obtained, the arrangement of each mandrel can be determined. Therefore, even if the number of winding turns of the optical fiber is increased, the winding angle of the optical fiber around the mandrel does not decrease, so that the bending loss can be efficiently and accurately obtained. Also, since bending is applied to the optical fiber from the downstream side to the upstream side, the tension generated in the optical fiber can be evened out, and locations where excessive tension is applied can be eliminated.

[0011] (2) In one aspect of the bending device for measuring bending loss according to the present disclosure, the bending device has guides for ensuring the supply height of the optical fiber toward the mandrel and the discharge height of the optical fiber away from the mandrel, respectively. It is possible to maintain the supply position and discharge position of the optical fiber, contributing to accurate measurement of bending loss.

[0012] (3) In one aspect of the bending applying device for measuring bending loss of the present disclosure, the guides are arranged in parallel along a direction intersecting the longitudinal direction of the optical fiber. Since bending can be simultaneously applied to a plurality of optical fibers using a mandrel, the efficiency of measuring the bending loss of the optical fiber is improved.

[0014] ( 4 ) In one aspect of the bending test device of the present disclosure, it is a bending test device including any of the bending applying devices for measuring bending loss, and has a tension applying mechanism for applying tension to the optical fiber toward the mandrel. It is possible to prevent loosening of the optical fiber when winding the optical fiber around the mandrel.

[0015] ( 5 ) In one aspect of the bending test device of the present disclosure, the bending test device includes at least an upstream bending applying device located upstream in the longitudinal direction of the optical fiber and a downstream bending applying device located downstream of the upstream bending applying device, and the mandrel of the downstream bending applying device is formed with a larger diameter than the mandrel of the upstream bending applying device, and the mandrel of the downstream bending applying device is moved in the second direction prior to the mandrel of the upstream bending applying device to apply bending to the optical fiber. Since the mandrel is composed of two types of diameters and bending is applied by moving in order from the larger-diameter mandrel, it is possible to measure the bending loss for a plurality of bending diameters, and the number of measurement times for the reference can be reduced. As a result, the time required for measuring the bending loss of the optical fiber can be shortened.

[0016] ( 6 ) In one aspect of the bending test device of the present disclosure, it has an arithmetic unit for obtaining the bending loss based on the length of the optical fiber to which bending is applied. By determining the length of the optical fiber to which bending is applied and converting it in terms of the number of turns, such as one turn or ten turns, the bending loss can be easily determined.

[0017] [Details of Embodiments of the Present Disclosure] Hereinafter, with reference to the accompanying drawings, specific examples of a bending application device and a bending test device for measuring bending loss according to the present disclosure will be described. FIG. 1 is a schematic configuration diagram of a bending test device 1 according to one aspect of the present disclosure. As shown in FIG. 1, the bending test device 1 includes a feeding unit 10, a dancer roller 20, a bending application device 30, a fiber catcher 70, and a power meter 80. The dancer roller 20 corresponds to the tension application mechanism of the present disclosure, and the bending application device 30 corresponds to the bending application device for measuring bending loss of the present disclosure.

[0018] The optical fiber F is pre-manufactured and is attached to the feeding unit 10 in a state of being wound around a bobbin 11. A light source 12 for inputting light to one end of the optical fiber F is installed in the feeding unit 10. The optical fiber F fed out from the bobbin 11 of the feeding unit 10 is sent to the bending application device 30 while being loaded with tension by the dancer roller 20 and is fixed to the fiber catcher 70.

[0019] In the bending application device 30, bending can be applied to the optical fiber F using a fixed mandrel 55 and a moving mandrel 65, which will be described later. The optical fiber F fixed to the fiber catcher 70 is connected to the power meter 80. The power meter 80 has, for example, a light receiving unit 81 and a calculation unit 82. In the light receiving unit 81, the power of the light output from the other end of the optical fiber F is measured. The calculation unit 82 obtains the bending loss of the optical fiber F based on the power of the light measured by the light receiving unit 81 and the length of the optical fiber F to which bending is applied by the bending application device 30.

[0020] The bending applying device 30 has a guide 31 between it and the dancer roller 20, and also has a guide 36 between it and the fiber catcher 70, in addition to the fixed mandrel 55 and the moving mandrel 65. The guide 31 ensures the supply height of the optical fiber F towards the bending applying device 30, and the guide 36 ensures the discharge height of the optical fiber F away from the bending applying device 30.

