Patent Application
20150185523
The present invention relates to a light modulation method, a light modulation program, a light modulation device, and a light irradiation device using the same, which modulate a phase of light such as laser light with a modulation pattern presented on a plurality of pixels of a spatial light modulator.
A spatial light modulator (SLM: Spatial Light Modulator) is an optical device used for control of light. In particular, a phase-modulation type spatial light modulator is to modulate a phase of input light, and output phase-modulated light, and is capable of not modulating an amplitude, and changing only a phase of the input light, to output the light (refer to, for example, Patent Document 1, and Non-Patent Documents 1 to 5).
As one of the features of this phase-modulation type SLM, it is included that it is possible to shape its wave front by modulating a phase of light, so as to generate multispot light condensing points having different spatial positions from a single light source and at temporally same timing. By use of multispot simultaneous irradiation of light with a multispot pattern generated by a phase-modulation type SLM, it is possible to execute, for example, simultaneous processing at a plurality of positions in laser processing, simultaneous observation of a plurality of positions in the purpose of a laser scanning microscope, and the like without loss of light amount.
As an example of utilization of a phase-modulation type SLM, a case where a multispot irradiation pattern with 10 points is generated by performing phase modulation onto laser light supplied from a single laser light source by the SLM, to perform multispot simultaneous processing of a processing object by use of this irradiation pattern will be considered. In this case, as compared with the conventional laser processing using only one light condensing point by a laser light source, there is the advantage that a processing speed for an object increases tenfold by use of the phase-modulation type SLM.
In a phase-modulation type SLM, there are advantages that it is possible to achieve speed-up of laser processing, etc., by parallel processing utilizing multispot simultaneous irradiation as described above, and the like. On the other hand, in laser light irradiation performed by use of an SLM in this way, in addition to a desired irradiation pattern due to phase-modulated laser light output from the SLM, unexpected laser light irradiation due to undesired zeroth-order light generated by the SLM may become a problem in some cases.
Here, undesired zeroth-order light is basically generated by a light component which is not modulated in the SLM. Such a light component is condensed as unexpected light on a focal position on which a plane wave is condensed by a lens in the case, for example, where the lens is disposed at the subsequent stage of the SLM. When such undesired zeroth-order light is generated, in the case where laser light modulated by a phase-modulation type SLM is utilized, the problems such as, for example, causing unexpected processing onto an object other than a planned processing point in laser processing, variation and deterioration of the observation conditions for an object due to the influence of the undesired zeroth-order light in a laser scanning microscope, and the like are caused.
The present invention has been achieved in order to solve the above-described problem, and an object thereof is to provide a light modulation method, a light modulation program, a light modulation device, and a light irradiation device which are capable of suppressing the generation of undesired zeroth-order light by an SLM.
In order to achieve the above-described object, a light modulation method according to the present invention, (1) which uses a phase-modulation type spatial light modulator having a plurality of two-dimensionally arrayed pixels, modulating a phase of input light for each pixel with a modulation pattern presented on the plurality of pixels, and outputting phase-modulated light, the light modulation method includes (2) a modulation pattern setting step of setting a target modulation pattern for modulating the phase of the light in the spatial light modulator, (3) a correction coefficient setting step of setting a correction coefficient α of α≧1 according to pixel structure characteristics of the spatial light modulator and pattern characteristics of the target modulation pattern, for the target modulation pattern, (4) a modulation pattern correction step of determining a corrected modulation pattern to be presented on the plurality of pixels of the spatial light modulator by multiplying the target modulation pattern by the correction coefficient α, and (5) a modulation pattern presentation step of presenting the corrected modulation pattern on the plurality of pixels of the spatial light modulator.
A light modulation program according to the present invention, (1) which uses a phase-modulation type spatial light modulator having a plurality of two-dimensionally arrayed pixels, modulating a phase of input light for each pixel with a modulation pattern presented on the plurality of pixels, and outputting phase-modulated light, the light modulation program makes a computer execute (2) modulation pattern setting processing of setting a target modulation pattern for modulating the phase of the light in the spatial light modulator, (3) correction coefficient setting processing of setting a correction coefficient α of α≧1 according to pixel structure characteristics of the spatial light modulator and pattern characteristics of the target modulation pattern, for the target modulation pattern, (4) modulation pattern correction processing of determining a corrected modulation pattern to be presented on the plurality of pixels of the spatial light modulator by multiplying the target modulation pattern by the correction coefficient α, and (5) modulation pattern presentation processing of presenting the corrected modulation pattern on the plurality of pixels of the spatial light modulator.
A light modulation device according to the present invention includes (a) a phase-modulation type spatial light modulator having a plurality of two-dimensionally arrayed pixels, modulating a phase of input light for each pixel with a modulation pattern presented on the plurality of pixels, and outputting phase-modulated light, (b) modulation pattern setting means setting a target modulation pattern for modulating the phase of the light in the spatial light modulator, (c) correction coefficient setting means setting a correction coefficient α of α≧1 according to pixel structure characteristics of the spatial light modulator and pattern characteristics of the target modulation pattern, for the target modulation pattern, and (d) modulation pattern correction means determining a corrected modulation pattern to be presented on the plurality of pixels of the spatial light modulator by multiplying the target modulation pattern by the correction coefficient α.
In the light modulation method, the light modulation program, and the light modulation device described above, with respect to the phase modulation patterns to be presented on the spatial light modulator, a target modulation pattern is set so as to correspond to a desired irradiation pattern or the like of light such as laser light. Then, with respect to the phase modulation of light which is actually executed in the spatial light modulator with this target modulation pattern, the two-dimensional pixel structure characteristics of the plurality of pixels in the spatial light modulator, and the pattern characteristics of the target modulation pattern are focused, and a correction coefficient α of 1 or more (α≧1) is set according to these pixel structure characteristics and pattern characteristics. In accordance with such a configuration, a corrected modulation pattern generated by multiplying the target modulation pattern by the correction coefficient α is presented on the plurality of pixels of the spatial light modulator, thereby it is possible to suppress the generation of undesired zeroth-order light in phase modulation of light in the spatial light modulator.
