JP3701875B2 - Photonic crystal fiber connection method, connection structure thereof, and components of the connection structure - Google Patents

Description

【００３９】
計測結果を表１に示す。
【００４０】
同表によれば、接続例２及び３は、接続例１よりも接続損失が非常に低いことが分かる。また、ＰＣファイバ１０と被接続光ファイバ２０との接続部の接続損失が５．４７ｄＢ（接続例１）であるのに対し、ＰＣファイバ１０のＭＦＤ（ｄ₁）に近い寸法のＭＦＤ（ｄ₃）を有するバッファ光ファイバ３０と被接続光ファイバ２０との接続部における接続損失が１．２２ｄＢ（接続例２）であることから、接続損失はＰＣファイバ１０の接続部において大きくなることが分かる。さらに、接続例１の接続損失が５．４７ｄＢであるのに対し、ＰＣファイバ１０とバッファ光ファイバ３０との接続部の接続損失が２．０１ｄＢ（接続例２及び３）であることから、特にこのＰＣファイバ１０とバッファ光ファイバ３０との接続部において接続損失の低減が図られていることが分かる。接続例１では、ＰＣファイバ１０のＭＦＤ（ｄ₁）と被接続光ファイバ２０のＭＦＤ（ｄ₂）との差が非常に大きいために、接続部において多大の光が放射により散逸して大きな接続損失を生じたものであると考えられる。これに対し、接続例２及び３では、接続部が２カ所設けられることとなるものの、ＰＣファイバ１０と被接続光ファイバ２０との間にＭＦＤ（ｄ₃）がそれらのものの中間の寸法であるバッファ光ファイバ３０が介設されていることにより、各接続部でファイバ間のＭＦＤの差が小さくなり、それによって光の放射による散逸が著しく抑制され（特にＰＣファイバ１０とバッファ光ファイバ３０との接続部において）、接続例１に比べてトータルの接続損失は低く抑えられたものであると考えられる。
【００４１】
また、接続例３は、接続例２よりも接続損失が低いことが分かる。接続例２では、バッファ光ファイバ３０と被接続光ファイバ２０との接続部でＭＦＤの差が大きいために、光が放射により散逸して相対的に大きな接続損失を生じたものであると考えられる。これに対し、接続例３では、接続部におけるバッファ光ファイバ３０のＭＦＤと被接続光ファイバ２０のＭＦＤとの差が小さくなっているために、光の放射による散逸が抑止されて接続損失が低くなったものであると考えられる。
【図面の簡単な説明】
【図１】 本発明の実施形態におけるフォトニッククリスタルファイバの斜視図である。
【図２】 本発明の実施形態における光ファイバの斜視図である。
【図３】 本発明の実施形態におけるバッファ光ファイバの斜視図である。
【図４】 本発明の実施形態におけるフォトニッククリスタルファイバの接続構造体を形成するための構成部材の側面図である。
【図５】 本発明の実施形態におけるフォトニッククリスタルファイバの接続構造体の側面図である。
【図６】 本発明の他の実施形態におけるフォトニッククリスタルファイバの接続構造体の側面図である。
【図７】 実施例におけるフォトニッククリスタルファイバの接続構造体の側面図である。
【図８】 従来例におけるフォトニッククリスタルファイバの接続構造体の側面図である。
【図９】 光ファイバの接続構造体の側面図である。
【符号の説明】
１０ フォトニッククリスタルファイバ
１１，２１，３１ コア
１２，２２，３２ クラッド
１３ 被覆部
１４ フォトニッククリスタルファイバ接続端
２０ 被接続光ファイバ
２３ 被接続光ファイバ接続端
３０ バッファ光ファイバ
３３ バッファ光ファイバ一端
３４ バッファ光ファイバ他端
ｃ 接続部
ｄ_l，ｄ_s，ｄ₁〜ｄ₃ モードフィールド径
ｆ₁，ｆ₂ 光ファイバ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for connecting a photonic crystal fiber (hereinafter referred to as “PC (photonic crystal) fiber”), a connection structure thereof, and a component of the connection structure.
