JP2014509756A - Double-cell liquid crystal device with rapid switching - Google Patents

Abstract

The liquid crystal device includes a first liquid crystal cell and a second liquid crystal cell that are arranged in a layered structure so that light passing through the first liquid crystal cell reaches the second liquid crystal cell. Each of the first liquid crystal cell and the second liquid crystal cell can be individually controlled between a relaxation state in which the liquid crystal cell exhibits a first birefringence and a switching state in which the liquid crystal cell exhibits a second birefringence. The transition of the first liquid crystal cell from the relaxed state to the switched state results in a change in the total birefringence of the liquid crystal device from the first total birefringence to the second total birefringence, and the liquid crystal device is in the first light modulation state. The transition from the second light modulation state to the second light modulation state and the subsequent transition of the second liquid crystal cell from the relaxed state to the switched state is the total birefringence of the liquid crystal device from the second total birefringence to the first total birefringence. A change in refractive index is caused, whereby the liquid crystal device transitions back from the second light modulation state to the first light modulation state.
[Selection] Figure 3a

Description

  The present invention relates to a liquid crystal device for modulating light passing therethrough. The invention further relates to a method for controlling such a liquid crystal device.

In many applications, rapid switching between a transparent (“light”) state and an opaque (“dark”) state is desirable.
The liquid crystal device is used as an optical shutter that realizes switching between a bright state and a dark state, for example. In particular, a conventional nematic liquid crystal material that is currently widely used in various liquid crystal displays and available electronic driving technologies. It has been found difficult to achieve sufficiently rapid switching speeds using. In particular, the relaxation of nematic liquid crystal materials is a slow process.
Many solutions have been proposed and tried to increase the switching speed of liquid crystal devices, but it turns out that it is difficult to achieve switching in a short time from dark to light and from light to dark simultaneously. doing.

  It is an object of the present invention to address the above-described problems of the prior art, and the present invention is an improvement that is configured to allow faster switching speeds between bright and dark states. Provided liquid crystal device.

  According to the first embodiment of the present invention, therefore, a liquid crystal device for modulating light passing therethrough, the liquid crystal device comprising a plurality of liquid crystal molecules sandwiched between a pair of first substrates. A first liquid crystal cell having a liquid crystal material, and a second liquid crystal cell having a liquid crystal material including a plurality of liquid crystal molecules sandwiched between a pair of second substrates, the first liquid crystal cell and the second liquid crystal cell The liquid crystal cell is arranged in a layered structure so that light passing through the first liquid crystal cell reaches the second liquid crystal cell, and each of the first liquid crystal cell and the second liquid crystal cell is a liquid crystal cell Is individually controllable between a relaxed state in which the first birefringence index is displayed and a switching state in which the liquid crystal cell exhibits the second birefringence index, and the liquid crystal cell is in the relaxed state with the second liquid crystal cell remaining in the relaxed state. When the first liquid crystal cell transitions from the relaxed state to the switched state The total birefringence of the liquid crystal device changes from the first total birefringence to the second total birefringence, the liquid crystal device transitions from the first light modulation state to the second light modulation state, and then When the first liquid crystal cell remains in the switched state and the second liquid crystal cell transitions from the relaxed state to the switched state, the total birefringence of the liquid crystal device is changed from the second total birefringence to the first total birefringence. A liquid crystal device is provided, wherein the liquid crystal device is arranged and configured to change so that the liquid crystal device changes from the second light modulation state to the first light modulation state. .

A nematic liquid crystal cell with uniform orientation functions optically as a uniaxial (birefringent) optical plate with an optical axis that matches the preferred orientation direction of the liquid crystal molecules in the cell. When such a liquid crystal cell is inserted between two intersecting polarizing plates, the luminous intensity l transmitted through the cell and the polarizing plate is aligned at an optical axis of 45 ° with respect to the transmission direction of the polarizing plate. Is simply given by the following equation:

l = l ₀ sin ² δ / 2

Here, δ = 2πdΔn / λ, the birefringence index _{Δn = n e -n 0 (n} e and _{n 0} are其s is the refractive index of the extraordinary ray and ordinary ray of the liquid crystal material) cell phase delay by Where λ is the wavelength of the light source.

Two liquid crystal cells each having a birefringence index Δn ₁ = n _e1 −n ₀₁ and Δn ₂ = n _e2 −n ₀₂ and thicknesses d ₁ and d ₂ are aligned parallel to each other, and each optical axis Is superimposed as a layered structure, the total phase delay of the two cells is given by:

δ _total = δ ₁ + δ ₂ = 2π (d ₁ Δn ₁ + d ₂ Δn ₂ ) / λ

However, if the optical axis of the cell is 90 °, the total phase delay of the two liquid crystal cells is

δ _total = δ ₁ −δ ₂ = 2π (d ₁ Δn ₁ −d ₂ Δn ₂ ) / λ,

Or may be expressed as a sum as follows:

δ _total = δ ₁ + (− δ ₂ ) = 2π [d ₁ Δn ₁ + d ₂ (−Δn ₂ )] / λ,

Here, Δn ₂ has a negative sign. This is a notation used as a background to the application of the present invention.

  The cell gap thickness in this dual cell device is a constant parameter of the cell, i.e. independent of the applied electric field. On the other hand, the birefringence of the cell can be controlled by applying an electric field. Thus, it is contemplated that “birefringence” and “phase retardation” are synonymous with liquid crystal devices in accordance with various aspects of the present invention.

  Further, the “relaxed” state has a meaning as an “electric field off” state in which the electric field applied by switching does not exist in the liquid crystal device, and the “switched” state indicates that the electric field applied by switching is in the liquid crystal device. Has the meaning of the “electric field on” state.

