Optical connector

Abstract

The purpose of the present invention is to provide an optical connector with which it is possible to suppress reflection at a connecting part.　This optical connector 1 comprises a multi-core fiber 10 having a plurality of cores 11, and a ferrule 20 that includes a through-hole 23 into which one end side of the multi-core fiber 10 is inserted, wherein: an end face 25 of the ferrule 20 overlaps with a spherical plane SS that contacts, on a center axis 23C of the through-hole 23, an inclined plane FS which inclines with respect to a perpendicular plane FP perpendicular to the center axis; an end face 15 on one side of the multi-core fiber 10 inclines to the same side as the side on which the inclined plane FS inclines with respect to the perpendicular plane FP; and when the radius of curvature of the spherical plane SS is defined as B (mm), an eccentricity amount that is the distance to a top position TP protruding most from a line CL going through the center axis 23C and connecting the center line 23C, the spherical plane SS, and edges ED of the end face 25 in a cross-section perpendicular to the inclined plane FS is defined as C (μm), and the distance between the center axis 23C and the center of the core 11 positioned most separated from the center axis 23C when viewed along the center axis 23C is defined as x (μm), the following expression is satisfied.

Description

Optical Connector

[0001] The present invention relates to an optical connector.

[0002] Multicore fibers having multiple cores arranged in a cladding are known. Patent Document 1 listed below describes an optical connector that connects a pair of multicore fibers by pressing their end faces together. Patent Document 1 describes conditions for connecting the cores of the multicore fibers through physical contact. The end face of this multicore fiber is formed into a curved surface with a convex center, with the end face being approximately perpendicular to the longitudinal direction of the multicore fiber. This optical connector is sometimes called a UPC connector (Ultra-Physical Contact Connector).

[0003] U.S. Patent No. 10,989,882

[0004] Incidentally, in a sensor that measures strain and the like using an optical fiber, it is required that reflection at the optical connector connecting the optical fibers be small, and therefore an angled physical contact (APC) connector, in which the end face of the optical fiber is inclined with respect to a plane perpendicular to the longitudinal direction of the optical fiber, is sometimes used. For this reason, even when a multicore fiber is used in a sensor, it is required that reflection at the optical connector be small, and therefore it is preferable to use an APC connector. Even when multicore fibers are connected to each other using an APC connector, it is preferable that reflection be suppressed by physical contact between the respective cores. However, the above-mentioned Patent Document 1 does not consider APC connectors.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical connector that can suppress reflection at the connection portion.

[0006] In order to achieve the above object, a first aspect of the present invention comprises a multicore fiber having a plurality of cores, and a ferrule including a through hole into which one end side of the multicore fiber is inserted, wherein an end face of the ferrule overlaps with a spherical surface that is tangent on the central axis to an inclined plane that is inclined with respect to a vertical plane perpendicular to the central axis of the through hole, and the end face on the one end side of the multicore fiber is inclined to the same side as the side on which the inclined plane is inclined with respect to the vertical plane, and a radius of curvature of the spherical surface is B (mm), an amount of eccentricity that is a distance from a vertex position that protrudes most from a line that connects an intersection point of the central axis and the spherical surface to an edge of the end face in a cross section that passes through the central axis and is perpendicular to the inclined plane is C (μm), and a distance between the central axis and the center of the core that is located farthest from the central axis when viewed along the central axis is x, The optical connector is characterized by satisfying the following.

[0007] When connecting a pair of optical connectors in which the ends of the ferrules that house one end of a multicore fiber are polished at an angle, the inventors have thoroughly studied the conditions under which the cores of each fiber come into physical contact. As a result, they have found that if each optical connector satisfies the above formula, the cores of each opposing multicore fiber come into physical contact. Therefore, the optical connector of the present invention can suppress reflection at the connection portion of the multicore fiber.

[0008] Furthermore, aspect 2 of the present invention is The optical connector according to aspect 1 satisfies the following conditions:

[0009] In addition to the condition of the above-described aspect 1, when at least one of the optical connectors satisfies this condition, the cores of the opposing multicore fibers are in stronger physical contact with each other, and reflection at the connection portion of the multicore fibers can be further suppressed.

