Optical connection assembly

Abstract

An optical connection assembly according to the present disclosure comprises: first and second optical connectors each having a ferrule assembly, a plug frame, and an elastic member; and an adapter. The ferrule assembly includes a ferrule and a ferrule flange, and is housed in the plug frame. The adapter has an adapter body and a sleeve formed integrally with the adapter body or a sleeve holder for holding the sleeve. The adapter body has a first internal space, a second internal space, a first opening, and a second opening. The sleeve has pull-out strength sufficient to maintain a mounted state in which the ferrule assembly of the first optical connector is in contact with the sleeve and the plug frame, and the ferrule assembly of the second optical connector is in contact with only the sleeve.

Description

Optical connection assembly ,

[0005]

[0001] The present disclosure relates to an optical connection assembly. This application claims priority based on Japanese Patent Application No. 2024-198087 filed on November 13, 2024, and incorporates all the descriptions set forth in the above-mentioned Japanese application.

[0002] When connecting optical fibers such as polarization-maintaining optical fibers (PMF), multi-core optical fibers (MCF), and bundle fibers by a connector, in order to align the arrangement of all components including the core on the fiber cross-section in two optical fibers, it is necessary to adjust the rotation angle of these optical fibers around the fiber axis. In the optical connectors shown in Non-Patent Document 1 and Patent Document 1, a ferrule attached to the tip of an optical fiber is fixed to a metal flange. This metal flange contacts the angle reference surface of a plug frame that functions as a housing using an elastic member such as a spring material, thereby adjusting the angle of the optical fiber.

[0003] At the time of connector connection, optical connectors attached to the tips of two optical fibers that require the above-described rotational alignment for optical connection are mounted in an adapter so as to face each other. A sleeve is disposed in the adapter, and at the time of mounting, the tips of the ferrules of these optical connectors are inserted into the sleeve from different directions. When the mounting of the plug frame to the adapter is completed with the tips of the ferrules abutted against each other in the sleeve, the ferrule retreats (flange back) and enters a floating state. In the floating state, since the ferrule is rotationally fixed only by the sleeve, it becomes difficult for an external force applied to the plug frame to be transmitted to the ferrule.

[0004] International Publication No. WO2018 / 180898, Japanese Unexamined Patent Application Publication No. 2015-059941

[0005] T. Morishima, et al., “Simple-StructureLC-Type Multi-Core Fiber Connector with Low Insertion Loss,” inOpt. Fiber Commun. Conf.(OFC) (2020), p. Th3I.2.

[0006] The optical connection assembly of the present disclosure comprises a first optical connector, a second optical connector, and an adapter. Each of the first and second optical connectors has a ferrule assembly and a plug frame. The ferrule assembly consists of a ferrule and a ferrule flange and is housed within the plug frame. The ferrule is attached to the end of an optical fiber. The ferrule flange holds the ferrule with the optical fiber passing through it and has a flange portion that abuts against the inner wall surface of the plug frame. The adapter has an adapter body and a sleeve or a sleeve holder that holds the sleeve. The adapter body has a first internal space, a second internal space, a first opening, and a second opening. The first internal space houses a portion of the first optical connector. The second internal space houses a portion of the second optical connector. The first opening allows a portion of the first optical connector to be introduced into the first internal space. The second opening allows a portion of the second optical connector to be introduced into the second internal space. A sleeve or sleeve holder is installed between the first internal space and the second internal space, and the ends of the ferrules of the first and second optical connectors are inserted into the sleeve.

[0007] In the optical connection assembly of this disclosure, each of the first optical connector and the second optical connector includes an elastic member housed within a plug frame and providing a biasing force to the ferrule flange. A sleeve or sleeve holder is formed integrally with the adapter body. The sleeve is fixed in a state where the ferrule assembly of the first optical connector is in contact with both the sleeve and the inner wall of the plug frame when the first optical connector is mounted on the adapter body before the second optical connector. The sleeve has pull-out strength to maintain a mounting state in which the ferrule assembly of the second optical connector is fixed in contact with the sleeve only.

[0008] Figure 1 is a diagram illustrating the assembly process of the optical connection assembly and its components according to the present disclosure. Figure 2 is a diagram illustrating the structure of a modified ferrule assembly and various assembly processes. Figure 3 is a front view of a ferrule assembly to which various optical fibers are applied as the optical fibers to be connected in the optical connection assembly according to the present disclosure. Figure 4 is a diagram illustrating the cross-sectional structure of the components of the optical connection assembly according to the present disclosure and a method for measuring the pull-out strength of one of the components, a sleeve. Figure 5 is a diagram illustrating the change in the orientation of the optical connector during the insertion process into the adapter in the assembly process of the optical connection assembly according to the present disclosure. Figure 6 is a graph plotting the relationship between the change in sleeve pull-out strength and insertion loss for two types of adapter samples with different structures. Figure 7 is a graph plotting the relationship between the number of insertions and removals of the optical connector and insertion loss for two types of integrated adapter samples having sleeves with different pull-out strengths.

