HEAD-UP DISPLAY APPARATUS, DISPLAY METHOD, AND DISPLAY SYSTEM

Abstract

One example display apparatus includes a multi-focus image generation device with a plurality of different focal lengths, configured to generate a first plurality of images, where focal planes of the first plurality of images are located in different positions. The example display apparatus includes a light diffuser screen, disposed on an image plane of the multi-focus image generation device, and configured to receive the first plurality of images, and diffuse light beams of the first plurality of images to generate a second plurality of images. The example display apparatus includes an optical image device, configured to image light beams of the second plurality of images to form a third plurality of images with different imaging distances.

Claims

1. A display apparatus, comprising: a multi-focus image generation device with a plurality of different focal lengths, configured to generate a first plurality of images, wherein focal planes of the first plurality of images are located in different positions; a light diffuser screen, disposed on an image plane of the multi-focus image generation device, and configured to: receive the first plurality of images; and diffuse light beams of the first plurality of images to generate a second plurality of images; and an optical image device, configured to image light beams of the second plurality of images to form a third plurality of images with different imaging distances.

2. The display apparatus according to claim 1, wherein the multi-focus image generation device comprises: an image generation element, configured to generate a fourth plurality of images; and a spatial light modulator, disposed on an optical path between the image generation element and the light diffuser screen, and configured to load different phase information to optical waves of the fourth plurality of images to enable the multi-focus image generation device to generate different images at different focal lengths.

3. The display apparatus according to claim 1, wherein the multi-focus image generation device comprises: an image generation element, configured to generate a fourth plurality of images; and a zoom liquid lens, disposed on an optical path between the image generation element and the light diffuser screen, wherein the multi-focus image generation device generates different images at different focal lengths by changing curvature of a light-exiting surface.

4. The display apparatus according to claim 1, wherein the display apparatus further comprises: a time sequence control device, configured to control a moment at which one of the first plurality of images is switched to and a moment at which one of the plurality of focal lengths is switched to, to enable the multi-focus image generation device to generate different images at different focal lengths.

5. The display apparatus according to claim 4, wherein the multi-focus image generation device comprises: an image generation element, configured to generate a fourth plurality of images; and a spatial light modulator, disposed on an optical path between the image generation element and the light diffuser screen, wherein the spatial light modulator loads different phase information at different moments to optical waves of the fourth plurality of images to allow the fourth plurality of images generated at different moments to correspond to different focal lengths, wherein the time sequence control device is configured to control a moment at which one of the fourth plurality of images is switched to and a moment at which the phase information is switched to, allowing the multi-focus image generation device to generate different images at different focal lengths.

6. The display apparatus according to claim 4, wherein the multi-focus image generation device comprises: an image generation element, configured to generate a fourth plurality of images; and a zoom liquid lens, disposed on an optical path between the image generation element and the light diffuser screen, wherein curvature of a light-exiting surface of the zoom liquid lens at different moments is different, allowing the fourth plurality of images generated at different moments to correspond to different focal lengths, wherein the time sequence control device is configured to control a moment at which one of the fourth plurality of images is switched to and a moment at which the curvature is switched to, allowing the multi-focus image generation device to generate different images at different focal lengths.

7. The display apparatus according to claim 4, wherein the multi-focus image generation device comprises: an image generation element, configured to generate a fourth plurality of images; a fixed-focus lens, disposed on an optical path between the image generation element and the light diffuser screen; and a first driving device, connected to the fixed-focus lens, wherein the first driving device drives the fixed-focus lens to move to different positions at different moments, to generate the fourth plurality of images at different moments to correspond to different focal lengths, wherein the time sequence control device is configured to control a moment at which one of the fourth plurality of images is switched to and a moment at which one of the positions is switched to, allowing the multi-focus image generation device to generate different images at different focal lengths.

8. The display apparatus according to claim 1, wherein the multi-focus image generation device comprises: an image generation element, having a plurality of image generation areas; and a spatial light modulator, disposed on an optical path between the image generation element and the light diffuser screen, wherein the spatial light modulator has a plurality of modulation areas, each modulation area corresponds to one image generation area, and the plurality of modulation areas load different phase information to optical waves of images generated in corresponding image generation areas, allowing a plurality of images generated by the image generation element at a same moment to correspond to different focal lengths.

9. The display apparatus according to claim 1, wherein the multi-focus image generation device comprises: an image generation element, having a plurality of image generation areas; and a zoom liquid lens, disposed on an optical path between the image generation element and the light diffuser screen, wherein the zoom liquid lens has a plurality of lens areas, each lens area corresponds to one image generation area, and curvature of light-exiting surfaces of the plurality of lens areas is different, allowing a plurality of images generated by the image generation element at a same moment to correspond to different focal lengths.

10. The display apparatus according to claim 1, further comprising: a second driving device, connected to the light diffuser screen, wherein the second driving device controls the light diffuser screen to move to an image plane of an image generated by the multi-focus image generation device.

11. The display apparatus according to claim 1, comprising a plurality of light diffuser screens, each light diffuser screen corresponds to one image plane of an image generated by the multi-focus image generation device, and different light diffuser screens are located on different image planes.

12. A display method, applied to a display apparatus, comprising: generating, by a multi-focus image generation device, a first plurality of images, wherein the multi-focus image generation device has a plurality of different focal lengths, and focal planes of the first plurality of images are located in different positions; receiving, by a light diffuser screen disposed on an image plane of the multi-focus image generation device, the first plurality of images; diffusing light beams of the first plurality of images to generate a second plurality of images; and imaging, by an optical imaging device, light beams of the second plurality of images to form a third plurality of images with different imaging distances.

13. The display method according to claim 12, wherein the display method comprises: generating a fourth plurality of images; and loading different phase information to optical waves of the fourth plurality of images to enable the multi-focus image generation device to generate different images at different focal lengths.

14. The display method according to claim 12, wherein the display method comprises: generating a fourth plurality of images; and changing curvature of a light-exiting surface to generate different images at different focal lengths.

15. The display method according to claim 12, wherein the display method further comprises: controlling a moment at which one of the first plurality of images is switched to and a moment at which one of the plurality of focal lengths is switched to, to generate different images at different focal lengths.

16. The display method according to claim 12, wherein the light diffuser screen is connected to a second driving device, and wherein the display method further comprises: when a focal length of the multi-focus image generation device is converted, controlling, by the second driving device, the light diffuser screen to move to an image plane of an image generated by the multi-focus image generation device.

