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

Abstract

To provide an optical fiber connection body of lower connection loss and a method for manufacturing an optical fiber connection body that makes it possible to manufacture an optical fiber connection body of lower connection loss.SOLUTION: An optical fiber connection body comprises: a hollow core fiber having a hollow core part; a solid core fiber having a solid core part; and a connection bridge having first and second connection end faces and propagating light between the first and the second connection end faces. The hollow core fiber and the solid core fiber are connected with the connection bridge interposed therebetween. The first connection end face of the connection bridge and the first end face of the hollow core fiber are connected together. The numerical aperture of the connection bridge at the first connection end face and the numerical aperture of the hollow core fiber at the first end face are appropriately the same.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.

[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 non-linearity 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 splicing 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 Literature

[0006]

Non-Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In an optical fiber connector in which a hollow core fiber and a solid core fiber are connected, an even lower connection loss is 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 lower connection loss and a method for manufacturing an optical fiber connector capable of manufacturing an optical fiber connector with a lower connection loss.

Means for Solving the Problems

[0009] In order to solve the above-described problems and achieve the object, one aspect of the present invention includes a hollow core fiber having a hollow core portion, a solid core fiber having a solid core portion, and a connection bridge having a first connection end face and a second connection end face, and propagating light between the first connection end face and the second connection end face. The hollow core fiber and the solid core fiber are connected with the connection bridge interposed therebetween, the first connection end face of the connection bridge and the first end face of the hollow core fiber are connected, and the numerical aperture of the connection bridge at the first connection end face and the numerical aperture of the hollow core fiber at the first end face are substantially the same. It is an optical fiber connector.

[0010] The difference between the numerical aperture of the connection bridge at the first connection end face and the numerical aperture of the hollow core fiber at the first end face may be within ±0.05.

[0011] The second connection end face of the connection bridge is connected to the second end face of the solid core fiber, and the numerical aperture of the connection bridge at the second connection end face and the numerical aperture of the solid core fiber at the second end face may be substantially the same.

[0012] The difference between the numerical aperture of the connection bridge at the second connection end face and the numerical aperture of the solid core fiber at the second end face may be within ±0.05.

[0013] The connection bridge may be a solid core fiber shorter than the hollow core fiber and the solid core fiber.

[0014] The connection bridge may have a substantially linear shape.

[0015] The numerical aperture of the connection bridge may change stepwise in the longitudinal direction.

[0016] The numerical aperture of the connection bridge may change continuously in the longitudinal direction.

[0017] One aspect of the present invention is a manufacturing method of an optical fiber connector, comprising: a preparation step of preparing a hollow core fiber having a hollow core portion, a solid core fiber having a solid core portion, and a connection bridge having a first connection end face and a second connection end face, and propagating light between the first connection end face and the second connection end face; and a connection step of connecting the hollow core fiber and the solid core fiber with the connection bridge interposed therebetween. In the connection step, the first connection end face of the connection bridge is connected to the first end face of the hollow core fiber, and the numerical aperture of the connection bridge at the first connection end face and the numerical aperture of the hollow core fiber at the first end face are substantially the same.

Effect of the Invention

[0018] According to the present invention, there is an effect that an optical fiber connector with lower connection loss can be realized.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note 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.

[0021] In this specification, when the maximum incident angle at which light input from air to an optical fiber is totally reflected in the core is θmax, the upper limit value of θmax is defined as the numerical aperture 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.

[0022] (Embodiment 1) FIG. 1 is a schematic cross-sectional view of a surface including a central axis extending in the longitudinal direction 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 connection bridge 30.

[0023] The hollow-core fiber 10 has an outer portion 11 and a hollow-core portion 12 extending along the longitudinal direction. 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 a first end face 10a at the longitudinal end. 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.

[0024] 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 capillaries for realizing antiresonant-type optical confinement.

[0025] The solid-core fiber 20 has a cladding portion 21 and a solid-core portion 22 extending along the longitudinal direction. The cladding portion 21 is a structure surrounding 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 a second end face 20a at the longitudinal end. 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.