[0009] The inventors, after examining the above-mentioned prior art, discovered the following problems. In conventional optical connection assemblies, optical connectors attached to the ends of two optical fibers, each requiring rotational alignment for optical connection, are mounted on an adapter with a sleeve inside. In this case, the arrangement of all components, including the core, on the fiber cross-section must be matched for the two optical fibers whose ends abut against each other within the sleeve. In operating environments that include attaching and detaching optical connectors, maintaining the reproducibility of the matched arrangement of all components, including the core, is important for reducing variations in the insertion loss of the optical connector.

[0010] Adapters with a sleeve positioned inside employ either a separate structure in which the adapter is composed of multiple components and the sleeve holder is incorporated during the adapter assembly process, as disclosed in Patent Document 2, or an integrated structure in which the sleeve or the sleeve holder that holds the sleeve is formed integrally with the adapter body.

[0011] In adapters employing a separate structure, a gap exists between the adapter body and the sleeve holder inside the adapter, allowing the sleeve holder to move even after the adapter is assembled. In this situation, when either optical connector is inserted into the adapter, the external force during insertion may cause the sleeve holder to move relative to the adapter body. The ferrule of the subsequently inserted optical connector will be held only by the sleeve, and in this case, the ferrule of the later-inserted optical connector will inevitably undergo changes in posture, such as rotation or tilting, in order to follow the displacement of the sleeve.

[0012] In adapters employing a one-piece structure, repeated attachment and detachment of the optical connector to the adapter generates rotational force on the ferrule due to flange back within the plug frame. This is because the rotation of the spring material, caused by changes in its shape such as contraction and extension during flange back, is transmitted to the ferrule. In such a situation, an increase in connection loss between the two optically connected fibers is unavoidable due to the ferrules abutting against each other.

[0013] This disclosure was made to solve the problems described above and aims to provide an optical connection assembly with a structure that effectively reduces variations in the insertion loss of an optical connector under operating conditions, including the insertion and removal of the optical connector.

[0014] The optical connection assembly of this disclosure effectively reduces variations in the insertion loss of the optical connector under operating conditions, including the insertion and removal of the optical connector.

[0015] The contents of this disclosed embodiment will be explained.

[0016] (1) The optical connection assembly of the present disclosure comprises a first optical connector, a second optical connector, and an adapter. Each of the first and second optical connectors has a ferrule assembly and a plug frame. The ferrule assembly consists of a ferrule and a ferrule flange and is housed within the plug frame. The ferrule is attached to the end of an optical fiber. The ferrule flange holds the ferrule with the optical fiber passing through it. The adapter has an adapter body and a sleeve or a sleeve holder that holds the sleeve. The adapter body has a first internal space, a second internal space, a first opening, and a second opening. The first internal space houses a portion of the first optical connector. The second internal space houses a portion of the second optical connector. The first opening allows a portion of the first optical connector to be introduced into the first internal space. The second opening allows a portion of the second optical connector to be introduced into the second internal space. The sleeve or sleeve holder is installed between the first and second internal spaces, and the ends of the ferrules of the first and second optical connectors are inserted into the sleeve.

[0017] In the optical connection assembly of this disclosure, each of the first optical connector and the second optical connector includes an elastic member housed within a plug frame and providing a biasing force to the ferrule flange. The sleeve or sleeve holder is formed integrally with the adapter body.

[0018] In the optical connection assembly of this disclosure, the sleeve has sufficient pull strength to maintain the ferrule assemblies of the first and second optical connectors in a specific mounting position. Specifically, the sleeve is fixed in a state where the ferrule assembly of the first optical connector is in contact with both the sleeve and the inner wall of the plug frame when the first optical connector is mounted on the adapter body before the second optical connector. The sleeve has sufficient pull strength to maintain a mounting position in which the ferrule assembly of the second optical connector is fixed in contact with only the sleeve. In this specification, the state in which the ferrule assembly of the first optical connector is fixed in contact with both the sleeve and the inner wall of the plug frame is referred to as the non-floating state. The state in which the ferrule assembly of the second optical connector is fixed in contact with only the sleeve is referred to as the floating state.

[0019] According to the optical connection assembly of this disclosure, in the plug frame of the first optical connector, which is first mounted on the adapter, the tip of the ferrule enters the sleeve due to the biasing force of the elastic member on the ferrule assembly, and the ferrule flange is maintained in an angled position by the plug frame. In this state, in order to cause flange back with respect to the ferrule assembly of the first optical connector, a force exceeding the biasing force of the elastic member and the frictional force between the sleeve and the ferrule (maximum frictional force defined by the static friction coefficient) must be applied. In the second optical connector, which is later inserted into the adapter, the ferrule enters the sleeve while receiving a frictional force from the sleeve (frictional force defined by the dynamic friction coefficient) as the plug frame is pushed in, and abuts against the ferrule of the first optical connector. In order to mount the second optical connector on the adapter, the plug frame needs to be pushed in further from the point where the ferrules abut. At this time, the biasing force (restoring force) of the elastic member of the second optical connector increases due to further compression.

