Multi-pulse light source and multi-pulse light generation method

Abstract

To provide a multi-pulse light source with which it is possible to realize dispersion compensation in which the attenuation of peak intensity is suppressed.SOLUTION: A multi-pulse light source 1 comprises: a delay addition unit 4 for adding a delay to a plurality of wavelength components that differs for each wavelength component; and a dispersion compensation unit 6 for compensating the plurality of wavelength components for the dispersion per wavelength component. The dispersion compensation unit 6 includes a spectroscopic element 61 for spectrally separating the plurality of wavelength components into respective wavelength components, a first optical pulse group La1 that includes one or more wavelength components among the plurality of wavelength components, a second optical pulse group La2 that includes one or more wavelength components differing from the one or more wavelength components, a separation optical element 63 for guiding to respectively different optical paths; a first spatial optical modulator 65 which the first optical pulse group La1 enters, and which compensates the first optical pulse group La1 for the dispersion per wavelength component, and a second spatial optical modulator 66 which the second optical pulse group La2 enters, and which compensates the second optical pulse group La2 for the dispersion per wavelength component.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a multi-pulse light source and a multi-pulse light generation method.

Background Art

[0002] Non-Patent Document 1 describes an example of a multi-pulse light source. Pulse light from a broadband light source is split into a plurality of wavelength components by a waveguide diffraction grating. By transmitting the split plurality of wavelength components in fibers having different lengths, different delays are imparted to each of them. Then, by combining the plurality of wavelength components with a multiplexer, multi-pulse light in which a plurality of pulse lights having different central wavelengths are arranged at predetermined time intervals is generated.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the multi-pulse light source described in Non-Patent Document 1, when a delay is imparted to each of a plurality of wavelength components, due to wavelength dispersion, the pulse width of the multi-pulse light after combination spreads. Specifically, characteristic quantities such as the peak intensity, full width at half maximum, and peak time interval of the multi-pulse light change greatly. And the degree of these changes differs for each pulse.

[0005] Therefore, it is conceivable to compensate for the dispersion of multi-pulse light for each wavelength component. For example, a plurality of wavelength components are spectrally separated into respective wavelength components, and the modulation surface of the spatial light modulator is divided into a plurality of modulation regions along the spectral direction. Then, each of the plurality of modulation regions is made to receive each wavelength component corresponding thereto, and a modulation pattern for compensating for dispersion for each wavelength component is displayed in each modulation region. However, when using a single spatial light modulator in which a plurality of modulation regions corresponding to a plurality of wavelength components respectively are arranged only in the spectral direction of incident light, there is a limit to the effect of dispersion compensation due to the constraint of wavelength resolution.

[0006] An object of the present invention is to provide a multi-pulse light source and a multi-pulse light generation method capable of more effectively compensating for the dispersion of multi-pulse light having different central wavelengths for each pulse.

Means for Solving the Problems

[0007] The multi-pulse light source of the present invention includes a pulse light source that generates pulse light separable into a plurality of wavelength components having different central wavelengths, a delay imparting unit that imparts different delays for each wavelength component to the plurality of wavelength components, and a dispersion compensation unit that compensates for dispersion for each wavelength component with respect to the plurality of wavelength components. The dispersion compensation unit includes a spectroscopic element that spectrally separates the plurality of wavelength components into respective wavelength components, a separation optical element that is provided in front of or behind the spectroscopic element and guides a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components to different optical paths, a first spatial light modulator that includes a first modulation region where the first wavelength component group is incident and performs modulation for compensating for dispersion for each wavelength component with respect to the first wavelength component group, and a second spatial light modulator that includes a second modulation region where the second wavelength component group is incident and performs modulation for compensating for dispersion for each wavelength component with respect to the second wavelength component group.

[0008] In the above-described multi-pulse light source, the pulsed light output from the pulse light source is input to the delay imparting unit, and different delays are imparted to each wavelength component, thereby generating multi-pulse light including a plurality of pulses having mutually different central wavelengths. Further, this multi-pulse light source includes a dispersion compensation unit that compensates for dispersion for each wavelength component. In the dispersion compensation unit, a first wavelength component group is incident on a first spatial light modulator, and a second wavelength component group is incident on a second spatial light modulator. Then, for each of the respective wavelength component groups, the dispersion for each wavelength component is compensated. Thereby, compared with the case of using a single spatial light modulator, the wavelength resolution for each wavelength component is improved, and the maximum dispersion compensation amount can be greatly improved. As a result, the dispersion of the multi-pulse light having different central wavelengths for each pulse can be compensated more effectively for each pulse.

[0009] The multi-pulse light source of the present invention includes a pulse light source that generates pulsed light separable into a plurality of wavelength components having different central wavelengths, a delay imparting unit that imparts different delays to each wavelength component with respect to the plurality of wavelength components, and a dispersion compensation unit that compensates for dispersion for each wavelength component with respect to the plurality of wavelength components. The dispersion compensation unit includes a spectroscopic element that spectroscopically separates a plurality of wavelength components into respective wavelength components, a separation optical element that is provided in front of or behind the spectroscopic element and guides a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the wavelength components included in the first wavelength component group to different optical paths, a first modulation region that is incident on the first wavelength component group and performs modulation for compensating for dispersion for each wavelength component with respect to the first wavelength component group, and a second modulation region that is incident on the second wavelength component group and performs modulation for compensating for dispersion for each wavelength component with respect to the second wavelength component group, and a spatial light modulator including the first modulation region and the second modulation region are arranged side by side along a direction intersecting the respective spectroscopic directions of the first wavelength component group and the second wavelength component group when they are incident on the first modulation region and the second modulation region, respectively.

[0010] In the above-described multi-pulse light source, the pulsed light output from the pulse light source is input to the delay imparting unit, and different delays are imparted for each wavelength component, thereby generating multi-pulse light including a plurality of pulses having different center wavelengths. Further, this multi-pulse light source includes a dispersion compensation unit that compensates for dispersion for each wavelength component. In the spatial light modulator of the dispersion compensation unit, the first modulation region and the second modulation region are arranged along a direction intersecting the respective spectral directions of the first wavelength component group and the second wavelength component group when they are incident on the first modulation region and the second modulation region, respectively. Thereby, compared with the case where a plurality of modulation regions corresponding to a plurality of wavelength components are arranged only in the spectral direction of the incident light, the wavelength resolution for each wavelength component is improved, and the maximum dispersion compensation amount can be significantly improved. As a result, the dispersion of the multi-pulse light having different center wavelengths for each pulse can be compensated more effectively for each pulse.

[0011] In the above-described multi-pulse light source, the spectroscopic element may include a diffraction grating. In this case, by using the diffraction grating, a plurality of wavelength components can be appropriately spectroscopically analyzed and then incident on the spatial light modulator. Also, the spectroscopic element can be simply configured.

[0012] In the above-described multi-pulse light source, the separation optical element may include a dichroic mirror. In this case, by using the dichroic mirror, a plurality of wavelength components can be reflected or transmitted according to the wavelength range, and the first wavelength component group and the second wavelength component group can be preferably separated. Also, the separation optical element can be simply configured.

[0013] The above multi-pulse light source further includes a polarization control unit that makes the polarization directions of one or more wavelength components included in the first wavelength component group and the polarization directions of one or more wavelength components included in the second wavelength component group orthogonal to each other before entering the separation optical element, and a wave plate provided on the optical path between the separation optical element and the first modulation region that rotates the polarization direction of the first wavelength component group by 90°. The separation optical element may include a polarization beam splitter or a birefringent crystal. In this case, after the polarization direction is controlled by the polarization control unit, by using a polarization beam splitter or a birefringent crystal, the first wavelength component group and the second wavelength component group can be guided to different optical paths according to the polarization direction. Then, by passing the first wavelength component group through the wave plate, the polarization direction of the first wavelength component group is made to coincide with the polarization direction of the second wavelength component group, and then the first wavelength component group and the second wavelength component group can be incident on the spatial light modulator.

[0014] In the above multi-pulse light source, the delay imparting unit may also serve as the polarization control unit. In this case, the number of necessary components can be reduced and the multi-pulse light source can be simplified.

