JPH0652351B2 - Light modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light modulation element, particularly a desired diffraction phenomenon for incident light by controlling the 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 element that causes

<Prior Art> Conventionally well-known light modulation elements include a pair of polarizing plates arranged so that their polarization directions are direct light, and a pair of transparent substrates arranged between the pair of polarizing plates facing each other. It is composed of a device in which liquid crystal is enclosed by applying alignment processing orthogonal to each other on the substrate surface, and the incident light is modulated by switching the alignment state of the 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 display element in which a dye is mixed in a liquid crystal molecule. The transmittance was about 75% at best.

Meanwhile, Japanese Patent Publication No. 53-3928 and USP 4,25
No. 1,137, etc., a display element or a color filter element in which a reflection type or transmission type phase diffraction grating and a liquid crystal are combined is disclosed. The elements disclosed in these are certainly excellent in luminous flux utilization efficiency, but the element disclosed in Japanese Patent Publication No. 53-3928 shows only a decorative effect.
It is not satisfactory as a display element for displaying characters or images or a light modulator for transmitting and blocking a light flux.
In the color filter device disclosed in USP 4,251,137, diffraction gratings are formed on a pair of opposed substrate surfaces so that their arrangement directions are orthogonal to each other, and liquid crystals are filled between the substrates to align liquid crystal molecules. The refractive index is changed by controlling the state, and the spectral transmittance characteristics are made variable by changing the difference in refractive index between the substance forming the diffraction grating and the liquid crystal, which is excellent in luminous flux utilization efficiency and high as a variable color filter. Have performance. However, a light modulation element using this type of diffraction grating needs to block diffracted light of other orders when using diffracted light of a specific order as modulated light. However, depending on the device configuration, it may not be possible to arrange this type of optical system or mask. Further, when white light is used as incident light like the elements disclosed in Japanese Patent Publication No. 53-3928 and USP 4,251,137, unnecessary diffracted light is generated because a large amount of diffracted light is emitted and its spread is large. The high-order diffracted light that has been spectrally separated cannot be completely removed, and spreads like a rainbow, which causes a reduction in display quality when used for a display element or the like.

<Summary of the Invention> An object of the present invention is to provide a light modulation element which has high light utilization efficiency and enables high quality display when used as a display element in view of the above-mentioned conventional problems. .

In order to achieve the above object, the light modulation element according to the present invention,
In an element that performs optical modulation by controlling the phase difference of a phase type diffraction grating, a plurality of diffraction grating groups are configured so that their lattice constants are random.

Further features of the present invention will be apparent from the examples shown below.

<Example> FIG. 1 is a principle diagram of light modulation of a light modulation element according to the present invention.
Is a variable refractive index material, 2 is a diffraction grating, 5 is incident light, 6 and 6'are orthogonal polarization components of the incident light 5, and A is a grating constant of the diffraction grating 2 and represents a pitch. T indicates the height of the diffraction grating 2.

Here, if the difference between the refractive index of the variable refractive index material 1 and the refractive index of the material forming the diffraction grating 2 is Δn and the wavelength of the incident light 5 is λ, then a rectangular diffraction grating as shown in FIG. 1 is formed. The diffraction efficiency η ₀ of the zero-order transmitted diffracted light in the light modulator is approximately represented by the following expression (1).

Further, for example, when the diffraction grating 2 has a triangular wave shape or a sine wave shape, the diffraction efficiency η ₀ in each case is as follows (2)
It becomes like the formula and the formula (3).

As can be understood from the above formulas (1) to (3), the refractive index difference Δ
By changing n, the diffraction efficiency η ₀ of the zero-order transmitted diffracted light can be made variable, and the zero-order light intensity can be controlled from 0 to a predetermined value. For example, in the above formula (1), Δn = 0
At that time, the diffraction efficiency becomes η ₀ = 1 and the incident light 5 in FIG. 1 passes through the element. or When (m = 0, 1, 2, ...), η ₀ = 0, and all incident light 5 is emitted from the element as high-order diffracted light, and zero-order light does not exist.

