Spatial light modulation device

Abstract

The present disclosure relates to a spatial light modulation device, comprising: a light modulation section including a plurality of pixels; a first driver that supplies a first potential to the light modulation unit; a second driver that supplies a second potential to the light modulation unit; and a voltage control section that supplies a third potential controlled in three stages to the light modulation section, in which the pixel includes: a first transistor whose conductive state is controlled by a first potential applied to a gate terminal thereof; a second transistor whose conductive state is controlled by a second potential applied to a gate terminal thereof when the conductive state of the first transistor is on; and a liquid crystal element in which a ferroelectric liquid crystal is interposed between a first electrode, a potential of which is set according to a conductive state of the second transistor, and a second electrode supplied with a third potential and facing the first electrode.

Description

Technical Field

[0001] The present disclosure relates to a spatial light modulation device. Background Art

[0002] Generally, a spatial light modulation device used in an image projection device such as a projector or a holographic display is called a spatial light modulator (SLM), and is used to spatially modulate the phase or amplitude of coherent light using a liquid crystal cell. An example of an SLM using a liquid crystal cell is a reflective SLM using Liquid Crystal On Silicon (LCOS).

[0003] In a reflective SLM, pixels are formed on silicon, where a liquid crystal layer is provided between a transparent electrode and a reflective electrode, and input light passing through the transparent electrode and the liquid crystal layer is reflected by the reflective electrode of each pixel to output modulated light. For example, when outputting two-level modulated light, ferroelectric liquid crystal (FLC) having spontaneous polarization is often used for the liquid crystal layer.

[0004] Pixels of an SLM having FLC can be formed based on, for example, dynamic random access memory (DRAM) cells or static random access memory (SRAM) cells. In the pixel circuit, the potential of the reflective electrode is controlled to 0 or the power supply potential according to data, and a voltage between the reflective electrode and the transparent electrode is applied to the liquid crystal layer formed by FLC. When the applied voltage reaches the driving voltage of FLC, the polarization direction of FLC can be reversed. Therefore, in order to make the voltage between the reflective electrode and the transparent electrode large enough, the potential of the transparent electrode is usually fixed at half of the power supply potential. In addition, it is desirable that the pixels are small. For example, the pixel pitch required to achieve a practically sufficient viewing angle of 30° in a holographic display is 1 μm.

[0005] [Prior Art Documents]

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. Hei 11-509647.

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-21159.

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2017-129746. Summary of the Invention

[0009] However, in an SLM having an FLC, there is a problem in that it is difficult to obtain a driving voltage for driving the FLC while attempting to narrow the pixel pitch (e.g., 1-μm pitch). Narrowing the pixel pitch means miniaturizing the transistors in the pixel circuit. However, generally, the breakdown voltage capability of a transistor decreases as it is miniaturized. Therefore, when the pixel pitch is narrowed, it is necessary to lower the power supply potential. In addition, since the potential of the transparent electrode is fixed at half of the power supply potential regardless of whether the potential of the reflective electrode is controlled to 0 or the power supply potential, the voltage between the reflective electrode and the transparent electrode is at most only half of the amplitude of the power supply potential. Therefore, as the pixel pitch is narrowed, it becomes difficult to obtain a voltage sufficient to reverse the polarization direction of the FLC.

[0010] In addition, for example, a pixel circuit based on a DRAM cell is configured to control the potential of the reflective electrode by a single transistor, whereby the area of the pixel can be made small. However, for an FLC with a large reverse current, even if it can be driven with a voltage capable of reversing the polarization, a sufficiently large driving current cannot be obtained, and the reversal takes time, resulting in a slow frame rate.

[0011] In addition, for example, a pixel circuit based on an SRAM cell can suppress a decrease in the frame rate by assigning data writing to the pixel and driving of the FLC to other transistors. However, since it has a configuration including a plurality of transistors, the area of the pixel increases.

[0012] An advantage of the present disclosure is to provide a spatial light modulation device capable of applying a sufficient voltage to a liquid crystal while suppressing an increase in the pixel area.

[0013] Additional features and advantages of the present disclosure will be set forth in the following description, and in part will be apparent from the description, or may be learned by practice of the present disclosure. These and other advantages of the present disclosure will be realized and obtained by the structure particularly pointed out in the specification and claims and the drawings.

[0014] To achieve these and other advantages, and in accordance with the purpose of the present disclosure, as embodied and broadly described herein, a spatial light modulation device includes: a light modulation unit including a plurality of pixels; a first driver that supplies a first potential to the light modulation unit; a second driver that supplies a second potential to the light modulation unit; and a voltage control unit that supplies a third potential to the light modulation unit for three-level control, wherein the pixel includes: a first transistor whose conduction state is controlled by a first potential applied to its gate terminal; a second transistor whose conduction state is controlled by a second potential applied to its gate terminal when the conduction state of the first transistor is on; and a liquid crystal element, wherein ferroelectric liquid crystal is interposed between a first electrode and a second electrode, the potential of the first electrode is set according to the conduction state of the second transistor, and the second electrode is supplied with the third potential and faces the first electrode.