17. The display method according to claim 16, wherein the controlling, by the second driving device, the light diffuser screen to move to an image plane of an image generated by the multi-focus image generation device comprises: determining an imaging distance V of the display apparatus based on the focal length of the multi-focus image generation device, wherein the imaging distance V is a distance between an image plane of the optical imaging device and an optical center of the optical image device, and then a distance S between a center of the light diffuser screen and the optical center of the optical image device is calculated according to the following formula, $S=\frac{\mathrm{fV}}{V-f},$ wherein f is a focal length of the optical image device; and driving, by the second driving device, the light diffuser screen to move to a position in which a distance to the optical center of the optical image device is S.

18. The display method according to claim 12, wherein the display method further comprises: projecting an image generated by the multi-focus image generation device to a corresponding light diffuser screen.

19. A display system, comprising: a display apparatus comprising: a multi-focus image generation device with a plurality of different focal lengths, configured to generate a first plurality of images, wherein focal planes of the first plurality of images are located in different positions; a light diffuser screen, disposed on an image plane of the multi-focus image generation device, and configured to: receive the first plurality of images; and diffuse light beams of the first plurality of images to generate a second plurality of images; and an optical imaging device, configured to image light beams of the second plurality of images to form a third plurality of images with different imaging distances; and a reflector, wherein the reflector is located on an imaging optical path of the optical imaging device.

20. The display system according to claim 19, wherein: the display apparatus is installed in a cab; and the reflector is a windshield installed in the cab.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0045] FIG. 1 is a schematic diagram of a structure of a head-up display apparatus in the conventional technology;

[0046] FIG. 2 is a schematic diagram of a structure of a head-up display apparatus applied in a cab according to an embodiment of this application;

[0047] FIG. 3 is a schematic diagram of a structure of a head-up display apparatus according to an embodiment of this application;

[0048] FIG. 4 is a block diagram of a structure of a head-up display apparatus according to an embodiment of this application;

[0049] FIG. 5 is a schematic diagram of a principle of changing a focal length of a multi-focus image generation unit by a spatial light modulator according to an embodiment of this application;

[0050] FIG. 6a is a schematic diagram of a principle of changing a focal length of a multi-focus image generation unit by a zoom liquid lens according to an embodiment of this application;

[0051] FIG. 6b is a schematic diagram of a structure of a zoom liquid lens according to an embodiment of this application;

[0052] FIG. 7 is a schematic diagram of a principle of changing a focal length of a multi-focus image generation unit by a fixed-focus lens according to an embodiment of this application;

[0053] FIG. 8 is a schematic diagram of a structure of dividing a pyramid image into a plurality of parts according to an embodiment of this application;

[0054] FIG. 9 is a schematic diagram of a structure of a plurality of light diffuser screens in a head-up display apparatus according to an embodiment of this application;

[0055] FIG. 10 is a schematic diagram of a structure of a head-up display apparatus according to an embodiment of this application;

[0056] FIG. 11 is a schematic diagram of a structure of a plurality of image generation areas in an image generation element according to an embodiment of this application;

[0057] FIG. 12 is a schematic diagram of a principle of changing a focal length of a multi-focus image generation unit by a spatial light modulator according to an embodiment of this application;

[0058] FIG. 13 is a schematic diagram of a principle of changing a focal length of a multi-focus image generation unit by a zoom liquid lens according to an embodiment of this application;

[0059] FIG. 14 is a schematic diagram of a principle of changing a focal length of a multi-focus image generation unit by a spatial light modulator according to an embodiment of this application;

[0060] FIG. 15 is a schematic diagram of a principle of changing a focal length of a multi-focus image generation unit by a zoom liquid lens according to an embodiment of this application;

[0061] FIG. 16 is a schematic diagram of a structure of a light diffuser screen according to an embodiment of this application;

[0062] FIG. 17 is a schematic diagram of a structure of a light diffuser screen according to an embodiment of this application; and

[0063] FIG. 18 is a flow block diagram of a display method for a head-up display apparatus according to an embodiment of this application.

REFERENCE NUMERALS

[0064] 01—first projection module; 02—second projection module; 03—penetrating diffusion plate; 04—polarizing beam splitter; 05—free form mirror; 06—extinction mechanism; A1—far distance image; A2—near distance image; 1—multi-focus image generation unit; 101—image generation element; 102—focal length conversion element; 1021—spatial light modulator; 1021A—first modulation area; 1021B—second modulation area; 1022—zoom liquid lens; 1022A—first lens area; 1022B—second lens area; 1023—fixed-focus lens; 2—light diffuser screen; 21—nano scattering coating; 22—liquid crystal molecular cooling coating; 201—first light diffuser screen; 202—second light diffuser screen; 3—optical imaging unit; 4—time sequence control unit; 5—windshield; 61—first image; 62—second image; 7—light-exiting surface; 8—permanent magnet; 9—coil; 10—drive cavity; 11—optical cavity.

DESCRIPTION OF EMBODIMENTS

[0065] Embodiments of this application relate to a head-up display apparatus, a display method, and a display system. The following describes in detail the head-up display apparatus, the display method, and the display system with reference to the accompanying drawings.

[0066] According to one aspect, an embodiment of this application provides a head-up display apparatus that can implement multi-screen display and has a simple structure. Referring to FIG. 2 and FIG. 3, the head-up display apparatus includes a multi-focus image generation unit 1, a light diffuser screen 2, and an optical imaging unit 3. The multi-focus image generation unit 1 has a plurality of different focal lengths and is configured to generate a plurality of images, and focal planes of the plurality of images are located in different positions (the multi-focus image generation unit 1 shown in FIG. 3 has a first focal plane F1 and a second focal plane F2). The light diffuser screen 2 is disposed on an image plane of the multi-focus image generation unit 1, and is configured to receive the plurality of images generated by the multi-focus image generation unit 1, and diffuse light beams of the plurality of images. The optical imaging unit 3 is configured to image a plurality of images projected to the light diffuser screen 2 to form a plurality of images with different imaging distances (FIG. 3 shows forming of a first image 61 with a first imaging distance V1 and a second image 62 with a second imaging distance V2). A focal plane is a plane that is perpendicular to an optical axis of the multi-focus image generation unit and includes a focal point. An image plane is an imaging plane of an image generated by the multi-focus image generation unit, and the focal plane and the image plane may be located in different spatial positions, or may be located in a same spatial position.

