Light modulation device and control method of spatial light modulator

Abstract

The light modulation device includes a light source, a control unit, and a spatial light modulator. The light source outputs laser light having an intensity corresponding to a set intensity. The spatial light modulator includes a plurality of pixel electrodes, a liquid crystal layer, a driving unit, and a cooling unit. The liquid crystal layer modulates the phase of the laser light in accordance with the size of an electric field formed by each of the plurality of pixel electrodes. The driving unit applies a voltage to the plurality of pixel electrodes. The cooling unit cools the liquid crystal layer such that the temperature of the liquid crystal layer approaches a set temperature. The control unit determines the set temperature of the cooling unit on the basis of the set intensity of the laser light.

Description

Technical Field

[0001] The present invention relates to a light modulation device and a control method of a spatial light modulator. This application claims priority based on Japanese application No. 2022-149927 filed on September 21, 2022, and all the contents described in the above Japanese application are cited. Background Art

[0002] Patent document 1 discloses a spatial light modulation device and a spatial light modulation method. The spatial light modulation device modulates the phase of incident light for each of a plurality of pixels arranged in one dimension or two dimensions. The spatial light modulation device comprises a liquid crystal layer, a temperature sensor, a plurality of pixel electrodes and a voltage generating unit. The liquid crystal layer modulates the phase of the incident light according to the magnitude of an applied electric field. The temperature sensor generates a signal corresponding to the temperature of the liquid crystal layer, namely a temperature signal. A pixel electrode is provided in each pixel, and a voltage for generating an applied electric field is applied to the liquid crystal layer. The voltage generating unit supplies voltage to the plurality of pixel electrodes. The voltage generating unit has a storage mechanism. The storage mechanism pre-stores one or more coefficients contained in a function representing the correlation between the temperature change of the liquid crystal layer relative to a reference temperature and the change in the phase modulation amount in the liquid crystal layer. The voltage generating unit uses the temperature indicated by the temperature signal provided by the temperature sensor and the one or more coefficients to perform an operation for correcting the magnitude of the voltage.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-168391 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] At present, there is a known technology for modulating the phase of light by a spatial light modulator (SLM). A liquid crystal type spatial light modulator has a liquid crystal layer and a plurality of pixel electrodes arranged along the liquid crystal layer. When a voltage is applied to the pixel electrode, the liquid crystal molecules rotate according to the magnitude of the voltage, and the birefringence of the liquid crystal changes. When light is incident on the liquid crystal layer, the phase of the light inside the liquid crystal layer changes, and light with a phase difference relative to the incident light is emitted to the outside. The relationship between the magnitude of the applied voltage and the phase difference of the emitted light before and after the application of the voltage, that is, the phase modulation amount, is represented by the phase modulation characteristics of the spatial light modulator. In the phase modulation characteristics, the relationship between the phase modulation amount and the applied voltage is nonlinear. In order to easily convert such a nonlinear relationship, a lookup table (LUT) is used that displays the correspondence between the grayscale value representing the phase modulation amount and the applied voltage.

[0008] When the temperature of the liquid crystal layer changes, the relationship between the phase modulation amount and the applied voltage changes. That is, even when a certain constant voltage is applied, the phase modulation amount varies depending on the temperature of the liquid crystal layer at that time. In the spatial light modulation device and spatial light modulation method disclosed in Patent Document 1, the magnitude of the applied voltage is corrected using the temperature of the liquid crystal layer detected by a temperature sensor based on the correlation between the temperature change amount of the liquid crystal layer relative to the reference temperature and the change amount of the phase modulation amount in the liquid crystal layer.

[0009] However, in most cases, the temperature sensor is arranged at a position away from the liquid crystal layer, such as on the back side of the spatial light modulator opposite to the light incident surface. Therefore, various components such as the substrate are interposed between the liquid crystal layer and the temperature sensor, and the temperature detected by the temperature sensor deviates from the temperature of the liquid crystal layer. In particular, when the intensity of the light incident on the liquid crystal layer increases, the temperature of the liquid crystal layer rises significantly due to the energy of the light, and the deviation of the temperature between the liquid crystal layer and the temperature sensor increases. If the deviation of the temperature between the liquid crystal layer and the temperature sensor is large, it is difficult to correctly correct the magnitude of the applied voltage even if the temperature detected by the temperature sensor is used. As a result, the actual phase modulation amount deviates from the target phase modulation amount. Depending on the purpose of using the spatial light modulator, such a phenomenon will cause serious problems. For example, in laser processing, when the laser output from the laser light source is irradiated to the workpiece via the spatial light modulator, the deviation of the phase modulation amount will have a significant impact on the processing accuracy. When a spatial light modulator is used in a microscope or an ophthalmoscope, there is a concern that a useful observation image cannot be obtained depending on the temperature at which it is used.

[0010] An object of the present invention is to provide an optical modulation device and a control method of a spatial light modulator that can reduce the deviation of an actual phase modulation amount from a target phase modulation amount.

[0011] Technical means of solving problems

[0012] [1] A first light modulation device according to one embodiment of the present invention includes a light source, a spatial light modulator, and a control unit. The light source outputs light having an intensity corresponding to a set intensity. The spatial light modulator includes a plurality of pixel electrodes, a liquid crystal layer, a drive unit, and a cooling unit. The plurality of pixel electrodes are arranged one-dimensionally or two-dimensionally. The liquid crystal layer modulates the phase of light according to the magnitude of the electric field formed by each pixel electrode. The drive unit applies a voltage to the plurality of pixel electrodes. The cooling unit cools the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature. The control unit determines a set temperature of the cooling unit. The control unit determines the set temperature based on the set intensity.

[0013] [2] A first control method for a spatial light modulator according to an embodiment of the present invention is a method for controlling a spatial light modulator. The spatial light modulator includes a plurality of pixel electrodes, a liquid crystal layer, a driving unit, and a cooling unit. The plurality of pixel electrodes are arranged one-dimensionally or two-dimensionally. The liquid crystal layer modulates the phase of light according to the magnitude of the electric field formed by each pixel electrode. The driving unit applies a voltage to the plurality of pixel electrodes. The cooling unit cools the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature. The first control method includes a determining step of determining a set temperature of the cooling unit, and a light input step of inputting light having an intensity corresponding to the set intensity into the liquid crystal layer. In the determining step, the set temperature is determined based on the set intensity.

[0014] As described above, when the intensity of light incident on the liquid crystal layer increases, the temperature of the liquid crystal layer increases significantly due to the energy of the light, and the deviation of the temperature between the liquid crystal layer and the temperature sensor increases. Therefore, in the first light modulation device and the first control method, in the control unit or the determination step, the set temperature of the cooling unit is determined based on the set intensity of light in such a manner that the set temperature of the cooling unit is lower than the set temperature as the set intensity of light input to the liquid crystal layer increases when the temperature of the liquid crystal layer approaches the set temperature. Thus, since the temperature of the liquid crystal layer can be made close to a constant regardless of the intensity of light incident on the liquid crystal layer, the magnitude of the applied voltage can be correctly set, and the actual phase modulation amount can be made close to the target phase modulation amount with good accuracy. Therefore, according to the first light modulation device and the first control method, the deviation of the actual phase modulation amount from the target phase modulation amount can be reduced. In addition, in the first light modulation device and the first control method, for example, the relationship between the phase modulation amount and the magnitude of the applied voltage is set based on the specified temperature instead of the set temperature.

[0015] [3] In the first light modulation device of the above-mentioned [1], the control unit may pre-store a data table showing the relationship between the setting intensity and the setting temperature, and determine the setting temperature using the data table. [4] Alternatively, in the first light modulation device of the above-mentioned [1], the control unit may pre-store a calculation formula showing the relationship between the setting intensity and the setting temperature, and determine the setting temperature using the calculation formula. In any of these cases, the control unit can easily determine the setting temperature based on the setting intensity. Similarly, [5] In the determination step of the first control method of the above-mentioned [2], the setting temperature may be determined using a data table showing the relationship between the setting intensity and the setting temperature. [6] Alternatively, in the determination step of the first control method of the above-mentioned [2], the setting temperature may be determined using a calculation formula showing the relationship between the setting intensity and the setting temperature. In any of these cases, in the determination step, the setting temperature may be easily determined based on the setting intensity.

