Optical fiber connector and manufacturing method thereof

Abstract

To provide an optical fiber connector with a simple configuration, and a simple manufacturing method thereof.SOLUTION: The optical fiber connector is a connector that optically connects a hole-core fiber with a hole core and an optical fiber with a core. The optical fiber connector includes: a first ferrule into which the end of the hollow-core fiber is inserted and fixed; a second ferrule into which the end of the optical fiber is inserted and fixed; and a fitting member with a hole into which the first ferrule and the second ferrule are inserted. The end surface of the hollow-core fiber and the end surface of the optical fiber face each other inside the hole of the fitting member.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 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 hollow core fiber is an optical fiber having a hollow core portion (hollow core portion) not filled with a solid medium. The hollow core fiber is an optical fiber having ultimate low nonlinearity and is considered to have the potential to break through the limit of the transmission capacity when using a solid core fiber.

[0004] In practical use, the hollow 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). As a method for manufacturing such an optical fiber connector, for example, a technique of connecting a hollow core fiber and a solid core fiber with a mode field adapter interposed therebetween is disclosed (Patent Document 1). The mode field adapter is configured to change the mode field diameter of the guided light between the mode field diameter of the hollow core fiber and the mode field diameter of the solid core fiber. According to Patent Document 1, the transmission loss due to the connection between the hollow core fiber and the solid core fiber is reduced by the mode field adapter.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] For the connection between a hollow core fiber and a solid core fiber, and for the connection between hollow core fibers, a simpler configuration and manufacturing method are required.

[0008] The present invention has been made in view of the above, and an object thereof is to provide an optical fiber connector with a simple configuration and a simple manufacturing method therefor.

Means for Solving the Problems

[0009] 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 an optical fiber having a core portion are optically connected, the optical fiber connector including a first ferrule into which a tip end portion of the hollow core fiber is inserted and fixed, a second ferrule into which a tip end portion of the optical fiber is inserted and fixed, and a fitting member having a hole into which the first ferrule and the second ferrule are inserted, and the optical fiber connector is configured such that a tip end surface of the hollow core fiber and a tip end surface of the optical fiber face each other inside the hole of the fitting member.

[0010] A gap may be formed between the tip end surface of the hollow core fiber and the tip end surface of the optical fiber.

[0011] The numerical aperture of the hollow core fiber and the numerical aperture of the optical fiber may be substantially the same.

[0012] The optical fiber may be a solid core fiber having a solid core portion.

[0013] An antireflection coating may be provided on the tip surface of the solid core fiber.

[0014] The tip surface of the solid core fiber may be inclined with respect to the central axis of the solid core fiber.

[0015] The optical fiber connector further includes a bent sleeve, the tip surface of the hollow core fiber is substantially perpendicular to the central axis of the hollow core fiber, the tip surface of the solid core fiber is inclined with respect to the central axis of the solid core fiber, and the solid core fiber and the hollow core fiber may be supported by the hole of the fitting member in a state of being inserted into the hole of the fitting member.

[0016] The first ferrule and the second ferrule may be fixed to the fitting member.

[0017] A heat dissipation mechanism for thermally connecting to the fitting member may be provided.

[0018] 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 an optical fiber having a core portion are optically connected. The tip end portion of the hollow core fiber is inserted and fixed into a first ferrule, the tip end portion of the optical fiber is inserted and fixed into a second ferrule, the first ferrule and the second ferrule are inserted into the hole of a fitting member, and the tip surface of the hollow core fiber and the tip surface of the optical fiber are opposed to each other inside the hole of the fitting member.

Advantages of the Invention

[0019] According to the present invention, there is an effect that an optical fiber connector with a simple configuration and a simple manufacturing method thereof can be realized.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to 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.

[0022] Further, in this specification, assuming that the maximum incident angle at which light input from air into the optical fiber undergoes total internal reflection 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 divergence angle of the light when the light is output from the end face of the optical fiber into the air. The divergence 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.

[0023] (Embodiment 1) FIG. 1 is a schematic diagram of a part of an optical fiber connector according to Embodiment 1, cut away by a plane including the central axis. The optical fiber connector 100 includes a hollow-core fiber 10, a solid-core fiber 20, a first ferrule 30, a second ferrule 40, and a sleeve 50. 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. The solid-core fiber 20 is an example of an optical fiber having a core portion.

