JP4614027B2 - Optical multilayer structure, optical switching element, and image display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical multilayer structure having a function of reflecting or transmitting incident light, an optical switching element using the same, and an image display device.
[0002]
[Prior art]
In recent years, the importance of a display as a display device for video information has increased, and as an element for this display, an optical switching element (such as an optical communication, optical storage device, optical printer, etc.) that operates at high speed ( Development of light bulbs is demanded. Conventionally, as this type of element, those using liquid crystals, those using micromirrors (DMD; Digital Micro Miror Device, digital micromirror device, registered trademark of Texas Instruments Incorporated), those using diffraction gratings (GLV) : Grating Light Valve, SLM (Silicon Light Machine).
[0003]
In GLV, a diffraction grating is manufactured with a MEMS (Micro Electro Mechanical Systems) structure, and a high-speed light switching element of 10 ns is realized with electrostatic force. The DMD also performs switching by moving a mirror in the MEMS structure. Although a display such as a projector can be realized using these devices, the liquid crystal and the DMD have a low operation speed. Therefore, in order to realize a display as a light valve, a two-dimensional arrangement is required, and the structure becomes complicated. . On the other hand, since the GLV is a high-speed drive type, a projection display can be realized by scanning a one-dimensional array.
[0004]
However, since the GLV has a diffraction grating structure, there are complexity such that it is necessary to make six elements for one pixel and to combine the diffracted light emitted in two directions into one by some optical system.
[0005]
  Examples of what can be realized with a simple configuration include those disclosed in US Pat. No. 5,589,974 and US Pat. This light valve, GroupPlate (refractive index n_S) With a refractive index of √n_SThe light-transmitting thin film is provided. In this element, an optical signal is transmitted or reflected by driving the thin film using electrostatic force and changing the distance between the substrate and the thin film, that is, the size of the gap. Here, the refractive index of the thin film is the refractive index n of the substrate._S√n_SIt is said that high contrast light modulation can be performed by satisfying such a relationship.
[0006]
[Problems to be solved by the invention]
However, in the element configured as described above, the refractive index n of the substrate_SIf is not a large value such as “4”, there is a problem that it cannot be realized in the visible light region. That is, when considering that it is a structure as a light-transmitting thin film, silicon nitride (Si_ThreeN_Four) (Refractive index n = 2.0) is desirable, and in that case, the refractive index n of the substrate_S= 4. In the visible light region, such a transparent substrate is difficult to obtain and the choice of materials is narrow. In communication wavelengths such as infrared rays, it can be realized by using germanium (Ge) (n = 4) or the like. However, it is considered that it is difficult to apply in practical use as a display or the like.
[0007]
The present invention has been made in view of such problems, and a first object thereof is a simple configuration, a small size and a light weight, and flexibility in selection of constituent materials, and a high-speed response even in the visible light region. It is possible to provide an optical multilayer structure that can be suitably used for an image display device.
[0008]
A second object of the present invention is to provide an optical switching element and an image display device capable of high-speed response using the optical multilayer structure.
[0010]
[Means for Solving the Problems]
  The optical multilayer structure according to the present invention comprises:TransparencyOn the bright substrate, the first transparent layer and the second transparent layer in contact with the transparent substrate, having a size capable of causing a light interference phenomenon and having a variable size, a third transparent layer, and a second transparent layer 4 transparent layersThisIt has a structure arranged in the order ofAnd a driving means for changing the optical size of the gap, the transparent substrate being a glass substrate, and the first transparent layer being a TiO 2 ₂ Membrane and MgF ₂ Composite layer consisting of film, second transparent layer as TiO ₂ TiO 2 film and third transparent layer ₂ The film and the fourth transparent layer are MgF ₂ The optical film thickness of each of the first transparent layer, the second transparent layer, the third transparent layer, and the fourth transparent layer is set to λ / 4 or λ. / 4 is an odd multiple (λ is the wavelength of the incident light), and the optical size of the gap is set between the odd multiple of λ / 4 and the even multiple of λ / 4 (including 0) by the driving means. By changing binary or continuously, the amount of reflection or transmission of visible light incident from the transparent substrate side or the opposite side of the transparent substrate is changed binaryly or continuously.It is what I did.
[0011]
  According to the present inventionLightThe switching element of the present inventionLight ofA multilayer structure and a driving means for changing the optical size of the gap in the optical multilayer structure.is there.
[0012]
  According to the present inventionPaintingAn image display device according to the present invention.LightA plurality of switching elements are arranged one-dimensionally or two-dimensionally, and a two-dimensional image is displayed by irradiating light of three primary colors and scanning with a scanner.
[0014]
  According to the present inventionLightIn the multi-layered structure, the size of the gap between the first transparent layer and the second transparent layer is narrower than, for example, “λ / 2” (λ is the wavelength of incident light), preferably “λ / Switching between “4” and “0” changes the amount of reflection or transmission of light incident from the transparent substrate side or the opposite side of the transparent substrate.And wideA substantially uniform reflection or transmission characteristic can be obtained over a wide wavelength range.
[0015]
  According to the present inventionLightIn the switching element, the switching operation is performed on the incident light by changing the optical size of the gap portion of the optical multilayer structure by the driving means.
[0016]
  According to the present inventionPaintingIn the image display device, a two-dimensional image is displayed by irradiating a plurality of optical switching elements of the present invention arranged one-dimensionally or two-dimensionally with light.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
[First Embodiment]
1 and 2 show a basic configuration of the optical multilayer structure 1 according to the first embodiment of the present invention. Of these, FIG. 1 shows a state in which a later-described gap portion 12 exists in the optical multilayer structure 1, and FIG. 2 shows a state in which there is no gap portion in the optical multilayer structure 1. The optical multilayer structure 1 is specifically used as, for example, an optical switching element, and an image display device can be configured by arranging a plurality of optical switching elements in a one-dimensional array.