[0016] [7] In any of the first light modulation devices of [1], [3] and [4] above, the set temperature may be proportional to the set intensity. [8] Similarly, in any of the first control methods of [2], [5] and [6] above, the set temperature may be proportional to the set intensity. According to the present inventors' understanding, the temperature of the liquid crystal layer deviates in proportion to the intensity of light input to the liquid crystal layer relative to the temperature detected by the temperature sensor. By determining the set temperature of the cooling unit in proportion to the set intensity of light, the temperature of the liquid crystal layer can be made closer to a constant regardless of the intensity of light incident on the liquid crystal layer, and the actual phase modulation amount can be made closer to the target phase modulation amount with better accuracy. Therefore, the deviation of the actual phase modulation amount from the target phase modulation amount can be further reduced.

[0017] [9] A second light modulation device according to an embodiment of the present invention includes a light source, a spatial light modulator, and a control unit. The light source outputs light having an intensity corresponding to a set intensity. The spatial light modulator includes a plurality of pixel electrodes, a liquid crystal layer, a drive unit, and a cooling unit. The plurality of pixel electrodes are arranged one-dimensionally or two-dimensionally. The liquid crystal layer modulates the phase of light according to the magnitude of an electric field formed by each pixel electrode. The drive unit applies a voltage to the plurality of pixel electrodes. The cooling unit cools the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature. The control unit determines the magnitude of the voltage applied to the plurality of pixel electrodes. The control unit determines the magnitude of the voltage so that when the phase of each pixel of the liquid crystal layer is set to a specified phase, the larger the set intensity, the larger the voltage corresponding to the specified phase.

[0018]

[10] A second control method for a spatial light modulator according to an embodiment of the present invention is a method for controlling a spatial light modulator. The spatial light modulator includes a plurality of pixel electrodes, a liquid crystal layer, a driving unit, and a cooling unit. The plurality of pixel electrodes are arranged one-dimensionally or two-dimensionally. The liquid crystal layer modulates the phase of light according to the magnitude of an electric field formed by each pixel electrode. The driving unit applies a voltage to the plurality of pixel electrodes. The cooling unit cools the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature. The second control method includes a determination step for determining the magnitude of a voltage applied to each pixel electrode, and a light input step for inputting light having an intensity corresponding to the set intensity into the liquid crystal layer. In the determination step, the magnitude of the voltage is determined in such a manner that, when the phase of each pixel of the liquid crystal layer is set to a specified phase, the larger the set intensity, the larger the voltage corresponding to the specified phase.

[0019] As described above, when the intensity of light incident on the liquid crystal layer increases, the temperature of the liquid crystal layer rises significantly due to the energy of the light, and the temperature deviation between the liquid crystal layer and the temperature sensor increases. In addition, since the refractive index of the liquid crystal decreases as the temperature increases, the phase modulation amount caused by the liquid crystal layer when a certain voltage is applied decreases as the temperature of the liquid crystal layer increases (that is, the intensity of the light input to the liquid crystal layer increases). Therefore, in the second light modulation device and the second control method, in the control unit or the determination step, the voltage is determined in such a way that when the phase of each pixel of the liquid crystal layer is set to a specified phase, the larger the set intensity of the light input to the liquid crystal layer, the larger the voltage corresponding to the specified phase. Thus, even if the temperature of the liquid crystal layer changes with the change in the intensity of the light incident on the liquid crystal layer, the actual phase modulation amount can be made close to the target phase modulation amount with good accuracy. Therefore, according to the second light modulation device and the second control method, the deviation of the actual phase modulation amount from the target phase modulation amount can be reduced.

[0020]

[11] In the second light modulation device of the above-mentioned [9], the control unit may have correlation data, which shows the correlation between the total number of grayscales used in the lookup table showing the relationship between the size of the display voltage and each of the plurality of grayscale values ​​and the set intensity. The control unit may use the correlation data to determine the total number of grayscales used in the lookup table based on the set intensity. In this case, the control unit can easily determine the size of the voltage according to the set intensity.

[12] Similarly, in the determination step of the second control method of the above-mentioned

[10] , there may be correlation data showing the correlation between the total number of grayscales used in the lookup table showing the relationship between the size of the display voltage and each of the plurality of grayscale values ​​and the set intensity. In the determination step, the correlation data may be used to determine the total number of grayscales used in the lookup table based on the set intensity. In this case, in the determination step, the size of the voltage can be easily determined according to the set intensity.

[0021]

[13] In the second optical modulator of the above-mentioned

[11] , the control unit may have reference data showing the correspondence between the phase modulation amount caused by the liquid crystal layer and each grayscale value of the lookup table, and the input value of the phase modulation amount may be displayed from the external input of the optical modulator, and the input value may be converted into a grayscale value using the reference data. In this case, a person using the second optical modulator can freely set the phase modulation amount.

[14] Similarly, in the determination step of the second control method of the above-mentioned

[12] , the input value of the phase modulation amount may be displayed from the external input of the optical modulator, and the input value may be converted into a grayscale value using the reference data showing the correspondence between the phase modulation amount caused by the liquid crystal layer and each grayscale value of the lookup table. In this case, a person using the second control method can freely set the phase modulation amount.

[0022]

[15] In the second light modulation device of the above-mentioned [9], the control unit may use correlation data showing the correlation between the total grayscale number and the set intensity to determine, based on the set intensity, a lookup table used in a plurality of lookup tables showing the relationship between the magnitude of the display voltage and each of the plurality of grayscale values ​​and the total grayscale numbers being different from each other. In this case, the control unit can easily determine the magnitude of the voltage according to the set intensity.

[16] Similarly, in the determination step of the above-mentioned second control method of

[10] , the correlation data showing the correlation between the total grayscale number and the set intensity may be used to determine, based on the set intensity, a lookup table used in a plurality of lookup tables showing the relationship between the magnitude of the display voltage and each of the plurality of grayscale values ​​and the total grayscale numbers being different from each other. In this case, in the determination step, the magnitude of the voltage may be easily determined according to the set intensity.

[0023]

[17] In the second optical modulator of the above-mentioned

[15] , the control unit may have a plurality of reference data showing the correspondence between the phase modulation amount caused by the display liquid crystal layer and each grayscale value of each of the plurality of lookup tables, and the input value of the phase modulation amount is displayed from the external input of the optical modulator, and the input value is converted into a grayscale value using the reference data corresponding to the above-mentioned lookup table used among the plurality of reference data. In this case, the person using the second optical modulator can freely set the phase modulation amount.

[18] Similarly, in the determination step of the second control method of the above-mentioned

[16] , the input value of the phase modulation amount can be displayed from the external input of the optical modulator, and the input value is converted into a grayscale value using the reference data corresponding to the above-mentioned lookup table used among the plurality of reference data showing the correspondence between the phase modulation amount caused by the display liquid crystal layer and each grayscale value of each of the plurality of lookup tables. In this case, the person using the second control method can freely set the phase modulation amount.

[0024] Effects of the Invention

[0025] According to the present invention, it is possible to provide an optical modulation device and a method for controlling a spatial light modulator that can reduce the deviation of an actual phase modulation amount from a target phase modulation amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram schematically showing the structure of the light modulation device according to the first embodiment of the present invention.

[0027] Figure 2 This is a diagram schematically showing the cross-sectional structure of a light modulation element.

[0028] Figure 3 This is a diagram of a plurality of pixel electrodes observed from the normal direction of the light incident and outgoing surfaces.

[0029] Figure 4 This is a perspective view showing the appearance of a container that accommodates the spatial light modulator.

[0030] Figure 5It is a perspective view showing the structure of a spatial light modulator.

[0031] Figure 6 is a diagram showing an example of a lookup table.

[0032] Figure 7 This is a diagram schematically showing the configuration of a test device for investigating the relationship between the phase modulation amount of a light modulator and the voltage applied to a pixel electrode.

[0033] Figure 8 This is a diagram showing an example of the relationship between the grayscale value corresponding to the phase change amount and the light intensity measured by the power meter.

[0034] Fig. 9 This is a diagram showing the results of measuring the relationship between the grayscale value input to the light modulation element and the phase modulation amount.

[0035] Fig.10 It is a diagram showing the relationship between the grayscale value and the phase modulation amount.

[0036] Fig.11 This is a diagram showing the relationship between the grayscale value and the phase modulation amount when the temperature of the liquid crystal layer is controlled to 20° C. and 25° C.