A light irradiation device according to the present invention includes a light source which supplies light serving as a modulation object, and a light modulation device having the above-described configuration including a phase-modulation type spatial light modulator which modulates a phase of the light supplied from the light source, and outputs the phase-modulated light. Further, in the case where the light serving as a modulation object is laser light, a laser light irradiation device includes a laser light source which supplies laser light, and a light modulation device having the above-described configuration including a phase-modulation type spatial light modulator which modulates a phase of the laser light supplied from the laser light source, and outputs the phase-modulated laser light.
In accordance with such a configuration, in the light modulation device including the phase-modulation type spatial light modulator, a modulation pattern corrected by multiplying the target modulation pattern by the correction coefficient α is presented on the plurality of pixels of the spatial light modulator, thereby it is possible to suppress the generation of undesired zeroth-order light in phase modulation of light, and it is possible to appropriately achieve operations such as irradiation of light onto an object with a desired irradiation pattern, and processing, observation, etc. of the object by irradiation. Such a light irradiation device is available as, for example, a laser processing device, a laser microscope, a laser manipulation device, or as an aberration correction device for a laser scanning ophthalmoscope or the like.
In accordance with the light modulation method, the light modulation program, the light modulation device, and the light irradiation device using the same of the present invention, a target modulation pattern is set with respect to a modulation pattern to be presented on the spatial light modulator, and a correction coefficient α of 1 or more is set according to the pixel structure characteristics of the plurality of pixels in the spatial light modulator, and the pattern characteristics of the target modulation pattern, and a modulation pattern corrected by multiplying the target modulation pattern by the correction coefficient α is presented on the spatial light modulator, thereby it is possible to inhibit the generation of undesired zeroth-order light in phase modulation of light in the spatial light modulator.
Hereinafter, embodiments of a light modulation method, a light modulation program, a light modulation device, and a light irradiation device according to the present invention will be described in detail with reference to the drawings. In addition, in the description of the drawings, the same components are denoted by the same reference symbols, and overlapping descriptions thereof will be omitted. Further, the dimensional ratios in the drawings are not necessarily matched to those in the description.
First, the basic configurations of a light modulation device and a light irradiation device including the light modulation device according to the present invention will be described along with their configuration examples. Here, the descriptions are made below assuming mainly laser light as light serving as a modulation object by a spatial light modulator. However, the light serving as a modulation object is not limited to laser light.
In the configuration shown in
The laser light source 10 is laser light supply means for supplying laser light such as pulsed laser light for irradiating the object 50 on the stage 58. The laser light output from the laser light source 10 is expanded by a beam expander 11, and is thereafter input to the light modulation device 2A including a spatial light modulator (SLM) 20 via reflecting mirrors 12 and 13.
The light modulation device 2A according to the present embodiment includes the spatial light modulator 20, a light modulator driving device 28, and a light modulation control device 30. The SLM 20 is a phase-modulation type spatial light modulator having a plurality of two-dimensionally arrayed pixels, and modulates a phase of input laser light for each pixel with a two-dimensional modulation pattern presented on the plurality of pixels, and outputs the phase-modulated laser light. In such a configuration, for example, a phase modulation pattern such as a hologram (CGH: Computer Generated Hologram) which is determined by a numerical calculation is presented on the SLM 20, and with this modulation pattern, light condensing irradiation of the laser light onto a set light condensing point is controlled.
Further, the spatial light modulator 20 is drive-controlled by the light modulation control device 30 via the driving device 28. The control device 30 performs generation and storage of a CGH to be presented on the SLM 20, transmission of a necessary signal to the driving device 28, and the like. Further, the driving device 28 converts the signal of the CGH transmitted from the control device 30 into a voltage instruction value with reference to a LUT (Look Up Table), and then performs an instruction to apply a voltage to the SLM 20. The LUT used here is, for example, a reference table which is used at the time of converting an input signal from the control device 30 corresponding to a phase value into a voltage instruction value in order to correct a nonlinear response, etc., to a voltage that a liquid crystal used for the SLM 20 has. In addition, the detailed configuration and the like of the light modulation device 2A including the SLM 20, the driving device 28, and the control device 30 will be described later.
This spatial light modulator 20 may be a reflective type, or may be a transmissive type.
The laser light which is phase-modulated into a predetermined pattern in the spatial light modulator 20, to be output is propagated to an objective lens 53 by a 4f optical system composed of lenses 51 and 52. Then, a single light condensing point or a plurality of light condensing points which are set on the surface or the inside of the irradiation object 50 are irradiated with the laser light by this objective lens 53.
In addition, the configuration of the optical system in the laser light irradiation device 1A is specifically not limited to the configuration shown in
Further, the movable stage 58 which moves the irradiation object 50 may be configured, for example, such that this stage is a fixed stage, or a movable stage moving in only an optical axis direction, and a movable mechanism, a Galvano mirror, or the like may be provided on the optical system side. Further, as the laser light source 10, a pulsed laser light source, for example, such as Nd:YAG laser light source, a femtosecond laser light source, which supplies pulsed laser light is preferably used.
