LIQUID CRYSTAL GRATING AND STEREOSCOPIC DISPLAY DEVICE

Provided are a liquid crystal grating and a stereoscopic display device. The liquid crystal grating includes at least one liquid crystal cell. A liquid crystal cell includes a first substrate, first electrodes, a first alignment layer, a liquid crystal layer and a second substrate which are disposed sequentially. In a first state, the liquid crystal cell includes multiple first grating units which are arranged along a first direction, and a first grating unit includes multiple first electrodes which are disposed at intervals from each other along the first direction. Along the first direction, a first electric field is formed between two closest first electrodes which are located in two adjacent first grating units, respectively, and in the liquid crystal cell, an alignment direction of the first alignment layer is the same as an electric field direction of the first electric field.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to Chinese Patent Application No. 202310341673.2 filed Mar. 31, 2023, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to the field of display technologies and, in particular, to a liquid crystal grating and a stereoscopic display device.

BACKGROUND

Since the two-dimensional display is difficult to clearly express three-dimensional depth information accurately, people have been continuously investigating a display technology that can display stereoscopic scenes, that is, the three-dimensional image display technology. The holographic three-dimensional display technology utilizes the diffraction or interference of light to record the amplitude and phase information of object light, and then reconstructs the information of the object light through the diffraction of light. The holographic three-dimensional display technology is the only real three-dimensional display technology among various display methods.

When displaying a three-dimensional image, the stereoscopic display device forms a left-eye image and a right-eye image through the diffraction function of a liquid crystal grating after a spatial light modulator (SLM) performs phase modulation and amplitude modulation on optical signals. How to improve the display effect has become an urgent problem to be solved.

SUMMARY

The present disclosure provides a liquid crystal grating and a stereoscopic display device so that the adverse impact of a transverse electric field on the rotation of liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

In a first aspect, an embodiment of the present disclosure provides a liquid crystal grating. The liquid crystal grating includes at least one liquid crystal cell. A liquid crystal cell includes a first substrate, first electrodes, a first alignment layer, a liquid crystal layer and a second substrate which are disposed sequentially. In a first state, the liquid crystal cell includes multiple first grating units which are arranged along a first direction, and a first grating unit includes multiple first electrodes which are disposed at intervals from each other along the first direction.

Along the first direction, a first electric field is formed between two closest first electrodes which are located in two adjacent first grating units, respectively, and in the liquid crystal cell, an alignment direction of the first alignment layer is the same as an electric field direction of the first electric field.

In a second aspect, an embodiment of the present disclosure provides a stereoscopic display device. The stereoscopic display device includes a light source, a spatial light modulator and a gating component which are disposed sequentially.

The gating component includes at least one liquid crystal grating according to the first aspect.

According to the liquid crystal grating provided in the embodiment of the present disclosure, the electric field direction of the first electric field is the same as the alignment direction of the first alignment layer. Therefore, the electric field direction affecting liquid crystal molecules close to the first alignment layer is towards the alignment direction of the first alignment layer, and will not be towards the direction opposite to the alignment direction of the first alignment layer; the liquid crystal molecules close the first alignment layer will not flip to an opposite direction, so that the adverse impact of the transverse electric field on the rotation of the liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

DETAILED DESCRIPTION

Hereinafter the present disclosure will be further described in detail in conjunction with the drawings and embodiments. It is to be understood that the specific embodiments set forth below are intended to illustrate and not to limit the present disclosure. Additionally, it is to be noted that for ease of description, only part, not all, of structures related to the present disclosure are illustrated in the drawings.

FIG.1is a sectional view of a liquid crystal grating in the research process. Referring toFIG.1, a liquid crystal grating includes a first substrate11, a second substrate12and a liquid crystal layer30. The liquid crystal layer30is located between the first substrate11and the second substrate12. The liquid crystal layer30includes liquid crystal molecules. The liquid crystal grating includes multiple grating units40. The grating units40are arranged along a first direction X, and a grating unit40includes multiple first electrodes21and a first second electrode22. The first electrodes21are located between the first substrate11and the liquid crystal layer30. The first electrodes21are disposed at intervals from each other, and the first electrodes21are disposed along the first direction X. Along the first direction X, a certain distance exists between two adjacent first electrodes21. The grating units40share the same one second electrode22, and the second electrode22is a whole-surface electrode.

FIG.2is a diagram showing the voltage distribution of a first electrode and the voltage distribution of a second electrode of a liquid crystal grating in the research process. Referring toFIG.1andFIG.2, according to the related research, it is found that a voltage difference exists between a first electrode21and the second electrode22during stereoscopic display. A longitudinal electric field formed by the first electrode and the second electrode can drive liquid crystal molecules to rotate. At least two first electrodes21have different voltages, and then longitudinal electric fields of different intensities which are arranged along the first direction X are formed. The longitudinal electric fields of different intensities cause liquid crystal molecules to rotate by different angles, forming a refractive index gradient, and multiple grating units40which are arranged along the first direction X are formed. Therefore, a grating unit40may also include liquid crystal molecules. However, a transverse electric field is formed between first electrodes21of different voltages. The transverse electric field will lead to a flexoelectric effect of liquid crystal molecules, changing the rotation behavior of the liquid crystal molecules. As a result, the liquid crystal molecules in the liquid crystal grating cannot flip in conformity to the ideal situation while rotating towards the direction opposite to a pre-tilt angle, leading to the problem of antiphase domains.

Referring toFIG.1andFIG.2, according to the related research, it is found that some regions in the liquid crystal grating are in an undesirable state. It is further found that along the first direction X, a first electric field TE1is formed between two closest first electrodes21which are located in two adjacent grating units40respectively. The first electric field TE1is a transverse electric field. The liquid crystal grating includes a first alignment layer31. The first alignment layer31is located between the first electrodes21and the liquid crystal layer30. In some regions of the liquid crystal grating, an alignment direction R1of the first alignment layer31is opposite to an electric field direction of the first electric field TE1. Under the combined impact of the first electric field TE1and the longitudinal electric field, a liquid crystal molecule in region S1rotates along the direction of the arrow inFIG.1and flips to an opposite direction, resulting in a bubble-like antiphase domain in region S1. The liquid crystal molecule in region S1is close to the first electrode21. The first alignment layer31may be in direct contact with the first electrodes21. In other implementations, a protective layer may further be disposed between the first alignment layer31and the first electrodes21. The first alignment layer31is located on a side of the protective layer away from the first electrodes21. The protective layer provides a flat surface for the first alignment layer31to improve the flatness of the first alignment layer31.

