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

Abstract

To provide an optical fiber connection body with which connection losses when fusion connected are reduced, and a method for manufacturing the optical fiber connection body.SOLUTION: Provided is 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 fusion-connected together. A first characteristics matching part constituting a shorter hollow core than the hollow core part is provided on the side of the hollow core part adjoining the solid core fiber in the longer direction, and a second characteristics matching part constituting a shorter solid core than the solid core part is provided on the side of the solid core part adjoining the hollow core fiber in the longer direction. The difference between the optical characteristics of the hollow core fiber in the first characteristics matching part and the optical characteristics of the solid core fiber in the second characteristics matching part is smaller than the difference between the optical characteristics of the hollow core fiber in the hollow core part and the optical characteristics of the solid core fiber in the second characteristics matching part.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 in the core portion is well known. The solid core portion is also called a solid core.

[0003] On the other hand, a holey core fiber is an optical fiber having a holey core portion (holey core portion) not filled with a solid medium. The holey 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 holey 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).

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] In an optical fiber connector in which a hollow core fiber and a solid core fiber are connected, it is important to reduce the connection loss between the hollow core portion and the solid core portion. In particular, reduction of the connection loss when fusion splicing is performed 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 in which the connection loss when fusion splicing is reduced, and a method for manufacturing the same.

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 a solid core fiber having a solid core portion are fusion spliced, wherein on a side of the hollow core portion adjacent to the solid core fiber in the longitudinal direction, a first characteristic matching portion that is a hollow core shorter than the hollow core portion is provided, and on a side of the solid core portion adjacent to the hollow core fiber in the longitudinal direction, a second characteristic matching portion that is a solid core shorter than the solid core portion is provided, and a difference between an optical characteristic of the hollow core fiber in the first characteristic matching portion and an optical characteristic of the solid core fiber in the second characteristic matching portion is smaller than a difference between an optical characteristic of the hollow core fiber in the hollow core portion and an optical characteristic of the solid core fiber in the second characteristic matching portion.

[0010] In the first characteristic matching portion, the optical characteristic of the hollow core fiber may continuously change from the hollow core portion toward the solid core fiber.

[0011] The optical characteristic may be a numerical aperture.

[0012] One aspect of the present invention is a method for manufacturing an optical fiber connector including a fusion connection step of fusion-connecting a hole-core fiber having a hole core portion and a solid-core fiber having a solid core portion, wherein on a side of the solid core portion adjacent to an end face of the solid-core fiber in a longitudinal direction, a second characteristic matching portion which is a solid core shorter than the solid core portion is provided, the fusion connection step includes a deformation step of heating a vicinity of an end face of the hole-core fiber in the longitudinal direction to deform the vicinity of the end face, and a connection step of connecting the end face of the solid-core fiber and the end face of the hole-core fiber, in the deformation step, by heating and deforming the hole core portion, a first characteristic matching portion which is a hole core shorter than the hole core portion is formed, and a difference between an optical characteristic of the hole-core fiber in the first characteristic matching portion and an optical characteristic of the solid-core fiber in the second characteristic matching portion is smaller than a difference between an optical characteristic of the hole-core fiber in the hole core portion and an optical characteristic of the solid-core fiber in the second characteristic matching portion.

[0013] The second characteristic matching portion of the solid-core fiber may be designed in consideration of a change in an optical characteristic of the hole-core fiber due to deformation of the hole core portion in the fusion connection step.

[0014] The optical characteristic may be a numerical aperture.

Advantages of the Invention

[0015] According to the present invention, there is an effect that an optical fiber connector with reduced connection loss when fusion-connected can be realized.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

DETAILED DESCRIPTION OF THE INVENTION

[0017] 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 given 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.

[0018] In this specification, when 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 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.

[0019] (Embodiment) FIG. 1 is a schematic cross-sectional view of a surface including the central axis of an optical fiber connector according to an embodiment. The optical fiber connector 100 includes a hollow-core fiber 10 and a solid-core fiber 20. The optical fiber connector 100 is an optical fiber connector in which the hollow-core fiber 10 and the solid-core fiber 20 are fusion-connected.

[0020] 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.

[0021] 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.

[0022] The hollow-core portion 12 includes a hollow-core portion 12a and a first characteristic matching portion 12b. Also, the hollow-core fiber 10 includes a fixed portion 10a including the hollow-core portion 12a and a deformed portion 10b including the first characteristic matching portion 12b. The hollow-core portion 12a has a constant shape in the longitudinal direction. As a result, the fixed portion 10a is a hollow-core fiber having a constant numerical aperture in the longitudinal direction.

