Floating display device and multi-layer display device having the same

Abstract

The present invention relates to a floating display device and a multi-layer display apparatus including the floating display device, the floating display device comprising: an image display unit having a display surface for an image and emitting display light constituting an initial image from the display surface; and an optical system defining an object plane and an image plane and arranged to receive the display light emitted from the display surface at the object plane, the optical system including a plurality of light groups arranged to have the ability to focus different light rays in a first direction and a second direction respectively perpendicular to an optical axis of the floating display device, the optical system having an aperture stop to confine the light rays from the object plane in the second direction, the display light propagating through the optical system forms a floating image at an image plane in air, and the image-side opening angle in the first direction is larger than the image-side opening angle in the second direction.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments described herein relate generally to optical three-dimensional display technology, and more particularly to floating display devices and multi-layer display apparatus including the floating display devices. [Background technology]

[0002] Among many display technologies, the floating display technology can make images float in the air, giving the viewer a strong visual impact and a tactile experience that is real or not, and has attracted the attention of many researchers.

[0003] Traditional floating display technology is realized by using a retroreflective screen, a two-layer plane mirror array, a concave mirror, or an integrated imaging method. However, the advantages of the retroreflective screen or the two-layer plane mirror array are that it can realize a floating display image with a large field of view and no aberration, and the disadvantages are that the processing process of the retroreflective screen or the two-layer plane mirror array is complicated, the cost is high, and multiple reflections are required, which causes ghost imaging problems at some observation angles. The main problem with the concave mirror realizing a floating image is that under the condition of meeting a large field of view, it is difficult to eliminate aberrations such as field curvature and distortion, and the imaging quality is poor. The integrated imaging method requires many micro-display units to be projected into the space to form a floating image, which makes it difficult to achieve high resolution, and at the same time, the cost of the screen is too high. Therefore, new technological solutions for floating displays are needed in the field. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE DISCLOSURE Exemplary embodiments of the present invention aim to provide a floating display device that can form floating images in the air, while at the same time having low manufacturing costs and more flexible optical layout. [Means for solving the problem]

[0005] Specifically, an exemplary embodiment of the present invention provides a floating display device comprising: an image display unit having a display surface for an image, and emitting display light constituting an initial image from the display surface; and an optical system defining an object surface and an image plane, and arranged to receive the display light emitted from the display surface at the object surface, the optical system including a plurality of light groups arranged to have the ability to focus different light rays in a first direction and a second direction, each of which is perpendicular to an optical axis of the floating display device; the optical system having an aperture stop to confine light rays from the object surface in the second direction; the display light is propagated through the optical system, and then a floating image is formed at the image plane in the air, and an image-side opening angle in the first direction is larger than an image-side opening angle in the second direction.

[0006] According to another exemplary embodiment of the present invention, there is provided a multi-layer display device, comprising: a floating display device according to the above exemplary embodiment; and a transparent display component arranged optically downstream of the floating display device, the transparent display component having a display surface at a position different from the image plane.

[0007] Other features and aspects will become apparent from the following detailed description, the drawings, and the claims. [Brief description of the drawings]

[0008] The invention will be better understood by describing exemplary embodiments thereof with reference to the accompanying drawings, in which:

[0009] [Figure 1] 1 shows a schematic block diagram of a floating display device 100 according to an embodiment of the present invention. [Diagram 2] 1A and 1B show schematic diagrams of the principle of light ray propagation in horizontal and vertical directions, respectively, of an optical system 110 in a floating display device 100 according to an embodiment of the present invention. [Diagram 3]1A and 1B show schematic diagrams of component placement and light propagation of an optical system 110 in a floating display device 100 according to an embodiment of the present invention in the horizontal and vertical directions, respectively. [Figure 4] 2 shows a schematic diagram of component placement and ray propagation of an optical system 210 according to the alternative embodiment in a first direction and a second direction, respectively. [Diagram 5] 3 shows a schematic diagram of component placement and ray propagation of an optical system 310 according to a further embodiment in a first direction and in a second direction, respectively. [Figure 6] 6 shows a schematic diagram of an optical system 610 according to a first embodiment of the present invention and light rays propagating in the yz plane. [Figure 7] 1 shows an exemplary structure in which a one-dimensional optical element is integrally formed with a one-dimensional retroreflective screen. [Figure 8] 8 shows a schematic diagram of an optical system 810 according to a second embodiment of the present invention and light rays propagating in the yz plane. [Figure 9] An example of a one-dimensional grating transmission array structure 802 is shown. [Figure 10] 10 shows a schematic diagram of an optical system 1010 according to a third embodiment of the present invention and light rays propagating in the yz plane. [Figure 11] 11 shows a schematic diagram of an optical system 1110 according to a fourth embodiment of the present invention and light rays propagating in the yz plane. [Figure 12] 1 shows an exemplary structure of a one-dimensional retroreflective screen. [Figure 13] 13 shows a schematic diagram of an optical system 1310 according to a fifth embodiment of the present invention and light rays propagating in the yz plane. [Figure 14] 14 shows a schematic diagram of an optical system 1410 according to a sixth embodiment of the present invention and light rays propagating in the yz plane. [Figure 15] 15 shows a schematic diagram of an optical system 1510 according to a seventh embodiment of the present invention and light rays propagating in the yz plane. [Figure 16] 16 shows a schematic diagram of an optical system 1610 according to an eighth embodiment of the present invention and light rays propagating in the yz plane. [Figure 17]17 shows a schematic diagram of an optical system 1710 according to a ninth embodiment of the present invention and light rays propagating in the yz plane. [Figure 18] 18 shows a schematic diagram of a multi-layer display device 1800 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Specific embodiments of the present invention will be described below. However, in the specific description of these embodiments, it should be noted that in the present specification, in order to be concise, it is not possible to completely describe all the features of the actual embodiments. It should be understood that in the process of actually implementing any embodiment, in the process of any engineering or design project, various specific decisions are often made to meet system-related or commercial-related constraints in order to achieve the specific goals of the developer, and this may change from one embodiment to another. It should also be understood that such development may require complex and lengthy efforts, but for those skilled in the art related to the contents disclosed in the present invention, some of the changes in design, manufacturing, production, etc. made based on the technical contents disclosed in this disclosure are merely existing technical means, and should not be understood as insufficient in the contents of the present disclosure.

