JPH0776812B2 - Light modulator - Google Patents

Description

The present invention relates to a light modulator, and more particularly to an incident light by controlling a refractive index of a refractive index variable substance by combining a diffraction grating and a refractive index variable substance. The present invention relates to a light modulation device that causes a desired diffraction phenomenon.

(Prior Art) As a well-known light modulator, a pair of polarizing plates arranged so that their polarization directions are orthogonal to each other and a pair of transparent substrates arranged between the pair of polarizing plates are opposed to each other. It consists of a device in which liquid crystal is enclosed by applying alignment treatment to the substrate surface at right angles to each other, and the incident light is modulated by switching the alignment state of this liquid crystal between a twisted state and a state perpendicular to the substrate surface. There is a so-called TN (twisted nematic) type liquid crystal display element. This type of display element is used in a wide variety of fields because of its simple structure and easy driving. The transmittance at the time of transmission was poor, and it could not be said to be a preferable optical modulator in terms of luminous flux utilization efficiency.

Further, as a display element of the same type using liquid crystal, there is a so-called guest-host mode liquid crystal element in which a dye is mixed in liquid crystal molecules. The transmittance was about 75% at best.

On the other hand, Japanese Patent Publication No. 53-3928, USP 4,251,137 and the like disclose a display element and a variable subtractive color filter element in which a reflection type or transmission type phase diffraction grating and a liquid crystal are combined. Although these disclosed elements are certainly excellent in luminous flux utilization efficiency, the elements disclosed in Japanese Patent Publication No. 53-3928 show only a decorative effect and are display elements for displaying characters and images. It was not satisfactory as an optical modulator for transmitting and blocking a light flux. In addition, the variable subtractive color filter element disclosed in USP 4,251,137 forms a diffraction grating on a pair of opposing substrate surfaces so that their arrangement directions are orthogonal to each other, and liquid crystal is filled between the substrates to adjust the alignment state of liquid crystal molecules. By controlling the refractive index, the spectral transmittance characteristics can be made variable by changing the refractive index difference between the substance that forms the diffraction grating and the liquid crystal, and it has high luminous flux utilization efficiency and high performance as a variable subtractive color filter. Have.

However, although this variable subtractive filter mainly displays the desired three primary colors R, G, B or their complementary colors C, M, Y, etc., they cannot be displayed by changing the density with the same color. It was

(Problems to be Solved by the Invention) The present invention has a high light utilization efficiency with respect to incident light having an arbitrary polarization characteristic, and is capable of displaying a display state of a display pattern with multi-stage density. The purpose is to provide a device.

(Means for Solving Problems) Two diffraction grating structures each having a transparent member and a liquid crystal alternately arranged are provided, and the two diffraction grating structures are arranged so that the directions of the grating grooves of the two diffraction grating structures are orthogonal to each other. The two diffraction grating structures are overlapped, and one of the two diffraction grating structures is used to diffract one polarization component of the polarization components of the incident light which are orthogonal to each other, while allowing the other polarization component to pass through, and In the light modulation device showing the first state in which the other polarization component of the incident light is allowed to pass through and the other polarization component of the incident light is diffracted by using the other of the diffraction grating structure of The structure allows the one polarization component to be diffracted and the other polarization component to pass through, and the other diffraction grating structure to pass both the one polarization component and the other polarization component. The second state, and the one diffraction grating structure allows both of the one polarization component and the other polarization component to pass through, and the other diffraction grating structure allows the one polarization component and the other polarization component to pass through. A means for controlling the alignment directions of the liquid crystals of the two diffraction grating structures is provided so as to generate the third state in which both of them pass through.

Besides, the features of the present invention are described in the embodiments.

(Embodiment) FIG. 1 is a perspective view of an optical modulator according to an embodiment of the present invention. In the figure, 12 and 15 are transparent electrodes, 13 is a transparent diffraction grating, and 1
Reference numeral 4 is a liquid crystal as a refractive index variable material, and 16 and 17 are transparent substrates, and these elements constitute a first light modulation section 8-1. Reference numeral 8-2 is a second light modulator having the same function as the light modulator 8-1.

In the second light modulator 8-2, 12 'and 15' are transparent electrodes, 13 'is a transparent diffraction grating, 14' is a liquid crystal as a refractive index variable substance, and 16 'and 17' are transparent substrates.

