JP2004163653A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide such a compact optical device serving as a compact color image display device that includes a light control device which has high light utilization efficiency, is easily controlled, is easily manufactured and has a high resolution, and that has a simple optical system and high resolution. <P>SOLUTION: A section of a diffraction grating is composed by arranging in parallel a plurality of optical elements 61 and 62 having a light reflection surface. The light control device is so composed that the diffraction angle is changed by changing the position of the predetermined optical element 62 in the one section by an electric control in the depth direction of the groove as the diffraction grating, and changing the grating interval by a multiple of integer (twice in the present case) by using such composition. Diffracted light is allowed to pass or intercepted at an aperture 13, and thus a one-dimensional or a two-dimensional image is displayed in which respective sections are used as pixels. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical device using a light control device that spatially and temporally controls emitted light with respect to incident light, and more specifically, uses a light control device using diffraction of light. The present invention relates to an optical device, for example, an image display device.
[0002]
[Prior art]
A device that spatially and temporally controls light emitted with respect to incident light is sometimes called a spatial light modulator or a light valve (light valve), and is used for an image display device or the like. Conventionally, as this type of device, a device using a liquid crystal, a device using a variable-shape reflector, or a device in which a large number of tiltable minute reflectors are arranged are known.
[0003]
A method using a diffraction grating is also known. According to Patent Literature 1, a plurality of beam-shaped reflective elements are arranged on a substrate in parallel at a predetermined height from the substrate, and an electrode formed on the beam-shaped reflective element and an electrode formed on the substrate are arranged in parallel. By applying a predetermined voltage between them, the distance between the beam-shaped reflection element and the substrate is controlled to a predetermined value, and thus, only the 0th-order reflected diffraction light is generated with respect to the incident light, It is possible to switch the case where the above reflected diffraction light occurs. Needless to say, since the diffracted light has different diffraction directions depending on the diffraction order, if an appropriate aperture is provided to take in only the reflected light in a specific direction, for example, only the first-order reflected diffracted light, the height of the beam-shaped reflecting element can be increased. By switching by electric control, the light state and the dark state of light can be switched. This patent document also discloses a method in which these beam-shaped reflection elements can be tilted about their longitudinal direction as an axis, and a blazed diffraction grating is formed when these beam-shaped reflection elements are inclined. An optical modulator using such a diffraction grating may be called a grating light valve.
[0004]
Patent Document 1 discloses a method of using such an optical modulator in a color image display device, and the above-described light corresponding to each of red (R), green (G), and blue (B). It is said that a color image can be obtained by providing a modulator and illuminating with white light.
[0005]
Patent Literature 2 and Patent Literature 3 each include an optical modulator similar to the above, corresponding to each of red (R), green (G), and blue (B). B shows a method of obtaining a color image by illuminating with independent light sources.
[0006]
[Patent Document 1]
JP 2002-503351 A
[Patent Document 2]
US Patent No. 5,808,797
[Patent Document 3]
US Pat. No. 6,219,015
[Problems to be solved by the invention]
When the spatial light modulator is used for an image display device, a printer, and the like, high-speed operation is an essential requirement. In Patent Literature 1 and Patent Literatures 2 and 3, the operation is performed at high speed, and it is sufficiently possible to use it for an image display device or the like. However, in the case where the beam-shaped reflecting element is configured to move up and down in parallel to the substrate, the diffraction grating is a so-called rectangular diffraction grating, and the diffraction efficiency of plus or minus first-order diffracted light is at most about 40%. If both the plus and minus first-order diffracted lights are taken in, the light utilization efficiency can be up to about 80%. However, needless to say, the directions of the plus and minus first-order diffracted lights are different. The system becomes complicated. On the other hand, if the configuration is such that the 0th-order diffracted light is taken in, even in the state where the first-order or higher reflected diffracted light is generated, a substantial equivalent of the 0th-order diffracted light is generated, and when viewed through the aperture, the contrast between light and dark is reduced. bad. Further, when the beam-shaped reflecting element is inclined to form a blazed diffraction grating, either plus or minus diffracted light is strongly generated, and a diffraction efficiency close to 100% can be obtained for a specific wavelength. Desirable, but extremely difficult to manufacture and difficult to control.
