Optical amplification device and optical amplification method

Abstract

To provide a light amplification device that amplifies multiple pulse lights with different wavelengths into pulse lights with high peak energy.SOLUTION: A light amplification device 1 includes: an optical fiber amplification unit 11 that amplifies two pulse laser lights having at least a first wavelength λ1 and a second wavelength λ2 that are different from each other while propagating the two pulse laser lights with a time difference and outputs first amplified light and second amplified light that are amplified lights of the pulse laser lights; and an optical distance adjustment unit 12 that differentiates optical distances at which the first amplified light and the second amplified light that are emitted from the optical fiber amplification unit propagate and superimposes the first amplified light and the second amplified light on each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical amplifier. and an optical amplification method Regarding. This application claims priority based on Japanese Patent Application No. 2020-191940, filed on November 18, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, pulse laser systems have been known that amplify time-separated pulsed light and then recombine it (for example, Patent Document 1). However, they do not amplify multiple pulsed light beams with different wavelengths into pulsed light beams each having a high peak energy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japan Special Publication No. 2014-522097 Summary of the Invention

[0004] An optical amplification device according to a first aspect includes an optical fiber amplifier that amplifies two pulsed laser beams having at least a first wavelength λ1 and a second wavelength λ2 that are different from each other while propagating them with a time difference, and outputs first amplified light and second amplified light, which are the amplified light of the pulsed laser beams, respectively; and an optical distance adjustment unit that differentiates the optical distances over which the first amplified light and the second amplified light emitted from the optical fiber amplifier propagate, and superimposes the first amplified light and the second amplified light. [Brief explanation of the drawings]

[0005] [Figure 1] 1 is a block diagram schematically illustrating a configuration of a main part of an optical amplifier according to a first embodiment. [Figure 2A] FIG. 4 is a diagram schematically showing the relationship between the first pulse laser beam and the second pulse laser beam and time. [Figure 2B]FIG. 4 is a diagram schematically showing the relationship between the first pulse laser beam and the second pulse laser beam and time. [Figure 3A] 1 is a block diagram schematically illustrating a configuration of a main part of an optical amplifier according to a first embodiment. [Figure 3B] 1 is a block diagram schematically illustrating a configuration of a main part of an optical amplifier according to a first embodiment. [Figure 4] FIG. 10 is a block diagram schematically illustrating the configuration of a main part of an optical amplifier according to a second embodiment. [Figure 5] FIG. 10 is a block diagram schematically illustrating the configuration of a main part of an optical amplifier according to a third embodiment. [Figure 6A] FIG. 10 is a block diagram schematically illustrating the configuration of a main part of an optical amplifier according to a fourth embodiment. [Figure 6B] FIG. 10 is a block diagram schematically illustrating the configuration of a main part of an optical amplifier according to a fourth embodiment. [Figure 7] FIG. 10 is a block diagram schematically illustrating a configuration of a main part of an optical amplifier according to a second embodiment. [Figure 8] FIG. 10 is a block diagram schematically illustrating the configuration of a main part of an optical amplifier according to a fifth embodiment. [Figure 9] FIG. 10 is a block diagram schematically illustrating the configuration of a main part of an optical amplifier according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] An optical amplifying device according to an embodiment of the present invention includes an optical fiber amplifier for amplifying at least two pulsed laser beams having a first wavelength λ1 and a second wavelength λ2 that are different from each other, and an optical distance adjuster for superimposing the amplified first amplified beam and the second amplified beam. The optical fiber amplifier amplifies and outputs the two pulsed laser beams while propagating them with a time difference. The optical distance adjuster is configured to differentiate the optical distances over which the first amplified beam and the second amplified beam emitted from the optical fiber amplifier propagate. This makes it possible to avoid spectral distortion and the generation of unnecessary spectral components due to nonlinear optical processes (such as four-wave mixing (FWM), cross-phase modulation (XPM), and stimulated Raman scattering (SRS)) occurring within the optical fiber amplifier when multiple pulsed laser beams having different wavelengths are simultaneously amplified in a single optical fiber amplifier. By superimposing the two pulsed laser beams amplified with a time difference by the optical distance adjuster, the two pulsed laser beams can be output in a state in which spectral distortion and the generation of unnecessary spectral components are suppressed. This will be explained in detail below.

[0007] First Embodiment An optical amplifier according to a first embodiment will be described with reference to the drawings. Note that this embodiment is specifically described to facilitate understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0008] Fig. 1 is a block diagram showing a schematic example of a configuration of the main parts of an optical amplifier 1. For convenience of explanation, a Cartesian coordinate system consisting of an X-axis, a Y-axis, and a Z-axis is set as shown in Fig. 1. Fig. 1 shows a case where the X-axis is set along the propagation direction of the laser pulse light, the Y-axis is set perpendicular to the X-axis and points upward on the page, and the Z-axis is set perpendicular to the X-axis and Y-axis and points toward the front of the page.

[0009] The optical amplifier 1 has an optical fiber amplifier 11, an optical distance adjuster 12, and a deflector 13. The incident unit 10 is connected to a light source 3. The light source 3 has a first light source 301 and a second light source 302. The first light source 301 and the second light source 302 are each controlled by a controller 4 to output pulsed laser light.