[0037] Fig.12 This is a diagram showing an example of the relationship between the light intensity of the test light and the maximum phase modulation amount of the light modulator when the set temperature of the cooling unit is set to 20° C. and 25° C.

[0038] Fig.13 This is a diagram showing an example of the relationship between the set intensity of the laser light and the set temperature of the cooling unit so as to make the phase modulation amount constant.

[0039] Fig.14 This is a flowchart showing the control method of the spatial light modulator according to the first embodiment.

[0040] Fig.15 This is a diagram showing an example of the relationship between the grayscale value and the phase modulation amount.

[0041] Fig.16 is a graph showing an example of correlation data.

[0042] Fig.17 (a) and (b) are diagrams showing examples of reference data.

[0043] Fig.18 This is a flowchart showing a method for controlling the spatial light modulator according to the second embodiment. DETAILED DESCRIPTION

[0044] Hereinafter, embodiments of the light modulation device and the control method of the spatial light modulator of 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 repeated descriptions are omitted.

[0045] [First embodiment]

[0046] Figure 1 FIG. 1 is a diagram schematically showing the structure of an optical modulation device 1A according to a first embodiment of the present invention. Figure 1 As shown, the light modulation device 1A of this embodiment includes a light source 3, a mirror 4, an imaging optical system 5, a condenser lens 6, a control unit 7 (control unit), and a spatial light modulator 10. The light modulation device 1A of this embodiment irradiates the laser light La output from the light source 3 to the object to be processed, i.e., the object B, via the spatial light modulator 10, in laser processing, for example. Alternatively, the light modulation device 1A of this embodiment irradiates the laser light La output from the light source 3 to the object to be observed, i.e., the object B, via the spatial light modulator 10, in a microscope such as a fluorescence microscope, for example.

[0047] The light source 3 outputs a laser La. The light source 3 is configured, for example, to output a single wavelength and linearly polarized laser La. The light source 3 is configured, for example, to repeatedly output a laser La having a pulse waveform having an extremely small time width such as a picosecond level or a femtosecond level. The wavelength of the laser La is, for example, 1030 nm. The pulse width of the laser La is, for example, 10 picoseconds. The pulse repetition frequency of the laser La is, for example, 1 MHz. The light source 3 is configured in a manner that can change the intensity of the laser La, and a signal indicating a set intensity is input from the outside of the optical modulation device 1A or the control unit 7, and the laser La having an intensity corresponding to the set intensity is output. The intensity described here refers to the peak intensity of each pulse. Alternatively, the intensity described here may also refer to the time average value of the light intensity within a certain period.

[0048] The mirror 4 is arranged opposite to the light incident and output surface 11a of the spatial light modulator 10. The mirror 4 is, for example, a prism type, and has two flat reflecting surfaces 41 and 42. The reflecting surface 41 is arranged on the optical path between the light source 3 and the light incident and output surface 11a of the spatial light modulator 10, and optically couples the light source 3 with the light incident and output surface 11a. The laser light La output from the light source 3 is reflected by the reflecting surface 41 and reaches the light incident and output surface 11a. The incident direction of the laser light La to the light incident and output surface 11a is inclined relative to the normal direction of the light incident and output surface 11a. The reflecting surface 42 is arranged on the optical path between the light incident and output surface 11a and the imaging optical system 5, and optically couples the light incident and output surface 11a and the imaging optical system 5. The modulated laser light Lb output from the light incident and output surface 11a is reflected by the reflecting surface 42 and reaches the imaging optical system 5. The emission direction of the laser light Lb from the light incident and output surface 11a is inclined toward the opposite side to the laser light La relative to the normal direction of the light incident and output surface 11a. In one example, a portion of the optical axis between the light source 3 and the reflecting surface 41 close to the reflecting surface 41 is located on the same straight line as a portion of the optical axis between the reflecting surface 42 and the imaging optical system 5 close to the reflecting surface 42.

[0049] The imaging optical system 5 optically couples the light incident and output surfaces 11a of the spatial light modulator 10 and the condenser lens 6. The imaging optical system 5 is configured to include, for example, a pair of lenses 51 and 52. The lenses 51 and 52 are arranged on the optical axis between the reflection surface 42 and the condenser lens 6. The lenses 51 and 52 constitute, for example, a bilateral telecentric optical system.

[0050] The condenser lens (objective lens) 6 condenses the modulated laser light Lb output from the light incident and output surface 11 a of the spatial light modulator 10 toward the object B. The condenser lens 6 is optically coupled to the light incident and output surface 11 a via the imaging optical system 5 and the reflection surface 42 .

[0051] The spatial light modulator 10 includes a light modulator 11, a temperature adjustment unit 16, and an external control substrate 17 (control unit). The light modulator 11 includes a plurality of pixels arranged one-dimensionally or two-dimensionally, and modulates the phase of the laser light La input to the light incident and output surfaces 11a for each pixel to generate modulated laser light Lb. The light modulator 11 of this embodiment has a reflective structure, but the light modulator 11 may also have a transmissive structure.

[0052] Figure 2 1 is a diagram schematically showing the cross-sectional structure of the light modulator 11. Figure 2 As shown, the light modulator 11 includes a silicon substrate 110, a glass substrate 112, a transparent conductive film 113, a plurality of pixel electrodes 114, a liquid crystal layer 115, a transparent layer (phase shift layer) 116, a dielectric multilayer film (reflective layer) 117, a light shielding layer 118, and a drive circuit layer 119 (control unit). The transparent layer 116 may not be provided.

[0053] The glass substrate 112 has a surface 112a and a back surface 112b. The surface 112a of the glass substrate 112 constitutes the light incident and output surface 11a of the light modulator 11. The glass substrate 112 allows the laser light La incident from the light incident and output surface 11a (surface 112a) to pass into the light modulator 11. The transparent conductive film 113 is provided on the back surface 112b of the glass substrate 112 and is mainly composed of a conductive material (e.g., ITO) that transmits the laser light La.

[0054] Figure 3 11 is a diagram showing a plurality of pixel electrodes 114 viewed from the normal direction of the light incident and emitting surface 11a. Figure 3 As shown, a plurality of pixel electrodes 114 are arranged one-dimensionally or two-dimensionally to form a plurality of pixels of the light modulator 11. Each pixel electrode 114 is made of a metal material such as aluminum, for example, and their surfaces are processed to be flat and smooth. The plurality of pixel electrodes 114 are driven by an active matrix circuit (driving unit) provided in a driving circuit layer 119. The active matrix circuit is provided between the plurality of pixel electrodes 114 and the silicon substrate 110, and applies a voltage of a magnitude corresponding to the phase modulation amount required for each pixel to each pixel electrode 114. The active matrix circuit has, for example: a first driver circuit that applies a voltage to each pixel column arranged in the X-axis direction; and a second driver circuit that applies a voltage to each pixel column arranged in the Y-axis direction. Voltage is applied to the pixel electrodes 114 of the pixels specified by the first and second driver circuits.

[0055] The liquid crystal layer 115 is disposed between the transparent conductive film 113 and the pixel electrode 114, and modulates the phase of the laser light La according to the magnitude of the electric field formed by each pixel electrode 114. When a voltage is applied to a certain pixel electrode 114 through the active matrix circuit, an electric field is formed between the transparent conductive film 113 and the pixel electrode 114. The electric field is applied to each of the dielectric multilayer film 117 and the liquid crystal layer 115 in a ratio corresponding to the respective thicknesses. Then, the arrangement direction of the liquid crystal molecules changes according to the magnitude of the electric field applied to the liquid crystal layer 115. When the laser light La passes through the glass substrate 112 and the transparent conductive film 113 and is incident on the liquid crystal layer 115, the laser light La is phase-modulated by the liquid crystal molecules while passing through the liquid crystal layer 115. After being reflected by the dielectric multilayer film 117, the laser light La is phase-modulated again by the liquid crystal layer 115 and extracted as the laser light Lb.

[0056] In this embodiment, the liquid crystal layer 115 is configured to include alignment films 115a and 115b. The alignment films 115a and 115b are formed on both end surfaces of the liquid crystal layer 115 to align the liquid crystal molecules in a certain direction. The alignment films 115a and 115b are made of a polymer material such as polyimide, and the contact surface with the liquid crystal layer 115 is subjected to a rubbing treatment or the like.

