JPH0731318B2 - Light modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light modulator, and more particularly, to an optical display that uses a diffraction grating and a variable-refractive-index material such as a liquid crystal to perform light modulation such as passing or blocking of light. The present invention relates to an optical modulator suitable for devices for optical recording, optical recording, optical coupling, optical communication, and optical calculation.

(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, a so-called guest-host mode liquid crystal element in which a dye is mixed with liquid crystal molecules is used. The transmittance was about 70% 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 the elements disclosed in these are certainly excellent in luminous flux utilization efficiency, the element disclosed in Japanese Patent Publication No. 53-3928 shows only a decorative effect, and is a display element for displaying characters and images. It was not satisfactory as an optical modulator for transmitting and blocking a light flux. In the variable subtractive color filter element disclosed in USP 4,251,137, at least one has a refractive index variable substance, for example, liquid crystal filled between substrates having an optically isotropic diffraction grating structure, and an electric field is applied to the liquid crystal. The refractive index of the liquid crystal is thereby changed, and a first device for modulating light by utilizing the diffraction effect of the diffraction grating and a pair of opposing substrate surfaces for modulating incident light having an arbitrary polarization component A diffraction grating is formed so that the alignment directions are orthogonal to each other, and the liquid crystal is filled between the substrates to change the refractive index by controlling the alignment state of liquid crystal molecules, and the difference in the refractive index between the substance forming the diffraction grating and the liquid crystal. There is a second device that makes the spectral transmittance characteristic variable by changing. In the second device, since the diffraction gratings are formed on the surfaces of the pair of opposed substrates so that the arrangement directions thereof are orthogonal to each other, the distance between the electrodes of the pair of opposed substrates is at least the diffraction of the first variable subtractive filter. There is a drawback that the distance is more than twice that of the grating and the electric field strength, which is the refractive index control means of the refractive index variable substance, is reduced to 1/2 or less. In addition, since the two layers of the diffraction grating are overlapped, the alignment direction of the liquid crystal in the boundary region is disturbed, and the effective diffraction grating height is reduced.

(Problems to be Solved by the Invention) The present invention has a high light utilization efficiency with respect to incident light having arbitrary polarization characteristics, a low driving voltage, and a simple structure that does not reduce the effective diffraction grating height. It is an object of the present invention to provide a light modulator of

(Means for Solving Problems) First and second substrates each having an electrode formed thereon, transparent electrode members, and liquid crystal and transparent members arranged alternately, respectively.
A first and a second diffraction grating structure, and the first and second diffraction grating structures are arranged via the electrode member so that the directions of the grating grooves of the first and the second diffraction grating structures are orthogonal to each other. The first and second diffraction grating structures that are overlapped with each other and are overlapped with each other via the electrode member are sandwiched by the first and second substrates, and are sandwiched between the electrode of the first substrate and the electrode member. Changing the alignment direction of the liquid crystal of the first diffraction grating structure sandwiched between the first substrate and the electrode member by applying electrolysis,
By applying an electric field between the electrode of the second substrate and the electrode member, the orientation direction of the liquid crystal of the second diffraction grating structure sandwiched between the second substrate and the electrode member is changed.

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

(Embodiment) FIG. 1 is an explanatory view of the principle of light modulation of the light modulator of the present invention. In the figure, reference numeral 15 is a transparent electrode, 13 is a transparent diffraction grating, 14 is a liquid crystal as a refractive index variable substance, 16 is a transparent substrate, and these elements constitute the first light modulator 8-1. 8-
Reference numeral 2 is a second light modulator having the same function as the light modulator 8-1. 1
5'is a transparent electrode, 13 'is a transparent diffraction grating, 14' is a liquid crystal as a refractive index variable substance, and 16 'is a transparent substrate.

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 liquid crystal 14 and the transparent diffraction grating (member) 13 constitute one element of the first diffraction grating structure, and the liquid crystal 14 'and the transparent diffraction grating (member) 13' constitute one element of the second diffraction grating structure. Are configured. The transparent substrate 16 corresponds to the first substrate and the transparent substrate 16 'corresponds to the second substrate.

26 is incident light having an arbitrary polarization component, 27 and 27 'are polarization components orthogonal to each other in the incident light 26, 27 is a polarization component parallel to the paper surface, and 27' is a polarization component perpendicular to the paper surface. . The liquid crystals 14 and 14 'have an optical axis in the grating groove direction of the diffraction gratings 13 and 13'. The refractive index of the liquid crystals 14 and 14 'is controlled by applying an electric field between the transparent electrodes 15 and (15').