[0015] In the above multi-pulse light source, the delay imparting unit has a plurality of polarization maintaining fibers that respectively propagate a plurality of wavelength components, the lengths of the plurality of polarization maintaining fibers are different from each other, and between the light input end and the light output end of the plurality of polarization maintaining fibers, the polarization plane of the polarization maintaining fiber that propagates the wavelength components included in the first wavelength component group may be rotated by 90° with respect to the polarization plane of the polarization maintaining fiber that propagates the wavelength components included in the second wavelength component group. In this case, while imparting a delay according to the length of the polarization maintaining fiber, the polarization directions of one or more wavelength components included in the first wavelength component group and the polarization directions of one or more wavelength components included in the second wavelength component group can be preferably adjusted.

[0016] In the above-described multi-pulse light source, the dispersion compensation unit may be arranged at the subsequent stage of the delay imparting unit. In this case, for each of a plurality of wavelength components (pulses) in which different wavelength dispersions are generated due to different delays being imparted to each other, since dispersion compensation is directly performed, the effect of dispersion compensation for each individual wavelength component (pulse) can be efficiently confirmed.

[0017] In the above-described multi-pulse light source, the delay imparting unit may have a plurality of optical fibers having different lengths from each other and propagating a plurality of wavelength components respectively. In this case, since a delay can be imparted according to the length of the optical fiber, the delay imparting unit can be simply configured.

[0018] The multi-pulse light generation method of the present invention includes a pulse light generation step of generating pulse light separable into a plurality of wavelength components having different center wavelengths, a delay imparting step of imparting different delays for each wavelength component to the plurality of wavelength components, and a dispersion compensation step of compensating for dispersion for each wavelength component with respect to the plurality of wavelength components, before or after the delay imparting step. The dispersion compensation step includes a spectroscopic step of splitting the plurality of wavelength components into respective wavelength components, and a separation step of guiding, to different optical paths, a first wavelength component group including one or more wavelength components and a second wavelength component group including one or more wavelength components different from the wavelength components included in the first wavelength component group, among the plurality of wavelength components, before or after the spectroscopic step, and a modulation step of performing modulation for compensating for dispersion for each wavelength component with respect to the first wavelength component group in a first spatial light modulator having a first modulation region where the first wavelength component group is incident, and performing modulation for compensating for dispersion for each wavelength component with respect to the second wavelength component group in a second spatial light modulator having a second modulation region where the second wavelength component group is incident.

[0019] In the multi-pulse light generation method of the present invention, different delays are imparted to the pulse light generated in the pulse light generation step for each wavelength component in the delay imparting step. Thereby, multi-pulse light including a plurality of pulses having mutually different center wavelengths is generated. Further, this multi-pulse light generation method includes a dispersion compensation step of compensating for dispersion for each wavelength component. In the dispersion compensation step, a first wavelength component group is incident on a first spatial light modulator, and a second wavelength component group is incident on a second spatial light modulator. Then, for each of the respective wavelength component groups, dispersion for each wavelength component is compensated. Thereby, compared with the case of using a single spatial light modulator, the wavelength resolution for each wavelength component is improved, and the maximum dispersion compensation amount can be significantly improved. As a result, the dispersion of the multi-pulse light having different center wavelengths for each pulse can be compensated more effectively for each pulse.

[0020] The multi-pulse light generation method of the present invention includes a pulse light generation step of generating pulse light separable into a plurality of wavelength components having different center wavelengths, a delay imparting step of imparting different delays for each wavelength component to the plurality of wavelength components, and a dispersion compensation step of compensating for dispersion for each wavelength component for the plurality of wavelength components before or after the delay imparting step. The dispersion compensation step includes a spectral splitting step of splitting the plurality of wavelength components into respective wavelength components, and before or after the spectral splitting step, a first wavelength component group including one or more wavelength components among the plurality of wavelength components, and a second wavelength component group including one or more wavelength components different from the wavelength components included in the first wavelength component group are respectively guided to different optical paths in a separation step, a first modulation region on which the first wavelength component group is incident, and a second modulation region on which the second wavelength component group is incident, and in a spatial light modulator in which the first modulation region and the second modulation region are arranged along a direction intersecting the respective spectral splitting directions of the first wavelength component group and the second wavelength component group when the first wavelength component group and the second wavelength component group are respectively incident thereon, a modulation step of performing modulation for compensating for dispersion for each wavelength component for the first wavelength component group and the second wavelength component group.

[0021] In the multi-pulse light generation method of the present invention, different delays are imparted to the pulse light generated in the pulse light generation step for each wavelength component in the delay imparting step. Thereby, multi-pulse light including a plurality of pulses having mutually different center wavelengths is generated. Further, this multi-pulse light generation method includes a dispersion compensation step of compensating for dispersion for each wavelength component. In the dispersion compensation step, the first modulation region and the second modulation region are arranged along a direction intersecting the respective spectral directions of the first wavelength component group and the second wavelength component group when they are incident on the first modulation region and the second modulation region, respectively. Thereby, the wavelength resolution for each wavelength component is improved as compared with the case where a plurality of modulation regions corresponding to a plurality of wavelength components are arranged only in the spectral direction of the incident light, and the maximum dispersion compensation amount can be significantly improved. As a result, the dispersion of the multi-pulse light having different center wavelengths for each pulse can be compensated more effectively for each pulse.

Advantages of the Invention

[0022] According to the present invention, it is possible to provide a multi-pulse light source and a multi-pulse light generation method capable of more effectively compensating for the dispersion of multi-pulse light having different center wavelengths for each pulse for each pulse.

Brief Description of the Drawings

[0023]

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[0024] Hereinafter, with reference to the drawings, preferred embodiments of the present disclosure will be described in detail. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted. [First Embodiment]

[0025] FIG. 1 is a diagram schematically showing the configuration of the multi-pulse light source 1 according to the first embodiment. As shown in FIG. 1, the multi-pulse light source 1 according to the present embodiment includes a pulse light source 2, a spectroscopic unit 3, a delay imparting unit 4, a coupling unit 5, and a dispersion compensation unit 6, and they are optically coupled. The pulse light source 2 is a light source that emits a single pulse light L1. The pulse light source 2 is, for example, a laser light source, and emits near-infrared ultrashort pulse light in the femtosecond region or picosecond region. Specifically, the pulse light source 2 is constituted by, for example, a titanium sapphire laser, a Yb:YAG laser, a Yb fiber laser, an Er fiber laser, a Tm fiber laser, or the like. The pulse light L1 is light having a certain spread in the wavelength range that can be separated into a plurality of wavelength components having different central wavelengths. In other words, the pulse light L1 includes a plurality of wavelength components having different central wavelengths.

[0026] The spectroscopic unit 3 is a part that spectroscopically divides the pulse light L1 into a plurality of wavelength components. FIG. 2 is a diagram showing an example of the spectroscopic unit 3, the delay imparting unit 4, and the coupling unit 5. As shown in FIG. 2, the spectroscopic unit 3 includes, for example, an arrayed waveguide grating 31. The spectroscopic unit 3 may consist only of the arrayed waveguide grating 31. The arrayed waveguide grating 31 is a spectroscopic element that spatially separates the plurality of wavelength components included in the pulse light L1 for each wavelength and makes each of them an independent optical pulse La (see FIG. 1), and makes them incident on the subsequent delay imparting unit 4 respectively. That is, the arrayed waveguide grating 31 generates a plurality of optical pulses La having different central wavelengths from each other.

[0027] The delay imparting section 4 is a section that imparts different delays to each of the plurality of wavelength components (optical pulses La) spectrally decomposed by the spectral section 3. The delay imparting section 4 includes, for example, a plurality of optical fibers 41. The delay imparting section 4 may consist only of the plurality of optical fibers 41. The number of optical fibers 41 is equal to the number of wavelength components spectrally decomposed by the spectral section 3. The plurality of optical fibers 41 are, for example, single mode fibers, photonic crystal fibers, etc. The lengths of the plurality of optical fibers 41 are different from each other. Each optical pulse La is delayed by a different amount according to the difference in the lengths of the plurality of optical fibers 41. Also, the shape of each optical pulse La changes according to the dispersion of each optical fiber 41 while propagating through each of the plurality of optical fibers 41. Since the lengths of the plurality of optical fibers 41 are different from each other, the dispersions of the plurality of optical pulses La after propagating through each of the plurality of optical fibers 41 are also different from each other. Therefore, the change in the shape of the pulse that occurs while each optical pulse La propagates through each of the plurality of optical fibers 41 is also different for each optical pulse La.

