JP2002353539A - Fiber-optic laser device and fiber-optic laser system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of excitation wavelength arrangement not being optimized for Raman amplification, in the desired wide band since a conventional spectral distribution is not fully controlled. SOLUTION: There are provided a laser light source 100 for generating a laser beam of a wavelength λ1, a chirp fiber grating 121 of first reflectivity with respect to a wavelength λ2, a nonlinear optical fiber 110 containing an active medium for activating nonlinear effect, and a chirp fiber grating 122, which is, together with an optical resonator regulated for the nonlinear optical fiber, positioned to face the chirp fiber grating 121 so as to sandwich the nonlinear optical fiber, and has a second reflectivity with respect to the wavelength λ2 to reflect the laser beam of wavelength λ2 while output a part of it. A desired laser beam expanded to a range of wide wavelength band is provided from the laser beam of arbitrary first wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber laser device utilizing non-linear effects (stimulated Raman scattering, stimulated Brillouin scattering, etc.), and more particularly to realizing broadband Raman amplification and gain flattening in an optical communication system. A possible fiber laser device and a fiber laser system.

[0002]

2. Description of the Related Art There are Raman fiber lasers and amplifiers as fiber laser devices utilizing the nonlinear effect.

In a Raman fiber laser and an amplifier, when high-power excitation light is input to a silica-based optical fiber, stimulated Raman scattering due to the interaction between light and optical phonons (lattice vibration) has a longer wavelength than the excitation light. The gain is provided on the side, and the laser light is oscillated and amplified by the nonlinear effect.

Here, a wavelength difference in stimulated Raman scattering is called a Raman shift amount, and when fused silica is used, a maximum wideband gain is obtained at a Raman shift amount of 13.2 THz. Unlike fiber lasers and amplifiers that use the stimulated emission effect, there is a feature that by selecting the wavelength of the pump light, laser light having a desired wavelength shifted by the Raman shift amount can be oscillated and amplified.

For example, in the case of a silica-based fiber, laser beams having wavelengths of 1.12 μm and 1.66 μm are obtained by excitation light having wavelengths of 1.06 μm and 1.55 μm, respectively. Further, when the core which forms the center of the silica-based fiber is doped with Ge, the gain in stimulated Raman scattering increases, and when P or B is doped heavily, the amount of Raman shift changes and the gain increases.

If the pumping light has a high power, it is possible to generate n (here, n is an integer of 2 or more) stimulated Raman scattering in a cascade, and to shift by n Raman shifts. Some lasers can obtain laser light of a desired wavelength.

For example, as shown in US Pat. No. 5,323,404, in a cascade Raman fiber laser, a plurality of n resonators corresponding to the amount of Raman shift of a silica-based fiber form n pairs of fiber gratings. It is configured using.

Here, as shown in FIG. 11, wavelengths of 1117 nm, 1175 nm,
Each resonator is defined by four pairs of fiber gratings that reflect laser beams of 0 nm and 1315 nm. With the excitation light having a wavelength of 1064 nm input to the optical fiber, laser light having a wavelength of 1117 nm corresponding to the amount of Raman shift is converted into fiber gratings 1021 and 1022.
Then, a laser beam having a wavelength of 1117 nm causes a laser beam having a wavelength of 1175 nm corresponding to the amount of Raman shift to be oscillated between the fiber gratings 1031 and 1032, and a laser beam having a wavelength of 1240 nm and 1315 nm is sequentially converted into a fiber grating 1041. , 1042
And between 1051 and 1052. The fiber grating 1052 has a low reflectance compared to other fiber gratings having a high reflectance,
A 315 nm laser beam is output to the outside.

At present, in optical communication systems, WDM
(Wavelength Division Multi
multiplexing) and DWD with wavelength multiplexing
M (Dense WDM) is being used to increase the capacity, and broadband amplification technology using Raman amplification is expected.

For example, "H. Kidrof, et,
al. , IEEE Photonics Tech
nol. Lett. , Vol 11, no. 5,
pp. 530, 1999. Raman amplification can be easily changed by changing the pump wavelength, so if the Raman fiber amplifier is simultaneously pumped with pump light of different wavelengths, the wavelength shifts according to the difference in pump wavelength. Gain distributions, and several tens to one
It has been demonstrated that a wide band of about 00 nm can be achieved.

However, when the band of the pump light source becomes very wide, the energy of the short-wavelength pump light component is lost to the long-wavelength pump light component due to the stimulated Raman scattering effect between the pump lights. A flat gain distribution cannot be obtained in a wide band. For this reason, when using a broadband pump light source that broadens the Raman fiber amplifier, it is necessary to set the spectral power density of the pump light to an asymmetric pump wavelength arrangement in which short wavelength components increase.

In order to perform Raman amplification in an optical fiber, high pump power is indispensable. As in the case of stimulated Raman scattering, by inputting high-power excitation light to a silica-based optical fiber, stimulated Brillouin scattering due to the interaction between light and acoustic phonons is lower than the excitation light by about 10 GHz in the Brillouin shift amount. The laser beam oscillates (amplifies) due to its nonlinear effect by giving a narrow band gain at the frequency.
Is done. Here, in the case of stimulated Brillouin scattering, since it is back scattering, it has a gain only in the opposite direction to the excitation light. Stimulated Brillouin scattering occurs at lower pump powers than stimulated Raman scattering and can be harmful in optical communication systems. This can be solved by broadening the bandwidth of high-power excitation light having a narrow spectral width. When the spectrum width of the excitation light is wider than the spectrum width of the gain in stimulated Brillouin scattering, stimulated Brillouin scattering is suppressed, and high-power excitation light can be used.

