JPS61149933A - Driving method of optical modulating element - Google Patents

Abstract

PURPOSE:To obtain high-speed responsiveness and high-density picture elements by impressing an electric signal of the polarity reverse from the signal polarity in the stage of writing to a data line to which fresh picture element information is to be rewritten to an optical modulating element made into the matrix electrode construction in which a bistable optical modulating element is used. CONSTITUTION:Scanning lines and data lines are provided and the optical material having bistability to an electric field, for example, a ferroelectric liquid crystal is disposed between said lines. The erasing state for orienting the liquid crystal corresponding to the part to be rewritten with the fresh picture image information and erasing partially the previously written picture image by impressing the scanning selection signal in the stage of writing respectively to the prescribed scanning line and the data line to be rewritten with the fresh picture image information and the electric signal of the polarity reverse from the polarity of an information selection signal to said lines and the step for impressing the scanning selection signal to the scanning line of the part to be rewritten with the fresh image information and impressing the information selection signal to orient the liquid crystal to the 2nd stable state in accordance with the picture image information to be rewritten to the data line in synchronization with the scanning signal are provided. Such method is widely used for an optical shutter, display, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving an optical modulation element, and more particularly to a method for time-divisional driving of an optical modulation element such as a display element or an optical shutter array.

Conventionally, scanning lines and data lines are arranged in a matrix,
2. Description of the Related Art Liquid crystal display elements are well known in which a liquid crystal compound is filled between electrodes to form a large number of pixels to display images or information. As a driving method for this display element, time-division driving is adopted, in which address signals are selectively and periodically applied to the scanning lines, and predetermined information signals are selectively applied in parallel to the data lines in synchronization with the address signals. However, this display element and its driving method had major and fatal drawbacks as described below.

That is, it is difficult to increase the pixel density or enlarge the screen. Among conventional liquid crystals, most of the liquid crystals used in practical use as display elements are, for example, M, 5ch, because they have a relatively high response speed and low power consumption.
dt and W, written by He1frich'''Applied
Physics Letters” Vo 18.
/164 (1971, 2, 15), P127-128 "Voltage-Dependen tOpt
ical Activity of a Twist
d Namatic Liquid Crystal”
T N (twistednemati)
c) type liquid crystal is used, and this type of liquid crystal forms a structure (helical structure) in which nematic liquid crystal molecules with positive dielectric anisotropy are twisted in the thickness direction of the liquid crystal layer in the absence of an electric field. The liquid crystal molecules form a structure arranged in parallel on both electrode surfaces. On the other hand, when an electric field is applied, nematic liquid crystals with positive dielectric anisotropy are aligned in the direction of the electric field, resulting in light modulation. When a display element is constructed using this type of liquid crystal with a matrix electrode structure, the area where both the scanning line and the data line are selected (selection point) is
A voltage higher than the threshold required to align the liquid crystal molecules perpendicular to the electrode surface is applied, and no voltage is applied to areas where both the scanning line and the data line are not selected (non-selected points), so the liquid crystal molecules are aligned perpendicularly to the electrode surface. It maintains a stable parallel arrangement with respect to In addition to arranging linear polarizers in a cross nicol relationship above and below such a liquid crystal cell, it is not possible to use it as a pixel element because light does not pass through selected points and light passes through non-selected points. It becomes possible. However, when a matrix electrode structure is configured, there is a finite area in which scanning lines are selected and data lines are not selected, or in areas where scanning lines are not selected and data lines are selected (so-called "one half-selected point"). The electric field becomes hotter.The difference between the voltage applied to the selected point and the voltage applied to the half-selected point is sufficiently large, and the voltage threshold required to align the liquid crystal molecules perpendicular to the electric field is set to an intermediate voltage value. If so, the display element operates normally, but if the number of scanning lines (N) is increased, the entire screen (1
While scanning a selected point (frame), the time (duty ratio) during which an effective electric field is present at one selected point decreases at a rate of N. For this reason, when repeated scanning is performed, the effective voltage difference between selected points and non-selected points becomes smaller as the number of scanning lines increases, resulting in lower image contrast and crosstalk. This is a drawback that is difficult to avoid. This phenomenon occurs in liquid crystals that do not have bistability ([
The stable state is when the liquid crystal molecules are aligned horizontally with respect to the polar plane, and they are aligned vertically only while an electric field is effectively applied. ,
This is essentially an unavoidable problem that arises when repeated scanning is performed. To improve this point, the voltage averaging method%2
Frequency drive methods and multiple matrix methods have already been proposed, but all of these methods are insufficient and have reached a plateau due to larger screens and higher density display elements, and the inability to increase the number of scanning lines sufficiently. The current situation is that

It is an object of the present invention to provide a novel method for driving a liquid crystal element that solves all the problems in conventional liquid crystal display elements or liquid crystal optical shutters.