[0015] It should be understood that the foregoing general description and the following detailed description are both exemplary and explanatory and are intended to provide further explanation of the claimed present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings are included to provide a further understanding of the present disclosure and are incorporated into and constitute a part of this specification. The drawings illustrate embodiments of the present disclosure and, together with the description, are used to explain the principles of the present disclosure. In the drawings:

[0017] Figure 1 is a block diagram showing the configuration of a spatial light modulation device according to an embodiment of the present disclosure;

[0018] Figure 2 is a partial cross-sectional view showing the configuration of the light modulation unit;

[0019] Figure 3 is a diagram showing an example of the circuit configuration of the reverse voltage generation unit;

[0020] Figure 4 is a diagram showing the circuit configuration of the pixel;

[0021] Figure 5 is a diagram showing a first example of the potential transition in the pixel;

[0022] Figure 6 is a diagram showing a second example of the potential transition in the pixel;

[0023] Figure 7 is a diagram showing a third example of the potential transition in the pixel;

[0024] Figure 8 is a diagram showing a fourth example of the potential transition in the pixel;

[0025] Figure 9 A diagram showing a list of operations of pixels;

[0026] Figure 10A and Figure 10B is a diagram showing a specific example of a voltage control method; and

[0027] Figure 11 is a diagram showing a modified example of the circuit configuration of a pixel. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments described below are examples and should not be construed as being limited by this description.

[0029] Figure 1 is a block diagram showing the configuration of a spatial light modulation device according to an embodiment of the present disclosure. The spatial light modulation device 100 is, for example, equipped in an image projection device such as a holographic display, and spatially modulates the phase of input light and then outputs it. Figure 1 The shown spatial light modulation device 100 has a light modulation unit 110, a gate driver 120, a source driver 130, a reverse voltage control unit 140, and a reverse voltage generation unit 150.

[0030] The light modulation unit 110 includes a pixel array in which a plurality of pixels 115 are two-dimensionally arranged in the row direction and the column direction. The light modulation unit 110 drives the liquid crystal elements of each pixel 115 according to the data written to each pixel 115 by the source driver 130, and spatially modulates the input light of each pixel 115.

[0031] Specifically, the light modulation unit 110 has Figure 2 the shown structure. Figure 2 is a diagram showing a partial cross-section of the light modulation unit. As Figure 2 shown, the light modulation unit 110 is formed such that a pixel circuit 220, a reflective electrode 230, an alignment layer 241, a liquid crystal layer 250, an alignment layer 242, a transparent electrode 260, and a cover glass 270 are stacked on a silicon substrate 210. The pixel circuit 220 and the reflective electrode 230 are mounted for each pixel 115.

[0032] The pixel circuit 220 is connected to the gate driver 120 and the source driver 130, and is a circuit including two transistors (such as metal-oxide-semiconductor field-effect transistors (MOSFETs)). The pixel circuit 220 controls the potential of the reflective electrode 230 by switching the conductive states of the two transistors, thereby controlling the writing of data to the pixel 115.

[0033] The reflective electrode 230 is an electrode formed of a metal such as aluminum, for example, and reflects the input light that passes through the cover glass 270, the transparent electrode 260, and the liquid crystal layer 250. The liquid crystal layer 250 is sandwiched between the reflective electrode 230 and the transparent electrode 260 facing the reflective electrode 230, thereby forming the liquid crystal element of the pixel 115. The potential of the reflective electrode 230 is controlled by the pixel circuit 220 to be a potential that varies with the data.

[0034] The alignment layers 241 and 242 are in direct contact with the liquid crystal layer 250 and are arranged in a predetermined direction to form a group of liquid crystal molecules of the liquid crystal layer 250.

[0035] The liquid crystal layer 250 is formed using ferroelectric liquid crystal (FLC) having spontaneous polarization, and when the voltage between the reflective electrode 230 and the transparent electrode 260 reaches the driving voltage, the polarization direction is reversed in the pixel 115. The liquid crystal layer 250 changes the transmittance of the input light according to the polarization direction of each pixel 115.

[0036] The transparent electrode 260 is a transparent electrode formed of, for example, indium tin oxide (ITO), and transmits the input light and the reflected light from the reflective electrode 230. The transparent electrode 260 is a single film-shaped electrode facing the plurality of reflective electrodes 230 mounted for each pixel 115, and is connected to the reverse voltage generation unit 150. The potential of the transparent electrode 260 is controlled by the reverse voltage control unit 140 and the reverse voltage generation unit 150 in three stages of a positive power supply potential, 0, and a negative power supply potential.

[0037] The cover glass 270 is a transparent member that covers the transparent electrode 260 and protects the surface of the light modulation unit 110. The input light input to the light modulation unit 110 is incident on the cover glass 270 from the outside, and the reflected light reflected by the reflective electrode 230 is output to the outside through the cover glass 270.

[0038] Back to Figure 1 , the gate driver 120 sequentially applies a gate voltage to the pixel array of the light modulation unit 110 one row at a time, and controls whether to write data to the pixel 115 to which the gate voltage is applied.

[0039] When writing data to each column of the pixel array of the light modulation unit 110, the source driver 130 supplies a data voltage according to the data and controls the potential of the reflective electrode 230 provided in the pixel 115.

