Optical connector boots

Abstract

This optical connector boot protects an optical fiber extending from an end of an optical connector, and comprises a boot body having formed therein a center hole into which the optical fiber is inserted, and a cylindrical straight portion extending from the rear end of the boot body and communicating with the center hole. The boot body includes a slit that is opened in the outer circumferential surface of the boot body and extends toward the center hole. When L is the length of the straight portion, Z is the section modulus of the straight portion, and E is the modulus of longitudinal elasticity of the straight portion, then L[mm] / (Z[mm3] × E[MPa]) ≥ 1.25 [ / mm2MPa].

Description

[Technical Field]

[0001] The present invention relates to a boot for an optical connector. This application claims priority based on Japanese Patent Application No. 2022-103566, filed on June 28, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] To ensure the quality of optical connectors, tests based on the Telcordia standard (hereinafter referred to as Telcordia tests) have been conducted. In Telcordia tests, the optical fiber extending from the optical connector is bent in multiple directions. The transmission loss (bending loss) that occurs when the optical fiber is bent in each direction is measured, and it is determined whether the bending loss meets the standard. More specifically, two types of tensile loads, low and high, are applied to the optical fiber in each direction, and the bending loss is evaluated for each of the two types of tensile loads.

[0003] A boot is generally attached to the rear end of an optical fiber connector to reduce bending loss. For example, Patent Document 1 discloses a configuration in which multiple radially extending slits are arranged at intervals along the longitudinal direction of the boot. With this configuration, when the optical fiber is bent, the wall surfaces of the slits come into contact with each other, thereby suppressing bending of the optical fiber and the bending loss caused by the bending. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2016-184009 Summary of the Invention [Problem to be solved by the invention]

[0005] During the Telcordia test, the boot bends elastically depending on the magnitude of the load. In other words, when the load is small, the boot bends less. With conventional boots, when the load is relatively small, the load causes the optical fiber to bend radially, but the boot does not bend sufficiently, resulting in the boot bending less than the optical fiber. In this case, a sharp bend occurs in the optical fiber at the rear end (free end) of the boot, which tends to increase bending loss. Due to this phenomenon, in the Telcordia test, even if the standard at high loads is met, the standard at low loads may not be met.

[0006] To solve the above problem, it is possible to adjust the length of the boot to make it easier to bend, but this method would increase the length of the boot, hindering the miniaturization of the optical connector.

[0007] The present invention has been made in consideration of the above circumstances, and has as its object to provide an optical connector boot that can suppress bending loss of an optical fiber in a low load test and reduce its length at the same time. [Means for solving the problem]

[0008] In order to solve the above problems, a first aspect of the present invention is a boot for an optical connector that protects an optical fiber extending from an end of an optical connector, the boot comprising: a boot body having a central hole through which the optical fiber is inserted; and a cylindrical straight portion extending from a rear end of the boot body and communicating with the central hole, the boot body having a slit that opens on an outer peripheral surface of the boot body and extends toward the central hole, and wherein, when the length of the straight portion is L, the section modulus of the straight portion is Z, and the longitudinal elastic modulus of the straight portion is E, L [mm] / (Z [mm 3 ]×E[MPa])≧1.25[ / mm 2 These are boots for optical connectors that meet the requirements of [MPa].

[0009] Furthermore, aspect 2 of the present invention is a boot for an optical connector according to aspect 1, wherein the outer surface of the boot body has a first tapered portion and a second tapered portion connected to the rear end of the first tapered portion and the front end of the straight portion, and the first tapered portion and the second tapered portion are inclined so that the outer diameter becomes smaller toward the rear.

[0010] A third aspect of the present invention is the boot for an optical connector of the first or second aspect, wherein the boot body and the straight portion are integrally formed from the same material.

[0011] A fourth aspect of the present invention is the boot for an optical connector according to any one of the first to third aspects, wherein the slit extends around the entire circumference of the boot body.

[0012] Furthermore, aspect 5 of the present invention is a boot for an optical connector, which is any one of aspects 1 to 4, wherein the boot body has two slits including the slit and two thin-walled portions located between the two slits and the central hole, the two slits are arranged at a distance from each other in the longitudinal direction of the central hole, and the radial thickness of the thin-walled portion located at the rear of the two thin-walled portions is less than or equal to the radial thickness of the thin-walled portion located at the front.

