Ambient light optics for head mounted display

1. An apparatus for a head mounted display (“HMD”) comprising:

a display module for launching computer generated image (“CGI”) light along a forward propagating path;

an eyepiece optically coupled to receive the CGI light and direct the CGI light to an eye-ward region of the eyepiece;

a switchable hologram disposed along a surface of the eyepiece, wherein the switchable hologram is configured to redirect ambient light propagating toward the eyepiece, when activated;

a controller coupled to the switchable hologram to activate and deactivate the switchable hologram; and

a light sensing module coupled to the controller and positioned to sense the ambient light, wherein the controller is coupled to activate and deactivate the switchable hologram in response to ambient light data generated by the light sensing module.

2. The apparatus of claim 1 further comprising a second switchable hologram coupled outside the external surface of the eyepiece and coupled to be activated and deactivated by the controller, wherein the switchable hologram is configured to diffuse ambient light when activated, and wherein the second switchable hologram is configured to, when activated, divert a selected visible spectrum of the ambient light in a pattern that directs the selected visible spectrum of the ambient light away from the eye-ward region.

3. The apparatus of claim 2 , wherein a transparent dielectric substrate is layered between the switchable hologram and the second switchable hologram.

4. The apparatus of claim 2 , wherein the switchable hologram is coupled above a top side of the eyepiece.

5. The apparatus of claim 2 , wherein the second switchable hologram is coupled in front of an external scene-side of the eyepiece.

6. The apparatus of claim 1 , wherein the switchable hologram appears virtually transparent to visible spectrums of the ambient light, when the switchable hologram is deactivated.

7. The apparatus of claim 1 , wherein the controller is coupled to activate the switchable hologram at different activation levels, and wherein the switchable hologram is configured to modulate a level of diffusion of the switchable hologram in response to the different activation levels.

8. The apparatus of claim 1 , wherein the switchable hologram is configured to divert a selected spectrum of the ambient light away from the eye-ward region, when activated by the controller.

9. The apparatus of claim 8 , wherein the controller is configured to activate the switchable hologram when a threshold value of the selected spectrum of the ambient light is measured by the light sensing module.

10. The apparatus of claim 8 , wherein the selected spectrum of the ambient light includes ultraviolet light.

11. The apparatus of claim 1 , wherein the switchable hologram includes holographic polymer dispersed liquid crystal (“H-PDLC”).

12. A method of redirecting light propagating toward an eyepiece of a head mounted display (“HMD”), the method comprising:

measuring ambient light;

analyzing a measurement of the ambient light; and

activating a switchable hologram in response to said analyzing the measurement of the ambient light, wherein the switchable hologram is positioned outside a surface of the eyepiece of the HMD, and wherein the switchable hologram is configured to, when activated, redirect at least a portion of the ambient light that is propagating toward the eyepiece.

13. The method of claim 12 , wherein said analyzing the measurement includes determining if the measurement includes a threshold value of a specific spectrum of the ambient light, and wherein the switchable hologram is configured to divert the specific visible spectrum away from an eye-ward region.

14. The method of claim 13 , wherein the specific spectrum includes ultraviolet light.

15. The method of claim 12 , wherein the switchable hologram is configured to diffuse the ambient light.

16. The method of claim 15 , wherein activating the switchable hologram includes activating the switchable hologram at different activation levels, and wherein the switchable hologram is configured to modulate a level of diffusion of the switchable hologram in response to being activated at the different activation levels.

17. The method of claim 12 further comprising activating a second switchable hologram in response to said analyzing the measurement of the ambient light, wherein the second switchable hologram is positioned outside the external surface of the eyepiece of the HMD, and wherein the second switchable hologram is configured to divert a specific visible spectrum of the ambient light away from the eye-ward region.

18. The method of claim 17 , wherein a transparent dielectric substrate is layered between the switchable hologram and the second switchable hologram.

19. The method of claim 12 , wherein the switchable hologram includes holographic polymer dispersed liquid crystal (“H-PDLC”).