[0019]
The optical multilayer structure 1 of the present embodiment has a first transparent layer 11 in contact with the transparent substrate 10 on a transparent substrate 10 made of a nonmetallic transparent material, and has a size capable of causing a light interference phenomenon. In addition, the gap portion 12 whose size can be changed and the second transparent layer 13 are arranged in this order.
[0020]
Here, the refractive index of the transparent substrate 10 is n_S, The refractive index of the first transparent layer 11 is n₁, The refractive index of the second transparent layer 13 is n₂, The following relations (1) and (2) are established. That is, in this optical multilayer structure 1, the refractive index relationship is arranged on the transparent substrate 10 in the order of the first transparent layer 11 having a high refractive index, the gap portion 12, and the second transparent layer 13 having a low refractive index. It has been established. The reason why this relational expression is established will be described later.
[0021]
n_S<N₁And n₁> N₂... (1)
[0022]
n₂= N₁/ √n_S... (2)
[0023]
Specific materials include, for example, a transparent glass substrate or a transparent plastic substrate as the transparent substrate 10, and titanium oxide (TiO 2) as the first transparent layer 11.₂) (N₁= 2.4), silicon nitride (Si_ThreeN_Four) (N₁= 2.0), zinc oxide (ZnO) (n₁= 2.0), niobium oxide (Nb)₂O_Five) (N₁= 2.2), tantalum oxide (Ta₂O_Five) (N₁= 2.1), silicon oxide (SiO) (n₁= 2.0), tin oxide (SnO₂) (N₁= 2.0), ITO (Indium-Tin Oxide) (n₁= 2.0), and the second transparent layer 13 is silicon oxide (SiO 2).₂) (N₂= 1.46), bismuth oxide (Bi₂O_Three) (N₂= 1.91), magnesium fluoride (MgF)₂) (N₂= 1.38), alumina (Al₂O_Three) (N₂= 1.67).
[0024]
Optical film thickness d of the first transparent layer 11 and the second transparent layer 13₁, D₂Is “λ / 4” or “odd multiple of λ / 4” (λ is the wavelength of the incident light). These film thicknesses d₁, D₂May not be strictly “λ / 4” but may be a value in the vicinity of λ / 4. This is because, for example, the optical thickness of the first transparent layer 11 is thicker than λ / 4, so that the second transparent layer 13 can be made thinner, etc., and the above equation (2). Even if the refractive index is slightly deviated from, the film thickness may be adjustable.₁, D₂Is slightly deviated from λ / 4. The same applies to other embodiments. Therefore, in this specification, the expression “λ / 4” includes the case of “approximately λ / 4”.
[0025]
The first transparent layer 11 and the second transparent layer 13 may be a composite layer composed of two or more layers having different optical characteristics. In this case, the synthesized optical characteristics in the composite layer are used. (Optical admittance) needs to have the same characteristics as in the case of a single layer.
[0026]
The size of the gap portion 12 (the distance between the first transparent layer 11 and the second transparent layer 13) can be changed by a driving unit described later. The medium that fills the gap 12 may be gas or liquid as long as it is transparent. Examples of the gas include air (refractive index n with respect to sodium D line (589.3 nm))._D= 1.0), nitrogen (N₂) (N_D= 1.0) and the like as water (n_D= 1.333), silicone oil (n_D= 1.4-1.7), ethyl alcohol (n_D= 1.3618), glycerin (n_D= 1.4730), Joodomethane (n_D= 1.737). The gap 12 can be in a vacuum state.
[0027]
The optical size of the gap 12 changes in a binary or continuous manner between “odd multiple of λ / 4” and “even multiple of λ / 4 (including 0)”. . As a result, the amount of reflected or transmitted incident light changes in a binary or continuous manner. As in the case of the film thicknesses of the first transparent layer 11 and the second transparent layer 13, even if there is a slight deviation from a multiple of λ / 4, there is a slight change in the film thickness or refractive index of other layers. Since it can be complemented, the expression “λ / 4” includes the case of “approximately λ / 4”.
[0028]
The optical multilayer structure 1 having the gap 12 can be manufactured by the manufacturing process shown in FIGS. First, as shown in FIG. 3A, TiO 2 is formed on a transparent substrate 10 made of glass, for example, by sputtering.₂The first transparent layer 11 is formed, and then, as shown in FIG. 3B, amorphous silicon (a−) as a sacrificial layer is formed by, for example, a CVD (Chemical Vapor Deposition) method. Si) film 12a is formed. Subsequently, as shown in FIG. 3C, a photoresist film 14 having a pattern shape of the gap 12 is formed, and this photoresist film 14 is used as a mask as shown in FIG. The amorphous silicon (a-Si) film 12a is selectively removed by RIE (Reactive Ion Etching).
[0029]
Next, after removing the photoresist film 14 as shown in FIG. 4A, Bi is formed by sputtering, for example, as shown in FIG. 4B.₂O_ThreeA second transparent layer 13 made of is formed. Next, as shown in FIG. 4C, the amorphous silicon (a-Si) film 12a is removed by dry etching. Thereby, the optical multilayer structure 1 provided with the gap | interval part 12 is producible.