[0010] In addition, in a third aspect of the present invention, when the deviation amount of the angle formed by the inclined plane and the vertical plane from 8 degrees is Δθ, 3. The optical connector according to claim 1, wherein the following is satisfied:

[0011] Generally, in an APC connector, the angle of the inclined plane relative to the vertical plane is approximately 8 degrees. This is specified in IEC 61755-3-2 and JIS C5965-3-2. When the deviation Δθ of the inclined plane from 8 degrees satisfies the above formula, and the deviation Δθ is constant, the eccentricity C can be reduced by reducing the radius of curvature B (mm). Alternatively, when the deviation Δθ of the inclined plane from 8 degrees satisfies the above formula, the radius of curvature B (mm) and the eccentricity C (μm) can more easily satisfy the formula of aspect 1.

[0012] Furthermore, aspect 4 of the present invention is an optical connector according to any one of aspects 1 to 3, further comprising a guide key arranged parallel to the longitudinal direction of the through hole on a housing to which the ferrule is fixed, and characterized in that a key error, which is the angle between the perpendicular to the inclined plane and the central axis of the through hole when viewed along a direction perpendicular to a plane passing through the central axis of the guide key and the central axis of the through hole, is 0.4 degrees or less.

[0013] The optical connector may be provided with the above-mentioned guide key. However, due to manufacturing variations, etc., when the optical connector is placed with the guide key facing upward and viewed from the side, the direction perpendicular to the inclined plane may be shifted in the up / down direction with respect to the longitudinal direction of the through hole indicated by the guide key. If the key error, which is the amount of this shift, is 0.4 degrees or less, reflection at the connection portion of the multicore fiber can be further suppressed.

[0014] A fifth aspect of the present invention is the optical connector according to any one of the first to fourth aspects, wherein the diameter of the ferrule is 2.5 mm.

[0015] As described above, according to the present invention, an optical connector capable of suppressing reflection at a connection portion can be provided.

[0016] 1 is a diagram showing an outline of an optical connector according to an embodiment of the present invention; FIG. 2 is a diagram showing a cross section perpendicular to the longitudinal direction of the multicore fiber of FIG. 1; FIG. 3 is a cross section showing the state of the tip of the ferrule of FIG. 1; FIG. 4 is a cross section showing the state of optical connectors being connected to each other; FIG. 5 is a diagram showing the relationship between the radius of curvature and the amount of eccentricity of the ferrule end face for physical contact between opposing cores of the multicore fiber; FIG. 6 is a diagram showing the relationship between the angle between the inclined plane and the vertical plane of the ferrule end face and the radius of curvature and the amount of eccentricity; FIG. 7 is a diagram showing a key error; and FIG. 8 is a diagram showing the relationship between the key error and loss due to light reflection at the connection portion when connecting a pair of optical connectors.

[0017] Hereinafter, embodiments for carrying out the optical connector according to the present invention will be illustrated with reference to the accompanying drawings. The embodiments illustrated below are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention can be modified and improved from the following embodiments without departing from the spirit thereof. Furthermore, in this specification, the dimensions of each component may be exaggerated to facilitate understanding.

[0018] Fig. 1 is a diagram showing an outline of an optical connector according to this embodiment. As shown in Fig. 1, the optical connector 1 according to this embodiment mainly comprises a multicore fiber 10, a ferrule 20, and a housing 30. An example of the optical connector 1 according to this embodiment is an SC connector (Subscriber Connector), as shown in Fig. 1.

[0019] The housing 30 accommodates the ferrule 20, and one end side including the tip portion 22 of the ferrule 20 protrudes from one opening 31 of the housing 30. The multicore fiber 10 protrudes from the side of the housing 30 opposite to the side from which the ferrule 20 protrudes. A guide key 32 is provided on a side surface of the housing 30 parallel to the longitudinal direction of a through hole 23 of the ferrule 20, which will be described later. Therefore, a central axis 32C of the guide key is parallel to the longitudinal direction of the through hole 23. An engagement claw 33 is provided on the other side surface of the housing 30.