That is, a broadband laser light is effective as a pump light source for Raman amplification in an optical communication system. For example, as shown in "IEICE Technical Report LQE2000-61", by connecting a single mode fiber to a Raman fiber laser, an ultra-wide band CW (Continuous) having an output power of about 100 nm and an output power of about 2 W is connected.
Wave) light is obtained. However, since the spectral distribution is not sufficiently controlled, it is not optimized as a pump wavelength arrangement for performing a desired broadband Raman amplification.
Further, it is necessary to arrange the pumping wavelength so that the gain becomes flat in the Raman amplification.

[0014]

In order to obtain a wide band laser light, there is a method utilizing a nonlinear effect. Stimulated Brillouin scattering is useful as Brillouin lasers and amplifiers. By generating stimulated Brillouin scattering in a cascade, multi-wavelength oscillation is realized at intervals of about 10 GHz. In addition, the spectrum width is expanded in the optical fiber due to other nonlinear effects such as four-wave mixing, self-phase modulation, and cross-phase modulation. For example, “P.
L. Baldeck and R.A. R. Alfa
no. Lightwave Technology.
vol. LT-5, no. 12, pp. 17
12, 1987. As the picosecond pulse pump light propagates through the multimode fiber, the cascaded stimulated Raman scattering, four-wave mixing, self-phase modulation, and crossing occur when the peak intensity of the pump light increases. It has been observed that as a result of the combination of phase modulation, the spectrum of the excitation light spreads over a wide band. In addition, when high-power pumping light is introduced into the Fabry-Perot cavity by the CW, cascaded stimulated Brillouin scattering and simultaneous four-wave mixing between laser beams propagating in the same direction simultaneously cause a longer wavelength side than the pumping light. In some cases, multi-wavelength laser light shifted to the shorter wavelength side (Stokes shift and anti-Stokes shift) is generated.

However, in order to realize broadband Raman amplification and flatten gain in an optical communication system, the spectrum of a high-power pump light is broadened by a nonlinear effect in an optical fiber and the spectrum distribution is controlled. It is important to.

Therefore, the fiber laser device according to the present invention is characterized by a resonator configuration in which a spectrum is actively expanded and output by a nonlinear effect up to a pump wavelength arrangement optimal for a desired broadband Raman amplification.

The resonator is constituted by a Fabry-Perot resonator using a pair of mirrors or a fiber grating reflecting means for reflecting laser light only in an arbitrary wide wavelength range, and cascaded stimulated Brillouin scattering and other nonlinear effects. The laser light is oscillated while being confined in an arbitrary wide wavelength range. Furthermore, in order to obtain a flat gain distribution of Raman amplification, the reflectance spectral distribution in one of the reflecting means is arbitrarily set, and the spectral power density of the laser light oscillating between the pair of reflecting means is adjusted. I have.
In this way, the laser light spreads within a wide wavelength range due to the non-linear effect, and the spectral distribution of the laser light to be easily output can be optimized by changing the spectral distribution of the reflectance in the reflection means. It is.

As the reflection means, a chirped fiber grating that reflects laser light in a wide wavelength range is suitable. The chirped fiber grating has a linear wavelength change in the fiber grating because the refractive index is given to the optical fiber to form a diffraction grating, and the frequency interval of the change in the refractive index is gradually changed. Further, in order to arbitrarily set the spectral distribution of the reflectance, the magnitude of the change in the refractive index changes, and the reflectance changes with the wavelength.

[0019]

According to a first aspect of the present invention, there is provided a fiber laser device for inputting a laser beam having an arbitrary first wavelength and amplifying a laser beam having a different second wavelength. A laser light source for generating a laser beam having the first wavelength, a first reflection means having a first reflectance for the second wavelength, and an active medium for activating a non-linear effect. Optical fiber, and an optical resonator is defined in the nonlinear optical fiber, is disposed at a position facing the first reflection means so as to sandwich the nonlinear optical fiber, and a second A second reflection means having a reflectance of 2 and reflecting the laser light having the second wavelength and outputting a part of the laser light having the second wavelength. And the second reflecting means, The optical resonator reflects laser light in a wide wavelength range including a wavelength, and the optical resonator amplifies the laser light having the second wavelength with the laser light having the first wavelength, and the second cavity is amplified by a nonlinear effect. Laser light having a wavelength spreads over a wide wavelength range and oscillates.

In a fiber laser device according to a second aspect of the present invention, an optical resonator is defined in the nonlinear optical fiber,
A wavelength band is disposed at a position facing the first reflection means so as to sandwich the nonlinear optical fiber, has a third reflectance with respect to the second wavelength, and has a narrow wavelength range centered on the second wavelength. And a third reflecting means for reflecting the laser light.

In a fiber laser device according to a third aspect of the present invention, an optical resonator is defined in the nonlinear optical fiber,
It is arranged on both sides to sandwich the nonlinear optical fiber,
Third and fourth reflection means respectively having third and fourth reflectances with respect to the second wavelength and reflecting laser light in a narrow wavelength range around the second wavelength. It is.

According to a fourth aspect of the present invention, in the fiber laser device, the nonlinear optical fiber includes a rare earth element that activates a stimulated emission effect by the laser light having the first wavelength. The laser light having the second wavelength is amplified inside the optical resonator by the laser light having the first wavelength.

In a fiber laser device according to a fifth aspect of the present invention, an optical resonator is defined in the nonlinear optical fiber,
It is arranged on both sides to sandwich the nonlinear optical fiber,
The optical device further includes a plurality of pairs of reflecting means for reflecting the laser light having the first wavelength or more and the second wavelength or less, and the laser light having the first wavelength is scattered inside the optical resonator by a cascaded nonlinear effect. This is for amplifying the laser light having the second wavelength.

