JPS62150331A - Driving method for optical modulation element - Google Patents

Abstract

PURPOSE:To prevent a phenomenon by which a display state is inverted to other display state in the course of scanning for writing one picture, by setting the maximum pulse width of a voltage waveform which is applied continuously to a picture element on a scan electrode line to which a scan non-selecting signal is applied, to 2 times or 2.5 times of a pulse at the time of writing. CONSTITUTION:The titled element is provided with an electric signal having the first phase t1 having a voltage for applying an electric field in one direction so that a liquid crystal is oriented in the first stable state by a scan electrode by which a liquid crystalement having a ferroelectric liquid crystal having at least two stable states against an electric field, and an electric signal of the signal electrode, and the third phase t3 having a voltage for assisting to orient again the liquid crystal to the second stable state in accordance with the electric signal of the signal electrode. Also, in the second phase t2, the titled element is driven by applying an electric signal having the voltage polarity being opposite to that of an electric signal which has been applied to the first phase t1, based on prescribed information, to a signal electrode group. The voltage waveform is 2V0, and -2V0, in case of a phase (time) t1 and t2, and in case of t3, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for driving an optical modulation element, and more particularly to a method for driving a ferroelectric liquid crystal element having a small number of (two stable states).

[Description of prior art]

Conventionally, liquid crystal display elements are well known in which a group of scanning electrodes and a group of signal electrodes are configured in a matrix, and a liquid crystal compound is filled between the electrodes to form a large number of pixels to display a single image or information. ing.

The driving method for this display element is a time-sharing method in which an address signal is selectively and periodically applied to a group of scanning electrodes, and a predetermined information signal is selectively applied in parallel to a group of signal electrodes in synchronization with the address signal. drive is used.

For practical purposes, most of these are, for example, ``Applied Physics Letters''.

(“Applied Rhysi, 6s Let
ter”) 1971, No. 18(4) 1'27-1
M, 5chadt (M, 5chadt) published on page 28
) and W, He1frich (W, He1frich
) co-authored ``Voltage Dependant φ Optical Activity of a Twisted Nematic Liquid Base Crystal''.

("Voltage Dependent 0pti
cal Activit7of a Twist
d Nematic Liquid Crystal
T N (twistedne
matic) type liquid crystal.

In recent years, the use of bistable liquid crystal elements as an improved version of conventional liquid crystal elements has been proposed by both C1ark and Lagewall in Japanese Patent Application Laid-open No. 107216/1983 and US Pat. Fourth
36'79'' No. 24, etc. As the bistable liquid crystal, chiral smemitic C is generally used.
Emphasis with phase (SmC') or H phase (SmH'')
When an electrically conductive liquid crystal is used and in these states assumes either a first optically stable state or a second optically stable state in response to an applied electric field, and when no electric field is applied. It has the property of maintaining its state, that is, it has stability; it also responds quickly to the change in electric field, and is expected to be widely used in fields such as high-speed and memory-type display devices.

[Problems that tsutsui attempts to solve]

However, problems arise when the number of display pixels is extremely large and high-speed driving is required. That is, the threshold voltage for providing the first stable state in a ferroelectric liquid crystal cell having bistability for a predetermined voltage application time is -Vt.
hl and the threshold voltage for providing the second stable state is +V'th2, even if these threshold voltages are not exceeded, if the voltage continues to be applied for a long time, the display written to the pixel A state (eg, a white state) may be reversed to another display state (eg, a black state). 1 shows the threshold characteristics of a bistable ferroelectric liquid crystal cell.

Figure 1 shows DOBAMBC (1 in the figure) as a ferroelectric liquid crystal.
2) and HOBACPC (l'l in the figure) are plotted of the application time dependence of the threshold voltage (vth) required for switching.

As is clear from FIG. 1, it is understood that the threshold value vth has application time dependence, and roughly speaking, the shorter the application time, the steeper the slope.

From this, when applied to an element that has an extremely large number of scanning lines and is driven at high speed, ``For example, even if a certain pixel is switched to the bright state during scanning, it will always be less than vth after the next scanning.'' It can be seen that if the information signal continues to be applied, there is a risk that the pixel will be inverted to a dark state during the completion of scanning one screen.