[0010] The first light source 301 outputs a first pulse laser beam having a first wavelength λ1 to an optical path 311. The second light source 302 outputs a second pulse laser beam having a second wavelength λ2, which is different from the first wavelength λ1, to an optical path 312. The first light source 301 and the second light source 302 have various circuits for supplying power. For example, a semiconductor laser (laser diode) can be used as each of the first light source 301 and the second light source 302. The first pulse laser beam and the second pulse laser beam are controlled by a control unit 4, which will be described later, and are output with a time difference τ. This time difference τ is larger than the pulse width of either the first pulse laser beam from the first light source 301 or the second pulse laser beam from the second light source 302. The first pulse laser beam and the second pulse laser beam propagate along the same optical path by the multiplexer 310 and enter the incident unit 10. In the following description, an example will be given in which the first wavelength λ1 is shorter than the second wavelength λ2 and the first pulse laser beam is output after a certain time has elapsed since the second pulse laser beam was output. FIGS. 2A and 2B schematically show the relationship between the first and second pulse laser beams and time. In FIG. 2A, the horizontal axis represents time, and the time difference between the peak of the first pulse laser beam A1 and the peak of the second pulse laser beam A2 is τ. The first and second pulse laser beams output from the light source 3 propagate in the state shown in FIG. 2A. Furthermore, the first pulsed laser beam and the second pulsed laser beam can be linearly polarized by disposing a polarizing plate between combiner 310 and incident unit 10 of light source 3 in Fig. 1. This polarizing plate is disposed so that the electric field oscillation directions of the first pulsed laser beam and the second pulsed laser beam combined by combiner 310 are both aligned along the plane of the drawing.

[0011] The optical fiber amplifier 11 is a fiber doped with a rare earth element, such as a single-mode fiber that pumps the rare earth element using a known core pumping method or a double-clad fiber that pumps the rare earth element using a clad pumping method. Examples of rare earth elements that can be used include ytterbium (Yb), erbium (Er), praseodymium (Pr), neodymium (Nd), and thulium (Tm). For example, the optical fiber amplifier 11 may be a fiber doped with ytterbium, a fiber doped with erbium, or a fiber co-doped with erbium and ytterbium.

[0012] The rare earth element in the optical fiber amplifier 11 is excited by pumping light output from a pumping light source (not shown) for exciting the optical fiber amplifier 11. In this state, the first pulse laser light and the second pulse laser light are incident on the optical fiber amplifier 11 with the time difference τ described above. The optical fiber amplifier 11 amplifies the incident first pulse laser light and outputs the first amplified light from the output unit 19. The optical fiber amplifier 11 amplifies the incident second pulse laser light and outputs the second amplified light from the output unit 19. The first pulse laser light and the second pulse laser light propagate through the optical fiber amplifier 11 with the time difference τ. As described above, the time difference τ is larger than the pulse width of both the first pulse laser light from the first light source 301 and the second pulse laser light from the second light source 302, and therefore no nonlinear interaction occurs between the first pulse laser light and the second pulse laser light propagating through the optical fiber amplifier 11. In other words, the first pulse laser light and the second pulse laser light propagate through the optical fiber amplifier 11 with a sufficient time difference so that no nonlinear interaction occurs between them. The first amplified light and the second amplified light are also output from the optical fiber amplifier 11 with the above-mentioned time difference τ. Therefore, the first amplified light and the second amplified light output from the optical fiber amplifier 11 have the relationship shown in FIG. 2A.

[0013] The optical distance adjustment unit 12 is configured so that the first amplified light and the second amplified light emitted from the optical fiber amplifier 11 propagate over different optical distances. The optical distance adjustment unit 12 superimposes the first amplified light and the second amplified light that have propagated over different optical distances. The optical distance adjustment unit 12 is configured, for example, by multiple reflecting members, or multiple diffraction gratings and reflecting members. When the optical distance adjustment unit 12 is configured with multiple reflecting members, as will be described in detail below, different optical distances are achieved by arranging the reflecting unit (first reflecting unit) that reflects the first amplified light and the reflecting unit (second reflecting unit) that reflects the second amplified light at different distances from the output position of the optical fiber amplifier 11. When the difference in optical distance caused by the arrangement of the first reflecting unit and the second reflecting unit causes the time difference occurring when the first amplified light and the second amplified light propagate respectively to be the time difference τ described above, the first amplified light and the second amplified light output from the optical distance adjustment unit 12 are completely superimposed. FIG. 2B , with time represented on the horizontal axis, shows a state in which the first amplified light and the second amplified light are completely superimposed, i.e., the time difference between the peaks of the first pulse laser light A1 and the second pulse laser light A2 is zero. When optical distance adjustment unit 12 is configured with multiple diffraction gratings and a reflecting member, as will be described in detail below, the first amplified light and the second amplified light pass through the diffraction grating, propagate along different optical paths, and are reflected by the reflecting member. The first amplified light and the second amplified light reflected by the reflecting member pass through the diffraction grating again and exit optical distance adjustment unit 12. When the time difference τ occurs when the first amplified light and the second amplified light propagate due to a difference in optical distance caused by passing through the diffraction grating, the first amplified light and the second amplified light exiting optical distance adjustment unit 12 are completely superimposed, as shown in FIG. 2B .

