JP2004163652A - Light controlling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simply structured light controlling device in which light is controlled spatially and timely at a high speed, whose light is utilized at a high efficiency, whose control is easy, and whose manufacturing is easy and inexpensive. <P>SOLUTION: In the light controlling device, optical elements 61 and 62 having a light reflection surface are arranged in parallel so as to compose a section of a diffraction grating. The position of the predetermined optical element 62 in the one section varies in the direction of the depth as of the diffraction grating by means of an electric control. The grating interval of the diffraction grating is varied by a multiple of integer (2 times in the present case) by using such composition, thus the diffraction angle of a predetermined diffraction order is varied. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light control device that spatially and temporally controls emitted light with respect to incident light, and more specifically, to a light control device using light diffraction.
[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]
Further, a device using a controllable diffraction grating is also known. For example, in Patent Document 1, a first electrode and a second electrode are formed on a first surface and a second surface of a variable-shape object which face each other, respectively, and a predetermined voltage is applied to these electrodes to form a cycle. A method is disclosed in which a variable electric field is formed, the shape-variable object is formed into a blazed diffraction grating, and the applied voltage is controlled to vary the blaze angle of the diffraction grating.
[0004]
Further, Patent Document 2 discloses that a large number of electrodes are formed in parallel on a deformable object, thereby forming a diffraction grating, and by applying a predetermined voltage to these electrodes, the distance between the electrodes is made variable. Thus, a method of forming a diffraction grating having a variable period is disclosed.
[0005]
Further, as a method using a diffraction grating, a method disclosed in Patent Document 3 is known. According to Patent Literature 3, a plurality of beam-shaped reflective elements are arranged on a substrate in parallel with a predetermined height from the substrate, and an electrode formed on these beam-shaped reflective elements 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.
[0006]
Further, in Patent Document 4, for the purpose of use for an optical switch used in optical communication, and in Patent Document 5, for the purpose of displaying a stereoscopic image, a plurality of beams corresponding to the beam-shaped reflective elements described in Patent Document 3 are used. Are controlled independently of each other, thereby forming an arbitrary wavefront.
[0007]
[Patent Document 1]
US Patent No. 4,011,009
[Patent Document 2]
US Patent No. 5,115,344
[Patent Document 3]
Japanese Unexamined Patent Publication No. 2002-503351
[Patent Document 4]
US Pat. No. 6,268,952
[Patent Document 5]
JP-A-2002-162599
[Non-patent document 1]
H. Dammann, "Blazed Synthetic Phase-Only Holograms", Optik, vol. 31 pp. 95-104 (1970)
[0013]
[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. According to Patent Documents 1 and 2, it is extremely difficult to obtain a necessary high speed because the deformable object includes an operation of volumetrically compressing the deformable object. Further, in the case of Patent Literature 1, the use efficiency of light is high because a blazed diffraction grating is formed, but the period (grating interval) of the diffraction grating is fixed. On the other hand, in the case of Patent Document 2, although the period as a grating is variable, a blazed diffraction grating cannot be formed.
[0014]
The device described in Patent Document 3 operates at a high speed and can be sufficiently used 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.
[0015]
In Patent Literatures 4 and 5, a plurality of ribbons each corresponding to a beam-shaped reflective element are driven while being kept parallel to the substrate. However, it is necessary to control each ribbon independently and at a height from the substrate to a predetermined value instead of a simple binary value as disclosed in Patent Document 3. This is extremely difficult in terms of manufacturing and control. If possible, it requires enormous manufacturing costs and a large control system.
[0016]
The present invention has been made in view of such a problem of the related art, and its object is to operate at a high speed, have a high light use efficiency, and a simple configuration of an optical system using the light. An object of the present invention is to provide a light control device that is easy to control, easy to manufacture, and inexpensive, and that spatially and temporally controls light.
[0017]
[Means for Solving the Problems]
The light control device of the present invention that achieves the above object is characterized in that the grating interval of the diffraction grating is changed by an integral multiple so that the diffraction angle of a predetermined diffraction order changes.