Another object of the present invention is to provide a method for driving a liquid crystal element having high-speed response.

Another object of the present invention is to provide a method for driving a liquid crystal device having a high density of pixels.

That is, an object of the present invention is to drive an optical modulation element having a structure including a scanning line and a data line, and an optical modulation material having bistability with respect to an electric field arranged between the scanning line and the data line. In the method, the polarity and opposite polarity of the scan selection signal and the information selection signal at the time of writing the new image quality information to the selected scan line and the data line to be rewritten, respectively. By applying an electric signal, the optical modulation material corresponding to the part where the new image information is to be rewritten is oriented to the first stable state, and the image information written in the previous writing step is partially rewritten. applying a scanning selection signal to the scan line of the part where new image information is to be rewritten, and orienting the optical modulation substance to a second stable state in accordance with the rewritten image information to the data line; This is achieved by a method of driving an optical modulation element comprising a partial writing step of applying an information selection signal in synchronization with the scanning selection signal.

The optical modulation material used in the driving method of the present invention has a bistable state consisting of a first optically stable state and a second optically stable state with respect to an electric field, and in particular has a bistable state with respect to an electric field as described above. A liquid crystal with bistability is used.

As a liquid crystal having bistability that can be used in the driving method of the present invention, a chiral smectic C-phase (8mC) or H-phase (SmH'') liquid crystal having ferroelectricity is suitable. For dielectric liquid crystals, please see @LE JOUR
NAL DFi PHYSIQUELETTBR8”
36 (L-69) 1975, [Ferroele
ctricLiquid Crystals J:
” Applied Physics Letters
”36 (11) 1980 “Submicro
5econd B15tableBlectroopt
ic 8witching in Liquid Cr
ystalsJ: 0 Solid State Physics” 16 (141) 198
1r liquid crystal" and the like, and the ferroelectric liquid crystal disclosed in these documents can be used in the present invention.

In addition, in the present invention, in addition to the above-mentioned 8mC" and SmH", K, chiral smect I phase (8mI), J phase (SmJ
”), G phase (8mG”), F phase (SmF”), carbon phase (S
mK”) can be used.

FIG. 1 schematically depicts an example of a ferroelectric liquid crystal cell. 11 and 11' are In2O3, 5n02 or IT
It is a substrate (glass plate) coated with a transparent electrode such as O (Indium-Tin Oxide), between which is sealed an 8mC" phase or SmH" phase liquid crystal oriented so that the layer 12 is perpendicular to the glass surface. There is.

A thick line 13 represents a liquid crystal molecule, and this liquid crystal molecule 13 has a dipole moment 14 (on P) in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 11 and 11, the liquid crystal molecules 13
The orientation direction of the liquid crystal molecules 13 can be changed so that the helical structure of the liquid crystal molecules is unraveled and all of the dipole moments 14 are oriented in the direction of the electric field. The liquid crystal molecules 13 have an elongated shape and exhibit high refractive anisotropy in the major and minor axis directions. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, the polarity of voltage application can be adjusted. It is easily understood that the liquid crystal modulation element has optical characteristics that change depending on the change in the optical characteristics. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ), the helical structure of the liquid crystal molecules unravels (non-helical structure) even when no electric field is applied, as shown in Figure 2, and its dipole The moment P or P' is either upward (24) or downward (24'). When such a cell is given an electric field E or E' with a different polarity above a certain threshold value as shown in FIG. 2, the dipole moment will move upward 24 or downward 2
4', and depending on the orientation, the liquid crystal molecules are oriented either in the first stable state 23 or in the second stable state 7!123'. There are two advantages to using a ferroelectric liquid crystal like this as a light modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability. To explain the second point with reference to FIG. 2, for example, when an electric field E is applied, the liquid molecules are oriented in a first stable state 23, and this state remains stable even when the electric field is turned off. When an electric field E' in the opposite direction is applied, the liquid crystal molecules are oriented to a second stable state 23 and change their orientation, but they remain in this state 1114 VC even after the electric field is turned off.

Further, as long as the applied electric field E does not exceed a certain threshold value, each orientation state 11AIIC is maintained.