[0014] The deflection element 13 is provided in the optical path between the optical fiber amplifier 11 and the optical distance adjuster 12. The deflection element 13 is, for example, a polarizing beam splitter (PBS) or a branching optical element configured by an optical member having a transmitting section and a reflecting section. The deflection element 13 changes the propagation direction of the first amplified light and the second amplified light from the optical distance adjuster 12. The first amplified light and the second amplified light, whose propagation direction has been changed by the deflection element 13, are output from the output section 20. Depending on the positional relationship between the optical fiber amplifier section 11 and the optical distance adjuster section 12, the optical amplifier 1 may be configured without the deflector element 13.

[0015] The control unit 4 is a processor having a microprocessor and its peripheral circuits, etc., and controls each unit of the optical amplifier 1 by reading and executing a control program stored in advance in a storage medium (not shown, for example, a flash memory, etc.). The control unit 4 may be configured with a CPU, an ASIC, a programmable MPU, etc. The control unit 4 controls the degree of superposition of the first amplified light and the second amplified light output from the optical distance adjustment unit 12 by controlling the time difference when the first pulsed laser light and the second pulsed laser light are output from the first light source 301 and the second light source 302, respectively. When this time difference τ is controlled so that the optical distance difference in the optical distance adjustment unit 12 becomes equal to the time difference generated when the first amplified light and the second amplified light propagate, the first amplified light and the second amplified light output from the optical distance adjustment unit 12 are completely superimposed.

[0016] A specific example of the optical amplifying device 1 described above will be described below. Example 1 The optical amplifying device 1 will be described in the case where the optical distance adjusting section 12-1 has a first reflecting section that reflects the first amplified light and a second reflecting section that reflects the second amplified light. 3A is a block diagram schematically illustrating the configuration of the main parts of the optical amplifier 1 according to the first embodiment. The optical amplifier 1 includes an optical fiber amplifier 11, an optical distance adjuster 12-1, a deflector 13-1, a polarization adjuster 14, a light source 3, and a controller 4. The optical fiber amplifier 11, the light source 3, and the controller 4 have the same configurations as those described with reference to FIG. 1. The optical amplifier 1 does not necessarily have to include the light source 3 and the controller 4.

[0017] The deflection element 13-1 is a polarizing beam splitter (PBS). The deflection element 13-1 reflects the S-polarized component of the first amplified light and the second amplified light output from the optical fiber amplifier 11 and transmits the P-polarized component. The P-polarized first amplified light and the second amplified light that have passed through the deflection element 13-1 propagate along the X direction in the figure. The polarization adjustment element 14 is disposed between the optical fiber amplifier 11 and the optical distance adjustment unit 12-1. Here, we consider the case where a 45-degree Faraday rotator is used as the polarization adjustment element 14. The electric field oscillation direction (polarization direction) of the linearly polarized (P-polarized) first amplified light and the second amplified light output from the deflection element 13-1 is rotated by 45 degrees by the polarization adjustment element 14. In addition to a Faraday rotator, a quarter-wave plate can be used as the polarization adjustment element 14.

[0018] The first amplified light and the second amplified light, whose electric field oscillation direction has been rotated 45° by the polarization state adjusting element 14, are incident on the optical distance adjusting unit 12-1. The optical distance adjusting unit 12-1 has a first reflecting unit 121 that transmits the second amplified light of the second wavelength λ1 and reflects the first amplified light of the first wavelength λ1, and a second reflecting unit 122 that reflects the second amplified light of the second wavelength λ2. The first reflecting unit 121 and the second reflecting unit 122 are narrowband reflecting mirrors in which a dielectric thin film is formed on the surface (a surface parallel to the YZ plane) of an optically transparent substrate made of glass or other material. A short-pass filter, a long-pass filter, or the like can also be used. A wideband mirror with small wavelength dependency can also be used for the second reflecting unit 122. As described above, the first reflecting unit 121 and the second reflecting unit 122 are arranged at positions different distances from the output position of the optical fiber amplifier 11. 3A , first reflecting unit 121 is disposed on the negative side in the X direction relative to second reflecting unit 122. When controller 4 controls the emission timings of the first and second pulse laser beams so that the time it takes for the second amplified beam to travel back and forth between first reflecting unit 121 and second reflecting unit 122 is equal to the time difference τ between when the second pulse laser beam is output from light source 3 and when the first pulse laser beam is emitted, the first amplified beam and the second amplified beam are emitted from optical distance adjustment unit 12-1 on the negative side in the X direction in a state where they are completely superimposed on each other. That is, by controlling the time difference between when the first pulse laser beam is emitted from first light source 301 and when the second pulse laser beam is emitted from second light source 302 by controller 4, the degree of superimposition of the first amplified beam and the second amplified beam can be controlled. As shown in FIG. 3B, the first reflecting portion 121 and the second reflecting portion 122 may be provided on the first surface (negative side in the X direction) and the second surface (positive side in the X direction), respectively, of a single light-transmitting member 123 made of, for example, glass or the like.