[0028] Each optical pulse La that has passed through each of the plurality of optical fibers 41 is incident on the combining section 5. The combining section 5 includes, for example, an arrayed waveguide grating 51 different from the arrayed waveguide grating 31. The combining section 5 may consist only of the arrayed waveguide grating 51. The arrayed waveguide grating 51 multiplexes the plurality of optical pulses La that have passed through the optical fibers 41 onto one optical path. That is, the arrayed waveguide grating 51 generates a multi-pulse light Lb (see FIG. 1) including a plurality of optical pulses La having different center wavelengths and having a time interval with each other.

[0029] Referring to FIG. 1 again. The dispersion compensation section 6 is a section that compensates for the wavelength dispersion generated in the plurality of optical pulses La between the pulse light source 2 and the dispersion compensation section 6 (mainly the delay imparting section 4). Specifically, the dispersion compensation section 6 suppresses the change in the shape of each optical pulse La by individually compensating for the wavelength dispersion of each optical pulse La. The dispersion compensation section 6 generates a dispersion-compensated multi-pulse light Lc obtained by dispersion-compensating the multi-pulse light Lb.

[0030] FIG. 3 shows a configuration diagram of the dispersion compensation unit 6 according to the first embodiment. The dispersion compensation unit 6 includes a spectroscopic element 61, a lens 62, a separation optical element 63, a first spatial light modulator 65, and a second spatial light modulator 66. In the first embodiment, the spectroscopic element 61 includes a diffraction grating 61a. As an example, the spectroscopic element 61 may consist only of the diffraction grating 61a. Further, the separation optical element 63 includes a dichroic mirror 63a. As an example, the separation optical element 63 may consist only of the dichroic mirror 63a. Here, the direction in which the multi-pulse light Lb is incident is defined as the Z-axis direction, the horizontal direction in the plane orthogonal to the Z-axis direction is defined as the X-axis direction, and the vertical direction is defined as the Y-axis direction. In the dispersion compensation unit 6, the multi-pulse light Lb is incident on the diffraction grating 61a along the Z-axis direction. The diffraction grating 61a spatially disperses each optical pulse La included in the multi-pulse light Lb. The dispersion direction coincides with the X-axis direction. Note that the spectroscopic element 61 may include other optical components such as a prism instead of the diffraction grating 61a or together with the diffraction grating 61a. Each optical pulse La is parallelized in the XZ plane by the lens 62 and reaches the dichroic mirror 63a as parallel light. The lens 62 may be a convex lens made of a light transmissive member, a concave mirror having a concave light reflecting surface, or a cylindrical lens.

[0031] The separation optical element 63 is arranged at the subsequent stage of the spectroscopic element 61 via the lens 62. The dichroic mirror 63a reflects a first optical pulse group (first wavelength component group) La1 including one or more optical pulses La among the plurality of optical pulses La, and transmits a second optical pulse group (second wavelength component group) La2 including one or more optical pulses La different from the optical pulses La included in the first optical pulse group La1, thereby guiding the first optical pulse group La1 and the second optical pulse group La2 to different optical paths respectively. Specifically, the dichroic mirror 63a guides the first optical pulse group La1 to an optical path along the X-axis direction. At this time, the spectroscopic direction of the first optical pulse group La1 is converted from the X-axis direction to the Z-axis direction due to reflection. Also, the dichroic mirror 63a guides the second optical pulse group La2 to an optical path along the Z-axis direction. At this time, the spectroscopic direction of the second optical pulse group La2 remains in the X-axis direction. The first optical pulse group La1 is incident on the first spatial light modulator 65, and the second optical pulse group La2 is incident on the second spatial light modulator 66 which is separate from the first spatial light modulator 65. The first spatial light modulator 65 is arranged on the optical path of the first optical pulse group La1 and is optically coupled to the dichroic mirror 63a via the optical path. The second spatial light modulator 66 is arranged on the optical path of the second optical pulse group La2 and is optically coupled to the dichroic mirror 63a via the optical path. When the number of the optical pulses La is 4 and their central wavelengths are λ1, λ2, λ3, and λ4 respectively, the optical pulse La with wavelength λ1 and the optical pulse La with wavelength λ2 may be included in the first optical pulse group La1, and the optical pulse La with wavelength λ3 and the optical pulse La with wavelength λ4 may be included in the second optical pulse group La2. However, the first optical pulse group La1 and the second optical pulse group La2 only need to include one or more optical pulses La, and the number of the optical pulses La constituting each wavelength component group is not limited to this. Also, in the following description, the magnitude relationship of the wavelengths λ1, λ2, λ3, and λ4 will be described as λ1 < λ2 < λ3 < λ4, but the magnitude relationship of the wavelengths λ1, λ2, λ3, and λ4 is not limited to this and is arbitrary.

[0032] The first spatial light modulator 65 and the second spatial light modulator 66 are optically coupled to the dichroic mirror 63a. The first spatial light modulator 65 modulates the phase of each optical pulse La included in the first optical pulse group La1 for each wavelength included in each optical pulse La. The first spatial light modulator 65 is, for example, of the LCOS (Liquid crystal on silicon) type that performs only phase modulation. Note that the first spatial light modulator 65 may perform only intensity modulation, or may perform both phase modulation and intensity modulation. Also, although FIG. 3 shows the reflective first spatial light modulator 65, the first spatial light modulator 65 may be transmissive. The second spatial light modulator 66 modulates the phase of each optical pulse La included in the second optical pulse group La2 for each wavelength included in each optical pulse La. Other configurations of the second spatial light modulator 66 are the same as those of the first spatial light modulator 65.

[0033] As shown in FIG. 3, the first spatial light modulator 65 has a modulation surface 65a (first modulation region) defined in the YZ plane. In the modulation surface 65a, a plurality of pixels are arranged two-dimensionally. In the modulation surface 65a, the same number of modulation regions as the optical pulses La included in the first optical pulse group La1 are arranged side by side in the Z-axis direction and extend in the Y-axis direction. FIG. 4(a) is a diagram showing an example of the modulation surface 65a. The example shown in FIG. 4(a) shows the case where the first optical pulse group La1 includes two optical pulses La. In this case, in the modulation surface 65a, two modulation regions 65aa and 65ab are arranged side by side in the Z-axis direction and extend in the Y-axis direction. Each of the modulation region 65aa and the modulation region 65ab receives the optical pulse La corresponding to each of the optical pulses La included in the first optical pulse group La1.

[0034] FIG. 4(a) shows the phase distribution on the modulation plane 65a by the shade of color. In the figure, the darker the color, the closer the phase value is to 2π (rad), and the lighter the color, the closer the phase value is to 0 (rad). A phase modulation pattern is displayed in each of the modulation region 65aa and the modulation region 65ab. The phase modulation pattern changes along the Z-axis direction and is constant in the Y-axis direction. In the phase modulation pattern, the larger the modulation amount of the phase, the larger the dispersion that can be compensated. In the example shown in FIG. 4(a), the phase modulation amount of the phase modulation pattern displayed in the modulation region 65ab is larger than that of the modulation region 65aa. Therefore, the dispersion compensation amount for the optical pulse La incident on the modulation region 65ab is larger than the dispersion compensation amount for the optical pulse La incident on the modulation region 65aa.

[0035] As shown in FIG. 3, the second spatial light modulator 66 has a modulation plane 66a (second modulation region) in the same manner as the first spatial light modulator 65. A plurality of pixels are two-dimensionally arranged on the modulation plane 66a. On the modulation plane 66a, the same number of modulation regions as the optical pulses La included in the second optical pulse group La2 are arranged side by side in the X-axis direction and extend in the Y-axis direction. FIG. 4(b) is a diagram showing an example of the modulation plane 66a. The example shown in FIG. 4(b) shows the case where the second optical pulse group La2 includes two optical pulses La. In this case, on the modulation plane 66a, two modulation regions 66aa and 66ab are arranged along the X-axis direction. In each of the modulation region 66aa and the modulation region 66ab, the optical pulse La corresponding to each optical pulse La included in the second optical pulse group La2 is incident.