[0067] The head-up display apparatus uses the multi-focus image generation unit with a plurality of different focal lengths, and the multi-focus image generation unit can generate a plurality of images. Focal planes of the plurality of images are located in different positions. In this way, image planes of the plurality of images are also located in different positions, so that light diffuser screens that receive the images generated by the multi-focus image generation unit and amplify the received images have different distances from the optical imaging unit. Referring to FIG. 3, according to a formula

[00002]$\frac{1}{f}=\frac{1}{S}+\frac{1}{V},$

f is a focal length of the optical imaging unit 3, S is a distance between an optical center of the optical imaging unit 3 and a center of the light diffuser screen 2, and V is an imaging distance of the optical imaging unit 3. According to the formula, when a relative distance between the light diffuser screen and the optical imaging unit is different, an imaging distance of the optical imaging unit is different. Therefore, the multi-focus image generation unit with a plurality of different focal lengths can be used to implement multi-screen display.

[0068] Because there is one multi-focus image generation unit 1 provided in this embodiment of this application, multi-screen display is implemented by changing a focal length. Compared with a structure shown in FIG. 1 in the conventional technology, a structure of an entire head-up display apparatus is simplified. Correspondingly, a volume of the head-up display apparatus is also smaller, and a miniaturization design requirement is met.

[0069] The following describes specific implementations of implementing multi-screen display.

Implementation 1

[0070] Referring to FIG. 4, the head-up display apparatus further includes a time sequence control unit 4. The multi-focus image generation unit generates one image at a time, and one image corresponds to one focal length. The time sequence control unit 4 is configured to control a moment at which one of the plurality of images generated by the multi-focus image generation unit 1 is switched to and a moment at which one of the plurality of focal lengths is switched to, so that the moment at which one of the plurality of images is switched to and the moment at which one of the focal lengths is switched to are equal, and are less than or equal to reaction time of a human eye.

[0071] For example, at a first moment, the multi-focus image generation unit generates a first image, and the first image corresponds to a first focal length. At a second moment, the multi-focus image generation unit generates a second image, and the second image corresponds to a second focal length. The time sequence control unit controls moments at which the first image and the second image are switched to, and moments at which the first focal length and the second focal length are switched to. Both the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to are less than or equal to the reaction time of the human eye. That is, the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to are very short, and cannot be identified by the human eye. In this way, it is felt that dual-screen display is formed at a same time.

[0072] It should be noted that, according to ergonomics, the reaction time of the human eye is about 0.2 seconds to 0.25 seconds.

Implementation 2

[0073] The multi-focus image generation unit simultaneously generates a plurality of images, and has a plurality of different focal lengths at a same time. The plurality of images correspond to different focal lengths. In this way, multi-screen display is formed at a same moment.

[0074] For example, at a moment, the multi-focus image generation unit simultaneously generates a first image and a second image, the first image corresponds to a first focal length, the second image corresponds to a second focal length, and double-screen display is seen by the human eye at this moment.

Implementation 3

[0075] The head-up display apparatus further includes a time sequence control unit 4. The multi-focus image generation unit simultaneously generates a plurality of images, has a plurality of different focal lengths at a same time, and the plurality of images correspond to different focal lengths. The time sequence control unit 4 is configured to control a moment at which one of the plurality of images generated by the multi-focus image generation unit 1 is switched to and a moment at which one of the plurality of focal lengths is switched to, so that the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to are equal, and are less than or equal to reaction time of a human eye.

[0076] For example, at a first moment, the multi-focus image generation unit simultaneously generates a first image and a second image, the first image corresponds to a first focal length, and the second image corresponds to a second focal length. At a second moment, the multi-focus image generation unit simultaneously generates a third image and a fourth image, the third image corresponds to a third focal length, and the fourth image corresponds to a fourth focal length. The time sequence control unit controls moments at which the first image and the third image are switched to, and moments at which the first focal length and the third focal length are switched to, and controls moments at which the second image and the fourth image are switched to, and moments at which the second focal length and the fourth focal length are switched to. Both the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to are less than or equal to the reaction time of the human eye. That is, the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to are very short, and cannot be identified by the human eye. In this way, it is felt that four-screen display is formed at a same time.

[0077] To clearly describe the three implementations, the following first describes implementation 1 in detail, then describes implementation 2 in detail, and finally describes implementation 3 in detail.

[0078] Related Solutions of Implementation 1

[0079] Referring to FIG. 3, when the focal length of the multi-focus image generation unit 1 is F1, after a first image generated by the multi-focus image generation unit 1 passes through the light diffuser screen 2 and the optical imaging unit 3, a first image 61 with an imaging distance V1 is formed. When the focal length of the multi-focus image generation unit 1 is F2, after a second image generated by the multi-focus image generation unit 1 passes through the light diffuser screen 2 and the optical imaging unit 3, a second image 62 with an imaging distance V2 is formed, and double-screen display is shown in the figure. By analogy, when there are N focal lengths of the multi-focus image generation unit (N is an integer greater than 2), corresponding N-screen display is formed. During specific implementation, if the first image is navigation image information, the first imaging displays corresponding guidance image information; and if the second image is instrument image information, the second imaging displays corresponding instrument image information. Time for switching the first image to the second image and time for switching the focal length F1 to the focal length F2 are less than or equal to the reaction time of the human eye. Therefore, the guidance image information and the instrument image information are simultaneously displayed to the human eye.

[0080] Referring to FIG. 2, the multi-focus image generation unit 1 includes an image generation element 101 and a focal length conversion element 102. The image generation element 101 is configured to generate a plurality of images, and the time sequence control unit 4 is configured to control a moment at which one of the plurality of images generated by the image generation element 101 is switched to. The time sequence control unit 4 is configured to control the focal length conversion element 102 to convert a focal length of the image generation element 101, so that the multi-focus image generation unit has a plurality of different focal lengths.

[0081] A structure of the focal length conversion element 102 has a plurality of cases, which are explained and described in the following by using three embodiments.

Embodiment 1

[0082] Referring to FIG. 5, the focal length conversion element includes a spatial light modulator 1021. The spatial light modulator 1021 is disposed on an optical path between the image generation element and the light diffuser screen. The spatial light modulator 1021 loads different phase information at different moments to optical waves of the images generated by the image generation element 101, so that a plurality of images generated by the image generation element 101 at different moments correspond to different focal lengths. The time sequence control unit is configured to control a moment at which the phase information is switched to, and the moment at which the phase information is switched to is equal to the moment at which one of the images is switched to.

