JP5384059B2 - Fiber laser resonator and laser oscillation method using fiber laser resonator - Google Patents

Description

  The present invention relates to a fiber laser resonator and a laser oscillation method using the fiber laser resonator. More specifically, the present invention relates to a laser beam using a nonlinear optical effect generated by a gain fiber disposed in the fiber laser resonator. The present invention relates to a fiber laser resonator capable of generating and suppressing generation of unnecessary laser light and a laser oscillation method using the fiber laser resonator.

  In recent years, fiber laser resonators constructed using gain fibers in which laser-active elements are added to optical fiber glass used in optical communications have become microfabrication technologies in the electronics industry such as semiconductor manufacturing processes. Various proposals have been made with the aim of application.

Specifically, the gain fiber is configured such that the optical waveguide layer of the optical fiber is doped with rare earth ions such as erbium (Er) ions and yttrium (Yb) ions as an active medium of the laser. Is.

Here, the above-described conventional fiber laser resonator propagates high-intensity light. At this time, since the cross-sectional area is small and high-intensity light is confined in an elongated gain fiber, various types are used. It is known that a nonlinear optical effect is induced.

  For example, when Raman scattering occurs in the fiber laser resonator, Stokes light that is Stokes-shifted to a wavelength shifted by the phonon frequency specific to the material of the fiber material of the gain fiber with respect to the signal light is generated.

  This nonlinear effect due to Raman scattering dissipates energy from the signal light, and is usually regarded as a problem with fiber laser resonators. However, it is possible to actively use this to extend the oscillation wavelength. It is.

  For example, a fiber laser resonator composed of a gain fiber and a plurality of fiber Bragg gratings (FBGs) is configured, and the fundamental wave is resonated by the inner resonator and the Stokes light is resonated by the outer resonator. Thus, Non-Patent Document 1 discloses a technique for performing laser oscillation at a Stokes-shifted wavelength.

  According to the fiber laser resonator using the nonlinear effect due to such Raman scattering, for example, when a quartz fiber added with yttrium (Yb) ions is used as a gain fiber, when 1080 nm light is generated as a fundamental wave, Since light having a wavelength of about 1140 nm is generated as the primary Stokes light and light having a wavelength of about 1210 nm is generated as the secondary Stokes light, various types of light having a wavelength different from the original wavelength of the emitted ions can be oscillated. It becomes possible.

However, since fiber Bragg gratings and mirrors reflect only a certain band, it is impossible to change the reflection band greatly using these.

  In other words, the spectrum to be oscillated depends on the reflection characteristics of the fiber Bragg grating and mirror, and it is not easy to control the wavelength, such as oscillating light of different wavelengths, once the fiber laser resonator is configured. There was a problem.

In addition, since the fiber laser resonator generates laser light that generally shows a broad emission spectrum, when a reflective element having a wide wavelength range is used, oscillation occurs in a wide band. It is not suitable for applications where a laser beam with a narrow line width is required.

  Here, Non-Patent Document 2 discloses a mirror that places a prism inside a fiber laser resonator, confines the fundamental wave by a method of configuring the fiber laser resonator with a diffraction angle corresponding to the wavelength to be extracted, and transmits Stokes light. In this example, only the wavelength tunable Stokes light is extracted from the optical fiber. However, the line width is limited by the prism dispersion, so it is generally broad, and the mechanical rotation mechanism exists in the fiber laser resonator. In addition, there is a problem that it is mechanically unstable.

On the other hand, as another problem of the fiber laser resonator, there is a problem of having strong amplified spontaneous emission (ASE) noise.

  The ASE noise may cause problems such as a decrease in efficiency and an increase in noise because spontaneously scattered light is amplified in the gain fiber laser and excitation energy becomes noise and energy to signal light relatively decreases. In particular, this is a problem in a fiber laser resonator in which excitation light is confined in a small-diameter gain fiber.

More specifically, in a fiber laser resonator that has been subjected to a pulse operation, particularly when the repetition frequency is low, the ASE noise rapidly increases between pulses.

  Here, as a technique for reducing the ASE noise, there is a technique in which the ASE noise is taken out of the fiber laser resonator before the ASE noise grows.

  In the well-known Fabry-Perot type fiber laser resonator, band reflection elements such as fiber Bragg gratings and narrow band mirrors are arranged in the fiber laser resonator, and the laser of the reflection band of those elements. Since only light returns to the fiber laser resonator and is amplified, an increase in ASE noise can be suppressed.

However, since such a band reflection element has a fixed reflection band or can be adjusted only slightly, the broadband property which is one of the characteristics of the fiber laser resonator is completely impaired. It was a new problem that would end up.

Also, in applications such as spectroscopy where signal light requires extremely high spectral purity, very low output ASE noise that cannot be avoided even with a continuous wave fiber laser resonator may affect the measurement. There was a problem that there was.

In order to reduce such noise, a technology for constructing a tunable fiber laser resonator by combining an acousto-optic tunable filter (AOTF) configured with a crystal having birefringence and a gain fiber, Although disclosed in Non-Patent Document 3 shown below, a technique for controlling including a nonlinear optical effect derived from a gain fiber is not shown.

In addition, Patent Documents 1 to 3 shown below disclose technologies in which an acoustooptic wavelength tunable filter is disposed in a wavelength tunable solid fiber laser resonator and wavelength tuning is realized by an external electric signal. This is intended only for tuning the oscillation wavelength of a solid-state laser.
S. A. Skubchenko, M.M. Y. Vyatkin, D.C. V. Gapontsev, IEEE Photon, Technol. Lett. 16, 1014 (2004) R. H. Stolen, C.I. Lin, J. et al. Shah, R .; F. Leheny, IEEE J.M. Quantum Electron. 14, 860 (1978) D. A. Smith, M.M. W. Maeda, J .; J. et al. Johnson, J.M. S. Patel, M.M. A. Saifi, A .; Von Lehman, Opt. Lett. 16, 387 (1991) JP-A-8-139398 JP-A-9-298331 JP 9-298332 A

  The present invention has been made in view of the above-described various problems of the prior art, and an object of the present invention is to tune the wavelength range of laser light oscillated by utilizing optical nonlinearity. The present invention intends to provide a fiber laser resonator and a laser oscillation method using the fiber laser resonator so as to maintain a broadband property in a wavelength range.

