JPH0259721A - lcd light bulb - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical recording type liquid crystal having a photoconductor layer and a liquid crystal layer [Prior art] An optical recording type liquid crystal having a conventional photoconductor layer and a liquid crystal layer The light valve may be, for example, an EEE Transacti
ons on ElectronDevice
Vol, ED-22No.

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ringent Liquid-CrystaI
Light Valve for Col.

As shown in the ``Symbology Display'', recording was performed using a liquid crystal vibrator i-knot field effect mode.

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology uses a CRT as a source of the light beam that irradiates the photoconductor layer of the liquid crystal light valve, and the phosphor coated on the CRT tube surface is Since the afterglow characteristic is set relatively long, nearly static driving is possible; however, when performing serial scanning with a light source such as a laser beam, it is not possible to perform nearly static driving as described above. This poses a problem in that it becomes impossible to maintain the optical response of the liquid crystal for a long period of time, and the contrast of the displayed image is significantly reduced.

Therefore, the present invention solves these problems,
The purpose is to provide an optical recording type liquid crystal light valve that can obtain good contrast even when serially scanned with a laser beam or the like.

[Means for Solving the Problems] The liquid crystal light valve of the present invention is an optical recording type liquid crystal light valve that has a photoconductor layer and a liquid crystal layer between a pair of electrodes and forms an image optically. The liquid crystal layer is formed of a liquid crystal having positive dielectric anisotropy, and applying an electric field higher than a crossover frequency of the dielectric anisotropy of the liquid crystal to the liquid crystal light valve via the pair of electrodes, The method is characterized in that pixels are formed in the liquid crystal layer by irradiating the photoconductor layer with a pulsed light beam to change the frequency component of the electric field applied to the liquid crystal layer.

[Example] An example of the liquid crystal light valve of the present invention is shown in Figures 1 to 3.
This will be explained according to the diagram.

As shown in FIG. 2, the liquid crystal light valve includes a transparent electrode 201 made of IT○ formed on a transparent substrate 201, a photoconductive layer 203, and a light separation mirror 20 made of a dielectric multilayer film.
4. Thereafter, a nematic liquid crystal 207 having positive dielectric constant anisotropy is sealed through a transparent substrate 206 formed with ITO 205 as a counter substrate. FIG. 3 shows the frequency characteristics of the dielectric constant of the nematic liquid crystal 207 used in this example. As can be seen from FIG. 3, the nematic liquid crystal 207 has a point at which the dielectric constant anisotropy becomes 0 at the crossover frequency f=fO.
The frequency of the electric field applied to the liquid crystal light valve via fO5 is set to be higher than this crossover frequency fO. Further, 208 is a light beam irradiated onto the photoconductor layer;
209 indicates a readout light. Table 1 shows the detailed configuration of the liquid crystal light valve. In this example, an amorphous silicon PIN structure was adopted as the photoconductor layer.
A single layer of amorphous silicon may be used, or other materials such as CdS, Se, O.P.C., single crystal silicon, and BSO may also be used.

Table 1 The operating principle of the liquid crystal light valve shown in this embodiment will be explained with reference to FIG. Assuming that the electric field applied to the liquid crystal layer via the transparent electrodes 202 and 205 is VEX, and the impedances of the photoconductor layer and the liquid crystal layer are ZP, C, ZL, and C, respectively, a light beam 208 is applied to the photoconductor layer 203. When not irradiated, the liquid crystal layer has ZL, C/ (ZP, C+ZL, C) XVEX
An electric field of -.-(1) is applied. However, ZP and C in equation 1) indicate the impedance of the photoconductor layer when no light is irradiated. Therefore, an electric field equivalent to (1) is applied to the liquid crystal layer, but as mentioned above, VE
Since the frequency of X is set higher than the crossover frequency of the liquid crystal, the dielectric anisotropy of the liquid crystal becomes negative, and the long axis of the liquid crystal molecules remains perpendicular to the direction of the electric field, so that no display is performed. On the other hand, when the photoconductor layer is irradiated with a pulsed light beam at 1=10, the electric fields VL and C applied to the liquid crystal change as shown in FIG. 1(a). The time indicated by τ in Figure 1(a) is approximately equal to the time constant determined by the resistivity and permittivity of the liquid crystal, and no matter how short the light pulse is, as long as it is within this period, the charge injected into the liquid crystal layer will be absorbed by the liquid crystal. The electric field applied to both ends of the liquid crystal layer changes the offset value and amplitude of its waveform. The waveform shown in FIG. 1(a) has two types of frequency components: the frequency of the electric field applied from the power source and the frequency induced by fluctuations in the electric field intensity due to the irradiation of the optical pulse. The frequency component caused by the irradiation of the latter optical pulse is determined by the time constant τ determined by the specific resistance and dielectric constant of the liquid crystal mentioned above.
Since this time constant τ is usually about several m5ec to several hundred m5eC, the frequency component induced by light pulse irradiation ranges from several Hz to several KHz, which is the crossover frequency of the liquid crystal used in this example. The following can be done. Therefore, when irradiated with light, the dielectric anisotropy of the liquid crystal becomes positive and the long axes of the liquid crystal molecules are aligned parallel to the applied electric field. On the other hand, as the intensity of the electric field applied to the liquid crystal increases with light irradiation, the effect of the frequency component below the crossover frequency and the ECB (el
electrically controlled b
The two effects (i.e., i.e., irefringence) act synergistically to achieve optical recording. After light irradiation, after a period of about τ after the electric field is applied to the liquid crystal, the amplitude of VL and C becomes less than the threshold electric field of the liquid crystal, and the response of the liquid crystal due to the ECB effect cannot be expected, but the attenuation of VL and C The electric field is exponential, and the electric field of the low frequency component caused by the optical pulse irradiation continues to be applied for a long time even after the time constant τ has been exceeded. Therefore, the liquid crystal continues to maintain an ON state for a relatively long time after being irradiated with a light pulse. When the liquid crystal light valve shown in this example is driven based on this principle, the afterglow characteristic is improved, so even when recording is performed by scanning the laser light source at high speed, a very high contrast display is possible. Ta.

[Effects of the Invention] As described above, according to the present invention, it is possible to drive the liquid crystal by adding the effect of dielectric anisotropy in addition to the ECB effect, so that the afterglow characteristics after light irradiation are improved. Unlike the prior art, there is no significant decrease in contrast, and sufficient contrast can be obtained even when an image is formed by scanning a laser light source or the like at high speed. In addition, because of the added effect of dielectric anisotropy, it is now possible to drive the liquid crystal sufficiently even with a low-energy light source.
We were also able to contribute from the perspective of reducing recording energy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an electric field applied to a liquid crystal layer of a liquid crystal light valve in an embodiment of the present invention. FIG. 2 is a cross-sectional view of a liquid crystal light valve according to the present invention. FIG. 3 is a diagram showing frequency characteristics of dielectric constant anisotropy of a liquid crystal according to an example of the present invention. Applicant: Seiko Epson Co., Ltd. agent, patent attorney, Nozomi Uecomb, and 1 other person

Claims (1)

[Claims] In an optical recording type liquid crystal light valve that has a photoconductor layer and a liquid crystal layer between a pair of electrodes and forms an image optically, the liquid crystal layer is made of liquid crystal with positive dielectric anisotropy. By applying an electric field higher than the crossover frequency of the dielectric anisotropy of the liquid crystal to the liquid crystal light valve via the pair of electrodes, and irradiating the photoconductor layer with a pulsed light beam. A liquid crystal light valve characterized in that pixels are formed in the liquid crystal layer by changing the frequency component of an electric field applied to the liquid crystal layer.