JP2651171B2 - Optical modulation element and optical modulation method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulation element having a simple configuration and capable of performing high-sensitivity display, and an optical modulation method suitable for the optical modulation element.

[Conventional technology and problems]

A recording medium having a birefringence is applied with an electric field to perform display by using a change in the birefringence. For example, PLZT, LiNbO ₃
And the like using a ferroelectric material such as a liquid crystal and a ferroelectric liquid crystal. As these display methods, what is specifically performed is that linearly polarized light obtained by a polarizing plate or the like is incident, the polarization direction is changed by the birefringence of the recording medium and the change of the optical axis, and then the polarizing plate is re-exposed. This is a method of reading as a contrast by passing light through the like.

However, this method requires an optical thickness sufficient to obtain a sufficient birefringence effect in order to read the display state, which is not preferable in terms of sensitivity.

In addition, when this method is used, there is also a problem that the amount of transmitted light is reduced and the contrast is reduced because two polarizing plates are used.

[Object of the invention]

Accordingly, an object of the present invention is to provide a new optical modulation element capable of displaying a high amount of transmitted light and high contrast, and an optical modulation method suitable for the element.

[Means and Actions for Solving the Problems] In the present invention, a compound capable of controlling the anisotropy of the refractive index by an electric field is used as an optical modulation layer, and the optical thickness of the optical modulation layer (nd: n is a refractive index) Rate and d are thicknesses).

Specifically, the present invention provides an optical modulation element in which a reflection layer is disposed directly or via an insulating alignment control layer on both sides of the optical modulation layer and the optical modulation layer, and an optical modulation element of the optical modulation element. An object of the present invention is to provide an optical modulation element having means for controlling the thickness to identify a difference in the reflectance of read light incident on the optical modulation layer.

The means for controlling the optical thickness of the optical modulation layer is provided by changing the refractive index or the anisotropy of the refractive index of the optical modulation layer. Specifically, the refractive index is changed by the phase transition of the optical modulation layer, and the anisotropy of the refractive index is changed by an electric field and a magnetic field.

The method of changing the anisotropy of the refractive index by an electric field is particularly preferable because it can be modulated at high speed and consumes little energy.

The compound capable of controlling the anisotropy of the refractive index by an electric field is a liquid crystal, a ferroelectric liquid crystal,
Polymer liquid crystals are mentioned.

The liquid crystal layer used in the present invention includes SmC ^* , SmH ^* , SmF ^* , SmJ ^* ,
It can be a chiral smectic phase or a nematic phase such as SmK ^* , SmI ^* or SmG ^* .

Nematic liquid crystal with Δε> O Nematic liquid crystal with Δε <O Ferroelectric liquid crystal Polymer liquid crystal having a nematic phase of Δε> O Polymer liquid crystal having a nematic phase of Δε <O Ferroelectric polymer liquid crystal Therefore, in the present invention, an optical modulation element having the above-described compound is arranged as shown in FIG. 1 to form an optical modulation element.

In FIG. 1, reference numeral 1 denotes an optical modulation layer, 2 denotes an insulating orientation control layer, 3 denotes a semi-transmissive reflective layer, 4 denotes an electrode, 5 denotes a transparent substrate, 6
Is a polarizing plate, 7 is a spacer, and 8 is a reflective layer.

When the optical modulation layer used in the present invention is heated once and then gradually cooled, an optical modulation layer horizontally oriented with respect to the electrode can be formed (see FIG. 2 (a)).

Next, when an electric field is applied between the four electrodes, the optical modulation layer changes as shown in FIG. 2 (b). Therefore, the present invention performs display using the difference between the two optical modulation states.

Specifically, the following steps are performed (see FIG. 3).

First, light is incident from the polarizing plate 6 side. Then, the light passes through the semi-transmissive reflection layer 3 and reaches the electrode / reflection layer 9. Light is reflected by the reflective layer 9, and as a result, the reflected light returns to the semi-transmissive reflective layer 3 again.
In this case, if the optical thickness between 3 and 9 is controlled so that the incident light and the light reflected by the electrode / reflection layer 9 interfere with each other, the light does not pass through the semi-transmissive reflection layer 3 and the light does not pass through the layer. The light also reflects at 3, and reciprocates between the semi-transmissive reflective layer 3 and the electrode / reflective layer 9, and only when the optical path length is significantly increased, passes through 3 and is detected as reflected light. In the present invention, such a state is called a multiple reflection state. The multiple reflection state is possible even when the semi-transmissive reflection layer 3 does not exist, but it is preferable that the multiple reflection state exists in order to obtain a multiple reflection device efficiently. If 3 is not present, the refractive index of 4
Set to satisfy the non-reflection condition with a refractive index of 2,1 (4
Index of refraction x 9 index of refraction = (average index of refraction of 2,1,2) ² )
Then, a multiple reflection state occurs between 4 and 9.