[0010]
In the case where the optical modulator or the light valve disclosed in the above patent document is used for a color image display device, as shown in these patent documents, R (red), G (green), and B (blue) are used. It is possible to provide corresponding optical modulators. In this case, a so-called three-plate type in which independent optical modulators corresponding to R, G, and B are provided, or minute R, G, and B corresponding regions are adjacent to each other. Thus, a so-called single-plate type in which a large number are arranged can be used. In any case, it is preferable that the optical modulator can be optimally designed for each of R, G, and B. However, although the three-plate type is relatively easy to manufacture each optical modulator and is preferable in terms of image quality, it is inevitable that the optical system becomes complicated and the color image display device becomes large-sized and expensive. Further, the single-panel type is easy to miniaturize as a color image display device, but it is difficult to manufacture an optical modulator, and is disadvantageous in terms of resolution as compared with the three-panel type.
[0011]
The present invention has been made in view of such problems of the prior art, and has as its object to provide a light control device (light control device) that has high light use efficiency, is easy to control, and is easy to manufacture and inexpensive. The present invention is to provide an optical device such as a color image display device which includes a modulator, and has a simple optical system, a small size and a high resolution as an optical device using the same.
[0012]
[Means for Solving the Problems]
The optical device according to the present invention for achieving the above object includes a light control device configured to change the grating interval of the diffraction grating by an integral multiple so that the diffraction angle of a predetermined diffraction order changes. Things.
[0013]
Another optical device according to the present invention is a light control device configured to change a diffraction angle of a predetermined diffraction order by changing a grating interval of a diffraction grating by an integral multiple, and a diffraction surface of the light control device. A lens serving as an object plane and an aperture placed in a focal plane of the lens are included.
[0014]
In this case, the diffraction surface of the light control device is illuminated by an illumination system having a light source that emits white light, and information corresponding to the wavelength band is sent to the light control device in a temporally separated manner. It is desirable to control the position of the opening to a corresponding position.
[0015]
The optical device as described above can be configured as, for example, a color image display device.
[0016]
In the present invention, the grating interval of the diffraction grating is changed by an integral multiple, and includes a light control device configured to change a diffraction angle of a predetermined diffraction order, and the diffraction surface of the light control device is defined as an object surface. Since the lens includes a lens and an aperture placed in the focal plane of the lens, the diffraction angle of each section of the light control device is controlled in accordance with pixel information or the like, so that each section is a one-dimensional or two-dimensional pixel. Images can be displayed.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of an optical device according to the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a perspective view of a module of a light control device used in the optical device of the present invention. A light control unit main body 2, electronic circuits 3 and 3 ′ necessary for driving the light control unit main body 2 are provided on a support substrate 1. Although not shown, an electrical contact for connecting to a power supply required for driving the module, an optical device using the module, for example, an electrical contact with an external circuit required for incorporating the module into an image display device, and the like Is arranged. The light control unit main body 2 has a plurality of sections 4, and each section is two-dimensionally arranged. In some cases, each section may be a one-dimensional array. Each section 4 corresponds to one pixel when this module is applied to an image display device.
[0019]
FIG. 2 is a view showing a state where one section 5 of the section 4 is enlarged and viewed from above, and a plurality of optical elements 6 are arranged in parallel.
