Optical fiber connection body and method for manufacturing optical fiber connection body

Abstract

To provide an optical fiber connection body in which back reflection is suppressed and connection loss is reduced, and a method for manufacturing the optical fiber connection body.SOLUTION: An optical fiber connection body where a hollow core fiber having a hollow core part and a solid core fiber having a solid core part are optically connected together, has a first end face which is inclined with respect to a center axis of the solid core fiber. The solid core fiber and the hollow core fiber are arranged so that the first end face and the second end face of the hollow core fiber face each other. A center axis of the solid core fiber and a center axis of the hollow core fiber are not parallel to each other. An optical axis of light propagated through the solid core fiber, outputted, and entering the hollow core fiber appropriately coincides with the center axis of the hollow core fiber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical fiber connector and a method for manufacturing the optical fiber connector.

Background Art

[0002] As an optical fiber, a solid core fiber having a solid core portion whose core portion is made of a solid medium such as glass is well known. The solid core portion is also called a solid core.

[0003] On the other hand, a hole core fiber is an optical fiber having a hole-shaped core portion (hole core portion) not filled with a solid medium. The hole core fiber is an optical fiber having ultimate low non-linearity, and is considered to have the possibility of breaking through the limit of the transmission capacity when a solid core fiber is used.

[0004] In practical use, the hole core fiber may be connected to a solid core fiber by fusion splicing or mechanical splice connection to form an optical fiber connector (Patent Documents 1 to 3, Non-Patent Document 1). In this case, since the refractive index n1 of the hole core portion of the hole core fiber is usually the refractive index of air, n1 = 1.002. On the other hand, since the refractive index n2 of the solid core portion of the solid core fiber is, for example, the refractive index of silica glass, n2 = 1.462. In this case, due to the difference in refractive index between the two, a refractive index boundary surface exists at the connection portion. The existence of such a boundary surface means that backward traveling light (backward reflected light) that travels backward with respect to the traveling direction of light at the boundary surface and propagates through the solid core portion may be generated. The existence of such backward reflection leads to degradation of the signal light in optical transmission, so the realization of large-capacity communication expected by using the hole core fiber in a transmission network may be difficult.

[0005] As a technique for suppressing or preventing backward reflection, when a hollow-core fiber and a solid-core fiber are connector-connected, a technique of applying an antireflection (AR) coating to the end face of the solid-core portion is disclosed. However, since the AR coating is vulnerable to heat, it is considered difficult to apply when the hollow-core fiber and the solid-core fiber are fusion-connected.

[0006] On the other hand, Patent Document 1 describes that it is obliquely arranged such that there is an angle between the longitudinal axis of the hollow-core waveguide and the longitudinal axis of the solid-core waveguide. It is described that this avoids or reduces the transmission loss caused by refraction at the facet when the two facet ends are joined. Similarly, Patent Document 2 describes that an angled splice may exist between two optical fibers to reduce unwanted backward reflection. It is also described that the angled splice may be characterized by a shallower angle (for example, 3° or 4°), and the difficulty of maintaining low transmission loss through the angled splice may increase with the required angle.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0008]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described above, in an optical fiber connector in which a hollow-core fiber and a solid-core fiber are connected, it is important to suppress back reflection due to the difference in refractive index between the hollow-core portion and the solid-core portion, and it is also important to reduce connection loss.

[0010] The present invention has been made in view of the above, and an object thereof is to provide an optical fiber connector in which back reflection is suppressed and connection loss is reduced, and a method for manufacturing the same.

Means for Solving the Problems

[0011] In order to solve the above-described problems and achieve the object, one aspect of the present invention is an optical fiber connector in which a hollow-core fiber having a hollow-core portion and a solid-core fiber having a solid-core portion are optically connected, wherein the solid-core fiber has a first end face inclined with respect to the central axis of the solid-core fiber, and the solid-core fiber and the hollow-core fiber are arranged such that the first end face faces the second end face of the hollow-core fiber, the central axis of the solid-core fiber and the central axis of the hollow-core fiber are non-parallel, and an optical axis of light that propagates through the solid-core fiber, is output, and is input to the hollow-core fiber substantially coincides with the central axis of the hollow-core fiber.