[0019] The first amplified light and second amplified light emitted from the optical distance adjusting unit 12-1 propagate in the negative direction of the X axis, and the polarization adjusting element 14 rotates the electric field oscillation direction by 45° to become S-polarized light. That is, the polarization adjusting element 14 rotates the electric field oscillation direction by 90° in both directions. The first amplified light and second amplified light, which have become S-polarized light, are reflected by the deflecting element 13-1 and propagate in the negative Y direction, and are emitted from the output unit 20 to the outside of the optical amplifying device 1.

[0020] Example 2 Next, an optical amplifying device 1 of a second embodiment will be described with reference to Fig. 4. In the optical amplifying device 1 of the second embodiment, the optical distance adjusting unit 12-2 has a first reflecting unit 221 that reflects the first amplified light and transmits the second amplified light, and a second reflecting unit 222 that reflects the second amplified light. The optical amplifying device 1 of the second embodiment is the same as the optical amplifying device 1 of the first embodiment, except that the optical distance adjusting unit 12-2 has a different configuration from the optical distance adjusting unit 12-1 of the first embodiment. The optical distance adjustment unit 12-2 is a volume holographic diffraction grating (VBG: Volume Bragg Grating), and is configured by a grating with a first reflecting unit 221 that reflects the first amplified light and transmits the second amplified light, and a second reflecting unit 222 that reflects the second amplified light. The first reflecting unit 221 and the second reflecting unit 222 are formed at positions that are different distances from the output position of the optical fiber amplifier 11, similar to the first reflecting unit 121 and the second reflecting unit 122 in Example 1. In the example shown in FIG. 4, the first reflecting unit 221 is positioned on the negative side in the X direction relative to the second reflecting unit 222. When controller 4 controls the emission timings of the first pulse laser beam and the second pulse laser beam so that the time it takes for the second amplified beam to travel back and forth between first reflector 221 and second reflector 222 is equal to the time difference between when the second pulse laser beam is output from light source 3 and when the first pulse laser beam is output, the first amplified beam and the second amplified beam are emitted from optical distance adjuster 12-2 to the negative side in the X direction in a state where they are completely superimposed on each other. That is, also in Example 2, controller 4 controls the time difference between when the first pulse laser beam is output from first light source 301 and when the second pulse laser beam is output from second light source 302, thereby controlling the degree of superimposition of the first amplified beam and the second amplified beam. The optical distance adjustment unit 12-2 may be configured by a CVBG (Chirped Volume Bragg Grating).

[0021] Example 3 Next, an optical amplifying device 1 of Example 3 will be described with reference to Fig. 5. In the optical amplifying device 1 of Example 3, the optical distance adjusting unit 12-3 has a first reflecting unit 321 that reflects the first amplified light and transmits the second amplified light, and a second reflecting unit 322 that reflects the second amplified light. Example 3 is the same as the optical amplifying device 1 of Example 1, except that the configuration is different from that of the optical distance adjusting unit 12-1 of Example 1. The optical distance adjustment unit 12-3 is a fiber Bragg grating (FBG) element, and is configured by a grating engraved on an optical fiber, which has a first reflecting unit 321 that reflects the first amplified light and transmits the second amplified light, and a second reflecting unit 322 that reflects the second amplified light. The first reflecting unit 321 and the second reflecting unit 322 are formed at positions that are different distances from the output position of the optical fiber amplifier 11. In the example shown in FIG. 5 , the first reflecting unit 321 is disposed on the negative side in the X direction relative to the second reflecting unit 322. When the control unit 4 controls the emission timing of the first pulse laser light and the second pulse laser light so that the time it takes for the second amplified light to travel back and forth between the first reflecting unit 321 and the second reflecting unit 322 is equal to the time difference τ between when the second pulse laser light is output from the light source 3 and when the first pulse laser light is output, the first amplified light and the second amplified light are output from the optical distance adjustment unit 12-3 on the negative side in the X direction in a state where they are completely superimposed on each other. That is, also in the third embodiment, the control unit 4 controls the time difference between the emission of the first pulse laser light from the first light source 301 and the emission of the second pulse laser light from the second light source 302, thereby controlling the degree of superposition of the first amplified light and the second amplified light.

[0022] In Example 3, the optical distance adjustment unit 12-3 is made of fiber. In the optical distance adjustment unit 12-3, the length of the fiber on the optical fiber amplifier 11 side of the first reflector 321 can be configured to be short, for example, about 10 cm. Since the length of the fiber in the optical distance adjustment unit 12-3 is short, the nonlinear interaction between the first amplified light and the second amplified light in this portion is extremely small and negligible. In Example 3, the optical distance adjustment unit 12-3 can be arranged so that the distance between the first reflector 321 and the second reflector 322 is large, which makes it relatively easy to increase the difference in optical distance between the first amplified light and the second amplified light. For example, if the distance between the first reflector 321 and the second reflector 322 is 20 cm, the time difference τ corresponds to about 2 ns.

