ELECTRONICALLY DIMMABLE OPTICAL DEVICE

• US 20140340728A1
• Filed: 07/29/2014
• Published: 11/20/2014
• Est. Priority Date: 01/31/2012
• Status: Active Grant

• Current Assignee: Alphamicron Incorporated
• Original Assignee: Alphamicron Incorporated
• Inventors: TAHERI, Bahman
• Granted Patent: US 9,304,333 B2
• Time in Patent Office: Days
• US Class Current: 359/250
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: G02B 27/281 used for attenuating light intensity, e.g. comprising rotatable polarising elements
• CPC Class Codes: G02B 5/3025 Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state G02B5/3008, G02B5/3016 take precedence
• CPC Class Codes: G02F 1/0136 for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation G02F1/0353 takes precedence
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 1/133531 characterised by the arrangement of polariser or analyser axes
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/13475 in which at least one liquid crystal cell or layer is doped with a pleochroic dye, e.g. GH-LC cell G02F1/13476 takes precedence
• CPC Class Codes: G02F 2203/01 transmissive
• CPC Class Codes: G02F 2203/02 reflective
• CPC Class Codes: G02F 2203/62 Switchable arrangements whereby the element being usually not switchable

Abstract

An electronically dimmable optical device, including, in sequence, an active absorbing polarizer; a first static reflective polarizer; an active polarization rotator; and a second static reflective polarizer; configured so that the reflectivity and/or transmissivity of the device can be controlled (increased or decreased) by application of a voltage across the active absorbing polarizer and/or the active polarization rotator. One or more polarization levels can be selected by controlling the voltage at the active absorptive polarizer such that setting the active absorptive polarizer to a selected polarization level determines the brightness of an image produced by the device.

Claims

1. An electronically dimmable optical device, comprising:

a. an active absorbing polarizer;

b. a first static reflective polarizer;

c. an active polarization rotator; and

d. a second static reflective polarizer;

configured so that the reflectivity and/or transmissivity of said device can be controlled (increased or decreased) by application of a voltage across the active absorbing polarizer and the active polarization rotator.

2. The optical device of claim 1, wherein the device further comprises a beam stop adjacent the second static reflective polarizer to absorb any light that reaches it.

3. The optical device of claim 1, wherein

a. the active absorbing polarizer has an absorptive axis in an x-direction when activated by application of a voltage,

b. the first static reflective polarizer has a reflective axis in the x-direction,

c. the active polarization rotator rotates the polarization axis of incident light by 90°

when activated by application of a voltage,

d. the second static reflective polarizer has a reflective axis in a y-direction,

so that upon application of the voltage, the reflectivity of the optical device is reduced.

4. The optical device of claim 1, wherein

a. the active absorbing polarizer has an absorptive axis in an x-direction when activated,

b. the first and second static reflective polarizers have a reflective axis in the x-direction,

c. the active polarization rotator rotates the polarization axis of incident light by 90°

when in a non-activated state,

so that upon application of the voltage, the reflectivity of the optical device is reduced.

5. The optical device of claim 1, wherein the device is a dimmable mirror that reflects a selective wavelength of visible spectrum.

6. The optical device of claim 1, wherein the device is a dimmable mirror that absorbs a selective wavelength of the visible spectrum.

7. The optical device of claim 1, wherein the device is a transmissive device that has minimum transmissivity when the device is not activated by application of a voltage.

8. The optical device of claim 1, wherein the device is a transmissive device that has minimum transmissivity when a maximum voltage is applied across the active absorbing polarizer and/or the active polarization rotator.

9. The optical device of claim 1, wherein the reflectivity/transmissivity of the device is controlled automatically, manually, or with a combination of both automatic and manual controls.

10. The optical device of claim 1, wherein the device reflects more than 50% of incident light when it is in its maximum reflectivity state.

11. The optical device of claim 1, wherein the swing (or contrast) between its maximum and minimum reflective states is more than 50%.

12. The optical device of claim 1, wherein the device reflects less than 20% of incident light when it is in its minimum reflectivity state.

13. The optical device of claim 1, wherein a selected polarization level is selected by controlling the voltage at said active absorptive polarizer and wherein setting said active absorptive polarizer to said selected polarization level determines the brightness of an image produced by said device.

14. The optical device of claim 1, further comprising a controller, controlling said active absorptive polarizer,

wherein said controller is coupled with said active absorptive polarizer,

wherein said active absorptive polarizer is divided into two or more sections, and

wherein said controller sets each of said sections to a respective polarization level.

15. The optical device of claim 1, further comprising at least one light detector coupled with a controller, wherein said at least one light detector provides at least one light-intensity value, wherein said controller sets said active absorptive polarizer to a selected polarization level according to said at least one light-intensity value.

16. The optical device of claim 1, wherein the device further comprises a display placed on the non-viewing side of the optical device and wherein at least a portion of light emitted from the display is transmitted to a viewing surface of the optical device.

17. The optical device of claim 1 for use as a rearview or side-view mirror of a vehicle.

18. A method of reducing light reflected from an optical device, said method comprising using the optical device of claim 1 and applying a voltage to said optical device to alter the reflectivity of the optical device.

19. The method of claim 18, wherein the method comprises:

setting the active polarizer to be in a non-absorptive state when not energized, and to absorb an x-direction polarization of incident light and transmit a y-direction polarization when energized by application of a voltage,

setting the first reflective polarizer to reflect the same x-direction polarization that the active polarizer absorbs,

setting the second reflective polarizer to reflect the orthogonally opposite y-direction polarization of light,

setting the active polarization rotator to have no effect when non-energized and to rotate the polarization direction of light by 90°

when energized by a maximum voltage.

20. The method of claim 18, comprising:

setting a viewing surface active polarizer to be in a non-absorptive state when not energized, and to absorb an x-direction polarization of incident light and transmit a y-direction polarization when energized by application of voltage,

setting the first and second static reflective polarizers to reflect said x-direction polarization of light,

setting the active polarization rotator to have no effect when energized by a maximum voltage but to rotate the polarization direction of light by 90°

when in a non-energized state.

21. A device for reflecting light at variable intensity by application of a variable voltage to the device, said device comprising:

a viewing surface having an active absorptive polarizer, adjacent a first static (non-switchable) reflective polarizer, adjacent an active (electrically switchable) polarization rotator, adjacent a second static (non-switchable) reflective polarizer,

configured such that the device has maximum reflectivity when the device is in an unenergized state,

and the device has minimum reflectivity when the device is activated by a maximum voltage applied to the active polarizer and/or the active polarization rotator.

22. (canceled)