JP2002277647A - Method for manufacturing double clad fiber and double clad fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a double clad fiber 1 consisting of a core 11 which excitation light crosses with a high probability and improved in amplifi cation efficiency of signal light, and 1st clad 12 and 2nd clad 13. SOLUTION: The double clad fiber of which the 1st clad 12 is constituted of a 1st and 2nd layers is manufactured by drawing a preform 2 is prepared by a core part forming process for arranging a core rod 21a on an approximately center in a cylindrical support pipe 24, and a 2nd layer part forming process for disposing a 2nd layer rod 23a having a refractive index different from that of a 1st layer rod 22a in a closest state and then coating the preform 2 with resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a double-clad fiber having a core and first and second claddings.

[0002]

2. Description of the Related Art Conventionally, a double clad fiber used for a fiber laser or a fiber amplifier has been known. The double clad fiber is composed of a core made of SiO ₂ doped with an excitation light active material and a core surrounding the core. A first clad made of SiO ₂ covering the first clad and a second clad made of a resin covering the periphery of the first clad. In this double-clad fiber, while the signal light propagates in the core, the pump light for exciting the signal light propagates in the first clad, so that the pump light crosses the core every time the pump light crosses the core. The active substance is activated, and as a result, the signal light is amplified.

[0003]

By the way, a double clad fiber in which the boundary between the first clad and the second clad is formed in a circular shape concentric with the core in the cross section of the fiber, the pumping light propagating in the first clad. However, there is a problem that the excitation light-active substance is not activated because the laser beam orbits around the core and hardly crosses the core, so that signal light propagating in the core cannot be greatly amplified.

Therefore, in order to increase the probability that the pumping light crosses the core, a double clad fiber in which the boundary between the first clad and the second clad has a square cross section, for example, has been proposed. In this double-clad fiber, since the pump light is suppressed from circling around the core, the probability of crossing the core is higher than that of the double-clad fiber in which the boundary shape is formed in a circular shape. It will be improved.

However, even a double-clad fiber having a square boundary shape has a 45
Under the unique condition that the excitation light travels at an angle of °, there is a disadvantage that the excitation light goes around the core and hardly crosses the core.

In order to manufacture a double-clad fiber having a square boundary shape, a preform for forming a core and a first clad is formed so that the cross-sectional shape of the preform is substantially square. Need to be subjected to a grinding process, which is very complicated and increases the manufacturing cost.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a double-clad fiber in which pump light has a high probability of crossing the core, and thus has improved signal light amplification efficiency. It is to provide at low cost.

[0008]

According to a first aspect of the present invention, there is provided a core which extends in a central axis direction of a fiber and through which a signal light propagates, and which covers the periphery of the core and excites the signal light. A first cladding for propagating excitation light to be propagated, and a second cladding for covering the periphery of the first cladding; the first cladding covering a periphery of the core; and a covering of the periphery of the first layer. And a preform manufacturing step for manufacturing a preform for forming the core and the first clad, which is directed to a method for manufacturing a double-clad fiber constituted by a second layer having a different refractive index from the first layer. And a drawing step of heating and stretching the preform to draw a fiber, and a coating step of forming the second clad by coating the outer periphery of the drawn fiber with a resin. The method.

[0009] In the preform manufacturing step, at least one core rod is provided substantially at the center of the hole of the cylindrical support tube, thereby forming the core portion serving as the core. Forming a plurality of first-layer rods having a different refractive index from the support tube with a predetermined gap between the core portion in the hole of the support tube and the inner peripheral surface of the support tube. A first layer portion forming a first layer portion serving as a first layer of the first clad by disposing the first layer portion in a close-packed state; and an outer periphery of the first layer portion and an inner periphery of the support tube. A plurality of second-layer rods having the same refractive index as the support tube are arranged in a close-packed manner between the second tube and the support tube, so that the second layer serving as the second layer of the first clad together with the support tube is provided. And forming a second layer portion forming step of forming a portion. Here, it is preferable that the core is doped with an excitation light active substance activated by excitation light. For this purpose, a rod doped with the excitation light active substance may be used as the core rod. The excitation light active substance may be a rare earth element such as erbium (Er) or neodymium (Nd).