[0021] As shown in FIG. 2A, the bending applying device 30 has, for example, a base plate 51 that is rectangular in a front view. A plurality (for example, five) of through grooves 52 are provided at equal intervals in the base plate 51. Each through groove 52 extends along a direction (the vertical direction shown in the figure) orthogonal to the longitudinal direction (the left - right direction shown in FIG. 2A) of the optical fiber F from the guide 31 to the guide 36 described in FIG. 1, and all of them are formed through the base plate 51.

[0022] A plurality (for example, seven) of fixed mandrels 55 are provided at equal intervals in the base plate 51. The fixed mandrel 55 is rotatably supported via bearings on a rotating shaft provided in the base plate 51, but the fixed mandrel 55 is fixed on the base plate 51 and does not move in the vertical direction shown in the figure. The fixed mandrels 55 are arranged one by one adjacent to the through grooves 52 along the longitudinal direction of the optical fiber F. The diameter (2r) of the fixed mandrel 55 is selected from, for example, 10 mm, 15 mm, 20 mm, 30 mm, and 60 mm.

[0023] Also, as shown in FIG. 2B, the bending applying device 30 has a slide plate 61, for example, on the back side of the base plate 51. A plurality (for example, six) of moving mandrels 65 are provided at equal intervals in the slide plate 61. In FIG. 2B, an example of two slide plates 61 each mounting three moving mandrels 65 is described, but it may be configured with one slide plate 61 mounting, for example, six moving mandrels 65.

[0024] Each moving mandrel 65 is rotatably supported via bearings on a rotating shaft provided on the slide plate 61. Each rotating shaft is disposed within the through groove 52, and the moving mandrels 65 are arranged one by one adjacent to the fixed mandrel 55. The diameter (2r) of the moving mandrel 65 is set to be the same as the diameter of the adjacent fixed mandrel 55, and for example, any one of 10 mm, 15 mm, 20 mm, 30 mm, 60 mm is selected. It is preferable that both the fixed mandrel 55 and the moving mandrel 65 are rotatably supported, but it is not necessary to rotate if the mandrel surface is slippery and smooth.

[0025] The slide plate 61 is movable along the vertical direction shown in FIG. 2A by the motor 62. When the moving mandrel 65 is positioned at one end of the through groove 52 as shown in FIG. 2A (corresponding to the reference position where no bending is applied to the optical fiber of the present disclosure), and the optical fiber F is being fed out from the guide 31 toward the guide 36, when the motor 62 is driven, each moving mandrel 65 moves downward along the through groove 52 as shown in FIG. 2C. In the case of FIG. 2C, the outer periphery of the adjacent fixed mandrel 55 and the outer periphery of the moving mandrel 65 are arranged at a predetermined interval so as to face each other without contact. The optical fiber F is wound around the outer periphery of the moving mandrel 65 and bends upward, and around the outer periphery of the fixed mandrel 55 to its right and bends downward.

[0026] Thereafter, when the moving mandrel 65 moves to, for example, the other end of the through groove 52 (corresponding to the forward position for applying bending to the optical fiber of the present disclosure) as shown in FIG. 2D, the adjacent fixed mandrel 55 and the moving mandrel 65 are arranged at a predetermined interval such that their outer circumferences face each other without contact, and the fixed mandrel 55 is arranged above and the moving mandrel 65 is arranged below in an alternating manner with respect to the left - right direction. In this case, the optical fiber F is wound around the outer circumference of each moving mandrel 65, bends upward at an angle that does not exceed 180 degrees but is close to 180 degrees, and also bends downward at an angle close to 180 degrees at the fixed mandrel 55 adjacent to the right of this moving mandrel 65. As a result, the optical fiber F is bent by being sandwiched between the adjacent fixed mandrel 55 and the moving mandrel 65.

[0027] In this way, by moving the moving mandrel 65 to the forward position and sandwiching it with the fixed mandrel 55 to apply bending loss to the optical fiber F, it is not necessary for the operator to hook the optical fiber on the mandrel, and the operation does not become troublesome. Here, when the moving mandrel 65 is moved to the forward position shown in FIG. 2D, a predetermined relational expression is established by the fixed mandrel 55 around which the optical fiber F is wound and the moving mandrel 65.

