JP3827819B2 - Fiber laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fiber laser, and more particularly to a fiber laser from which high-power laser light can be obtained.
[0002]
[Prior art]
FIG. 4 shows the structure of a conventional fiber laser. This fiber laser is composed of a pump light source 11 and a laser fiber 12.
The laser optical fiber used as the laser fiber 12 is a single mode optical fiber having a core made of a rare earth element-doped quartz glass obtained by adding (doping) a rare earth element such as erbium (Er) or neodymium (Nd) to quartz glass. It has been known.
When pump light enters the laser fiber 12 from the pump light source 11, the rare earth element ions added to the core of the laser fiber 12 are excited while the pump light is transmitted through the laser fiber 12 to a certain length. Then, laser oscillation occurs, and laser light is emitted from the emission end 14. For example, when a laser beam having a wavelength of 0.85 μm is incident as pump light from the pump light source 11, a laser beam having a wavelength of 1.06 μm is emitted from the emission end 14.
[0003]
However, a single mode optical fiber having a core made of rare earth element-doped silica glass has a small core diameter, so the coupling efficiency of pump light to the core is low, and the power density in the core cannot be sufficiently increased. The laser oscillation output cannot be increased sufficiently.
[0004]
A double clad type laser optical fiber as shown in FIG. 5 has been proposed as a device capable of solving this inconvenience and outputting high-power laser light.
This has a core 1 made of quartz glass doped with rare earth elements and having an outer diameter C of 3 to 12 μm, and a first clad having a large diameter of about 400 μm and made of pure quartz glass surrounding the core 21 ( And a second cladding (coating layer) 23 having an outer diameter B of about 500 μm made of a resin having a lower refractive index than pure quartz, for example, a fluorine-containing acrylate resin, provided on the outer periphery of the first cladding 22. It has.
[0005]
In this laser optical fiber, the core diameter is relatively large, the coupling efficiency of the pump light is increased, and a considerable portion of the pump light incident on the first clad 22 having a large diameter passes through the first clad 22 and the core 21. It is said that high-power laser light can be obtained by being amplified in the core 21 while propagating. Further, in this double-clad type laser optical fiber, one that has improved efficiency by decentering the core or making the outer shape rectangular is proposed.
However, even if such a double clad laser optical fiber is used, the output is not sufficient, and it may not be suitable for use depending on the application.
[0006]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to obtain a fiber laser that can oscillate even higher-power laser light.
[0007]
Such problems include a main laser fiber, one or more pumping fibers coupled via a coupler in the length direction of the main laser fiber, an amplification pump light source that makes amplification pump light incident on the pumping fiber, A fiber laser having a main pump light source for entering main pump light from an incident end of the main laser fiber,
The main laser fiber includes a core added with a rare earth element, a first clad surrounding the core, and a second resin made of a resin having a refractive index lower than that of the first clad provided on the first clad. Consisting of clad,
The pumping fiber comprises a core and a clad made of a resin having a refractive index lower than that of the core provided on the core.
The refractive index of the first cladding of the main laser fiber and the refractive index of the core of the pumping fiber are equal,
In the coupler, the first cladding exposed by peeling off the second cladding of the main laser fiber and the core exposed by peeling off the cladding of the pumping fiber are arranged in parallel and in contact with the second cladding. This is solved by a fiber laser characterized in that it is provided with a collective coating layer formed by being coated again with the same material as that of the cladding.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of the structure of the fiber laser of the present invention.
Reference numeral 31 in the figure denotes a main pump light source, and a main laser fiber 32 is connected to the main pump light source 31.
The main laser fiber 32 is connected to an amplification pumping fiber 35 via a plurality of couplers 36, and an amplification pump light source 37 is provided at the incident end of the amplification pumping fiber 35.
The main laser fiber 32 forms an amplifying unit between the plurality of couplers 36.
[0009]
In the fiber laser having such a configuration, the main pump light generated from the main pump light source 31 enters the incident end of the main laser fiber 32 and propagates through the main laser fiber 32, while the pumping fiber from the amplification pump light source 37. The amplifying pump light incident on 35 is coupled to the main pump light in the coupler 36.
That is, when the main pump light propagates through the main laser fiber 32, it is amplified by the amplification pump light as needed. As a result, high-power laser light can be emitted from the output end 34.