[0083] As shown in FIG. 5, at a first moment, when phase information loaded by the spatial light modulator 1021 to an optical wave of an image generated by the image generation element is first phase information, and a focal length of the image generated by the image generation element is F1, the image is imaged on a first image plane. At a second moment, when phase information loaded by the spatial light modulator to an optical wave of an image generated by the image generation element is second phase information, and a focal length of the image generated by the image generation element is F2, the image is imaged on a second image plane. A time difference between the first moment and the second moment is less than or equal to the reaction time of the human eye (that is, moments at which the first phase information and the second phase information are switched to, and moments at which the first image and the second image are switched to are less than or equal to the reaction time of the human eye). In this way, double-screen display is seen by the human eye. It can be learned from the figure that, when the first phase information and the second phase information loaded by the spatial light modulator to the optical waves of the images generated by the image generation element are different, a focal length size, a focal plane position, and an image plane position are changed.

[0084] The spatial light modulator may be a spatial light modulator based on a microlens array, or may be a liquid crystal spatial light modulator. For example, a liquid crystal on silicon (LCoS) spatial light modulator implements modulation of each pixel by changing a voltage value of the pixel, so as to modulate an optical wave of the image generation element, and change a focal length of the image generation element.

[0085] A moment at which the phase information is switched to and loaded by the spatial light modulator to the optical waves of the images generated by the image generation element is less than or equal to the reaction time of the human eye, so that it is felt that there is multi-screen display at a same time.

Embodiment 2

[0086] Referring to FIG. 6a and FIG. 6b, the focal length conversion element includes a zoom liquid lens 1022. The zoom liquid lens 1022 is disposed on an optical path between the image generation element and the light diffuser screen. Curvature of a light-exiting surface of the zoom liquid lens at different moments is different, so that a plurality of images generated by the image generation element at different moments correspond to different focal lengths. The time sequence control unit is configured to control a moment at which the curvature is switched to, and the moment at which the curvature is switched to is equal to the moment at which one of the images is switched to.

[0087] FIG. 6b is a schematic diagram of a structure of the zoom liquid lens. A drive cavity 10 communicates with an optical cavity 11, that is, liquid in the drive cavity 10 and liquid in the optical cavity 11 can flow between the two cavities. When the liquid in the optical cavity 11 changes, surface tension of a light-exiting surface 7 changes, so that curvature of the light-exiting surface 7 changes. A permanent magnet 8 and a coil 9 form a power source, configured to drive flowing between the liquid in the optical cavity 11 and the liquid in the drive cavity 10.

[0088] As shown in FIG. 6b, at a first moment, after the coil 9 is connected to a first current, a magnetic field generated by the coil 9 is different from a magnetic field generated by the permanent magnet 8, and the permanent magnet 8 is attracted to move downward, so that a volume of the drive cavity 10 is reduced, and the liquid in the drive cavity 10 flows to the optical cavity 11, causing deformation of the light-exiting surface 7 to form first curvature (shown by a solid line), so that a focal length of the zoom liquid lens is F1. At a second moment, after the coil 9 is connected to a second current, a magnetic field generated by the coil 9 is different from a magnetic field generated by the permanent magnet 8, and the permanent magnet 8 is attracted to move downward, so that a volume of the drive cavity 10 is reduced, and the liquid in the drive cavity 10 flows to the optical cavity 11, causing deformation of the light-exiting surface 7 to form second curvature (shown by a dashed line), so that a focal length of the zoom liquid lens is F2. A value of the second current is greater than a value of the first current. A time difference between the first moment and the second moment is less than or equal to the reaction time of the human eye (that is, moments at which the first curvature and the second curvature are switched to, and moments at which the first image and the second image are switched to are less than or equal to the reaction time of the human eye). In this way, double-screen display is seen by the human eye. It can be learned from the figure that, when the curvature of the light-exiting surface of the zoom liquid lens is different, a focal length size, a focal plane position, and an image plane position are changed.

Embodiment 3

[0089] Referring to FIG. 7, the focal length conversion element includes a fixed-focus lens 1023 and a first driving unit (not shown in the figure). The fixed-focus lens is disposed on an optical path between the image generation element and the light diffuser screen. The first driving unit is connected to the fixed-focus lens, and the time sequence control unit is configured to control the first driving unit to move the fixed-focus lens to different positions at different moments, so that a plurality of images generated by the image generation element at different moments correspond to different focal lengths.

[0090] As shown in FIG. 7, at a first moment, when the first driving unit drives the fixed-focus lens to move to a first position (shown by a dashed line), a focal length of a first image generated by the image generation element is F1, and imaging of the first image is performed on a first image plane. At a second moment, when the first driving unit drives the fixed-focus lens to move to a second position (shown by a solid line), a focal length of a second image generated by the image generation element is F2, and imaging of the second image is performed on a second image plane. A time difference between the first moment and the second moment is less than or equal to the reaction time of the human eye (moments at which the first position and the second position are switched to, and moments at which the first image and the second image are switched to are less than or equal to the reaction time of the human eye). In this way, double-screen display is seen by the human eye. It can be learned from the figure that, when the fixed-focus lens moves to different positions, a focal length size, a focal plane position, and an image plane position of the multi-focus image generation unit are changed.

[0091] The first driving unit in embodiment 3 has a plurality of structures. For example, the first driving unit includes a driving motor, and the driving motor is connected to the fixed-focus lens to drive the fixed-focus lens to move. For another example, the first driving unit includes a telescopic cylinder, and the telescopic cylinder is connected to the fixed-focus lens to drive the fixed-focus lens to move. Any structure that can drive the fixed-focus lens to move falls within the protection scope of this application.

[0092] The fixed-focus lens may be disposed on a mobile station, and the first driving unit is connected to the mobile station to drive the mobile station to move, so as to drive the fixed-focus lens to move. The fixed-focus lens is generally made of a glass material, and the first driving unit is directly connected to the fixed-focus lens, which requires a relatively high connection structure. Therefore, the fixed-focus lens is installed on the mobile station.

[0093] The foregoing three embodiments are only used as some implementations of the focal length conversion element, and the focal length of the image generation element may be changed in another implementation.

[0094] Because the focal length of the multi-focus image generation unit is constantly converted, an image plane position of an image generated by the multi-focus image generation unit is also constantly changing, and the light diffuser screen 2 needs to be able to receive imaging of the multi-focus image generation unit in real time. The light diffuser screen 2 has the following two implementation structures.