According to the first aspect of the present invention, since the first clad is composed of the first layer and the second layer having different refractive indices, the excitation light propagating in the first clad is formed by the first clad. When traveling from the layer to the second layer or from the second layer to the first layer, the light is refracted at the boundary due to the difference in refractive index between the two layers. Therefore, the pumping light propagates in the first cladding while forming an extremely random trajectory in the fiber cross section. As a result, the probability that the pumping light passes through the core is increased, and the signal light of the signal light propagating through the core is increased. The amplification efficiency is improved.

Here, the first layer and the second layer have different refractive indices from each other, and the difference between the refractive indices of the first and second layers is almost the same as that of the excitation light at the boundary between the two layers. The first layer may have a higher refractive index than the second layer, or the second layer may have a higher refractive index than the first layer, as long as it does not reflect light.

The boundary shape between the first layer and the second layer of the first cladding in the cross section of the fiber is not particularly limited, and may be, for example, a rectangle such as a square or an ellipse. . Furthermore, the boundary shape in the cross section of the fiber between the first clad and the second clad is not particularly limited. For example, the boundary shape may be a rectangle such as a square, an ellipse, or a circle. Good.

In the double clad fiber according to the present invention, a preform is manufactured by disposing the rods for the core and the first and second layers in a cylindrical support tube in the closest density. , By drawing and coating. This eliminates the need for grinding, which was required when manufacturing a conventional double-clad fiber, thereby reducing manufacturing costs. In addition, the first layer rod and the second layer rod are adjusted only by adjusting the arrangement positions of the first layer rod and the second layer rod in the support tube, and the first layer rod and the second layer rod are adjusted.
The shape of the boundary between the layer portion and the second layer portion can be formed in any shape. For example, if the shape of the boundary portion is formed into a polygonal shape such as a triangle or a square or an elliptical shape in the fiber cross section, the first layer and the second layer in the fiber cross section of the double clad fiber obtained by drawing this preform are drawn. The boundary shape between the two layers is formed in a polygonal shape such as the triangle or the square, an elliptical shape, or the like. For this reason, a double-clad fiber with improved signal light amplification efficiency can be manufactured at low cost.

According to the first aspect of the present invention, for example, in the preform manufacturing process, the boundary between the first layer portion and the second layer portion in the cross section of the preform includes the first layer portion. A mixed layer in which rods and second layer rods are alternately arranged along the boundary may be provided.

In the double clad fiber manufactured by the method according to the second aspect of the present invention, the first layer rod and the second layer rod are formed along the boundary between the first layer part and the second layer part. By alternately arranging preforms, the first
The boundary between the layer and the second layer is formed in a wave shape. Thereby, the trajectory of the pumping light propagating in the first clad composed of the first and second layers is further randomized, and as a result, the probability that the pumping light crosses the core is drastically improved.

According to a third aspect of the present invention, in the preform manufacturing step, the first layer portion is different from the first layer rod forming the first layer portion in the vicinity of the boundary with the second layer portion in the first layer portion. A different refractive index portion provided with at least one rod having a refractive index may be provided. Here, the rod having a refractive index different from that of the first layer rod may be, for example, a second layer rod.

In the double clad fiber manufactured by the method according to the third aspect of the present invention, a portion having a different refractive index from the first layer (a different refractive index portion) is provided in the first layer of the first clad. As a result, the excitation light is refracted at the different refractive index portion and proceeds. Thereby, the randomization of the trajectory of the excitation light is further promoted, and the probability that the excitation light crosses the core is dramatically improved.

Further, by providing the different refractive index portion in the vicinity of the boundary between the first layer and the second layer, randomization of the trajectory of the excitation light is further promoted. That is, for example, if the different refractive index portion is set near the core, the distance between the boundary between the first clad and the second clad and the different refractive index portion becomes wider. There is a possibility that the excitation light may circulate between the portions. Therefore, a different refractive index portion is provided near the boundary between the first layer portion and the second layer portion in the first layer portion of the preform, which is located at a position away from the core, so that the boundary between the first clad and the second clad has By narrowing the interval between the refractive index portions, it is possible to effectively refract the excitation light circling near the boundary between the first cladding and the second cladding at the different refractive index portions. Thus, randomization of the trajectory of the excitation light is further promoted.

