JP2003233024A - Optical multilayered structure, optical switching element using the same, and picture display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical multilayered structure which has less reflection boundary surfaces and has a simple arrangement. <P>SOLUTION: An optical multilayered structure 1 has an arrangement where a first transparent layer 11 brought into contact with a substrate 10 used as an incidence medium, a gap part 12 which has a size allowing the occurrence of an interference phenomenon of light and can change the size, a second layer 13 being absorbent of light, and a third layer 14 being absorbent of light are arranged on the substrate 10 in order, and the optical multilayered structure modulates incident light from the substrate 10 side. They are set so as to satisfy formula (5) where nS and n<SB>1</SB>are refractive indexes of the substrate 10 and the first layer 11, respectively, and N<SB>2</SB>(=n<SB>2</SB>-i k<SB>2</SB>, n<SB>2</SB>is the refractive index, k<SB>2</SB>is the attenuation coefficient, and i is the imaginary unit) and N<SB>3</SB>(=n<SB>3</SB>-i k<SB>3</SB>, n<SB>3</SB>is the refractive index, k<SB>3</SB>is the attenuation coefficient, and i is the imaginary unit) are complex indexes of refraction of the second layer and the third layer, respectively. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multilayer structure having a function of reflecting, transmitting or absorbing incident light, an optical switching element using the optical multilayer structure and an image display device.

[0002]

2. Description of the Related Art In recent years, the importance of a display as a display device for video information is increasing, and it operates at high speed as an element for this display and further as an element for optical communication, an optical storage device, an optical printer and the like. There is a demand for the development of an optical switching element (light valve) that does. Conventionally, as this type of element, an element using a liquid crystal or an element using a micromirror (DMD: Digital Micro Miror D
evice, digital micromirror device, registered trademark of Texas Instruments), and one using a diffraction grating (GLV: Grating Light Valve, manufactured by SLM (Silicon Light Machine)).

GLV uses a diffraction grating as a MEMS (Micro Elec
tro Mechanical Systems) structure, and electrostatic force 10
A high-speed light switching element of ns is realized. D
The MD also has a MEMS structure and performs switching by moving a mirror. Although a display such as a projector can be realized by using these devices, since the liquid crystal and the DMD have a low operation speed, a two-dimensional array is required to realize the display as a light valve, which complicates the structure. . On the other hand, since GLV is a high-speed drive type, a projection display can be realized by scanning a one-dimensional array.

However, since the GLV has a diffraction grating structure, there are complications such as it being necessary to form six elements for one pixel and to combine diffracted light emitted in two directions into one by some optical system. There is.

As a device which can be realized with a simple structure, US Pat. No. 5,589,974 and US Pat.
No. 00,761. This light valve has a structure in which a translucent thin film having a refractive index of √n _S is provided on a substrate (refractive index n _S ) with a gap (gap layer) interposed therebetween. In this element, an optical signal is transmitted or reflected by driving a thin film using electrostatic force and changing the distance between the substrate and the thin film, that is, the size of a gap. Here, the refractive index of the thin film is √n _S with respect to the refractive index n _{S of the} substrate, and it is said that high contrast optical modulation can be performed by satisfying such a relationship.

[0006]

However, in the element having the above-mentioned structure, the substrate cannot be realized in the visible light region unless the refractive index n _{S of the} substrate is a large value such as "4". There is. That is, considering that the translucent thin film is a structure, a material such as silicon nitride (Si ₃ N ₄ ) (refractive index n = 2.0) is desirable, but in that case, the refractive index of the substrate is n _S = 4. In the visible region, the choice of such materials is narrow. For communication wavelengths such as infrared rays, germanium (Ge) (n =
4), silicon (Si) (n≈4), and the like.

Therefore, the same applicant as the present applicant first
The first layer, which absorbs light, causes the light interference phenomenon on the substrate.
A gap that has a size that can be crushed and whose size is variable
Section and an optical multilayer structure having a structure in which a second layer is provided
Structure, optical switching element using the same, and image display
Proposed a device (Japanese Patent Application No. 2000-219599)
book). The proposed optical multilayer structure absorbs light on the substrate.
The first layer, the gap, and the second layer that have
It has a structure that is set up. Also, with this optical multilayer structure
Is the complex index of the substrate N_S(= N_S-I ・ k_S, N_S
Is the refractive index, k_SIs the extinction coefficient, i is the imaginary unit), the first layer
The complex refractive index of N₁(= N₁-I ・ k₁, N ₁Is refraction
Rate, k₁Is the extinction coefficient), and the refractive index of the second layer is n₂,incident
When the refractive index of the medium is 1.0, the relation of the following equation (2)
Is configured to meet.

[0008]

[Equation 2]

According to the proposed optical multilayer structure, a high-speed response which is sufficient for constructing a two-dimensional image display device is possible, and an optical switching element can be realized with a simple structure in principle. . Furthermore, since it is possible to switch between light reflection and light absorption, it is possible to extremely easily perform processing of unnecessary light which is a problem in realizing the image display device. Therefore, this optical switching element can be suitably used for a direct-view / reflection-type image display device.

By the way, the above-mentioned proposed optical multilayer structure is
The light incident from the second layer side (the side opposite to the substrate) of the optical multilayer structure is modulated. Therefore, when an optical switching element or an image display device is constructed using this optical multilayer structure, a second optical multilayer structure is formed in order to protect and seal the optical multilayer structure formed on the substrate. A transparent one must be used as an additional substrate arranged on the layer side. In the case of color display, a color filter or the like is formed on this transparent additional substrate. However, since the reflective interfaces are increased by disposing the transparent additional substrate, reflection at these interfaces becomes a problem, and it may be necessary to take measures such as mounting an antireflection film.

The present invention has been made in view of the above problems, and an object thereof is to provide an optical multilayer structure having a small number of reflective interfaces and a simple structure, an optical switching element using the same, and an image display device. is there.