Embodiment 1

[0095] Referring to FIG. 2 and FIG. 3, the head-up display apparatus further includes a second driving unit (not shown in the figure), the second driving unit is connected to the light diffuser screen, and the second driving unit controls the light diffuser screen to move to an image plane of an image generated by the multi-focus image generation unit. In FIG. 3, a solid line indicates that the light diffuser screen is located on a first image plane when the multi-focus image generation unit has a first focal length F1. In FIG. 3, a dashed line indicates that the light diffuser screen is located on a second image plane when the multi-focus image generation unit has a second focal length F2.

[0096] That is, the second driving unit drives the light diffuser screen to move along an imaging optical path of the multi-focus image generation unit (in a P direction in FIG. 3), so as to receive imaging of the multi-focus image generation unit at different moments.

[0097] In addition, the second driving unit can drive the light diffuser screen to move continuously along the imaging optical path of the multi-focus image generation unit. In this design, the following technical effect can be further achieved: Referring to FIG. 8, if a pyramid needs to be imaged, a pyramid image is divided into a plurality of parts (12 parts are displayed in the figure). The multi-focus image generation unit displays one part of the image at a time, the part continuously switches from the top to the bottom of the pyramid, and focal lengths of each two parts of the image are continuously changed. The second driving unit drives the light diffuser screen to move continuously, so that a final pyramid image seen by the human eye appears in a three-dimensional structure, which has depth information and improves user experience.

Embodiment 2

[0098] Referring to FIG. 9, there are a plurality of light diffuser screens, each light diffuser screen corresponds to one image plane of images generated by the multi-focus image generation unit, and different light diffuser screens are located on different image planes.

[0099] That is, there are a plurality of light diffuser screens, each light diffuser screen is fixed, and each light diffuser screen is disposed on a corresponding image plane. For example, the head-up display apparatus shown in FIG. 9 includes a first light diffuser screen 201 and a second light diffuser screen 202. The first light diffuser screen 201 is disposed in an image plane position in which a focal length of the multi-focus image generation unit is F1, and the second light diffuser screen 202 is disposed in an image plane position in which a focal length of the multi-focus image generation unit is F2.

[0100] A movable light diffuser screen structure shown in FIG. 3 has a simpler structure and occupies less space than a plurality of fixed light diffuser screen structures shown in FIG. 9. Therefore, this application is preferably implemented by using the second driving unit to drive the light diffuser screen to move.

[0101] Related Solutions of Implementation 2

[0102] Referring to FIG. 10, the multi-focus image generation unit 1 includes an image generation element 101 and a focal length conversion element 102, and the image generation element 101 has a plurality of image generation areas (FIG. 10 and FIG. 11 show a first image generation area P1 and a second image generation area P2). The focal length conversion element 102 is configured to simultaneously change focal lengths of the plurality of image generation areas, so that the plurality of image generation areas have different focal lengths.

[0103] A structure of the focal length conversion element 102 has a plurality of cases, which are explained and described in the following by using two embodiments.

Embodiment 1

[0104] Referring to FIG. 12, the focal length conversion element 102 includes a spatial light modulator 1021. The spatial light modulator is disposed on an optical path between the image generation element and the light diffuser screen. The spatial light modulator has a plurality of modulation areas, each modulation area corresponds to one image generation area, and the plurality of modulation areas load different phase information to optical waves of images generated in corresponding image generation areas, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths.

[0105] As shown in FIG. 12, the spatial light modulator includes a first modulation area 1021A and a second modulation area 1021B, the first modulation area 1021A corresponds to the first image generation area P1, and the second modulation area 1021B corresponds to the second image generation area P2. When phase information loaded by the first modulation area 1021A to an optical wave of a first image generated by the first image generation area P1 is first phase information, a focal length of the first image generated by the first image generation area P1 is F1, and imaging of the first image is performed on a first image plane. At a same moment, when phase information loaded by the second modulation area 1021B to an optical wave of a second image generated by the second image generation area P2 is second phase information, a focal length of the second image generated by the second image generation area P2 is F2, and imaging of the second image is performed on a second image plane. It can be learned from the figure that when the first phase information and the second phase information of the optical waves loaded by the first modulation area 1021A and the second modulation area 1021B to the images generated by the corresponding image generation areas are different, a focal length size, a focal plane position, and an image plane position are changed, thereby implementing multi-screen display at a same time.

Embodiment 2

[0106] Referring to FIG. 13, the focal length conversion element 102 includes a zoom liquid lens 1022. The zoom liquid lens 1022 is disposed on an optical path between the image generation element and the light diffuser screen. The zoom liquid lens 1022 has a plurality of lens areas, each lens area corresponds to one image generation area, and curvature of light-exiting surfaces of the plurality of lens areas is different, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths.

[0107] As shown in FIG. 13, the zoom liquid lens 1022 includes a first lens area 1022A and a second lens area 1022B, the first lens area 1022A corresponds to the first image generation area P1, and the second lens area 1022B corresponds to the second image generation area P2. Curvature of a light-exiting surface of the first lens area 1022A is first curvature, and a focal length of a first image generated by the first image generation area P1 is F1, so that imaging of the first image is performed on a first image plane. At a same moment, curvature of a light-exiting surface of the second lens area 1022B is second curvature, and a focal length of a second image generated by the second image generation area P2 is F2, so that imaging of the second image is performed on a second image plane. It can be learned from the figure that, when the curvature of the first lens area 1022A and the second lens area 1022B is different, a focal length size, a focal plane position, and an image plane position are changed, thereby implementing multi-screen display at a same time.

[0108] In some implementations, there are a plurality of light diffuser screens, each light diffuser screen corresponds to one image plane of images generated by the multi-focus image generation unit, and different light diffuser screens are located on different image planes.

[0109] That is, there are a plurality of light diffuser screens, each light diffuser screen is fixed, and each light diffuser screen is disposed on a corresponding image plane.

[0110] Related Solutions of Implementation 3

[0111] The multi-focus image generation unit includes an image generation element and a focal length conversion element, the image generation element has a plurality of image generation areas, and the focal length conversion element is configured to simultaneously modulate focal lengths of the plurality of image generation areas, so that the plurality of image generation areas have different focal lengths. In addition, the head-up display apparatus further includes a time sequence control unit, where the time sequence control unit is configured to control a moment at which one of images generated in the image generation areas is switched to and a moment at which one of the focal lengths is switched to, so that the moment at which one of the plurality of images is switched to and the moment at which one of the focal lengths is switched to are equal, and are less than or equal to the reaction time of the human eye.

[0112] A structure of the focal length conversion element 102 has a plurality of cases, which are explained and described in the following by using two embodiments.

