Optical fiber connector and method for manufacturing an optical fiber connector

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

[0004]

[0001] The present invention relates to an optical fiber connector and a method for manufacturing an 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. ​​​​​​​​​​One technique disclosed for suppressing or preventing back reflection involves applying an anti-reflective (AR) coating to the end face of the solid core when connecting a hollow core fiber and a solid core fiber using a connector. However, since AR coatings are susceptible to heat, their application is considered difficult when fusion splicing hollow core fibers and solid core fibers.

[0006] In contrast, Patent Document 1 describes that the longitudinal axis of the hollow core waveguide and the longitudinal axis of the solid core waveguide are angled so that there is an angle between them. It is stated that this avoids or reduces transmission loss caused by refraction in the facet when the two facet ends are coupled. Similarly, Patent Document 2 describes that an angled splice may exist between two optical fibers to reduce undesirable back reflection. It is also stated that the angled splice may feature a shallower angle (e.g., 3° ​​or 4°), and that 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] Special Publication No. 2022-502716 [Patent Document 2] Special Publication No. 2023-507373 [Patent Document 3] Japanese Patent Publication No. 2023-003952 [Non-patent literature]

[0008] [Non-Patent Document 1] Kazunori Mukasa, "Hollow Core Fiber Cable," Furukawa Electric Times, No. 140 (July 2021), pp. 32-39. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] As mentioned above, in optical fiber connectors where 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 and the solid core, and it is also important to reduce connection loss.

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

[0011] To solve the above-mentioned problems and achieve the objective, 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 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 and output and input to the hollow core fiber substantially coincides with the central axis of the hollow core fiber.

[0012] The optical fiber connector further comprises a bent sleeve, the second end face of which 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 while 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.

[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 such 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 with suppressed back reflection and reduced connection loss can be realized.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view of a plane including the central axis of the optical fiber connector according to Embodiment 1. [Figure 2] FIG. 2 is a diagram showing an example of a light beam output after propagating through a solid core fiber. [Figure 3] FIG. 3 is a diagram showing an example of a light beam that can be input and propagated through a solid core fiber. [Figure 4] FIG. 4 is a schematic cross-sectional view of a plane including the central axis of the optical fiber connector according to Embodiment 2. [Figure 5] FIG. 5 is a schematic cross-sectional view of a plane including the central axis of the optical fiber connector according to Embodiment 3.

Embodiments for Carrying Out the Invention

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

[0019] Also, in this specification, when the maximum incident angle at which light input from air into the 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 angular spread of the light when the light is output from the end face of the optical fiber into the air. The angular spread 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 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, it 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 porous core fiber 10 is, for example, a photonic bandgap fiber (PBGF). In this case, the outer portion 11 has vacancies to achieve photonic band-type optical confinement. Alternatively, the porous core fiber 10 may be an antiresonant fiber. In this case, the outer portion 11 has a tubular body to achieve 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 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 glass. The solid core fiber 20 has an end face 20a at the end in the longitudinal direction. The end face 20a is an example of a first end face. The solid core fiber 20 is a single-mode optical fiber that propagates light in a single mode at wavelengths in the 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, it 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, for example, so that the return loss of back reflection is -20 dB or less, but is, for example, greater than 0° and less than or equal to ~15°, preferably between 1° and ~8° or between 1° and ~4°.

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

[0027] The hollow core fiber 10 is supported by the sleeve 30 while inserted into the first part 31. The solid core fiber 20 is supported by the sleeve 30 while inserted into the second part 32. The sleeve 30 positions the solid core fiber 20 and the hollow core fiber 10 so that their end faces 20a and end face 10a face each other. 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 this embodiment, the central axes X1 and X2 form the bending angle described above.

[0028] The hollow core fiber 10 and the solid core fiber 20 may be fixed to the sleeve 30, for example, with an adhesive. Furthermore, a connector housing may be 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 connected via a connector.

[0029] In the optical fiber connector 100, when 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 with the central axis X2. Here, the angle between the optical light L1 and the central axis X2 is an angle that follows 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 tilted by 2 × θ1 with respect to the central axis X2 of the solid core fiber 20, so back reflection is suppressed.