[0020] From the above, in order for flange back to occur in the ferrule assembly of the first optical connector which is mounted on the adapter first, the elastic member of the second optical connector, which is further compressed when mounted on the adapter, must have a biasing force that exceeds the sum of the biasing force of the elastic member of the first optical connector, the maximum frictional force applied to the ferrule, and the dynamic frictional force applied to the ferrule of the second optical connector. This means that the attitude of the ferrule assembly of the first optical connector which is mounted on the adapter first can be controlled by adjusting the pull-out strength of the sleeve, which directly affects the magnitude of the frictional force. In other words, if the pull-out strength of the sleeve is appropriately adjusted, it becomes possible to cause flange back only in the ferrule assembly of the second optical connector. In such a configuration, the first optical connector which is mounted on the adapter first is not affected by the rotational force caused by the change in shape of the elastic member, such as contraction and expansion. As a result, the fluctuation in optical fiber connection loss (insertion loss of the optical connector) caused by the change in shape of the elastic member is reduced for the optical connection assembly as a whole.

[0021] The pull-out strength of the sleeve is equal to the magnitude of the frictional force applied from the sleeve to the ferrule along the longitudinal direction of the ferrule. Whether or not a ferrule inserted into a sleeve rotates is determined by the magnitude of the frictional force applied from the sleeve to the ferrule along the circumferential direction of the ferrule and the magnitude of the rotational force caused by the change in shape of the elastic member. From this, it can be concluded that although the direction of the frictional force received from the sleeve differs between movement along the longitudinal direction of the ferrule and rotation in the circumferential direction, there is a strong correlation between the pull-out strength and the frictional force (rotational fixing force) required to prevent the rotation of the ferrule.

[0022] According to the optical connection assembly of this disclosure, the sleeve or sleeve holder that holds the sleeve, which is positioned within the adapter, is formed integrally with the adapter body, and there is virtually no positional variation of the sleeve within the adapter body. This effectively reduces variations in connection loss between the two abutted optical fibers, even when at least one of the first optical connector and the second optical connector is attached to or detached from the adapter. The statement that the sleeve or sleeve holder is formed integrally with the adapter body means that the sleeve or sleeve holder has a surface that is continuous with the inner wall surface of the adapter body defining the first and second internal spaces. Therefore, in this specification, the sleeve or sleeve holder formed integrally with the adapter body does not include a structure (separate structure) that is incorporated into the adapter body as a separate component during the assembly process of the adapter body, which is composed of multiple components.

[0023] (2) In (1) above, the pull strength of the sleeve may be 1.5 N or more. In this case, the ferrule assembly of the first optical connector, which is attached to the adapter first, is fixed in contact with both the sleeve and the inner wall of the plug frame. The sleeve can reliably maintain a mounting state in which the ferrule assembly of the second optical connector, which is attached later, is fixed in contact only with the sleeve.

[0024] (3) In (1) or (2) above, the elastic member may be a spring material arranged to surround the optical fiber. In this case, the first optical connector and the second optical connector can be obtained at low cost without complicating the structure.

[0025] (4) In any of (1) to (3) above, the plug frames of the first optical connector and the second optical connector may each have a positioning portion into which a ferrule flange, which is biased by an elastic member, is abutted. In this case, within the plug frame of the first optical connector after both the first optical connector and the second optical connector have been mounted on the adapter, the orientation of the ferrule assembly is maintained such that the tip of the ferrule is in contact with the tip of the ferrule of the second optical connector within the sleeve, and the ferrule flange is in contact with the positioning portion.

[0026] (5) In (4) above, within the plug frame of the second optical connector, the orientation of the ferrule assembly is maintained such that the tip of the ferrule is in contact with the tip of the ferrule of the first optical connector within the sleeve, and the ferrule flange is physically separated from the positioning part (floating state). In this case, the influence of external forces on the plug frame of the second optical connector is reduced. When the ferrule assembly of the first optical connector of the pair of optical connectors mounted on the adapter is set to the floating state, even when an external force is applied to at least one of the plug frame and the adapter, the ferrule assembly of the floating optical connector can follow the orientation and fiber axis of the non-floating ferrule assembly in the second optical connector. Therefore, the contact state of the tips of the ferrule assemblies is maintained, and the increase in connection loss between the two abutted optical fibers is reduced.

[0027] Each of the embodiments listed above is applicable to each of the remaining embodiments, or to all combinations of these remaining embodiments.

[0028] [Details of Embodiments of the Disclosure] Specific examples of optical connection assemblies relating to the Disclosure will be described in detail below with reference to the accompanying drawings. The present invention is not limited to these examples, and is intended to include all modifications within the meaning and scope of the claims, as indicated by the claims. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0029] Figure 1 is a diagram illustrating the assembly process of the optical connection assembly 1 and its components according to the present disclosure (referred to as "assembly process" in Figure 1). The upper part of Figure 1 (referred to as "optical connection assembly" in Figure 1) shows a diagram illustrating the assembly process of an example of the optical connection assembly 1 according to the present disclosure. The lower part of Figure 1 (referred to as "ferrule assembly" in Figure 1) shows a diagram illustrating the assembly configuration of an example of a ferrule assembly 100 as a component of the optical connection assembly 1.

[0030] The optical connection assembly 1 shown in the upper part of Figure 1 comprises a first optical connector 10A, a second optical connector 10B, and an adapter 600, which are attached to the ends of two optical fibers 50 that require rotational alignment for optical connection. In the example shown in the upper part of Figure 1, the second optical connector 10B is attached to the adapter 600 before the first optical connector 10A, but the order of attachment may be reversed. LC, SC, and MU type optical connectors are applicable to both the first optical connector 10A and the second optical connector 10B. Unless otherwise specified herein, an LC type optical connector is meant as a representative example. The optical fibers 50 to which the optical connection assembly 1 of this disclosure is applied include, for example, PMF, MCF, and bundled fibers.

