JP2016051018A - Pulse light fairing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse light fairing device that allows a waveform of an optical pulse to be highly accurately made similar to a desired shape.SOLUTION: A pulse light fairing device 1A comprises: a spectroscopic element 12; a spatial optical modulator 16; and a control unit 20 that controls a phase pattern to be presented to the spatial optical modulator 16. The control unit 20 is cause the spatial optical modulator 16 to present the phase pattern including an intensity modulation pattern for giving input pulse light La an intensity spectrum having a mountain waveform and a valley waveform alternately repeated and a phase spectrum having a wavelength interval in which the phase stays almost constant repeated. A boundary wavelength between adjacent wavelength intervals is included in a wavelength range of the valley waveform.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pulsed light shaping device.

  Non-Patent Document 1 discloses a technique for controlling the shape of an optical pulse using a spatial light modulator (SLM). In this document 1, input light is split by a diffraction grating, and the split light is guided to a two-dimensional LCOS (Liquid Crystal on Silicon) type spatial light modulator. The waveform of the output pulse light is controlled by modulating the phase spectrum and intensity spectrum of the input light in the spatial light modulator. A blazed diffraction grating pattern or a binary diffraction grating pattern is adopted as the intensity spectrum modulation method.

Eugene Frumker and Yaron Silberberg, “Phase and amplitude pulse shaping with two-dimensional phase-only spatial light modulators,” J. Opt. Soc. Am. B, vol. 24, No. 12 (2007)

  As a technique for controlling the waveform of the ultrashort pulse light, there is a technique of modulating the phase spectrum and the intensity spectrum of an optical pulse by a spatial light modulator. In this technique, it is desirable that the optical pulse waveform be brought close to a desired shape with high accuracy. It is an object of the present invention to provide a pulsed light shaping device that can accurately approximate the waveform of an optical pulse to a desired shape.

  In order to solve the above-described problem, a first pulsed light shaping device according to the present invention is a pulsed light shaping device that generates output pulsed light having a waveform different from the input pulsed light from input pulsed light, A spectroscopic element that splits input pulse light for each wavelength component, a phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component, and spatial light And a control unit that provides a control signal for controlling the phase pattern presented to the modulator to the spatial light modulator, and the combined light obtained by combining the wavelength components modulated by the spatial light modulator is a pulse light shaping device. The control unit outputs, to the combined light, an intensity modulation pattern for giving the combined light an intensity spectrum in which a peak waveform and a valley waveform are alternately repeated, and a phase spectrum that repeats a wavelength section in which the phase is substantially constant. A phase pattern including a phase modulation pattern to be obtained is presented to the spatial light modulator, a boundary wavelength between adjacent wavelength sections is included in the wavelength range of the valley waveform, and the control unit includes a blazed diffraction grating An intensity modulation pattern is presented in each modulation region, and the amplitude of the blazed diffraction grating is variable.

  The second pulsed light shaping device according to the present invention is a pulsed light shaping device that generates output pulsed light having a waveform different from the input pulsed light from the input pulsed light. A spectral element that divides into two, a phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component, and a phase presented to the spatial light modulator A control unit that provides a control signal for controlling the pattern to the spatial light modulator, and the combined light in which the respective wavelength components modulated by the spatial light modulator are combined is output from the pulse light shaping device. An intensity modulation pattern for giving the combined light an intensity spectrum in which peak and valley waveforms are alternately repeated, and a phase modulation pattern for giving the combined light a phase spectrum that repeats a wavelength section having a substantially constant phase. A phase pattern including the first and second phase patterns is presented to the spatial light modulator, and the boundary wavelength of the adjacent wavelength sections is included in the wavelength range of the valley waveform, and the control unit includes the phase of the intensity modulation pattern in each modulation region. The pixel value of the phase modulation image based on the modulation amount is corrected according to each wavelength corresponding to each modulation region.

  The third pulse light shaping device according to the present invention is a pulse light shaping device that generates output pulse light having a waveform different from that of the input pulse light from the input pulse light. A spectral element that divides into two, a phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component, and a phase presented to the spatial light modulator A control unit that provides a control signal for controlling the pattern to the spatial light modulator, and the combined light in which the respective wavelength components modulated by the spatial light modulator are combined is output from the pulse light shaping device. An intensity modulation pattern for giving the combined light an intensity spectrum in which peak and valley waveforms are alternately repeated, and a phase modulation pattern for giving the combined light a phase spectrum that repeats a wavelength section having a substantially constant phase. A phase pattern that includes a horn pattern is presented to the spatial light modulator, and a boundary wavelength between adjacent wavelength sections is included in the wavelength range of the valley waveform, and the control unit generates a pattern for intensity modulation including a blazed diffraction grating. In addition to presenting each modulation region, the period of the blazed diffraction grating is corrected according to the size of each wavelength corresponding to each modulation region.

  A fourth pulse light shaping device according to the present invention is a pulse light shaping device that generates output pulse light having a waveform different from the input pulse light from the input pulse light. A spectral element that divides into two, a phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component, and a phase presented to the spatial light modulator A control unit that provides a control signal for controlling the pattern to the spatial light modulator, and the combined light in which the respective wavelength components modulated by the spatial light modulator are combined is output from the pulse light shaping device. An intensity modulation pattern for giving the combined light an intensity spectrum in which peak and valley waveforms are alternately repeated, and a phase modulation pattern for giving the combined light a phase spectrum that repeats a wavelength section having a substantially constant phase. The phase pattern including the waveform is presented to the spatial light modulator, the boundary wavelength between adjacent wavelength sections is included in the wavelength range of the valley waveform, and the control unit modulates the periodic intensity modulation pattern In addition to being presented in the region, a phase bias corresponding to the amplitude of the intensity modulation pattern in each modulation region is added to the amount of phase modulation in each modulation region.