The multiple reflection state is also related to the wavelength (λ) of the incident light arbitrarily determined from the value of the optical thickness. Since the optical path length is significantly increased, even the slightest incident light is absorbed in the multiple reflection layer. When there is a substance, that is, by adding a light-absorbing substance to the layer, the amount of light that can be detected as reflected light with respect to the incident light can be minimized (that is, the reflectance can be minimized). .

Second, when the molecular state of the optical modulation layer is changed by an electric field with reference to the first state, the reflected light can pass through the semi-transmissive reflection layer 3. Then, when the light amount at that time is identified as a reflectance and expressed as a difference in contrast from that in the first state, display can be performed. As described above, by comparing the contrast between the first state and the second state, it is possible to obtain an unprecedented high-sensitivity identification state.

The display method described above is an example in which display is performed with a difference in contrast between when the reflectance is minimal and when the reflectance is increased, but in the present invention, on the contrary, the reflectance is initially high. A state may be selected, and display may be performed with a difference in contrast when the reflectance is gradually lowered.

In the case where a compound having a negative birefringence and a compound Δε capable of changing the birefringence by an electric field is used as the optical modulation layer, it is preferable that the birefringence be vertically aligned.

The value of the variation Δnd of the optical thickness in the present invention is, as a result of an experiment, preferably 0.2 μm or less, more preferably 0.001 μm or less.
0.20.2 μm. That is, high sensitivity and high contrast can be obtained even when the physical thickness d is used with a very small value in a compound having ordinary refractive index anisotropy (Δn = 0.001 to 0.5). The larger Δn is, the smaller the physical thickness d can be. Preferably, d = 1 μm.
m or less, more preferably 100 to 8000 °.

Further, in order to make the contrast clearer, a dye as a substance that absorbs light may be added to the display layer. Examples of the additive include the following.

However, it is not limited to the exemplified dye.

The semi-transmissive reflective layer 3 in the present invention has a transmittance of 5 to 95% and a film thickness of 10 to 2000, more preferably 50 to 800.
For example, a layer of a metal thin film such as aluminum, gold, silver, or copper, or an inorganic oxide film having a thickness of 10 to 5000 mm, or a high refractive index compound such as ZnS can be used.

In FIG. 1, a transparent substrate 5 is coated with a transparent electrode or electrode 4 made of a thin film such as In ₂ O ₃ , SnO ₂ or ITO (Indium-Tin Oxide). A thin film of a polymer such as polyimide is rubbed with a gauze, an acetate flocking cloth or the like, and an insulating alignment control layer 2 for arranging liquid crystals in the rubbing direction is formed thereon. Further, as the insulating layer, for example, silicon oxide, silicon carbide containing hydrogen, silicon oxide, boron nitride, boron nitride containing hydrogen, cerium oxide, aluminum oxide, zirconium oxide, titanium oxide, and fluorine oxide Form an inorganic material insulating layer such as magnesium, on which polyvinyl alcohol, polyimide, polyamide imide, polyester imide, polyparaxylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate,
An organic insulating substance such as polyamide, polystyrene, cellulose resin, melamine resin, urea resin, acrylic resin, and photoresist resin may be used as an orientation control layer, and an insulating orientation control layer may be formed in two layers. It may be an insulating orientation control layer or a single layer of an organic substance insulating orientation control layer. Further, the orientation control layer disposed on the substrate may be provided only on one side substrate. If this insulating orientation control layer is inorganic, it can be formed by vapor deposition, etc., and if it is organic,
Using a solution in which an organic insulating substance is dissolved or a precursor solution thereof (0.1 to 20% by weight, preferably 0.2 to 10% by weight in a solvent), a spinner coating method, a dip coating method, a screen printing method, a spray coating method, It can be formed by applying by a roll coating method or the like, and curing under predetermined curing conditions (for example, heating). The thickness of the insulating orientation control layer is usually from 20 to
1μ, preferably 30 ° to 5000 °, more preferably 50 °
~ 3000Å is suitable.

In FIG. 1, a transparent substrate 5 and a reflective layer 8 are kept at an arbitrary distance by a spacer 7. For example, there is a method in which a transparent substrate 5 and a reflective layer 8 are sandwiched between silica beads and alumina beads having a predetermined diameter as spacers, and the periphery is sealed with a sealing material, for example, an epoxy-based adhesive. In addition, a polymer film, glass fiber, or the like may be used as the spacer.