According to a sixth aspect of the present invention, in the fiber laser device, at least one of the pair of the first and second reflecting means has a change in the refractive index change, and the change in the refractive index with respect to the wavelength. The reflectance changes.

In a fiber laser device according to a seventh aspect of the present invention, the reflectance of the one reflecting means gradually increases as the wavelength is longer than the second wavelength and shorter.

[0026] A fiber laser system according to claim 8 of the present invention is a fiber laser device according to any one of claims 1 to 7, which outputs broadband laser light;
Optical transmission means for transmitting the wavelength multiplexed signal light, and a broadband laser light output from the fiber laser device,
Laser coupling means for introducing the light into the light transmission means.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Embodiment 1 A fiber laser device according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a fiber laser device according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 100 denotes a wavelength λ1 (= 10
64 nm) Nd: YAG laser (laser light source), 11
0 is a silica fiber (non-linear optical fiber), 111 is a fiber grating that reflects laser light of wavelength λ1, and 121 and 122 are laser lights of a wide wavelength range Δλ1 (= 20 nm) including wavelength λ2 (= 1116 nm). A pair of chirped fiber gratings (reflecting means).

Here, the fiber grating 111,
Reference numerals 121 and 122 are formed in a quartz-based fiber.
The fiber grating 111 has a reflectance of 99% or more with respect to the laser beam having the wavelength λ1.

The spectral distribution of the reflectance in the chirped fiber gratings 121 and 122 has a wide band as shown in FIGS. 2A and 2B, respectively. Note that the arrangement of the fiber grating 111 may be replaced with the chirped fiber grating 122 in some cases.

Next, the operation of the fiber laser device according to the first embodiment will be described with reference to the drawings.

As shown in FIG. 1, a laser beam having a wavelength of λ 1 having a high power and a CW is input from a Nd: YAG laser 100 to a quartz-based fiber 110. Here, Nd: YAG
Since the laser 100 has an optical system as a laser input means, the laser light having the wavelength λ1
Has been introduced to the core.

The wavelength λ input to the silica-based fiber 110
One laser beam propagates through the core of the silica-based fiber 110. In addition, the silica-based fiber 110 is propagated by the fiber grating 111 in a folded manner, and
0 stimulated Raman scattering is more activated. At this time, a pair of chirped fiber gratings 121 and 122
Since the silica-based fiber 110 is provided inside the optical resonator defined by the formula (1), the laser light having the wavelength λ1 is transmitted through the silica-based fiber 110 as excitation light for stimulated Raman scattering.
Give gain near. As a result, due to stimulated Raman scattering, a pair of chirped fiber gratings 121,
The laser light having the wavelength λ2 is oscillated between the pulses 122.

Further, since the pair of chirped fiber gratings 121 and 122 reflect the laser light of a wide wavelength range Δλ1, the laser light of the wavelength λ2 is transmitted as the excitation light of stimulated Brillouin scattering through the quartz-based fiber 110. , A narrow band gain is provided at a frequency lower than the wavelength λ2 by about 10 GHz. As a result, stimulated Brillouin scattering causes a pair of chirped fiber gratings 12
Multi-wavelength laser light is oscillated one after another at intervals of about 10 GHz over wavelength λ2 between 1 and 122, and the laser light of wavelength λ2 spreads within a wide wavelength range Δλl.

Further, as a result of the combination of stimulated Brillouin scattering of the cascade and other nonlinear effects, for example, due to four-wave mixing between laser beams simultaneously propagating in the same direction, a multi-wavelength laser within a wide wavelength range Δλl is obtained. Light may be generated. Due to these non-linear effects, laser light is oscillated between a pair of chirped fiber gratings 121 and 122 in a wide wavelength range Δλl.

Chirped fiber grating 122
As shown in FIG. 2A, since the laser output means has a low reflectance, a part of the laser light inside the optical resonator is transmitted from the quartz-based fiber 110 through the chirped fiber grating 122. Is output. The spectrum distribution of the output laser light has a wide band as shown in FIG.

As described above, in the fiber laser device according to the first embodiment, the laser light having the wavelength λ1 and extending into a desired wide wavelength range is obtained.

Embodiment 2 Embodiment 2 A fiber laser device according to Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 4 is a diagram showing a configuration of a fiber laser device according to Embodiment 2 of the present invention.

In FIG. 4, reference numeral 200 denotes a wavelength λ1 (= 13
15 nm) Raman fiber laser (laser light source), 2
10 is a silica fiber (non-linear optical fiber), 211
Is a pair of chirped fiber gratings (reflecting means) that reflect laser light of a wide wavelength range Δλ1 (= 30 nm) including a wavelength λ2 (= 1395 nm), and 231 and 222 are fiber gratings 221 and 222. Is a fiber grating (reflecting means) that reflects laser light in a narrow wavelength range Δλs around the wavelength λ2.

Here, the fiber gratings 211 and 221 and 222 and 231 are formed on the quartz fiber 210. The fiber grating 211 has a reflectance of 99% or more with respect to the laser beam having the wavelength λ1. As in the case of the first embodiment, the spectral distribution of the reflectance in the chirped fiber gratings 221 and 222 has a wide band as shown in FIGS. 2A and 2B, respectively. Further, the spectral distribution of the reflectance in the fiber grating 231 has a narrow band as shown in FIG. The arrangement of the fiber grating 211 may be replaced with the chirped fiber grating 222 or between the pair of chirped fiber gratings 221 and 222.

