KR101876257B1

KR101876257B1 - Fiber laser device

Info

Publication number: KR101876257B1
Application number: KR1020160033822A
Authority: KR
Inventors: 마사쿠니 미무로
Original assignee: 가부시키가이샤후지쿠라
Priority date: 2015-03-24
Filing date: 2016-03-22
Publication date: 2018-07-09
Also published as: TW201640764A; JP2016180844A; KR20160114519A; JP6140750B2; TWI575827B

Abstract

A fiber laser apparatus comprising: a first optical amplifier for outputting light of a first wavelength; A first wavelength filter optically coupled to the first optical amplifier and transmitting light of the first wavelength and blocking light of wavelengths other than the first wavelength; A first Raman wavelength conversion unit optically coupled to the first wavelength filter to generate an inductive Raman scattering effect and to convert output light from the first wavelength filter into light having a second wavelength longer than the first wavelength; A second wavelength filter optically coupled to the first Raman wavelength converter and transmitting light of the second wavelength and blocking light of a wavelength other than the second wavelength; A second optical amplifier optically coupled to the second wavelength filter and amplifying output light from the second wavelength filter; A second Raman wavelength conversion unit optically coupled to the second optical amplifier to convert the output light from the second optical amplifier into light having a third wavelength longer than the second wavelength, And a third wavelength filter that is optically coupled to the second Raman wavelength conversion unit, transmits the third wavelength light, and blocks light having a wavelength other than the third wavelength.

Description

FIBER LASER DEVICE

The present invention relates to a fiber laser device.

A fiber laser device having a pulse oscillator, a first wavelength filter, a wavelength converter, a second wavelength filter, and an optical fiber amplifier is disclosed in Patent Document 1 below.

In this fiber laser device, the pulse light output from the pulse oscillator passes through the first wavelength filter and enters the wavelength converter. The wavelength is converted into a wavelength within the gain wavelength band of the optical fiber amplifier so that the wavelength can be amplified to a desired output by a downstream optical fiber amplifier. The pulse light whose wavelength has been converted by the wavelength converter passes through the second wavelength filter. On the other hand, the pulse light whose wavelength has not been converted by the wavelength converter is blocked by the second wavelength filter. The pulse light transmitted through the second wavelength filter is amplified and output to a desired output by an optical fiber amplifier, and is used for laser processing or the like.

On the other hand, the reflected light from the surface to be processed is amplified by being transmitted through the optical fiber amplifier, becomes the high-intensity reflected light, and enters the second wavelength filter. Since the wavelength of the reflected light matches the wavelength of the output light incident on the optical fiber amplifier from the wavelength converter, the reflected light passes through the second wavelength filter and enters the wavelength converter. The reflected light transmitted through the wavelength converter is incident on the first wavelength filter, but the wavelength of the reflected light is blocked by the first wavelength filter because it differs from the wavelength of the original output light output from the pulse oscillator. In this manner, since the reflection light can be prevented from entering the pulse oscillator, it is possible to prevent the components in the pulse oscillator from being broken by the reflected light.

- Patent Document 1: Japanese Patent No. 5198292

2. Description of the Related Art In recent years, the use of fiber laser devices has been diversified and a fiber laser device for outputting laser light on the longer wavelength side than the conventional one is sometimes required. However, there is a limitation in increasing the wavelength of light obtained by the optical fiber amplifier. Therefore, in the fiber laser device of Patent Document 1, there is a problem that laser light having a desired wavelength on the long wavelength side can not be obtained. Therefore, it is required to provide a fiber laser device capable of obtaining a laser beam having a desired wavelength on the long wavelength side while suppressing the influence of reflected light on a signal light generating portion such as a pulse oscillator.

An object of the present invention is to provide a fiber laser device capable of obtaining a laser beam having a desired wavelength on a longer wavelength side while suppressing the influence of reflected light on a signal light generating portion, .