[0026] The connection bridge 30 extends in the longitudinal direction and has a first connection end face 30a and a second connection end face 30b at the longitudinal ends. The connection bridge 30 is configured to propagate light between the first connection end face 30a and the second connection end face 30b. In the present embodiment, the connection bridge 30 is a solid core fiber having a cladding portion 31 and a solid core portion 32. The cladding portion 31 is a structure surrounding the periphery of the solid core portion 32 and is made of, for example, silica glass. The solid core portion 32 has a maximum refractive index higher than that of the cladding portion 31 and is made of, for example, silica glass.

[0027] The hollow core fiber 10 and the solid core fiber 20 are connected with the connection bridge 30 interposed therebetween. Specifically, the first connection end face 30a of the connection bridge 30 and the first end face 10a of the hollow core fiber are connected. Also, the second connection end face 30b of the connection bridge 30 and the second end face 20a of the solid core fiber 20 are connected. Note that the connection of each end face is a fusion connection or a mechanical splice connection. If it is a fusion connection or a mechanical splice connection, a connection having high power resistance and long-term reliability can be realized.

[0028] Here, regarding the first connection end face 30a and the first end face 10a connected to each other, the numerical aperture of the connection bridge 30 at the first connection end face 30a and the numerical aperture of the hollow core fiber 10 at the first end face 10a are substantially the same. Here, substantially the same means, for example, a case where the difference between the numerical aperture of the connection bridge 30 at the first connection end face 30a and the numerical aperture of the hollow core fiber 10 at the first end face 10a is within ±0.05.

[0029] Note that the numerical aperture of the hollow-core fiber is usually smaller than that of a general single-mode solid-core fiber having a mode field diameter of a similar value. Therefore, the connection bridge 30 may be configured using, for example, a solid-core fiber having a relatively small numerical aperture but a relatively large mode field diameter. However, such a solid-core fiber is weak against bending. Therefore, if such a solid-core fiber is used to form a long connection bridge, the connection bridge is likely to have bending loss due to bending during handling and has low practicality. Therefore, it is preferable from the viewpoint of reducing bending loss that the length of the connection bridge 30 is relatively short. For example, the connection bridge 30 is a solid-core fiber shorter than the hollow-core fiber 10 and the solid-core fiber 20. Also, for example, the length of the connection bridge 30 is 100 mm or less, more preferably 10 mm or less, 7 mm or less, or 5 mm or less. Further, the connection bridge 30 may have a substantially linear shape. Thereby, bending loss is suppressed. Note that the connection bridge 30 having a substantially linear shape means, for example, a shape with a bending radius of 100 mm or more.

[0030] In the optical fiber connector 100 according to the first embodiment configured as described above, regarding the first connection end face 30a and the first end face 10a connected to each other, since the numerical aperture of the connection bridge 30 at the first connection end face 30a and the numerical aperture of the hollow-core fiber 10 at the first end face 10a are substantially the same, low connection loss is achieved.

[0031] Hereinafter, a specific description will be given. FIG. 2 is a diagram showing an example of the relationship between the mode field diameter (MFD) and the numerical aperture (NA) in a single-mode optical fiber. Note that all the optical fibers shown in FIG. 2 are solid-core fibers. Also, MFD and NA are values at a wavelength of 1550 nm. As shown in FIG. 2, in an optical fiber, although the mode field diameter and the numerical aperture have a high correlation, they do not necessarily correspond one-to-one.

[0032] In the above-described known art, when connecting a hole-core fiber and a solid-core fiber, in order to achieve low connection loss, the mode field diameters of both are made to match.

[0033] In contrast, the present inventor earnestly studied in order to achieve further lower connection loss between a hole-core fiber and a solid-core fiber, and found the following. That is, the inventor found that in order to achieve low connection loss, it is important to match the numerical apertures of both. Even if the mode field diameters of both match, if the numerical apertures are different, the effect of improving the connection loss is limited. Even if the mode field diameters of both are different, if the numerical apertures match, the connection loss is small.

[0034] The present inventor conducted the following experiment. First, several solid-core fibers and a photonic bandgap fiber as a hole-core fiber were prepared, and the solid-core fiber and the photonic bandgap fiber were mechanically spliced. Then, the connection loss due to this mechanical splicing was measured.