[0023] The first characteristic matching portion 12b is located on the side of the hollow-core portion 12 adjacent to the solid-core fiber 20. The first characteristic matching portion 12b is a hollow-core shorter than the hollow-core portion 12a, and the numerical aperture in the first characteristic matching portion 12b is different from the numerical aperture in the hollow-core portion 12a. Also, the first characteristic matching portion 12b continuously changes in shape from the hollow-core portion 12a toward the solid-core fiber 20 in the longitudinal direction. As a result, in the first characteristic matching portion 12b, the hollow-core fiber 10 has a continuously changing numerical aperture from the hollow-core portion 12a toward the solid-core fiber 20 in the longitudinal direction. The first characteristic matching portion 12b is an example of a first characteristic matching portion provided on the side of the hollow-core portion adjacent to the solid-core fiber in the longitudinal direction.

[0024] The solid-core fiber 20 has a cladding portion 21, a solid-core portion 22, and a second characteristic matching portion 23 extending along the longitudinal direction. The cladding portion 21 is a structure surrounding the solid-core portion 22 and the second characteristic matching portion 23 and is made of, for example, silica-based glass. The solid-core portion 22 has a maximum refractive index higher than the refractive index of the cladding portion 21 and is made of, for example, silica-based glass.

[0025] The second characteristic matching section 23 has a maximum refractive index higher than that of the clad section 21 and is made of, for example, silica-based glass. The second characteristic matching section 23 is located on the side adjacent to the hollow core fiber 10 with respect to the solid core section 22 in the longitudinal direction. The second characteristic matching section 23 is a solid core shorter than the solid core section 22, and the numerical aperture in the second characteristic matching section 23 is smaller than the numerical aperture in the solid core section 22. Such a numerical aperture can be realized by making the refractive index of the second characteristic matching section 23 smaller than the refractive index of the solid core section 22 or making the core diameter of the second characteristic matching section 23 larger than the core diameter of the solid core section 22. The second characteristic matching section 23 is an example of the second characteristic matching section provided on the side adjacent to the hollow core fiber in the longitudinal direction of the solid core section.

[0026] Here, the difference between the numerical aperture in the first characteristic matching section 12b and the numerical aperture in the second characteristic matching section 23 is smaller than the difference between the numerical aperture in the hollow core section 12a and the numerical aperture in the second characteristic matching section 23. Therefore, the connection loss in the optical fiber connector 100 is smaller than that when the hollow core section 12a and the second characteristic matching section 23 are directly fusion-spliced. As a result, the connection loss of the optical fiber connector 100 is reduced when fusion-spliced.

[0027] Furthermore, in the deformation section 10b of the hollow core fiber 10, the numerical aperture continuously changes from the hollow core section 12a toward the solid core fiber 20. As a result, the connection loss is reduced compared to the case where the numerical aperture changes discontinuously.

[0028] Next, a method for manufacturing the optical fiber connector 100 will be described. FIG. 2 is a flowchart for explaining the method for manufacturing the optical fiber connector 100.

[0029] In this manufacturing method, for example, a fusion splicing process of fusion splicing the solid core fiber 20 and the shaped hole core fiber is performed using a commercially available fusion splicer. Here, the shaped hole core fiber is a hole core fiber in which the hole core portion has a constant shape in the longitudinal direction, like the shaped portion 10a of the hole core fiber 10. The shaped hole core fiber becomes the hole core fiber 10 in the optical fiber connector 100 by the fusion splicing process. Further, the second characteristic matching portion 23 of the solid core fiber 20 is provided on the side of the solid core portion 22 adjacent to the end face of the solid core fiber 20 in the longitudinal direction.

[0030] In the fusion splicing process, the vicinity of the end face of the solid core fiber 20 and the vicinity of the end face of the shaped hole core fiber are heated and melted by the discharge from the discharge rod of the fusion splicer. A deformation process of deforming the vicinity of the end face of the shaped hole core fiber is executed by this heating and melting (step S101). By this deformation process, the vicinity of the end face of the shaped hole core fiber becomes the deformed portion 10b, and the shaped hole core fiber becomes the shape of the hole core fiber 10. Note that for the solid core fiber 20 as well, deformation occurs in the vicinity of its end face due to heating and melting.

[0031] In the fusion splicing process, simultaneously with step S101, a connection process of butting the end face of the heated and melted solid core fiber 20 and the end face of the shaped hole core fiber that has become the shape of the hole core fiber 10 and connecting the two is executed (step S102). At this time, the deformation in the vicinity of the end face of the solid core fiber 20 due to heating and melting substantially returns to its original state. Thereby, the optical fiber connector 100 is completed.

[0032] Here, the present inventor examined the change in the numerical aperture due to thermal deformation when heating the vicinity of the end face using 19 PBGFs as the shaped hole core fiber. The results are shown in FIG. 3. Here, the horizontal axis represents the heating amount (arbitrary unit: A.U.), and the vertical axis represents the numerical aperture (NA) of each PBGF. The NA of the PBGFs before heating was about 0.108 on average. As shown in FIG. 3, the NA of the PBGFs with a small heating amount is the same as before heating, but as the heating amount increases, the NA decreases, and it was confirmed that when the heating amount exceeds a certain level, the NA does not fall below about 0.1 and the change saturates.