[0040] The reverse voltage control unit 140 controls the reverse voltage to set the potential of the transparent electrode 260 to a desired potential. Specifically, when the frame of the display data starts, the reverse voltage control unit 140 controls to supply the negative power supply potential as the reverse voltage to the transparent electrode 260, thereby resetting the polarization directions of the liquid crystal elements of all the pixels 115. Then, while performing data writing to each pixel 115, the reverse voltage control unit 140 controls to supply 0 as the reverse voltage to the transparent electrode 260, and when the data writing to all the pixels 115 is completed, the reverse voltage control unit 140 controls to supply the positive power supply potential as the reverse voltage to the transparent electrode 260. In this way, the reverse voltage control unit 140 operates to supply three stages of reverse voltage to the transparent electrode 260 and controls the potential of the transparent electrode 260 in three stages (i.e., the positive power supply potential, 0, and the negative power supply potential).

[0041] The reverse voltage generation unit 150 supplies the reverse voltage to the transparent electrode 260 according to the control of the reverse voltage control unit 140. That is, the reverse voltage generation unit 150 supplies three types of reverse voltages (i.e., the positive power supply potential, 0, and the negative power supply potential) to the transparent electrode 260. Specifically, the reverse voltage generation unit 150 has, for example, a circuit configuration as shown in Figure 3 below. As shown in Figure 3 below, the reverse voltage generation unit 150 has inverter circuits 151 to 153, a voltage divider circuit 154, and transmission gate circuits 155 and 156.

[0042] The inverter circuit 151 is connected to the positive power supply potential +VDD and the ground potential GND, and supplies its output voltage to the voltage divider circuit 154.

[0043] The inverter circuit 152 is connected to the positive power supply potential +VDD and the ground potential GND, and supplies its output voltage to the transmission gate circuit 155.

[0044] The inverter circuit 153 is connected to the ground potential GND and the negative power supply potential -VDD, and supplies its output voltage to the transmission gate circuit 156.

[0045] The voltage divider circuit 154 has resistor elements with a resistance value ratio of 2:1, and divides the voltage between the output potential of the inverter circuit 151 and the negative power supply potential -VDD, and supplies its output voltage to the inverter circuit 153.

[0046] The transmission gate circuit 155 switches whether to supply the output voltage of the inverter circuit 152 to the transparent electrode 260.

[0047] The transmission gate circuit 156 switches whether to supply the output voltage of the inverter circuit 153 to the transparent electrode 260.

[0048] The reverse voltage control unit 140 controls the operations of the inverter circuits 151, 152, and 153 and the transmission gate circuits 155 and 156 such that the reverse voltage generation unit 150 supplies one of the positive power supply potential +VDD, 0, and the negative power supply potential -VDD as a reverse voltage to the transparent electrode 260.

[0049] The configuration of the pixel 115 of the light modulation unit 110 will be described in more detail. Figure 4 It is a diagram showing the circuit configuration of the pixel. Figure 4 The shown pixel 115 has transistors 301 and 302 and a liquid crystal element 303.

[0050] The transistor 301 is, for example, a field effect transistor such as a MOSFET, and has a gate terminal connected to the gate driver 120, a source terminal connected to the source driver 130, and a drain terminal connected to the node A. Therefore, the transistor 301 is controlled to be in its conductive state by the write voltage from the gate driver 120, and when the conductive state is on, the voltage of the node A is set by the data voltage from the source driver 130. Since the node A is the node connected to the gate terminal of the transistor 302, a gate voltage that varies with the voltage of the node A is applied to the gate terminal of the transistor 302.

[0051] The transistor 302 is, for example, a field effect transistor such as a MOSFET, and has a gate terminal connected to the node A, a source terminal connected to the ground electrode, and a drain terminal connected to the node B. Therefore, the transistor 302 is controlled to be in its conductive state by the voltage from the node A, and when the conductive state is on, the voltage of the node B is set by the ground voltage from the ground electrode. Since the node B is the node connected to the reflective electrode 230 of the liquid crystal element 303, when the conductive state of the transistor 302 is on, the potential of the reflective electrode 230 of the liquid crystal element 303 is set to 0 in the same manner as the node B.

[0052] The liquid crystal element 303 is composed of a liquid crystal layer 250 interposed between the reflective electrode 230 and the transparent electrode 260, and the liquid crystal layer 250 is driven by the voltage between the reflective electrode 230 and the transparent electrode 260. That is, when the voltage between the reflective electrode 230 and the transparent electrode 260 reaches the driving voltage, the liquid crystal element 303 can reverse the polarization direction of the liquid crystal molecules constituting the liquid crystal layer 250.

[0053] When the transistor 302 is in the conductive state, the polarization direction of the liquid crystal element 303 is reset to the initial state, the potential VB of the node B is controlled to 0, and the reverse voltage becomes the negative power supply potential. Thereafter, when the transistor 302 is in the non-conductive state, the node B is in the high impedance (Hi-Z) state, and the reverse voltage becomes the positive power supply potential, the polarization direction of the liquid crystal element 303 is maintained or reversed according to the potential state of the reflective electrode 230.

[0054] In this way, since the pixel 115 is composed of two transistors 301 and 302 and the liquid crystal element 303, the increase in the pixel area is suppressed to the minimum. Specifically, since the pixel circuit 220 needs to be equipped with two transistors 301 and 302, the circuit size of the pixel circuit 220 is small, and the manufacturing cost of the spatial light modulation device 100 can be reduced.

[0055] Specifically describe writing data into the pixel 115 configured as above. First, for example, describe the case where the polarization direction of the liquid crystal element 303 is set to, for example, the "-" direction in order to write the data "0" into the pixel 115.