[0036] In Fig. 4(b), the phase distribution on the modulation surface 66a is shown by the shade of color. In the figure, the darker the color, the closer the phase value is to 2π (rad), and the lighter the color, the closer the phase value is to 0 (rad). Phase modulation patterns are displayed in each of the modulation regions 66aa and 66ab. The phase modulation pattern changes along the X-axis direction and is constant in the Y-axis direction. In the example shown in Fig. 4(b), the amount of phase modulation of the phase modulation pattern displayed in the modulation region 66ab is larger than that of the modulation region 66aa. Further, when compared with Fig. 4(a), the amount of phase modulation of the phase modulation pattern increases in the order of the modulation regions 65aa, 65ab, 66aa, and 66ab. That is, the dispersion compensation amount increases in the order of the modulation regions 65aa, 65ab, 66aa, and 66ab. In the delay imparting unit 4, when using a plurality of optical fibers 41 having different lengths, the longer the length of the optical fiber 41, the larger the wavelength dispersion of the optical pulse La that has passed through the optical fiber 41. Therefore, by making the optical pulse La that has passed through the longest optical fiber 41 enter the modulation region 66ab and making the optical pulse La that has passed through the shortest optical fiber 41 enter the modulation region 65aa, dispersion compensation is performed with a magnitude corresponding to the wavelength dispersion of each optical pulse La.

[0037] Referring to Fig. 3 again. The first optical pulse group La1 modulated and reflected by the first spatial light modulator 65 and the second optical pulse group La2 modulated and reflected by the second spatial light modulator 66 are guided back onto one common optical path by the dichroic mirror 63a. The plurality of optical pulses La are focused on a single point on the diffraction grating 61a by the lens 62. At this time, the lens 62 functions as a condensing optical system for condensing each optical pulse La. The diffraction grating 61a functions as a multiplexing optical system for multiplexing the plurality of optical pulses La. That is, by these lens 62 and diffraction grating 61a, each optical pulse La is condensed and multiplexed with each other to become the multi-pulse light Lc after dispersion compensation.

[0038] The dispersion compensation unit 6 is not limited to the configuration of FIG. 3. For example, the spectroscopic element 61 (diffraction grating 61a) may be arranged after the separation optical element 63 (dichroic mirror 63a), and each optical pulse La included in the multi-pulse light Lb may be separated into a first optical pulse group La1 and a second optical pulse group La2 by the dichroic mirror 63a and then guided, and then each optical pulse La included in each optical pulse group La1, La2 may be spectroscopically analyzed by the diffraction grating 61a.

[0039] In addition to the first optical pulse group La1 and the second optical pulse group La2, there may be a third optical pulse group. For this purpose, for example, in FIG. 3, by newly adding a dichroic mirror between the lens 62 and the dichroic mirror 63a, the third wavelength component group may be guided to an optical path different from the first optical pulse group La1 and the second optical pulse group La2. In that case, it is preferable to further provide a spatial light modulator corresponding to the third optical pulse group.

[0040] The multi-pulse light generation method using the multi-pulse light source 1 described above will be described. FIG. 5 is a flowchart showing the multi-pulse light generation method of the present embodiment. First, a pulse light L1 separable into a plurality of optical pulses La having different central wavelengths is generated by the pulse light source 2 (pulse light generation step ST1). Next, the pulse light L1 is spectroscopically analyzed into a plurality of wavelength components by the spectroscopic unit 3, thereby generating a plurality of optical pulses La having different central wavelengths from each other (spectroscopic analysis step ST2). Subsequently, in the delay imparting unit 4, the plurality of optical pulses La respectively pass through a plurality of optical fibers 41 having different lengths. As a result, different delays are imparted to each of the plurality of optical pulses La for each optical pulse La (delay imparting step ST3). Subsequently, the plurality of optical pulses La that have respectively passed through the optical fibers 41 are combined on one optical path at the combining unit 5. As a result, a multi-pulse light Lb including a plurality of optical pulses La having different central wavelengths from each other and having a time interval from each other is generated (combining step ST4).

[0041] Subsequently, in the dispersion compensation unit 6, dispersion is compensated for each of the plurality of optical pulses La (dispersion compensation step ST5). In this example, the dispersion compensation step ST5 is performed after the combining step ST4, but the dispersion compensation step ST5 may be performed between the pulsed light generation step ST1 and the splitting step ST2.

[0042] The dispersion compensation step ST5 includes a splitting step ST51, a separation step ST52, and a modulation step ST53. In the splitting step ST51, each optical pulse La is split by the splitting element 61. In the separation step ST52, the separation optical element 63 guides the first optical pulse group La1 including one or more optical pulses La among the plurality of optical pulses La and the second optical pulse group La2 including one or more optical pulses La different from the optical pulses La constituting the first optical pulse group La1 to different optical paths. In this example, the separation step ST52 is performed after the splitting step ST51, but the separation step ST52 may be performed first, and then the splitting step ST51 may be performed.

[0043] In the modulation step ST53, modulation for compensating the dispersion for each optical pulse La is performed on the first optical pulse group La1 in the spatial light modulator 65 having the modulation surface 65a on which the first optical pulse group La1 is incident. At the same time, modulation for compensating the dispersion for each optical pulse La is performed on the second optical pulse group La2 in the spatial light modulator 66 having the modulation surface 66a on which the second optical pulse group La2 is incident.

[0044] The effects obtained by the multi-pulse light source 1 and the multi-pulse light generation method of the present embodiment described above will be described together with a comparative example. FIG. 6 shows the phase distribution on the modulation surface 7a as a comparative example, indicated by the shade of color. In the example shown in FIG. 6, four optical pulses La enter a single spatial light modulator without being separated into a first optical pulse group La1 and a second optical pulse group La2. Therefore, on the modulation surface 7a, four modulation regions 7aa, 7ab, 7ac, and 7ad corresponding to the plurality of optical pulses La respectively are arranged along the spectral direction on a single modulation surface 7a. Here, the wavelength resolution in the spatial light modulator is a value obtained by dividing the wavelength band of the incident light by the number of pixels of the modulation surface in the spectral direction. In the present embodiment, dispersion compensation is performed using two spatial light modulators such as the first spatial light modulator 65 and the second spatial light modulator 66. As is clear from comparing FIGS. 4(a) and 4(b) with FIG. 6, in that case, compared with the case of using a single spatial light modulator, the width in the spectral direction of the modulation region corresponding to each optical pulse La is doubled, and the number of pixels in the same direction is also doubled. Therefore, the wavelength resolution is also improved by a factor of two.

[0045] Thus, in the multi-pulse light source 1 and the multi-pulse light generation method of the present embodiment, the wavelength resolution for each optical pulse La is improved compared with the case of using a single spatial light modulator. As a result, the maximum dispersion compensation amount can be significantly improved. Consequently, the dispersion of the multi-pulse light Lb having different center wavelengths for each optical pulse La can be compensated more effectively for each optical pulse La.

[0046] As another comparative example, FIG. 7 shows a diagram in which the first spatial light modulator 65 and the second spatial light modulator 66 are arranged in parallel in the spectral direction. In this comparative example, the separation optical element 63 is not provided, and the multi-pulse light Lb is incident on the first spatial light modulator 65 and the second spatial light modulator 66 without being separated into the first light pulse group La1 and the second light pulse group La2. In this case, a dead space D is generated between the modulation surface 65a of the first spatial light modulator 65 and the modulation surface 66a of the second spatial light modulator 66. Since the light incident on the dead space D is not modulated, in order to modulate all the bands of each light pulse La, as shown in FIG. 3, the separation optical element 63 guides the first light pulse group La1 and the second light pulse group La2 to different optical paths, respectively, and then the first spatial light modulator 65 and the second spatial light modulator 66 are arranged on each optical path.

[0047] In the present embodiment, the spectroscopic element 61 includes a diffraction grating 61a. By using the diffraction grating 61a, a plurality of light pulses La, that is, a plurality of wavelength components can be appropriately spectroscopically separated and then incident on the first spatial light modulator 65 and the second spatial light modulator 66. In addition, the spectroscopic element 61 can be simply configured.