FIG.3is a sectional view of a liquid crystal grating according to an embodiment of the present disclosure, andFIG.4is a diagram showing the voltage distribution of first electrodes and the voltage distribution of a second electrode of a liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.3andFIG.4, the liquid crystal grating includes at least one liquid crystal cell100. A liquid crystal cell100includes a first substrate11, first electrodes21, a first alignment layer31, a liquid crystal layer30and a second substrate12which are disposed sequentially. In a first state ST1, the liquid crystal cell100includes multiple first grating units401which are arranged along the first direction X. A first grating unit401includes multiple first electrodes21which are disposed at intervals along the first direction X. Along the first direction X, a certain distance exists between two adjacent first electrodes21. Along the first direction X, a first electric field TE1is formed between two closest first electrodes21which are located in two adjacent first grating units401respectively. In the liquid crystal cell100, an alignment direction R1of the first alignment layer31is the same as an electric field direction of the first electric field TEL

According to the liquid crystal grating provided in the embodiment of the present disclosure, the electric field direction of the first electric field TE1is the same as the alignment direction R1of the first alignment layer31. Therefore, the electric field direction affecting liquid crystal molecules close to the first alignment layer31is towards the alignment direction R1of the first alignment layer31, and will not be towards the direction opposite to the alignment direction of the first alignment layer31; the liquid crystal molecules close to the first alignment layer31will not flip to an opposite direction, so that the adverse impact of the transverse electric field on the rotation of the liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.3andFIG.4, the liquid crystal cell100further includes a second electrode22. The second electrode22is located between the second substrate12and the liquid crystal layer30. During stereoscopic display, a voltage difference exists between a first electrode21and the second electrode22. A longitudinal electric field formed between the first electrode21and the second electrode22can drive liquid crystal molecules to rotate, and multiple first grating units401are formed. The first grating units401are arranged repeatedly along the first direction X. The liquid crystal gating is used for light diffraction and deflection. When stereoscopic display is not performed, no first grating unit401is formed, and the liquid crystal grating is not configured for or assists in light diffraction and deflection. The direction of the longitudinal electric field may be a third direction Z or the opposite direction of the third direction Z.

Optionally, referring toFIG.3, the same first grating unit401includes multiple first electrode groups51which are arranged along the first direction X. A first electrode group51includes at least one first electrode21and at least one second electrode22. In the same first electrode group51, a first electrode21at least partially overlaps a second electrode22; that is, a first electrode21overlaps a second electrode22, or a first electrode21partially overlaps a second electrode22. The voltage difference between the first electrode21and the second electrode22is a first voltage difference. The longitudinal electric field formed by the first voltage difference can drive liquid crystal molecules to rotate. The first voltage difference is a difference between a voltage of a first electrode21and a voltage of a second electrode22in the first grating unit401, that is, the first voltage difference is a voltage of a first electrode21minus a voltage of the second electrode22.

Exemplarily, referring toFIG.3, a first electrode group51includes a first electrode21and a second electrode22. The first voltage difference exists between voltages of a first electrode21and a second electrode22in the same first electrode group501. In other implementations, a first electrode group51includes multiple first electrodes21and a second electrode22.

Optionally, referring toFIG.3andFIG.4, various first voltage differences have the same polarity. Longitudinal electric fields (longitudinal electric fields illustrated by arrows inFIG.3) formed by first electrodes21and the second electrode22have the same electric field direction. The longitudinal electric fields formed by the first electrodes21and the second electrodes22drives liquid crystal molecules to rotate towards the same direction.

Exemplarily, referring toFIG.3andFIG.4, multiple first electrodes21includes first sub-first electrodes211, second sub-first electrodes212, third sub-first electrodes213and fourth sub-first electrodes214. A voltage of a first sub-first electrode211is greater than the voltage of the second electrode22, and a positive first voltage difference is formed between the first sub-first electrode211and the second electrode22. A voltage of a second sub-first electrode212is greater than the voltage of the second electrode22, and a positive first voltage difference is formed between the second sub-first electrode212and the second electrode22. A voltage of a third sub-first electrode213is greater than the voltage of the second electrode22, and a positive first voltage difference is formed between the third sub-first electrode213and the second electrode22. A voltage of a fourth sub-first electrode214is greater than the voltage of the second electrode22, and a positive first voltage difference is formed between the fourth sub-first electrode214and the second electrode22. Arrows inFIG.3represent longitudinal electric fields, and the thickness of the arrows indicates the intensity of the longitudinal electric fields. The thicker the arrow, the stronger the longitudinal electric field, the larger the first voltage difference.

Optionally, referring toFIG.3andFIG.4, in the same first grating unit401, along the first direction X, various first voltage differences gradually decrease, intensities of longitudinal electric fields formed by various first electrode groups51gradually decrease, and rotation angles of liquid crystal molecules gradually decrease. In other implementations, in the same first grating unit401, along the first direction X, first voltage differences gradually increase, and thus the alignment direction R1of the first alignment layer31is changed accordingly so that the alignment direction R1is the same as the electric direction of the first electric field TE1. It is to be understood that in the same first grating unit401, due to the gradual increase or gradual decrease of the first voltage differences along the first direction X, a jump occurs in first voltage differences of two adjacent first grating units401. Accordingly, refractive indexes formed by liquid crystal molecules gradually change in the same first grating unit401, and a jump occurs in refractive indexes at the boundary of two adjacent first grating units401, and thus a grating with the diffraction function is formed.

Exemplarily, referring toFIG.3andFIG.4, a first grating unit401includes M (exemplarily, M=4 inFIG.3) first electrode groups51, where M is a positive integer larger than 1. In the same first grating unit401, along the first direction X, first voltage differences corresponding to the first first electrode group51to the M-th first electrode group51change linearly. In the same first grating unit401, intensities of longitudinal electric fields formed by various first electrode groups51increase or decrease linearly. Since the rotation angle of liquid crystal molecules is in direct proportion to the intensity of the longitudinal electric field, various first voltage differences which change linearly result in refractive indexes of liquid crystal molecules which change linearly, so that the optical path is simplified. In other implementations, the first voltage differences corresponding to the first first electrode group51to the M-th first electrode group51change in other rules.

Optionally, referring toFIG.3, multiple first grating units401share one second electrode22. Along a direction perpendicular to a plane where the first substrate11is located, the second electrode22overlaps first electrodes21in multiple first grating units401. The second electrode22may be a whole-surface electrode.

FIG.5is a sectional view of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.6is a diagram showing the voltage distribution of first electrodes and the voltage distribution of second electrodes of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.5andFIG.6, the liquid crystal cell100further includes a second alignment layer32. The second alignment layer32is located between second electrodes22and the liquid crystal layer30. In the first state ST1, a first grating unit401includes multiple second electrodes22which are disposed at intervals from each other, and the second electrodes22are disposed along the first direction X. Along the first direction X, a certain distance exists between two adjacent second electrodes22. Along the first direction X, a second electric field TE2is formed between two closest second electrodes22which are located in two adjacent first grating units401respectively. The second electric field TE2is a transverse electric field. In the liquid crystal cell100, an alignment direction R2of the second alignment layer32is the same as an electric field direction of the second electric field TE2. In the embodiment of the present disclosure, the electric field direction of the second electric field TE2is the same as the alignment direction R2of the second alignment layer32. Therefore, the electric field direction affecting liquid crystal molecules close to the second alignment layer32is towards the alignment direction R2of the second alignment layer32, and will not be towards the direction opposite to the alignment direction of the second alignment layer32; the liquid crystal molecules close to the second alignment layer will not flip to an opposite direction, so that the adverse impact of the transverse electric field on the rotation of the liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.5andFIG.6, at least two first electrodes21exist and have different voltages, and a transverse electric field is generated between the first electrodes21. At least two second electrodes22exist and have different voltages, and a transverse electric field is generated between the second electrodes22. In this manner, transverse electric fields are distributed on first electrodes21and second electrodes22, that is, transverse electric fields are distributed on the first substrate11and the second substrate12, rather than concentrated on a single substrate (substrates include the first substrate11and the second substrate12), so that the intensity of the transverse electric field on a single substrate is reduced. Therefore, the adverse impact of the transverse electric field on the rotation of liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.5andFIG.6, in the same first grating unit401, at least two first electrodes21have different voltages, and at least two second electrodes22have different voltages. In the same first grating unit401, transverse electric fields are distributed on the first substrate11and the second substrate12, so that the adverse impact of the transverse electric field on the rotation of liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.1andFIG.2, a voltage of the first sub-first electrode211is +1V, a voltage of the second sub-first electrode212is +2V, a voltage of the third sub-first electrode213is +3V, and a voltage of the fourth sub-first electrode214is +4V. The voltage of the second electrode22is 0V. A voltage difference formed between the first sub-first electrode211and the second electrode22is 1V, a voltage difference formed between the second sub-first electrode212and the second electrode22is 2V, a voltage difference formed between the third sub-first electrode213and the second electrode22is 3V, and a voltage difference formed between the fourth sub-first electrode214and the second electrode22is 4V. A voltage difference formed between the fourth sub-first electrode214and a first sub-first electrode211in an adjacent grating unit40is 3V. The transverse electric field formed between the first electrodes21is relatively strong. When the alignment direction R1of the first alignment layer31is opposite to the electric field direction of the first electric field TE1, the higher the electric field intensity of the first electric field TE1is, the easier it is to cause liquid crystal molecules to fail to flip in conformity to the ideal situation; and the liquid crystal molecules rotate to a direction opposite to a pre-tilt angle, resulting in the problem of antiphase domains.