[0020]
3A and 4 are cross-sectional views of the section 5 (cross-sectional views along the line AA 'in FIG. 2). In FIG. 3A, reference numeral 7 denotes a substrate of the light control unit main body 2, on which strip-shaped pieces 61, 62 serving as the optical element 6 are provided with a predetermined gap. They are arranged at a predetermined angle φ. The widths of the strip-shaped pieces 61 and 62 are made equal, and the width (projected width) when viewed perpendicular to the substrate 7 is d. Although not shown, the strips 61 and 62 are supported on the substrate 7 at both ends. An electrode layer 8 is formed on one surface of the substrate 7 via an insulating layer 9 as necessary. As shown in more detail in FIG. 3B, an electrode layer 10 is formed on the upper surface of the strip-shaped element 61 and a light reflection layer 11 is further formed on the upper surface thereof. The reflection layer 11 is formed. The electrode layer 10 may also be a layer of a metal, for example, aluminum, chromium, gold, or the like, also serving as the light reflection layer 11. The strip-shaped pieces 61 and 62 are configured to be elastically deformable like a leaf spring, and may be made of, for example, polyimide, silicon, silicon nitride, or the like. Further, a rib 12 is formed on the substrate 7 at a position corresponding to the side of the strip-shaped element 61 closer to the substrate.
[0021]
Such a structure can be realized using a generally known manufacturing technique of a semiconductor integrated circuit (IC) or a micromachine (micromachine or MEMS). In this case, a silicon wafer is used for the substrate 7. The insulating layer 9 can be a silicon oxide film layer, and the electrode layers 8 and 10 can be metal films. In the case where a metal film is formed by vapor deposition or the like which also serves as the electrode layer 10 and the light reflection layer 11, since no electrode is required for the strip-shaped piece 62, the metal deposition film formed on the strip-shaped piece 62 is A treatment to electrically insulate the metal deposition film formed on the strip-shaped piece 61 is performed.
[0022]
Next, the operation of each section 4 (5) of the light control unit having such a structure will be described. FIG. 4 shows a state where a predetermined voltage is applied between the electrode layer 8 and the electrode layer 10 of the strip-shaped element 61. That is, when a predetermined voltage is applied to the electrode layer 8 and the electrode layer 10 in the state of FIG. 3A, an electrostatic attraction acts between the electrodes 8 and 10, and the elastically deformable strip-shaped piece 61 becomes , Except for the both ends, moves toward the substrate 7, and the side closer to the substrate 7 hits the rib 12 and stops. At this time, the strip-shaped piece 61 is connected to the strip-shaped piece 62 and substantially forms one surface.
[0023]
Assuming that the state of FIG. 3A is state I and the state of FIG. 4 is state II, in the case of state I, the strip-shaped pieces 61 and 62 in the section 5 constitute a blazed diffraction grating with a grating interval d. I do. On the other hand, in the case of the state II, since one set of the strip-shaped pieces 61 and 62 substantially constitute one surface, it is necessary to form a blazed diffraction grating with a grating interval of 2d together with another set of the strip-shaped pieces. become. In general, when light having a wavelength λ is perpendicularly incident on a diffraction grating having a grating interval D, the following equation is established, where the diffraction angle is ψ and the diffraction order is m.
[0024]
D · sinψ = mλ (1)
Now, when the diffraction order angle of diffraction smallest except 0-order is considered for the case of 1, in the case of state I, with respect to m = 1, when the diffraction angle at that time with the theta _1,
sin θ ₁ = λ / d (2)
Become whereas, if the state II, with respect to m = 1, when the diffraction angle at that time and theta _2,
sin θ ₂ = λ / 2d (3)
Because
sin θ ₁ = ₂ sin θ ₂ (4)
And when θ ₁ and θ ₂ are small,
θ ₁ ≒ 2θ ₂ (5)
It becomes.
[0025]
Therefore, when the state I, even the smallest diffraction angle, is approximately twice the theta _2. Therefore, the opening for taking light into subsequent optical system, by providing the opening 13 as capture diffracted light theta ₂ direction only, if the status I, what order diffracted light in theta ₂ direction No light enters the opening 13 because it does not exit. Needless to say, in the case of the state II, the first-order diffracted light passes through the aperture 13. Moreover, because they become a blazed diffraction grating, taking the grating depth h ₂ as shown in FIG. 4 to lambda / 2, a nearly 100% diffraction efficiency is extremely high primary diffraction efficiency, ideally. At this time, diffracted light of other orders including the minus order is hardly generated, so that most of the diffracted light is concentrated on the aperture 13 and the light use efficiency is increased. At the same time, it is only necessary to provide one of the optical systems following the light control unit main body 2 as the opening 13, so that the configuration of the optical system following this can be simplified.