[0057] The transparent layer 116 is provided at the interface of the liquid crystal layer 115 so that the peaks of the laser light La incident from the glass substrate 112 and the laser light La reflected by the dielectric multilayer film 117 do not overlap each other. The optical film thickness of the transparent layer 116 is set to be equal to or greater than the wavelength of the laser light La. Alternatively, the optical film thickness of the transparent layer 116 is set to be equal to or greater than (τ×c) / 30, with the pulse width of the laser light La being τ and the speed of light being c. The constituent material of the transparent layer 116 mainly includes, for example, SiO 2 and / or Nb 2 O 5 As mentioned above, the transparent layer 116 may not be provided.

[0058] The dielectric multilayer film 117 is provided between the liquid crystal layer 115 and the light shielding layer 118 (if the transparent layer 116 is provided, between the transparent layer 116 and the light shielding layer 118). The dielectric multilayer film 117 reflects the laser light La at a high reflectivity of, for example, more than 99%. The constituent material of the dielectric multilayer film 117 is, for example, SiO 2 With TiO 2 The constituent material of the dielectric multilayer film 117 is not particularly limited to this, and TiO 2 Using HfO 2 , or replace SiO 2 Using MgF 2 etc., make appropriate changes.

[0059] The light shielding layer 118 is disposed between the dielectric multilayer film 117 and the pixel electrodes 114, and is directly formed on the surfaces of the plurality of pixel electrodes 114. The light shielding layer 118 suppresses the occurrence of light leakage.

[0060] Figure 4 It is a perspective view showing the appearance of a container 20 that accommodates the spatial light modulator 10 . Figure 4The container 20 shown has a shell 21, a heat sink 22, and a fan 23. The shell 21 is a hollow container that is roughly rectangular or roughly cubic. The shell 21 is made of metal, for example. The shell 21 has a pair of side surfaces 21a and 21b arranged along a certain direction D1. In addition, the shell 21 has an optical window 21c on each of the side surfaces 21a and 21b. Only the optical window 21c of the side surface 21a is shown in the figure. The optical window 21c of the side surface 21a is opposite to the optical window 21c of the side surface 21b in the direction D1. The shell 21 has a pair of side surfaces 21d and 21e arranged along a direction D2 that intersects the direction D1. The heat sink 22 and the fan 23 are installed on one side surface 21d of the side surfaces 21d and 21e. The heat sink 22 has a plurality of protrusions on the outer surface. The heat sink 22 is fixed in a state of being inserted into a rectangular opening 21f formed on the side surface 21d. The fan 23 is configured in a manner that covers the outer surface of the heat sink 22. The fan 23 is fixed to the side surface 21 d . The fan 23 sends air to the outer surface of the radiator 22 to cool the radiator 22 .

[0061] Figure 5 1 is a perspective view showing the structure of the spatial light modulator 10. The spatial light modulator 10 is accommodated in a container 20 together with the mirror 4 described above. Figure 5 The spatial light modulator 10 shown includes a light modulation element 11 , a substrate 12 , a metal block 13 , a temperature sensor 14 , and a cooling unit 15 .

[0062] The substrate 12 has a first surface 12a and a second surface 12b. The first surface 12a is opposite to the mirror 4. The second surface 12b is opposite to the first surface 12a and is opposite to the heat sink 22. The light modulator 11 is configured so that light enters the output surface 11a (reference Figure 2 ) is mounted on the first surface 12a of the substrate 12 in a manner opposite to the mirror 4.

[0063] A substantially rectangular opening 12c is formed on the substrate 12. When viewed from the normal direction of the first surface 12a and the second surface 12b, the opening 12c overlaps with the light modulator 11. The back surface 11b of the light modulator 11 is exposed from the opening 12c. The back surface 11b is the surface on the opposite side to the light incident and exiting surface 11a. The metal block 13 is arranged in the opening 12c. The metal block 13 is thermally coupled or connected to the back surface 11b of the light modulator 11. The metal block 13 is, for example, a copper block.

[0064] The temperature sensor 14 and the cooling unit 15 constitute Figure 1 The temperature sensor 14 detects the temperature of the liquid crystal layer 115 (refer to Figure 2) of the surrounding temperature of the liquid crystal layer 115. The temperature sensor 14 is, for example, a thermistor, and changes its resistance value according to the surrounding temperature of the liquid crystal layer 115. In the example shown in the figure, the temperature sensor 14 is arranged inside the metal block 13, but the temperature sensor 14 only needs to be arranged near the light modulating element 11, and can also be arranged outside the metal block 13 (for example, on the substrate 12). In the present invention, the temperature of the liquid crystal layer 115 is not limited to the actual temperature of the liquid crystal layer 115, but also includes the surrounding temperature of the liquid crystal layer 115.

[0065] The cooling unit 15 is arranged at a position sandwiching the metal block 13 with the light modulator 11. The cooling unit 15 includes, for example, a Peltier element. The heat absorbing surface of the Peltier element is thermally coupled or in contact with the metal block 13. The heat dissipating surface of the Peltier element is thermally coupled or in contact with the inner surface 22a of the heat sink 22. The inner surface 22a of the heat sink 22 is the surface opposite to the outer surface provided with a plurality of protrusions. The cooling unit 15 cools the light modulator 11 (particularly the liquid crystal layer 115). The cooling unit 15 is controlled, for example, by a control driver circuit provided on the substrate 12. The cooling unit 15 cools the liquid crystal layer 115 through the metal block 13 in such a manner that the temperature detected by the temperature sensor 14 approaches the set temperature. As a result, the actual temperature of the liquid crystal layer 115 also approaches the set temperature.

[0066] From light source 3 (reference Figure 1 ) The laser light La outputted from the housing 21 passes through the optical window 21c on the side surface 21b of the housing 21 and reaches the reflecting surface 41 of the mirror 4. The laser light La is reflected by the reflecting surface 41 and is incident on the light incident and outputting surface 11a of the light modulating element 11. The light modulating element 11 modulates the phase of the laser light La for each pixel. The modulated laser light Lb outputted from the light modulating element 11 is reflected by the reflecting surface 42 of the mirror 4. The laser light Lb passes through the optical window 21c on the side surface 21a of the housing 21 and is outputted to the outside of the housing 21 ( Figure 1 The imaging optical system 5 is shown.

[0067] Reference again Figure 1, the control unit 7 of the present embodiment is described. The control unit 7 can be physically constructed as a common computer including a processor (CPU), a main storage device such as ROM and RAM, an input device such as a keyboard, a mouse and a touch screen, an output device such as a display (including a touch screen), an auxiliary storage device such as a hard disk, etc. The control unit 7 is electrically connected to the light source 3, the light modulator 11 and the temperature adjustment unit 16. The control unit 7 provides information A1 to the light source 3 via the external control substrate 17, or receives information A1 from the light source 3. Information A1 is information related to the set intensity of the laser La. In addition, the control unit 7 provides information A2 to the light modulator 11 via the external control substrate 17. Information A2 is information related to the grayscale value of the phase modulation amount set as the target in each of the multiple pixels displayed in the light modulator 11. In addition, the control unit 7 provides information A3 to the control driver circuit of the temperature adjustment unit 16 via the external control substrate 17. Information A3 is information related to the set temperature of the cooling unit 15.

[0068] Generally speaking, the phase modulation amount of each pixel of the light modulator 11 has a nonlinear relationship with the magnitude of the voltage applied to each pixel electrode 114. Therefore, the external control substrate 17 has a lookup table for converting the grayscale value input from the control unit 7 into the magnitude of the voltage. The external control substrate 17 converts the grayscale value into an analog voltage value using the lookup table, and inputs the analog voltage value to the drive circuit layer 119. Figure 6 : is a diagram showing an example of a lookup table. The lookup table can store analog voltage values ​​as input values ​​(DA input values) to a digital / analog converter. The grayscale value is a digital signal with a total grayscale number of N (0 to N-1), and in this embodiment, N=256. The pixel input values ​​of all N grayscales from 0 to N-1 show a phase modulation amount of 1 cycle of 0 to 2π. Figure 6The phase modulation amount is also displayed for reference, but the driving circuit layer 119 does not have information related to the phase modulation amount. The driving circuit layer 119 applies a voltage to the pixel electrode 114 of each pixel based on the analog voltage value input to each pixel. As described later, since the refractive index of the liquid crystal layer 115 decreases as the temperature increases, the phase modulation amount caused by the liquid crystal layer 115 when a voltage of a certain magnitude is applied decreases as the temperature of the liquid crystal layer 115 increases. Therefore, the external control substrate 17 has a lookup table that is different for each temperature of the liquid crystal layer 115. The driving circuit layer 119 may also have a lookup table. In this case, the driving circuit layer 119 converts the grayscale value input from the control unit 7 into an analog voltage value using the lookup table. Then, the driving circuit layer 119 applies a voltage to the pixel electrode 114 of each pixel based on the converted analog voltage value. Alternatively, the control unit 7 may also have a lookup table. In this case, the control unit 7 converts the grayscale value into an analog voltage value using the lookup table. Then, the driving circuit layer 119 applies a voltage to the pixel electrode 114 of each pixel based on the analog voltage value input from the control unit 7 .