Exemplarily, referring toFIG.5andFIG.6, multiple second electrodes22include first sub-second electrodes221, second sub-second electrodes222, third sub-second electrodes223and fourth sub-second electrodes224. The voltage of the first sub-first electrode211is +0.5V, the voltage of the second sub-first electrode212is +1V, the voltage of the third sub-first electrode213is +1.5V, and the voltage of the fourth sub-first electrode214is +2V. A voltage of a first sub-second electrode221is −0.5V, a voltage of a second sub-second electrode222is −1V, a voltage of a third sub-second electrode223is −1.5V, and a voltage of a fourth sub-second electrode224is −2V. A voltage difference formed between the first sub-first electrode211and the first sub-second electrode221is 1V, a voltage difference formed between the second sub-first electrode212and the second sub-second electrode222is 2V, a voltage difference formed between the third sub-first electrode213and the third sub-second electrode223is 3V, and a voltage difference formed between the fourth sub-first electrode214and the fourth sub-second electrode224is 4V. The voltage difference formed between the fourth sub-first electrode214and the first sub-first electrode211in the adjacent grating unit40is 1.5V. A voltage difference formed between the fourth sub-second electrode224and a first sub-second electrode221in an adjacent grating unit is 1.5V. In this manner, the transverse electric field formed between first electrodes21is reduced; even the alignment direction R1of the first alignment layer31is opposite to the electric field direction of the first electric field TE1, the adverse impact of the transverse electric field on the rotation of liquid crystal molecules can be reduced, and thus the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.5andFIG.6, in various grating units40(including first grating units401), first electrodes21of the same ordinal number have the same voltage, and second electrodes22of the same ordinal number have the same voltage. Multiple first electrodes21in various grating units40have the same voltage distribution rule, and multiple second electrodes22in various gating units40have the same voltage distribution rule. Therefore, first electrodes21having the same voltage in multiple grating units40may be connected to the same power supply terminal, and second electrodes22having the same voltage in multiple grating units may be connected to the same power supply terminal, so that the number of power supply terminals is reduced. The ordinal number of a first electrode21or the ordinal number of a second electrode22in a grating unit40refers to the ranking of the first electrode21or the ranking of the second electrode22in the grating unit40. The voltage distribution rule of first electrodes21or the voltage distribution rule of second electrodes22refers to a distribution rule of voltages of multiple first electrodes21or a distribution rule of voltages of multiple second electrodes22along the first direction X.

Exemplarily, referring toFIG.5andFIG.6, grating units40include first grating sub-units41and second grating sub-units42. A first grating sub-unit41and a second grating sub-unit42each include four electrode groups50. Each of electrode groups50(including first electrode groups51) includes a first electrode21and a second electrode22. In a grating unit40, four first electrodes21are arranged in order, and four second electrodes22are arranged in order. The first first electrode21in a first grating subunit41has the same voltage as the first first electrode21in a second grating subunit42, and the second first electrode21in the first grating subunit41has the same voltage as the second first electrode21in the second grating subunit42. The first second electrode22in the first grating subunit41has the same voltage as the first second electrode22in the second grating subunit42, and the second second electrode22in the first grating subunit41has the same voltage as the second second electrode22in the second grating subunit42.

FIG.7is a diagram showing the three-dimensional structure of another liquid crystal grating according to an embodiment of the present disclosure,FIG.8is a sectional view of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.9is a diagram showing the operating process of a liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.7toFIG.9, the liquid crystal grating includes two liquid crystal cells100which are stacked. The two liquid crystal cells100are a first liquid crystal cell101and a second liquid crystal cell102respectively. In the first state ST1, the first liquid crystal cell101includes first grating units401, and any two first electrodes21in the second liquid crystal cell102have the same voltage. In the second liquid crystal cell102, voltage differences formed between any two first electrodes21and the second electrode22are the same, and electric field intensities of longitudinal electric fields formed between any two first electrodes21and the second electrode22are the same. Along the first direction X, intensities of longitudinal electric fields do not change. Due to the same intensity of longitudinal electric fields, liquid crystal molecules rotate by the same angle, no refractive index gradient is formed, and no grating having the diffraction function is formed. Therefore, the second liquid crystal cell102will not cause diffraction and deflection of light passing through the second liquid crystal cell102.

Exemplarily, referring toFIG.7toFIG.9, the two liquid crystal cells100are stacked along an optical axis of the liquid crystal grating, and light passes through the two liquid crystal cells100. That is, the same light passes through both the first liquid crystal cell101and the second liquid crystal cell102. The optical axis of the liquid crystal grating is perpendicular to the plane where the first substrate11is located. Dashed arrows inFIG.9represent the propagation direction of light. The vertically incident light, after passing through the first liquid crystal cell101and the second liquid crystal cell102, is deflected towards the right side. In the first state ST1, in the first liquid crystal cell101, the voltage of the first electrode21is a positive voltage, and the voltage of the second electrode22is 0V. A first longitudinal electric field VE1is formed between the first electrode21and the second electrode22, and a direction of the first longitudinal electric field VE1is the third direction Z, pointing from the first electrode21to the second electrode22. Along the first direction X, intensities of first longitudinal electric fields VE1gradually decrease. The first longitudinal electric fields VE1of different intensities cause liquid crystal molecules to rotate by different angles, so that a refractive index gradient is formed, and multiple first grating units401which are arranged along the first direction X are formed. The first grating units401form a grating having the diffraction and deflection function. In the embodiment of the present disclosure, the first liquid crystal cell101is configured for deflecting light. In the first liquid crystal cell101, the alignment direction R1of the first alignment layer31is the same as the electric field direction of the first electric field TEL The alignment direction of the first alignment layer31in the first liquid crystal101is denoted as a first alignment direction R11. In the first state ST1, in the first liquid crystal cell101, the first alignment direction R11is the same as the electric field direction of the first electric field TE1.