Embodiment 1

[0113] Referring to FIG. 14, the focal length conversion element includes a spatial light modulator 1021. The spatial light modulator is disposed on an optical path between the image generation element and the light diffuser screen. The spatial light modulator has a plurality of modulation areas, each modulation area corresponds to one image generation area, and the plurality of modulation areas load different phase information to optical waves of images generated in corresponding image generation areas, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths. In addition, the time sequence control unit controls the image generation areas and loads different phase information at different moments to optical waves of images generated by the image generation areas, so that a plurality of images generated by the image generation areas at different moments correspond to different focal lengths.

[0114] As shown in FIG. 14, the spatial light modulator includes a first modulation area 1021A and a second modulation area 1021B, the first modulation area 1021A corresponds to a first image generation area P1, and the second modulation area 1021B corresponds to a second image generation area P2. At a first moment, when phase information loaded by the first modulation area 1021A to an optical wave of a first image generated by the first image generation area P1 is first phase information, a focal length of the first image generated by the first image generation area P1 is F1, and imaging of the first image is performed on a first image plane. At the first moment, when phase information loaded by the second modulation area 1021B to an optical wave of a second image generated by the second image generation area P2 is second phase information, a focal length of the second image generated by the second image generation area P2 is F2, and imaging of the second image is performed on a second image plane. At a second moment, when phase information loaded by the first modulation area 1021A to an optical wave of a third image generated by the first image generation area P1 is third phase information, a focal length of the third image generated by the first image generation area P1 is F3, and imaging of the third image is performed on a third image plane. At the second moment, when phase information loaded by the second modulation area 1021B to an optical wave of a fourth image generated by the second image generation area P2 is fourth phase information, a focal length of the fourth image generated by the second image generation area P2 is F2, and imaging of the fourth image is performed on a fourth image plane. A time difference between the first moment and the second moment is less than or equal to the reaction time of the human eye (moments at which the first phase information and the third phase information are switched to, moments at which the second phase information and the fourth phase information are switched to, and moments at which the first image and the second image are switched to are less than or equal to the reaction time of the human eye). In this way, four-screen display is seen by the human eye.

Embodiment 2

[0115] Referring to FIG. 15, the focal length conversion element 102 includes a zoom liquid lens 1022. The zoom liquid lens 1022 is disposed on an optical path between the image generation element and the light diffuser screen. The zoom liquid lens 1022 has a plurality of lens areas, each lens area corresponds to one image generation area, and curvature of light-exiting surfaces of the plurality of lens areas is different, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths. In addition, the time sequence control unit controls the image generation areas. The curvature of the light-exiting surfaces of the plurality of lens areas at different moments is different, so that a plurality of images generated by the image generation areas at different moments correspond to different focal lengths.

[0116] As shown in FIG. 15, the zoom liquid lens 1022 includes a first lens area 1022A and a second lens area 1022B, the first lens area 1022A corresponds to a first image generation area P1, and the second lens area 1022B corresponds to a second image generation area P2. At a first moment, curvature of a light-exiting surface of the first lens area 1022A is first curvature, and a focal length of a first image generated by the first image generation area P1 is F1, so that imaging of the first image is performed on a first image plane. At the first moment, curvature of a light-exiting surface of the second lens area 1022B is second curvature, and a focal length of a second image generated by the second image generation area P2 is F2, so that imaging of the second image is performed on a second image plane. At a second moment, curvature of a light-exiting surface of the first lens area 1022A is third curvature, and a focal length of a third image generated by the first image generation area P1 is F3, so that imaging of the third image is performed on a third image plane. At the second moment, curvature of a light-exiting surface of the second lens area 1022B is fourth curvature, and a focal length of a fourth image generated by the second image generation area P2 is F2, so that imaging of the fourth image is performed on a fourth image plane. A time difference between the first moment and the second moment is less than or equal to the reaction time of the human eye (moments at which the first curvature and the third curvature are switched to, moments at which the second curvature and the fourth curvature are switched to, and moments at which the first image and the second image are switched to are less than or equal to the reaction time of the human eye). In this way, four-screen display is seen by the human eye.

[0117] In some implementations, there are a plurality of light diffuser screens, each light diffuser screen is connected to a second driving unit, and the second driving unit controls the light diffuser screen to move to an image plane of an image generated by the multi-focus image generation unit.

[0118] For example, a structure shown in FIG. 14 may include two light diffuser screens, which are respectively a first light diffuser screen and a second light diffuser screen, and there are two second driving units, which are respectively a second driving unit A and a second driving unit B. The second driving unit A may drive the first light diffuser screen to move between the first image plane and the third image plane, and the second driving unit B may drive the second light diffuser screen to move between the second image plane and the fourth image plane.

[0119] The foregoing describes a specific structure that may be implemented for the second driving unit, and details are not described herein again.

[0120] In the foregoing implementation 1, implementation 2, and implementation 3, the light diffuser screen is used to implement diffuse reflection by using a concave-convex structure disposed on a scattering surface, to implement an expanded image. However, roughness of a scattering surface of an existing light diffuser screen is large, and is basically at a scale of dozens of microns. Therefore, an image formed in this way has a blurred edge and obvious granular sensation, and high-definition display cannot be implemented.

[0121] To improve visual experience, for example, referring to FIG. 16, a nano scattering coating 21 is formed on a scattering surface of the light diffuser screen 2 provided in this embodiment of this application, and a size of nano-particles of the nano scattering coating 21 is approximately close to a micron scale, to reduce surface roughness of the light diffuser screen. For another example, referring to FIG. 17, a liquid crystal molecular cooling coating 22 is formed on the scattering surface of the light diffuser screen 2. The liquid crystal molecular cooling coating is formed on the scattering surface of the light diffuser screen, to reduce roughness of the scattering surface of the light diffuser screen, so that an image magnified by the optical imaging unit does not have a blurred edge, obvious noise, and granular sensation. For another example, the light diffuser screen is made of glass ceramics. Diffusion is implemented by using a microcrystalline molecule in the glass ceramics. The microcrystalline molecule is at a nanometer scale, and after being magnified by the optical imaging unit, an image has no obvious noise and granular sensation, thereby forming high-definition display.

[0122] The optical imaging unit 3 has a plurality of implementable structures. For example, the optical imaging unit 3 includes an aspherical reflector. For another example, the optical imaging unit 3 includes an aspherical reflector and a convex mirror that are stacked. For another example, the optical imaging unit 3 includes an aspherical reflector and a concave mirror that are stacked. Certainly, the optical imaging unit 3 may alternatively include another optical element. A specific structure of the optical imaging unit is not limited in this application, and any structure falls within the protection scope of this application.