[0031] The adapter 600 has an adapter body 610 in which a sleeve or a sleeve holder for holding the sleeve is integrally formed inside. Inside the adapter body 610, there is a first internal space for housing a part of the first optical connector 10A and a second internal space for housing a part of the second optical connector 10B. The adapter body 610 is provided with a first opening 620a for introducing a part of the first optical connector 10A into the first internal space and a second opening 620b for introducing a part of the second optical connector 10B into the second internal space.

[0032] The first optical connector 10A and the second optical connector 10B have the same structure. As an example, the first optical connector 10A has a plug frame that functions as a housing. The plug frame is composed of a front housing 20 and a rear housing 30. Inside this plug frame is a ferrule assembly 100 including a ferrule 110 and an elastic member, such as a spring, for stably maintaining the housing position of the ferrule assembly 100. The tip portion of the optical fiber 50, including the end face, corresponds to a glass fiber 51 from which the resin coating has been removed, and the ferrule 110 is attached to the glass fiber 51. A boot 40 is attached to the rear housing 30 to protect the optical fiber 50 extending from the rear housing 30.

[0033] As shown in the lower part of Figure 1, the ferrule assembly 100 consists of a ferrule 110 attached to the tip of the glass fiber 51 from which the resin coating has been removed, and a ferrule flange 130, for example, made of metal. The ferrule flange 130 has a flange portion 130A and a body portion 130B for restricting the rotation of the ferrule assembly 100. The flange portion 130A has a flange front surface 130a that abuts against a positioning portion in the plug frame, and a flange rear surface 130b that receives a biasing force from an elastic member such as a spring from the rear. In a structure in which the ferrule is fixed with the ferrule flange 130, the rear end of the ferrule 110 is inserted into the ferrule flange 130.

[0034] Specifically, in the assembly process of the ferrule assembly 100, first, with the ferrule 110 attached to the glass fiber 51 corresponding to the tip of the optical fiber 50, the optical fiber 50 is aligned. Aligning the optical fiber 50 means rotating the optical fiber 50 along the direction indicated by arrow S1. During the alignment process, the optical fiber 50 remains in a state where it has passed through the through-hole of the ferrule flange 130. Once the alignment process is complete, the rear end of the ferrule 110 attached to the tip of the optical fiber 50 is press-fitted into the through-hole of the ferrule flange 130 from the front surface 130a of the flange toward the rear surface 130b of the flange.

[0035] The ferrule flange 130 constituting the ferrule assembly 100 shown in the lower part of Figure 1 has a structure in which the flange portion 130A and the body portion 130B are a single component. The ferrule flange 130 may be composed of multiple components, as shown in the upper part of Figure 2. Figure 2 is a diagram for illustrating the structure of a modified ferrule assembly 100A and various assembly processes (indicated as "Modified Ferrule Assembly and Assembly Process" in Figure 2). The upper part of Figure 2 (indicated as "Structure" in Figure 2) shows the structure of a modified ferrule assembly 100A. The middle part of Figure 2 (indicated as "Assembly Process 1" in Figure 2) and the lower part of Figure 2 (indicated as "Assembly Process 2" in Figure 2) show the assembly process up to the point in which the ferrule assembly 100A is attached to the glass fiber 51 corresponding to the tip portion of the optical fiber 50.

[0036] As shown in the upper part of Figure 2, the ferrule assembly 100A consists of a ferrule 110 and a ferrule flange 131 that are attached to a glass fiber 51 corresponding to the tip portion of the optical fiber 50. The ferrule flange 131 consists of a physically separable flange portion 131A and a body portion 131B. The ferrule 110 has a through hole into which the tip portion of the optical fiber 50 is inserted. The flange portion 131A has a flange front surface 131a and a flange rear surface 131b, and a through hole is provided between the flange front surface 131a and the flange rear surface 131b into which the tip of the body portion 131B is press-fitted. The body portion 131B has a through hole into which the rear end of the ferrule is press-fitted with the optical fiber 50 passing through it.

[0037] In the example of the assembly process shown in the middle of Figure 2, the structure that will become the ferrule assembly 100A is assembled before it is attached to the glass fiber 51, which corresponds to the tip of the optical fiber 50. During assembly, the front end of the body portion 131B is press-fitted into the through hole of the flange portion 131A, from the rear surface 131b of the flange toward the front surface 131a of the flange. Subsequently, the rear end of the ferrule 110 is press-fitted into the through hole of the body portion 131B, from the front surface 131a of the flange toward the rear surface 131b of the flange. Once the alignment of the optical fiber 50, which is performed by rotating the optical fiber 50 by a predetermined angle in the direction indicated by arrow S1, is completed, the ferrule 110 of the already assembled ferrule assembly 100A is attached to the tip of the aligned optical fiber 50.

[0038] In the example assembly process shown in the lower part of Figure 2, the structure consisting of the ferrule 110 and the body portion 131B is attached to the tip of the optical fiber 50, and the optical fiber 50 is aligned, i.e., rotated along the direction indicated by arrow S1. The ferrule 110 is press-fitted into the through-hole of the body portion 131B while attached to the glass fiber 51 corresponding to the tip of the optical fiber 50. During alignment, the optical fiber 50 remains in a state where it has passed through the through-hole of the already assembled structure consisting of the ferrule 110 and the body portion 131B. Once the alignment is complete, the body portion 131B of the structure (ferrule 110 and body portion 131B) attached to the tip of the optical fiber 50 is press-fitted into the through-hole of the flange portion 131A.