[0030]
In the optical multilayer structure 1 of the present embodiment, the amount of reflection or transmission of light incident from the transparent substrate 10 side or the opposite side to the transparent substrate 10 is changed by changing the optical size of the gap 12. It is something to be made. Specifically, the optical size of the gap portion 12 is set between an odd multiple of λ / 4 and an even multiple of λ / 4 (including 0) (for example, “λ / 4” and “0”). The amount of reflection or transmission of incident light is changed in a binary or continuous manner by changing in a binary or continuous manner.
[0031]
Next, the significance of the equations (1) and (2) will be described with reference to FIGS. 5 (A) and 5 (B) and FIGS. 6 (A) and 6 (B).
[0032]
The filter characteristics of the optical multilayer structure 1 as described above can be explained by optical admittance. The optical admittance y has the same value as the complex refractive index N (= n−i · k, where n is the refractive index and k is the extinction coefficient). For example, the admittance of air is y (air) = 1, n (air) = 1, and the admittance of glass is y (glass) = 1.52 and n (glass) = 1.52.
[0033]
  TransparentOn the boardTransparentWhen the optical film is formed, the film thickness is shown on the optical admittance diagram as shown in FIG.increase ofAs a result, the trajectory moves in an arc. Here, the horizontal axis is the real axis of admittance (R_e), The vertical axis is the imaginary axis of admittance (I_m) Respectively. For example, n = y = 2.40 TiO on a glass substrate with n = y = 1.52.₂And the like, the locus of the synthetic optical admittance moves while drawing an arc from the point of y = 1.52 as the film thickness increases. If TiO₂When the optical film thickness of λ / 4 is λ / 4, the locus of the synthetic admittance results in a point of 3.79 on the real axis (λ / 4 law). This is TiO / 4 film thickness on a glass substrate (transparent substrate)₂It is a synthetic admittance when a film (first transparent layer) is formed. That is, when this structure is viewed from above, it is as if viewing an integrated substrate with n = 3.79. Since the reflectance at this time is obtained by the following equation (3) at the interface with air, the reflectance R = 33.9%.
[0034]
R = (n−1 / n + 1)²... (3)
[0035]
  Next, when a film (second transparent layer) of n = y = 1.947 is further formed on the optical multilayer structure by an optical film thickness = λ / 4, the film is 3 on the optical admittance diagram. .The locus moves clockwise from the 79 point. The composite admittance is Y = 1.0, which is 1.0 on the real axis. That is, since the synthetic admittance = the synthetic refractive index is equivalent to 1.0, that is, equivalent to air, there is no reflection at the interface, so-called V coat reflection.PreventionIt can be regarded as a membrane. This is the reflection characteristic when the optical multilayer structure 1 is in the state shown in FIG.
[0036]
  On the other hand, the TiO₂When a gap portion of n = 1 (air) is provided on the film (n = 2.4) (first transparent layer) by the optical film thickness = λ / 4, the synthetic admittance is As shown in FIGS. 6A and 6B, Y₂= 0.2638. Further, a film of n = y = 1.947 (second transparent layer) is formed on the gap.ButOptical film thickness = λ / 4 onlyExistenceThen, the synthetic admittance is Y_Three= 14.37, which is 14.37 on the real axis. The reflectivity at that time is Y in the above equation (3)._Three= 14.37. At this time, the reflectance R is 76%. This is a characteristic when the optical multilayer structure 1 is in the state shown in FIG. From the above, when the air layer of the gap 12 is changed from “0” to an optical film thickness of “λ / 4” (that is, switching from the state of FIG. 2 to the state of FIG. 1), the reflectance is “ It turns out that it changes from "0%" to "76%."
[0037]
Where Y₁= N₁ ²/ N_s, Y_Three'= N₂ ²  / Y₁= N₂ ²・ N_s/ N₁(See FIG. 5A). In order to realize such characteristics, Y_Three‘= 1.0 (the admittance of air) should be n₂ ²・ N_s/ N₁ ²= 1.0, that is, the above equation (2), that is, n₂= N₁/ √n_SIt is sufficient if the relationship is established. Even if these refractive indexes are not strictly in this relationship, it is possible to make up a little with the film thickness or the like.
[0038]
〔Concrete example〕
7A and 7B show a glass substrate (n) as the transparent substrate 10 in the optical multilayer structure 1 of the present embodiment._S= 1.52), TiO as the first transparent layer 11₂Membrane (n₁= 2.32), the air layer (n_D= 1.00), Bi as the second transparent layer 13₂O_ThreeFilm (refractive index n₂= 1.92) represents the relationship between the wavelength of incident light (design wavelength 550 nm) and the reflectance. Here, FIG. 7A shows the case where the optical film thickness of the gap (air layer) is “λ / 2” (physical thickness = 275 nm) and “λ / 4” (137.5 nm). B) represents the characteristics when the optical film thickness of the gap (air layer) is “0” and “λ / 4”, respectively.
[0039]
8A to 8C show these optical admittance diagrams. FIG. 8A shows the optical film thickness of the gap (air layer) as “λ / 2”, and FIG. The optical thickness of the gap (air layer) is “λ / 4”, and FIG. 8C shows the case where the optical thickness of the gap (air layer) is “0”.
[0040]
As is apparent from the characteristic diagram shown in FIG. 7, in the optical multilayer structure 1 of the present embodiment, when the optical film thickness of the gap (air layer) 12 is “λ / 2”, the incident light ( Low reflection characteristics with respect to the wavelength λ), high reflection characteristics when the optical thickness of the gap 12 is “λ / 4”, and low reflection characteristics when the optical thickness of the gap 12 is 0. I understand that. That is, when the optical film thickness of the gap 12 is switched between an odd multiple of “λ / 4” and an even multiple of “λ / 4” (including 0), the high reflection characteristics and the low reflection characteristics alternate. Will be shown. Even when the optical film thickness is “λ / 2” even when the optical film thickness is “λ / 2”, the V coat reflection characteristic is exhibited for a specific wavelength (550 nm). The V-shaped characteristic becomes smooth, becomes almost flat, and the band with a reflectance of 0% becomes wider.