  The present invention has been made in view of the above-mentioned various problems of the prior art, and its object is to reduce the ASE noise generated in the fiber laser resonator. An object of the present invention is to provide a fiber laser resonator and a laser oscillation method using the fiber laser resonator.

  In order to achieve the above object, according to the present invention, an acoustooptic wavelength tunable filter is inserted into a fiber laser resonator, and the intensity of light other than laser light having a desired wavelength generated in the fiber laser resonator is arbitrarily set. It is designed to be controllable.

Therefore, according to the present invention, when laser oscillation is performed by designating a wavelength at which gain of the gain fiber exists, a laser having a narrow line width corresponding to the transmission spectrum width of the acoustooptic wavelength tunable filter is oscillated. At this time, by applying the one whose reflection factor is slightly reduced with respect to the wavelength, it is possible to oscillate at the fundamental wave, and the electric signal to be applied to the acoustooptic wavelength tunable filter. When the frequency is increased or decreased, the wavelength can be varied within the gain range of the gain fiber, and the broadband property of the wavelength range can be maintained.

  Further, according to the present invention, since no mechanical movement is performed, laser oscillation that is mechanically stable and highly reproducible can be realized, and ASE noise generated in the fiber laser resonator is reduced. be able to.

That is, the fiber laser resonator according to the first aspect of the present invention includes a first feedback element that reflects light having a wide wavelength range with a high reflectivity, and a gain that is disposed after the first feedback element. A fiber, a light source that inputs excitation light to the gain fiber from the outside of the fiber laser resonator, and an acoustooptic that is arranged downstream of the gain fiber and diffracts light having a wavelength according to the frequency of the supplied RF signal A fiber comprising: a wavelength tunable filter; an RF power source that supplies an RF signal to the acoustooptic wavelength tunable filter; and a second feedback element that partially reflects light diffracted by the acoustooptic wavelength tunable filter. a laser resonator, light and diffraction wavelength der other than the diffraction wavelength is light not more diffracted to the acoustic-optic tunable filter The but light not diffracted by the diffraction efficiency is output to the outside without being amplified by the fiber laser cavity, the acousto-optic light more diffracted to the wavelength tunable filter, is partially reflected in the second feedback element Light that is amplified by reciprocating between the second feedback element and the first feedback element and is not partially reflected by the second feedback element is output to the outside of the fiber laser resonator. is there.

According to a second aspect of the present invention, there is provided a fiber laser resonator comprising: a first feedback element that reflects light having a broadband wavelength with high reflectivity; and a gain disposed at a stage subsequent to the first feedback element. A fiber, a light source that inputs excitation light to the gain fiber from the outside of the fiber laser resonator, and an acoustooptic that is arranged downstream of the gain fiber and diffracts light having a wavelength according to the frequency of the supplied RF signal A fiber comprising: a wavelength tunable filter; an RF power source that supplies an RF signal to the acoustooptic wavelength tunable filter; and a second feedback element that totally reflects light diffracted by the acoustooptic wavelength tunable filter. a laser resonator, light diffracted by the acousto-optic tunable filter, the second is totally reflected in the second feedback element Is amplified back and forth between the feedback element and the first feedback element, except the diffraction wavelength including Stokes light generated in the fiber laser resonator is a light not more diffracted to the acoustic-optic tunable filter light and is a diffraction wavelength not diffracted by the diffraction efficiency of light is obtained by the so that the output to the outside of the fiber laser cavity.

According to a third aspect of the present invention, there is provided a fiber laser resonator according to a third aspect of the present invention, wherein a first feedback element that reflects light having a wide wavelength range with a high reflectivity and a gain disposed at a subsequent stage of the first feedback element. The fiber, the light source that inputs the excitation light to the gain fiber from the outside of the fiber laser resonator, and the frequency of a plurality of types of RF signals that are arranged at the subsequent stage of the gain fiber and that are supplied with different frequencies, respectively. An acousto-optic wavelength tunable filter that diffracts light of different wavelengths, an RF power source that supplies a plurality of types of RF signals having different frequencies to the acousto-optic wavelength tunable filter, and different wavelengths diffracted by the acousto-optic tunable filter among the light, a second for partially reflecting light of a different wavelength from the said predetermined wavelength with the totally reflecting light of a predetermined wavelength Instead a fiber laser resonator, characterized in that it comprises an element, is a light and diffraction wavelengths other than the diffracted wavelength is light not more diffracted to the acoustic-optic tunable filter is not diffracted by the diffraction efficiency of light is output to the outside without being amplified by the fiber laser cavity, among more diffracted light to the acousto-optic tunable filter, the light of the predetermined wavelength is totally reflected at the second feedback element Of the light that is amplified by reciprocating between the second feedback element and the first feedback element and diffracted by the acoustooptic wavelength tunable filter, light having a wavelength different from the predetermined wavelength Is partially reflected by the second feedback element, amplified by reciprocating between the second feedback element and the first feedback element, and partially reflected by the second feedback element. Isa is not light, is obtained so as to be outputted to the outside of the fiber laser cavity.

According to a fourth aspect of the present invention, there is provided a fiber laser resonator according to a first feedback element that reflects light having a wide wavelength range with high reflectivity, and a gain disposed at a subsequent stage of the first feedback element. The fiber, the light source that inputs the excitation light to the gain fiber from the outside of the fiber laser resonator, and the frequency of a plurality of types of RF signals that are arranged at the subsequent stage of the gain fiber and that are supplied with different frequencies, respectively. An acousto-optic wavelength tunable filter that diffracts light of different wavelengths, an RF power source that supplies a plurality of types of RF signals having different frequencies to the acousto-optic wavelength tunable filter, and different wavelengths diffracted by the acousto-optic tunable filter a fiber laser resonator and having a second feedback element which totally reflects the light, the acousto-optic Light diffracted in the length variable filter is totally reflected in the second feedback element is amplified back and forth between the second feedback element and the first feedback element, the acoustic-optic tunable filter so that it is light and diffraction wavelengths other than the diffracted wavelength including Stokes light generated in the fiber laser resonator is a light not diffracted light not diffracted by the diffraction efficiency is output to the outside of the fiber laser resonator in It is a thing.