  In the first to fourth pulse light shaping devices described above, first, after the input pulse light is dispersed for each wavelength component by the spectroscopic element, the phase and intensity of each wavelength component are modulated in each modulation region of the spatial light modulator. Is done. The spatial light modulator presents a phase pattern including an intensity modulation pattern and a phase modulation pattern. The intensity modulation pattern gives the combined light an intensity spectrum in which a peak waveform and a valley waveform are alternately repeated (for example, including a sine wave component). In addition, the phase modulation pattern gives the combined light a phase spectrum that repeats a wavelength interval in which the phase is substantially constant.

  Here, high-order components that cause noise may occur in the output pulse light, but such high-order components cause a sudden phase change at the boundary between adjacent wavelength sections in the phase spectrum as described above. Is considered to be the cause. In the first to fourth pulse light shaping devices described above, since the boundary wavelength between adjacent wavelength sections is included in the wavelength range of the valley waveform, the light intensity in the region where the phase changes rapidly is relatively suppressed. be able to. Therefore, according to these pulse light shaping devices, it is possible to reduce the higher order components and bring the output pulse light close to a desired shape with high accuracy.

  In the first pulsed light shaping device, the control unit presents an intensity modulation pattern including a blazed diffraction grating in each modulation region, and the amplitude of the blazed diffraction grating is variable. As described above, when the intensity modulation pattern includes the blazed diffraction grating, the intensity spectrum can be suitably modulated into the above waveform. In addition, the modulation of the intensity spectrum always involves optical loss, but since the amplitude of the blazed diffraction grating is variable, the balance between the intensity modulation amount and the optical loss is appropriately adjusted to avoid excessive optical loss, The intensity spectrum can be modulated with sufficient accuracy.

  Further, in the second pulse light shaping device, the control unit corrects the pixel value of the phase modulation image based on the phase modulation amount of the intensity modulation pattern in each modulation region according to each wavelength corresponding to each modulation region. To do. According to the knowledge of the present inventor, in the spatial light modulator, the amount of phase modulation for performing a certain intensity modulation is the same, but the pixel value of the phase modulation image created based on the amount is the wavelength. Slightly different. Therefore, by correcting the pixel value of the phase modulation image based on the phase modulation amount in accordance with each wavelength corresponding to each modulation region, intensity modulation at each wavelength is performed more accurately, and the waveform of the optical pulse has a desired shape. Can be brought closer to accuracy.

  Further, in the third pulse light shaping device, the control unit presents the intensity modulation pattern including the blazed diffraction grating to each modulation region, and sets the period of the blazed diffraction grating in accordance with each wavelength corresponding to each modulation region. to correct. According to the knowledge of the present inventors, when the wavelength of incident light is different, the diffraction angle by the blazed diffraction grating having the same period may be slightly different. Therefore, in consideration of the wavelength dependence of the period of the blazed diffraction grating, the diffraction angle at each wavelength can be matched by correcting the period of the blazed diffraction grating according to each wavelength corresponding to each modulation region. Even when light is used as output light, the intensity spectrum can be modulated with high accuracy.

  Further, in the fourth pulse light shaping device, the control unit presents a periodic intensity modulation pattern in each modulation area and a phase bias corresponding to the amplitude of the intensity modulation pattern in each modulation area. Is added to the phase modulation amount. This phase bias is, for example, a bias in which the centers of modulation amplitudes coincide with each other in each modulation region. As a result, a state where the intensity spectrum modulation pattern does not affect the phase spectrum modulation pattern can be realized, and the waveform of the optical pulse can be brought closer to a desired shape with higher accuracy.

  According to the pulsed light shaping device of the present invention, the waveform of an optical pulse can be brought close to a desired shape with high accuracy.