A transparent electrode 15 (15 ') is provided on the transparent substrate 16 (16'). The diffraction grating 13 (13 ') is formed on the transparent electrode 15 (15') by a method such as photolithography, etching and lift-off. The grating grooves of the diffraction gratings 13 and 13 'are arranged so as to be orthogonal to each other. Here, the diffraction gratings 13 and 13 'correspond to transparent members. Diffraction grating 13
(13 ') and liquid crystal 14 (14') form an element of the diffraction grating structure.

FIG. 2 is an operation explanatory view of the optical modulator shown in FIG. 1, 8-1 is a first optical modulator of the first layer, and 8-2 is a second optical modulator of the second layer. is there. Reference numeral 26 is incident light, and 27 and 27 'are polarization components of the incident light 26 which are orthogonal to each other, 27 is a polarization component parallel to the paper surface, and 27' is a polarization component perpendicular to the paper surface.
13 and 13 'are diffraction gratings and 14 and 14' are liquid crystals.
4, 14 'have an optical axis in the lattice groove direction. The refractive index of the liquid crystals 14 and 14 'with respect to each polarization component is controlled by applying an electric field between the transparent electrodes 12 and 15 and between the transparent electrodes 12' and 15 'by a liquid crystal drive circuit (not shown). It controls by changing the optical axis direction.

In a static state in which no electric field is applied, in the first-layer light modulator 8-1, the polarization component 27 'of the incident light 26 feels the extraordinary refractive index n _e of the liquid crystal 14, and the polarization component 27 is the liquid crystal. 14 ordinary refractive index n _o of
Feel Further, second layer at the light modulating unit 8-2, the polarization component 27 'LCD 14' felt ordinary refractive index n _'o of the polarization components
27 feel _e 'extraordinary refractive index n' of the liquid crystal 14. Where 1
The refractive index of the member forming the diffraction grating of the light modulation section 8-1 of the layer is n _g , the refractive index of the member forming the diffraction grating of the light modulation section of the second layer 8-2 is n ′ _g , and the incident light Is λ, and the thicknesses of the diffraction gratings of the first-layer and second-layer optical modulators 8-1 and 8-2 are respectively
T, T ′, the difference in refractive index between the liquid crystal and the member of the diffraction grating is Δn, Δ
If n ′, the diffraction efficiencies η _o and η ′ _o of the zero-order transmitted diffracted light in the diffraction grating of each layer are approximately expressed by the following equations (1) and (1) ′ when the diffraction grating shape is rectangular. Can be represented.

From the above equation, when Δn = 0 or Δn ′ = 0, η _o = 1 or η ′ _o = 1 and ΔnT = (1/2 + m) λ, or Δn ′
It can be seen that η _o = 0 or η ′ _o = 0 when the condition of T ′ = (1/2 + m) λ (m = 0,1,2,3 ...) is satisfied.

If by satisfying n _o = n _g In the first layer of the optical modulation unit 8-1 polarization component 27 flowed through, the other 27 'is modulated in accordance with equation (1). Even in the light modulation section 8-2 of the second layer, if _n'o = _n'g is satisfied, the polarization component 27 'passes through and the other 27 is modulated according to the equation (1)'. .

Next, when an electric field is applied to the liquid crystals 14 and 14 ′,
The direction of the 14 'optical axis changes and the polarization component 2
Since the refractive indexes 7 and 27 'feel change, the modulations according to the equations (1) and (1)' are performed in the light modulating portions of the first and second layers, respectively.

For example, when the optical axis directions (orientation directions) of the liquid crystals 14 and 14 'are perpendicular to the diffraction grating surface, that is, in the incident direction of the light beam, the polarization components 27 and 27' are the light modulation portions 8 of the first and second layers. -1,8
At -2, the ordinary refractive index n _o of the liquid crystal is all felt, and it passes through it to become zero-order transmitted light. Therefore, by applying an electric field, it is possible to control the transmittance of the zero-order transmitted diffracted light having a desired polarization characteristic.
In the above description, the zero-order diffracted light was considered as the modulated light, but it goes without saying that higher-order diffracted light can be used.

Examples of the variable refractive index medium include liquid crystal, PLZT, and LiNb.
O ₃ , LiTaO ₃ , TiO ₂ , PMMA, CCl ₄ , KDP, ADP, ZnO, BaTiO ₃ , Bi ₁₂ Si
O ₂₀ , Ba ₂ NaNb ₅ O ₁₅ , MnBi, EuO, CS ₂ , Gd ₂ (MoO ₄ ) ₃ , Bi ₄ Ti ₃ O
₁₂ , CuCl, CaAs, ZnTe, As ₂ Se ₃ , Se, AsGeSeS, DKDP, MNA, mNA, U
Examples include REA and photoresist.