[0002]
[Prior art]
When a pair of optical fibers f ₁ and f ₂ having different mode field diameters d ₁ and d _s (hereinafter referred to as “MFD”) are connected, the two fibers f ₁ and f ₂ are simply fused and connected, as shown in FIG. As shown in FIG. 3, light emission occurs at the connection part c, which causes a great connection loss. On the other hand, by setting the heating time at the time of fusion splicing longer, setting the heating temperature higher, or additionally heating the connecting portion c, as shown in FIG. Germanium (Ge) doped in the cores of both fibers f ₁ and f ₂ in part c is diffused to the clad side to enlarge each MFD, and the size difference between them is reduced to reduce the connection loss. There is an optical fiber connection method. Similarly, by heating the connection end of the optical fiber f ₂ having the smaller MFD, germanium (Ge) doped in the core is diffused to the clad side as shown in FIG. There is also an optical fiber connection method that expands and connects it to the connection end of the optical fiber f ₁ having the larger MFD.
[0003]
[Problems to be solved by the invention]
By the way, in recent years, a PC fiber is attracting attention as an optical fiber exhibiting a large chromatic dispersion. The PC fiber includes a solid or hollow core extending in the longitudinal direction at the fiber center, and a clad having a large number of pores provided to cover the core and extending along the core. It constitutes a photonic crystal structure in which the refractive index fluctuates two-dimensionally.
[0004]
When such a PC fiber having an MFD of about 3 to 5 μm is connected to an optical fiber having an MFD of about 10 μm, the connection loss cannot be kept low depending on the connection method as described above. There's a problem. That is, in the PC fiber in which germanium (Ge) or the like is not doped in the core, both the core and the clad are composed only of quartz (SiO ₂ ), but the clad has a large number of pores, so In addition, the refractive index is equivalently low, so that light is propagated in the core due to the total reflection phenomenon, and light is propagated in the core due to the effect of the photonic crystal structure of the cladding. It cannot be said that germanium (Ge) or the like can be diffused into the material, and if the connection end of this PC fiber is heated for a long time or at a high temperature in order to expand the MFD, a large number of pores in the cladding are sealed. As a result, the connection end becomes a quartz lump, and light is diffused therefrom, which causes a large connection loss. A PC fiber having a core doped with germanium (Ge) or the like has a large number of pores around the core, so that the diffusion of germanium (Ge) or the like cannot be performed smoothly.
[0005]
The present invention has been made in view of this point, and an object of the present invention is to connect a PC fiber having a relatively small MFD to a connected optical fiber having a relatively large MFD with low connection loss. And it is providing the structural member which forms the connection structure of such a connection structure body of PC fiber.
[0006]
[Means for Solving the Problems]
In the present invention, the PC fiber is connected to the connected optical fiber through a buffer optical fiber having an MFD intermediate between the MFD of the PC fiber and the MFD of the connected optical fiber.
[0007]
Specifically, the invention of the present application is
A PC fiber comprising a solid or hollow core extending longitudinally in the fiber center, a cladding having a plurality of pores provided to cover the core and extending along the core, and an MFD of the PC fiber A connected optical fiber having a larger MFD,
A buffer comprising a core forming the center of the fiber and a solid clad provided so as to cover the core, and having a mode field diameter intermediate between the mode field diameter of the PC fiber and the mode field diameter of the connected optical fiber The connection end of the PC fiber is connected to one end of the optical fiber by fusion at a temperature at which the pores of the cladding are not crushed by heat, while the connection end of the optical fiber to be connected is connected to the other end of the buffer optical fiber. Is connected.
[0008]
When a PC fiber with a relatively small MFD and a connected optical fiber with a relatively large MFD are directly connected, if the difference between them is large, a large amount of light is dissipated by radiation at the connecting portion, resulting in a large connection loss. However, according to the above connection method, although two connection portions are provided, the total connection loss is larger than that in the case where the PC fiber and the optical fiber to be connected are directly connected as described above. Will be kept low. Although the reason for this is not clear, a buffer optical fiber having an MFD intermediate size between the PC fiber and the optical fiber to be connected is interposed between the PC fiber and the optical fiber to be connected, so that the difference in MFD between the fibers at each connection portion. It is presumed that this is because the dissipation due to the radiation of light is remarkably suppressed.
[0009]
In order to reduce the connection loss, it is effective to reduce the connection loss at the connection portion of the PC fiber that usually generates a large connection loss. For this purpose, the MFD of the PC fiber and the buffer optical fiber are reduced. It is preferable to make MFD close.
