Refractive index matching material, optical fiber connection structure, and method of arranging refractive index matching material

Abstract

To provide a refractive index matching material that can improve the visibility of the refractive index matching material. [Solution] The refractive index matching material 60, which is placed between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30, is a composition containing a silicone resin and a coloring agent, wherein the coloring agent has an absorption rate of 10% or less in the near-infrared wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30, and an absorption rate of 20% or more in the visible wavelength band.

Description

[[Technical Field]]

[0001] The present disclosure relates to a refractive index matching material, an optical fiber connection structure, and a method for arranging a refractive index matching material. [[Background Art]]

[0002] As methods for connecting one optical fiber to another optical fiber, a method of directly butting optical fibers against each other and a method of butting ferrules having optical fibers inserted thereinto against each other are known. These methods are commonly used as methods for physically connecting optical fibers, and examples thereof include mechanical splice connection and optical connector connection. Generally, for permanent connections, mechanical splice connection is effective, while optical connector connection is effective when frequent attachment and detachment are performed.

[0003] In both mechanical splice connection and optical connector connection, the connection is physically performed by applying an axial pressing force to the end faces of the optical fibers. However, in the case of optical connector connection, since optical fibers are generally brittle and weak, inserting and protecting the optical fiber in a ferrule enables physical contact between the end faces of the optical fibers.

[0004] In the above physical connection, the end face shape of the optical fiber greatly affects the connection characteristics. For example, if the angle of the end face is deviated, or if the end face shape is rough, it is conceivable that air may enter between the butted end portions of the optical fibers. As a result, there arises a problem that Fresnel reflection increases at the connection end face, and connection loss increases.

[0005] In order to solve such problems, technologies related to refractive index matching materials arranged between butted end portions of optical fibers are known. For example, Patent Document 1 discloses an optical connection structure in which a solid adhesive connecting member having refractive index matching properties is interposed in close contact as a single layer between end faces of mutually opposing optical transmission media, or between an end face of an optical transmission medium and an optical component. [[Prior Art Documents]] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4332490 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the prior art described in Patent Document 1 involved arranging a transparent refractive index matching material as an adhesive connecting member for the purpose of reducing light loss. Because such refractive index matching materials are very small and thin, there was a problem in that their transparency made it difficult to visually confirm their presence once they were in place. Therefore, it was not easy to confirm whether or not the refractive index matching material was in place. Thus, there was room for improvement regarding the visibility of the refractive index matching material.

[0008] This disclosure aims to provide a refractive index matching material capable of improving the visibility of the refractive index matching material, a connection structure for optical fibers, and a method for arranging the refractive index matching material. [Means for solving the problem]

[0009] The means to achieve the above objectives are as follows:

[0010] (1) A refractive index matching material disposed between the first end face of the first optical fiber and the second end face of the second optical fiber, A composition comprising a silicone resin and a colorant, The coloring agent has an absorption rate of 10% or less in the near-infrared wavelength band of optical communication using the first optical fiber and the second optical fiber, and an absorption rate of 20% or more in the visible wavelength band. Refractive index matching material. (2) A refractive index matching material as described in (1) above, The adhesive strength is included in the range of 5N or less. Refractive index matching material. (3) A refractive index matching material as described in (1) or (2) above, Hardened and integrally disposed with respect to at least one of the first end face and the second end face, Refractive index matching material. (4) A refractive index matching material described in any one of (1) to (3) above, The wavelength band of the optical communication is included in the range of 850 nm to 980 nm within the near-infrared wavelength band. Refractive index matching material. (5) A refractive index matching material as described in any one of (1) to (4) above, The first optical fiber having the first end face, A first ferrule holding the previously reviewed first optical fiber, The second optical fiber having the second end face, A second ferrule that holds the aforementioned second optical fiber, A connector that connects the first ferrule and the second ferrule to each other, Equipped with, Optical fiber connection structure. (6) The connection structure described in (5) above, The refractive index matching material is filled in at least one of the first internal void between the first tip and the first end face of the first ferrule and the second internal void between the second tip and the second end face of the second ferrule. Connection structure. (7) A connection structure as described in (5) or (6) above, The refractive index of the core wire of the first optical fiber is lower than the refractive index of the refractive index matching material. The refractive index of the core wire of the second optical fiber is higher than the refractive index of the refractive index matching material. Connection structure. (8) A step of applying a liquid silicone resin containing a coloring agent having an absorption rate of 10% or less in the near-infrared wavelength band and an absorption rate of 20% or more in the visible wavelength band to at least one of the first end face of the first optical fiber and the second end face of the second optical fiber, A step of curing the applied liquid, a step of connecting said first optical fiber and said second optical fiber to each other by a connector, and integrally disposing, between said first end face and said second end face, a refractive index matching material which is a composition containing said cured silicone resin and said colorant; comprising a method for arranging a refractive index matching material.

Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a refractive index matching material capable of improving the visibility of the refractive index matching material, an optical fiber connection structure, and a method for arranging a refractive index matching material.

Brief Description of Drawings

[0012] [Figure 1] It is a schematic diagram showing an example of a configuration for realizing the optical fiber connection structure according to the first embodiment of the present disclosure. [Figure 2] It is a schematic diagram showing an example of a cross section of the optical fiber connection structure according to the first embodiment of the present disclosure. [Figure 3] It is a schematic diagram showing an enlarged view of only a part of the configuration of the connection structure of FIG. 2. [Figure 4A] It is a schematic diagram showing an example of a cross section when the first optical fiber is held by the first ferrule. [Figure 4B] It is a schematic diagram showing an example of a cross section when the second optical fiber is held by the second ferrule. [Figure 5] It is a schematic diagram showing an example of a refractive index matching material integrated with the end face of the ferrule. [Figure 6] It is a graph diagram showing a first example of the optical characteristics of the refractive index matching material according to the first example. [Figure 7] It is a graph diagram showing a second example of the optical characteristics of the refractive index matching material according to the first example. [Figure 8] It is a graph diagram for explaining insertion loss due to reflection of the refractive index matching material according to the first example. [Figure 9] It is a graph diagram obtained by enlarging a part of the horizontal axis of the graph of FIG. 8. [Figure 10]This graph shows the results of evaluating the insertion loss of the refractive index matching material according to the first embodiment. [Figure 11] This graph shows a first example of the mechanical properties of a refractive index matching material according to the first embodiment. [Figure 12] This graph shows a second example of the mechanical properties of the refractive index matching material according to the first embodiment. [Figure 13] This graph shows a third example of the mechanical properties of the refractive index matching material according to the first embodiment. [Figure 14] This graph shows an example of the optical properties of the refractive index matching material according to the second embodiment. [Modes for carrying out the invention]

[0013] In the following, one embodiment of this disclosure will be mainly described with reference to the attached drawings.

[0014] (First Embodiment) Figure 1 is a schematic diagram showing an example of a configuration for realizing the optical fiber connection structure 1 according to the first embodiment of this disclosure. Figure 2 is a schematic diagram showing an example of a cross-section of the optical fiber connection structure 1 according to the first embodiment of this disclosure. Figure 1 shows that the first optical fiber 10 and the second optical fiber 30 are arranged separately from each other along the axial direction before realizing the connection structure 1 shown in Figure 2.