[0123] According to another aspect, an embodiment of this application further provides a display system, where the display system includes a reflector and the head-up display apparatus provided in the foregoing embodiments, and the reflector is located on an imaging optical path of an optical imaging unit. That is, an image formed by an optical imaging element of the head-up display apparatus may be reflected into a human eye by using the reflector.

[0124] It should be noted that the display system may be installed in a driving device, or the display system may be installed in a teaching device.

[0125] When the display system is installed in the driving device, a windshield can be used as the reflector, or the reflector can be disposed alone. This application preferably uses the windshield as the reflector.

[0126] The head-up display apparatus provided in the foregoing embodiments is used in the display system, and an image generation unit in the head-up display apparatus is a multi-focus image generation unit, that is, has a plurality of different focal lengths, and can generate a plurality of images. In this way, multi-screen display can be implemented, and the display system is a single optical machine structure (one multi-focus image generation unit) with a simple structure and a corresponding decreased volume.

[0127] According to still another aspect, an embodiment of this application further provides a display method for a head-up display apparatus. Referring to FIG. 18, the display method includes:

[0128] S01. A multi-focus image generation unit generates a plurality of images, where the multi-focus image generation unit has a plurality of different focal lengths, and focal planes of the plurality of images are located in different positions.

[0129] S02. A light diffuser screen disposed on an image plane of the multi-focus image generation unit receives the plurality of images generated by the multi-focus image generation unit, and diffuses light beams of the plurality of images.

[0130] S03. An optical imaging unit images a plurality of images projected to the light diffuser screen to form a plurality of images with different imaging distances.

[0131] That is, an image generation unit in the display method is a multi-focus image generation unit, the multi-focus image generation unit can generate a plurality of images, and focal planes of the plurality of images are located in different positions. In this way, a plurality of images with different imaging distances are formed, and multi-screen display is implemented. Compared with an existing technology of implementing multi-screen display by using a plurality of image generation units with different focal lengths, one multi-focus image generation unit replaces the plurality of image generation units with different focal lengths.

[0132] The display method may be implemented in the following three implementations to implement multi-screen display at a same time. The following separately describes the three implementations.

[0133] First Implementation

[0134] In this implementation, the head-up display apparatus further includes a time sequence control unit. The display method includes: The time sequence control unit controls a moment at which one of the plurality of images generated by the multi-focus image generation unit is switched to and a moment at which one of the plurality of focal lengths is switched to, so that the moment at which one of the plurality of images is switched to and the moment at which one of the focal lengths is switched to are equal, and are less than or equal to reaction time of a human eye.

[0135] The time sequence control unit controls the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to, so that the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to are less than or equal to the reaction time of the human eye. That is, the moment at which one of the images is switched to and the moment at which one of the focal lengths is switched to are very short, and cannot be identified by the human eye. In this way, the human eye feels that there is multi-screen display at a same time.

[0136] In some embodiments, the multi-focus image generation unit includes an image generation element and a spatial light modulator. In some other embodiments, a multi-focal image generation unit includes an image generation element and a zoom liquid lens. In some other embodiments, the multi-focus image generation unit includes an image generation element, a fixed-focus lens, and a first driving unit. The image generation element can generate a plurality of images. The time sequence control unit controls a moment at which one of the plurality of images generated by the image generation element is switched to, and the moment at which one of the images of the image generation element is switched to is less than or equal to the reaction time of the human eye. The spatial light modulator, the zoom liquid lens, the fixed-focus lens, and the first driving unit are configured to change a focal length of the image generation element.

[0137] When the multi-focus image generation unit includes an image generation element and a spatial light modulator, the display method includes: The spatial light modulator loads different phase information at different moments to optical waves of the images generated by the image generation element, so that a plurality of images generated by the image generation element at different moments correspond to different focal lengths. The time sequence control unit controls a moment at which one of the images generated by the image generation element is switched to and a moment at which the phase information is switched to, and the moment at which the phase information is switched to is equal to the moment at which one of the images is switched to. Different phase information is loaded at different moments to the optical waves of the images generated by the image generation element, so as to change the focal length of the image generation element, and finally, the plurality of images generated by the image generation element at different moments correspond to different focal lengths. The moment at which the phase information is switched to is equal to the moment at which one of the images is switched to, and are less than or equal to the reaction time of the human eye. In this way, the human eye feels that there is multi-screen display at a same time.

[0138] When the multi-focus image generation unit includes an image generation element and a zoom liquid lens, the display method includes: Curvature of a light-exiting surface of the zoom liquid lens at different moments is different, so that a plurality of images generated by the image generation element at different moments correspond to different focal lengths. The time sequence control unit controls a moment at which one of the images generated by the image generation element is switched to and a moment at which the curvature is switched to, and the moment at which the curvature is switched to is equal to the moment at which one of the images is switched to. The curvature of the light-exiting surface of the zoom liquid lens at different moments is different, which can change the focal length of the image generation element, and finally, the plurality of images generated by the image generation element at different moments correspond to different focal lengths. The moment at which the curvature is switched to is equal to the moment at which one of the images is switched to, and are less than or equal to the reaction time of the human eye. In this way, the human eye feels that there is multi-screen display at a same time.

[0139] When the multi-focus image generation unit includes an image generation element, a fixed-focus lens, and a first driving unit connected to the fixed-focus lens, the display method includes: The first driving unit drives the fixed-focus lens to move to different positions at different moments, so that a plurality of images generated by the image generation element at different moments correspond to different focal lengths. The time sequence control unit controls a moment at which one of the images generated by the image generation element is switched to and a moment at which one of the positions is switched to, and the moment at which one of the positions is switched to is equal to the moment at which one of the images is switched to. The first driving unit drives the fixed-focus lens at different moments to move to different positions, to change the focal length of the image generation element, and finally, the plurality of images generated by the image generation element at different moments correspond to different focal lengths. The moment at which one of the positions of the fixed-focus lens is switched to is equal to the moment at which one of the images is switched to, and are less than or equal to the reaction time of the human eye. In this way, the human eye feels that there is multi-screen display at a same time.

[0140] In this implementation, the light diffuser screen is connected to a second driving unit. The display method further includes: When a focal length of the multi-focus image generation unit is converted, the second driving unit controls the light diffuser screen to move to an image plane of an image generated by the multi-focus image generation unit.