The fourth and fifth aspects of the present invention relate to a double-clad fiber. Specifically, the fourth aspect of the present invention relates to a core extending in a central axis direction of a fiber and transmitting a signal light. A double clad fiber including a first clad that covers the periphery of a core and through which pumping light that excites the signal light propagates, and a second clad that covers the periphery of the first clad. A first layer covering the periphery of the core; and a first layer covering the periphery of the first layer and covering the first layer.
And a second layer having a different refractive index from the layer.

It is a specific matter that the boundary between the first layer and the second layer of the first cladding in the fiber cross section is formed in a wave shape.

According to the fourth aspect of the present invention, the excitation light propagating in the first clad while being refracted at the boundary between the first layer and the second layer having different refractive indices is formed by the first layer and the second layer. Is formed in a wave shape, and propagates in the first clad while forming an extremely random trajectory. As a result, the probability that the pump light crosses the core is greatly improved, and the efficiency of amplifying the signal light of the double clad fiber is greatly improved.

According to a fifth aspect of the present invention, there is provided a core which extends in the central axis direction of the fiber and through which the signal light propagates, a first clad which covers the periphery of the core and through which the pump light for exciting the signal light propagates, A double clad fiber having a second clad covering the periphery of the first clad;
The clad includes a first layer covering the periphery of the core and a second layer covering the periphery of the first layer and having a different refractive index from the first layer.

The first section of the first cladding in the cross section of the fiber is located near the boundary with the second layer in the first layer.
It is a specific matter to form a different refractive index portion having a different refractive index from the layer. Here, the refractive index of the different refractive index portion may be the same as the refractive index of the second layer.

According to the fifth aspect of the present invention, a different refractive index portion having a different refractive index from the first layer is formed in the first layer of the first cladding near the boundary with the second layer. The excitation light is refracted at the different refractive index portion. Thereby, the first
The randomization of the trajectory of the excitation light propagating in the clad is further promoted, and the probability that the excitation light crosses the core is dramatically improved.

[0025]

As described above, according to the double clad fiber of the present invention, the first clad is composed of the first layer and the second layer having different refractive indices from each other. The excitation light thus refracted at the boundary between the first and second layers of the first clad when traveling from the first layer to the second layer or from the second layer to the first layer due to a difference in refractive index between the two layers. Thereby, the pumping light can be propagated in the first clad while forming an extremely random trajectory in the fiber cross section. As a result, the probability that the pumping light passes through the core is increased, and the pumping light propagates through the core. The amplification efficiency of the signal light can be improved. In addition, the first layer and the second layer
A boundary with the layer is formed in a wave shape in the cross section of the fiber, or a different refractive index portion having a different refractive index from the first layer is formed in the first layer near the boundary with the second layer. This makes the trajectory of the excitation light more random,
As a result, the amplification efficiency of the signal light propagating through the core can be greatly improved.

A preform for producing the above-mentioned double clad fiber is produced simply by disposing the rods for the core and the first and second layers in the cylindrical support tube in the closest density. Therefore, the fabrication is easy, and the cross-sectional shape of the boundary between the first layer portion and the second layer portion can be formed in an arbitrary shape. Thus, the manufacturing cost of the double-clad fiber can be reduced, and a double-clad fiber with improved amplification efficiency of the signal light propagating through the core can be provided at low cost. In addition, the first in the double clad fiber
Since the cross-sectional shape of the boundary between the layers and the second layer and the different refractive index portion are formed only by adjusting the arrangement positions of the first and second layer rods, the amplification efficiency of the signal light is significantly increased. An improved double clad fiber can be manufactured at low cost.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 shows a cross section of a double clad fiber 1 according to a first embodiment of the present invention.
This is composed of a core 11 through which signal light propagates, and a core 1
The first cladding 12 covers the periphery of the first cladding 12 and in which the pumping light for exciting the signal light propagates, and the second cladding 13 covers the periphery of the first cladding 12.

The core 11 is a single mode core made of SiO ₂ , and is disposed so as to extend substantially in the center of the fiber in the direction of the central axis of the fiber. The core 11 has Ge so as to have a higher refractive index than the first clad 12.
And a rare earth element (for example, Er, Yb, Nd, or the like) which is an excitation light active material so that the signal light propagating in the core 11 is amplified by the excitation light propagating in the first clad 12. Is doped.

