EP4652495A1

EP4652495A1 - An optical device and an imaging optical system for a head-up display

Info

Publication number: EP4652495A1
Application number: EP24744968.9A
Authority: EP
Inventors: Anna-Karin HOLMÉR
Original assignee: Saab AB
Current assignee: Saab AB
Priority date: 2023-01-16
Filing date: 2024-01-16
Publication date: 2025-11-26
Also published as: SE547322C2; SE2300002A1; WO2024155220A1

Abstract

An imaging optic system (200a), wherein the optical device (100a, 100b) comprises: a first substrate (102a) comprising: a first array of lenses (104) comprising a first collimating lens (106a) and a second collimating lens (106b). The first collimating lens (106a) and the second collimating lens (106b) have a first focal length (Fl). A second substrate (102b) comprising a second array of lenses (108) opposite to the first array (104). The second array of lenses (108) comprises a first imaging lens (110a) a second imaging lens (110b); and wherein the first imaging lens (110a) have a second focal length (F2) and the second imaging lens (110b) have a third focal length (F3), wherein the third focal length (F3) is different from the second focal length (F2). The disclosure further relates to an imaging optical system (200a) for a HUD.

Description

An optical device and an imaging optical system for a head-up display

Technical field

The present disclosure relates to an optical device and an imaging optical system for a head-up display, HUD. In particular, but not exclusively, the disclosed technology relates to an optical device and a projecting optical system for a HUD.

Background art

A problem with the solutions of the prior art is that the HUD optics between the image source and the eye box contains a high number of optical elements, as well as complicated and advanced optical elements. There is thus a need for improvement to reduce the cost and/or the volume and weight of HUD systems. One way to do this is to increase the degrees of freedom in the design of the optical system, by allowing the display surface, which is projected by the HUD system, to be curved instead of flat. This has been shown to allow for considerable simplification of the HUD projecting optics. The transformation of a flat display surface into a curved display surface has also been shown, using a relay optical system, which may also include a magnification of the emitting display surface. However, such a relay optical system usually takes up a large volume and includes multiple optical components. Also, the transformation from flat display surface to a curved image plane of the same, is generally limited to generate a mainly spherical image plane. Also, the spherical image plane is generally a convex plane, i.e., from the view of the projecting HUD optics, the vertex of the curved image plane is closer to the HUD optics than the points on the surface which are at a radially larger distance from the optical axis. Such a curved image plane is only simplifying the following HUD optics in some specific cases. This limitation could be overcome by, for example, using a face plate that is put on a flat display plane and via the optical fibers of the face plate, transforming the flat image plane (display plane) into an arbitrarily curved image plane, that can be projected by the following HUD optics. However, in order for the face plate solution to work, the flat surface of the face plate must coincide within a fairly small tolerance to the flat, image emitting plane (of the display). A display usually has to include several surfaces, e.g. filters and protective glass, between the emitting surface of the display component and its outer, accessible surface.

This invention relates to an optical device, which, in a very compact way, images the flat emitting image surface of the image generating element, i.e. the display, into an arbitrarily curved or shaped image plane, which in turn is serving as input to the following projecting optics of the HUD system. Thus, a "virtual" curved display is created which allows increased degree of freedom in the design and optimization of the HUD system.

It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above mentioned problem.

According to a first aspect there is provided an optical device, for an imaging or projecting optical system. The optical device comprises a first substrate and a second substrate. The first substrate comprising a first array of lenses comprising a first collimating lens and a second collimating lens. The first collimating lens and the second collimating lens both have a first focal length. The second substrate comprising a second array of lenses opposite to the first array, wherein the second array of lenses comprises a first imaging lens and a second imaging lens. The first imaging lens has a second focal length and the second imaging lens has a third focal length, wherein the third focal length is different from the second focal length. The collimating lenses of the first array are in alignment with the corresponding imaging lenses of the second array of lenses.

This enables a curved image plane to be generated, on which light from light sources, e.g., micro LEDs, may be imaged.

In one example embodiment, the focusing lenses and the imaging lenses are centered but do not have a common optical axis.

According to some embodiments, in the first array of lenses and the second array of lenses are parallel to each other.