[0013] Furthermore, aspect 6 of the present invention is a boot for an optical connector according to any one of aspects 1 to 5, wherein the boot body has a plurality of slits including the slit, the plurality of slits are arranged at intervals in the longitudinal direction of the central hole, and the slit located furthest to the rear of the plurality of slits is connected to the central hole. [Effects of the Invention]

[0014] According to the above aspect of the present invention, it is possible to provide an optical connector boot that can suppress bending loss of an optical fiber in a low load test and reduce its length at the same time. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view showing an optical connector according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II shown in FIG. [Figure 3] 1 is a perspective view showing an optical connector boot according to an embodiment of the present invention; [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV shown in FIG. [Figure 5A] FIG. 4 is a cross-sectional view taken along the line VA-VA shown in FIG. [Figure 5B] FIG. 4 is a cross-sectional view taken along line VB-VB shown in FIG. [Figure 5C] FIG. 4 is a cross-sectional view taken along the line VC-VC shown in FIG. [Figure 5D] FIG. 4 is a cross-sectional view taken along line VD-VD shown in FIG. [Figure 6] FIG. 1 shows the Telcordia test. DETAILED DESCRIPTION OF THE INVENTION

[0016] An optical connector boot 10 according to an embodiment of the present invention and an optical connector 1 using the optical connector boot 10 will be described below with reference to the drawings.

[0017] As shown in FIGS. 1 and 2, the optical connector 1 according to this embodiment includes an optical connector boot 10, a housing 60, and a case 70. As shown in FIG. 2, the housing 60 houses a ferrule 20, a holding member 30, a spring push 40, and a biasing member 50. Hereinafter, the optical connector boot 10 may be simply referred to as the "boot 10." Note that the configuration of the optical connector 1 other than the boot 10 is merely an example and can be modified as appropriate. The optical connector 1 holds an optical fiber F. The optical fiber F extends from an end of the optical connector 1. As shown in FIG. 2, the boot 10 includes a boot body 11 and a straight portion 12. The boot body 11 and the straight portion 12 are cylindrical. The boot body 11 has a central hole 13, and the straight portion 12 has a communicating hole 17. The communicating hole 17 is communicated with the central hole 13. The optical fiber F is inserted through the central hole 13 and the communicating hole 17.

[0018] (direction definition) In this embodiment, the direction parallel to the central axis O of the central hole 13 of the boot 10 is referred to as the X direction, axial direction X, or longitudinal direction X. The direction in which the optical fiber F extends from the optical connector 1 along the longitudinal direction X is referred to as the -X direction or rearward. The communication hole 17 opens toward the rear. The direction opposite to the -X direction is referred to as the +X direction or forward. A cross section perpendicular to the longitudinal direction X is referred to as a transverse cross section. A direction perpendicular to the central axis O of the central hole 13 as viewed from the longitudinal direction X is referred to as a radial direction. A direction approaching the central axis O along the radial direction is referred to as a radially inner direction, and a direction away from the central axis O is referred to as a radially outer direction. A direction going around the central axis O as viewed from the longitudinal direction X is referred to as a circumferential direction. Hereinafter, a dimension in the longitudinal direction X may be simply referred to as a "length."

[0019] As shown in Fig. 2, the ferrule 20 has a connection end face 20a with a fiber hole 21 opening therein. The optical fiber F according to this embodiment includes an embedded fiber F1 that is inserted into the fiber hole 21 and fixed therein, and a connection fiber F2 that is connected to the rear end of the embedded fiber F1. The embedded fiber F1 and the connection fiber F2 are connected by, for example, fusion splicing. The embedded fiber F1 is fixed in the fiber hole 21 with the tip of the embedded fiber F1 positioned at the connection end face 20a.

[0020] The holding member 30 is formed with a holding hole 31 that opens forward, and a through hole 32 that opens into the holding hole 31 and extends rearward. The holding member 30 holds the ferrule 20 by inserting the rear end of the ferrule 20 into the holding hole 31. An optical fiber F (embedded fiber F1) is inserted into the through hole 32. The holding member 30 has a biased surface 30a that faces rearward. The rear end of the holding member 30 according to this embodiment is formed with a plurality of protrusions 33 that protrude radially outward from the outer circumferential surface of the holding member 30.

[0021] The spring push 40 is disposed behind the holding member 30. The spring push 40 has a through hole 41 formed therein, which penetrates the spring push 40 in the longitudinal direction X. The optical fiber F (connection fiber F2) is inserted into the through hole 41. The spring push 40 has a biasing surface 40a facing forward. A rear end of the spring push 40 is formed with a plurality of fixing protrusions 42 that protrude radially outward from the outer circumferential surface of the spring push 40. Although detailed illustration is omitted, the multiple fixing protrusions 42 are arranged at intervals in the circumferential direction.

