Projection device and head-up display system

Abstract

The invention discloses a projection device and a head-up display system, image sources in the projection device comprise a first image source, a second image source and a third image source, and liquid crystal gratings comprise three liquid crystal gratings which are respectively arranged at a first input end, a second input end and a third input end of a beam combiner; a first color light beam emitted by the first image source enters the first liquid crystal grating, and enters the beam combiner after the transmission direction of the first color light beam is modulated by the first liquid crystal grating; a second color light beam emitted by the second image source enters the second liquid crystal grating, and enters the beam combiner after the transmission direction of the second color light beam is modulated by the second liquid crystal grating; a third color light beam emitted by a third image source enters a third liquid crystal grating, and enters the beam combiner after the transmission direction is modulated by the third liquid crystal grating, that is, light deflection can be realized by modulation of the three different color light beams by the corresponding liquid crystal gratings, so that a color image formed by the beam combiner enters human eyes; the projection device is simple in structure, low in cost and high in reliability.

Description

Technical Field

[0001] The present invention relates to the field of display technology, and in particular to a projection device and a head-up display system. Background Art

[0002] Head-Up Display (HUD) is a transparent display technology that projects key driving information in front of the driver's line of sight. This information can include vehicle speed, navigation instructions, and warning signals. With HUD, the driver can quickly obtain the required information without having to look down at the dashboard. The working principle of HUD is mainly to project image information onto a translucent reflector (such as a windshield) through a projector, and the reflector then reflects the image into the driver's line of sight. In this way, the driver can see the required driving information while keeping his line of sight unchanged.

[0003] At present, in the image source of the HUD system, different color light beams are each controlled by a display panel, and the viewing angle can only be controlled by mechanical rotation. Finally, they are combined into the required color image through a beam splitter prism. Such a structure is complex, costly and has poor reliability. Summary of the invention

[0004] The present invention provides a projection device and a head-up display system. By setting a liquid crystal grating, light beams of different colors emitted by an image source can be modulated to achieve light beam deflection. The projection device has a simple structure, low cost and high reliability.

[0005] In a first aspect, an embodiment of the present invention provides a projection device, including an image source, a liquid crystal grating and a beam combiner, wherein the image source includes a first image source, a second image source and a third image source, and the liquid crystal grating includes a first liquid crystal grating, a second liquid crystal grating and a third liquid crystal grating respectively arranged at a first input end, a second input end and a third input end of the beam combiner;

[0006] The first color light beam emitted by the first image source is incident on the first liquid crystal grating, and is incident on the beam combining mirror after the transmission direction is modulated by the first liquid crystal grating;

[0007] The second color light beam emitted by the second image source is incident on the second liquid crystal grating, and is incident on the beam combining mirror after the transmission direction is modulated by the second liquid crystal grating;

[0008] The third color light beam emitted by the third image source is incident on the third liquid crystal grating, and is incident on the beam combining mirror after the transmission direction is modulated by the third liquid crystal grating;

[0009] The beam combiner combines the first color light beam, the second color light beam and the third color light beam to form a color image which is emitted in the same direction.

[0010] In a second aspect, an embodiment of the present invention further provides a head-up display system, comprising the projection device described in the first aspect.

[0011] According to the technical solution provided by the embodiment of the present invention, three light beams of different colors emitted by three image sources are respectively incident on corresponding liquid crystal gratings, so that the liquid crystal grating can deflect the light beams, and the deflection angle of the light beams is controllable. The three light beams of different colors modulated by the liquid crystal grating are combined by a beam combiner to form a color image, which are emitted in the same direction and then incident on the human eye so that the user can view the driving information. The projection device has a simple structure, low cost and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural schematic diagram of a projection device provided in the prior art;

[0013] Figure 2 A schematic structural diagram of a first projection device provided by an embodiment of the present invention;

[0014] Figure 3 A schematic structural diagram of a second projection device provided by an embodiment of the present invention;

[0015] Figure 4 A schematic structural diagram of a third projection device provided by an embodiment of the present invention;

[0016] Figure 5 A partial top view schematic diagram of a liquid crystal grating provided by an embodiment of the present invention;

[0017] Figure 6 for Figure 5 A first cross-sectional schematic diagram of the corresponding liquid crystal grating along the section line AA';

[0018] Figure 7 for Figure 5 A second cross-sectional schematic diagram of the corresponding liquid crystal grating along the section line AA';

[0019] Figure 8 A schematic diagram of the cross-sectional structure of a liquid crystal grating during the inventor's research process;

[0020] Fig. 9 A schematic diagram of voltage distribution of a first gate electrode and a second gate electrode of a liquid crystal grating during research by the inventor;

[0021] Fig.10 for Figure 5 A third cross-sectional schematic diagram of the corresponding liquid crystal grating along the section line AA';

[0022] Fig.11A schematic diagram of voltage distribution of a first gate electrode and a second gate electrode of a liquid crystal grating provided in an embodiment of the present invention;

[0023] Fig.12 for Figure 5 A schematic diagram of a fourth cross-sectional structure of the corresponding liquid crystal grating along the section line AA';

[0024] Fig.13 A schematic diagram of voltage distribution of a first gate electrode and a second gate electrode of another liquid crystal grating provided by an embodiment of the present invention;

[0025] Fig.14 for Figure 5 A schematic diagram of a fifth cross-sectional structure of the corresponding liquid crystal grating along the section line AA';

[0026] Fig.15 A schematic diagram of the structure of a head-up display system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0028] Figure 1 FIG. 1 is a schematic diagram of a structure of a projection device provided in the prior art. Figure 1 As shown, the inventors have found that the red light beam a', green light beam b' and blue light beam c' emitted by the image source need to be deflected by a reflector 1000 and a spatial light modulation module 2000, that is, the viewing angle is controlled by mechanical rotation, and the modulated light beams of different colors pass through a dichroic prism to form a color picture. Such a system is complex, costly and has poor reliability.

[0029] Based on the above research findings, the inventors further developed the technical solution in the embodiment of the present invention, by setting a liquid crystal grating between the image source and the beam combiner, so that the liquid crystal grating can deflect the light before it enters the beam combiner, thereby realizing the control of the light deflection angle, and then the deflected light beams of different colors are combined by the beam combiner to form a color image, which are emitted in the same direction and incident on the human eye, so that the user can view the driving information. Such a projection device has a simple structure, low cost and high reliability.