[0048] In the present embodiment, the separation optical element 63 includes a dichroic mirror 63a. By using the dichroic mirror 63a, a plurality of light pulses La (wavelength components) can be reflected or transmitted according to the wavelength range, and the first light pulse group La1 and the second light pulse group La2 can be preferably separated. In addition, the separation optical element 63 can be simply configured.

[0049] In the present embodiment, the dispersion compensation unit 6 is arranged at the subsequent stage of the delay imparting unit 4. Thereby, direct dispersion compensation can be performed for each of a plurality of light pulses La (wavelength components) in which different wavelength dispersions are generated due to different delays being imparted to each other. Therefore, the effect of dispersion compensation for each light pulse La (wavelength component) can be efficiently confirmed.

[0050] In this embodiment, the delay imparting unit 4 has a plurality of optical fibers 41 with different lengths that respectively propagate a plurality of wavelength components. As a result, a delay can be imparted according to the length of the optical fiber 41, so that the delay imparting unit 4 can be simply configured. [Second Embodiment]

[0051] FIG. 8 shows a configuration diagram of the dispersion compensation unit 6A according to the second embodiment. In the second embodiment, the configurations of the pulse light source 2, the splitting unit 3, the delay imparting unit 4, and the coupling unit 5 are the same as those in the first embodiment. The dispersion compensation unit 6A includes a diffraction element 61A, a lens 62, a separation optical element 63A, and a spatial light modulator 67. Different from the first embodiment in FIG. 3, the separation optical element 63A is arranged in front of the diffraction element 61A. In the second embodiment, as an example, the diffraction element 61A includes a first diffraction grating 61b and a second diffraction grating 61c. The first diffraction grating 61b and the second diffraction grating 61c are arranged side by side along the Y-axis direction. Also, as an example, the separation optical element 63A includes a dichroic mirror 63b and a mirror 63c. The dichroic mirror 63b and the mirror 63c are arranged side by side along the Y-axis direction. The first diffraction grating 61b is arranged on the optical path between the dichroic mirror 63b and the spatial light modulator 67. The second diffraction grating 61c is arranged on the optical path between the mirror 63c and the spatial light modulator 67.

[0052] The multi-pulse light Lb input to the dispersion compensation unit 6A first enters the dichroic mirror 63b. The dichroic mirror 63b transmits the first optical pulse group La1 and reflects the second optical pulse group La2 in the Y-axis direction toward the mirror 63c. Thereafter, the mirror 63c reflects the second optical pulse group La2 reflected by the dichroic mirror 63b in the Z-axis direction, which is a direction parallel to the optical path of the first optical pulse group La1. As a result, the first optical pulse group La1 and the second optical pulse group La2 are guided along different optical paths.

[0053] The first folding grating 61b spatially disperses each optical pulse La included in the first optical pulse group La1. The second folding grating 61c spatially disperses each optical pulse La included in the second optical pulse group La2. The dispersion direction is the X-axis direction. Since the first optical pulse group La1 and the second optical pulse group La2 are arranged along the Y-axis direction, the dispersion direction of these optical pulse groups La1, La2 and the direction in which these optical pulse groups La1, La2 are arranged intersect each other. The lens 62 is disposed on the optical path between the dispersive element 61A and the spatial light modulator 67. The dispersed first optical pulse group La1 and second optical pulse group La2 are parallelized mainly in the XZ plane by the lens 62 and enter the modulation plane 67a of the spatial light modulator 67.

[0054] FIG. 9 is a diagram showing an example of the modulation plane 67a. As shown in FIG. 9, the modulation plane 67a extends along the X-axis and the Y-axis. A plurality of pixels are two-dimensionally arranged on the modulation plane 67a. Further, the modulation plane 67a includes a first modulation region 67a1 where the first optical pulse group La1 is incident and a second modulation region 67a2 where the second optical pulse group La2 is incident. The first modulation region 67a1 and the second modulation region 67a2 are arranged along the Y-axis direction. That is, the first modulation region 67a1 and the second modulation region 67a2 are arranged along the direction intersecting the respective dispersion directions of the first optical pulse group La1 and the second optical pulse group La2 when they are incident on the first modulation region 67a1 and the second modulation region 67a2, respectively.

[0055] The example shown in FIG. 9 shows a case where the first optical pulse group La1 includes two optical pulses La, and the second optical pulse group La2 includes two optical pulses La. In this case, in the first modulation region 67a1, the modulation region 67aa and the modulation region 67ab are arranged side by side in the X-axis direction and extend in the Y-axis direction. In each of the modulation region 67aa and the modulation region 67ab, the corresponding optical pulse La among the optical pulses La included in the first optical pulse group La1 is incident. In the second modulation region 67a2, the modulation region 67ac and the modulation region 67ad are arranged side by side in the X-axis direction and extend in the Y-axis direction. In each of the modulation region 67ac and the modulation region 67ad, the corresponding optical pulse La among the optical pulses La included in the second optical pulse group La2 is incident.

[0056] In FIG. 9, the phase distribution on the modulation plane 67a is shown by the shade of color. In the figure, the darker the color, the closer the phase value is to 2π (rad), and the lighter the color, the closer the phase value is to 0 (rad). A phase modulation pattern is displayed in each of the modulation regions 67aa, 67ab, 67ac, and 67ad. The phase modulation pattern changes along the X-axis direction and is constant in the Y-axis direction. In the phase modulation pattern, the larger the modulation amount of the phase, the greater the dispersion can be compensated. In the example shown in FIG. 9, the phase modulation amount of the phase modulation pattern displayed in the modulation region 67ad is the largest, and the phase modulation amount of the phase modulation pattern displayed in the modulation region 67aa is the smallest. Therefore, the dispersion compensation amount for the optical pulse La incident on the modulation region 67ad is larger than the dispersion compensation amount for the optical pulse La incident on the modulation region 65aa.

[0057] Referring to FIG. 8 again, the first optical pulse group La1 and the second optical pulse group La2 that are modulated and reflected by the spatial light modulator 67 are focused by the lens 62 at a single point on the diffraction gratings 61b and 61c. The diffraction grating 61b functions as a multiplexing optical system and multiplexes one or more optical pulses La that constitute the first optical pulse group La1. The diffraction grating 61c also functions as a multiplexing optical system and multiplexes one or more optical pulses La that constitute the second optical pulse group La2. The first optical pulse group La1 and the second optical pulse group La2 are guided again onto a common optical path by the dichroic mirror 63b and become the multi-pulse light Lc after dispersion compensation.

[0058] A method for generating multi-pulse light using the dispersion compensation unit 6A of this embodiment will be described. FIG. 10 is a flowchart showing the method for generating multi-pulse light of this embodiment. Note that the pulse light generation step ST1, the splitting step ST2, the delay application step ST3, and the combining step ST4 are the same as those in the first embodiment, so the description thereof will be omitted.

[0059] After the combining step ST4, in the dispersion compensation unit 6A, dispersion is compensated for each optical pulse La among the plurality of optical pulses La (dispersion compensation step ST5A). Note that in this example, the dispersion compensation step ST5A is performed after the combining step ST4, but the dispersion compensation step ST5A may be performed between the pulse light generation step ST1 and the splitting step ST2.

[0060] The dispersion compensation step ST5A includes a separation step ST54, a splitting step ST55, and a modulation step ST56. In the separation step ST54, the separation optical element 63A guides the first optical pulse group La1 including one or more optical pulses La and the second optical pulse group La2 including one or more optical pulses La different from the optical pulses La constituting the first optical pulse group La1 onto different optical paths, respectively, among the plurality of optical pulses La. In the splitting step ST55, each optical pulse La is split by the splitting element 61A. Note that in this example, the splitting step ST55 is performed after the separation step ST54, but the splitting step ST55 may be performed first, and then the separation step ST54 may be performed.

[0061] In modulation step ST56, in a spatial light modulator 67 having a modulation plane 67a including a first modulation region 67a1 into which a first optical pulse group La1 is incident and a second modulation region 67a2 into which a second optical pulse group La2 is incident, modulation for compensating for dispersion for each optical pulse La is performed on the first optical pulse group La1 and the second optical pulse group La2. As described above, the first modulation region 67a1 and the second modulation region 67a2 are arranged along a direction intersecting the respective spectral directions of the first optical pulse group La1 and the second optical pulse group La2 when the first optical pulse group La1 and the second optical pulse group La2 are incident on the first modulation region 67a1 and the second modulation region 67a2, respectively.