[0028] Specifically, as shown in FIG. 3 which is an enlarged view of the forward position shown in FIG. 2D, focus on the moving mandrel 65 at the central position among the three continuously arranged fixed mandrels 55, the moving mandrel 65, and the fixed mandrel 55. The optical fiber F approaches downward from the fixed mandrel 55 on the left, starts to contact this moving mandrel 65 at the upstream contact point T1, and then winds around the outer circumference of the moving mandrel 65. Then, it starts to separate from this moving mandrel 65 at the downstream contact point T2 and approaches the fixed mandrel 55 on the right upward. In addition, in this specification, the pay - out side of the optical fiber is defined as the upstream side, and the side where the optical fiber is fixed by the fiber catcher is defined as the downstream side.

[0029] If the radii of both the fixed mandrel 55 and the movable mandrel 65 are the same and equal to r, the horizontal axial distance between adjacent mandrels shown in Fig. 3 can be expressed as 2r + d. Here, this horizontal direction is the same as the left - right direction in Fig. 2A, and in a plane orthogonal to the rotation axis of the mandrel of the present disclosure (a plane with the rotation axis of the mandrel as the normal), it corresponds to the first direction connecting the upstream contact point T1 where the optical fiber begins to contact the mandrel located at the center and the downstream contact point T2 where the optical fiber begins to separate from the mandrel located at the center.

[0030] Also, the vertical axial distance between adjacent mandrels shown in Fig. 3 can be expressed as s. Here, this vertical direction is the same as the up - down direction in Fig. 2A, and in a plane orthogonal to the rotation axis of the mandrel of the present disclosure, it corresponds to the second direction orthogonal to the first direction. And when the diameter of the optical fiber F is D (D ≤ d), the distance between the common internal tangent of the fixed mandrel 55 and the movable mandrel 65 as seen from the center position of the optical fiber F is the length of the straight line BC in the right - angled triangle ABC shown in Fig. 3. BC 2 = AB 2 - AC 2 In this case, AB 2 is (2r + d) 2 + s 2 、AC 2 is (2r + D) 2 Therefore, the length of the straight line BC can be expressed by Equation (1).

[0031]

Equation (1)

[0032] On the other hand, when the angle between the vertical direction of adjacent mandrels shown in Fig. 3 and the common internal tangent of the fixed mandrel 55 and the movable mandrel 65 as seen from the center position of the optical fiber F is θ (0° ≤ θ < 90°), the length of the straight line BC is the sum of AC * tanθ and s / cosθ, and thus can be expressed by Equation (2).

Equation (2)

[0033] Therefore, the number 3 can be obtained from these numbers 1 and 2.

Number

[0034] In this way, if the horizontal axial center distance 2r + d and the vertical axial center distance s between adjacent mandrels shown in FIG. 3 are obtained such that θ satisfies the number 3, the arrangements of the fixed mandrel 55 and the moving mandrel 65 can be determined. Therefore, even if the number of winding turns of the optical fiber F is increased, the winding angle of the optical fiber F with respect to the fixed mandrel 55 and the moving mandrel 65 does not decrease, so that the bending loss can be efficiently and accurately obtained.

[0035] Note that the winding angle of the optical fiber F with respect to the moving mandrel 65 is represented by 180° - 2θ. When θ is 0°, the winding angle of the optical fiber F becomes 180°, which is an ideal winding state. When the bending applying device 30 is used, the ratio of the difference between the winding length in the ideal winding state and the actual winding length to the winding length in the ideal winding state is, for example, within 50% (2θ / 180° ≤ 0.5). Preferably, the arrangements of the fixed mandrel 55 and the moving mandrel 65 are determined so as to satisfy within 10% (2θ / 180° ≤ 0.1), and more preferably within 2% (2θ / 180° ≤ 0.02). That is, the fixed mandrel 55 and the moving mandrel 65 are arranged such that θ is 0° or more and 45° or less, preferably θ is 0° or more and 9° or less, and more preferably θ is 0° or more and 1.8° or less. By setting θ within the above range, it is possible to secure the length of the optical fiber F to which bending is applied without excessively increasing the number of the fixed mandrel 55 and the moving mandrel 65. Note that the length of the optical fiber F to which bending is imparted by the bending imparting device 30 can be determined from the respective winding angles of the fixed mandrel 55 and the moving mandrel 65 of the bending imparting device 30. That is, θ is calculated using Equation 3. For the mandrels at both ends of the bending imparting device 30, the length of the optical fiber F to which bending is imparted by the mandrel is rπ(90° - θ) / 180° respectively, and for the mandrels other than both ends, the length of the optical fiber F to which bending is imparted by the mandrel is rπ(180° - 2θ) / 180° respectively. Therefore, the length of the optical fiber F to which bending is imparted by the bending imparting device 30 can be obtained by summing these up.

