Micromechanical optical switch and flat panel display

• US 5,771,321 A
• Filed: 01/04/1996
• Issued: 06/23/1998
• Est. Priority Date: 01/04/1996
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Stern, Ernest
• Primary Examiner(s): Ngo, John
• Application Number:
  US08/582,790
• Time in Patent Office: 901 Days
• Field of Search: 385/37, 385/16, 385/18, 385/25, 385/26, 385/42, 385/40, 385/41, 385/48, 385/146, 385/901
• US Class Current: 385/31
• CPC Class Codes: G02B 26/02 for controlling the intensity of light G02B26/004 takes precedence
• CPC Class Codes: G02B 6/35 having switching means by changing the optical properties of the medium G02F1/00
• CPC Class Codes: G02B 6/3522 the optical element enabling or impairing total internal reflection using evanescent coupling G02B6/3536
• CPC Class Codes: G02B 6/3558 1xN switch, i.e. one input and a selectable single output of N possible outputs
• CPC Class Codes: G02B 6/357 Electrostatic force electrostatic forces controlling reflecting elements in general G02B26/0841
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 3/2074 using sub-pixels
• CPC Class Codes: G09G 3/3473 based on light coupled out of a light guide, e.g. due to scattering, by contracting the light guide with external means
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

The invention provides an optical coupling switch and flat panel display including an array of such optical coupling switches. The optical coupling switch includes a light storage plate adapted to set up conditions for total internal reflection such that light injected into the plate is internally reflected. A light tap is disposed proximal to a coupling surface of the light storage plate for coupling internally reflected light out of the light storage plate and into the light tap when the light tap is brought into contact with the light storage plate coupling surface. The light tap is capable of movement in a direction perpendicular to the light storage plate in response to an applied electrostatic force. The optical coupling switch includes a scattering mechanism, such as a scattering surface or scattering medium, for scattering light in the light tap into a viewing volume. With this configuration, the optical coupling switch provides an elegantly uncomplicated geometry that accommodates a range of actuation schemes for efficiently producing high-speed optical switching. Also provided is an optical display in which an array of light taps are disposed proximal to a light storage plate coupling surface. Each light tap is adapted to move in response to an applied electrostatic force in a direction perpendicular to the coupling surface, and each light tap includes a scattering surface for scattering coupled light. A light source is disposed at an edge of the light storage plate for injecting light into the plate. Control circuitry is provided connected to the array of light taps for applying an electrostatic force to selected one or more of the light taps in the array.

Claims

1. An optical coupling switch comprising:

a light storage plate having a coupling surface, the light storage plate being adapted to internally reflect light injected into the plate;

a light tap disposed in a selected spaced relationship with the light storage plate coupling surface for coupling internally reflected light out of the light storage plate and into the light tap when the light tap is brought into coupling proximity with the light storage plate coupling surface, the light tap including actuation means responsive to an applied electric field for causing the light tap to move to positions toward and away from the light storage plate coupling surface, and the light tap being configured with a stress condition that is selected to constrain movement of the tap in response to an applied electric field to only designated stable positions; and

scattering means configured to enable coupled light to penetrate the light tap, for scattering light that is coupled into the light tap.

2. The optical switch of claim 1 wherein the scattering means comprises a scattering surface.

3. The optical switch of claim 2 wherein the scattering surface comprises a textured surface of the light tap.

4. The optical switch of claim 3 wherein the light tap textured surface comprises surface asperities.

5. The optical switch of claim 3 wherein the light tap textured surface comprises a surface grating.

6. The optical switch of claim 1 wherein the scattering means comprises a scattering medium.

7. The optical switch of claim 6 wherein the scattering medium comprises a fluorescent medium.

8. The optical switch of claim 6 wherein the scattering medium comprises a luminescent medium.

9. The optical switch of claim 6 wherein the scattering medium comprises a translucent medium.

10. The optical switch of claim 1 wherein the light storage plate comprises at least one coupling mesa located on the coupling surface in correspondence with the light tap to define the coupling proximity between the light tap and the light storage plate.

11. The optical switch of claim 1 wherein the light tap comprises at least one light tap mesa located on the light tap in correspondence with the light storage plate coupling surface to define the coupling proximity between the light tap and the light storage plate.

12. The optical switch of claim 1 wherein the light tap is characterized by an internal mechanical restoring force that opposes an electrostatic force generated in response to an applied electric field, and wherein the light tap is mechanically biased in coupling proximity with the light storage plate by the mechanical restoring force and is moved out of coupling proximity with the light storage plate by an applied electric field.

13. The optical switch of claim 1 wherein the light tap is characterized by an internal mechanical restoring force that opposes an electrostatic force generated in response to an applied electric field, and wherein the light tap is mechanically biased out of coupling proximity with the light storage plate by the mechanical restoring force and is moved into coupling proximity with the light storage plate by an applied electric field.

14. The optical switch of claim 1 wherein the light tap is biased in coupling proximity with the light storage plate by an applied electric field and is moved out of coupling proximity with the light storage plate by an applied electric field.