[0033] Therefore, as the solid core fiber 20, it is preferable that the second characteristic matching portion 23 is set in consideration of the change in the numerical aperture due to the deformation of the hole core portion when applying the heating amount for proper fusion splicing in the fusion splicing process. That is, for example, if the numerical aperture of the shaped hole core fiber decreases by 0.08 due to the heating amount applied for proper fusion splicing with the solid core fiber 20 and becomes a deformed portion, then in consideration of this decrease, as the second characteristic matching portion 23, one having a numerical aperture set to be 0.08 smaller than the numerical aperture of the shaped hole core fiber may be used. Thereby, after deformation by heating, the numerical aperture in the first characteristic matching portion 12b becomes an appropriate numerical aperture with respect to the second characteristic matching portion 23, so that the connection loss with the second characteristic matching portion 23 of the solid core fiber 20 can be reduced.

[0034] In addition, in the above embodiment, the difference between the numerical aperture of the hole core fiber 10 in the first characteristic matching portion 12b and the numerical aperture of the solid core fiber 20 in the second characteristic matching portion 23 is made smaller than the difference between the numerical aperture of the hole core fiber 10 in the hole core portion 12a and the numerical aperture of the solid core fiber 20 in the second characteristic matching portion 23. However, the optical characteristics of reducing the difference in this way are not limited to the numerical aperture, and may be, for example, the mode field diameter. Therefore, for example, the second characteristic matching portion 23 of the solid core fiber 20 may be designed in consideration of the change in the mode field diameter of the hole core fiber due to the deformation of the hole core portion in the fusion splicing process.

[0035] Further, in the above embodiment, in the first characteristic matching portion 12b of the hole-core fiber 10, the numerical aperture continuously changes from the hole-core portion 12a toward the solid-core fiber 20, but it may change stepwise if the step is small enough.

[0036] Also, the present invention is not limited to the above embodiment. Combinations of the above-described components configured as appropriate are also included in the present invention. 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 embodiment, and various changes are possible.

Explanation of Reference Numerals

[0037] 10: Hole-core fiber 10a: Fixed portion 10b: Deformed portion 11: Outer portion 12, 12a: Hole-core portion 12b: First characteristic matching portion 20: Solid-core fiber 21: Cladding portion 22: Solid-core portion 23: Second characteristic matching portion 100: Optical fiber connector

Claims

1. 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 fusion-connected, wherein a first characteristic matching portion, which is a hollow core shorter than the hollow-core portion, is provided on a side of the hollow-core portion adjacent to the solid-core fiber in the longitudinal direction, a second characteristic matching portion, which is a solid core shorter than the solid-core portion, is provided on a side of the solid-core portion adjacent to the hollow-core fiber in the longitudinal direction, and a difference between the optical characteristics of the hollow-core fiber in the first characteristic matching portion and the optical characteristics of the solid-core fiber in the second characteristic matching portion is smaller than a difference between the optical characteristics of the hollow-core fiber in the hollow-core portion and the optical characteristics of the solid-core fiber in the second characteristic matching portion. Optical fiber connector.

2. In the hollow-core fiber, in the first characteristic matching portion, the optical characteristics continuously change from the hollow-core portion toward the solid-core fiber. The optical fiber connector according to Claim 1.

3. The optical characteristic is a numerical aperture. The optical fiber connector according to Claim 1 or 2.

4. A method for manufacturing an optical fiber connector, comprising a fusion-connection step of fusion-connecting a hollow-core fiber having a hollow-core portion and a solid-core fiber having a solid-core portion, wherein a second characteristic matching portion, which is a solid core shorter than the solid-core portion, is provided on a side of the solid-core portion adjacent to an end face of the solid-core fiber in the longitudinal direction, the fusion-connection step includes a deformation step of heating a vicinity of an end face of the hollow-core fiber in the longitudinal direction to deform the vicinity of the end face, and a connection step of connecting the end face of the solid-core fiber and the end face of the hollow-core fiber, and in the deformation step, a first characteristic matching portion, which is a hollow core shorter than the hollow-core portion, is formed by heating and deforming the hollow-core portion, and a difference between the optical characteristics of the hollow-core fiber in the first characteristic matching portion and the optical characteristics of the solid-core fiber in the second characteristic matching portion is smaller than a difference between the optical characteristics of the hollow-core fiber in the hollow-core portion and the optical characteristics of the solid-core fiber in the second characteristic matching portion. Method for manufacturing an optical fiber connector.

5. The second characteristic matching part of the solid core fiber is designed in consideration of the change in the optical characteristics of the hollow core fiber due to the deformation of the hollow core part in the fusion splicing process. The method for manufacturing an optical fiber connector according to claim 4.

6. The optical characteristic is the numerical aperture. The method for manufacturing an optical fiber connector according to claim 4 or 5.

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