[0011] Unless otherwise defined, technical or scientific terms used in the claims and the specification shall have the ordinary meaning as understood by a person of ordinary skill in the art to which the invention pertains. The terms "first", "second" and similar terms used in the specification and claims of the present invention patent application do not denote any order, quantity or importance, but are merely used to distinguish different components. The terms "one" and "1" do not denote a quantity limitation, but indicate the presence of at least one. The terms "comprise" and similar terms such as "include" and "include" mean that the element or object preceding "comprise" or "include" includes the elements or objects listed after "comprise" or "include" and equivalent elements, but do not exclude other elements or objects. The terms "connect" and similar terms such as "connect" and "connect" do not limit the connection to a physical or mechanical connection, nor to a direct or indirect connection. The term "A is approximately equal to B" means that the tolerances in the process manufacturing are taken into consideration, i.e., the numerical values ​​of A and B are within ±10% of each other.

[0012] FIG. 1 shows a schematic block diagram of a floating display device 100 according to an embodiment of the present invention. Referring to FIG. 1, a floating display device 100 according to an embodiment of the present invention may include an image display unit 120 and an optical system 110. The image display unit 120 has a display surface of an image, and emits display light constituting an initial image from the display surface. The image display unit 120 may adopt a direct light-emitting display method or an indirect projection method to display or project an image on the display surface. The optical system 110 is disposed optically downstream of the image display unit 120 to receive the display light, and has an object surface and an image surface. The object surface is disposed on the display surface of the image display unit 120 to receive the original light constituting the initial image on the object surface, and then the original light can be modulated through the optical system 110 to form a floating image (also called an aerial image) on the image surface in the air. Alternatively, there may be one or more relay optical systems between the image display unit 120 and the optical system 110 that can image the display surface of the image display unit 120 onto the object plane of the optical system 110, in which case the object plane of the optical system 110 may be located at an image plane onto which the display surface of the image display unit 120 is imaged by one or more relay optical systems.

[0013] FIG. 2 shows a schematic diagram of the principle of light propagation in the horizontal and vertical directions, respectively, of the optical system 110 of the floating display device 100 according to an embodiment of the present invention. For ease of explanation, light is considered to propagate along an optical path from an optically "upstream" position to an optically "downstream" position in a light beam. Thus, the relative positions of optical elements in an optical path can also be described in these two terms. For example, in Figure 2, object plane 10 is located optically upstream of the aperture stop as well as optically upstream of light groups 101 or 102, with the aperture stop being optically upstream of the first light group 101.

[0014] 2, the optical system 110 may include multiple light groups. The multiple light groups are arranged to have different light beam focusing capabilities in a first direction and a second direction. The first direction and the second direction may each be perpendicular to an optical axis of the optical system 110. The first direction and the second direction may be perpendicular to each other. As an example, the first direction may be horizontal (x-direction), the second direction may be vertical (y-direction), and the optical axis is along the z-direction as shown in the figure.

[0015] In particular, the optical system 110 has an aperture stop to confine light rays from the object plane 10 in the vertical direction (y direction). In some embodiments of the present invention, the aperture stop can refer to the location in the optical system 110 where the light passing size in the y direction is the smallest. In the horizontal direction (x direction), the aperture stop does not substantially function or can confine light rays from the object plane 10 to a small extent. In other words, the aperture stop has a relatively small light passing size in the y direction and a relatively large light passing size in the x direction. For those skilled in the art, the function of the aperture stop can be realized by one optical element of a plurality of optical groups, as long as the optical element can confine light rays in the y direction, in which case the optical system 110 may not have a separate aperture stop. Therefore, the aperture stop is shown alone in FIG. 2 for the purpose of more clearly explaining the principle of the present invention, not for the purpose of limitation, and is shown in a dashed frame.

[0016] The display light from the image display unit 120 is propagated through an aperture stop and multiple light groups to form a floating image at an image plane 20 in the air, where the image side opening angle α in the x-direction is greater than the image side opening angle β in the y-direction.

[0017] The multiple light groups may include at least a first light group 101 and a second light group 102. The first light group 101 may be disposed optically downstream of the aperture stop and may include a one-dimensional optical element having a positive focal degree to focus light rays in the y-direction. The second light group 102 may include a conjugate imaging element having a one-dimensional diffraction grating structure to focus light rays in the x-direction. For example, the conjugate imaging element having a one-dimensional diffraction grating structure may be a one-dimensional retroreflective screen, a one-dimensional grating transmission array, a one-dimensional holographic diffraction grating, etc. The advantage of adopting such a conjugate imaging element is that the positional relationship (object and image) is conjugate, the image does not expand, and there is no aberration.

[0018] The second light group 102 may be provided between the first light group 101 and the object plane 10, or may be provided between the first light group 101 and the image plane 20. The present invention does not intend to specify the positional relationship between the first light group 101 and the second light group 102, and FIG. 2 only shows an example in which the second light group is provided between the first light group 101 and the image plane 20.

[0019] The optical system 110 in the floating display device 100 according to an exemplary embodiment of the present invention has been described above. In this optical system 110, the image side opening angle at which a point on the subject plane 10 is imaged by a plurality of light groups along the x direction is relatively large (preferably 30 degrees or more) to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20. The image side opening angle at which a point on the subject plane 10 is imaged by a plurality of light groups along the y direction is relatively small, preferably 30 degrees or less.

[0020] FIG. 3 shows a schematic diagram of component layout and light propagation of an optical system 110 in a floating display device 100 according to an embodiment of the present invention in the horizontal and vertical directions, respectively.

[0021] The aperture stop can have a relatively large light-passing hole diameter Dx in the x direction so as not to restrict the light rays in the x direction, thereby obtaining a sufficiently large opening angle in the x direction, thereby satisfying the binocular parallax condition and realizing a floating display.

[0022] The aperture stop can have a relatively small light-passing hole diameter Dy in the y direction so as to restrict the light beam in the y direction, thereby selecting different parts of the light beam to participate in imaging, and improving the imaging quality of off-axis points.