[0030] The above is the core idea of ​​the present invention. The technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Figure 2 A schematic diagram of the structure of a first projection device provided by an embodiment of the present invention is shown in FIG. Figure 2 As shown, the projection device 100 includes an image source 10, a liquid crystal grating 20 and a beam combiner 30. The image source 10 includes a first image source 101, a second image source 102 and a third image source 103. The liquid crystal grating 20 includes a first liquid crystal grating 201, a second liquid crystal grating 202 and a third liquid crystal grating 203 respectively arranged at a first input end 301-1, a second input end 301-2 and a third input end 301-3 of the beam combiner 30. The first color light beam a emitted by the first image source 101 is incident on the first liquid crystal grating 201. The crystal grating 201 modulates the transmission direction and then enters the beam combiner 30; the second color light beam b emitted by the second image source 102 is incident on the second liquid crystal grating 202, and then is incident on the beam combiner 30 after being modulated by the second liquid crystal grating 202 in terms of transmission direction; the third color light beam c emitted by the third image source 103 is incident on the third liquid crystal grating 203, and then is incident on the beam combiner 30 after being modulated by the third liquid crystal grating 203 in terms of transmission direction; the beam combiner 30 combines the first color light beam a, the second color light beam b and the third color light beam c into a color image and emits them in the same direction.

[0032] Specifically, the image source 10 can be understood as a picture generation unit (PGU) for emitting a light beam of at least one color. In this embodiment, the image source 10 includes a first image source 101 emitting a first color light beam a, a second image source 102 emitting a second color light beam b, and a third image source 103 emitting a third color light beam c. The colors of the light beams emitted by the three image sources are all different. Exemplarily, the first color light beam a can be a red light beam, the second color light beam b can be a green light beam, and the third color light beam c can be a blue light beam, and the beam combiner 30 can output a color image.

[0033] Specifically, since the liquid crystal grating 20 can deflect light beams of different polarization states at different angles, the light beam can be deflected by controlling the arrangement of liquid crystal molecules in the liquid crystal grating 20, and thus the deflection of the light beam emission direction can be achieved without the aid of a mechanical structure. In the liquid crystal grating 20, the arrangement of the liquid crystal molecules can change under the action of an electric field. Furthermore, a liquid crystal grating 20 is arranged between the image source 10 and the beam combiner 30, and the image source 10 corresponds to the liquid crystal grating 20 one-to-one, and the liquid crystal grating 20 corresponds to the input end of the beam combiner 30 one-to-one, so that the three color light beams emitted by the three image sources 101, 102 and 103 are respectively incident on the three liquid crystal gratings 201, 202 and 203, and are respectively incident on the beam combiner 30 after the transmission direction is modulated by the liquid crystal grating 20, that is, the first color light beam a emitted by the first image source 101 is incident on the first liquid crystal grating 201, and is incident on the first liquid crystal grating 201 after the transmission direction is modulated by the liquid crystal grating 20. The grating 201 modulates the transmission direction and then enters the beam combiner 30; the second color light beam b emitted by the second image source 102 is incident on the second liquid crystal grating 202, and then is incident on the beam combiner 30 after being modulated by the second liquid crystal grating 202; the third color light beam c emitted by the third image source 103 is incident on the third liquid crystal grating 203, and then is incident on the beam combiner 30 after being modulated by the third liquid crystal grating 203. The beam combiner 30 combines the three color light beams into a color image and emits it in the same direction, and then it enters the human eye so that the user can view the relevant information.

[0034] As a comparative example, the embodiment of the present invention adopts a liquid crystal grating 20 to replace the reflector and the spatial light modulation module in the prior art. On the one hand, it can reduce the number of components, thereby simplifying the structure of the projection device and realizing the miniaturization of the projection device. On the other hand, the reliability of light deflection achieved by the liquid crystal grating is high.

[0035] In the projection device provided by the embodiment of the present invention, three light beams of different colors emitted by three image sources are respectively incident on corresponding liquid crystal gratings, so that the liquid crystal grating can deflect the light beams, and the deflection angle of the light beams is controllable. The three light beams of different colors modulated by the liquid crystal grating are combined by a beam combiner to form a color image, which are emitted in the same direction and then incident on the human eye so that the user can view driving information. Such a projection device has a simple structure, low cost and high reliability.

[0036] Optionally, the grating periods of the first liquid crystal grating 201 , the second liquid crystal grating 202 and the third liquid crystal grating 203 are the same.

[0037] Specifically, the grating period of the liquid crystal grating 20 determines the deflection angle of the light. The grating periods of the first liquid crystal grating 201, the second liquid crystal grating 202 and the third liquid crystal grating 203 are the same, so that on the one hand, the setting method is simple and the cost is low, and on the other hand, it is conducive to ensuring that the color images formed by the three different color light beams after being modulated by the liquid crystal grating 20 and combined by the beam combining mirror 30 are emitted in the same direction, thereby improving the projection effect of the projection device.

[0038] Optionally, the wavelength of the first color light beam a is λ1, the wavelength of the second color light beam b is λ2, the wavelength of the third color light beam c is λ3, the grating period of the first liquid crystal grating 201 is d1, the grating period of the second liquid crystal grating 202 is d2, and the grating period of the third liquid crystal grating 203 is d3, d1 / λ1=d2 / λ2=d3 / λ3.

[0039] Specifically, the ratio of the grating period to the light wavelength affects the diffraction characteristics of the grating, including the diffraction angle and diffraction efficiency. According to the grating equation dsin(θ)=mλ, where m is the diffraction order, it can be seen that the diffraction angle θ is related to the grating period d and the light wavelength λ, and the ratio of the grating period d to the light wavelength λ determines the deflection angle of the diffracted light.

[0040] Specifically, by setting d1 / λ1=d2 / λ2=d3 / λ3, that is, if the wavelength λ1 of the first color light beam a is larger, the grating period d1 of the first liquid crystal grating 201 is also larger, and if the wavelength λ3 of the third color light beam c is smaller, the grating period d3 of the third liquid crystal grating 203 is also smaller. This is conducive to ensuring that the three different colors of light are combined by the beam combiner to form a color image and are emitted in the same direction, that is, the light emission angles are matched, thereby improving the display effect.

[0041] Optionally, λ1>λ2>λ3, that is, the first color light beam a can be a red light beam, the second color light beam b can be a green light beam, and the third color light beam c can be a blue light beam. To ensure that the three different color lights are combined by the beam combiner 30 to form a color image and are emitted in the same direction, in addition, since λ1>λ2>λ3, according to d1 / λ1=d2 / λ2=d3 / λ3, d1>d2>d3 can be set.

[0042] Optional, Figure 3 A schematic diagram of the structure of a second projection device provided by an embodiment of the present invention is shown in FIG. Figure 3 As shown, at least one of the first liquid crystal grating 201 , the second liquid crystal grating 202 and the third liquid crystal grating 203 includes at least two sub-liquid crystal gratings 200 stacked together.