[0041]
Thus, in this embodiment, high-contrast modulation can be performed even in the visible light region such as 550 nm. Moreover, since it has a simple configuration and the moving range of the movable part is at most “λ / 2”, a high-speed response is possible. Therefore, by using this optical multilayer structure 1, a high-speed optical switching element and an image display device can be realized.
[0042]
[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG. 9 and FIG. In the first embodiment, the structure capable of changing the reflection characteristics in a specific wavelength range has been described. However, in the present embodiment, a uniform wavelength (flat) in a broad wavelength range is almost uniform. The reflection characteristics can be changed.
[0043]
The optical multilayer structure 2 according to the present embodiment has a first transparent layer 21 and a second transparent layer 22 in contact with the transparent substrate 20 on the transparent substrate 20 made of a non-metallic transparent material. The gap 23, the third transparent layer 24, and the fourth transparent layer 25, which have a size that can be raised and whose size is variable, are arranged in this order. Here, FIG. 9 shows a state where a later-described gap portion 23 exists in the optical multilayer structure 2, and FIG. 10 shows a state where there is no gap portion of the optical multilayer structure 2.
[0044]
In the present embodiment, the refractive index of the transparent substrate 20 is n_S, The refractive index of the first transparent layer is n₁, The refractive index of the second transparent layer is n₂, The refractive index of the third transparent layer is n_Three, The refractive index of the fourth transparent layer is n_FourIs set so that the relationship of the following formula (4) is established.
[0045]
n_S<N₁<N₂≒ n_ThreeAnd n_Four<N₁... (4)
[0046]
Specific materials include, for example, a transparent glass substrate or a transparent plastic substrate as the transparent substrate 20, and Al as the first transparent layer 21.₂O_ThreeMembrane (n₁= 1.67), the second transparent layer 22 is TiO₂Membrane (n₂= 2.4) As the third transparent layer 24, TiO₂Membrane (n_Three= 2.4), the fourth transparent layer 25 is MgF₂Membrane (n_Four= 1.38). Optical film thickness n of the first transparent layer 21 to the fourth transparent layer 25₁d₁, N₂d₂, N_Threed_Three, N_Fourd_FourIs “λ / 4” or “odd multiple of λ / 4” (λ is the wavelength of the incident light).
[0047]
The first transparent layer 21 to the fourth transparent layer 25 may be a composite layer composed of two or more layers having different optical characteristics. In this case, the synthesized optical characteristics (optical admittance) in the composite layer are used. ) Must have the same characteristics as a single layer.
[0048]
Similar to the gap portion 12 of the first embodiment, the size of the gap portion 23 (the distance between the second transparent layer 22 and the third transparent layer 24) can be changed by the driving means described later. . The medium for filling the gap 23 is the same as that for the gap 12.
[0049]
In the optical multilayer structure 2 of the present embodiment, since the above equation (4) is established, the reflection characteristic can be obtained in a wide band, and the size of the gap portion 23 can be changed to change the transparent substrate 20 side or transparent The amount of reflection or transmission of light incident from the side opposite to the substrate 20 is changed. More specifically, as in the first embodiment, the optical size of the gap 23 is set to “ By changing binary or continuously between “odd multiple of λ / 4” and “even multiple of λ / 4 (including 0)”, the amount of reflection or transmission of incident light is binary. Or it changes continuously.
[0050]
FIG. 11 shows a glass substrate (n) as the transparent substrate 20 in the optical multilayer structure 2 of the present embodiment._S= 1.52), TiO as the first transparent layer 21₂Membrane and MgF₂(Magnesium fluoride) film (composite refractive index n₁= 1.7, corresponding to the composite film thickness λ / 4), and TiO as the second transparent layer 22₂Film (refractive index n₂= 2.32), the air layer as the gap layer 23, and TiO as the third transparent layer 24₂Film (refractive index n_Three= 2.32), MgF as the fourth transparent layer 25₂Film (refractive index n_Four= 1.38) is a characteristic diagram showing the relationship between the wavelength (design wavelength) of incident light and the reflectance. Here, FIG. 11 shows the characteristics when the optical film thickness of the gap (air layer) 23 is “λ / 4” (physical thickness = 137.5 nm), and the optical film thickness of the gap (air layer) 23. Shows the characteristics when is 0.
[0051]
12A and 12B show these optical admittance diagrams. FIG. 12A shows an optical film thickness of the gap (air layer) 23 of “0” and FIG. 12B. Indicates the case where the optical film thickness of the gap (air layer) 23 is “λ / 4”.
[0052]
As is apparent from the characteristic diagram of FIG. 11, in the optical multilayer structure 2 of the present embodiment, when the optical film thickness of the gap (air layer) 23 is “λ / 4”, it covers a wide band. It can be seen that when the high reflection characteristic (approximately 60%) and the optical film thickness of the gap 23 are “0”, flat low reflection characteristics (approximately 0%) are exhibited over a wide band.