[0062] The effects obtained by the second embodiment described above will be described. Here, similar to the first embodiment, a comparison is made between the resolution for each optical pulse La on the modulation surface 67a of this embodiment and the resolution for each optical pulse La on the modulation surface 7a shown in FIG. 6. As described above, in the example shown in FIG. 6, four optical pulses La are incident on a single spatial light modulator without being separated into the first optical pulse group La1 and the second optical pulse group La2. Therefore, on the modulation surface 7a, four modulation regions 7aa, 7ab, 7ac, and 7ad corresponding to the plurality of optical pulses La are arranged side by side along the spectral direction on a single modulation surface 7a. On the other hand, in the dispersion compensation unit 6A according to the second embodiment, the multi-pulse light Lb is separated into the first optical pulse group La1 and the second optical pulse group La2, and then the first optical pulse group La1 is made incident on the first modulation region 67a1 of the spatial light modulator 67, and the second optical pulse group La2 is made incident on the second modulation region 67a2 of the spatial light modulator 67. The first modulation region 67a1 and the second modulation region 67a2 are arranged side by side along a direction intersecting the spectral directions of the first optical pulse group La1 and the second optical pulse group La2 when they are respectively incident on the first modulation region 67a1 and the second modulation region 67a2. Therefore, as is clear from comparing FIG. 9 and FIG. 6, the width in the spectral direction of the modulation region corresponding to each optical pulse La is doubled, and the number of pixels in the modulation region in the same direction is also doubled. As described above, the wavelength resolution in the spatial light modulator is a value obtained by dividing the wavelength band of the incident light by the number of pixels of the modulation surface in the spectral direction. Therefore, the wavelength resolution is improved by a factor of two.

[0063] Thus, according to the multi-pulse light source and the multi-pulse light generation method of the second embodiment, since the wavelength resolution for each optical pulse La in the spatial light modulator is improved, the maximum dispersion compensation amount can be significantly improved. As a result, the dispersion of the multi-pulse light Lb having different center wavelengths for each optical pulse La can be compensated more effectively for each optical pulse La. [Modification Example]

[0064] FIG. 11 shows the configuration of the dispersion compensation unit 6B according to a modification of the second embodiment. The dispersion compensation unit 6B of the modification has a separation optical element 63B instead of the separation optical element 63A (dichroic mirror 63b and mirror 63c) of the second embodiment. The separation optical element 63B includes a polarization beam splitter 63d and a mirror 63e. Note that the separation optical element 63B may include a birefringent crystal instead of the polarization beam splitter 63d. The dispersion compensation unit 6B further has a wave plate 64. The wave plate 64 is disposed on the optical path of the first optical pulse group La1 between the separation optical element 63B and the spectroscopic element 61A.

[0065] The multi-pulse light source of this modification further includes a polarization control unit 42. The other configurations of the multi-pulse light source of this modification, excluding the dispersion compensation unit 6B and the polarization control unit 42, are the same as those of the first embodiment. The polarization control unit 42 orthogonalizes the polarization directions of one or more optical pulses La included in the first optical pulse group La1 and the polarization directions of one or more optical pulses La included in the second optical pulse group La2 before the light enters the separation optical element 63B. The polarization control unit 42 includes, for example, the same number of polarization-maintaining fibers as the plurality of optical pulses La. Between the optical input end and the optical output end of the plurality of polarization-maintaining fibers, the polarization plane of the polarization-maintaining fiber that propagates the optical pulse La that will later be guided as the first optical pulse group La1 rotates 90° in the clockwise or counterclockwise direction with respect to the polarization plane of the polarization-maintaining fiber that propagates the optical pulse La that will later be guided as the second optical pulse group La2. By transmitting each optical pulse La in the corresponding polarization-maintaining fiber, the polarization direction of each optical pulse La that will later be guided as the first optical pulse group La1 and the polarization direction of each optical pulse La that will later be guided as the second optical pulse group La2 can be controlled to be orthogonal. Note that the plurality of optical fibers 41 shown in FIG. 2 may be the plurality of polarization-maintaining fibers. In that case, the delay imparting unit 4 also serves as the polarization control unit 42. And the lengths of the plurality of polarization-maintaining fibers are different from each other.

[0066] The multi-pulse light Lb including a plurality of optical pulses La polarization-controlled by the polarization control unit 42 is incident on a polarization beam splitter 63d (or a birefringent crystal). The polarization beam splitter 63d (or the birefringent crystal) transmits the first optical pulse group La1 and reflects the second optical pulse group La2 toward the mirror 63e in the Y-axis direction. Thereafter, the mirror 63e reflects the second optical pulse group La2 in the Z-axis direction, which is a direction parallel to the optical path of the first optical pulse group La1. As a result, the first optical pulse group La1 and the second optical pulse group La2 are guided along different optical paths.

[0067] The first optical pulse group La1 is incident on a wave plate 64. By the wave plate 64, the polarization direction of the first optical pulse group La1 is rotated 90° in the clockwise direction or the counterclockwise direction. Thereby, the polarization direction of the first optical pulse group La1 coincides with the polarization direction of the second optical pulse group La2.

[0068] Also in the dispersion compensation unit 6 according to the first embodiment shown in FIG. 3, similar to this modified example, instead of the dichroic mirror 63a, a polarization beam splitter 63d (or a birefringent crystal) and a mirror 63e may be used. In that case, the multi-pulse light source 1 may further include a polarization control unit 42. The polarization control unit 42 orthogonalizes the polarization direction of the optical pulse La included in the first optical pulse group La1 and the polarization direction of the optical pulse La included in the second optical pulse group La2 before the plurality of optical pulses La are incident on the polarization beam splitter 63d (or the birefringent crystal). The polarization beam splitter 63d (or the birefringent crystal) guides the first optical pulse group La1 and the second optical pulse group La2 along different optical paths based on the polarization direction.

[0069] When using a polarization beam splitter 63d (or a birefringent crystal) and a mirror 63e instead of the dichroic mirror 63a, the dispersion compensation unit 6 may further have a wave plate 64 between the separation optical element 63 and the first spatial light modulator 65.

[0070] According to the multi-pulse light source of this modification example, after the polarization control unit 42 controls the polarization direction, by using the polarization beam splitter 63d (or birefringent crystal) and the mirror 63e, the first optical pulse group La1 and the second optical pulse group La2 can be guided along different optical paths according to the polarization direction. Then, by passing the first optical pulse group La1 through the wave plate 64, the polarization direction of the first optical pulse group La1 is made to coincide with the polarization direction of the second optical pulse group La2, and then the first optical pulse group La1 and the second optical pulse group La2 can be made incident on the spatial light modulator 67.

[0071] As described above, the delay imparting unit 4 may also serve as the polarization control unit 42. Thereby, the number of necessary components can be reduced and the multi-pulse light source can be simplified.

[0072] As described above, the polarization control unit 42 has a plurality of polarization maintaining fibers that respectively propagate a plurality of optical pulses La. The lengths of the plurality of polarization maintaining fibers are different from each other. Between the optical input end and the optical output end of the plurality of polarization maintaining fibers, the polarization plane of the polarization maintaining fiber that propagates the optical pulse La included in the first optical pulse group La1 is rotated 90° in the clockwise direction or the counterclockwise direction with respect to the polarization plane of the polarization maintaining fiber that propagates the optical pulse La included in the second optical pulse group La2. In this case, while imparting a delay according to the length of the polarization maintaining fiber, the polarization direction of one or more optical pulses La included in the first optical pulse group La1 and the polarization direction of one or more optical pulses La included in the second optical pulse group La2 can be suitably adjusted. [Embodiment]

[0073] First, estimate the necessary dispersion compensation amount. Assuming that the refractive index of the optical fiber 41 is 1.5, the time interval between the plurality of optical pulses La is dt, and the step value of the length of the plurality of optical fibers 41 is L, the following formula holds. Here, C is the speed of light. dt = n·L / C For example, in order to set the time interval dt of the plurality of optical pulses La included in the multi-pulse light Lb to 3 ns, it is advisable to increase the lengths of the plurality of optical fibers 41 in increments of 0.6 m. In order to set the time interval dt to 5 ns, it is advisable to increase the lengths of the plurality of optical fibers 41 in increments of 1 m. The time intervals such as 3 ns to 5 ns correspond to the fluorescence lifetime and are suitable values when the multi-pulse light Lb is used for fluorescence observation. If the number of optical pulses La is 4 and the length of the shortest optical fiber 41 is 0.5 m, the length of the longest optical fiber 41 will be 3.5 m. Converting this length into dispersion results in 70000 fs 2 (assuming the second-order dispersion β2 of the optical fiber 41 is 20 ps 2 / km). It is desirable to compensate for this dispersion as much as possible.