According to an aspect of the present invention, there is provided a fiber laser apparatus including a first optical amplifier for outputting light of a first wavelength, a second optical amplifier optically coupled to the first optical amplifier, A first wavelength filter for blocking light having a wavelength other than the first wavelength; A first Raman wavelength conversion unit optically coupled to the first wavelength filter and expressing an induced Raman scattering effect and converting output light from the first wavelength filter into light having a second wavelength longer than the first wavelength; A second wavelength filter optically coupled to the first Raman wavelength converter and transmitting light of the second wavelength and blocking light of a wavelength other than the second wavelength; A second optical amplifier optically coupled to the second wavelength filter, the second optical amplifier amplifying output light from the second wavelength filter; A second Raman wavelength conversion unit optically coupled to the second optical amplifier to convert the output light from the second optical amplifier into light having a third wavelength longer than the second wavelength, And a third wavelength filter that is optically coupled to the second Raman wavelength conversion unit, transmits the third wavelength light, and blocks light having a wavelength other than the third wavelength.

The wavelength of the output light from the second optical amplifier is shifted to the long wavelength side and the light of the second wavelength is shifted to the second wavelength side by the third wavelength < RTI ID = 0.0 > As shown in FIG. Therefore, even if the second optical amplifier alone has a limitation on the long wavelength, output light with a longer wavelength can be obtained as compared with a conventional apparatus that does not include the second Raman wavelength converter.

On the other hand, when the reflected light of the third wavelength reflected from the irradiated object returns from the irradiated object, the light passes through the third wavelength filter and is incident on the second Raman wavelength converter. Here, the wavelength of the reflected light is also shifted to the long wavelength side, and the reflected light of the longer wavelength is incident on the second optical amplifier. The reflected light is amplified by the second optical amplifier, but the wavelength of the reflected light amplified by the second optical amplifier is longer than the third wavelength and is different from the wavelength (second wavelength) of the light converted by the first Raman wavelength converter Therefore, the reflected light amplified by the second optical amplifier can not pass through the second wavelength filter. Further, even if the second wavelength component is included in the reflected light and the second wavelength component can pass through the second wavelength filter, the second wavelength component can not pass through the first wavelength filter.

As described above, according to the fiber laser device of this embodiment, it is possible to obtain a desired output light having a longer wavelength, which can not be obtained only by the second optical amplifier, and at the same time, the influence of the reflected light on the first optical amplifier can be reliably suppressed.

The first Raman wavelength converter may include a first optical fiber, and the second Raman wavelength converter may comprise a second optical fiber.

In this case, the core diameter of the second optical fiber may be larger than the core diameter of the first optical fiber, and the length of the second optical fiber may be shorter than the length of the first optical fiber.

Wavelength conversion by inductive Raman scattering occurs when a strong incident light is incident to a nonlinear medium such that it exceeds a predetermined threshold value (Raman threshold value). Particularly, when the peak power density (= peak power / core cross section) of light is high and the fiber length is long, the wavelength conversion is more likely to occur. In the case of the above-described fiber laser device, since the incident light to the second Raman wavelength converter is amplified by the second optical amplifier, the peak power is larger than the incident light to the first Raman wavelength converter. Therefore, if the fiber length and the core cross-sectional area are the same, high-order unnecessary Raman scattering may occur in the second Raman wavelength converter. Therefore, according to the above arrangement, unnecessary high-order Raman scattering in the second Raman wavelength converter can be suppressed.

The second optical amplifier may include Yb doped fiber as the amplification fiber, and the wavelength of the light output from the second optical amplifier may be longer than 1060 nm.