It is preferable for a Kti cell to be as thin as possible in order to effectively realize fast response speed and bistability, and generally 0.5μ to 20μ, and 0.5μ to 5μ are suitable. There is. A liquid crystal electro-optical device using this type of ferroelectric liquid crystal and having an IJ electrode structure has been proposed, for example, in US Pat. No. 4,367,924 by Clark and Ragaval.

A preferred example of the driving method of the present invention is shown in FIG.

FIG. 3(A) Fi is a schematic diagram of a cell 31 having a matrix pixel structure in which a bistable optical modulation material is sandwiched between a scanning line (scanning electrode group) and a data line (signal electrode group).

32 is a scanning electrode group, and 33 is a signal electrode group.

Now, to simplify the explanation, an example will be shown in which a black and white binary signal is displayed. In FIG. 3(A), it is assumed that the pixels indicated by diagonal lines correspond to "black" and the other pixels correspond to "white". First, to align the screen to "white" (this step is referred to as an erase step), the bistable optical modulating material can be aligned to the first stable 11. To do this, apply a signal of a predetermined voltage pulse (e.g. +2vo, time width Δt) to all scanning electrode groups, and apply a signal of a predetermined pulse (e.g. voltage -VO%Δt) to the entire scanning electrode group button. do it. That is, in this erasing step, an electrical signal of opposite polarity to the scanning selection signal during the writing step is applied to the scanning electrode group, and an electrical signal of opposite polarity to the information selection signal (writing signal) during the writing step is applied to the signal electrode group. are applied synchronously.

Figures 3 (B)-(a') and (B)-(b) show the electrical signal for opening the selected scanning electrode (scanning selection signal) and the signal for opening the other scanning electrodes (unselected scanning electrodes), respectively. The applied electrical signals are shown in Figures 3 (B)-(c) and (B).
)-(d) are the electrical signals (Vo applied at the information selection signal phase Tl) applied to the signal electrodes that are selected (this is black) and are not selected (this is white)
Represents the electrical signal applied to the signal electrode. Figure 3 (B)
-(a) to (d) The horizontal axis represents time and the vertical axis represents voltage. T1 and T2 represent the phase at which the information signal (and scanning signal) is applied and the phase at which the auxiliary signal is applied, respectively. In this example, an example where T2=Δt is shown.

32 scanning electrode groups are sequentially selected. Now, the threshold voltage at the application time Δt to give the first stable state (white) of the liquid crystal cell with bistability is -vtb, and the threshold voltage at the application time Δt to give the stable state (black) of ts2 is -vtb. If the threshold voltage of is vthl, the electric signal given to the selected scanning electrode is as shown in FIG. 3(B)-(a). The voltage is such that In addition, the other scanning electrodes are the third
As shown in Figures (B)-(b), it is in a grounded state and the electrical signal is 0. On the other hand, the electric signal Fi applied to the selected signal electrode is vo in phase t1 and -vo in phase 12, as shown in FIGS. 3(B)-(C)', and is applied to the unselected signal electrode. The electrical signal is -vo in phase TIVC and +vo in phase T2, as shown in FIGS. 3(B)-(d). In the above, the voltage value ■o is Vo<Vthl<3V0 and -vo>-
vth2>-3V, is set to a desired value that satisfies the following.

FIG. 3(C) shows the voltage waveform applied to each pixel when such an electric signal is applied.

In FIG. 3(C), (a) and (b) are on the selected scanning line, respectively, and "black" and "white" are displayed on the pixels to be displayed, and (C) and (d) ) are voltage waveforms applied to pixels on each unselected scanning line.

In the first phase T1, the information selection signal vo is applied to a pixel on the scanning line to which the scanning selection signal -2■o is applied and whose display is "black", and therefore the threshold voltage vth1 is applied to this pixel. A voltage exceeding 30 is applied to orient the bistable liquid crystal to a second optically stable state and the pixel will be written "black" K (writing step). Furthermore, in the case of a pixel that exists on the same scanning line and is to be displayed as "white", the applied voltage in the first phase T1 is a voltage vo that does not exceed the threshold voltage vth1. It remains stable, ie white.

On the other hand, on unselected scanning lines, the voltages applied to all pixels are either 2 or 0, and neither exceeds the threshold voltage. Therefore, the liquid crystal molecules maintain the orientation corresponding to the signal state when scanned without changing the orientation state. That is, when the scanning electrode is selected in the optically stable state of one side in which "white" K is aligned, a signal for one line is written in the first phase T1, and the frame ends. Even after that, the signal state can be maintained.