The configuration of the phase-modulation type spatial light modulator 20 used in the laser light irradiation device 1A and the light modulation device 2A shown in
In this configuration example, the SLM 20 has a silicon substrate 21, and a liquid crystal layer 22 provided on the silicon substrate 21. Further, the SLM 20 further has a pixel electrode group 23 disposed between the silicon substrate 21 and the liquid crystal layer 22, and an electrode 24 which is provided at a position sandwiching the liquid crystal layer 22 with the pixel electrode group 23. The pixel electrode group 23 is composed of a plurality of pixel electrodes 23a for applying a voltage to the liquid crystal layer 22. These plurality of pixel electrodes 23a are two-dimensionally arrayed in a plurality of rows and a plurality of columns, thereby defining a two-dimensional pixel structure by a plurality of pixels composing the SLM 20.
On the other hand, the electrode 24 is, for example, formed of a metal film vapor-deposited on one surface of a glass substrate 25, and this metal film is optically transparent. The glass substrate 25 is supported on the silicon substrate 21 via a spacer 26 such that the above-described one surface of the substrate 25 and the silicon substrate 21 face each other. Further, the liquid phase layer 22 is configured so as to fill a liquid crystal between the silicon substrate 21 and the glass substrate 25.
In the SLM 20 including this configuration, an analog signal voltage for each pixel output from the driving device 28 is applied between the corresponding pixel electrode 23a and the electrode 24. Thereby, an electric field is generated in the liquid crystal layer 22 sandwiched between the pixel electrode group 23 and the electrode 24. Then, as shown in (b) in
Here, in the case where laser light irradiation is performed by use of the phase-modulation type SLM 20 having the plurality of two-dimensionally arrayed pixels as in the configuration example shown in
In addition, in this configuration, the light modulation control device 30 in which design, correction, storage, and the like of a modulation pattern (CGH) are carried out may be composed of a computer, for example. Further, respective devices such as an input device 37 used for inputting information, instructions, and the like necessary for light modulation control, and a display device 38 used for displaying information for an operator are connected to this control device 30 as needed.
The modulation pattern setting unit 31 is modulation pattern setting means (a modulation pattern setting step) for setting a target modulation pattern for modulating a phase of laser light in the SLM 20 with respect to the SLM 20 having the plurality of pixels two-dimensionally arrayed. A CGH used as a target modulation pattern may be prepared, for example, by the design methods described in Non-Patent Documents 1 to 4 with reference to a desired reconstructed pattern in laser light irradiation, etc. The design of a CGH in the setting unit 31 using these methods is carried out under ideal conditions under which undesired zeroth-order light is not generated.
The correction coefficient setting unit 32 is correction coefficient setting means (a correction coefficient setting step) for setting a correction coefficient α of 1 or more (α≧1) according to the pixel structure characteristics of the SLM 20 (refer to
Further, a correction coefficient storage unit 33 and a correction coefficient derivation unit 34 are provided for the correction coefficient setting unit 32. The correction coefficient storage unit 33 is storage means for storing a correction coefficient α which is determined in advance according to the pattern characteristics of the target modulation pattern so as to correspond to the target modulation pattern. Further, the correction coefficient derivation unit 34 is derivation means (a correction coefficient derivation step) for determining a correction coefficient α according to the pattern characteristics of the target modulation pattern with reference to the target modulation pattern. The setting unit 32 uses the storage unit 33 or the derivation unit 34 as needed, to acquire a correction coefficient α corresponding to a target modulation pattern.
The modulation pattern correction unit 35 is modulation pattern correction means (a modulation pattern correction step) for determining a corrected modulation pattern to be actually presented on the plurality of pixels of the SLM 20 by multiplying the target modulation pattern by the correction coefficient α. Here, given that a two-dimensional pixel position on a plane (modulation plane) perpendicular to an optical axis of each pixel composing the SLM 20 is (x, y), a target modulation pattern prepared in the setting unit 31 is φCGH(x, y), and a corrected modulation pattern in the correction unit 35 is φSLM(x, y), the corrected modulation pattern φSLM is determined as follows.
φSLM(x,y)=φCGH(x,y)×α
The light modulator drive control unit 36 is drive control means (a modulation pattern presentation step) which drive-controls the SLM 20 via the driving device 28, to present the corrected modulation pattern φSLM created by the modulation pattern correction unit 35, on the plurality of pixels of the SLM 20. This drive control unit 36 is provided as needed in accordance with the detailed configuration of the light modulation device 2A including the SLM 20, the driving device 28, and the control device 30.
It is possible to achieve processing corresponding to the light modulation method executed in the light modulation control device 30 shown in
Further, the above-described program for causing the CPU to execute the respective processing for a laser light modulating operation by use of the SLM 20, in particular, for design and correction of a modulation pattern to be presented on the SLM 20 may be recorded on a computer-readable recording medium, to be distributed. As such a recording medium, for example, a magnetic medium such as a hard disk or a flexible disk, an optical medium such as a CD-ROM or a DVD-ROM, a magnetooptic medium such as a floptical disk, or a hardware device such as a RAM, a ROM, or a semiconductor nonvolatile memory which is specially arranged so as to execute or store program instructions, and the like, are included.
The effects of the light modulation method, the light modulation program, the light modulation device 2A, and the laser light irradiation device 1A according to the present embodiment will be described.
In the light modulation method, the light modulation program, and the light modulation device 2A shown in
In accordance with such a configuration, in the modulation pattern correction unit 35, a corrected modulation pattern φSLM is created by multiplying the target modulation pattern φCGH by the correction coefficient α, and the corrected modulation pattern φSLM is presented on the plurality of pixels of the SLM 20, thereby it is possible to suppress the generation of undesired zeroth-order light in phase modulation of laser light in the SLM 20. Further, in accordance with this, it is possible to appropriately and accurately achieve a phase modulation operation of laser light in the SLM 20, and control of an irradiation pattern of the laser light for the object 50 thereby.