When the reflected light of the third wavelength from the irradiated object returns from the irradiated object, it passes through the third wavelength filter and is incident on the second Raman wavelength converter. At this time, the reflected light passes through the second Raman wavelength converter, the wavelength of the reflected light further shifts to the long wavelength side, and the reflected light shifted to the longer wavelength enters the second optical amplifier. Here, the Yb doped fiber tends to have a lower gain as the gain peak is longer than 1060 nm at 1030 nm and 1060 nm. Therefore, when the wavelength of the output light from the second optical amplifier is longer than 1060 nm when the Yb doped fiber is used, the amplification of the reflected light returning from the second optical amplifier to the input side is suppressed and the influence of the reflected light to the first optical amplifier is further suppressed can do.

And the V value of the optical fiber reaching the output fiber from the input fiber to the second Raman wavelength converter is less than 2.4.

According to this configuration, since the output obtained from the fiber laser device is a single mode output, the beam quality is improved.

A polarization-maintaining fiber may be used at least in part and a single polarization may be output.

According to this configuration, it is possible to cope with a use in which a single polarized light is required as output light.

According to this aspect, it is possible to realize a fiber laser device capable of obtaining a laser beam having a desired wavelength on the longer wavelength side while suppressing the influence of reflected light on the signal light generating portion.

1 is a schematic configuration diagram of a fiber laser device according to a first embodiment.
2 is a diagram showing the wavelengths of respective lights after the output of the pulse oscillator, after the output of the first Raman wavelength converter, and after the output of the second Raman wavelength converter.
3A is a diagram showing the transmission characteristics of the first wavelength filter.
3B is a view showing the transmission characteristics of the second wavelength filter.
3C is a diagram showing transmission characteristics of the third wavelength filter.
4 is a schematic configuration diagram of a fiber laser device according to the second embodiment.
5 is a schematic configuration diagram of a modified example of the fiber laser device according to the second embodiment.
6 is a schematic configuration diagram of a modified example of the fiber laser device according to the second embodiment.

[First Embodiment]

Hereinafter, a first embodiment of the present invention will be described with reference to Figs. 1 and 2. Fig.

The fiber laser device according to the present embodiment is an example of a pulsed fiber laser device preferable for use in applications such as laser processing. However, the application is not limited to laser processing.

Fig. 1 is a schematic configuration diagram of a fiber laser device according to the present embodiment.

1, the fiber laser device 1 includes a pulse oscillator (first optical amplifier) 2, a first wavelength filter 3, a first Raman wavelength converter 4, a second wavelength filter 5, an optical amplifier (second optical amplifier) 6, a second Raman wavelength converter 7, and a third wavelength filter 8.

2, the first wavelength? 1, which is the wavelength of the output light from the pulse oscillator 2 in the fiber laser device 1, is shifted toward the longer wavelength side by the first Raman wavelength conversion section 4, And the second wavelength? 2 is further shifted to the long wavelength side by the second Raman wavelength conversion section 7 to become the third wavelength? 3 after passing through the optical amplifier 6.

The pulse oscillator 2 outputs pulse light of the first wavelength? 1. For the pulse oscillator 2, for example, a known pulse oscillator such as a Fabry-Perot type fiber laser or a fiber ring laser is used. Although not described in detail, the pulse oscillator 2 includes, for example, an excitation light source, a rare-earth added fiber, and an optical switch. The excitation light from the excitation light source excites rare-earth ions in the rare earth-doped fiber to emit spontaneously emitted light. The spontaneous emission light is amplified and propagated in the optical fiber and outputted. The output light from the rare-earth added fiber is switched by the optical switch to become a pulse light. In this embodiment, Yb fiber is used as the rare-earth added fiber, and the gain band is about 1030 to 1100 nm. Therefore, the first wavelength is, for example, about 1030 nm in the case of the shortest wavelength side.

The first wavelength filter (3) is optically coupled to the pulse oscillator (2). The first wavelength filter 3 is constituted by, for example, a band-pass filter. The first wavelength filter 3 transmits light in the vicinity of 1030 nm which is an example of the first wavelength lambda 1 and blocks light in a wavelength other than the first wavelength lambda 1 as shown in the transmission characteristic in Fig.