[0043] Specifically, the first liquid crystal grating 201, the second liquid crystal grating 202 and the third liquid crystal grating 203 all include two stacked sub-liquid crystal gratings 200 as an example for explanation, that is, each liquid crystal grating 20 includes two sub-liquid crystal gratings 200, which can increase the deflection angle of the liquid crystal grating to the light, improve the deflection effect, and thus enhance the display effect.

[0044] It should be noted that each liquid crystal grating 20 may include three or more sub-liquid crystal gratings 200. In addition, any one of the first liquid crystal grating 201, the second liquid crystal grating 202 and the third liquid crystal grating 203 may include at least two sub-liquid crystal gratings 200, or any two of the first liquid crystal grating 201, the second liquid crystal grating 202 and the third liquid crystal grating 203 may include at least two sub-liquid crystal gratings 200. In this way, on the one hand, diversified settings of the projection device can be achieved, and on the other hand, the deflection angle of the liquid crystal grating to the light can be increased to enhance the display effect.

[0045] Optional, Figure 4 A schematic diagram of the structure of a third projection device provided by an embodiment of the present invention is shown in FIG. Figure 4 As shown, continue to refer to Figure 2 and Figure 4 The beam combining mirror 30 includes a color combining prism 301, and the color combining prism 301 includes a first color combining surface 3011 and a second color combining surface 3012. The first color combining surface 3011 reflects the first color light beam a and transmits the second color light beam b. The second color combining surface 3012 reflects the third color light beam c and transmits the second color light beam b. The first color light beam a is incident from the first input end 301-1 of the color combining prism 301 into the color combining prism 301, and is reflected from the first color combining surface 3011. The output end of the color combining prism 301 is emitted; the second color light beam b is incident into the color combining prism 301 from the second input end 301-2 of the color combining prism 301, and is emitted from the output end of the color combining prism 301 after being transmitted through the first color combining surface 3011 and the second color combining surface 3012; the third color light beam c is incident into the color combining prism 301 from the third input end 301-3 of the color combining prism 301, and is emitted from the output end of the color combining prism 301 after being reflected through the second color combining surface 3012.

[0046] Specifically, the first color light beam a is incident into the color combining prism 301 from the first input end 301-1 of the color combining prism 301, and after being reflected by the first color combining surface 3011, it can be directly emitted from the output end of the color combining prism 301, or the light beam reflected by the first color combining surface 3011 can be emitted after being transmitted through the second color combining surface 3012. The third color light beam c is incident into the color combining prism 301 from the third input end 301-3 of the color combining prism 301, and after being reflected by the second color combining surface 3012, it can be directly emitted from the output end of the color combining prism 301, or the light beam reflected by the second color combining surface 3012 can be emitted after being transmitted through the first color combining surface 3011. The second color light beam b is incident into the color combining prism 301 from the second input end 301-2 of the color combining prism 301, and is emitted from the output end of the color combining prism 301 after being transmitted through the first color combining surface 3011 and the second color combining surface 3012. In this way, the three color light beams form a color image, which is emitted from the output end of the color combining prism 301 in the same direction and then incident on the human eye.

[0047] For example, continue to refer to Figure 2 The cross-sectional view of the color combining prism 301 may be a rectangle, and the first color combining plane 3011 and the second color combining plane 3012 may be diagonals of the rectangle, respectively.

[0048] For example, continue to refer to Figure 4 The color combining prism 301 can be formed by gluing together a plurality of triangular prisms.

[0049] Optional, Figure 5 A partial top view schematic diagram of a liquid crystal grating provided by an embodiment of the present invention, Figure 6 for Figure 5 The first cross-sectional schematic diagram of the corresponding liquid crystal grating along the section line AA' is as follows: Figure 5 and Figure 6 As shown, the liquid crystal grating 20 includes a first substrate 20-1 and a second substrate 20-2 which are arranged opposite to each other, and a liquid crystal layer 20-3 located between the first substrate 20-1 and the second substrate 20-2; a plurality of supporting structures 20-4 are included between the first substrate 20-1 and the second substrate 20-2; the first substrate 20-1 includes a driving electrode layer 20-5 on the side close to the second substrate 20-2, and the driving electrode layer 20-5 includes a plurality of gate electrodes 205 extending along a first direction (the Y direction as shown in the figure) and arranged along a second direction (the X direction as shown in the figure); wherein the first substrate 20-1 also includes an auxiliary structure 20-6, at least part of the auxiliary structure 20-6 is located between at least part of the gate electrode 205 and the supporting structure 20-4, the first direction Y and the second direction X are both parallel to the plane where the first substrate 20-1 is located, and the first direction Y and the second direction X intersect.

[0050] Specifically, the first substrate 20-1 and the second substrate 20-2 may be glass substrates for protecting the film structure in the liquid crystal grating. The liquid crystal layer 20-3 between the first substrate 20-1 and the second substrate 20-2 includes liquid crystal molecules. The plurality of support structures 20-4 disposed between the first substrate 20-1 and the second substrate 20-2 are used to support the first substrate 20-1 and the second substrate 20-2 to form a filling space for the liquid crystal layer 20-3.

[0051] Exemplarily, the shape of the support structure 20-4 can be columnar or strip-shaped (such as a retaining wall), etc. The embodiment of the present invention is described using the shape of the support structure 20-4 as a truncated cone as an example. Exemplarily, the cross-sectional view of the support structure 20-4 is an inverted trapezoid.

[0052] Specifically, the driving electrode layer 20-5 includes a plurality of gate electrodes 205, that is, the gate electrodes 205 can be independently arranged, and the side of the second substrate 20-2 close to the supporting structure 20-4 includes a common electrode layer 20-7, and the common electrode layer 20-7 can be a common electrode arranged on the entire surface. There is a voltage difference between the common electrode and the gate electrode 205, so that the longitudinal electric field formed by the common electrode and the gate electrode 205 can drive the liquid crystal molecules in the liquid crystal layer 20-3 to rotate, and thus can deflect the light incident on the liquid crystal grating 20.

[0053] Specifically, the first substrate 20-1 also includes an auxiliary structure 20-6, and at least part of the auxiliary structure 20-6 is located between at least part of the gate electrode 205 and the supporting structure 20-4. That is, by setting the auxiliary structure 20-6, the thickness of the inorganic layer between the supporting structure 20-4 and the first substrate 20-1 can be increased, thereby improving the compressive strength of the liquid crystal grating 20. In this way, during the preparation or use of the liquid crystal grating, when the supporting structure 20-4 is subjected to external pressure, the gate electrode 205 will not be broken, which is conducive to ensuring the stability of the liquid crystal grating.