[0026]
In the case of state I, since the grating depth h ₁ becomes lambda / 4, but also strongly to generate diffracted light other than the primary, including zero order, showing only first-order diffracted light in FIG. 3 (a).
[0027]
As described above, the light incident on the light control unit main body 2 is controlled for each of the sections 4 to be in any one of the state I, ie, the dark state, and the state II, ie, the bright state.
[0028]
In the above description, it is assumed that the number of grating periods is sufficiently large, but for diffracted light of a certain diffraction order, the angular distribution depends on the number of grating periods. The diffracted light of that order is concentrated. In FIG. 4, three periods are used, but if the number is further increased, it is preferable because the intensity of light passing through the opening 13 having a certain width increases. However, for application to an image display device or the like, three cycles are sufficient for practical use.
[0029]
Further, in FIG. 4, one period of the grating is shown to be constituted by two strip-shaped pieces. However, it is also possible to constitute three or more strip-shaped pieces. For example, in the case of the three strips, the first-order diffraction angle in the state I is about three times the diffraction angle in the state II, which is preferable in terms of the contrast ratio, but the height control of the middle strip is preferable. Is difficult, and the manufacturing is complicated, and thus the cost is high. Practically, it may be composed of two strip-shaped pieces.
[0030]
Next, an embodiment in which the optical device of the present invention is implemented as an image display device or the like including the above-described light control device will be described with reference to FIGS. 5, 6, 7, and 8. FIG. In FIG. 5, reference numeral 20 denotes the above-described light control device, which is viewed from the side. The direction of the groove as the diffraction grating of each section 4 of the light control unit main body 2 is arranged to be perpendicular to the paper surface.
[0031]
In the following, the light control unit main body 2 is referred to as an optical modulator 2. Reference numerals 21 and 22 constitute an illumination system for illuminating the optical modulator 2, reference numeral 21 denotes a white light source, and reference numeral 22 denotes a collimating lens which also serves as a light collector. As the light source 21, a lamp having a light emitting portion as small as possible, for example, a lamp having a sharp discharge electrode is preferable. Alternatively, a multi-line laser having oscillation lines for R, G, and B may be used. In this case, a beam expanding optical system (not shown) is used to obtain a necessary light beam diameter. Although the collimator lens 22 is shown as a single lens in FIG. 5, it is desirable that the collimator lens 22 has been corrected for aberration. Therefore, the collimator lens 22 generally includes a plurality of lens elements. The optical axis 23 of this illumination system forms an angle θ with an optical axis 25 of an imaging lens 24 described later.
[0032]
The light modulator 2 illuminated in this manner is temporally controlled for each section (pixel) 4 based on image information to be displayed. In the state II shown in FIG. First-order) diffracted light 26 is strongly generated. In FIG. 4, the incident light is assumed to enter vertically for the sake of simplicity. However, the function of the diffraction grating is not limited to this, and generally, as shown in FIG. The diffraction angle θ ′ has the following relationship, where D is the lattice spacing, m is the diffraction order, and λ is the wavelength of light.
[0033]
D (sin θ + sin θ ′) = mλ (6)
However, here, it is assumed that the angles θ and θ ′ are positive in the clockwise direction with respect to the normal 91 of the diffraction surface.
[0034]
Therefore, it is also possible to set the diffraction angle θ ′ to 0 for an incident angle θ that is not a certain wavelength λ, 0, and FIG. 5 shows this state. The diffracted light 26 emitted from the section 4 in the state II enters the imaging lens 24, passes through the aperture 27, and forms an image on the image plane 28. Although the imaging lens 24 is shown as a single lens in the figure, it generally comprises a plurality of lens elements for aberration correction. The aperture 27 has its center on the optical axis 25 and is arranged on the rear focal plane of the imaging lens 24. The opening 27 is connected to an opening moving device 29 and can be moved perpendicular to the optical axis 25.