The first Raman wavelength converter 4 is optically coupled to the first wavelength filter 3. The first Raman wavelength conversion unit 4 is composed of an optical fiber (first optical fiber) that exhibits an induced Raman scattering effect when high power light is incident. The power of the light generated by the inductive Raman scattering can be adjusted by the core diameter or fiber length of the optical fiber. The first Raman wavelength conversion section 4 converts the output light from the first wavelength filter 3 into light of a second wavelength lambda 2 longer than the first wavelength lambda 1. The wavelength of the output light from the first wavelength filter 3 can be shifted by about 50 nm on the long wavelength side in the first Raman wavelength conversion section 4. [ As a result, light of a wavelength of 1030 to 1100 nm is converted into light of a wavelength of 1080 to 1150 nm by the first Raman wavelength conversion section (4). Considering from the shortest wavelength side, for example, light having a wavelength of 1030 nm (? 1) is converted into light having a wavelength of 1080 nm (? 2).

The second wavelength filter (5) is optically coupled to the first Raman wavelength converter (4). The second wavelength filter 5 is constituted by, for example, a band-pass filter. The second wavelength filter 5 transmits light in the vicinity of 1080 nm which is an example of the second wavelength lambda 2 and blocks light in a wavelength other than the second wavelength lambda 2 as shown in the transmission characteristic in Fig.

The optical amplifier 6 is optically coupled to the second wavelength filter 5 to amplify the light output from the second wavelength filter 5. The optical amplifier 6 includes, for example, an excitation light source including a plurality of laser diodes and an amplification fiber composed of Yb-doped fiber doped with Yb as a rare-earth element, although a detailed description will be omitted. The excitation light from the excitation light source is absorbed by Yb in the amplifying fiber to form an inversion distribution and induction emission occurs. Thereby, the laser light propagated in the core is amplified and output as a laser output. The wavelength band of the light output from the optical amplifier 6 is 1080 to 1100 nm. The light output from the optical amplifier 6 is 1080 nm which is the second wavelength? 2 when considered from the shortest wavelength side.

The second Raman wavelength converter 7 is optically coupled to the optical amplifier 6. [ The second Raman wavelength conversion unit 7 is composed of an optical fiber (second optical fiber) that exhibits an induced Raman scattering effect when high power light is incident. The power of the light generated by the inductive Raman scattering can be adjusted by the core diameter or fiber length of the optical fiber. The second Raman wavelength converter 7 converts the output light from the optical amplifier 6 into light of a third wavelength lambda 3 longer than the second wavelength lambda 2. The wavelength of the output light from the optical amplifier 6 can be shifted by about 50 nm toward the long wavelength side in the second Raman wavelength conversion section 7.

As a result, light of wavelength 1080 to 1100 nm is converted into light of wavelengths 1130 to 1150 nm by the second Raman wavelength conversion unit 7. Considering the shortest wavelength side, for example, light in the vicinity of the wavelength 1080 nm (? 2) is converted into light in the vicinity of the wavelength 1130 nm (? 3).

The third wavelength filter 8 is optically coupled to the second Raman wavelength converter 7. The third wavelength filter 8 is constituted by, for example, a band-pass filter. The third wavelength filter 8 transmits light in the vicinity of 1130 nm which is an example of the third wavelength lambda 3 and blocks light in a wavelength other than the third wavelength lambda 3 as shown in the transmission characteristic in Fig. 3C.

Table 1 summarizes the wavelength characteristics of the respective components described above.

Hereinafter, the operation of the fiber laser device 1 of the present embodiment will be described with reference to Table 1.

First, attention is paid to output light. The light of the first wavelength? 1 (for example, 1030 nm) outputted from the pulse oscillator 2 is transmitted through the first wavelength filter 3 and the wavelength is converted by the first Raman wavelength conversion unit 4 to be converted into the second wavelength? For example, 1080 nm). At this time, the wavelengths of all the lights are not changed and a part of the light of the first wavelength lambda 1 remains, while the light of the first wavelength lambda 1 is blocked by the second wavelength filter 5 of the subsequent stage.

