Illumination system using optical feedback

• US 6,507,419 B1
• Filed: 03/23/2000
• Issued: 01/14/2003
• Est. Priority Date: 03/23/1999
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: DigiLens Inc
• Inventors: Adams, Michael R., Nabors, C. David, Popovich, Milan M., Storey, John J., Waldern, Jonathan D.
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): BOUTSIKARIS, LEONIDAS
• Application Number:
  US09/533,608
• Time in Patent Office: 1,027 Days
• Field of Search: 359/4, 359/5, 359/6, 359/7, 359/15, 359/24, 359/562, 359/566, 359/567, 359/568, 359/576
• US Class Current: 359/15
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02F 1/13318 Circuits comprising a photodetector
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals

Abstract

Disclosed is an illumination system using optical feedback to maintain a predetermined illumination output. The illumination system employs an electrically controllable optical filter for filtering light incident thereon. The illumination system also includes a light detector for detecting at least a portion of the light filtered by the electrically controllable optical filter. The light detector is in data communication with the electrically controllable optical filter. Some or all light filtered by the electrically controllable optical filter is detected by the light detector, which, in turn generates a corresponding signal that is compared to at least one predetermined value. If the signal generated by the light detector differs when compared to the at least one predetermined value, one or more filtering characteristics of electrically controllable optical filter are varied which, in turn, varies the amount of light filtered by the electrically controllable optical filter. The filtering characteristics of the electrically controllable optical filter continue to be varied until the signal generated by the light etector substantially matches the at least one predetermined value.

Claims

1. An apparatus comprising:

an electrically controllable optical filter comprising an electrically switchable holographic optical element, wherein the electrically switchable holographic optical element is switchable between active and inactive states, wherein the electrically switchable holographic optical element is configured to receive incident light and one or more control signals, wherein the electrically switchable holographic optical element outputs light in response to receiving the incident light and the one or more control signals, wherein the output light comprises only a portion of the incident light, wherein the portion of incident light varies according to the one or more control signals received by the electrically switchable holographic optical element;

a light detector, wherein the light detector is configured to detect a portion of output light, wherein the light detector is configured to generate an output signal in response to detecting the portion of output light, and;

a control signal circuit coupled between the light detector and the electrically switchable holographic optical element, wherein the control signal circuit is configured to generate the one or more control signals in response to the light detector generating the output signal.

2. The apparatus of claim 1 wherein the portion of the incident light varies in accordance with a magnitude of one or more of the control signals.

3. The apparatus of claim 1 wherein the electrically controllable optical filter comprises an electrically switchable liquid crystal optical element.

4. The apparatus of claim 1 wherein the electrically switchable holographic optical element comprises a holographic recording medium that records a hologram, wherein the holographic recording medium comprises:

a monomer dipentaeryiritol hydroxypentaacrylate;

a liquid crystal;

a cross-linking monomer;

a coinitiator; and

a photoinitiator dye.

5. The apparatus of claim 1 wherein the electrically switchable holographic optical element comprises a hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer dispersed liquid crystal material comprising, before exposure:

a polymerizable monomer;

a liquid crystal;

a cross-linking monomer;

a coinitiator; and

a photoinitiator dye.

6. The apparatus of claim 1 further comprising a beamsplitter configured to receive and deflect the portion of the output light, wherein the light detector detects the portion of the output light after being deflected by the beamsplitter.

7. The apparatus of claim 6 further comprising a collection lens positioned between the beamsplitter and the light detector, wherein the collection lens is configured to receive and collect the portion of the output light after being deflected by the beamsplitter, wherein the light detector detects the portion of output light after being collected by the collection lens.

8. The apparatus of claim 1 further comprising a condenser lens, wherein the condenser lens is configured to collimate the incident light before the electrically controllable optical filter receives the incident light.

9. The apparatus of claim 1 wherein the portion of incident light varies by intensity.

10. The apparatus of claim 1 wherein the portion of incident light varies by bandwidth.

11. The apparatus of claim 1 wherein the portion of incident light varies by intensity and bandwidth.

12. The apparatus of claim 1 further comprising a digital reflective display, wherein the digital reflective display is configured to receive a portion of the output light.