[0022] The housing 60 is a cylindrical member and houses the ferrule 20, the holding member 30, and the spring push 40. The case 70 is also a cylindrical member and houses the housing 60. Although detailed illustration is omitted, the spring push 40 is fixed inside the housing 60.

[0023] The biasing member 50 is sandwiched between the biased surface 30a of the holding member 30 and the biasing surface 40a of the spring push 40. The biasing member 50 is compressed between the biased surface 30a and the biasing surface 40a, thereby biasing the ferrule 20 forward via the holding member 30. A coil spring, for example, can be used as the biasing member 50. In addition, a restricting protrusion 61 that protrudes radially inward from the inner circumferential surface of the housing 60 is formed at the front end of the housing 60 according to this embodiment. The restricting protrusion 61 abuts against the front surface of the holding member 30 to prevent the holding member 30 and the ferrule 20 from falling forward from the housing 60.

[0024] In this embodiment, the splice point P where the embedded fiber F1 and the connection fiber F2 are connected is protected by a heat-shrink sleeve 80. The heat-shrink sleeve 80 is a tubular member that can be shrunk by heating. The heat-shrink sleeve 80 is heat-shrunk so that the splice point P where the embedded fiber F1 and the connection fiber F2 are connected is located inside the heat-shrink sleeve 80. Furthermore, the heat-shrink sleeve 80 according to this embodiment is heat-shrunk so as to tighten the protrusion 33 of the holding member 30, thereby fixing the heat-shrink sleeve 80 to the rear end of the holding member 30. As shown in the example of FIG. 2, a tensile strength member 81 may be housed inside the heat-shrink sleeve 80 so as to be placed next to the splice point P. This configuration allows the splice point P to be protected more reliably.

[0025] The boot 10 serves to protect the optical fiber F (connection fiber F2) extending rearward from the optical connector 1. More specifically, the boot 10 is configured to elastically deform in accordance with the bending of the optical fiber F when a tensile load in the radial direction is applied to the optical fiber F (see also FIG. 6). The boot 10 serves to elastically absorb the bending of the optical fiber F and make the bending of the optical fiber F gentler. In other words, the boot 10 serves to reduce the curvature of the optical fiber F.

[0026] 2, 3, and 4, the straight portion 12 extends rearward from the rear end of the boot body 11. The boot body 11 and the straight portion 12 are configured to be elastically deformable. As will be described in detail below, the boot body 11 elastically absorbs a high load when applied to the optical fiber F, thereby suppressing bending of the optical fiber F. The straight portion 12 elastically absorbs a low load when applied to the optical fiber F, thereby suppressing bending of the optical fiber F.

[0027] In this embodiment, the boot body 11 and the straight portion 12 are integrally formed from the same material. For example, an elastomer resin can be used as the material for forming the boot body 11 and the straight portion 12. Examples of elastomer resins include TPE (ThermoPlastic Elastomer), TPS (Thermoplastic Styrenic Elastomer), and TPV (Thermoplastic vulcanizates, dynamically crosslinked thermoplastic elastomer).

[0028] As shown in Figures 5A to 5D, the center hole 13 and the communicating holes 17 have a substantially circular shape in cross-sectional view. In this specification, the term "substantially circular shape" also includes cases where the shape can be considered circular if manufacturing errors and elastic deformation are ignored. The center hole 13 is located at the center of the boot body 11 in the radial direction. The communicating holes 17 are located at the center of the straight portion 12 in the radial direction. As shown in Fig. 4, the diameter of the communicating hole 17 according to this embodiment is approximately constant at Φ4 in the longitudinal direction X. In other words, the inner diameter of the straight portion 12 according to this embodiment is approximately constant at Φ4 in the longitudinal direction X. Note that in this specification, the term "approximately constant" also includes cases where the diameter can be considered constant if manufacturing errors and elastic deformation are ignored. The inner diameter Φ4 of the straight portion 12 is, for example, about 1.6 mm.

