RU2697888C1 - Control method of ferroelectric liquid crystal gate - Google Patents

Abstract

FIELD: control systems.

SUBSTANCE: invention relates to liquid crystal structures. Method consists in fact, that on the ferroelectric liquid crystal (FLC) gate is alternatively supplied with electric signal with one polarity and locking electric signal with opposite (opposite) polarity to obtain maximum and minimum values of optical passage of FLC of gate, wherein the electrical signal is supplied in the form of a series of electric pulses of short duration, the total area of which is equal to the area of the information electrical signal due to variation by parameters of information and locking electrical signals. In this case, zero average current is provided through the FLC gate for the complete control period, which leads to the absence of constant volumetric ion charge in the FLC layer and ensures correct operation of the FLC of the gate at arbitrary duration of the information electric signal.

EFFECT: broader functional capabilities of controlling the ferroelectric liquid crystal (FLC) gate by providing the method at an arbitrary duration of the information signal.

1 cl, 5 dwg

Description

FIELD OF THE INVENTION

The invention relates to liquid crystal structures, and more specifically, to ferroelectric liquid crystal structures, and can be used to create high-speed low-voltage optical light modulators, including energy-efficient optical shutters for active stereo glasses with high optical efficiency when viewing stereo images of short (millisecond) duration.

State of the art

In liquid crystal (LC) optical shutters (binary amplitude light modulators), the operation of the LC layer located between the input and output polarizers consists in changing the state of polarization of the transmitted light under the influence of a control electric field, which occurs in the LC layer when an external control voltage is applied to the transparent electrodes adjacent to the LCD layer on both sides.

The implementation of methods for controlling LCD elements (optical shutters) should not lead to degradation of the properties of the LCD layers during long-term operation. The most significant degradation factor is the formation of ions in the LC layer [1-3]. If a constant electric current flows in the LC layer for a sufficiently long time, then ions can primarily arise due to the electrolysis of impurities in the LC material. Ions can also occur during the flow of direct current and in a pure LC substance; ion sources can be orienting dielectric layers adjacent to the LC layer. At a sufficiently high concentration of ions, the space charge created by them substantially distorts the configuration of the lines of force of the control electric field in the LC layer, which leads to disruption of the operation of the LC shutter until its complete cessation at a sufficiently large amount of ion charge.

To prevent degradation of the LC layers, it is necessary to control the LCD shutter by providing a zero average value of direct current in the LCD layer for a fairly short period of time (comparable to the time the LCD shutter switches from the state with maximum optical transmission and vice versa).

There is a method [4] for controlling a nematic liquid crystal (NLC) shutter, which consists in the fact that in successive control cycles alternating values of the maximum and minimum optical transmittance of the NLC shutter are obtained, applying a control voltage to the electric input from the output of the electronic control unit, in (2n-1) -th and (2n + 1) -th clocks, to obtain the maximum value of the optical transmittance of the NLC shutter, the control voltage of the first (minimum of the initial or zero) level, respectively, of positive and negative polarity, and in the (2n) and (2n + 2) -th clock cycles, to obtain a zero value of the optical transmission of the NLC shutter, a second (maximum) level control voltage of respectively positive and negative polarity.

The known method provides zero average direct current through the NLC layer for 4 cycles of operation, during which the first and second pair of unipolar voltage levels corresponding to the first (maximum) and second (minimum) value of the optical transmission of the NLC shutter act on the NLC layer. This control method with a zero average voltage for 4 cycles of operation is based on the fact that the NLC layer is non-polar, since the NLC gate changes the optical transmittance when only the control voltage level changes, regardless of its polarity.

However, this known control method is not suitable for ferroelectric liquid crystal (FLC) gates, since the FLC layer is polar, i.e. its optical state changes only when the polarity of the applied voltage changes with a level that exceeds the threshold of operation of the FLC shutter.

The closest in technical essence to the claimed method is a method [5] for controlling an FLC shutter, which consists in the fact that in successive control cycles alternating values of the maximum and minimum optical transmittance of the FLC shutter are obtained, applying a control voltage to the electrical input from the output of the electronic control unit in this case, in (2n-1) -th clocks, to obtain the maximum value of the optical transmission of the FLC shutter, an information signal from the first (positive) polarity, and in (2n) cycles, to obtain the minimum optical transmittance of the FLC shutter, a blocking signal with a second (negative) polarity is supplied to its electrical input, the potential of the common input of the FLC shutter being set equal to the zero potential of the total output of the electronic unit management.