1 is a diagram schematically showing a configuration of a pulsed light shaping device according to an embodiment of the present invention. It is a figure which shows the modulation surface of a spatial light modulator. (A) It is a graph which shows the example of the combination of a phase spectrum and an intensity spectrum. (B) It is a graph which shows the time waveform of the output pulse light implement | achieved by the combination of the phase spectrum and intensity spectrum which were shown to (a). (A) It is a graph which shows the example of the combination of a phase spectrum and an intensity spectrum. (B) It is a graph which shows the time waveform of the output pulse light implement | achieved by the combination of the phase spectrum and intensity spectrum which were shown to (a). It is a figure which shows the phase modulation pattern for implement | achieving the phase spectrum shown by Fig.3 (a) and Fig.4 (a) visually. (A) It is a graph which shows the example of the combination of a phase spectrum and an intensity spectrum. (B) It is a graph which shows the time waveform of the output pulse light implement | achieved by the combination of the phase spectrum and intensity spectrum which were shown to (a). (A) It is a figure which shows the intensity | strength modulation pattern for implement | achieving the intensity | strength spectrum shown by Fig.6 (a) visually. (B) A phase pattern in which the phase modulation pattern shown in FIG. 5B and the intensity modulation pattern shown in FIG. It is a figure for demonstrating the difference in the amount of diffracted light by the difference in the amplitude of a blazed diffraction grating. It is a graph which shows an example of the change of an intensity spectrum using the amplitude change of a blazed diffraction grating. It is a figure which shows an example of the characteristic referred in the case of modulation intensity operation. It is a figure for demonstrating the difference in the amplitude of a blazed diffraction grating when the amount of diffraction light is made equal in a mutually different wavelength. It is a figure for demonstrating the difference in the period of a blazed diffraction grating when the amount of diffraction light is made equal in a mutually different wavelength. (A) The blazed diffraction grating shown in FIG. (B) The blazed diffraction grating shown in FIG. (C) FIG. 13B shows a plot in which the bias components are added so that the average values of FIGS. 13A and 13B are aligned. It is a graph which shows the phase spectrum which concerns on one modification. FIG. 11 is a graph showing a change in characteristics shown in FIG. 10 according to a modification. FIG. (A) rectangular phase modulation pattern, (b) cosine waveform type intensity modulation pattern, and (c) these patterns, which are capable of realizing highly accurate intensity spectrum modulation, created by the method of the embodiment. It is a figure which shows an example of the phase pattern by which synthesize | combined. It is a graph which shows the superposition of (a) phase spectrum, (b) intensity spectrum, and (c) phase spectrum and intensity spectrum which are realized by each pattern shown in FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a pulsed light shaping device according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a diagram schematically showing a configuration of a pulsed light shaping device 1A according to an embodiment of the present invention. This pulsed light shaping device 1A simultaneously performs phase modulation and intensity modulation in a spatial light modulator, thereby generating output pulsed light Ld having an arbitrary time waveform different from the input pulsed light La from the input pulsed light La. This is a so-called SLM pulse shaper. As the input pulsed light La, for example, coherent pulsed light output from a solid-state laser is used. As shown in FIG. 1, the pulsed light shaping device 1 </ b> A of the present embodiment includes an optical system 10 and a control unit 20. The optical system 10 includes a spectroscopic element 12, a curved mirror 14, and a spatial light modulator 16.

  The spectroscopic element 12 splits the input pulsed light La for each wavelength component. The spectroscopic element 12 has, for example, a diffraction grating formed on a plate surface. The input pulsed light La is incident obliquely on the diffraction grating and is split into a plurality of wavelength components. The pulsed light Lb including the plurality of wavelength components reaches the curved mirror 14. The pulsed light Lb is reflected by the curved mirror 14 and reaches the spatial light modulator 16.

  The spatial light modulator 16 is a phase modulation type. In one embodiment, the spatial light modulator 16 is of the LCOS type. FIG. 2 is a diagram showing the modulation surface 17 of the spatial light modulator 16. As shown in FIG. 2, a plurality of modulation regions 17 a are arranged along a certain direction A on the modulation surface 17, and each modulation region 17 a extends in a direction B intersecting the direction A. This direction A is a spectral direction by the spectral element 12. Therefore, each of the dispersed wavelength components is incident on each of the plurality of modulation regions 17a. The spatial light modulator 16 modulates the phase and intensity of each incident wavelength component in each modulation region 17a. Since the spatial light modulator 16 of the present embodiment is a phase modulation type, the intensity modulation is realized by a phase pattern (phase image) presented on the modulation surface 17.

  The pulsed light Lc including each wavelength component modulated by the spatial light modulator 16 is reflected again by the curved mirror 14 and reaches the spectroscopic element 12. In the spectroscopic element 12, the plurality of wavelength components of the pulsed light Lc are combined with each other. This combined light is output from the pulsed light shaping device 1A as output pulsed light Ld.

  The control unit 20 is electrically connected to the spatial light modulator 16 and provides a control signal for controlling the phase pattern presented to the spatial light modulator 16 to the spatial light modulator. The control unit 20 includes an arbitrary waveform input unit 21, a phase spectrum design unit 22, a phase / intensity spectrum design unit 23, a phase pattern design unit 24, and a time waveform selection unit 25. The arbitrary waveform input unit 21 receives input or selection of an arbitrary pulse time waveform from the operator. The operator inputs a desired pulse time waveform to the arbitrary waveform input unit 21 or selects a desired pulse time waveform from a plurality of presented pulse time waveforms.

  Information on the pulse time waveform is given to the phase spectrum design unit 22. The phase spectrum design unit 22 selects a phase spectrum of the output pulsed light Ld for realizing the pulse time waveform from a plurality of phase spectra prepared in advance, or based on the input pulse time waveform. calculate. Further, the phase spectrum design unit 22 sets a phase pattern based on the identified phase spectrum.

  Information on the pulse time waveform is also given to the phase / intensity spectrum design unit 23. The phase / intensity spectrum design unit 23 selects or inputs a phase spectrum and an intensity spectrum of the output pulsed light Ld for realizing the pulse time waveform from a plurality of phase spectra and intensity spectra prepared in advance. Based on the pulse time waveform thus calculated. The phase pattern design unit 24 sets a phase pattern for realizing the phase spectrum and the intensity spectrum obtained by the phase / intensity spectrum design unit 23. The phase pattern setting method in the phase pattern design unit 24 will be described in detail later.