[0015] Figure 3 is a schematic diagram showing only a portion of the configuration of connection structure 1 in Figure 2 in an enlarged view. Figure 4A is a schematic diagram showing an example of a cross-section when the first optical fiber 10 is held in the first ferrule 20. Figure 4B is a schematic diagram showing an example of a cross-section when the second optical fiber 30 is held in the second ferrule 40.

[0016] As shown in Figures 2 and 3, the optical fiber connection structure 1 includes a first optical fiber 10 having a first end face S1 and a first ferrule 20 that holds the first optical fiber 10. The connection structure 1 also includes a second optical fiber 30 having a second end face S2 and a second ferrule 40 that holds the second optical fiber 30. The connection structure 1 includes a connector 50 that connects the first ferrule 20 and the second ferrule 40 to each other. The connection structure 1 also includes a refractive index matching material 60 that is placed between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30.

[0017] The optical fiber connection structure 1 is placed within an optical network intended for the transmission of optical signals. This optical network may include, for example, one intended for the short-distance transmission of optical signals. This optical network may include an in-vehicle optical network, but is not limited to this; it may also include other networks intended for short-distance transmission. For example, this optical network may be used in sensor systems or medical equipment systems other than vehicles, or it may include a home network. Alternatively, this optical network may include an optical communication network intended for long-distance transmission, such as the Internet.

[0018] The connection structure 1, having a first optical fiber 10 and a second optical fiber 30, is used for optical communication that transmits optical signals in a predetermined wavelength band in an optical network such as an in-vehicle optical network. The wavelength band for optical communication in the optical network in which the connection structure 1 is used includes, for example, the near-infrared wavelength band. This wavelength band may be included in the range of 850 nm to 980 nm.

[0019] In connection structure 1, the first optical fiber 10 and the second optical fiber 30 are arranged such that the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30 face each other in the axial direction. The refractive index matching material 60 is arranged to fill the space between the opposing first end faces S1 and the second end faces S2. In connection structure 1, an optical signal may be transmitted from the first optical fiber 10 to the second optical fiber 30 via the refractive index matching material 60. Conversely, an optical signal may be transmitted from the second optical fiber 30 to the first optical fiber 10 via the refractive index matching material 60.

[0020] The first optical fiber 10 and the second optical fiber 30 may have different core (core) refractive indices. For example, the refractive index of the core of the first optical fiber 10 is lower than that of the refractive index matching material 60. For example, the refractive index of the core of the second optical fiber 30 is higher than that of the refractive index matching material 60. The first optical fiber 10 and the second optical fiber 20 may be different types of optical fibers.

[0021] The first optical fiber 10 includes, for example, a POF (Plastic Optical Fiber). The POF may include a graded-index POF or a step-index POF. The transmission mode of the POF may be single-mode or multi-mode. The refractive index at the radial center of the core of the first optical fiber 10 is, for example, in the range of 1.34 to 1.36.

[0022] The first ferrule 20 is a component that precisely aligns the first end face S1 of the first optical fiber 10 and improves the transmission efficiency of optical signals at the optical connection with the second optical fiber 30. The first ferrule 20 is made of a material such as resin, ceramic, or metal. The first ferrule 20 has a central hole 21 that holds the core and cladding of the first optical fiber 10. The tip face S3 of the first ferrule 20 is configured as a curved surface having a predetermined radius of curvature R1.

[0023] As shown in Figure 4A, the entire first ferrule 20 holding the first optical fiber 10 has a circular shape with a diameter d1 in cross-sectional view. The first ferrule 20 positions the core and cladding of the first optical fiber 10 at its radial center. The entire core and cladding of the first optical fiber 10 has a circular shape with a diameter d2 in cross-sectional view.

[0024] The second optical fiber 30 includes, for example, a GOF (Gango of Fiber). The GOF may include a graded-index GOF or a step-index GOF. The transmission mode of the GOF may be single-mode or multi-mode. The refractive index at the radial center of the core of the second optical fiber 30 is, for example, in the range of 1.45 to 1.47.

[0025] As shown in Figure 3, the second ferrule 40 is a component that precisely aligns the second end face S2 of the second optical fiber 30 and improves the transmission efficiency of optical signals at the optical connection with the first optical fiber 10. The second ferrule 40 is made of a material such as resin, ceramic, or metal. The second ferrule 40 has a central hole 41 that holds the core and cladding of the second optical fiber 30. The tip face S4 of the second ferrule 40 is configured as a curved surface having a predetermined radius of curvature R2.

[0026] As shown in Figure 4B, the entire second ferrule 40 holding the second optical fiber 30 has a circular shape with a diameter d3 in cross-sectional view. The second ferrule 40 positions the core and cladding of the second optical fiber 30 at its radial center. The entire core and cladding of the second optical fiber 30 has a circular shape with a diameter d4 in cross-sectional view.

[0027] As shown in Figure 2, the connector 50 is a connecting member for precisely aligning the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30 to efficiently transmit optical signals. The connector 50 includes a male first connector 51 attached to a first ferrule 20 that holds the first optical fiber 10, and a female second connector 52 attached to a second ferrule 40 that holds the second optical fiber 30.

[0028] The first connector 51 and the second connector 52 have, for example, a latch mechanism or clip for detachably engaging or mating with each other. When the first connector 51 and the second connector 52 engage or mate with each other, the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30 face each other in close proximity.

[0029] The refractive index matching material 60 is, for example, a composition containing a silicone resin. The refractive index matching material 60 is, for example, made of silicone rubber. The refractive index matching material 60 is used, for example, in optical communication using a first optical fiber 10 and a second optical fiber 30 in a wavelength band including the near-infrared wavelength band. In the refractive index matching material 60, in the wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30, the refractive index of the silicone resin is, for example, in the range of 1.39 to 1.43, more preferably 1.39 to 1.41.

[0030] In the refractive index matching material 60, for example, at a thickness of 0.4 mm, the haze value is in the range of 1.0% or less, more preferably 0.6% or less, and even more preferably 0.4% to 0.6%. The adhesive strength of the refractive index matching material 60 is in the range of 5 N or less, more preferably 1 N to 5 N. On the other hand, in the refractive index matching material 60, the elastic modulus of the silicone resin is in the range of 0.1 MPa to 10 MPa, more preferably 0.1 MPa to 1.0 MPa. The refractive index matching material 60 has stronger elasticity than adhesiveness. The refractive index matching material 60 is, for example, a member with a relatively low elastic modulus and a softness similar to rubber.

[0031] As shown in Figure 3, the refractive index matching material 60 is hardened and integrally disposed with respect to at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30. For example, the refractive index matching material 60 may be integrally disposed with the tip face S3 in the first ferrule 20, where the first end face S1 of the first optical fiber 10 is located near the tip of the central hole 21. The refractive index matching material 60 may also be integrally disposed with the first end face S1, which is fixed in the first ferrule 20, via the first ferrule 20.