[0074] Fig. 12 shows the configuration of the multi-pulse light source 1A according to the embodiment. The pulse light source 2 is a laser light source that emits near-infrared pulse light L1 in the femtosecond region. The pulse light L1 has a wavelength band spread that can be separated into four optical pulses La with central wavelengths of λ1: 938 nm, λ2: 1013 nm, λ3: 1088 nm, and λ4: 1163 nm. Subsequently, the pulse light L1 is split into four optical pulses La by the splitting unit 3. The splitting unit 3 is a dichroic mirror array, and the four split optical pulses La are incident on the delay imparting unit 4.

[0075] The delay imparting unit 4 includes four optical fibers 41 with different lengths. As shown in Fig. 13, in this embodiment, the optical pulse La with wavelength λ1 is incident on the shortest optical fiber 41, and in the order of wavelengths λ2, λ3, and λ4, the lengths of the incident optical fibers 41 are gradually increased. The length of the shortest optical fiber 41 is 0.5 m, and it is increased in increments of 1 m from there. That is, the length of the longest optical fiber 41 is 3.5 m.

[0076] Referring to Fig. 12 again, each optical pulse La that has passed through the delay imparting unit 4 is combined at the combining unit 5 to form the multi-pulse light Lb. Thereafter, dispersion compensation is performed by the dispersion compensation unit 6A according to the second embodiment, and the multi-pulse light Lc after dispersion compensation is generated.

[0077] Fig. 14 shows the temporal intensity waveforms (broken lines) of the respective optical pulses La before entering the delay imparting section 4 and the temporal intensity waveforms (solid lines) of the respective optical pulses La after dispersion compensation. Fig. 14(a) shows the results according to the comparative example. In the comparative example, a spatial light modulator 7 (see Fig. 6) in which a plurality of modulation regions respectively corresponding to the plurality of optical pulses La are arranged only in the spectral direction of each optical pulse La when entering the modulation surface is used. Then, without using the separation optical element 63, the multi-pulse light Lb is made to enter the modulation surface 7a of the spatial light modulator 7 without separating it into the first optical pulse group La1 and the second optical pulse group La2. On the other hand, Fig. 14(b) shows the results when the dispersion compensation section 6 according to the second embodiment is used. In both the examples and the comparative example, the number of pixels in the spectral direction of the spatial light modulators 67 and 7 is set to 1280, and the optical resolution is set to 23.7 μm. Also, the grating density in the diffraction gratings 61b and 61c of the examples is set to 1100 lines / mm, and the grating density in the diffraction grating of the comparative example is set to 600 lines / mm.

[0078] When the peak intensity of each optical pulse La before entering the delay imparting unit 4 is set to 100%, the peak intensity of each optical pulse La after dispersion compensation is 97% at wavelength λ1, 80% at wavelength λ2, 57% at wavelength λ3, and 37% at wavelength λ4 in Fig. 14(a). On the other hand, in Fig. 14(b), it is 99% at wavelength λ1, 94% at wavelength λ2, 86% at wavelength λ3, and 75% at wavelength λ4. That is, it can be seen that in the embodiment, the attenuation of the peak intensity is significantly suppressed compared with the comparative example. This is due to the difference in the wavelength resolution of each modulation region in the spatial light modulator. In the comparative example, the number of pixels in the spectral direction per modulation region is 1280 / 4 = 320, and the wavelength resolution of each modulation region is 0.234 nm obtained by dividing the wavelength band 75 nm of one optical pulse La by the number of pixels 320. In contrast, in the embodiment, the number of pixels in the spectral direction per modulation region is 1280 / 2 = 640, and the wavelength resolution of each modulation region is 0.117 nm obtained by dividing the wavelength band 75 nm of one optical pulse La by the number of pixels 640. Thus, in the embodiment, the wavelength resolution is twice that of the comparative example. Although the configuration of the second embodiment is adopted in this embodiment, the wavelength resolution is the same value even in the first embodiment, so the same dispersion compensation effect as in this embodiment can be obtained also in the first embodiment. [Application Example]

[0079] The multi-pulse light sources according to the first and second embodiments can be applied to a multimodal microscope. In recent years, instead of conventional fluorescence observation, non-linear optical microscopes based on phenomena such as multi-photon excitation and high-order harmonic generation have attracted attention. A microscope having a function of discriminating a plurality of different targets by discriminating light responses based on a plurality of observation modalities such as multi-photon excitation and high-order harmonic generation is called a multimodal microscope. In multimodal observation, since pulsed light of a wide range of wavelengths corresponding to a plurality of different observation modalities is used, a multi-pulse light source is useful. However, when the shapes of the respective light pulses La of the multi-pulse light Lb are different from each other due to wavelength dispersion, different peak intensities will result for each target, and stable measurement cannot be performed. Therefore, by using the multi-pulse light sources according to the first and second embodiments, the dispersion of multi-pulse light having different center wavelengths for each pulse can be compensated more effectively for each pulse, so that multimodal observation can be performed stably.

Explanation of Signs

[0080] 1... Multi-pulse light source, 2... Pulse light source, 4... Delay imparting section, 41... Optical fiber, 42... Polarization control section, 6... Dispersion compensation section, 61... Spectroscopic element, 61a... Diffraction grating, 63... Separation optical element, 63a... Dichroic mirror, 63b... Dichroic mirror, 63c... Mirror, 63d... Polarizing beam splitter, 64... Wave plate, 65... First spatial light modulator, 66... Second spatial light modulator, 67... Spatial light modulator, 67a1... First modulation region, 67a2... Second modulation region, L1... Pulse light, La1... First wavelength component group, La2... Second wavelength component group.

Claims

1. A pulse light source that generates pulse light separable into a plurality of wavelength components having different central wavelengths, a delay imparting unit that imparts different delays to each of the plurality of wavelength components to create a time interval between the plurality of wavelength components, and a dispersion compensation unit that compensates for dispersion for each of the plurality of wavelength components, wherein the dispersion compensation unit includes a spectroscopic element that spectroscopically separates the plurality of wavelength components into respective wavelength components, a separation optical element provided in front of or behind the spectroscopic element that guides a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components to different optical paths, a first spatial light modulator that includes a first modulation region where the first wavelength component group is incident and performs modulation for compensating for dispersion for each wavelength component of the first wavelength component group, and a second spatial light modulator that includes a second modulation region where the second wavelength component group is incident and performs modulation for compensating for dispersion for each wavelength component of the second wavelength component group, a multi-pulse light source.

2. A pulse light source that generates pulse light separable into a plurality of wavelength components having different central wavelengths, a delay imparting unit that imparts different delays to each of the plurality of wavelength components to create a time interval between the plurality of wavelength components, and a dispersion compensation unit that compensates for dispersion for each of the plurality of wavelength components, wherein the dispersion compensation unit includes a spectroscopic element that spectroscopically separates the plurality of wavelength components into respective wavelength components, a separation optical element provided in front of or behind the spectroscopic element that guides a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components to different optical paths, and a spatial light modulator that includes a first modulation region where the first wavelength component group is incident and performs modulation for compensating for dispersion for each wavelength component of the first wavelength component group, and a second modulation region where the second wavelength component group is incident and performs modulation for compensating for dispersion for each wavelength component of the second wavelength component group, wherein the first modulation region and the second modulation region are arranged side by side along a direction intersecting the respective spectroscopic directions of the first wavelength component group and the second wavelength component group when the first wavelength component group and the second wavelength component group are incident on the first modulation region and the second modulation region, respectively, a multi-pulse light source.

3. The spectroscopic element includes a diffraction grating, and the multi-pulse light source according to claim 1 or 2.

4. The separation optical element includes a dichroic mirror, and the multi-pulse light source according to any one of claims 1 to 3.