  The time waveform selection unit 25 selects either the phase pattern set by the phase spectrum design unit 22 or the phase pattern set by the phase pattern design unit 24. The time waveform selection unit 25 selects a phase pattern based on, for example, the intensity loss amount of the output pulsed light Ld with respect to the input pulsed light La and waveform accuracy information unique to each phase pattern. Then, a control signal indicating the selected phase pattern is provided to the spatial light modulator 16.

  Here, the phase pattern setting method in the phase / intensity spectrum design unit 23 will be described in detail. The control unit 20 of the present embodiment provides a phase pattern for phase modulation (hereinafter referred to as a phase modulation pattern) for providing an appropriate phase spectrum to the output pulse light Ld and an appropriate intensity spectrum to the output pulse light Ld. Therefore, the spatial light modulator 16 is caused to present a phase pattern including a phase pattern for intensity modulation (hereinafter referred to as an intensity modulation pattern).

  FIG. 3A and FIG. 4A are graphs showing examples of combinations of a phase spectrum and an intensity spectrum. 3B and 4B show time waveforms of the output pulsed light Ld realized by the combination of the phase spectrum and the intensity spectrum shown in FIGS. 3A and 4A, respectively. It is a graph which shows. FIGS. 5A and 5B are diagrams visually showing phase modulation patterns for realizing the phase spectra shown in FIGS. 3A and 4A, respectively. . 3A and 4A, graphs G11 and G21 indicate phase spectra, graphs G12 and G22 indicate intensity spectra, the horizontal axis indicates wavelength (nm), and the left vertical axis indicates The intensity value (arbitrary unit) of the intensity spectrum is shown, and the right vertical axis shows the phase value (rad) of the phase spectrum. In FIGS. 3B and 4B, the horizontal axis represents time (femtoseconds), and the vertical axis represents light intensity (arbitrary unit). 5A and 5B, the direction A is the spectral direction and represents the arrangement direction of the plurality of modulation regions 17a shown in FIG. 2, and the phase modulation amount depends on the color density. The darker the color is, the closer it is to 0π (rad), and the thinner, the closer it is to 2π (rad).

  In the example shown in FIGS. 3A and 5A, the phase spectrum and the phase modulation pattern are constant regardless of the wavelength, and the intensity spectrum is not modulated and has a single peak. It has a spectral shape peculiar to laser light. In this case, as shown in FIG. 3B, the time waveform of the output pulsed light Ld is a single pulse having a steep single peak P1. On the other hand, in the example shown in FIGS. 4A and 5B, the phase of the phase spectrum and the phase modulation pattern changes periodically and discretely over a certain wavelength band. Specifically, in the phase spectrum and the phase modulation pattern, a wavelength section having a constant phase value ph1 and a wavelength section having a constant phase value ph2 (<ph1) are alternately repeated. The intensity spectrum is the same as that shown in FIG. In this case, as shown in FIG. 4B, the time waveform of the output pulse light Ld is a double pulse having two steep peaks P2 and P3.

  In this way, by using the spatial light modulator 16 to provide a phase spectrum that periodically repeats two phase values, the output pulse light Ld that is a double pulse is preferably generated from the input pulse light La that is a single pulse. can do. Note that this is merely an example, and the time waveform of the output pulsed light Ld can be shaped into an arbitrary shape by various phase spectra that repeat a wavelength interval in which the phase is substantially constant.

  Here, referring to FIG. 4B, it can be seen that small peak waveforms (beats) B1 appear periodically in addition to the output pulsed light Ld which is a double pulse. This peak waveform B1 is considered to be caused by a high-frequency component included in the phase modulation pattern. That is, in the phase modulation pattern that repeats the wavelength section D in which the phase is substantially constant, the phase value changes abruptly at the wavelength at the boundary of the wavelength section, so that a high frequency component is included in the vicinity of the wavelength. This high-frequency component causes an unintended high-order component (peak waveform B1). Since this higher-order component becomes noise with respect to the output pulsed light Ld, it is desirable to remove it.

  FIG. 6A is a graph showing an example of a combination of a phase spectrum and an intensity spectrum for solving the above problem. FIG. 6B is a graph showing a time waveform of the output pulsed light Ld realized by the combination of the phase spectrum and the intensity spectrum shown in FIG. In FIG. 6A, a graph G31 indicates a phase spectrum, a graph G32 indicates an intensity spectrum, a horizontal axis indicates a wavelength (nm), and a left vertical axis indicates an intensity value (arbitrary unit) of the intensity spectrum. The right vertical axis indicates the phase value (rad) of the phase spectrum. In FIG. 6B, the horizontal axis represents time (femtosecond), and the vertical axis represents light intensity (arbitrary unit). As shown in FIG. 6 (a), in this example, the phase spectrum is the same as that shown in FIG. 4 (a), but the intensity spectrum is different from that shown in FIG. 4 (a). . That is, in this intensity spectrum, the intensity periodically changes, and a peak waveform (peak waveform) and a valley waveform (bottom waveform) are alternately repeated.

  FIG. 7A is a diagram visibly showing an intensity modulation pattern for realizing the intensity spectrum shown in FIG. In FIG. 7A, the direction A is the spectral direction and represents the arrangement direction of the plurality of modulation regions 17a shown in FIG. 2, and the phase modulation amount is represented by color shading. It is closer to (rad) and closer to 2π (rad) as it is thinner.