[0012] The optical fiber connector further includes a bent sleeve, the second end face is substantially perpendicular to the central axis of the hollow-core fiber, and the solid-core fiber and the hollow-core fiber may be supported by the sleeve in a state of being inserted into the sleeve.

[0013] The second end face is inclined with respect to the central axis of the hollow-core fiber, and the first end face and the second end face may be in contact with each other.

[0014] On the side of the solid core portion adjacent to the first end face in the longitudinal direction, a low NA portion which is a solid core shorter than the solid core portion is provided, and the numerical aperture in the low NA portion may be smaller than the numerical aperture in the solid core portion.

[0015] One aspect of the present invention is a method for manufacturing an optical fiber connector in which a hollow core fiber having a hollow core portion and a solid core fiber having a solid core portion are optically connected, and the solid core fiber has a first end face inclined with respect to the central axis of the solid core fiber. The method includes making the central axis of the solid core fiber and the central axis of the hollow core fiber non-parallel, and arranging the solid core fiber and the hollow core fiber so that the first end face and the second end face of the hollow core fiber face each other.

Advantages of the Invention

[0016] According to the present invention, there is an effect that an optical fiber connector in which back reflection is suppressed and connection loss is reduced can be realized.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiments described below. In each drawing, the same or corresponding components are appropriately denoted by the same reference numerals. In this specification, the cut-off wavelength or the effective cut-off wavelength refers to the cable cut-off wavelength (λcc) defined in ITU-T G.650.1 of the International Telecommunication Union (ITU). In addition, for terms not specifically defined in this specification, the definitions and measurement methods in G.650.1 and G.650.2 shall apply.

[0019] In this specification, assuming that the maximum incident angle at which light input from air into an optical fiber is totally reflected within the core is θmax, the upper limit value of θmax is defined as the numerical aperture (NA) of the optical fiber. Note that this θmax is the same as the spread angle of light when the light is output from the end face of the optical fiber into the air. The spread angle is defined as the angular width at which the power for each emission angle of the light beam output from the end face of the optical fiber becomes 1% of the peak power.

[0020] (Embodiment 1) FIG. 1 is a schematic cross-sectional view of a surface including the central axis of an optical fiber connector according to Embodiment 1. The optical fiber connector 100 includes a hollow-core fiber 10, a solid-core fiber 20, and a sleeve 30. The optical fiber connector 100 is an optical fiber connector in which the hollow-core fiber 10 and the solid-core fiber 20 are optically connected.

[0021] The hollow-core fiber 10 has an outer portion 11 extending along the longitudinal direction and a hollow-core portion 12. The outer portion 11 is a structure surrounding the hollow-core portion 12 and is made of, for example, silica-based glass. The hollow-core fiber 10 has an end face 10a at the longitudinal end. The end face 10a is an example of a second end face. The hollow-core fiber 10 is, for example, a single-mode optical fiber that propagates light in a single mode at a wavelength in a communication wavelength band such as 1550 nm.

[0022] The central axis X1 is the central axis of the hollow-core fiber 10 and, in this embodiment, is also the central axis of the hollow-core portion 12. In this embodiment, the end face 10a is substantially perpendicular to the central axis X1. Substantially perpendicular means that the angle with respect to the central axis X1 is within the range of ±1°.

[0023] The hollow-core fiber 10 is, for example, a photonic bandgap fiber (PBGF). In this case, the outer portion 11 has holes for realizing photonic band-type optical confinement. Also, the hollow-core fiber 10 may be an antiresonant fiber. In this case, the outer portion 11 has a tubular body for realizing antiresonant-type optical confinement.

[0024] The solid-core fiber 20 has a cladding portion 21 and a solid-core portion 22 that extend along the longitudinal direction. The cladding portion 21 is a structure that surrounds the solid-core portion 22 and is made of, for example, silica-based glass. The solid-core portion 22 has a maximum refractive index higher than that of the cladding portion 21 and is made of, for example, silica-based glass. The solid-core fiber 20 has an end face 20a at the longitudinal end. The end face 20a is an example of the first end face. The solid-core fiber 20 is, for example, a single-mode optical fiber that propagates light in a single mode at a wavelength in a communication wavelength band such as 1550 nm.