[0032] Alternatively, the refractive index matching material 60 may be integrally disposed with the tip surface S4 in the second ferrule 40, where the second end surface S2 of the second optical fiber 30 is located near the tip of the central hole 41. The refractive index matching material 60 may also be integrally disposed with the second end surface S2, which is fixed in the second ferrule 40, via the second ferrule 40. The refractive index matching material 60 is disposed with a thickness w between the first end surface S1 of the first optical fiber 10 and the second end surface S2 of the second optical fiber 30.

[0033] The first end face S1 of the first optical fiber 10 is located on the opposite side of the second optical fiber 30 from the first tip T1 of the first ferrule 20. In the axial direction, the first end face S1 is located inside the central hole 21 of the first ferrule 20 from the first tip T1. The first end face S1 is not flush with the tip face S3 of the first ferrule 20, but is positioned one step recessed inside the central hole 21 from the tip face S3. That is, a first gap V1 having a gap width g1 along the axial direction is located between the first end face S1 and the first tip T1.

[0034] The second end face S2 of the second optical fiber 30 is located on the opposite side from the first optical fiber 10 from the second tip T2 of the second ferrule 40. In the axial direction, the second end face S2 is located inside the central hole 41 of the second ferrule 40 from the second tip T2. The second end face S2 is not flush with the tip face S4 of the second ferrule 40, but is positioned one step recessed inside the central hole 41 from the tip face S4. That is, a second gap V2 with a gap width g2 along the axial direction is located between the second end face S2 and the second tip T2.

[0035] The refractive index matching material 60 is filled in at least one of the internal first void V1 between the first tip T1 and the first end face S1, and the internal second void V2 between the second tip T2 and the second end face S2. In Figure 3, for the purpose of simplifying the illustration, the placement of the refractive index matching material 60 in both the first void V1 and the second void V2 is omitted. However, the elastic refractive index matching material 60 deforms under the compressive force F acting on the first ferrule 20 and the second ferrule 40 in the connection structure 1, and fills at least one of the first void V1 and the second void V2. For example, the refractive index matching material 60 may be placed along the entire optical path of the optical signal from the first tip T1 to the first end face S1, or along the entire optical path of the optical signal from the second tip T2 to the second end face S2.

[0036] In the connection structure 1 having the refractive index matching material 60 as described above, the surface roughness of at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30 may be in the range of 0.01 μm or more and 0.03 μm or less. For example, even if the surface roughness of the first end face S1 of the first optical fiber 10 is in the range of 0.01 μm or more and 0.03 μm or less, the refractive index matching material 60 filling the first void V1 may deform to match the shape of the first end face S1, thereby filling the rough surface of the first end face S1. For example, even if the surface roughness of the second end face S2 of the second optical fiber 30 is in the range of 0.01 μm or more and 0.03 μm or less, the refractive index matching material 60 filling the second void V2 may deform to match the shape of the second end face S2, thereby filling the rough surface of the second end face S2.

[0037] The method for arranging the refractive index matching material 60 as described above comprises several steps. For example, the arrangement method includes a step of applying a liquid silicone resin, in which the refractive index is in the range of 1.39 to 1.43, more preferably 1.39 to 1.41, in the wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30, to at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30. In this step, for example, the tip face S3 of the first ferrule 20 that holds the first optical fiber 10 may be immersed in the liquid and the liquid may transfer to the tip face S3. For example, the tip face S4 of the second ferrule 40 that holds the second optical fiber 30 may be immersed in the liquid and the liquid may transfer to the tip face S4.

[0038] Next, the arrangement method includes a step of curing the applied liquid. In this step, for example, the liquid may be cured in a state where it is integrally arranged with the tip surface S3 of the first ferrule 20 that holds the first optical fiber 10. For example, the liquid may be cured in a state where it is integrally arranged with the tip surface S4 of the second ferrule 40 that holds the second optical fiber 30.

[0039] Figure 5 is a schematic diagram showing an example of a refractive index matching material 60 integrated with the tip surface of a ferrule. For example, the refractive index matching material 60 may be integrated with the tip surface S3 of the first ferrule 20 through a process of curing the liquid. For example, the refractive index matching material 60 may be integrated with the tip surface S4 of the second ferrule 40 through a process of curing the liquid.

[0040] The arrangement method includes connecting the first optical fiber 10 and the second optical fiber 30 to each other with a connector 50, and integrally arranging a refractive index matching material 60, which is a composition containing cured silicone resin, between the first end face S1 and the second end face S2. This step realizes the arrangement of the refractive index matching material 60 between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30, as schematically shown in Figures 2 and 3.

[0041] According to the first embodiment described above, the refractive index matching of the refractive index matching material 60 with respect to the optical fiber can be improved. In the refractive index matching material 60, the refractive index of the silicone resin is included in the range of 1.39 to 1.43 in the wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30. As a result, compared to conventional refractive index matching materials that have a refractive index of about 1.46 to match the GOF, for example, the refractive index matching material 60 can improve the refractive index matching with other types of optical fibers whose core refractive index is less than 1.4.

[0042] The refractive index of the refractive index matching material 60 is an intermediate value between a refractive index of approximately 1.46 and a refractive index of approximately 1.35. Therefore, the refractive index matching material 60 can achieve an intermediate refractive index between, for example, the first optical fiber 10 as a POF and the second optical fiber 30 as a GOF, whose core refractive indices are different, thereby enabling a low-loss optical connection in the connection structure 1 that is independent of the type of optical fiber being connected.

[0043] The refractive index matching material 60 can reduce a significant decrease in refractive index matching by having a refractive index close to the respective refractive index of each optical fiber, even when, for example, both the first optical fiber 10 and the second optical fiber 30 have a refractive index of approximately 1.46 in their cores, or when they have a refractive index of approximately 1.35 in their cores. The refractive index matching material 60 can reduce Fresnel reflection at interfaces with POF and GOF, for example. In other words, the refractive index matching material 60 can achieve low-loss connections to POF and GOF.

[0044] In the refractive index matching material 60, the haze value at a thickness of 0.4 mm falls within the range of 1.0% or less. The refractive index matching material 60 can also improve the transmittance of light in the wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30. The refractive index matching material 60 can reduce absorption loss, reflection loss, or scattering loss of light propagating between the first optical fiber 10 and the second optical fiber 30. As a result, the refractive index matching material 60 can reduce the decrease in the intensity of the optical signal propagating between the first optical fiber 10 and the second optical fiber 30.

[0045] The refractive index matching material 60 has an adhesive strength within the range of 5N or less. This allows the refractive index matching material 60 to be constructed to be solid and tacky, but with reduced adhesiveness. Therefore, the refractive index matching material 60 can improve connection stability in repeated optical connections with one of the first optical fiber 10 and the second optical fiber 30, for example, when it is cured and integrally placed on the other. The refractive index matching material 60 can achieve stable and repeated connections with the other.

[0046] For example, the refractive index matching material described in Patent Document 1 is adhesive. Therefore, this refractive index matching material is prone to connection failures during repeated connections at the connection point with the optical fiber. The refractive index matching material 60 solves these conventional problems and enables stable, repeated connections.