The diffraction grating in this embodiment is not limited to the rectangular shape, but may be a triangular shape or a sinusoidal shape.

With the above configuration, the light passing through the light modulation device is controlled to electrically display the display pattern.

FIG. 3 is an explanatory diagram of display patterns and wiring patterns according to an embodiment of the present invention. In the figure, 8-1 and 8-2 are the same first and second light modulators as shown in FIG. 2, respectively. 31,3
2, 33 and 34 are substrates having transparent electrodes. Each transparent substrate 31, 32, 33, 34 has a wiring pattern A, B, C corresponding to the display pattern 310, a wiring pattern D corresponding to the common electrode pattern 320, a wiring pattern E corresponding to the common electrode pattern 330, and a display pattern. Wiring patterns A ′, B ′, C ′ corresponding to 340 (A _{1 to} C ₃ ) are provided.

FIG. 4 is an explanatory diagram of the wiring in which the display pattern and the common electrode pattern of FIG. 3 are developed, and the reference numerals correspond to the reference numerals of FIG. 3, respectively. In FIG. 4, 40 is a power source.

In this embodiment, A to D, B to D, C of the first light modulator 8-1
The presence or absence of an electric field between D to D causes the presence or absence of light diffraction in the diffraction grating portion corresponding to each display pattern connected to the wirings A, B, and C, which causes the display pattern to change in brightness.
Further, in the second light modulator 8-2, A'to E, B'to E, C '
Display pattern pairs (A ₁ , B ₁ , C ₁ ), (A ₂ , B ₂ , C ₂ ) connected to wirings A ′, B ′, C ′ depending on the presence or absence of an electric field between E to E
Presence or absence of light diffraction occurs in the diffraction grating portion corresponding to (A ₃ , B ₃ , C ₃ ), which causes a change in lightness and darkness in each set of display patterns.

In this embodiment, the density of the display pattern of the light modulator is controlled by individually controlling the presence or absence of light diffraction in the first and second light modulators 8-1, 8-2 by a liquid crystal drive circuit (not shown). ing. Each transparent electrode, connection and liquid crystal drive circuit is a light modulator 8-
A control means for controlling the optical axis (orientation direction) of the 1,8-2 liquid crystal is configured. The display state of the display pattern for this density control is shown in Table 1. In Table 1, "light" is 85-90%, "medium" is "50-55%", and "dark" is 10%.
It shows a transmittance of about 20%.

As shown in Table-1, in this embodiment, the light utilization efficiency is high, and the transmittance in the display state of the display pattern can be displayed in multiple stages.

(Effects of the Invention) According to the present invention, a high light utilization efficiency is obtained for incident light having an arbitrary polarization characteristic, and the display state of a display pattern is displayed in three levels of density: bright, medium, and dark. Can be done.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is an explanatory view of the operation of FIG. 1, FIG. 3 is an explanatory view showing a relationship between a display pattern and a wiring pattern of the present invention, and FIG. FIG. 4 is an explanatory diagram of a wiring pattern of FIG. In the figure, 8-1, 8-2 are the first and second light modulators, 12, 12 ', 15, 15' are transparent electrodes, 16, 16 ', 17,
17 'is a transparent substrate, 13 and 13' are diffraction gratings, 14 and 14 'are liquid crystals,
31, 32, 33, 34 are substrates having transparent electrodes, 310, 340 are display pattern portions, 320, 330 are common electrode patterns, A, B, C, D, E,
A ', B', C'are wiring patterns.

Claims (1)

[Claims] 1. A diffraction grating structure comprising two transparent members and liquid crystals alternately arranged, wherein the two diffraction grating structures are arranged such that the directions of the grating grooves of the two diffraction grating structures are orthogonal to each other. One of the two diffraction grating structures is superposed, one of the polarization components of the incident light orthogonal to each other is diffracted, and the other polarization component is allowed to pass therethrough. In the light modulator showing the first state in which the other polarization component of the incident light is allowed to pass through while the other polarization component of the incident light is allowed to pass by using the other, the one of the one diffraction grating structure is used to A second state in which a polarized light component is diffracted and the other polarized light component is allowed to pass through, and the other diffraction grating structure causes both of the one polarized light component and the other polarized light component to pass through; A third state in which one of the one polarization component and the other polarization component is allowed to pass by one diffraction grating structure, and both the one polarization component and the other polarization component are allowed to pass by the other diffraction grating structure. An optical modulator comprising means for controlling the alignment direction of the liquid crystal having the two diffraction grating structures so as to generate