[0054] Specifically, the auxiliary structure may be an insulating layer and / or a driving electrode layer. In a feasible embodiment, the auxiliary structure 20-6 may be an insulating layer, that is, the structure between the first substrate 20-1 and the supporting structure 20-4 is "insulating layer-driving electrode layer-insulating layer". As another feasible embodiment, the auxiliary structure 20-6 may be a driving electrode layer, that is, the structure between the first substrate 20-1 and the supporting structure 20-4 is "insulating layer-driving electrode layer-insulating layer-driving electrode layer". As another feasible embodiment, the auxiliary structure 20-6 may be an insulating layer and a driving electrode layer, that is, the structure between the first substrate 20-1 and the supporting structure 20-4 is "insulating layer-driving electrode layer-insulating layer-driving electrode layer-insulating layer". In this way, on the one hand, the pressure resistance of the liquid crystal grating can be improved, the stability and reliability of the liquid crystal grating can be ensured, and on the other hand, the diversified design of the liquid crystal grating can be realized.

[0055] Exemplarily, the side of the first substrate 20-1 close to the second substrate 20-2 and the side of the second substrate 20-2 close to the first substrate 20-1 may also include a dielectric layer. By providing the dielectric layer, on the one hand, the liquid crystal grating 20 can be protected from being damaged by the external environment, and on the other hand, the charges between the electrodes can be effectively isolated to prevent the leakage of charges and the occurrence of arcs, thereby ensuring that the liquid crystal grating 20 can work normally.

[0056] Optional, continue to refer to Figure 6 The liquid crystal grating 20 further includes a first insulating layer 20-8 located between the driving electrode layer 101 and the first substrate 10. Providing the first insulating layer 20-8 is beneficial to improving the uniformity of the driving electrode layer and avoiding defects of the driving electrode layer.

[0057] Optional, continue to refer to Figure 6 , the auxiliary structure 20 - 6 includes an insulating layer.

[0058] Specifically, the auxiliary structure 20-6 includes an insulating layer, that is, the structure between the first substrate 20-1 and the support structure 20-4 can be "insulating layer-driving electrode layer-insulating layer", so that the side of the support structure 20-4 close to the first substrate 20-1 is directly in contact with the insulating layer, and the auxiliary structure 20-6 can increase the overall thickness of the inorganic layer, and when the support structure 20-4 is subjected to external pressure, it can play a buffering role to prevent the gate electrode 205 from being broken. In addition, the auxiliary structure 20-6 can cover the exposed surface of the gate electrode 205, for example, protect the side of the gate electrode 205 to avoid scratching the gate electrode 205; on the other hand, the auxiliary structure 20-6 is in contact with the first insulating layer 20-8, which can play an auxiliary support role, thereby improving the stability and reliability of the liquid crystal grating.

[0059] Optional, Figure 7 for Figure 5 The corresponding second cross-sectional diagram of the liquid crystal grating along the section line AA' is as follows: Figure 7 As shown, along the third direction (Z direction shown in the figure), the auxiliary structure 20 - 6 overlaps with at least two gate electrodes 205 , and the third direction Z is the direction from the second substrate 20 - 2 to the first substrate 20 - 1 .

[0060] Specifically, along the third direction Z, the auxiliary structure 20-6 overlaps with at least two gate electrodes 205, that is, the auxiliary structure 20-6 can be independently arranged, and the width of each auxiliary structure 20-6 can be greater than or equal to the width of at least two gate electrodes 205, so as to completely cover the support structure 20-4, and then when the support structure 20-4 is subjected to external pressure, the buffering capacity and the bearing capacity can be improved, and the probability of the gate electrode 205 being disconnected can be reduced, which is beneficial to improving the stability and reliability of the liquid crystal grating. In addition, the auxiliary structure 20-6 can, on the one hand, cover the exposed surface of the gate electrode 205, for example, protect the side of the gate electrode 205 to avoid scratching the gate electrode 205; on the other hand, the auxiliary structure 20-6 can contact with the insulating layer 20-8, so as to play the role of auxiliary support, thereby improving the stability and reliability of the liquid crystal grating. It should be noted that in this embodiment, the auxiliary structure 20-6 is independently arranged, rather than being arranged on the entire surface, which is beneficial to stress release and avoids cracks or crack transmission when the support structure 20-4 is subjected to pressure.

[0061] It should be noted that the liquid crystal grating 20 may also include an alignment layer 210, and the alignment layer 210 may be located between the auxiliary structure 20-6 and the liquid crystal molecules, so that on the one hand, the liquid crystal molecules can be prevented from contacting the gate electrode 205, and on the other hand, the initial arrangement direction of the liquid crystal molecules can be controlled by the alignment layer 20-9. It can be understood that the side of the second substrate 20-2 close to the liquid crystal molecules and other drawings of the embodiments of the present invention may include an alignment layer, which is not shown in the drawings of other embodiments.

[0062] Optional, Figure 8 A schematic diagram of the cross-sectional structure of a liquid crystal grating during the inventor's research process; Fig. 9The present invention is a schematic diagram of voltage distribution of the first gate electrode and the second gate electrode of a liquid crystal grating in the process of research by the inventor. The liquid crystal grating 20 includes a first substrate 20-1 and a second substrate 20-2 arranged opposite to each other, and a liquid crystal layer 20-3 located between the first substrate 20-1 and the second substrate 20-2, and the liquid crystal layer 20-3 includes liquid crystal molecules. The liquid crystal grating includes a plurality of grating units 21. The plurality of grating units 21 are arranged along a first direction X, and the grating unit 21 includes a plurality of first gate electrodes 206 and a second gate electrode 22. The plurality of first gate electrodes 206 are located between the first substrate 20-1 and the liquid crystal layer 20-3. The plurality of first gate electrodes 206 are arranged spaced apart from each other along the first direction X. Along the first direction X, two adjacent first gate electrodes 206 are spaced apart by a certain distance. The plurality of grating units 21 share the same second gate electrode 22, and the second gate electrode 22 is a whole-surface electrode.

[0063] Continue to refer Figure 8 and Fig. 9 After research, the inventors found that there is a voltage difference between the first gate electrode 206 and the second gate electrode 22, and the longitudinal electric field formed by the first gate electrode 206 and the second gate electrode 22 can drive the liquid crystal molecules to rotate. There are at least two first gate electrodes 206 with different voltages, thereby forming longitudinal electric fields of different strengths arranged along the first direction X. The longitudinal electric fields of different strengths cause the liquid crystal molecules to rotate at different angles, thereby forming a refractive index gradient, forming a plurality of grating units 21 arranged along the first direction X, so the grating unit 21 can also include liquid crystal molecules. However, a transverse electric field is formed between the first gate electrodes 206 with different voltages. The existence of the transverse electric field will cause the liquid crystal molecules to produce an electric bending effect, change the rotation behavior of the liquid crystal molecules, and the liquid crystal molecules in the liquid crystal grating cannot be flipped according to the ideal situation. The liquid crystal molecules rotate in the direction opposite to the pretilt angle, resulting in a reverse domain problem.