[0029] As shown in FIG. 2, the boot body 11 is formed with an insertion hole 15 that opens forward. The insertion hole 15 is connected to the central hole 13. The rear end of the spring pusher 40 is inserted into the insertion hole 15. As shown in FIG. 3, the boot body 11 is formed with a plurality of fixing holes 15a that open into the insertion hole 15 and extend radially outward to the outer circumferential surface of the boot body 11. In this embodiment, the number of fixing holes 15a is the same as the number of fixing protrusions 42 described above. The fixing holes 15a are arranged at intervals in the circumferential direction. As shown in FIG. 2, the boot body 11 according to this embodiment is attached to the rear end of the spring pusher 40 by inserting the fixing protrusions 42 one by one into the fixing holes 15a.

[0030] As shown in Fig. 4, the outer peripheral surface of boot body 11 according to this embodiment has a non-tapered portion 11c, a first tapered portion 11a connected to the rear end of non-tapered portion 11c, and a second tapered portion 11b connected to the rear end of first tapered portion 11a and the front end of straight portion 12. As shown in Figs. 5A to 5C, each of non-tapered portion 11c, first tapered portion 11a, and second tapered portion 11b has a substantially circular shape in cross section. Also, as shown in Fig. 5D, the outer peripheral surface of straight portion 12 has a substantially circular shape in cross section.

[0031] As shown in FIG. 4, the outer diameter of the non-tapered portion 11c is substantially constant in the longitudinal direction X. The first tapered portion 11a and the second tapered portion 11b are inclined so that the outer diameter (diameter) decreases toward the rear. The inclination of the second tapered portion 11b with respect to the longitudinal direction X is greater than the inclination of the first tapered portion 11a with respect to the longitudinal direction X. The outer diameter of the straight portion 12 is substantially constant in the longitudinal direction X. The outer diameter Φ1 of the non-tapered portion 11c (the front end of the first tapered portion 11a) is, for example, approximately 6.2 mm. The outer diameter Φ2 of the rear end of the first tapered portion 11a (the front end of the second tapered portion 11b) is, for example, approximately 4.06 mm. The outer diameter Φ3 of the straight portion 12 (the rear end of the second tapered portion 11b) is, for example, approximately 1.6 mm. The length L1 (dimension in the longitudinal direction X) of the first tapered portion 11a is, for example, about 11.3 mm. The length L2 of the second tapered portion 11b is, for example, about 0.8 mm. The length L of the straight portion 12 is, for example, about 2.5 mm.

[0032] As shown in FIGS. 3 and 4 , the boot body 11 is formed with a plurality of (six in the illustrated example) slits 14 that open to the outer circumferential surface of the boot body 11 and extend radially inward toward the center hole 13. The plurality of slits 14 are spaced apart in the longitudinal direction X. Hereinafter, the six slits 14 will be referred to, in order from front to rear, as a first slit 14A, a second slit 14B, a third slit 14C, a fourth slit 14D, a fifth slit 14E, and a sixth slit 14F. In this embodiment, the first slit 14A opens into the non-tapered portion 11c. The second slit 14B, the third slit 14C, the fourth slit 14D, and the fifth slit 14E open into the first tapered portion 11a. The sixth slit 14F opens at the boundary between the first tapered portion 11a and the second tapered portion 11b. 3, each of the slits 14A to 14F extends around the entire circumference of the boot body 11. In other words, each of the slits 14A to 14F opens in the outer circumferential surface of the boot body 11 in an annular shape.

[0033] The boot body 11 has the slits 14A to 14F formed therein, which allows the boot body 11 to perform the aforementioned function, i.e., to elastically absorb a heavy load when the load is applied to the optical fiber F. Specifically, when a heavy load is applied to the optical fiber F and the boot body 11 is bent to a certain extent or more, the wall surfaces of the slits 14A to 14F come into contact with each other in the longitudinal direction X, as shown in Fig. 6. The wall surfaces of the slits 14A to 14F come into contact with each other, thereby suppressing bending of the boot body 11 and the optical fiber F inserted therein. Furthermore, the slits 14A to 14F extend around the entire circumference of the boot body 11, which reduces the circumferential dependency (bending directionality) of the bendability of the boot body 11.

[0034] As shown in FIG. 4, the slits 14A to 14F are formed, so that the thickness of the boot body 11 at the portions where the slits 14A to 14F are formed (the radial distance between the outer peripheral surface of the boot body 11 and the central hole 13) is smaller than the thickness of the portions where the slits 14A to 14F are not formed. Hereinafter, each of the multiple portions of the boot body 11 located between the multiple slits 14A to 14F and the central hole 13 in the radial direction will be referred to as a thin-walled portion 16. In particular, the portion located between the first slit 14A and the central hole 13 in the radial direction will be referred to as a first thin-walled portion 16A, and the portion located between the second slit 14B and the central hole 13 will be referred to as a second thin-walled portion 16B. Similarly, the portions located between the third slit 14C to the sixth slit 14F and the central hole 13 will be referred to as a third thin-walled portion 16C to a sixth thin-walled portion 16F, respectively (see also FIG. 5C).