[0025] The central axis X2 is the central axis of the solid-core fiber 20 and, in this embodiment, is also the central axis of the solid-core portion 22. In this embodiment, the end face 20a is inclined by an inclination angle θ1 with respect to a virtual plane VS1 perpendicular to the central axis X1. The inclination angle θ1 is set so that, for example, the reflection attenuation amount of the rear reflection is -20 dB or less, and is, for example, greater than 0° to 15° or less, preferably 1° or more to 8° or less, or 1° or more to 4° or less.

[0026] The sleeve 30 includes a cylindrical first portion 31 into which the hollow-core fiber 10 can be inserted, and a cylindrical second portion 32 into which the solid-core fiber 20 can be inserted. In the sleeve 30, the first portion 31 and the second portion 32 are bent at a predetermined bending angle. The predetermined bending angle will be described later. Note that the sleeve 30 is made of, for example, ceramics, metal, or resin.

[0027] The hollow-core fiber 10 is supported by the sleeve 30 in a state of being inserted into the first portion 31. The solid-core fiber 20 is supported by the sleeve 30 in a state of being inserted into the second portion 32. The solid-core fiber 20 and the hollow-core fiber 10 are arranged such that the end face 20a and the end face 10a face each other by the sleeve 30. In this state, the central axis X1 of the hollow-core fiber 10 and the central axis X2 of the solid-core fiber 20 are non-parallel, and in the present embodiment, the central axis X1 and the central axis X2 form the above-described bending angle.

[0028] Note that the hollow-core fiber 10 and the solid-core fiber 20 may be fixed to the sleeve 30 with, for example, an adhesive or the like. Further, a connector housing is attached to each of the hollow-core fiber 10 and the solid-core fiber 20, and the hollow-core fiber 10 and the solid-core fiber 20 may be connector-connected.

[0029] In the optical fiber connector 100, when the optical light L1 propagates through the solid-core portion 22 of the solid-core fiber 20 and is output from the end face 20a, the optical light L1 travels non-parallel to the central axis X2, that is, at an angle to the central axis X2. Here, the angle formed by the optical light L1 and the central axis X2 is an angle that conforms to Snell's law. On the other hand, the reflected light generated at the end face 20a due to the optical light L1 travels in a direction inclined by 2×θ1 with respect to the central axis X2 of the solid-core fiber 20, so that the back reflection is suppressed.

[0030] Thereafter, the light L1 travels and enters the hollow-core fiber 10. Here, the bending angle in the sleeve 30 is set such that the optical axis of the light L1 entering the hollow-core fiber 10 coincides with the central axis X1 of the hollow-core fiber 10. Thereby, the loss when the light L1 enters the hollow-core fiber 10 is reduced. Such reduction of loss contributes to the reduction of connection loss.

[0031] As described above, in the optical fiber connector 100, back reflection is suppressed and connection loss is reduced.

[0032] Also, in the optical fiber connector 100, since the end face 10a of the hollow-core fiber 10 is substantially perpendicular to the central axis X1, the step of obliquely cutting the hollow-core fiber 10 becomes unnecessary.

[0033] When manufacturing the optical fiber connector 100, the central axis X2 of the solid-core fiber 20 and the central axis X1 of the hollow-core fiber 10 are made non-parallel, and the solid-core fiber 20 and the hollow-core fiber 10 are arranged such that the end face 20a and the end face 10a face each other. To realize these steps, for example, a sleeve 30 is prepared, the hollow-core fiber 10 is inserted and fixed in the first part 31 of the sleeve 30, and the solid-core fiber 20 is inserted and fixed in the second part of the sleeve 30.

[0034] (Difference in the angle of light due to input or output with respect to the solid-core fiber) FIG. 2 is a diagram showing an example of the beam of light propagated through the solid-core fiber and output. As shown in FIG. 2, the light L1 propagated through the solid-core portion 22 of the solid-core fiber 20 and output from the end face 20a travels in a direction in which the optical axis is inclined with respect to the central axis X2 according to Snell's law. The beam B1 of the light L1 spreads as the light L1 travels. The optical axis of the light L1 and the spread of the beam B1 depend on the inclination angle θ1 of the end face 20a (see FIG. 1) and the numerical aperture of the solid-core fiber 20.