Now, FIG. 3A shows an example of an image forming process in which one screen is formed by the erasing step and writing step in this manner. Next, an example of partially rewriting this screen is shown in FIG. 3(D). As shown in the figure, when rewriting the X-Y area consisting of the scanning line
An electric signal (for example, 2Vo shown in FIG. 4) having a polarity opposite to that of the scan selection signal (for example, 2Vo shown in FIG. 4) during the previous write step is applied to 1182 and 83 at 1 o'clock or sequentially, The part to be rewritten (X-Y area) The data line 11 corresponding to the IC and the electric signal (for example, By applying -Vo in step 1 shown in FIG. 4, it is possible to erase only a partial part of one screen, that is, the XY region (partial erasing step).

Next, the data lines of the area partially erased in this way are processed in the same manner as in the previous write step, that is, an information selection signal (+Vo) and an information non-selection signal (-Vo) according to the rewritten image information. VO) -2v.

By applying the signal in synchronization with the scan selection signal of , it is possible to write in this area (partial write step).

On the other hand, the area where rewriting is not performed, that is, the X'-Y' region consisting of the scanning line X' and the data line Y' is
In order to maintain the written state of each pixel in the -Y' region, an electric signal lower than the threshold voltage of the ferroelectric liquid crystal is applied to each pixel in this region.

Specifically, during the partial erasing step, the t-scanning signal (for example, as shown in FIG. Apply an electric signal having the same polarity as the voltage (Vo 2Vo) shown in FIG. Scan selection signal during write step (e.g. * M 4 Figure 'IC' f Sx * 82-83
(7) -2VO) (!: Apply an electric signal of the same polarity (for example, -Vo of I3 shown in Fig. 4) for M periods. Also, the potential of the scanning line corresponding to this X'-Y region teeth,
A reference potential (for example, 0 volts) is used.

FIG. 4 shows the drive signals described above in chronological order. 81 to SS are electric signals b I applied to the scanning electrodes.
With electric signals applied to signal electrodes I and I3, pixels A, C, and D shown in FIGS. 3(A) and (D), respectively,
This is the voltage waveform applied to C and DVC.

Further, in the present invention, a rewritten portion can be specified using a cursor.

Now, the switching mechanism of ferroelectric liquid crystals due to electric fields in a bistable state is not necessarily clear microscopically, but generally, after switching to a predetermined stable state with a strong electric field for a predetermined time, there is no electric field at all. If it is applied and left in a strong state, it is possible to maintain that state semi-permanently; voltage), if an electric field of opposite polarity is applied for a long time, the orientation state will be reversed again to the opposite stable state, resulting in incorrect information display and modulation. Phenomena that cannot be achieved may occur. The present inventors believe that the ease with which the orientation state transition reversal phenomenon (a type of crosstalk) occurs due to the long-term application of such a weak electric field is influenced by the substrate surface material, roughness, liquid crystal material, etc. We have recognized this, but we have not yet fully understood it quantitatively. However, it has been confirmed that when a uniaxial substrate treatment for aligning liquid crystal molecules is performed, such as rubbing or oblique evaporation of SiO, etc., the tendency for the above-mentioned inversion phenomenon to occur tends to increase. In particular, it was confirmed that this tendency appears more strongly when the temperature is 1 higher than when the temperature is lower.

In any case, in order to achieve correct information display or modulation, it is preferable to avoid applying an electric field in a fixed direction for a long time.

Therefore, the second phase T2 in the driving method of the present invention is a phase that prevents the continued application of a weak electric field in a certain direction, and a preferable example thereof is shown in FIG. 3(B)-(
As shown in C) and (d), a signal with a different polarity from the information signal applied to the signal electrode group at phase T1 ((C) corresponds to black, (d) corresponds to white) is applied at phase T2IC. It is something to do. For example, when trying to display the pattern shown in FIG. 3(A), if a driving method without phase T2 is used, the pixel becomes black when scanning electrode S1 is scanned.
After S2, the electric signal applied to the signal electrode IIK is:

-vo continues and the voltage is applied to the pixel as it is, so there is a high possibility that the pixel will eventually turn white.