13. The apparatus of claim 1 further comprising an array of switchable micro-mirrors wherein the array of switchable micro-mirrors is configured to receive a portion of the output light.

14. The apparatus of claim 1:

wherein the electrically controllable optical filter is configured to receive a first set of control signals, wherein the output light comprises only a first bandwidth portion of the incident light, wherein the first bandwidth portion of incident light varies in intensity according to the first set of control signals received by the electrically controllable optical filter;

wherein the electrically controllable optical filter is configured to receive a second set of control signals, wherein the output light comprises only a second bandwidth portion of the incident light, wherein the second bandwidth portion of incident light varies in intensity according to the second set of control signals received by the electrically controllable optical filter;

wherein the electrically controllable optical filter is configured to receive a third set of control signals, wherein the output light comprises only a third bandwidth portion of the incident light, wherein the third bandwidth portion of incident light varies in intensity according to the third set of control signals received by the electrically controllable optical filter;

wherein the first, second, and third bandwidths are distinct from each other.

15. The apparatus of claim 14:

wherein the first bandwidth portion of incident light varies in intensity according to one of the first set of control signals received by the electrically controllable optical filter;

wherein the second bandwidth portion of incident light varies in intensity according to one of the second set of control signals received by the electrically controllable optical filter;

wherein the third bandwidth portion of incident light varies in intensity according to one of the third set of control signals received by the electrically controllable optical filter.

16. The apparatus of claim 14:

wherein the first bandwidth portion of incident light varies in intensity according to a magnitude of one of the first set of control signals received by the electrically controllable optical filter;

wherein the second bandwidth portion of incident light varies in intensity according to a magnitude of one of the second set of control signals received by the electrically controllable optical filter;

wherein the third bandwidth portion of incident light varies in intensity according to a magnitude of one of the third set of control signals received by the electrically controllable optical filter.

17. The apparatus of claim 14 wherein the electrically controllable optical filter is configured to diffract the incident light received thereon.

18. The apparatus of claim 17 wherein the output light comprises only a diffracted portion of the incident light.

19. The apparatus of claim 14 wherein the electrically controllable optical filter is configured to sequentially and cyclically receive the first, second, and sets of control signals.

20. The apparatus of claim 1 wherein the electrically controllable optical filter comprises a first holographic optical element having front and back oppositely facing surfaces, wherein the first holographic optical element is switchable between active and inactive states, wherein the first optical element diffracts first bandwidth light incident on the front surface thereof when operating in the active state, wherein the first bandwidth light diffracted by the first holographic optical element emerges from the back surface thereof, and wherein the first holographic optical element transmits first bandwidth light without substantial alteration when operating in the inactive state.

21. The apparatus of claim 20 wherein the electrically controllable optical filter comprises a second holographic optical element having front and back oppositely facing surfaces, wherein the second holographic optical element is switchable between active and inactive states, wherein the second holographic optical element diffracts second bandwidth light incident on the front surface thereof when operating in the active state, wherein second bandwidth light diffracted by the second holographic optical element emerges from the back surface thereof, and wherein the second holographic optical element transmits second bandwidth light without substantial alteration when operating in the inactive state, wherein the first and second holographic optical elements are positioned adjacent each other, and wherein first and second bandwidth lights are distinct from each other.

22. The apparatus of claim 21 wherein the front surfaces of the first and second holographic optical elements are aligned orthogonal to a common axis so that the back surface of the first holographic optical element faces the front surface of the second holographic optical element.

23. The apparatus of claim 22 further comprising a polarization rotation device positioned between the first and second holographic optical elements, wherein each of the first and second holographic optical elements comprise a diffraction grating, wherein the first and second holographic optical elements are configured so that the diffraction gratings thereof are disposed parallel to each other.

24. The apparatus of claim 22 wherein the first holographic optical element comprises a first diffraction grating, wherein the second holographic optical element comprises a second diffraction grating, and wherein the first diffraction grating is disposed orthogonal to the second diffraction grating.