[0035] 5A is a cross-sectional view taken along line VA-VA in FIG. 3, showing a region in which first slit 14A is formed in the longitudinal direction. As shown in FIG. 5A, first slit 14A does not communicate with central hole 13. First thin-walled portion 16A has a substantially annular shape in cross section. Although not shown in detail, second slit 14B to fourth slit 14D do not communicate with central hole 13, similar to first slit 14A. Second thin-walled portion 16B to fourth thin-walled portion 16D each have a substantially annular shape in cross section, similar to first thin-walled portion 16A. In this specification, the term "substantially annular" also includes cases where the shape can be considered to be annular if manufacturing errors and elastic deformation are ignored.

[0036] 5B is a cross-sectional view taken along line VB-VB in FIG. 3, showing a region in which fifth slit 14E is formed in the longitudinal direction. As shown in FIG. 5B, fifth slit 14E, unlike slits 14A to 14D, is connected to center hole 13 at a portion in the circumferential direction. As a result, fifth thin-walled portion 16E does not have an annular shape in cross section. Specifically, fifth thin-walled portion 16E according to this embodiment includes two portions 16EA and 16EB that are spaced apart from each other in the circumferential direction. In other words, fifth thin-walled portion 16E has an annular shape with a portion in the circumferential direction that is hollowed out. 5C is a cross-sectional view taken along line VC-VC in FIG. 3, showing a cross-sectional view of a region in which sixth slit 14F is formed in the longitudinal direction. As shown in FIG. 5C, sixth slit 14F, like fifth slit 14E, is connected to center hole 13 in a portion in the circumferential direction. As a result, sixth thin-walled portion 16F does not have an annular shape in cross section, but includes two portions 16FA and 16FB that are spaced apart in the circumferential direction. In other words, sixth thin-walled portion 16F has an annular shape with a portion in the circumferential direction removed.

[0037] As described above, by adopting a configuration in which the slits 14E, 14F located at the rear end of the boot body 11 communicate with the central hole 13, the rigidity of the rear end of the boot body 11 can be reduced. This makes the rear portion of the boot body 11 more easily bent in the radial direction than the front portion of the boot body 11, making it easier to reduce the curvature of the optical fiber F when a load is applied. Note that, as shown in FIGS. 5B and 5C , in this embodiment, the positions of the fifth thin-walled portions 16EA, 16EB and the sixth thin-walled portions 16FA, 16FB are offset by 90° in the circumferential direction. This makes it possible to suppress an increase in the bending directionality of the boot body 11, which would be caused by the thin-walled portions 16E, 16F being partially hollowed out in the circumferential direction.

[0038] As shown in FIG. 4, the thin-walled portions 16A to 16F according to this embodiment are designed so that the thickness of the thin-walled portions 16 in the radial direction gradually decreases toward the rear. Hereinafter, the radial thickness of the thin-walled portions 16 will also be referred to as the "thickness of the thin-walled portions 16." In other words, for each of two thin-walled portions 16 adjacent to each other in the longitudinal direction X, the thickness of the thin-walled portion 16 located rearward is equal to or less than the thickness of the thin-walled portion 16 located forward. In this embodiment, when the outer diameters of the first thin-walled portion 16A to the sixth thin-walled portion 16F are ΦA to ΦF (see also FIG. 5C), respectively, the following relationship holds: ΦA ≥ ΦB ≥ ΦC ≥ ΦD ≥ ΦE ≥ ΦF. The outer diameter ΦA of the first thin-walled portion 16A is, for example, approximately 4.8 mm. The outer diameter ΦB of the second thin-walled portion 16B is, for example, approximately 2.6 mm. The outer diameter ΦC of the third thin-walled portion 16C is, for example, approximately 2.2 mm. The outer diameter ΦD of the fourth thin portion 16D is, for example, about 2.2 mm. The outer diameter ΦE of the fifth thin portion 16E is, for example, about 1.6 mm. The outer diameter ΦF of the sixth thin portion 16F (see FIG. 5C) is, for example, about 1.6 mm.