[0030] Subsequently, the optical fiber L1 travels and enters the hollow core fiber 10. Here, the bending angle in the sleeve 30 is set so that the optical axis of the optical fiber L1 entering the hollow core fiber 10 coincides with the central axis X1 of the hollow core fiber 10. This reduces the loss when the optical fiber L1 enters the hollow core fiber 10. Such loss reduction contributes to a reduction in connection loss.

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

[0032] Furthermore, in the optical fiber connector 100, the end face 10a of the hollow core fiber 10 is approximately perpendicular to the central axis X1, thus eliminating the need for the process of cutting the hollow core fiber 10 at an angle.

[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 so that their end faces 20a and 10a face each other. To achieve these steps, for example, a sleeve 30 can be prepared, the hollow core fiber 10 can be inserted and fixed into the first part 31 of the sleeve 30, and the solid core fiber 20 can be inserted and fixed into the second part of the sleeve 30.

[0034] (Differences in the angle of light due to input or output to a solid core fiber) Figure 2 shows an example of a beam of light output after propagating through a solid core fiber. As shown in Figure 2, the light L1 output from the end face 20a after propagating through the solid core portion 22 of the solid core fiber 20 propagates in a direction in which the optical axis is tilted with respect to the central axis X2, according to Snell's law. The beam B1 of light L1 spreads as the light L1 propagates. The optical axis of light L1 and the spread of beam B1 depend on the tilt angle θ1 of the end face 20a (see Figure 1) and the numerical aperture of the solid core fiber 20.

[0035] In contrast, Figure 3 shows an example of a beam of light that can be input into and propagated in a solid core fiber. The light L2 that can be input into and propagated in the solid core fiber 20 is light that travels in a direction in which the optical axis is tilted in the opposite direction to the light L1 shown in Figure 2 with respect to the central axis X2, according to Snell's law, and the spread of the beam B2 of 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 Figure 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 great, 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 be close. For example, if the refractive index of the solid core portion 22 is 1.462 and the tilt angle θ1 is, for example, 4°, then the distance between the end face 10a and the end face 20a is preferably, for example, 100 μm or less.

[0037] Furthermore, the cladding portion 21 of the solid core fiber 20 shown in Figure 1, which is 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) Figure 4 is a schematic cross-sectional view of the optical fiber connector according to Embodiment 2 in a plane including the central axis. The optical fiber connector 200 comprises a hollow core fiber 10A and a solid core fiber 20. The solid core fiber 20 is the same as the solid core fiber 20 shown in Figure 1, so its description is omitted.

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

[0040] The central axis X1A is the central axis of the hollow core fiber 10A, and in this embodiment, it is also the central axis of the hollow core portion 12. In this embodiment, the end face 10Aa is inclined by an 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 faces 10Aa and 20a are connected by fusion splicing or mechanical splicing.

[0042] Here, the tilt 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 and is output, and 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, back reflection is suppressed and connection loss is reduced, similar to the optical fiber connector 100 according to Embodiment 1. 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) Figure 5 is a schematic cross-sectional view of the optical fiber connector according to Embodiment 3 in a plane including the central axis. The optical fiber connector 300 comprises 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 wavelengths in the communication wavelength band, such as 1550 nm. The cladding portion 21 and the solid core portion 22 are the same as those of the solid core fiber 20 shown in Figure 1, so their description 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 achieved by making the refractive index of the low NA portion 23 smaller than that of the solid core portion 22, or by making the core diameter of the low NA portion 23 larger than that 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, for example, so that the return loss of back reflection is -20 dB or less, but is a smaller value than the inclination angle θ1 shown in Figure 1, for example, greater than 0° and less than or equal to ~10°, preferably between 1° and ~8° or between 1° and ~4°.

[0048] The perforated core fiber 10B, like the perforated core fiber 10 shown in Figure 4, has an outer portion 11 and a perforated core portion 12 that extend along the longitudinal direction. The perforated core fiber 10B has an end face 10Ba at its longitudinal end. End face 10Ba is an example of a second end face. The perforated core fiber 10B is a single-mode optical fiber that propagates light in a single mode at wavelengths in the 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, it is also the central axis of the hollow core portion 12. In this embodiment, the end face 10Ba is inclined by an 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 faces 10Ba and 20Aa are connected by fusion splicing or mechanical splicing.