[0056] Figure 5 is a diagram showing a first example of the transition of the potential of each node in the pixel. In Figure 5 the transitions of the data voltage VDATA, the write voltage VWRITE, the reverse voltage VOPP, the potential VA of the node A, and the potential VB of the node B are shown in order from the top. The data voltage VDATA is controlled by the source driver 130, the write voltage VWRITE is controlled by the gate driver 120, and the reverse voltage VOPP is controlled by the reverse voltage control unit 140 and the reverse voltage generation unit 150.

[0057] The first example is, for example, the case where the data "0" of the previous frame is written into the pixel 115 at the start of a frame (i.e., time t0), and the polarization direction of the liquid crystal element 303 is "-". In this case, when the frame starts at time t0, the potential VB of the node B equal to the potential of the reflective electrode 230 is the positive power supply potential +VDD.

[0058] From time t0 to time t1, the reverse voltage VOPP is continuously set to the positive power supply potential +VDD from the previous frame, and the potential of the transparent electrode 260 becomes the positive power supply potential +VDD. Then, from time t1 to time t2, the reverse voltage VOPP is set to 0, so that the potentials of the transparent electrode 260 and the reflective electrode 230 become 0. In addition, although the reverse voltage VOPP is set to 0 from time t1 to time t2 in this case, the reverse voltage VOPP can be set to the positive power supply potential +VDD until time t2.

[0059] From time t2 to time t3, the polarization direction of the liquid crystal element 303 is reset to the initial state of the "-" direction. Specifically, the reverse voltage VOPP is set to the negative power supply potential -VDD, and the write voltage VWRITE is set to the positive power supply potential +VDD. By setting the write voltage VWRITE to the positive power supply potential +VDD, the conduction state of the transistor 301 is turned on, and before data writing, the potential VA of the node A is set to a high potential by the data voltage VDATA set to the positive power supply potential +VDD. As a result, the conduction state of the transistor 302 is turned on, and the potential VB of the node B is set to 0 by the ground potential from the ground electrode.

[0060] Therefore, the potential of the transparent electrode 260 is set to the negative power supply potential -VDD equal to the reverse voltage VOPP, and the potential of the reflective electrode 230 is set to 0 equal to the potential VB of the node B, so that the amplitude of the voltage between the reflective electrode 230 and the transparent electrode 260 becomes equal to the amplitude of the power supply potential. As a result, by making the amplitude of the power supply potential greater than the driving voltage of the liquid crystal layer 250, the polarization direction of the liquid crystal element 303 can be reset from time t2 to time t3. Here, since the data "0" was written in the previous frame, the polarization direction of the liquid crystal element 303 is the "-" direction, and even if reset, the polarization direction of the liquid crystal element 303 will not change.

[0061] From time t3 to time t4, the reverse voltage VOPP is set to 0, so the potential of the transparent electrode 260 becomes 0. As a result, the amplitude of the voltage between the reflective electrode 230 and the transparent electrode 260 becomes 0, but the polarization direction of the liquid crystal element 303 remains in the "-" direction.

[0062] From time t4 to time t5, while setting the write voltage VWRITE to the positive power supply potential +VDD, the data voltage VDATA is set to 0 corresponding to the data "0". As a result, the potential VA of the node A is set to 0 by the data voltage VDATA, the conduction state of the transistor 302 is cut off, and the node B becomes a high impedance (Hi-Z) state. As a result, the pixel 115 is set to the data "0".

[0063] From time t5 to time t6, the write voltage VWRITE returns to 0, and the conduction state of the transistor 301 is cut off. Even after the conduction state of the transistor 301 is cut off, the potential VA of the node A remains at 0. Thereafter, from time t6 to time t8, each potential passes (or remains unchanged) without change.

[0064] From time t8 to time t9, the polarization direction of the liquid crystal element 303 is set to reflect the data set in the pixel 115. Specifically, the reverse voltage VOPP is set to the positive power supply potential +VDD. By setting the reverse voltage VOPP to the positive power supply potential +VDD, the potential of the transparent electrode 260 becomes the positive power supply potential +VDD. In addition, since the conduction state of the transistor 302 is off, the potential VB of the node B in the high impedance Hi-Z state is not affected by the ground electrode and rises to the same positive power supply potential +VDD as the potential of the transparent electrode 260.

[0065] Therefore, since the potential of the transparent electrode 260 is set to the positive power supply potential +VDD equal to the reverse voltage VOPP, and the potential of the reflection electrode 230 rises to the positive power supply potential +VDD equal to the potential VB of the node B, the amplitude of the voltage between the reflection electrode 230 and the transparent electrode 260 becomes a small value close to 0. Therefore, when the voltage between the reflection electrode 230 and the transparent electrode 260 does not reach the driving voltage of the liquid crystal layer 250, the polarization direction of the liquid crystal element 303 is maintained. That is, in the liquid crystal element 303, the polarization direction is maintained in the "-" direction corresponding to the data "0".

[0066] Figure 6 is a diagram showing a second example of the transition of the potential of each node in the pixel. Similar to Figure 5 , in Figure 6 , the transitions of the data voltage VDATA, the write voltage VWRITE, the reverse voltage VOPP, the potential VA of the node A, and the potential VB of the node B are shown in order from the top.

[0067] The second example is a case where, for example, at the start of a frame (i.e., time t0), the data "1" of the previous frame is written into the pixel 115, and the polarization direction of the liquid crystal element 303 is in the "+" direction. In this case, when the frame starts at time t0, the potential VB of the node B equal to the potential of the reflection electrode 230 is 0.