[0010]
Further, when the refractive index adjusting component such as germanium (Ge) is doped in the core of the buffer optical fiber, the refractive index adjusting component is connected to the other end of the buffer optical fiber that is the connection end with the connected optical fiber. It is preferable to perform a heat treatment for diffusing to the solid clad. In this way, the refractive index adjusting component such as germanium (Ge) doped in the core at the other end of the buffer optical fiber diffuses into the solid cladding, so that the MFD at the other end of the buffer optical fiber is The difference between the optical fiber and the MFD of the optical fiber to be connected is reduced, whereby the dissipation due to the radiation of light is reduced, and the connection loss at those connection parts is kept low. Here, the heat treatment may be performed before connection to the connected optical fiber, may be performed while connected to the connected optical fiber, and may be performed after connection to the connected optical fiber. Good.
[0011]
And by the connection method as described above, a solid or hollow core extending in the longitudinal direction in the fiber center and a clad provided so as to cover the core and having a plurality of pores extending along the core are provided. Between the PC fiber and the optical fiber to be connected, a core that forms the center of the fiber and a solid clad provided so as to cover the core, and between the MFD of the PC fiber and the MFD of the optical fiber to be connected A PC fiber connection structure in which a buffer optical fiber having an MFD is interposed is formed.
[0012]
Further, in order to form such a PC fiber connection structure, it has a solid or hollow core extending in the longitudinal direction at the fiber center and a plurality of pores provided so as to cover the core and extending along the core. One end of a PC fiber having a cladding and a connecting end of the PC fiber are connected by fusion at a temperature at which the pores of the cladding are not crushed by heat, so that the core that forms the center of the fiber and the core are covered. What is necessary is just to use the structural member which consists of a buffer optical fiber which has a solid clad provided and has a mode field diameter larger than the mode field diameter of the PC fiber.
[0013]
Further, even in this component, when the refractive index adjusting component such as germanium (Ge) is doped in the core of the buffer optical fiber, the refractive index adjusting component diffuses into the cladding at the other end of the buffer optical fiber. It is preferable that it is the structure which has.
[0014]
Here, if the PC fiber has a solid or hollow core extending in the longitudinal direction at the fiber center and a clad provided with a large number of pores extending along the core so as to cover the core There is no particular limitation.
[0015]
The optical fiber to be connected and the buffer optical fiber connected to the PC fiber are not particularly limited, and are 1.3 μm zero dispersion wavelength fiber, 1.55 μm dispersion shift fiber, non-zero dispersion shift fiber, dispersion compensation fiber, rare earth element What is necessary is just an optical fiber provided with cores, such as a doped fiber and a polarization-maintaining fiber, and the solid clad provided so that the core may be covered.
[0016]
The connection between the PC fiber and the buffer optical fiber is performed by fusion by low temperature heating. Further, the connection between the buffer optical fiber and the optical fiber to be connected may be performed by fusion by heating, or may be performed by butting using a connector.
[0017]
【The invention's effect】
As described above, according to the invention of the present application, the buffer optical fiber in which the MFD is an intermediate size between the PC fiber having a relatively small MFD and the connected optical fiber having a relatively large MFD. Although two connecting portions are provided, the total connection loss can be suppressed lower than when the PC fiber and the optical fiber to be connected are directly connected.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for connecting PC fibers according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0019]
(Configuration of each fiber)
FIG. 1 shows a PC fiber 10. The PC fiber 10 is made of quartz (SiO ₂ ), and has a solid core 11 extending in the longitudinal direction at the center of the fiber and a large number of pores provided so as to cover the core 11 and extending along the core 11. A clad 12 and a covering part 13 provided so as to cover the clad 12 are provided. The clad 12 constitutes a photonic crystal structure in which the refractive index periodically fluctuates two-dimensionally, and the signal light is confined and propagated in the core 11 surrounded by the photonic crystal structure. Become. The fiber diameter of the PC fiber 10 is 125 μm, and the MFD (d ₁ ) is slightly larger than the core diameter and is about 3 μm.
[0020]
FIG. 2 shows the connected optical fiber 20. This be-connected optical fiber 20, a quartz (SiO ₂₎ made of a core 21 which germanium (Ge) doped extending fiber center in the longitudinal direction, made of quartz is provided so as to cover the core 21 (SiO ₂₎ The cladding 22 is provided. The signal light is confined and propagated in the core 21 having a high refractive index. The fiber diameter of the connected optical fiber 20 is 125 μm, and the MFD (d ₂ ) is slightly larger than the core diameter and is about 10 μm.
[0021]
FIG. 3 shows the buffer optical fiber 30. The buffer optical fiber 30 has the same configuration as the optical fiber 20 to be connected except that the MFD (d ₃ ) is about 3 μm (however, larger than the MFD (d ₁ ) of the PC fiber 10). The function is also the same.