[0020] Fig. 2 is a diagram showing a cross section perpendicular to the longitudinal direction of the multi-core fiber 10 in Fig. 1. The multi-core fiber 10 includes a plurality of cores 11, a cladding 12, an inner coating layer 13, and an outer coating layer 14.

[0021] In the multicore fiber 10 of this embodiment, one core 11 is arranged at a center 10C of the multicore fiber 10, and the other six cores 11 are arranged on the same circle centered on the center 10C. That is, the multiple cores 11 of the multicore fiber 10 of this embodiment are arranged in a so-called 1-6 arrangement. The center 10C coincides with the center of the cladding 12. The diameter of the core 11 is, for example, 4 μm or more and 10 μm or less. The inter-core distance is, for example, 35 μm. In this case, the distance from the center 10C to the core 11 located on the outer periphery side is 35 μm. The six cores 11 arranged on the outer periphery side may be arranged so as to be twisted along the longitudinal direction of the multicore fiber 10.

[0022] The clad 12 surrounds the outer periphery of each core 11. The diameter of the clad 12 is, for example, 125 μm.

[0023] The refractive index of each core 11 is higher than the refractive index of the cladding 12. The core 11 is made of silica glass doped with a dopant such as germanium that increases the refractive index, and the cladding 12 is made of silica glass that does not have any dopant added. Alternatively, the core 11 may be made of silica glass that does not have any dopant added, and the cladding 12 may be made of silica glass that has a dopant such as fluorine that decreases the refractive index.

[0024] The inner coating layer 13 coats the outer peripheral surface of the cladding 12, and the outer coating layer 14 coats the outer peripheral surface of the inner coating layer 13. The inner coating layer 13 and the outer coating layer 14 are each made of a resin such as an ultraviolet curable resin, and the inner coating layer 13 and the outer coating layer 14 are made of different resins.

[0025] The ferrule 20 of this embodiment includes a cylindrical main body 21 and a cylindrical tip portion 22 that extends from one end of the main body 21 and has a smaller diameter than the main body 21. For example, the diameter of the ferrule 20 is 2.5 mm. The through holes 23 of the main body 21 and the tip portion 22 have the same diameter. One end of the multicore fiber 10, from which the inner coating layer 13 and the outer coating layer 14 have been stripped, is inserted into the through hole 23. In this embodiment, one end face 15 of the multicore fiber 10 is located within the through hole 23 of the ferrule 20 and is slightly recessed from the end face 25 of the ferrule 20. The ferrule 20 is made of a material that is lower in hardness than the cladding 12 of the multicore fiber 10. An example of such a material is zirconia.

[0026] 3 is a cross-sectional view showing the state of the tip of the ferrule 20 in FIG. 1. As shown in FIG. 3, an inclined plane FS is assumed to be inclined with respect to a vertical plane FP perpendicular to the central axis 23C of the through-hole 23, and a spherical surface SS is assumed to be tangent to this inclined plane FS on the central axis 23C. The end face 25 of the ferrule 20 overlaps this spherical surface SS. Therefore, the end face 25 is part of a spherical surface formed in a convex shape and is inclined with respect to the vertical plane FP. In this embodiment, the inclination of the inclined plane FS with respect to the vertical plane FP is 8 degrees.

[0027] The opening of the through hole 23 is located approximately in the center of the end face 25 having such an inclined spherical shape. Therefore, the multicore fiber 10 can be seen by looking into the through hole 23. The multicore fiber 10 is inserted into the through hole 23 so that the central axis of the multicore fiber 10 located in the through hole 23 coincides with the central axis 23C of the through hole 23. Therefore, the center 10C of the multicore fiber 10 shown in FIG. 2 is located on the central axis 23C. Furthermore, the end face 15 of the multicore fiber 10 is inclined with respect to the vertical plane FP on the same side as the inclined plane FS. The average inclination of this end face 15 with respect to the vertical plane FP is preferably the same as the inclination of the inclined plane FS with respect to the vertical plane FP. Furthermore, although this end face 15 may be an inclined plane as described above, it is preferably a spherical surface. In this case, it is more preferable that the radius of curvature of the end face 15 is the same as the radius of curvature of the spherical surface SS.

