JP2006017816A - Joint structure of optical fiber, optical fiber component and dispersion-compensated fiber module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joint structure which has a small loss and is applicable to connect optical fibers of different mode field diameters together or to connect a dispersion-compensated fiber module and an output transmission fiber. <P>SOLUTION: In the joint structure of a 1st optical fiber 1 and a 2nd optical fiber 2 having mode field diameters different with each other, a holy fiber 3 having the core 5 of a refractive index higher than the clad which has at least three or more holes 7 is inserted between these 1st and 2nd optical fibers. One end 9 of this holy fiber is connected to the end of the 1st optical fiber of a small mode field diameter with the holes held therein. A hole diameter reduced section 8 is formed gradually decreasing the hole diameter at the other end of the holy fiber, and this end 10 of the holy fiber is connected to an end of the 2nd optical fiber having a larger mode field diameter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of fusion splicing optical fibers having different mode field diameters (hereinafter referred to as MFDs) with low loss, and this connection method includes, for example, special optical fibers and optical components and normal transmission light. It is used for connection to a fiber, connection to a dispersion compensation fiber and a dispersion compensation fiber module, a 1.3 μm band zero dispersion single mode optical fiber, or a 1.55 μm band non-zero dispersion single mode optical fiber. More specifically, the present invention uses an optical fiber having a small MFD, an optical fiber having a small MFD, an optical component, and a holey fiber having an MFD equivalent to a dispersion compensating fiber between these optical fibers or optical components. The present invention relates to a technique for connecting a dispersion compensating fiber and a fiber with a large MFD with low loss.

In order to increase the capacity of an optical fiber transmission system, studies on wavelength division multiplexing transmission and high-speed transmission are underway. Residual dispersion compensation technology is important for speeding up.
The 1.3 μm band zero-dispersion single-mode optical fiber (S-SMF) that has already been installed in a wide range has a wavelength dispersion of about +17 ps / nm / km in the 1.55 μm band, so it can be transmitted at high speed. Then, the transmission distance is limited. Various non-zero dispersion-shifted optical fibers (NZ-DSFs) also have smaller chromatic dispersion than S-SMF, but the transmission distance is also limited in high-speed transmission. End up. Therefore, a dispersion compensation device is indispensable for increasing the transmission speed and extending the distance.
So far, dispersion compensation fiber modules capable of simultaneously compensating for the dispersion slope and dispersion have been developed and put into practical use for various transmission optical fibers.
These dispersion compensating fibers are generally modularized and inserted into a terminal station of a transmission line. For this reason, the same S-SMF (or NZ-DSF) as the transmission line is fused and connected to both ends of the dispersion compensating fiber with low loss. When inserting into the transmission line, the same type of fiber is connected (connector or fused). Connection).

In the dispersion compensating fiber, in order to increase the chromatic dispersion that can be compensated per unit length, the core / cladding relative refractive index difference is increased and the core diameter is reduced. For example, the relative refractive index difference of the core / cladding of the dispersion compensating fiber is 1 to 2%, which is three times or more of S-SMF. Further, since the core diameter of the central portion is also less than or equal to half of S-SMF, MFD is about 5 μm, which is about half of S-SMF.
For this reason, conventionally, the dispersion compensation fiber and the S-SMF are fusion spliced and the connection portion is heated to expand the MFD of the dispersion compensation fiber to reduce the connection loss, or between the dispersion compensation fiber and the S-SMF. In addition, a method has been adopted in which an intermediate optical fiber having a structure in which the core is easily diffused is interposed (see, for example, Patent Document 1).

  On the other hand, in recent years, a new fiber called a holey fiber has been developed. This holey fiber is a general term for optical fibers having holes, and is also called a photonic crystal fiber (PCF) or a micro structured fiber. This holey fiber can realize characteristics that cannot be realized by a conventional core / cladding structure, and is expected as various types of functional fibers and future transmission fibers (for example, see Non-Patent Document 1).