[Means for Solving the Problems] and [Operation] The purpose of the present invention is to provide a novel method for driving a liquid crystal element that solves the problems in conventional liquid crystal display elements or liquid crystal optical shutters as described above. It is in. Another object of the present invention is to provide a method for driving a liquid crystal element with high-speed response.

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

The present invention provides a matrix pixel structure in which an optical modulation material having at least two stable states is arranged between crossed scanning electrode groups and signal electrode groups, and pixels are defined at intersections of the scanning electrode groups and signal electrode groups. In the method for driving an optical modulation element, all or a predetermined portion of the pixels on the scan electrode line of the matrix pixel structure are covered with the optical modulation material during a writing period to the pixels on the scan electrode line selected in the matrix pixel structure. the first of
a first phase in which all or a predetermined portion of the pixels on the scanning electrode line are brought into a display state based on a stable state of the optical modulating substance; and a second phase t2 that does not determine the display state of the pixel between the first phase t1 and the third phase t3. ing.

In a preferred embodiment of the present invention, a scanning electrode group is sequentially and periodically selected based on a scanning signal, a signal electrode group facing the scanning electrode group and selected based on a predetermined information signal, and a gap between the two electrodes. orienting the liquid crystal to a first stable state by means of a selected scanning electrode of a liquid crystal element having at least a ferroelectric liquid crystal held at a constant temperature and having at least two stable states with respect to an electric field, and an electric signal of a signal electrode. a first phase t1 having a voltage that provides an electric field in one direction; and a third phase t3 having a voltage that assists in reorienting the liquid crystal to a second stable state in response to an electric signal from a signal electrode. Electricity 7 with
L4M, and furthermore, in a second phase t2, an electric signal having a voltage polarity opposite to that of the electric signal applied to the signal electrode group in the first phase t1 based on predetermined information is applied. It can be driven by adding

〔Example〕

The optical modulation substance used in the driving method of the present invention has at least two stable states, and in particular takes either a first optically stable state or a second optically stable state depending on the applied electric field. . That is, a substance having a bistable state with respect to an electric field, particularly a liquid crystal having such a property, is used.

As the liquid crystal having bistability that can be used in the driving method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable, among which chiral smectic C phase (SmC') and H phase (SmH ') LCD is suitable.

This ferroelectric liquid crystal is described in “Le Journal de Physique: Rutile” (“Le Journal de Physiove 1
etter") 36 @ (L-69), 1975's "Ferroelectric Kai Liquid Crystals" (rF
error electric liquid crystal
als J); “Applied Physics φ Letters”.

(“Applied Physics Letters
” ) Volume 36 (No. 11) 1980 “Submicron Second Contest Bi-Stipple Electro-Optic Switching in Fist Liquid Crystals J
(r Submicro 5econd B15t
able Electra optie Switch
ng in Liquid CrystalsJ')
``Solid State Physics'' 16 (141) 1981 ``Liquid Crystal'' etc., and the ferroelectric liquid crystal disclosed in these documents can be used in the present invention.

More specifically, an example of a ferroelectric liquid crystal compound used in the method of the present invention is decyloxyhenzylidene-y-amino-2-methylbutylcinnamate (DOBAMBC).
, hexyloxyhensi-richin-y-amino-2-chloropropylcinnamate (HOBACPC) and 4
-O-(2-methyl)-butylresolsiliten-4'-
Examples include octylaniline (MBRA8).

When constructing an element using these materials, the element is supported by a copper block or the like with a heater embedded in it, as necessary, in order to maintain the temperature at which the liquid crystal compound becomes the SmC' phase or SmH' phase. can do.

Further, in the present invention, in addition to the above-mentioned SmC' and SmH' +7), it is also possible to use ferroelectric liquid crystals that appear in chiral smectic F phase, ■ phase, J phase, G phase, or other phases.