Here, when the incident light 5 having a plurality of wavelength components is incident on the light modulation element of FIG. 1, in addition to the zero-order transmitted diffracted light, higher-order diffracted light such as ± 1st order, ± 2nd order as shown in the figure is generated. The generated diffracted light of each order forms a spectrum by the emitted light of each wavelength component. The zero-order transmitted diffracted light is naturally emitted in the traveling direction of the incident light 5 without depending on the wavelength, and the higher-order diffracted light is emitted in the direction depending on the wavelength λ and the value of the pitch Λ which is the lattice constant. Is.

Therefore, when the zero-order transmitted diffracted light is used as the modulated light and is applied to, for example, a display element, the above-described wavelength-separated diffracted light looks like a rainbow and deteriorates display quality. In order to solve this problem, in the present invention, the diffraction grating of the element as shown in FIG. 1 is composed of a plurality of diffraction grating groups in the display area when applied to the display element, and each diffraction grating is formed. It is arranged so that the lattice pitch Λ of the group is random. As a result, the direction of emission of unnecessary diffracted light such as the above-mentioned rainbow which causes deterioration of display quality is made random, and the unnecessary diffracted light is superposed on each other, thereby substantially suppressing the generation of rainbow. Therefore, the image quality can be improved only by the characteristics of the element itself without using a special optical system or a light-shielding means such as a mask unlike the prior art. Therefore, the degree of freedom of the optical device to which the present light modulation element can be applied is significantly increased as compared with the conventional one.

Further, as a further feature of the present light modulation element, the characteristics of the zero-order transmitted diffracted light, which is the modulated light, can be roughly adjusted by making the grating shapes, the heights T, etc. in the respective diffraction grating groups substantially the same. It is preferable to make them uniform and maintain the display quality.

Hereinafter, the present invention will be described in detail with reference to specific examples.

FIG. 2 is a diagram showing an example of a modulator of the optical modulator according to the present invention. The same members as those in FIG. 1 are designated by the same reference numerals. In the figure, 4 is a transparent electrode and 7 is a liquid crystal.

In this embodiment, the liquid crystal 7 is used as the refractive index variable substance, and the liquid crystal 1 is filled in the groove (recess) of the rectangular diffraction grating 2 existing between the pair of transparent substrates 1 on which the transparent electrodes 4 are formed. is there. Here, a nematic liquid crystal having a positive dielectric property or the like is suitable as the liquid crystal 7, and the liquid crystal 7 shown in FIG. 2 will be described as a positive dielectric nematic liquid crystal. The liquid crystal 7 is aligned in the groove direction of the diffraction grating 2 (perpendicular to the paper surface), and by applying an electric field between the transparent electrodes 4, the alignment direction is changed to the array surface of the diffraction grating 2, that is, the electric field direction. At this time, light polarized in the optical axis rotation plane of the liquid crystal 7, the refractive index between the ordinary refractive index n _o and the extraordinary refractive index n _e of the liquid crystal 7 in accordance with the angle between the optical axis of the liquid crystal 7 Feel When this refractive index is represented by the effective refractive index n _LC of the liquid crystal and the refractive index of the diffraction grating 2 is represented by ng, the refractive index difference Δn is expressed by the following equation (4).

Δn = | n _LC −ng | (4) Therefore, the light modulation can be performed by changing the diffraction efficiency η ₀ of the zero-order transmitted diffracted light according to the above equations (1) to (3).

If the incident light is linearly polarized light through a polarizer or the like, it can be modulated by a single-layer optical modulator as shown in FIGS. 1 and 2, but the incident light has a random polarization plane. In the case where it has, since the single-layer element exerts a diffracting action on only one polarization component of the polarization components 6 and 6 ′ orthogonal to each other as shown in FIG. It becomes transparent. An element configured to solve this problem and to be able to modulate light of any polarization characteristic is shown below.

FIG. 3 shows a light modulator in which two elements are superposed so that the arrangement directions of the diffraction gratings are orthogonal to each other based on the element of FIG. 2 as a basic structure. In the figure, the same members as those in FIG. Put the numbers.