[0053]
[Modification]
In the optical multilayer structure shown in FIG. 13, a metal film having a film thickness of, for example, 100 nm or more and an aluminum (Al) layer 10a are formed on a transparent substrate 10 made of glass, and the first transparent layer 11 has a film thickness of 52. 67nm TiO₂The film, the second transparent layer 13 is made of TiO 2 with a film thickness of 32.29 nm.₂Film 13a, SiO. Film thickness of 114.72 nm₂Film 13b, TiO with a film thickness of 53.08 nm₂Film 13c and 19.53 nm thick SiO₂This is formed by a multilayer film made of the film 13d. When the aluminum layer 10a is 100 nm or more, light transmission is almost zero. In addition, providing an antireflection film on a non-transmitting film means that reflection is zero and all of the light is absorbed by the aluminum layer 10a. Furthermore, from the characteristics of aluminum itself, it is easy in design to make the reflectivity in the high reflection state when the antireflection characteristic is destroyed to be close to 100% with a small number of layers.
[0054]
FIG. 14 shows the result of simulation when the gap 12 is changed in this optical multilayer structure. Incident light is on the opposite side of the aluminum layer 10a (the uppermost SiO 2 layer).₂Incident from the side of the film 13d. The gap 12 is the second SiO2 from the top layer.₂Even if the film 13b is replaced, similar characteristics can be obtained. FIG. 15 shows the reflection characteristics at that time. The design wavelength at this time was 550 nm, and the film thickness of each layer is shown in the figure.
[0055]
The gap 12 in FIGS. 14 and 15 is assumed to be air or vacuum having a refractive index of 1.0. However, since this requires a somewhat complicated process to perform experimentally, instead of the gap. , Low refractive index material SiO₂The experiment was conducted using. The film configuration at this time is as shown in FIG. 16. FIG. 17 shows the result of the simulation, and FIG. 18 and FIG. 19 show the measurement results of the actual film formed. This shows that the simulation results and the actual measurement results are in good agreement. At this time, since the light is set to be incident from the glass substrate side, the reflection of about 4% on the surface is large in the actual measurement value. Some other deviation can be eliminated by controlling the film thickness while optically monitoring during film formation.
[0056]
FIG. 20 shows the reflection characteristics when the gap portion 12 is 386 nm and FIG. 21 is also 1485 nm in the optical multilayer structure shown in FIG. It can be seen that the width of the low reflection band in FIGS. 20 and 21 is narrower than the example of FIG. 14 (the gap 12 is 110.46 nm). That is, the larger the gap 12, the narrower the width of the low reflection region becomes, especially at 1500 nm or more, and the margin becomes low during manufacturing, which makes it difficult to handle. Therefore, the size of the gap 12 is less than 1500 nm, preferably within 500 nm. If it is this grade, it can produce without much problem.
[0057]
In the optical multilayer structure shown in FIG. 22, the first transparent layer 11 is directly formed on the transparent substrate 10 made of glass with a 40.89 nm-thick TiO 2 film.₂The film and the second transparent layer 13 are made of TiO 2 with a film thickness of 32.62 nm.₂Film 13a, 77.14 nm thick SiO₂Film 13b, TiO with a film thickness of 39.40 nm₂Film 13c and SiO with a film thickness of 163.13 nm₂This is formed by a multilayer film made of the film 13d. FIG. 23 shows the result of the simulation. The design wavelength at this time was 550 nm. Unlike the example of FIG. 13, since there is no light absorption film (aluminum layer) on the transparent substrate 10, the reflectance in the reflection band is low, but the transmitted light escapes without being absorbed by the multilayer structure. The body itself can be prevented from having heat.
[0058]
In the above embodiment, the gap portion of the optical multilayer structure is a single layer, but a plurality of layers, for example, two layers as shown in FIG. 24 may be provided. That is, on the transparent substrate 10, the first transparent layer 11, the first gap 12, the second transparent layer 13, the second gap 30, and the third transparent layer 31 are formed in this order, and the second The transparent layer 13 and the third transparent layer 31 are supported by supports 15 and 32 made of, for example, silicon nitride.
[0059]
In this optical multilayer structure, the intermediate second transparent layer 13 is displaced up and down, and one gap between the first gap 12 and the second gap 30 is narrowed, so that the other gap is widened. As a result, the reflection characteristics change.
[0060]
[Driving method]
Next, specific means for changing the size of the gaps 12 and 23 in the optical multilayer structures 1 and 2 will be described.
[0061]
FIG. 25 shows an example in which the optical multilayer structure is driven by static electricity. In this optical multilayer structure, electrodes 16a and 16a made of, for example, aluminum are provided on both sides of the first transparent layer 11 on the transparent substrate 10, respectively, and the second transparent layer 13 is made of, for example, silicon nitride (Si_ThreeN_Four), And electrodes 16b and 16b are formed at positions facing the electrodes 16a and 16a of the support 15.
[0062]
In this optical multilayer structure, the optical film thickness of the gap portion 12 is set to, for example, “λ / 4” and “0” by the electrostatic attraction generated by the potential difference caused by the voltage application to the electrodes 16a and 16a and the electrodes 16b and 16b. Or in a binary manner between “λ / 4” and “λ / 2”. Of course, by continuously changing the voltage application to the electrodes 16a and 16a and the electrodes 16b and 16b, the size of the gap 12 is continuously changed within a certain range of values, and the incident light is reflected or transmitted. Alternatively, the amount of absorption or the like can be changed continuously (analog).
[0063]
In addition, the method shown in FIGS. 26 and 27 may be used to drive the optical multilayer structure with static electricity. In the optical multilayer structure 1 shown in FIG. 26, a transparent conductive film 17a made of, for example, ITO (Indium-Tin Oxide) is provided on the first transparent layer 11 on the transparent substrate 10, and, for example, SiO 2₂The second transparent layer 13 is formed in a cross-linked structure, and a transparent conductive film 17b made of ITO is provided on the inner surface of the second transparent layer 13.