The first clad 12 covers the periphery of the core 11 and extends in the direction of the central axis of the fiber. The cross-sectional shape of the first clad 12 is 125 μm, which is the same as the outer diameter of an ordinary communication optical fiber. Is formed in a circular shape.
The first cladding 12 includes a first layer 12a that covers the outer periphery of the core 11 inside the fiber radial direction and a second layer 12a that covers the outer periphery of the first layer 12a outside the fiber radial direction.
b. The first layer 12a is made of SiO ₂
In order to make the refractive index lower than that of the core 11, a relatively low concentration of Ge is doped, and pure SiO
_The refractive index is higher than ₂ . On the other hand, the second layer 1
2b is also made of SiO ₂ , but is made of pure SiO ₂ so as to have a different refractive index from the first layer 12a. Thereby, the refractive index of the second layer 12b becomes the first layer 1
2a. A boundary 16 between the first layer 12a and the second layer 12b is formed in a substantially square shape in the cross section of the fiber, and each side of the square is formed in a wavy shape (see a dashed line in the figure). The boundary 1
The shape of the cross section of the fiber 6 is not limited to the square shape shown in FIG. 1, but may be a polygonal shape such as a hexagonal shape or an elliptical shape.

The second clad 13 is disposed so as to extend in the central axis direction of the fiber while covering the outer periphery of the first clad 12. The second clad 13 is formed of an ultraviolet-curable resin. Thus, the refractive index is significantly lower than that of the second layer 12b of the first clad.

Next, a method of manufacturing the double clad fiber 1 will be described with reference to FIG. FIG.
Are the core of the double clad fiber 1 and the first clad 1
2 shows a preform 2 for forming the preform 2, wherein the double-clad fiber 1 is a preform producing step for producing the preform 2, and drawing is performed by heating and stretching the preform 2 to draw a fiber. Process and
A coating step of coating the outer periphery of the drawn fiber with an ultraviolet curable resin in the drawing step. Since the preform 2 is symmetric, the right half of the preform 2 is not shown in FIG.

First, the preform manufacturing process will be described. A cylindrical support tube 24 made of pure SiO ₂ and having a substantially circular cross section is prepared, and a round bar-shaped SiO ₂ core is formed substantially in the center of the support tube 24. One of the rods 21a is provided to form a core portion that becomes the core 11 of the double clad fiber 1 (core portion forming step). The core rod 21a is preferably made of a material doped with Ge or the like which increases the refractive index and the rare earth element in advance. Further, the core portion may be formed by arranging a plurality of core rods 21a at a substantially center in the support tube 24 in a close-packed manner.

Next, a predetermined gap is formed around the outer periphery of the core rod 21a in the support tube 24 from the inner peripheral surface of the support tube 24 to form a round rod-shaped first layer rod 22a made of SiO ₂ 22a. Are arranged in a close-packed manner so that the first layer 12a of the first clad of the double-clad fiber 1 is formed.
Is formed (first layer portion forming step).
At this time, the first cladding rod 22a is disposed such that the first layer portion 22 has a substantially square shape in a cross section of the fiber. It should be noted that the first layer rod 22a may be one doped with Ge at a relatively low concentration.

The first tube in the support tube 24
And the surrounding layer portion 22, between the inner peripheral surface of the support tube 24, the SiO ₂ manufactured by the second layer for the rod 23a of the rod-shaped by a plurality of arranged, the first of the double clad fiber 1
The first layer portion 23 which becomes a part of the second layer 12b of the clad is formed (second layer portion forming step). The second layer rod 23
a it may be used made of pure SiO _2.

As shown in FIG. 3, the boundary S between the first layer portion 22 and the second layer portion 23 has the first
A mixed layer 25 in which the layer rods 22a and the second layer rods 23a are alternately arranged along the boundary S is provided.

Thus, each of the core rod 21a and the first and second layer rods 22a and 23a is
The preform 2 provided in the preform 4 is produced (preform production step). There is no limitation on the order of the core part forming step, the first layer part forming step, and the second layer part forming step.

Then, the preform 2 is heated and drawn in a drawing furnace (not shown) to form a fiber (drawing step). As a result, the first and second layer rods 22a and 23a are fused together and the first clad 12
Of the first layer 12a and a part of the second layer 12b, and the core rod 21a forms the core 11. In addition, the support pipe 24 is provided with the second layer 12b.
Form part of Then, the outer periphery of the drawn fiber is coated with an ultraviolet curable resin to form the second clad 13 (coating step), and the double clad fiber 1 shown in FIG. 1 is manufactured.