With the configuration as in the present embodiment, the polarization components of the incident light which are orthogonal to each other are independently modulated by the corresponding diffraction gratings, so that the incident light is entirely modulated.

4 and 5 are schematic views showing the state of the diffraction grating of the light modulation element according to the present invention. Here, for example, the pitches of the diffraction grating are randomly arranged within a predetermined display pattern area. .

Next, a production example of the present light modulation element and a result of performance evaluation will be described.

ITO transparent electrodes are formed on a pair of ordinary glass substrates,
Far UV photo resist ODUR1013 on one substrate
After manufacturing a diffraction grating using (Tokyo Ohka), a pair of glass substrates are bonded together so that the ITO transparent electrodes face each other, and a positive dielectric nematic liquid crystal RO-TN403 (manufactured by Roche) is enclosed to provide a light modulation element. Was formed. At this time, when the diffraction grating is formed by exposing a far-ultraviolet photoresist to form a diffraction grating, it is exposed through a mask of a random pitch grating pattern so that the pitch of the diffraction grating becomes random in the display pattern area. . Therefore, the thickness of the diffraction grating in this embodiment is 1.5 μm, the pitch is 1.2 to 3.0 μm, and the ratio of the line width (width of the convex portion) of the grating to the pitch is 0.5 to 0.65.
Then, a rectangular diffraction grating is used. Furthermore, the ordinary refractive index n ₀ of RO-TN403 for light with a wavelength of 589.3 nm is n ₀ = 1.
53, the extraordinary refractive index n _e is n _e = 1.78, and the refractive index n _{g of} ODUR1013 for light of the same wavelength is n _g = 1.53.

Here, in a static state in which the electric field is OFF, the RO-TN40
3 is oriented in the groove direction of each diffraction grating, and when white light linearly polarized in a direction parallel to the groove direction of the diffraction grating is used as incident light and is incident on the element, the incident light is RO-
Zero order transmitted diffracted light feel extraordinary refractive index n _e of TN403 became blue emitted light. Also, by applying an electric field, RO-TN
The orientation direction of 403 was made to coincide with the direction of the electric field, the incident light feels the ordinary refractive index n _o of the RO-TN403, has passed all incident light element in order to be n _{o =} n _g as described above A transparent state was obtained. At this time, in the static state, high-order diffracted light other than the zero-order transmitted diffracted light that is the modulated light is emitted from each diffraction grating group, but because multiple diffraction grating groups are arranged at random , The high-order diffracted lights emitted from the respective diffraction grating groups were agitated with each other, and virtually no rainbow or diffraction image was visible. Therefore, using this element as a display element is extremely effective in view of high light utilization efficiency and emission of a desired color, and high-quality display can be achieved.

Next, another specific example will be described.

A ZrO ₂ diffraction grating was formed on one of the ITO transparent electrode-attached glass substrates by the ion etching method, and the other ITO transparent electrode-attached glass substrate and the transparent electrode surface were attached so as to face each other to form a positive dielectric constant. Nematic liquid crystal R
An optical modulator was formed by encapsulating O-TN407 (manufactured by Roche). In the diffraction grating of this embodiment, of course, a plurality of diffraction grating groups are formed with different pitches of the diffraction gratings. The thickness of each diffraction grating is 1.6 μm, and the pitch is 1.2 to 3.0 μm. , The ratio of the line width of the grid to the pitch is
It was set to 0.5 to 0.65. Furthermore, RO for wavelength 580 nm
Ordinary refractive index _{n o} of -TN407 is _{n o} = 1.53, the extraordinary refractive index _{n e} is _{n e} = 1.79, the refractive index _{n g} of ZrO ₂ relative to the wavelength is _{n g} = 1.53.

When light similar to that in the above-mentioned embodiment was applied to the device of this embodiment and modulation was performed, zero-order emission light showed magenta color in a static state, and a predetermined amount of electric field was applied to the RO-TN4.
In the state in which 07 was oriented in the direction of the electric field, the zero-order emitted light showed a cyan color. Furthermore, in the intermediate state between the above two states (RO-TN407 is tilted and oriented), the emitted light showed a yellow color.