  For example, as shown in FIG. 7A, the intensity spectrum shown in FIG. 6A is obtained by using a blazed diffraction grating (sawtooth groove) in which the amplitude is set for each of the plurality of modulation regions 17a. The intensity modulation pattern is preferably realized by cosine modulation by presenting the intensity modulation pattern in each modulation region 17a. The arrangement direction of the gratings in the blazed diffraction grating intersects with the arrangement direction of the plurality of modulation regions 17a. FIG. 7B is a phase pattern in which the phase modulation pattern shown in FIG. 5B and the intensity modulation pattern shown in FIG. The control unit 20 causes the spatial light modulator 16 to present this phase pattern.

  Here, referring to FIG. 6A, the wavelength of the boundary between the wavelength sections D adjacent to each other in the phase spectrum is included in the wavelength range of the valley waveform of the intensity spectrum. In other words, the bottom wavelength of the intensity spectrum is located in or near the wavelength region where the phase changes rapidly in the phase spectrum. A plurality of peaks (maximum portions) of the intensity spectrum that change periodically are located in each wavelength section D of the phase spectrum (between rising and falling or between falling and rising).

  Thereby, the intensity can be relatively suppressed at a wavelength whose phase changes rapidly in the phase spectrum, that is, a wavelength including a high frequency component, and the intensity can be increased in a wavelength region not including a high frequency component (a phase is constant). Therefore, higher-order components in the phase spectrum (the peak waveform B1 shown in FIG. 4B) can be effectively removed, and the time waveform of the output pulsed light Ld can be brought close to a desired shape (FIG. 6 (b)). In this embodiment, the wavelength range of the valley waveform is a range including a minimum point, and refers to a range from one inflection point to the other inflection point.

Here, in order to bring the time waveform of the output pulsed light Ld closer to a desired shape with higher accuracy, it is considered that the intensity spectrum is made smooth with respect to the wavelength axis and the intensity modulation resolution is increased. There are the following four methods for increasing the modulation accuracy of the intensity spectrum.
・ Amplitude operation of blazed diffraction grating ・ Consideration of wavelength dependency of phase modulation amount ・ Consideration of wavelength dependency of period of blazed diffraction grating ・ Bias modulation according to modulation amplitude amount of blazed diffraction grating Explained.

(1) Amplitude operation of blazed diffraction grating In this embodiment, intensity modulation in each modulation region 17a is realized by a blazed diffraction grating. By making the amplitude of the blazed diffraction grating variable, intensity modulation at each wavelength can be performed with higher accuracy. FIG. 8 is a diagram for explaining the difference in the amount of diffracted light due to the difference in amplitude of the blazed diffraction grating. Assume that at a certain wavelength (for example, 800 nm), the blazed diffraction grating GR1 (amplitude A1) shown in FIG. At this time, if the diffracted light amount of the blazed diffraction grating GR2 shown in FIG. 8B is to be set to a value smaller than 90%, for example 60%, the amplitude A2 of the blazed diffraction grating GR2 is made smaller than the amplitude A1. good.

  FIG. 9 is a graph showing an example of a change in intensity spectrum using the amplitude change of such a blazed diffraction grating. In FIG. 9, the horizontal axis indicates the wavelength (nm) and the vertical axis indicates the intensity (arbitrary unit). Graphs G41 to G45 are intensity spectra, and the intensity of the minimum portion in the valley waveform (hereinafter referred to as bottom intensity) gradually decreases as the graph G41 shifts to G45. For example, the graph G41 is an intensity spectrum when the intensity modulation is not performed, and is the same as the graph G22 of FIG. The graph G45 is an intensity spectrum in the case where the bottom intensity is almost zero, and is the same as the graph G32 in FIG. With the intensity spectrum shown in the graph G45, higher-order components contained in the phase spectrum can be most effectively removed.

  Further, when the input pulse light La is given an intensity spectrum that alternately repeats a peak waveform and a valley waveform as in the present embodiment, the light intensity is attenuated in the valley waveform portion, so there is always a light loss. For example, the peak intensity of the double pulse shown in FIG. 4B is about 1.8, but the peak intensity of the double pulse shown in FIG. 6B is about 1.2. In many cases, in order to obtain the output pulsed light Ld having sufficient light intensity, it is desired that the intensity of the output pulsed light Ld is not as small as possible with respect to the intensity of the input pulsed light La. Therefore, it is preferable to set the bottom intensity to such a size that excessive light loss can be avoided while reducing higher-order components included in the phase spectrum to an acceptable level. Since it is considered that the size allowed for the high-order component varies depending on the scene and situation in which the pulse light shaping device 1A is used, such a bottom intensity can be obtained by operating the user with the amplitude of the blazed diffraction grating being variable. Can be suitably set.

  FIG. 10 is a diagram illustrating an example of characteristics referred to when the modulation intensity is manipulated as described above. The horizontal axis of FIG. 10 represents light loss due to intensity modulation, and the left vertical axis represents light intensity. The graph G51 in the figure shows the peak height Pm of the double pulse, and the graph G52 shows the peak height Ps of the largest of the higher order components. The vertical axis on the right side and the graph G53 in the figure indicate the ratio (%) of the peak height Ps of the higher order component to the peak height Pm of the double pulse.