A laser oscillation method using the fiber laser resonator according to claim 5 of the present invention is a laser oscillation method using the fiber laser resonator according to claim 1 of the present invention. light is a light and diffraction wavelengths other than the diffracted wavelength not diffracted by the diffraction efficiency is a light not more diffracted to the optical wavelength variable filter is output to the outside without being amplified by the fiber laser cavity, the acousto-optic light more diffracted wavelength tunable filter, is partially reflected in the second feedback element is amplified back and forth between the second feedback element and the first feedback element, said second feedback Light that is not partially reflected by the element is output to the outside of the fiber laser resonator .

The laser oscillation method using the fiber laser resonator according to a sixth aspect of the present invention, there is provided a laser oscillation method using the fiber laser resonator according to claim 2 of the present invention, the acoustic The light diffracted by the optical wavelength tunable filter is totally reflected by the second feedback element, amplified by reciprocating between the second feedback element and the first feedback element, and the acoustooptic wavelength variable. light is a light and diffraction wavelengths other than the diffracted wavelength including Stokes light generated in the fiber laser resonator is a light not more diffracted to the filter not diffracted by the diffraction efficiency is output to the outside of the fiber laser resonator It was made to do.

A laser oscillation method using the fiber laser resonator according to claim 7 of the present invention is a laser oscillation method using the fiber laser resonator according to claim 3 of the present invention. light is a light and diffraction wavelengths other than the diffracted wavelength not diffracted by the diffraction efficiency is a light not more diffracted to the optical wavelength variable filter is output to the outside without being amplified by the fiber laser cavity, the acousto-optic among the more diffracted light in the wavelength tunable filter, the light of the predetermined wavelength, reciprocates between the second is totally reflected in the feedback element and the second feedback element and the first feedback element Of the light amplified and diffracted by the acousto-optic wavelength tunable filter, light having a wavelength different from the predetermined wavelength is partially reflected in the second feedback element. Isa is being amplified back and forth between the second feedback element and the first feedback element, so that the second is not partially reflecting the feedback element light is output to the outside of the fiber laser resonator It is a thing.

The laser oscillation method using the fiber laser resonator according to claim 8 of the present invention, there is provided a laser oscillation method using the fiber laser resonator according to a fourth aspect of the present invention, the acoustic The light diffracted by the optical wavelength tunable filter is totally reflected by the second feedback element, amplified by reciprocating between the second feedback element and the first feedback element, and the acoustooptic wavelength variable. Light other than the diffraction wavelength including Stokes light generated in the fiber laser resonator, which is light that has not been diffracted by the filter, and light that is a diffraction wavelength but is not diffracted by the diffraction efficiency are output to the outside of the fiber laser resonator. It is what I did.

  Since the present invention is configured as described above, a fiber laser resonator that retains broadband characteristics in the wavelength range by expanding the tuning wavelength range of laser light oscillated by utilizing optical nonlinearity. In addition, it is possible to provide a laser oscillation method using a fiber laser resonator.

  Further, since the present invention is configured as described above, it is possible to provide a fiber laser resonator in which ASE noise generated in the fiber laser resonator is reduced and a laser oscillation method using the fiber laser resonator. There is an excellent effect of being able to.

  Hereinafter, embodiments of a fiber laser resonator and a laser oscillation method using the fiber laser resonator according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram of a conceptual configuration of a fiber laser resonator 10 according to the first embodiment of the present invention. The fiber laser resonator 10 according to the first embodiment of the present invention includes: A so-called Fabry-Perot resonator, which is a laser beam generated by an excitation semiconductor laser light source 26 (described later) between an output mirror 12 which is a reflection element and a fiber Bragg grating (FBG) 14. A coupler 16 that introduces light into a gain fiber 18 (described later), an end of which is connected to the coupler 16 and a core of the optical fiber is doped with a laser active medium, and is generated by a semiconductor laser source 26 for excitation. A gain fiber 18 that is pumped by pump light and outputs laser light, and an end of the gain fiber 18 The laser beam connected to 18b and output from the gain fiber 18 to the collimator lens 22 (described later), and the laser beam disposed after the coupler 20 and emitted from the coupler 20 Is arranged between the collimating lens 22 that makes the parallel light, the collimating lens 22 on the optical path of the fiber laser resonator 10 and the output mirror 12, and receives a high-frequency signal (RF signal) from a high-frequency power source (RF power source) (not shown). An acoustooptic wavelength tunable filter 24 that can diffract laser light having a predetermined wavelength when supplied is configured.

  In the laser resonator 10, the excitation light is generated by an excitation semiconductor laser light source 26 disposed outside the laser resonator 10, and the excitation semiconductor laser light source 26 has no gain substance. It is connected to the coupler 16 via a passive fiber 28.

  That is, the excitation light generated by the excitation semiconductor laser light source 26 enters the coupler 16 disposed in the fiber laser resonator 10 via the passive fiber 28.

  Further, an RF power source (not shown) is disposed in the vicinity of the acousto-optic wavelength tunable filter 24 as means for inputting an RF signal to the acousto-optic wavelength tunable filter 24. The RF power source is acoustically operated by a personal computer (not shown). The frequency of the RF signal supplied to the optical wavelength variable filter 24 can be controlled.

  The laser light diffracted inside the acoustooptic wavelength tunable filter 24 is determined by the frequency of the RF signal supplied from such an RF power source.

  The diffracted light that is the laser light diffracted by the acousto-optic tunable filter 24 is reflected into the fiber laser resonator 10 in accordance with the reflectance of the output mirror 12, and the fiber in accordance with the transmittance of the output mirror 12. The light is emitted to the outside of the laser resonator 10.

  On the other hand, non-diffracted light that is not diffracted by the acoustooptic wavelength tunable filter 24 is output to the outside of the fiber laser resonator 10.

In the present embodiment, the output mirror 12, which is one feedback element, is configured to have a reflectance of 30% and a transmittance of 70% for light having a wavelength of 1030 nm.

  In the present embodiment, the fiber Bragg grating 14 as the other feedback element is one that can reflect light with a wide wavelength range with high reflectivity. Specifically, the fiber Bragg grating 14 is light with a wavelength of 1030 nm. The wavelength can be specified by having a reflectivity of 99%.

  Furthermore, as the gain fiber 18, ytterbium (Yb) is used as a gain medium in the present embodiment, and a gain fiber having a wavelength range of 1000 to 1120 nm is used.

  Furthermore, in the present embodiment, a spatial acoustooptic wavelength tunable filter is used as the acoustooptic wavelength tunable filter 24.

  In the present embodiment, the excitation semiconductor laser light source 26 generates laser light having a wavelength of 975 nm as excitation light.