[0035] In contrast, FIG. 3 is a diagram showing an example of a beam of light that can be input to and propagated through a solid core fiber. The light L2 that can be input to and propagated through the solid core fiber 20 is light that travels in a direction inclined with respect to the optical axis in the opposite direction to the light L1 shown in FIG. 2 with respect to the central axis X2 in accordance with Snell's law, and the spread of the beam B2 of the light L2 is also limited to a spread angle corresponding to the numerical aperture in the solid core fiber 20.

[0036] Therefore, in the case of the optical fiber connector 100 shown in FIG. 1, if the distance between the end face 10a of the hollow core fiber 10 and the end face 20a of the solid core fiber 20 is too large, the connection loss when light propagates from the hollow core fiber 10 to the solid core fiber 20 may increase. Therefore, it is preferable that the distance between the end face 10a of the hollow core fiber 10 and the end face 20a of the solid core fiber 20 is as close as possible. For example, when the refractive index of the solid core portion 22 is 1.462 and the inclination angle θ1 is, for example, 4°, the distance between the end face 10a and the end face 20a is preferably, for example, 100 μm or less.

[0037] Note that, in the solid core fiber 20 shown in FIG. 1, the cladding portion 21 of the portion close to the end face 10a of the hollow core fiber 10 may be cut to make it easier to bring the hollow core fiber 10 closer to the solid core fiber 20.

[0038] (Embodiment 2) FIG. 4 is a schematic cross-sectional view of a plane including the central axis of the optical fiber connector according to Embodiment 2. The optical fiber connector 200 includes a hollow core fiber 10A and a solid core fiber 20. Since the solid core fiber 20 is the same as the solid core fiber 20 shown in FIG. 1, the description thereof is omitted.

[0039] The hollow-core fiber 10A has an outer portion 11 and a hollow-core portion 12 that extend along the longitudinal direction, similar to the hollow-core fiber 10 shown in FIG. 1. The hollow-core fiber 10A has an end face 10Aa at the longitudinal end. The end face 10Aa is an example of a second end face. The hollow-core fiber 10A is a single-mode optical fiber that propagates light in a single mode at a wavelength in a communication wavelength band such as 1550 nm.

[0040] The central axis X1A is the central axis of the hollow-core fiber 10A and is also the central axis of the hollow-core portion 12 in the present embodiment. In the present embodiment, the end face 10Aa is inclined by an inclination angle θ2 with respect to a virtual plane VS2 perpendicular to the central axis X1A. The central axis X1A and the central axis X2 of the solid-core fiber 20 are non-parallel.

[0041] The end face 10Aa of the hollow-core fiber 10A and the end face 20a of the solid-core fiber 20 face each other and are in contact. For example, the end face 10Aa and the end face 20a are connected by fusion splicing or mechanical splice connection.

[0042] Here, the inclination angle θ2 in the hollow-core fiber 10A is set so that the optical axis of the light that propagates through the solid-core fiber 20, is output, and is input to the hollow-core fiber 10A coincides with the central axis X1A of the hollow-core fiber 10A.

[0043] In the optical fiber connector 200 configured as described above, similar to the optical fiber connector 100 according to Embodiment 1, back reflection is suppressed and connection loss is reduced. Furthermore, since the end face 10Aa of the hollow-core fiber 10A and the end face 20a of the solid-core fiber 20 are joined, physical connection strength is ensured.

[0044] (Embodiment 3) FIG. 5 is a schematic cross-sectional view of a plane including the central axis of the optical fiber connector according to Embodiment 3. The optical fiber connector 300 includes a hollow-core fiber 10B and a solid-core fiber 20A.

[0045] The solid core fiber 20A has a cladding portion 21, a solid core portion 22, a low NA portion 23, and an end face 20Aa. The end face 20Aa is an example of a first end face. The solid core fiber 20A is a single-mode optical fiber that propagates light in a single mode at a wavelength in a communication wavelength band such as 1550 nm. The cladding portion 21 and the solid core portion 22 are the same as the cladding portion 21 and the solid core portion 22 of the solid core fiber 20 shown in FIG. 1, and thus the description thereof is omitted.

