Folded viewing optics with an optical retarder on a simple surface
A folded-lens system is used in an artificial-reality headset. The folded-lens system has a first mirror, a second mirror, and a quarter-wave plate between the first mirror and the second mirror. The first mirror and the second mirror are not strongly curved, which enables the quarter-wave plate to be on a flat surface.
1. A system comprising:
a display, wherein the display is an optical display emitting light;
a first lens, the first lens comprising a first reflective surface facing the display;
a second lens, the second lens comprising a second reflective surface facing a user's eye, wherein:
the first lens is between the second lens and the display; and
a z-distance from the second reflective surface to the display is equal to or less than 15 mm and is equal to or greater than 5 mm; and
a flat optical retarder between the first lens and the second lens.
2. The system of claim 1 , wherein the flat optical retarder is on a simple surface.
3. The system of claim 1 , wherein the flat optical retarder is a quarter-wave retarder.
4. The system of claim 1 , further comprising a linear polarizer and a quarter-wave plate.
5. The system of claim 1 , wherein the first reflective surface is a partial mirror.
6. The system of claim 5 , wherein the partial mirror has a transmission of 50%+/−10%.
7. The system of claim 1 , wherein the second reflective surface comprises a reflective polarizer.
8. The system of claim 1 , wherein:
the display has a diagonal length, and the diagonal length is equal to or greater than 1.8 inches and equal to or less than 3 inches; and
the flat optical retarder is characterized by a diameter or a diagonal length greater than the diagonal length of the display.
9. The system of claim 1 , wherein the first lens has a surface roughness less than 3 nm.
10. The system of claim 1 , wherein the first lens is configured to move to compensate for optical vision of a user.
11. The system of claim 1 , wherein the system has a focal length equal to or greater than 20 mm and equal to or less than 30 mm.
12. The system of claim 1 , wherein a sag-to-diameter ratio for the first lens is equal to or less than 0.15.
13. The system of claim 1 , wherein the first reflective surface and the second reflective surface are curved surfaces.
14. A lens system, the lens system comprising:
a first lens, wherein the first lens has a partial reflector on a compound curved surface facing a display;
a second lens having a reflective surface facing an eye of a user of the lens system; and
flat optical retarder,
wherein:
the flat optical retarder is between the first lens and the second lens;
the first lens is between the second lens and the display; and
the lens system has:
a focal length equal to or greater than 20 mm and equal to or less than 30 mm;
a field of view that is greater than +/−45 degrees in a horizontal plane;
a z-distance that is equal to or less than 15 mm and equal to or greater than 5 mm from the reflective surface of the second lens to the display; and
a size of the display equal to or greater than 1.8 inches diagonal and equal to or less than 3 inches diagonal.
15. The lens system of claim 14 , wherein the flat optical retarder is within 26 nm of a quarter wavelength of a peak emission of a light in the display.
16. The lens system of claim 14 , further comprising a quarter-wave plate, wherein the quarter-wave plate and the flat optical retarder are identical and clocked by 90 degrees, +1-5 degrees.
17. The lens system of claim 14 , wherein the reflective surface of the second lens comprises a reflective polarizer.
18. A method comprising:
transmitting light from a display to a partial reflector on a first surface of a first lens, the first surface facing the display;
transmitting light from the partial reflector to a flat quarter-wave plate;
reflecting light passing through the flat quarter-wave plate by a polarization reflector on a second surface of a second lens, the second surface facing a user's eye, wherein a z-distance from the second surface of the second lens to the display is equal to or less than 15 mm and is equal to or greater than 5 mm;
transmitting light through the flat quarter-wave plate a second time;
reflecting light using the partial reflector;
passing light through the flat quarter-wave plate a third time; and
transmitting light through the polarization reflector after transmitting light through the flat quarter-wave plate the third time.
19. The method of claim 18 , further comprising moving the first lens in relation to the second lens for vision correction.
20. The method of claim 19 , wherein the first lens is moved no more than 2.5 mm to compensate for −8 to +4 diopter prescriptions.