The voltage of all first electrodes21in the second liquid crystal cell102is 0V, the voltage of the second electrode22is 0V, and no longitudinal electric field is formed between the first electrodes21and the second electrode22. Along the first direction X, intensities of longitudinal electric fields do not change. In other implementations, the voltage of all electrodes21in the second liquid crystal cell102is 1V, the voltage of the second electrode22is 0V, and the voltage difference formed between the first electrodes21and the second electrode22is 1V. Along the first direction X, intensities of longitudinal electric fields do not change, so that no refractive index gradient is formed. In the first state ST1, the second liquid crystal cell102is not used for light deflection. In the second liquid crystal cell102, since all first electrodes21have the same voltage, no transverse electric field is generated between adjacent first electrodes21, so that the adverse impact of the transverse electric field on the rotation of liquid crystal molecules is avoided, and in the first state ST1, the problem of antiphase domains will not occur in the second liquid crystal cell102. In the second state, the first liquid crystal cell101is not used for light deflection, while the second liquid crystal cell102is used for light deflection, so that the function of light deflection is split by two liquid crystal cells100and performed in two states in a time-division manner, respectively, and in the liquid crystal cell100(including the first liquid crystal cell101in the first state and the second liquid crystal cell102in the second state) mainly for diffraction and deflection, the alignment direction R1of the first alignment layer31is the same as the electric field direction of the first electric field TEL Therefore, the adverse impact of the transverse electric field on the rotation of liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

FIG.10is a sectional view of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.11is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.10andFIG.11, in the second state ST2, the second liquid crystal cell102includes at least one second grating unit402. A second grating unit402includes multiple first electrodes21which are disposed at intervals from each other along the first direction. A voltage variation trend of the multiple first electrodes21of the second grating unit402in the second state ST2is opposite to a voltage variation trend of first electrodes21of the first grating unit401in the first state ST1. In the second state ST2, a third electric field TE3is formed between two closest first electrodes21which are located in two adjacent second grating units402, respectively. The third electric field TE3is a transverse electric field. In the second liquid crystal cell102, the alignment direction of the first alignment layer31is the same as an electric field direction of the third electric field TE3. In the embodiment of the present disclosure, in the second liquid crystal cell102, the electric field direction of the third electric field TE3is the same as the alignment direction of the first alignment layer31. Therefore, the electric field direction affecting liquid crystal molecules close to the first alignment layer31is towards the alignment direction of the first alignment layer31, and will not be towards the direction opposite to the alignment direction of the first alignment layer31; the liquid crystal molecules close to the first alignment layer31will not flip to an opposite direction, so that the adverse impact of the transverse electric field on the rotation of the liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.10andFIG.11, in the second state ST2, in the second liquid crystal cell102, a second longitudinal electric field VE2is formed between a first electrode21and the second electrode22. A direction of the second longitudinal electric field VE2is the third direction Z pointing from the first electrode21to the second electrode22. Along the first direction X, intensities of second longitudinal electric fields VE2gradually increase. The second longitudinal electric fields VE2of different intensities cause liquid crystal molecules to rotate by different angles, so that a refractive index gradient is formed, and multiple second grating units402which are arranged along the first direction X are formed. The second grating units402form a grating having the diffraction and deflection function. In the embodiment of the present disclosure, the second liquid crystal cell102is used for deflecting light. In the second liquid crystal cell102, the alignment direction R1of the first alignment layer31is the same as the electric field direction of the first electric field TE1. The alignment direction of the first alignment layer31in the second liquid crystal102is denoted as a second alignment direction R21. In the second state ST2, in the second liquid crystal cell102, the second alignment direction R21is the same as the electric field direction of the third electric field TE3.

In the second state ST2, any two first electrodes21in the first liquid crystal cell101have the same voltage. In the first liquid crystal cell101, voltage differences formed between any two first electrodes21and the second electrode22are the same, and electric field intensities of longitudinal electric fields formed between any two first electrodes21and the second electrode22are the same. Along the first direction X, intensities of longitudinal electric fields do not change. Due to the same intensity of longitudinal electric fields, liquid crystal molecules rotate by the same angle, no refractive index gradient is formed, and no grating having the diffraction function is formed. Therefore, in the second state ST2, the first liquid crystal cell101will not cause diffraction and deflection of light passing through the first liquid crystal cell101. In the first liquid crystal cell101, since all first electrodes21have the same voltage, no transverse electric field is generated between adjacent first electrodes21, so that the adverse impact of the transverse electric field on the rotation of liquid crystal molecules is avoided, and in the second state ST2, the problem of antiphase domains will not occur in the first liquid crystal cell101. The function of setting the first liquid crystal cell101and the second liquid crystal cell102is not repeated here, and reference may be made to the description of the embodiments related toFIG.7toFIG.9.

Through the preceding embodiments, the liquid crystal grating can provide images to the left eye and the right eye separately, while the problem of antiphase domains is avoided; at the same time, the refresh frequency of a liquid crystal cell can be reduced and thus power consumption can be reduced.

Exemplarily, referring toFIG.7toFIG.11, along the same first direction X, in the first state ST1, the voltage variation trend of first electrodes21in the first grating unit401is gradual decrease. In the second state ST2, the voltage variation trend of first electrodes21in the second grating unit402is gradual increase.

FIG.12is a sectional view of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.13is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.12andFIG.13, the liquid crystal grating includes two liquid crystal cells100which are stacked, and the two liquid crystal cells100are a first liquid crystal cell101and a second liquid crystal cell102respectively. In the first state ST1, the first liquid crystal cell101includes first grating units401, and the second liquid crystal cell102includes at least one third grating unit403. A third grating unit403includes multiple first electrodes21which are disposed at intervals from each other along the first direction X. Referring toFIG.12andFIG.13, along the first direction X, a fourth electric field TE4is formed between two adjacent first electrodes21which are located in the same third grating unit403, and an electric field direction of the fourth electric field TE4is opposite to the electric field direction of the first electric field TEL In the embodiment of the present disclosure, in the first state ST1, along the first direction X, a voltage variation trend of first electrodes21in a first grating unit401is the same as a voltage variation trend of first electrodes21in a third grating unit403. The first liquid crystal cell101and the second liquid crystal cell102are both used for deflecting light to the first side of the optical axis of the liquid crystal grating. In the first state ST1, the first liquid crystal cell101is configured for light diffraction and deflection, and the second liquid crystal cell102assists in light deflection. The first liquid crystal cell101roughly deflects light to a preset position or by a preset angle as soon as possible, and the second liquid crystal cell102subtly corrects the deflection angle so that light is deflected to the preset position or by the preset angle.

Optionally, referring toFIG.12andFIG.13, along the first direction X, a fifth electric field TE5is formed between two closest first electrodes21which are located in two adjacent third grating units403respectively. The fifth electric field TE5is a transverse electric field. In the second liquid crystal cell102, the alignment direction R1(that is, the second alignment direction R21) of the first alignment layer31is opposite to an electric field direction of the fifth electric field TE5. An absolute value of the fifth electric field TE5is smaller than an absolute value of the first electric field TEL In the embodiment of the present disclosure, on the one hand, in the first state ST1, the second liquid crystal cell102assists in light deflection, and the second liquid crystal cell102and the first liquid crystal cell101causes the same light deflection direction. On the other hand, the electric field intensity of the fifth electric field TE5is relatively low; even if the second alignment direction R21is opposite to the electric field direction of the fifth electric field TE5, the intensity of the fifth electric field TE5is lower than the intensity of a transverse threshold electric field which will cause liquid crystal molecules to flip to an opposite direction, and the value of the fifth electric field TE5is smaller than the value of the transverse electric field when bubble domains are generated; therefore, in the second liquid crystal cell102, liquid crystal molecules close to the first alignment layer31will not flip to an opposite direction, so that the adverse impact of the transverse electric field on the rotation of the liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