[0024] The hollow-core fiber 10 has an outer portion 11 extending along the longitudinal direction, a hollow-core portion 12, and a coating 13. The outer portion 11 is a structure surrounding the periphery of the hollow-core portion 12 and is made of, for example, silica-based glass. The coating 13 surrounds the outer periphery of the outer portion 11. However, at the tip of the hollow-core fiber 10, the coating 13 does not exist and the outer portion 11 is exposed. The coating 13 is made of, for example, resin. The hollow-core fiber 10 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.

[0025] 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.

[0026] The solid-core fiber 20 has a cladding portion 21, a solid-core portion 22, and a coating 23 that extend along the longitudinal direction. The cladding portion 21 is a structure that surrounds the periphery of 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 portion 22 is an example of a core portion. The coating 23 surrounds the outer periphery of the cladding portion 21. However, at the tip of the solid-core fiber 20, the coating 23 does not exist and the cladding portion 21 is exposed. The coating is made of, for example, resin. The solid-core fiber 20 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.

[0027] The first ferrule 30 is a cylindrical member. A portion of the outer side 11 of the tip of the hollow-core fiber 10 where it is exposed and a part of the coating 13 are inserted into the first ferrule 30. Also, the hollow-core fiber 10 is fixed to the first ferrule 30 with an adhesive or the like. The first ferrule 30 is made of, for example, ceramics, metal, or resin.

[0028] The second ferrule 40 is a cylindrical member. A portion of the cladding portion 21 of the tip of the solid-core fiber 20 where it is exposed and a part of the coating 23 are inserted into the second ferrule 40. Also, the solid-core fiber 20 is fixed to the second ferrule 40 with an adhesive or the like. The second ferrule 40 is made of, for example, resin, ceramics, metal, or resin.

[0029] The sleeve 50 is a cylindrical member having a hole into which the first ferrule 30 and the second ferrule 40 are inserted. Inside the hole of the sleeve 50, the tip surface of the hollow-core fiber 10 and the tip surface of the solid-core fiber 20 face each other and are abutted in this embodiment. The sleeve 50 is made of, for example, ceramics, metal, or resin. The sleeve 50 is an example of a fitting member.

[0030] Note that the inner diameter of the hole of the sleeve 50 is preferably such that the difference from the outer diameter of the first ferrule 30 and the outer diameter of the second ferrule 40 is small, and the difference is set to an appropriate amount so that insertion is easy.

[0031] In the optical fiber connector 100 configured as described above, the hollow-core fiber 10 and the solid-core fiber 20 are connected with a simple configuration. In particular, in the hollow-core fiber 10, since the hollow-core portion 12 is a space, it is not necessary to have a precise structure such as PC (Physical Contact) connection when abutting the end faces against each other as in the case of solid-core fibers. Therefore, the end face treatment of the hollow-core fiber 10 in the optical fiber connector 100 may be simple. Since such a simple end face treatment is sufficient, for example, even when constructing an optical fiber in the field, the optical fiber connector 100 can be connected in a short time without the need for special equipment or tools.

[0032] When manufacturing the optical fiber connector 100, for example, the following steps are performed. First, a part of the coating 13 is removed at the tip of the hollow-core fiber 10 to expose a part of the outer portion 11. Subsequently, the tip of the hollow-core fiber 10 is inserted and fixed into the first ferrule 30. Also, a part of the coating 23 is removed at the tip of the solid-core fiber 20 to expose a part of the cladding portion 21. Subsequently, the tip of the solid-core fiber 20 is inserted and fixed into the second ferrule 40. Note that thereafter, the tip end face of the solid-core fiber 20 may be polished together with the second ferrule 40 to enhance smoothness. Then, the first ferrule 30 and the second ferrule 40 are inserted into the hole of the sleeve 50, and the tip end face of the hollow-core fiber 10 and the tip end face of the solid-core fiber 20 are faced to each other inside this hole.