[0028] When optical connectors 1 having such a configuration are connected to each other, an adapter is used that has a pair of guide grooves into which the guide keys 32 of each optical connector 1 are fitted and a pair of engagement holes into which the engagement claws 33 of each optical connector 1 are engaged when the optical connectors 1 are opposed to each other. Fig. 4 is a cross-sectional view showing how the optical connectors are connected to each other. Note that Fig. 4 only shows the tips of the ferrules 20 and the multi-core fibers 10. When a pair of optical connectors 1 is fixed to the adapter, as shown in Fig. 4, the end faces 25 of the tip portions 22 of the opposing ferrules 20 are pressed against each other, causing the tip portions 22 to deform slightly, so that the end faces 15 of the multi-core fibers 10 come into contact with each other, thereby connecting the multi-core fibers 10 to each other. For example, when the diameter of the ferrules 20 is 2.5 mm, if the force pressing the end faces 25 against each other is 7.8 N or more and 11.8 N or less, reflection at the connection portion of the multi-core fibers 10 can be further suppressed.

[0029] Next, a description will be given of the conditions under which the opposing cores 11 of the pair of multi-core fibers 10 are in appropriate physical contact with each other when the optical connectors 1 are connected to each other.

[0030] First, the radius of curvature of the spherical surface SS shown in FIG. 3 is defined as B (mm). When the optical connector 1 is viewed in a cross section passing through the central axis 23C and perpendicular to the inclined plane FS, the cross section shown in FIG. 3 is obtained. Therefore, in the cross section of FIG. 3, the vertex position TP of the spherical surface SS is defined as the position that protrudes most from the line CL connecting the edge ED of the end face 25. The eccentricity C (μm) of the vertex position TP is defined as the distance between the intersection CP of the central axis 23C of the through hole 23 and the spherical surface SS and the vertex position TP. When viewed along the central axis 23C, the distance between the central axis 23C and the center of the core 11 located farthest from the central axis 23C is defined as x (μm). When the center 10C of the multicore fiber is located on the central axis 23C of the through hole 23 as described above, x in FIG. 2 corresponds to the distance x (μm).

[0031] As described above, the end face 15 of the multi-core fiber 10 is slightly recessed from the end face 25 of the ferrule 20, and this recession amount is a maximum value A maximum(nm), and the maximum value A maximum (nm) is determined in accordance with IEC 61755-3-2 so as to satisfy the following formula (1):

[0032] FIG. 5 shows the relationship between the radius of curvature B (mm) and the amount of eccentricity C (μm) at the end face 25 of the ferrule 20 for physical contact between opposing cores of a multicore fiber. First, a first optical connector 1 was prepared, having a ferrule 20 with a radius of curvature B (mm) of 10.5 (mm) and an amount of eccentricity C (μm) of 126.4 (μm). Next, multiple second optical connectors 1 were prepared to be connected to this first optical connector 1. Then, the second optical connector 1 was connected to the first optical connector 1, and the return loss was measured. Multiple second optical connectors 1 with a return loss of 55 dB, which is close to the upper limit of the return loss of a typical APC connector, were selected. The return loss is a quantity that indicates the ratio of the power of reflected return light to the power of incident light. Next, fitting was performed based on the radius of curvature B (mm) and the amount of eccentricity C (μm) at the end face 25 of the ferrule 20 of each of the selected second optical connectors 1, resulting in the thin solid line a in FIG. 5. In addition, the radius of curvature B (mm) and the eccentricity C (μm) of one optical connector 1 are substituted into equation (1), and A obtained from equation (1) is maximum The relationship between the radius of curvature B (mm) and the amount of eccentricity C (μm) that is the same as the radius of curvature B (mm) (nm) is shown by the thin dashed line b in Figure 5. Therefore, when one optical connector 1 having a ferrule 20 whose end face 25 has a radius of curvature B (mm) and amount of eccentricity C (μm) located on the dashed line b is connected to another optical connector 1 having a ferrule 20 whose end face 25 has a radius of curvature B (mm) and amount of eccentricity C (μm) located on the solid line a, the return loss is expected to be 55 dB. Furthermore, if the radius of curvature B (mm) and amount of eccentricity C (μm) of the end face 25 of the ferrule 20 in the other optical connector 1 to be connected to this one optical connector 1 are located below the solid line a, the return loss is expected to be 55 dB or more. If the return loss is 55 dB or more, it can be said that reflection at the connection is sufficiently suppressed.