Next, the operation of the fiber laser device according to the second embodiment will be described with reference to the drawings.

As shown in FIG. 4, a CW, high-power laser beam having a wavelength λ 1 is input from a Raman fiber laser 200 to a silica-based fiber 210. Here, since the Raman fiber laser 200 has an optical fiber as the laser input means, the laser light of the wavelength λ1 is introduced into the core of the silica-based fiber 210.

The wavelength λ input to the silica-based fiber 210
One laser beam propagates through the core of the silica-based fiber 210. The silica-based fiber 210 is propagated by the fiber grating 211 in a folded manner, and
0 stimulated Raman scattering is more activated. At this time, since the silica-based fiber 210 is inside the optical resonator defined by the chirped fiber grating 221 and the fiber grating 231, the laser light having the wavelength λ1 propagates through the silica-based fiber 210 as excitation light of stimulated Raman scattering. In this case, a gain is provided near the wavelength λ2. as a result,
Due to stimulated Raman scattering, laser light having a wavelength λ2 is oscillated between the chirped fiber grating 221 and the fiber grating 231.

Further, since the pair of chirped fiber gratings 221 and 222 reflect the laser light in the wide wavelength range Δλ1, the laser light having the wavelength λ2 is transmitted as the excitation light for stimulated Brillouin scattering through the quartz-based fiber 210. , A narrow band gain is provided at a frequency lower than the wavelength λ2 by about 10 GHz.

Here, laser light in a narrow wavelength range Δλs is oscillated around the wavelength λ2 by the fiber grating 231 to further stimulate stimulated Brillouin scattering of the silica fiber 210. As a result, a pair of chirped fiber gratings 221 and 22 are generated by stimulated Brillouin scattering.
The laser light of multiple wavelengths is oscillated one after another at intervals of about 10 GHz above the wavelength λ2 between the two, and the laser light of the wavelength λ2 spreads within a wide wavelength range Δλ1.

Further, as a result of the combination of stimulated Brillouin scattering of the cascade and other nonlinear effects, for example, four-wave mixing between laser beams simultaneously propagating in the same direction causes a multi-wavelength laser within a wide wavelength range Δλ1. Light may be generated. Due to these nonlinear effects, laser light is oscillated between the pair of chirped fiber gratings 221 and 222 in a wide wavelength range Δλ1.

Chirp fiber grating 222
Has a low reflectance as a laser output means,
Part of the laser light inside the optical resonator is output from the silica-based fiber 210 via the chirped fiber grating 222. As in the case of the first embodiment, the spectrum distribution of the output laser light has a wide band as shown in FIG.

As described above, in the fiber laser device according to the second embodiment, the laser light having the wavelength λ1 and extending in a desired wide wavelength range is obtained.

Embodiment 3 Embodiment 3 A fiber laser device according to Embodiment 3 of the present invention will be described with reference to the drawings. FIG. 6 is a diagram showing a configuration of a fiber laser device according to Embodiment 3 of the present invention.

In FIG. 6, reference numeral 300 denotes a wavelength λ1 (= 13
85 nm) Raman fiber laser (laser light source), 3
Reference numeral 10 denotes a silica-based fiber (non-linear optical fiber), 311
Is a fiber grating that reflects laser light of wavelength λ1, 321 and 322 are a pair of chirped fiber gratings (reflecting means) 331 that reflect laser light of a wide wavelength range Δλ1 (= 40 nm) including wavelength λ2 (= 1480 nm). Reference numeral 332 denotes a pair of fiber gratings (reflecting means) for reflecting laser light in a narrow wavelength range Δλs around the wavelength λ2.

Here, the fiber gratings 311 and 321 and 322 and 331 and 332 are
10 is formed. Fiber grating 311
Has a reflectance of 99% or more with respect to the laser beam having the wavelength λ1. As in the first embodiment, the spectral distribution of the reflectance in the chirped fiber gratings 321 and 322 has a wide band as shown in FIGS. 2A and 2B, respectively. In addition, fiber grating 33
The spectral distribution of the reflectance at 1 and 332 has a narrow band as shown in FIG. 5A or 5B, respectively. If the fiber grating 331 is as shown in FIG. 332 is (b) or (a). The arrangement of the fiber grating 311 may be replaced with the chirped fiber grating 322, or the fiber grating 332 and the chirped fiber grating 322 may be replaced.
May be replaced between the two.

Next, the operation of the fiber laser device according to the third embodiment will be described with reference to the drawings.

As shown in FIG. 6, a CW high-power laser beam having a wavelength λ 1 is input from a Raman fiber laser 300 to a silica-based fiber 310. Here, since the Raman fiber laser 300 has an optical fiber as the laser input means, the laser light of the wavelength λ1 is introduced into the core of the silica-based fiber 310.

The wavelength λ input to the silica-based fiber 310
One laser beam propagates through the core of the silica-based fiber 310. The quartz fiber 310 is folded back by the fiber grating 311, and the quartz fiber 31
0 stimulated Raman scattering is more activated. At this time, the silica-based fiber 3 is placed inside the optical resonator defined by the fiber grating 332 and the fiber grating 331.
Since there is 10, the laser light having the wavelength λ1 has gain near the wavelength λ2 when propagating through the silica-based fiber 310 as excitation light for stimulated Raman scattering. As a result, laser light having a wavelength λ2 is oscillated between the chirped fiber grating 321 and the fiber grating 331 by stimulated Raman scattering.