[0068] From time t0 to time t1, the reverse voltage VOPP is continuously set to the positive power supply potential +VDD from the previous frame, and the potential of the transparent electrode 260 becomes the positive power supply potential +VDD. Then, from time t1 to time t2, the reverse voltage VOPP is set to 0, and thus, the potentials of the transparent electrode 260 and the reflection electrode 230 become 0.

[0069] From time t2 to time t3, the polarization direction of the liquid crystal element 303 is reset to the initial state of the "-" direction. Specifically, the reverse voltage VOPP is set to the negative power supply potential -VDD, and the write voltage VWRITE is set to the positive power supply potential +VDD. By setting the write voltage VWRITE to the positive power supply potential +VDD, the conduction state of the transistor 301 is turned on, and before data writing, the potential VA of the node A is set to a high potential by the data voltage VDATA set to the positive power supply potential +VDD. As a result, the conduction state of the transistor 302 is turned on, and the potential VB of the node B is set to 0 by the ground potential from the ground electrode.

[0070] Therefore, the potential of the transparent electrode 260 is set to the negative power supply potential -VDD equal to the reverse voltage VOPP, and the potential of the reflective electrode 230 is set to 0 equal to the potential VB of the node B, so that the amplitude of the voltage between the reflective electrode 230 and the transparent electrode 260 becomes equal to the amplitude of the power supply potential. As a result, by making the amplitude of the power supply potential greater than the driving voltage of the liquid crystal layer 250, the polarization direction of the liquid crystal element 303 can be reset from time t2 to time t3. Here, since the data "1" was written in the previous frame, the polarization direction of the liquid crystal element 303 is the "+" direction opposite to the "-" direction, and the polarization direction of the liquid crystal element 303 is reversed by the reset. That is, the polarization direction of the liquid crystal element 303 is reset to the "-" direction corresponding to the data "0".

[0071] Thereafter, as in the first example above, from time t4 to time t5, the conduction state of the transistor 302 is turned off, and the pixel 115 is set to the state in which the data "0" is set. Then, from time t8 to time t9, the reverse voltage VOPP is set to the positive power supply potential +VDD so that the potential of the transparent electrode 260 becomes the positive power supply potential +VDD, and the potential of the reflective electrode 230 rises to the positive power supply potential +VDD. As a result, when the voltage between the reflective electrode 230 and the transparent electrode 260 does not reach the driving voltage of the liquid crystal layer 250, the polarization direction of the liquid crystal element 303 is maintained. That is, in the liquid crystal element 303, the polarization direction is maintained in the state of the "-" direction corresponding to the data "0".

[0072] Hereinafter, a case is described in which the polarization direction of the liquid crystal element 303 is set to the "+" direction opposite to the "-" direction in order to write the data "1" into the pixel 115, for example.

[0073] Figure 7 is a diagram showing a third example of the potential transition of each node in the pixel. Similar to Figure 5 , in Figure 7The transitions of the data voltage VDATA, the write voltage VWRITE, the reverse voltage VOPP, the potential VA of node A, and the potential VB of node B are shown in order from the top.

[0074] A third example is a case where, for example, at the start of a frame (i.e., time t0), the data “0” of the previous frame is written to pixel 115, and the polarization direction of liquid crystal element 303 is in the “−” direction. In this case, when the frame starts at time t0, the potential VB of node B, which is equal to the potential of reflection electrode 230, is the positive power supply potential +VDD.

[0075] From time t0 to time t1, the reverse voltage VOPP is continuously set to the positive power supply potential +VDD from the previous frame, and the potential of transparent electrode 260 becomes the positive power supply potential +VDD. Then, from time t1 to time t2, the reverse voltage VOPP is set to 0. Therefore, the potentials of transparent electrode 260 and reflection electrode 230 become 0.

[0076] From time t2 to time t3, the polarization direction of liquid crystal element 303 is reset to the initial state in the “−” direction. Specifically, the reverse voltage VOPP is set to the negative power supply potential −VDD, and the write voltage VWRITE is set to the positive power supply potential +VDD. By setting the write voltage VWRITE to the positive power supply potential +VDD, the conduction state of transistor 301 is turned on, and before data writing, the potential VA of node A is set to the positive power supply potential +VDD by the data voltage VDATA set to the positive power supply potential +VDD. As a result, the conduction state of transistor 302 is turned on, and the potential VB of node B is set to 0 by the ground potential from the ground electrode.

[0077] Therefore, the potential of transparent electrode 260 is set to the negative power supply potential −VDD equal to the reverse voltage VOPP, and the potential of reflection electrode 230 is set to 0 equal to the potential VB of node B, so that the amplitude of the voltage between reflection electrode 230 and transparent electrode 260 becomes equal to the amplitude of the power supply potential. As a result, by making the amplitude of the power supply potential greater than the amplitude of the drive voltage of liquid crystal layer 250, the polarization direction of liquid crystal element 303 can be reset from time t2 to time t3. Here, since the data “0” was written in the previous frame, the polarization direction of liquid crystal element 303 is in the “−” direction, and even if reset, the polarization direction of liquid crystal element 303 does not change.

[0078] From time t3 to time t4, the reverse voltage VOPP is set to 0. Therefore, the potential of transparent electrode 260 becomes 0. As a result, the amplitude of the voltage between reflection electrode 230 and transparent electrode 260 becomes 0, but the polarization direction of liquid crystal element 303 remains in the “−” direction.

