Head-up display

A head-up display for a vehicle having a window, the head-up display comprising:

• a picture generating unit arranged to output pictures, wherein each picture comprises a first picture component and a second picture component;
• and
• a projection engine arranged to receive the pictures output by the picture generating unit and project the pictures onto the window of the vehicle in order to form a first virtual image of the first picture component at a first virtual image distance and a second virtual image of the second picture component at a second virtual image distance, wherein light of the first picture component is polarised in a first polarisation direction and light of the second picture component is polarised in a second polarisation direction perpendicular to the first polarisation direction,
• wherein the projection engine comprises polarisation-selective mirror having:
• (i) a first surface arranged to receive and reflect light of the first picture component and transmit light of the second picture component, and (ii) a second surface arranged to receive and reflect light of the second picture component, wherein the first surface has first optical power in the first polarisation direction and the second surface has second optical power in the second polarisation direction such that the first virtual image distance is different to the second virtual image distance.

A method of providing a head-up display for a vehicle having a window, the method comprising:

• providing a plurality of pictures, each picture comprising a first picture component and a second picture component;
• projecting the pictures onto the window of the vehicle in order to form a first virtual image of the first picture component at a first virtual image distance from a viewing plane and a second virtual image of the second picture component at a second virtual image distance from the viewing plane, wherein light of the first picture component is polarised in a first polarisation direction and light of the second picture component is polarised in a second polarisation direction perpendicular to the first polarisation direction,
• wherein the projection comprises receiving light of the first picture component and light of the second picture component at a polarisation-selective mirror having:
• (i) a first surface arranged to receive and reflect light of the first picture component and transmit light of the second picture component, and (ii) a second surface arranged to receive and reflect light of the second picture component, wherein the first surface has first optical power in the first polarisation direction and the second surface has second optical power in the second polarisation direction such that the first virtual image distance is not equal to the second virtual image distance, and
• wherein the light of the first picture component forms a first light footprint on the optical element and light of the second picture component forms a second light footprint on the optical element, wherein the first light footprint and second light footprint at least partially overlap.