[0069] Figure 7 1 is a diagram schematically showing the structure of the test device 2. The test device 2 is a device for investigating the relationship between the phase modulation amount of the light modulator 11 and the voltage applied to the pixel electrode 114. The test device 2 includes a laser light source 31, a 1 / 2 wavelength plate 32, a polarizing beam splitter 33, a light absorber 34, a beam expander 35, a dielectric mirror 36a, a dielectric mirror 36b, a homogenizer 37, a polarizing beam splitter 38, a light absorber 39, an aperture 40, and a power meter 43.

[0070] The laser light source 31 outputs a test light Lc simulating the laser light La. The test light Lc is incident on the polarization beam splitter 33 after passing through the 1 / 2 wavelength plate 32. The polarization direction of the test light Lc is adjusted in the 1 / 2 wavelength plate 32, and only the first polarization component having a predetermined polarization direction in the test light Lc passes through the polarization beam splitter 33. The second polarization component other than the first polarization component in the test light Lc is reflected by the polarization beam splitter 33 and absorbed by the light absorber 34. The polarization direction of the test light Lc is rotated by 45° relative to the orientation direction of the liquid crystal in the liquid crystal layer 115 of the light modulator 11 by the 1 / 2 wavelength plate 32 and the polarization beam splitter 33.

[0071] In order to make the beam diameter of the test light Lc match the size of the modulation surface of the light modulator 11 (for example, 16 mm×12.8 mm), the beam expander 35 expands the beam diameter of the test light Lc. The beam diameter of the test light Lc before expansion is, for example, 7 mm. When the size of the modulation surface of the light modulator 11 is, for example, 16 mm×12.8 mm, the beam diameter of the test light Lc after expansion is, for example, 11 mm. The beam expander 35 can be composed of a combination of a concave lens and a convex lens, for example. The test light Lc with the expanded beam diameter is introduced into the homogenizer 37 through the dielectric mirrors 36a and 36b. The test light Lc passes through the homogenizer 37 and has a uniform light intensity distribution in an area of ​​a specific shape (for example, a circle).

[0072] The mirror 4 housed in the container 20 is arranged on the optical axis between the homogenizer 37 and the polarizing beam splitter 38. The test light Lc output from the homogenizer 37 is reflected by the mirror 4 and input to the light modulator 11. At this time, the polarization direction of the modulated test light Ld is rotated according to the phase modulation amount given by the light modulator 11. The modulated test light Ld output from the light modulator 11 is reflected by the mirror 4 and reaches the polarizing beam splitter 38. Only the specified polarization component in the test light Ld passes through the polarizing beam splitter 38, and then passes through the aperture 40 and is input to the power meter 43. The opening diameter of the aperture 40 is, for example, 6 mm. The other components of the test light Ld except the specified polarization component are reflected by the polarizing beam splitter 38 and absorbed by the light absorber 39. The power meter 43 measures the light intensity of the test light Ld that has passed through the aperture 40. In the test device 2, the amount of polarization components of the test light Ld passing through the polarization beam splitter 38 and the aperture 40 changes according to the phase modulation amount given by the light modulator 11. Therefore, the phase change amount in the light modulator 11 is observed as the intensity change amount in the power meter 43.

[0073] Figure 8 θ is a graph showing an example of the relationship between the grayscale value corresponding to the phase change amount and the light intensity measured by the power meter 43. The light intensity I measured by the power meter 43 is expressed by the following equation (1). θ is the phase modulation amount, I n is a constant.

[0074] [Number 1]

[0075] I=I n cos 2 θ…(1)

[0076] Fig. 9 This is a graph showing the results of measuring the relationship between the grayscale value and the phase modulation amount input to the optical modulator 11 using a test light Lc with a pulse width of 10 picoseconds, a wavelength of 1030nm, and a repetition frequency of 1MHz. The horizontal axis represents the grayscale value, and the vertical axis represents the phase modulation amount (πrad). Fig. 9As shown, the grayscale value has a substantially linear relationship with the phase modulation amount. Fig.10 The horizontal axis is the phase modulation amount (πrad), and the vertical axis is the grayscale value, which shows the relationship between the grayscale value and the phase modulation amount. Fig.10 The grayscale value used to obtain the target phase modulation amount can be obtained by using the graph shown in the figure. For example, if the linear function is used to approximate Fig.10 From the graph shown in FIG. 1 , the following formula (2) can be obtained.

[0077] [Number 2]

[0078] Grayscale value = 117 × phase modulation amount…(2)

[0079] According to the formula (2), for example, 2×117=234 is obtained as the grayscale value for obtaining a phase modulation amount of 2π (rad).

[0080] Here, the temperature of the liquid crystal layer 115 changes with the change of the ambient temperature or the irradiation of the laser La. Since the refractive index of the liquid crystal layer 115 decreases as the temperature of the liquid crystal layer 115 increases, the phase modulation amount caused by the liquid crystal layer 115 when a certain voltage is applied decreases as the temperature of the liquid crystal layer 115 increases. Fig.11 As an example, FIG. 1 is a diagram showing the relationship between the grayscale value and the phase modulation amount when the temperature of the liquid crystal layer 115 is controlled to 20° C. and 25° C. Fig.11 As shown, the higher the temperature of the liquid crystal layer 115, the smaller the phase modulation amount relative to the grayscale value. Therefore, the temperature of the liquid crystal layer 115 is made close to the set temperature by the cooling unit 15, and the temperature of the liquid crystal layer 115 is kept constant. In this way, the phase modulation amount can be controlled with high accuracy.

[0081] However, the temperature sensor 14 of the present embodiment is arranged inside the metal block 13. Thus, in most cases, the temperature sensor 14 is arranged at a position away from the liquid crystal layer 115. Therefore, various components such as the silicon substrate 110, the dielectric multilayer film 117, and the drive circuit layer 119 are interposed between the liquid crystal layer 115 and the temperature sensor 14, and the temperature detected by the temperature sensor 14 deviates from the temperature of the liquid crystal layer 115. In particular, when the intensity of the laser light La incident on the liquid crystal layer 115 increases, the temperature of the liquid crystal layer 115 rises significantly due to the energy of the laser light La, and the deviation of the temperature between the liquid crystal layer 115 and the temperature sensor 14 increases. If the deviation of the temperature between the liquid crystal layer 115 and the temperature sensor 14 is large, it is difficult to correctly set the magnitude of the applied voltage even if the temperature of the liquid crystal layer 115 detected by the temperature sensor 14 is used. As a result, the actual phase modulation amount deviates from the target phase modulation amount.

[0082] Therefore, the control unit 7 of the present embodiment determines the set temperature of the cooling unit 15 based on the set intensity of the laser La. That is, the control unit 7 determines the set temperature of the cooling unit 15 based on the set intensity of the laser La in such a manner that the set temperature of the cooling unit 15 becomes lower than the specified temperature as the set intensity of the laser La increases when the temperature of the liquid crystal layer 115 approaches the specified temperature. In other words, the control unit 7 determines the set temperature of the cooling unit 15 based on the set intensity of the laser La in such a manner that the set temperature of the cooling unit 15 becomes lower than the specified temperature when the temperature of the liquid crystal layer 115 approaches the specified temperature, and in such a manner that the difference between the set temperature of the cooling unit 15 and the specified temperature becomes larger as the set intensity of the laser La increases. The lookup table shows the relationship between the phase modulation amount and the magnitude of the applied voltage at a specified temperature such as room temperature, rather than the relationship between the set temperature of the cooling unit 15 and the magnitude of the applied voltage. Alternatively, the lookup table shows the relationship between the phase modulation amount and the magnitude of the applied voltage at the set temperature of the cooling unit 15 when the set intensity of the laser La is assumed to be zero.