[0046] The low NA portion 23 is provided on the side adjacent to the end face 20Aa in the longitudinal direction. The low NA portion 23 is shorter than the solid core portion 22 in the longitudinal direction. The numerical aperture in the low NA portion 23 is smaller than the numerical aperture in the solid core portion 22. Such a numerical aperture can be realized by making the refractive index of the low NA portion 23 smaller than the refractive index of the solid core portion 22 or making the core diameter of the low NA portion 23 larger than the core diameter of the solid core portion 22.

[0047] The central axis X2A is the central axis of the solid core fiber 20A, and in this embodiment, it is also the central axis of the solid core portion 22 and the low NA portion 23. In this embodiment, the end face 20Aa is inclined by an inclination angle θ3 with respect to a virtual plane VS3 perpendicular to the central axis X2A. The inclination angle θ3 is set such that, for example, the reflection attenuation amount of the rear reflection is -20 dB or less, and is a value smaller than the inclination angle θ1 shown in FIG. 1, and is, for example, larger than 0° and 10° or less, preferably 1° or more and 8° or less, or 1° or more and 4° or less.

[0048] The hole core fiber 10B has an outer portion 11 and a hole core portion 12 that extend along the longitudinal direction, similar to the hole core fiber 10 shown in FIG. 4. The hole core fiber 10B has an end face 10Ba at the longitudinal end. The end face 10Ba is an example of a second end face. The hole core fiber 10B is a single-mode optical fiber that propagates light in a single mode at a wavelength in a communication wavelength band such as 1550 nm.

[0049] The central axis X1B is the central axis of the hollow-core fiber 10B and, in this embodiment, is also the central axis of the hollow-core portion 12. In this embodiment, the end face 10Ba is inclined by an inclination angle θ4 with respect to a virtual plane VS4 perpendicular to the central axis X1B. The central axis X1B and the central axis X2A of the solid-core fiber 20A are non-parallel.

[0050] The end face 10Ba of the hollow-core fiber 10B and the end face 20Aa of the solid-core fiber 20A face each other and are in contact. For example, the end face 10Ba and the end face 20Aa are connected by fusion splicing or mechanical splice connection.

[0051] Here, the inclination angle θ4 in the hollow-core fiber 10B is set so that the optical axis of the light that propagates through the solid-core fiber 20A, is output, and is input to the hollow-core fiber 10B coincides with the central axis X1A of the hollow-core fiber 10A.

[0052] In the optical fiber connector 300 configured as described above, similar to the optical fiber connector 200 according to Embodiment 2, back reflection is suppressed and connection loss is reduced, and since the end face 10Ba of the hollow-core fiber 10B and the end face 20Aa of the solid-core fiber 20A are joined, physical connection strength is ensured.

[0053] Furthermore, in the optical fiber connector 300, a low-NA portion 23 is provided, and the numerical aperture in the low-NA portion 23 of the solid-core fiber 20A is smaller than the numerical aperture in the solid-core portion 22. Thereby, the value of the tilt angle θ3 necessary to obtain the effect of suppressing back reflection to the same extent as in the case of the solid-core fiber 20 may be smaller than the tilt angle θ1 in the solid-core fiber 20. As a result, the tilt angle θ4 in the hole-core fiber 10A may also be smaller than the tilt angle θ2 in the hole-core fiber 10. Therefore, the difference D2 between the tip side and the base end side of the end face 10Aa in the hole-core fiber 10A may be smaller than the difference D1 (see FIG. 4) between the tip side and the base end side of the end face 10a in the hole-core fiber 10. Thus, the connection loss of the light that propagates through the hole-core fiber 10B and is output and then input to the solid-core fiber 20A is further reduced.

[0054] In the above embodiment, the optical axis of the light that propagates through the solid-core fiber and is output and then input to the hole-core fiber coincides with the central axis of the hole-core fiber. However, they do not have to completely coincide, and it is sufficient if they substantially coincide. Substantially coincide means that the positional deviation between the optical axis and the central axis is within a range of ±5 μm, and the angular deviation is within a range of ±3°.