[0141] In a process in which the second driving unit drives the light diffuser screen to move, a position to which the light diffuser screen moves needs to be determined. Therefore, that the second driving unit controls the light diffuser screen to move to an image plane of an image generated by the multi-focus image generation unit includes:

[0142] S11. Determine an imaging distance V of the head-up display apparatus based on a focal length of the multi-focus image generation unit, where the imaging distance V is a distance between an image plane of the optical imaging unit and an optical center of the optical imaging unit.

[0143] S12. Then calculate a distance S between a center of the light diffuser screen and the optical center of the optical imaging unit according to the following formula,

[00003]$S=\frac{\mathrm{fV}}{V-f};$

where f is a focal length of the optical imaging unit.

[0144] S13. The second driving unit drives the light diffuser screen to move to a position in which a distance to the optical center of the optical imaging unit is S.

[0145] After the optical imaging unit is determined, a distance between the light diffuser screen and the optical imaging unit and an imaging distance of the optical imaging unit meet

[00004]$\frac{1}{f}=\frac{1}{S}+\frac{1}{V}.$

Therefore, the position to which the light diffuser screen moves may be determined according to this formula.

[0146] In this implementation, the head-up display apparatus further includes a plurality of light diffuser screens (that is, the second driving unit is not included), and each light diffuser screen corresponds to one image plane of images generated by the multi-focus image generation unit. The display method further includes: projecting images generated by the multi-focus image generation unit at different moments to corresponding light diffuser screens.

[0147] Second Implementation

[0148] In this implementation, the multi-focus image generation unit simultaneously generates a plurality of images and has a plurality of different focal lengths, so as to implement multi-screen display at a same time.

[0149] In some embodiments, the multi-focus image generation unit includes an image generation element and a spatial light modulator. In some other embodiments, a focal image generation unit includes an image generation element and a zoom liquid lens. The image generation element has a plurality of image generation areas, and can simultaneously generate a plurality of images.

[0150] When the multi-focus image generation unit includes an image generation element and a spatial light modulator, the spatial light modulator has a plurality of modulation areas, and each modulation area corresponds to one image generation area. The display method includes: simultaneously generating images in the plurality of image generation areas, where the plurality of modulation areas load different phase information to optical waves of images generated in corresponding image generation areas, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths. Each modulation area loads different phase information at a same moment to an optical wave of an image generated by a corresponding image generation area, so that the plurality of image generation areas have different focal lengths, and multi-screen display is implemented at a same time.

[0151] When the multi-focus image generation unit includes an image generation element and a zoom liquid lens, the zoom liquid lens has a plurality of lens areas, and each lens area corresponds to one image generation area. The display method includes: simultaneously generating images in the plurality of image generation areas, where curvature of light-exiting surfaces of the plurality of lens areas is different, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths. Curvature of a light-exiting surface of each lens area at a same moment is different, so that the plurality of image generation areas have different focal lengths, and multi-screen display is implemented at a same time.

[0152] Because the image generation element has a plurality of image generation areas, the spatial light modulator has a plurality of modulation areas, and the zoom liquid lens has a plurality of lens areas, a plurality of corresponding light diffuser screens are also disposed, and each light diffuser screen corresponds to one image plane of images generated by the multi-focus image generation unit. The display method further includes: projecting images generated by the multi-focus image generation unit at a same moment to corresponding light diffuser screens.

[0153] In addition, when the spatial light modulator loads phase information to the optical waves of the images generated by the image generation element, Fresnel phase information may be loaded to convert a focal length of the image generation element.

[0154] A radius r.sub.m of an m.sup.th ring of a Fresnel phase is r.sub.m=√{square root over (2mfλ)}; and λ is a wavelength of the optical wave of the image generated by the image generation element, and f is a focal length of a Fresnel lens equivalent to the Fresnel phase.

[0155] Third Implementation

[0156] In this implementation, the multi-focus image generation unit simultaneously generates a plurality of images and has a plurality of different focal lengths. The head-up display apparatus further includes a time sequence control unit. The time sequence control unit is configured to control a moment at which one of the plurality of images generated by the multi-focus image generation unit is switched to and a moment at which one of the plurality of focal lengths is switched to, so that the moment at which one of the plurality of images is switched to and the moment at which one of the focal lengths is switched to are equal, and are less than or equal to the reaction time of the human eye, so as to implement multi-screen display at a same time.

[0157] In some embodiments, the multi-focus image generation unit includes an image generation element and a spatial light modulator. In some other embodiments, a focal image generation unit includes an image generation element and a zoom liquid lens. The image generation element has a plurality of image generation areas, and can simultaneously generate a plurality of images.

[0158] When the multi-focus image generation unit includes an image generation element and a spatial light modulator, the spatial light modulator has a plurality of modulation areas, and each modulation area corresponds to one image generation area. The display method includes: simultaneously generating images in the plurality of image generation areas, where the plurality of modulation areas load different phase information to optical waves of images generated in corresponding image generation areas, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths. In addition, the time sequence control unit controls a moment at which one of the images generated by the image generation areas is switched to and a moment at which phase information in the modulation areas is switched to, and the moment at which one of the images is switched to and the moment at which the phase information is switched to are equal, and are less than or equal to the reaction time of the human eye.

[0159] When the multi-focus image generation unit includes an image generation element and a zoom liquid lens, the zoom liquid lens has a plurality of lens areas, and each lens area corresponds to one image generation area. The display method includes: simultaneously generating images in the plurality of image generation areas, where curvature of light-exiting surfaces of the plurality of lens areas is different, so that a plurality of images generated by the image generation element at a same moment correspond to different focal lengths. In addition, the time sequence control unit controls a moment at which one of images generated by the image generation areas is switched to and a moment at which curvature of the lens areas is switched to, and the moment at which one of the images is switched to and the moment at which the curvature is switched to are equal, and are less than or equal to the reaction time of the human eye.

[0160] In this implementation, there may be a plurality of light diffuser screens, and each light diffuser screen is connected to one second driving unit. A position to which the second driving unit drives the light diffuser screen to move is described above, and details are not described herein again.

[0161] In this implementation, the spatial light modulator may load Fresnel phase information to the optical wave of the image generated by the image generation element, so as to convert a focal length of the image generation element.

[0162] In the descriptions of this specification, the described specific features, structures, materials, or characteristics may be combined in a proper manner in any one or more of embodiments or examples.

[0163] The foregoing descriptions are merely specific implementations of this application, but are not intended to limit the protection scope of this application. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in this application shall fall within the protection scope of this application. Therefore, the protection scope of this application shall be subject to the protection scope of the claims.