[0039] Figure 3 is a front view of a ferrule assembly 100 to which various optical fibers are applied as the optical fibers 50 to be connected in the optical connection assembly 1 of the present disclosure (referred to as "optical fiber" in Figure 3). In the example shown in Figure 3, a ferrule flange 130 is applied in which the flange portion 130A and the body portion 130B are a single component. The upper part of Figure 3 (referred to as "Type 1" in Figure 3) shows an example of the application of MCF 50A as an example of the optical fiber 50. The middle part of Figure 3 (referred to as "Type 2" in Figure 3) shows an example of the application of PMF 50B as an example of the optical fiber 50. The lower part of Figure 3 (referred to as "Type 3" in Figure 3) shows an example of the application of bundle fiber 50C as an example of the optical fiber 50.

[0040] The front view of the ferrule assembly 100 shown in the upper part of Figure 3 shows the end face of the MCF 50A, which is an optical fiber 50 that requires alignment, a ferrule 110 attached to a glass fiber 51A corresponding to the tip portion of the MCF 50A, and a ferrule flange 130 (essentially flange portion 130A) into which the rear end of the ferrule 110 is press-fitted. The MCF 50A comprises a plurality of cores 52A each extending along the fiber axis AX, which is the central axis of the MCF 50A, and a common cladding 53A surrounding each of the plurality of cores 52A. Line LA indicates the reference orientation for rotation alignment of the MCF 50A, i.e., the orientation with a rotation angle of 0°. Line LR is the installation reference line of the ferrule assembly 100, i.e., the rotation angle reference of the ferrule flange 130, along the edge of the flange portion 130A. In the ferrule assembly 100 including the aligned MCF 50A, lines LA and LR are parallel.

[0041] The front view of the ferrule assembly 100 shown in the middle of Figure 3 shows the end face of the PMF 50B, which is an optical fiber 50 that needs to be aligned, a ferrule 110 attached to a glass fiber 51B corresponding to the tip portion of the PMF 50B, and a ferrule flange 130 (essentially a flange portion 130A) into which the rear end of the ferrule 110 is press-fitted. The PMF 50B comprises a core 52B extending along the fiber axis AX, which is the central axis of the PMF 50B, stress-applying portions 54 arranged to sandwich the core 52B, and a common cladding 53B surrounding the core 52B and the stress-applying portions 54, respectively. In the ferrule assembly 100 including the aligned PMF 50B, the lines LA and LR are parallel.

[0042] The front view of the ferrule assembly 100 shown in the lower part of Figure 3 shows the end face of the bundle fiber 50C, which is an optical fiber 50 that needs to be aligned, a ferrule 110 to which glass fibers 510 corresponding to the tip portions of the multiple single-core optical fibers 500 constituting the bundle fiber 50C are integrally attached, and a ferrule flange 130 (substantially the flange portion 130A) to which the rear end of the ferrule 110 is press-fitted. Each of the multiple single-core optical fibers 500 is composed of a glass fiber 510 and a resin coating, and each glass fiber 510 has a core 520 and a cladding 530. The glass fibers 510 bundled by the ferrule 110 constitute the glass fiber 51C. The arrangement of the core 520 in the bundled state of the multiple glass fibers 510 substantially corresponds to the core arrangement of the MCF 50A described above. In the ferrule assembly 100 including the aligned bundle fiber 50C, lines LA and LR are parallel.

[0043] FIG. 4 is a diagram for explaining the cross-sectional structure of the components of the optical connection assembly 1 of the present disclosure and the method for measuring the extraction strength of the sleeve 120B, which is one of the components (in FIG. 4, denoted as "cross-sectional structure"). In the example shown in FIG. 4, the ferrule flange 130 in which the flange portion 130A and the body portion 130B are one member is applied. In the upper part of FIG. 4 (denoted as "adapter" in FIG. 4), the cross-sectional structure of the adapter 600, which is one of the components, along the line I-I shown in FIG. 1 is shown. In the middle part of FIG. 4 (denoted as "connector" in FIG. 4), the cross-sectional structures of the first optical connector 10A and the second optical connector 10B, which are one of the components, along the line II-II shown in FIG. 1 are shown. In the lower part of FIG. 4 (denoted as "extraction strength test" in FIG. 4), a diagram for explaining the method for measuring the extraction strength of the sleeve 120B, which is one of the components, is shown.

[0044] As shown in the upper part of FIG. 4, inside the adapter body 610 that constitutes the adapter 600, there are an inner wall surface 630a that defines a first internal space for housing a part of the first optical connector 10A, an inner wall surface 630b that defines a second internal space for housing a part of the second optical connector 10B, a first opening 620a for introducing a part of the first optical connector 10A into the first internal space, and a second opening 620b for introducing a part of the second optical connector 10B into the second internal space. The sleeve holder 120A is disposed between the first internal space and the second internal space, and the adapter body 610 and the sleeve holder 120A are integrally formed.