[0033] Next, one optical connector 1 was prepared, which had a ferrule 20 with a curvature radius B (mm) of 9.1 (mm) and an eccentricity C (μm) of 50.4 (μm). A plurality of other optical connectors 1 to be connected to this one optical connector 1 were also prepared. Then, the other optical connector 1 was connected to the one optical connector 1, and the return loss was measured, and a plurality of other optical connectors 1 with a return loss of 55 dB were extracted. Next, fitting was performed based on the curvature radius B (mm) and the eccentricity C (μm) at the end face 25 of the ferrule 20 of each of the extracted other optical connectors 1, resulting in the thick solid line c in Figure 5. Furthermore, the curvature radius B (mm) and the eccentricity C (μm) of the one optical connector 1 were substituted into equation (1), and the A obtained by equation (1) was calculated. maximum The relationship between the radius of curvature B (mm) and the amount of eccentricity C (μm) that is the same as the radius of curvature B (mm) and amount of eccentricity C (μm) is shown by the thick dashed line d in Figure 5. Therefore, when one optical connector 1 having a ferrule 20 whose end face 25 has a radius of curvature B (mm) and amount of eccentricity C (μm) located on dashed line d is connected to another optical connector 1 having a ferrule 20 whose end face 25 has a radius of curvature B (mm) and amount of eccentricity C (μm) located on solid line c, it is considered that the return loss will be 55 dB. Furthermore, if the radius of curvature B (mm) and amount of eccentricity C (μm) of the end face 25 of the ferrule 20 in the other optical connector 1 to be connected to this one optical connector 1 are located below solid line c, it is considered that the return loss will be 55 dB or more.

[0034] As described above, the shape of the end face 25 of the ferrule 20 of the other optical connector 1 that is connected to one optical connector 1 having a ferrule 20 located on dashed line b and that has a return loss of 55 dB or more must be located within a relatively narrow region below solid line a. In contrast, the shape of the end face 25 of the ferrule 20 of the other optical connector 1 that is connected to one optical connector 1 having a ferrule 20 located on dashed line d and that has a return loss of 55 dB or more must be located within a relatively wide region below solid line c. Therefore, by reducing the eccentricity of dashed line b and moving dashed line b downward, solid line a moves upward. This expands the range of curvature radius B (mm) and eccentricity C (μm) that the shape of the end face 25 of the ferrule 20 of the other optical connector 1 can take. Therefore, by repeating this process and finding and fitting the points where dashed line b and solid line a intersect for each curvature radius, the dashed-dotted line e is obtained. Furthermore, if the eccentricity of dashed line d is increased and dashed line d is moved upward, solid line c will move downward. Repeating this process to find and fit the point where dashed line d and solid line c intersect for each radius of curvature results in dashed-dotted line e. Therefore, when connecting a pair of optical connectors 1 in which the radius of curvature B (mm) and eccentricity C (μm) of the end face 25 of the ferrule 20 are in a range equal to or less than dashed-dotted line e, the return loss can be suppressed to 55 dB or more.

[0035] The relationship between the radius of curvature B (mm) and the amount of eccentricity C (μm) in the region below the dashed dotted line e is given by the following formula (2):

[0036] Therefore, by connecting a pair of optical connectors 1 in which the radius of curvature B (mm) and eccentricity C (μm) of the end face 25 of the ferrule 20 satisfy formula (2), reflection at the connection portion is sufficiently suppressed. Thus, in an APC connector using a multicore fiber 10, the end face 25 of the ferrule 20 is spherically polished, so the end face 15 of the multicore fiber 10 can also be spherical, and a discrepancy in the angle at the end face can occur between the core 11 located at the center and the core 11 located on the outer periphery. In this case, some of the cores 11 located on the outer periphery may have a higher return loss than the core 11 located at the center, while others may have a lower return loss. Here, if the return loss is 55 dB or more, all of the cores 11 can approach the return loss range of 60 dB or more, which is defined by the standards (IEC 61755-2-2 and JIS C5965-2-2). Therefore, reflection at the connection portion can be sufficiently suppressed.