[0033] Note that the numerical aperture of the solid core fiber 20 and the numerical aperture of the hollow core fiber 10 are preferably substantially the same. For the solid core fiber and the hollow core fiber, even if, for example, the mode field diameters are made to coincide, the numerical aperture of the hollow core fiber tends to be smaller than the numerical aperture of the solid core fiber, so the reduction of the connection loss may be limited. In this regard, if the numerical aperture of the solid core fiber 20 and the numerical aperture of the hollow core fiber 10 are substantially the same, the connection loss can be further reduced. Note that "substantially the same" means, for example, that the difference in the numerical aperture is within ±0.05.

[0034] Also, in the present embodiment, the solid core fiber 20 may be replaced with a hollow core fiber having a hollow core portion.

[0035] (Embodiment 2) FIG. 2 is a schematic diagram of a part of an optical fiber connector according to Embodiment 2, cut away by a plane including the central axis. The optical fiber connector 200 is different from the optical fiber connector 100 shown in FIG. 1 in that a gap G is formed between the tip surface of the hollow core fiber 10 and the tip surface of the solid core fiber 20.

[0036] In the optical fiber connector 200, one of the optical fibers to be connected is the hollow core fiber 10, and the hollow core fiber 10 has a relatively small numerical aperture. Therefore, even with such a gap G, the connection loss is relatively small. Also, like the optical fiber connector 100, the structure and manufacturing method are simple. Further, the same effect can be obtained even if the solid core fiber 20 is replaced with a hollow core fiber having a hollow core portion.

[0037] Here, according to the investigation by the present inventor, in an optical fiber connector such as the optical fiber connectors 100 and 200, since the hollow core fiber 10 has a relatively small numerical aperture even with a gap G as shown in FIG. 2, and since the hollow core fiber 10 has a relatively large mode field diameter even with a radial optical axis deviation (offset) between the hollow core fiber 10 and the solid core fiber 20, it was confirmed that the connection loss is relatively small.

[0038] Figure 3 is a diagram showing an example of the relationship between the size of the gap (GAP) and the connection loss (Loss) in an optical fiber connector. Further, Figure 4 is a diagram showing an example of the relationship between the size of the offset (OFFSET) and the connection loss (Loss) in an optical fiber connector. In both Figures 3 and 4, the broken line is the calculated value of the characteristics when solid core fibers, which are single mode optical fibers, are connected. Also, the solid line is the calculated value when hole core fibers, which are single mode optical fibers, are connected, the dashed-dotted line is the calculated value when a hole core fiber, which is a single mode optical fiber, and a solid core fiber are connected, and the data points are the measured values. As shown in Figures 3 and 4, it was confirmed that the connection loss is relatively small even when the gap or offset is relatively large in the case of connecting hole core fibers to each other. Also, in the case of connecting a hole core fiber and a solid core fiber, it was confirmed that the connection loss is relatively small even when the gap or offset is relatively large.

[0039] (Embodiment 3) Figure 5 is a schematic diagram of a part of the optical fiber connector according to Embodiment 3, cut away by a plane including the central axis. The optical fiber connector 300 has a configuration in which, in the optical fiber connector 200 shown in Figure 2, the solid core fiber 20 is replaced with a solid core fiber 20A and an antireflection coating 60 is added.

[0040] The solid core fiber 20A has a cladding portion 21, a solid core portion 22, and a low NA portion 22a. The solid core fiber 20A 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. Since 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 Figure 1, the description thereof is omitted.

[0041] The low-NA portion 22a is provided on the side adjacent to the tip surface of the solid-core fiber 20A in the longitudinal direction. The low-NA portion 22a is shorter than the solid-core portion 22 in the longitudinal direction. The numerical aperture in the low-NA portion 22a 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 22a smaller than the refractive index of the solid-core portion 22 or by making the core diameter of the low-NA portion 22a larger than the core diameter of the solid-core portion 22.

[0042] The anti-reflection coating 60 is provided on the tip surface of the solid-core fiber 20A. The anti-reflection coating 60 is also called an AR (Anti-Reflection) coating.

[0043] In the optical fiber connector 300 configured as described above, the same effects as those of the optical fiber connector 200 according to Embodiment 2 can be obtained. Further, even if the numerical aperture in the solid-core portion 22 of the solid-core fiber 20A and the numerical aperture of the hole-core fiber 10 do not substantially match, the numerical aperture in the low-NA portion 22a of the solid-core fiber 20A and the numerical aperture of the hole-core fiber 10 can be made to substantially match. Therefore, it is suitable for further reducing the connection loss, and the degree of freedom of the numerical aperture in the solid-core portion 22 of the solid-core fiber 20A is increased. Further, in the optical fiber connector 300, since the anti-reflection coating 60 is provided on the tip surface of the solid-core fiber 20A, reflection at the tip surface of the solid-core fiber 20A can be prevented.