[0047] The refractive index matching material 60 is hardened and integrally disposed on at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30. This allows the refractive index matching material 60 to be stably positioned on at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30. Therefore, the refractive index matching material 60 is stably positioned between the first optical fiber 10 and the second optical fiber 30 in the connection structure 1, and the reliability of the optical connection between the first optical fiber 10 and the second optical fiber 30 via the refractive index matching material 60 can be improved.

[0048] The wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30 includes the near-infrared wavelength band. The refractive index matching material 60 can be applied to optical networks intended for the transmission of optical signals. The refractive index matching material 60 can be applied to optical networks intended for the short-distance transmission of optical signals, such as automotive optical networks. The refractive index matching material 60 can be applied to optical networks intended for the long-distance transmission of optical signals, such as the general internet.

[0049] The wavelength range of optical communication using the first optical fiber 10 and the second optical fiber 30 is within the range of 850 nm to 980 nm. This makes the refractive index matching material 60 applicable to optical networks intended for short-distance transmission of optical signals, including automotive optical networks.

[0050] The optical fiber connection structure 1 includes a first ferrule 20 that holds a first optical fiber 10 having a first end face S1, a second ferrule 40 that holds a second optical fiber 30 having a second end face S2, and a connector 50 that connects the first ferrule 20 and the second ferrule 40 to each other. In addition, the connection structure 1 includes a refractive index matching material 60 that is placed between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30.

[0051] As a result, the connection structure 1 can improve the refractive index matching of the refractive index matching material 60 with respect to the first optical fiber 10 and the second optical fiber 30, thereby improving the refractive index matching of the refractive index matching material 60 with respect to the optical fibers. The connection structure 1 can achieve a low-loss and stable optical connection between the first optical fiber 10 and the second optical fiber 30 via the refractive index matching material 60.

[0052] In connection structure 1, the first end face S1 of the first optical fiber 10 is located on the opposite side of the second optical fiber 30 from the first tip T1 of the first ferrule 20. As a result, connection structure 1 does not configure the first end face S1 to be flush with the tip face S3 of the first ferrule 20, but rather to be positioned one step recessed inward from the tip face S3 within the central hole 21. Therefore, even when connection structure 1 is installed in an environment with severe vibration, such as an in-vehicle optical network, the sliding of the first end face S1 of the first optical fiber 10 against other objects is reduced, thereby preventing abrasion or damage.

[0053] In connection structure 1, the second end face S2 of the second optical fiber 30 is located on the opposite side from the first optical fiber 10 from the second tip T2 of the second ferrule 40. As a result, connection structure 1 does not configure the second end face S2 to be flush with the tip face S4 of the second ferrule 40, but rather to be positioned one step recessed inward from the tip face S4 within the central hole 41. Therefore, even when connection structure 1 is installed in an environment with severe vibration, such as an in-vehicle optical network, the sliding of the second end face S2 of the second optical fiber 30 against other objects is reduced, thereby preventing abrasion or damage.

[0054] The refractive index matching material 60 is filled in at least one of the first internal void V1 between the first tip T1 and the first end face S1, and the second internal void V2 between the second tip T2 and the second end face S2. This makes it possible to place the refractive index matching material 60 along the entire optical path of the optical signal, for example, from the first tip T1 to the first end face S1. In this case, the refractive index matching material 60 can improve the refractive index matching of the first void V1 with respect to the first optical fiber 10 compared to the case where air is interposed in the first void V1. Therefore, the refractive index matching material 60 can realize a low-loss optical connection between the first optical fiber 10 and the second optical fiber 30.

[0055] The refractive index matching material 60 can also be placed, for example, along the entire optical path of the optical signal from the second tip T2 to the second end face S2. In this case, the refractive index matching material 60 can improve the refractive index matching of the second air gap V2 with respect to the second optical fiber 30 compared to the case where air is interposed in the second air gap V2. Therefore, the refractive index matching material 60 can realize a low-loss optical connection between the first optical fiber 10 and the second optical fiber 30.

[0056] The refractive index of the core wire of the first optical fiber 10 is lower than the refractive index of the refractive index matching material 60. The refractive index of the core wire of the second optical fiber 30 is higher than the refractive index of the refractive index matching material 60. As a result, the refractive index of the refractive index matching material 60 has a value between the refractive index of the core wire of the first optical fiber 10 and the refractive index of the core wire of the second optical fiber 30. Therefore, the refractive index matching material 60 can, for example, achieve an intermediate refractive index between the first optical fiber 10 and the second optical fiber 30, whose core refractive indices are different from each other, and in the connection structure 1, it is possible to achieve a low-loss optical connection that is independent of the type of optical fiber being connected.

[0057] According to the first embodiment described above, the ability of the refractive index matching material 60 to follow the end face shape of the optical fiber can be improved. In the refractive index matching material 60, the elastic modulus of the silicone resin is in the range of 0.1 MPa to 10 MPa. As a result, the refractive index matching material 60 can be configured as a composition containing a silicone resin, such as silicone rubber. The refractive index matching material 60 can be configured as a member having a relatively low elastic modulus and a softness similar to that of rubber.

[0058] As described above, the refractive index matching material 60 can be flexibly deformed to match the end face shape of the optical fiber to be connected. The refractive index matching material 60 can follow any end face shape of the optical fiber, enabling low-loss optical connection that is independent of the end face shape of the optical fiber to be connected. Even if the end face of the optical fiber is rough, the refractive index matching material 60 can flexibly deform to match the uneven shape of the rough surface and fill the gaps in the uneven shape. Therefore, the refractive index matching material 60 eliminates the need for conventional methods such as polishing or laser shaping of the end face of the optical fiber to smooth the end face.

[0059] The refractive index matching material 60 eliminates the need for smoothing the end face of the optical fiber, thereby mitigating the problem of increased costs associated with processes and equipment that have occurred in conventional methods. In addition, the refractive index matching material 60 also reduces the problem of contamination of the optical fiber tip by polishing debris or evaporated components from the laser. As a result, the refractive index matching material 60 enables low-cost and low-loss optical connections compared to conventional technologies that use polishing or laser shaping.

[0060] The refractive index matching material 60 is positioned as an optical connecting member between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30, thereby reducing physical contact between the ends of the first optical fiber 10 and the second optical fiber 30. Therefore, the refractive index matching material 60 also functions as a protective film for the end faces of the optical fibers, protecting these ends. The refractive index matching material 60 reduces the occurrence of damage by avoiding physical contact between the optical fibers that are connected to each other, thereby reducing the increase in loss in the optical connection. As a result, the refractive index matching material 60 can reduce fluctuations in connection loss due to vibration, even when it is placed in an environment with severe vibration, such as an in-vehicle optical network.

[0061] In connection structure 1, the surface roughness of at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30 is in the range of 0.01 μm or more and 0.03 μm or less. Connection structure 1 can achieve low-loss optical connection by placing the refractive index matching material 60 not only on smoothed end faces with a surface roughness of less than 0.01 μm, but also on unsmoothed end faces.

[0062] The connection structure 1 can flexibly deform the refractive index matching material 60 to match the uneven shape of the rough end face of the optical fiber, even if the end face is rough, and can fill the gaps in the uneven shape. The connection structure 1 eliminates the need for conventional methods such as polishing or laser shaping of the end face of the optical fiber to smooth the end face.