  In the present invention, the relaxation of the liquid crystal material in the liquid crystal cell (the duration of this relaxation is determined by the thickness of the cell gap and the anchoring strength, and the viscosity and elastic constant of the liquid crystal material) Recognize that this is a factor that limits the switching speed between dark states and that this relaxation process is optically "cancelled" by properly arranging two appropriate liquid crystal cells in succession. Based on what you are doing. The inventor of the present invention further enables the total birefringence of two liquid crystal cells arranged in succession to change the liquid crystal device (such as dark and bright) 2 by actively switching the individual liquid crystal cells. It is understood that it can be used to switch between two light modulation states. Also, the liquid crystal cell can relax at the same time while allowing the liquid crystal device to remain in one of the light modulation states, which is the state in which the liquid crystal device can be actively switched again between the two light modulation states. It is in.

  Thus, both switching from the first modulation state of the liquid crystal device to the second modulation state of the liquid crystal device and switching back to the first modulation state activate the liquid crystal molecules in each liquid crystal cell by applying an electric field. This is achieved using a rapid process for reorienting the target.

  Once the liquid crystal device is relaxed to return from the switched state to the relaxed state in the first light modulation state of the liquid crystal device, the liquid crystal device controls the first liquid crystal cell from the relaxed state to the switched state by The state is switched to the second modulation state again.

  In the liquid crystal device according to various embodiments of the present invention, the liquid crystal molecules of the first and second liquid crystal cells are substantially parallel to each other in the relaxed state of the first and second liquid crystal cells. When the first liquid crystal cell is controlled by applying an electric field inside the liquid crystal cell and transitions to the switching state, the orientation of the liquid crystal molecules in the first liquid crystal cell changes, and again, the liquid crystal molecules are almost parallel to each other. In other common orientation directions, the birefringence of the first liquid crystal cell will change more than in the relaxed state. This will result in a change in the birefringence of the first liquid crystal cell and a change in the total birefringence of the liquid crystal device since the second liquid crystal device remains in a relaxed state.

  Due to this change in the total birefringence of the liquid crystal device, the light intensity level passing through the first and second liquid crystal cells disposed between the intersecting polarizing plates further changes, for example, from the first light modulation state to the second light modulation state. Bring about a transition to

  It should be noted that this birefringence-based control for the transitioned light intensity level is quite different from the polarization control performed by a gradually changing waveguide through a liquid crystal cell, for example in a twisted nematic cell. It is. The use of this birefringence-based control of the liquid crystal device according to various embodiments of the present invention allows a design that is selected such that the first and second light modulation states described above are in a light / dark state. To. This means, for example, whether the simultaneous relaxation of the first and second liquid crystal cells occurs in the dark state or the bright state, depending on the design of the liquid crystal cell. As a result, utilizing the birefringence-based control of the liquid crystal cell allows the characteristics of the liquid crystal cell to adapt to various requirements, such as optical performance, production yield, structural stability, and the like. Furthermore, the sensitivity of deviation between the polarizing plate, the analyzer and the liquid crystal cell is reduced.

Each of the first liquid crystal cell and the second liquid crystal cell is a so-called meaning that the liquid crystal molecules are reoriented in one plane perpendicular to the substrate of the liquid crystal cell when an electric field is applied as described above. It is advantageously configured for “out-of-plane” switching.
The liquid crystal material of the first and second liquid crystal cells is advantageous in the nematic phase (relative to the expected operating state of the liquid crystal device).

  It is desirable to cause simultaneous relaxation of the first liquid crystal cell and the second liquid crystal cell from the switched state to the relaxed state by a method that is not optically noticeable to the user of the liquid crystal device. For this purpose, the first liquid crystal cell and the second liquid crystal cell may have a birefringence of the first liquid crystal cell during simultaneous relaxation from the switching state to the relaxation state of the first liquid crystal cell and the second liquid crystal cell. And the sum of the birefringence of the second liquid crystal cell are arranged and configured so as to remain substantially constant as the first total birefringence.

  The total birefringence of this device remains constant due to the birefringence correction effect that occurs during the relaxation process in the cell. A characteristic characteristic of the relaxation process in the cell is that the birefringence of the first liquid crystal cell increases / decreases while the birefringence of the second liquid crystal cell decreases / increases, and is constant with respect to the total birefringence. Is to make the relaxation process invisible.

In principle, the liquid crystal device may be controlled by control means arranged outside the liquid crystal device. However, the first liquid crystal cell includes a first control electrode and a second control electrode, and the first control electrode and the second control electrode of the first liquid crystal cell are the first control electrode and the second control electrode of the first liquid crystal cell. The first liquid crystal cell is arranged to be controlled from a relaxed state to a switched state by applying a voltage to the control electrode, and the second liquid crystal cell includes the first control electrode and the first control electrode. The first control electrode and the second control electrode of the second liquid crystal cell by applying a voltage between the first control electrode and the second control electrode of the second liquid crystal cell. The liquid crystal device is advantageously configured to be arranged to allow the two liquid crystal cells to be controlled from the relaxed state to the switched state.
Such control electrodes are advantageously arranged to provide out-of-plane switching of the liquid crystal cell described above.

  According to various embodiments of the present invention, a first birefringence of the first liquid crystal cell is not zero, and a first birefringence of the second liquid crystal cell is substantially zero, and the first liquid crystal cell The second liquid crystal cell is arranged so that the first total birefringence does not become zero.