An optical multilayer structure according to the present invention has a transparent first layer on one surface of a substrate which also serves as an incident medium, and a gap portion having a size capable of causing a light interference phenomenon and having a variable size. , Has a structure in which a second layer and a third layer that absorbs light are arranged, and modulates the light incident from the substrate side.

In the optical multilayer structure according to the present invention, the refractive index of the substrate is n _S , the refractive index of the first layer is n ₁ , and the complex refractive index of the second layer is N ₂ (= n ₂ −i · k). ₂ , n ₂ is the refractive index, k
₂ is the extinction coefficient, i is the imaginary unit), the complex refractive index of the third layer is N ₃ (= n ₃ −i · k ₃ , n ₃ is the refractive index, k ₃ is the extinction coefficient, i is the imaginary unit) ), It is preferable that the relationship of the following expression (3) is satisfied.

[0014]

[Equation 3]

The optical switching element according to the present invention has a transparent first layer on one surface of a substrate which also serves as an incident medium, a gap portion having a size capable of causing a light interference phenomenon, and having a variable size. In order to change the optical size of the optical multi-layer structure that has the structure in which the second layer and the third layer that absorbs light are arranged, and that modulates the light incident from the substrate side, and the gap portion. And a driving means of.

The image display device according to the present invention displays a two-dimensional image by irradiating a plurality of one-dimensionally or two-dimensionally arranged optical switching elements with light. On one surface of the substrate which also serves as a transparent first layer, a transparent layer having a size capable of causing a light interference phenomenon and having a variable size, a second layer and a third layer having a light absorption property. It has a structure in which layers are arranged, and is provided with an optical multilayer structure for modulating light incident from the substrate side, and a driving means for changing the optical size of the gap.

In the optical multi-layer structure according to the present invention, light is incident from the substrate side, and the optical size of the gap portion is set to "λ /
4 "(where λ is the design wavelength of the incident light) and an even multiple of" λ / 4 "(including 0) are binary or continuously changed to reflect or transmit the incident light. Alternatively, the amount of absorption changes binary or continuously.

In the optical switching element according to the present invention, light is incident from the substrate side, and the optical size of the gap portion of the optical multilayer structure is changed by the driving means, so that the switching operation can be performed with respect to the incident light. Done.

In the image display device according to the present invention, a two-dimensional image is displayed by irradiating the plurality of optical switching elements of the present invention arranged in one or two dimensions with light from the substrate side. .

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 and 2 show the basic structure of an optical multilayer structure 1 according to an embodiment of the present invention. FIG. 1 shows a gap 12 which will be described later in the optical multilayer structure 1.
2 is present, and FIG. 2 shows a state when there is no gap 12 of the optical multilayer structure 1 and there is a low reflection. The optical multilayer structure 1 is specifically used, for example, as an optical switching element, and an image display device can be configured by arranging a plurality of the optical switching elements in one dimension or two dimensions.

This optical multilayer structure 1 has a transparent first layer 11 in contact with the substrate 10 on one surface of the substrate 10 which also serves as an incident medium, and a size capable of causing a light interference phenomenon. There is absorption of light, which is in contact with the gap 12 whose size can be changed, the first layer 11 and the second layer 13 formed on the opposite side with the gap 12 interposed therebetween, and the second layer 13. The third layer 14 is arranged in this order.

The substrate 10 also serves as an incident medium for the light incident on the first layer 11, and is made of, for example, silicon oxide (Si).
It may be made of a transparent material such as O ₂ ), glass or plastic.

The first layer 11 is made of a transparent material such as an oxide material or a nitride material. For example, titanium oxide (TiO ₂ ) (n ₁ = 2.4), silicon nitride (S
i ₃ N ₄ ) (n ₁ = 2.0), aluminum nitride (Al
N) (n ₁ = 2.16), niobium oxide (Nb ₂ O ₅ ).
(N ₁ = 2.2), tantalum oxide (Ta ₂ O ₅ ) (n ₁
= 2.1) or the like.

Optical thickness n ₁ · d of the first layer 11
₁ is less than or equal to "λ / 4" (λ is the design wavelength of incident light). The reason will be described later.

The gap 12 is formed by a driving means described later.
Its optical size (of the first layer 11 and the second layer 13
Interval) is set to be variable. Gap 12
The medium for filling the liquid may be gas or liquid as long as it is transparent.
As the gas, for example, air (sodium D line (58
Refractive index n for 9.3 nm)_D= 1.0), nitrogen (N
₂) (N_D= 1.0) and the like, the liquid is water (n_D=
1.333), silicone oil (n_D= 1.4-1.
7), ethyl alcohol (n_D= 1.3618), green
Serine (n_D= 1.4730), jod methane (n_D
= 1.737) and the like. In addition, the gap 12
It can also be in a vacuum state. In this embodiment, the gap
The part 12 is filled with air.

The optical size of the gap 12 is "λ / 4".
Between "an odd multiple of .lambda." And "an even multiple of .lambda. / 4 (including 0)". As a result, the amount of reflection, transmission, or absorption of incident light changes binary or continuously. As in the case of the film thicknesses of the first layer 11 and the second layer 13, even if the film thickness is slightly different from the multiple of λ / 4, it can be complemented by a slight change in the film thickness or the refractive index of the other layers. Therefore, the expression “λ / 4” includes the case of “approximately λ / 4”.

It should be noted that "λ / 4" in the notation in this specification may not be strictly "λ / 4", but may be a value in the vicinity thereof. This is because, for example, the optical thickness of one layer becomes thicker than λ / 4, which can be complemented by making the other layer thinner, and the refractive index can be slightly calculated from the formula (4) described later. This is because the film thickness can be adjusted in some cases even when there is a deviation. Therefore, in this specification, the expression “λ / 4” also includes the case of “approximately λ / 4”.