Optionally, referring toFIG.12andFIG.13, the same third grating unit403includes multiple second electrode groups52which are arranged along the first direction X. A second electrode52includes at least one first electrode21and at least one second electrode22. In the same second electrode group52, the first electrode21at least partially overlaps the second electrode22. The first electrode21overlaps the second electrode22, or the first electrode21partially overlaps the second electrode22. A voltage difference formed between the first electrode21and the second electrode22is a second voltage difference, and a sixth electric field VE6is formed between the first electrode21and the second electrode22. The sixth electric field VE6is a longitudinal electric field. The absolute value of the fifth electric field TE5is smaller than an absolute value of a maximum value of the sixth electric field TE6. The second voltage difference is a difference between the voltage of the first electrode21and the voltage of the second electrode22in the third grating unit403, that is, the second voltage difference is the voltage of the first electrode21minus the voltage of the second electrode22. It is to be understood that along the first direction X, the distance between two adjacent first electrodes21is relatively small, so that an electric field of a higher intensity is easy to generate under a given voltage difference (such as 1V). Along the third direction Z, since a certain cell thickness needs to be kept for the liquid crystal layer30, the distance between the first electrode21and the second electrode22is relatively large, so that an electric field of a lower intensity is easy to generate under a given voltage difference (such as 1V). In the embodiment of the present disclosure, the absolute value of the fifth electric field TE5is smaller than the absolute value of the maximum value of the sixth electric field VE6, and the electric field intensity of the fifth electric field TE5is much lower than the electric field intensity of the first electric field TEL Even if the second alignment direction R21is opposite to the electric field direction of the fifth electric field TE5, the problem of antiphase domains will not occur in the second liquid crystal cell102.

Optionally, referring toFIG.12andFIG.13, the liquid crystal layer30includes liquid crystal molecules. The absolute value of the maximum value of the sixth electric field VE6is smaller than a threshold electric field value for driving the liquid crystal molecules to rotate. The absolute value of the maximum value of the sixth electric field VE6is smaller than a value of a longitudinal electric field when bubble domains are generated. In the second liquid crystal cell102, liquid crystal molecules close to the first alignment layer31will not flip to an opposite direction, so that the adverse impact of the transverse electric field on the rotation of the liquid crystal molecules is reduced and the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.12andFIG.13, in the first state ST1, in the second liquid crystal cell102, the voltage of the second electrode22is a common voltage. The voltage of the second electrode22may be, for example, a ground voltage or 0V, so that voltages of a positive frame and a negative frame may be exactly symmetrical. When the voltage of the second electrode22is 0V, the absolute value of the sixth electric field VE6is in direct proportion to the absolute value of the voltage of the second electrode22. The larger the absolute value of the sixth electric field VE6, the larger the absolute value of the voltage of the second electrode22; the smaller the absolute value of the sixth electric field VE6, the smaller the absolute value of the voltage of the second electrode22. When the voltage of the second electrode22is 0V and the voltage of the sixth electric field VE6is a non-negative voltage (including 0V and a positive voltage), the voltage of the first electrode21(that is, the first sub-first electrode211inFIG.12) corresponding to the maximum value of the sixth electric field VE6is denoted as V1. The voltage difference between the first sub-first electrode211and the second electrode22satisfies that V1−0=V1. The voltage of the first electrode21(that is, the fourth sub-first electrode214inFIG.12) corresponding to the minimum value of the sixth electric field VE6is denoted as V2, and V2=V. The voltage difference between the fourth sub-first electrode214and the second electrode22satisfies that V2−0=V2=0V. A transverse voltage difference corresponding to the fifth electric field TE5satisfies that V1−V2=V1−0=V1.

Optionally, referring toFIG.12andFIG.13, the number of first electrodes21in a first grating unit401is the same as the number of first electrodes21in a third grating unit403. In the two liquid crystal cells100, the division of the first grating unit401and the third grating unit403remains unchanged, so that antiphase domains are avoided, and at the same time, the two liquid crystal cells100assist each other in deflecting light, reducing the burden on a single liquid crystal cell100; moreover, the two liquid crystal cells100may use two circuits having the same function, so that the difficulty of circuit design is reduced.

Exemplarily, referring toFIG.12andFIG.13, the number of first grating units401is the same as the number of third grating units403. First electrodes21having the same voltage in multiple first grating units401may be connected to the same power supply terminal, and second electrodes22having the same voltage in multiple third grating units403may be connected to the same power supply terminal, so that the number of power supply terminals is reduced.

In other implementations, the sixth electric field VE6may also not drive liquid crystal molecules to rotate, so that no refractive index gradient is formed, and no grating having the diffraction function is formed. The second liquid crystal cell102may not cause diffraction and deflection of light passing through the second liquid crystal cell102.

It is to be noted that in the embodiment,FIG.12andFIG.13represent current states of the two liquid crystal cells100in the same frame, that is, states of the two liquid crystal cells100when an image is provided to one eye, that is, states of the two liquid crystal cells100in the same frame. At this time, the first liquid crystal cell101is configured for light deflection. Of course, in some embodiments of the present disclosure, when another frame of image is displayed, the liquid crystal grating is used for providing the image to the other eye. At this time, states of the two liquid crystal cells100are swapped, that is, the second liquid crystal cell102is configured for light deflection. At this time, the second liquid crystal cell102needs to be set by referring to the preceding requirements for the first liquid crystal cell101, and the first liquid crystal cell101needs to be set by referring to the requirements for the second liquid crystal cell102in the preceding embodiment. In addition, the voltage variation trend of first electrodes21in the same grating unit40in the first liquid crystal cell101and the voltage variation trend of first electrodes21in the same grating unit40in the second liquid crystal cell102are gradual increase along the first direction X.

FIG.14is a sectional view of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.15is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.14andFIG.15, the number of first grating units401in the first liquid crystal cell101is larger than the number of third grating units403in the second liquid crystal cell102. Along the first direction X, a change period of the first longitudinal electric field VE1is smaller than a change period of the sixth electric field VE6. The sixth electric field VE6changes slowly, resulting in a smaller number of fifth electric fields TE5, so that the adverse impact of the fifth electric field TE5on the rotation of liquid crystal molecules is reduced, and the problem of antiphase domains is alleviated.

Exemplarily, referring toFIG.14andFIG.15, the number of first electrodes21in a first grating unit401is smaller than the number of first electrodes21in a third grating unit403. The number of first grating units401in the first liquid crystal cell101is L times the number of third grating units403in the second liquid crystal cell102, where L is a positive integer greater than 1.

FIG.16is a sectional view of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.17is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.16andFIG.17, in the first state ST1, the first liquid crystal cell101includes multiple first grating units401, and the second liquid crystal cell102includes a third grating unit403. In the third grating unit403, voltages from the first first electrode21to the last first electrode21gradually increase or gradually decrease. In the embodiment of the present disclosure, since only one third grating unit403exists, no fifth electric field TE5is generated, so that the adverse impact of the fifth electric field TE5on the rotation of liquid crystal molecules is reduced, and the problem of antiphase domains in the second liquid crystal cell is avoided.

That is, only one third grating unit403exists in the second liquid crystal cell102, that is, all first electrodes21in the second liquid crystal cell102form a grating unit40. Along the first direction X, the voltage variation trend of all the first electrodes21in the second liquid crystal cell102is a gradual change.