[0064] Continue to refer Figure 8 and Fig. 9 After research, the inventors found that some areas in the liquid crystal grating are in an undesirable state. The inventors further found that along the first direction X, a first electric field TE1 is formed between two first gate electrodes 206 that are located in two adjacent grating units 21 and are closest to each other. The first electric field TE1 is a transverse electric field. The liquid crystal grating includes a first alignment layer 20-9, and the first alignment layer 20-9 is located between the first gate electrode 206 and the liquid crystal layer 20-3. In some areas of the liquid crystal grating, the alignment direction R1 of the first alignment layer 20-9 is opposite to the electric field direction of the first electric field TE1. Under the combined influence of the first electric field TE1 and the longitudinal electric field, the liquid crystal molecules at the S1 region are aligned along Figure 8The liquid crystal molecules in the S1 region are rotated in the direction of the arrow and flipped in the opposite direction, generating a bubble-shaped inversion domain in the S1 region. The liquid crystal molecules in the S1 region are close to the first gate electrode 206. The first alignment layer 20-9 may be in direct contact with the first gate electrode 206. In other embodiments, a protective layer may be provided between the first alignment layer 20-9 and the first gate electrode 206. The first alignment layer 20-9 is located on a side of the protective layer away from the first gate electrode 206. The protective layer provides a flat surface for the first alignment layer 20-9, thereby improving the flatness of the first alignment layer 20-9.

[0065] Fig.10 for Figure 5 The corresponding third cross-sectional schematic diagram of the liquid crystal grating along the section line AA', Fig.11 A schematic diagram of voltage distribution of a first gate electrode and a second gate electrode of a liquid crystal grating provided in an embodiment of the present invention, with reference to Fig.10 and Fig.11 The liquid crystal grating 20 includes a first substrate 20-1 and a second substrate 20-2 which are arranged opposite to each other, and a liquid crystal layer 20-3 located between the first substrate 20-1 and the second substrate 20-2. The first substrate 20-1 includes a first gate electrode 206 and a first alignment layer 20-9 which are arranged in sequence on a side close to the liquid crystal layer 20-3. In the first state ST1, the liquid crystal grating 20 includes a plurality of grating units 21 arranged along a first direction X, and the grating unit 21 includes a plurality of first gate electrodes 206 which are arranged spaced apart from each other along the first direction X. Along the first direction X, a certain distance is spaced between two adjacent first gate electrodes 206. Along the first direction X, a first electric field TE1 is formed between two first gate electrodes 206 which are located in two adjacent grating units 21 and are closest to each other. The alignment direction R1 of the first alignment layer 20-9 is the same as the electric field direction of the first electric field TE1.

[0066] Specifically, the electric field direction of the first electric field TE1 is the same as the alignment direction R1 of the first alignment layer 20-9. The electric field direction to which the liquid crystal molecules adjacent to the first alignment layer 20-9 are subjected is toward the alignment direction R1 of the first alignment layer 20-9, and not in the opposite direction of the alignment of the first alignment layer 20-9. The liquid crystal molecules adjacent to the first alignment layer 20-9 will not produce reverse flipping, thereby reducing the adverse effect of the lateral electric field on the rotation of the liquid crystal molecules and improving the reverse domain problem.

[0067] For example, continue to refer to Fig.10 and Fig.11 The liquid crystal grating 20 further includes a second gate electrode 22, and the second gate electrode 22 is located between the second substrate 20-2 and the liquid crystal layer 20-3. The longitudinal electric field formed by the first gate electrode 206 and the second gate electrode 22 can drive the liquid crystal molecules to rotate, forming a plurality of grating units 21, and the plurality of grating units 21 are repeatedly arranged along the first direction X. The liquid crystal grating is used for diffraction and deflection of light.

[0068] Optional, continue to refer to Fig.10 The liquid crystal grating 20 further includes a second gate electrode 22, and the second gate electrode 22 is located between the second substrate 20-2 and the liquid crystal layer 20-3; the same grating unit 21 includes a plurality of first electrode groups 51 arranged along the first direction X, and the first electrode group 51 includes at least one first gate electrode 206 and at least one second gate electrode 22. In the same first electrode group 51, the first gate electrode 206 and the second gate electrode 22 at least partially overlap, and the voltage difference between the two is the first voltage difference.

[0069] Specifically, the longitudinal electric field formed by the first voltage difference can drive the liquid crystal molecules to rotate. The first voltage difference is the difference between the voltage of the first gate electrode 206 and the voltage of the second gate electrode 22 in the grating unit 21, that is, the first voltage difference is the voltage of the first gate electrode 206 minus the voltage of the second gate electrode 22.

[0070] For example, continue to refer to Fig.10 , a first electrode group 51 includes a first gate electrode 21 and a second gate electrode 22. A first voltage difference exists between the voltages of the first gate electrode 206 and the second gate electrode 22 in the same first electrode group 51. In other embodiments, a first electrode group 51 includes a plurality of first gate electrodes 206 and one second gate electrode 22.

[0071] Optional, Fig.12 for Figure 5 The corresponding schematic diagram of the fourth cross-sectional structure of the liquid crystal grating along the cross-sectional line AA', Fig.13 A schematic diagram of voltage distribution of a first gate electrode and a second gate electrode of another liquid crystal grating provided by an embodiment of the present invention is shown in FIG. Fig.12 and Fig.13 As shown, the liquid crystal grating 20 also includes a second alignment layer 32, and the second alignment layer 32 is located between the second gate electrode 22 and the liquid crystal layer 20-3; in the first state ST1, the grating unit 20 includes a plurality of second gate electrodes 22 spaced apart from each other along the first direction X; along the first direction X, a second electric field TE2 is formed between two second gate electrodes 22 that are respectively located in two adjacent grating units 21 and are closest to each other, and the alignment direction of the second alignment layer 32 is the same as the electric field direction of the second electric field TE2.

[0072] Specifically, the electric field direction of the second electric field TE2 is the same as the alignment direction R2 of the second alignment layer 32. The electric field direction to which the liquid crystal molecules adjacent to the second alignment layer 32 are subjected is toward the alignment direction R2 of the second alignment layer 32, and not in the opposite direction of the alignment of the second alignment layer 32. The liquid crystal molecules adjacent to the second alignment layer 32 will not flip in the reverse direction, thereby reducing the adverse effect of the lateral electric field on the rotation of the liquid crystal molecules and improving the reverse domain problem.