Further, since the pair of chirped fiber gratings 321 and 322 reflect the laser light in the wide wavelength range Δλ1, the laser light having the wavelength λ2 is transmitted as the excitation light for stimulated Brillouin scattering through the quartz fiber 310. , A narrow band gain is provided at a frequency lower than the wavelength λ2 by about 10 GHz. Here, the fiber gratings 331 and 332 narrow the wavelength range Δλ around the wavelength λ2.
The laser beam of s is oscillated, and the stimulated Brillouin scattering of the quartz fiber 310 is further activated. As a result, laser light of multiple wavelengths is oscillated one after another at intervals of about 10 GHz between the pair of chirped fiber gratings 321 and 322 due to stimulated Brillouin scattering.
The second laser beam spreads within a wide wavelength range Δλl.

Also, as a result of the combination of stimulated Brillouin scattering of the cascade with other nonlinear effects, for example, due to four-wave mixing between laser beams simultaneously propagating in the same direction, a multi-wavelength laser within a wide wavelength range Δλl is obtained. Light may be generated. Due to these nonlinear effects, laser light is oscillated between a pair of chirped fiber gratings 321 and 322 in a wide wavelength range Δλl.

Chirp fiber grating 322
Has a low reflectance as a laser output means,
Part of the laser light inside the optical resonator is output from the silica-based fiber via the chirped fiber grating 322. As in the case of the first embodiment, the spectrum distribution of the output laser light has a wide band as shown in FIG.

As described above, in the fiber laser device according to the third embodiment, the laser light having the wavelength λ1 and extending in the desired wide wavelength range is obtained.

Embodiment 4 FIG. Embodiment 4 A fiber laser device according to Embodiment 4 of the present invention will be described with reference to the drawings.

In the structures of the first to third embodiments, when the silica-based fiber contains a rare earth element that activates the stimulated emission effect by the laser beam having the wavelength λ1, the stimulated emission effect becomes larger than the nonlinear effect. Since the stimulated emission effect has a gain of the wavelength λ2 instead of the nonlinear effect, a similar effect can be obtained. For example, in a configuration similar to that of FIG. 1, 100 is a Raman fiber laser (laser light source) having a wavelength of λ1 (= 1480 nm), and 110 is a rare-earth-doped fiber (non-linear Fiber), 111 is wavelength λ1
Fiber grating that reflects the laser light of
Reference numerals 1 and 122 denote a pair of chirped fiber gratings (reflecting means) that reflect laser light in a wide wavelength range Δλ1 (= 10 nm) including the wavelength λ2 (= 1550 nm).

Next, the operation of the fiber laser device according to the fourth embodiment will be described with reference to the drawings.

As shown in FIG. 1, a laser beam having a wavelength of λ 1 having a high power and a CW is input from a Raman fiber laser 100 to a silica-based fiber 110. Here, the laser light having the wavelength λ1 is introduced into the core of the silica-based fiber 110.

The wavelength λ input to the silica-based fiber 110
One laser beam propagates through the core of the silica-based fiber 110. In addition, the silica-based fiber 110 is propagated by the fiber grating 111 in a folded manner, and
0 stimulates the stimulated release effect. At this time, the laser light having the wavelength λ1 has a gain near the wavelength λ2 when propagating through the quartz-based fiber 110 as excitation light for stimulated emission. As a result, laser light having a wavelength λ2 is oscillated between the pair of chirped fiber gratings 121 and 122 by stimulated emission.

Further, when the laser beam having the wavelength λ2 propagates through the silica-based fiber 110 as excitation light for stimulated Brillouin scattering, it has a narrow band gain at a frequency lower than the wavelength λ2 by about 10 GHz. As a result, stimulated Brillouin scattering causes a pair of chirped fiber gratings 12
Multi-wavelength laser light is oscillated one after another at intervals of about 10 GHz over wavelength λ2 between 1 and 122, and the laser light of wavelength λ2 spreads within a wide wavelength range Δλl.

Further, as a result of combining the cascaded stimulated Brillouin scattering with other nonlinear effects, multi-wavelength laser light may be generated within a wide wavelength range Δλ1 in some cases. Due to these non-linear effects, a wide wavelength range Δ between the pair of chirped fiber gratings 121 and 122.
Laser light is oscillated in the range of λ1.

Chirp fiber grating 122
A part of the laser light inside the optical resonator is output from the silica-based fiber 110 through the optical fiber. As in the case of the first embodiment, the spectrum distribution of the output laser light has a wide band as shown in FIG.

Embodiment 5 Embodiment 5 A fiber laser device according to Embodiment 5 of the present invention will be described with reference to the drawings. FIG. 7 is a diagram showing a configuration of a fiber laser device according to Embodiment 5 of the present invention.

In the configuration of the first to third embodiments, a plurality of pairs of laser light beams having a wavelength of λ1 or more and a wavelength of λ2 or less are reflected so as to define an optical resonator in a silica-based fiber. When a chirped fiber grating (reflection means) is provided, a similar effect can be obtained.

For example, in the configuration shown in FIG.
Is a Yb-doped fiber laser (laser light source) having a wavelength of λ1 (= 1064 nm), 410 is a silica-based fiber (non-linear optical fiber), 411 is a fiber grating that reflects laser light having a wavelength of λ1, 421 and 422 are wavelengths of λ
2 (= 1480 nm) and a wide wavelength range Δλl (= 50
431) is a fiber grating that reflects laser light in a narrow wavelength range Δλs around a wavelength λ2, and 441 and 442 are wavelength gratings λ3 (= 111).
A pair of fiber gratings 451 and 452 that reflect laser light of 6 nm) have a wavelength λ4 (= 1175n).
m) a pair of fiber gratings for reflecting laser light, 461 and 462 are a pair of fiber gratings for reflecting laser light of wavelength λ5 (= 1240 nm),
Reference numerals 471 and 472 denote a pair of fiber gratings that reflect laser light having a wavelength λ6 (= 1315 nm).
Reference numerals 1 and 482 denote a pair of fiber gratings that reflect laser light having a wavelength of λ7 (= 1395 nm).