[0023] Example 4 6A and 6B, an optical amplifier 1 according to a fourth embodiment will be described. In the optical amplifier 1 according to the fourth embodiment, the polarization adjusting element 14 is not provided, and the deflector 13-4 and the optical distance adjusting unit 12-4 are different from the deflector 13-1 and the optical distance adjusting unit 12-1 of the first embodiment, respectively. The deflecting element 13-4 is a mirror with high reflectivity. In Example 4, as schematically shown in Fig. 6B, the first amplified light and the second amplified light from the optical fiber amplifier 11 pass through the upper part (+ side in the Z direction) of the deflecting element 13-4, enter the optical distance adjustment unit 12-4, have their optical axis heights shifted to the - side in the Z direction, and then exit from the optical distance adjustment unit 12-4 and are reflected by the deflecting element 13-4. Note that in Fig. 6B, the arrows shown by solid lines indicate the propagation paths of the first amplified light and the second amplified light.

[0024] The optical distance adjustment unit 12-4 includes a grating pair having a first grating 421 and a second grating 422, and a reflector 423. The first grating 421 deflects the first amplified light and the second amplified light that pass through the upper part of the deflection element 13-4 and enters it at different angles, and outputs the light toward the second grating 422. The second grating 422 outputs the first amplified light and the second amplified light deflected by the first grating 421 toward the reflector 423 so that the light becomes parallel. As described above, the second wavelength λ2 is longer than the first wavelength λ1, and therefore the second amplified light deflected by the first grating 421 propagates along the optical path L2, and the first amplified light propagates along the optical path L1, before entering the second grating 422. These beams are deflected by second grating 422 to become parallel to each other, enter reflector 423, and are shifted in height in the negative Z direction upon reflection (see FIG. 6B ). Then, they return along the optical paths along which they propagated, converge to the same optical path at first grating 421, and are then emitted from optical distance adjustment unit 12-4. As a result, the optical distance traveled by the second amplified beam is longer than the optical distance traveled by the first amplified beam. Therefore, the second amplified beam takes longer to pass through optical distance adjustment unit 12-4 than the first amplified beam. When this time difference becomes the time difference τ at the time of emission from light source 3, the first amplified beam and the second amplified beam are emitted from optical distance adjustment unit 12-4 in a state where they are completely superimposed on each other. That is, in Example 4 as well, the degree of superimposition of the first amplified beam and the second amplified beam can be controlled by controlling the time difference between the emission of the first pulsed laser beam from first light source 301 and the emission of the second pulsed laser beam from second light source 302 using control unit 4.

[0025] For example, when a grating with a line density of 1600 / mm is used with an incident angle of 58° and a grating spacing of 1 cm for amplified light with a wavelength of 1060 nm, the dispersion D2 is approximately 1.2 ps / nm. Therefore, if the difference between the first wavelength λ1 and the second wavelength λ2 is 10 nm and the spacing between the two gratings is 10 cm, a time difference of 120 ps can be generated between the first amplified light and the second amplified light. When the control unit 4 controls the time difference between the emission of the first pulse laser light and the emission of the second pulse laser light to 120 ps, the first amplified light and the second amplified light can be completely superimposed.

[0026] The reflecting unit 423 is a roof mirror that makes incident light and reflected light parallel to each other, and reflects the first amplified light and the second amplified light, which are parallel to each other, while maintaining their parallel relationship. In the fourth embodiment, the reflecting unit 423 can be moved (shifted) in a direction perpendicular to the dispersion direction of the grating (i.e., the Z direction) with respect to the incident direction of the first amplified light and the second amplified light.

[0027] The first amplified light and second amplified light that have exited the optical distance adjustment unit 12-4 propagate toward the deflection element 13-4. As described above, the first amplified light and second amplified light that have been reflected by the reflector 423 propagate further in the negative Z direction than when they exited the optical fiber amplifier 11, and are then incident on the deflection element 13-4 and reflected toward the positive Y direction. As a result, the first amplified light and second amplified light are output from the output unit 20.

[0028] In the first embodiment and examples described above, an example has been given in which two laser pulse beams with different wavelengths are emitted from light source 3. However, three or more laser pulse beams may be emitted from light source 3. For example, when three laser pulse beams are emitted, light source 3 further includes a third light source that emits a third laser pulse beam with a third wavelength λ3. The first, second, and third laser pulse beams emitted from light source 3 are incident on optical fiber amplifier 11 with a time difference between them, propagate, and are amplified into first amplified beam, second amplified beam, and third amplified beam. Optical distance adjustment unit 12 is configured so that the propagation distance of the third amplified beam is different from that of the first amplified beam and the second amplified beam, thereby enabling the first amplified beam, the second amplified beam, and the third amplified beam to be superimposed. In this case, the optical distance adjustment unit 12 of Examples 1 to 3 includes, in addition to the first reflecting unit and the second reflecting unit, a third reflecting unit that reflects the third amplified light, and the first reflecting unit, the second reflecting unit, and the third reflecting unit are arranged at positions that are different distances from the output position of the optical fiber amplifier 11. The controller 4 controls the timing at which the light source 3 emits laser pulse light based on a time difference that corresponds to the difference in optical distance among the first amplified light, the second amplified light, and the third amplified light, which occurs due to the difference in the arrangement positions of the first reflecting unit, the second reflecting unit, and the third reflecting unit, thereby making it possible to change the degree of superposition of the first amplified light, the second amplified light, and the third amplified light when they are emitted from the optical distance adjustment unit 12.