[0018]
In this case, it is desirable that the diffraction grating is a blazed type or a diffraction grating that approximates the blazed type.
[0019]
Further, by changing the grating interval of the diffraction grating twice, the diffraction angle of the predetermined diffraction order can be changed by about twice.
[0020]
As the diffraction grating that approximates the blazed type, a diffraction grating that approximates the blazed type with a step-like shape can be used.
[0021]
Also, for example, a plurality of optical elements having a light-reflective surface are arranged in parallel to constitute one section of a diffraction grating, and predetermined optical elements in one section are electrically controlled in a depth direction of a groove as a diffraction grating. It can be configured such that the position changes.
[0022]
In addition, one section of the diffraction grating may be arranged one-dimensionally or two-dimensionally, and each section may be independently controlled.
[0023]
In the present invention, the grating interval of the diffraction grating is changed by an integral multiple, so that the diffraction angle of the predetermined diffraction order is changed. For example, a spatial light modulator or the like capable of binary control can be configured.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a light control device according to the present invention will be described with reference to the drawings.
[0025]
FIG. 1 shows a perspective view of an embodiment in which the light control device of the present invention is implemented as a module. On a support substrate 1, a light control unit main body 2, electronic circuits 3 and 3 'necessary for driving the light control unit main body 2, and 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.
[0026]
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.
[0027]
[First Embodiment]
FIGS. 3A and 4 show the first embodiment of the configuration of the section 5 as a cross-sectional view of the section 5 (a cross-sectional view 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.
[0028]
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.
[0029]
Next, the operation of the light control device of the present embodiment 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.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
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).
[0034]
As described above, according to the present invention, the light incident on the light control unit main body 2 is controlled for each of the sections 4 to one of the state I, ie, the dark state, and the state II, ie, the bright state.
[0035]
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.
[0036]
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.
[0037]
[Second embodiment]
5 and 6 show the second embodiment of the configuration of the section 5 (FIG. 2) as a cross-sectional view of the section 5 (a cross-sectional view along the line AA ′ in FIG. 2). In FIG. 5, reference numeral 7 denotes a substrate of the light control unit main body 2, on which pieces 63, 64 having a stepped cross section as the optical element 6 are arranged with a predetermined gap. The step-like pieces 63 and 64 have the same shape, and have surfaces parallel to the substrate 7, 631 and 632, and 641 and 642, respectively.
[0038]
Here, the stepped segments 63 and 64, vertically seen width substrate 7 (projected width) d, the surface 631 and the surface 632, the difference in height between the surface 641 and the surface 642 and _{h 3.} The other components are the same as those of the first embodiment. The step-shaped element 63 corresponds to the strip-shaped element 61, and the step-shaped element 64 corresponds to the strip-shaped element 62.
[0039]
Next, the operation of the light control device of the present embodiment will be described. FIG. 6 shows a state where a predetermined voltage is applied between the electrode layer 8 and the electrode layer 10 (see FIG. 3B) provided on the step-like piece 63. That is, when a predetermined voltage is applied to the electrode layer 8 and the electrode layer 10 in the state of FIG. 5, an electrostatic attraction acts between the electrodes 8 and 10, and the elastically deformable step-like piece 63 is moved at both ends thereof. It moves in the direction of the substrate 7 except for the portion, and the side closer to the substrate 7 hits the rib 12 and stops. At this time, the step-like element 63 moves by 2 × h _3, and takes a form in which the slope is approximated by four steps in combination with the step-like element 64. These drawings 5, but are drawn larger h ₃ for clarity in FIG. 6, in practice, when considering a visible light as the incident light, h ₃ is roughly 0.1μm or less, the width Since d can be set to about 10 μm, the step-like pieces 63 and 64 are close to a plane, and even if there is a step, the step-like pieces 63 and 64 can be sufficiently elastically deformed.