The second layer 13 is made of metal such as tungsten (W), tantalum (Ta), titanium (Ti), metal nitride such as titanium nitride (TiN), or germanium (G).
It may be made of a material that absorbs light, such as a semiconductor such as e). Note that an example of the material of the second layer 13 will be described later with reference to FIG. 7.

The third layer 14 is a metal oxide such as chromium oxide (CrO), a metal nitride such as titanium nitride (TiN),
Carbide such as carbon (C), graphite (graphite), silicon carbide (SiC) or silicon (Si)
It may be made of a material that absorbs light, such as a semiconductor. Note that an example of the material of the third layer 14 will be described later with reference to FIG. 7.

The third layer 14 preferably has a thickness that does not transmit light. This is because the incident light is absorbed by the third layer 14 at the time of low reflection, and there is no possibility of generating stray light or the like.

The first layer 11, the second layer 13 and the third layer 14 may be a composite layer composed of two or more layers having different optical characteristics, but in this case, the composite layer It is necessary that the combined optical characteristics have the same characteristics as those of the single layer.

Next, with reference to FIGS. 3 and 4, and FIG. 5, conditions to be satisfied by the optical constants of the respective layers described above in order to realize the above optical multilayer structure 1 will be described. 3 and 4 used in the following description,
Although the optical multilayer structure 1 shown in FIGS. 1 and 2 is shown, the substrate 10 as an incident medium is indicated by a dotted line, the transparent first layer 11 is the uppermost layer, and the optical layer 1 is an optical layer for the sake of clarity. The third layer 14 having the above absorption is shown as the bottom layer in the reverse order of FIGS. 1 and 2.

In this embodiment, as shown in FIGS. 3 and 4, the transparent substrate 10 having a refractive index of n _S is an incident medium, and the transparent first layer having a refractive index of n ₁ is used. 11 is the uppermost layer, and the second layer 13 and the lowermost third layer 14
And are made of a material that absorbs light. FIG. 3 shows a state where there is a gap portion 12 and high reflection, and FIG. 4 shows the gap portion 1.
There is no 2 and the state at the time of low reflection is shown.

First, when there is no gap 12 shown in FIG.
In the case of low reflection, that is, the first layer 11 and the second layer
Optical add of respective material of layer 12 and third layer 14
Substrate is a synthetic optical admittance that combines Mittance.
10 optical admittances (n _STo be equal to)
By doing so, the reflectance for the design wavelength can be made zero.
It Here, the optical admittance y is the complex refractive index N
(= N−i · k, n is the refractive index, k is the extinction coefficient, and i is the imaginary number
Unit) and the value is the same. For example, the admittance of air
S is y (air) = 1, n (air) = 1, glass admittance
The ratio is y (glass) = 1.52, n (glass) =
It is 1.52.

That is, n₁Transparent first with a refractive index of
Layer 11 of the (n _S, 0) point (board
10 optical admittance, which is equivalent to the refractive index)
As shown in FIG. 5, the locus of movement is n on the real axis Re (Y).
_SAnd n₁ ²/ N_S, And the center C is (n₁ ²+
n_S ²) / 2n_S, Radius r is (n₁ ²-N_S ²) / 2n
_SArc a. Where the optics of the material of the third layer 14
Admittance y₃(= Complex refractive index N₃(= N₃-I
k₃, N₃Is the refractive index, k₃Is the extinction coefficient, i is the imaginary unit
Position)) is inside the arc a in FIG. 5 and outside the arc a,
Optical admittance y of the material of the second layer 13₂(= Complex
Refractive index N₂(= N₂-I ・ k₂, N₂Is the refractive index, k ₂Is
Extinction coefficient, i is an imaginary unit)), the third layer
14 and second layer 13 combined optical admittance y
₃₂Is the optical admittance y of the third layer 14.₃Depart from
Then, as the film thickness of the second layer 13 increases, a gentle curve
, And the optical admittance y of the second layer 13₂Return to
To do. Optical admittance y of the third layer 14₃And the second
Optical admittance y of layer 13₂Means that of the first layer 11
Since it is located on the opposite side across the arc a, the third layer 1
4 and second layer 13 combined optical admittance y₃₂Is
The arc a of the first layer 11 must be crossed. Thus, the third
Synthetic optical admittance y of the layer 14 and the second layer 13₃₂
Becomes a value at the intersection with the arc a of the first layer 11.
Moreover, the film thickness of the second layer 13 can be determined. Third
Synthetic optical array of layer 14, second layer 13 and first layer 11
Domittance changes from this intersection to the arc a of the first layer 11.
Move along. Therefore, the first layer 11 and the second layer
The combined optical admittance of 12 and the third layer 14 is
Optical admittance of substrate 10 (n_SIs equal to)
Thus, the film thickness of the first layer 11 can be determined.

[0037] Thus, the optical admittance y ₃ of the third layer 14 and the optical admittance y ₂ of the second layer 13, opposite side of the arc a which depends on the optical properties of the first layer 11 Therefore, there is always a combination of film thicknesses such that the reflectance with respect to the design wavelength is 0. The optical admittance y ₃ of the third layer 14 may be inside or outside the arc a.

The third layer 14 for satisfying such conditions
The relationship between the optical constants of the second layer 13 and the second layer 13 is expressed by the following equation (4). However, by arranging a material having another optical constant very thinly, the third layer 14, the second layer 13, and the first layer 13 can be formed.
Since the combined optical admittance of the layer 11 of n may be reduced to n _S , it may not be necessary to completely satisfy the equation (4). Therefore, it is sufficient if the equation (4) is substantially satisfied.

[0039]

[Equation 4]

In FIG. 5, the optical film thickness n ₁ · d ₁ of the first layer 11 is the first layer 1 starting from (n _S , 0).
The arc a of 1 becomes a semicircle (n ₁ ² / n on the real axis)
_S ), it becomes “λ / 4” (λ is the design wavelength of the incident light). Since the combined optical admittance y _{32 of} the third layer 14 and the second layer 13 crosses the arc a of the first layer 11 in the middle of the semicircle, the optical film of the first layer 11 is formed. Thickness n ₁
・ D ₁ is less than or equal to “λ / 4”.