[0045] The sleeve 120B is inserted into the sleeve holder 120A that is integrally formed with the adapter body 610. The sleeve 120B shown in the upper part of FIG. 4 is a split sleeve with a slit, but it may also be a solid bore without a slit. The sleeve holder 120A may function as a sleeve.

[0046] As shown in the middle section of Figure 4, the first optical connector 10A and the second optical connector 10B each have a plug frame for stably housing the ferrule assembly 100 attached to the tip of the optical fiber 50. This plug frame consists of a front housing 20 and a rear housing 30 fitted into the front housing 20. The tip of the ferrule 110, which constitutes part of the ferrule assembly 100, protrudes from the front opening of the front housing 20. The inner wall surface of the front housing 20 is provided with a positioning portion 20A, which has an inclined surface to which the flange portion 130A of the ferrule flange 130 constituting the ferrule assembly 100 abuts, and a positioning portion 20B, which has a flat surface. The portion that functions as a positioning portion may be only the positioning portion 20A or only the positioning portion 20B. When the portion that functions as a positioning portion is either the positioning portion 20A or the positioning portion 20B, the ferrule assembly 100 is positioned by being sandwiched between the positioning portion and the inner wall surface of the housing space.

[0047] Inside the rear housing 30 is a spring material 140, which acts as an elastic member that applies a biasing force to the flange portion 130A. The spring material 140 has a shape that spirally surrounds the body portion 130B along the longitudinal direction of the optical fiber 50. When the rear housing 30 is inserted into the front housing 20 from the rear, the spring material 140 is compressed by being sandwiched between the ferrule assembly 100 housed in the front housing 20 and the rear of the rear housing 30. A through hole is provided in the rear of the rear housing 30 for pulling out the optical fiber 50. The portion of the optical fiber 50 that is pulled out from the rear housing 30 is protected by a boot 40. The flange portion 130A of the ferrule assembly 100 receives a biasing force (restoring force of the spring material 140) from the spring material 140, and the front flange surface 130a of the flange portion 130A is pressed against the positioning portion 20A and positioning portion 20B of the front housing 20. In the example shown in the middle of Figure 4, a pair of positioning parts 20A and 20B are shown, but one or more positioning parts may be provided on the inner wall surface of the front housing 20 to correspond to the shape of the flange front surface 130a of the flange portion 130A.

[0048] The extraction strength of the sleeve 120B is measured by using the pin gauges 700A and 700B arranged so as to sandwich the sleeve 120B, as shown in the lower part of FIG. 4. Specifically, as shown in the upper part within the lower part of FIG. 4, the tip portion of the pin gauge 700A is inserted into the sleeve 120B from the first end of the sleeve 120B, and the tip portion of the pin gauge 700B is inserted into the sleeve 120B from the second end of the sleeve 120B. Subsequently, as shown in the lower part within the lower part of FIG. 4, in the measurement of the extraction strength of the sleeve 120B, with the tip portion of the pin gauge 700B inserted into the sleeve 120B held by the sleeve holder 120A, the force (frictional force) when the tip portion of the pin gauge 700A is pulled out of the sleeve 120B in the direction indicated by the arrow S2 is measured. As an example, when each of the first optical connector 10A and the second optical connector 10B is an LC type optical connector, the diameter of the ferrule 110 is 1.25 mm (cited from the international standard "IEC61754-20"). In this case, for each of the two prepared pin gauges 700A and 700B, the outer diameter CK of the tip portion is 1.2488 mm or more and 1.2492 mm or less, the length CN of the tip portion is 4.2 mm or more and 15 mm or less, the surface roughness Ra of the tip portion is less than 0.2 μm, and the roundness (cylindricity) of the cross-sectional shape at the tip portion is less than 0.5 μm. As described above, since there is a strong correlation between the rotational fixing force for preventing the rotation of the ferrule 110 within the sleeve 120B and the extraction strength, it is desirable that the value of the extraction strength be large. The extraction strength defined by the international standard "IEC61754-20" is 1 N or more and 2.5 N or less.

[0049] In the optical connection assembly 1 of the present disclosure, the sleeve 120B is set to an extraction strength for maintaining different postures as shown in the lower part of FIG. 5 (step ST3) between the ferrule assembly 100 of the first optical connector 10A and the ferrule assembly 100 of the second optical connector 10B within the range of 1 N or more and 2.5 N or less defined by the international standard "IEC61754-20".

[0050] Figure 5 is a diagram illustrating the change in the orientation of the ferrule assembly 100 of the first optical connector 10A and the ferrule assembly 100 of the second optical connector 10B during the insertion step into the adapter 600 in the assembly process of the optical connection assembly 1 of the present disclosure (referred to as "insertion step" in Figure 5). In the example shown in Figure 5, a ferrule flange 130 in which the flange portion 130A and the body portion 130B are a single component is applied. The upper part of Figure 5 (referred to as "step ST1" in Figure 5) shows the state in which the first optical connector 10A is attached to the adapter 600 first, of the two optical connectors 10B. The middle section of Figure 5 (labeled "Step ST2" in Figure 5) shows the state in which the tip of the ferrule assembly 100 of the first optical connector 10A, which was previously attached to the adapter 600, (the tip of the ferrule 110) of the second optical connector 10B, which was inserted into the adapter 600 after the first optical connector 10A, is in contact with the tip of the ferrule assembly 100 of the second optical connector 10B, which was inserted into the adapter 600 following the first optical connector 10A. The lower section of Figure 5 (labeled "Step ST3" in Figure 5) shows the orientation of the ferrule assembly 100 of the first optical connector 10A and the ferrule assembly 100 of the second optical connector 10B, both of which are attached to the adapter 600, within the adapter 600.