In addition, the electrode 4 is connected to a marine power supply by a lead wire. A polarizing plate 6 is attached to the outside of the transparent substrate 5.

Further, the reflection layer 8 is, for example, a metal substrate, and can be formed so as to have both the function as the electrode 4 and the function as the original reflection layer. (FIG. 3) Similarly, if the surface of the electrode 4 provided on the reflection layer 8 side is made to function as a reflection layer, the reflection layer 8 may not be provided.

On the other hand, of the electrodes 4, at least the electrode on the side on which light is incident needs to be a transparent electrode.

Further, the electrodes 4 may be formed in a matrix as shown in FIG. At this time, the display change portion in the optical modulation layer is the S portion (selected pixel) in FIG. 4B, and the molecular state at that time is compared with the N portion (non-selected pixel). The result is as shown in FIG.

FIG. 5 shows another embodiment of the present invention. As shown in FIG. 5, the present invention can be practiced by providing a photoconductive layer in an optical modulation element. In this example, a dielectric mirror is used as the reflection layer.

 Hereinafter, the present invention will be described in more detail by way of examples.

Example 1 A transparent electrode 4 made of ITO was formed on a glass substrate 5,
Further, a translucent Au layer 3 of about 400 mm or less having a thickness of 500 mm or less was formed by vapor deposition. A polyamic acid solution (PIQ manufactured by Hitachi Chemical Co., Ltd .: nonvolatile content: 3 wt%) was spin-coated at 3000 rpm by a spinner coater. It was applied over a period of seconds and heated at 120 ° C. for 30 minutes, at 200 ° C. for 60 minutes, and at 350 ° C. for 30 minutes. The thickness of the obtained polyimide film was about 500 mm.

Next, photosensitive polyimide was spin-coated, exposed to light in the form of stripes, and excess portions were etched with an alkaline solution. It was fired at 200-350 ° C. to obtain a film having a thickness of about 2000 mm.

This polyimide alignment film was uniaxially aligned by a rubbing method.

Next, a polyamic acid solution was spin-coated on the smooth aluminum substrate 9 in the same manner as described above, followed by baking to obtain a polyimide alignment film. This alignment film was also subjected to a uniaxial alignment treatment by a rubbing method, and bonded so that the orientation of the glass-ITO substrate 5 and the alignment treatment direction coincided with each other.

A cell obtained by adding 0.1 wt% of the above-described exemplary dye (E) to E7 nematic liquid crystal manufactured by BDH was sealed in the cell at atmospheric pressure by degassing the inside of the cell. (FIG. 3) The cell was heated to an isotropic layer and then gradually cooled to obtain a uniaxially horizontally oriented optical modulation layer. The thickness of this optical modulation layer was about 2000 mm. In this state, the reflectance for 500 nm linearly polarized light was measured and found to be about 5%.

Next, a voltage of 10 V was applied between the ITO transparent electrode and the aluminum substrate, and the reflectance for light of 500 nm was measured. The reflectance was 15%.

Example 2 A cell prepared in the same manner as in Example 1 was charged with CS-CS-
1011 The same dye 9 as in Example 1 was added to ferroelectric liquid crystal at 0.1 wt%.
The added one was enclosed. The temperature was raised to the isotropic layer, and the sample was gradually cooled to obtain an oriented sample. At this time, the position of the polarizing plate was bonded so as to coincide with the optical axis of CS-1011 to which a voltage of 10 V was applied. The reflectance at this time was 3% at 500 nm.

Next, when a reverse voltage was applied, the reflectance became 10%.

Example 3 SiO ₂ was vapor-deposited on a glass substrate 5 on which a transparent electrode 4 made of ITO patterned in a stripe pattern was formed. On this SiO ₂ film 2, a translucent Au layer 3 having a thickness of about 400 ° and a thickness of 500 ° or less was formed by vapor deposition.
Next, a polyamic acid solution (non-volatile content: 1.5 wt%) was spin-coated and baked at 120 to 350 ° C. to form a polyimide alignment film. This was subjected to a uniaxial orientation treatment by a rubbing method.

Next, a polyamic acid solution (nonvolatile content: 1.5 wt%) was spin-coated on the glass substrate 10 on which Al was vapor-deposited in a stripe shape, and baked at 120 to 350 ° C. to obtain a polyimide alignment film 2.

Next, a spacer 7 was formed from photosensitive polyimide in the same manner as in Example 1, and then baked and subjected to a uniaxial orientation treatment.