  Referring to FIG. 10, as the optical loss due to intensity modulation increases, the peak height Pm of the double pulse shown in the graph G51 decreases, and the peak height Ps of the higher order component shown in the graph G52 also decreases. Then, referring to the ratio of higher-order components (graph G53), it can be seen that the ratio decreases as the optical loss due to intensity modulation increases. That is, as the bottom intensity is decreased, the optical loss is increased, but higher-order components are suppressed and the ratio of the peak height Ps is decreased. Conversely, if the bottom intensity is relatively large, higher order components increase and the ratio of the peak height Ps increases, but light loss due to intensity modulation can be reduced. When the control unit 20 is configured so that the user can select the bottom intensity at which the ratio of the peak height Ps of the higher-order component is the smallest within the allowable optical loss range with reference to such a graph, for example. good. For example, in the example shown in FIG. 10, when the intensity loss of about 50% is allowed, the peak of the higher order component hardly appears. On the other hand, when the intensity modulation is not performed, a high-order component peak of about 11% appears. The advantage of this method (1) is that the amount of intensity loss can be reduced arbitrarily by the user determining the required waveform accuracy.

(2) Considering the wavelength dependence of the phase modulation amount In the present embodiment, intensity modulation is performed in each corresponding modulation region 17a for each of the dispersed wavelengths. However, in the spatial light modulator 16, if the wavelength of the incident light is different, the pixel values of the phase modulation image for the same phase pattern may be slightly different. In such a case, the control unit 20 considers the wavelength dependence of the pixel value of the phase modulation image, and determines the pixel value of the phase modulation image based on the phase modulation amount of the intensity modulation pattern in each modulation region 17a. Correction may be made according to each wavelength corresponding to the modulation region 17a. Thereby, intensity modulation at each wavelength can be performed with higher accuracy.

  FIG. 11 is a diagram for explaining a difference in amplitude of a blazed diffraction grating when the amount of diffracted light is made equal at different wavelengths (for example, the amount of diffracted light is 90%). FIG. 11A shows a case where the wavelength is 800 nm, for example, and FIG. 11B shows a case where the wavelength is 810 nm, for example. At this time, when each amplitude is corrected according to each wavelength, the amplitude A4 of the blazed diffraction grating GR4 shown in FIG. 11B is smaller than the amplitude A3 of the blazed diffraction grating GR3 shown in FIG. .

(3) Considering the wavelength dependence of the period of the blazed diffraction grating In this embodiment, intensity modulation in each modulation region 17a is realized by a blazed diffraction grating. However, in the spatial light modulator 16, when the wavelength of the incident light is different, the diffraction angle by the blazed diffraction grating having the same period may be slightly different. In such a case, the control unit 20 may correct the period of the blazed diffraction grating in accordance with each wavelength corresponding to each modulation region 17a in consideration of the wavelength dependence of the period of the blazed diffraction grating. Thereby, the diffraction angles at the respective wavelengths can be matched, and the intensity spectrum can be modulated with high accuracy even when the primary light is used as the output light.

  FIG. 12 is a diagram for explaining the difference in the period of the blazed diffraction grating when the diffraction angles are made equal at different wavelengths. FIG. 12A shows a case where the wavelength is 800 nm, for example, and FIG. 12B shows a case where the wavelength is 810 nm, for example. At this time, the period T2 of the blazed diffraction grating GR6 shown in FIG. 12B may be made smaller than the period T1 of the blazed diffraction grating GR5 shown in FIG.

(4) Bias modulation in accordance with the modulation amplitude amount of the blazed diffraction grating The control unit 20 of the present embodiment presents each modulation region 17a with a periodic intensity modulation pattern such as a blazed diffraction grating. For example, when applying the methods shown in the above (1) to (3), the amplitude of the periodic intensity modulation pattern in each modulation region 17a may be changed. At this time, for example, the amplitude of the intensity modulation pattern can be suitably changed by changing the maximum phase value with a certain phase value as a reference. However, in such a system, the average phase value fluctuates, and the intensity spectrum modulation pattern affects the phase spectrum modulation amount. Therefore, the control unit 20 may add a phase bias corresponding to the amplitude of the intensity modulation pattern in each modulation region 17a to the phase modulation amount of each modulation region 17a.

  Here, an example of adding such a phase bias in the method shown in (3) above will be described. FIG. 13 (a) shows the blazed diffraction grating GR5 shown in FIG. 12 (a), and FIG. 13 (b) shows the blazed diffraction grating GR6 shown in FIG. 12 (b). When a phase bias is applied to the blazed diffraction grating GR6 in order to make the phase average values of the blazed diffraction gratings GR5 and GR6 uniform, the result is as shown in FIG. In the blazed diffraction grating GR7 shown in FIG. 13 (c), an arbitrary phase bias is uniformly applied, so that the average phase value becomes PH1, which substantially matches the average phase value of the blazed diffraction grating GR5. Yes. In other words, the centers of the modulation amplitudes (straight line E in the figure) substantially coincide with each other in the blazed diffraction gratings GR5 and GR6. In this way, by applying a phase bias of an appropriate magnitude according to the degree of change in amplitude, the fluctuation of the average phase value is suppressed, and the intensity spectrum modulation pattern is maintained while the intensity spectrum modulation pattern is maintained. It is possible to prevent the modulation amount from being affected.

  As described above, in the pulsed light shaping device 1A of the present embodiment, as shown in FIG. 6A, the wavelength at the boundary between adjacent wavelength sections in the phase spectrum is a trough waveform of the intensity spectrum. It is included in the wavelength range. Thereby, it is possible to relatively suppress the light intensity at a wavelength at which the phase rapidly changes in the phase spectrum. Therefore, it is possible to reduce high-order components of the phase spectrum and bring the time waveform of the output pulsed light Ld close to a desired shape with high accuracy.