Further, in the laser light irradiation device 1A shown in
Here, with respect to setting of a correction coefficient α in the correction coefficient setting unit 32, the configuration may be used in which the correction coefficient storage unit 33 which stores the correction coefficient α which is determined in advance according to the pattern characteristics so as to correspond to the target modulation pattern is provided, and the correction coefficient α is set in the setting unit 32 according to a coefficient read out from the storage unit 33. In this way, pattern characteristics of a modulation pattern to be presented on the SLM 20 are evaluated in advance, a coefficient α is determined according to the pattern characteristics, to be stored as coefficient data in the storage unit 33, and the coefficient data is read out as needed, to be set as a correction coefficient α, thereby it is possible to appropriately set the correction coefficient α corresponding to the target modulation pattern.
Or, with respect to setting of a correction coefficient α, the configuration may be used in which the correction coefficient derivation unit 34 which determines the correction coefficient α by a predetermined calculation or the like according to the pattern characteristics with reference to the target modulation pattern is provided, and the correction coefficient α is set in the setting unit 32 according to a coefficient determined by the derivation unit 34. In this way, pattern characteristics are evaluated by a calculation or the like with reference to a target modulation pattern which is set as a modulation pattern to be presented on the SLM 20, and a coefficient is determined according to the pattern characteristics, to set a correction coefficient α, thereby it is also possible to appropriately set the correction coefficient α corresponding to the target modulation pattern.
Further, the configuration may be used in which the correction coefficient α is set as a coefficient α(x, y) for each pixel dependent on a two-dimensional pixel position (x, y) of each of the plurality of pixels in the SLM 20. In the phase modulation pattern to be presented on the SLM 20, a case where a value of the correction coefficient α by which the modulation pattern is to be multiplied varies depending on a pixel position (x, y) in accordance with its specific pattern configuration may be considered. In contrast, with the configuration in which it is possible to set the correction coefficient α as a coefficient α(x, y) for each pixel as described above, thereby it is possible to appropriately execute correction of the modulation pattern. In this case, the corrected modulation pattern φSLM is determined as follows.
φSLM(x,y)=φCGH(x,y)×α(x,y)
Here, in the case where the dependence of a correction coefficient α on a pixel position is low or the like, a correction coefficient α may be a constant value independent of a pixel position.
Further, with respect to the pattern characteristics of the modulation pattern to be referenced in setting of a correction coefficient α, specifically, the configuration may be used in which a coefficient set according to spatial frequency characteristics of the target modulation pattern is used as the correction coefficient α. Or, the configuration may be used in which a coefficient set according to a point having a maximum diffraction angle in a reconstructed pattern of laser light phase-modulated with the target modulation pattern is used as the correction coefficient α. In this case, in particular, a coefficient set according to a distance between the point having the maximum diffraction angle in the reconstructed pattern of the laser light phase-modulated with the target modulation pattern and a light condensing point of zeroth-order light is preferably used as a correction coefficient α. In addition, a method of setting a correction coefficient α, or the like will be further described later in detail.
The phase modulation of laser light, the design and correction of a modulation pattern, and the like in the laser light irradiation device 1A and the light modulation device 2A shown in
First, generation of undesired zeroth-order light in phase modulation of laser light using the SLM 20 having the plurality of two-dimensionally arrayed pixels will be described. Undesired zeroth-order light is, as described above, generated by a light component which is not modulated in the SLM 20 due to the two-dimensional pixel structure or the like of the SLM 20. Such a light component is condensed as unexpected light on a focal position in the case, for example, where a lens is disposed at the subsequent stage of the SLM. In addition, in reality, because a wave front of output light is distorted by a distortion or the like in the SLM 20, a light condensing position of the undesired zeroth-order light may be slightly shifted from the above-described focal position in some cases.
The reason for that undesired zeroth-order light is called “unexpected light” is because this zeroth-order light is not generated at a stage of design or simulation of a CGH carried out under ideal conditions. Here,
A reconstructed pattern of laser light is determined by simulation by use of a target modulation pattern designed as described above, thereby reconstructing a multispot pattern which is the same as that in (a) in
The existence of such undesired zeroth-order light becomes a problem, particularly, in the case where a multispot laser light irradiation pattern is created to perform processing, and the like of an object. For example, in the case where a desired one-point laser light irradiation pattern and an undesired zeroth-order light spot pattern are reconstructed by the SLM 20, provided that the light component of 99% in the laser light is diffracted, and the light component of 1% becomes undesired zeroth-order light, an S/N ratio is to be 99. In such a case, provided that the energy of the undesired zeroth-order light is made to be less than or equal to a processing threshold value for an object by adjusting, etc., a light amount of the laser light input to the SLM, by utilizing that high S/N ratio, it is possible to avoid the influence of the undesired zeroth-order light.
Next, in consideration of the case where a desired 99-point laser light irradiation pattern and an undesired zeroth-order light pattern are reconstructed by the SLM 20, provided that the light component of 1% is diffracted to each point in the 99-point irradiation pattern, and the light component of 1% becomes undesired zeroth-order light, an S/N ratio per point is 1. In such a case, it is impossible to avoid the influence of the undesired zeroth-order light by merely adjusting a light amount of the laser light input to the SLM, and for example, an operation that, such as, the undesired zeroth-order light is masked to be blocked by any method, or a Fresnel lens pattern is added to a CGH presented on the SLM, thereby shifting reconstruction positions of the undesired zeroth-order light and the CGH in the optical axis direction, which defocuses the zeroth-order light on the reconstruction plane of the CGH, is required.