When the liquid crystal device according to these embodiments is installed between crossed polarizers, it is preferably equal to approximately 45 °, but the transmission direction of one polarizer changing within the range 0 ° <φ <90 ° Provided with at least one optical axis of the first liquid crystal cell or the second liquid crystal cell having an angle φ, the first modulation state is a bright state (when both the first liquid crystal cell and the second liquid crystal cell are in a relaxed state). Will.
Further, in these embodiments, the second birefringence of the first liquid crystal cell is substantially zero, and the second total birefringence is substantially zero. This results in a dark state when the second modulation state is properly placed between the crossed polarizing plates.

  According to an embodiment of the present invention, the first liquid crystal cell is planarly aligned in a relaxed state so that the liquid crystal molecules contained in the first liquid crystal cell are arranged substantially parallel to the pair of first substrates. The second liquid crystal cell has a configuration in which the liquid crystal molecules included in the second liquid crystal cell are vertically aligned in a relaxed state so that the liquid crystal molecules are disposed substantially perpendicular to the pair of second substrates.

  In the following, a liquid crystal cell in a planar alignment configuration in a relaxed state is referred to as a “PA cell”, and a liquid crystal cell in a vertical alignment configuration in a relaxed state is referred to as a “VA cell”. A liquid crystal device in which the first liquid crystal cell is a PA cell and the second liquid crystal cell is a VA cell is called a VA / PA double cell device.

  The liquid crystal molecules contained in the VA cell can advantageously exhibit negative dielectric anisotropy, so that the first control electrode is disposed on the first substrate of the first liquid crystal cell and the second control electrode In the second substrate of the first liquid crystal cell. As a result, the liquid crystal molecules in the VA cell are arranged in a state where the liquid crystal molecules arranged in parallel to the substrate are arranged on a plane from a state in which the liquid crystal molecules are arranged in a vertical direction (a state in which the birefringence is substantially equal to zero). Thus, the birefringence is controlled to a non-zero state.

Further, the liquid crystal molecules of the VA cell can exhibit positive dielectric anisotropy, and in this case, the first and second control electrodes are arranged on the same substrate to create a so-called in-plane magnetic field or fringe electric field.
In the VA cell, when the VA cell is in the switching state, the liquid crystal molecules in the VA cell are oriented in substantially the same direction as the liquid crystal molecules in the PA cell when the PA cell is in the relaxed state in the VA / PA dual cell apparatus. Constructed advantageously.

According to various embodiments of the liquid crystal device according to the present invention, the magnitude of the first birefringence of the first liquid crystal cell is approximately equal to the magnitude of the first birefringence of the second liquid crystal cell.
In particular, the first liquid crystal cell and the second liquid crystal cell may have substantially the same configuration with respect to liquid crystal materials such as cell gap, anchoring characteristics, and electrode structure. This is so that the total birefringence of the liquid crystal device remains constant during the simultaneous relaxation of the liquid crystal cell (during the simultaneous transition from the switched state of the first liquid crystal cell and the second liquid crystal cell to the relaxed state). Would make it easier to design.

  (The first birefringence index of the first liquid crystal cell is approximately equal to the first birefringence index of the second liquid crystal cell.) For these embodiments of the liquid crystal device according to the present invention, the first The liquid crystal cell and the second liquid crystal cell are arranged such that when the first liquid crystal cell is in a relaxed state and the second liquid crystal cell is in a relaxed state, the total birefringence of the liquid crystal device is substantially zero. Arranged in relation to each other. For example, the optical axis of the first liquid crystal cell is substantially perpendicular to the optical axis of the second liquid crystal cell.

  When the liquid crystal device according to these embodiments is arranged between crossed polarizing plates, the first light modulation state (when both the first liquid crystal cell and the second liquid crystal cell are in a relaxed state) The birefringence is almost zero and the incident light will be in the dark state because it does not pass through the crossed polarizers with the liquid crystal device inserted in between.

  Further, in these embodiments (the first birefringence of the first liquid crystal cell is approximately equal to the first birefringence of the second liquid crystal cell). In these embodiments, the first liquid crystal cell and the second liquid crystal cell In the liquid crystal cell, when the first liquid crystal cell is in the second state (switched state) and the second liquid crystal cell is in the first state (relaxed state), the total birefringence does not become substantially zero. Are arranged in relation to each other. Therefore, when the first liquid crystal cell is controlled to transition from the relaxed state to the switched state, the total birefringence of the liquid crystal device is not zero, which means that the incident light passes through the intersecting polarizing plates, It means that the liquid crystal device transits to a bright state by the liquid crystal device. At this time, as is well known to those skilled in the art, it is necessary that the crossed polarizing plates be appropriately arranged in the in-plane direction of the liquid crystal molecules.

  According to one embodiment of the present invention, each of the first liquid crystal cell and the second liquid crystal cell has a planar alignment configuration in a relaxed state, and each of the first liquid crystal cell and the second liquid crystal cell. The liquid crystal molecules contained therein are arranged almost in parallel with the respective substrates. In other words, both the first liquid crystal cell and the second liquid crystal cell are PA cells, and the liquid crystal device is a PA / PA double cell device.

  In the case of this PA / PA double cell device, the first birefringence of the first liquid crystal cell is not zero and is substantially equal to the first birefringence of the second liquid crystal cell. This means that when the first liquid crystal cell is switched from the relaxed state to the switched state, the birefringence of the first liquid crystal cell changes, which means that the total birefringence of the liquid crystal device is not zero, This means that the liquid crystal device is transitioning from the dark state to the bright state.

  Each liquid crystal cell of the PA / PA double cell device is advantageously switched from a planar alignment state to a vertical alignment state in which the liquid crystal molecules contained in the liquid crystal cell are aligned substantially perpendicular to the substrate. Configured.