This holey fiber is produced, for example, by providing appropriate holes in the clad portion of a normal 1.3 μm band zero-dispersion single mode optical fiber base material, and reduces bending loss while maintaining a predetermined MFD. It is something that can be done.
When connecting a photonic crystal fiber and a connected fiber having a relatively large MFD, a method of inserting and connecting a buffer optical fiber having an intermediate MFD to both optical fibers is disclosed in Patent Document 2 and Patent It is disclosed in Document 3.
JP-A-8-190030 Takemi Hasegawa, et al “Novel hole-assisted lightguide fiber exhibiting large anomalous dispersion and low below 1dB / km”, Optical Fiber Communication (OFC) 2001, PD5 (2001) JP 2002-243971 A Japanese Patent Laid-Open No. 2002-243972

The conventional method of expanding the MFD by heating an optical fiber has been difficult to apply to an optical fiber in which loss occurs due to heating.
In addition, when the intermediate fiber is used, the MFD difference between the intermediate fiber and the S-SMF is about 5 μm. Therefore, even if the MFD is expanded, there is a limit in reducing the connection loss due to mismatch of the field distribution. The total loss at both ends of the intermediate fiber was about 0.2 to 0.3 dB.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a connection structure that can be connected with low loss in connection between optical fibers having different MFDs or connection between a dispersion compensating fiber and a lead-out transmission fiber.

In order to achieve the above object, the present invention provides a connection structure of first and second optical fibers each having a different MFD, and has a refractive index higher than that of the cladding portion between the first and second optical fibers. A holey fiber having a core part and having at least three holes in the cladding part is inserted, and one end surface of the holey fiber is a first optical fiber having a small MFD among the first and second optical fibers. The other end of the holey fiber is connected to the other end surface of the holey fiber, and a hole gradually decreasing portion is formed by gradually reducing the hole diameter of the holey fiber. An optical fiber connection structure is provided which is connected to one end face of two optical fibers.
In the optical fiber connection structure of the present invention, it is preferable that the first optical fiber is a dispersion compensating fiber and the second optical fiber is a 1.3 μm band zero dispersion single mode optical fiber.
In the connection structure, it is preferable that a relative refractive index difference of the core portion with respect to the cladding portion other than the hole portion of the holey fiber is 0.3% to 0.4%.
In the connection structure, the difference between the MFD of one end face of the holey fiber and the MFD of the dispersion compensating fiber is within ± 1.0 μm, and the MFD of the other end face of the holey fiber and the 1.3 μm band zero-dispersion single mode light The difference from the MFD of the fiber is preferably within ± 0.5 μm.
In the optical fiber connection structure of the present invention, it is preferable that the first optical fiber is a dispersion compensating fiber and the second optical fiber is a 1.55 μm band non-zero dispersion single mode optical fiber.
In the connection structure, it is preferable that the relative refractive index difference of the core portion with respect to the cladding portion other than the hole portion of the holey fiber is 0.3% to 0.5%.
In the connection structure, the difference between the MFD on one end face of the holey fiber and the MFD of the dispersion compensating fiber is within ± 1.0 μm, and the MFD on the other end face of the holey fiber and the non-zero dispersion single mode in the 1.55 μm band The difference from the MFD of the optical fiber is preferably within ± 0.5 μm.

The present invention also provides an optical fiber type optical component having the above-described optical fiber connection structure according to the present invention.
The present invention also provides a dispersion compensating fiber module having the above-described optical fiber connection structure according to the present invention.