Further, in the above description, the multispot processing by the laser light is shown, however, generation of undesired zeroth-order light by the SLM becomes a problem, in addition to multispot processing, for the purpose of application using multispot such as a multispot laser scanning microscope, or further, in aberration correction of a single point such as a laser scanning ophthalmoscope, light condensing point position movement, and the like, and moreover, presents a problem on the overall purpose of performing phase modulation of laser light by the SLM such as correlation and LG beam reconstruction.
Such undesired zeroth-order light by the SLM is generated because the modulation pattern to be actually presented on the SLM is changed from the target modulation pattern designed under the ideal conditions due to the pixel structure characteristics held by the plurality of pixels of the SLM, and the phase modulation characteristics. Such a change in the modulation pattern in the SLM may be, for example, due to the influence of a pixel gap in the pixel structure of the SLM shown in
As the influence of a pixel gap in phase modulation in the SLM, in detail, for example, it may be considered that, because the liquid crystal in the pixel gap does not receive a voltage by the pixel electrode, phase modulation is not performed onto the light input to the pixel gap (Non-Patent Document 5). In this case, it has been considered that light components which have not been phase modulated in the pixel gap are condensed to become undesired zeroth-order light.
Meanwhile, it has been found out that, in reality, the influence by crosstalk between the pixels of the SLM by expansion of an electric field due to a pixel gap is great. This is because, a uniform voltage is applied to the electrode on the glass substrate side with respect to the structure which is partitioned in pixel units on the silicon substrate side, and therefore, crosstalk between the pixels of the SLM is caused by expansion of an electric field in the electrode on the glass substrate side. That is, in the liquid crystal in the pixel gap, although phase modulation is performed onto input laser light, the behavior becomes unstable under the influence of the adjacent pixels, and, as a result, the phase of the laser light input to the pixel gap becomes an unexpected value. In particular, in the case where a potential difference between a pixel and an adjacent pixel is large, a strong potential difference is generated laterally, and not only the pixel gap, but also the behavior of the liquid crystal inside the pixels may become unstable.
In the case where a phase pattern of such a blazed diffraction grating is presented on the SLM under the ideal conditions, undesired zeroth-order light is not generated in phase-modulated light output from the SLM. In contrast, when a phase modulation pattern is actually presented on the SLM, the presented pattern does not become an ideal stepwise phase pattern by crosstalk between the pixels due to the influence of the pixel structure including a pixel gap in the SLM, but a blunt shaped pattern as shown on the dashed line graph P2 of (b) in
In the laser light irradiation device 1A and the light modulation device 2A shown in
In addition, with respect to the phase modulation pattern to be presented on the SLM 20, the phase pattern for expressing the blazed diffraction grating is exemplified in
The suppression effect on undesired zeroth-order light from the SLM by the above-described correction formula of a modulation pattern using a correction coefficient α
φSLM(x,y)=φCGH(x,y)×α
was verified by use of a blazed diffraction grating phase modulation pattern.
In the verification results shown in
In addition, here, the verification was carried out with the patterns having only one spatial frequency component, however, an actual pattern such as a CGH has a plurality of spatial frequency components, and is influenced by a main spatial frequency component. A main spatial frequency component is composed of the outermost reconstructed point in many cases, meanwhile, for example, in the case where the energy of the outermost point is low, the influence by that point is small, and a point with a large diffraction angle and high energy after that outermost point have an influence as a main component.
Next, the effects of the correction coefficient α in the case where a complicated pattern other than a blazed diffraction grating is used were verified. In detail, phase modulation patterns corresponding to rectangular multispot reconstructed patterns with 2×2 points, 16×16 points, and 32×32 points at equal point intervals, which are respectively shown in
In the verification results shown in
Further, the values of the correction coefficient α by which the diffraction efficiency of the zeroth-order light is minimized are respectively α=1, 1.10, and 1.28 on the graphs B1, B2, and B3, which were different values according to a modulation pattern. Further, the diffraction efficiencies of the zeroth-order light at this time are respectively 0.8%, 0.7%, and 0.7%, that is generation of undesired zeroth-order light is suppressed in each case as compared with the case where the correction coefficient is α=1. In this way, it is possible to easily suppress the generation of zeroth-order light by multiplying the phase modulation pattern presented on the SLM by a correction coefficient α set according to its pattern characteristics.
Next, verification of the effect of a correction coefficient α was carried out with respect to the multispot reconstructed patterns of which the positions of the outermost reconstructed point are equal. In detail, phase modulation patterns corresponding to rectangular multispot reconstructed patterns with 20×20 points, 10×10 points, and 2×2 points of which the positions of the outermost reconstructed points (corresponding to a point having a maximum diffraction angle in a reconstructed pattern) are equal, and which are respectively shown in
In the verification results shown in
The setting and derivation of the correction coefficient α with respect to the target modulation pattern will be described. As shown in the respective specific examples described above, the optimum correction coefficient α is different for each CGH serving as a modulation pattern, and a coefficient α by which the intensity of zeroth-order light is minimized exists for each CGH. It is possible to determine an optimum correction coefficient α for a modulation pattern on the basis of a measurement result by use of an evaluation optical system or a calculation result by simulation or the like.
Then, the phase-modulated reflected laser light output from the SLM 20 is reflected by the half mirror 63, to be imaged as its light condensing reconstructed image by a photodetector 68 via a lens 64 and an aperture 65. With this reconstructed image of the laser light, it is possible to evaluate light condensing control of the laser light by phase modulation in the SLM 20, and a generation status of undesired zeroth-order light, and derive a correction coefficient α by conditions, for example, under which the intensity of zeroth-order light is minimized, and the like.