  When the second PA cell is switched from the relaxed state to the switched state while the first PA cell remains switched, that is, when the planar orientation of the second PA cell is adjusted from the planar orientation to the magnetic field induced vertical orientation, the PA / PA double cell is obtained. The device is switched back from the bright state to the dark state. Even if the cell is switched off in this state, the relaxation process in the cell will not be visible to the observer due to the birefringence correction effect. Here, both cells of the dual cell device in the relaxed state are in a state of being switched again.

  In the PA / PA double cell device, the liquid crystal molecules contained in each liquid crystal cell advantageously exhibit a positive dielectric anisotropy, and each liquid crystal cell is arranged on a first substrate. An electrode and a second control electrode disposed on the second substrate may be advantageously included. Thereby, the liquid crystal molecules in each liquid crystal cell can be controlled from the planarly aligned relaxed state (birefringence index is not zero) to the vertically aligned switching state where the birefringence index is substantially zero.

  According to various embodiments of the present invention, in both the first liquid crystal cell and the second liquid crystal cell, the liquid crystal molecules contained in the first liquid crystal cell are arranged substantially perpendicular to the first and second substrates. Thus, it is a vertical alignment configuration in the relaxed state. In other words, both the first liquid crystal cell and the second liquid crystal cell are VA cells, which means that the liquid crystal device is a VA / VA double cell device.

  In this VA / VA double cell device, the liquid crystal molecules contained in the VA cell advantageously exhibit a negative or positive dielectric anisotropy, as in the VA / PA double cell device described above, and The liquid crystal molecules can include first and second control electrodes arranged appropriately.

  According to a second embodiment of the present invention, there is a method for controlling the operation of the liquid crystal device according to the first embodiment of the present invention, wherein the method allows the first liquid crystal cell to remain in the switched state while the second liquid crystal cell remains in the switching state. The cell is controlled from the relaxed state to the switched state, and the second liquid crystal cell is controlled from the relaxed state to the switched state while the first liquid crystal cell remains in the switched state, and the first liquid crystal cell and the first liquid crystal cell A method comprising the steps of simultaneously controlling two liquid crystal cells to relax from their respective switching states to their respective relaxation states is provided.

  Each of the first liquid crystal cell and the second liquid crystal cell is such that the total birefringence of the liquid crystal device remains substantially constant during relaxation of the first liquid crystal cell and the second liquid crystal cell. , It is advantageously controlled to relax from each switching state to each relaxation state.

  The effects obtained by the various embodiments and the second embodiment of the present invention are substantially the same as those described above for the first embodiment of the present invention.

  As described above, in the first embodiment of the present invention, the first liquid crystal cell and the second liquid crystal cell are arranged as a layered structure so that light passing through the first liquid crystal cell reaches the second liquid crystal cell. It is related with the liquid crystal device containing. Each of the first liquid crystal cell and the second liquid crystal cell can be individually controlled between a relaxed state in which the liquid crystal cell exhibits a first birefringence and a switching state in which the liquid crystal cell exhibits a second birefringence. The transition of the first liquid crystal cell from the state to the switched state results in a change in the total birefringence of the liquid crystal device from the first total birefringence to the second total birefringence, and the liquid crystal device is moved from the first light modulation state. The transition to the second light modulation state and the subsequent transition of the second liquid crystal cell from the relaxed state to the switched state is the total birefringence of the liquid crystal device from the second total birefringence to the first total birefringence. Causing a change in rate, whereby the liquid crystal device transitions back from the second light modulation state to the first light modulation state.

These and other aspects of the invention will be described in more detail with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention.
FIG. 1 is a schematic perspective view of a liquid crystal device according to various embodiments of the present invention. FIG. 2 is a diagram schematically illustrating an exemplary driving method of the liquid crystal device according to the first embodiment of the present invention. 3a to 3d are diagrams schematically showing the state of the liquid crystal device at various stages of the driving method of FIG. 2 according to the first embodiment of the present invention. FIG. 4 is a diagram schematically illustrating an exemplary driving method of the liquid crystal device according to the second embodiment of the present invention. FIGS. 5a to 5d are diagrams schematically showing the state of the liquid crystal device at various stages of the driving scheme of FIG. 4 according to the second embodiment of the present invention.

  FIG. 1 is a schematic perspective view of a liquid crystal device 1 according to various embodiments of the present invention. This liquid crystal device 1 is layered between crossed polarizing plates 4 and 5 (“polarizing plate” 4 is closest to the light source 7 and “analyzer” 5 is closest to the observer 8). The first liquid crystal cell 2 and the second liquid crystal cell 3 are included. The polarization directions of the polarizing plate 4 and the analyzer 5 are indicated by broken lines in FIG. Each of the first liquid crystal cell and the second liquid crystal cell is individually between a relaxation state in which the liquid crystal cell exhibits a first birefringence and a switching state in which the liquid crystal cell exhibits a second birefringence different from the first birefringence. Can be controlled.

  When the light from the light source 7 that passes through the polarizing plate 4 and is linearly polarized in the direction shown in FIG. 1 passes through the first liquid crystal cell 2 and the second liquid crystal cell 3, the birefringence of the first liquid crystal cell 2. And an overall phase delay, expressed as the sum of the birefringence of the second liquid crystal cell 3. When the total birefringence is zero, the light never passes through the analyzer 5, but when the total birefringence is not zero, at least a part of the light passes through the analyzer 5 and reaches the observer 8. The polarization state of the light is corrected, and the birefringence state of the optical axis becomes an appropriate orientation with respect to the transmission direction of the polarizing plate 4.

