High efficiency pancake lens
An example apparatus may include a display, a beamsplitter having a first region and a second region, and a reflective polarizer. The reflectance of the second region of the beamsplitter may be appreciably greater than the reflectance of the first region; for example, at least approximately 20% greater. In some examples, the second region may be a peripheral region surrounding a generally centrally located first region. An example apparatus may be configured so that at least some light emitted by the display is transmitted through the first region of the beamsplitter, reflects from the reflective polarizer, reflects from the second region of the beamsplitter, and is then directed through the reflective polarizer to an eye of a user when the user wears the apparatus. Other devices, methods, systems, and computer-readable media are also disclosed.
1. An apparatus comprising:
a display;
a beamsplitter comprising a first region and a second region; and
a reflective polarizer;
wherein:
the first region of the beamsplitter has a first reflectance;
the second region of the beamsplitter has a second reflectance;
the second reflectance is at least 20% greater than the first reflectance for at least one wavelength of visible light; and
the apparatus is configured so that a light ray emitted by the display is transmitted through the first region of the beamsplitter, reflects from the reflective polarizer, reflects from the second region of the beamsplitter, and is transmitted through the reflective polarizer.
2. The apparatus of claim 1 , wherein the second reflectance is at least 30% greater than the first reflectance.
3. The apparatus of claim 1 , wherein:
the first reflectance is between 30% and 70%; and
the second reflectance is greater than 80%.
4. The apparatus of claim 3 , wherein the first reflectance is between 40% and 60%.
5. The apparatus of claim 3 , wherein the second reflectance is greater than 90%.
6. The apparatus of claim 1 , wherein the apparatus is configured so that the light ray emitted from the display has a circular polarization.
7. The apparatus of claim 1 , further comprising an optical retarder located between the beamsplitter and the reflective polarizer.
8. The apparatus of claim 7 , wherein the apparatus is configured so that:
the light ray has a first transmission through the optical retarder after passing through the first region of the beamsplitter; and
the light ray has a first linear polarization after the first transmission through the optical retarder.
9. The apparatus of claim 8 , wherein the apparatus is further configured so that the light ray is transmitted through the optical retarder a second time after reflection from the second region of the beamsplitter.
10. The apparatus of claim 1 , wherein the display is a liquid crystal display.
11. The apparatus of claim 1 , wherein the apparatus is a head-mounted device.
12. The apparatus of claim 1 , wherein the apparatus is an augmented reality device or a virtual reality device.
13. The apparatus of claim 1 , wherein:
the beamsplitter includes a layer formed on an optical element; and
the optical element includes a lens.
14. The apparatus of claim 13 , wherein:
the layer has a first thickness in the first region;
the layer has a second thickness in the second region; and
the second thickness is greater than the first thickness.
15. The apparatus of claim 1 , wherein:
the first region of the beamsplitter is partially reflective and partially transmissive; and
the second region of the beamsplitter is essentially reflective.
16. The apparatus of claim 1 , wherein:
the first region comprises a partially transmissive optical film; and
the second region comprises a reflective metal film.
17. A method, comprising:
emitting light from a display;
transmitting the light through a first region of a beamsplitter;
reflecting the light from a reflective polarizer; and
directing the light from a second region of the beamsplitter through the reflective polarizer and towards an eye of a user, wherein:
the first region of the beamsplitter has a first reflectance for the light of greater than 90%; and
the second region of the beamsplitter has a second reflectance for the light of less than 70%.
18. The method of claim 17 , wherein:
the method is performed by a head mounted device; and
the method further includes displaying an augmented reality image or a virtual reality image to the user using the light.
19. The method of claim 17 , wherein the light passes through an optical retarder before passing through the reflective polarizer.
20. A method, comprising:
emitting light having a first circular polarization from a display;
transmitting the light through a first region of a beamsplitter;
reflecting the light from a reflective polarizer; and
reflecting the light from a second region of the beamsplitter through the reflective polarizer and towards an eye of a user, wherein
the light has a second circular polarization when the light is transmitted through the reflective polarizer;
the first region of the beamsplitter has a first reflectance;
the second region of the beamsplitter has a second reflectance; and
the second reflectance is greater than the first reflectance.