In addition, as the photodetector 68 that detects a light condensing reconstructed image, for example, a camera, a photodiode (PD), or the like may be used. Further, with respect to the configuration of an optical system including a spatial filter, a lens, a mirror, and the like, various configurations other than the example shown in
After an object modulation pattern is set, a value of a correction coefficient α for first evaluation for the pattern is set (S104), and a corrected modulation pattern φSLM
φSLM(x,y)=φCGH(x,y)×α
is determined by multiplying the modulation pattern φCGH by the correction coefficient α (S105). Then, this corrected modulation pattern φSLM is presented on the SLM, to measure the intensity I0 of zeroth-order light at that time (S106).
Moreover, the measured intensity value I0 is compared with the intensity minimum value Imin of the zeroth-order light at that point of time (S107). As a result of the comparison, in the case of I0<Imin, with the evaluated coefficient value α being set to a set value αD=αDesire of the correction coefficient α (αD=α), and Imin=I0, the intensity minimum value Imin of the zeroth-order light is replaced (S108). When it is I0≧Imin, the coefficient αD and the searched value Imin of the intensity minimum value are left as they are.
Then, with respect to the correction coefficient α for the modulation pattern, it is confirmed whether or not the evaluations with all the search values are completed (S109), and when it is not completed, a value of the correction coefficient α to be evaluated is changed (S104), and the measurement and evaluation shown in Steps S104 to S108 are repeatedly executed. When the evaluations for the correction coefficient α with all the search values are completed, a correction coefficient α for a modulation pattern serving as an object is determined, then the search is completed. Such derivation processing of a correction coefficient α can be manually executed by an operator, or automatically executed by use of a predetermined derivation program.
In addition, with respect to evaluation of undesired zeroth-order light and setting of a correction coefficient α for a phase modulation pattern to be presented on the SLM, as described above for
Further, in the case where there are a plurality of modulation patterns serving as setting objects for a correction coefficient α, as shown in a flowchart of
Or, in the case where there are a plurality of modulation patterns, as shown in a flowchart of
In addition, with respect to evaluation of undesired zeroth-order light generated in the SLM, and setting of a correction coefficient α, the configuration in which a light condensing reconstructed image of phase-modulated laser light is detected by the photodetector 68 is exemplified in the evaluation optical system of
Further, in the case where setting of a correction coefficient α is carried out for each of the plurality of phase modulation patterns used in the light modulation device 2A, as shown in
Further, for example, in the case where a coefficient set according to a point having a maximum diffraction angle in a reconstructed pattern is used, an optical system as in
Such an LUT is stored, for example, in the correction coefficient storage unit 33 in the configuration shown in
Here, with respect to pattern characteristics of a phase modulation pattern to be referenced at the time of setting a correction coefficient α, in the case where evaluation of undesired zeroth-order light and determination of a correction coefficient α are carried out by use of an evaluation optical system as described above, the pattern characteristics are taken into account through the evaluation and determination processing, to set a correction coefficient α corresponding to the pattern characteristics.
Further, as a correction coefficient α corresponding to the pattern characteristics, as described above, a coefficient set according to spatial frequency characteristics of the target modulation pattern may be used. For example, as shown in the graph of
Further, as a correction coefficient α, a coefficient set according to a point having a maximum diffraction angle in a reconstructed pattern of laser light phase-modulated with the target modulation pattern may be used. Further, in this case, for example, as a correction coefficient α, a coefficient set according to a distance between the point having the maximum diffraction angle in the reconstructed pattern of the laser light phase-modulated with the target modulation pattern and a light condensing point of zeroth-order light is preferably used.
For example, as shown in the graph of
Further, as described above, in addition to the configuration in which zeroth-order light is reduced by applying a correction coefficient α to a modulation pattern, a lens effect with a Fresnel lens pattern, a Fresnel zone plate, or the like may be given to a CGH as a modulation pattern, thereby defocusing the reconstruction position of the CGH and the zeroth-order light. Here, in the case where the intensity of undesired zeroth-order light is high, in order to prevent the influence of interference with a desired irradiation pattern of laser light, it is necessary to defocus the zeroth-order light at the CGH reconstruction position in a large way by enlarging a focal length of the Fresnel lens.
In such a case, because a phase of the Fresnel lens is increased by the square of a distance from the central portion, its phase gradient becomes steeper at the peripheral portion. Therefore, the influence may be exercised on the phase expression ability of the SLM, such as a lowering in the diffraction efficiency at the peripheral portion. In contrast, in the configuration in which a correction coefficient α is applied as described above, because the intensity of zeroth-order light is suppressed to be low, a focal length of the Fresnel lens becomes short, and its phase gradient becomes gradual. In accordance with this, it is expected to reduce the burden of the SLM.
Or, in addition to the configuration in which zeroth-order light is reduced by applying a correction coefficient α, a shielding plate or the like may be further disposed at a predetermined position of the optical system, thereby blocking zeroth-order light. In this case, because the intensity of the zeroth-order light is suppressed to be low by the correction coefficient α, an effect such as prevention of processing onto the shielding plate by the zeroth-order light is expected.
Further, a target modulation pattern φCGH(x, y) is usually designed within a range of phase values of 0 to 2π (rad), however, in the case of multiplying a correction coefficient α as described above, the phase values in the modulation pattern φSLM(x, y) obtained as a result may exceed the range of 0 to 2π (rad). Accordingly, as the spatial light modulator 20 used in the light modulation device 2A, it is preferable to use a modulator which is capable of expressing a phase whose position modulation amount exceeds a range of phase values set in normal CGH design.
Further, the light modulation method using a correction coefficient α as described above may be applied to stealth dicing laser processing of forming a modified layer by condensing laser light on the inside of an object such as silicon. In such laser processing, spherical aberration is caused by refractive-index mismatching, and the deeper the light condensing position is, the higher the influence by aberration is. Then, it has been proposed to carry out a correction of spherical aberration by use of an SLM (for example, refer to Patent Document 1).