[0035] FIG. 3 is a diagram showing an example of the relationship between the mode field diameter, the numerical aperture, and the connection loss as a result of the above experiment. The data points indicated by circles in FIG. 3 show the mode field diameter and the numerical aperture of the solid-core fiber, and the numbers near the data points indicate the connection loss when connected with the mode field diameter matching that of the photonic bandgap fiber. Also, the data points indicated by double circles in FIG. 3 show the mode field diameter and the numerical aperture of the solid-core fiber, and the numbers near the data points indicate the connection loss when connected with the numerical aperture matching that of the photonic bandgap fiber.

[0036] As can be seen from FIG. 3, the connection loss when connecting with the same mode field diameter as the photonic bandgap fiber was 1.15 dB, but the connection loss when connecting with the same numerical aperture as the photonic bandgap fiber was even lower, at 0.95 dB or 0.65 dB. That is, it was confirmed that in order to achieve an even lower connection loss between the holey-core fiber and the solid-core fiber, it is important to match the numerical apertures of both.

[0037] Note that the optical fiber connector 100 according to the present embodiment can be manufactured, for example, by the following procedure. First, prepare the holey-core fiber 10, the solid-core fiber 20, and the connection bridge 30 (an example of the preparation process). Subsequently, connect the holey-core fiber 10 and the solid-core fiber 20 with the connection bridge 30 interposed therebetween (an example of the connection process). At this time, connect the first connection end face 30a of the connection bridge 30 and the first end face 10a of the holey-core fiber 10, and connect the second connection end face 30b of the connection bridge 30 and the second end face 20a of the solid-core fiber 20.

[0038] Alternatively, first prepare the solid-core fiber 20 and the long solid-core fiber that is the raw material of the connection bridge 30, connect the solid-core fiber 20 and the long solid-core fiber, and then cut the long solid-core fiber to an appropriate length to form the connection bridge 30. In this case, the process of cutting the long solid-core fiber is a process included in the preparation process.

[0039] (Embodiment 2) FIG. 4 is a schematic cross-sectional view of a plane including the central axis extending in the longitudinal direction of the optical fiber connector according to Embodiment 2. The optical fiber connector 100A has a configuration in which the connection bridge 30 of the optical fiber connector 100 according to Embodiment 1 shown in FIG. 1 is replaced with a connection bridge 30A.

[0040] The connection bridge 30A extends in the longitudinal direction and has a first connection end face 30Aa and a second connection end face 30Ab at the longitudinal ends. The connection bridge 30A is configured to propagate light between the first connection end face 30Aa and the second connection end face 30Ab. In the present embodiment, the connection bridge 30A is a solid core fiber having a cladding portion 31A and a solid core portion 32A. The cladding portion 31A is a structure surrounding the solid core portion 32A and is made of, for example, silica glass. The solid core portion 32A has a maximum refractive index higher than that of the cladding portion 31A and is made of, for example, silica glass.

[0041] The connection bridge 30A has a continuously changing numerical aperture in the longitudinal direction. Specifically, in the connection bridge 30A, the numerical aperture at the first connection end face 30Aa is smaller than the numerical aperture at the second connection end face 30Ab, and the numerical aperture changes continuously from the first connection end face 30Aa towards the second connection end face 30Ab between the first connection end face 30Aa and the second connection end face 30Ab. Note that the connection bridge 30A may be a solid core fiber shorter than the hollow core fiber 10 and the solid core fiber 20, or may have a length of 100 mm or less or 10 mm or less. Also, the connection bridge 30A may have a substantially linear shape.

[0042] In the present embodiment, the hollow core fiber 10 and the solid core fiber 20 are connected with the connection bridge 30A interposed therebetween. Specifically, the first connection end face 30Aa and the first end face 10a are connected, and the second connection end face 30Ab and the second end face 20a are connected. Note that the connection of each end face is a fusion connection or a mechanical splice connection.