The light of the second wavelength? 2 output from the first Raman wavelength conversion section 4 is transmitted through the second wavelength filter 5 and amplified by the optical amplifier 6, Is converted into a light of a third wavelength lambda 3 (for example, 1130 nm). Here, as in the first Raman wavelength conversion section 4, the wavelengths of all the lights are not changed, and a part of the light of the second wavelength? 2 remains, while the light of the second wavelength? 2 is blocked by the third wavelength filter 8 . The light of the third wavelength? 3 outputted from the second Raman wavelength converter 7 is transmitted through the third wavelength filter 8 and outputted. The output light is irradiated on the surface to be processed, for example, and used for laser processing.

Next, attention is paid to reflected light. The reflected light of the third wavelength? 3 from the surface to be processed passes through the third wavelength filter 8 and is incident on the second Raman wavelength conversion section 7. Here, the wavelength of the reflected light is further shifted from the third wavelength? 3 to the long wavelength side, and the longer wavelength reflected light is incident on the optical amplifier 6.

This reflected light is amplified by the optical amplifier 6, but the light amplified by the optical amplifier 6 is blocked by the second wavelength filter 5 and is not returned any more. If light of the second wavelength coexists in the reflected light and light of the second wavelength transmits the second wavelength filter 5, the light is blocked by the first wavelength filter 3 and returns to the pulse oscillator 2 Do not come.

As described above, the fiber laser device 1 of the present embodiment is provided with the second Raman wavelength conversion section 7 at the rear stage of the optical amplifier 6, so that even if the optical amplifier 6 alone has a limitation in the wavelength of light, And the second Raman wavelength converter 7, it is possible to obtain an output light having a long wavelength. Specifically, an optical amplifier using Yb-doped fiber as an amplifying fiber is advantageous in that the output power is easily improved and the beam quality is excellent. On the other hand, since the gain peak is near 1030 nm and 1060 nm, as the wavelength becomes longer than 1060 nm The gain tends to be lowered. Therefore, it is difficult to amplify light having a wavelength of 1100 nm or more. Therefore, this type of fiber laser apparatus has a problem that it can not be used for applications requiring a wavelength of 1100 nm or more. In this regard, according to the fiber laser device 1 of the present embodiment, output light having a wavelength exceeding 1100 nm can be obtained as described above. As described above, according to the present embodiment, it is possible to obtain a desired output light of a longer wavelength, which can not be obtained only by the optical amplifier 6, and at the same time to suppress the influence of the reflected light on the pulse oscillator 2, (1) can be realized.

In addition, the core diameter and fiber length of the optical fiber in each Raman wavelength conversion unit can be appropriately set for the purpose of, for example, adjustment of the optical power in which the inductive Raman scattering occurs. However, the core diameter of the optical fiber (second optical fiber) constituting the second Raman wavelength conversion section 7 is made larger than the core diameter of the optical fiber (first optical fiber) constituting the first Raman wavelength conversion section 4, The following effects can be obtained by making the length of the optical fibers constituting the 2 Raman wavelength converter 7 smaller than the length of the optical fibers constituting the first Raman wavelength converter 4:

Wavelength conversion by inductive Raman scattering occurs when a strong incident light is incident to a nonlinear medium such that it exceeds a predetermined threshold value (Raman threshold value). Particularly, when the peak power density (= peak power / core cross section) of light is high and the length of the fiber is long, the wavelength conversion is likely to occur relatively. Here, when A = peak power x (fiber length) / (cross-sectional area of core), when A exceeds a predetermined threshold value, Raman light of an arbitrary wavelength is generated. For example, let A 2 be the threshold at which the second Raman light is generated, A 3 be the threshold at which the third Raman light occurs, ... , let A be a threshold value at which n-th Raman light is generated, A2 <A3 <... <An.