[0063] Connection structure 1 eliminates the need for smoothing the end face of the optical fiber, thereby mitigating the problem of increased costs associated with processes and equipment that occurred in conventional methods. In addition, connection structure 1 also reduces the problem of contamination of the optical fiber tip by polishing debris or evaporated components from the laser. As a result, connection structure 1 can achieve low-cost and low-loss optical connections compared to conventional technologies that use polishing or laser shaping.

[0064] In the first embodiment described above, the refractive index matching material 60 was described as a composition containing a silicone resin, but it is not limited thereto. The refractive index matching material 60 may be a composition containing a resin other than a silicone resin, or it may be composed of a material different from a resin.

[0065] In the first embodiment described above, the refractive index of the silicone resin is described as being in the range of 1.39 to 1.43 in the wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30, but it is not limited to this. The refractive index of the silicone resin may be in other numerical ranges.

[0066] In the first embodiment described above, the elastic modulus of the silicone resin was described as being in the range of 0.1 MPa to 10 MPa, but it is not limited to this. The elastic modulus of the silicone resin may be in other numerical ranges.

[0067] In the first embodiment described above, the haze value for a thickness of 0.4 mm was described as being within the range of 1.0% or less, but this is not limited to this. The haze value may be within other numerical ranges.

[0068] In the first embodiment described above, the adhesive strength was described as being within the range of 5N or less, but it is not limited to this. The adhesive strength may be within other numerical ranges.

[0069] In the first embodiment described above, the refractive index matching material 60 is cured and integrally disposed with respect to the first end face S1 of the first optical fiber 10 or the second end face S2 of the second optical fiber 30, but the embodiment is not limited to this. The refractive index matching material 60 may be cured and integrally disposed with respect to both the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30.

[0070] In the first embodiment described above, the wavelength band for optical communication using the first optical fiber 10 and the second optical fiber 30 was described as including the near-infrared wavelength band, but is not limited thereto. The wavelength band may include any other wavelength bands that can be used to realize optical communication using optical fibers. For example, the wavelength band may include other infrared wavelength bands other than the near-infrared wavelength band, or it may include the visible wavelength band.

[0071] In the first embodiment described above, the wavelength band for optical communication using the first optical fiber 10 and the second optical fiber 30 was described as being in the range of 850 nm to 980 nm, but it is not limited to this. This wavelength band may be included in any other near-infrared wavelength band that can realize optical communication using optical fibers. For example, this wavelength band may be included in the optical communication wavelength band that includes 1550 nm or 1310 nm. This optical communication wavelength band may include, for example, the O band, E band, S band, C band, L band, or U band.

[0072] In the first embodiment described above, the optical fiber connection structure 1 was described as having a structure in which a first ferrule 20 that holds a first optical fiber 10 and a second ferrule 40 that holds a second optical fiber 30 are connected to each other by a connector 50, but it is not limited to this. The connection structure 1 may have any other structure in which a refractive index matching material 60 can be placed between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30.

[0073] In the first embodiment described above, the surface roughness of at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30 was described as being in the range of 0.01 μm or more and 0.03 μm or less, but is not limited to this. The surface roughness of at least one of the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30 may be in other numerical ranges.

[0074] In the first embodiment described above, the first end face S1 of the first optical fiber 10 is located on the opposite side of the second optical fiber 30 from the first tip T1 of the first ferrule 20, but this is not limited to this. The first end face S1 may be flush with the tip face S3 of the first ferrule 20, which includes the first tip T1, or it may be located on the side of the tip face S3 that is closer to the second optical fiber 30.

[0075] In the first embodiment described above, the second end face S2 of the second optical fiber 30 is located on the opposite side from the first optical fiber 10 to the second tip T2 of the second ferrule 40, but this is not limited to this. The second end face S2 may be flush with the tip face S4 of the second ferrule 40, which includes the second tip T2, or it may be located on the side of the tip face S4 that is closer to the first optical fiber 10.

[0076] In the first embodiment described above, both the first end face S1 and the second end face S2 are located inside the corresponding ferrule, but are not limited thereto. At least one of the first end face S1 and the second end face S2 may be flush with the leading edge of the corresponding ferrule, or it may be located outside of the leading edge.

[0077] In the first embodiment described above, the refractive index matching material 60 is described as filling at least one of the first internal void V1 between the first tip T1 and the first end face S1 and the second internal void V2 between the second tip T2 and the second end face S2, but is not limited thereto. The refractive index matching material 60 does not have to fill either the first void V1 or the second void V2.

[0078] In the first embodiment described above, the refractive index of the core wire of the first optical fiber 10 is lower than that of the refractive index matching material 60, and the refractive index of the core wire of the second optical fiber 30 is higher than that of the refractive index matching material 60. However, the embodiment is not limited to this. The refractive index of the core wire of the first optical fiber 10 and the refractive index of the core wire of the second optical fiber 30 may both be lower than or higher than that of the refractive index matching material 60. Alternatively, at least one of the refractive index of the core wire of the first optical fiber 10 and the refractive index of the core wire of the second optical fiber 30 may be the same as that of the refractive index matching material 60.

[0079] (Second Embodiment) In the first embodiment described above, the refractive index matching material 60 was described as a composition containing a silicone resin, but it is not limited thereto. The refractive index matching material 60 according to the second embodiment of this disclosure differs from the first embodiment in that it is a composition containing a colorant in addition to a silicone resin. Other configurations, functions, effects, and modifications are the same as in the first embodiment, and corresponding descriptions also apply to the refractive index matching material 60 according to the second embodiment. In the following, components the same as in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted. The differences from the first embodiment will be mainly described.

[0080] The refractive index matching material 60 is, for example, a composition comprising a silicone resin and a coloring agent. The refractive index matching material 60 is, for example, configured as silicone rubber colored with a coloring agent. The refractive index matching material 60 is used, for example, in optical communication using a first optical fiber 10 and a second optical fiber 30 in a wavelength band including the near-infrared wavelength band. The wavelength band of said optical communication is, for example, included in the range of 850 nm to 980 nm within the near-infrared wavelength band.

[0081] The coloring agent contained in the refractive index matching material 60 may be a dye or a pigment. The coloring agent may include, for example, ink. The coloring agent may have an absorption rate of 10% or less in the near-infrared wavelength band and an absorption rate of 20% or more in the visible wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30.

[0082] The method for arranging the refractive index matching material 60 as described above comprises several steps. For example, the arrangement method includes a step of applying a liquid silicone resin containing a coloring agent that has an absorption rate of 10% or less in the near-infrared wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30, and an absorption rate of 20% or more in the visible wavelength band, to at least one of the first end face S1 of the first optical fiber 10 and the second optical fiber 30 and the second end face S2 of the second optical fiber 30. In this step, for example, the tip face S3 of the first ferrule 20 that holds the first optical fiber 10 may be immersed in the liquid and the liquid may transfer to the tip face S3. For example, the tip face S4 of the second ferrule 40 that holds the second optical fiber 30 may be immersed in the liquid and the liquid may transfer to the tip face S4.

