Head-up display and means of transportation comprising a head-up display

1. A head-up display, comprising:

an imaging unit for generating an image; and

an optical system for projecting the image onto a projection surface, wherein the optical system comprises at least a first minor, a curved second minor arranged adjacent to the first minor, and a selectively reflective element configured in an optical path between the first mirror and the second minor, wherein the reflective element comprises a direction-selective reflector configured to reflect light for a first range of angles, and configured to be transparent for a second range of angles, and wherein the optical system is configured such that light emitted from the imaging unit is:

directed to pass through the selectively reflective element;

reflected off the first mirror towards the selectively reflective element;

reflected by the selectively reflective element towards the second mirror; and

reflected by the second minor towards the selectively reflective element, and passed through to be directed to the projection surface.

2. The head-up display according to claim 1 , wherein the first range of angles comprise 40° to 60° and the second range of angles comprise 0° to 25°.

3. The head-up display according to claim 1 , wherein the direction- selective reflector is configured as a reflective volume grating.

4. The head-up display according to claim 3 , wherein the reflective volume grating comprises an additional optical function.

5. The head-up display according to claim 4 , wherein the reflective volume grating comprises a lens function.

6. The head-up display according to claim 1 , wherein the direction-selective reflector comprises a substrate with a multilayer thin-film coating.

7. The head-up display according to claim 6 , wherein at least a portion of the substrate is configured as a lens.

8. The head-up display according to claim 1 , wherein the selectively reflective element comprises a polarization-selective reflector, and wherein a quarter-wave plate is configured in front of each of the first minor and the second mirror.

9. The head-up display according to claim 1 , wherein the selectively reflective element is substantially vertically aligned.

10. The head-up display according to claim 1 , wherein the selectively reflective element is curved.

11. A method of operating a head-up display, comprising:

projecting, via an optical system, an image for a projection surface, wherein the optical system comprises at least a first minor, a curved second minor arranged adjacent to the first minor, and a selectively reflective element configured in an optical path between the first mirror and the second mirror, wherein the reflective element comprises a direction-selective reflector configured to reflect light for a first range of angles, and configured to be transparent for a second range of angles;

directing, via the optical system, emitted light from the image to pass through the selectively reflective element;

reflecting, via the optical system, the emitted light from the image off the first minor towards the selectively reflective element;

reflecting, via the optical system, the emitted light from the image by the selectively reflective element towards the second mirror; and

reflecting, via the optical system, emitted light from the image by the second mirror towards the selectively reflective element, and passing the emitted light through the selectively reflective element to be directed to the projection surface.

12. The method according to claim 11 , wherein the first range of angles comprise 40° to 60° and the second range of angles comprise 0° to 25°.

13. The method according to claim 11 , wherein the direction-selective reflector is configured as a reflective volume grating.

14. The method according to claim 11 , wherein the direction-selective reflector comprises a substrate with a multilayer thin-film coating.

15. The method according to claim 14 , wherein at least a portion of the substrate is configured as a lens.

16. The method according to claim 11 , wherein the selectively reflective element comprises a polarization-selective reflector, and wherein a quarter-wave plate is configured in front of each of the first mirror and the second minor.

17. The method according to claim 11 , wherein the selectively reflective element is curved.

18. A vehicle, comprising:

a head-up display, comprising:

an imaging unit for generating an image; and

an optical system for projecting the image onto a projection surface for the vehicle, wherein the optical system comprises at least a first minor, a curved second minor arranged adjacent to the first mirror, and a selectively reflective element configured in an optical path between the first minor and the second mirror, wherein the reflective element comprises a direction-selective reflector configured to reflect light for a first range of angles, and configured to be transparent for a second range of angles, and

wherein the optical system is configured such that light emitted from the imaging unit is:

directed to pass through the selectively reflective element;

reflected off the first mirror towards the selectively reflective element;

reflected by the selectively reflective element towards the second mirror; and

reflected by the second minor towards the selectively reflective element, and passed through to be directed to the projection surface.