[0083] Specifically, the control unit 7 holds in advance a data table showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15. The control unit 7 determines the set temperature of the cooling unit 15 by referring to the data table based on the known set intensity of the laser La. Alternatively, the control unit 7 holds in advance a calculation formula (for example, the following formula (3)) showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15. The control unit 7 determines the set temperature of the cooling unit 15 by applying the known set intensity of the laser La to the calculation formula. Maintaining the calculation formula means maintaining the coefficients included in the calculation formula.

[0084] Fig.12 2 is a diagram showing an example of the relationship between the light intensity of the test light Lc and the maximum phase modulation amount of the light modulator 11 when the set temperature of the cooling unit 15 is set to 20° C. and 25° C. Fig.12 In the figure, the horizontal axis represents the light intensity (W) of the test light Lc, and the vertical axis represents the maximum phase modulation amount (πrad). The plot P1 in the figure shows the measured value of the maximum phase modulation amount when the set temperature of the cooling unit 15 is set to 20°C, and Q1 is its approximate straight line. The plot P2 in the figure shows the measured value of the maximum phase modulation amount when the set temperature of the cooling unit 15 is set to 25°C, and Q2 is its approximate straight line. The figure also shows the approximate straight line Q3 when the set temperature of the cooling unit 15 is set to 23°C.

[0085] Depend on Fig.12It can be seen that, under the condition that the set temperature of the cooling unit 15 is the same, the greater the light intensity of the test light Lc, the smaller the maximum phase modulation amount of the light modulator 11. Therefore, the light intensity of the test light Lc and the maximum phase modulation amount of the light modulator 11 have a substantially linear relationship. Under the condition that the light intensity of the test light Lc is the same, the greater the set temperature of the cooling unit 15, the smaller the maximum phase modulation amount. For example, in this example, the maximum phase modulation amount when the set temperature is 25°C and the light intensity of the test light Lc is 10W is 2.105π (rad). The maximum phase modulation amount when the set temperature is 25°C and the light intensity of the test light Lc is 75W is 2.066π (rad). The maximum phase modulation amount when the set temperature is 20°C and the light intensity of the test light Lc is 10W is 2.193π (rad). The maximum phase modulation amount when the set temperature is 20°C and the light intensity of the test light Lc is 75W is 2.167π (rad). As can be seen from this, even when the light intensity of the laser light La varies, the maximum phase modulation amount of the light modulator 11 can be corrected by controlling the set temperature of the cooling unit 15. That is, by filling the gaps between the approximate straight lines Q1 to Q3 corresponding to the respective temperatures and changing the set temperature of the cooling unit 15 in accordance with the change in the set intensity of the laser light La, the phase modulation amount can be stabilized even when the set intensity of the laser light La is changed.

[0086] Fig.13 This is a diagram showing an example of the relationship between the set intensity of the laser La that can make the phase modulation amount constant and the set temperature of the cooling unit 15. In this figure, the horizontal axis represents the set intensity of the laser La (W), and the vertical axis represents the set temperature of the cooling unit 15 (°C). The plot P4 in the figure shows the measured value of the set temperature relative to the set intensity when the phase modulation amount is kept constant. Q4 in the figure is its approximate straight line. The approximate straight line Q4 can be obtained, for example, by the following formula (3). T is the set temperature of the cooling unit 15 (°C), and I is the set intensity of the laser La (W).

[0087] [Number 3]

[0088] T=-0.0241×I+24.773…(3)

[0089] As can be seen from formula (3), the set temperature of the cooling unit 15 is proportional to the set intensity of the laser La. According to formula (3), for example, by setting the set temperature of the cooling unit 15 to 24.5°C when the set intensity of the laser La is 10W and setting the set temperature of the cooling unit 15 to 23°C when the set intensity of the laser La is 75W, the respective phase modulation amounts are made substantially equal.

[0090] The degree of increase in the temperature of the liquid crystal layer 115 relative to the set intensity of the laser La varies depending on the conditions (pulse width, wavelength, and repetition frequency, etc.) of the laser La. Therefore, the degree of change in the phase modulation amount relative to the set intensity of the laser La also varies depending on the form of the laser La. Therefore, a plurality of data tables showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15 or a calculation formula showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15 may be prepared according to the number of combinations of the conditions of the laser La.

[0091] Fig.14 1 is a flowchart showing a control method of the spatial light modulator 10 of the present embodiment. First, the control unit 7 determines the set temperature of the cooling unit 15 based on the set intensity of the laser La in such a manner that when the temperature of the liquid crystal layer 115 is brought close to the prescribed temperature, the greater the set intensity of the laser La, the lower the set temperature is set to (determine step S11). At this time, the control unit 7 refers to a data table showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15, and determines the set temperature of the cooling unit 15 based on the known set intensity of the laser La. Alternatively, the control unit 7 determines the set temperature of the cooling unit 15 by applying the known set intensity of the laser La to a calculation formula showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15.

[0092] Next, laser light La having an intensity corresponding to the above-mentioned set intensity is input to the liquid crystal layer 115 of the light modulator 11 (light input step S12 ). The laser light La is phase-modulated for each pixel in the liquid crystal layer 115 , and the light modulator 11 outputs the modulated laser light Lb.

[0093] The effects that can be obtained by the light modulation device 1A of the present embodiment and the control method of the spatial light modulator 10 of the present embodiment described above are summarized as follows. In the light modulation device 1A of the present embodiment and the control method of the spatial light modulator 10 of the present embodiment, in the control unit 7 or the determination step S11, the set temperature of the cooling unit 15 is determined based on the set intensity of the laser La so that when the temperature of the liquid crystal layer 115 is brought close to the predetermined temperature, the greater the set intensity of the laser La input to the liquid crystal layer 115, the lower the set temperature of the cooling unit 15 is. As a result, the temperature of the liquid crystal layer 115 can be made close to a constant regardless of the intensity of the laser La incident on the liquid crystal layer 115. As a result, even if a common lookup table is used, the magnitude of the applied voltage can be accurately set, and the actual phase modulation amount can be made close to the target phase modulation amount with good accuracy. Therefore, according to the light modulation device 1A of the present embodiment and the control method of the spatial light modulator 10 of the present embodiment, the deviation of the actual phase modulation amount from the target phase modulation amount can be reduced. Furthermore, unlike the second embodiment described below, the reference data (reference data) showing the correspondence between the phase modulation amount and the grayscale value can be used in common regardless of the intensity of the laser light La. Fig.17 ).

[0094] As in the present embodiment, the control unit 7 may retain in advance a data table showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15, and determine the set temperature using the data table. Alternatively, the control unit 7 may retain in advance a calculation formula showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15, and determine the set temperature using the calculation formula. In any of these cases, the control unit 7 can easily determine the set temperature of the cooling unit 15 based on the set intensity of the laser La. Similarly, in the determination step S11, the set temperature of the cooling unit 15 may be determined using a data table showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15. Alternatively, in the determination step S11, the set temperature of the cooling unit 15 may be determined using a calculation formula showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15. In any of these cases, in the determination step S11, the set temperature of the cooling unit 15 may be easily determined based on the set intensity of the laser La. The external control substrate 17 or the drive circuit layer 119 of the optical modulation element 11 may also have the function of the control unit 7.

[0095] As in the present embodiment, the set temperature of the cooling unit 15 may be proportional to the set intensity of the laser light La. According to the knowledge of the present inventors, the temperature of the liquid crystal layer 115 deviates from the temperature detected by the temperature sensor 14 in proportion to the intensity of the laser light La input to the liquid crystal layer 115. By determining the set temperature of the cooling unit 15 in proportion to the set intensity of the laser light La, the temperature of the liquid crystal layer 115 can be made closer to a constant regardless of the intensity of the laser light La incident on the liquid crystal layer 115. As a result, the actual phase modulation amount can be made closer to the target phase modulation amount with better accuracy. Therefore, the deviation of the actual phase modulation amount from the target phase modulation amount can be further reduced.