[0083] Next, the arrangement method includes a step of curing the applied liquid. In this step, for example, the liquid may be cured in a state where it is integrally arranged with the tip surface S3 of the first ferrule 20 that holds the first optical fiber 10. For example, the liquid may be cured in a state where it is integrally arranged with the tip surface S4 of the second ferrule 40 that holds the second optical fiber 30.

[0084] For example, the refractive index matching material 60 may be integrated with the tip surface S3 of the first ferrule 20 through a process of curing the liquid. For example, the refractive index matching material 60 may be integrated with the tip surface S4 of the second ferrule 40 through a process of curing the liquid.

[0085] The arrangement method includes connecting the first optical fiber 10 and the second optical fiber 30 to each other using a connector 50, and integrally arranging a refractive index matching material 60, which is a composition containing cured silicone resin and a coloring agent, between the first end face S1 and the second end face S2. This step realizes the arrangement of the refractive index matching material 60 between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30, as schematically shown in Figures 2 and 3.

[0086] According to the second embodiment described above, the visibility of the refractive index matching material 60 can be improved. In the refractive index matching material 60, the coloring agent has an absorption rate of 10% or less in the near-infrared wavelength band of optical communication using the first optical fiber 10 and the second optical fiber 30, and an absorption rate of 20% or more in the visible wavelength band. As a result, the refractive index matching material 60, with the coloring agent added, can be configured as a connecting member that has light absorption in the visible wavelength band but high transmittance in the near-infrared wavelength band.

[0087] Therefore, the refractive index matching material 60 reduces the loss of optical signals in optical communication, and by having a color, it facilitates visual confirmation when placed between the first end face S1 and the second end face S2. Even if the refractive index matching material 60 is very small and thin, it has absorption properties for visible light, making it easy to confirm the presence or absence of the refractive index matching material 60 by recognizing its color. The refractive index matching material 60 also facilitates visual confirmation of placement even in repeated connections.

[0088] In the second embodiment described above, the coloring agent was described as having an absorption rate of 10% or less in the near-infrared wavelength band and an absorption rate of 20% or more in the visible wavelength band for optical communication using the first optical fiber 10 and the second optical fiber 30, but it is not limited to this. The absorption rate of the coloring agent may be greater than 10% in the near-infrared wavelength band and less than 20% in the visible wavelength band. [Examples]

[0089] The refractive index matching material 60 according to this embodiment will be described in more detail below with reference to the following examples, but this disclosure is not limited in any way to the following examples. The numerical values ​​described in the examples are merely examples and do not limit the scope of this disclosure. The scope of this disclosure should be determined based on the description in the claims. In the following, components similar to those in the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted.

[0090] (First embodiment) The first embodiment relates to the refractive index matching material 60 according to the first embodiment. The refractive index matching material 60 according to the first embodiment is a heat-curable silicone rubber composed of two components, component A and component B. Component A contains a vinyl silicone component and a Pt catalyst. Component B contains a vinyl silicone component, a silicone crosslinking agent, and a silane coupling agent. The refractive index matching material 60 is a transparent rubber-like substance obtained by heat-curing a two-component heat-curable adhesive liquid silicone rubber (TSE3033) manufactured by Momentive, which consists of component A as the main component and component B as the curing agent. Table 1 below shows the oven conditions and curing results when heat-curing TSE3033.

[0091] [Table 1]

[0092] Figure 6 is a graph showing a first example of the optical properties of the refractive index matching material 60 according to the first embodiment. Figure 7 is a graph showing a second example of the optical properties of the refractive index matching material 60 according to the first embodiment.

[0093] To obtain the optical properties data shown in Figures 6 and 7, a sample sheet of refractive index matching material 60 was prepared. The sample sheet preparation process includes a first step of stirring and degassing the two components of silicone, agent A and agent B, in a planetary stirrer. The sample sheet preparation process includes a second step of defining the film thickness with a spacer and forming a film by sandwiching the product from the first step between PEPE-treated glass / release film. The sample sheet preparation process includes a third step of heating and curing the product from the second step in an oven at 100°C for 30 minutes. The sample sheet preparation process includes a fourth step of transferring the product to a release film to obtain a sample sheet. The sample sheet preparation process includes a fifth step of shaping the sample sheet obtained in the fourth step.

[0094] Figure 6 shows graphs illustrating the wavelength dependence of the light transmittance T (%) and reflectance R (%) of the obtained sample sheet, measured with three different mixing ratios of agent A and agent B. The target thickness of the sample sheet was 0.4 mm. For TSE3033, three levels of mixing ratios of agent A and agent B were set: A / B = 1 / 2 (AB12), 1 / 1 (AB11), and 2 / 1 (AB21). In Figure 6, "IT" represents the graph of the wavelength dependence of the light transmittance T (%). "IR" represents the graph of the wavelength dependence of the light reflectance R (%).

[0095] As shown in Figure 6, the light transmittance T(%) of the sample sheet remains high, exceeding 94.0% across the entire range of measured wavelengths. On the other hand, the light reflectance R(%) of the sample sheet remains low, around 5.50%, across the entire range of measured wavelengths. At a wavelength of 980 nm, the sample sheet exhibits a high light transmittance T(%) exceeding 94.0% and a low light reflectance R(%) around 5.50%.

[0096] Figure 7 shows graphs illustrating the wavelength dependence of the light absorption rate (%) of the obtained sample sheet, measured with three different mixing ratios of agent A and agent B. The target thickness of the sample sheet was 0.4 mm. For TSE3033, three levels of mixing ratios of agent A and agent B were set: A / B = 1 / 2 (AB12), 1 / 1 (AB11), and 2 / 1 (AB21). In Figure 7, "AB" represents the graph of the wavelength dependence of the light absorption rate (%).

[0097] As shown in Figure 7, the light absorption rate of the sample sheet remains close to zero in the range of 850 nm to 980 nm. At a wavelength of 980 nm, the sample sheet shows almost no film absorption. The light absorption rate of the sample sheet also remains close to zero in the optical communication wavelength band around 1310 nm.

[0098] Table 2 below summarizes the optical properties of the sample sheet at a wavelength of 980 nm. As shown in Table 2, the sample sheet exhibits optical properties that show almost no film absorption at a wavelength of 980 nm, which is included in the near-infrared wavelength band, with a refractive index n of approximately 1.40.

[0099] [Table 2]

[0100] Figure 8 is a graph illustrating the insertion loss due to reflection of the refractive index matching material 60 according to the first embodiment. Figure 9 is a graph showing an enlarged portion of the horizontal axis of the graph in Figure 8. Figures 8 and 9 show graphs of the insertion loss when light propagates from one of the first optical fiber 10 and the second optical fiber 30 to the other, simulated by changing the refractive index n0 of the space between the first optical fiber 10 and the second optical fiber 30. The insertion loss includes losses due to two reflections: a first Fresnel reflection occurring at the first boundary between the first optical fiber 10 and the space, and a second Fresnel reflection occurring at the second boundary between the second optical fiber 30 and the space.