[0023] In some embodiments of the present invention, the aperture diameter Dx of the aperture stop can be larger than the height A of the object plane (i.e., display surface) in the x-direction, i.e. Dx>A. In this way, it can be ensured that the image plane rays parallel to the main optical axis pass through the aperture stop, because the edge image rays in the x-direction cannot enter the human eye, otherwise the complete floating image cannot be observed.

[0024] The distance between the aperture stop and the focal plane of the first light group 101 is d, and the light passing size in the y direction is Dy, which is smaller than the light passing size in the y direction of other optical elements in the optical system 110 and satisfies the following condition: Dy≧h / f*d where h is the y-direction length of the floating image, and f is the focal length of the first light group 101. In this way, it can be ensured that the image plane light rays parallel to the main optical axis pass through the aperture stop, because the edge image light rays in the y direction cannot enter the human eye, otherwise the complete floating image cannot be observed.

[0025] In some embodiments of the present invention, the aperture stop can be left between the first light group 101 and the object plane 10. Alternatively, the aperture stop can be placed within a ±f range centered on the focal plane of the first light group 101, since the y-size of the aperture stop is no larger than the image height in the y-direction of the floating image.

[0026] In some embodiments of the present invention, the vertical magnification in the x direction of the optical system 110 is βx=1, and the vertical magnification in the y direction of the optical system 110 is βy≧1, but this is not limiting. An advantage of this arrangement is that if the vertical magnification in the y direction is βy>1, that is, the optical system 110 has an amplification function with respect to the object plane in the y direction, the object plane can be set relatively small, thereby reducing the volume of the entire apparatus.

[0027] Alternatively, in some embodiments, optical system 110 can further include a third light group. The third light group can be disposed optically upstream of first light group 101 (i.e., between first light group 101 and object plane 10) and can include a one-dimensional optical element with positive focal power to modulate light rays from the display surface (i.e., object plane 10 of optical system 110) in a second direction (y-direction).

[0028] 4 shows a schematic diagram of the component arrangement and light propagation of the optical system 210 according to the alternative embodiment in the first direction and the second direction, respectively. Some details of the optical system 210 are the same as those of the optical system 110 described with reference to FIGS. 1-3 above, and will be omitted here. The following mainly describes the differences of the optical system 210.

[0029] 4, the third optical group 103 can be disposed between the second optical group 102 and the object plane 10, and includes at least one one-dimensional optical element to adjust the light beam in the y-direction. The design of the third optical group 103 aims to balance the focal distribution of the optical system, make the layout of the optical system more flexible, and further reduce the aberration and improve the imaging quality.

[0030] In the y direction, the light passing size D1 of the first light group 101 may be equal to or larger than the light passing size D3 of the third light group 103. The focal length f1 of the first light group 101 may be equal to or larger than the focal length f3 of the third light group 103. Alternatively, the distance d1 between the image plane 20 and the first light group 101 is within 1 times the focal length of the first light group 101, i.e., d1≦f1. Alternatively, the function of the aperture stop can be achieved by a conjugate imaging element having a one-dimensional diffraction grating structure in the second light group 102.

[0031] Alternatively, in some further embodiments, the one-dimensional optical element in the third light group 103 can function as the aperture stop, and thus the third light group 103 (particularly the one-dimensional optical element) can be integrated with the aperture stop as a single optical component. Referring to FIG. 5, a schematic diagram of the component arrangement and ray propagation of the optical system 310 according to a further embodiment is shown in the first direction and the second direction, respectively. As shown in FIG. 5, the one-dimensional optical element in the third light group 103 is an aperture stop. The light-passing hole diameter Dx of the one-dimensional optical element in the third light group 103 may be larger than the height A in the x-direction of the object plane (i.e., the display surface), i.e. Dx>A. In this way, it can be ensured that the image plane rays parallel to the main optical axis pass through the aperture stop, because the edge image rays in the x-direction cannot enter the human eye, otherwise a complete floating image cannot be observed. The distance between the one-dimensional optical element of the third light group 103 and the focal plane of the first light group 101 is d, and the light passing size in the y direction is Dy, which satisfies the following condition. Dy≧h / f*d where h is the y-direction length of the floating image, and f is the focal length of the first light group 101. In this way, it can be ensured that the image plane light rays parallel to the main optical axis pass through the aperture stop, because the edge image light rays in the y direction cannot enter the human eye, otherwise the complete floating image cannot be observed.

[0032] Alternatively, the one-dimensional optical elements of the third light group 103 can be located within a range of ±f centered on the focal plane of the first light group 101 .

[0033] In some embodiments of the present invention, the first light group 101 and the third light group 103 can be arranged substantially symmetrically along the optical axis with respect to the conjugate imaging element, and the focal length of the first light group 101 can be approximately equal to the focal length of the third light group 103. Preferably, the focal length between the conjugate imaging element and the object point on the optical axis on the object plane 10 is approximately equal to the focal length of the third light group 103. optical path length is the distance between the conjugate imaging element and the image point on the optical axis on the image plane 20. optical path length is approximately equal to

[0034] Alternatively, the aperture stop can be located in the object-side focal plane of the first light group 101 while at the same time being located in the image-side focal plane of the third light group 103 .

[0035] Below, some examples of optical systems in floating display devices according to embodiments of the present invention are described.

[0036] First Example 6 shows a schematic diagram of an optical system 610 according to a first embodiment of the present invention and light propagating in the yz plane. Some details of the optical system 610 in the floating display device according to the first embodiment are the same as the optical system 110 described with reference to FIGS. 2-3 above, and are omitted here. The following mainly describes the differences of the optical system 610 in the first embodiment.

[0037] In this example, the optical system 610 may include an aperture stop 601, a spectroscopic mirror 602, and an imaging unit 603. In particular, a one-dimensional optical element (e.g., a lens) in the first light group and a conjugate imaging element (e.g., a one-dimensional retroreflective screen) having a one-dimensional diffraction grating structure in the second light group are integrally molded as a cylindrical sawtooth diffraction grating, i.e., an imaging unit 603. One direction of the imaging unit 603 is a curved surface, and the other direction is a one-dimensional sawtooth structure, which is an isosceles triangle structure with a apex angle of 90 degrees, as shown in FIG.