[0079] From time t4 to time t5, while setting the write voltage VWRITE to the positive power supply potential +VDD, the data voltage VDATA is set to the positive power supply potential +VDD corresponding to the data "1". As a result, the potential VA of node A is set to a high potential by the data voltage VDATA, and the conduction state of transistor 302 is turned on. As a result, pixel 115 is set to the data "1".

[0080] From time t5 to time t6, the write voltage VWRITE returns to 0, and the conduction state of transistor 301 is cut off. Even after the conduction state of transistor 301 is cut off, the potential VA of node A remains in the high potential state. Thereafter, from time t6 to time t8, each potential passes (or remains) unchanged.

[0081] From time t8 to time t9, the polarization direction of liquid crystal element 303 is set to reflect the data set in pixel 115. Specifically, the reverse voltage VOPP is set to the positive power supply potential +VDD. By setting the reverse voltage VOPP to the positive power supply potential +VDD, the potential of transparent electrode 260 becomes the positive power supply potential +VDD. In addition, since the conduction state of transistor 302 is on, the potential VB of node B remains at 0 regardless of the potential of transparent electrode 260.

[0082] Therefore, since the potential of transparent electrode 260 is set to the positive power supply potential +VDD equal to the reverse voltage VOPP, and the potential of reflective electrode 230 is set to 0 equal to the potential VB of node B, the amplitude of the voltage between reflective electrode 230 and transparent electrode 260 becomes equal to the amplitude of the power supply potential. Therefore, by making the amplitude of the power supply potential greater than the driving voltage of liquid crystal layer 250, the polarization direction of liquid crystal element 303 can be reversed. That is, the polarization direction of liquid crystal element 303 reset to the "-" direction can be reversed to the "+" direction corresponding to the data "1".

[0083] Figure 8 is a diagram showing a fourth example of the transition of the potential of each node in a pixel. Similar to Figure 5 ,in Figure 8 the transitions of the data voltage VDATA, the write voltage VWRITE, the reverse voltage VOPP, the potential VA of node A, and the potential VB of node B are shown in order from the top.

[0084] The fourth example is a case where, for example, at the start of a frame (i.e., time t0), the data "1" of the previous frame is written into pixel 115, and the polarization direction of liquid crystal element 303 is in the "+" direction. In this case, when the frame starts at time t0, the potential VB of node B equal to the potential of reflective electrode 230 is 0.

[0085] From time t0 to time t1, the reverse voltage VOPP is continuously set to the positive power supply potential +VDD from the previous frame, and the potential of the transparent electrode 260 becomes the positive power supply potential +VDD. Then, from time t1 to time t2, the reverse voltage VOPP is set to 0. Therefore, the potentials of the transparent electrode 260 and the reflective electrode 230 become 0.

[0086] From time t2 to time t3, the polarization direction of the liquid crystal element 303 is reset to the initial state in the "-" direction. Specifically, the reverse voltage VOPP is set to the negative power supply potential -VDD, and the write voltage VWRITE is set to the positive power supply potential +VDD. By setting the write voltage VWRITE to the positive power supply potential +VDD, the conduction state of the transistor 301 is turned on, and before data writing, the potential VA of the node A is set to a high potential by the data voltage VDATA set to the positive power supply potential +VDD. As a result, the conduction state of the transistor 302 is turned on, and the potential VB of the node B is set to 0 by the ground potential from the ground electrode.

[0087] Therefore, the potential of the transparent electrode 260 is set to the negative power supply potential -VDD equal to the reverse voltage VOPP, and the potential of the reflective electrode 230 is set to 0 equal to the potential VB of the node B, so that the amplitude of the voltage between the reflective electrode 230 and the transparent electrode 260 becomes equal to the amplitude of the power supply potential. As a result, by making the amplitude of the power supply potential greater than the driving voltage of the liquid crystal layer 250, the polarization direction of the liquid crystal element 303 can be reset from time t2 to time t3. Here, since the data "1" was written in the previous frame, the polarization direction of the liquid crystal element 303 is in the "+" direction, and the polarization direction of the liquid crystal element 303 is reversed by the reset. That is, the polarization direction of the liquid crystal element 303 is reset to the "-" direction corresponding to the data "0".

[0088] Thereafter, as in the above third example, from time t4 to time t5, the conduction state of the transistor 302 is turned on, and the pixel 115 is set to the state in which the data "1" is set. Then, at time t8 to time t9, the reverse voltage VOPP is set to the positive power supply potential +VDD, so that the potential of the transparent electrode 260 becomes the positive power supply potential +VDD, and the potential of the reflective electrode 230 remains at 0. As a result, the amplitude of the voltage between the reflective electrode 230 and the transparent electrode 260 becomes equal to the amplitude of the power supply potential, and the polarization direction of the liquid crystal element 303 is reversed. That is, in the liquid crystal element 303, the polarization direction is set to the "+" direction corresponding to the data "1".

[0089] As Figure 9 shown, the transition of the potential in the above pixel 115 is summarized. Figure 9Shows the data voltage, write voltage, reverse voltage, potential of the node, conduction state of the transistor, and polarization direction of the liquid crystal element at each time in Figures 5 to 8 .

