JP2003227944A - Doubly clad fiber and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a doubly clad fiber in which the productivity is excellent, the amounts of wasted first clad material and necessary second clad material are small, further, a fracture of the corner part of the first clad does not become a start point of a clack generation. <P>SOLUTION: The doubly clad fiber 10 is provided with a core 11 which serves as an optical waveguide in which an optical amplifying component is doped, the first clad 12 which is given so as to coat a core 11, and the second clad 13 which is given so as to coat the first clad. The first clad 12 is so formed that the outer shape at the section of the fiber is made by removing bow-shaped parts from a circular form along the circumference of the circle with intervals. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a core forming an optical waveguide doped with an optical amplification component, a first cladding provided so as to cover the core, and a first cladding provided so as to cover the first cladding. The excitation light incident on the first cladding propagates in the region surrounded by the second cladding while being repeatedly reflected at the interface between the first cladding and the second cladding. The present invention relates to a double-clad fiber configured to activate an optical amplification component of the core when passing through the core, and to amplify the light guided by the activated optical amplification component, and a manufacturing method thereof.

[0002]

2. Description of the Related Art A double-clad fiber is known as an optical fiber used for a core-pumped and core-outputted fiber laser. This double-clad fiber is composed of a core forming the center of the fiber, a first clad having a relatively high refractive index provided so as to cover the core, and a relatively provided first clad having a relatively high refractive index. The second cladding having a low refractive index is provided, and the excitation light incident on the first cladding propagates in the region surrounded by the second cladding while being repeatedly reflected at the interface between the first cladding and the second cladding. , When the excitation light passes through the core, the rare earth element such as Nd or Er which is doped in the core is made into an inverted distribution state excited by outermost shell electrons, and the light guided through the core is amplified by the stimulated emission. Is.

However, when the outer shape of the first clad in the cross section of the fiber is a circle concentric with the core,
The excitation light propagating in the region surrounded by the clad circulates around the core and hardly passes through the core.
There is a problem that the rare earth element doped in the core cannot be sufficiently in an inverted distribution state, and the light guided in the core cannot be greatly amplified.

As a solution to this problem, a double clad fiber structure is known in which the outer shape of the first clad in the cross section of the fiber is square.

Japanese Patent No. 2781399 discloses a double clad fiber structure in which the outer shape of the first clad in the cross section of the fiber is rectangular.

[0006]

By the way, when manufacturing a double-clad fiber, it is usually necessary to fabricate a preform whose outer shape is substantially similar to that of the first clad and to draw the preform. Manufactured by. Then, in the double clad fiber in which the outer shape of the first clad in the cross section of the fiber is rectangular,
A preform is produced by polishing a cylindrical rod material, but since the polishing amount of the cylindrical rod material is large, the productivity is low, and the wasteful first clad material is increased and the required second clad material is increased. In addition, since the corners of the preform are likely to be damaged, there is a problem that it may become a starting point of crack generation after being formed into a fiber.

The present invention has been made in view of the above points, and it is an object of the present invention that the productivity is good and the wasteful first clad material and the necessary second clad material are small. Another object of the present invention is to provide a double-clad fiber and a method for manufacturing the same, in which a defect in a corner portion of the first cladding does not become a starting point of crack generation.

[0008]

According to the present invention, the outer shape of the first clad in the fiber cross section is formed by removing a circular arc from the circular shape at intervals along the circumference thereof.

Specifically, a core forming an optical waveguide doped with an optical amplification component, a first clad provided so as to cover the core, and a first clad provided so as to cover the first clad. The excitation light incident on the first clad propagates in a region surrounded by the second clad while repeating reflection at the interface between the first clad and the second clad. Presupposes a double-clad fiber configured to activate an optical amplification component of the core as it passes through the core, and the activated optical amplification component amplifies light guided through the core. . The first clad is characterized in that the outer shape in the cross section of the fiber is formed in a shape in which an arcuate shape is removed from the circular shape at intervals along the circumference thereof.

According to the above construction, the outer shape of the first clad in the cross section of the fiber is formed by removing the arcuate shape from the circular shape at intervals along the circumference, so that the rod material is polished or the like. When making a preform,
As the outer shape is formed in a rectangular shape, the amount of removal from the cylindrical rod material by polishing or the like is unnecessary, so that the productivity is good, and the waste of the first clad material is small, and the required second clad material is required. The amount of clad material is also small, and the corners are not formed on the preform, and the corners are not damaged and become the starting point of crack generation after forming a fiber.