[0096] [Second embodiment]

[0097] Next, a second embodiment of the present invention is described. In this embodiment, the control unit 7 determines the magnitude of the voltage applied to the plurality of pixel electrodes 114 instead of determining the set temperature of the cooling unit 15. That is, the control unit 7 determines the magnitude of the voltage applied to the plurality of pixel electrodes 114 in such a manner that when the phase of each pixel of the liquid crystal layer 115 is set to a predetermined phase, the greater the set intensity of the laser light La, the greater the voltage corresponding to the predetermined phase.

[0098] Fig.15 This is a diagram showing an example of the relationship between grayscale value and phase modulation amount. The horizontal axis represents grayscale value, and the vertical axis represents phase modulation amount (πrad). In this diagram, an approximate straight line Q5 representing the relationship when the light intensity of laser La is 10W, and an approximate straight line Q6 representing the relationship when the light intensity of laser La is 100W are shown. Fig.15 It can be seen that, when the grayscale value is the same, the phase modulation amount decreases as the light intensity of the laser La increases. The reason for this is that, as described in the first embodiment, as the light intensity of the laser La increases, the temperature of the liquid crystal layer 115 deviates from the set temperature of the cooling unit 15 and increases, and the refractive index of the liquid crystal layer 115 decreases accordingly. Therefore, in this embodiment, as the set intensity of the laser La increases, the applied voltage corresponding to the specified phase increases, and the phase modulation amount is kept constant regardless of the change in the set intensity of the laser La.

[0099] Specifically, the control unit 7 holds correlation data in advance, and the correlation data is displayed in a lookup table (for example, reference table 110 ) showing the relationship between the magnitude of the voltage applied to the pixel electrode 114 and each of the plurality of grayscale values, which is held by the external control substrate 17. Figure 6 ) and the correlation between the total number of grayscales used in and the set intensity of laser La. Fig.16is a graph showing an example of such correlation data. In this graph, the horizontal axis represents the light intensity of the laser La, and the vertical axis represents the total number of grayscales. In the figure, plot P7 shows the measured value of the grayscale value relative to the set intensity of the laser La when the phase modulation amount is kept constant. Q7 in the figure is its approximate straight line. Fig.16 As shown, when the phase modulation amount is constant, the set intensity of laser La and the grayscale value have a substantially linear relationship. The control unit 7 uses such correlation data to determine the total number of grayscales used in the lookup table held by the external control substrate 17 based on the set intensity of laser La.

[0100] Furthermore, the control unit 7 has reference data showing the correspondence between the phase modulation amount by the liquid crystal layer 115 and each grayscale value of the lookup table. Fig.17 (a) and (b) are diagrams showing examples of such reference data. Fig.17 The reference data shown in (a) shows the correspondence between the phase modulation amounts of 0 (rad) to 2.1π (rad) and the grayscale values ​​of 0 to 244 when the total grayscale number is 245. Fig.17 The reference data shown in (b) shows the correspondence between the phase modulation amount 0 (rad) to 2.1π (rad) and the grayscale value 0 to 250 when the total grayscale number is 251. Fig.16 The correlation data shown in the figure are obtained by setting the total grayscale number to 245 when the intensity of the laser La is set to 70W. Fig.17 In addition, the control unit 7 refers to the reference data shown in (a). Fig.16 The correlation data shown in the figure are obtained by setting the total grayscale number to 251 when the intensity of the laser La is set to 140W. Fig.17 The reference data shown in (b).

[0101] The control unit 7 of this embodiment receives an input value indicating a target phase modulation amount from the outside of the optical modulation device 1A. The control unit 7 uses Fig.17 The control unit 7 converts the input value into a grayscale value. The control unit 7 provides the converted grayscale value to the light modulation element 11. The light modulation element 11 determines the applied voltage corresponding to the grayscale value using the lookup table and applies the applied voltage to the pixel electrode 114.

[0102] Fig.181 is a flowchart showing a control method of the spatial light modulator 10 of the present embodiment. First, the control unit 7 determines the magnitude of the voltage applied to each pixel electrode 114 in such a manner that, when the phase of each pixel of the liquid crystal layer 115 is set to a predetermined phase, the greater the set intensity of the laser light La, the greater the voltage corresponding to the predetermined phase (determination step S21). At this time, the control unit 7 uses a lookup table (e.g., reference table 114) indicating the relationship between the magnitude of the display applied voltage and each of the plurality of grayscale values. Figure 6 ) and the correlation data of the total grayscale number used in the setting intensity of the laser La (for example, reference Fig.16 ), based on the set intensity of the laser La, the total number of grayscales used in the lookup table is determined. Furthermore, the control unit 7 has reference data (e.g., reference 1) that shows the correspondence between the phase modulation amount caused by the liquid crystal layer 115 and each grayscale value in the lookup table. Fig.17 ), and the input value of the phase modulation amount is displayed from the external input of the optical modulation device 1A, and the input value is converted into a grayscale value using reference data.

[0103] Next, laser light La having an intensity corresponding to the above-mentioned set intensity is input to the liquid crystal layer 115 of the light modulator 11 (light input step S22 ). The laser light La is phase-modulated for each pixel in the liquid crystal layer 115 , and the light modulator 11 outputs the modulated laser light Lb.

[0104] The effects obtained by the light modulation device 1A of the present embodiment and the control method of the spatial light modulator 10 of the present embodiment described above are summarized as follows. As described above, when the intensity of the laser light La incident on the liquid crystal layer 115 increases, the temperature of the liquid crystal layer 115 increases significantly due to the energy of the laser light La, and the temperature deviation between the liquid crystal layer 115 and the temperature sensor 14 increases. Since the refractive index of the liquid crystal decreases as the temperature increases, the phase modulation amount caused by the liquid crystal layer 115 when a certain voltage is applied decreases as the temperature of the liquid crystal layer 115 increases (that is, the intensity of the laser light La input to the liquid crystal layer 115 increases). Therefore, in the light modulation device 1A of the present embodiment and the control method of the spatial light modulator 10 of the present embodiment, the magnitude of the voltage applied to each pixel electrode 114 is determined in the control unit 7 or the determination step S21 so that when the phase of each pixel of the liquid crystal layer 115 is set to a predetermined phase, the larger the set intensity of the laser light La, the larger the voltage corresponding to the predetermined phase. Thus, even if the temperature of the liquid crystal layer 115 changes with the intensity of the laser light La, the actual phase modulation amount can be made close to the target phase modulation amount with good accuracy. Therefore, according to the light modulation device 1A of this embodiment and the control method of the spatial light modulator 10 of this embodiment, the deviation of the actual phase modulation amount from the target phase modulation amount can be reduced.

[0105] As in the present embodiment, the control unit 7 or the determination step S21 can use the correlation data indicating the correlation between the total number of grayscales used in the lookup table showing the relationship between the magnitude of the voltage applied to each pixel electrode 114 and each of the plurality of grayscale values ​​and the set intensity of the laser La to determine the total number of grayscales used in the lookup table based on the set intensity of the laser La. In this case, the magnitude of the applied voltage can be easily determined according to the set intensity of the laser La in the control unit 7 or the determination step S21.

[0106] As in this embodiment, in the control unit 7 or in the determination step S21, an input value of the display phase modulation amount can be input from the outside of the light modulation device 1A, and the input value can be converted into a grayscale value using reference data corresponding to the phase modulation amount caused by the display liquid crystal layer 115 and each grayscale value of the lookup table. In this case, a person who uses the light modulation device 1A (or the control method) can freely set the phase modulation amount. In this embodiment, the external control substrate 17 or the drive circuit layer 119 of the light modulation element 11 can also have the function of the control unit 7.

[0107] [Modifications]

[0108] In the above-mentioned second embodiment, the control unit 7 uses the correlation data showing the correlation between the total grayscale number used in the lookup table and the set intensity of the laser La to determine the total grayscale number based on the set intensity of the laser La. In contrast, in this variant, the control unit 7 maintains a plurality of lookup tables with different total grayscale numbers. The fact that the control unit 7 has the correlation data showing the correlation between the total grayscale number and the set intensity of the laser La is the same as in the second embodiment. The control unit 7 of this variant uses the correlation data to determine the lookup table used in the plurality of lookup tables based on the set intensity of the laser La, and provides the lookup table to the external control substrate 17. Then, the control unit 7 displays the input value of the phase modulation amount from the external input of the optical modulation device 1A, as in the second embodiment. The control unit 7 maintains a plurality of reference data showing the correspondence between the phase modulation amount caused by the liquid crystal layer 115 and each grayscale value of each of the plurality of lookup tables. The control unit 7 uses the reference data corresponding to the lookup table used among the plurality of reference data to convert the input value into a grayscale value.