[0029] According to the above-described first embodiment, the following effects can be obtained. (1) The optical amplifier 1 includes an optical fiber amplifier 11 and an optical distance adjuster 12. The optical fiber amplifier 11 amplifies two pulsed laser beams (first pulsed laser beam, second pulsed laser beam) having at least a first wavelength λ1 and a second wavelength λ2 that are different from each other while they propagate with a time difference τ, and outputs first amplified beam and second amplified beam, which are the amplified beams of the first pulsed laser beam and the second pulsed laser beam, respectively. The optical distance adjuster 12 differentiates the optical distances over which the first amplified beam and the second amplified beam emitted from the optical fiber amplifier 11 propagate, thereby superimposing the first amplified beam and the second amplified beam. By amplifying multiple pulsed laser beams having different wavelengths in the single optical fiber amplifier 11 with a time difference τ, spectral distortion and the generation of unnecessary spectral components due to nonlinear optical processes within the optical fiber amplifier 11 can be suppressed. As a result, first amplified beam and second amplified beam with high peak energies can be obtained. Furthermore, the optical distance adjusting unit 12 can superimpose and output a plurality of amplified lights with high peak energy, in which spectral disturbance and the occurrence of unnecessary spectral components are suppressed.

[0030] (2) The optical amplifier 1 includes a control unit 4 that controls the degree of superposition of the pulses of the first amplified light and the second amplified light emitted from the optical distance adjustment unit 12. Specifically, the control unit 4 controls the time difference τ between the pulses of the first pulsed laser light from the first light source 301 and the second pulsed laser light from the second light source 302. This cancels out the time difference that occurs in the optical distance adjustment unit 12 when the first amplified light and the second amplified light propagate through different optical distances, making it possible to superpose the first amplified light and the second amplified light.

[0031] (3) The time difference τ is larger than the pulse widths of the first pulse laser beam from the first light source 301 and the second pulse laser beam from the second light source 302. This prevents the first pulse laser beam and the second pulse laser beam from overlapping in time, allowing the optical fiber amplifier 11 to amplify the pulses without causing nonlinear interaction between the pulses.

[0032] Second Embodiment An optical amplifier device according to the second embodiment will be described with reference to the drawings. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and differences will be mainly described. Points that are not specifically described are the same as those in the first embodiment.

[0033] 7 is a block diagram schematically showing the configuration of the main part of the optical amplifier 100 according to the second embodiment. In FIG. 7, an orthogonal coordinate system consisting of X, Y, and Z axes is set, similar to FIG. The optical amplifier 100 includes a wavelength converter 6 in addition to the optical fiber amplifier 11, optical distance adjuster 12, deflector 13, light source 3, and controller 4 included in the optical amplifier 1 of the first embodiment.

[0034] The wavelength conversion unit 6 is provided between the deflection element 13 and the output unit 20, and generates pulsed laser light having a predetermined wavelength from the first amplified light and the second amplified light. The wavelength conversion unit 6 is made of, for example, organic crystals such as DAST (4-dimethylamino-N-methyl-4-stilbazaliumtosylate), LBO (LiBO), BBO (β-BaBO), CLBO (CsLiBO), 10 The wavelength converter 6 is formed of a nonlinear crystal such as lithium niobate (LiNbO3), lithium niobate (LiNbO3), or the like. When the first amplified light and the second amplified light superimposed by the optical distance adjusting unit 12 as described in the first embodiment pass through the wavelength converter 6, harmonics, sum frequencies, difference frequencies, etc. are generated by nonlinear interaction, and wavelength-converted light is generated as pulsed laser light having a wavelength different from the wavelengths of the first pulsed laser light and the second pulsed laser light from the light source 3. When the first amplified light and the second amplified light are not superimposed, no nonlinear interaction occurs in the wavelength converter 6, and therefore no wavelength-converted light is generated.

[0035] As described in the first embodiment, the control unit 4 controls the degree of superposition of the first amplified light and the second amplified light emitted from the optical distance adjustment unit 12 by controlling the time difference between the emission of the first pulse laser light and the emission of the second pulse laser light. By performing the above control, the control unit 4 can control the output of wavelength-converted light generated in the wavelength conversion unit 6. For example, the control unit 4 can control whether or not to output wavelength-converted light by controlling the time difference between the emission of the first pulse laser light and the emission of the second pulse laser light.

[0036] A specific example of the optical amplifying device 100 according to the second embodiment will now be described. Example 5 Example 5, which is a first example of the optical amplifier 100 in the second embodiment, will be described. 8 is a block diagram showing a schematic configuration of a main part of an optical amplifier 100 according to a fifth embodiment. The optical amplifier 100 of the first example includes an optical fiber amplifier 11, an optical distance adjuster 12, a deflector 13, a light source 3, a controller 4, and a wavelength converter 6-1.