[0038] 6, the light beam emitted from the object plane 10 is filtered by an aperture stop and enters the spectroscopic mirror 602, and the partial light for imaging is reflected by the one-dimensional sawtooth structure of the imaging unit 603 via the spectroscopic mirror 602, and the light reflected from the one-dimensional sawtooth structure is transmitted to the image plane 20 via the spectroscopic mirror 602 to form a floating image. Alternatively, the object plane 10 and the image plane 20 are both at 2f (double focal length) of the imaging unit 603, where f is the focal length of the imaging unit 603 in the second direction (y direction).

[0039] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 610 along the x direction is relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20. The image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 610 along the y direction is relatively large, so that high imaging quality can be obtained.

[0040] Second example 8 shows a schematic diagram of an optical system 810 according to a second embodiment of the present invention and light propagating in the yz plane. Some details of the optical system 810 in the floating display device according to the second embodiment are the same as the optical system 110 described with reference to FIGS. 2-3 above, and are omitted here. The following mainly describes the differences of the optical system 810 in the second embodiment.

[0041] In this example, the optical system 810 may include a cylindrical lens 801 (first light group), a one-dimensional grating transmission array structure 802 (second light group), and an aperture stop 803. The distance between the cylindrical lens and the object plane may be set within the range of f (1x focal length) to 2f (2x focal length) of the cylindrical lens, so that the optical system 810 forms a magnified floating image in the y direction. As shown in FIG. 9 as an example of the one-dimensional grating transmission array structure 802, the one-dimensional grating transmission array structure may be constructed by bonding together several parallel glass plates, and the bonding surfaces are plated with a metal reflective film, where the object point o is optically conjugated with the image point o', and the object plane of the structure is equal in size to the image plane, and there is no aberration.

[0042] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 810 along the x direction is relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20. The image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 810 along the y direction is relatively small, so that high imaging quality can be obtained.

[0043] Third example Fig. 10 shows a schematic diagram of an optical system 1010 according to a third embodiment of the present invention and light rays propagate in the yz plane. Some details of the optical system 1010 in the floating display device according to the third embodiment are the same as the optical system 210 described with reference to Fig. 4 above, and are omitted here. The following mainly describes the differences of the optical system 1010 of the third embodiment.

[0044] In this example, optical system 1010 may include a freeform mirror 1001 (first optical group), a one-dimensional grating transmission array structure 1002 (second optical group), a one-dimensional optical element 1003, and an aperture stop 1004. As shown, the freeform mirror 1001 may be positioned optically downstream of the one-dimensional grating transmission array structure 1002 and positioned to reflect light transmitted from the one-dimensional grating transmission array structure 1002 to the image plane 20.

[0045] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 810 along the x-direction is made relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20, and the technical effect is produced that this floating image has parallax in the x-direction while forming a certain angle with the optical system 1010.

[0046] Fourth example 11 shows a schematic diagram of an optical system 1110 according to a fourth embodiment of the present invention and light rays propagating in the yz plane. Some details of the optical system 1110 in the floating display device according to the fourth embodiment are the same as the optical system 110 or 210 described with reference to FIGS. 2-4 above, and are omitted here. The following mainly describes the differences of the optical system 1110 in the fourth embodiment.

[0047] In this example, the conjugate imaging element in the second light group 102 can function as the aperture stop described above, so the second light group (particularly the conjugate imaging element) 102 can be formed integrally with the aperture stop as a single optical component. Referring to FIG. 11, the optical system 1110 can include a freeform mirror 1101 (first light group), a one-dimensional retroreflective screen 1102 (second light group and aperture stop), a one-dimensional optical element 1103 (third light group), and a half mirror 1004. The half mirror 1004 may be arranged optically downstream of the one-dimensional optical element 1103, and arranged to reflect light from the one-dimensional optical element 1103 to the conjugate imaging element (the one-dimensional retroreflective screen 1102) and transmit light reflected from the one-dimensional retroreflective screen 1102 to the freeform mirror 1101. The freeform mirror 1101 may be disposed optically downstream of the half mirror 1104 and disposed so as to reflect light transmitted from the half mirror 1104 to the image plane 20. An example of a one-dimensional retroreflective screen 1102 is shown in Fig. 12, in which a light ray arbitrarily irradiated onto the surface of the one-dimensional retroreflective screen is partially reflected according to the original angle.

[0048] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1110 along the x direction is relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20. The image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1110 along the y direction is relatively small, so that high imaging quality can be obtained.

[0049] Fifth case 13 shows a schematic diagram of an optical system 1310 according to a fifth embodiment of the present invention and light rays propagating in the yz plane. Some details of the optical system 1310 in the floating display device according to the fifth embodiment are the same as the optical system 110 or 210 described with reference to FIGS. 2-4 above, and are omitted here. The following mainly describes the differences of the optical system 1310 in the fifth embodiment.

[0050] In this example, the optical system 1310 may include a first concave mirror 1301 (first light group), a one-dimensional retroreflective screen 1302 (second light group and aperture stop), a second concave mirror 1303 (third light group), a first spectral plate 1304, and a second spectral plate 1305. The first concave mirror 1301 is disposed between the object plane 10 and the image plane 20, with its concave surface facing the image plane 20. The first concave mirror may be an iso-thickness structure with a 50 / 50 spectral film applied to its upper surface. The concave surface of the second concave mirror 1303 faces the one-dimensional retroreflective screen 1302. The first spectral plate 1304 is provided at an angle between the object plane 10 and the first concave mirror 1301, and between the one-dimensional retroreflective screen 1302 and the second concave mirror 1303. The spectroscopic plane is disposed between the first concave mirror 1301 and the image plane 20 .