In the above configuration, in the fiber laser resonator 10 according to the first embodiment of the present invention, when an RF signal is input to the acoustooptic wavelength tunable filter 24 from the RF power supply, the acoustooptic wavelength tunable filter 24 is Only the light determined by the frequency of the acoustic wave generated in the acousto-optic tunable filter 24 is diffracted according to the frequency of the more input RF signal.

  On the other hand, the pumping light generated by the pumping semiconductor laser light source 26 is incident on the gain fiber 18 from the end 18a of the gain fiber 18 via the passive fiber 28 and the coupler 16, and the laser activity of the gain fiber 18 is caused by this pumping light. The medium is excited.

The fiber laser resonator 10 is configured for the diffracted light of the acoustooptic wavelength tunable filter 24 between the fiber Bragg grating 14 and the output mirror 12. Although the gain fiber 18 has a wide gain wavelength band, only the limited narrow wavelength region is diffracted by the wavelength tunable filter 24 and can circulate inside the fiber laser resonator 10. Only the selected narrow band light is emitted as laser light from the output mirror 12 to the outside.

Next, the operation of the above-described fiber laser resonator 10 will be described in more detail. The acoustooptic wavelength tunable filter 24 is used, for example, in a laser resonator disclosed in JP-A-9-172215. Since the same configuration as that of the acoustooptic wavelength tunable filter may be used, detailed description of the configuration and operation related to the same will be omitted.

  In the following description, a case where laser light having a wavelength of 1030 nm (hereinafter referred to as laser light λ1 as appropriate) is output from the output mirror 12 as diffracted light will be described.

Thus, in order to obtain the laser light λ1 having a wavelength of 1030 nm as diffracted light, a TeO ₂ crystal or the like is used as the acoustooptic wavelength variable filter 24, and the frequency of the RF signal supplied from the RF power source is the laser having the wavelength of 1030 nm. A frequency suitable for diffracting the light λ1 is set.

First, the excitation semiconductor laser light source 26 is driven to oscillate laser light, and the laser light is incident on the coupler 16 through the passive fiber 28 as excitation light.

  The excitation light incident on the coupler 16 enters the gain fiber 18 from the coupler 16 through the end 18 a of the gain fiber 18, and the laser active medium is excited in the gain fiber 18.

  The laser light is emitted from the end 18 b of the gain fiber 18, passes through the coupler 20, and is collected by the collimating lens 22.

  The laser light converted into parallel light by the collimator lens 22 is incident on the acoustooptic wavelength variable filter 24.

  At this time, the acoustooptic wavelength tunable filter 24 is supplied with an RF signal having a frequency suitable for diffracting the laser beam λ1 having a wavelength of 1030 nm from the RF power source. The light λ 1 is diffracted, and the laser light λ 1 that is the diffracted diffracted light reaches the output mirror 12.

  Here, in the present embodiment, the output mirror 12 has a reflectance of 30% and a transmittance of 70% with respect to the light having a wavelength of 1030 nm, that is, the laser light λ1 that is diffracted light. The laser light λ1 that has reached the output mirror 12 is reflected by the output mirror 12 according to the above-described reflectance and returned to the fiber Bragg grating 14, and is transmitted through the output mirror 12 according to the above-described transmittance and passed through the fiber. The light is emitted to the outside of the laser resonator 10.

That is, a part of the laser light λ1 reaching the output mirror 12 is reflected by the output mirror 12, passes through the acoustooptic wavelength tunable filter 24, the collimator lens 22 and the coupler 20 again, and ends 18b of the gain fiber 18 More incident on the gain fiber 18.

  Further, the laser light λ1 that has passed through the gain fiber 18 is emitted from the end 18a of the gain fiber 18 and enters the coupler 16.

  Next, the laser light λ1 emitted from the coupler 16 reaches the fiber Bragg grating 14.

  Of the laser light reaching the fiber Bragg grating 14, only the laser light λ1 is reflected by the fiber Bragg grating 14 and is incident on the coupler 16 again. Similarly to the above, the laser light λ1 is emitted from the coupler 16 and gained. The laser beam λ 1 enters the gain fiber 18 from the end 18 b of the fiber 18, and is emitted from the end 18 b of the gain fiber 18, passes through the coupler 20 and the collimating lens 22, and reaches the acoustooptic wavelength tunable filter 24. Become.

  As described above, since the RF signal having a frequency suitable for diffracting the laser beam λ1 is supplied from the RF power source to the acoustooptic wavelength tunable filter 24, the laser beam λ1 is diffracted by the acoustooptic wavelength tunable filter 24. The diffracted light reaches the output mirror 12.

  In this way, the laser beam λ1 is amplified by reciprocating between the output mirror 12 and the fiber Bragg grating 14 in the fiber laser resonator 10.

By the way, the intensity of the laser light amplified in the fiber laser resonator 10 in a state where the laser light that becomes the fundamental wave as described above, that is, the laser light λ1 is confined in the fiber laser resonator 10 and oscillated. When the value exceeds the threshold value for the occurrence of Raman scattering, the first-order Stokes light S1, which is light that is wavelength-shifted by an amount corresponding to the phonon frequency of the gain medium of the gain fiber, compared with the laser light that is the fundamental wave, It is newly generated inside the fiber laser resonator 10.

  In the present embodiment, since the RF signal that diffracts only the laser beam λ1 serving as the fundamental wave is supplied to the acoustooptic wavelength tunable filter 24, the first-order Stokes light S1 generated in this way is the acoustooptic wavelength tunable. The light is not diffracted by the filter 24 and is emitted from the acousto-optic wavelength tunable filter 24 to the outside of the fiber laser resonator 10 as non-diffracted light.

Here, FIG. 2 shows the state of the reflectance of the output mirror in the fiber laser resonator, the state of the acoustooptic wavelength tunable filter (the type of laser light diffracted by the acoustooptic wavelength tunable filter), and the fiber laser. A chart summarizing explanatory diagrams conceptually showing the output intensities of diffracted light and non-diffracted light output from the resonator is shown.

  FIG. 3 is a conceptual explanatory diagram illustrating diffracted light and non-diffracted light output from the fiber laser resonator 10 according to the present embodiment.