[0035]
Next, the operation of the optical system in the state of FIG. 5 will be described. Now, assuming that the white light source 21 is small enough to be regarded as a point light source for simplicity, the light emitted from the white light source 21 is illuminated by the collimator lens 22 into a parallel light flux to illuminate the light modulator 2. If the incident angle θ and the wavelength λ _G are selected so that 2d sin θ = λ _G , the first-order diffraction angle θ ′ of the diffracted light 26 emitted from the section 4 in the state II becomes 0 for the wavelength λ _G. On the other hand, no diffraction light of any order is emitted in the direction of θ ′ = 0 from the section 4 in the state I shown in FIG. The wavelength λ _G is a specific wavelength among the wavelengths of the light emitted from the white light source 21, and when the present invention is used for a color image display device, the wavelength λ _G is the center wavelength of the G (green) band. For light other than the wavelength λ _G , the diffraction angle θ ′ has a certain inclination with respect to the optical axis 25. However, due to the aperture 27 placed on the rear focal plane of the imaging lens 24, the diffracted light having a certain inclination or more is limited. In other words, the light can pass through the opening 27 is limited to light having a wavelength around lambda _G. Increasing the aperture 27 widens the wavelength band of the light passing therethrough, and at the same time brightens the light. However, if it is too large, the color reproducibility when displaying a color image is degraded. Further, the aperture 27 placed on the rear focal plane of the imaging lens 24 fulfills the function of the aperture 13 shown in FIGS. 3A and 4 for all the sections 4 and if the aperture is too large. There is a possibility that the diffracted light generated in the state I is taken in. When the white light source 21 is not a point light source but has a certain size, even if the light source 21 is a monochromatic light source, the aperture 27 acts as a brightness stop. The size of the opening 27 is determined.
[0036]
As can be understood from the above description, if the aperture 27 is set to an appropriate size, among the sections 4 (pixels) of the optical modulator 2, from the section in the state II (bright state), the opening 27 wavelength diffracted light in the vicinity of lambda _G is generated that passes through, forms an image on the image plane 28. At this time, by controlling the time ratio between the state I (dark) and the state II (bright) within a unit time for each section, a bright and dark gradation can be obtained.
[0037]
6, whereas the a state 5 corresponds to the wavelength lambda _G, shows a state corresponding to the wavelength lambda _B. The wavelength λ _B is a specific wavelength among the wavelengths of light emitted from the white light source 21, and is the center wavelength of the B (blue) band when the present invention is used for a color image display device. Since λ _B <λ _G , the first-order diffraction angle θ ′ with respect to λ _B is negative, and the opening 27 is moved upward by approximately | f sin θ ′ | in FIG. Here, f is the focal length of the imaging lens 24. Other configurations, operations, and operations are the same as those in FIG.
[0038]
Further, FIG. 7 shows a state corresponding to the wavelength lambda _R. The wavelength λ _R is a specific wavelength among the wavelengths of light emitted from the white light source 21, and is the center wavelength of the R (red) band when the present invention is used for a color image display device. Since λ _G <λ _R , the first-order diffraction angle θ ′ with respect to λ _R becomes positive, and the opening 27 is moved downward by approximately fsin θ ′ by the opening moving device 29 in FIG. Other configurations, operations, and operations are the same as those in FIG.
[0039]
As described above, the states corresponding to R, G, and B are realized by moving the opening 27. That is, when an R signal is being sent to the optical modulator 2, the aperture 27 is in the state shown in FIG. 7, and when a G signal is being sent to the optical modulator 2, the aperture 27 is in the state shown in FIG. When the signal B is sent to the container 2, the opening moving device 29 is controlled so that the opening 27 is in the state shown in FIG. The movement of the opening 27 can be realized by using a piezoelectric element, a voice coil, or the like, or by opening three or more openings at three different distances from the center of the disk and rotating the disk with a motor. realizable. Instead of using mechanical means, the opening may be formed by, for example, a liquid crystal panel, an electrochromic element, or the like, and may be electrically movable. In any case, by switching these three states at a high speed, a color image can be displayed.