[0051] Alternatively, the first spectral plate 1304 may be a polarizing spectral film, and the second spectral plate 1305 may be a polarizing spectral plate. In this case, the optical system 1310 may further include a first quarter-wave plate 1306, a second quarter-wave plate 1307, and a third quarter-wave plate 1308. In particular, the second light group (the conjugate imaging element therein) and the aperture stop are integrated into a single component, the one-dimensional retroreflective screen 1302. That is, the one-dimensional retroreflective screen simultaneously performs the function of the aperture stop described above. The first quarter-wave plate 1306 may be provided between the second concave mirror 1303 and the polarizing spectral film. The second quarter-wave plate 1307 may be provided between the one-dimensional retroreflective screen 1302 and the polarizing spectral film. The third quarter-wave plate 1308 may be provided between the first concave mirror 1301 and the polarizing spectral plate. The second quarter-wave plate 1307 may be provided in the same inclination manner as the first spectral plate 1304. The optical axes of the second quarter-wave plate 1307 and the third quarter-wave plate 1308 are provided perpendicular to each other.

[0052] When the display surface of the image display unit 120 is placed or relayed to the object surface of the optical system 1310, the s-polarized light emitted from the display surface is reflected by the polarizing spectroscopic film and irradiated onto the second concave mirror 1303. The light reflected by the second concave mirror 1303 passes through the first quarter-wave plate 1306 to be converted into p-polarized light, passes through the polarizing spectroscopic film and the second quarter-wave plate 1307, and is transmitted to the one-dimensional retroreflective screen 1302. The light is reflected by the one-dimensional retroreflective screen 1302, passes through the second quarter-wave plate 1307 again to be converted into s-polarized light, and is reflected by the polarizing spectroscopic film. The light reflected by the polarizing spectroscopic film passes through the second quarter-wave plate 1307 again and is irradiated onto the first concave mirror 1301, a part of the light passes through the first concave mirror 1301 and is irradiated onto the third quarter-wave plate 1308, the light is still s-polarized after passing through the third quarter-wave plate 1308, and is reflected by the polarizing spectroscopic plate. The light reflected by the polarizing spectroscopic plate is irradiated to the first concave mirror 1301 and reflected again, passes through the second quarter-wave plate 1308 and becomes p-polarized, passes through the polarizing spectroscopic plate and is emitted, forming a floating image on the image plane 20 in the air.

[0053] The polarizing spectroscopic film, the polarizing spectroscopic plate, the first ¼ wavelength plate 1306, the second ¼ wavelength plate 1307 and the third ¼ wavelength plate 1308 are used to improve the optical efficiency of the optical system and to eliminate the effects of unnecessary light rays (e.g., external light rays), but are not necessarily required, and those skilled in the art can understand that an optical system that does not use these optical elements is sufficient to achieve the purpose of forming a floating image.

[0054] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1310 along the x direction is relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20. The image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1310 along the y direction is relatively small, so that high imaging quality can be obtained. The optical system 1310 is a pure reflection structure, has no chromatic aberration, and is easy to realize large-scale production.

[0055] Sixth example 14 shows a schematic diagram of an optical system 1410 according to a sixth embodiment of the present invention and light rays propagating in the yz plane. Some details of the optical system 1410 in the floating display device according to the sixth embodiment are the same as the optical system 110 or 210 described with reference to Figs. 2-4 above and the optical system 1310 described with reference to Fig. 13 above, and are omitted here. The following mainly describes the differences of the optical system 1410 of the sixth embodiment.

[0056] In this example, the optical system 1410 may include a convex lens 1401, a one-dimensional retroreflective screen 1402 (a second light group and an aperture stop), a concave mirror 1403, a splitter mirror 1404, and a correction lens 1405. The convex lens 1401 is disposed between the object plane 10 and the image plane 20, with its convex surface facing the object plane 10. The concave surface of the concave mirror 1403 faces the one-dimensional retroreflective screen 1402. The splitter mirror 1404 is provided at an angle between the object plane 10 and the convex lens 1401, and between the one-dimensional retroreflective screen 1402 and the concave mirror 1403. The correction lens 1405 is provided between the splitter mirror 1404 and the one-dimensional retroreflective screen 1402 so as to correct the aberration of the optical system 1410. The correction lens 1405 may be a positive lens or a negative lens. In this example, a first light group is formed by the convex lens 1401 and the corrector lens 1405, and a third light group is formed by the concave mirror 1403 and the corrector lens 1405. In other words, in this example, the corrector lens 1405 can be used simultaneously as an optical element in the first light group and as an optical element in the third light group.

[0057] Alternatively, the splitting mirror 1404 may be a polarizing splitting film. In this case, the optical system 1410 may further include a first quarter-wave plate 1406 and a second quarter-wave plate 1407. In particular, the second light group (the conjugate imaging element therein) and the aperture stop are integrated into a single component, the one-dimensional retroreflective screen 1402. In other words, the one-dimensional retroreflective screen 1402 also simultaneously performs the function of the aperture stop described above.

[0058] When the display surface of the image display unit 120 is placed or relayed to the object surface of the optical system 1310, the s-polarized light emitted from the display surface is reflected by the polarizing and splitting film and irradiated onto the concave mirror 1403. The light reflected by the concave mirror 1403 passes through the first quarter-wave plate 1406 to be converted into p-polarized light, passes through the polarizing and splitting film and the second quarter-wave plate 1407, and is transmitted to the one-dimensional retroreflective screen 1302. The light passing through the correction lens 1405 is reflected by the one-dimensional retroreflective screen 1402, passes through the correction lens 1405 again, passes through the second quarter-wave plate 1407 to be converted into s-polarized light, and is reflected by the polarizing and splitting film. The light reflected by the polarizing and splitting film passes through the convex lens 1401 to be condensed onto the image plane 20 in the air, forming a floating image.

[0059] The polarizing spectroscopic film, the first 1 / 4 wavelength plate 1406, and the second 1 / 4 wavelength plate 1407 are used to improve the optical efficiency of the optical system and to eliminate the effects of unnecessary light rays (e.g., external light rays), but are not necessarily required, and those skilled in the art can understand that an optical system that does not use these optical elements is sufficient to achieve the purpose of forming a floating image.

[0060] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1410 along the x direction is relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20. The image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1410 along the y direction is relatively small, so that high imaging quality can be obtained.