[0073] For example, continue to refer to Fig.12 and Fig.13 , there are at least two first gate electrodes 206 with different voltages, and a transverse electric field is generated between the first gate electrodes 206. There are at least two second gate electrodes 22 with different voltages, and a transverse electric field is generated between the second gate electrodes 22. Thus, the transverse electric field is dispersed in the first gate electrode 206 and the second gate electrode 22, and the transverse electric field is dispersed in the first substrate 20-1 and the second substrate 20-2, rather than concentrated on one substrate (the substrate includes the first substrate 20-1 and the second substrate 20-2), thereby reducing the transverse electric field strength of a single substrate. Reduce the adverse effect of the transverse electric field on the rotation of the liquid crystal molecules and improve the reverse domain problem.

[0074] For example, continue to refer to Fig.12 and Fig.13 In the same grating unit 21, there are at least two first grating electrodes 206 with different voltages, and there are at least two second grating electrodes 22 with different voltages. In the same grating unit 21, the lateral electric field is dispersed between the first substrate 20-1 and the second substrate 20-2, reducing the adverse effect of the lateral electric field on the rotation of the liquid crystal molecules and improving the reverse domain problem.

[0075] For example, continue to refer to Figure 8 and Fig. 9 , the voltage of the first sub-first gate electrode 211 is +1V, the voltage of the second sub-first gate electrode 212 is +2V, the voltage of the third sub-first gate electrode 213 is +3V, and the voltage of the fourth sub-first gate electrode 214 is +4V. The voltage of the second gate electrode 22 is 0V. The voltage difference formed between the first sub-first gate electrode 211 and the second gate electrode 22 is 1V, the voltage difference formed between the second sub-first gate electrode 212 and the second gate electrode 22 is 2V, the voltage difference formed between the third sub-first gate electrode 213 and the second gate electrode 22 is 3V, and the voltage difference formed between the fourth sub-first gate electrode 214 and the second gate electrode 22 is 4V. The voltage difference formed between the fourth sub-first gate electrode 214 and the first sub-first gate electrode 211 in the adjacent grating unit 21 is 3V. The lateral electric field formed between the first gate electrodes 206 is relatively large. When the alignment direction R1 of the first alignment layer 20-9 is opposite to the electric field direction of the first electric field TE1, the greater the electric field strength of the first electric field TE1, the more likely it is that the liquid crystal molecules cannot flip according to the ideal situation, and the liquid crystal molecules rotate in the direction opposite to the pretilt angle, resulting in a reverse domain problem.

[0076] Exemplary, reference Fig.12 and Fig.13, the plurality of second gate electrodes 22 include a first sub-second gate electrode 221, a second sub-second gate electrode 222, a third sub-second gate electrode 223, and a fourth sub-second gate electrode 224. The voltage of the first sub-first gate electrode 211 is +0.5V, the voltage of the second sub-first gate electrode 212 is +1V, the voltage of the third sub-first gate electrode 213 is +1.5V, and the voltage of the fourth sub-first gate electrode 214 is +2V. The voltage of the first sub-second gate electrode 221 is -0.5V, the voltage of the second sub-second gate electrode 222 is -1V, the voltage of the third sub-second gate electrode 223 is -1.5V, and the voltage of the fourth sub-second gate electrode 224 is -2V. The voltage difference formed between the first sub-first gate electrode 211 and the first sub-second gate electrode 221 is 1V, the voltage difference formed between the second sub-first gate electrode 212 and the second sub-second gate electrode 222 is 2V, the voltage difference formed between the third sub-first gate electrode 213 and the third sub-second gate electrode 223 is 3V, and the voltage difference formed between the fourth sub-first gate electrode 214 and the fourth sub-second gate electrode 224 is 4V. The voltage difference formed between the fourth sub-first gate electrode 214 and the first sub-first gate electrode 211 in the adjacent grating unit 21 is 1.5V. The voltage difference formed between the fourth sub-second gate electrode 224 and the first sub-second gate electrode 221 in the adjacent grating unit 21 is 1.5V. The lateral electric field formed between the first gate electrodes 206 is reduced, and even when the alignment direction R1 of the first alignment layer 20-9 is opposite to the electric field direction of the first electric field TE1, the adverse effect of the lateral electric field on the rotation of the liquid crystal molecules can be reduced, thereby improving the reverse domain problem.

[0077] Exemplary, reference Fig.12 and Fig.13 In each grating unit 21, the first gate electrodes 206 with the same ordinal number have the same voltage, and the second gate electrodes 22 with the same ordinal number have the same voltage. The voltage distribution law of the multiple first gate electrodes 206 in each grating unit 21 is the same, and the voltage distribution law of the multiple second gate electrodes 22 in each grating unit 21 is the same, so that the first gate electrodes 206 with the same voltage in the multiple grating units 21 can be connected to the same power supply terminal, and the second gate electrodes 22 with the same voltage in the multiple grating units 21 can be connected to the same power supply terminal, thereby reducing the number of power supply terminals. Among them, the ordinal number of the first gate electrode 206 or the second gate electrode 22 in the grating unit 21 refers to the number of the first gate electrode 206 or the second gate electrode 22 in the grating unit 21. Among them, the voltage distribution law of the first gate electrode 206 or the second gate electrode 22 refers to the distribution law of the voltage of the multiple first gate electrodes 206 or the multiple second gate electrodes 22 along the first direction X.

[0078] For example, see reference Fig.12 and Fig.13, the grating unit 21 includes a first sub-grating unit 21-1 and a second sub-grating unit 21-2. The first sub-grating unit 21-1 and the second sub-grating unit 21-2 each include four electrode groups 50. One electrode group 50 (including the first electrode group 51) includes a first gate electrode 206 and a second gate electrode 22. In the grating unit 21, the four first gate electrodes 206 are arranged in sequence, and the four second gate electrodes 22 are arranged in sequence. The first first gate electrode 206 in the first sub-grating unit 21-1 and the first first gate electrode 206 in the second sub-grating unit 21-2 have the same voltage, and the second first gate electrode 206 in the first sub-grating unit 21-1 and the second first gate electrode 206 in the second sub-grating unit 21-2 have the same voltage. The first second gate electrode 22 in the first sub-grating unit 21-1 has the same voltage as the first second gate electrode 22 in the second sub-grating unit 21-2, and the second second gate electrode 22 in the first sub-grating unit 21-1 has the same voltage as the second second gate electrode 22 in the second sub-grating unit 21-2.