In the column (a) of FIG. 2 described above, the state of the reflectance of the output mirror 12 in the fiber laser resonator 10 and the state of the acoustooptic wavelength tunable filter 24 (the laser beam diffracted by the acoustooptic wavelength tunable filter 24). 2), and an explanatory diagram conceptually showing the output intensities of the diffracted light and the non-diffracted light output from the fiber laser resonator 10 is shown. As shown in FIG. 3, in the fiber laser resonator 10, an output mirror 12 that partially reflects the laser beam λ1 is used, and further, the acoustooptic wavelength tunable filter 24 is diffracted so that only the laser beam λ1 is diffracted. Since the RF signal is supplied to, the first-order Stokes light S1 is obtained as non-diffracted light, and the laser light λ1 is obtained as diffracted light.

  Since the primary Stokes light S1 is emitted from the acousto-optic wavelength tunable filter 24 as non-diffracted light, it returns to the fiber laser resonator 10 and is output to the outside without being amplified. It is weak and has a broad waveform.

  On the other hand, since the laser light λ1 that is diffracted light is amplified and emitted in the fiber laser resonator 10, the intensity of the obtained light is strong and has a waveform with a narrow line width.

Thus, according to the above-described fiber laser resonator 10 according to the present embodiment, there is no mechanical movable part without performing an operation such as changing the angle of the members constituting the fiber laser resonator 10. Using the element, it is possible to separate laser light such as first-order Stokes light generated by the nonlinear optical effect and laser light that is a fundamental wave, while giving high loss to ASE noise, Since the resonance wavelength of the signal light can be controlled by the RF signal, a fiber laser resonator that becomes a low-noise wavelength tunable laser device can be realized as a result.

  Further, according to the fiber laser resonator 10 according to the above-described embodiment, the laser generated by deriving from the signal light by the nonlinear optical effect is controlled by the frequency of the RF signal supplied to the acoustooptic wavelength tunable filter 24. It is also possible to diffract the light by the acoustooptic wavelength tunable filter 24.

  That is, in the fiber laser resonator 10, the control of the wavelength of the laser beam output from the fiber laser resonator 10 and the extraction of the laser beam to the outside are controlled by the frequency of the RF signal supplied to the acoustooptic wavelength tunable filter 24. can do.

Next, a fiber laser resonator 200 according to a second embodiment of the present invention will be described with reference to FIG.

  The fiber laser resonator 200 is different from the fiber laser resonator 10 according to the first embodiment in that an output mirror 220 is provided instead of the output mirror 12 and two different types of the acoustooptic wavelength tunable filter 24 are provided. This is different from the point that an RF signal having a frequency of 1 is given.

  In the following description, the same or equivalent components as those of the fiber laser resonator according to the first embodiment of the present invention described with reference to FIGS. 1 to 3 are the same as those used above. Detailed description of the configuration and operation will be omitted as appropriate by using reference numerals.

  The output mirror 220 in the fiber laser resonator 200 is totally reflected with respect to the laser light λ1 generated in the fiber laser resonator 200, and is part of the primary Stokes light S1 generated in the fiber laser resonator 200. A mirror configured to reflect.

  The RF signals having two different frequencies given to the acoustooptic wavelength tunable filter 24 are an RF signal having a frequency required for diffracting the laser light λ1 and an RF signal having a frequency required for diffracting the first-order Stokes light S1. Signal.

  That is, the fiber laser resonator 200 is intended to output the primary Stokes light S1 from the output mirror 220 to the outside of the fiber laser resonator 200.

  For this reason, the acousto-optic wavelength tunable filter 24 has two different RF signals having a frequency suitable for diffracting the laser light λ1 and an RF signal having a frequency suitable for diffracting the laser light as the first-order Stokes light. RF signals of various frequencies will be supplied.

Hereinafter, the operation of the fiber laser resonator 200 will be described in detail. Since the laser light λ1 generated in the fiber laser resonator 200 having the above-described configuration is totally reflected by the output mirror 220, the above-described first operation is performed. Based on the same principle as that of the fiber laser resonator 10 according to the embodiment, amplification is performed by reciprocating between the output mirror 220 and the FBG 14, and amplification is continued without being output from the output mirror 220.

  Then, when the intensity of the amplified laser light λ1 exceeds the threshold value of the occurrence of Raman scattering, the first-order Stokes light that is wavelength-shifted by an amount corresponding to the phonon frequency of the medium of the gain fiber compared to the fundamental wave. S1 is newly generated inside the fiber laser resonator 200.

  In the fiber laser resonator 200, since the RF signal is supplied to the acoustooptic wavelength tunable filter 24 so that the first-order Stokes light S1 is also diffracted in the same manner as the laser light λ1, the inside of the fiber laser resonator 200 in this way. The first-order Stokes light S1 generated in the diffracted light is diffracted by the acousto-optic tunable filter 24 and emitted as second diffracted light to the output mirror 220. A part of the reflected light is reflected by the output mirror 220 and a part thereof is a fiber laser. The light is emitted to the outside of the resonator 200.

In the column (c) of FIG. 2 described above, the state of the reflectance of the output mirror 220 in the fiber laser resonator 200 and the state of the acoustooptic wavelength tunable filter 24 (the laser beam diffracted by the acoustooptic wavelength tunable filter 24). 2), and an explanatory diagram conceptually showing the output intensities of the diffracted light and the non-diffracted light output from the fiber laser resonator 200, and the column (c) in FIG. As shown in FIG. 4, in the fiber laser resonator 200, an output mirror 220 that totally reflects the laser light λ1 and partially reflects the primary Stokes light S1 is used. Since the RF signal is supplied to the acoustooptic wavelength tunable filter 24 so as to diffract the secondary Stokes light S1, the laser light λ1 and the primary Stokes light S1 are diffracted. The laser beam λ1 which is obtained as diffracted light together with the optical beam S1 and is emitted from the acoustooptic wavelength tunable filter 24 is totally reflected by the output mirror 220 and fed back into the fiber laser resonator 200. The first-order Stokes light S1, which is the diffracted light emitted from the optical wavelength tunable filter 24, is output to the outside of the fiber laser resonator 200 as laser light having a strong intensity and a waveform with a narrow line width.

Further, in the fiber laser resonator 200, the intensity of the primary Stokes light S1 amplified in the fiber laser resonator 200 is generated by Raman scattering based on the same principle as that of the primary Stokes light S1 described above. The second-order Stokes light S2, which is light that is wavelength-shifted by an amount corresponding to the phonon frequency of the medium of the gain fiber as compared with the first-order Stokes light S1, is generated inside the fiber laser resonator 200. Newly occurs.