[0061] In the above fifth and sixth examples, the optical system 1310 or 1410 may be a symmetrical structure, and the one-dimensional retroreflective screen 1302 or 1402 in the second light group is located at the middle position of the optical system 1310 or 1410, i.e., between the conjugate imaging element and the object plane. optical path length is the distance between the conjugate imaging element and the image plane. optical path lengthIn addition, the focal length of the first light group is approximately equal to the focal length of the third light group, and the object plane 10 and the image plane 20 are approximately equal in size.

[0062] Seventh example Fig. 15 shows a schematic diagram of an optical system 1510 according to a seventh embodiment of the present invention and light rays propagate in the yz plane. Some details of the optical system 1510 in the floating display device according to the seventh embodiment are the same as the optical system 310 described with reference to Fig. 5 above, and are omitted here. The following mainly describes the differences of the optical system 1510 of the seventh embodiment.

[0063] In this example, the optical system 1510 may include a plano-convex cylindrical mirror 1501 (first optical group), a sawtooth diffraction grating 1502 (second optical group), a cylindrical concave mirror 1503 (third optical group and aperture stop), a polarizing spectroscopic plate 1504, a first polarizing plate 1505, a second polarizing plate 1506, a first quarter-wave plate 1507, and a second quarter-wave plate 1508. In particular, the third optical group (i.e., the one-dimensional optical elements therein) and the aperture stop are integrated into a single component, namely, the cylindrical concave mirror 1503 with its concave surface facing the object plane 10. That is, the cylindrical concave mirror 1503 simultaneously functions as an aperture stop in the y-direction. The conjugate imaging element is a sawtooth diffraction grating 1502 arranged to face the image plane 20, and the one-dimensional optical element of the first light group is a plano-convex cylindrical mirror 1501 arranged between the image plane 20 and the sawtooth diffraction grating 1502, with the planar side of the plano-convex cylindrical mirror 1501 facing the image plane 20 and the convex side of the plano-convex cylindrical mirror 1501 facing the sawtooth diffraction grating 1502. The polarizing splitter plate 1504 is provided at an angle between the object plane 10 and the cylindrical concave mirror 1503, and between the sawtooth diffraction grating 1502 and the plano-convex cylindrical mirror 1506. The first polarizing plate 1505 is provided between the object plane 10 and the polarizing splitter plate 1504 to convert the light from the object plane 10 into p-polarized light. The second polarizing plate 1506 is provided optically downstream of the plano-convex cylindrical mirror 1501 to block the transmission of s-polarized light. The first quarter-wave plate 1507 is disposed between the cylindrical concave mirror 1503 and the polarizing splitter plate 1504 so as to convert the light reflected from the cylindrical concave mirror 1503 into s-polarized light. The second quarter-wave plate 1508 is disposed between the polarizing splitter plate 1504 and the sawtooth diffraction grating 1502 so as to convert the light reflected from the sawtooth diffraction grating 1502 into p-polarized light.

[0064] When the display surface of the image display unit is placed or relayed to the subject plane of the optical system 1510, the light emitted from the display surface passes through the first polarizing plate 1505 to be converted to p-polarized light, and passes through the polarizing spectroscopic plate 1504, which transmits p-polarized light and reflects s-polarized light, so that the light emitted from the display surface passes through the polarizing spectroscopic plate 1504 and is irradiated onto the cylindrical concave mirror 1503 through the first 1 / 4 wave plate 1507. The light beam returning from the cylindrical concave mirror 1503 passes through the first quarter-wave plate 1507 again to be converted into s-polarized light, is reflected by the polarizing spectroscopic plate 1504, and is irradiated onto the sawtooth diffraction grating 1502 through the second quarter-wave plate. The light beam reflected from the sawtooth diffraction grating 1502 passes through the second quarter-wave plate 1508 again to be converted into p-polarized light, passes through the polarizing spectroscopic plate 1504, and is irradiated onto the plano-convex cylindrical mirror 1506. Finally, the light beam passes through the plano-convex cylindrical mirror 1501 to form a floating image on the image plane 20 in the air. The function of the second polarizing plate 1506 is to transmit only p-polarized light and filter out stray light of s-polarized light, and when external light is incident on the sawtooth diffraction grating 1502, it can be combined with the second quarter-wave plate 1508 to eliminate the influence of external light.

[0065] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1510 along the x direction is relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20. The image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1510 along the y direction is relatively small, so that high imaging quality can be obtained.

[0066] Eighth example Fig. 16 shows a schematic diagram of an optical system 1610 according to an eighth embodiment of the present invention and light rays propagate in the yz plane. Some details of the optical system 1610 in the floating display device according to the eighth embodiment are the same as the optical system 310 described with reference to Fig. 5 above, and are omitted here. The following mainly describes the differences of the optical system 1610 of the eighth embodiment.

[0067] In this example, the optical system 1610 may include a plano-convex cylindrical mirror 1601 (first light group), a one-dimensional retro-reflective screen 1602 (second light group), a cylindrical concave mirror 1603 (third light group and aperture stop), a polarizing and splitting film 1604, a splitting mirror 1605, a first polarizing plate 1606, a second polarizing plate 1607, and a first quarter-wave plate 1608. In particular, the third light group (i.e., the one-dimensional optical elements therein) and the aperture stop are integrated into a single component, i.e., the cylindrical concave mirror 1603 with its concave surface facing the object plane 10. That is, the cylindrical concave mirror 1603 simultaneously functions as an aperture stop in the y direction. The conjugate imaging element having a one-dimensional diffraction grating structure is a one-dimensional retroreflective screen 1602, and the one-dimensional optical element in the first light group is a plano-convex cylindrical mirror 1601 arranged between the image plane 20 and a polarizing splitting film 1604, with the planar side of the plano-convex cylindrical mirror 1601 facing the image plane 20 and the convex side of the plano-convex cylindrical mirror 1601 facing the polarizing splitting film 1604. The splitting mirror 1605 is provided at an angle between the object plane 10 and the cylindrical concave mirror 1603 so as to transmit light from the object plane 10 to the cylindrical concave mirror 1603 and reflect light reflected from the cylindrical concave mirror 1603 to the one-dimensional retroreflective screen 1602. The polarizing splitting film 1604 is provided at an angle between the splitting mirror 1605 and the one-dimensional retroreflective screen 1602 so as to pass p-polarized light and reflect s-polarized light. The polarizing splitting film 1604 reflects the s-polarized light reflected from the one-dimensional retroreflective screen 1602 to the plano-convex cylindrical mirror 1601. The first polarizing plate 1606 is provided between the splitting mirror 1605 and the polarizing splitting film 1604 so as to convert the light from the object plane 10 into p-polarized light. The quarter-wave plate 1608 is provided between the polarizing splitting film 1604 and the one-dimensional retroreflective screen 1602 so as to convert the light reflected from the one-dimensional retroreflective screen 1602 into s-polarized light. The second polarizing plate 1607 is provided optically downstream of the plano-convex cylindrical mirror 1601 so as to pass the s-polarized light.