[0079] Optional, Fig.14 for Figure 5 The corresponding fifth cross-sectional structure diagram of the liquid crystal grating along the cross-sectional line AA' is as follows: Fig.14 As shown, the liquid crystal grating 20 includes a first substrate 20-1 and a second substrate 20-2 which are arranged opposite to each other, and a liquid crystal layer 20-3 located between the first substrate 20-1 and the second substrate 20-2; a plurality of grating units 21 are arranged along a first direction X, including a plurality of first gate electrodes 206 and a plurality of second gate electrodes 22; the plurality of first gate electrodes 206 are located between the first substrate 20-1 and the liquid crystal layer 20-3, and are spaced apart from each other along the first direction X; the plurality of second gate electrodes 22 are located between the second substrate 20-2 and the liquid crystal layer 20-3, and are spaced apart from each other along the first direction X; there are at least two first gate electrodes 206 having different voltages, and there are at least two second gate electrodes 22 having different voltages.

[0080] Specifically, there are at least two first gate electrodes 206 with different voltages, and a transverse electric field is generated between the first gate electrodes 206. There are at least two second gate electrodes 22 with different voltages, and a transverse electric field is generated between the second gate electrodes 22. Thus, the transverse electric field is dispersed between the first gate electrode 206 and the second gate electrode 22, and the transverse electric field is dispersed between the first substrate 20-1 and the second substrate 20-2, rather than being concentrated on one substrate (the substrate includes the first substrate 20-1 and the second substrate 20-2), thereby reducing the transverse electric field strength of a single substrate. Reduce the adverse effect of the transverse electric field on the rotation of the liquid crystal molecules, and improve the reverse domain problem.

[0081] For example, continue to refer to Fig.14The longitudinal electric field formed by the first gate electrode 206 and the second gate electrode 22 can drive the liquid crystal molecules to rotate, forming a plurality of grating units 21, and the plurality of grating units 21 are repeatedly arranged along the first direction X. The liquid crystal grating is used for light diffraction and deflection. The direction of the longitudinal electric field can be the third direction Z or the opposite direction of the third direction Z.

[0082] For example, continue to refer to Fig.14 In the same grating unit 21, there are at least two first grating electrodes 206 with different voltages, and there are at least two second grating electrodes 22 with different voltages. In the same grating unit 21, the lateral electric field is dispersed between the first substrate 20-1 and the second substrate 20-2, reducing the adverse effect of the lateral electric field on the rotation of the liquid crystal molecules and improving the reverse domain problem.

[0083] Optional, continue to refer to Fig.14 The same grating unit 21 includes a plurality of electrode groups 50 arranged along the first direction X, and the electrode group 50 includes at least one first gate electrode 206 and at least one second gate electrode 22; in the same electrode group 50, the first gate electrode 206 and the second gate electrode 22 at least partially overlap, and the voltage difference between the two is the first voltage difference.

[0084] Specifically, the longitudinal electric field formed by the first voltage difference can drive the liquid crystal molecules to rotate. The first voltage difference is the difference between the voltage of the first gate electrode 206 and the voltage of the second gate electrode 22, that is, the first voltage difference is the voltage of the first gate electrode 206 minus the voltage of the second gate electrode 22.

[0085] For example, continue to refer to Fig.14 , an electrode group 50 includes a first gate electrode 206 and a second gate electrode 22. A first voltage difference exists between the voltages of the first gate electrode 206 and the second gate electrode 22 in the same electrode group 50. In other embodiments, an electrode group 50 includes a plurality of first gate electrodes 206 and one second gate electrode 22.

[0086] In summary, in the projection device provided by the embodiment of the present invention, the three different color light beams emitted by the three image sources are respectively incident on the corresponding liquid crystal gratings, so that the liquid crystal grating can deflect the light beams, and the deflection angle of the light beams is controllable. The three different color light beams modulated by the liquid crystal grating are combined by the beam combiner to form a color image and emitted in the same direction, and then incident on the human eye, so that the user can refer to the driving information. In this way, the projection device has a simple structure, low cost and high reliability. In addition, at least one of the first liquid crystal grating, the second liquid crystal grating and the third liquid crystal grating includes at least two stacked sub-liquid crystal gratings, so that the deflection angle of the liquid crystal grating to the light can be increased, the deflection effect is improved, and the display effect is improved.

[0087] Based on the same inventive concept, an embodiment of the present invention further provides a head-up display system, which includes the projection device described in the above implementation. Therefore, the head-up display system provided by the embodiment of the present invention also has the above-mentioned beneficial effects, which will not be repeated here.

[0088] Fig.15 A schematic diagram of the structure of a head-up display system provided by an embodiment of the present invention is shown in FIG. Fig.15 As shown, the head-up display system also includes an eye tracking device (not shown in the figure), which is used to determine the observation position of the eye 501 of the user 500. The projection device 100 adjusts the signal of the liquid crystal grating according to the observation position of the eye 501 to make the image light incident on the human eye.

[0089] Specifically, the eye tracking device can detect the driver's line of sight and attention in real time, and then determine the observation position of the user 500's eyeball 501. The projection device 100 adjusts the signal that controls the liquid crystal grating according to the observation position of the eyeball 501. This can ensure that the image light is always within the user's field of view on the one hand, and on the other hand, it can always monitor the information required by the driver, so as to display the most critical information at the right time and position, thereby improving information transmission efficiency and improving user experience.

[0090] Optional, continue to refer to Fig.15 The head-up display system further includes at least one reflector 300 , and the image light output by the projection device is reflected by the reflector 300 and the windshield 400 and is incident on the human eye.

[0091] Specifically, the image light emitted by the projection device is reflected by the reflector 300 and then incident on the windshield 400 , and the windshield 400 reflects the light to the user's field of vision, so that the user can see the relevant information.

[0092] Optional, continue to refer to Fig.15 The reflector 300 includes a first curved reflector 301 and a second curved reflector 302. The image light output by the projection device 100 is reflected by the first curved reflector 301, the second curved reflector 302 and the windshield 400 in sequence and then enters the human eye.

[0093] Specifically, the image light emitted by the projection device is reflected by the first curved reflector 301 to the second curved reflector 302, and then reflected by the second curved reflector 302 to the windshield 400, and finally reflected by the windshield 400 to enter the human eye. By setting the first curved reflector 301 and the second curved reflector 302, on the one hand, the transmission direction of the light can be changed to provide a longer projection distance and a larger field of view. On the other hand, the first curved reflector 301 and the second curved reflector 302 can be adapted to the size and curvature of the windshield, which is conducive to the image being correctly reflected on the windshield and forming a clear virtual image within the driver's field of vision.