[0039] By adopting a configuration in which the thickness gradually decreases toward the rearwardly located thin-walled portion 16, it is possible to realize a rigidity distribution in the boot body 11 in which the rigidity gradually decreases from the front to the rear, thereby more effectively suppressing the curvature of the optical fiber F when a load is applied.

[0040] Incidentally, when the tensile load applied to the optical fiber F is small, the bending of the boot body 11 also becomes small. If the boot 10 only has the boot body 11, when the tensile load is relatively small, the load causes the optical fiber F to tend to bend in the radial direction, but the boot body 11 does not bend sufficiently, and the bending of the boot body 11 may become smaller than the bending of the optical fiber F. In this case, a sharp bend occurs in the optical fiber F at the rear end (free end) of the boot body 11, and bending loss is likely to increase.

[0041] Therefore, the boot body 11 according to this embodiment has a straight portion 12 connected to the rear end of the boot body 11. When a small load is applied to the optical fiber F, the straight portion 12 elastically receives the optical fiber F at the rear end of the boot body 11 and plays a role in suppressing an increase in the curvature of the optical fiber F.

[0042] As a result of extensive research by the inventors of the present application, it has been found that the bending loss of the optical fiber F when a low load is applied can be suppressed by adjusting the length L of the straight portion 12, the section modulus Z of the straight portion 12, and the modulus of longitudinal elasticity (Young's modulus) E of the straight portion 12. It is believed that increasing the value of the length L increases the contact area between the optical fiber F and the straight portion 12, making it easier to suppress bending of the optical fiber F even when a low load is applied. It is also believed that decreasing the values ​​of the section modulus Z and the modulus of longitudinal elasticity E makes the straight portion 12 more flexible, allowing the straight portion 12 to bend so as to follow the bending of the optical fiber F. [Example]

[0043] Hereinafter, using specific examples, conditions that preferably hold regarding the length L of the straight portion 12, the section modulus Z, and the modulus of longitudinal elasticity E will be described. Note that the present invention is not limited to the following examples.

[0044] Example 1 A plurality of boots 10 were prepared, each having a different length L of the straight portion 12 and a different thickness of the straight portion 12. The straight portion 12 of each of the boots 10 had a common modulus of longitudinal elasticity E of 7.2 MPa and a common inner diameter Φ4 of 0.9 mm. The "thickness of the straight portion 12" refers to the radial distance between the communicating hole 17 and the outer circumferential surface of the straight portion 12 (see FIG. 4), and is expressed as (Φ3 - Φ4) / 2.

[0045] An optical connector 1 was assembled using each boot 10, and a Telcordia test was performed on each optical connector 1. As shown in Figure 6, in the Telcordia test, a load was applied to the optical fiber F in a direction perpendicular to the longitudinal direction X (i.e., the radial direction). More specifically, two types of loads, a high load (0.7 kg) and a low load (0.25 kg), were applied to each of eight directions perpendicular to the longitudinal direction X, and the bending loss was evaluated for each of the two types of loads. In addition, for each optical connector 1, a simulation was performed to determine how much the position of the rear end (free end) of the straight portion 12 would be displaced in the radial direction when a load of 1 g was applied to the optical fiber F. In addition, the value of parameter A, defined by the following equation a, was calculated for each optical connector 1 (straight portion 12). a:A[ / mm 2 MPa]=L[mm] / (Z[mm 3 ]×E [MPa]) L: Length of straight section 12 Z: Section modulus of straight section 12 E: Modulus of longitudinal elasticity of the straight section 12 Table 1 is a table summarizing the test results, the simulation results, and the calculated values ​​of the parameter A.

[0046] [Table 1]

[0047] In Table 1, for each of the 36 combinations of the length L and thickness of the straight portion 12, the calculated value of parameter A is shown in the upper row, the simulated value of the displacement of the straight portion 12 is shown in the middle row, and the evaluation result of bending loss in the low-load test is shown in the lower row. The "evaluation result of bending loss in the low-load test" was rated "good" when the maximum value of bending loss in eight directions was 0.50 dB or less, and "poor" when the maximum value of bending loss exceeded 0.50 dB. Note that the evaluation result of bending loss in the high-load test was "good" for all boots 10, so it is not shown here. Furthermore, since the straight portion 12 according to this embodiment has a substantially cylindrical shape, the section modulus Z was calculated using the following formula b. Table 2 summarizes the calculated values ​​of the section modulus Z. As mentioned above, the inner diameter Φ4 of the multiple boots 10 is common to all of the boots 10, at 0.9 mm, and the thickness was changed by changing the size of Φ3. b:Z=(π / 32)×(Φ3 4 -Φ4 4 ) / Φ3