According to some embodiments, the collimating lenses of the first array of lenses and/or the imaging lenses of the second array of lenses are micro-lenses.

According to some embodiments, each imaging lens is either a positive lens, negative lens, or a flat lens.

According to some embodiments, the distance between the first array of lenses and the second array of lenses are within the range of 0.01 - 10 mm to each other. A shorter distance reduce crosstalk between the pixels. According to some embodiments, the imaging lenses and the collimating lenses are centered but do not have a common optical axis,

The focusing lenses in the second array of lenses may be made off axis in relation to the collimating lenses. This enabling tailoring of the direction of the emitted cone angle to fit the acceptance angle of the following projecting optics thus enabling the following projecting optical system to directing the light towards, e.g., an eyebox of a HUD. Most HUD systems are off axis systems, with inherent non-telecentricity in the image plane. A typical chief ray angle of exitance of an off-axis HUD system lays between 15 and 20 degrees and is quite constant over the surface.

Said feature may also give a magnification between the display area and the curved imaged display plane area (not to confuse with magnification of the individual pixels). This is usually and advantage since commercially available micro-LEDs may be too small for this type of application. However, if the imaged display plane curvature is concave as seen from the projection optics of a HUD (i.e., with the vertex of the curved surface farthest away from the following optics), the imaged size of the display is reduced, which is usually not what is desired.

According to some embodiments, the collimating lenses and/or the imaging lenses are meta-lenses. The use if meta-lenses enables manufacturing an optical device as one component, and it also make the alignment of the two parts more easily.

Another advantages using meta-lenses, is that a meta-lens can have a numerical aperture, NA, as high as 0.85, i.e. a half cone angle of more than 50 degrees, and diffraction limited performance at NA 0.8 is reported. The thinness of the meta-lens allows the use of very high NA and a compact solution. The larger NA allows light from a larger cone to be gathered from the emitting pixel, e.g. a micro-LED pixel. The use of meta-lenses gives a large degree of freedom to design the emission of the display, i.e., cone angle and fill factor, for an efficient use of energy in a HUD optical system.

During use of meta-lenses, the wavefront can be well controlled, including amplitude, phase and polarization. The image can therefore be tailored to a specific pattern rather than a point. For example, a point could be imaged to an M-shape. It is therefore possible to have a constant imaged pixel size, regardless of the focus length of the lens. The display can be calibrated pixel by pixel to yield a homogeneous luminance. Another advantage of using meta-surfaces and meta-lenses technology is that it is very suitable for vertical integration with CMOS technology, i.e., micro-LED and OLED displays (see the second aspect of this disclosure further down). CMOS and meta-surfaces can be manufactured using the same lithographic manufacturing technique. Rather than manufacturing the display and electronics and then the "optics", the meta-lenses are included in the display manufacturing process. Thus, alignment is given inherently.

According to some embodiments, the first substrate comprises a first surface and a second surface, wherein the first surface and second surface of said first substrate are on opposite sides of the first substrate, and the second surface of the first substrate is facing the second substrate, wherein the first surface of the first substrate comprises a meta-lens surface.

According to some embodiments, the second substrate comprises a first surface and a second surface, wherein the first surface and second surface of said second substrate are on opposite sides of the second substrate, and the first surface of the second substrate (102b) is facing the first substrate, wherein the second surface of the second substrate comprises a meta-lens surface.

According to some embodiments, the first substrate and the second substrate constitute a common substrate. By having the one substrate instead of two substrates, the manufacturing process is simplified. Another advantage is that the gap between the first array of lenses and the second array of lenses is eliminated, i.e., 0 mm. Further, no air, or other gases, is located between the first array of lenses and the second array of lenses.

According to a second aspect there is provided an imaging optical system for a head-up display, HUD, comprising: a display unit comprising a plurality of pixels; a curved image plane defined by a plane comprising the focal points of the imaging lenses; and an optical device according to any of the first aspect; wherein the first array of lenses of the optical device is parallel with and mounted to the display unit, and each pixel of the display unit have a common optical axis with a corresponding collimating lens, wherein each collimating lens collimates light from the corresponding pixel, and each imaging lens focus the light from the corresponding collimating lens onto the curved image plane.