The known method is characterized by insufficient functionality: a zero average level of control electric voltage is achieved only when working with the same duration of information and blocking electrical signals of the same shape. With varying durations (forms) of information and blocking signals, the known method does not allow providing a zero average value of direct current through the FLC layer for any number of consecutive clock cycles. For example, when using an optical shutter in stereo glasses when observing stereo images using LCD monitors in the widespread 3D Vision computer system [6], the generation time of light fluxes of angle images is about 3 ms at a frame frequency of 100 Hz. Therefore, with a formal duration of each frame of 10 ms, the change of image information between frames takes 7 ms due to the specifics of the operation of stereoscopic LCD monitors with sequential playback of angle images. During the change of images, both shutters of the stereo glasses must be closed so as not to worsen the contrast of the stereo image played during the remaining 3 ms of each frame. Since the open state time of each optical shutter of stereo glasses is 3 ms, and the closed state is 7 ms, for the FLC shutter in this case the duration of the control electric signal with one polarity (providing the open state of the shutter) will be more than two times shorter than the duration of the control an electrical signal with the opposite polarity (providing a closed state of the shutter). Therefore, the average value of the current through the FLC gate will significantly differ from zero, which will result in degradation of the stereo image due to degradation of the FLC (due to the accumulation of an ion charge), and subsequently to complete cessation of the operation of the FLC shutter due to the blocking of the control voltage field by the field constant ionic charge in the FLC layer.

Disclosure of invention

The objective of the invention is to expand the functionality of the method by ensuring its operation with an arbitrary duration of the information signal.

The problem in the control method of the FLC shutter, which consists in the fact that in successive control cycles receive alternating values of the maximum and minimum optical transmittance of the FLC shutter, applying to its electrical input a control voltage from the output of the electronic control unit, while in (2n- 1) -th steps to obtain the maximum value of the optical transmittance of the FLC gate to its electrical input serves an information signal with the first (positive) polarity, and in (2n) -th In order to obtain the minimum value of the optical transmittance of the FLC shutter, a locking signal with a second (negative) polarity is supplied to its electrical input, and the potential of the common input of the FLC shutter is set equal to zero potential of the total output of the electronic control unit, it is decided that the locking signal has the form of a sequence of N electric blocking pulses whose parameters satisfy three conditions.

выбрана больше времени

переходного оптического отклика СЖК затвора на ступенчатое изменение амплитуды управляющего сигнала. Это обеспечивает переход СЖК затвора в требуемое закрытое состояние (с минимальным оптическим пропусканием) в течение действия каждого запирающего импульса.The first condition is for an arbitrary (ith) blocking electric pulse, the duration

more time selected

transitional optical response of the FLC shutter to a step change in the amplitude of the control signal. This ensures the transition of the FLC shutter to the required closed state (with minimal optical transmission) during the action of each blocking pulse.

между соседними (i и i+1) запирающими импульсами выбран меньше времени

переходного оптического отклика СЖК элемента на ступенчатое изменение амплитуды управляющего сигнала. Это условие соответствует отсутствию выхода слоя СЖК из состояния с минимальным оптическим пропусканием во временном промежутке между двумя соседними запирающими импульсами.The second condition is the time interval

between adjacent (i and i + 1) blocking pulses less time is chosen

transitional optical response of the FLC element to a step change in the amplitude of the control signal. This condition corresponds to the absence of the exit of the FLC layer from the state with minimal optical transmission in the time interval between two adjacent blocking pulses.

The third condition is the integral of the sum of functions describing the shape (instantaneous amplitudes versus time) of all the locking pulses, equal in magnitude to the integral of the function describing the shape (instantaneous amplitude) of the information signal. This condition is achieved by selecting the level of the instantaneous amplitude of the information signal and the levels (form) of the blocking pulses, taking into account the fact that, above certain instantaneous levels of the information or blocking signals, the maximum or minimum optical transmittance is reached, which does not change with a further increase in these levels.