Note that the m2 diagram is a schematic depiction of an example of a ferroelectric liquid crystal cell. 21a and 21b are I n203゜3 n02 and I
A substrate (glass plate) coated with a transparent electrode such as TO (indium tin oxide), between which a liquid crystal molecular layer 22 is oriented perpendicular to the glass surface.
'' phase liquid crystal is sealed. The thick line 23 represents the liquid crystal molecule, and this liquid crystal molecule 23 has a dipole moment (P) 14 in the direction perpendicular to the molecule. When a voltage above a certain threshold is applied between the electrodes on the substrates 21a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and the dipole moment The orientation direction can be changed.The liquid crystal molecules 23 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. It is easy to understand that if the arranged polarizer is turned off, it becomes a liquid crystal optical modulation element whose optical properties change depending on the polarity of applied voltage.Furthermore, if the thickness of the liquid crystal cell is made sufficiently thin (for example, L). As shown in Fig. 3, the helical structure of the liquid crystal molecules is unraveled even when no electric field is applied, and the dipole moment Pa or pb is either upward (34a) or downward (34b). .In such a cell, an electric field E of different polarity above a certain threshold value is applied as shown in Fig. 3.
When a or Eb is applied for a predetermined time, the dipole moment moves upward 34 in response to the electric field vector of the electric field Ea or Eb.
a or downward 34b, and accordingly, the liquid crystal molecules are aligned in either the first stable state 33a or the second stable state 33b.

There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has a bistable state. To explain the second point with reference to FIG. 2, for example, when the electric field Ea is applied, the liquid crystal molecules are aligned in a first stable state 33a, and this state remains stable even when the electric field is turned off. Furthermore, when an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented to the second stable state 33b and the orientation of the molecules is changed.
It remains in this state even if the electric field is turned off. Further, as long as the applied electric field Ea does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, generally 0.5
A range of 1 to 20 strands is suitable, especially a range of 1 to 5 strands.

Preferred specific examples of the driving method of the present invention will be explained with reference to FIGS. 4 to 7.

FIG. 4 is a schematic diagram of a cell 41 having a matrix electrode structure in which a ferroelectric liquid crystal compound is sandwiched between. 42 is a scanning electrode group, and 43 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. 4, it is assumed that the pixels indicated by diagonal lines correspond to "black" and the others correspond to "white". Fifth
Figures (a) and (b) respectively show the scan selection signal given to the selected scan electrode and the scan non-selection signal given to the other scan electrodes (unselected scan electrodes).
Figures (C) and (d) represent an information selection signal applied to a selected signal electrode and an information non-selection signal applied to an unselected signal electrode, respectively.These information selection signals and information non-selection signals are different from each other. The voltage waveforms have the same polarity in the first phase t1. In FIGS. 5(a) to 5(d), the horizontal axis represents time and the vertical axis represents voltage. tl within the write period.

t2 and t3 are the first. In this example, tl=t2=t3 indicates the second and third phases.

Writing periods are sequentially selected for the scan electrode group 42 .

Now, the threshold voltage at the application time Δt to give the first stable state (this is white) of a liquid crystal cell having bistability is -vt hl, and the second stable state (this is black) is set as -vt hl. ) is the threshold voltage at the application time Δt to give Vt h
If it is 2.

The electrical signals given to the selected scanning electrodes are shown in Figure 5 (
As shown in a), the phase (time) tl and t2-c are 2V
Q is a voltage waveform such that 5-phase t3-c' is -2vO. For other scanning types and poles, see Figure 5(b)
As shown in the figure, it is in a grounded state and the electrical signal is 0.

On the other hand, the electrical signal given to the selected signal electrode is
As shown in Figure (C), the voltage is 1 in the phase t1, and -vO in the phases t2 and t3. Further, the electrical signal applied to the unselected signal electrodes is 10 at phase t1, as shown in FIG. 5(d). In the above,
The voltage value vO is v□<vt h2<3v□ and -3v(,<
-vt hl<-VQ is set to a desired value.

FIG. 6 shows the voltage waveform applied to each pixel when such an electric signal is applied.

In FIG. 6, (a) and (b) are on the selected scanning electrode, respectively, and "black" and "white J" are displayed on the pixel to be displayed, and (c) and (d) are respectively selected. This is the voltage waveform applied to the pixels on the scan electrodes that are not connected.
As is clear from the figure, all or a predetermined portion of the pixels on the selected scan electrode have a threshold voltage of −V at the first phase t1.
Since a voltage of -3vo exceeding thl is applied, it is first aligned to -white. This is called the erasure phase. Among these pixels, the pixel to be displayed as "black" is transferred to the other optically stable state ("black") because a voltage 3VQ exceeding the threshold voltage Vt h2 is applied at the third phase t3. This is defined as the display selection phase. In addition, it exists on the same scanning electrode, and
In the pixel to be displayed as "white", the applied voltage in the third phase t3 is a voltage vo that does not exceed the threshold voltage -vth, so the pixel remains in one optically stable state.