Further, in the double clad fiber having a square or polygonal outer shape in the cross section of the first clad, since the surface tension tends to cause twisting and deformation during the drawing process at the time of manufacture, the outer shape is It is not possible to draw the wire while monitoring the (diameter), and it is difficult to draw the core so that the core is positioned in a predetermined center, for example. However, according to the double-clad fiber of the present invention, the first clad shape, that is, the outer shape of the first clad in the cross section of the fiber is formed into a shape in which the arcuate shape is removed from the circular shape along the circumferential direction to form the outer shape. Since the arcuate portion remains, the surface tension at the time of wire drawing is relatively stable, and it becomes easy to position the core in a predetermined center for wire drawing.

The double-clad fiber of the present invention has a core forming portion which becomes the core and a first cladding forming portion which covers the core forming portion and becomes the first cladding. A preparatory step of preparing a reform, and a drawing step of performing a drawing process of heating and stretching the preform to reduce its diameter, wherein the preform has a circular outer shape in a cross section thereof. Can be manufactured by forming the arc shape into a shape in which arcuate shapes are removed at intervals along the circumference.

By the way, as a technique for suppressing the generation of a component of the excitation light propagating in the region surrounded by the second cladding, which circulates around the core, Japanese Patent No. 3039993 discloses that the fiber crosses the first cladding. A structure of a double-clad fiber in which the outer shape of the surface is formed into a non-rectangular or convex polygonal shape is disclosed. Also, Japanese Patent Laid-Open No. 9-1942
Japanese Laid-Open Patent Publication No. 25 discloses a double clad fiber structure in which the outer shape of the first clad in the cross section of the fiber is formed in a non-geometrical shape. Then, when connecting the double-clad fiber and a general optical fiber, usually, the connection ends of both fibers are melted and spliced,
In the double clad fiber in which the outer shape of the first clad in the cross section of the fiber is formed in a non-geometrical shape, the shape change in the fiber radial direction of the first clad when the splicing end is melted is anisotropic due to the effect of surface tension. Has sex
As a result, the position of the core deviates from the center, and there is a problem that fiber connection work becomes difficult.

On the other hand, according to the present invention, the core may be provided so as to be disposed at the position of the center of gravity of the outer shape of the first clad in the cross section of the fiber. According to this configuration, when the connection end is melted, the shape change of the first cladding in the radial direction of the fiber has anisotropy due to the effect of surface tension when the connection end is melted. Since the movement of the core arranged at the position of the center of gravity in the cross section of the fiber is small, the workability of the fiber connection work is improved.

In this case, the outer shape of the first clad in the cross section of the fiber may have a rotational symmetry. According to this structure, the degree of anisotropy of the shape change of the first cladding in the radial direction of the fiber when the connection end is melted is reduced, so that the movement of the core becomes smaller and the workability of the fiber connection work is improved. It will be better.

The present invention may be arranged such that the outer shape of the first clad in the cross section of the fiber is formed into a substantially rectangular shape having four arcs. When connecting a double-clad fiber to an ordinary optical fiber, the cores are generally abutted against each other while observing the side surface, but the core position is visually confirmed by observing the side surface depending on the outer shape of the cross section of the first clad. However, when the outer shape is a substantially rectangular shape, the visibility of the position of the core is excellent, so that the workability of the fiber connection work is improved.

[0017]

As described above, according to the present invention,
Since the outer shape of the first clad in the cross section of the fiber is formed by removing the arc shape along the circumference from the circle at intervals, the amount of removal by polishing or the like from the cylindrical rod material during manufacturing is small. The productivity is good and the amount of wasted first and second cladding materials is small, and it becomes the starting point of crack generation after the corners of the preform are missing and become fibers. There is no such thing. Moreover, since the circular arc portion remains in the outer contour of the fiber cross section of the first cladding, the surface tension during the drawing process during manufacturing is relatively stable, and the core can be positioned, for example, at a predetermined center for drawing. It will be easy.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a double clad fiber 10 according to an embodiment of the present invention.

This double-clad fiber 10 has a core 11 which is the center of the fiber, a first clad 12 provided so as to cover the core 11, and a second clad 13 provided so as to cover the first clad 12. And consists of.

The core 11 is made of germanium (Ge),
The optical waveguide is made of quartz (SiO ₂ ) doped with an optical amplification component such as erbium (Er). The outer shape of the core 11 in the cross section of the fiber is circular.