In the double clad fiber 1 according to the present embodiment, the first clad 12 has the first clad 12 having different refractive indexes.
Excitation light propagating in the first cladding 12 is formed by the first layer 1a and the second layer 12b.
When traveling from 2a to the second layer 12b or from the second layer 12b to the first layer 12a, the light is refracted at the boundary due to the difference in the refractive index between the two layers 12a and 12b. Therefore, the pumping light propagates in the first clad 12 while forming an extremely random trajectory in the fiber cross section. As a result, the probability that the pumping light passes through the core 11 is increased, and the pumping light propagates through the core 11. The amplification efficiency of the signal light can be improved. In particular, the first layer 12a and the second layer 12b
Is formed in a wave shape, so that the trajectory of the pumping light propagating in the first clad 12 is further randomized. As a result, the probability that the pumping light crosses the core 11 is dramatically improved. Can be done.

The boundary shape between the first clad 12 and the second clad 13 in the cross section of the fiber is a circular shape having a diameter of 125 μm, which is the same as the outer diameter of a normal optical fiber for communication. The heat capacity of the clad fiber 1 and the optical fiber for communication and the molten state when heated are the same. Accordingly, when the double-clad fiber 1 and the communication optical fiber are fusion-spliced, the flow of the glass at the time of heating and melting is prevented, and the cores of the two fibers are not axially displaced.
Both fibers can be connected with low loss. Further, since the outer diameter difference between the double clad fiber 1 and the optical fiber for communication is relatively small, it is not necessary to change the structure of the V-block used for axial alignment when connecting the two fibers.

The double clad fiber 1 according to the present invention has a rod 21 for a core and a first and a second layer 21.
a, 22a, and 23a are each replaced with a cylindrical support tube 24.
The preform 2 is manufactured only by arranging the preform 2 at a predetermined position in a close-packed state, and the preform 2 is manufactured by drawing and resin coating. For this reason, the manufacturing cost of the double clad fiber 1 can be reduced.

The cross-sectional shape of the boundary 16 between the first layer 12a and the second layer 12b of the double clad fiber 1 is as follows:
The shape of the boundary portion S between the first layer portion 22 and the second layer portion 23 in the preform 2 is determined.
The shape of the boundary portion S between the layer portion 22 and the second layer portion 23 is the first shape.
An arbitrary shape can be formed only by adjusting the arrangement of the layer and the second layer rods 22a and 23a. Also,
The wave shape at the boundary 16 between the first layer 12a and the second layer 12b in the double clad fiber 1 is the same as the boundary S between the first layer 22 and the second layer 23 in the preform 2 and the first layer. Rod 22a and second layer rod 23
This is formed only by providing the boundary layer 25 in which “a” and “a” are alternately arranged. For this reason, the double-clad fiber 1 in which the probability that the pumping light crosses the core 11 is further increased can be manufactured at extremely low cost.

<Second Embodiment> FIG. 4 shows a double clad fiber 3 according to a second embodiment of the present invention, which comprises a second layer 1 in a first layer 12a of a first clad.
Near the boundary 17 with the second layer 12b, the second layer 12b of the first clad
Forming the different refractive index portion 12c having the same refractive index as that of the first layer 12a and the boundary 17 between the first layer 12a and the second layer 12b.
However, the difference from the first embodiment is that the height difference is smaller than the corrugated unevenness at the boundary 16 of the first embodiment. Other configurations are the same as those in the first embodiment, and thus the same members are denoted by the same reference numerals and description thereof will be omitted.

Next, a method for manufacturing the double clad fiber 3 according to the second embodiment will be described with reference to FIG. Note that the right half of the preform 4 is not shown in FIG.

The rod-shaped core rod 21a and the first and second layer rods 2a are provided in a cylindrical support tube 24.
A preform manufacturing step of manufacturing the preform 4 by disposing the preforms 4a and 3a in a close-packed state; a drawing step of drawing the preform 4; and an ultraviolet-curing resin around the drawn fiber. The point of having a coating step of coating is the same as in the first embodiment,
The arrangement positions of the first and second layer rods 22a and 23a arranged in the preform manufacturing process are different from those of the first embodiment.