According to the present invention, it is possible to easily obtain a low-loss connection structure when connecting optical fibers or optical components having significantly different MFDs.
For example, in a structure in which a dispersion compensating fiber having a small MFD and a transmission fiber for a large MFD are connected, a core portion having a refractive index higher than that of the cladding portion is provided between the dispersion compensating fiber and the transmission fiber for a lead. Insert a holey fiber having at least three holes in the cladding, connect one end face of the holey fiber to the dispersion compensating fiber while holding the hole, and set the hole diameter at the other end of the holey fiber. By providing a gradually decreasing hole gradually decreasing portion, expanding the MFD of the other end surface to have a value equivalent to the MFD of the transmission fiber, and connecting the other end surface to one end surface of the transmission fiber, It became possible to obtain a low-loss connection structure. As a result, the loss of the dispersion compensating fiber module including the splicing loss of the lead fiber can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view of an essential part showing an embodiment of an optical fiber connection structure according to the present invention. In FIG. 1, reference numeral 1 denotes a first optical fiber, 2 denotes a second optical fiber, 3 denotes a holey fiber, The core portion of the first optical fiber 1, 5 is the core portion of the holey fiber 3, 6 is the core portion of the second optical fiber 2, 7 is a hole, 8 is a gradually decreasing portion of the hole, and 9 is one of the holey fibers 3. An end surface, 10 is the other end surface of the holey fiber 3, 11 is a first fusion splicing portion, and 12 is a second fusion splicing portion.

  The connection structure of this embodiment has a core portion 5 having a higher refractive index than the cladding portion between the first optical fiber 1 and the second optical fiber 2 having different MFDs, and at least three or more in the cladding portion. A holey fiber 3 having holes 7 is inserted, and one end surface 9 of the holey fiber 3 is fusion-bonded to one end surface of the first optical fiber 1 having a small MFD to form a first fusion-bonding portion 11. At the other end of the holey fiber 3, a hole gradually decreasing portion 8 in which the hole diameter of the holey fiber 3 is gradually reduced is provided, and the other end surface 10 of the holey fiber 3 is connected to one end surface of the second optical fiber 2 having a large MFD. The second fusion splicing portion 12 is formed by fusion splicing.

  Although it does not specifically limit as said 1st optical fiber 1, For example, in the production use of a dispersion compensation fiber module, a dispersion compensation fiber is mentioned. In order to increase the chromatic dispersion that can be compensated per unit length, the dispersion compensating fiber has a higher core / cladding relative refractive index difference and a smaller core diameter than a normal transmission fiber. Is smaller than the MFD of a general transmission optical fiber.

  The second optical fiber 2 can be used by appropriately selecting from optical fibers having an MFD larger than the MFD of the first optical fiber 1. For example, when the dispersion compensating fiber is used as the first optical fiber 1, S-SMF, NZ-DSF, or the like is used as the second optical fiber 2.

  As the holey fiber 3, one having a core part 5 having a higher refractive index than the cladding part and having at least three holes 7 in the cladding part can be appropriately selected and used. The remaining MFD of the one end face 9 is close to the MFD of the first optical fiber 1, and the MFD of the other end face 10 in which the holes 7 are crushed by the hole gradually decreasing portion 8 is the MFD of the second optical fiber 2. A holey fiber 3 having a value close to is preferable.

  At the other end of the holey fiber 3, there is provided a hole gradually decreasing portion 8 in which the hole diameter of the holey fiber 3 is gradually reduced. The hole gradually decreasing portion 8 is heated while the other end portion is appropriately moved when the other end portion is subjected to discharge heating or burner heating, and the hole 7 is gradually reduced along the longitudinal direction so as to be near the other end face 10. Thus, the voids 7 can be formed. The hole gradually decreasing portion 8 formed in this way gradually expands toward the other end surface 10, and the other end surface 10 can have an MFD comparable to the MFD of the second optical fiber 2.

