Head-up display with diffuser

1. A head-up display for a windscreen having spatially variant optical power, the head-up display comprising:

a diffuser arranged to display an image, wherein the diffuser has a curved surface shaped to compensate for the spatially variant optical power of the windscreen; and

a holographic projector configured to project the image for display onto the curved surface of the diffuser such that the image is in non-planar focus on the curved surface of the diffuser, the holographic projector comprising:

a spatial light modulator arranged to apply a phase-delay distribution to incident light, wherein the phase-delay distribution comprises phase-only data representative of an object and phase-only data arranged to provide a lensing effect adapted to bring the image to a non-planar focus on the curved surface of the diffuser; and

Fourier transform means arranged to perform a Fourier transform of phase modulated light received from the spatial light modulator and form the image in non-planar focus on the curved surface of the diffuser.

2. The head-up display of claim 1 , further comprising a mirror arranged to receive light from the diffuser and redirect the received light onto the windscreen.

3. The head-up display of claim 2 , wherein the mirror has optical power.

4. The head-up display of claim 3 , wherein the mirror is a parabolic mirror.

5. The head-up display of claim 1 , wherein the windscreen forms part of an optical system arranged to form a virtual image of the real image displayed by the diffuser.

6. The head-up display of claim 1 , further comprising a laser arranged to produce the incident light for the spatial light modulator.

7. A method of manufacturing the head-up display of claim 1 , the method comprising:

shaping the curved surface of the diffuser to compensate for the spatially variant optical power of the windscreen.

8. The head-up display of claim 1 , wherein the Fourier transform means is a physical lens.

9. The head-up display of claim 1 , wherein the Fourier transform means is a phase-only lens implemented on the spatial light modulator.

10. A method of forming a virtual image for a head-up display using an optical system comprising a windscreen having spatially variant optical power, the method comprising:

displaying a real image in non-planar focus on a curved surface of a diffuser by projecting the real image onto the curved surface of the diffuser, wherein the curved surface of the diffuser is shaped to compensate for the spatially variant optical power of the windscreen, and wherein projecting the image in non-planar focus onto the curved surface of the diffuser comprises:

illuminating a spatial light modulator with incident light to apply a phase-delay distribution to the incident light, wherein the phase-delay distribution comprises phase-only data representative of an object and phase-only data arranged to provide a lensing effect adapted to bring the real image to a non-planar focus on the curved surface of the diffuser; and

performing a Fourier transform of the phase modulated light received from the spatial light modulator and forming the image in non-planar focus on the curved surface of the diffuser; and

forming a virtual image of the real image using the optical system comprising the windscreen.

11. The method of claim 10 , wherein the optical system further comprises a mirror, and forming the virtual image comprises receiving light from the diffuser at the mirror and redirecting the received light onto the windscreen using the mirror.

12. The method of claim 11 , wherein the mirror has optical power.

13. The method of claim 12 , wherein the mirror is a parabolic mirror.

14. The method of claim 10 , wherein the incident light is produced by a laser.