[0064]
In this optical multilayer structure, the optical film thickness of the gap portion 12 can be switched by electrostatic attraction generated by a potential difference caused by voltage application between the transparent conductive films 17a and 17b.
[0065]
In the optical multilayer structure shown in FIG. 27, a conductive film made of, for example, aluminum (Al) is provided between the first transparent layer 12 and the transparent substrate 10 instead of the transparent conductive film 17a of the optical multilayer structure of FIG. 17c is provided.
[0066]
In addition to such static electricity, the optical multilayer structure can be driven by various methods such as a method using a micromachine such as a toggle mechanism or a piezoelectric element, a method using a magnetic force, and a method using a shape memory alloy. FIGS. 28A and 28B show a mode of driving using magnetic force. In this optical multilayer structure, a magnetic layer 40 made of a magnetic material such as cobalt (Co) having an opening is provided on the second transparent layer 13 and an electromagnetic coil 41 is provided below the transparent substrate 10. By switching the electromagnetic coil 41 on and off, the gap 12 is switched between, for example, “λ / 2” (FIG. 28A) and “0” (FIG. 28B). Thereby, the reflectance can be changed.
[0067]
[Optical switching device]
[0068]
FIG. 29 illustrates a configuration of an optical switching device 100 using the optical multilayer structure 1. In the optical switching device 100, a plurality (four in the figure) of optical switching elements 100A to 100D are arranged in a one-dimensional array on a transparent substrate 101 made of glass, for example. In addition, it is good also as a structure arrange | positioned not only in one dimension but in two dimensions. In this optical switching device 100, for example, TiO along one direction (element arrangement direction) of the surface of the transparent substrate 101.₂A film 102 is formed. TiO₂On the film 102, for example, an ITO (Indium-Tin Oxide: indium and tin oxide mixed film) film 103 is formed. These TiO₂The film 102 and the ITO film 103 correspond to the first transparent layer of the first embodiment.
[0069]
On the transparent substrate 101, TiO₂In the direction orthogonal to the film 102 and the ITO film 103, a plurality of Bi₂O_ThreeA membrane 105 is provided. Bi₂O_ThreeAn ITO film 106 as a transparent conductive film is formed outside the film 105. These ITO films 106 and Bi₂O_ThreeThe film 105 corresponds to the second transparent layer of the first embodiment, and has a crosslinked structure at a position across the ITO film 103. The optical film thickness of the first transparent layer and the second transparent layer is, for example, “λ / 4” (λ is the wavelength of incident light (550 nm)). Between the ITO film 103 and the ITO film 106, a gap 104 whose size changes in accordance with the switching operation (on / off) is provided. The optical film thickness of the gap 104 changes between, for example, “λ / 4” (137.5 nm) and “0” with respect to the wavelength of incident light (λ = 550 nm).
[0070]
In the optical switching elements 100A to 100D, the optical film thickness of the gap 104 is set to, for example, “λ / 4” and “0” by electrostatic attraction generated by a potential difference caused by voltage application to the transparent conductive film (ITO films 103 and 106). To switch between. In FIG. 29, the optical switching elements 100A and 100C are in the state where the gap 104 is “0” (ie, the low reflection state), and the optical switching elements 100B and 100D are in the state where the gap 104 is “λ / 4” (ie, the high Reflection state). The transparent conductive film (ITO films 103 and 106) and a voltage application device (not shown) constitute the “driving means” of the present invention.
[0071]
In this optical switching device 100, when the ITO film 103 on the first transparent layer side is grounded to have a potential of 0V and a voltage of, for example, + 12V is applied to the ITO film 106 formed on the second transparent layer side, the potential difference As a result, an electrostatic attractive force is generated between the ITO films 103 and 106. In FIG. 29, the ITO films 103 and 106 are brought into close contact like the optical switching elements 100A and 100C, and the gap 104 is in a "0" state. In this state, the incident light P₁Passes through the multilayer structure, and further passes through the transparent substrate 21 to transmit the transmitted light P.₂It becomes.
[0072]
Next, when the transparent conductive film 106 on the second transparent layer side is grounded and the potential is set to 0 V, the electrostatic attractive force between the ITO films 103 and 106 disappears, and in FIG. 29, the ITO film as in the optical switching elements 100B and 100D. 103 and 106 are separated from each other, and the gap 12 is in a state of “λ / 4”. In this state, the incident light P₁Is reflected and reflected light P_ThreeIt becomes.
[0073]
Thus, in the present embodiment, the incident light P in each of the optical switching elements 100A to 100D.₁By switching the gap portion to binary by electrostatic force, the transmitted light P₂And reflected light P_ThreeThe two directions can be switched and taken out. Of course, the incident light P can be obtained by continuously changing the size of the gap as described above.₁Transmitted light P₂Reflected light P_ThreeIt is also possible to switch continuously.
[0074]
In these optical switching elements 100A to 100D, since the distance that the movable part has to move is at most about “λ / 2 (or λ / 4)” of incident light, the response speed is sufficiently high to about 10 ns. It is. Therefore, a display light valve can be realized with a one-dimensional array structure.
[0075]
In addition, in the present embodiment, if a plurality of optical switching elements are assigned to one pixel, they can be independently driven. Therefore, when performing gradation display of image display as an image display device, a method using time division In addition to this, gradation display by area is also possible.