In the case of the fiber laser device 1 according to the present embodiment, since the incident light to the second Raman wavelength conversion section 7 is amplified by the optical amplifier 6, the peak power is lower than the incident light to the first Raman wavelength conversion section 4 Big. Therefore, if the fiber length and the core cross-sectional area are the same, a high-order unnecessary Raman scattering may occur in the second Raman wavelength conversion part 7. Therefore, the core diameter of the optical fiber constituting the second Raman wavelength converter 7 is made larger than the core diameter of the optical fiber constituting the first Raman wavelength converter 4, and the second Raman wavelength converter 7 If the length of the optical fiber is made shorter than the length of the optical fiber constituting the first Raman wavelength converter 4, unnecessary high-order inductive Raman scattering in the second Raman wavelength converter 7 can be suppressed.

As in this embodiment, the wavelength of the output light from the optical amplifier 6 is preferably longer than 1060 nm. This is because the influence of the reflected light on the pulse oscillator 2 can be more reliably suppressed if the wavelength of the output light from the optical amplifier 6 is longer than 1060 nm. In other words, the reflected light returned from the surface to be processed passes through the second Raman wavelength converter 7, whereby the wavelength shifts to the longer wavelength side, and the reflected light shifted to a longer wavelength enters the optical amplifier 6. Here, as described above, the Yb doped fiber tends to have a lower gain as the wavelength becomes longer than 1060 nm. Therefore, if the wavelength of the output light from the optical amplifier 6 is longer than 1060 nm, the amplification of the reflected light returning from the optical amplifier 6 to the pulse oscillator 2 side is suppressed.

And the V value of the optical fiber reaching the output fiber from the input fiber to the second Raman wavelength converter 7 is preferably smaller than 2.4. In this case, since the output obtained from the fiber laser device 1 is a single mode output, the beam quality is improved.

[Second Embodiment]

Hereinafter, a second embodiment of the present invention will be described with reference to FIG.

The basic structure of the fiber laser device according to the second embodiment is the same as that of the fiber laser device of the first embodiment, except that it is a single polarized laser capable of obtaining a single polarized output, which is different from the first embodiment.

In FIG. 4, the same components as those in FIG. 1 used in the first embodiment are denoted by the same reference numerals, and a description thereof will be omitted.

4, the fiber laser device 11 according to the present embodiment is provided with the polarizer 12 between the second wavelength filter 5 and the optical amplifier 6. [ The polarizer 12 is a device that monopolizes random polarized light. As the spatial polarizer, a polarization splitter such as Glan-Thompson prism, Glan-Taylor prism, or Glan-laser prism is used. As the fiber polarizer, a polarization maintaining fiber having a birefringence higher than usual is used. In the fiber polarizer, for example, by using the difference in bending loss between the slow axis and the fast axis of the optical fiber and changing the warpage of the fiber, for example, the loss of the slow axis is set to 0, the loss of the fast axis is set to 20 dB, Thereby obtaining a single polarized state.

In Fig. 4, the portion from the pulse oscillator 2 to the second wavelength filter 5 is a random polarization portion 13 that handles random polarized light. The portion from the polarizer 12 to the third wavelength filter 8 is a single polarization section 14 that handles a single polarization. A normal optical fiber 16 can be used in the random polarization section 13. [ On the other hand, in the single polarization section 14, it is necessary to use the polarization-maintaining fiber 17. As the polarization maintaining fibers 17, for example, PANDA fibers may be used.

The rest of the configuration is the same as that of the first embodiment.

It is possible to realize the fiber laser device 11 capable of obtaining the desired output light of a long wavelength and simultaneously suppressing the influence of the reflected light on the pulse oscillator in the present embodiment as well as achieving the same effect as in the first embodiment . Further, according to this embodiment, it is possible to cope with a use in which a single polarization laser is required.