In this design, the excessive transverse electric field between two grating units40in the second liquid crystal cell102is directly avoided, so that the second liquid crystal cell102is used for assisting the first liquid crystal cell101in light deflection, and the occurrence of antiphase domains in the second liquid crystal cell102is avoided.

FIG.18is a sectional view of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.19is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.18andFIG.19, the liquid crystal grating includes two liquid crystal cells100which are stacked, and the two liquid crystal cells100are a first liquid crystal cell101and a second liquid crystal cell102respectively. In the first state ST1, the first liquid crystal cell101includes first grating units401, and the second liquid crystal cell102includes at least one third grating unit403. A third grating unit403includes multiple first electrodes21which are disposed at intervals from each other along the first direction X. Along the first direction X, a fifth electric field TE5is formed between two closest first electrodes21which are located in two adjacent third grating units403respectively. In the second liquid crystal cell102, the alignment direction R1(that is, the second alignment direction R21) of the first alignment layer31is opposite to the electric field direction of the fifth electric field TE5. The second alignment direction R21is the same as the electric field direction of the fifth electric field TE5. In the second liquid crystal cell102, the electric field direction affecting liquid crystal molecules close to the first alignment layer31is towards the second alignment direction R21, so that the liquid crystal molecules close to the first alignment layer31do not flip to an opposite direction. In the embodiment of the present disclosure, in the first state ST1, along the first direction X, the voltage variation trend of first electrodes21in the first grating unit401is opposite to the voltage variation trend of first electrodes21in a third grating unit403. The first liquid crystal cell101is used for deflecting light towards the first side of the optical axis of the liquid crystal grating, and the second liquid crystal cell102is used for deflecting light towards the second side of the optical axis of the liquid crystal grating. In the first state ST1, the first liquid crystal cell101is mainly configured for light diffraction and deflection, and the second liquid crystal cell102assists in light deflection.

Optionally, referring toFIG.18andFIG.19, the alignment direction R1of the first alignment layer31in the first liquid crystal cell101is different from the alignment direction R1of the first alignment layer31in the second liquid crystal cell102, that is, the first alignment direction R11is different from the second alignment direction R21. In the first state ST1, the electric field direction of the first electric field TE1is opposite to the electric field direction of the fifth electric field TE5. In the first state ST1, the voltage of a first electrode21in the first liquid crystal cell101and the voltage of a first electrode21in the second liquid crystal cell102have opposite polarities. The direction of the first longitudinal electric field VE1is the third direction Z, in the first liquid crystal cell101, pointing from the first electrode21to the second electrode22. Along the first direction X, intensities of first longitudinal electric fields VE1gradually decrease. The first longitudinal electric fields VE1of different intensities cause liquid crystal molecules to rotate by different angles, so that a refractive index gradient is formed. In the embodiment of the present disclosure, the first liquid crystal cell101is mainly configured for deflecting light. The direction of the sixth electric field VE6is the opposite direction of the third direction Z, in the first liquid crystal cell102, pointing from the second electrode22to the first electrode21. Along the first direction X, intensities of sixth longitudinal electric fields VE6gradually decrease. The sixth longitudinal electric fields VE6of different intensities cause liquid crystal molecules to rotate by different angles, so that a refractive index gradient is formed. In the embodiment of the present disclosure, the second liquid crystal cell102assists in deflecting light. In the embodiment of the present disclosure, in the first liquid crystal cell101, the electric field direction of the first electric field TE1is the same as the first alignment direction R11, so that the problem of antiphase domains will not occur in the first liquid crystal cell101. In the second liquid crystal cell102, the electric field direction of the fifth electric field TE5is the same as the second alignment direction R21, so that the problem of antiphase domains will not occur in the second liquid crystal cell102.

Exemplarily, referring toFIG.18andFIG.19, the first alignment direction R11is opposite to the second alignment direction R21, the electric field direction of the fourth electric field TE4is opposite to the electric field direction of the first electric field TE1, and the electric field direction of the first longitudinal electric field VE1is opposite to the electric field direction of the sixth electric field VE6. In the first state ST1, along the first direction X, the voltage variation trend of the first electrodes21in the first grating unit401is the same as the voltage variation trend of the first electrodes21in the third grating unit403. The first liquid crystal cell101and the second liquid crystal cell102are both used for deflecting light to the first side of the optical axis of the liquid crystal grating.

In the first state ST1, the voltage of the first electrode21in the first grating unit401may be a positive voltage or a negative voltage. A detailed explanation is provided below. The first state ST1represents current states of the two liquid crystal cells100in the same frame F (for example, in a first frame F1). In the first state ST1, the first liquid crystal cell101is configured for deflecting light, while the second liquid crystal cell102is not used for or assists in deflecting light. The second state ST2represents current states of the two liquid crystal cells100in the same frame F (for example, in a second frame F2). In the second state ST2, the second liquid crystal cell102is configured for deflecting light, while the first liquid crystal cell101is not used for or assists in deflecting light.

Exemplarily, referring toFIG.8andFIG.9, in the first state ST1, along the first direction X, voltages of first electrodes21in the first grating unit401gradually decrease, and the voltages of the first electrodes21in the first grating unit401are positive voltages.

FIG.20is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.8andFIG.20, in the first state ST1, along the first direction X, the voltages of the first electrodes21in the first grating unit401gradually decrease, and the voltages of the first electrodes21in the first grating unit401are negative voltages. The electric direction of the first electric field TE1is the same as the first alignment direction R11, so that the problem of antiphase domains will not occur in the first liquid crystal cell101.

In addition to containing liquid crystal molecules, the liquid crystal layer30also includes impurities, which will move towards the first electrode21or the second electrode22under the action of an electric field. Therefore, when the same liquid crystal cell100operates in a manner of positive-negative frame transformation, the direction of a longitudinal electric field formed by the positive frames may be opposite to the direction of a longitudinal electric field formed by the negative frames, so that in the positive frames, the impurities move towards the first electrode21, and in the negative frames, the impurities move towards the second electrode22; or in the positive frames, the impurities move towards the second electrode22, and in the negative frames, the impurities move towards the first electrode21; in this manner, the impurities are prevented from accumulating on one side. A detailed explanation of the first liquid crystal cell101working in a positive frame and a negative frame is provided below.

Exemplarily, referring toFIG.9, in the first liquid crystal cell101, the impurities in the liquid crystal layer30move towards the second electrode22side driven by the longitudinal electric field towards the third direction Z. Referring toFIG.20, in the first liquid crystal cell101, the impurities in the liquid crystal layer30move towards the first electrode21side driven by the longitudinal electric field towards the opposite direction of the third direction Z. The operating time of the liquid crystal grating includes multiple frames, and in different frames, the longitudinal electric field in the first liquid crystal cell101may be alternately towards the third direction Z and the opposite direction of the third direction Z so that the impurities are prevented from accumulating on one side.

In the second state ST2, the voltage of the first electrode21in the second grating unit402may be a positive voltage or a negative voltage. A detailed explanation is provided below.

Exemplarily, referring toFIG.10andFIG.11, in the second state ST2, along the first direction X, voltages of first electrodes21in the second grating unit402gradually increase, and the voltages of the first electrodes21in the second grating unit402are positive voltages.

FIG.21is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.10andFIG.21, in the second state ST2, along the first direction X, the voltages of the first electrodes21in the first grating unit402gradually increase, and the voltages of the first electrodes21in the second grating unit402are negative voltages. The electric direction of the third electric field TE3is the same as the second alignment direction R21, so that the problem of antiphase domains will not occur in the second liquid crystal cell102.