[0094] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A projection device, characterized in that: It includes an image source, a liquid crystal grating and a beam combiner, wherein the image source includes a first image source, a second image source and a third image source, and the liquid crystal grating includes a first liquid crystal grating, a second liquid crystal grating and a third liquid crystal grating respectively arranged at a first input end, a second input end and a third input end of the beam combiner; The first color light beam emitted by the first image source is incident on the first liquid crystal grating, and is incident on the beam combining mirror after the transmission direction is modulated by the first liquid crystal grating; The second color light beam emitted by the second image source is incident on the second liquid crystal grating, and is incident on the beam combining mirror after the transmission direction is modulated by the second liquid crystal grating; The third color light beam emitted by the third image source is incident on the third liquid crystal grating, and is incident on the beam combining mirror after the transmission direction is modulated by the third liquid crystal grating; The beam combiner combines the first color light beam, the second color light beam and the third color light beam to form a color image which is emitted in the same direction.

2. The projection device according to claim 1, characterized in that: The grating periods of the first liquid crystal grating, the second liquid crystal grating and the third liquid crystal grating are the same.

3. The projection device according to claim 1, characterized in that: The wavelength of the first color light beam is λ1, the wavelength of the second color light beam is λ2, the wavelength of the third color light beam is λ3, the grating period of the first liquid crystal grating is d1, the grating period of the second liquid crystal grating is d2, the grating period of the third liquid crystal grating is d3, d1 / λ1=d2 / λ2=d3 / λ3.

4. The projection device according to claim 3, characterized in that: λ1>λ2>λ3.

5. The projection device according to claim 1, characterized in that: At least one of the first liquid crystal grating, the second liquid crystal grating, and the third liquid crystal grating includes at least two sub-liquid crystal gratings stacked together.

6. The projection device according to claim 1, characterized in that: The beam combining mirror comprises a color combining prism, wherein the color combining prism comprises a first color combining surface and a second color combining surface, wherein the first color combining surface reflects the first color light beam and transmits the second color light beam, and the second color combining surface reflects the third color light beam and transmits the second color light beam; The first color light beam is incident into the color combining prism from the first input end of the color combining prism, and is emitted from the output end of the color combining prism after being reflected by the first color combining surface; The second color light beam is incident into the color combining prism from the second input end of the color combining prism, and is emitted from the output end of the color combining prism after being transmitted through the first color combining surface and the second color combining surface; The third color light beam is incident into the color combining prism from the third input end of the color combining prism, and is emitted from the output end of the color combining prism after being reflected by the second color combining surface.

7. The projection device according to claim 1, characterized in that: The liquid crystal grating comprises a first substrate and a second substrate which are arranged opposite to each other, and a liquid crystal layer located between the first substrate and the second substrate; A plurality of supporting structures are included between the first substrate and the second substrate; The first substrate comprises a driving electrode layer on a side close to the second substrate, and the driving electrode layer comprises a plurality of gate electrodes extending along a first direction and arranged along a second direction; The first substrate further includes an auxiliary structure, at least part of the auxiliary structure is located between at least part of the gate electrode and the support structure, the first direction and the second direction are both parallel to the plane where the first substrate is located, and the first direction and the second direction intersect.

8. The projection device according to claim 7, characterized in that: The auxiliary structure includes an insulating layer.

9. The projection device according to claim 7, characterized in that: Along a third direction, the auxiliary structure overlaps with at least two of the gate electrodes, and the third direction is a direction from the second substrate to the first substrate.

10. The projection device according to claim 1, characterized in that: The liquid crystal grating comprises a first substrate and a second substrate which are arranged opposite to each other, and a liquid crystal layer located between the first substrate and the second substrate, and a side of the first substrate close to the liquid crystal layer comprises a first gate electrode and a first alignment layer which are arranged in sequence; in a first state, the liquid crystal grating comprises a plurality of grating units arranged along a first direction, and the grating units comprise a plurality of first gate electrodes which are arranged along the first direction and spaced from each other; Along the first direction, a first electric field is formed between two first gate electrodes which are respectively located in two adjacent grating units and are closest to each other, and the alignment direction of the first alignment layer is the same as the electric field direction of the first electric field.

11. The projection device according to claim 10, characterized in that: The liquid crystal grating further includes a second gate electrode, and the second gate electrode is located between the second substrate and the liquid crystal layer; The same grating unit includes multiple first electrode groups arranged along the first direction, and the first electrode group includes at least one first gate electrode and at least one second gate electrode; in the same first electrode group, the first gate electrode and the second gate electrode at least partially overlap, and the voltage difference between the two is the first voltage difference.

12. The projection device according to claim 11, characterized in that: The liquid crystal grating further comprises a second alignment layer, wherein the second alignment layer is located between the second gate electrode and the liquid crystal layer; The grating unit includes a plurality of second grating electrodes arranged spaced apart from each other along the first direction; Along the first direction, a second electric field is formed between two second gate electrodes which are respectively located in two adjacent grating units and are closest to each other, and the alignment direction of the second alignment layer is the same as the electric field direction of the second electric field.

13. The projection device according to claim 1, characterized in that: The liquid crystal grating comprises a first substrate and a second substrate which are arranged opposite to each other, and a liquid crystal layer located between the first substrate and the second substrate; A plurality of grating units are arranged along a first direction, and include a plurality of first grating electrodes and a plurality of second grating electrodes; the plurality of first grating electrodes are located between the first substrate and the liquid crystal layer, and are spaced apart from each other along the first direction; the plurality of second grating electrodes are located between the second substrate and the liquid crystal layer, and are spaced apart from each other along the first direction; There are at least two of the first gate electrodes having different voltages, and there are at least two of the second gate electrodes having different voltages.

14. The projection device according to claim 13, characterized in that: The same grating unit includes multiple electrode groups arranged along the first direction, and the electrode groups include at least one first gate electrode and at least one second gate electrode; in the same electrode group, the first gate electrode and the second gate electrode at least partially overlap, and the voltage difference between the two is the first voltage difference.

15. A head-up display system, characterized in that: The invention comprises the projection device according to any one of claims 1 to 14.

16. The head-up display system according to claim 15, characterized in that: It also includes an eye tracking device, which is used to determine the viewing position of the user's eyes. The projection device adjusts the signal controlling the liquid crystal grating according to the viewing position of the eyes so that the image light is incident on the human eye.

17. The head-up display system according to claim 15, characterized in that: It also includes at least one reflector, and the image light output by the projection device is reflected by the reflector and the windshield and incident on the human eye.

18. The head-up display system according to claim 17, characterized in that: The reflector includes a first curved reflector and a second curved reflector. The image light output by the projection device is reflected by the first curved reflector, the second curved reflector and the windshield in sequence and then enters the human eye.

Images