[0036] (Example 1) Figs. 4 to 7 are diagrams showing an example of a method for measuring the bending loss of an optical fiber. In this example, an upstream bending imparting device 30a is provided near the pay-out section 10 described in Fig. 1, a downstream bending imparting device 30c is provided near the fiber catcher 70, and further, a middle-stream bending imparting device 30b is provided between the upstream bending imparting device 30a and the downstream bending imparting device 30c.

[0037] The upstream bending imparting device 30a has guides 31 and 32, and between the guides 31 and 32, it has a fixed mandrel 53 and a moving mandrel 63 with a diameter (2r) of, for example, 15 mm each. The middle-stream bending imparting device 30b has guides 33 and 34, and between the guides 33 and 34, it has a fixed mandrel 54 and a moving mandrel 64 with a diameter (2r) of, for example, 20 mm each. The downstream bending imparting device 30c has guides 35 and 36, and between the guides 35 and 36, it has a fixed mandrel 55 and a moving mandrel 65 with a diameter (2r) of, for example, 30 mm each.

[0038] First, the optical fiber F fed out from the feeding section 10 is fed out from the guide 31 toward the guide 36 while applying tension with the dancer roller 20, and fixed to the fiber catcher 70 (fiber fixing step). In this case, as shown in FIG. 4, each of the moving mandrels 63, 64, 65 is arranged at the reference position, and the optical fiber F is fixed to the fiber catcher 70 through between each mandrel without being sandwiched by adjacent mandrels. One end of this optical fiber F is connected to the power meter 80.

[0039] Next, for example, without moving each of the moving mandrels 63, 64, 65 from the reference position, that is, without applying bending to the optical fiber F, the bending loss of the optical fiber F is obtained with the power meter 80 (reference measurement step). Subsequently, as shown in FIG. 5, the large-diameter moving mandrel 65 by the downstream bending device 30c is moved to the forward position. As a result, the optical fiber F bends upward at a predetermined angle (for example, 180 degrees) with the moving mandrel 65, and bends downward at a predetermined angle (for example, 180 degrees) with the adjacent fixed mandrel 55, and the optical fiber F is sandwiched between the adjacent moving mandrel 65 and fixed mandrel 55 to apply bending to the optical fiber F. Then, with the bending applied by the large-diameter fixed mandrel 55 and moving mandrel 65, the bending loss of the optical fiber F is obtained with the power meter 80 (large-diameter bending loss measurement step).

[0040] Next, as shown in FIG. 6, the medium-diameter moving mandrel 64 by the middle-stream bending device 30b is also moved to the forward position. As a result, the optical fiber F is sandwiched between the adjacent moving mandrel 64 and fixed mandrel 54 to apply bending to the optical fiber F (middle-stream bending application step). Then, with the bending applied by the large-diameter fixed mandrel 55 and moving mandrel 65, as well as the medium-diameter fixed mandrel 54 and moving mandrel 64, the bending loss of the optical fiber F is obtained with the power meter 80. In this case, the bending loss when bending is applied by the medium-diameter fixed mandrel 54 and moving mandrel 64 can be obtained (medium-diameter bending loss measurement step).

[0041] Thereafter, as shown in FIG. 7, the small-diameter moving mandrel 63 by the upstream bending device 30a is also moved to the forward position, and the optical fiber F is bent by the large-diameter fixed mandrel 55, the moving mandrel 65, the medium-diameter fixed mandrel 54, the moving mandrel 64, and in addition, the small-diameter fixed mandrel 53 and the moving mandrel 63. In this state, the bending loss of the optical fiber F is obtained with the power meter 80. In this case, the bending loss when bending is applied by the small-diameter fixed mandrel 53 and the moving mandrel 63 can be obtained (small-diameter bending loss measurement step).

[0042] In this way, since bending is applied to the optical fiber F from the downstream side to the upstream side, the tension generated in the optical fiber F can be evened out, and a location where excessive tension is applied can be eliminated. Also, since the mandrels are configured with three types of diameters and bending is applied by moving them in the order of the large-diameter moving mandrel 65, the medium-diameter moving mandrel 64, and the small-diameter moving mandrel 63, the bending loss for a plurality of bending diameters can be measured, and the number of reference measurements can be reduced. Thereby, the time required for measuring the bending loss of the optical fiber F can be shortened.