On the other hand, as shown in FIG. 3, when the gap portion 12 is provided, the first layer 11, the gap portion 12 and the second layer 1 are provided.
The combined optical admittance of the third and third layers 14 does not result in a refractive index n _S of the substrate 10 and is highly reflective.

That is, in this optical multilayer structure 1, when the gap 12 between the first layer 11 and the second layer 13 is "0", it serves as an antireflection film, and the gap becomes the design wavelength. On the other hand, when it is optically approximately λ / 4, it becomes a reflective film. That is, by making the interval variable between “0” and “λ / 4”, it is possible to realize an optical switching element whose reflectance can be changed to “0” and “70%” or more as described later. You can In order to make the size of the gap 12 variable, the substrate 1
0 and at least one of the first layer 11 and the second
Of at least one of the third layer 13 and the third layer 14 of at least a part of ITO (Indium-Tin Oxide) (n
= 2.0) and other methods, such as driving by static electricity, including a transparent conductive film. The transparent conductive film may be made of tin oxide (SnO ₂ ) (n = 2.0) or zinc oxide (ZnO) (n = 2.0) in addition to ITO.

By the way, in the above equation (4), the equal sign indicates that the optical characteristic of the second layer 13 is equal to the optical characteristic of the third layer 14, that is, as shown in FIG. This corresponds to the case where the second layer 13 is omitted in 3. In the optical admittance diagram of FIG.
This corresponds to the case where the optical admittance y ₃ of the layer 14 is on the arc a of the first layer 11.

As a combination of materials for such an optical multi-layer structure, it is sufficient that the above constraints are satisfied, and the degree of freedom in selection is wide. In FIG. 7, the substrate 10 is SiO ₂ .
It can be used as the curve a (corresponding to the arc a in FIG. 5) representing the optical admittance diagram of the first layer 11 when the first layer 11 is TiO ₂ , and as the second layer 13 and the third layer 14. It also shows the optical admittance (equivalent to the complex refractive index) of various materials. A combination of the material inside and outside the curve (semicircle) a in FIG. 7 finds a design that realizes the optical multilayer structure described above. Table 1
Represents an example thereof. The optical characteristics in Table 1 are based on Palik's literature values (ED Palik, Ha
ndbook of Optical Constants of Solids, Academic Pr
ess).

[0045]

[Table 1]

Here, the substrate 10 is made of quartz (Si
O₂), TiO as the first layer 11 ₂Layers, gaps 12 and
The air layer (n = 1.00) and the second layer 13 are
A carbon layer was used as the Gusten layer and the third layer 14.
As described above, the third layer 14 made of a carbon layer is light-sensitive.
The film thickness is such that it does not pass through
m and above. The reason is that the carb of the third layer 14 is
Film thickness of 100 nm, 300 nm and sufficiently thick
For each case, we investigated the reflection characteristics at low reflection.
However, as shown in FIG. 8, a film thickness of 300 nm is sufficient.
This is because the reflection characteristics are almost the same as those of the thick case.
In addition, in FIG. 8, the curve 8A is for a film thickness of 100 nm.
Curve 8B when the film thickness is 300 nm, and curve 8C
Indicates that the film thickness is sufficiently thick.

FIG. 9 shows a result of simulating the relationship between the wavelength of the incident light (design wavelength 550 nm) and the reflectance with such a configuration. Here, the curve 9A has an optical film thickness of the gap 12 (air layer) of “0” (low reflection side), and the curve 9B has an optical film thickness of “λ / 4” (138 nm).
The characteristics in the case of (high reflection side) are shown. Figure 9
As can be seen from the figure, at the design wavelength of 550 nm, the reflection characteristics are 0% at low reflection and 73% at high reflection. FIG. 10 shows a combined optical admittance diagram at the time of low reflection, where the combined optical admittance is 1.
It can be seen that this results in 46 (refractive index of the substrate 10). On the other hand, FIG. 11 shows a combined optical admittance diagram at the time of high reflection, and the combined optical admittance does not result in the refractive index of the substrate 10.

As can be seen from the optical admittance (equivalent to complex refractive index) of various materials shown in FIG.
The same characteristics can be obtained by using germanium, tantalum, titanium or the like instead of tungsten as the material of the layer 13. The substrate 10 may also be glass or plastic.

Table 2 shows the optical characteristics of the second layer 13 in the case of the equal sign in the above formula (4), that is, the third layer 1
7 shows an example of a configuration (see FIG. 6) in which the second layer 13 is omitted by making the optical characteristics equal to those of No. 4 in FIG.

[0050]

[Table 2]

Here, as the substrate 10, quartz (Si
O₂), TiO as the first layer 11 ₂Layers, gaps 12 and
And using the air layer (n = 1.00) is similar to the example in Table 1.
Similarly, but omitting the second layer 13 and replacing the third layer 14 with
Then, a silicon (Si) crystal is used. From Figure 7
, The optical admittance of the silicon crystal (complex
Folding rate and equivalent) are almost₂First layer consisting of layers 1
It is on the optical admittance curve a of 1.

FIG. 12 shows a result of simulating the relationship between the wavelength of the incident light (design wavelength 550 nm) and the reflectance with the configuration shown in Table 2. Where curve 1
2A has an optical film thickness of the gap 12 (air layer) of "0" (low reflection side), and curve 12B has an optical film thickness of "λ / 4" (138n).
m) (high reflection side).
As can be seen from FIG. 12, at the design wavelength of 550 nm, 0.2% at low reflection and 76% at high reflection are shown.

In the optical multilayer structure 1 of the present embodiment, light is made incident from the substrate 10 side, and the optical size of the gap portion 12 is set to an odd multiple of λ / 4 and an even multiple of λ / 4 (0. (For example, between “λ / 4” and “0”), the amount of reflection, transmission, or absorption of incident light is changed. It is a thing.