According to some embodiments, the focal length of each imaging lens of the second array is based on the distance between the imaging lens and a corresponding point in the curved image plane. According to some embodiments, the optical system comprises a diffuser in the curved image plane. In one example embodiment, when the optical system comprises a diffuser, the curved image plane is a physical surface.

According to some embodiments, the diffuser has a flat surface and a curved diffusing surface.

According to some embodiments, the diffuser has a grating structure.

In one example embodiment, the diffuser is surface diffuser.

According to some embodiments, the ratio of the pixel pitch of the pixels in the array of pixels and the pixel size is in the range of 1-5.

According to some embodiments, the pixels comprise micro-LEDs.

In one example embodiment, each pixel comprises a plurality of micro-LEDs. In one example, a pixel may have the size of 40pm.

According to some embodiments, the first array of lenses is integrated to the display unit.

Another example of advantages of meta-surface and meta-lens technology is that a very high numerical aperture, NA, can be achieved. A high NA is suitable for a lens integrated on a display pixel in that it can gather light from a very large cone angle and generate a small spot size, if required.

According to some embodiments, the display unit comprises a meta-lens surface, positioned on the surface of the display unit, which is facing the first lens array

Effects and features of the second aspect are to a large extent analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect.

The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure. Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

[Terminology]

The term curved image plane is to be interpreted as a curved object plane in the vocabulary of optical design. Further, the curved image plane may be a physical or a nonphysical entity, i.e., a curved surface or a virtual curved image plane. The curved image plane is a plane in space defined by the focal points of the focusing lenses.

The terms meta surfaces, meta-lens surface are used interchangeably. These terms are to be interpreted as a surface comprising meta-lenses.

Brief of the

The above objects, as well as additional objects, features and advantages of the present disclosure will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

Figure la shows a perspective side view of the optical device according to an embodiment of the present disclosure.

Figure lb shows a perspective side view of the optical device according to an embodiment of the present disclosure.

Figure 2a shows a perspective side view of the imaging optical system according to an embodiment of the present disclosure. Figure 2b shows a perspective side view of the imaging optical system according to an embodiment of the present disclosure.

Detailed description

The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.

Figure 1 shows the first aspect of this disclosure, which is an optical device 100a, for an imaging optic system 200a; 200b (shown in Fig. 2a-2b). The optical device 100a comprises a first substrate 102a and a second substrate 102b. The first substrate 102a comprising a first array of lenses 104 which comprising a first collimating lens 106a and a second collimating lens 106b. The first collimating lens 106a and the second collimating lens 106b both have a first focal length Fl. The second substrate 102b comprising a second array of lenses 108 opposite to the first array of lenses 104. The second array of lenses 108 comprises a first imaging lens 110a and a second imaging lens 110b. The first imaging lens 110a have a second focal length F2 and the second imaging lens 110b have a third focal length F3, wherein the third focal length F3 is different from the second focal length F2. The collimating lenses 106a, 106b of the first array 104 are in alignment with the corresponding imaging lenses 110a, 110b of the second array of lenses 108.

In one example embodiment, the first array of lenses 104 and the second array of lenses 108 are parallel to each other.

In one example embodiment, the collimating lenses 106a, 106b of the first array of lenses 104 and the imaging lenses 110a, 110b of the second array of lenses 108 are microlenses.

In one example embodiment, each imaging lens 110a, 110b is a positive lens. As seen in the figure, each imaging lens 110a, 110b is substantially a focusing lens, which gather the rays of light (indicated by dashed arrows) at a focal plane defined by the second focal length F2 and third focal length F3.

In one example embodiment (not shown, but similar to the embodiment shown in Fig. la), each imaging lens 110a, 110b may be a negative lens. In that case each imaging lens is a diverging lens, spreading the light and creating a virtual image at a focal plane defined by the second focal length and third focal length and located at a negative distance, i.e., to the left of the element 102b, as seen from the following projecting HUD optical system.

In one example embodiment, the distance between the first array of lenses 104 and the second array of lenses 108 is 5 mm. In another example embodiment, the distance between the first array of lenses 104 and the second array of lenses 108 are within the range of the range is 0.01-5 mm, or 5-10 mm.