A detailed explanation of the second liquid crystal cell102working in a positive frame and a negative frame is provided below. Exemplarily, referring toFIG.11, in the second liquid crystal cell102, the impurities in the liquid crystal layer30move towards the second electrode22side driven by the longitudinal electric field towards the third direction Z. Referring toFIG.21, in the second liquid crystal cell102, the impurities in the liquid crystal layer30move towards the first electrode21side driven by the longitudinal electric field towards the opposite direction of the third direction Z. The operating time of the liquid crystal grating includes multiple frames, and in different frames, the longitudinal electric field in the second liquid crystal cell102may be alternately towards the third direction Z and the opposite direction of the third direction Z so that the impurities are prevented from accumulating on one side.

In the preceding embodiments, the first alignment direction R11is different from the second alignment direction R21. In other implementations, the first alignment direction R11may be the same as the second alignment direction R21.

FIG.22is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.22, the first alignment direction R11is the same as the second alignment direction R21. The electric field direction of the first longitudinal electric field VE1is the opposite direction of the third direction Z. In the first state ST1, along the first direction X, voltages of first electrodes21in the first grating unit401gradually increase, and the voltages of the first electrodes21in the first grating unit401are negative voltages. The electric direction of the first electric field TE1is the same as the first alignment direction R11, so that the problem of antiphase domains will not occur in the first liquid crystal cell101.

FIG.23is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.23, the first alignment direction R11is the same as the second alignment direction R21. The electric field direction of the second longitudinal electric field VE2is the opposite direction of the third direction Z. In the second state ST2, along the first direction X, voltages of first electrodes21in the second grating unit402gradually increase, and the voltages of the first electrodes21in the second grating unit402are negative voltages. The electric direction of the third electric field TE3is the same as the second alignment direction R21, so that the problem of antiphase domains will not occur in the second liquid crystal cell102.

In an implementation, the liquid crystal cell100may include multiple first electrodes21and multiple second electrodes22. A detailed explanation based on the alignment direction and the electric field direction in the liquid crystal cell100of this structure is provided below.

FIG.24is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.5andFIG.24, in the first state ST1, in the first liquid crystal cell101, the first alignment direction R11is the same as the electric direction of the first electric field TE1, so that liquid crystal molecules close to the first alignment layer31will not flip to an opposite direction. The alignment direction of the second alignment layer32in the first liquid crystal101is denoted as a third alignment direction R12. In the first state ST1, in the first liquid crystal cell101, the third alignment direction R12is the same as the electric field direction of the second electric field TE2, so that liquid crystal molecules close to the second alignment layer32will not flip to an opposite direction. The first alignment direction R11is opposite to the third alignment direction R12.

FIG.25is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.5andFIG.25, in the second state ST2, in the second liquid crystal cell102, the second alignment direction R21is the same as the electric direction of the third electric field TE3, so that liquid crystal molecules close to the first alignment layer31will not flip to an opposite direction. The alignment direction of the second alignment layer32in the second liquid crystal102is denoted as a fourth alignment direction R22. In the second state ST2, in the second liquid crystal cell102, the fourth alignment direction R22is the same as an electric field direction of a seventh electric field TE7, so that liquid crystal molecules close to the second alignment layer32will not flip to an opposite direction. The second alignment direction R21is opposite to the fourth alignment direction R22. In the second liquid crystal cell102, in the second state ST2, along the first direction X, the seventh electric field TE7is formed between two closest second electrodes22which are located in two adjacent grating units40respectively. The seventh electric field TE7is a transverse electric field.

FIG.26is a timing graph showing the operations of a liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.7toFIG.11andFIG.26, the liquid crystal grating includes two liquid crystal cells100which are stacked. The operating time of the liquid crystal grating includes multiple frames F. In the same frame F, one of the two liquid crystal cells100is configured for light diffraction and deflection, and the other one of the two liquid crystal cells100is not configured for or assists in light diffraction and deflection. The deflection angle of light is mainly determined by one of the two liquid crystal cells100.

Exemplarily, referring toFIG.26, a frame F refers to a time period during which light of a color illuminates an eye of the observer. For a scheme using three primary colors, that is, red, green and blue (RGB), for color display, a complete image during stereoscopic display requires six frames. These six frames are a left-eye green frame LG, a left-eye blue frame LB, a left-eye red frame LR, a right-eye green frame RG, a right-eye blue frame RB and a right-eye red frame RR, respectively. Dashed boxes inFIG.26indicate that the liquid crystal cell is not used for or assists in light deflection. For example, in the left-eye green frame LG, the first liquid crystal cell101is mainly configured for diffracting and deflecting light to the left eye of the observer, and the second liquid crystal cell102is not used for or assists in light deflection. In the right-eye green frame RG, the first liquid crystal cell101is not used for or assists in light deflection, and the second liquid crystal cell102is mainly configured for diffracting and deflecting light to the right eye of the observer.

Optionally, referring toFIG.7toFIG.11andFIG.26, the two liquid crystal cells100are the first liquid crystal cell101and the second liquid crystal cell102respectively. The multiple frames F include first frames F1and second frames F2, and the second frames F2are placed after the first frames F1. In the first frames F1, the first liquid crystal cell101operates in the first state ST1and is configured mainly to diffract and deflect light towards the first side of the optical axis of the liquid crystal grating. In the second frames F2, the second liquid crystal cell102operates in the second state ST2and is configured mainly to diffract and deflect light towards the second side of the optical axis of the liquid crystal grating, where the first side and the second side are located at two opposite sides of the optical axis of the liquid crystal grating. The optical axis of the liquid crystal grating is perpendicular to the plane where the first substrate11is located.

Exemplarily, referring toFIG.7toFIG.9andFIG.26, in the first frames F1, the first liquid crystal cell101operates in the first state ST1, and the first liquid crystal cell101is configured mainly to diffract and deflect light towards the first side of the optical axis of the liquid crystal grating. The first side of the optical axis of the liquid crystal grating is the right side of the optical axis of the liquid crystal grating. For the observer facing the direction of light propagation, green light (green light is used for illustration but is not limiting) is deflected into the left eye of the observer.

Exemplarily, referring toFIG.10,FIG.11andFIG.26, in the second frames F2, the second liquid crystal cell102operates in the second state ST2, and the second liquid crystal cell102is configured mainly to diffract and deflect light towards the second side of the optical axis of the liquid crystal grating. The second side of the optical axis of the liquid crystal grating is the left side of the optical axis of the liquid crystal grating. For the observer facing the direction of light propagation, green light (green light is used for illustration but is not limiting) is deflected into the right eye of the observer.

Optionally, referring toFIG.7toFIG.11andFIG.26, in the first frames F1, in the same first grating unit401of the first liquid crystal cell101, voltages of various first electrodes21gradually decrease along the first direction. The first liquid crystal cell101is configured mainly to diffract and deflect light towards the first side of the optical axis of the liquid crystal grating. In the second frames F2, in the same second grating unit402of the second liquid crystal cell102, voltages of various first electrodes21gradually increase along the first direction X. The second liquid crystal cell102is configured mainly to diffract and deflect light towards the second side of the optical axis of the liquid crystal grating.

Optionally, referring toFIG.7toFIG.11andFIG.26, the voltages of the first electrodes21in the first liquid crystal cell101in the first frames F1have the same polarity as the voltages of the first electrodes21in the second liquid crystal cell102in the second frames F2. In an example, the voltages of the first electrodes21in the first liquid crystal cell101in the first frames F1are positive voltages, and the voltages of the first electrodes21in the second liquid crystal cell102in the second frames F2are negative voltages.