5. A pulse light source that generates pulse light separable into a plurality of wavelength components having different center wavelengths, A delay imparting unit that imparts different delays for each wavelength component to the plurality of wavelength components, A dispersion compensation unit that compensates for dispersion for each wavelength component with respect to the plurality of wavelength components, A spectroscopic element that spectrally separates the plurality of wavelength components into respective wavelength components, A separation optical element provided in front of or behind the spectroscopic element, guiding a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components to different optical paths, A first spatial light modulator including a first modulation region that receives the first wavelength component group and performs modulation for compensating for dispersion for each wavelength component with respect to the first wavelength component group, A second spatial light modulator including a second modulation region that receives the second wavelength component group and performs modulation for compensating for dispersion for each wavelength component with respect to the second wavelength component group, and the dispersion compensation unit having the same, A polarization control unit that orthogonalizes the polarization directions of the one or more wavelength components included in the first wavelength component group and the polarization directions of the one or more wavelength components included in the second wavelength component group before the light enters the separation optical element, A wavelength plate provided on the optical path between the separation optical element and the first modulation region, and rotating the polarization direction of the first wavelength component group by 90°, The separation optical element includes a polarization beam splitter or a birefringent crystal, and the multi-pulse light source.

6. A pulse light source that generates pulse light separable into a plurality of wavelength components having different center wavelengths, A delay imparting unit that imparts different delays for each wavelength component to the plurality of wavelength components, A dispersion compensation unit that compensates for dispersion for each wavelength component with respect to the plurality of wavelength components, A spectroscopic element that spectrally separates the plurality of wavelength components into respective wavelength components, A separation optical element provided in front of or behind the spectroscopic element, guiding a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components to different optical paths, A first modulation region where the first wavelength component group is incident and modulation is performed to compensate for dispersion for each wavelength component with respect to the first wavelength component group, and a second modulation region where the second wavelength component group is incident and modulation is performed to compensate for dispersion for each wavelength component with respect to the second wavelength component group, and a spatial light modulator including the same. The first modulation region and the second modulation region are arranged side by side along a direction intersecting each spectral direction of the first wavelength component group and the second wavelength component group when they are incident on the first modulation region and the second modulation region, respectively, the dispersion compensation unit. A polarization control unit that orthogonalizes the polarization direction of the one or more wavelength components included in the first wavelength component group and the polarization direction of the one or more wavelength components included in the second wavelength component group before being incident on the separation optical element. A wavelength plate provided on the optical path between the separation optical element and the first modulation region, which rotates the polarization direction of the first wavelength component group by 90°. The separation optical element includes a polarization beam splitter or a birefringent crystal, a multi-pulse light source.

7. The multi-pulse light source according to claim 5 or 6, wherein the delay imparting unit also serves as the polarization control unit.

8. The delay imparting unit has a plurality of polarization-maintaining fibers that respectively propagate the plurality of wavelength components, the lengths of the plurality of polarization-maintaining fibers are different from each other, and between the optical input end and the optical output end of the plurality of polarization-maintaining fibers, the polarization plane of the polarization-maintaining fiber that propagates the wavelength component included in the first wavelength component group is rotated by 90° with respect to the polarization plane of the polarization-maintaining fiber that propagates the wavelength component included in the second wavelength component group, the multi-pulse light source according to claim 7.

9. The multi-pulse light source according to any one of claims 1 to 8, wherein the dispersion compensation unit is arranged at a subsequent stage of the delay imparting unit.

10. The multi-pulse light source according to any one of claims 1 to 7, 9, wherein the delay imparting unit has a plurality of optical fibers with different lengths that respectively propagate the plurality of wavelength components.

11. A pulse light generation step of generating pulse light separable into a plurality of wavelength components having different center wavelengths, A delay imparting step of imparting different delays to each of the plurality of wavelength components to cause a time interval between the plurality of wavelength components. Before or after the delay application step, a dispersion compensation step of compensating for dispersion for each wavelength component of the plurality of wavelength components is provided. The dispersion compensation step includes: a spectral splitting step of splitting the plurality of wavelength components into respective wavelength components; before or after the spectral splitting step, a separation step of guiding, into different optical paths, a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components; a modulation step of performing modulation for compensating for dispersion for each wavelength component on the first wavelength component group in a first spatial light modulator having a first modulation region into which the first wavelength component group is incident, and performing modulation for compensating for dispersion for each wavelength component on the second wavelength component group in a second spatial light modulator having a second modulation region into which the second wavelength component group is incident, the multi-pulse light generation method.

12. a pulse light generation step of generating pulse light separable into a plurality of wavelength components having different center wavelengths; a delay application step of causing a time interval to occur between the plurality of wavelength components by applying different delays to each of the plurality of wavelength components; before or after the delay application step, a dispersion compensation step of compensating for dispersion for each wavelength component of the plurality of wavelength components is provided. The dispersion compensation step includes: a spectral splitting step of splitting the plurality of wavelength components into respective wavelength components; before or after the spectral splitting step, a separation step of guiding, into different optical paths, a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components; a modulation step of performing modulation for compensating for dispersion for each wavelength component on the first wavelength component group and the second wavelength component group in a spatial light modulator having a first modulation region into which the first wavelength component group is incident and a second modulation region into which the second wavelength component group is incident, the first modulation region and the second modulation region being arranged side by side along a direction intersecting each spectral splitting direction of the first wavelength component group and the second wavelength component group when the first wavelength component group and the second wavelength component group are incident on the first modulation region and the second modulation region, respectively, the multi-pulse light generation method.

13. a pulse light generation step of generating pulse light separable into a plurality of wavelength components having different center wavelengths; a delay imparting step of imparting different delays for each wavelength component to the plurality of wavelength components; a dispersion compensation step of compensating for dispersion for each wavelength component with respect to the plurality of wavelength components, before or after the delay imparting step, a spectral splitting step of splitting the plurality of wavelength components into respective wavelength components; a separation step of guiding, before or after the spectral splitting step, a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components to different optical paths; a modulation step of performing modulation for compensating for dispersion for each wavelength component with respect to the first wavelength component group in a first spatial light modulator having a first modulation region into which the first wavelength component group is incident, and performing modulation for compensating for dispersion for each wavelength component with respect to the second wavelength component group in a second spatial light modulator having a second modulation region into which the second wavelength component group is incident, the dispersion compensation step including: a step of making orthogonal the polarization directions of the one or more wavelength components included in the first wavelength component group and the polarization directions of the one or more wavelength components included in the second wavelength component group before the dispersion compensation step; the dispersion compensation step further includes a step of rotating the polarization direction of the first wavelength component group by 90° by a wave plate provided on an optical path between a separation optical element including a polarization beam splitter or a birefringent crystal and the first modulation region, a multi-pulse light generation method.

14. a pulse light generation step of generating pulse light separable into a plurality of wavelength components having different center wavelengths; a delay imparting step of imparting different delays for each wavelength component to the plurality of wavelength components; a dispersion compensation step of compensating for dispersion for each wavelength component with respect to the plurality of wavelength components, before or after the delay imparting step, a spectral splitting step of splitting the plurality of wavelength components into respective wavelength components; a separation step of guiding, before or after the spectral splitting step, a first wavelength component group including one or more wavelength components among the plurality of wavelength components and a second wavelength component group including one or more wavelength components different from the one or more wavelength components to different optical paths; A spatial light modulator having a first modulation region into which the first wavelength component group is incident and a second modulation region into which the second wavelength component group is incident, the first modulation region and the second modulation region being arranged side by side along a direction intersecting the respective spectral directions of the first wavelength component group and the second wavelength component group when they are incident on the first modulation region and the second modulation region, respectively, the method comprising a modulation step of performing modulation for compensating for dispersion for each wavelength component with respect to the first wavelength component group and the second wavelength component group, and the dispersion compensation step. Before the dispersion compensation step, a step of making the polarization direction of the one or more wavelength components included in the first wavelength component group orthogonal to the polarization direction of the one or more wavelength components included in the second wavelength component group. The dispersion compensation step further includes a step of rotating the polarization direction of the first wavelength component group by 90° by a wave plate provided on the optical path between a polarization beam splitter or a separation optical element including a birefringent crystal and the first modulation region, the multi-pulse light generation method.

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