[0043] In Example 1, the reference measurement step and the bending loss measurement step were carried out in this order. However, they can also be carried out in the order of the bending loss measurement step and the reference measurement step, and the reference measurement step may be carried out after bending is applied. Also, although an example of a mandrel with a bearing has been described, when the moving mandrel 65 is moved in order from the fiber catcher 70 side toward the pay-out section 10 side, it is also applicable to a mandrel without a bearing.

[0044] (Example 2) In FIG. 1, an example in which one optical fiber F is sent out from one pay-out section 10 to the bending device 30 has been described. However, as described above, when a mandrel is used instead of a roller for the bending device 30, a plurality of pay-out sections may be arranged in parallel along a direction intersecting the longitudinal direction of the optical fiber F.

[0045] Specifically, as shown in FIG. 8, if the guide 41 is arranged in parallel with the guide 31 and the guide 46 is arranged in parallel with the guide 36, for the optical fiber F going from the guide 31 to the guide 36 and also for the optical fiber F going from the guide 41 to the guide 46, bending can be applied using the fixed mandrel 55 and the moving mandrel 65. Therefore, the efficiency of measuring the bending loss of the optical fiber F is improved.

[0046] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present disclosure is shown not by the above meaning but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Description of Reference Numerals

[0047] 1... Bending test apparatus, 10... Pay-out section, 11... Bobbin, 12... Light source, 20... Dancer roller (tension applying mechanism), 30, 30a, 30b, 30c... Bending applying device (bending applying device for measuring bending loss), 31, 32, 33, 34, 35, 36, 41, 46... Guides, 51... Base plate, 52... Through groove, 53, 54, 55... Fixed mandrels, 61... Slide plate, 62... Motor, 63, 64, 65... Moving mandrels, 70... Fiber catcher, 80... Power meter, 81... Light receiving section, 82... Calculation section, F... Optical fiber.

Claims

1. A bending device having at least three mandrels, which bends an optical fiber by winding the fed optical fiber around the mandrels, wherein the mandrels are arranged alternately at a predetermined interval such that the outer circumferences of adjacent mandrels in the longitudinal direction of the optical fiber face each other without contact, with the diameter of the optical fiber being D and the radius of the mandrel being r. In a plane perpendicular to the rotation axis of the mandrel, taking the first direction as the direction connecting the upstream contact point where the optical fiber wound around the central mandrel among three mandrels of the same diameter arranged continuously along the longitudinal direction of the optical fiber starts to contact the central mandrel and the downstream contact point where the optical fiber wound around the central mandrel starts to separate from the central mandrel, the interval between adjacent mandrels in the first direction is 2r + d. Taking the second direction as the direction perpendicular to the first direction in a plane perpendicular to the rotation axis of the mandrel, the interval between adjacent mandrels in the second direction is s, and the angle θ formed between the second direction and the common internal tangent of adjacent mandrels viewed at the center position of the optical fiber is 0 degrees or more and 45 degrees or less. each adjacent mandrel is a fixed mandrel that does not move and a moving mandrel that is configured to be movable between a reference position where no bending is applied to the optical fiber and a forward position where bending is applied to the optical fiber with respect to the fixed mandrel, A bending device for measuring bending loss, in which among a plurality of the moving mandrels, the moving mandrel located on the downstream side in the longitudinal direction of the optical fiber is moved earlier than the moving mandrel located on the upstream side to apply bending to the optical fiber. Here, the angle θ satisfies the following formula (3). 【Mathematics 3】

2. The bending device for measuring bending loss according to claim 1, further comprising guides for ensuring the supply height of the optical fiber toward the mandrel and the discharge height of the optical fiber away from the mandrel, respectively.

3. The bending device for measuring bending loss according to claim 2, wherein the guides are arranged in parallel along a direction intersecting the longitudinal direction of the optical fiber.

4. A bending test device comprising the bending device for measuring bending loss according to any one of claims 1 to 3. A bending test apparatus having a tension applying mechanism for applying tension to the optical fiber toward the mandrel.

5. The bending test apparatus includes at least an upstream bending applying device located on the upstream side in the longitudinal direction of the optical fiber and a downstream bending applying device located on the downstream side of the upstream bending applying device, and the mandrel of the downstream bending applying device is formed with a larger diameter than the mandrel of the upstream bending applying device. The bending test apparatus according to claim 4, wherein the mandrel of the downstream bending applying device is moved in the second direction prior to the mandrel of the upstream bending applying device to apply bending to the optical fiber.

6. The bending test apparatus according to claim 4 or claim 5, further comprising an arithmetic unit configured to obtain a bending loss based on a length of the optical fiber to which bending is applied.

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