  As described above, since the total birefringence corresponds to the sum of the birefringence of the first liquid crystal cell 2 and the birefringence of the second liquid crystal cell 3, the total birefringence is naturally the first liquid crystal cell 2. It is controlled by controlling either the second liquid crystal cell 3 or the second liquid crystal cell 3. By appropriately configuring the first liquid crystal cell 2 and the second liquid crystal cell 3, the liquid crystal device 1 can be actively switched between the dark state and the bright state, and thus can return to the dark state. Means that one state transition in the nematic liquid crystal takes place much faster than with a single cell liquid crystal device, usually very slow, caused by elastic relaxation of the liquid crystal material. As will be described in more detail below, in various embodiments of the liquid crystal device according to the present invention, the first liquid crystal cell 2 and the second liquid crystal cell 3 can be switched if both liquid crystal cells are switched so as to be relaxed. The double cell liquid crystal device 1 is configured to be in the same light modulation state (such as bright or dark). In this way, the liquid crystal device 1 can be relaxed during a switching event, and switching between light modulation states can always be active, which means that liquid crystal molecules along a selected direction. Brought about by the application of electric fields in parallel.

Two exemplary embodiments and driving schemes of the liquid crystal device in FIG. 1 are described below.
First, exemplary driving schemes of the VA / PA double cell device 10 and the VA / PA double cell device 10 will be described with reference to FIGS. 2 and 3a to d. 3A to 3D are cross-sectional views represented by exploded views of the liquid crystal device 1 of FIG. 1 in a cross section taken along the line AA ′ of FIG.

Referring first to FIG. 3a, the VA / PA dual cell apparatus 10 is schematically shown with no control voltage applied. The VA / PA double cell device 10 includes a first liquid crystal cell 11 and a second liquid crystal cell 12 arranged as a layered structure between crossed polarizing plates 4 and 5. The first liquid crystal cell 11 includes a nematic liquid crystal material sandwiched between the first substrate 14 and the second substrate 15. As schematically shown in FIG. 3a, in order to align the liquid crystal molecules 18 of the liquid crystal material in a plane orientation, the first control electrode 16 is formed on the side of the substrate 14, 15 facing this nematic liquid crystal material. And a second control electrode 17 and an alignment layer (not shown). It should be noted that the liquid crystal molecules 18 are arranged at an angle of about 45 ° with respect to the polarization direction of the incident light determined by the polarizing plate 4. In this configuration, the liquid crystal material in the first liquid crystal cell 11 will exhibit a constant non-zero birefringence Δn _PA .

The second liquid crystal cell 12 further includes a nematic liquid crystal material sandwiched between the first substrate 19 and the second substrate 20 (same as the material included in the first liquid crystal cell 11). As schematically shown in FIG. 3a, in order to align the liquid crystal molecules 23 of the liquid crystal material in a vertical (homeotropic) alignment, a first control electrode 21, a second control electrode 22, and an alignment layer (not shown) Are provided on the sides of the substrates 19, 20 facing this nematic liquid crystal material. In this configuration, the liquid crystal material in the second liquid crystal cell 12 will exhibit a zero birefringence Δn _VA = 0.

After introducing the VA / PA double cell device 10 in FIGS. 3a-d, an exemplary drive scheme for controlling the VA / PA double cell device 10 between different light modulation states (dark and light) is provided. 2 and FIGS. 3a-d will now be described.
In FIG. 2, a voltage V _PA supplied across the electrodes 16 and 17 of the first liquid crystal cell 11 (PA cell) and a voltage V _VA supplied across the electrodes 21 and 22 of the second liquid crystal cell 12 (VA cell) are represented. It is shown in the upper two figures as shown.
In the lower figure, the birefringence of the PA cell 11 (broken line) generated by supplying the voltages V _PA and V _VA to the PA cell 11 and the VA cell 12 shown in FIG. The birefringence (dotted line) and the optical response (solid line) of the VA / PA double cell device 10 are shown.

Between time t ₀ and time t ₁ , the voltage V _PA applied to the PA cell 11 is 0 V, and the voltage V _VA applied to the VA cell 12 is also 0 V, and the VA / PA double cell apparatus 10 is planarly aligned. FIG. 3 a shows the liquid crystal molecules 18 of the PA cell 11 in FIG. 3 and the liquid crystal molecules 23 of the PA cell 11 in the vertical alignment. In this state, the total birefringence is not zero (Δn _{tot =} Δn _PA + Δn _VA ≠ 0), and this is because the optical axis of the PA cell 11 is in an appropriate orientation with respect to the polarization direction of the polarizing plate 4 It means that the light passes through the crossed polarizing plates 4 and 5 into which the VA / PA double cell device 10 is inserted. Therefore, the apparatus 10 is in a bright state (BRIGHT) as shown in FIG. 2 in order to transmit incident light from the light source 7.

At time t ₁ , a voltage is applied to the PA cell 11 to reorient the liquid crystal molecules 18 to a vertical alignment, as schematically shown in FIG. 3b. The voltage V _VA applied to the VA cell 12 is still 0 V (or at least low enough to prevent the liquid crystal molecules 23 in the VA cell 12 from being realigned). By applying a voltage to the PA cell 11, when the liquid crystal molecules 18 in the PA cell 11 is changed, the birefringence of the PA cell 11 is switched from the [Delta] n _PA ≠ 0 to [Delta] n _PA * = 0. As shown schematically in FIG. 2, this switching is relatively fast and results in a total birefringence transition such that Δn _tot = Δn _{PA *} + Δn _VA = 0. As a result, the light passing through the polarizing plate 4 in FIG. 3b will pass through the PA cell 11 and VA cell 12 without a change in polarization state, which is illustrated in FIG. This means that it is switched to the dark state (DARK) as further shown in FIG.