That is, the preform 4 according to the second embodiment has a round bar-shaped Si
A single core rod 21a made of O _{2 is} provided to form a core portion that becomes the core 11 of the double clad fiber 3 (core portion forming step). The support tube 24 is provided around the outer periphery of the core rod 21a in the support tube 24.
A plurality of round rod-shaped first layer rods 22a made of SiO ₂ are arranged in a close-packed manner with a predetermined gap from the inner peripheral surface of the first clad of the double clad fiber 3 to form a first clad.
A first layer portion 22 to be the layer 12a is formed (first layer portion forming step). At this time, the first cladding rod 22a
Are arranged such that the first layer portion 22 has a substantially square cross section. Also, the second layer portion 23 in the first layer portion 22
Specifically, one rod 23a for the second layer is disposed near each of the four corners of the first layer portion 22 having a substantially square cross section. A different refractive index portion to be the different refractive index portion 12c of the double clad fiber 3 is formed.

Next, between the periphery of the first layer portion 22 in the support tube 24 and the inner peripheral surface of the support tube 24, a plurality of rod-shaped second rods 23a made of SiO ₂ are formed. By disposing the first layer portion 23, the first layer portion 23 to be the second layer 12b of the first clad is formed (second layer portion forming step). At this time, as shown in FIG. 6 in an enlarged manner, only the first layer rod 22a is arranged in the closest position on one side of the boundary portion S, and the first layer rod 22a is disposed on the other side of the boundary portion S. Double-layer rod 23
The first layer rods 22a and the second layer rods 23a are individually arranged so that only the a is arranged in the closest density, and the boundary portion S is formed.

Thus, the preform 4 in which the core rod 21a and the first and second layer rods 22a and 23a are disposed in the support tube 24 is manufactured (preform manufacturing step). In addition, the core part forming step,
The order in which the first layer portion forming step and the second layer portion forming step are performed is not limited.

The double clad fiber 3 shown in FIG. 4 is manufactured by subjecting the preform 4 thus obtained to a drawing step and a coating step.

The double clad fiber 3 according to the second embodiment has a different refractive index from the first layer 12a in the first layer 12a of the first clad (having the same refractive index as the second layer 12b). Since the different refractive index portion 12c is formed, the excitation light propagating in the first clad 12 is refracted in the different refractive index portion 12c. Thereby, the randomization of the trajectory of the excitation light is further promoted, and the probability that the excitation light crosses the core 11 can be improved. Further, the different refractive index portion 12c is formed in the first layer 12a near the boundary 17 with the second layer 12b, and the different refractive index portion 12c and the boundary between the first clad 12 and the second clad 13 are formed. By narrowing the gap between the first cladding 12 and the second cladding 13, the pumping light circling near the boundary between the first cladding 12 and the second cladding 13 can be effectively refracted by the different refractive index portion 12 c. Thus, the randomization of the trajectory of the excitation light can be further promoted.

Further, the preform manufacturing step includes the steps of:
And first and second layer rods 22a, 23a, 24a
Are simply arranged in the support tube 24, so that the different refractive index portion 12c of the double clad fiber 3
Also, in the preform manufacturing step, the first layer 22
In the vicinity of the boundary with the second layer portion 23, it is only necessary to provide a different refractive index portion in which one second layer rod 23a forming the second layer portion 23 is provided, and the different refractive index portion is provided. 12
The production of c can be performed very easily. As a result, the double clad fiber 3 can be manufactured at low cost.

<Other Embodiments> It should be noted that the present invention is not limited to the above-described embodiments, but includes various other embodiments. That is, in the above embodiment, the first-layer rod 22a and the second-layer rod 23a are each in the form of a round bar. However, the present invention is not limited to this. For example, as shown in FIG. , 23
b may be used. When the first-layer rod 22b or the second-layer rod 23b having such a regular hexagonal cross-sectional shape is provided in the support tube 24, the first-layer rod 22b or the second-layer rod 23b is What is necessary is just to arrange in order so that side surfaces may contact mutually. In this case, the first layer rods 22b and the like can be disposed without forming a gap between the adjacent first layer rods 22b and the like. The first layer rod 22b and the second layer rod 23 are provided at the boundary S between the first layer part 22 and the second layer part 23.
b are mixed layers 25 alternately arranged along the boundary S
May be provided. As shown in FIG. 8, only the first-layer rod 22b is arranged in the closest place on one side of the boundary S, and the second-layer rod is disposed on the other side of the boundary S. The first layer rod 22b and the second layer rod 23b may be individually arranged to form the boundary portion S, such that only the second layer 23b is arranged in the closest density.