[0010]
The main laser fiber 32 is a double clad laser optical fiber shown in FIG. 5, and a thick first clad (large clad) 22 and a second clad (coating layer) 23 are sequentially provided around the core 21. It is what was done.
The core 21 is made of glass such as quartz glass, fluoride glass such as zirconium fluoride, calcium fluoride, or the like doped with rare earth elements such as Nd (neodymium) or Er (erbium). It is made of the undoped glass. In this example, Er is added to the core 21.
The second cladding 23 is made of a resin having a refractive index lower than those of these glasses, for example, a fluorine-containing acrylate resin.
An example using quartz glass will be described below.
[0011]
The outer diameter C of the core 21 is 5 to 100 μm, the outer diameter A of the first cladding 22 is 200 to 500 μm, and the outer diameter B of the second cladding 23 is about 300 to 600 μm.
Since the outer diameter A of the first cladding 22 is set to be sufficiently large to be about 4 to 40 times the outer diameter C of the core 21, the first cladding 22 is referred to as a large diameter cladding.
In this way, the outer diameter A of the first cladding 22 is designed to be sufficiently large, and high-power laser light is obtained while most of the main pump light incident on the first cladding 22 propagates through the core 21. It is something that can be done.
In this example, the outer diameter C of the core 21 is 12 μm, the outer diameter A of the first cladding 22 is 400 μm, and the outer diameter B of the second cladding 23 is 500 μm.
Further, the outer shape of the first cladding 22 may be circular as shown in FIG. 5, or may be oval or rectangular. Since the density of light passing through the core 21 is remarkably increased when the oval shape or the rectangular shape is used, the efficiency is better.
In the case of an ellipse, for example, the major axis diameter is 400 μm and the minor axis diameter is 200 μm. In the case of a rectangle, for example, it is 400 × 200 μm.
[0012]
The double clad laser optical fiber used for the main laser fiber 32 can be manufactured as follows, for example.
First, a porous preform to be the core 21 is prepared by the VAD method or the like, this porous preform is immersed in an aqueous solution of a rare earth element compound, for example, erbium chloride, and the preform is impregnated with the rare earth element compound. This is heated to form a transparent glass to obtain a core glass rod.
Next, porous glass particles to be the first cladding 22 are deposited on the core glass rod by the VAD method or the like, and this is heated and transparentized to obtain a glass base material.
[0013]
Next, this glass preform is melt-spun to form an element fiber composed of the core 21 and the first cladding 22. Next, this element fiber is covered with a synthetic resin to be the second cladding 23.
[0014]
As shown in FIG. 2, the pumping fiber 35 includes a core 41 made of pure quartz glass having an outer diameter A ′ of about 400 μm, and a resin provided on the outer periphery of the core 41 with a refractive index lower than that of pure quartz, such as fluorine. The clad (coating layer) 42 having an outer diameter B ′ of about 500 μm made of a contained acrylate resin is used.
[0015]
The fiber having the structure shown in FIG. 2 constituting the pumping fiber 35 is obtained by forming a glass preform made of pure quartz glass, melt spinning it, and then coating with a synthetic resin to be the clad 42.
[0016]
FIG. 3 is a sectional view of the coupler 36.
In this coupler 36, the first cladding 22 exposed by peeling off the second cladding 23 of the main laser fiber 32 by about 20 mm and the core 41 exposed by peeling off the cladding 42 of the pumping fiber 35 by about 20 mm are arranged in parallel. In a contact state, a collective coating layer 38 formed by re-coating with the same material as that of the second clad 23 and the clad 42 is provided thereon.
[0017]
In this coupler 36, the first cladding 22 of the main laser fiber 32 and the core 41 of the pumping fiber 35 are in contact with each other.
The first cladding 22 and the core 41 are both made of pure quartz glass and have the same refractive index. Therefore, the amplification pump light propagating through the core 41 of the pumping fiber 35 oozes from the core 41 into the first clad 22 and further penetrates into the core 21 from the first clad 22.
[0018]
As described above, the pumping fiber 35 has a structure in which the amplification pump light propagating through the core 41 easily oozes out into the first cladding 22 in contact with the core 41.