As described above, in the present embodiment, since the incident light from the substrate 10 side is modulated, the substrate 10
It becomes possible to serve as the transparent protective substrate of the optical multilayer structure 1 by itself. Therefore, it is not necessary to dispose another transparent protective substrate on the substrate 10 side (the side on which light is incident), and the number of reflective interfaces can be reduced. Furthermore, when an image display device is formed by using this optical multilayer structure 1, a color filter or the like can be directly formed on the other surface of the substrate 10, and a transparent protective substrate on which the color filter is formed is a separate component. There is no need to prepare as. Further, the protective member on the second layer 14 side of the optical multilayer structure 1 does not need to be a transparent substrate because light does not enter, and an opaque material such as an inexpensive metal plate may be used. You may arrange.

Further, even in the visible light region such as 550 nm, the reflectance at the time of low reflection can be almost 0 and the reflectance at the time of high reflection can be 70% or more, so that a high contrast of about 1000: 1 can be obtained. A display is feasible. Moreover, since the structure is simple, it can be manufactured more easily than a diffraction grating structure such as GLV or a complicated three-dimensional structure such as DMD. Further, the GLV requires six lattice-shaped ribbons for each pixel, but in the present embodiment, only one ribbon is required, so that the configuration is simple and can be made small. Further, since the moving range of the movable part is at most "λ / 2", high-speed response of 10 ns level becomes possible. Therefore, when it is used as a light valve for display, it can be realized with a simple structure of a one-dimensional array as described later.

Furthermore, the optical multilayer structure 1 of the present embodiment
Is essentially different from a narrow band transmission filter having a structure in which a gap is sandwiched by a metal thin film or a reflective layer, that is, a Fabry-Perot type filter, and therefore the bandwidth of the low reflection band can be widened. Therefore, it is possible to take a relatively wide margin of the film thickness control at the time of manufacturing, and the degree of freedom in design is increased.

Further, in the present embodiment, the complex refractive indexes of the second layer 13 and the third layer 14 need only be values satisfying certain conditions, so that the degree of freedom in selecting materials is widened. Furthermore, since the third layer 14 has a thickness that does not transmit light, incident light is absorbed by the third layer 14 at the time of low reflection, and there is no fear of generating stray light or the like.

As described above, by using the optical multilayer structure 1 of the present embodiment, it is possible to realize an optical switching element and an image display device which are small in size at high speed and have improved reliability. Details of these will be described later.

[Driving Method] Next, the above optical multilayer structure 1
A specific means for changing the size of the gap portion 12 will be described.

FIG. 13 shows an example of driving an optical multilayer structure by static electricity. In this optical multilayer structure, electrodes 16a, 16a made of, for example, aluminum are provided on both sides of a first layer 11 on a transparent substrate 10, and the second layer 13 and the third layer 14 are made of, for example, silicon nitride. Supported by a support 15 made of (Si ₃ N ₄ ),
The electrodes 16b and 16b are formed on the support 15 at positions facing the electrodes 16a and 16a.

In this optical multilayer structure, the electrodes 16a, 1
6a and the electrodes 16b, 16b are electrostatically attracted to each other by an electrostatic attraction force to cause the optical film thickness of the gap 12 to fall between, for example, "λ / 4" and "0", or "λ".
Binary switching between “/ 4” and “λ / 2”. Of course, by continuously changing the voltage applied to the electrodes 16a, 16a and the electrodes 16b, 16b, the size of the gap 12 is continuously changed within a certain range, and the incident light is reflected or transmitted. Alternatively, the amount of absorption or the like can be changed continuously (analogically).

Other than the method of driving the optical multilayer structure by static electricity, the method shown in FIGS. 14 and 15 may be used. The optical multi-layer structure 1 shown in FIG. 14 has, for example, an ITO (Indi
a transparent conductive film 17a made of um-Tin Oxide) is provided, and the second layer 13 and the third layer 14 are formed in a cross-linked structure, and ITO is also formed on the outer surfaces of the second layer 13 and the third layer 14. A transparent conductive film 17b made of is provided.

In this optical multilayer structure, the transparent conductive film 17 is used.
The optical film thickness of the gap portion 12 can be switched by the electrostatic attraction generated by the potential difference due to the voltage application between a and 17b.

In the optical multilayer structure shown in FIG. 15, the structure shown in FIG.
In place of the transparent conductive film 17a of the optical multi-layer structure of 3, a high refractive index transparent conductive film such as ITO is provided as the conductive first layer 11.

In addition to such static electricity, various methods can be considered for driving the optical multilayer structure, such as a method using a micromachine such as a toggle mechanism or a piezoelectric element, a method using magnetic force, or a method using a shape memory alloy. 16 (A) and 16 (B) 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 third layer 14, and an electromagnetic coil 41 is provided below the substrate 10. By switching the electromagnetic coil 41 on and off, the gap of the gap 12 is set to, for example, "λ / 4" (see FIG. 1).
6 (A)) and "0" (FIG. 16 (B)) can be switched to change the reflectance.

[Optical Switching Device] FIG. 17 shows a configuration of an optical switching device 100 using the optical multilayer structure 1. A plurality of optical switching devices 100 (four in the figure) are provided on a substrate 110 made of glass, for example.
The optical switching elements 100A to 100D are arranged in a one-dimensional array. In addition, it is not limited to one-dimensional
It may be arranged in a dimension. In this optical switching device 100, for example, the ITO film 111A and the TiO ₂ film are arranged along one direction (element arrangement direction) of one surface of the substrate 110.
The film 111B is formed. This ITO film 111A
And the TiO ₂ film 111B correspond to the first layer 11 in the above-described embodiment.