[0048] [Table 2]

[0049] As shown in Table 1, the larger the value of parameter A, the greater the displacement of the straight portion 12 when a load of 1 g is applied. In other words, a positive correlation is observed between parameter A and the displacement of the straight portion 12. This supports the idea that by increasing the value of parameter A, the straight portion 12 can be bent to follow the bending of the optical fiber F, even when an extremely low load, such as 1 g, is applied to the optical fiber F.

[0050] Furthermore, as shown in Table 1, for boots 10 with a parameter A value of 1.25 or more, the bending loss in the low load test was evaluated as "good." On the other hand, for boots 10 with a parameter A value of less than 1.25, the bending loss in the low load test was evaluated as "poor." In this way, by making the parameter A value 1.25 or more, the bending loss of the optical fiber F in the low load test can be suppressed.

[0051] Example 2 Similar to the above-described Example (Example 1), a plurality of boots 10 were prepared, each having a different length L and thickness of the straight portion 12, but with a common inner diameter Φ4 of 0.9 mm. In this Example, unlike the above-described Example (Example 1), the Young's modulus E of the straight portion 12 was common to all of the plurality of boots 10, being 3.9 MPa. Table 3 is a table summarizing the results of the low load test, the results of the simulation, and the calculated value of the parameter A for the boot 10 according to this Example.

[0052] [Table 3]

[0053] In this example as well, the larger the value of parameter A, the greater the displacement of the straight portion 12 when a load of 1 g is applied. Furthermore, in boots 10 for which the value of parameter A is 1.25 or more, the bending loss in the low load test is evaluated as "good." On the other hand, in boots 10 for which the value of parameter A is less than 1.25, the bending loss in the low load test is evaluated as "poor." In other words, even in this example, in which the Young's modulus E of the straight portion 12 is different from that of Example 1, by setting the value of parameter A to 1.25 or more, the bending loss of the optical fiber F in the low load test can be suppressed.

[0054] In light of the above, in this embodiment, a boot 10 for an optical connector that protects an optical fiber F extending from an end of an optical connector 1 includes a boot body 11 having a central hole 13 through which the optical fiber F is inserted, and a cylindrical straight portion 12 that extends from the rear end of the boot body 11 and communicates with the central hole 13, and the boot body 11 has a slit 14 that opens on the outer peripheral surface of the boot body 11 and extends toward the central hole 13, and when the length of the straight portion 12 is L, the section modulus of the straight portion 12 is Z, and the longitudinal elastic modulus of the straight portion 12 is E, L [mm] / (Z [mm 3 ]×E[MPa])≧1.25[ / mm 2 The present invention proposes an optical connector boot 10 that satisfies the above requirements.

[0055] This configuration makes it possible to suppress the bending loss of the optical fiber F in a low-load test. Furthermore, to achieve L / ZE≧1.25, it is also possible to employ a method of reducing the section modulus Z or the Young's modulus E of the straight portion 12, in addition to a method of increasing the length L of the straight portion 12. In other words, by adjusting the section modulus Z and the Young's modulus E of the straight portion 12, it is possible to suppress the bending loss of the optical fiber F without excessively increasing the value of the length L of the straight portion 12. This makes it possible to achieve both suppression of the bending loss of the optical fiber F and a reduction in the length of the boot 10.

[0056] The outer peripheral surface of the boot 10 may have a first tapered portion 11a and a second tapered portion 11b connected to the rear end of the first tapered portion 11a and the front end of the straight portion 12, and the first tapered portion 11a and the second tapered portion 11b may be inclined so that their outer diameters decrease toward the rear. This configuration allows the boot body 11 to achieve a section modulus distribution in which the section modulus gradually decreases from the front to the rear. This effectively reduces the curvature of the optical fiber F when a load is applied. Furthermore, the provision of the second tapered portion 11b prevents discontinuous bending at the connection between the boot body 11 and the straight portion 12.

[0057] The boot body 11 and the straight portion 12 may be integrally formed from the same material. This configuration makes it easy to manufacture the boot 10 having the boot body 11 and the straight portion 12.

[0058] The slit 14 may also extend around the entire circumference of the boot body 11. This configuration can reduce the bending directionality of the boot body 11 (boot 10).

