JP2004133276A - Method for splicing photonic crystal fiber and splicing structure of photonic crystal fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent increase of splicing loss in splicing photonic crystal fibers 1 by a mechanical splice 9. <P>SOLUTION: In a method for splicing photonic crystal fibers, the splicing end faces 13, 13 of a pair of fibers 1, 1 are butted against each other in a capillary 9 and the butted splicing faces 13, 13 are adhered to each other with an adhesive. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for connecting a photonic crystal fiber and a connection structure thereof.
[0002]
[Prior art]
Conventionally, a method using a mechanical splice has been known as a method of connecting end faces of optical fibers by abutting each other. As the mechanical splice, a substrate in which a V-groove into which a bare fiber is inserted is formed, a pressing member superposed on the substrate, and a U-shaped clamp member sandwiching the superposed substrate and the pressing member. Is known (see, for example, Patent Document 1). In this device, a bare fiber is inserted from both sides of a V-groove and their connection end faces are abutted with each other. In this state, a substrate and a holding member are overlapped, and these are sandwiched by a clamp member to form a pair of optical fibers. To make a connection.
[0003]
Further, as a mechanical splice different from this, a glass splice (capillary) made of glass is known, in which a bare fiber is inserted from each of both ends of the above-mentioned capillary, and these are inserted inside the capillary. The end faces are abutted and connected.
[0004]
In any of the above mechanical splices, in order to reduce the connection loss caused by reflection at the connection end face, the refractive index of the optical fiber is substantially the same as the refractive index of the core portion at the abutting portion where the connection end faces of the optical fiber abut. Is filled with a refractive index matching agent (matching oil) having
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. Hei 9-31836
[Problems to be solved by the invention]
By the way, the optical fiber has a core portion and a clad portion, but as a different fiber, a solid core portion formed at the center of the fiber, and a core portion provided around the core portion and provided in the core portion. A photonic crystal fiber including a porous portion having a large number of pores extending along the same is known.
[0007]
This device transmits light by confining light in a core surrounded by a porous portion.However, it is possible to freely control the wavelength dispersion of light by changing the size of pores and the interval between the pores. Therefore, communication in a new wavelength range, which cannot be realized by the conventional optical fiber, is possible, and high-speed communication and cost reduction are expected.
[0008]
When trying to connect the photonic crystal fibers to each other or to connect the photonic crystal fiber and the optical fiber by the mechanical splice, the matching oil enters into the inside of the photonic crystal fiber from the opening of each pore at the end face of the fiber. Become. Since the matching oil has substantially the same refractive index as the core, if the matching oil enters the pores, the signal light propagating in the core leaks out in the radial direction. A large loss will occur in some parts. Further, if the matching oil flows in the longitudinal direction in each of the pores, signal light leaks at portions other than the connection portion of the fiber, which may cause deterioration of transmission loss.
[0009]
The present invention has been made in view of such circumstances, and an object of the present invention is to prevent an increase in connection loss when connecting a photonic crystal fiber by a mechanical splice. is there.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a capillary is used as a mechanical splice, and the connection end faces of the butted fibers in the capillary are bonded with an adhesive.
[0011]
Specifically, the first invention is characterized in that at least one fiber has a solid core portion forming the center of the fiber and a plurality of thin fibers provided so as to surround the core portion and extend along the core portion. The present invention relates to a photonic crystal fiber connection method for connecting a pair of fibers, which are photonic crystal fibers having a porous portion having holes, to each other using a capillary.
[0012]
In the connection method according to the first invention, the pair of fibers are inserted from both ends of the capillary, respectively, and the butting step of butting the connection end faces of the fibers in the capillary is performed. A bonding step of bonding the connection end surfaces with an adhesive.
[0013]
According to this configuration, when connecting the photonic crystal fibers to each other or the photonic crystal fiber and the optical fiber, the connection end faces of the pair of fibers abut against each other in the capillary, and the abutted connection end faces. Are bonded with an adhesive.
[0014]
For this reason, no air layer or the like is interposed between the connection end faces, thereby suppressing reflection at the connection end faces. Further, since the refractive index matching agent is not required, the refractive index matching agent is prevented from entering the pores from the openings of the pores at the connection end face of the photonic crystal fiber. Further, the curing of the adhesive prevents the adhesive from penetrating deep into each pore of the photonic crystal fiber. Thus, even when the photonic crystal fiber is connected by a mechanical splice, an increase in connection loss is prevented.
[0015]
In addition, since the openings of the respective pores at the connection end face of the photonic crystal fiber are also closed, moisture is prevented from entering into the respective pores even in a humid heat environment, and a decrease in transmission loss is suppressed. You.
[0016]
Here, while the capillary is made of a transparent material, and the adhesive is an ultraviolet-curable adhesive, before the butting step, including an injection step of injecting the ultraviolet-curable adhesive into the capillary, The bonding step, after the butting step, by irradiating ultraviolet rays from the outside of the capillary toward the butting portion where the connection end faces are butted in the capillary, thereby curing the ultraviolet curable adhesive. The step of bonding the connection end faces may be performed.