[0022]
(Fiber connection method)
First, as shown in FIG. 4, one end 33 of the buffer optical fiber 30 is connected to the connection end 14 of the PC fiber 10. At this time, the cores 11 and 31 of both fibers 10 and 30 are made to coincide and overlap. Further, this connection is performed by heating and melting the connection end 14 of the PC fiber 10 and the one end 33 of the buffer optical fiber 30 at a temperature at which the porous portion 12 of the PC fiber 10 is not crushed by heat. The connection body of the PC fiber 10 and the buffer optical fiber 30 is a constituent member for forming a connection structure of the PC fiber 10 described later.
[0023]
Next, as shown in FIG. 5, the connection end 23 of the connected optical fiber 20 is connected to the other end 34 of the buffer optical fiber 30. At this time, the central axes of both fibers 20 and 30 are made to coincide. Further, this connection is performed by heating and melting the other end 34 of the buffer optical fiber 30 and the connection end 23 of the optical fiber 20 to be connected. Further, by additionally heating the connecting portions of these fibers 20 and 30, germanium (Ge) doped in the cores 21 and 31 of both fibers 20 and 30 is diffused into the clads 22 and 32, thereby both fibers 20 and 30 are diffused. , 30 are expanded so that they are almost identical.
[0024]
As described above, the PC in which the buffer optical fiber 30 having the MFD (d ₃ ) larger than the MFD (d ₁ ) of the PC fiber 10 is interposed between the PC fiber 10 and the connected optical fiber 20. A connection structure of the fiber 10 is formed.
[0025]
Since the buffer optical fiber 30 causes a transmission loss, its length is limited. That is, the connection loss when the PC fiber 10 and the optical fiber 20 to be connected are directly connected without using the buffer optical fiber 30 is A (dB), and the connection loss when the buffer optical fiber 30 is used is B (dB). Then, (AB) (dB) is a connection loss that can be reduced by using the buffer optical fiber 30, and when the transmission loss of the buffer optical fiber 30 is C (dB / km), the buffer optical fiber If the length of 30 becomes longer than (A−B) / C (km), the reduced connection loss will be offset by the transmission loss of the buffer optical fiber 30. However, in actuality, it is sufficient that the buffer optical fiber 30 has a length of about 1 m even in consideration of the workability of connection with the PC fiber 10 and the connected optical fiber 20. Since the transmission loss can be considered to be approximately 0.001 dB or less, the transmission loss of the buffer optical fiber 30 is practically negligible.
[0026]
(Action / Effect)
According to the connection method of the PC fiber 10 described above, the MFD (d ₂ ) is between the PC fiber 10 having a relatively small MFD (d ₁ ) and the connected optical fiber 20 having a relatively large MFD (d ₂ ). However, as compared with the case where the PC fiber 10 and the optical fiber 20 to be connected are directly connected, the buffer optical fiber 30 having an intermediate size between them is provided, so that two connecting portions are provided. The total connection loss can be kept low.
[0027]
Further, after the connection between the buffer optical fiber 30 and the optical fiber 20 to be connected, the connecting portion is subjected to additional heating, so that germanium (Ge) doped in the cores 21 and 31 of both fibers 20 and 30 is applied. Is diffused into the claddings 22 and 32, and the MFDs of the other end 34 of the buffer optical fiber 30 and the connection end 23 of the connected optical fiber 20 are enlarged so that they are substantially the same, thereby dissipating the light due to radiation. As a result, the connection loss at these connecting portions is reduced.
[0028]
(Other embodiments)
In the above embodiment, the solid-core PC fiber 10 is used, but the present invention is not limited to this, and a hollow-core PC fiber may be used.
[0029]
In the above embodiment, the core 11 of the PC fiber 10 is made of quartz (SiO ₂ ). However, the core 11 is not limited to this, and is made of quartz (SiO ₂ ) doped with germanium (Ge) or the like. Also good.
[0030]
Moreover, in the said embodiment, although the buffer optical fiber 30 and the to-be-connected optical fiber 20 were connected by fusion | fusion by heating, it is not limited to this in particular, You may connect by butt | matching using a connector.
[0031]
Moreover, in the said embodiment, in order to diffuse the germanium (Ge) doped by the cores 21 and 31 of the buffer optical fiber 30 and the to-be-connected optical fiber 20 in the claddings 22 and 32, after connecting both the fibers 20 and 30, Although the process of additionally heating the connection portion is performed, the present invention is not particularly limited to this, and the heating temperature may be set higher or the heating time may be set longer during the connection by fusion.