[0068] When the display surface of the image display unit is provided on the object surface 10 of the optical system 1610, the light emitted from the display surface passes through the splitter mirror 1605, is irradiated to the cylindrical concave mirror 1603, is reflected by the concave mirror 1603, is irradiated again to the splitter mirror 1605, and is reflected by the polarizing plate 1606 for passing the light beam in the p-polarized state. The p-polarized light passes through the polarizing splitter film (passes the p-light and reflects the s-light) and is irradiated to the quarter-wave plate 1608, and the light beam is reflected by the one-dimensional retroreflective screen 1602, and then passes through the quarter-wave plate 1608 again to become s-polarized light. The s-polarized light is reflected by the polarizing splitter film 1604, is irradiated to the lens 1601, and is emitted through the second polarizing plate 1607 to form a floating image in the air. The second polarizing plate 1607 may pass the s-polarized light. Since the absorption axis directions of the second polarizing plate 1607 and the first polarizing plate 1606 are perpendicular to each other, it is possible to prevent large-angle light rays emitted from the display surface from passing directly through the second polarizing plate 1607 and the first polarizing plate 1606 and entering the human eye, thereby preventing ghost imaging from being created.

[0069] In this way, the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1510 along the x direction is relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20, and the image side opening angle of a point on the display surface of the image display unit 120 formed by the optical system 1610 along the y direction is relatively small, so that high imaging quality is obtained.

[0070] Ninth case 17 shows a schematic diagram of an optical system 1710 according to a ninth embodiment of the present invention and light rays propagating in the yz plane. Some details of the optical system 1710 in the floating display device according to the ninth embodiment are the same as the optical system 310 described with reference to FIG. 5 above, and are omitted here. The following mainly describes the differences of the optical system 1710 of the ninth embodiment.

[0071] In this example, the optical system 1710 may include a spectral concave mirror 1701 (first light group), a one-dimensional retro-reflective screen 1702 (second light group), a cylindrical concave mirror 1703 (third light group and aperture stop), a spectral plate 1704, a polarizing spectral plate 1705, a first polarizing plate 1706, a first quarter-wave plate 1707, and a second quarter-wave plate 1708. In particular, the third light group (i.e., the one-dimensional optical elements therein) and the aperture stop are integrated into a single component, namely, the cylindrical concave mirror 1703 with its concave surface facing the object plane 10. That is, the cylindrical concave mirror 1703 simultaneously functions as an aperture stop in the y-direction. The phase conjugate optical element is a one-dimensional retroreflective screen 1702, and the one-dimensional optical element in the first optical group is a spectroscopic concave mirror 1701 arranged between a spectroscopic plate 1704 and a polarizing spectroscopic plate 1705, with the concave surface of the spectroscopic concave mirror 1701 facing towards the image plane 20.

[0072] The spectral flat plate 1704 is provided at an angle between the subject plane 10 and the cylindrical concave mirror 1703 so as to transmit light from the subject plane 10 to the cylindrical concave mirror 1703 and reflect light reflected from the cylindrical concave mirror 1703 to the one-dimensional retroreflective screen 1701. The polarizing spectral flat plate 1705 is provided at an angle between the spectral concave mirror 1701 and the image plane 20 so as to transmit p-polarized light and reflect s-polarized light, and reflects s-polarized light reflected from the one-dimensional retroreflective screen 1702 to the spectral concave mirror 1701. The first polarizing plate 1706 is provided between the subject plane 10 and the polarizing spectral flat plate 1704 so as to convert light from the subject plane 10 to p-polarized light. The first quarter-wave plate 1707 is provided between the spectral flat plate 1704 and the spectral concave mirror 1701. The second quarter wave plate 1708 is disposed between the polarizing spectroscopic plate 1705 and the spectroscopic concave mirror 1701 .

[0073] When the display surface of the image display unit is provided on the object plane 10 of the optical system 1410, the light emitted from the display surface passes through 1706 (quarter-wave plate + polarizing plate), the outgoing light is p-polarized light, passes through the spectral plate 1704, and is irradiated onto the cylindrical concave reflecting mirror 1703. The light is reflected by the cylindrical concave reflecting mirror 1703, then reflected by the spectral plate 1704, and irradiated onto the first quarter-wave plate 1707, which converts the p-polarized light into circularly polarized light, and is irradiated onto the spectral concave mirror 1701. The spectral concave mirror 1701 is a flat plate structure of constant thickness with a constant curvature, and a half mirror is plated on its surface. After passing through the spectroscopic concave mirror 1701, the light is irradiated onto the second quarter-wave plate 1708, which converts the circularly polarized light into s-polarized light, reflected by the polarizing spectroscopic plate 1705, irradiated onto and reflected by the one-dimensional retroreflective screen 1702, reflected by the polarizing spectroscopic plate a second time, and then passed through the second quarter-wave plate 1708 to be converted into circularly polarized light. Some of the light is reflected by the spectroscopic concave mirror 1701, passed through the second quarter-wave plate 1708 again to be converted into p-polarized light, and emitted by the polarizing spectroscopic plate 1705, forming an image floating in the air.

[0074] In this way, the image-side opening angle at which a point on the display surface of the image display unit 120 is imaged by the optical system 1710 along the x-direction is made relatively large to satisfy the binocular parallax condition, so that a floating image can be formed on the image plane 20.

