JPH0652353B2 - Light modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light modulation element, and more particularly to a light modulation element that causes a desired diffraction phenomenon in incident light by controlling the refractive index of liquid crystal by combining a diffraction grating and liquid crystal. Regarding

<Prior Art> Conventionally well-known light modulation elements include a pair of polarizing plates arranged so that polarization directions thereof are orthogonal to each other, and a pair of transparent substrates arranged between the pair of polarizing plates and facing each other. It is composed of a device in which liquid crystal is enclosed by subjecting the surfaces to mutually orthogonal alignment processing, and the incident light is modulated by switching the alignment state of this liquid crystal between a twisted state and a state oriented perpendicular to the substrate surface. There is a so-called TN (twist nematic) liquid crystal display element. This type of display element is widely used because of its simple structure and easy driving.
Since the light beams are transmitted and blocked by using two polarizing plates, the transmittance at the time of erasing, that is, at the time of transmitting light is poor, and it cannot be said to be a preferable light modulator in terms of light beam 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 70% at best.

Meanwhile, Japanese Patent Publication No. 53-3928 and USP 4,25
No. 1,137, etc., a display element and a color filter element in which a reflection type or transmission type phase diffraction grating and a liquid crystal are combined are 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 was not satisfactory as a display element for displaying characters or images or an intermodulation element for transmitting or blocking a light beam.
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, since the light modulation element using the conventional diffraction grating of this kind generally diffracts the incident light even in the static state, when it is actually used as a display element, the non-display state, that is, the incident light flux is It was necessary to constantly apply a voltage or the like in order to maintain the state of being completely transparent. Therefore, there are problems that are unfavorable for a display device, such as a large amount of power being consumed and the transmission characteristics of the device in the non-display state being unstable due to the alignment state of the liquid crystal and the like.

<Summary of Invention> An object of the present invention is to provide a light modulation element suitable for use as a display element, in which a stable non-display state is obtained in view of the above-mentioned conventional problems.

In order to achieve the above object, the light modulation element according to the present invention,
An element having a phase type diffraction grating composed of a predetermined member, a liquid crystal existing in a groove portion of the diffraction grating, and a control means for changing an alignment state of the liquid crystal, wherein the control means is an electrode provided on a side surface of the diffraction grating. It is characterized by having.

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

<Example> FIGS. 1A and 1B are schematic views showing an example of an optical modulator according to the present invention, in which 1 is a transparent substrate, 2 is a transparent electrode, and 3 is a transparent substrate.
Is a transparent insulating film, 4 is a liquid crystal, 5 is a transparent insulator forming a diffraction grating, and 6 is a transparent protective film which also serves as an insulating film. 7 is a switch,
8 is a driving power source, 9 is incident light, 10 is zero-order diffracted light, and 10 '.
Indicates high-order diffracted light.

Here, FIG. 1A shows a state in which the switch 7 is OFF and no electric field is applied, and FIG. 1B shows a state in which the switch 7 is ON and an electric field is applied, and in the present embodiment. As the liquid crystal 1, a positive dielectric nematic liquid crystal is used.

In the light modulation element of this embodiment, a transparent insulating film is formed on one surface of each of a pair of transparent substrates 1, and a rectangular diffraction pattern is formed on the transparent insulating film 3 of one transparent substrate 1 by a transparent insulator 5. A grating is formed, a transparent electrode 2 is provided on a side surface of the diffraction grating and an interface between the transparent insulating film 3 and the diffraction grating, and the diffraction grating is covered with a transparent protective film 6 to form a transparent substrate 1 having the diffraction grating. The other transparent substrate 1 is bonded so that the transparent protective film 3 faces it, and the liquid crystal 4 is sealed in the gap. In addition, the transparent electrodes 2 of the adjacent convex portions are connected to the driving power source 8 via the lead wire.
And the switch 7. Further, the transparent insulating film 3 is subjected to vertical alignment treatment, and the molecules of the liquid crystal 4 are vertically aligned, that is, so-called homeotropic alignment.

The function of the present light modulation element will be described below.

In the state shown in FIG. 1A, that is, in the state where the switch 7 is OFF and no voltage is applied between the transparent electrodes 2, the liquid crystal 4 is homeotropically aligned as described above, and the substrate 1
The long axis is oriented in a direction perpendicular to. At this time, the incident light 9 is normal refractive index n _o of the liquid crystal 4 regardless of its polarization state
Therefore, if the film thickness of the transparent electrode 2 and the transparent protective film 6 is sufficiently smaller than the line width of the diffraction grating (width of the convex portion),
By keeping the refractive index n _g of the transparent insulator 5 is set equal to the ordinary refractive index n _o of the liquid crystal 4, the incident light 9 is passed through the present device without receiving the diffraction action, as the zero-order output light 10 Emit.

On the other hand, the state shown in FIG. 1 (B), that is, the switch 7 is turned on.
With a predetermined voltage applied between the transparent electrodes 2,
The major axes of the molecules of the liquid crystal 4 are aligned with the direction of the electric field, and are aligned in a direction parallel to the surface of the substrate 1 (homogeneous alignment) as shown in the figure. At this time, among the polarization components of the incident light 9, the polarization component in the same direction as the alignment direction of the liquid crystal 4 has an extraordinary refractive index n _{e of the} liquid crystal 4.
Feel Therefore, the optical path length difference between the optical path length when the light of the polarization component passes through the liquid crystal 4 and the optical path length when passing through the transparent insulator 5 is just λ / 2 (λ is the wavelength of the incident light). Therefore, the extraordinary refractive index n _e of the liquid crystal 4 and the refractive index n _e of the transparent insulator 5
By setting _g and the height T of the diffraction grating, the incident light 9 does not become the zero-order emitted light 10 but all becomes the higher-order diffracted light 10 '. The diffraction angle (emission angle) of the high-order diffracted light 10 'depends on the wavelength λ and the pitch of the diffraction grating.