  Since the secondary Stokes light S2 is emitted without being diffracted by the acoustooptic wavelength tunable filter 24, it is emitted outside the fiber laser resonator 200 as non-diffracted light (see FIG. 4).

  The column (c) in FIG. 2 shows the waveform of the secondary Stokes light emitted from the acoustooptic wavelength tunable filter 24. The secondary Stokes light is a fiber laser resonator 200. Since the laser beam is emitted outside the fiber laser resonator 200 without being amplified, the output intensity is weak and the light has a broad waveform.

As described above, in addition to the effects obtained by the fiber laser resonator 10 according to the first embodiment, in the fiber laser resonator 200 according to the second embodiment, the primary Stokes light having a narrow line width is acoustically generated. It can be extracted as diffracted light from the optical wavelength variable filter 24.

  That is, by appropriately selecting the frequency of the RF signal supplied to the acousto-optic wavelength tunable filter 24, it becomes possible to extend the oscillation wavelength of the gain fiber. It is possible to realize a fiber laser resonator that generates narrow-line-width laser light that oscillates at a wavelength and that can tune the wavelength.

As described above, since the fiber laser resonators 10 and 200 are configured using elements that do not have mechanical movable parts, a series of fiber laser resonators are different from conventional fiber laser resonators using gain fibers. Therefore, it is possible to realize a fiber laser resonator having high mechanical stability and high reproducibility.

  Furthermore, operating the acousto-optic wavelength tunable filter 24 in the fiber laser resonators 10 and 200 gives an arbitrary spectral profile to the Q value of the resonator, so various functions are added as a laser oscillation device. It becomes possible to do.

In general, the parameters for controlling the acousto-optic tunable filter 24 include the frequency and input intensity of an input RF signal.

Since the frequency of the RF signal is uniquely determined with respect to the wavelength of the diffracted laser beam, the diffracted wavelength for the laser beam is selected according to the input RF frequency.

The input intensity of the RF signal determines the diffraction efficiency of the laser beam in the acoustooptic wavelength tunable filter 24. Here, when the diffraction efficiency is high, the loss of the fiber laser resonator is low. Further, when the diffraction efficiency is low, the loss of the fiber laser resonator becomes large, which means that the overall gain is reduced.

On the other hand, the gain of the gain fiber, which is a laser medium, depends on the wavelength, and even if the gain is within a wavelength range, there are high gain and low gain depending on the wavelength.

Furthermore, since other components of the fiber laser resonator can be said to have a dependency on the wavelength, the loss is generally reduced at a certain wavelength, and the loss is increased at a certain wavelength. .

Accordingly, both the acousto-optic wavelength tunable filter 24 and the entire fiber laser resonator have a high gain wavelength and a low wavelength depending on the wavelength.

In general, the higher the gain, the easier it is to extract the output intensity from the laser.

Therefore, in the above-described fiber laser resonator according to the present invention, if the diffraction efficiency is finely controlled for each wavelength by the input intensity of the RF signal, the gain of the entire fiber laser resonator can be set so as not to depend on the wavelength. Even if any wavelength is selected in the wavelength variable region, a constant intensity can always be output.

Furthermore, this method can give an arbitrary wavelength dependency to the output intensity.

Furthermore, according to the fiber laser resonators 10 and 200, the wavelength of the extracted Stokes light also changes by changing the resonance wavelength of the fundamental wave, so that the high nonlinear optical effect of the gain fiber is positively achieved with a simple configuration. Therefore, the wavelength range that can be generated by the gain fiber 18 can be extended.

  Furthermore, since the fiber laser resonators 10 and 200 can suppress unnecessary spectrum light output from the gain fiber 18 by disposing the output mirrors 12 and 220 after the acoustooptic wavelength tunable filter 24, spectroscopy or the like. It is also suitable for applications that dislike spectral noise.

Each embodiment described above can be modified as shown in the following (1) to (6).

  (1) In the fiber laser resonator 10 according to the first embodiment described above, the output mirror 12 that partially reflects the generated laser light λ1 is used. However, the present invention is not limited to this. Thus, an output mirror 120 that totally reflects the laser beam λ1 may be used as in the fiber laser resonator 100 illustrated in FIG. 5 which is a modification of the fiber laser resonator 10.

  More specifically, the fiber laser resonator 100 differs from the fiber laser resonator 10 according to the first embodiment only in that an output mirror 120 is provided instead of the output mirror 12.

  In the following description, the same or equivalent configuration as the fiber laser resonator 10 described with reference to FIGS. 1 to 3 is indicated by using the same reference numerals as those used above. Detailed description of the configuration and operation will be omitted as appropriate.

  Here, the operation of the fiber laser resonator 100 will be described. The laser light λ1 generated in the fiber laser resonator 100 is totally reflected by the output mirror 120 and reciprocates between the output mirror 120 and the fiber Bragg grating 14. Will continue to amplify.

  The primary Stokes light S1 generated in the fiber laser resonator 100 is emitted as non-diffracted light from the acoustooptic wavelength variable filter 24 to the outside of the fiber laser resonator 100. The first-order Stokes light S1 that is non-diffracted light emitted to the outside is laser light having a strong output intensity and a broad waveform shape as shown in the column (b) of FIG.

  On the other hand, since the laser light λ1 that is diffracted light is totally reflected by the output mirror 120, the output intensity of the diffracted light output from the output mirror 120 becomes weak.

  Therefore, according to the fiber laser resonator 100 described above, the primary Stokes light S1 can be output to the outside of the fiber laser resonator 100.

  (2) The laser resonator 200 according to the second embodiment uses the output mirror 220 that totally reflects the generated laser light λ1 and partially reflects the primary Stokes light S1. However, the present invention is not limited to this, and both of the laser beam λ1 and the primary Stokes beam S1 are used as in a laser resonator 300 illustrated in FIG. 6 which is a modification of the fiber laser resonator 200. Alternatively, an output mirror 320 that totally reflects the light may be used.

  More specifically, the fiber laser resonator 300 differs from the fiber laser resonator 200 according to the second embodiment described above only in that an output mirror 320 is provided instead of the output mirror 220.

  In the following description, the same or corresponding configuration as the fiber laser resonator 200 described with reference to FIGS. 1 to 4 is indicated by using the same reference numerals as those used above. Detailed description of the configuration and operation will be omitted as appropriate.