In one example embodiment, the imaging lenses 110a, 110b and the collimating lenses 106a, 106b are centered but do not have a common optical axis.

Figure lb shows one embodiment of the first aspect of this disclosure, which is an optical device 100a, for an imaging optic system 200b (shown in Fig. 2b).

In one example embodiment, the first substrate 102a comprises a first surface 103a and a second surface 103b, wherein the first surface 103a and second surface 103b are on opposite sides of the first substrate 102a, and the second surface 103b of the first substrate 102a is facing the second substrate 102b. The first surface 103a of the first substrate (102a) comprises a meta-lens surface.

In one example embodiment, the second substrate 102b comprises a first surface 109a and a second surface 109b. The first surface 109a and second surface 109b are on opposite sides of the second substrate 102b, and the first surface 109a of the second substrate 102b is facing the first substrate 102a, wherein the second surface 109b of the second substrate 102b comprises a meta-lens surface.

In one example embodiment, the distance between the first array of lenses 104 and the second array of lenses 108 is equal to 0 mm.

Figure 2a shows the second aspect of this disclosure, which is an imaging optical system 200a for a HUD. The imaging optical system 200a comprising a display unit 120, a curved image plane 130, and an optical device 100a according to any of the first aspects.

The display unit 120 comprising a plurality of pixels 122a, 122b, and the curved image plane 130 is defined by a plane comprising the focal points of the imaging lenses. The first array of lenses 104 of the optical device 100a is parallel with the display unit 120 and mounted to the display unit 120. Each pixel 122a, 122b of the display unit 120 have a common optical axis with a corresponding collimating lens 106a, 106b. Each collimating lens 106a, 106b collimates light from the corresponding pixel 122a, 122b. Each imaging lens 110a, 110b focus the light from the corresponding collimating lens 106a, 106b onto the curved image plane 130.

In one example embodiment, each focal length of the second array F2, F3 is based on the distance d2, d3 between the imaging lens 110a, 110b and a corresponding point in the curved image plane 130.

In one example embodiment, the optical system 200a comprises a diffuser 140 in the curved image plane 130.

In one example embodiment, the diffuser 140 has a flat surface and a curved diffusing surface. The curved diffusing surface coincides with the curved image plane

In one example embodiment, the diffuser 140 has a grating structure.

In one example embodiment, the ratio of the pixel pitch of the pixels in the array of pixels and the pixel size is 2.5.

In one example embodiment, the pixels 122a, 122b comprises micro-LEDs.

Figure 2b shows one embodiment of the second aspect of this disclosure. Fig. 2b show an imaging optical system 200b for a HUD comprising a display unit 120, a curved image plane 130, and an optical device 100b, wherein the an optical device 100b is similar to the optical device 100a disclosed in relation with the embodiment in Fig la.

In one example embodiment, the optical device 100b of the optical system 200b comprising that the collimating lenses 106a, 106b and imaging lenses 110a, 110b are metalenses, and the first surface 103a of the first substrate 102a and the second surface 109b of the second substrate 102b comprises meta-lens surfaces on which the meta-lenses are located.

In one example embodiment, the distance between the first array of lenses 104 and the second array of lenses 108 is 0 mm.

In one example embodiment, the first array of lenses 104 is integrated to the display unit 120.

The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. For example, the first lens array substrate 102a or 102b could be integrated to the display unit 120, such that the distance dl is zero. In another example, the first lens array substrate is integrated to the display unit, and followed by a protective glass, which is place in between the first and second lens array, thus making the second lens array substrate interchangeable. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.

Claims

1. An optical device (100a, 100b), for an imaging optic system (200a), wherein the optical device (100a, 100b) comprises: a first substrate (102a) comprising: a first array of lenses (104) comprising: a first collimating lens (106a); and a second collimating lens (106b), wherein the first collimating lens (106a) and the second collimating lens (106b) both have a first focal length (Fl); a second substrate (102b) comprising: a second array of lenses (108) opposite to the first array (104), wherein the second array of lenses (108) comprises: a first imaging lens (110a); and a second imaging lens (110b); and wherein the first imaging lens (110a) have a second focal length (F2) and the second imaging lens (110b) have a third focal length (F3), wherein the third focal length (F3) is different from the second focal length (F2), and the collimating lenses (106a, 106b) of the first array (104) are in alignment with the corresponding imaging lenses (110a, 110b) of the second array of lenses (108).