Here, all the fiber gratings are formed on the silica-based fiber 410. Fiber gratings 411 and 441, 442 and 451, 452 and 461, 462 and 471, 472 and 481, 482
It has a reflectance of 99% or more for the laser light of each wavelength. As in the case of the first embodiment, the spectral distribution of the reflectance in the chirped fiber gratings 421 and 422 has a wide band as shown in FIGS. As in the case of the second embodiment, the spectral distribution of the reflectance in the fiber grating 431 has a narrow band as shown in FIG. 5A or 5B. The arrangement of the fiber grating 411 may be replaced with the chirped fiber grating 422 or between the fiber grating 431 and the chirped fiber grating 422.

Next, the operation of the fiber laser device according to the fifth embodiment will be described with reference to the drawings.

As shown in FIG. 7, a laser beam having a wavelength of λ1 having a high power and a CW is input from a Yb-doped fiber laser 400 to a silica-based fiber 410. Here, since the Yb-doped fiber laser 400 has an optical fiber as the laser input means, the laser light of the wavelength λ1 is introduced into the core of the silica-based fiber 410.

The wavelength λ input to the silica-based fiber 410
One laser beam propagates through the core of the silica-based fiber 410. The silica fiber 410 is folded back by the fiber grating 411, and the silica fiber 41
0 activates the nonlinear effect more. At this time, the wavelength λ
The laser beam 1 has a gain near the wavelength λ3 when propagating through the silica-based fiber 410 as excitation light of stimulated Raman scattering. As a result, laser light of wavelength λ3 is oscillated between the pair of fiber gratings 441 and 442 by stimulated Raman scattering.

The pair of fiber gratings 44
1, 442, a pair of fiber gratings 451, 452, and a pair of fiber gratings 4
61, 462, a pair of fiber gratings 461,
462, a pair of fiber gratings 471, 47
2. Since the silica-based fiber 410 is inside the optical resonator defined by the pair of fiber gratings 481 and 482, laser light having a wavelength λ2 between the chirped fiber grating 421 and the fiber grating 431 due to cascade stimulated Raman scattering. Is oscillated.

Further, when the laser light having the wavelength λ2 propagates through the silica-based fiber 410 as excitation light for stimulated Brillouin scattering, it has a narrow band gain at a frequency lower than the wavelength λ2 by about 10 GHz. Here, laser light in a narrow wavelength range Δλs is oscillated around the wavelength λ2 by the fiber grating 431, and the stimulated Brillouin scattering of the silica-based fiber 410 is further activated. As a result, the pair of chirped fiber gratings 421, 4
The laser light of multiple wavelengths is oscillated one after another at intervals of about 10 GHz above the wavelength λ2 between the laser beams 22, and the laser light of the wavelength λ2 spreads within a wide wavelength range Δλl.

Further, as a result of the combination of stimulated Brillouin scattering of the cascade and other nonlinear effects, multi-wavelength laser light may be generated within a wide wavelength range Δλ1 in some cases. Due to these non-linear effects, laser light is oscillated between a pair of chirped fiber gratings in a wide wavelength range Δλl.

[0077] Chirped fiber grating 422
A part of the laser light inside the optical resonator is output from the silica-based fiber 410 through the optical fiber. As in the case of the first embodiment, the spectrum distribution of the output laser light has a wide band as shown in FIG.

Embodiment 6 FIG. Embodiment 6 A fiber laser device according to Embodiment 6 of the present invention will be described with reference to the drawings.

In the structures of the first to fifth embodiments, the chirped fiber grating can obtain the same effect when the reflectance changes with respect to the wavelength. For example, in a configuration similar to the second embodiment shown in FIG. 4, a pair of chirped fiber gratings 221 and 222 are provided.
On the other hand, for example, the spectral distribution of the reflectance in the chirped fiber grating 222 has a wide band as shown in FIG.

Chirp fiber grating 222
When the reflectance distribution is constant within a wide wavelength range Δλ1 as shown in FIG. 2B, the laser light on the short wavelength side becomes the excitation light in the stimulated Brillouin scattering of the cascade. Therefore, as shown in FIG. 3, the shorter the wavelength, the higher the output power through the chirped fiber grating 222.

On the other hand, when the reflectance distribution in the chirped fiber grating 222 gradually increases as the wavelength becomes shorter than the wavelength λ2 as shown in FIG. 8, the stimulated Brillouin scattering of the cascade occurs. In FIG. 9, since the laser light on the short wavelength side oscillates with high power, the stimulated Brillouin scattering of the cascade is activated, and the shorter the wavelength, the higher the reflectivity of the fiber grating 222. As described above, the power of the laser beam is output through the chirped fiber grating 222 at a substantially constant power within a wide wavelength range Δλl. In this way, the spectral distribution of the reflectance in the chirped fiber grating 222 is arbitrarily set, and the spectral power density of the laser light oscillating between the pair of reflecting means is adjusted.

Embodiment 7 FIG. Embodiment 7 A fiber laser system according to Embodiment 7 of the present invention will be described with reference to the drawings. FIG. 10 is a diagram showing a configuration of a fiber laser system according to Embodiment 7 of the present invention.