In addition, as described above, the structure of the main laser fiber 32 is a structure in which a considerable portion of the pump light incident on the first cladding 22 easily penetrates into the core 21 from the first cladding 22.
In other words, the combination makes it easy for the pump light for amplification to penetrate the core 21 via the core 41 and the second cladding 23. As a result, tens to 100% of the pump light for amplification is coupled to the main pump light. And can be amplified efficiently.
[0019]
The installation interval of the coupler 36 is adjusted so that the amplification pump light enters from the next coupler 36 when the amplification effect of the amplification pump light incident from one coupler 36 is used up.
Usually, about 2 to 50 sets of the coupler 36, the pumping fiber 35, and the amplifying pump light source 37 are provided for one fiber laser.
The installation interval of the coupler 36 is several m to several tens m as the fiber length.
In this example, ten sets of couplers 36, pumping fibers 35, and amplification pump light sources 37 are used, the fiber length a from the main pump light source 31 shown in FIG. 1 to the first coupler 36 is 50 m, and the distance between the couplers 36 is The fiber length b is 50 m, and the fiber length c from the coupler 36 on the output end 34 side to the output end 34 is 50 m.
[0020]
As the main pump light source 31 and the amplification pump light source 37, a semiconductor laser that generates laser light having a wavelength of 0.5 to 1.49 μm as pump light is preferably used.
[0021]
(Test example)
A fiber laser similar to that in the above example is configured, and laser light having a wavelength of 0.85 μm and an output of 10 w is incident on the laser fiber 32 as the main pump light from the main pump light source 31, and the pumping fiber 35 and coupler are coupled from the amplification pump light source 37. When a laser beam having a wavelength of 0.85 μm and an output of 5 w is incident on the laser fiber 32 as an amplification pump light through 36, a laser beam having a wavelength of 1.06 μm is obtained from the output end 34 with an output of 30 w, and a high-power fiber laser It was confirmed that.
[0022]
【The invention's effect】
As described above, in the fiber laser of the present invention, a laser fiber that can make pump light incident with high coupling efficiency and can sufficiently increase its power density is used as a main laser fiber, a core as a pumping fiber, and a core. Since a coupler was constructed by using a structure provided with a coating layer, removing the coating layer made of these synthetic resins, and contacting a portion made of a quartz material having an equal refractive index, an amplification pump light source Thus, the amplification pump light incident on the pumping fiber can be efficiently coupled to the main pump light propagating through the main laser fiber.
Thus, by efficiently amplifying the main pump light as needed with the amplification pump light, a high-power, high-condensing fiber laser can be configured.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a fiber laser of the present invention.
FIG. 2 is a cross-sectional view showing an example of a pumping fiber used in the fiber laser of the present invention.
FIG. 3 is a cross-sectional view showing an example of the structure of the fiber laser coupler of the present invention.
FIG. 4 is a schematic configuration diagram showing an example of a conventional fiber laser.
FIG. 5 is a cross-sectional view showing an example of a double clad laser optical fiber used as a main laser fiber of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 21 ... Core, 22 ... 1st clad (large diameter clad), 23 ... 2nd clad (coating layer), 31 ... Main pump light source, 32 ... Main laser fiber, 35 ... Pumping fiber, 36 ... Coupler, 37 ... For amplification Pump light source, 41 ... core, 42 ... clad (coating layer)

Claims (1)

A main laser fiber, one or more pumping fibers coupled in the length direction of the main laser fiber via a coupler, an amplifying pump light source for amplifying the pumping light into the pumping fiber, and the main laser fiber A fiber laser having a main pump light source for entering the main pump light from the incident end of
The main laser fiber includes a core added with a rare earth element, a first clad surrounding the core, and a second resin made of a resin having a refractive index lower than that of the first clad provided on the first clad. Consisting of clad,
The pumping fiber comprises a core and a clad made of a resin having a refractive index lower than that of the core provided on the core.
The refractive index of the first cladding of the main laser fiber and the refractive index of the core of the pumping fiber are equal,
In the coupler, the first cladding exposed by peeling off the second cladding of the main laser fiber and the core exposed by peeling off the cladding of the pumping fiber are arranged in parallel and in contact with the second cladding. A fiber laser comprising a collective coating layer formed by being coated again with the same material as that of the cladding.

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