  Here, the operation of the fiber laser resonator 300 will be described. The laser light λ1 and the primary Stokes light S1 generated in the fiber laser resonator 300 are totally reflected by the output mirror 320, and the output mirror 320, the fiber Bragg grating 14, and the like. It continues to amplify by reciprocating between.

  Since the laser light λ1 and the primary Stokes light S1 generated in the fiber laser resonator 300 continue to be amplified without being extracted to the outside, the output intensity of the diffracted light output from the output mirror 320 is weak. Become.

  The fiber laser resonator 300 also generates secondary Stokes light S2 from the amplified primary Stokes light S1 based on the same principle as the fiber laser resonator 200.

  Such secondary Stokes light S2 is laser light having a strong output intensity and a broad waveform shape as shown in the column (d) of FIG.

  Therefore, according to the fiber laser resonator 300 described above, the secondary Stokes light S2 can be output to the outside of the fiber laser resonator 300.

  (3) In each of the above-described embodiments, the fiber laser resonator of each of the above-described embodiments is configured by a Fabry-Perot resonator using a reflective element that reflects light having a wide wavelength range. Of course, the laser resonator according to each of the above embodiments may be configured by a ring resonator using a partially coupled device.

  (4) In each of the above-described embodiments, one of the feedback elements constituting the fiber laser resonator is a mirror and the other is a fiber Bragg grating, but it is of course not limited thereto. For example, a fiber Bragg grating may be used for both feedback elements, or an element such as a fiber loop may be applied.

  (5) In each of the above-described embodiments and modifications, the description has been given of the case where an acousto-optic wavelength tunable filter for spatial waveguide is used. However, the present invention is not limited to this. An acousto-optic wavelength tunable filter may be used.

  (6) In each of the above-described embodiments and modifications, a case has been described in which RF signals of two types of frequencies are supplied from the RF power source to the acoustooptic wavelength tunable filter 24. However, the present invention is not limited to this. Of course, three or more types of RF signals having a plurality of types of frequencies are supplied to the acoustooptic wavelength tunable filter 24, and the reflectivities of the output mirrors 12, 120, 220, and 320 are selected according to the RF signals. A plurality of types of laser light may be output from the mirrors 12, 120, 220, and 320 as diffracted light of the acoustooptic wavelength tunable filter 24, and a plurality of types of laser light may be output from the acoustooptic wavelength tunable filter 24. You may make it output as diffracted light.

  (7) In each of the above-described embodiments and modifications, the diffracted light diffracted by the acousto-optic wavelength tunable filter is directly incident on the output mirror. However, the present invention is not limited to this. In addition, a dispersion correcting prism for correcting the dispersion of the diffracted light may be provided between the acoustooptic wavelength tunable filter and the output mirror.

  In FIG. 7, a fiber laser resonator 400 is illustrated. The laser resonator 400 is different from the laser resonator 10 according to the first embodiment only in that a correction prism 402 is provided between the output mirror 12 and the acoustooptic wavelength tunable filter 24.

  As described above, by arranging the correction prism between the output mirror and the acoustooptic wavelength tunable filter, the directivity of the laser light emitted from the output mirror can be made constant.

  (8) In each of the above-described embodiments and modifications, the case where the light output is taken out from the output mirror disposed on the acousto-optic wavelength tunable filter side has been described. However, the present invention is not limited to this. The diffracted light circulating through the laser resonator may be taken out from a feedback element disposed on the opposite side with the acoustooptic wavelength tunable filter and the gain fiber interposed therebetween.

  (9) You may make it combine suitably the embodiment shown above and the modification shown in said (1) thru | or (8).

  The present invention can be used for a laser oscillation device used in a field that dislikes spectral noise such as a spectroscopic device.

FIG. 1 is an explanatory diagram of a conceptual configuration of a fiber laser resonator according to a first embodiment of the present invention. FIG. 2 shows the state of reflectance of the output mirror in the fiber laser resonator, the state of the acoustooptic wavelength tunable filter (shows the type of laser light diffracted by the acoustooptic wavelength tunable filter), and the output from the fiber laser resonator. Is a chart summarizing explanatory diagrams conceptually showing the output intensities of diffracted light and non-diffracted light, and the column (a) relates to the fiber laser resonator according to the first embodiment, and The column (b) relates to a modification of the fiber laser resonator according to the first embodiment, and the column (c) relates to a fiber laser resonator according to the second embodiment. The column (d) relates to a modification of the fiber laser resonator according to the second embodiment. FIG. 3 is a conceptual explanatory diagram illustrating diffracted light and non-diffracted light output from the fiber laser resonator according to the first embodiment of the present invention. FIG. 4 is a conceptual explanatory diagram illustrating diffracted light and non-diffracted light output from the fiber laser resonator according to the second embodiment of the present invention. FIG. 5 is a conceptual explanatory diagram illustrating diffracted light and non-diffracted light output from a laser resonator which is a modification of the fiber laser resonator according to the first embodiment of the present invention. FIG. 6 is a conceptual explanatory diagram illustrating diffracted light and non-diffracted light output from a laser resonator which is a modification of the fiber laser resonator according to the second embodiment of the present invention. FIG. 7 is a conceptual explanatory diagram illustrating a fiber laser resonator which is a modification of the laser resonator according to the first embodiment of the present invention.

Explanation of symbols

10, 100, 200, 300 Fiber laser resonator 12, 120, 220, 320 Output mirror 14 Fiber Bragg grating (FBG)
16, 20 coupler 18 gain fiber 22 collimating lens 24 acousto-optic tunable filter (AOTF)
26 Excited semiconductor light source 28 Passive fiber

Claims (8)