[0090] It can be seen from Figure 9 that in the case of writing data "0" to pixel 115 and the case of writing data "1" to pixel 115, the reverse voltage VOPP changes in the same way. That is, from time t2 to time t3, when the polarization direction of the liquid crystal element 303 is reset, the reverse voltage VOPP is set to the negative power supply potential -VDD, and from time t3 to time t8, when setting data "0" or "1" to pixel 115, the reverse voltage VOPP is set to 0. In addition, after time t8 when setting the polarization direction of the liquid crystal element 303 according to the data, the reverse voltage VOPP is set to the positive power supply potential +VDD.

[0091] Furthermore, from time t2 to time t3, the conduction states of transistors 301 and 302 both become on, and the potential VB of node B becomes 0, so that regardless of the polarization direction before time t2, the polarization direction of the liquid crystal element 303 is reset to, for example, the "-" direction (represented by "-" in Figure 9 ). Therefore, data can be written to pixel 115 without being affected by the previous frame, and the input light to the light modulation unit 110 can be reliably spatially modulated.

[0092] In addition, from time t4 to time t5, the conduction state of transistor 301 becomes on, and the potential VA of node A is set to 0 or a high potential (represented by "H" in Figure 9 ) according to the data voltage VDATA. As a result, the conduction state of transistor 302 after time t4 is determined, and it is set whether the potential VB of node B is maintained at the ground potential or rises according to the potential of the transparent electrode 260. Therefore, data "0" or "1" is set to pixel 115.

[0093] Furthermore, from time t8 to time t9, the potential VB of node B becomes a potential that changes according to the data set to pixel 115, and the amplitude of the voltage between the reflective electrode 230 and the transparent electrode 260 (i.e., the difference between the potential VB of node B and the reverse voltage VOPP) becomes approximately 0 or a value equal to the power supply potential. When the amplitude of this voltage is approximately 0, the liquid crystal layer 250 is not driven, and the polarization direction of the liquid crystal element 303 remains in the "-" state without change. In addition, when the amplitude of this voltage is equal to the power supply potential, the liquid crystal layer 250 is driven so that the polarization direction of the liquid crystal element 303 is reversed from "-" to "+". In this way, when the polarization direction of the liquid crystal element 303 is reversed, a voltage equal to the power supply potential can be applied, so that a sufficiently large voltage can be applied to the liquid crystal layer 250 to reverse the polarization direction.

[0094] In addition, since the optical modulation unit 110 includes a pixel array in which a plurality of pixels 115 are two-dimensionally arranged in the row direction and the column direction, data writing to each pixel 115 is performed sequentially. At this time, the polarization directions of the pixels 115 in all rows can be reset simultaneously, and then data is written to the pixels 115 row by row. Specific examples are described below.

[0095] As Figure 10A shown, in the case where the pixel array of the optical modulation unit 110 has pixels 115 of, for example, M rows and N columns (where M and N are integers of 2 or more), the write voltages VWRITE supplied from the gate driver 120 to the pixel circuits 220 of each row are respectively referred to as voltages VW#1 to VW#M, and the data voltages VDATA supplied from the source driver 130 to the pixel circuits 220 of each column are respectively referred to as voltages VD#1 to VD#N. A reverse voltage VOPP is supplied from the reverse voltage generation unit 150 to one transparent electrode 260 facing the pixel circuit 220 and the reflection electrode 230.

[0096] As Figure 10B shown, in the pixel array, at time (or interval) TR, the polarization directions of all pixels 115 are reset. That is, the write voltages VW#1 to VW#M of all rows are set to the positive power supply potential +VDD, and the reverse voltage VOPP is set to the negative power supply potential -VDD, so that the polarization directions of all pixels 115 are reset to the initial state.

[0097] Then, while setting the reverse voltage VOPP to 0, data is set row by row in the pixel circuit 220. That is, at time (or interval) T1, the write voltage VW#1 supplied to the pixel circuit 220 of the first row becomes the positive power supply potential +VDD, and during this period, the data voltages VD#1 to VD#N are supplied to the pixel circuits 220 of each column in the first row. In addition, at time (or interval) T2, the write voltage VW#2 supplied to the pixel circuit 220 of the second row becomes the positive power supply potential +VDD, and during this period, the data voltages VD#1 to VD#N are supplied to the pixel circuits 220 of each column in the second row. Thereafter, the same data setting is performed, and at time (or interval) TM, the write voltage VW#M supplied to the pixel circuit 220 of the Mth row becomes the positive power supply potential +VDD, and during this period, the data voltages VD#1 to VD#N are supplied to the pixel circuits 220 of each column in the Mth row.

[0098] When the data setting for the pixel circuits 220 of all the rows is completed, the reverse voltage VOPP is set to the positive power supply potential +VDD. Accordingly, the polarization direction of each pixel 115 is maintained or reversed according to the data set in each pixel circuit 220, and modulation of the input light in the entire light modulation unit 110 is performed.

[0099] In this way, by commonly controlling the reverse voltage VOPP supplied to the transparent electrodes 260 of the plurality of pixels 115, the polarization directions in the plurality of pixels 115 can be individually controlled.

[0100] As described above, according to the present embodiment, the pixels of the light modulation unit include: two transistors that switch their conductive states according to a write voltage and a data voltage; and a liquid crystal element in which ferroelectric liquid crystal is sandwiched between a reflection electrode whose potential is controlled by the transistor and a reflection electrode whose potential is controlled in three stages. Further, for each frame, the polarization direction of the liquid crystal element is reset, and then data is written into the pixel to set the polarization direction. Accordingly, the liquid crystal element can be driven by a voltage equal to the power supply potential, and a sufficient voltage can be applied to the liquid crystal while suppressing an increase in the pixel area.