[0101] In the simulations used to obtain the data shown in Figures 8 and 9, the refractive index n1 of the first optical fiber 10 and the second optical fiber 30 were set to 1.346. When n0=1, i.e., when air is interposed in the space between the first optical fiber 10 and the second optical fiber 30, the insertion loss increases to approximately 0.19 dB, which is large. On the other hand, when n0=1.4, i.e., when refractive index matching material 60 is interposed in the space between the first optical fiber 10 and the second optical fiber 30, the insertion loss is less than 0.01 dB, which is sufficiently small.

[0102] Figure 10 is a graph showing the evaluation of the insertion loss of the refractive index matching material 60 according to the first embodiment. The vertical axis of Figure 10 shows the power (mW) of the light output from one of the first optical fiber 10 and the second optical fiber 30 when light is propagated from one to the other. In this evaluation, the refractive index matching material 60 according to the first embodiment is placed between the first end face S1 of the first optical fiber 10 and the second end face S2 of the second optical fiber 30. The thickness w of the refractive index matching material 60 is 0.05 mm. When the first end face S1 and the second end face S2 of the first optical fiber 10 and the second optical fiber 30 are positioned facing each other axially with the refractive index matching material 60 according to the first embodiment in between, they are pressed against the refractive index matching material 60 with a pressing force F of 10 N.

[0103] The first optical fiber 10 is, for example, a graded-index POF with a length of 2 m. In the first optical fiber 10, the diameter d2 is 0.49 mm. The diameter of the core of the first optical fiber 10 is 0.055 mm. The refractive index of the core of the first optical fiber 10 is 1.346 at the radial center of the core and gradually decreases from the center of the core toward the radial side. In the first ferrule 20, the diameter d1 is 1.25 mm. The radius of curvature R1 is 10 mm. The gap width g1 is 0.01 mm.

[0104] The second optical fiber 30 is, for example, a graded-index POF with a length of 2 m. In the second optical fiber 30, the diameter d4 is 0.49 mm. The core diameter of the second optical fiber 30 is 0.055 mm. The refractive index of the core of the second optical fiber 30 is 1.346 at the radial center of the core and gradually decreases from the center outward in the radial direction. In the second ferrule 40, the diameter d3 is 1.25 mm. The radius of curvature R2 is 10 mm. The gap width g2 is 0.01 mm.

[0105] Under the conditions described above, the light power (mW) when the refractive index matching material 60 according to the first embodiment is placed between the first end face S1 and the second end face S2 is shown relative to the light power (mW) when butt contact is performed. Butt contact means that the first end face S1 and the second end face S2 are directly butted together without any gap. Compared to the case of butt contact, the light power (mW) was reduced by only about 0.02 dB.

[0106] On the other hand, the optical power (mW) in the comparative example, where an air gap is formed without placing the refractive index matching material 60 according to the first embodiment between the first end face S1 and the second end face S2, is shown relative to the optical power (mW) when butt contact is used. Compared to the case of butt contact, the optical power (mW) was reduced by 0.15 dB. Comparing this comparative example with the case where the refractive index matching material 60 according to the first embodiment is placed, it was confirmed that placing the refractive index matching material 60 between the first end face S1 and the second end face S2 reduces the insertion loss and approximates the optical power (mW) to the value when butt contact is used.

[0107] Figure 11 is a graph showing a first example of the mechanical properties of the refractive index matching material 60 according to the first embodiment. Figure 12 is a graph showing a second example of the mechanical properties of the refractive index matching material 60 according to the first embodiment. Tensile tests were performed using the refractive index matching material 60 to obtain the mechanical property data shown in Figures 11 and 12. A dumbbell-shaped specimen of type 8 was used as the standard dumbbell-shaped test specimen for tensile tests.

[0108] Figure 11 shows the stress (N / mm²) of the refractive index matching material 60. 2 Figure 12 shows the graph of the displacement (strain) dependence of the material when the mixing ratio of agent A and agent B is changed in three patterns. In TSE3033, the mixing ratio of agent A and agent B was set to three levels: A / B = 1 / 2 (AB12), 1 / 1 (AB11), and 2 / 1 (AB21). Figure 12 shows the graph of the dependence of the elastic modulus (MPa) of refractive index matching material 60 on the mixing ratio.

[0109] Table 3 below summarizes the mechanical properties of the refractive index matching material 60. As shown in Figures 11 and 12, and Table 3, the elastic modulus (MPa) of the refractive index matching material 60 tends to increase when a relatively larger amount of component B, which contains the crosslinking agent, is mixed in. However, even in that case, it remains below 1 MPa at all three levels.

[0110] [Table 3]

[0111] Figure 13 is a graph showing a third example of the mechanical properties of the refractive index matching material 60 according to the first embodiment. Figure 13 shows data of the optical output (dBm) measured when the end face of an optical fiber was roughened with a polishing film. To obtain the mechanical property data in Figure 13, an AB11 mixing ratio was achieved in TSE3033. More specifically, the liquid agent was sandwiched between fluorine-treated glass with a 0.05 mm spacer and heated and cured at 80°C for 1 hour. The conditions for roughening the end face of the optical fiber on which the obtained refractive index matching material 60 is placed and the optical output (dBm) are summarized in Table 4 below.

[0112] [Table 4]

[0113] In Table 4, column 1 shows the results when the surface roughness and optical output of the end face of an optical fiber to which the refractive index matching material 60 is to be placed are measured without processing with a polishing film. Columns 2 and 3 show the results when the surface roughness and optical output of the end face of an optical fiber to which the refractive index matching material 60 is to be placed are measured after the end face of the optical fiber is roughened with a polishing film under different conditions.

[0114] As shown in Figure 13 and Table 4, the optical output (dBm) of the optical fiber with an unroughened end face was approximately -2.0 dBm both before and after the placement of the refractive index matching material 60. On the other hand, as the end face of the optical fiber became rougher, the optical output (dBm) decreased further, resulting in an increase in insertion loss. In contrast, when the refractive index matching material 60 was placed on the roughened end face of the optical fiber, it flexibly deformed to conform to the roughened surface shape, resulting in an increase in the optical output (dBm) compared to before placement. The difference in optical output (dBm) before and after the placement of the refractive index matching material 60 increased as the end face of the optical fiber became rougher. Thus, the effect of improving refractive index matching by the elastic refractive index matching material 60 is obtained.

[0115] To evaluate the adhesive strength of the refractive index matching material 60 according to the first embodiment, measurements were performed using the following method.

[0116] A tacking tester (model number: TAC-1000, manufactured by Resca Co., Ltd.) was used to measure the adhesive strength. A 5mm diameter SUS (stainless steel) rod was used as a probe. The actual measurements were performed using the tacking tester, following the procedure below.

[0117] First, the refractive index matching material 60, which is the sample, is placed on the stage. The probe is brought into contact with the adhesive surface of the refractive index matching material 60 from above at a set speed. At this time, the tacking test machine performs load control and penetration depth control processing. The probe is brought into contact with the surface of the refractive index matching material 60 at a constant speed, held at 50 gf for 15 seconds, and then pulled up at a constant speed. When the probe is released from the refractive index matching material 60 at the set speed, the probe encounters resistance due to the adhesive force. This resistance generated during the pull-up is recorded as the load (N) value. This load value becomes the tack value (adhesion force).

[0118] The measurement conditions were as follows: the probe pressing speed was 1 mm / sec, and the probe withdrawal speed was 2 mm / sec.