[0043] Also, in this embodiment as well, the number of openings of the connection bridge 30A on the first connection end face 30a connected to each other is substantially the same as the number of openings of the hollow-core fiber 10 on the first end face 10a. Further, in this embodiment, the number of openings of the connection bridge 30A on the second connection end face 30Ab connected to each other may also be substantially the same as the number of openings of the solid-core fiber 20 on the second end face 20a. Also in this case, "substantially the same" means, for example, the case where the difference in the number of openings is within ±0.05.

[0044] In the optical fiber connector 100A according to Embodiment 2 configured as described above, the same effects as those of the optical fiber connector 100 according to Embodiment 1 can be obtained, and for example, low connection loss is achieved. Further, in the optical fiber connector 100A, since the number of openings continuously changes in the longitudinal direction, the difference between the number of openings of the connection bridge 30A on the first connection end face 30a and the number of openings of the hollow-core fiber 10 on the first end face 10a, and the difference between the number of openings of the connection bridge 30 on the second connection end face 30Ab and the number of openings of the solid-core fiber 20 on the second end face 20a can be reduced simultaneously. As a result, further lower connection loss is achieved as compared with the optical fiber connector 100.

[0045] Note that the connection bridge 30A can be formed, for example, by subjecting a solid-core fiber having a constant number of openings in the longitudinal direction to a heat treatment. In this case, for example, after connecting a solid-core fiber that becomes the raw material of the connection bridge to the solid-core fiber 20, the solid-core fiber may be subjected to a heat treatment to form the connection bridge 30A.

[0046] (Embodiment 3) FIG. 5 is a schematic cross-sectional view of a plane including the central axis extending in the longitudinal direction of the optical fiber connector according to Embodiment 3. The optical fiber connector 100B has a configuration in which the connection bridge 30 of the optical fiber connector 100 according to Embodiment 1 shown in FIG. 1 is replaced with a connection bridge 30B.

[0047] The connection bridge 30B extends in the longitudinal direction and has a first connection end face 30Ba and a second connection end face 30Bb at the longitudinal ends. The connection bridge 30B is configured to propagate light between the first connection end face 30Ba and the second connection end face 30Bb. In the present embodiment, the connection bridge 30B is a solid core fiber having a cladding portion 31A and a solid core portion 32B. The cladding portion 31B is a structure surrounding the solid core portion 32B and is made of, for example, silica glass. The solid core portion 32B has a maximum refractive index higher than that of the cladding portion 31B and is made of, for example, silica glass.

[0048] The connection bridge 30B has a stepwise change in the numerical aperture in the longitudinal direction. Specifically, in the connection bridge 30B, the numerical aperture at the first connection end face 30Ba is smaller than that at the second connection end face 30Bb, and the numerical aperture changes in such a manner that it increases stepwise from the first connection end face 30Ba toward the second connection end face 30Bb between the first connection end face 30Ba and the second connection end face 30Bb. Note that the connection bridge 30B may be a solid core fiber shorter than the hollow core fiber 10 and the solid core fiber 20, or may have a length of 100 mm or less or 10 mm or less. Also, the connection bridge 30B may have a substantially linear shape.

[0049] In the present embodiment, the hollow core fiber 10 and the solid core fiber 20 are connected with the connection bridge 30B interposed therebetween. Specifically, the first connection end face 30Ba and the first end face 10a are connected, and the second connection end face 30Bb and the second end face 20a are connected. Note that the connection of each end face is a fusion connection or a mechanical splice connection.

[0050] And also in the present embodiment, the numerical aperture of the connection bridge 30B at the mutually connected first connection end face 30a is substantially the same as the numerical aperture of the hollow core fiber 10 at the first end face 10a. Also, in the present embodiment, the numerical aperture of the connection bridge 30 at the mutually connected second connection end face 30Bb may be substantially the same as the numerical aperture of the solid core fiber 20 at the second end face 20a.

[0051] Even in the optical fiber connector 100B according to Embodiment 3 configured as described above, the difference between the numerical aperture of the connection bridge 30B at the first connection end face 30Ba and the numerical aperture of the hole core fiber 10 at the first end face 10a, and the difference between the numerical aperture of the connection bridge 30B at the second connection end face 30Bb and the numerical aperture of the solid core fiber 20 at the second end face 20a can be simultaneously reduced. As a result, further lower connection loss is achieved as compared with the optical fiber connector 100.