Optionally, referring toFIG.7toFIG.11, an extension direction of the first electrodes21in the first liquid crystal cell101is the same as an extension direction of the first electrodes21in the second liquid crystal cell102. The first electrodes21in the first liquid crystal cell101are set to be parallel to the first electrodes21in the second liquid crystal cell102. The first electrodes21in the first liquid crystal cell101and the first electrodes21in the second liquid crystal cell102are all extend along a second direction Y. The first liquid crystal cell101and the second liquid crystal cell102form a liquid crystal grating.

It is to be noted that in addition to the use of two liquid crystal cells100to form a liquid crystal grating in the preceding embodiments, in other implementations, one liquid crystal cell100may also be used for forming a liquid crystal grating. When one liquid crystal cell100is used for forming a liquid crystal grating, the voltage variation trend of first electrodes21needs to be controlled so that the direction of the first electric field TE1is the same as the alignment direction of the first alignment layer31.

FIG.27is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure, andFIG.28is a diagram showing the operating process of another liquid crystal grating according to an embodiment of the present disclosure. Referring toFIG.3,FIG.27andFIG.28, two first states ST1includes a first sub-state ST11and a second sub-state ST12. That is, two first states ST1are a first sub-state ST11and a second sub-state ST12respectively. The first sub-state ST11represents the current state of a single liquid crystal cell100in the frame F (for example, in a first frame F1). In the first sub-state ST11, the liquid crystal cell100diffracts and deflects light towards the first side of the optical axis of the liquid crystal grating. The second sub-state ST12represents the current state of a single liquid crystal cell100in the same frame F (for example, in a second frame F2). In the second sub-state ST12, the liquid crystal cell100diffracts and deflects light towards the second side of the optical axis of the liquid crystal grating. In the same liquid crystal cell100, the polarity of voltages of first electrodes21in the first sub-state ST11is opposite to the polarity of the voltages of the first electrodes21in the second sub-state ST12. In the same liquid crystal cell100, the electric field direction of the first electric field TE1in the first sub-state ST11is the same as the electric field direction of the first electric field TE1in the second sub-state ST12. In the first sub-state ST11and the second sub-state ST12, the direction of the first electric field TE1is the same as the alignment direction of the first alignment layer31, so that liquid crystal molecules close to the first alignment layer31do not flip to an opposite direction, the adverse impact of the transverse electric field on the rotation of liquid crystal molecules is reduced, and the problem of antiphase domains is alleviated. In the embodiment of the present disclosure, in a single liquid crystal cell100, light deflection in two directions is achieved through positive-negative voltage switching, and the direction of the first electric field TE1is the same as the alignment direction of the first alignment layer31in two types of frames, so that liquid crystal molecules close to the first alignment layer31do not flip to an opposite direction, the adverse impact of the transverse electric field on the rotation of liquid crystal molecules is reduced, and the problem of antiphase domains is alleviated. The polarity of voltages of first electrodes21in the first sub-state ST11is opposite to the polarity of the voltages of the first electrodes21in the second sub-state ST12. Therefore, when the same liquid crystal cell100operates in a manner of positive-negative frame transformation, the direction of a longitudinal electric field formed in the positive frames may be opposite to the direction of a longitudinal electric field formed in the negative frames, so that in the positive frames, the impurities move towards the first electrode21, and in the negative frames, the impurities move towards the second electrode22; or in the positive frames, the impurities move towards the second electrode22, and in the negative frames, the impurities move towards the first electrode21; in this manner, the impurities are prevented from accumulating on one side. It is to be noted that in the embodiment of the present disclosure, the liquid crystal grating includes only one liquid crystal cell100, so that the thickness of the liquid crystal grating is reduced, light transmittance is improved, and costs of the liquid crystal grating are reduced.

Exemplarily, referring toFIG.3andFIG.27, in the first sub-state ST11, voltages of first electrodes21are positive voltages. In the same first grating unit401, the voltages of the first electrodes21gradually decrease along the first direction X. The liquid crystal cell100is configured to diffract and deflect light towards the first side of the optical axis of the liquid crystal grating. The first side of the optical axis of the liquid crystal grating is the right side of the optical axis of the liquid crystal grating. For the observer facing the direction of light propagation, the light is deflected into and enters the left eye of the observer.

Exemplarily, referring toFIG.3andFIG.28, in the second sub-state ST12, the voltages of the first electrodes21are negative voltages. In the same first grating unit401, the voltages of the first electrodes21gradually decrease along the first direction X. The liquid crystal cell100is configured to diffract and deflect light towards the second side of the optical axis of the liquid crystal grating. The second side of the optical axis of the liquid crystal grating is the left side of the optical axis of the liquid crystal grating. For the observer facing the direction of light propagation, the light is deflected into and enters the right eye of the observer.

FIG.29is a diagram of a stereoscopic display device according to an embodiment of the present disclosure. Referring toFIG.29, the stereoscopic display device includes a light source61, a spatial light modulator62and a gating component64which are disposed sequentially. The gating component64includes at least one liquid crystal grating in the preceding embodiments.

Exemplarily, referring toFIG.29, the light source61is used for emitting coherent backlight of three colors, that is, red light, green light and blue light, in a timing sequence. The spatial light modulator62includes a first spatial light modulator621for phase modulation and a second spatial light modulator622for amplitude modulation. The stereoscopic display device further includes a field lens63, which is located between the spatial light modulator62and the grating component64. The field lens63is at least used for improving the capability of edge light of light emitted by the spatial light modulator62of being incident into the grating component64. The grating component64is used for forming left-eye images and right-eye images based on the incident light.

Exemplarily, referring toFIG.29, the grating component64includes three liquid crystal gratings. The three liquid crystal gratings are a first liquid crystal grating641, a second liquid crystal grating642and a third liquid crystal grating643respectively. Any two of first electrodes21of the first liquid crystal grating641, first electrodes21of the second liquid crystal grating642and first electrodes21of the third liquid crystal grating643may have different extension directions. In other implementations, the grating component64may also include liquid crystal gratings of other numbers.

FIG.30is a diagram showing the structure of region S2inFIG.29. Referring toFIG.3,FIG.29andFIG.30, the first substrate11is located between the second substrate12and the spatial light modulator62in the same liquid crystal cell100. The first electrodes21are located between the second electrode22and the spatial light modulator62in the same liquid crystal cell100. In other implementations, the position of the first electrodes21and the position of the second electrode22may also be swapped, that is, the second substrate12is located between the first substrate11and the spatial light modulator62in the same liquid crystal cell100. The second electrode22is located between the first electrodes21and the spatial light modulator62in the same liquid crystal cell100. After the position of the first electrodes21and the position of the second electrode22are swapped, the propagation path and the deflection direction of light are not affected compared with before position swapping.

It is to be noted that the preceding are only preferred embodiments of the present disclosure and technical principles used therein. It is to be understood by those skilled in the art that the present disclosure is not limited to the embodiments described herein. Those skilled in the art can make various apparent modifications, adaptations, combinations and substitutions without departing from the scope of the present disclosure. Therefore, while the present disclosure has been described in detail through the preceding embodiments, the present disclosure is not limited to the preceding embodiments and may include more other equivalent embodiments without departing from the concept of the present disclosure. The scope of the present disclosure is determined by the scope of the appended claims.