At time t _2, the voltage applied to the VA cell 12, the liquid crystal molecules 23, as shown schematically in Figure 3c, reorienting the plane orientation. The voltage V _PA applied to the PA cell 11 is still applied so that the liquid crystal molecules 18 in the PA cell 11 remain in the vertical alignment. By applying a voltage VA cell 12, when the liquid crystal molecules 23 in the VA cell 12 is switched, the birefringence of the VA cell 12 is switched from [Delta] n _VA = 0 to _{Δn VA * = Δn PA ≠ 0} . As shown schematically in FIG. 2, this switching is relatively fast, resulting in a transition of the total birefringence of the cell such that Δn _tot = Δn _{PA *} + Δn _{VA *} = Δn _PA ≠ 0, This transition means that the light again passes through the crossed polarizers 4, 5 into which the VA / PA double cell device 10 is plugged, so this device 10 is shown in FIGS. As shown, it is in a bright state (BRIGHT).

At time t ₃ , the voltage is removed across both PA cell 11 and VA cell 12. As a result, the liquid crystal cells 11 and 12 are simultaneously relaxed to their respective relaxed states. As schematically shown in FIG. 3d, the liquid crystal molecules 18 in the PA cell 11 are relaxed to planar alignment, and the liquid crystal molecules 23 in the VA cell 12 are relaxed to vertical alignment. During this relaxation process, the birefringence of the PA cell 11 increases from Δn _{PA *} = 0 to Δn _PA ≠ 0, and the birefringence of the VA cell 12 increases from Δn _{VA *} = Δn _PA ≠ 0 to Δn _VA = 0. After decreasing and after a certain relaxation time, it returns to the relaxed state shown in FIG. 3a.

During this relaxation, the total birefringence Δn _tot remains substantially constant (and not zero) depending on the configuration of the PA cell 11 and the VA cell 12 and / or the applied control voltage. However, there is only a slight mismatch in the relaxation of the PA cell 11 and the VA cell 12, causing a change in transmitted light intensity, shown as a small “kink” 25 in FIG. Since this change can only take place in the order of ms and only in the bright state of the VA / PA dual cell device 10 in FIGS. 3a-d, this change will be hardly visible to the observer 8. . This change is expected to be avoided by optimizing the characteristics of the cell parameters and the driving method, or at least the influence can be ignored. While the liquid crystal device 1 is in the bright state, the change is expected. , Advantageous for applications with simultaneous relaxation (occurring at time t ₃ ). This is achieved using the VA / PA dual cell device 10 of FIGS.

Finally, at time _{t 4,} the voltage is again applied to the PA cell 11 returns the VA / PA dual cell system 10 in the dark state (DARK) shown in Figure 3b.

  With reference to FIGS. 4 and 5a to d, an exemplary driving scheme of the PA / PA double cell device 30 and the PA / PA double cell device 30 will be described below. Like FIGS. 3a-d, FIGS. 5a-d are cross-sectional views represented in exploded view of the embodiment of the liquid crystal device 1 of FIG. 1 in a cross-section along line A-A 'of FIG.

First, referring to FIG. 5a, a PA / PA double cell device 30 is schematically shown with no control voltage applied. The PA / PA double cell device 30 includes a first liquid crystal cell 31 and a second liquid crystal cell 32 arranged as a layered structure between the intersecting polarizing plates 4 and 5. The first liquid crystal cell 31 includes a nematic liquid crystal material sandwiched between the first substrate 14 and the second substrate 15. As schematically shown in FIG. 5a, in order to align the liquid crystal molecules 33 of the liquid crystal material in a plane orientation, the first control electrode 16 and the side surfaces of the substrates 14 and 15 facing the liquid crystal material A second control electrode 17 and an alignment layer (not shown) are provided. As schematically shown in FIG. 5a, the liquid crystal molecules 33 are parallel to the substrates 14 and 15 and parallel to the plane of the drawing. It should be noted that the liquid crystal molecules 33 are arranged at an angle of approximately 45 ° with respect to the polarization direction of the incident light determined by the polarizing plate 4. In this configuration, the liquid crystal material in the first liquid crystal cell 31 will exhibit a constant non-zero birefringence Δn _PA1 = Δn _PA .

The second liquid crystal cell 32 further includes a nematic liquid crystal material sandwiched between the first substrate 19 and the second substrate 20 (which is the same material included in the first liquid crystal cell 31). As schematically shown in FIG. 5a, in order to align the liquid crystal molecules 34 of the liquid crystal material in a planar alignment, the first control electrode 21, the second control electrode 22, and an alignment layer (not shown) Provided on the side of the substrates 19, 20 facing this liquid crystal material. As schematically shown in FIG. 5a, the liquid crystal molecules 34 are parallel to the substrates 19 and 20 and perpendicular to the plane of the drawing. It should be noted that the liquid crystal molecules 34 are approximately 90 ° parallel to the desired alignment direction of the liquid crystal molecules 33 in the liquid crystal cell 31. In this configuration, the liquid crystal material in the second liquid crystal cell 32 will exhibit a constant non-zero birefringence Δn _PA2 = Δn _PA . In this configuration of cell 32 with an optical axis that makes an angle of about 90 °, the negative sign, Δn _PA2 = −Δn _PA , should be considered. After introducing the PA / PA double cell device 30 in FIGS. 5a-d, an exemplary drive scheme for controlling the PA / PA double cell device 30 between different light modulation states (dark and light) is provided. , And will now be described with reference to FIGS. 4 and 5a-d.

In FIG. 4, the voltage V _PA1 supplied across the electrodes 16 and 17 of the first liquid crystal cell 31 and the voltage V _PA2 supplied across the electrodes 21 and 22 of the second liquid crystal cell 12 are the upper two as shown in the figure. Is shown in one figure.
In the lower figure, the birefringence (dashed line) of the first PA cell 31 generated by supplying such voltages V _PA1 and V _PA2 to the first PA cell 31 and the second PA cell 32 shown in FIG. The birefringence (dotted line) of the second PA cell 32 and the optical response (solid line) of the PA / PA double cell device 30 are shown.