2. The optical device (100a, 100b) according to claim 1, wherein in the first array of lenses (104) and the second array of lenses (108) are parallel to each other.

3. The optical device (100a, 100b) according to any of claim 1-2, wherein the collimating lenses (106a, 106b) of the first array of lenses (104) and/or imaging lenses (110a, 110b) of the second array of lenses (108) are micro-lenses.

4. The optical device (100a, 100b) according to any of the preceding claims, wherein each imaging lens (110a, 110b) is either of a positive lens, negative lens, and/or a flat lens.

5. The optical device (100a, 100b) according to any of the preceding claims, wherein the distance between the first array of lenses (104) and the second array of lenses (108) are within the range of 0.01 - 10 mm to each other.

6. The optical device (100a, 100b) according to any of the preceding claims, wherein the imaging lenses (110a, 110b) and the collimating lenses (106a, 106b) are centered but do not have a common optical axis,

7. The optical device (100a, 100b) according to any of the preceding claims, wherein the collimating lenses (106a, 106b) and/or imaging lenses (110a, 110b) are meta-lenses.

8. The optical device (100b) according to any of claim 1-4 and 7, wherein the first substrate (102a) comprises a first surface (103a) and a second surface (103b), wherein the first surface (103a) and second surface (103b) are on opposite sides of the first substrate (102a), and the second surface (103b) of the first substrate (102a) is facing the second substrate (102b), wherein the first surface (103a) of the first substrate (102a) comprises a meta-lens surface.

9. The optical device (100b) according to any of claim 1-4 and 7-8, wherein the second substrate (102b) comprises a first surface (109a) and a second surface (109b), wherein the first surface (109a) and second surface (109b) are on opposite sides of the second substrate (102b), and the first surface (109a) of the second substrate (102b) is facing the first substrate (102a), wherein the second surface (109b) of the second substrate (102b) comprises a meta-lens surface.

10. The optical device (100b) according to claim 8 and 9, wherein the first substrate (102a) and the second substrate (102b) constitute a common substrate (102).

11. An imaging optical system (200a) for a HUD, comprising: a display unit (120) comprising a plurality of pixels (122a, 122b); a curved image plane (130) defined by a plane comprising the focal points of the imaging lenses; and an optical device (100a, 100b) according to any of claim 1-10; wherein the first array of lenses (104) of the optical device (100, 100a) is parallel with and mounted to the display unit (120), and each pixel (122a, 122b) of the display unit (120) have a common optical axis with a corresponding collimating lens (106a, 106b), wherein each collimating lens (106a, 106b) collimates light from the corresponding pixel (122a, 122b), and each imaging lens (110a, 110b) focus the light from the corresponding collimating lens (106a, 106b) onto the curved image plane (130).

12. The imaging optical system (200a) according to claim 11, wherein the focal length of each imaging lens (110a, 110b) of the second array (F2,F3) is based on the distance (d2,d3) between the imaging lens (110a, 110b) and a corresponding point in the curved image plane (130).

13. The imaging optical system (200a) according to claim 11-12, wherein the optical system (200a) comprises a diffuser (140) in the curved image plane (130).

14. The imaging optical system (200a) according to claim 13, wherein the diffuser (140) has a flat surface and a curved diffusing surface.

15. The imaging optical system (200a) according to claim 12-14, wherein the diffuser (140) has a grating structure.

16. The imaging optical system (200a) according to claim 11-15, wherein the ratio of the pixel pitch of the pixels in the array of pixels and the pixel size is in the range of 1-5.

17. The imaging optic system (200a) according to claim 11-16, wherein the pixels (122a, 122b) comprises micro-LEDs.

18. The imaging optic system (200a) according to claim 11-17, wherein the first array of lenses (104) is integrated to the display unit (120).

19. The imaging optic system (300) according to claim 11-18, wherein the display unit (120) comprising a meta-lens surface, positioned on the surface of the display unit (120) which is facing the first lens array (108)