[0044] (Embodiment 4) FIG. 6 is a schematic diagram of a part of the optical fiber connector according to Embodiment 4, cut away by a plane including the central axis. The optical fiber connector 400 has a configuration in which an adhesive 70 is added to the optical fiber connector 200 shown in FIG. 2.

[0045] The adhesive 70 is provided so as to fill the gaps between the first ferrule 30 and the sleeve 50 and between the second ferrule 40 and the sleeve 50. Thereby, the first ferrule 30 and the second ferrule 40 are fixed to the sleeve 50.

[0046] In the optical fiber connector 400 configured as described above, the same effects as those of the optical fiber connector 200 according to the second embodiment can be obtained. Furthermore, the hollow core fiber 10 and the solid core fiber 20 can be semi-permanently connected.

[0047] In this embodiment, the first ferrule 30 and the second ferrule 40 are fixed to the sleeve 50 by the adhesive 70, but the fixing may be performed in other ways such as laser welding.

[0048] (Embodiment 5) FIG. 7 is a schematic view of a part of the optical fiber connector according to the fifth embodiment, cut away by a plane including the central axis. The optical fiber connector 500 has a configuration in which a heat dissipation mechanism 80 is added to the optical fiber connector 200 shown in FIG. 2.

[0049] The heat dissipation mechanism 80 is thermally connected to the sleeve 50. The heat dissipation mechanism is, for example, a heat sink in the shape of a metal block having heat dissipation fins, a liquid-cooled heat dissipation mechanism capable of circulating a coolant inside, or the like.

[0050] In the optical fiber connector 500 configured as described above, the same effects as those of the optical fiber connector 200 according to the second embodiment can be obtained. Furthermore, even if heat is generated due to the connection loss between the hollow core fiber 10 and the solid core fiber 20, appropriate heat treatment can be performed by the heat dissipation mechanism 80. For example, when high-power light such as 100 W passes through the optical fiber connector 500, even if the connection loss is 0.1 dB, the power of the heat generated due to the connection loss is as large as about 2 W. Even in this case, since the heat generated by the heat dissipation mechanism 80 is appropriately processed, excessive temperature rise of the optical fiber connector 500 and damage caused thereby can be suppressed or prevented.

[0051] (Embodiment 6) FIG. 8 is a schematic view of a part of the optical fiber connector according to Embodiment 6, cut away by a plane including the central axis. The optical fiber connector 600 has a configuration in which the solid core fiber 20 in the optical fiber connector 200 shown in FIG. 2 is replaced with a solid core fiber 20B, the second ferrule 40 is replaced with a second ferrule 40B, and further the sleeve 50 is replaced with a sleeve 50B.

[0052] The sleeve 50B has a first portion 51 and a second portion 52. The central axis of the first portion 51 and the central axis of the second portion 52 are non-parallel, and the sleeve 50B has a bent shape. The sleeve 50B is an example of a bent fitting member.

[0053] The hollow core fiber 10 is supported by the sleeve 50B in a state of being inserted into the hole of the first portion 51 of the sleeve 50B. The solid core fiber 20B is supported by the sleeve 50B in a state of being inserted into the hole of the second portion 52 of the sleeve 50B.

[0054] Here, the front end face of the hollow core fiber 10 is substantially perpendicular to the central axis of the hollow core fiber 10, whereas the front end face of the solid core fiber 20B is inclined with respect to the central axis of the solid core fiber 20B. Also, the front end face of the second ferrule 40B is inclined in the same manner as the front end face of the solid core fiber 20B.

[0055] Since the end face of the solid core fiber 20B is inclined with respect to the central axis of the solid core fiber 20B, the light L that propagates through and is output from the solid core fiber 20B travels in a direction inclined by a certain angle with respect to the central axis of the solid core fiber 20B. This angle is an angle that conforms to Snell's law according to the effective refractive index of the solid core fiber 20B and the refractive index of air. Thus, since the end face of the solid core fiber 20B is inclined with respect to the central axis of the solid core fiber 20B, the light reflected at the end face of the solid core fiber 20B is suppressed from coupling to the solid core portion 22 of the solid core fiber 20B and propagating again.