  Further, as described in the method (1) above, the control unit 20 can present the intensity modulation pattern including the blazed diffraction grating in each modulation region 17a, and can change the amplitude of the blazed diffraction grating. preferable. Thus, the intensity spectrum can be suitably modulated by including the blazed diffraction grating in the intensity modulation pattern. Modulation of the intensity spectrum always involves optical loss, but since the amplitude of the blazed diffraction grating is variable, the intensity is adjusted while appropriately adjusting the balance between the intensity modulation amount and the optical loss to avoid excessive optical loss. By modulating the spectrum with sufficient accuracy, the time waveform of the output pulsed light Ld can be brought close to a desired shape with high accuracy.

  Further, as described in the above method (2), the control unit 20 corresponds the pixel value of the phase modulation image to each modulation region 17a based on the phase modulation amount of the intensity modulation pattern in each modulation region 17a. It is preferable to correct according to each wavelength. According to the knowledge of the present inventors, in the spatial light modulator, the pixel value of the phase modulation image corresponding to the phase modulation amount for performing a certain intensity modulation slightly varies depending on the wavelength. Accordingly, by correcting the pixel value corresponding to each wavelength corresponding to each modulation region 17a, intensity modulation at each wavelength is performed with higher accuracy, and the waveform of the output pulsed light Ld is made closer to a desired shape with higher accuracy. be able to.

  Further, as described in the method (3) above, the control unit 20 preferably corrects the period of the blazed diffraction grating included in the intensity modulation pattern according to each wavelength corresponding to each modulation region 17a. According to the knowledge of the present inventors, when the wavelength of incident light is different, the diffraction angle by the blazed diffraction grating having the same period may be slightly different. Therefore, the diffraction angle at each wavelength can be kept constant by correcting the period of the blazed diffraction grating pattern in accordance with each wavelength corresponding to each modulation region 17a. As a result, by using the method (3), even when the primary light is used as the output light, the waveform of the output pulsed light Ld can be brought closer to the desired shape more accurately without reducing the intensity modulation accuracy.

  Further, as described in the above method (4), the control unit 20 preferably adds a phase bias corresponding to the amplitude of the intensity modulation pattern in each modulation region 17a to the phase modulation amount of each modulation region 17a. . This can prevent the intensity spectrum modulation pattern from affecting the phase spectrum modulation amount while maintaining the intensity spectrum modulation accuracy.

(Modification)
In the above embodiment, a phase spectrum that periodically repeats two phase values has been exemplified, but by optimizing the phase spectrum, most of the role of waveform control is assigned to the phase spectrum, and the control amount in the intensity spectrum is reduced. The optical loss can be further reduced by reducing the size.

  FIG. 14 is a graph showing a phase spectrum according to a modification of the embodiment. In FIG. 14, the horizontal axis indicates the wavelength (nm) and the vertical axis indicates the phase (rad). A graph G61 shows the phase spectrum of the above embodiment used as the initial phase spectrum, and a graph G62 shows the optimized phase spectrum. In this modification, for example, a double pulse waveform is set as a desired time waveform, and the phase for realizing the desired time waveform is optimized by using a numerical calculation method such as an iterative Fourier method (IFTA) for the phase spectrum. Obtain the spectrum. Graph G62 shows, as an example, a phase spectrum after performing 20 calculations by IFTA.

  FIG. 15 is a graph showing changes in the characteristics shown in FIG. 10 according to this modification. The horizontal axis in FIG. 15 represents the optical loss due to intensity modulation, and the vertical axis represents the ratio (%) of the peak height Ps of the higher order component to the peak height Pm of the double pulse. A graph G71 is the same as the graph G53 of FIG. 10, and shows the characteristics according to the above embodiment. A graph G72 represents the characteristics according to this modification. As shown in FIG. 15, in this modification, the ratio of the peak height Ps with the same optical loss is significantly smaller than that in the above embodiment. Thus, according to the present modification, the peak height of the higher-order component can be effectively reduced within the allowable light loss range.

(Example)
An example of the above embodiment will be described. FIG. 16 shows (a) a rectangular phase modulation pattern, (b) a cosine waveform type intensity modulation pattern, and (c) created by the method of the above embodiment and capable of realizing highly accurate intensity spectrum modulation. It is a figure which shows an example of the phase pattern by which these patterns were synthesize | combined. FIG. 17 is a graph showing (a) a phase spectrum, (b) an intensity spectrum, and (c) a superposition of the phase spectrum and the intensity spectrum realized by each pattern shown in FIG. In FIG. 16, the wavelength axis direction is the spectral direction and represents the arrangement direction A of the plurality of modulation regions 17 a shown in FIG. 2, and the phase modulation amount is represented by color shading. The smaller the phase and the thinner the phase.

  Since these patterns are created on the assumption that zero-order light is used, in the wavelength region of a mountain waveform where intensity modulation is not necessary, for example, in the vicinity of a wavelength of 800 nm in FIG. The diffraction grating pattern is not presented. On the other hand, in the wavelength region of the valley waveform where intensity modulation is performed, the blazed diffraction grating pattern corresponding to the modulation amount is confirmed as a striped pattern.