On the substrate 110, a plurality of tungsten (W) films 113 are arranged in a direction orthogonal to the ITO film 111A and the silicon nitride film 111B. The carbon (C) film 11 is provided outside the tungsten film 113.
4 are provided. The tungsten film 113 and the carbon film 114 correspond to the second layer 13 and the third layer 14 of the above-described embodiment, respectively. TiO ₂ film 11
Between 1B and the tungsten film 113, a gap 112 whose size changes according to a switching operation (ON / OFF) is provided. The optical film thickness of the gap 112 changes with respect to the wavelength of incident light (λ = 550 nm), for example, between “λ / 4” (138 nm) and “0”.

Optical switching elements 100A to 100D
Is, for example, the ITO film 111A and the tungsten film 11
The optical film thickness of the gap 12 is switched between, for example, "λ / 4" and "0" by the electrostatic attractive force generated by the potential difference due to the voltage application to 3. In FIG. 17, in the optical switching elements 100A and 100C, the gap 12 is in the state of “0” (that is, in the low reflection state), the optical switching element 100.
B and 100D show the state where the gap portion 12 is "λ / 4" (that is, the high reflection state). The ITO film 111
The A and tungsten films 113 and the voltage application device (not shown) constitute the "driving means" of the present invention.

In this optical switching device 100, the IT
The O film 111A is grounded to have a potential of 0 V, and the second layer 13
When a voltage of, for example, +12 V is applied to the tungsten film 113 corresponding to, an electrostatic attraction is generated between the ITO film 111A and the tungsten film 113 due to the potential difference, and
7, the first layer and the second layer are in close contact with each other like the optical switching elements 100A and 100C, and the gap 112 is "0".
It becomes the state of. In this state, the incident light P ₁ passes through the multilayer structure and is further absorbed by the carbon film 114 corresponding to the third layer 14.

Next, the transparent conductive film 106 on the second layer side is contacted.
When the ground potential is set to 0 V, TaN _XMembrane 102 and ITO
The electrostatic attraction between the film 106 and the film 106 disappears, and in FIG.
As with the first elements such as the switching elements 100B and 100D
The gap between the second layer and the second layer is "λ / 4".
It becomes a state. In this state, the incident light P₁Is reflected and anti
Light P₃Becomes

In this way, in the present embodiment, in each of the optical switching elements 100A to 100D, the gap of the incident light P ₁ is switched to the binary value by the electrostatic force so that there is no reflected light and the reflected light P. It can be taken out by switching to a binary value where ₃ occurs. Of course, by continuously changing the size of the gap as described above, it is possible to continuously switch the incident light P ₁ from the state without reflection to the state in which the reflected light P ₃ is generated.

These optical switching elements 100A to 10A
At 0D, the distance that the movable portion has to move is about “λ / 2 (or λ / 4)” of the incident light even if it is large, so that the response speed is sufficiently high as about 10 ns.
Therefore, a light valve for display can be realized with a one-dimensional array structure.

In addition, in the present embodiment, if a plurality of optical switching elements are assigned to one pixel, they can be driven independently of each other. Therefore, when performing gradation display of image display as an image display device, Not only the method by division but also gradation display by area is possible.

[Image Display Device] FIG. 18 shows an example of an image display device using the optical switching device 100.
It shows the configuration of the projection display. Here, the optical switching elements 100A to 100D
An example in which the reflected light P ₃ from P is used for image display will be described.

This projection display comprises light sources 200a, 200b and 200c made of lasers of red (R), green (G) and blue (B) colors, and an optical switching element array 201a provided corresponding to each light source. 201
b, 201c, dichroic mirrors 202a, 202
b, 202c, a projection lens 203, a galvanometer mirror 204 as a one-axis 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 one in which a plurality of the above-mentioned switching elements are arranged in a direction perpendicular to the plane of the drawing, and the necessary number of pixels, for example, 1000, are arranged one-dimensionally, and thereby a light valve is configured. ing.

In this projection display,
The light emitted from the light sources 200a, 200b, and 200c for each of the RGB colors is converted into the optical switching element array 201a and
It is incident on 201b and 201c. In addition, it is preferable that the incident angle is as close to 0 as possible so that the influence of polarization is not exerted, and the incident angle is vertical. The reflected light P ₃ from each optical switching element is reflected by the dichroic mirror 2
The light is focused on the projection lens 203 by 02a, 202b, and 202c. Projection lens 20
The light condensed at 3 is scanned by the galvano mirror 204 and projected on the projection screen 205 as a two-dimensional image.

As described above, in this projection display, a plurality of optical switching elements are arranged in a one-dimensional array, RGB light is emitted respectively, and the switched light is scanned by a one-axis scanner to produce a two-dimensional image. Can be displayed.

Further, in the present embodiment, since the reflectance at the time of low reflection can be set to 0.1% or less and the reflectance at the time of high reflection can be set to 70% or more, a high contrast of about 1,000 to 1 can be obtained. Since it is possible to display and the characteristics can be obtained at the position where light is vertically incident on the element,
When assembling the optical system, it is not necessary to consider polarization and the like, and the configuration is simple.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-described embodiments and modifications, and various modifications can be made. For example, in the above-described embodiment, a display having a configuration in which a laser is used as a light source to scan a light valve in a one-dimensional array has been described. However, as shown in FIG. 19, a two-dimensionally arranged optical switching device. It is also possible to adopt a configuration in which light is emitted from the white light source 207 to 206 and an image is displayed on the projection screen 208.

In the above embodiment, an example of using a glass substrate as the substrate has been described, but as shown in FIG. 20, for example, a flexible substrate 209 having a thickness of 2 mm or less is used. A paper-like display may be used so that the image can be viewed directly.

Further, in the above-mentioned embodiment, the light source of each color of RGB is used, but color display may be performed by using a color filter. In that case, as shown in FIG. 21, the optical switching element 100 using the above optical multilayer structure on one surface 110A of the substrate 110.
And the color filter 120 on the other surface 110B.
R, 120G, and 120B can be formed. Further, it is possible to provide the antireflection film 130 on the other surface 110B of the substrate 110.

Further, in the above 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 is used to draw an image on a photosensitive drum and other than the display. It is also possible to apply to various devices such as optical printers.