[0032]
Moreover, in the said embodiment, although germanium (Ge) doped by the cores 21 and 31 of both the buffer optical fiber 30 and the to-be-connected optical fiber 20 was diffused in the clads 22 and 32, it is not limited to this especially. In addition, only the other end 34 of the buffer optical fiber 30 before connection is heated to diffuse germanium (Ge) doped in the core 31 into the clad 32, and as shown in FIG. May be connected to the connection end 23 of the optical fiber 20 to be connected.
[0033]
【Example】
PC fiber 10 having an outer fiber diameter of 100 μm, a cladding pore diameter of 1.28 μm, a triangular lattice pitch of 2.16 μm formed by the pores, an MFD (d ₁ ) of about 3 μm, and an MFD (d ₂ ) of 10.8 μm Is connected to the single-mode connected optical fiber 20 (1.3 μm zero-dispersion wavelength single-mode fiber) by the methods of the following three connection examples, and light having a wavelength of 1.55 μm from the connected optical fiber 20 side. And the connection loss of each connection example was measured. In addition, about the thing (connection example 2 and 3) where two connection parts arise, the connection loss in each connection part was measured, and those sum was made into the total connection loss.
[0034]
(Connection example)
-Connection example 1
A connection example 1 is obtained by heating and melting the connection end 14 of the PC fiber 10 and the connection end 23 of the optical fiber 20 to be connected, and connecting them so that their central axes coincide as shown in FIG. It was. At this time, the heating temperature was set low so that the connection end 14 of the PC fiber 10 was not melted and the pores were not crushed.
[0035]
-Connection example 2-
A dispersion compensating fiber having a length of 1 m with MFD (d ₃ ) of 4.9 μm was prepared as the buffer optical fiber 30. Then, as shown in FIG. 7B, the connection end 14 of the PC fiber 10 and the one end 33 of the buffer optical fiber 30 are heated and melted so that they are abutted and connected so that their central axes coincide with each other, and the buffer light A connection example 2 was obtained by heating and melting the other end 34 of the fiber 30 and the connection end 23 of the optical fiber 20 to be connected and butting them so that their central axes coincided with each other. At this time, the connection condition of the PC fiber 10 to the buffer optical fiber 30 was the same as that of the connection example 1.
[0036]
-Connection example 3-
After measuring the connection loss in connection example 2, the connection part between the buffer optical fiber 30 and the optical fiber 20 to be connected is additionally heated, and germanium (Ge) doped in the respective cores 21 and 31 is applied to the claddings 22 and 32. As shown in FIG. 7C, a connection example 3 was used in which the MFD diameters of both were made substantially the same as shown in FIG.
[0037]
(Measurement result)
[0038]
[Table 1]

[0039]
Table 1 shows the measurement results.
[0040]
According to the table, it can be seen that connection examples 2 and 3 have a much lower connection loss than connection example 1. Further, while the connection loss of the connection portion between the PC fiber 10 and the optical fiber 20 to be connected is 5.47 dB (connection example 1), the MFD (d ₃ ) having a size close to the MFD (d ₁ ) of the PC fiber 10. ) Is 1.22 dB (connection example 2) at the connection portion between the buffer optical fiber 30 and the optical fiber 20 to be connected, and it can be seen that the connection loss increases at the connection portion of the PC fiber 10. Furthermore, since the connection loss of the connection example 1 is 5.47 dB, the connection loss of the connection portion between the PC fiber 10 and the buffer optical fiber 30 is 2.01 dB (connection examples 2 and 3). It can be seen that the connection loss is reduced at the connecting portion between the PC fiber 10 and the buffer optical fiber 30. In connection example 1, since the difference between the MFD (d ₁ ) of the PC fiber 10 and the MFD (d ₂ ) of the optical fiber 20 to be connected is very large, a large amount of light is dissipated due to radiation at the connection portion, resulting in a large connection. This is considered to have caused a loss. On the other hand, in connection examples 2 and 3, although two connecting portions are provided, MFD (d ₃ ) is an intermediate dimension between the PC fiber 10 and the optical fiber 20 to be connected. Since the buffer optical fiber 30 is interposed, the difference in MFD between the fibers at each connection portion is reduced, and thereby dissipation due to light emission is remarkably suppressed (particularly between the PC fiber 10 and the buffer optical fiber 30). In the connection portion), it is considered that the total connection loss is suppressed as compared with the connection example 1.