On the other hand, on the scan electrode that is not selected, the voltage applied to all pixels is ±V or O, neither of which exceeds the threshold voltage.Therefore, the liquid crystal molecules are scanned previously without changing their alignment state. The orientation corresponding to the current display state is maintained as is. That is, when a scanning electrode is selected, first, in a first phase t1, the selected pixel is aligned to the optically stable state "white" on one side, and then, in a third phase t3, the selected pixel is aligned on the other side. The signal is transferred to an optically stable state (black), a line's worth of signals are written, and the signal state can be maintained until the next frame is selected.

FIG. 7 shows the drive signals described above in chronological order. 5l-55 is a scanning signal applied to the scanning electrode, and 1
1 and 3 are information signals applied to the signal electrodes, and A and C are voltage waveforms applied to pixels A and C shown in FIG.

Now, the switching mechanism of a ferromagnetic liquid crystal in a bistable state due to an electric field is not necessarily clear microscopically, but generally a strong electric field for a predetermined period of time is applied to a predetermined (first) stable state. If the state is left in a state where no electric field is applied after switching, it is possible to maintain that state almost semi-permanently; For example, if an electric field of opposite polarity is applied for a long time even if the voltage is lower than vth, the orientation state will transition again to the opposite (second) stable state. As a result, it has been recognized that the likelihood of a situation in which correct information display or modulation cannot be achieved is affected by the substrate surface material, roughness, liquid crystal material, etc., but it has not yet been quantitatively understood. . 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 transition to occur tends to increase. It was also confirmed that this tendency was stronger at higher temperatures.

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

Therefore, in the driving method of the present invention, in the first phase t1 during scanning, all pixels on the scanning electrode are set to "white",
In the third phase t3, the corresponding pixel is rewritten as "black" according to the information, but in this embodiment, the voltage to make it "white" in the first phase t1 is -3VQ; The application time is Δt. On the other hand, the voltage required to rewrite to "black" is 3VQ, and its application time is Δt.

In addition, the voltage applied to each pixel at times other than scanning is at most i
±Vol, and the longest time for which it is continuously applied can be determined by providing an auxiliary phase (auxiliary signal application phase) that is the second phase in which the auxiliary signal that does not determine the display state of the pixel is applied. 71 shown in Figure 7, crosstalk does not occur at all, and once the scanning of the previous screen is completed, the information displayed as 1 is retained semi-permanently, so it has bistability. There is no need for a refresh unit at all as in a display element using a normal TN liquid crystal. Moreover, in the present invention, since the voltage waveform applied to the pixel when scanning is not selected is 2Δt at maximum,
It is possible to set a wide voltage margin during driving without causing an inversion phenomenon.

Example 1 About 300 polyimide films were formed using a spin cord on a set of glass plates in which transparent conductive films (ITO) were patterned to form a 500×500 matrix. Each substrate was rubbed with a roller whose back surface was wrapped with a terrene cloth, and the substrates were bonded together so that the rubbing direction matched to form a cell. The cell spacing at this time is approximately 1.6 g.

Desyloxybenzylidene, a ferroelectric liquid crystal, is used in this cell.
P'-amino-2-methylbutylcinname) (DO
BAMBC) was injected and slowly cooled from the heated molten state to obtain a uniform monodomain state in the SmC' state. Controlling the cell temperature at 70°C, based on the driving method shown in Figure 3, VQ = lOV, t 1 = j2 = t
When line sequential scanning was performed with the setting of 3 = Δt = 501 Lsec, an extremely good image was obtained.

Drive examples that are further improved from the drive example described above are shown in FIGS. 8 to 10.

8(a) and (b) respectively show the scan selection signal given to the selected scan electrode and the scan non-selection signal given to the other scan electrodes (unselected scan electrodes). t3 corresponds to the above-mentioned erasure phase and display selection phase. The phase t2 is the auxiliary phase (
In the 0-line driving example, which is the same as the applied voltage used in the driving example above, which is the auxiliary signal application phase), the fourth phase t4
As a result, it is possible to create an auxiliary phase that does not determine the display state of the pixel.