[0119] The adhesive strength of the refractive index matching material 60 was 5N or less when measured using a 5mm diameter SUS (stainless steel) rod as a probe. This result indicates that the refractive index matching material 60 has low adhesive strength. It was confirmed that the refractive index matching material 60 has the property of suppressing adhesive residue that occurs when using the material. The adhesive strength of the refractive index matching material 60 for each mixing ratio of agent A and agent B is summarized in Table 5 below. The thickness of the refractive index matching material 60 was 0.4mm.

[0120] [Table 5]

[0121] (Second example) The second embodiment relates to the refractive index matching material 60 according to the second embodiment. The contents described in the first embodiment also apply to the refractive index matching material 60 according to the second embodiment. In the following, the contents that are common to the first embodiment will be omitted from the explanation. The differences from the first embodiment will be mainly explained.

[0122] The refractive index matching material 60 according to the second embodiment is a heat-curing silicone rubber comprising, for example, two components, component A and component B, in addition to a coloring agent. Component A comprises, for example, a vinyl silicone component and a Pt catalyst. Component B comprises, for example, a vinyl silicone component, a silicone crosslinking agent, and a silane coupling agent. The refractive index matching material 60 is a colored rubber-like substance obtained by adding a coloring agent to a two-component heat-curing adhesive liquid silicone rubber (TSE3033) manufactured by Momentive, which consists of component A as the main component and component B as the curing agent, and then heat-curing it.

[0123] Figure 14 is a graph showing an example of the optical properties of the refractive index matching material 60 according to the second embodiment. In order to investigate the coloring of the refractive index matching material 60 according to the second embodiment, the refractive index matching material 60 was prepared by adding cyan, magenta, and yellow dyes to TSE3033. The refractive index matching material 60 was prepared using, for example, AB11. The refractive index matching material 60 was prepared by dropping one drop (0.02 g) of dye ink into 1 g of agent A and 1 g of agent B.

[0124] The stirring conditions included stirring at 2000 rpm and 10 kPa for 1.5 minutes. The liquid agent was sandwiched between fluorine-treated glass and heated and cured to a target film thickness of 0.4 mm at 100°C for 30 minutes. The mixed viscosity was 1 Pa·s. The refractive index matching material 60 was heated and cured in an oven at 100°C for 30 minutes, resulting in a film with a thickness w of approximately 0.4 mm.

[0125] In Figure 14, graph G1 shows the wavelength dependence of the light transmittance (%) of the refractive index matching material 60 when it contains cyan dye as a coloring agent. Graph G2 shows the wavelength dependence of the light transmittance (%) of the refractive index matching material 60 when it contains magenta dye as a coloring agent. Graph G3 shows the wavelength dependence of the light transmittance (%) of the refractive index matching material 60 when it contains yellow dye as a coloring agent. Graph G4 shows the wavelength dependence of the light transmittance (%) of the refractive index matching material 60 when it is colorless and transparent without containing any coloring agent.

[0126] Generally, each dye has complementary color absorption. For example, cyan dye has red as its complementary color and is likely to affect the transmission characteristics in the near-infrared wavelength band. Magenta dye has green as its complementary color and is less likely to affect the transmission characteristics in the near-infrared wavelength band. Yellow dye has blue as its complementary color and is hardly affected by the transmission characteristics in the near-infrared wavelength band. As shown in Figure 14, in graph G1, the light transmittance (%) decreases significantly at the wavelength of red light, and the tail of this decrease extends into the near-infrared wavelength band. On the other hand, in graphs G2 and G3, the light transmittance (%) in the near-infrared wavelength band remains approximately the same as the value in graph G4. Table 6 below summarizes the optical properties of refractive index matching material 60 at wavelengths of 850 nm and 980 nm.

[0127] [Table 6]

[0128] It will be apparent to those skilled in the art that this disclosure can be implemented in other predetermined forms besides the embodiments described above without deviating from its spirit or essential features. Therefore, the prior description is illustrative and not limiting. The scope of the disclosure is defined not by the prior description but by the added claims. Any modifications within their equivalent scope are included therein.

[0129] For example, the shape, pattern, size, arrangement, orientation, type, and number of each component described above are not limited to those shown in the above description and drawings. The shape, pattern, size, arrangement, orientation, type, and number of each component may be configured arbitrarily as long as they can achieve their function. Each component of the refractive index matching material 60 and the connecting structure 1 shown is a functional concept. The specific form of each component is not limited to those shown. [Explanation of symbols]

[0130] 1. Connection structure 10. First optical fiber 20 First ferrule 21 Center hole 30. Second optical fiber 40 Second ferrule 41 Center hole 50 connectors 51 First connector 52 Second connector 60 refractive index matching material F Pressing force G1, G2, G3, G4 graphs R1 radius of curvature R2 radius of curvature S1 1st end surface S2 2nd end face S3 tip surface S4 tip surface T1 First tip T2 Second tip V1 1st void V2 2nd void d1 diameter d2 diameter d3 diameter d4 diameter g1 Gap width g2 Gap width w thickness

Claims

1. A refractive index matching material disposed between the first end face of the first optical fiber and the second end face of the second optical fiber, A composition comprising a silicone resin and a colorant, The coloring agent has an absorption rate of 10% or less in the near-infrared wavelength band of optical communication using the first optical fiber and the second optical fiber, and an absorption rate of 20% or more in the visible wavelength band. Refractive index matching material.

2. A refractive index matching material according to claim 1, The adhesive strength is included in the range of 5N or less. Refractive index matching material.

3. A refractive index matching material according to claim 1, Hardened and integrally disposed with respect to at least one of the first end face and the second end face, Refractive index matching material.

4. A refractive index matching material according to any one of claims 1 to 3, The wavelength band of the optical communication is included in the range of 850 nm to 980 nm within the near-infrared wavelength band. Refractive index matching material.

5. A refractive index matching material according to any one of claims 1 to 3, The first optical fiber having the first end face, A first ferrule that holds the first optical fiber, The second optical fiber having the second end face, A second ferrule that holds the second optical fiber, A connector that connects the first ferrule and the second ferrule to each other, Equipped with, Optical fiber connection structure.

6. The connection structure according to claim 5, The refractive index matching material is filled in at least one of the first internal void between the first tip and the first end face of the first ferrule and the second internal void between the second tip and the second end face of the second ferrule. Connection structure.

7. The connection structure according to claim 5, The refractive index of the core wire of the first optical fiber is lower than the refractive index of the refractive index matching material. The refractive index of the core wire of the second optical fiber is higher than the refractive index of the refractive index matching material. Connection structure.

8. A step of applying a liquid silicone resin containing a coloring agent having an absorption rate of 10% or less in the near-infrared wavelength band and an absorption rate of 20% or more in the visible wavelength band to at least one of the first end face of the first optical fiber and the second end face of the second optical fiber, A step of curing the applied liquid, A step of connecting the first optical fiber and the second optical fiber with a connector, and integrally arranging a refractive index matching material, which is a composition containing the cured silicone resin and the coloring agent, between the first end face and the second end face, including, Method of arranging refractive index matching material.

Images