That is, the diffraction efficiency η _o of the zero-order transmitted diffracted light (emitted light 10 in the figure) in the rectangular diffraction grating as shown in FIGS. 1 (A) and (B) is approximated by the following equation (1). Can be expressed as
In order to set the diffraction efficiency η _o of the light of the predetermined wavelength λ to η _o ≈0, it is sufficient to satisfy the condition of the expression (2).

_{However, Δn = | n e -n g} | it is.

In FIG. 1 (B), among the polarization components of the incident light 9, the polarization component polarized in the direction perpendicular to the alignment direction of the liquid crystal 4, that is, the groove direction of the diffraction grating is the electric field in which the switch 7 is ON. even applied state, feel ordinary refractive index n _o of the liquid crystal 4. Therefore,
This polarization component of the incident light 9 cannot be modulated by the light modulator of this embodiment. Therefore, in order to modulate the incident light having an arbitrary polarization characteristic, for example, two elements as shown in FIG. 1 may be used so that they are superposed so that the arrangement directions of the diffraction gratings are orthogonal to each other. It is possible for each element to independently modulate polarization components that are orthogonal to each other.

As described above, in the light modulation element according to the present embodiment, when no electric field is applied, the "bright" state, that is, the total transmission state,
Since "dark", that is, a modulation state (display state) is obtained when an electric field is applied, current consumption in the normal state ("bright" state) is eliminated, and the degree of freedom in designing the drive circuit used to drive the element is increased. .

Also, the electrolytic corrosion rate of the transparent electrode is slowed down, and the reliability as an element is significantly improved. Therefore, the applicable range of the present light modulation element such as a display element, a color filter, an optical switch, etc. is greatly expanded.

Further, as a matter of course, unlike the display element using the conventional liquid crystal, the polarizing plate and the light absorbing substance (for example, dye) are not used, so that the luminous flux utilization efficiency is excellent.

As can be seen from FIG. 1, the diffraction grating forming the light modulation element according to the present invention is a so-called phase type diffraction grating consisting of a relief pattern of concavities and convexities. As a method of forming this kind of relief pattern, for example, a photolin There are various methods such as a method combining a graphic 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.

Further, in the present embodiment, an element having a rectangular shape as a diffraction grating is shown, but light can be modulated even if this shape has any shape. For example, a diffraction grating of various shapes such as a triangular wave shape, a sine wave shape, and an asymmetrical shape can be used, and the separation angle between the diffracted lights depends on the pitch of the diffraction grating and the wavelength of the incident light. The spectral transmittance characteristics mainly depend on the shape (waveform profile) and height T of the diffraction grating and the refractive index difference Δn. That is, the equation (1) representing the diffraction efficiency η _o of the zero-order transmitted diffracted light in the rectangular diffraction grating cannot be applied to the diffraction efficiency in the triangular wave-shaped or sinusoidal-shaped diffraction grating, and In this case, the equations corresponding to the respective diffraction grating shapes are used.

Further, although a so-called transmissive light modulation element is shown in this embodiment, it can be used as a reflective light modulation element. In this case, one of the pair of transparent electrodes 3 shown in FIG. 1 is composed of a member having a reflection characteristic in the used wavelength (band), or a reflective film is provided on the interface between the substrate 1 and the transparent electrode 3. It may be applied or a reflection film may be formed on the entire surface of the relief pattern having concaves and convexes forming a diffraction grating.

Further, in the element shown in FIG. 1, the transparent electrode 2 is also formed on the interface with the transparent protective film 3, but it is not always necessary to form the transparent electrode 2 on this interface. A so-called positive dielectric nematic liquid crystal such as an element is applied to a lateral electric field (substrate 1
It is only necessary to apply an electric field parallel to the plane. Therefore, it is usually sufficient that it is formed on the side wall of the transparent insulator forming the diffraction grating. Further, the means for controlling the alignment state of the liquid crystal is not limited to the electric field, and it is possible to use a control means for generating heat or a magnetic field, but in view of the element structure, the simplicity of the control method, the response characteristics, etc. And the control by the electric field is most preferable.

<Effects of the Invention> As described above, the light modulation element according to the present invention is an element suitable for a display element, a color filter, or the like that can obtain a total transmission state in a static state and can stabilize a non-display state. is there.

[Brief description of drawings]

1 (A) and 1 (B) are schematic views showing an embodiment of the light modulation element according to the present invention. FIG. 1 (A) shows a static state and FIG. 1 (B) shows a driving state. . 1 ... Transparent substrate 2 ... Transparent electrode 3 ... Transparent insulating film 4 ... Liquid crystal 5 ... Transparent insulator (diffraction grating) 6 ... Transparent protective film 7 ... Switch 8 ... Drive power supply 9 ... Incoming light 10 ... Zero-order diffracted light 10 '... High-order diffracted light

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Takayuki Ishii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yukitoshi Okubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (3)

[Claims] 1. An element having a diffraction grating made of a predetermined member, a liquid crystal existing in a groove portion of the diffraction grating, and a control means for changing an alignment state of the liquid crystal, wherein the control means is provided on a side surface of the diffraction grating. A light modulation element having an electrode provided. 2. The light modulation element according to claim 1, wherein the liquid crystal is a nematic liquid crystal having a positive dielectric property. 3. An optical modulator according to claim 2, wherein said control means is a means for applying an electric field and has an electrode on the side surface of the convex portion of said diffraction grating.