The voltage applied to all scanning electrode lines in the fourth phase t4 is Ov, and the auxiliary signal applied to the signal electrode is a voltage from ±vO having the opposite polarity to the voltage waveform applied in the third phase t3. applied.

When scanning is not selected, the voltage applied to each pixel is maximum 1±Vat.
The longest time for which ±vo is continuously applied is 2Δt at a location like lot, as shown in Figure 10, due to the auxiliary signals applied at phases t2 and t4, and this 2Δt occurs. The number of times is small, and 2Δt alternates,
Since the weak voltage applied to each pixel when scanning is not selected is small, crosstalk does not occur at all, and once the entire screen has been scanned, the displayed information is retained semi-permanently, which improves bistability. As in a display element using a normal TN liquid crystal, which does not have a refrigeration unit, it is not necessary at all.

Furthermore, in the present invention, the above-mentioned phase t4 may be before the above-mentioned phase L1.

11 to 13 show another embodiment of the present invention. FIGS. 11(a) and 11(b) respectively show a scan selection signal applied to a selected scan electrode and a scan non-selection signal applied to other scan electrodes (unselected scan electrodes). Phases t1 and t3 correspond to an erase phase and a display selection phase. Phases t2 and t4 are phase supplements that apply supplementary signals that do not determine the display state. As shown in FIG. 11(a), the scan selection signal applied to the selected scan electrode is 3VQ at phase (time) 11, O at phase (time) t2, -2VQ at phase t3, and O at phase t4. The voltage waveform is as follows. The other scanning electrodes are in a grounded state, as shown in FIG. 11(b), and receive an electrical signal O. On the other hand, as shown in FIG. 11(c), the information selection signal applied to the selected signal electrode is O at phase t1, -0 at phase t1, +Vo at phase t3, and +Vo at phase t4. −
It is vo. Further, the information non-selection signal given to the unselected signal electrode has a phase t1 as shown in FIG. 11(d).
0 at phase t2, +Vo at phase t3, -vo at phase t3, and VO at phase t4. Here, each phase is t1=t3, t2=t4, and 1/2tl=t2
It's Toshide. In the above, the voltage value Vo is set in the same manner as in the driving example described above. FIG. 12 shows the voltage waveform applied to each pixel when such an electric signal is applied.

In Fig. 12, (a) and (b) are on the selected scanning electrode, respectively, and "black" and "white" are displayed on the pixels to be displayed, and (C) and (d) are respectively selected. This is the voltage waveform applied to the pixels on the scan electrodes that are not connected. All or a given pixel on the selected scan electrode is
As in the driving example described above, the first phase t1 first aligns the colors to one white. Among these, for pixels that should be displayed as “black”, the third
is displayed in black based on the other optically stable state at phase t3. In addition, in the case of a pixel that exists on the same scanning electrode and is to be displayed as "white", the applied voltage at the third phase t3 is a voltage v□ that does not exceed the threshold voltage Vthl, so that the pixel is in one optically stable state. It remains there.

On the other hand, on the scan electrodes that are not selected, the voltages applied to all pixels are ±V or O, as in the driving example described above, and neither exceeds the threshold voltage. Therefore, the liquid crystal molecules maintain the orientation corresponding to the signal state when scanned last time without changing the orientation state.

That is, when the scanning electrode is selected, first the first phase t
1, - is aligned to one optically stable state "white", and then in a second phase t2, the selected pixel is transferred to the other optically stable state (black), and the -line segment is aligned to the optically stable state "white". After the signal is written, the signal state can be maintained until the next frame is selected.

FIG. 13 shows the drive signals described above in chronological order. S1 to S5 are electrical signals applied to the scanning electrodes,
1 and 13 are electrical signals applied to the signal electrodes, A and C
is the voltage waveform applied to pixels A and C shown in FIG.

In the tree embodiment, the voltage for making it "white" in the first phase t1 is -3VQ, and its application time is Δt. on the other hand,"
The "direct pressure" for rewriting to "black" is 3VQ, and its application time is also Δt. In addition, the voltage applied to each pixel except during scanning is a maximum of 1±Vol, and the longest time it is continuously applied is when the auxiliary signals are applied at 1 phase t2 and t4, for example, when the white signal - white signal is Even when scanning continuously, the voltage applied to each pixel is 2.5Δt, and the weak voltage applied to each pixel is small, so crosstalk does not occur at all, and once the entire screen has been scanned, the displayed information is
Retained semi-permanently.