[0101] Further, the transparent electrode 260 may be constituted by a single electrode as described in the above embodiment, or may be constituted by a plurality of electrodes divided into a plurality of parts in the row direction. In this case, the reverse voltage VOPP supplied from the reverse voltage generation unit 150 may also be supplied by dividing it into the same number as the number of divisions of the reverse electrode. Further, the timing at which the reverse voltage VOPP is set from 0 to the positive power supply potential +VDD in order to set the polarization direction according to the data written in the pixel may be different for each divided electrode. Accordingly, the number of pixels driven by the reverse voltage generation unit 150 for each reverse voltage is reduced, and the reverse voltage VOPP can be supplied with a larger margin.

[0102] Further, although the pixel 115 according to the above embodiment has two transistors 301 and 302 and a liquid crystal element 303, the pixel 115 may have other circuit elements. Figure 11 is a diagram showing a modified example of the pixel. In Figure 11 , the same components as those in Figure 4 are given the same reference numerals.

[0103] Figure 11 The pixel 115 shown has a configuration in which capacitors 311 and 312 are added to the pixel 115 shown in Figure 4 .

[0104] The capacitor 311 is inserted between the node A and the ground electrode. By installing the capacitor 311, when the potential VA of the node A is set to a high potential and then the conductive state of the transistor 301 is turned off, the high potential of the node A can be more stably maintained.

[0105] The capacitor 312 is installed between the node B and the reverse voltage in parallel with the liquid crystal element 303. By installing the capacitor 312, when the conductive state of the transistor 302 is turned off, the influence of the parasitic capacitance of the transistor 302 on the potential VB of the node B can be reduced, and the potential of the reflective electrode 230 can rise more stably according to the potential of the transparent electrode 260.

[0106] One of these capacitors 311 and 312 can be installed in the pixel 115. In addition, since the capacitors 311 and 312 are small circuit elements, the increase in the pixel area due to the installation of the capacitors 311 and 312 in the pixel 115 is limited.

[0107] In the above-described embodiment, when the pixel 115 is reset, the reverse voltage VOPP is set to the negative power supply potential -VDD, and when the polarization direction of the pixel 115 is set, the reverse voltage VOPP is set to the positive power supply potential +VDD. However, the setting of the reverse voltage VOPP is not limited to this. That is, for example, the reverse voltage VOPP can also be set to the positive power supply potential +VDD when resetting, and the reverse voltage VOPP can be set to the negative power supply potential -VDD when setting the polarization direction. In this case, by inverting other potentials such as the data voltage VDATA or by changing the orientation of the liquid crystal molecule group via the alignment layers 241 and 242, as in the above-described embodiment, the liquid crystal element can be driven by a voltage equal to the power supply potential.

[0108] According to the present disclosure as described above, a sufficient voltage can be applied to the liquid crystal while suppressing an increase in the pixel area.

[0109] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is intended to cover modifications and variations of the present disclosure as long as they fall within the scope of the appended claims and their equivalents.

[0110] Cross-reference to related applications

[0111] This application claims the benefit of priority of Japanese Patent Application No. 2023-223155, filed in Japan on December 28, 2023, the entire contents of which are incorporated herein by reference for all purposes as if fully set forth herein.

Claims

1. A spatial light modulation device, comprising: a light modulation unit, wherein the light modulation unit includes a plurality of pixels; a first driver that supplies a first potential to the light modulation unit; a second driver that supplies a second potential to the light modulation unit; as well as a voltage control unit that supplies a third potential controlled in three levels to the light modulation unit, Wherein, each pixel of the plurality of pixels comprises: a first transistor, a conduction state of the first transistor being controlled by a first potential applied to a gate terminal of the first transistor; a second transistor whose conduction state is controlled by a second potential applied to a gate terminal of the second transistor when the conduction state of the first transistor is on; and A liquid crystal element in which a ferroelectric liquid crystal is interposed between a first electrode whose potential is set according to the conductive state of the second transistor and a second electrode supplied with the third potential and facing the first electrode.

2. The spatial light modulation device according to claim 1, wherein: Each of the plurality of pixels further includes a capacitive element connected between the gate terminal of the second transistor and a ground electrode.

3. The spatial light modulation device according to claim 1, wherein: Each of the plurality of pixels further includes a capacitive element connected in parallel with the liquid crystal element.

4. The spatial light modulation device according to claim 1, wherein: The voltage control section is configured to supply the third potential of a first level to the second electrode to reset the polarization direction of the liquid crystal element, and then supply the third potential of a second level to the second electrode to set data to each of the plurality of pixels.

5. The spatial light modulation device according to claim 4, wherein: The voltage control unit is configured to supply the third potential of the third stage, which is positively reversed from the third potential of the first stage, to the second electrode, so as to maintain or reverse the polarization direction of the liquid crystal element according to the data set for each of the plurality of pixels.

6. The spatial light modulation device according to claim 1, wherein: The liquid crystal element is configured by interposing the ferroelectric liquid crystal between the first electrode installed for each pixel and the second electrode facing the first electrodes of the plurality of pixels in common.

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