[0017]
According to this configuration, when a pair of fibers is inserted from both ends of the capillary and their connection end faces are abutted in the capillary, an ultraviolet curing adhesive is previously injected into the capillary. An ultraviolet-curable adhesive is applied to the butted portions of the connection end surfaces in the capillary (between and around the connection end surfaces).
[0018]
In this state, ultraviolet light is irradiated from the outside of the capillary toward the butting portion of the connection end faces in the capillary. At this time, since the capillary is made of, for example, a transparent material such as glass, ultraviolet rays penetrate into the capillary, and the ultraviolet curable adhesive applied to the butted portion is cured. Thus, the connection end faces are bonded to each other, and the butted portion is fixed to the capillary.
[0019]
By injecting the ultraviolet curable adhesive into the capillary as described above, the connection operation of the pair of fibers can be performed extremely easily.
[0020]
As the adhesive, it is preferable to use an adhesive having a refractive index after curing equal to or less than the refractive index of the core of the fiber (photonic crystal fiber or optical fiber).
[0021]
This is because, in the present invention, the connection end faces are connected via an adhesive, and if the refractive index of the adhesive is higher than the refractive index of the core portion, the signal light is reflected at the connection end face of the fiber. This is because the connection loss increases.
[0022]
According to a second aspect of the invention, at least one fiber has a core portion formed as a center of the fiber and having a solid shape, and a porous portion having a plurality of pores provided so as to surround the core portion and extending along the core portion. The present invention relates to a photonic crystal fiber connection structure in which a pair of fibers, which are photonic crystal fibers each including a portion, are connected to each other by a capillary.
[0023]
The connection structure of the photonic crystal fiber according to the second invention is such that the connection end faces of a pair of fibers inserted from both ends of the capillary are bonded with an adhesive in a state where the connection end faces are abutted with each other in the capillary. It is.
[0024]
By doing so, as described above, the butted connection end faces are adhered to each other with the adhesive, so that no air layer or the like is interposed between the connection end faces, and thus, the connection end faces Reflection is suppressed. Further, by not using the refractive index matching agent, it is possible to prevent the refractive index matching agent from entering the pores from the openings of the pores on the connection end face of the photonic crystal fiber. Further, the curing of the adhesive prevents the adhesive from penetrating deep into each pore of the photonic crystal fiber. Thus, a connection structure of a photonic crystal fiber in which an increase in connection loss is prevented is realized.
[0025]
【The invention's effect】
As described above, according to the present invention, when connecting the photonic crystal fibers, the connection end faces abutted in the capillary are adhered to each other with an adhesive, so that a refractive index matching agent is not required, and the photonic crystal is spliced by a mechanical splice. Also when connecting a crystal fiber, it is possible to prevent an increase in connection loss.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0027]
(Configuration of photonic crystal fiber)
FIG. 1 shows a terminal portion of the photonic crystal fiber 1. The photonic crystal fiber 1 is made of quartz, plastic, or the like, and has a core 71 serving as the center of the fiber, a porous portion 8 provided so as to surround the core 71, and a porous portion 8 surrounding the core 8. And a covering portion 72 provided.
[0028]
The core portion 71 is formed solid, and the signal light is transmitted through the core portion 71 in the longitudinal direction. The core 71 may be doped with a functional material such as germanium (Ge).
[0029]
In the porous portion 8, a plurality of pores 8a extending along the core portion 71 are formed around the core portion 71, and the plurality of pores 8a form a triangular lattice in the fiber cross section. The arrangement forms a photonic crystal structure in the fiber radial direction. The signal light is confined in the core 71 by the porous portion 8.
[0030]
Such a photonic crystal fiber 1 may be manufactured as follows. That is, first, a cylindrical support tube, a plurality of capillaries, and one rod-shaped core member are prepared. Then, a preform is manufactured by filling the support tube with a plurality of capillaries and one core member. At this time, the core member is arranged at the center axis position of the support tube.
[0031]
Next, the above preform is set in a drawing machine, heated at a high temperature, and stretched at a high speed to reduce the diameter (to form a fiber). At the time of drawing, the drawn photonic crystal fiber (bare fiber 11) is coated with a resin.
[0032]
(Structure of mechanical splice)
The mechanical splice according to the present embodiment includes the capillary 9. As shown in FIG. 2, the capillary 9 is made of, for example, glass, and has a hole 91 slightly larger than the diameter of the bare fiber 11 and at both ends in the longitudinal direction facing the end. The diameter is a tapered portion 92 whose diameter increases. The capillary 9 is not filled with a refractive index matching agent (matching oil).
[0033]
(Fiber connection procedure)
Next, a procedure for connecting the pair of photonic crystal fibers 1 by the capillary 9 will be described. When connecting a pair of photonic crystal fibers 1, first, the resin coating 12 at the tip of each photonic crystal fiber 1 is peeled off to expose the bare fiber 11.