29. The apparatus of claim 1 wherein the electrically controllable element comprises a fist holographic optical element having front and back oppositely facing surfaces, wherein the first holographic optical element is switchable between active and inactive states, wherein the first optical element diffracts first bandwidth light incident on the front surface thereof when operating in the active state, wherein first bandwidth light diffracted by the first holographic optical element emerges from the front surface thereof, and wherein the first holographic optical element transmits first bandwidth light incident on the front surface thereof without substantial alteration when operating in the inactive state.

30. The apparatus of claim 29 wherein the electrically controllable element comprises a second holographic optical element having front and back oppositely facing surfaces, wherein the second holographic optical element is switchable between active and inactive states, wherein the second holographic optical element diffracts first bandwidth light incident on the front surface thereof when operating in the active state, wherein first bandwidth light diffracted by the second holographic optical element emerges from the front surface thereof, and wherein the second holographic optical element transmits first bandwidth light without substantial alteration when operating in the inactive state, wherein the first and second holographic optical elements are positioned adjacent each other.

25. An apparatus comprising:

an electrically controllable optical filter configured to receive incident light and one or more control signals, wherein the electrically controllable optical filter outputs light in response to receiving the incident light and the one or more control signals, wherein the output light comprises only a portion of the incident light, wherein the portion of incident light varies according to the one or more control signals received by the electrically controllable optical filter;

a light detector, wherein the light detector is configured to detect a portion of output light, wherein the light detector is configured to generate an output signal in response to detecting the portion of output light, and;

a control signal circuit coupled between the light detector and the electrically controllable optical filter, wherein the control signal circuit is configured to generate the one or more control signals in response to the light detector generating the output signal;

a first group of first, second, and third holographic optical elements electrically switchable between active and inactive states;

a second group of first, second, and third holographic optical elements electrically switchable between active and inactive states;

wherein each holographic optical element comprises front and back oppositely facing surfaces;

wherein each of the first holographic optical elements diffracts first bandwidth light incident on the front surface thereof when operating in the active state, wherein first bandwidth light diffracted by each of the first holographic optical elements emerges from the back surface thereof, and wherein each of the first holographic optical elements transmits first bandwidth light incident on the front surface thereof without substantial alteration when operating in the inactive state, wherein first bandwidth light transmitted by each of the first holographic optical elements emerges from the back surface thereof;

wherein each of the second holographic optical elements diffracts second bandwidth light incident on the front surface thereof when operating in the active state, wherein second bandwidth light diffracted by each of the second holographic optical elements emerges from the back surface thereof, and wherein each of the second holographic optical elements transmits second bandwidth light incident on the front surface thereof without substantial alteration when operating in the inactive state, wherein second bandwidth light transmitted by each of the second holographic optical elements emerges from the back surface thereof;

wherein each of the third holographic optical elements diffracts third bandwidth light incident on the front surface thereof when operating in the active state, wherein third bandwidth light diffracted by each of the third holographic optical elements emerges from the back surface thereof, and wherein each of the third holographic optical elements transmits third bandwidth light incident on the front surface thereof without substantial alteration when operating in the inactive state, wherein third bandwidth light transmitted by each of the third holographic optical elements emerges from the back surface thereof;

wherein the first and second groups of holographic optical elements are positioned adjacent each other;

wherein the first, second and third bandwidths are distinct from each other.

26. The apparatus of claim 25 wherein the front surface of each holographic optical element is aligned orthogonal to a common axis, wherein the front surfaces of each of the holographic optical elements of the second group faces the back surface of each of the holographic optical elements of the first group.

27. The apparatus of claim 26 further comprising a polarization rotation device positioned between the first and second groups of holographic optical elements, wherein each of the holographic optical elements comprises a diffraction grating, wherein all the holographic optical elements are positioned so that each diffraction grating is disposed parallel to the others.

28. The apparatus of claim 26 wherein each of the holographic optical element of the first group comprises a first grating, wherein the each of the second holographic optical elements of the second group comprises a second grating, and wherein the first and second groups of holographic optical elements are positioned so that the first gratings are disposed orthogonal to the second gratings.