In FIG. 10, reference numeral 500 denotes a broadband pump light source (fiber laser device) having any one of the first to sixth embodiments, and reference numeral 510 denotes an optical fiber for transmitting a signal light having a wavelength multiplexed at about 100 nm. (Optical transmission means),
Reference numeral 520 denotes a fiber coupler (laser coupling means) for introducing a laser beam of about 50 nm and a broad band output from the broad band excitation light source 500 into the optical fiber 510.

As shown in FIG. 10, the multiplexed signal light propagates through the optical fiber 510. The broadband laser light is output from the broadband pump light source 500 and coupled to the optical fiber 510 via the fiber coupler 520 in a direction opposite to the signal light. Further, when the spectrum width of the excitation light is wider than the spectrum width of the gain in stimulated Brillouin scattering, stimulated Brillouin scattering is suppressed, and high-power excitation light can be used. Note that the fiber coupler 520 is disposed in the optical fiber 510 so that the broadband laser light can sufficiently propagate, and the broadband laser light may be coupled in the same direction as the signal light.

The broadband laser light coupled to the optical fiber 510 propagates through the core of the optical fiber 510. At this time, when the broadband laser light propagates through the optical fiber 510 as excitation light of stimulated Raman scattering, it has a wideband gain of 100 nm or more corresponding to the wavelength multiplexed signal light. As a result, the optical fiber 510 is stimulated by stimulated Raman scattering.
The signal light having the wavelength multiplexed therein is subjected to Raman amplification.

In particular, when the broadband excitation light source 500 is the sixth embodiment, it is possible to easily optimize the spectral distribution of the output laser light by changing the spectral distribution of the reflectance in the reflection means. A flat gain distribution of Raman amplification can be obtained by setting the spectral power density of the pump light to an asymmetric pump wavelength arrangement in which short wavelength components increase.

[0087]

As described above, the fiber laser device according to claim 1 of the present invention amplifies a laser beam having an arbitrary first wavelength and amplifies a laser beam having a different second wavelength. , Includes a laser light source for generating a laser beam having the first wavelength, a first reflection unit having a first reflectance for the second wavelength, and an active medium for activating a nonlinear effect. An optical fiber for nonlinearity,
An optical resonator is defined in the nonlinear optical fiber, and is disposed at a position facing the first reflection means so as to sandwich the nonlinear optical fiber, and has a second reflectance with respect to the second wavelength. And a second reflecting means for reflecting the laser light having the second wavelength and outputting a part of the laser light having the second wavelength.
The reflection means reflects laser light in a wide wavelength range including the second wavelength, and the optical resonator amplifies the laser light having the second wavelength with the laser light having the first wavelength. At the same time, since the laser light having the second wavelength spreads and oscillates in a wide wavelength range due to the non-linear effect, the laser light has expanded from a laser light of any first wavelength to a desired wide wavelength range. This has the effect of obtaining light.

As described above, in the fiber laser device according to the second aspect of the present invention, an optical resonator is defined in the nonlinear optical fiber, and the first reflecting means is provided so as to sandwich the nonlinear optical fiber. Since it further includes a third reflecting means which is disposed at an opposite position, has a third reflectance with respect to the second wavelength, and reflects laser light in a narrow wavelength range around the second wavelength. The laser beam having an arbitrary first wavelength can obtain a laser beam spread within a desired wide wavelength range.

As described above, the fiber laser device according to claim 3 of the present invention defines an optical resonator in the nonlinear optical fiber, and is disposed on both sides of the nonlinear optical fiber so as to sandwich the nonlinear optical fiber. Third and fourth reflecting means having third and fourth reflectances for the second wavelength and reflecting laser light in a narrow wavelength range around the second wavelength are further provided. There is an effect that a laser beam spread within a desired wide wavelength range can be obtained from the laser beam of the first wavelength.

In the fiber laser device according to a fourth aspect of the present invention, as described above, the nonlinear optical fiber contains a rare earth element that activates the stimulated emission effect by the laser light having the first wavelength. Since the laser beam having the second wavelength is amplified inside the optical resonator by the laser beam having the first wavelength based on the stimulated emission effect, the laser beam having any first wavelength can be amplified to a desired wide wavelength. There is an effect that a laser beam spread within the range can be obtained.

As described above, the fiber laser device according to claim 5 of the present invention defines an optical resonator in the nonlinear optical fiber, and is disposed on both sides of the nonlinear optical fiber so as to sandwich the nonlinear optical fiber. A plurality of pairs of reflecting means for reflecting laser light having a wavelength equal to or greater than one wavelength and equal to or less than the second wavelength, wherein the laser light having the first wavelength is illuminated inside the optical resonator by a cascaded nonlinear effect; Since the laser light having the wavelength of .lamda. Is amplified, it is possible to obtain a laser light having an arbitrary first wavelength within a desired wide wavelength range.

As described above, the fiber laser device according to claim 6 of the present invention comprises a pair of the first and second pairs.
Of the reflecting means, at least one of the reflecting means has a change in the refractive index change and a change in the reflectance with respect to the wavelength. There is an effect that a laser beam spread within the range can be obtained.

As described above, in the fiber laser device according to claim 7 of the present invention, the one reflecting means includes:
Since the reflectivity gradually increases as the wavelength is shorter than or equal to the second wavelength, it is possible to obtain laser light having an arbitrary first wavelength within a desired wide wavelength range. It has the effect of being able to.

As described above, the fiber laser system according to the eighth aspect of the present invention includes a fiber laser device according to any one of the first to seventh aspects for outputting a broadband laser light, and a wavelength multiplexing apparatus. Optical transmission means for transmitting the converted signal light, and laser coupling means for introducing the broadband laser light output from the fiber laser device to the optical transmission means. It has the effect of being able to amplify.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a fiber laser device according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing a spectral distribution of reflectance in a chirped fiber grating of the fiber laser device according to Embodiment 1 of the present invention.