[0037] The wavelength conversion unit 6-1 has a first wavelength conversion unit 601 and a second wavelength conversion unit 602. The first wavelength conversion unit 601 is the above-mentioned nonlinear crystal. The first wavelength conversion unit 601 satisfies the phase matching condition for second harmonic generation of the first amplified light of the first wavelength λ1. The first wavelength conversion unit 601 does not satisfy the phase matching condition for second harmonic generation of the second amplified light of the second wavelength λ2. Therefore, of the first amplified light and second amplified light incident on the first wavelength conversion unit 601, a pulsed laser light of the second harmonic (wavelength λ1 / 2) of the first amplified light of the first wavelength λ1 is generated.

[0038] The second wavelength conversion unit 602 is also the above-mentioned nonlinear crystal. The second wavelength conversion unit 602 satisfies the phase matching condition for the sum frequency generation of the second harmonic (wavelength λ1 / 2) of the first amplified light and the second amplified light of the second wavelength λ2. As a result, when the second harmonic of the first amplified light and the second amplified light are superimposed and incident on the second wavelength conversion unit 602, a pulsed laser light of wavelength λ3 (1 / λ3 = 2 / λ1 + 1 / λ2) is generated, which is the sum frequency of the wavelength λ1 / 2 of the second harmonic of the first amplified light and the second wavelength λ2 of the second amplified light.

[0039] When the second harmonic of the first amplified light and the second amplified light are not superimposed, the second wavelength converter 602 does not cause the above-mentioned nonlinear interaction, and therefore a pulsed laser light of wavelength λ3 is not generated. For example, the control unit 4 can control whether or not a pulsed laser light of wavelength λ3 is generated by controlling the time difference between the emission of the first pulsed laser light and the emission of the second pulsed laser light.

[0040] Example 6 Next, a sixth embodiment, which is a second example of the optical amplifying device 100 according to the second embodiment, will be described. 9 is a block diagram showing a schematic configuration of the main parts of an optical amplifier 100 according to Example 6. The optical amplifier 100 of the second example includes an optical fiber amplifier 11, an optical distance adjuster 12, a deflector 13, a light source 3, a controller 4, and a wavelength converter 6-2.

[0041] The wavelength converter 6-2 includes a first wavelength converter 601, a third wavelength converter 603, and a fourth wavelength converter 604. The first wavelength converter 601 is similar to the first example described above and satisfies a phase matching condition for second harmonic generation of the first amplified light of the first wavelength λ1 to generate a second harmonic (wavelength λ1 / 2). The third wavelength converter 603 is a nonlinear crystal and satisfies a phase matching condition for second harmonic generation of the second amplified light of the second wavelength λ2 to generate a second harmonic (wavelength λ2 / 2). The fourth wavelength converter 604 is a nonlinear crystal and satisfies a phase matching condition for generating a sum frequency of the second harmonic (wavelength λ1 / 2) of the first amplified light and the second harmonic (wavelength λ2 / 2) of the second amplified light. Here, the wavelength λ4 of the sum frequency is given by λ4 = 2 / λ1 + 2 / λ2. For example, when the first wavelength λ1 is 1060 nm and the second wavelength λ2 is 1068 nm, wavelength-converted light with a wavelength of 266 nm is generated.

[0042] Therefore, when the first amplified light and the second amplified light are superimposed, the wavelength conversion unit generates light of wavelength λ4, whereas when the first amplified light and the second amplified light are not superimposed, light of this wavelength is not generated.

[0043] For example, the control unit 4 can control whether or not light with wavelength λ4 is generated by controlling the time difference between the emission of the first pulse laser beam and the emission of the second pulse laser beam.

[0044] According to the second embodiment described above, the following advantageous effects can be obtained. The optical amplifier 100 includes a wavelength conversion unit 6 that generates pulsed laser light having a predetermined wavelength from the first amplified light and the second amplified light. The control unit 4 of the optical amplifier 100 controls the degree of pulse superposition of the first amplified light and the second amplified light by controlling the time difference between the emission of the first pulsed laser light and the emission of the second pulsed laser light, thereby controlling the output of the pulsed laser light. This makes it possible to output wavelength-converted light in which spectral disturbance due to nonlinear interactions of the pulsed laser light in the optical fiber amplifier 11 is suppressed. The control unit 4 controls whether or not to output wavelength-converted light by controlling the time difference between the emission of the first pulsed laser light and the second pulsed laser light.

[0045] Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments that are conceivable within the scope of the technical idea of the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0046] 100...Optical amplifier 3…Light source 4...Control unit 6, 6-1, 6-2...wavelength conversion section 11...Optical fiber amplifier 12, 12-1, 12-2, 12-3, 12-4...Optical distance adjustment section 13, 13-1, 13-4...deflection element 14...Polarization state adjusting element 121, 221, 321...first reflection section 122, 222, 322...Second reflection section 421...1st Grating 422...Second Grating 423...Reflector 601...First wavelength conversion unit 602...second wavelength conversion unit 603...Third wavelength conversion unit 604...Fourth wavelength conversion unit

Claims

1. an optical fiber amplifier that amplifies at least two pulsed laser beams having a first wavelength λ1 and a second wavelength λ2 that are different from each other while propagating them with a time difference, and outputs first amplified light and second amplified light that are amplified light of the pulsed laser beams, respectively; an optical distance adjusting unit that changes the optical distances along which the first amplified light and the second amplified light emitted from the optical fiber amplifying unit propagate, and superimposes the first amplified light and the second amplified light; An optical amplifier comprising:

2. In the optical amplifier according to claim 1, an optical amplifier comprising, between the optical fiber amplifier and the optical distance adjuster, a deflector that changes the propagation direction of the first amplified light and the second amplified light from the optical distance adjuster;

3. In the optical amplifier according to claim 1 or 2, an optical distance adjusting unit that includes a first reflecting unit and a second reflecting unit that reflect the first amplified light and the second amplified light at positions that are different distances from the output position of the optical fiber amplifying unit,

4. In the optical amplifier according to claim 3, an optical amplifier device, wherein at least one of the first reflecting section and the second reflecting section is one of a narrowband reflecting mirror, a short-pass mirror, and a long-pass mirror that reflects the first amplified light and the second amplified light, respectively;

5. In the optical amplifier according to claim 3, The optical amplifier, wherein the first reflecting portion and the second reflecting portion are volume holographic diffraction gratings that reflect the first amplified light and the second amplified light, respectively.

6. In the optical amplifier according to claim 3, The optical amplifying device, wherein the first reflecting portion and the second reflecting portion are fiber Bragg grating elements that reflect the first amplified light and the second amplified light, respectively.

7. An optical amplifier according to any one of claims 3 to 6 dependent on claim 2, the first amplified light and the second amplified light are linearly polarized light having the same electric field oscillation direction, the deflecting element is a polarizing beam splitter; The optical amplifier further comprises a polarization state adjusting element between the deflection element and the optical distance adjusting unit, which rotates the electric field oscillation direction by 90° in a round trip.

8. In the optical amplifier according to claim 7, An optical amplifier, wherein the polarization adjusting element is a quarter-wave plate or a 45-degree Faraday rotator.

9. In the optical amplifier according to claim 2, the optical distance adjusting unit includes a first grating, a second grating, and a fourth reflecting unit; the fourth reflecting section is a roof mirror that reflects light parallel to the incident light and shifts in a direction perpendicular to the dispersion direction of the second grating, the first grating deflects the incident first amplified light and the incident second amplified light at different angles and outputs the deflected light toward the second grating; the second grating emits the deflected first amplified light and the deflected second amplified light toward the fourth reflector so as to be parallel to each other; the fourth reflecting section reflects the first amplified light and the second amplified light in a direction parallel to an incident direction, the second grating emits the first amplified light and the second amplified light from the fourth reflecting portion toward the first grating; the first grating emits the first amplified light and the second amplified light from the second grating toward the deflection element; The optical amplifying device, wherein the deflecting element reflects the first amplified light and the second amplified light from the first grating.

10. An optical amplifier according to any one of claims 1 to 9, an optical amplifier further comprising a first light source that outputs pulsed laser light of the first wavelength λ1 and a second light source that outputs pulsed laser light of the second wavelength λ2;

11. An optical amplifier according to any one of claims 1 to 10, An optical amplifying device further comprising a control unit that controls the degree of superposition of the pulses of the first amplified light and the second amplified light that are output from the optical distance adjustment unit.

12. An optical amplifier according to claim 11 dependent on claim 10, The control unit controls a time difference between pulses of the pulsed laser light from the first light source and pulsed laser light from the second light source.

13. The optical amplifier according to claim 12, an optical amplifier, wherein the time difference is greater than the pulse width of the pulsed laser light from the first light source and the pulsed laser light from the second light source;

14. An optical amplifier according to any one of claims 11 to 13, a wavelength conversion unit that generates pulsed laser light having a predetermined wavelength from the first amplified light and the second amplified light, The control unit controls the degree of pulse superposition of the first amplified light and the second amplified light, thereby controlling the output of pulsed laser light.

15. The optical amplifier according to claim 14, an optical amplifier device, wherein the wavelength conversion unit includes: a first wavelength conversion unit that satisfies a phase matching condition only for second harmonic generation of the first amplified light of the first wavelength λ1; and a second wavelength conversion unit that satisfies a phase matching condition for sum frequency generation of the second harmonic of the first amplified light of the first wavelength λ1 and the second amplified light of the second wavelength λ2.

16. The optical amplifier according to claim 14, an optical amplifier device, wherein the wavelength conversion unit includes: a first wavelength conversion unit that satisfies a phase matching condition for second harmonic generation of the first amplified light of the first wavelength λ1; a third wavelength conversion unit that satisfies a phase matching condition for second harmonic generation of the second amplified light of the second wavelength λ2; and a fourth wavelength conversion unit that generates a sum frequency of the second harmonic of the first amplified light of the first wavelength λ1 and the second harmonic of the second amplified light of the second wavelength λ2.

17. Using the optical amplifier according to claim 10, an optical amplification method for controlling a time difference between pulses of the pulsed laser light from the first light source and the pulsed laser light from the second light source, thereby controlling a degree of superposition of the first amplified light and the second amplified light output from an output section.

18. A method of amplifying two pulsed laser beams each having at least a first wavelength λ1 and a second wavelength λ2 different from each other while propagating them with a time difference, and outputting first amplified light and second amplified light which are amplified light of the pulsed laser beams; making the optical distances over which the first amplified light and the second amplified light propagate different from each other, and superimposing the first amplified light and the second amplified light.

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