[0076]
(Image display device)
FIG. 30 illustrates a configuration of a projection display as an example of an image display device using the optical switching device 100. Here, the reflected light P from the optical switching elements 100A to 100D_ThreeAn example in which is used for image display will be described.
[0077]
The projection display includes light sources 200a, 200b, and 200c made of lasers of red (R), green (G), and blue (B) colors, and optical switching element arrays 201a, 201b, and 201c provided corresponding to the light sources. A dichroic mirror 202a, 202b, 202c, a projection lens 203, a galvano mirror 204 as a uniaxial scanner, and a projection screen 205. The three primary colors may be cyan, magenta, and yellow in addition to red, green, and blue. Each of the switching element arrays 201a, 201b, and 201c is a one-dimensional array of a plurality of the above switching elements in the direction perpendicular to the paper, for example, the required number of pixels, for example, 1000. ing.
[0078]
In this projection display, the light emitted from the RGB light sources 200a, 200b, and 200c is incident on the optical switching element arrays 201a, 201b, and 201c, respectively. In addition, it is preferable to make this incident angle as close to 0 as possible and to make it enter perpendicularly so that the influence of polarization may not be exerted. Reflected light P from each optical switching element_ThreeIs condensed on the projection lens 203 by the dichroic mirrors 202a, 202b, 202c. The light condensed by the projection lens 203 is scanned by the galvanometer mirror 204 and projected onto the projection screen 205 as a two-dimensional image.
[0079]
As described above, in this projection display, a plurality of optical switching elements are arranged in a one-dimensional manner, RGB light is respectively irradiated, and the light after switching is scanned by a one-axis scanner to display a two-dimensional image. be able to.
[0080]
In the present embodiment, the reflectance at the time of low reflection can be 0.1% or less, and the reflectance at the time of high reflection can be 70% or more. Therefore, a high contrast display of about 1,000 to 1 can be achieved. In addition, since the characteristics can be obtained at a position where the light is perpendicularly incident on the element, it is not necessary to consider polarization or the like when assembling the optical system, and the configuration is simple.
[0081]
Although the present invention has been described with reference to the embodiment and the modification, the present invention is not limited to the embodiment and the modification, and various modifications can be made. For example, in the above-described embodiment, the display configured to scan a one-dimensional array of light valves using a laser as a light source has been described. However, as shown in FIG. 31, an optical switching device arranged in a two-dimensional manner. A configuration may also be adopted in which light is emitted from the white light source 207 to 206 and an image is displayed on the projection screen 208.
[0082]
In the above embodiment, an example in which a glass substrate is used as a transparent substrate has been described. However, as shown in FIG. 32, for example, a paper using a flexible (flexible) substrate 209 having a thickness of 2 mm or less. The image may be viewed directly by viewing.
[0083]
Furthermore, in the above-described embodiment, an example in which the optical multilayer structure of the present invention is used for a display has been described. However, for example, an optical printer other than a display can be used such as drawing an image on a photosensitive drum using an optical printer. It is also possible to apply to various devices such as.
[0084]
【The invention's effect】
  As described above, according to the optical multilayer structure and the optical switching element of the present invention,,whileIncident from the transparent substrate side or the opposite side of the transparent substrate by changing the size of the gapVisibleThe amount of light reflection or transmission can be changed, and a high-speed response is possible with a simple configuration, particularly in the visible light region.
[0085]
Further, according to the image display device of the present invention, the optical switching elements of the present invention are arranged one-dimensionally, and image display is performed using the optical switching device having this one-dimensional array structure. In addition, since the characteristics can be obtained at a position where light is incident perpendicularly to the element, it is not necessary to consider polarization or the like when assembling the optical system, and the configuration is simplified.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration when a gap portion of an optical multilayer structure according to a first embodiment of the present invention is “λ / 4”.
FIG. 2 is a cross-sectional view showing a configuration when the gap portion of the optical multilayer structure shown in FIG. 1 is “0”.
3 is a cross-sectional view for explaining a manufacturing process of the optical multilayer structure shown in FIG. 1. FIG.
4 is a plan view for explaining a process following the process of FIG. 3. FIG.
FIG. 5 is a diagram for explaining characteristics when the gap portion of the optical multilayer structure shown in FIG. 1 is “0”;
6 is a diagram for explaining the characteristics when the gap portion of the optical multilayer structure shown in FIG. 1 is “λ / 4”. FIG.
FIG. 7 is a diagram showing the reflection characteristics of the optical multilayer structure shown in FIG.
FIG. 8 is a diagram for explaining the reflection characteristics (optical admittance) of FIG. 7;
FIG. 9 is a cross-sectional view showing a configuration when the gap portion of the optical multilayer structure according to the second embodiment of the present invention is “λ / 4”.
10 is a cross-sectional view showing a configuration when the gap portion of the optical multilayer structure shown in FIG. 9 is “0”.
11 is a diagram showing the reflection characteristics of the optical multilayer structure shown in FIG. 9. FIG.
12 is a diagram for explaining reflection characteristics (optical admittance) of the optical multilayer structure of FIG. 11. FIG.
FIG. 13 is a cross-sectional view for explaining a modification of the first embodiment.
14 is a diagram illustrating reflection characteristics of the optical multilayer structure of FIG.
15 is a diagram illustrating reflection characteristics of the optical multilayer structure of FIG.
FIG. 16 is a cross-sectional view for explaining another modification of the first embodiment.
FIG. 17 is a diagram illustrating reflection characteristics (simulation) of the optical multilayer structure of FIG.