Here, in the above-described aberration correction, the deeper the processing depth is, the higher the spatial frequency of an aberration correction pattern is. In particular, a lens effect is given to the aberration correction pattern described in Patent Document 1 in order to reduce a spatial frequency. Therefore, a light condensing point of the corrected laser light is reconstructed at a position different from that of the zeroth-order light, and accordingly, there are two light condensing points of the undesired zeroth-order light and desired light condensing laser light, as a result, it is impossible to perform desired processing onto an object. In contrast, in the configuration in which a correction coefficient α is applied to a modulation pattern as described above, it is possible to perform laser processing under good conditions by reducing undesired zeroth-order light.
The suppression effect on undesired zeroth-order light from the SLM with a corrected modulation pattern using a coefficient α (α≧1) will be further described.
Further,
Here, an aperture is not disposed in front of a camera which is a photodetector, but a condenser lens of f=250 mm is used, to show the results obtained by an optical system which is equivalent to that of
With respect to the suppression effect on undesired zeroth-order light from the SLM with a corrected modulation pattern using a coefficient α, a result with a cylindrical lens pattern is shown as another example. Here, the cylindrical lens pattern can be expressed, for example, as follows.
φc(x,y)=π(y−y0)2/λf
Here, in the above-described formula, λ is a wavelength of light input to the SLM, and f is a focal length of the lens.
Further,
The light modulation method, the light modulation program, the light modulation device, and the light irradiation device according to the present invention are not limited to the above-described embodiment and the configuration examples, and various modifications are possible. For example, the configuration of the entire optical system including the light modulation device, the light source, and the like is not limited to the configuration example shown in
Further, as light serving as a modulation object by the spatial light modulator, laser light is mainly considered in the above-described embodiment, meanwhile, the present invention may be generally applied to light other than laser light. As such light, for example, coherent light output from a light source such as a laser light source, an LD, or an SLD, incoherent light output from a light source such as a lamp light source, and scattering light, fluorescence, and the like generated by laser light irradiation are included. Coherent light can be used for laser processing, for example. Further, light from a lamp light source, scattering light, fluorescence, and the like may be used for a microscope, or a light-receiving side of a laser ophthalmoscope, for example.
A light modulation method according to the above-described embodiment, (1) which uses a phase-modulation type spatial light modulator having a plurality of two-dimensionally arrayed pixels, modulating a phase of input light for each pixel with a modulation pattern presented on the plurality of pixels, and outputting phase-modulated light, the light modulation method includes (2) a modulation pattern setting step of setting a target modulation pattern for modulating the phase of the light in the spatial light modulator, (3) a correction coefficient setting step of setting a correction coefficient α of α≧1 according to pixel structure characteristics of the spatial light modulator and pattern characteristics of the target modulation pattern, for the target modulation pattern, (4) a modulation pattern correction step of determining a corrected modulation pattern to be presented on the plurality of pixels of the spatial light modulator by multiplying the target modulation pattern by the correction coefficient α, and (5) a modulation pattern presentation step of presenting the corrected modulation pattern on the plurality of pixels of the spatial light modulator.
A light modulation program according to the above-described embodiment, (1) which uses a phase-modulation type spatial light modulator having a plurality of two-dimensionally arrayed pixels, modulating a phase of input light for each pixel with a modulation pattern presented on the plurality of pixels, and outputting phase-modulated light, the light modulation program makes a computer execute (2) modulation pattern setting processing of setting a target modulation pattern for modulating the phase of the light in the spatial light modulator, (3) correction coefficient setting processing of setting a correction coefficient α of α≧1 according to pixel structure characteristics of the spatial light modulator and pattern characteristics of the target modulation pattern, for the target modulation pattern, (4) modulation pattern correction processing of determining a corrected modulation pattern to be presented on the plurality of pixels of the spatial light modulator by multiplying the target modulation pattern by the correction coefficient α, and (5) modulation pattern presentation processing of presenting the corrected modulation pattern on the plurality of pixels of the spatial light modulator.
A light modulation device according to the above-described embodiment includes (a) a phase-modulation type spatial light modulator having a plurality of two-dimensionally arrayed pixels, modulating a phase of input light for each pixel with a modulation pattern presented on the plurality of pixels, and outputting phase-modulated light, (b) modulation pattern setting means for setting a target modulation pattern for modulating the phase of the light in the spatial light modulator, (c) correction coefficient setting means for setting a correction coefficient α of α≧1 according to pixel structure characteristics of the spatial light modulator and pattern characteristics of the target modulation pattern, for the target modulation pattern, and (d) modulation pattern correction means for determining a corrected modulation pattern to be presented on the plurality of pixels of the spatial light modulator by multiplying the target modulation pattern by the correction coefficient α.
Here, with respect to setting of a correction coefficient, the light modulation method may use a configuration in which the correction coefficient α which is determined in advance according to the pattern characteristics so as to correspond to the target modulation pattern, to be stored in correction coefficient storage means is used, and the correction coefficient setting step sets the correction coefficient α according to a coefficient read out of the correction coefficient storage means. In the same way, the light modulation program may use a configuration in which the correction coefficient α which is determined in advance according to the pattern characteristics so as to correspond to the target modulation pattern, to be stored in the correction coefficient storage means is used, and the correction coefficient setting processing sets the correction coefficient α according to a coefficient read out of the correction coefficient storage means. In the same way, the light modulation device may use a configuration which includes correction coefficient storage means for storing the correction coefficient α which is determined in advance according to the pattern characteristics so as to correspond to the target modulation pattern, and the correction coefficient setting means sets the correction coefficient α according to a coefficient read out of the correction coefficient storage means.