Between time t ₀ and time t ₁ , the voltage V _PA1 applied to the first PA cell 31 is 0 V, and the voltage V _PA2 applied to the second PA cell 32 is also 0 V, and the PA / PA double cell device 30 is As shown in FIG. 5a, with liquid crystal molecules 33 in the first PA cell 31 in a planar orientation on the plane of the drawing and liquid crystal molecules 34 in a second PA cell 32 in the vertical orientation on the vertical plane of the drawing. It is in a state. In this state, the total birefringence is zero (Δn _tot = 0), meaning that no light passes through the crossed polarizing plates 4 and 5 into which the PA / PA double cell device 30 is inserted. Thus, the device 30 is in the dark state (DARK) as shown in FIG.

At time t ₁ , a voltage is applied to the first PA cell 31 to reorient the liquid crystal molecules 33 to a vertical alignment, as schematically shown in FIG. 5b. The voltage V _PA2 applied to the second PA cell 32 is still 0 V (or a voltage at least low enough not to reorient the liquid crystal molecules 34 in the second PA cell 32). By applying a voltage to the 1PA cell 31, when the liquid crystal molecules 33 in the 1PA cell 31 is switched, the birefringence index of the 1PA cell 31 is switched from the [Delta] n _PA1 ≠ 0 to Δn _PA1 * = 0. As shown schematically in FIG. 4, this switching is relatively fast and will result in a total birefringence transition such that Δn _tot ≠ 0, which is a PA / PA double cell. It means that the device 30 is switched to the bright state (BRIGHT) as further shown in FIG.

At time t _2, the voltage applied to the 2PA cell 32, the liquid crystal molecules 34, as shown schematically in Figure 5c, it is reoriented vertically aligned. The voltage V _PA1 applied to the first PA cell 31 is still applied so that the liquid crystal molecules 33 in the first PA cell 31 remain in the vertical alignment. When the liquid crystal molecules 34 in the second PA cell 32 are switched by applying a voltage to the second PA cell 32, the birefringence of the second PA cell 32 is changed from Δn _PA2 = −Δn _PA ≠ 0 to Δn _PA2 = 0. Can be switched. As shown schematically in FIG. 4, this switching is relatively fast and results in a transition of the total birefringence of the cell such that Δn _tot = 0, which transition is a PA / PA double cell. It means that the device 30 is in the dark state (DARK) as shown in FIGS.

At time t ₃ , the voltage is removed across both the first PA cell 31 and the second PA cell 32. As a result, the liquid crystal cells 31 and 32 are simultaneously relaxed to their respective relaxed states. As schematically shown in FIG. 5d, the liquid crystal molecules 33 in the first PA cell 31 are relaxed to a planar orientation on the plane of the drawing, and the liquid crystal molecules 34 in the second PA cell 32 are in the vertical plane of the drawing. Relaxed in the vertical orientation above. During this relaxation process, the birefringence of the first PA cell 31 increases from Δn _{PA1 *} = 0 to Δn _PA1 = Δn _PA ≠ 0, and the birefringence of the second PA cell 32 increases from Δn _{PA2 *} = 0 to Δn _PA2 = After increasing to -Δn _PA and after a certain relaxation time, it returns to the relaxation state shown in FIG. 5a.

During this relaxation, the total birefringence Δn _tot remains substantially constant (and not zero) depending on the configuration of the first PA cell 31 and the second PA cell 32 and / or the applied control voltage. As in the VA / PA dual cell apparatus 10 described above with reference to FIGS. 2 and 3a-d, there is only a slight mismatch in mitigating the first PA cell 31 and the second PA cell 32, and a small amount in FIG. It causes a change in transmitted light intensity, shown as “kink” 36.

Finally, at time _{t 4,} the voltage is again applied to the 1PA cell 31, returning the PA / PA dual cell system 30 in the bright state (BRIGHT) shown in Figure 5b.

  FIGS. 3a-d and FIGS. 5a-d are simplified schematic diagrams provided to illustrate various embodiments of the present invention, and note that the schematic diagrams do not depict actual conditions. Should. In particular, an actual liquid crystal cell includes much more layers of liquid crystal molecules so that any slight deflection closest to the substrate has a negligible effect on the birefringence of the liquid crystal cell.

Those skilled in the art will also recognize that other dual cell structures are within the scope of the invention as defined by the appended claims. For example, based on the detailed description provided above and the technical knowledge of those skilled in the art, one of ordinary skill in the art would consider a VA / VA dual cell device with similar characteristics as one of the PA / PA dual cell devices 30. It will be easy to recognize.
In addition, those skilled in the art can further select appropriate liquid crystal materials, cell dimensions, alignment layers, more complex driving schemes, etc. without undue burden.

  Those skilled in the art will recognize that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and changes, for example VA (s) in a VA / PA or VA / VA class of dual cell devices comprising a liquid crystal material with positive dielectric anisotropy due to an in-plane electric field or fringe region Cell switching is possible within the scope of the appended claims.

  In the claims, the word “comprising” does not exclude other elements or steps, and the “singular” indefinite article does not exclude a plurality. The mere fact that inventive features are recited in mutually different dependent claims does not indicate that a combination of these specified inventive matters is not used.