  The connection structure of this embodiment has a core portion 5 having a higher refractive index than the cladding portion between the first optical fiber 1 and the second optical fiber 2 having different MFDs, and at least three or more in the cladding portion. A holey fiber 3 having a hole 7 is inserted, and one end surface 9 of the holey fiber 3 is connected to the first optical fiber 1 having a small MFD in a state where the hole is held, and is connected to the other end of the holey fiber 3. The hole gradually decreasing portion 8 is provided, and the MFD of the other end face 10 is expanded so as to have an MFD equivalent to the second optical fiber 2 having a large MFD, and the other end face 10 is connected to one end face of the second optical fiber 2. By connecting, a low-loss connection structure can be obtained.

  In the connection structure of this embodiment, when a dispersion compensating fiber is used as the first optical fiber 1, S-SMF is used as the second optical fiber 2, and both are connected via the holey fiber 3, The difference between the MFD of the one end face 9 and the MFD of the dispersion compensating fiber (first optical fiber 1) is within ± 1.0 μm, and the MFD and S-SMF of the other end face 10 provided with the pore gradually decreasing portion 8 ( The difference from the MFD of the second optical fiber 2) is preferably within ± 0.5 μm. Moreover, it is preferable that the relative refractive index difference of the core part with respect to the cladding part other than the hole part of the holey fiber 3 is 0.3% to 0.4%.

  By using this connection structure, the first fusion splicing part 11 formed by fusion-bonding the dispersion compensating fiber as the first optical fiber 1 and the holey fiber 3 has a low connection of 0.1 dB or less. The second fusion splicing portion 12 formed by fusion splicing the other end face 10 of the holey fiber 3 and the S-SMF as the second optical fiber 2 is 0.05 dB. Since the connection loss can be made as low as possible, a connection structure with a low loss of 0.15 dB or less in total can be obtained.

  As the holey fiber 3 used for this connection structure, a holey fiber 3 manufactured by forming a predetermined number of holes at predetermined positions in a base material of the same quality as that of the S-SMF manufacturing base material and drawing the holes is used. preferable. In the holey fiber 3 manufactured in this way, the MFD of the one end face 9 where the holes 7 remain can be set to a value close to the MFD of the first optical fiber 1, and the holes gradually decrease by the holes gradually decreasing portion 8. The MFD of the other end face 10 crushed 7 can be a value close to the MFD of the S-SMF.

  In the connection structure of the present embodiment, when a dispersion compensating fiber is used as the first optical fiber 1 and NZ-DSF is used as the second optical fiber 2, both are connected via the holey fiber 3. 3 is less than ± 1.0 μm between the MFD of the one end face 9 and the MFD of the dispersion compensating fiber (first optical fiber 1), and the MFD and NZ− of the other end face 10 provided with the pore gradually decreasing portion 8 are provided. The difference from the MFD of the DSF (second optical fiber 2) is preferably within ± 0.5 μm. Further, the relative refractive index difference of the core portion with respect to the cladding portion other than the hole portion of the holey fiber 3 is preferably 0.3% to 0.5%.

  By using this connection structure, the first fusion splicing part 11 formed by fusion-bonding the dispersion compensating fiber as the first optical fiber 1 and the holey fiber 3 has a low connection of 0.1 dB or less. The second fusion splicing portion 12 formed by fusion splicing the other end face 10 of the holey fiber 3 and the NZ-DSF as the second optical fiber 2 is 0.05 dB. Since the connection loss can be made as low as possible, a connection structure with a low loss of 0.15 dB or less in total can be obtained.

  As the holey fiber 3 used for this connection structure, a holey fiber 3 manufactured by drilling a predetermined number and a predetermined number of holes in a base material similar to the base material for NZ-DSF manufacturing and drawing it is used. preferable. In the holey fiber 3 manufactured in this way, the MFD of the one end face 9 where the holes 7 remain can be set to a value close to the MFD of the first optical fiber 1, and the holes gradually decrease by the holes gradually decreasing portion 8. The MFD of the other end face 10 crushed 7 can be a value close to the MFD of the NZ-DSF.