[0051] As shown in step ST1 in the upper part of Figure 5, when the first optical connector 10A is inserted into the first internal space of the adapter body 610 through the first opening 620a, the tip of the ferrule 110 of the first optical connector 10A is inserted into the sleeve 120B held by the sleeve holder 120A which is integrally formed with the adapter body 610. Furthermore, as the plug frame of the first optical connector 10A is pushed into the first internal space of the adapter body 610, the ferrule 110 enters the sleeve 120B, and as a result the first optical connector 10A is mounted on the adapter body 610. At this time, the tip of the ferrule 110 is located in a region closer to the second internal space than to the center of the adapter, and the flange portion 130A is abutted against the positioning portion 20A and positioning portion 20B provided on the inner wall surface of the plug frame. In the first optical connector 10A, the biasing force received by the flange portion 130A from the spring material 140 is, for example, 4.66 N. At this time, the frictional force that the ferrule 110 receives from the sleeve 120B (split sleeve) when the ferrule is inserted is between 2N and 5N.

[0052] Next, the second optical connector 10B is inserted into the second internal space of the adapter body 610 through the second opening 620b along the direction indicated by arrow S3. As shown in step ST2 in the middle of Figure 5, once the second optical connector 10B is inserted into the second internal space of the adapter body 610 through the second opening 620b, the tip of the ferrule 110 of the second optical connector 10B is inserted into the sleeve 120B held by the sleeve holder 120A. Inside the sleeve 120B, the second optical connector 10B abuts against the tip of the ferrule 110 of the first optical connector 10A, which was previously attached to the adapter body 610. At this time, the biasing force received by the flange portion 130A from the spring material 140 of the second optical connector 10B is, for example, 4.66N. At this time, the frictional force received by the ferrule 110 from the sleeve 120B is between 1N and 2.5N, since the ferrule 110 of the first optical connector 10A has already been inserted.

[0053] After the ferrule 110 of the second optical connector 10B abuts against the ferrule 110 of the first optical connector 10A within the sleeve 120B, the plug frame of the second optical connector 10B is further pushed into the second internal space of the adapter body 610, thereby mounting the second optical connector 10B to the adapter body 610. At this time, as shown in step ST3 in the lower part of Figure 5, the ferrule assembly 100 of the second optical connector 10B can no longer move within the sleeve 120B along the direction of travel of the plug frame of the second optical connector, so the relative position between the ferrule assembly 100 and the positioning portions 20A and 20B provided on the inner wall surface of the plug frame changes. That is, in the second optical connector 10B, the ferrule assembly 100, with the tip of the ferrule 110 held in the sleeve 120B, enters a floating state where the flange portion 130A is separated from the positioning portions 20A and 20B. Assuming that the flange portion 130A of the ferrule assembly 100 is set back by about 1 mm relative to the positioning portions 20A and 20B, the biasing force of the spring material 140 in the contracted state of the second optical connector 10B is estimated to be about 6.29 N.

[0054] Figure 6 is a graph plotting the relationship between the change in sleeve pull-out strength and insertion loss for two types of adapter samples with different structures (labeled "Comparative Experiment (Structure)" in Figure 6). The upper part of Figure 6 (labeled "Integrated Adapter" in Figure 6) shows a graph plotting the experimental results for an adapter sample in which the sleeve holder 120A that holds the sleeve 120B is formed integrally with the adapter body 610. The lower part of Figure 6 (labeled "Built-in Adapter" in Figure 6) shows a graph plotting the experimental results for an adapter sample in which the sleeve holder 120A that holds the sleeve 120B is housed inside the adapter body 610 as a separate component.

[0055] The optical fiber 50 to which the provided optical connector is attached is an MCF having four cores. The number of samples for the integrated adapter is "12", and the number of samples for the embedded adapter is "6".

[0056] The graph in the upper part of Figure 6 plots the insertion loss at a wavelength of 1310 nm for each of the four cores, measured while varying the pull-out strength of the sleeve 120B for 12 samples of the integrated adapter. The graph in the lower part of Figure 6 plots the insertion loss at a wavelength of 1310 nm for each of the four cores, measured while varying the pull-out strength of the sleeve 120B for 6 samples of the embedded adapter. Insertion loss represents the connection loss between the two optical fibers with the two optical connectors attached to the adapter sample.

[0057] As can be seen from the comparison of the graphs shown in the upper and lower sections of Figure 6, with integrated adapters, it becomes easier to reduce the insertion loss to 0.5 dB or less as the pull-out strength value increases. With embedded adapters, the position of the sleeve holder built into the adapter body changes with ferrule insertion, so the insertion loss increases as the pull-out strength value decreases. In the case of embedded adapters, even with a high pull-out strength value, it was not possible to reduce the overall insertion loss to 0.5 dB or less.