[0041]
It can also be seen that connection example 3 has a lower connection loss than connection example 2. In connection example 2, since the MFD difference is large at the connection between the buffer optical fiber 30 and the optical fiber 20 to be connected, it is considered that light is dissipated by radiation and a relatively large connection loss occurs. . On the other hand, in connection example 3, since the difference between the MFD of the buffer optical fiber 30 and the MFD of the connected optical fiber 20 in the connection portion is small, dissipation due to light emission is suppressed and the connection loss is low. It is thought that it became.
[Brief description of the drawings]
FIG. 1 is a perspective view of a photonic crystal fiber according to an embodiment of the present invention.
FIG. 2 is a perspective view of an optical fiber in an embodiment of the present invention.
FIG. 3 is a perspective view of a buffer optical fiber according to an embodiment of the present invention.
FIG. 4 is a side view of components for forming a photonic crystal fiber connection structure in an embodiment of the present invention.
FIG. 5 is a side view of a photonic crystal fiber connection structure according to an embodiment of the present invention.
FIG. 6 is a side view of a photonic crystal fiber connection structure according to another embodiment of the present invention.
FIG. 7 is a side view of a photonic crystal fiber connection structure in an example.
FIG. 8 is a side view of a connection structure of photonic crystal fibers in a conventional example.
FIG. 9 is a side view of an optical fiber connection structure.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Photonic crystal fiber 11, 21, 31 Core 12, 22, 32 Cladding 13 Covering part 14 Photonic crystal fiber connection end 20 Connected optical fiber 23 Connected optical fiber connection end 30 Buffer optical fiber 33 Buffer optical fiber end 34 Buffer optical fiber and the other end c connected portion _{d l, d s, d 1} ~d 3 mode field diameter f _1, f ₂ optical fiber

Claims (6)

A photonic crystal fiber comprising a solid or hollow core extending longitudinally in the fiber center and a clad having a plurality of pores provided to cover the core and extending along the core. A method of connecting to a connected optical fiber having a mode field diameter larger than the mode field diameter of the fiber,
A mode field diameter intermediate between the mode field diameter of the photonic crystal fiber and the mode field diameter of the connected optical fiber, and a core that forms the center of the fiber and a solid clad provided to cover the core one end of the buffer optical fiber having a connection end of the photonic crystal fiber, while the pores of the cladding are connected by fusion at a temperature that does not collapse by heat, the object to be connected light to the other end of the buffer optical fiber A method for connecting photonic crystal fibers, comprising connecting ends of fibers.   2. The method of connecting photonic crystal fibers according to claim 1, wherein the other end of the buffer optical fiber is subjected to a heat treatment for diffusing the refractive index adjusting component doped in the core into the solid clad. . A photonic crystal fiber comprising a solid or hollow core extending longitudinally in the fiber center and a cladding having a plurality of pores provided to cover the core and extending along the core;
A connected optical fiber having a mode field diameter larger than the mode field diameter of the photonic crystal fiber;
One end is connected to the connection end of the photonic crystal fiber by fusion at a temperature at which the pores of the clad are not crushed by heat, while the other end is connected to the connection end of the optical fiber to be connected. And a solid clad provided so as to cover the core, and having a mode field diameter intermediate between the mode field diameter of the photonic crystal fiber and the mode field diameter of the connected optical fiber Optical fiber,
A photonic crystal fiber connection structure comprising:   The buffer optical fiber has a refractive index adjustment component doped in the core, and the refractive index adjustment component doped in the core is diffused in the solid cladding at the other end of the buffer optical fiber. The photonic crystal fiber connection structure according to claim 3, wherein: A photonic crystal fiber comprising a solid or hollow core extending longitudinally in the fiber center and a cladding having a plurality of pores provided to cover the core and extending along the core;
One end of the photonic crystal fiber is connected by fusion at a temperature at which the pores of the clad are not crushed by heat, and a solid clad provided to cover the core that forms the center of the fiber And a buffer optical fiber having a mode field diameter larger than that of the photonic crystal fiber,
A constituent member of a photonic crystal fiber connection structure comprising:   The buffer optical fiber has a refractive index adjustment component doped in the core, and the refractive index adjustment component doped in the core is diffused in the solid cladding at the other end of the buffer optical fiber. The constituent member of the connection structure of the photonic crystal fiber according to claim 5.

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