The present invention also provides an optical fiber type optical component having the above-described optical fiber connection structure according to the present invention.
Examples of MFDs that are significantly different from MFDs of ordinary transmission optical fibers include highly nonlinear fibers. However, the present invention provides a connection between a dispersion compensating fiber and a transmission optical fiber, and a connection between a highly nonlinear fiber and a transmission optical fiber. It is not limited to connection only. In the case of a combination having a very large MFD difference, the connection structure of the present invention is effective.

The present invention also provides a dispersion compensating fiber module having the above-described optical fiber connection structure according to the present invention. In this dispersion compensating fiber module, a dispersion compensating fiber having a length necessary for carrying out dispersion compensation of a transmission optical fiber is wound around a bobbin or the like, and S-SMF or NZ-DSF for feeding are provided at both ends of the dispersion compensating fiber. Is connected to the dispersion compensating fiber and the S-SMF or NZ-DSF via a holey fiber using the above-described optical fiber connection structure according to the present invention.
Since the dispersion compensating fiber module of the present invention is provided with the above-described optical fiber connection structure according to the present invention, dispersion compensation can be performed with low loss compared to the conventional product.

[Example 1]
In this example, as shown in FIG. 2, a holey fiber 20 having six holes 23 around a core 21 having a higher refractive index than that of the cladding portion 22 was used. The holey fiber 20 was made by punching holes at predetermined positions of the S-SMF manufacturing base material, and the base material was manufactured by the same method as that for drawing a normal transmission optical fiber.
The core portion 21 has a core-clad relative refractive index difference of Δ = 0.34%, which is equivalent to S-SMF. When there is no hole 23, it has optical characteristics, such as MFD equivalent to S-SMF, and a cutoff wavelength. Table 1 shows the hole diameter, hole interval, core diameter, and optical characteristics of the holey fiber 20.

No. shown in Table 1. 1 holey fiber was used when connecting the S-SMF dispersion compensating fiber to the S-SMF. Although the holey fiber 20 has a large MFD in the state without the holes 23, the holey fiber 20 is formed with six holes 23 close to the core portion 21 so that the MFD becomes small in the presence of the holes 23. ing.
Table 2 shows the characteristics of the dispersion compensating fiber for S-SMF. Table 3 shows the characteristics of the S-SMF used to lead the dispersion compensating fiber module using this dispersion compensating fiber.

  First, a dispersion compensating fiber having the characteristics shown in Table 2 and a holey fiber having the characteristics shown in Table 1 are fusion spliced using a commercially available fusion splicer. 1 fusion splicing part 27 was formed. The first fusion splicing portion 27 is connected to one end face of the dispersion compensating fiber 24 and one end face 26 of the holey fiber 20 while holding the holes 23 so as not to change the MFD of the holey fiber 20. The core 21 of the holey fiber 20 has a larger diameter than the core 25 of the dispersion compensating fiber 24. However, the MFD of the holey fiber 20 is 6.2 μm due to the air holes 23 in the vicinity of the core 21 of the holey fiber 20, and the MFD of the dispersion compensating fiber. The value is close to (5.4 μm). The connection loss of the first fusion splicing portion 27 was 0.08 dB.

Next, the other end portion of the holey fiber 20 is heated by the fusion splicer, and the hole 23 at the other end surface 31 is crushed in the longitudinal direction, while the hole 23 is completely crushed at the other end surface 31. 28 was formed. The MFD of the other end face 31 of the holey fiber 20 in which the holes 23 were completely crushed was 10 μm at a wavelength of 1.55 μm.
Next, as shown in FIG. 4, the second fusion splicing portion 32 was formed by fusing S-SMF 29 to the other end surface 31 of the holey fiber 20 in which the hole gradually decreasing portion 28 was formed. The second fusion splicing part 32 forms a hole gradually decreasing part 28, and the other end face 31 of the holey fiber 20 in which the hole 23 is completely crushed and the one end face of the S-SMF 29 are fusion spliced. In the second fusion splicing portion 32, the diameters of the core portion 21 of the holey fiber 20 and the core portion 30 of the S-SMF 29 are equal, and the respective MFDs are equal.