FIGS. 14 to 16 show another example of driving according to the present invention. FIG. 14(a) shows the scan selection signal applied to the selected scan electrode line at 2V□ with one phase t1.
, O1 at phase t2 and -2VQ at phase t3. FIG. 14(b) shows a scan non-selection signal applied to unselected scan electrode lines, which is O over phases t1, t2, and t3. FIG. 14(C) shows the information selection signal applied to the selected signal ° electrode at -V(
,, ■o at phases t2 and t3. Figure 14(d)
is the information non-selection signal applied to the signal electrode that is not selected, -vo at phase t1, vO at phase t2, and one
The voltage waveform is alternating with o.

FIG. 15(a) shows the voltage waveform when the aforementioned scanning selection signal and information selection signal are applied to the pixel in synchronization, and FIG. 15(b) shows the voltage waveform when the scanning selection signal and the information non-selection signal are applied to the pixel. It shows the voltage waveform when applied synchronously.

FIG. 15(c) shows the voltage waveform when the aforementioned scanning non-selection signal and information selection signal are applied to the pixel, and FIG.
) represents the voltage waveform when the scanning non-selection signal and the information non-selection signal are applied.

FIG. 16 shows the signal voltage described above in time series. In the figure, A is the time series waveform applied to pixel A in FIG. 4, and B is the time series waveform applied to pixel B in FIG. It represents a series waveform.

In this example as well, as can be seen from FIG. 16, the longest time applied to pixels when scanning is not selected can be set to 2Δt.

According to the present invention, even when a display panel using a ferroelectric liquid crystal element is driven at high speed, the maximum pulse of the '1f pressure waveform continues to be applied to the pixels on the scan electrode line to which the scan non-selection signal is applied. Since the width is twice or 2.5 times the pulse Δt during writing, it is possible to effectively prevent a phenomenon in which the display state is reversed to another display state during the writing scan of one screen.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the threshold characteristics of a ferroelectric liquid crystal. FIGS. 2 and 3 are perspective views schematically showing a ferroelectric liquid crystal element used in the present invention. FIG. 4 is a plan view of the matrix pixel structure used in the present invention. Figure 5 (
a) to (d), Fig. 8 (a) to (d), Fig. 11 (
a) to (d) and FIGS. 14(a) to (d) are explanatory diagrams showing voltage waveforms of signals applied to the electrodes, respectively. Figures 6(a) to (d), Figures 9(a) to (d), Figures 12(a) to (d), and Figures 15(a) to (d) are applied to the pixels, respectively. FIG. 2 is an explanatory diagram showing a voltage waveform of a signal. Figure 7. FIGS. 10, 13, and 16 are explanatory diagrams of voltage waveforms representing the aforementioned signals in time series. Figure 86 - VO Figure 2 10 VO

Claims (6)

[Claims] (1) An optical modulation material having at least two stable states is arranged between an intersecting scanning electrode group and a signal electrode group, and has a matrix pixel structure in which the intersection of the scanning electrode group and the signal electrode group is a pixel. In the method for driving a modulation element, all or a predetermined portion of the pixels on the scan electrode line are covered with the first layer of the optical modulation material during a writing period for the pixels on the scan electrode line selected in the matrix pixel structure. a first phase in which all or a predetermined portion of the pixels on the scanning electrode line are brought into a display state based on a stable state of the optical modulating substance; and a second phase that does not determine the display state of the pixel between the first phase and the third phase. . (2) The driving method according to claim 1, wherein a fourth phase that does not determine the display state of the pixel is provided before the first phase or after the third phase. (3) The driving method according to claim 1, wherein the optical modulating substance is a ferroelectric liquid crystal. (4) The driving method according to claim 3, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. (5) The driving method according to claim 1, wherein the chiral smectic liquid crystal is a chiral smectic liquid crystal with a non-helical structure. (6) The driving method according to claim 3, wherein the ferroelectric liquid crystal is in chiral smectic C phase or H phase.