Varying the levels of the information signal and the blocking pulses within the specified limits allows you to find a balance that provides integrated averaging of the positive (information) and negative (blocking) electrical control signals on the FLC layer.

As a result, the problem is solved by achieving a technical result, which consists in ensuring a zero average value of the control voltage on the FLC shutter for each full period of its switching (including obtaining the maximum and minimum optical states of the FLC shutter). Therefore, when implementing the method, a constant electric current does not occur in the FLC layer, and therefore, there are no violations in the required operation of the FLC shutter during its arbitrarily long operation for any duration of the information signal.

Brief Description of the Drawings

The invention is illustrated using the drawings, in the figures of which are presented:

FIG. 1 is a wiring diagram for connecting an FLC shutter to a control unit.

FIG. 2 is an optical diagram of an FLC shutter.

FIG. 3 is a diagram of the control electrical signals and the optical response of the FLC shutter.

FIG. 4, 5 - variants of the shape of the electric blocking pulses of rectangular and arbitrary shape.

DETAILED DESCRIPTION OF THE INVENTION

FLC shutter 1 (Fig. 1, 2) contains a layer 2 FLC, placed between transparent electrodes 3 ₁ and 3 ₂ deposited on the inner sides of the optical (glass) substrates 4 ₁ and 4 ₂ , on the outer sides of which are input and output mutually orthogonal linear polarizers P _in and P _out . The signal input S _FLC and the common input G _FLC FLC of the shutter are connected respectively to the signal S _control and common G _control outputs of the _control unit 5. The optical transmittance of the FLC shutter 1 is determined by the output intensity J _{out of} the light intensity with respect to the input intensity J _in intensity.

The way to control the FLC shutter is to obtain alternating maximum O _max and minimum O _min optical transmittance of the FLC shutter in successive clock cycles (Fig. 3), while in odd (2n-1) -th cycles to obtain the maximum optical transmittance values O _max to the signal input S _FLC FLC of the shutter 1 supply an information electric signal s (t) of positive polarity from the signal output S _{control of control} unit 5, and to obtain a minimum (zero) value O _{min of} optical transmittance during the rest of the time of odd (2n-1) clocks and for the total time of even (2n) clocks, a blocking signal is supplied to the signal input S _{FLC of the} FLC of gate 1 as a sequence of N pulses of negative polarity, of which the ith pulse (i = 1, 2, ..., N) is described by the function g _i (t). The potential of the common gate G _FFA FFA shutter in all cycles is set equal to zero potential overall yield G _conlrol control unit 5, and the parameters of the information and the locking electrical signals satisfy

- длительность i-го электрического запирающего импульса,

- время переходного оптического отклика СЖК затвора на скачкообразное изменение амплитуды электрического управляющего сигнала,

- интервал времени между соседними (i)-м и (i+1)-м электрическими запирающими импульсами.where l _FLC is the threshold of operation of the FLC shutter under the action of the amplitude of the electric control signal, regardless of its polarity,

- the duration of the i-th electric blocking pulse,

- the transition time of the optical response of the FLC shutter to an abrupt change in the amplitude of the electric control signal,

- the time interval between adjacent (i) th and (i + 1) th electrical blocking pulses.

с непрямоугольной формой.In FIG. 4 and 5 are examples of blocking electrical pulses, including pulses

with a non-rectangular shape.

между произвольными соседними (i и i+1) запирающими электрическими импульсами.When implementing the method, the relationships between the durations of processes in the FLC layer and the parameters (durations and amplitudes) of the control electronic signals given in relations (1) - (3) provide the required functional of the amplitude modulation of light fluxes when alternating open and closed states that are unequal in duration FLC shutter providing zero average (over the total period T _F electronic control signal) electric current. Indeed, the first condition in relation (1) means the opening of the FLC shutter during the action of the information electric signal s (t), since its instantaneous amplitude exceeds the threshold l of the _{FLC of the} FLC shutter. From the second condition of relation (1) and from relation (2) it follows that the FLC shutter under the influence of a discrete set of electric locking pulses goes into a practically continuous optical closed state, since the second condition in relation (1) and the first condition in relation (2) provide transition of the FLC shutter to the closed state during the instantaneous amplitude g _i (t) of an arbitrary (i-th) locking pulse, and the second condition in relation (2) means maintaining the FLC shutter in the closed state at time intervals

between arbitrary neighboring (i and i + 1) blocking electrical pulses.