  As described above, when the dispersion compensating fiber 24 and the S-SMF 29 are connected via the holey fiber 20, the total connection loss of the first fusion splicing portion 27 and the second fusion splicing portion 32 is 0.10 dB. Thus, a connection structure having a low loss of about half compared to the conventional connection loss was obtained.

[Example 2]
In this example, the dispersion compensation fiber 24 was the same as that of Example 1 except that the dispersion compensation fiber for S-SMF shown in Table 4 was used. Table 4 shows the characteristics of the dispersion compensating fiber 24 used in this example.

  The dispersion compensating fiber 24 having the characteristics shown in Table 4 and the holey fiber 20 having the characteristics shown in Table 1 are fusion-spliced using a commercially available fusion splicer, and a first fusion splice 27 as shown in FIG. Formed. The first fusion splicing portion 27 is connected to one end face of the dispersion compensating fiber 24 and one end face 26 of the holey fiber 20 while holding the holes 23 so as not to change the MFD of the holey fiber 20. The core 21 of the holey fiber 20 has a larger diameter than the core 25 of the dispersion compensating fiber 24. However, the MFD of the holey fiber 20 is 6.2 μm due to the air holes 23 in the vicinity of the core 21 of the holey fiber 20, and the MFD of the dispersion compensating fiber. The value is close to (5.6 μm). The connection loss of the first fusion splicing portion 27 was 0.04 dB.

Next, the other end portion of the holey fiber 20 is heated by the fusion splicer, and the hole 23 at the other end surface 31 is crushed in the longitudinal direction, while the hole 23 is completely crushed at the other end surface 31. 28 was formed. The MFD of the other end face 31 of the holey fiber 20 in which the holes 23 were completely crushed was 10 μm at a wavelength of 1.55 μm.
Next, as shown in FIG. 4, the second fusion splicing portion 32 was formed by fusing S-SMF 29 to the other end surface 31 of the holey fiber 20 in which the hole gradually decreasing portion 28 was formed. The second fusion splicing part 32 forms a hole gradually decreasing part 28, and the other end face 31 of the holey fiber 20 in which the hole 23 is completely crushed and the one end face of the S-SMF 29 are fusion spliced. In the second fusion splicing portion 32, the diameters of the core portion 21 of the holey fiber 20 and the core portion 30 of the S-SMF 29 are equal, and the respective MFDs are equal.

  Thus, when the dispersion compensating fiber 24 and the S-SMF 29 are connected via the holey fiber 20, the connection loss of the first fusion splicing portion 27 and the second fusion splicing portion 32 is 0.06 dB in total. Thus, a connection structure having a low loss compared to the conventional connection loss was obtained.

[Example 3]
In the same manner as in Example 1, a holey fiber having a structure as shown in FIG. 2 was produced. The core portion has Δ = 0.40%, which is slightly higher in core-clad relative refractive index difference than S-SMF. When there was no void | hole, the base material which has MFD equivalent to NZ-DSF was used. Table 5 shows the hole diameter, hole interval, core diameter, and optical characteristics of the manufactured holey fiber.

No. shown in Table 5 Using the holey fiber of No. 2, the dispersion compensation fiber for NZ-DSF was connected to the NZ-DSF.
Table 6 shows the characteristics of the dispersion compensating fiber for NZ-DSF. Table 7 shows the characteristics of the NZ-DSF used to lead out the dispersion compensating fiber module using this dispersion compensating fiber.