The pulsed light shaping device according to the present invention is not limited to the above-described embodiment, and various other modifications are possible. For example, although the blazed diffraction grating is applied as the intensity modulation pattern in the embodiment and the modification, various periodic patterns can be applied to the intensity modulation pattern. For example, the following diffraction gratings can be used as an intensity modulation pattern.
・ Sine wave type diffraction grating (sinusoidal groove)
・ Binary diffraction grating (rectangular groove)
In the blazed diffraction grating used in the above embodiment, both 0th-order light and 1st-order light can be used. On the other hand, the sine wave type diffraction grating and the binary type diffraction grating are mainly used when the 0th order light is used, and the light use efficiency is inferior when the 1st order light is used.

  DESCRIPTION OF SYMBOLS 1A ... Pulse light shaping device, 10 ... Optical system, 12 ... Spectral element, 14 ... Curved surface mirror, 16 ... Spatial light modulator, 17 ... Modulation surface, 17a ... Modulation area, 20 ... Control part, 21 ... Arbitrary waveform input part , 22 ... Phase spectrum design unit, 23 ... Phase / intensity spectrum design unit, 24 ... Phase pattern design unit, 25 ... Time waveform selection unit, A1 to A4 ... Amplitude, B1 ... Unnecessary higher order components included in the time waveform , GR1 to GR7, blazed diffraction grating, La, input pulse light, Ld, output pulse light, PH1, phase average value of blazed diffraction grating.

Claims (4)

A pulse light shaping device that generates an output pulse light having a waveform different from that of the input pulse light from the input pulse light,
A spectroscopic element that divides the input pulsed light into wavelength components;
A phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component;
A controller that provides the spatial light modulator with a control signal for controlling a phase pattern presented to the spatial light modulator;
With
A combined light obtained by combining the wavelength components modulated by the spatial light modulator is output from the pulse light shaping device,
The control unit provides the combined light with an intensity modulation pattern for giving the combined light an intensity spectrum in which a peak waveform and a valley waveform are alternately repeated, and a phase spectrum repeating a wavelength section in which the phase is substantially constant. The phase pattern including a phase modulation pattern for presenting the spatial light modulator,
A boundary wavelength of the wavelength sections adjacent to each other is included in the wavelength range of the valley waveform,
The control unit causes the intensity modulation pattern including a blazed diffraction grating to be presented in each modulation region, and the amplitude of the blazed diffraction grating is variable. A pulse light shaping device that generates an output pulse light having a waveform different from that of the input pulse light from the input pulse light,
A spectroscopic element that divides the input pulsed light into wavelength components;
A phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component;
A controller that provides the spatial light modulator with a control signal for controlling a phase pattern presented to the spatial light modulator;
With
A combined light obtained by combining the wavelength components modulated by the spatial light modulator is output from the pulse light shaping device,
The control unit provides the combined light with an intensity modulation pattern for giving the combined light an intensity spectrum in which a peak waveform and a valley waveform are alternately repeated, and a phase spectrum repeating a wavelength section in which the phase is substantially constant. The phase pattern including a phase modulation pattern for presenting the spatial light modulator,
A boundary wavelength of the wavelength sections adjacent to each other is included in the wavelength range of the valley waveform,
The control unit corrects the pixel value of the phase modulation image based on the phase modulation amount of the intensity modulation pattern in each modulation region in accordance with each wavelength corresponding to each modulation region. Shaping device. A pulse light shaping device that generates an output pulse light having a waveform different from that of the input pulse light from the input pulse light,
A spectroscopic element that divides the input pulsed light into wavelength components;
A phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component;
A controller that provides the spatial light modulator with a control signal for controlling a phase pattern presented to the spatial light modulator;
With
A combined light obtained by combining the wavelength components modulated by the spatial light modulator is output from the pulse light shaping device,
The control unit provides the combined light with an intensity modulation pattern for giving the combined light an intensity spectrum in which a peak waveform and a valley waveform are alternately repeated, and a phase spectrum repeating a wavelength section in which the phase is substantially constant. The phase pattern including a phase modulation pattern for presenting the spatial light modulator,
A boundary wavelength of the wavelength sections adjacent to each other is included in the wavelength range of the valley waveform,
The control unit presents the intensity modulation pattern including a blazed diffraction grating to each modulation region, and corrects the period of the blazed diffraction grating according to the size of each wavelength corresponding to each modulation region. A pulsed light shaping device. A pulse light shaping device that generates an output pulse light having a waveform different from that of the input pulse light from the input pulse light,
A spectroscopic element that divides the input pulsed light into wavelength components;
A phase modulation type spatial light modulator that has a plurality of modulation regions corresponding to each wavelength component and modulates the phase and intensity of each wavelength component;
A controller that provides the spatial light modulator with a control signal for controlling a phase pattern presented to the spatial light modulator;
With
A combined light obtained by combining the wavelength components modulated by the spatial light modulator is output from the pulse light shaping device,
The control unit provides the combined light with an intensity modulation pattern for giving the combined light an intensity spectrum in which a peak waveform and a valley waveform are alternately repeated, and a phase spectrum repeating a wavelength section in which the phase is substantially constant. The phase pattern including a phase modulation pattern for presenting the spatial light modulator,
A boundary wavelength of the wavelength sections adjacent to each other is included in the wavelength range of the valley waveform,
The control unit presents a periodic intensity modulation pattern in each modulation region, and adds a phase bias corresponding to the amplitude of the intensity modulation pattern in each modulation region to the phase modulation amount of each modulation region. A pulsed light shaping device.