Claims (14)

A liquid crystal device for modulating light passing through the liquid crystal device,
A first liquid crystal cell having a liquid crystal material including a plurality of liquid crystal molecules sandwiched between a pair of first substrates; and
A second liquid crystal cell having a liquid crystal material including a plurality of liquid crystal molecules sandwiched between a pair of second substrates,
The first liquid crystal cell and the second liquid crystal cell are arranged in a layered structure such that light passing through the first liquid crystal cell reaches the second liquid crystal cell, and
Each of the first liquid crystal cell and the second liquid crystal cell can be individually controlled between a relaxation state in which the liquid crystal cell exhibits a first birefringence and a switching state in which the liquid crystal cell exhibits a second birefringence. ,
The liquid crystal cell
When the first liquid crystal cell transitions from the relaxed state to the switched state while the second liquid crystal cell remains in the relaxed state, the total birefringence of the liquid crystal device is changed from the first total birefringence to the second total birefringence. The liquid crystal device transitions from the first light modulation state to the second light modulation state, and
Thereafter, the second liquid crystal cell transitions from the relaxed state to the switched state while the first liquid crystal cell remains in the switched state, whereby the total birefringence of the liquid crystal device is changed from the second total birefringence to the first total. A liquid crystal device, wherein the liquid crystal device is arranged and configured to change so as to change to a birefringence and return from the second light modulation state to the first light modulation state.   The first liquid crystal cell and the second liquid crystal cell are configured so that the birefringence of the first liquid crystal cell and the second liquid crystal cell are reduced during simultaneous relaxation from the switching state of the first liquid crystal cell and the second liquid crystal cell to the relaxation state. 2. The liquid crystal device according to claim 1, wherein the liquid crystal device is arranged and configured so that a sum of birefringences of the liquid crystal cell remains substantially constant as the first total birefringence. The first liquid crystal cell includes a first control electrode and a second control electrode, and the first control electrode and the second control electrode of the first liquid crystal cell are the first control electrode and the second control electrode of the first liquid crystal cell. Arranged to allow the first liquid crystal cell to be controlled from a relaxed state to a switched state by applying a voltage between and
The second liquid crystal cell includes a first control electrode and a second control electrode, and the first control electrode and the second control electrode of the second liquid crystal cell are the first control electrode and the second control electrode of the second liquid crystal cell. 3. The liquid crystal device according to claim 1, wherein the second liquid crystal cell is disposed so as to be controlled from a relaxed state to a switched state by applying a voltage between the first and second liquid crystal cells.   The first birefringence of the first liquid crystal cell is not zero, the first birefringence of the second liquid crystal cell is substantially zero, and the first liquid crystal cell and the second liquid crystal cell are 4. The liquid crystal device according to claim 1, wherein the liquid crystal device is arranged so that the total birefringence does not become zero. 5.   5. The liquid crystal device according to claim 4, wherein the second birefringence of the first liquid crystal cell is substantially zero, and the second total birefringence is substantially zero. The first liquid crystal cell has a configuration of planar alignment in a relaxed state such that liquid crystal molecules contained in the first liquid crystal cell are arranged substantially parallel to the pair of first substrates, and
5. The second liquid crystal cell is configured to be vertically aligned in a relaxed state so that liquid crystal molecules contained in the second liquid crystal cell are arranged substantially perpendicular to a pair of second substrates. Or 5. The liquid crystal device according to 5. The liquid crystal molecules contained in the second liquid crystal cell exhibit negative dielectric anisotropy,
7. The method according to claim 6, further comprising: a first control electrode disposed on the first substrate of the second liquid crystal cell; and a second control electrode disposed on the second substrate of the second liquid crystal cell. The liquid crystal device described.   The liquid crystal molecules included in the second liquid crystal cell exhibit a positive dielectric anisotropy, and the liquid crystal device is disposed on the first substrate of the second liquid crystal cell to generate an in-plane electric field. The liquid crystal device according to claim 6, comprising first and second control electrodes.   The first birefringence index of the first liquid crystal cell is substantially equal to the first birefringence index of the second liquid crystal cell, and the first liquid crystal cell and the second liquid crystal cell have a first total 4. The liquid crystal device according to claim 1, wherein the liquid crystal devices are disposed so as to be related to each other so that the birefringence is substantially zero.   The first liquid crystal cell and the second liquid crystal cell have a total birefringence that does not become substantially zero when the first liquid crystal cell is in a switching state and the second liquid crystal cell is in a relaxed state. The liquid crystal device according to claim 9, wherein the liquid crystal devices are arranged in relation to each other.   Each of the first liquid crystal cell and the second liquid crystal cell has a configuration of planar alignment in a relaxed state, and the liquid crystal molecules contained in each of the first liquid crystal cell and the second liquid crystal cell are respectively The liquid crystal device according to claim 9, wherein the liquid crystal device is disposed substantially parallel to the substrate.   Each of the first liquid crystal cell and the second liquid crystal cell has a vertically aligned configuration in a relaxed state, and the liquid crystal molecules contained in each of the first liquid crystal cell and the second liquid crystal cell are respectively The liquid crystal device according to claim 9, wherein the liquid crystal device is disposed substantially perpendicular to the substrate. A method for controlling the operation of the liquid crystal device according to claim 1, wherein the method comprises:
Controlling the first liquid crystal cell from the relaxed state to the switched state while allowing the second liquid crystal cell to remain in the switched state;
Controlling the second liquid crystal cell from the relaxed state to the switched state while allowing the first liquid crystal cell to remain in the switched state; and
A method comprising the steps of simultaneously controlling the first liquid crystal cell and the second liquid crystal cell to relax from each switching state to each relaxation state.   Each of the first liquid crystal cell and the second liquid crystal cell is such that the total birefringence of the liquid crystal device remains substantially constant during relaxation of the first liquid crystal cell and the second liquid crystal cell. 14. The method of claim 13, wherein the method is controlled to relax from each switching state to each relaxation state.

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