Optical device with one-way mirror
In some implementations, an optical device includes a one-way mirror formed by a polarization selective mirror and an absorptive polarizer. The absorptive polarizer has a transmission axis aligned with the transmission axis of the reflective polarizer. The one-way mirror may be provided on the world side of a head-mounted display system. Advantageously, the one-way mirror may reflect light from the world, which provides privacy and may improve the cosmetics of the display. In some implementations, the one-way mirror may include one or more of a depolarizer and a pair of opposing waveplates to improve alignment tolerances and reduce reflections to a viewer. In some implementations, the one-way mirror may form a compact integrated structure with a dimmer for reducing light transmitted to the viewer from the world.
1. An optical device that is wearable on a head of a user, the optical device comprising:
a one-way mirror arranged on a world side of the optical device, the one-way mirror comprising:
a depolarizer including at least one retarder having random optical axis orientations such that the depolarizer receives light from the world side of the optical device and randomizes a polarization of at least a portion of the received light;
a polarization selective mirror oriented to receive light from the depolarizer and configured to transmit, through the polarization selective mirror, a portion of the received light having randomized polarization, the polarization selective mirror having a transmission axis; and
an absorptive polarizer oriented to receive the light transmitted through the polarization selective mirror, the absorptive polarizer having a transmission axis aligned with the transmission axis of the polarization selective mirror,
wherein the polarization selective mirror is disposed between the depolarizer and the absorptive polarizer.
2. The optical device of claim 1 , wherein the depolarizer comprises a quarter waveplate.
3. The optical device of claim 1 , wherein the depolarizer comprises a super retarder.
4. The optical device of claim 1 , wherein the polarization selective mirror and the absorptive polarizer are spaced apart, and further comprising one or more retarders between the polarization selective mirror and the absorptive polarizer.
5. The optical device of claim 4 , wherein the one or more retarders comprise two spaced-apart quarter wave plates.
6. The optical device of claim 1 , wherein the polarization selective mirror comprises a reflective polarizer.
7. The optical device of claim 6 , wherein the reflective polarizer comprises a wire-grid polarizer.
8. The optical device of claim 7 , wherein the wire-grid polarizer comprises a nano-scale wire pattern with repeating parallel wires.
9. The optical device of claim 8 , wherein the wires of the wire pattern are each elongated parallel to the transmission axis of the polarization selective mirror.
10. The optical device of claim 6 , wherein the reflective polarizer comprises a multi-layer polarizer.
11. The optical device of claim 10 , wherein the multi-layer polarizer is configured to reflect incident light of a pre-determined wavelength.
12. The optical device of claim 10 , wherein the multi-layer polarizer comprises a plurality of polymer films.
13. The optical device of claim 10 , wherein the multi-layer polarizer reflects 50% or less of incident light with an electric field vector perpendicular to the transmission axis of the multi-layer polarizer.
14. The optical device of claim 10 , wherein the multi-layer polarizer reflects 30% to 40% of incident light with an electric field vector perpendicular to the transmission axis of the multi-layer polarizer.
15. The optical device of claim 1 , wherein the absorptive polarizer is configured to absorb linearly polarized light.
16. The optical device of claim 1 , wherein the optical device is a head-mounted display system, wherein the display system comprises a head-mounted display, and wherein the one-way mirror is disposed on the world side of the head-mounted display and opposite a user side of the display while the display is being worn by the user.
17. The optical device of claim 16 , wherein the display comprises an eyepiece including at least one waveguide that is configured to output, to the user, light conveying virtual content, wherein the at least one waveguide is at least partly transparent to transmit, to at least one eye of the user, at least a portion of the light that is transmitted through the polarization selective mirror, wherein the at least one waveguide includes a plurality of waveguides each configured to output light with a different amount of wavefront divergence than one or more other waveguides of the plurality of waveguides, and wherein different amounts of wavefront divergence correspond to different depth planes.
18. The optical device of claim 1 , further comprising an actively variable dimmer comprising the absorptive polarizer, an additional polarizer, and an array of liquid crystal elements disposed between the absorptive polarizer and the additional polarizer, wherein the actively variable dimmer is configured to variably dim at least a portion of the light from the world side that is transmitted through the one-way mirror and to transmit the dimmed light toward an eye of the user.