Further, in the double clad fiber 1 according to the first embodiment, the boundary between the first layer 12a and the second layer 12c is formed in a wavy shape in the cross section of the fiber, and the different refractive index portion 12c is formed as in the second embodiment. Although not provided, the double-clad fiber 1 according to the first embodiment may be provided with a different refractive index portion 12c.

[0054]

Next, an embodiment in which a double clad fiber is manufactured by the manufacturing method according to the present invention will be described.

<First Example> A first example is an example in which the double clad fiber 1 according to the first embodiment is manufactured (see FIGS. 1 and 2). Was used.

Support tube: φ25 mm × 1 t × 300 mmL core rod (specific refractive index difference Δ1.0% with respect to SiO ₂₎
(Ge-doped) and Yb-doped (10000 pp)
m)): φ1 mm × 300 mmL Rod for first layer (Δ0.5% (Ge-doped)): φ1 m
mx 300mmL Rod for second layer (Δ0.0%): φ1mm x 300mm
L Then, as shown in FIG. 2, one core rod 21a is disposed substantially at the center of the support tube 24 to form a core portion, and the first layer rod 21a is formed around the core rod 21a. The first layer portion 22 was formed by arranging the first layers 22a in a close-packed manner so as to have a substantially square cross section. Further, the second layer rod 23a was arranged between the first layer part 22 and the support tube 24 in the closest density to form the second layer part 23. At this time, the first layer rods 22a and the second layer rods 23a are alternately arranged along the boundary portion S at the boundary portion S between the first layer portion 22 and the second layer portion 23. A mixing section 25 was provided.

As shown in FIG. 9, tubular auxiliary pipes 5 and 5 were respectively attached to both ends of the preform 2 thus manufactured, and these were set on a lathe and subjected to chlorination (flow rate 50 sccm, 1000 ° C., 1000 ° C.). 1hr), and
A gauge pressure of -53 kPa (-4
After reducing the pressure to 00 mmHg, the end openings of the auxiliary pipes 5 were sealed.

Then, the preform 2 on which the auxiliary pipe 5 was attached was subjected to a drawing process to produce a fiber having an outer diameter of 125 μm. Further, the outer surface of the fiber was coated with an ultraviolet curable resin (a relative refractive index difference with respect to SiO ₂ -4.0%) to produce a double clad fiber 1.

<Second Example> A second example is an example in which the double clad fiber 3 according to the second embodiment is manufactured (see FIGS. 4 and 5). Was used.

Support tube: φ25 mm × 1 t × 300 mmL Core rod (Δ1.0% (Ge doped), Yb doped (10000 ppm)): φ1 mm × 300 mmL First layer rod: (Δ0.5% (Ge doped)) : Φ1
mm × 300mmL Rod for second layer: (Δ0.0%): φ1mm × 300m
mL The core rod 21a is disposed substantially at the center of the support tube 24 to form a core portion, and the first layer rod 22a is formed so as to have a substantially square cross section around the core rod 21a. By disposing the first layer portion 22
Was formed. At this time, one rod 23a for the second layer was disposed near each of the four corners in the first layer portion 22 having a substantially square cross section to form a different refractive index portion.

The first layer 22 and the support tube 2
The second layer portion 23 was formed by disposing the second layer rod 23 a between the inner layer 4 and the inner peripheral surface of the second layer portion 23. At this time, the first layer 2
The first layer rod 22a and the second layer rod 23a were individually provided without providing the mixed layer 25 at the boundary S between the second layer part 23 and the second layer part 23.

Auxiliary pipes 5 and 5 were attached to both ends of the preform 4 thus produced (see FIG. 9), set on a lathe and chlorinated (flow rate 50 scc).
m, 1000 ° C., 1 hr) and the above support tube 2
The inside of each of the auxiliary pipes 5 was sealed by reducing the pressure in the sample 4 to −53 kPa (−400 mmHg) with a gauge pressure. The preform 4 is formed by wire drawing to have an outer diameter of φ125 μm.
m, and a UV-curable resin (differential refractive index difference with respect to SiO ₂ -4.0%) was coated on the fiber to produce a double-clad fiber 3.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a double clad fiber according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a preform of the double clad fiber according to the first embodiment.