[0037] Furthermore, it is preferable that the radius of curvature B (mm) and the eccentricity C (μm) of the end face 25 of the ferrule 20 of at least one of the optical connectors 1 are located in the region below the dotted line f in Figure 5. This region is expressed by the following formula (3).

[0038] Of a pair of optical connectors 1 that satisfy the above formula (2), if the radius of curvature B (mm) and eccentricity C (μm) of the end face 25 of the ferrule 20 of at least one of the optical connectors 1 satisfy formula (3), it is possible to bring all cores 11 closer to the range of 60 dB or more, which is the return loss range specified by the above standard, and to further suppress reflection at the connection portion.

[0039] Next, we consider the angle of the inclined plane FS relative to the vertical plane FP. IEC 61755-3-2 and JIS C5965-3-2 stipulate that the angle of the inclined plane FS of an APC connector be 8 degrees. Therefore, the angle of the inclined plane FS of the end face 25 of the ferrule 20 of this embodiment relative to the vertical plane FP is also 8 degrees. Furthermore, when the above formula (2) is satisfied, and the radius of curvature B (mm) and eccentricity C (μm) of the end face 25 of the ferrule 20 also satisfy formula (2), the angle of the inclined plane FS relative to the vertical plane FP is often approximately 8 degrees. Therefore, we consider the deviation of the inclined plane FS from 8 degrees that satisfies formula (2). Figure 6 is a diagram showing the relationship between the angle of the inclined plane FS of the end face 25 of the ferrule 20 relative to the vertical plane FP and the radius of curvature B and eccentricity C. In FIG. 6 , the angle of the inclined plane FS from the vertical plane FP is referred to as the oblique grinding angle, the radius of curvature B is referred to as the curvature, and the amount of eccentricity C is referred to as the apex deviation. As shown in FIG. 6 , when the radius of curvature B (mm) is constant, the greater the deviation of the angle of the inclined plane FS from 8 degrees relative to the vertical plane FP, the greater the amount of eccentricity (μm). Furthermore, when the amount of eccentricity C (μm) is constant, the greater the deviation of the angle of the inclined plane FS from 8 degrees relative to the vertical plane FP, the smaller the radius of curvature B (mm). When this deviation Δθ is Δθ, it is preferable to satisfy the following formula (4). When the deviation Δθ of the inclined plane from 8 degrees satisfies formula (4), the amount of eccentricity C (μm) can be reduced by reducing the radius of curvature B (mm), provided that the deviation Δθ is constant. Alternatively, the radius of curvature B (mm) and the amount of eccentricity C (μm) can more easily satisfy formula (2).

[0040] Next, let us consider key error. As described above, the housing 30 is provided with a guide key 32 that indicates the longitudinal direction of the through hole 23 in the ferrule 20. FIG. 7 is a diagram illustrating the key error, in which the optical connector 1 is viewed along a direction perpendicular to a plane passing through the central axis 32C of the guide key 32 and the central axis 23C of the through hole 23. That is, the optical connector 1 is positioned with the guide key 32 facing upward, and the optical connector 1 is viewed from the side. The end face 25 is inclined toward the side on which the inclined plane FS is inclined. In this embodiment, the inclined plane FS is inclined toward the side toward which the optical connector 1 is viewed, with the vertical plane FP as the reference. Therefore, the end face 25 is visible in FIG. 3. Note that FIG. 3 is a cross-sectional view taken along a plane passing through the central axis 32C of the guide key 32 and the central axis 23C of the through hole 23. When viewing the optical connector 1 as shown in FIG. 7, the key error is the angle θ' between the perpendicular line FSV of the inclined plane FS and the central axis 23C of the through hole 23. Therefore, when viewing the optical connector 1 as shown in Figure 7, if a key error occurs, the perpendicular line FSV tilts upward or downward. Note that in Figure 7, each θ' is exaggerated to make the drawing easier to read. An error in the orientation of the end face 25 due to manufacturing errors of the optical connector 1 may cause an error in the orientation of the inclined plane FS, resulting in the above-mentioned key error. Figure 8 illustrates the relationship between the key error and loss due to light reflection at the connection when connecting a pair of optical connectors 1. As shown in Figure 8, if the key error is 0.4 degrees or less, the probability of reducing loss due to light reflection at the connection is increased when connecting optical connectors 1, allowing the return loss to be increased to more than 60 dB, and preventing the return loss from changing with each connection. Therefore, it can be seen that if the key error is 0.4 degrees or less, there is a tendency for the return loss to be stabilized while reducing loss.