[0075] Alternatively, in the above-mentioned exemplary embodiments and examples, if the object plane of the optical system 110 is flat, the optical system may have a field curvature in the y direction, so that the floating image may be formed as a curved surface. Therefore, to correct the field curvature in the y direction, the object plane of the optical system 110 may be provided as a curved surface in the y direction. For example, if the display surface of the image display unit 120 overlaps with the object plane of the optical system 110, the display surface may be provided as a curved surface. Alternatively, the display surface may be formed as a curved image on the object plane of the optical system 110 by a relay imaging unit.

[0076] According to another exemplary embodiment of the present invention, a multi-layer display device is also provided.

[0077] FIG. 18 shows a schematic diagram of a multi-layer display device 1800 according to an embodiment of the present invention. The multi-layer display device 1800 can include any of the floating display devices 1810 described above and a transparent display 1820. The transparent display component 1820 can be disposed optically downstream of the floating display device 1810. The display surface 30 of the transparent display component 1820 is located at a different location than the image plane 20. The transparent display component 1820 can have high transmittance, such as a transparent OLED / LED / LCD display or film (slide).

[0078] Above is a description of a multi-layer display device 1800 according to an embodiment of the present invention. By using the multi-layer display device 1800, the floating display device 1810 can form a floating image on the image plane 20, and the transparent display 1820 can display different information on the display surface 30. In this way, secondary information can be displayed on the display surface 30, and important information can be displayed on the image plane 20, thereby improving the efficiency and experience of people's information acquisition.

[0079] Above, the floating display device according to an exemplary embodiment of the present invention, the optical system used, and the multi-layer display device have been described in detail. The optical system in the floating display device is easy to process, can effectively reduce costs, and has a more flexible optical layout, eliminating the problem of ghost imaging in the prior art. Using the floating display device, the light field reconstruction in the air of the display surface is realized, which is a light field three-dimensional display technology. The image side opening angle at which the light beam on the display surface is imaged by the optical system along the first direction can be relatively large to satisfy the binocular parallax condition, thereby realizing the floating display of the image. In particular, with respect to the optical system in the floating display device of the present invention, the aperture stop described in this specification only plays the role of limiting light in the second direction, and the function of limiting light in the first direction may be played by a first light group or a conjugate imaging element having a one-dimensional diffraction grating structure. Compared with the conventional optical system, the optical element functioning as the aperture stop in the first and second directions does not have to be the same optical element.

[0080] It should be understood that the above description is general and not limiting. For example, the above-described examples (and / or various aspects thereof) may be used in conjunction with one another. Moreover, many modifications can be made to adapt a particular condition or material to the teachings of the various embodiments of the invention without departing from the scope of the invention. The sizes and types of materials described herein are used to define the parameters of the various embodiments of the invention, but the various examples are not meant to be limiting, but are illustrative examples. Many other examples will be apparent to those skilled in the art upon reading the above description. Thus, the scope of the various embodiments of the invention should be determined with reference to the appended claims and the full scope of equivalent forms claimed therein.

Claims

1. an image display unit having a display surface for displaying an image and emitting display light constituting an initial image from the display surface; an optical system defining an object plane and an image plane and positioned to receive the display light emanating from the display surface at the object plane; the optical system includes a plurality of light groups arranged to have a capability of focusing different light beams in a first direction and a second direction, each of the first direction and the second direction being orthogonal to an optical axis of the floating display device; At least one optical element included in the plurality of light groups is a conjugate imaging element having a one-dimensional diffraction grating structure, the optical system having an aperture stop to confine light rays from the object plane in the second direction; a floating image is formed at the image plane in the air after the display light is propagated through the optical system, and an image side opening angle in the first direction is larger than an image side opening angle in the second direction.

2. The plurality of light groups include a first optical group including a one-dimensional optical element for modulating light in the second direction; 2. The floating display device of claim 1, further comprising: a second light group including a conjugate imaging element having a one-dimensional diffraction grating structure to focus light rays in the first direction.

3. 3. The floating display device according to claim 2, wherein the aperture stop has a distance d from the focal plane of the first light group, and a light passing size Dy in the second direction, and the light passing size Dy satisfies the following condition: Dy ≧ h / f*d where h is the length of the floating image in the second direction and f is the focal length of the first light group.

4. 3. The floating display device of claim 2, wherein the one-dimensional optical element and the conjugate imaging element are integrally formed as a cylindrical sawtooth diffraction grating.

5. 3. The floating display device as claimed in claim 2, wherein the one-dimensional optical element is a cylindrical lens, and the conjugate imaging element is a one-dimensional diffraction grating transmission array structure.

6. 3. The floating display device of claim 2, wherein the optical system further comprises a third optical group including a one-dimensional optical element to modulate light rays from the object plane in the second direction.

7. 7. The floating display device of claim 6, wherein the one-dimensional optical element in the third optical group and the aperture stop are integrated into a single component.

8. 3. The floating display device of claim 2, wherein the conjugate imaging element having a one-dimensional grating structure and the aperture stop are integrated into a single component.

9. 7. The floating display device according to claim 6, wherein the first light group and the third light group are disposed approximately symmetrically along an optical axis with respect to the conjugate imaging element.

10. The optical system comprises:

3. The floating display device of claim 2, further comprising a spectroscopic mirror disposed along an optical path between the conjugate imaging element and the image display unit.

11. The optical system comprises: a waveplate disposed along the optical path between the conjugate imaging element and the spectroscopic mirror; and / or 11. The floating display device of claim 10, further comprising the spectroscopic mirror having a polarizing spectroscopic capability.

12. 2. The floating display device of claim 1, wherein a length of the floating image in the second direction is equal to or greater than a length of the initial image in the second direction.

13. 12. The floating display device of claim 2, wherein an optical path length between the conjugate imaging element and an object point on the optical axis on the object plane is approximately equal to an optical path length between the conjugate imaging element and an image point on the optical axis on the image plane.

14. 13. The floating display device of claim 1, wherein the object surface is arranged as a curved surface in the second direction.

15. A floating display device according to any one of claims 1 to 14; a transparent display component optically downstream of the floating display device, the transparent display component having a display surface at a different location than the image plane.

Images