First, a dispersion compensating fiber having the characteristics shown in Table 6 and a holey fiber having the characteristics shown in Table 5 were connected. At this time, as shown in FIG. 3, the connection was performed under the condition that the holes were held so as not to change the MFD of the holey fiber. The connection loss of the first fusion splicing portion was 0.14 dB.
Next, as shown in FIG. 4, the hole at the other end of the holey fiber is gradually crushed along the longitudinal direction using a fusion splicer, while the hole is completely crushed at the other end to completely reduce the hole. Formed. The MFD on the other end surface at this time was 9.6 μm at a wavelength of 1.55 μm.
Next, the other end surface of this holey fiber and one end surface of NZ-DSF having the characteristics shown in Table 7 were connected to form a second fusion splicing portion.
Thus, when the dispersion compensating fiber and the NZ-DSF are connected via the holey fiber, the connection loss of the first fusion splicing portion and the second fusion splicing portion is 0.15 dB in total, A connection structure with a low loss of about half of the connection loss was obtained.

It is a principal part side view which shows one Embodiment of the connection structure of this invention. It is an end view of the holey fiber produced in the Example. It is a block diagram which shows the vicinity of the 1st fusion splicing part among the connection structures produced in the Example. It is a block diagram which shows the vicinity of the 2nd fusion splicing part among the connection structures produced in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st optical fiber, 2 ... 2nd optical fiber, 3 ... Holey fiber, 4, 5, 6 ... Core part, 7 ... Hole, 8 ... Hole decreasing part, 9 ... One end surface, 10 ... Others End face 11... First fusion splicing part 12... Second fusion splicing part 20. Holey fiber 21. Core part 22. Cladding part 23. Core part, 26 ... one end face, 27 ... first fusion splicing part, 28 ... pore gradually decreasing part, 29 ... S-SMF, 30 ... core part, 31 ... other end face, 32 ... second fusion splicing part .

Claims (9)

  In the connection structure of the first and second optical fibers having different mode field diameters, a core portion having a refractive index higher than that of the cladding portion is provided between the first and second optical fibers, and at least in the cladding portion. A holey fiber having three or more holes is inserted, and one end surface of the holey fiber is inserted into one end surface of the first optical fiber having a small mode field diameter among the first and second optical fibers. The other end of the holey fiber is connected to the other end of the holey fiber, and a hole gradually decreasing portion is formed by gradually reducing the hole diameter of the holey fiber. The other end surface of the holey fiber is connected to the second optical fiber having a large mode field diameter. An optical fiber connection structure characterized by being connected to one end surface.   The optical fiber connection structure according to claim 1, wherein the first optical fiber is a dispersion compensating fiber, and the second optical fiber is a 1.3 μm band zero-dispersion single mode optical fiber.   The optical fiber connection structure according to claim 1 or 2, wherein a relative refractive index difference of the core portion with respect to the cladding portion other than the hole portion of the holey fiber is 0.3% to 0.4%.   The difference between the mode field diameter of one end face of the holey fiber and the mode field diameter of the dispersion compensating fiber is within ± 1.0 μm, and the mode field diameter of the other end face of the holey fiber is equal to the 1.3 μm band zero dispersion single mode. 4. The optical fiber connection structure according to claim 2, wherein a difference from a mode field diameter of the optical fiber is within ± 0.5 μm.   2. The optical fiber connection structure according to claim 1, wherein the first optical fiber is a dispersion compensating fiber, and the second optical fiber is a 1.55 μm band non-zero dispersion single mode optical fiber.   The optical fiber connection structure according to claim 5, wherein the relative refractive index difference of the core portion with respect to the cladding portion other than the hole portion of the holey fiber is 0.3% to 0.5%.   The difference between the mode field diameter of one end face of the holey fiber and the mode field diameter of the dispersion compensating fiber is within ± 1.0 μm, and the mode field diameter of the other end face of the holey fiber and the non-zero dispersion single in the 1.55 μm band 7. The optical fiber connection structure according to claim 5, wherein a difference from a mode field diameter of the mode optical fiber is within ± 0.5 μm.   An optical fiber type optical component having the optical fiber connection structure according to claim 1. A dispersion compensating fiber module comprising the optical fiber connection structure according to claim 1.

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