[0052] Note that the connection bridge 30B can be formed, for example, by connecting multiple solid core fibers with a constant numerical aperture in the longitudinal direction in multiple stages. Also, in this embodiment, although the numerical aperture of the connection bridge 30B changes in one step in the longitudinal direction, it may change in two or more steps.

[0053] Note that in the above embodiment, the numerical aperture of the connection bridge 30A in Embodiment 2 changes continuously in the longitudinal direction, and the numerical aperture of the connection bridge 30B in Embodiment 3 changes stepwise in the longitudinal direction. However, as a modification of these embodiments, a portion where the numerical aperture changes continuously and a portion where it changes stepwise may be mixed in the longitudinal direction of the connection bridge.

[0054] Also, in the above embodiment, the connection bridge is a solid core fiber, but the connection bridge is not limited to this, and for example, it may be configured using a coupling system using a lens. In this case, a GRIN (GRaded INdex) lens may be used as the lens.

[0055] Further, the present invention is not limited by the above embodiments. Those configured by appropriately combining the above-described components are also included in the present invention. Also, further effects and modifications can be easily derived by those skilled in the art. Therefore, a broader aspect of the present invention is not limited to the above embodiments, and various changes are possible.

Explanation of Reference Numerals

[0056] 10: Hollow-core fiber 10a: First end face 11: Outer part 12: Hollow-core part 20: Solid-core fiber 20a: Second end face 21, 31, 31A, 31B: Cladding parts 22, 32, 32A, 32B: Solid-core parts 30, 30A, 30B: Connection bridges 30a, 30Aa, 30Ba: First connection end face 30b, 30Ab, 30Bb: Second connection end face 100, 100A, 100B: Optical fiber connectors

Claims

1. A hollow-core fiber having a hollow-core portion, A solid-core fiber having a solid-core portion, A connection bridge having a first connection end face and a second connection end face, and propagating light between the first connection end face and the second connection end face, Comprising, The hollow-core fiber and the solid-core fiber are connected with the connection bridge interposed therebetween, The first connection end face of the connection bridge is connected to the first end face of the hollow-core fiber, The numerical aperture of the connection bridge at the first connection end face is substantially the same as the numerical aperture of the hollow-core fiber at the first end face Optical fiber connector.

2. The difference between the numerical aperture of the connection bridge at the first connection end face and the numerical aperture of the hollow-core fiber at the first end face is within ±0.05 The optical fiber connector according to Claim 1.

3. The second connection end face of the connection bridge is connected to the second end face of the solid-core fiber, The numerical aperture of the connection bridge at the second connection end face is substantially the same as the numerical aperture of the solid-core fiber at the second end face The optical fiber connector according to Claim 1.

4. The difference between the numerical aperture of the connection bridge at the second connection end face and the numerical aperture of the solid-core fiber at the second end face is within ±0.05 The optical fiber connector according to Claim 3.

5. The connection bridge is a solid-core fiber shorter than the hollow-core fiber and the solid-core fiber The optical fiber connector according to Claim 1.

6. The connection bridge has a substantially linear shape The optical fiber connector according to Claim 5.

7. The numerical aperture of the connection bridge changes stepwise in the longitudinal direction The optical fiber connector according to Claim 1.

8. The numerical aperture of the connection bridge changes continuously in the longitudinal direction The optical fiber connector according to Claim 1.

9. A preparation step of preparing a hollow-core fiber having a hollow-core portion, a solid-core fiber having a solid-core portion, a connection bridge having a first connection end face and a second connection end face, and propagating light between the first connection end face and the second connection end face, A connection step of connecting the hollow-core fiber and the solid-core fiber with the connection bridge interposed therebetween, Comprising, In the connection step, connect the first connection end face of the connection bridge and the first end face of the hole core fiber, the numerical aperture of the connection bridge at the first connection end face and the numerical aperture of the hole core fiber at the first end face are substantially the same A method for manufacturing an optical fiber connector.

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