A first feedback element that reflects light of a wide wavelength range with high reflectivity;
A gain fiber disposed downstream of the first feedback element;
A light source for inputting excitation light to the gain fiber from the outside of the fiber laser resonator;
An acousto-optic tunable filter that is disposed at the subsequent stage of the gain fiber and diffracts light having a wavelength corresponding to the frequency of the supplied RF signal;
An RF power source for supplying an RF signal to the acousto-optic tunable filter;
A fiber laser resonator comprising: a second feedback element that partially reflects the light diffracted by the acoustooptic wavelength tunable filter;
The acoustooptic the wavelength of light and diffraction wavelengths other than the diffracted wavelength is light not more diffracted to the variable filter not diffracted by the diffraction efficiency of light is output to the outside without being amplified by the fiber laser resonator,
The acousto-optic wavelength light more diffracted to the variable filter is amplified back and forth between the said is partially reflected at the second feedback element and the second feedback element and the first feedback element, said first 2. A fiber laser resonator, wherein light that is not partially reflected by the feedback element of 2 is output to the outside of the fiber laser resonator. A first feedback element that reflects light of a wide wavelength range with high reflectivity;
A gain fiber disposed downstream of the first feedback element;
A light source for inputting excitation light to the gain fiber from the outside of the fiber laser resonator;
An acousto-optic tunable filter that is disposed at the subsequent stage of the gain fiber and diffracts light having a wavelength corresponding to the frequency of the supplied RF signal;
An RF power source for supplying an RF signal to the acousto-optic tunable filter;
A fiber laser resonator, comprising: a second feedback element that totally reflects light diffracted by the acoustooptic wavelength tunable filter,
The light diffracted by the acousto-optic wavelength tunable filter is totally reflected by the second feedback element and amplified by reciprocating between the second feedback element and the first feedback element,
The acoustic-optic tunable filter is an optical and diffraction wavelengths other than the diffracted wavelengths including more Stokes light generated in the fiber laser resonator is a light that is not diffracted but are not diffracted by the diffraction efficiency light, fiber laser resonator fiber laser resonator, characterized in that to the outside Ru output. A first feedback element that reflects light of a wide wavelength range with high reflectivity;
A gain fiber disposed downstream of the first feedback element;
A light source for inputting excitation light to the gain fiber from the outside of the fiber laser resonator;
An acousto-optic tunable filter that diffracts light of different wavelengths according to the frequency of a plurality of types of RF signals having different frequencies that are disposed after the gain fiber and supplied,
An RF power source for supplying a plurality of types of RF signals having different frequencies to the acousto-optic tunable filter;
A second feedback element that totally reflects light having a predetermined wavelength among the light having different wavelengths diffracted by the acoustooptic wavelength tunable filter and partially reflects light having a wavelength different from the predetermined wavelength; A fiber laser resonator characterized by comprising:
The acoustooptic the wavelength of light and diffraction wavelengths other than the diffracted wavelength is light not more diffracted to the variable filter not diffracted by the diffraction efficiency of light is output to the outside without being amplified by the fiber laser resonator,
Among the more diffracted light to the acousto-optic tunable filter, the light of the predetermined wavelength, and said total reflection has been the second feedback element and the second feedback element and the first feedback element Of the light that is amplified back and forth and diffracted by the acousto-optic tunable filter, light having a wavelength different from the predetermined wavelength is partially reflected by the second feedback element, and the second feedback element. A fiber laser resonance characterized in that light which is amplified by reciprocating between a feedback element and the first feedback element and is not partially reflected by the second feedback element is output to the outside of the fiber laser resonator. vessel. A first feedback element that reflects light of a wide wavelength range with high reflectivity;
A gain fiber disposed downstream of the first feedback element;
A light source for inputting excitation light to the gain fiber from the outside of the fiber laser resonator;
An acousto-optic tunable filter that diffracts light of different wavelengths according to the frequency of a plurality of types of RF signals having different frequencies that are disposed after the gain fiber and supplied,
An RF power source for supplying a plurality of types of RF signals having different frequencies to the acousto-optic tunable filter;
A fiber laser resonator comprising: a second feedback element that totally reflects light of different wavelengths diffracted by the acoustooptic wavelength tunable filter,
The light diffracted by the acousto-optic tunable filter is totally reflected by the second feedback element and amplified by reciprocating between the second feedback element and the first feedback element,
Light other than the diffraction wavelength including Stokes light generated in the fiber laser resonator, which is light that has not been diffracted by the acousto-optic wavelength tunable filter, and light that is diffracted but not diffracted by the diffraction efficiency of the fiber laser resonator fiber laser resonator, characterized in that that will be output to the outside. A laser oscillation method using the fiber laser resonator according to claim 1,
The acoustooptic the wavelength of light and diffraction wavelengths other than the diffracted wavelength is light not more diffracted to the variable filter not diffracted by the diffraction efficiency of light is output to the outside without being amplified by the fiber laser resonator,
The acousto-optic wavelength light more diffracted to the variable filter is amplified back and forth between the said is partially reflected at the second feedback element and the second feedback element and the first feedback element, said first 2. A laser oscillation method using a fiber laser resonator, wherein light that is not partially reflected by the feedback element of 2 is output to the outside of the fiber laser resonator. A laser oscillation method using the fiber laser resonator according to claim 2,
The light diffracted by the acousto-optic wavelength tunable filter is totally reflected by the second feedback element and amplified by reciprocating between the second feedback element and the first feedback element,
The acoustic-optic tunable filter is an optical and diffraction wavelengths other than the diffracted wavelengths including more Stokes light generated in the fiber laser resonator is a light that is not diffracted but are not diffracted by the diffraction efficiency light, fiber laser resonator Laser oscillation method using a fiber laser resonator, characterized by being output to the outside of the laser. A laser oscillation method using the fiber laser resonator according to claim 3,
The acoustooptic the wavelength of light and diffraction wavelengths other than the diffracted wavelength is light not more diffracted to the variable filter not diffracted by the diffraction efficiency of light is output to the outside without being amplified by the fiber laser resonator,
Among the more diffracted light to the acousto-optic tunable filter, the light of the predetermined wavelength, and said total reflection has been the second feedback element and the second feedback element and the first feedback element Of the light that is amplified back and forth and diffracted by the acousto-optic tunable filter, light having a wavelength different from the predetermined wavelength is partially reflected by the second feedback element, and the second feedback element. Light which is amplified by reciprocating between a feedback element and the first feedback element and is not partially reflected by the second feedback element is output to the outside of the fiber laser resonator. Laser oscillation method using fiber laser resonator. A laser oscillation method using the fiber laser resonator according to claim 4,
The light diffracted by the acousto-optic tunable filter is totally reflected by the second feedback element and amplified by reciprocating between the second feedback element and the first feedback element,
Light other than the diffraction wavelength including Stokes light generated in the fiber laser resonator, which is light that has not been diffracted by the acousto-optic wavelength tunable filter, and light that is diffracted but not diffracted by the diffraction efficiency of the fiber laser resonator A laser oscillation method using a fiber laser resonator, characterized by being output to the outside .

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