FIG. 3 is a diagram showing a spectrum distribution of output laser light of the fiber laser device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a fiber laser device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a spectral distribution of reflectance in a fiber grating 231 of the fiber laser device according to Embodiment 2 of the present invention.

FIG. 6 is a diagram showing a configuration of a fiber laser device according to Embodiment 3 of the present invention.

FIG. 7 is a diagram showing a configuration of a fiber laser device according to Embodiment 5 of the present invention.

FIG. 8 is a diagram showing a spectral distribution of reflectance in a chirped fiber grating 222 of a fiber laser device according to Embodiment 6 of the present invention.

FIG. 9 is a diagram showing a spectrum distribution of output laser light of a fiber laser device according to Embodiment 6 of the present invention.

FIG. 10 is a diagram showing a configuration of a fiber laser system according to Embodiment 7 of the present invention.

FIG. 11 is a diagram showing a configuration of a conventional fiber laser device.

[Explanation of symbols]

100 Nd: YAG laser (laser light source) with wavelength λ1 (= 1064 nm), 110 silica-based fiber (non-linear optical fiber), 111 fiber grating, 1
21, 122 Chirped fiber grating (reflection means), 200 wavelength λ1 (= 1315 nm) Raman fiber laser (laser light source), 210 silica-based fiber (non-linear optical fiber), 211 fiber grating, 221, 222 chirped fiber grating (Reflection means), 231 fiber grating, 300 wavelength λ1 (= 1385 nm) Raman fiber laser (laser light source), 310 silica-based fiber (non-linear optical fiber), 311 fiber grating, 321, 322 chirped fiber grating (reflection means) ), 331, 332 A pair of fiber gratings, Y of 400 wavelength λ1 (= 1064 nm)
b-doped fiber laser (laser light source), 410 quartz-based fiber (non-linear optical fiber), 411 fiber grating, 421, 422 chirped fiber grating (reflection means), 431 fiber grating, 441, 442 fiber grating, 4
51, 452 fiber grating, 461, 46
2 fiber grating, 471, 472 fiber grating, 481, 482 fiber grating, 500 broadband excitation light source (laser output means),
510 Optical fiber (optical transmission means), 520 Fiber coupler (laser coupling means).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2K002 AA02 AB12 BA01 CA15 DA10 HA23 HA24 5F072 AB07 AB09 AK06 KK07 QQ06 QQ07 YY17

Claims (8)

[Claims] 1. A fiber laser device for inputting a laser beam having an arbitrary first wavelength and amplifying a laser beam having a different second wavelength, comprising: a laser light source for generating the laser beam having the first wavelength; A first reflecting means having a first reflectance for the second wavelength; a nonlinear optical fiber including an active medium for activating a nonlinear effect; and an optical resonator defined in the nonlinear optical fiber. A laser beam having a second reflectance with respect to the second wavelength and having the second wavelength is disposed at a position facing the first reflecting means so as to sandwich the nonlinear optical fiber. A second reflecting means for reflecting and outputting a part of the laser light having the second wavelength, wherein the pair of the first and second reflecting means have a wide wavelength range including the second wavelength. Reflecting the laser light in the region, the optical resonator, The laser light having the second wavelength is amplified by the laser light having the first wavelength, and the laser light having the second wavelength spreads and oscillates in a wide wavelength range due to a non-linear effect. Characteristic fiber laser device. 2. An optical resonator is defined in the nonlinear optical fiber, the optical resonator is arranged at a position facing the first reflecting means so as to sandwich the nonlinear optical fiber, and a second optical wavelength is defined with respect to the second wavelength. 2. The fiber laser device according to claim 1, further comprising third reflecting means having a reflectance of 3 and reflecting laser light in a narrow wavelength range around the second wavelength. 3. An optical resonator is defined in the non-linear optical fiber, and is disposed on both sides of the non-linear optical fiber so as to sandwich the non-linear optical fiber. 2. The fiber laser device according to claim 1, further comprising third and fourth reflection means for reflecting the laser light in a narrow wavelength range around the second wavelength. 4. The non-linear optical fiber includes a rare-earth element that activates a stimulated emission effect by the laser light having the first wavelength, and the first optical fiber based on the stimulated emission effect.
The fiber laser device according to any one of claims 1 to 3, wherein the laser light having the second wavelength is amplified inside the optical resonator by the laser light having the wavelength. 5. An optical resonator is defined in the non-linear optical fiber, and is disposed on both sides of the non-linear optical fiber so as to sandwich the non-linear optical fiber, and reflects laser light having the first wavelength or more and the second wavelength or less. The laser light having the first wavelength amplifies the laser light having the second wavelength inside the optical resonator by a cascaded nonlinear effect. The fiber laser device according to any one of claims 1 to 3. 6. A method according to claim 1, wherein at least one of the pair of first and second reflecting means has a change in the refractive index change and a change in the reflectance with respect to the wavelength. The fiber laser device according to any one of claims 1 to 5, wherein 7. The fiber laser device according to claim 6, wherein the reflectance of the one reflecting means gradually increases as the wavelength is longer than the second wavelength and shorter. 8. A fiber laser device according to claim 1, which outputs a broadband laser light, an optical transmission means for transmitting wavelength-multiplexed signal light, and said fiber laser device. And a laser coupling means for introducing broadband laser light output from the optical transmission means to the optical transmission means.