The first cladding 12 is made of pure quartz (SiO 2).
It is formed by ₂ ) and constitutes an excitation optical waveguide in which excitation light from an excitation light source is incident from an end face (not shown) and the excitation light propagates. The outer shape of the first clad 12 in the cross section of the fiber is formed into a substantially square shape by removing a concentric circle (for example, a diameter of 125 μm) from the core 11 and arcuate shapes having the same shape along the circumference of the core 11 at intervals. ing. That is, the outer shape of the first clad in the cross section of the fiber has the core 11 arranged at the center of gravity in the cross section of the fiber and has 90 ° rotational symmetry.

The second clad 13 constitutes a protective layer formed of, for example, an ultraviolet curable acrylic resin. The outer shape of the second clad 13 in the cross section of the fiber is formed in a circular shape concentric with the core 11.

The core 11, the first clad 12 and the second clad 13 have a structure in which the refractive index is higher from the inner side, and the excitation light incident on the first clad 12 is the second
The excitation light confined in the region surrounded by the clad 13 propagates by being repeatedly reflected at the interface between the first clad 12 and the second clad 13, and when passing through the core 11, light such as Er of the core 11 is transmitted. The amplification component is activated, and the activated optical amplification component amplifies the light guided through the core 11.

Next, a method of manufacturing the double clad fiber 10 will be described.

<Preparation Step> First, MCVD method, OV
A cylindrical rod made of quartz having a core forming portion 21 which becomes the core 11 at the central axis position as shown in FIG. 2A, in the same manner as in the known method of manufacturing a preform for optical fiber such as the D method and the VAD method. The material 200 is formed. At this time, the core forming portion 21 is doped with a predetermined element such as Ge or Er.

Then, as shown in FIG. 2 (b), the side surface of the cylindrical rod member 200 is polished to remove the circular cross section from the circular shape having the same arc shape at intervals along the circumference thereof. It is formed into a substantially square shape. At this time, from the viewpoint of productivity and reduction of the quartz material to be removed,
It is desirable to polish so that an arc of 50% or more of the circular circumference remains.

As described above, the core forming portion 21 whose outer cross-sectional shape is circular and the core forming portion 21 are formed.
The first clad forming portion 22 is formed so as to cover the above and is formed into a substantially square shape by removing the arcuate shape of the same shape from the circle in the cross section at intervals along the circumference thereof.
A preform 20 consisting of

<Drawing Step> The produced preform 20 is set in a drawing machine, and the preform 20 is drawn by heating to perform drawing processing for reducing the diameter. Here, the heating temperature of the drawing process is set so that the first cladding forming portion 22 becomes the first cladding 12 by the drawing process while the outer shape of the cross section is substantially maintained. Specifically, this temperature is the temperature on the lower limit side (1800 to 2000 ° C.) in the range of 1800 to 2100 ° C. which is the heating temperature for the drawing process when manufacturing an ordinary optical fiber. Therefore, at this time, the first cladding forming portion 22 keeps the outer shape of the first cladding 12 substantially unchanged.
Becomes That is, the first clad 12 is formed into a substantially square shape in which the outer shape of the first clad is substantially similar to that of the first clad forming portion and arcuate shapes of the same shape are removed at intervals along the circumference thereof. In addition, the core forming portion 21 includes the core 11
Is formed.

Next, an acrylic resin liquid added with a radical generator is attached to the surface of the drawn material, and it is cured by irradiating it with ultraviolet rays, and the first clad 1
2 A second clad 13 that covers and protects the surface is formed.

As described above, the core 11 at the center of the fiber, the first cladding 12 provided so as to cover the core 11, and the second cladding 13 provided so as to cover the first cladding 12. The double clad fiber 10 is manufactured.