[0041] As described above, in the optical connector 1 of this embodiment, the end face 25 of the ferrule 20 overlaps with the spherical surface SS, and the radius of curvature of this spherical surface SS is B (mm), the eccentricity C (μm) is the distance from the intersection CP of the central axis 23C and the spherical surface SS to the vertex position TP, and the distance x between the central axis 23C and the center of the core 11 located farthest from the central axis 23C satisfy formula (2). Therefore, by connecting such optical connectors 1 together, the cores 11 of the opposing multicore fibers 10 come into physical contact with each other, and reflection at the connection portion of the multicore fibers 10 can be suppressed.

[0042] Although the present invention has been described above using the above embodiment as an example, the present invention is not limited to the above embodiment.

[0043] In the above embodiment, the multi-core fiber 10 having seven cores 11 is exemplified, but the number of cores 11 is not limited to seven as long as it is plural. For example, the core 11 does not have to be disposed at the center of the cladding 12.

[0044] Furthermore, in the above embodiment, an example has been shown in which one end face 15 of the multicore fiber 10 is located inside the through-hole 23 of the ferrule 20 and is slightly recessed from the end face 25 of the ferrule 20. However, one end face 15 of the multicore fiber 10 may protrude slightly from the end face 25 of the ferrule 20. In this case, the protrusion amount of the multicore fiber 10 is 100 nm or less.

[0045] According to the present invention, an optical connector capable of suppressing reflection at a connection portion can be provided, and can be used in fields such as optical communications.

Claims

1. A multi-core fiber having a plurality of cores, A ferrule including a through-hole into which one end side of the multi-core fiber is inserted, Comprising, The end face of the ferrule overlaps a spherical surface that contacts on the central axis with respect to an inclined plane that is inclined with respect to a vertical plane perpendicular to the central axis of the through-hole, The end face of the one end side of the multi-core fiber is inclined to the same side as the side where the inclined plane is inclined with respect to the vertical plane, Let the radius of curvature of the spherical surface be B (mm), and the eccentricity C (μm) be the distance from the intersection of the central axis and the spherical surface to the vertex position that protrudes most from the line connecting the edge of the end face of the ferrule in a cross section passing through the central axis and perpendicular to the inclined plane. When the distance between the central axis and the center of the core located farthest from the central axis when viewed along the central axis is x, Satisfying An optical connector characterized by the above.

2. Satisfying The optical connector according to claim 1, characterized by the above.

3. When the deviation amount from 8 degrees of the angle formed by the inclined plane and the vertical plane is Δθ, Satisfying The optical connector according to claim 1 or 2, characterized by the above.

4. The optical connector further includes a guide key provided in parallel with the longitudinal direction of the through-hole in a housing to which the ferrule is fixed, The key error, which is the angle formed by the perpendicular line of the inclined plane and the central axis of the through-hole when viewed along a direction perpendicular to the plane passing through the central axis of the guide key and the central axis of the through-hole, is 0.4 degrees or less. The optical connector according to claim 1 or 2, characterized by the above.

5. The diameter of the ferrule is 2.5 mm The optical connector according to claim 1 or 2, characterized by the above.

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