18 is a diagram illustrating reflection characteristics (actual measurement values) of the optical multilayer structure of FIG. 16;
FIG. 19 is a diagram illustrating reflection characteristics (actual measurement values) of the optical multilayer structure of FIG.
20 is a diagram showing another reflection characteristic of the optical multilayer structure shown in FIG.
FIG. 21 is a diagram illustrating another reflection characteristic of the optical multilayer structure illustrated in FIG.
FIG. 22 is a cross-sectional view for explaining still another modification of the first embodiment.
FIG. 23 is a diagram illustrating reflection characteristics (simulation) of the optical multilayer structure of FIG.
FIG. 24 is a cross-sectional view for explaining still another modification of the first embodiment.
FIG. 25 is a cross-sectional view for explaining a method of driving the optical multilayer structure by static electricity.
FIG. 26 is a cross-sectional view for explaining another driving method by static electricity of the optical multilayer structure.
FIG. 27 is a cross-sectional view for explaining still another driving method by static electricity of the optical multilayer structure.
FIG. 28 is a cross-sectional view for explaining a magnetic driving method of the optical multilayer structure.
FIG. 29 is a diagram illustrating a configuration of an example of an optical switching device.
FIG. 30 is a diagram illustrating a configuration of an example of a display.
FIG. 31 is a diagram illustrating another example of the display.
FIG. 32 is a configuration diagram of a paper-like display.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 2 ... Optical multilayer structure, 10 ... Transparent substrate, 11, 21 ... 1st transparent layer, 12, 23 ... Gap part, 13, 22 ... 2nd transparent layer, 24 ... 3rd transparent layer, 25 ... Fourth transparent layer, 100—Optical switching device

Claims (5)

The transparency on the substrate, a first transparent layer in contact with the transparent substrate, the second transparent layer, its size is variable gap portion which has a size capable of causing an optical interference phenomenon, a third transparent layer, and and has a structure which is disposed a fourth transparent layer in the order of this, an optical multilayer structure having a driving means for changing an optical size of the gap portion,
The transparent substrate is a glass substrate, the first transparent layer is a composite layer composed of a TiO ₂ film and an MgF ₂ film, the second transparent layer is a TiO ₂ film, the third transparent layer is a TiO ₂ film, Each of the four transparent layers is composed of an MgF ₂ film and the gap portion is an air layer, and the first transparent layer, the second transparent layer, the third transparent layer, and the fourth transparent layer The optical film thickness is λ / 4 or an odd multiple of λ / 4 (λ is the wavelength of incident light),
By changing the optical size of the gap portion between the odd multiple of λ / 4 and the even multiple of λ / 4 (including 0) by the driving means in a binary or continuous manner, An optical multilayer structure that changes the amount of reflection or transmission of visible light incident from the transparent substrate side or the opposite side of the transparent substrate, in a binary or continuous manner . In each of the first transparent layer to the fourth transparent layer, at least two transparent layers sandwiching the gap portion, a part is made of a transparent conductive film, and the driving means is configured to apply a voltage to the transparent conductive film. The optical multilayer structure according to claim 1 , wherein the optical size of the gap is changed by an electrostatic force generated by application. The optical multilayer structure according to claim ₂ , wherein the transparent conductive film is formed of any one of ITO, SnO _2, and ZnO. The transparency on the substrate, a first transparent layer in contact with the transparent substrate, the second transparent layer, its size is variable gap portion which has a size capable of causing an optical interference phenomenon, a third transparent layer, and and has a structure which is disposed a fourth transparent layer in the order of this, an optical switching device having a driving means for changing an optical size of the gap portion,
The transparent substrate is a glass substrate, the first transparent layer is a composite layer composed of a TiO ₂ film and an MgF ₂ film, the second transparent layer is a TiO ₂ film, the third transparent layer is a TiO ₂ film, Each of the four transparent layers is composed of an MgF ₂ film and the gap portion is an air layer, and the first transparent layer, the second transparent layer, the third transparent layer, and the fourth transparent layer The optical film thickness is λ / 4 or an odd multiple of λ / 4 (λ is the wavelength of incident light),
By changing the optical size of the gap portion between the odd multiple of λ / 4 and the even multiple of λ / 4 (including 0) by the driving means in a binary or continuous manner, An optical switching element that changes the amount of reflection or transmission of visible light incident from the transparent substrate side or the opposite side of the transparent substrate in a binary or continuous manner . An image display device that displays a two-dimensional image by irradiating light to a plurality of optical switching elements arranged one-dimensionally or two-dimensionally,
The optical switching element, the transparency on the substrate, a first transparent layer in contact with the transparent substrate, the second transparent layer, its size is variable gap portion which has a size capable of causing an optical interference phenomenon, and has a structure which is disposed a third transparent layer, and the fourth transparent layer of in the order of this, a driving means for changing an optical size of the gap portion,
The transparent substrate is a glass substrate, the first transparent layer is a composite layer composed of a TiO ₂ film and an MgF ₂ film, the second transparent layer is a TiO ₂ film, the third transparent layer is a TiO ₂ film, Each of the four transparent layers is composed of an MgF ₂ film and the gap portion is an air layer, and the first transparent layer, the second transparent layer, the third transparent layer, and the fourth transparent layer The optical film thickness is λ / 4 or an odd multiple of λ / 4 (λ is the wavelength of incident light),
By changing the optical size of the gap portion between the odd multiple of λ / 4 and the even multiple of λ / 4 (including 0) by the driving means in a binary or continuous manner, An image display device that changes the amount of reflection or transmission of visible light incident from the transparent substrate side or the opposite side of the transparent substrate, in a binary or continuous manner .

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