In this embodiment, the screen is formed by an erasing step in which the entire screen becomes "white", and a writing step and K in which corresponding pixels are written as "black" in accordance with the information in the first phase Tl. In this case, the voltage for writing "black" K in the first phase T1 is 3vo, and the application time is Δt. Also, the voltage applied to each pixel during periods other than scanning is a maximum of 1±V,
1, and the longest time it is continuously applied is:
2Δt at 40 points shown in FIG. 4, and the most severe condition is when the information signal continues in the order of white → white → black, and the second "white" corresponds to the scanning time. This is still 4Δt (41), which is a short application time, and no crosstalk occurs at all. Once the entire screen has been scanned, the displayed information exhibits bistable property, which allows it to be retained semi-permanently. There is no need for a refresh unit at all as in a display element using a normal TN liquid crystal.

Now, the optimal time interval of the second phase T2 depends on the magnitude of the voltage applied to the signal electrode in this phase, and the voltage applied as an information signal in the first phase T1. When applying a voltage of opposite polarity, it is generally preferable to shorten the time interval when the voltage is large and to lengthen the time interval when the voltage is small; however, if the time interval is long, Buttons that scan the entire screen will take a long time. Therefore, it is preferable to set T2≦T.

FIGS. 5 and 6 show time-series representations of another example of the drive mode according to the present invention. In these driving forms, the threshold value for orientation transition is the pulse width Δ1 [whereas the value of vo is set to be a value between 1 Vol and 21 Vo10.

In FIG. 5, the signal for erasing the image is applied to the scanning electrode group in the erasing step as an electric signal of +■o and to the information signal electrode group as an electric signal of -Vo. Then, a scanning signal -vo is sequentially applied, and in synchronization with this scanning signal, an information selection signal 10Vo is applied to the signal electrode to perform writing in the state shown in FIG. 3(A).

Next, in the partial erasing step, the X-Y
-2Vo to the pixels written in the previous step in the area
The electrical signal VO is applied and erased at 1 o'clock (at this time, as shown in the example of erasure at 1 o'clock in Fig. 5, the electrical signal VO is sequentially applied to the scanning lines as a scanning song selection signal to perform a partial erasure step. ). Next, an electric signal corresponding to new image information is applied to the X-Y area to partially write the X-Y area into the state shown in FIG. 3(D).

The examples shown in FIGS. 5 and 6 are cases in which there is no auxiliary signal, and the example in FIG. 7 is a case in which there is an auxiliary signal. The voltage values of each drive pulse are shown in the figure, but in the example of FIG. 7, the erasing signals applied to the scanning electrode and the signal electrode during the erasing step have polarities reversed when writing information. water and the absolute value is smaller than that (lv
o), it is an electrical signal with a large pulse width (2Δt). In such an erasing method, the threshold voltage of the liquid crystal has pulse width dependence, and the width 2 Δt K vs. t threshold Vth″1 is such that vth=<!−v.

13 It is possible if it satisfies (7).

Also, in the partial erase step, -iv is applied to pixels in the Fix-y area.
o electric signal is applied to partially erase, and a new image is written in the X-Y area in the next partial writing step.

As an example of the ferroelectric liquid crystal compound, in addition to DOBAMBC used in Example 1, 1-hexyloxyhensyritene-P-amino-2-chloropropylcinnamate (HO
BACPC), 4-〇-(2-methyl)-phthylresorsilitin-4'-octylaniline (MBRA8)
etc. can be used. Further, as the ferroelectric liquid crystal, in addition to the above-mentioned SmC+ and 8mH'', phases such as chiral smectite phase, F phase, G phase, and J phase can be used.

When constructing an element using these materials, the element may be supported by a copper block with a heater embedded in it, if necessary, in order to maintain the temperature at which the liquid crystal compound enters the chiral smectate phase. can.

The method of the present invention can be widely applied to the field of optical shutters and displays such as liquid crystal-optical shutters and liquid crystal televisions.

Hereinafter, specific examples of the present invention will be shown.

Example 1 A polyimide film of approximately 30 OA was formed using a spin cord on one of the glass plates in which transparent conductive films (ITO) were patterned to form a 500×500 matrix. The substrate was rubbed with a roller whose surface was wrapped with a terrene cloth, and then bonded to the other substrate not coated with the polyimide film to form a cell. The cell spacing at this time is approximately 16μ. In this cell, a ferroelectric liquid crystal, desyloxybenzylidene-P, is used.
-amino-2-methylbutylcinnamate (DOBAM
BC) was injected and slowly cooled from the heated molten state to obtain a uniform monodomain state at 8 mC. Controlling the cell temperature at 70°C, based on the driving method shown in Figures 3 and 4, VO = 10 V, '14 =
When line sequential scanning was performed with T2=Δt=80 μsec, an extremely good image was formed, and when a part of this screen was then rewritten as a new image using the method shown in FIG. A good image with a rewritten screen was obtained.