[0056] Further, since the sleeve 50B directs the hollow core fiber 10 such that its central axis substantially coincides with the optical axis of the light L output from the solid core fiber 20B, an increase in the connection loss between the solid core fiber 20B and the hollow core fiber 10 with respect to the light L is suppressed.

[0057] Also, in the optical fiber connector 600, as in other embodiments, the hollow core fiber 10 and the solid core fiber 20B are connected with a simple configuration.

[0058] In the optical fiber connector 600, the sleeve 50B may be replaced with a non-bent sleeve. That is, even when a combination of a solid core fiber 20B whose end face is inclined with respect to the central axis, a hollow core fiber 10, and a non-bent sleeve is used, the hollow core fiber 10 and the solid core fiber 20B are connected with a simple configuration.

[0059] Furthermore, the present invention is not limited by the above-described embodiments. Those configured by appropriately combining the above-described components are also included in the present invention. For example, the antireflection coating and the low-NA portion in Embodiment 3 may be provided on the solid core fiber in other embodiments. Also, in Embodiments 4 and 5, the solid core fiber 20 may be replaced with a hollow core fiber having a hollow core portion. Further, additional effects and modification 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 embodiments, and various changes are possible.

Explanation of Signs

[0060] 10: Hollow core fiber 11: Outer portion 12: Hollow core portion 13, 23: Coating 20, 20A, 20B: Solid core fiber 21: Cladding portion 22: Solid core portion 22a: Low-NA portion 30: First ferrule 40, 40B: Second ferrule 50, 50B: Sleeve 51: First portion 52: Second portion 60: Antireflection coating 70: Adhesive 80: Heat dissipation mechanism 100, 200, 300, 400, 500: Optical fiber connector G: Gap L: Light

Claims

1. A hollow-core fiber having a hollow-core portion, An optical fiber having a core portion, An optical fiber connector in which they are optically connected, A first ferrule into which the tip of the hollow-core fiber is inserted and fixed, A second ferrule into which the tip of the optical fiber is inserted and fixed, A fitting member having a hole into which the first ferrule and the second ferrule are inserted, Comprising, with the tip surface of the hollow-core fiber and the tip surface of the optical fiber facing each other inside the hole of the fitting member Optical fiber connector.

2. A gap is formed between the tip surface of the hollow-core fiber and the tip surface of the optical fiber The optical fiber connector according to claim 1.

3. The numerical aperture of the hollow-core fiber and the numerical aperture of the optical fiber are substantially the same The optical fiber connector according to claim 1.

4. The optical fiber is a solid-core fiber having a solid-core portion The optical fiber connector according to claim 1.

5. An antireflection coating is provided on the tip surface of the solid-core fiber The optical fiber connector according to claim 4.

6. The tip surface of the solid-core fiber is inclined with respect to the central axis of the solid-core fiber The optical fiber connector according to claim 4.

7. The fitting member is bent, the tip surface of the hollow-core fiber is substantially perpendicular to the central axis of the hollow-core fiber, the tip surface of the solid-core fiber is inclined with respect to the central axis of the solid-core fiber, and the solid-core fiber and the hollow-core fiber are supported by the fitting member in a state of being inserted into the hole of the fitting member The optical fiber connector according to claim 4.

8. The first ferrule and the second ferrule are fixed to the fitting member The optical fiber connector according to claim 1.

9. A heat dissipation mechanism that thermally connects to the fitting member is provided The optical fiber connector according to claim 1.

10. A hollow-core fiber having a hollow-core portion, An optical fiber having a core portion, A method for manufacturing an optical fiber connector in which they are optically connected, Inserting and fixing the tip of the hollow-core fiber through the first ferrule, Inserting and fixing the tip of the optical fiber through the second ferrule, Insert the first ferrule and the second ferrule into the hole of the fitting member, and face the tip surface of the hollow core fiber and the tip surface of the optical fiber inside the hole of the fitting member. A method for manufacturing an optical fiber connector.

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