As described above, the light modulation element in this embodiment can select the emitted light of C, M, and Y by applying an electric field, and forms a variable color filter. Also, in the element of this example, no rainbow or diffraction image was observed as in the above example.

Although liquid crystal is used as the refractive index variable substance in the above description, it goes without saying that the present invention can be applied to other refractive index variable substances. For example, RLZ
T, LiNbO ₃ , LiTaO ₃ , TiO ₂ , PMM
A, CCl ₄ , KDP, ADP, ZnO, BaTi
O ₃ , Bi ₁₂ SiO ₂₀ , Ba ₂ NaNb ₅ O ₁₅ ,
MnBi, EuO, CS ₂ , Gd ₂ (M ₀ O ₄ ) ₃ , B
i ₄ Ti ₃ O ₁₂ , CuCl, CaAs, ZnTe, A
s ₂ Se ₃ , Se, AsGeSeS, DKDP, MN
A, mNA, UREA, photoresist, etc. may be mentioned. However, liquid crystals, especially nematic liquid crystals, can be said to be suitable materials for the present invention because they are easily available and easy to control, and the orientation can be regulated by a diffraction grating. or,
It is preferable to use the electric field control method as the control method in view of the response characteristics and the ease of driving as a display element. Still index variable material, a refractive index difference between the extraordinary refractive index n _e and ordinary index n _o is large is preferred, will enhance the degree of freedom of device structure and modulation function. Therefore, at this sense although also crystal and preferred materials, preferably the refractive index difference (n e _{-n o)} Good 0.2 or more substances. The diffraction grating may be produced by combining photolithography and dry etching, a replica method using a thermosetting resin or an ultraviolet curable resin, a cutting method using a ruling engine or an embossing method. There are various methods.

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 reflection type, the behavior of diffracted light inside the element becomes complicated, so in consideration of the design and practical application of the display element and the like, a transmissive type light modulation element may be used in the present invention. 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.

<Effects of the Invention> As described above, the light modulation element according to the present invention arranges a plurality of diffraction grating groups so that the grating pitches are random respectively, so that a rainbow, a diffraction image, and the like caused by the presence of unnecessary diffracted light are generated. It is a light modulation element that is substantially removed and has high light utilization efficiency and is capable of high-quality display when applied to a display element.

[Brief description of drawings]

FIG. 1 is a modulation principle diagram of an optical modulator according to the present invention. FIG. 2 is a schematic diagram showing an example of a modulator of the light modulator according to the present invention. FIG. 3 is a schematic diagram showing another example of the modulator of the light modulator according to the present invention. FIG. 4 and FIG. 5 are schematic views showing the states of the diffraction grating in the present light modulation element. 1 ... Refractive index variable substance, 2 ... Diffraction grating, 3 ... Transparent substrate, 4 ... Transparent electrode, 5 ... Incident light, 6, 6 '... Polarization components orthogonal to each other, 7 ... Liquid crystal, 8 ...... Modulation section.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G02F 1/1347 7348-2K

Claims (8)

[Claims] 1. An optical modulation element, which is an element that performs optical modulation by controlling the phase difference of a phase type diffraction grating, and is formed by a plurality of diffraction grating groups, and the lattice constant of which is random. 2. The light modulation element according to claim 1, wherein the phase type diffraction grating is composed of a relief pattern having a predetermined shape and a refractive index variable substance present in the concave portion of the relief pattern. 3. An optical modulator according to claim 1, wherein the plurality of diffraction grating groups have a constant grating shape and height. 4. The light modulation element according to claim 1, wherein the array directions of the plurality of diffraction grating groups are the same. 5. The light modulator according to claim 1, wherein zero-order diffracted light is used as the modulated light. 6. The light modulation element according to claim 2, wherein the variable refractive index substance is liquid crystal. 7. The light modulation element according to claim 1, wherein the substance forming the diffraction grating is transparent to a used wavelength. 8. The optical modulator according to claim 1, wherein an electric field is used when controlling the phase difference.