[0083]

As described above, according to the optical multilayer structure according to any one of claims 1 to 23 and the optical switching element according to claim 24, the incident light from the substrate side is prevented. Since the modulation is applied, the substrate itself can also serve as the transparent protective substrate of the optical multilayer structure. Therefore, it is not necessary to dispose another transparent protective substrate on the substrate side (the side on which light is incident), and the number of reflective interfaces can be reduced. Furthermore, in the case of forming an image display device using this optical multilayer structure or an optical switching element, a color filter or the like can be directly formed on the other surface of the substrate, and a transparent protective substrate having a color filter is formed. There is no need to prepare it as a separate part. Also,
The protection member on the second layer side of the optical multilayer structure does not need to be a transparent substrate because light does not enter, and an opaque material such as an inexpensive metal plate may be used, and any protection material may be arranged. Good.

Moreover, since the structure is simple, it can be manufactured more easily than a diffraction grating structure such as GLV or a complicated three-dimensional structure such as DMD. Further, the GLV requires six lattice-shaped ribbons for each pixel, but only one is required for the above optical multi-layer structure, so the structure is simple and can be made small. Further, by forming the structure in which the first layer, the second layer and the third layer are in contact with each other in this order on the substrate without the gap portion, it can be used as an antireflection film.

Further, the above-mentioned optical multilayer structure is a narrow band transmission filter having a structure in which the gap is sandwiched by a metal thin film or a reflection layer,
That is, since it is essentially different from the Fabry-Perot type, the bandwidth of the low reflection band can be widened. Therefore, it is possible to take a relatively wide margin of the film thickness control at the time of manufacturing, and the degree of freedom in design is increased.

In particular, according to the optical multilayer structure of the fifth aspect, since the third layer has a thickness that does not transmit light, incident light is absorbed by the third layer during low reflection, There is no need to worry about stray light.

Further, in particular, the optical multilayer structure according to claim 6.
According to the body, the refractive index of the substrate is n_S, The refractive index of the first layer
n₁, The complex refractive index of the second layer is N₂(= N₂-I
k₂, N ₂Is the refractive index, k₂Is the extinction coefficient, i is the imaginary unit
The complex refractive index of the third layer is N₃(= N₃-I
k₃, N₃Is the refractive index, k₃Is the extinction coefficient, i is the imaginary unit
Rank)) so that they meet certain conditions
Since it was configured, by changing the size of the gap
Change the amount of reflection, transmission or absorption of incident light.
Is possible and has a simple structure, particularly, for example, 550 nm
Even in the visible light range such as
0, the reflectance at high reflection can be 70% or more
It Therefore, a high contrast of about 1000: 1
A display is feasible. In addition, the second layer and
And the complex refractive index N of the third layer₂, N₃Satisfies certain conditions
Therefore, the flexibility of material selection is wide.
It

Particularly, according to the optical multilayer structure of the seventh aspect, since the optical characteristics of the second layer are made equal to the optical characteristics of the third layer and the second layer is omitted, The structure and manufacturing process can be simplified.

In addition, in particular, according to the optical multilayer structure of the ninth aspect, the optical size of the gap portion is binary between an odd multiple of λ / 4 and an even multiple of λ / 4. Alternatively, since it is changed continuously, the moving range of the movable part is at most "λ / 2", and high-speed response of 10 ns level becomes possible. Therefore, when used as a light valve for a display application, it can be realized with a simple structure of a one-dimensional array.

According to the image display device of any one of claims 25 to 27, the optical switching elements of the present invention are arranged one-dimensionally or two-dimensionally.
Since an image is displayed by using an optical switching device having a two-dimensional or two-dimensional array structure, it is possible to perform a high-contrast display and to obtain characteristics at a position where light is vertically incident on the device. Therefore, when assembling the optical system, it is not necessary to consider polarization etc.,
The configuration is simple.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration when a gap portion of an optical multilayer structure according to an embodiment of the present invention is “λ / 4”.

FIG. 2 shows a gap of “0” in the optical multilayer structure shown in FIG.
It is sectional drawing showing the structure at the time of.

3 shows the optical multilayer structure shown in FIG. 1 in which the substrate as an incident medium is indicated by a dotted line, the first layer is the uppermost layer, and the third layer is the lowermost layer, in the reverse order of FIG. It is the sectional view shown.

4 shows the optical multilayer structure shown in FIG. 2 in which the substrate as an incident medium is indicated by a dotted line, the first layer is the uppermost layer, and the third layer is the lowermost layer, in the reverse order of FIG. It is the sectional view shown.

FIG. 5 shows an optical admittance diagram where a transparent first layer having a refractive index of n ₁ is (n
It is a figure showing the locus | trajectory which passes along the point of ( _S , 0) (optical admittance of a board | substrate).

FIG. 6 is a view showing a modified example of the optical multilayer structure of FIG.

FIG. 7 is a plan view showing the substrate in the optical multilayer structure shown in FIG.
iO ₂ , the first when the first layer is formed of TiO ₂
It is a figure which shows together the optical admittance diagram of the layer of, and the optical admittance of various materials of.

FIG. 8 is a diagram showing reflection characteristics at the time of low reflection when the film thickness of the carbon layer of the third layer is changed to 100 nm, 300 nm and sufficiently thick in the configuration example shown in Table 1. is there.

FIG. 9 is a diagram showing the reflection characteristics of the configuration example shown in Table 1.

10 is a diagram showing optical admittance during low reflection in the example of FIG.

11 is a diagram illustrating optical admittance during high reflection in the example of FIG.

FIG. 12 is a diagram showing reflection characteristics of the configuration example shown in Table 2.

FIG. 13 is a cross-sectional view for explaining a method of driving an optical multilayer structure by static electricity.

FIG. 14 is a cross-sectional view for explaining another driving method of the optical multilayer structure by static electricity.