In the static state in which no electric field is applied, the polarization component 27 'of the incident light 26 is converted into the liquid crystal 14' in the second-layer light modulator 8-2.
And the polarization component 27 feels the extraordinary refractive index ne of the liquid crystal 14 '. Also, in the light modulation section 8-1 of the first layer,
The polarization component 27 'feels the extraordinary refractive index ne' of the liquid crystal 14, and the polarization component 27 feels the ordinary refractive index no 'of the liquid crystal 14. Here, the refractive index of the member forming the diffraction grating of the second-layer light modulation unit 8-2 is
ng, the refractive index of the member forming the refraction grating of the first-layer optical modulation unit 8-1 is n′g, the wavelength of incident light is λ, the second- and first-layer optical modulation units 8-2, 8 The thickness of the -1 diffraction grating is T,
T ′, the difference in refractive index between the liquid crystal and the diffraction grating member is Δn, Δ
If n ′, the diffraction efficiencies ηo and η′o of the zero-order transmitted diffracted light in the diffraction grating of each layer are approximately represented by the following equations (1) and (1) ′ when the diffraction grating shape is rectangular. be able to.

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

If no = ng is satisfied in the light modulation section 8-2 of the second layer, the polarization component 27 is passed through, and the other is modulated according to the equation (1). Even in the first-layer optical modulation section 8-1, n '
If o = n'g is satisfied, the polarization component 27 'will pass through and the other will be modulated according to the equation (1)'.

Next, when an electric field is applied to the liquid crystal of each layer, the direction of the optical axis of the liquid crystal changes, and the refractive index sensed by the polarization components 27 and 27 'changes accordingly. In the section, the modulation according to the equations (1) and (1) 'is performed.

For example, when the optical axis direction (orientation direction) of the liquid crystal of each layer is perpendicular to the diffraction grating surface, that is, the incident direction of the light flux, the polarization component 27
Numerals 27 'and 27' feel the ordinary refractive index no of the liquid crystal in the light modulating portions 8-2, 8-1 of the second and first layers, and pass through them 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. Although the zero-order diffracted light is considered as the modulated light in the above description, it goes without saying that the higher-order diffracted light can be used.

The refractive index variable medium may be, for example, liquid crystal, PLZT, 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.

2, 3, and 4 are schematic views of the essential parts of an embodiment of the present invention. In these embodiments, two light modulators 8
When the -1,8-2 are superposed on each other, the diffraction gratings 13,13 'are superposed with a transparent conductor plate (also referred to as a transparent electrode member) 22 interposed therebetween to simplify the entire apparatus.

2 shows a case where the diffraction grating has a rectangular shape, FIG. 3 shows a case where the diffraction grating has a triangular shape, and FIG.

In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

As described above, in this embodiment, the distance between the transparent electrodes is reduced by using the two light modulation portions and the transparent conductor plate shown in the explanatory diagram of the principle of light modulation shown in FIG. 1, that is, the voltage between the transparent conductor plate and the transparent electrode is reduced. Is applied to reduce the drive voltage, and when the liquid crystals with different optical axes are directly placed in contact with each other, the occurrence of a transition region where the optical axes are disturbed is prevented and the polarization state of the incident light is disturbed. Prevents and performs good optical modulation.

In this embodiment, a transmissive optical modulator is shown, but it is also possible to form a reflective element by providing a light reflecting film on one substrate, for example. However, in the case of the reflective type, the behavior of diffracted light in the element becomes complicated, so in consideration of the design and practical application of the display element and the like, in the present invention, the transmissive type light modulating element is used. desirable. In this case, as a matter of course, the diffraction grating, the variable refractive index material, the substrate, and the like are made of a member that is transparent to the used wavelength.

(Effect of the Invention) According to the present invention, as described above, when the two light modulation portions having the predetermined elements are superposed so that the grating grooves of the diffraction grating are orthogonal to the traveling direction of light, the transparent conductor plate By arranging, the driving voltage at the time of changing the refractive index of the refractive index variable substance is lowered, and the disturbance of the optical axis of the refractive index variable substance at the interface between the two light modulation sections is prevented, resulting in high light utilization efficiency. An optical modulator having a simple structure can be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of light modulation of the present invention, and FIGS. 2, 3, and 4 are explanatory views of the essential parts of another embodiment of the present invention. 8- in the figure
1, 8-2, are light modulation parts, 15, 15 ', 22 are transparent electrode members, 16,
16 'is a transparent substrate, 13 and 13' are diffraction gratings, 14 and 14 'are liquid crystals,
26 is incident light and 25 and 25 'are outgoing lights.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukitoshi Okubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference US Patent 4251137 (US, A)

Claims (1)

[Claims] 1. A first substrate and a second substrate each having an electrode formed thereon,
A transparent electrode member, and a first and a second diffraction grating structure in which liquid crystals and transparent members are alternately arranged, respectively.
The first and second diffraction grating structures are overlapped with each other via the electrode member so that the directions of the grating grooves of the second diffraction grating structure are orthogonal to each other, and the electrode member is formed by the first and second substrates. The first and second diffraction grating structures that are overlapped with each other are sandwiched, and sandwiched between the first substrate and the electrode member by applying an electric field between the electrode of the first substrate and the electrode member. By changing the alignment direction of the liquid crystal of the first diffraction grating structure and applying an electric field between the electrode of the second substrate and the electrode member, the liquid crystal sandwiched between the second substrate and the electrode member. An optical modulation device characterized by changing the alignment direction of liquid crystal having a second diffraction grating structure.