Atmospheric pressure was obtained by degassing the inside of the cell by adding 0.1 wt% of the same dye as in Example 1 to the BDH E7 nematic liquid crystal to the two substrates bonded together so that the alignment processing directions were aligned. Then, a polarizing plate was bonded so as to coincide with the optical axis. (FIG. 4 (a)) When a voltage of 10 V was applied to the transparent electrode and the Al electrode,
The reflectance at 500 nm in the S portion shown in FIG.
It was 5% in the N part.

Example 4 A transparent electrode 4 made of ITO was formed on a glass substrate 5,
Further, a polyamic acid solution is spin-coated on a translucent Au layer 3 having a thickness of 500 ° or less formed by vapor deposition.
It was baked at 0 ° C. to 350 ° C. to obtain a polyimide alignment film 2. The polyimide alignment film 2 was subjected to a uniaxial alignment treatment by a rubbing method.

Next, another glass substrate 10 having the ITO transparent electrode 4 formed thereon was coated with a polymer obtained by dispersing a photoconductor 14 made of CdS in a polymer, and dried. A dielectric mirror 13 was formed thereon by vapor deposition, and a spacer 7 was formed of photosensitive polyimide.

The above two substrates were adhered to each other, and 0.1% by weight of the same dye as in Example 1 was added to BDH E7 nematic liquid crystal, and the cell was degassed and sealed at atmospheric pressure. The polarizing plates were stuck together. (FIG. 5) When a voltage of 10 V was applied to the ITO electrodes 4 on the upper and lower substrates, writing light was irradiated from the photoconductive layer side, the state of the display layer was changed, and reading light was incident from the polarizing plate side. The reflectance of the liquid crystal layer of the writing light irradiation part is 10%, and the reflectance of the non-irradiation part is 5%.
It became.

〔The invention's effect〕

As described above, according to the present invention, since only one polarizing plate is required, it is possible to obtain an optical modulation element with small loss of light quantity and excellent contrast. Moreover, in the optical modulation element of the present invention, the contrast does not decrease even if the optical modulation layer is thinner than the conventional liquid crystal element, so that the driving voltage can be reduced.

Further, the present invention was able to provide an optical modulation method suitable for the optical modulation device of the present invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the optical modulation element of the present invention, FIG. 2 is a view showing the molecular state of the optical modulation layer in the present invention, and FIGS. 3 and 4 (a) are the present invention. FIG. 4 (b) is a diagram showing the configuration of scanning electrodes and signal electrodes arranged in a matrix, and FIG. 4 (c) is a diagram of the optical modulator in FIG. 4 (a). FIG. 5 shows a molecular state of an optical modulation layer. FIG. 5 is a view showing another embodiment of the optical modulation element of the present invention. DESCRIPTION OF SYMBOLS 1 ... Optical modulation layer, 2 ... Insulating orientation control layer 3 ... Semi-transmissive reflective layer, 4 ... Electrode 5 ... Transparent substrate, 6 ... Polarizing plate 7 ... Spacer, 8 ... Substrate 9 ... ... metal substrate, 10 ... scanning electrode 11 ... signal electrode, 12 ... dielectric mirror 13 ... photoconductive layer, 14 ... voltage applying device 15 ... writing light, 16 ... reading light

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshio Takasu 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-49-5060 (JP, A)

Claims (7)

(57) [Claims] 1. An optical modulation layer comprising a compound having birefringence and capable of changing birefringence and a substance absorbing incident light, wherein said optical modulation layer has an optical thickness capable of taking a multiple reflection state. An optical modulation element comprising: a layer; a unit for changing an optical thickness of the optical modulation layer; and a unit for identifying a reflected light amount when irradiated with light. 2. The optical modulator according to claim 1, wherein the compound having birefringence and capable of changing birefringence is a nematic liquid crystal. 3. The optical modulation device according to claim 1, wherein the compound having birefringence and capable of changing birefringence is a chiral smectic liquid crystal. 4. The chiral smectic liquid crystal comprises a chiral smectic C phase, a chiral smectic F phase, a chiral smectic I phase, a chiral smectic H phase, a chiral smectic J phase, a chiral smectic G phase,
4. The optical modulator according to claim 3, wherein the optical modulator is a liquid crystal having a chiral smectic K phase. 5. The optical modulation device according to claim 1, wherein the compound having birefringence and capable of changing birefringence is a polymer liquid crystal. 6. The optical modulation layer according to claim 1, wherein the change in optical thickness is 0.2.
2. The optical modulation element according to claim 1, wherein the optical modulation element has a diameter of not more than μm. 7. An optical modulation layer having a compound capable of changing birefringence and having birefringence and a substance absorbing incident light is set to have an optical thickness capable of taking a multiple reflection state. An optical modulation method characterized by changing a multiple reflection state by changing an optical thickness of an optical modulation layer, and controlling a reflected light amount when light is irradiated.