[0040]
When the present invention is applied to a monochrome image display device instead of a color image display device or a printer, only the state shown in FIG. 5 is sufficient, and needless to say, the aperture moving device 29 is not required. However, the wavelength is not limited to λ _G, appropriately set.
[0041]
The image plane 28 does not need to be a final image plane, for example, a display screen. The image plane 28 may be used as an intermediate image plane, and a zoom lens optical system or the like may be arranged thereafter to relay the image plane. .
[0042]
Further, when the sections 4 of the optical modulator 2 are two-dimensionally arranged, a two-dimensional image can be obtained with the above configuration, but the sections 4 of the optical modulator 2 are one-dimensionally arranged. In this case, a two-dimensional image may be obtained by adding a high-speed oscillating mirror (galvanometer mirror) or the like to the optical system. When used in a printer, a two-dimensional image can be obtained by moving or rotating the photoconductor placed at the position of the image plane 28.
[0043]
With the configuration described above, according to the present invention, a small and inexpensive optical device such as a high-resolution image display device or a printer can be realized with a simple optical system.
[0044]
【The invention's effect】
As is apparent from the above description, the optical device of the present invention includes a light control device configured to change the diffraction angle of a predetermined diffraction order by changing the grating interval of the diffraction grating by an integral multiple. Since it includes a lens whose object plane is the diffraction surface of the light control device and an aperture placed in the focal plane of the lens, the diffraction angle of each section of the light control device is controlled according to pixel information and the like. A one-dimensional or two-dimensional image can be displayed using each section as a pixel.
[Brief description of the drawings]
FIG. 1 is a perspective view of a module of a light control device used in an optical device of the present invention.
FIG. 2 is an enlarged view of one section of FIG. 1 viewed from above.
3A is a cross-sectional view showing the configuration of one section of the light control device of FIG. 1, and FIG. 3B is a cross-sectional view of an electrically controllable strip in the section.
FIG. 4 is a cross-sectional view similar to FIG. 3 (a) in a state where a voltage is applied to an electrically controllable strip-shaped piece in each section of the light control device of FIG. 1;
FIG. 5 is an optical path diagram of an embodiment in which the optical device of the present invention is implemented as an image display device including the light control device of FIG.
FIG. 6 is a view similar to FIG. 5 when using a wavelength different from that in FIG. 5;
FIG. 7 is a diagram similar to FIG. 5 when used for another wavelength different from those in FIGS. 5 and 6;
FIG. 8 is a diagram for explaining a relationship between an incident angle and a diffraction angle when light is incident at an angle other than perpendicular to the diffraction grating.
[Explanation of symbols]
1: Support substrate 2: Light control unit main body (light modulator)
3, 3 '... electronic circuit 4 ... section 5 ... one section 6 ... optical element 7 ... substrate 8 of light control unit main body ... electrode layer 9 ... insulating layer 10 ... electrode layer 11 ... light reflecting layer 12 ... rib 13 ... opening Reference Signs List 20 light control device 21 white light source 22 collimating lens 23 optical axis 24 of illumination system imaging lens 25 optical axis 26 of imaging lens diffracted light 27 aperture 28 image plane 29 aperture moving device 61 , 62: strip-shaped piece 91: normal to the diffraction surface

Claims (4)

An optical device comprising: a light control device configured to change a diffraction interval of a predetermined diffraction order by changing a grating interval of a diffraction grating by an integral multiple. A light control device configured to change a diffraction angle of a predetermined diffraction order by changing a grating interval of the diffraction grating by an integral multiple, a lens having a diffraction surface of the light control device as an object surface, and a focus of the lens. An optical device comprising an aperture placed in a plane. A diffraction surface of the light control device is illuminated by an illumination system having a light source that emits white light, and information corresponding to a wavelength band is sent to the light control device in a time-separated manner, at a position corresponding to the wavelength band. 3. The optical device according to claim 1, wherein a position of the opening is controlled. The optical device according to claim 3, wherein the optical device is configured as a color image display device.

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