дискретных запирающих импульсов с отрицательной полярностью. Варьирование уровнями информационного и запирающего электрических сигналов при выполнении соотношения (1) и варьирование длительностями и уровнями электрических запирающих импульсов при выполнении соотношения (2) математически обеспечивает выполнение соотношения (3). Выполнение соотношения (3) означает равенство средних (за период T_F управляющего электронного сигнала) значений энергии электрического поля, возникающих в слое СЖК под действием электрического управляющего напряжения положительной и отрицательной полярностей при точном воспроизведении оптическим откликом СЖК затвора требуемой формы электрического информационного сигнала. Соответствующий средний ток через слой СЖК равен нулю за каждый период T_F управляющего электрического сигнала, что обеспечивает бесперебойную работу СЖК затвора вследствие отсутствия в нем постоянного объемного электрического заряда.The fulfillment of relation (3) means that the area under the envelope of the information control signal s (t) with positive polarity is equal to the area under the general envelope of the entire population

discrete blocking pulses with negative polarity. Varying the levels of information and blocking electric signals when fulfilling relation (1) and varying the durations and levels of electric blocking pulses when fulfilling relation (2) mathematically ensures the fulfillment of relation (3). The fulfillment of relation (3) means the equality of the average (over the period T _{F of the} control electronic signal) values of the electric field energy arising in the FLC layer under the influence of the electric control voltage of positive and negative polarities when the optical response of the FLC shutter accurately reproduces the desired shape of the electric information signal. The corresponding average current through the FLC layer is zero for each period T _{F of the} control electric signal, which ensures uninterrupted operation of the FLC shutter due to the absence of a constant volume electric charge in it.

As a result, the problem of expanding the functionality of the method by ensuring its operation with an arbitrary duration of the information signal was solved.

LITERATURE

1. Dahl I., Lagerwall S.T., Skarp K. Simple model for the polarization reversal current in a ferroelectric liquid crystal // Physical Review A. 1987. - V. 36. - No. 9. - P. 4380-4390.

2. Perlmutter S.H., Doroski D., Moddel G. Degradation of liquid crystal device performance due to selective adsorption of ions // Appl. Phys. Lett. - 1996. - V. 69. - No. 9. - P. 1182-1184.

3. Neyts K., Beunis F. Ion transport and switching currents in smectic liquid crystal devices // Ferroelectrics. - 2006. - V. 344. - No. 1. - P. 255-266.

4. Lipton L., Ackerman M. Liquid crystal shutter system for stereoscopic and other applications // US Patent No. 4967268, publ. 10/30/1990.

5. RF patent No. 2512095, publ. 04/10/2014.

6. US patent No. 7724211, publ. 05/25/2010.

Claims (10)

A method of controlling a ferroelectric liquid crystal shutter, which consists in the fact that in successive control cycles, alternating values of the maximum and minimum optical transmittance of the ferroelectric liquid crystal shutter are obtained, applying a control voltage to the electric input from the output of the electronic control unit, while in odd cycles to obtain the maximum value of optical transmission serves information electric signal from the first (positive) polarity, and in even cycles to obtain the minimum optical transmittance of the ferroelectric liquid crystal shutter, an electrical locking signal with a second (negative) polarity is supplied to its electrical input, the potential of the common input of the ferroelectric liquid crystal shutter being set to zero potential of the total output of the electronic control unit characterized in that the electrical locking signal is supplied in the form of a sequence N FIR locking pulse parameters satisfy the relations

where s (t) is a function that describes the instantaneous amplitude of the electrical information signal, g _i (t) is a function that describes the instantaneous amplitude of the i-th electric blocking pulse (i = 1, 2, ..., N),

- the duration of the i-th electric blocking pulse,

- the transition time of the optical response of the ferroelectric liquid crystal shutter to a jump in the amplitude of the electric control signal,

- the time interval between adjacent (i) th and (i + 1) th electrical blocking pulses, l _FLC - the threshold of the ferroelectric liquid crystal shutter under the influence of the amplitude of the electric control signal, regardless of its polarity.

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