[0055] Also, in the above Embodiment 3, the numerical aperture changes stepwise between the solid-core portion 22 and the low-NA portion 23. However, it may change continuously, or a portion where the numerical aperture changes continuously and a portion where it changes stepwise may coexist.

[0056] Also, in the above-described Second and Third Embodiments, when the first end face of the solid core fiber and the second end face of the hollow core fiber are fusion-connected, for example, a fusion splicer is used. In this case, when the two optical fibers are brought close to each other so that the central axes form a desired angle and the first end face and the second face are brought into contact, due to the impact at the time of contact or the like, the end faces may be butted against each other in a state where the central axes are deviated from the desired angle, and may be fusion-connected as they are. In order to prevent such fusion connection from occurring with the angular deviation remaining, when bringing the two optical fibers close to each other, the angle formed by the central axes may be deviated from the desired angle by the amount of the assumed angular deviation, and the end faces may be butted against each other. For example, when it is assumed that the angle between the central axes deviates by 1° to the larger side at the time of contact between the end faces, and when fusion connection is desired with the angle between the central axes set to 4°, the angle between the central axes may be set to 3°, the end faces may be brought close to each other, and butted against each other.

[0057] Also, in the above-described embodiment, an AR coat may be applied to the end face of the solid core fiber.

[0058] Also, the present invention is not limited by the above-described embodiment. Those configured by appropriately combining the above-described constituent elements are also included in the present invention. Further, additional effects and modified examples can be easily derived by those skilled in the art. Therefore, a broader aspect of the present invention is not limited to the above-described embodiment, and various modifications are possible.

Description of Reference Numerals

[0059] 10, 10A, 10B: Hollow core fiber 10a, 10Aa, 10Ba, 20a, 20Aa: End face 11: Outer portion 12: Hollow core portion 20, 20A: Solid core fiber 21: Clad portion 22: Solid core portion 23: Low NA portion 30: Sleeve 31: First portion 32: Second part 100, 200, 300: Optical fiber connectors B1, B2: Beams L1, L2: Light VS1, VS2, VS3, VS4: Virtual planes X1, X1A, X1B, X2, X2A: Central axes

Claims

1. A hollow-core fiber having a hollow-core portion, A solid-core fiber having a solid-core portion, An optical fiber connector in which the hollow-core fiber and the solid-core fiber are optically connected, The solid-core fiber has a first end face inclined with respect to the central axis of the solid-core fiber, The solid-core fiber and the hollow-core fiber are arranged such that the first end face and the second end face of the hollow-core fiber face each other, The central axis of the solid-core fiber and the central axis of the hollow-core fiber are non-parallel, and the optical axis of the light propagating through the solid-core fiber, outputted therefrom, and inputted into the hollow-core fiber substantially coincides with the central axis of the hollow-core fiber Optical fiber connector.

2. Further comprising a bent sleeve, The second end face is substantially perpendicular to the central axis of the hollow-core fiber, The solid-core fiber and the hollow-core fiber are supported by the sleeve in a state of being inserted into the sleeve The optical fiber connector according to claim 1.

3. The second end face is inclined with respect to the central axis of the hollow-core fiber, The first end face and the second end face are in contact with each other. The optical fiber connector according to claim 1.

4. On the side of the solid-core portion adjacent to the first end face in the longitudinal direction, a low-NA portion, which is a solid-core shorter than the solid-core portion, is provided, The numerical aperture in the low-NA portion is smaller than the numerical aperture in the solid-core portion The optical fiber connector according to claim 3.

5. A hollow-core fiber having a hollow-core portion, A solid-core fiber having a solid-core portion, Are optically connected, A method for manufacturing an optical fiber connector in which the solid-core fiber has a first end face inclined with respect to the central axis of the solid-core fiber, Making the central axis of the solid-core fiber and the central axis of the hollow-core fiber non-parallel, Arranging the solid-core fiber and the hollow-core fiber such that the first end face and the second end face of the hollow-core fiber face each other Method for manufacturing an optical fiber connector.

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