According to the double-clad fiber 10 having the above-mentioned structure, the outer shape of the first clad 12 in the cross-section of the fiber is a circle in which the core 11 is a concentric circle, and an arcuate shape is removed at intervals along the circumference of the circle. Since it is formed on the pre-form 2
When 0 is manufactured, the polishing amount of the cylindrical rod member 200 is not required as much as the outer peripheral shape is rectangular, so that the productivity is good, and the waste of the first clad material is small and necessary. The amount of the second clad material to be used is also small, and the corner portion is not formed on the preform 20, and the corner portion is not damaged and becomes a starting point of crack generation after forming a fiber. Moreover, since the circular arc portion remains on the outer portion of the first clad 12 in the cross section of the fiber, the surface tension during the drawing process during manufacturing is relatively stable, and the core 11 can be easily positioned and drawn. Becomes

Further, since the outer shape of the first cladding 12 in the cross section of the fiber is such that the core 11 is arranged at the position of the center of gravity and it has 90 ° rotational symmetry, it is connected at the time of connection with a general optical fiber. The degree of anisotropy of the shape change of the first cladding 12 in the fiber radial direction due to the action of surface tension when the ends are melted is low, the movement of the core 11 is extremely small, and the workability of fiber connection work is good. Become.

Further, since the outer shape of the first clad 12 in the cross section of the fiber is formed into a substantially square shape having four arcs, the side surface of the core 11 can be observed at the time of connection with a general optical fiber. Since the visibility is excellent, the workability of the fiber connecting work is also improved in that respect.

In this embodiment, the first cladding 12
The outer shape of the cross section of the fiber is substantially square, but the shape is not particularly limited to this, and as shown in FIG. 3A, the first clad 32 may be a substantially equilateral triangle having 120 ° rotational symmetry. Alternatively, a substantially regular hexagonal one having 60 ° rotational symmetry may be used. Furthermore, FIG.
As shown in (b), if the outer shape of the first clad 42 in the cross-section of the fiber is a shape in which arcuate shapes are removed at intervals along the circumference from the circular shape, there is no rotational symmetry. May be

In the above embodiment, the core 12 is arranged at the center of gravity of the outer shape of the first clad in the cross section of the fiber and at the center of the fiber. However, the present invention is not limited to this, and the core is at the center of gravity. It may be absent or not at the center of the fiber.

[Brief description of drawings]

FIG. 1 is a perspective view of a double-clad fiber according to an embodiment of the present invention.

FIG. 2 is a perspective view of a cylindrical rod member and a preform.

FIG. 3 is a perspective view of a double-clad fiber according to another embodiment of the present invention.

[Explanation of symbols]

10, 30, 40 double clad fiber 11,31,41 core 12, 32, 42 1st clad 13, 33, 43 2nd clad 20 preform 21 core forming part 22 First clad forming part 200 cylindrical rod material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor ▲ Yoshi ▼ Minoru Ta             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Yoshihito Hirano             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Takayuki Yanagisawa             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Yasuharu Oyada             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F term (reference) 5F072 AB09 AK06 YY17

Claims (5)

[Claims] 1. A core forming an optical waveguide doped with an optical amplification component, a first clad provided so as to cover the core, and a second clad provided so as to cover the first clad. The excitation light incident on the first cladding propagates in the region surrounded by the second cladding while being repeatedly reflected at the interface between the first cladding and the second cladding, and the excitation light is transmitted to the core. A double-clad fiber configured to activate an optical amplification component of the core when passing through the optical fiber, and the activated optical amplification component amplifies light guided through the core, The clad is a double clad fiber characterized in that the outer shape in the cross section of the fiber is formed by removing a circular arc from the circular shape at intervals along the circumference thereof. 2. The double-clad fiber according to claim 1, wherein the core is provided so as to be disposed at a center of gravity of an outer shape in a fiber cross section of the first cladding. Double clad fiber. 3. The double clad fiber according to claim 2, wherein the outer shape of the first clad in the cross section of the fiber has rotational symmetry. 4. The double clad fiber according to claim 1, wherein the outer shape of the first clad in the cross section of the fiber is formed into a substantially rectangular shape having four arcs. 5. A core forming an optical waveguide doped with an optical amplification component, a first clad provided so as to cover the core, and a second clad provided so as to cover the first clad. The excitation light incident on the first clad propagates in a region surrounded by the second clad while being repeatedly reflected at an interface between the first clad and the second clad, and the excitation light is transmitted to the core. A method of manufacturing a double-clad fiber configured to activate an optical amplification component of the core when passing through, and the activated optical amplification component is configured to amplify light guided through the core, A preparatory step of preparing a preform having a core forming part to be the core and a first clad forming part to be the first clad provided so as to cover the core forming part; and heating the preform. Stretched to a small diameter And a wire drawing step for applying a wire drawing process, wherein the outer shape of the cross-section of the preform is formed in a shape in which arcuate shapes are removed from the circle at intervals along the circumference thereof. A method for producing a double-clad fiber which is a feature.