In this way, pattern characteristics of a modulation pattern to be presented on the spatial light modulator are evaluated in advance, a coefficient α is determined according to the pattern characteristics, to be stored as coefficient data in the storage means, and the coefficient data is read out as needed, to be set as a correction coefficient α, thereby it is possible to appropriately set the correction coefficient α corresponding to the target modulation pattern.
Or, with respect to setting of a correction coefficient, the light modulation method may use a configuration which includes a correction coefficient derivation step of determining the correction coefficient α according to the pattern characteristics with reference to the target modulation pattern, and the correction coefficient setting step sets the correction coefficient α according to a coefficient determined by the correction coefficient derivation step. In the same way, the light modulation program may use a configuration which includes correction coefficient derivation processing of determining the correction coefficient α according to the pattern characteristics with reference to the target modulation pattern, and the correction coefficient setting processing sets the correction coefficient α according to a coefficient determined by the correction coefficient derivation processing. In the same way, the light modulation device may use a configuration which includes correction coefficient derivation means for determining the correction coefficient α according to the pattern characteristics with reference to the target modulation pattern, and the correction coefficient setting means sets the correction coefficient α according to a coefficient determined by the correction coefficient derivation means.
In this way, the pattern characteristics are evaluated with reference to the target modulation pattern which is set as a modulation pattern to be presented on the spatial light modulator, and a coefficient α is determined according to the pattern characteristics, to set the correction coefficient α, thereby it is also possible to appropriately set the correction coefficient α corresponding to the target modulation pattern.
Further, with respect to a correction coefficient, the light modulation method may be configured such that, in the correction coefficient setting step, the correction coefficient α is set as a coefficient α(x, y) for each pixel dependent on a two-dimensional pixel position of each of the plurality of pixels in the spatial light modulator. In the same way, the light modulation program may be configured such that, in the correction coefficient setting processing, the correction coefficient α is set as a coefficient α(x, y) for each pixel dependent on a two-dimensional pixel position of each of the plurality of pixels in the spatial light modulator. In the same way, the light modulation device may be configured such that, in the correction coefficient setting means, the correction coefficient α is set as a coefficient α(x, y) for each pixel dependent on a two-dimensional pixel position of each of the plurality of pixels in the spatial light modulator.
In the phase modulation pattern to be presented on the spatial light modulator, a case where a value of the correction coefficient α by which the modulation pattern is to be multiplied varies depending on a pixel position (x, y) in accordance with its specific pattern configuration may be considered. In contrast, with the configuration in which it is possible to set the correction coefficient α as a coefficient α(x, y) for each pixel as described above, it is possible to appropriately execute correction of the modulation pattern even in a case where a value of an optimum correction coefficient α is dependent on a pixel position.
Further, with respect to the pattern characteristics of the modulation pattern to be referenced in setting of a correction coefficient α, specifically, the light modulation method may be configured such that, in the correction coefficient setting step, a coefficient set according to spatial frequency characteristics of the target modulation pattern is used as the correction coefficient α. In the same way, the light modulation program may be configured such that, in the correction coefficient setting processing, a coefficient set according to spatial frequency characteristics of the target modulation pattern is used as the correction coefficient α. In the same way, the light modulation device may be configured such that, in the correction coefficient setting means, a coefficient set according to spatial frequency characteristics of the target modulation pattern is used as the correction coefficient α.
Or, with respect to the pattern characteristics of the modulation pattern to be referenced in setting of a correction coefficient, the light modulation method may be configured such that, in the correction coefficient setting step, a coefficient set according to a point having a maximum diffraction angle in a reconstructed pattern of light phase-modulated with the target modulation pattern is used as the correction coefficient α. In the same way, the light modulation program may be configured such that, in the correction coefficient setting processing, a coefficient set according to a point having a maximum diffraction angle in a reconstructed pattern of light phase-modulated with the target modulation pattern is used as the correction coefficient α. In the same way, the light modulation device may be configured such that, in the correction coefficient setting means, a coefficient set according to a point having a maximum diffraction angle in a reconstructed pattern of light phase-modulated with the target modulation pattern is used as the correction coefficient α. Further, in this case, in setting of a correction coefficient particularly, a coefficient set according to a distance between the point having the maximum diffraction angle in the reconstructed pattern of the light phase-modulated with the target modulation pattern and a light condensing point of zeroth-order light is preferably used as the correction coefficient α.
The light irradiation device according to the above-described embodiment includes a light source which supplies light serving as a modulation object, and a light modulation device having the above-described configuration including a phase-modulation type spatial light modulator which modulates a phase of the light supplied from the light source, and outputs the phase-modulated light. Further, in the case where the light serving as a modulation object is laser light, the laser light irradiation device includes a laser light source which supplies laser light, and a light modulation device having the above-described configuration including a phase-modulation type spatial light modulator which modulates a phase of the laser light supplied from the laser light source, and outputs the phase-modulated laser light.
In accordance with such a configuration, in the light modulation device including the phase-modulation type spatial light modulator, a modulation pattern corrected by multiplying the target modulation pattern by the correction coefficient α is presented on the plurality of pixels of the spatial light modulator, thereby it is possible to suppress the generation of undesired zeroth-order light in phase modulation of light, and it is possible to appropriately achieve operations such as irradiation of light onto an object with a desired irradiation pattern, and processing, observation, etc. of the object by the irradiation. Such a light irradiation device is available as, for example, a laser processing device, a laser microscope, a laser manipulation device, or an aberration correction device for a laser scanning ophthalmoscope or the like.
The present invention is available as a light modulation method, a light modulation program, a light modulation device, and a light irradiation device which are capable of suppressing the generation of undesired zeroth-order light by an SLM.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-165722 | Jul 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/068742 | 7/9/2013 | WO | 00 |