[0058] Figure 7 is a graph plotting the relationship between the number of insertions and removals of the optical connector and the insertion loss for two types of integrated adapter samples with sleeves having different pull-out strengths (labeled "Comparative Experiment (Pull-out Strength)" in Figure 7). The upper part of Figure 7 (labeled "Pull-out Strength (1N-1.5N)" in Figure 7) shows a graph plotting the experimental results for an integrated adapter sample using sleeve 120B with a pull-out strength of 1N or more and less than 1.5N. The lower part of Figure 7 (labeled "Pull-out Strength (1.5N-2.5N)" in Figure 7) shows a graph plotting the experimental results for an integrated adapter sample using sleeve 120B with a pull-out strength of 1.5N or more and 2.5N or less.

[0059] The optical fiber 50 to which the prepared optical connector is attached is an MCF having four cores. The method for measuring the insertion loss is the same as in the comparative experiment shown in Figure 6.

[0060] Graphs G610A to G640A shown in the upper part of Figure 7 show the insertion loss for each of the four cores of the prepared MCF in relation to the number of insertion and removal cycles in insertion and removal experiments on sleeves with a pull-out strength of 1 N or more and less than 1.5 N. Graphs G610B to G640B shown in the lower part of Figure 7 show the insertion loss for each of the four cores of the prepared MCF in relation to the number of insertion and removal cycles in insertion and removal experiments on sleeves with a pull-out strength of 1.5 N or more and 2.5 N or less.

[0061] As can be seen from the comparison of the graphs shown in the upper and lower sections of Figure 7, for sleeves with a pull-out strength of 1 N or more but less than 1.5 N, the variation in insertion loss is greater than 0.5 dB for all cores. For sleeves with a pull-out strength of 1.5 N or more but less than 2.5 N, the insertion loss is less than 0.5 dB for all cores. Due to this significant difference, the pull-out strength of the sleeve may be 1.5 N or more. This significant difference is thought to be because, when the value of the rotational fixing force, which has a strong correlation with the pull-out strength, is small, the rotational force caused by the change in shape of the spring material, which repeatedly contracts and expands during attachment and detachment, greatly affects the orientation of the ferrule assembly. From this, it can be estimated that for sleeves with a pull-out strength of 1.5 N or more but less than 2.5 N, at least one of the two optical connectors mounted on the adapter is maintained in a non-floating state within the plug frame.

[0062] 1…Optical connection assembly 10A…First optical connector 10B…Second optical connector 20…Front housing 20A, 20B…Positioning section 30…Rear housing 40…Boot 50…Optical fiber 50A…MCF 50B…PMF 50C…Bundled fiber 51, 51A, 51B, 51C, 510…Glass fiber 52A, 52B, 520…Core 53A, 53B…Common cladding 54…Stress application section 100, 100A…Ferrule assembly 110…Ferrule 120A…Sleeve holder 120B…Sleeve 130, 131…Ferrule flange 130A, 131A…Flange section 130B, 131B…Body section 130a, 131a…Front of flange 130b, 131b…Rear of flange 140…Spring material 500...Single-core optical fiber 530...Cladding 600...Adapter 610...Adapter body 620a...First aperture 620b...Second aperture 630a, 630b...Inner wall surface 700A, 700B...Pin gauge AX...Fiber axis LA, LR...Wire S1, S2, S3...Arrow

Claims

1. A first optical connector and a second optical connector each having a ferrule assembly comprising a ferrule attached to the tip of an optical fiber and a ferrule flange that holds the ferrule while the optical fiber is passing through it, and a plug frame that houses the ferrule assembly; an adapter body having a first internal space that houses a part of the first optical connector, a second internal space that houses a part of the second optical connector, a first opening for introducing the part of the first optical connector into the first internal space, and a second opening for introducing the part of the second optical connector into the second internal space; and a sleeve or sleeve holder installed between the first internal space and the second internal space that holds the sleeve; each of the first optical connector and the second optical connector includes an elastic member housed in the plug frame that applies a biasing force to the ferrule flange, and the sleeve or sleeve holder is formed integrally with the adapter body. The sleeve is an optical connection assembly wherein, when the first optical connector is mounted on the adapter body before the second optical connector, the ferrule assembly of the first optical connector is fixed in contact with both the sleeve and the inner wall surface of the plug frame, and the sleeve has pull-out strength to maintain a mounting state in which the ferrule assembly of the second optical connector is fixed in contact only with the sleeve.

2. The optical connection assembly according to claim 1, wherein the pull strength of the sleeve is 1.5 N or more.

3. The optical connection assembly according to claim 1 or claim 2, wherein the elastic member is a spring material arranged to surround the optical fiber.

4. The optical connection assembly according to any one of claims 1 to 3, wherein the plug frame has a positioning portion into which the ferrule flange, which is biased by the elastic member, abuts, and within the plug frame of the first optical connector after both the first optical connector and the second optical connector are mounted on the adapter, the orientation of the ferrule assembly is maintained such that the tip of the ferrule is in contact with the tip of the ferrule of the second optical connector within the sleeve, and the ferrule flange is in contact with the positioning portion.

5. The optical connection assembly according to claim 4, wherein, within the plug frame of the second optical connector, the orientation of the ferrule assembly is maintained such that the tip of the ferrule is in contact with the tip of the ferrule of the first optical connector within the sleeve, and the ferrule flange is physically separated from the positioning portion.

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