[0034]
On the other hand, an ultraviolet curable adhesive is injected in advance at a substantially central position in the longitudinal direction of the capillary 9. This UV-curable adhesive preferably has a refractive index after curing equal to or less than the refractive index of the core 71 of the photonic crystal fiber 1.
[0035]
Then, the bare fibers 11 of the pair of fibers 1 and 1 are inserted from both ends of the capillary 9, and the connection end faces 13 and 13 of the two fibers 1 and 1 are butted together at a substantially central position in the longitudinal direction of the capillary 9. You. As a result, the ultraviolet curable adhesive adheres to and between the butted connection end faces 13 and 13.
[0036]
Next, ultraviolet light is irradiated from the outside of the capillary 9 toward the butting portion of the connection end faces 13, 13 butted in the capillary 9. As a result, the ultraviolet curable adhesive is cured, the connection end faces 13 of the pair of fibers 1 and 1 are adhered to each other, and the butted portion is fixed to the capillary 9. Thus, the connection of the fiber 1 is completed.
[0037]
As described above, according to the present embodiment, the connection end faces 13 and 13 of the pair of photonic crystal fibers 1 and 1 are butted with each other in the capillary 9, and the butted connection end faces 13 and 13 are bonded with an adhesive. Therefore, an air layer or the like does not intervene between the connection end face 13 and the connection end face 13, thereby suppressing reflection at the connection end face 13. Further, since the matching oil is not required, the matching oil is prevented from entering the fine holes 8a from the openings of the fine holes 8a in the connection end face 13 of the photonic crystal fiber 1. Further, the curing of the adhesive prevents the adhesive from penetrating deep into each of the pores 8a. Thus, even when the photonic crystal fiber 1 is connected by the capillary 9, an increase in connection loss can be prevented.
[0038]
Further, since the opening of each of the pores 8a on the connection end face of the photonic crystal fiber 1 is closed, moisture can be prevented from entering into each of the pores 8a even in a wet heat environment, and the transmission loss is reduced. Can also be suppressed.
[0039]
Further, when the photonic crystal fiber 1 is connected, the bare fiber 11 of the pair of fibers 1 is inserted into the capillary 9 by injecting an ultraviolet curable adhesive into the capillary 9 in advance. The connection of the fiber 1 is completed only by irradiating the fiber 1 with ultraviolet rays. Thus, the efficiency of the connection operation is improved.
[0040]
By setting the refractive index of the adhesive after curing to be equal to or less than the refractive index of the core 71 of the photonic crystal fiber 1, it is possible to suppress the reflection at the connection end face 13 of the photonic crystal fiber 1. it can. For example, when a fiber is connected by a capillary 9 using matching oil (refractive index: about 1.45), the return loss is about 60 to 70 dB, while the refractive index is about 1.425. When the fiber is connected by the capillary 9 using an adhesive, the return loss is about 40 dB, which is a practically acceptable level.
[0041]
In the above embodiment, the connection between the photonic crystal fibers 1 has been described, but the present invention is also applicable to the connection between the photonic crystal fiber 1 and an optical fiber having a core portion and a clad portion.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an end face of a photonic crystal fiber.
FIG. 2 is a cross-sectional view illustrating a fiber connection structure using a capillary.
[Explanation of symbols]
Reference Signs List 1 photonic crystal fiber 13 connection end face 71 core part 8 porous part 8a pore 9 capillary

Claims (4)

At least one of the fibers includes a core portion that is formed as a center of the fiber and is solid, and a porous portion that is provided so as to surround the core portion and has a plurality of pores extending along the core portion. A method for connecting a pair of fibers, each being a nic crystal fiber, to a photonic crystal fiber, wherein the pair of fibers is connected to each other using a capillary,
A butting step of inserting the pair of fibers from both ends of the capillary, and abutting the connection end faces of the fibers in the capillary,
And a bonding step of bonding the butted connection end faces with an adhesive. In claim 1,
The capillary is made of a transparent material, and the adhesive is an ultraviolet-curable adhesive,
Before the butting step, including an injection step of injecting the ultraviolet curing adhesive into the capillary,
In the bonding step, after the butting step, the ultraviolet curable adhesive is cured by irradiating ultraviolet rays from the outside of the capillary toward a butting portion where the connection end faces of the capillary are butted together. A method for connecting a photonic crystal fiber, comprising a step of bonding the connection end faces to each other. In claim 1,
A method for connecting a photonic crystal fiber, wherein an adhesive having a refractive index after curing equal to or lower than a refractive index of a core portion of the fiber is used. At least one of the fibers includes a core portion that is formed as a center of the fiber and is solid, and a porous portion that is provided so as to surround the core portion and has a plurality of pores extending along the core portion. A pair of fibers that are nick crystal fibers are a connection structure of photonic crystal fibers connected to each other by a capillary,
A connection structure for a photonic crystal fiber, wherein connection end faces of a pair of fibers inserted from both ends of the capillary are bonded with an adhesive in a state where the connection end faces abut each other in the capillary.

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