Although FIG. 4 shows an embodiment in which the polarizer 12 is disposed between the second wavelength filter 5 and the optical amplifier 6, the configuration in which the fiber laser device is a single polarization laser is not limited to this embodiment , For example, the configurations shown in Figs. 5 and 6 may be employed.

5, in the fiber laser apparatus 21 of the first modification, the polarizer 12 is provided between the pulse oscillator 2 and the first wavelength filter 3. In this case, the portion from the pulse oscillator 2 to the input of the polarizer 12 is a random polarization section 13 that handles random polarized light. The portion from the polarizer 12 to the third wavelength filter 8 is a single polarization section 14 that handles a single polarization. In the random polarization section 13, a normal optical fiber 16 is used. In the single polarization section 14, the polarization maintaining fibers 17 are used.

As shown in Fig. 6, the fiber laser device 31 of the second modification does not have a polarizer. In this case, from the pulse oscillator 2 to the third wavelength filter 8 are all the single polarization section 14 and the polarization maintaining fibers 17 are used for all the optical fibers.

The technical scope of the present invention is not limited to the above embodiment, and various changes can be made within the scope of the present invention.

For example, in the embodiment described above, the first and second Raman wavelength conversion units are formed of optical fibers, but the first and second Raman wavelength conversion units are not necessarily composed of optical fibers. As the first and second Raman wavelength conversion units, for example, nonlinear optical crystals that exhibit an induced Raman scattering effect may be used.

In addition, specific configurations of each component of the fiber laser device, and oscillation wavelength, amplification wavelength, transmission wavelength and blocking wavelength of the wavelength filter, and the like are not limited to those of the above-described embodiments, but can be appropriately changed.

[Industrial applicability]

INDUSTRIAL APPLICABILITY The present invention can be used, for example, in a fiber laser apparatus used for material processing and the like.

1, 11, 21, 31 ... Fiber laser device, 2 ... A pulse oscillator (first optical amplifier), 3 ... A first wavelength filter, 4 ... A first Raman wavelength converter 5, Second wavelength filter, 6 ... Optical amplifier (second optical amplifier), 7 ... A second Raman wavelength converter 8, Third wavelength filter, 17 ... Polarization retaining fibers.

Claims

A first optical amplifier for outputting light of a first wavelength;
A first wavelength filter optically coupled to the first optical amplifier and transmitting light of the first wavelength and blocking light of wavelengths other than the first wavelength;
A first Raman wavelength conversion unit optically coupled to the first wavelength filter and expressing an induced Raman scattering effect and converting output light from the first wavelength filter into light having a second wavelength longer than the first wavelength;
A second wavelength filter optically coupled to the first Raman wavelength converter and transmitting light of the second wavelength and blocking light of a wavelength other than the second wavelength;
A second optical amplifier optically coupled to the second wavelength filter and amplifying output light from the second wavelength filter;
A second Raman wavelength conversion unit optically coupled to the second optical amplifier to convert the output light from the second optical amplifier into light having a third wavelength longer than the second wavelength, And
A third wavelength filter optically coupled to the second Raman wavelength converter and transmitting light of the third wavelength and blocking light of wavelengths other than the third wavelength,
Lt; / RTI >
Wherein the first Raman wavelength converter comprises a first optical fiber, the second Raman wavelength converter comprises a second optical fiber,
The core diameter of the second optical fiber is larger than the core diameter of the first optical fiber,
The length of the second optical fiber is shorter than the length of the first optical fiber,
Fiber laser devices.

The method according to claim 1,
Wherein the second optical amplifier comprises Yb doped fiber as an amplifying fiber,
The wavelength of the light output from the second optical amplifier is longer than 1060 nm,
Fiber laser devices.

3. The method according to claim 1 or 2,
The normalized frequency V of the optical fiber reaching the output fiber from the input fiber to the second Raman wavelength converter is less than 2.4,
Fiber laser devices.

3. The method according to claim 1 or 2,
A polarization-maintaining fiber is used at least in part, and a single-
Fiber laser devices.

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