[0040]
Assuming that the state of FIG. 5 is state III and the state of FIG. 6 is state IV, in the case of state III, the step-like pieces 63 and 64 in the section 5 constitute a rectangular cross-section diffraction grating with a grating interval d. On the other hand, in the case of the state IV, since the set of step-like elements 63 and 64 forms a shape in which the slope is approximated by four steps, the blaze approximation type diffraction with a lattice spacing of 2d together with the other sets of step-like elements. A lattice will be constructed. The idea of approximating such a blaze shape by a step-like shape is known, and is described in, for example, Non-Patent Document 1. However, the idea as in the present embodiment is not suggested at all.
[0041]
The operation of the present embodiment is basically the same as that of the first embodiment. However, when the state II of the first embodiment is compared with the state IV of the present embodiment, in the present embodiment, the lattice shape is approximated by the blaze approximation. Because of the shape, the diffraction efficiency is slightly inferior, and if the number of grating periods is sufficiently large, it will be about 80% for a predetermined wavelength. If the number of steps approximating the blaze shape is increased, for example, if the number of steps is eight, it can be reduced to about 95%, but the manufacturing process becomes slightly complicated. In practice, four stages are often sufficient as shown in FIG.
[0042]
In the present embodiment, since the optical element is constituted by the surfaces 631, 632, 641, and 642 parallel to the substrate 7, the optical element is manufactured by using a semiconductor manufacturing technique, for example, in comparison with the first embodiment. Becomes easier.
[0043]
【The invention's effect】
As is clear from the above description, according to the light control device of the present invention, the grating interval of the diffraction grating is changed by an integral multiple to change the diffraction angle of the predetermined diffraction order. By arranging an aperture or the like that transmits the light of the order, the operation is fast, the light use efficiency is high, the configuration of the optical system using the light is simple, the control is easy, and the manufacturing is easy. It is possible to configure a light control device that controls light spatially and temporally, which is easy and inexpensive.
[Brief description of the drawings]
FIG. 1 is a perspective view of one embodiment in which a light control device of the present invention is implemented as a module.
FIG. 2 is an enlarged view of one section of FIG. 1 viewed from above.
FIG. 3A is a cross-sectional view showing the configuration of one section of the first embodiment of the present invention, 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 in a state where a voltage is applied to a strip-shaped piece that can be electrically controlled in each section of the first embodiment.
FIG. 5 is a sectional view showing a configuration of one section according to a second embodiment of the present invention.
FIG. 6 is a cross-sectional view similar to FIG. 3 in a state where a voltage is applied to an electrically controllable staircase element in each section of the second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Support board 2 ... Light control part main body 3, 3 '... Electronic circuit 4 ... Section 5 ... One division 6 ... Optical element 7 ... Light control part main body substrate 8 ... Electrode layer 9 ... Insulating layer 10 ... Electrode layer 11 ... Light reflecting layer 12 ... Rib 13 ... Openings 61 and 62 ... Strip-shaped pieces 63 and 64 ... Step-shaped pieces 631,632, 641 and 642 ... A plane parallel to the substrate

Claims (6)

An optical control device characterized in that a grating interval of a diffraction grating is changed by an integral multiple to change a diffraction angle of a predetermined diffraction order. The light control device according to claim 1, wherein the diffraction grating is a blazed type or a diffraction grating that approximates a blazed type. 2. The light control device according to claim 1, wherein the grating angle of the diffraction grating changes by a factor of two, so that the diffraction angle of a predetermined diffraction order changes by a factor of about two. 3. The light control device according to claim 2, wherein the light control device is a diffraction grating that approximates a blazed type with a step-like shape. A plurality of optical elements having a light reflecting surface are arranged in parallel to form one section of the diffraction grating, and a predetermined optical element in one section changes its position in the groove depth direction as a diffraction grating by electrical control. The light control device according to claim 1, wherein the light control device is a light control device. 2. The light control device according to claim 1, wherein a plurality of one section of the diffraction grating are arranged one-dimensionally or two-dimensionally, and each section is independently controlled.

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