[Brief explanation of drawings]

1 and 92 are perspective views of liquid crystal elements used in the driving method of the present invention. Figure 3 (A) and Figure 3 (D) F
i is a plan view of an electrode structure used in the driving method of the present invention; FIG. 3(B) (a) to (d) are explanatory diagrams showing waveforms of electrical signals applied to the electrodes. Figure 3 (C) (a)
~((D is an explanatory diagram showing the voltage waveform applied to the pixel. Fig. 4, Fig. 5, Fig. 6, and Fig. 7 show the voltage waveform when voltage is applied in time series. It is an explanatory diagram.Patent applicant: Canon Co., Ltd. 111+-+-+ Procedural amendment (mouse) April 7, 1985 Mr. Manabu Shiga, Commissioner of the Patent Office!, Indication of the case, 1982 Patent Patent No. 272357 2, Name of the invention Optical modulation element Driving method 3, relationship with the case of the person making the amendment Patent applicant address 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (1oo
) Canon Co., Ltd. Representative Ryu Kaku 3 Department 4, Agent address: Canon Co., Ltd., 3-30-2 Shimomaruko, Ota-ku, Tokyo 146 (telephone: 758-2111) 5, Specification subject to amendment 6, Contents of amendment (1) rH, 5cha on page 4, lines 7 to 12 of the specification
dL-...(twisted nematic) type"
``Applied Physics Letters Volume 1'' by M. Schitt (M, 5chadt) and Tableu, Helfrich (W. Heltr 1ch)
8. Number 4 (1971, 2, 15), page 12
7-128 (“Applied Physics L
ettars” Vol 8. No. 4 (1971, 2, 15), PL27-128
) (7) "Voltage - Dependent - Optical Activity - of a Twisted Nematic Liquid Number Crystal"("Voltage
-Dependent 0ptical Activities
Ty ofa Twisted Nematic Li
Quid Crystal”
TN) [Twisted Nematic
Nematic ) ] type”. (2) Same as above, page 8, line 17 to page 9, line 1 r ”L
E JOURNAL・l, 1quid Cr7st
als J;
URNAL DE PHYSIQUE LETTERS
”) 36 (L-69) 1975.r Ferroelectric Kid Bottle Linutarus J (rFerroel
etricLiquid Crystals J)
; “Applied Physics Letters”
s") 36 (11) 1980 r Submicro Second Bistiple Electro-optic Switching In-kai Liquid Crystals J (r Su
bmigro 5econd B15tableEle
ctrooptic Switching in
LiquidCrystalsJ ); Corrected as J.

Claims (7)

[Claims] (1) In a method for driving an optical modulation element having a structure in which a scanning line and a data line are arranged, and an optical modulation material having bistability with respect to an electric field is arranged between the scanning line and the data line, Applying electrical signals having polarities opposite to those of the scan selection signal and information selection signal during the write step, respectively, to the selected scanning line and the data line to which new image information is to be rewritten among the data lines. a partial erasing step of orienting the optical modulating material corresponding to the part where new image information is to be rewritten into a first stable state by partially erasing the image written in the previous writing step; Then, a scan selection signal is applied to the scan line of the part where new image information is to be rewritten, and an information selection signal is applied to the data line to orient the optical modulation material to a second stable state in accordance with the rewritten image information. 1. A method of driving an optical modulation element, comprising a partial writing step of applying the signal in synchronization with the signal. (2) At the time of the partial erasing step, an electric signal having the same polarity as the scanning signal at the time of the erasing step is applied to the data line corresponding to the part other than the part where new image information is to be rewritten. A method for driving an optical modulation element according to item 1. (3) At the time of the partial write step, an electric signal of the same polarity is applied to the data line corresponding to the part other than the part where new image information is to be rewritten, in synchronization with the scan selection signal at the time of the partial write step. A method for driving an optical modulation element according to scope 1 or 2. (4) The method for driving an optical modulation element according to claim 1, wherein the optical modulation substance is a ferroelectric liquid crystal. (5) The method for driving an optical modulation element according to claim 4, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. (6) The chiral smectate liquid crystal has a C phase, an H phase,
6. The method of driving an optical modulation element according to claim 5, wherein the optical modulation element is in G phase, I phase, J phase, F phase, or K phase. (7) The method for driving an optical modulation element according to claim 5, wherein the chiral smect liquid crystal has a non-helical structure.