FIG. 15 is a cross-sectional view for explaining still another driving method of the optical multilayer structure by static electricity.

FIG. 16 is a cross-sectional view for explaining a magnetic driving method of an optical multilayer structure.

FIG. 17 is a diagram illustrating a configuration of an example of an optical switching device.

FIG. 18 is a diagram illustrating a configuration of an example of a display.

FIG. 19 is a diagram illustrating another example of the display.

FIG. 20 is a configuration diagram of a paper-like display.

FIG. 21 is a diagram illustrating still another example of the display.

[Explanation of symbols]

1 ... Optical multilayer structure, 10, 110 ... Substrate, 11 ... First
Layer, 12, 112 ... gap part, 13 ... second layer, 14 ...
Second layer, 100 ... Optical switching device

Claims (27)

[Claims] 1. A transparent first layer, a gap having a size capable of causing a light interference phenomenon and having a variable size, a second layer, and a light on one surface of a substrate also serving as an incident medium. 2. An optical multi-layered structure having a structure in which a third layer having absorption is arranged, and modulating light incident from the substrate side. 2. The first layer on one surface of the substrate,
The optical multilayer structure according to claim 1, wherein the gap portion, the second layer, and the third layer are arranged in this order. 3. The optical multilayer structure according to claim 1, wherein the substrate is made of a transparent material. 4. The optical multilayer structure according to claim 1, wherein the second layer is made of a material that absorbs light. 5. The optical multilayer structure according to claim 1, wherein the third layer has a thickness that does not transmit light. 6. The refractive index of the substrate is n _S , the refractive index of the first layer is n ₁ , and the complex refractive index of the second layer is N ₂ (=
n ₂ −i · k ₂ and n ₂ are refractive indices, k ₂ is an extinction coefficient, i is an imaginary unit), and the complex refractive index of the third layer is N ₃ (= n _3).
-I · k ₃ , n ₃ is the refractive index, k ₃ is the extinction coefficient, and i is the imaginary unit), the relationship of the following equation (1) is satisfied. The optical multilayer structure according to claim 1, wherein: 7. The optical multilayer according to claim 1, wherein the optical properties of the second layer are made equal to the optical properties of the third layer, and the second layer is omitted. Structure. 8. An amount of reflection, transmission, or absorption of incident light is provided by having a driving unit that changes the optical size of the gap, and changing the size of the gap by the driving unit. The optical multi-layer structure according to claim 1, wherein 9. The optical size of the gap is set to an odd multiple of λ / 4 and an even multiple of λ / 4 (0
The amount of reflection, transmission or absorption of incident light is changed in a binary manner or continuously by changing it in a binary manner or in a continuous manner.
The optical multilayer structure described. 10. The optical thickness of the first layer is λ / 4.
The optical multilayer structure according to claim 1, wherein (λ is a design wavelength of incident light) or less. 11. At least one of the first layer, the second layer, and the third layer is a composite layer composed of two or more layers having different optical characteristics from each other. The optical multilayer structure according to claim 1, which is characterized in that. 12. At least one of the substrate and the first layer and at least one of the second layer and the third layer includes a transparent conductive film in at least a part thereof, 9. The optical multilayer structure according to claim 8, wherein the driving means changes the optical size of the gap portion by an electrostatic force generated by applying a voltage to the transparent conductive film. 13. The transparent conductive film is made of ITO, SnO ₂
13. The optical multilayer structure according to claim 12, wherein the optical multi-layer structure comprises any one of ZnO and ZnO. 14. The optical multilayer structure according to claim 1, wherein the substrate is made of any one of silicon oxide, glass and plastic. 15. The optical multilayer structure according to claim 1, wherein the first layer is made of any one of oxide and nitride. 16. The first layer is made of any one of silicon nitride, aluminum nitride, titanium oxide, niobium oxide and tantalum oxide.
The optical multilayer structure described. 17. The optical multilayer structure according to claim 1, wherein the second layer is made of any one of metal, metal oxide, metal nitride, carbide and semiconductor. 18. The optical multilayer structure according to claim 1, wherein the third layer is made of any one of metal, metal oxide, metal nitride, carbon (C), graphite, carbide and semiconductor. . 19. The substrate is made of any one of silicon oxide, glass and plastic, the first layer is made of titanium oxide, and the second layer is made of tungsten, germanium, tantalum or titanium. The optical multi-layer structure according to claim 1, wherein the third layer is made of any one of carbon and carbon. 20. The substrate is made of any one of silicon oxide, glass and plastic, the first layer is made of titanium oxide, the second layer is omitted, and the third layer is formed. The optical multi-layer structure according to claim 1, wherein is made of silicon (Si). 21. The optical multilayer structure according to claim 1, wherein the gap is filled with air or a transparent gas or liquid. 22. The optical multilayer structure according to claim 1, wherein the gap is in a vacuum state. 23. The optical multi-layer structure according to claim 8, wherein the driving means changes the optical size of the gap portion by using magnetic force. 24. On one surface of a substrate which also serves as an incident medium,
It has a structure in which a transparent first layer, a gap having a size capable of causing a light interference phenomenon and having a variable size, a second layer and a third layer having a light absorption are arranged. An optical switching element comprising: an optical multilayer structure that modulates light incident from the substrate side; and a driving unit that changes an optical size of the gap. 25. An image display device for displaying a two-dimensional image by irradiating a plurality of one-dimensionally or two-dimensionally arranged optical switching elements with light, wherein the optical switching elements also serve as an incident medium. On one side of the transparent first layer,
It has a structure in which a gap having a size capable of causing a light interference phenomenon and having a variable size, a second layer and a third layer having a light absorption are arranged, and the light is incident from the substrate side. An image display device, comprising: an optical multi-layer structure for modulating light; and a driving unit for changing the optical size of the gap. 26. The image display device according to claim 25, further comprising an antireflection film on the other surface of the substrate. 27. The image display device according to claim 25, further comprising a color filter on the other surface of the substrate.