[0051] Here, the tilt 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 and is output, and 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, back reflection is suppressed and connection loss is reduced, similar to the optical fiber connector 200 according to Embodiment 2. Furthermore, physical connection strength is ensured because the end face 10Ba of the hollow core fiber 10B and the end face 20Aa of the solid core fiber 20A are joined together.

[0053] Furthermore, the optical fiber connector 300 is provided with a low NA section 23, and the numerical aperture in the low NA section 23 of the solid core fiber 20A is smaller than the numerical aperture in the solid core section 22. As a result, the tilt angle θ3 required to obtain the same degree of back reflection suppression as in the case of the solid core fiber 20 can be smaller than the tilt angle θ1 in the solid core fiber 20. Consequently, the tilt angle θ4 in the open core fiber 10A can also be smaller than the tilt angle θ2 in the open core fiber 10. Therefore, the difference in distance D2 between the tip side and the base side of the end face 10Aa in the open core fiber 10A can be smaller than the difference in distance D1 (see Figure 4) between the tip side and the base side of the end face 10a in the open core fiber 10, thus further reducing the connection loss of the light propagating through the open core fiber 10B and outputting to the solid core fiber 20A.

[0054] In the above embodiment, the optical axis of the light propagating through the solid core fiber and outputting to the open core fiber coincides with the central axis of the open core fiber. However, it does not need to coincide perfectly; approximate coincidence is sufficient. Approximate coincidence means that the positional misalignment between the optical axis and the central axis is within ±5 μm, and the angular misalignment is within ±3°.

[0055] Furthermore, in the above embodiment 3, the numerical aperture changes stepwise between the solid core portion 22 and the low NA portion 23, but it may also change continuously, and portions where the numerical aperture changes continuously and portions where it changes stepwise may be mixed.

[0056] Furthermore, in embodiments 2 and 3 described above, when fusion splicing is performed between the first end face of a solid core fiber and the second end face of a hollow core fiber, a fusion splicer is used, for example. In this case, if both optical fibers are brought close together so that their central axes form a desired angle, and the first and second end faces are brought into contact, the end faces may come into contact with the central axes misaligned from the desired angle due to impact during contact, and the fusion splice may be performed in that state. To prevent such angular misalignment from occurring during fusion splicing, when bringing both optical fibers close together, the angle between their central axes may be set to be slightly different from the desired angle by the expected angular misalignment, and the end faces may be brought into contact. For example, if it is expected that the angle between the central axes will shift by 1° to the larger side when the end faces come into contact, and it is desired to fusion splice with an angle of 4° between the central axes, the angle between the central axes should be set to 3°, and the end faces should be brought close together and brought into contact.

[0057] Furthermore, in the above embodiment, an AR coating may be applied to the end face of the solid core fiber.

[0058] Furthermore, the present invention is not limited by the embodiments described above. Configurations that appropriately combine the above-described components are also included in the present invention. Moreover, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the embodiments described above, and various modifications are possible. [Explanation of symbols]

[0059] 10, 10A, 10B: Hollow core fiber 10a, 10Aa, 10Ba, 20a, 20Aa: End surface 11 :Outer part 12: Hollow core section 20, 20A: Solid core fiber 21: Clad section 22: Solid core section 23:Low NA section 30: Sleeves 31: Part 1 32: Part 2 100, 200, 300: Fiber optic connectors B1, B2: Beam L1, L2: light VS1, VS2, VS3, VS4: Virtual surfaces X1, X1A, X1B, X2, X2A: Center axis

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 optical fibers are 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 that propagates through the solid core fiber and is output to the hollow core fiber is substantially coincided with the central axis of the hollow core fiber. 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 over a surface. Optical fiber connector.

2. It also features a curved 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 while inserted into the sleeve. The optical fiber connector according to claim 1.

3. A low-NA portion, which is a solid core shorter than the solid core portion, is provided on the side of the solid core portion adjacent to the first end face in the longitudinal direction. 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 1.

4. A hollow core fiber having a hollow core portion, A solid core fiber having a solid core portion, They are optically connected, The solid core fiber is a first end face inclined with respect to the central axis of the solid core fiber, and the method for manufacturing an optical fiber connector is as follows: The central axis of the solid core fiber and the central axis of the hollow core fiber are made non-parallel, 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 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 over a surface. A method for manufacturing optical fiber connectors.

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