[0109] As in this modification, the control unit 7 or the determination step S21 can use the correlation data showing the correlation between the total grayscale number and the set intensity of the laser La to determine the lookup table to be used among the plurality of lookup tables having different total grayscale numbers based on the set intensity of the laser La. In this case, the control unit 7 or the determination step S21 can easily determine the magnitude of the applied voltage according to the set intensity of the laser La.

[0110] As in this modification, in the control unit 7 or in the determination step S21, an input value of the display phase modulation amount can be input from the outside of the light modulation device 1A, and the input value can be converted into a grayscale value using a reference data corresponding to the phase modulation amount caused by the display liquid crystal layer 115 and each grayscale value of each of the plurality of lookup tables, which corresponds to the reference data corresponding to the lookup table used. In this case, a person who uses the light modulation device 1A (or the control method) can freely set the phase modulation amount. In addition, in this modification, the external control substrate 17 or the drive circuit layer 119 of the light modulation element 11 can also have the function of the control unit 7.

[0111] The control method of the light modulation device and the spatial light modulator of the present invention is not limited to the above-mentioned embodiment, and various other modifications can be made. For example, the control unit of the light modulation device can also have the functions of the control unit 7 of the first embodiment and the functions of the control unit 7 of the second embodiment. That is, the control unit can simultaneously reduce the set temperature of the cooling unit 15 as the set intensity of the laser La increases, and increase the applied voltage corresponding to the specified phase as the set intensity of the laser La increases.

[0112] In the first embodiment described above, the control unit 7 determines the set temperature of the cooling unit 15 using a data table or a calculation formula showing the relationship between the set intensity of the laser La and the set temperature of the cooling unit 15, but the method of determining the set temperature of the cooling unit 15 is not limited to this. In the first embodiment described above, the set temperature of the cooling unit 15 is proportional to the set intensity of the laser La, but the relationship between the set temperature of the cooling unit 15 and the set intensity of the laser La is not limited to a proportional relationship.

[0113] In each of the above-mentioned embodiments, the Peltier element is exemplified as the cooling unit, but the cooling unit may have other structures (for example, water cooling by a water cooling plate, etc.).

[0114] Explanation of symbols

[0115] 1A...light modulation device, 2...test device, 3...light source, 4...mirror, 5...imaging optical system, 6...condensing lens, 7...control unit, 10...spatial light modulator, 11...light modulation element, 11a...light incident and exit surfaces, 11b...back surface, 12...substrate, 12a...first surface, 12b...second surface, 12c...opening, 13...metal block, 14...temperature sensor, 15...cooling unit, 16...temperature adjustment unit, 17...external control substrate, 20...container, 21...housing, 21a, 21b, 21d, 21e...side surfaces, 21c...optical window, 21f...opening, 22...heat sink, 23...fan, 31...laser light source, 32...1 / 2 wavelength plate, 33... 38…polarizing beam splitter, 34, 39…light absorber, 35…beam expander, 36a, 36b…dielectric mirror, 37…homogenizer, 40…aperture, 41, 42…reflecting surface, 43…power meter, 51, 52…lens, 110…silicon substrate, 112…glass substrate, 112a…surface, 112b…back surface, 113…transparent conductive film, 114…pixel electrode, 115…liquid crystal layer, 115a, 115b…alignment film, 116…transparent layer, 117…dielectric multilayer film, 118…light shielding film, 119…driving circuit layer, B…object, D1, D2…direction, La, Lb…laser, Lc, Ld…test light, Q1 to Q6…approximate straight line.

Claims

1. A light modulation device, wherein: have: a light source configured to output light having an intensity corresponding to a set intensity; A spatial light modulator comprising: a plurality of pixel electrodes arranged one-dimensionally or two-dimensionally, a liquid crystal layer configured to modulate the phase of the light according to the magnitude of the electric field formed by each of the plurality of pixel electrodes, a driving unit configured to apply a voltage to the plurality of pixel electrodes, and a cooling unit configured to cool the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature; and The control unit is configured to determine the set temperature of the cooling unit based on the set intensity.

2. The light modulation device according to claim 1, wherein: The control unit stores in advance a data table indicating the relationship between the set intensity and the set temperature, and determines the set temperature using the data table.

3. The light modulation device according to claim 1, wherein: The control unit stores in advance a calculation formula indicating the relationship between the set intensity and the set temperature, and determines the set temperature using the calculation formula.

4. The light modulation device according to any one of claims 1 to 3, wherein: The set temperature is proportional to the set intensity.

5. A light modulation device, wherein: have: a light source configured to output light having an intensity corresponding to a set intensity; A spatial light modulator comprising: a plurality of pixel electrodes arranged one-dimensionally or two-dimensionally, a liquid crystal layer configured to modulate the phase of the light according to the magnitude of the electric field formed by each of the plurality of pixel electrodes, a driving unit configured to apply a voltage to the plurality of pixel electrodes, and a cooling unit configured to cool the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature; and a control unit configured to determine the magnitude of the voltage applied to the plurality of pixel electrodes, When setting the phase of each pixel of the liquid crystal layer to a predetermined phase, the control unit determines the magnitude of the voltage so that the voltage corresponding to the predetermined phase becomes larger as the setting intensity becomes larger.

6. The light modulation device according to claim 5, wherein: The control unit has correlation data indicating the correlation between the total number of grayscales used in a lookup table indicating the relationship between the magnitude of the voltage and each of a plurality of grayscale values ​​and the set intensity, The control section determines the total number of grayscales used in the lookup table based on the set intensity using the correlation data.

7. The light modulation device according to claim 6, wherein: The control unit has reference data representing the correspondence between the phase modulation amount caused by the liquid crystal layer and the plurality of grayscale values ​​of the lookup table, and an input value representing the phase modulation amount is input from the outside of the light modulation device, and the input value is converted into a grayscale value using the reference data.

8. The light modulation device according to claim 5, wherein: The control unit uses correlation data indicating a correlation between the total grayscale number and the set intensity to determine, based on the set intensity, a lookup table to be used among a plurality of lookup tables indicating a relationship between the voltage and each of a plurality of grayscale values ​​and having different total grayscale numbers.

9. The light modulation device according to claim 8, wherein: The control unit has a plurality of reference data representing the correspondence between the phase modulation amount caused by the liquid crystal layer and the plurality of grayscale values ​​of the plurality of lookup tables, and an input value representing the phase modulation amount is input from the outside of the light modulation device, and the input value is converted into a grayscale value using the reference data corresponding to the lookup table used among the plurality of reference data.

10. A method for controlling a spatial light modulator, wherein: is a method for controlling a spatial light modulator, The spatial light modulator comprises: a plurality of pixel electrodes arranged one-dimensionally or two-dimensionally, a liquid crystal layer configured to modulate the phase of light according to the magnitude of the electric field formed by each of the plurality of pixel electrodes, a driving unit configured to apply voltage to the plurality of pixel electrodes, and a cooling unit configured to cool the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature. The control method of the spatial light modulator comprises: a determining step of determining the set temperature of the cooling unit; and a light input step of inputting light having an intensity corresponding to a set intensity into the liquid crystal layer, In the determining step, the set temperature is determined based on the set intensity.

11. A method for controlling a spatial light modulator, wherein: is a method for controlling a spatial light modulator, The spatial light modulator comprises: a plurality of pixel electrodes arranged one-dimensionally or two-dimensionally, a liquid crystal layer configured to modulate the phase of light according to the magnitude of the electric field formed by each of the plurality of pixel electrodes, a driving unit configured to apply voltage to the plurality of pixel electrodes, and a cooling unit configured to cool the liquid crystal layer in such a manner that the temperature of the liquid crystal layer approaches a set temperature. The control method of the spatial light modulator comprises: a determining step of determining the magnitude of the voltage applied to each pixel electrode; and a light input step of inputting light having an intensity corresponding to a set intensity into the liquid crystal layer, In the determination step, when the phase of each pixel of the liquid crystal layer is set to a predetermined phase, the magnitude of the voltage is determined in such a manner that the voltage corresponding to the predetermined phase becomes larger as the setting intensity becomes larger.

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