[0059] Furthermore, the boot body 11 has a plurality of slits 14A-14F and a plurality of thin-walled portions 16A-16F located between the plurality of slits 14A-14F and the central hole 13, the plurality of slits 14A-14F being spaced apart in the longitudinal direction X, and for each of two thin-walled portions 16 adjacent to each other in the longitudinal direction X, the thickness of the rearwardly positioned thin-walled portion 16 may be equal to or less than the thickness of the forwardly positioned thin-walled portion 16. This configuration makes it possible to achieve a rigidity distribution in the boot body 11 in which the rigidity gradually decreases from the front to the rear. This makes it possible to more effectively reduce the curvature of the optical fiber F when a load is applied.

[0060] Furthermore, the slit 14F located furthest to the rear among the plurality of slits 14A to 14F may be connected to the central hole 13. This configuration can reduce the rigidity of the rear end portion of the boot body 11. This makes the rear portion of the boot body 11 more easily bendable in the radial direction than the front portion of the boot body 11, making it easier to reduce the curvature of the optical fiber F when a load is applied.

[0061] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0062] For example, the boot body 11 and the straight portion 12 may be made of different materials.

[0063] The number and positions of the slits 14 in the boot body 11 can be changed as appropriate. The number and positions of the slits 14 communicating with the central hole 13 can be changed as appropriate. There may not be a slit 14 communicating with the central hole 13. For example, in the above-described embodiment, the fifth thin-walled portion 16E of the fifth slit 14E and the sixth thin-walled portion 16F of the sixth slit 14F may have a substantially annular shape in cross section.

[0064] Furthermore, there may be at least one pair of two adjacent thin-walled portions 16 in the longitudinal direction X that satisfies the relationship that "the thickness of the rearwardly positioned thin-walled portion 16 is equal to or less than the thickness of the forwardly positioned thin-walled portion 16." Alternatively, such a pair of two thin-walled portions 16 does not necessarily have to exist.

[0065] Alternatively, the boot body 11 may not have the slit 14 and the thin portion 16 formed therein.

[0066] Furthermore, the outer peripheral surface of the boot body 11 does not necessarily have to have the first tapered portion 11a or the second tapered portion 11b.

[0067] Moreover, the various dimensions L, L1, L2, Φ1 to Φ3, and ΦA to ΦF in the above embodiment are all examples and can be changed as appropriate.

[0068] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate, without departing from the spirit of the present invention. [Explanation of symbols]

[0069] 1...optical connector 10...boot (boot for optical connector) 11...boot body 11a...first tapered portion 11b...second tapered portion 12...straight portion 13...center hole 14...slit 16...thin portion X...longitudinal direction

Claims

1. An optical connector boot for protecting an optical fiber extending from an end of an optical connector, a boot body having a central hole through which the optical fiber is inserted; a cylindrical straight portion extending from a rear end of the boot body and communicating with the center hole; The boot body has a slit that opens on an outer circumferential surface of the boot body and extends toward the center hole, When the length of the straight portion is L, the section modulus of the straight portion is Z, and the longitudinal elastic modulus of the straight portion is E, L [mm] / (Z [mm ３ ]×E[MPa])≧1.25[ / mm ２ MPa] holds true. Boots for optical connectors.

2. The outer peripheral surface of the boot body has a first tapered portion and a second tapered portion connected to a rear end of the first tapered portion and a front end of the straight portion, The first tapered portion and the second tapered portion are inclined so that the outer diameters thereof become smaller toward the rear.

2. The boot for an optical connector according to claim 1.

3. The boot body and the straight portion are integrally formed from the same material.

3. The boot for an optical connector according to claim 1 or 2.

4. The slit extends around the entire circumference of the boot body.

3. The boot for an optical connector according to claim 1 or 2.

5. The boot body includes: Two slits including the slit; two thin-walled portions located between the two slits and the central hole, The two slits are arranged at an interval in the longitudinal direction of the central hole, 3. The optical connector boot according to claim 1, wherein the radial thickness of the rearwardly positioned thin-walled portion of the two thin-walled portions is equal to or less than the radial thickness of the forwardly positioned thin-walled portion.

6. The boot body has a plurality of slits including the slit, The plurality of slits are arranged at intervals in the longitudinal direction of the central hole, The rearmost slit among the plurality of slits communicates with the central hole.

3. The boot for an optical connector according to claim 1 or 2.

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