FIG. 3 is an enlarged sectional view showing a boundary portion between a first layer portion and a second layer portion.

FIG. 4 is a cross-sectional view showing a double clad fiber according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a preform of a double clad fiber according to a second embodiment.

FIG. 6 is a view corresponding to FIG. 3, showing a boundary portion between the first and second layers.

FIG. 7 shows a first example in which a rod having a regular hexagonal cross section is used.
FIG. 3 showing an example in which a mixed layer is provided at the boundary between the first and second layers.
FIG.

FIG. 8 shows a first example in which a rod having a regular hexagonal cross section is used.
FIG. 4 is a view corresponding to FIG. 3 showing a boundary portion between the first and second layers.

FIG. 9 is a longitudinal sectional view showing a preform to which an auxiliary pipe is attached.

[Explanation of symbols]

 1,3 Double clad fiber 2,4 Preform 11 Core 12 First clad 13 Second clad 22 First layer part 23 Second layer part 24 Support tube 25 Mixed layer 12a First layer 12b Second layer 12c Different refractive index part 21a Core rod (core part) 22a First layer rod 23a Second layer rod (different refractive index part) S Boundary part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Minoru Yoshi ▼ 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Co., Ltd. Itami Works F-term (reference) 2H050 AA09 AA11 AB05Z AC03 AC13 AC36 5F072 AB07 AK06

Claims (5)

[Claims] 1. A core extending in a central axis direction of a fiber, through which a signal light propagates, a first cladding that covers the periphery of the core, and through which an excitation light that excites the signal light propagates, and a first cladding that surrounds the first cladding. A first layer covering the periphery of the core, and a second layer covering the periphery of the first layer and having a different refractive index from the first layer. A method for producing a double-clad fiber, comprising: a preform producing step of producing a preform for forming the core and the first clad; and a drawing step of heating and stretching the preform to draw a fiber. A coating step of forming the second clad by coating the outer periphery of the drawn fiber with a resin, wherein the preform manufacturing step includes: A core portion forming step of forming a core portion serving as the core by disposing at least one core rod; and an inner peripheral surface of the support tube around the core portion in a hole of the support tube. A first layer portion that becomes a first layer of the first clad by arranging a plurality of first layer rods having a refractive index different from that of the support tube in a close-packed manner with a predetermined gap. Forming a first layer portion; and forming a first layer portion between an outer periphery of the first layer portion and an inner peripheral surface of the support tube.
By arranging a plurality of second layer rods having the same refractive index as that of the support tube in a close-packed state, a second layer portion forming the second layer of the first clad together with the support tube is formed. A method for producing a double-clad fiber, comprising a step of forming a layer portion. 2. The preform manufacturing process according to claim 1, wherein the first layer rod and the second layer rod are provided at a boundary between the first layer and the second layer in the cross section of the preform. A method of manufacturing a double-clad fiber, comprising providing mixed layers alternately arranged along a portion. 3. The method according to claim 1, wherein, in the preform manufacturing step, the first layer is formed near a boundary between the first layer and the second layer.
A method for manufacturing a double-clad fiber, comprising providing a different refractive index portion provided with at least one rod having a different refractive index from the layer rod. 4. A core extending in the direction of the central axis of the fiber, through which a signal light propagates, a first cladding that covers the periphery of the core, and through which pumping light for exciting the signal light propagates, and a first cladding that covers the periphery of the first cladding. A double-clad fiber comprising two clads, wherein the first clad includes a first layer covering a periphery of the core,
A second layer covering the periphery of the first layer and having a different refractive index from the first layer; and a first layer and a second layer of the first clad in a fiber cross section.
A double-clad fiber, wherein the boundary with the layer is formed in a wave shape. 5. A core extending in the direction of the central axis of the fiber, through which a signal light propagates, a first cladding that covers the periphery of the core and through which pumping light for exciting the signal light propagates, and a first cladding that covers the periphery of the first cladding. A double-clad fiber comprising two clads, wherein the first clad includes a first layer covering a periphery of the core,
A second layer covering the periphery of the first layer and having a refractive index different from that of the first layer, wherein a section of the fiber in the first layer of the first clad near the boundary with the second layer in the first layer. 3. A double-clad fiber, wherein a different refractive index portion having a different refractive index from the first layer is formed.