15. The optical switch of claim 1 further comprising a viewing plate disposed adjacent to the light tap.

16. The optical switch of claim 3 wherein the textured scattering surface of the light tap comprises a reflective scattering surface for reflectively scattering light coupled into the light tap back through the light storage plate to emerge into a viewing volume adjacent to the light storage plate.

17. The optical switch of claim 3 wherein the textured scattering surface of the light tap comprises a forward scattering surface for scattering light coupled into the light tap into a viewing volume adjacent to the light tap.

18. The optical switch of claim 17 further comprising a viewing plate, disposed adjacent to the light tap, through which the forward scattered light emerges into the viewing volume.

19. The optical switch of claim 18 wherein the viewing plate comprises a forward scattering surface for scattering light emerging through the viewing plate into the viewing volume.

20. The optical switch of claim 1 wherein the light tap comprises a conducting electrode.

21. The optical switch of claim 20 further comprising a conducting electrode disposed on the light storage plate in proximity with the light tap conducting electrode for generating an electrostatic force.

22. The optical switch of claim 18 wherein the light tap comprises a conducting electrode, and wherein the viewing plate comprises a conducting electrode disposed in proximity with the light tap conducting electrode for generating an electrostatic force.

23. The optical switch of claim 22 further comprising a conducting electrode disposed on the light storage plate in proximity with the light tap conducting electrode for generating an electrostatic force.

24. The optical switch of claim 20 further comprising an electret embedded in the light storage plate in proximity with the light tap conducting electrode for generating an electrostatic force.

25. The optical switch of claim 18 wherein the light tap comprises a conducting electrode, and wherein the viewing plate comprises an electret embedded in the viewing plate in proximity with to the light tap conducting electrode for generating an electrostatic force.

26. The optical switch of claim 1 wherein the scattering means comprises a Lambertian scattering surface.

27. The optical switch of claim 15 wherein the light tap is anchored to the viewing plate by at least one support located at a point on the tap that permits flexing of the tap, and wherein the viewing plate is secured to the light storage plate.

28. The optical switch of claim 27 further comprising a light source located at a peripheral edge of the light storage plate.

29. The optical switch of claim 1 wherein the light storage plate is formed of a glassy material.

30. The optical switch of claim 29 wherein the light storage plate is formed of quartz.

31. The optical switch of claim 1 wherein the light storage plate is formed of plastic.

32. The optical switch of either of claims 12 or 13 wherein the light tap is formed of silicon nitride.

33. The optical switch of claim 32 wherein the silicon nitride light tap is characterized as being in a state of internal tensile stress.

34. The optical switch of claim 1 wherein the light tap is formed of plastic.

35. The optical switch of claim 1 wherein the light tap is formed of a microelectronic material.

36. The optical switch of claim 15 wherein the viewing plate is formed of plastic.

37. The optical switch of claim 15 wherein the viewing plate is formed of a glassy material.

38. The optical switch of claim 37 wherein the viewing plate is formed of quartz.

39. The optical switch of claim 1 wherein the light tap further comprises protrusions on a surface of the light tap facing the light storage plate, the protrusions permitting coupling of light into the light tap but suppressing contact forces between the light tap and the light storage plate.

40. The optical coupling switch of claim 1 wherein the selected stress condition configuration of the light tap comprises a selected stress in a material layer of the light tap.

41. The optical coupling switch of claim 1 wherein the stress condition configuration of the light tap is selected to constrain movement of the tap in response to an applied electric field to only three designated stable positions.

42. The optical coupling switch of claim 1 wherein the stress condition configuration of the light tap is selected to constrain movement of the tap in response to an applied electric field to only two designated stable positions.

43. An optical display comprising:

a light storage plate having a coupling surface and a back surface, the light storage plate being adapted to internally reflect light injected into the plate;

an array of light taps disposed in a selected spaced relationship with the light storage plate coupling surface for coupling internally reflected light out of the light storage plate into one or more light taps in the array when one or more of the light taps are in coupling proximity with the light storage plate, each light tap including a scattering surface configured to enable coupled light to penetrate the light tap, for scattering light that is coupled into the light tap, each light tap further including actuation means responsive to an applied electric field for causing the light tap to move to positions toward and away from the light storage plate coupling surface, and each light tap being configured with a stress condition that is selected to constrain movement of the tap in response to an applied electric field to only designated stable positions;

a light source disposed at an edge of the light storage plate for injecting light into the plate; and

control circuitry connected to the array of light taps for applying an electric field to selected one or more of the light taps in the array.

44. The optical display of claim 43 wherein each light tap is characterized by an internal mechanical restoring force that opposes an electrostatic force generated in response to an applied electric field, and wherein each light tap is mechanically biased in coupling proximity with the light storage plate by the mechanical restoring force and is moved out of coupling proximity with the light storage plate by an applied electric field.

45. The optical switch of claim 43 wherein each light tap is biased in coupling proximity with the light storage plate by an applied electric field and is moved out of coupling proximity with the light storage plate by an applied electric field.

46. The optical display of claim 43 wherein the light storage plate comprises an array of coupling mesas on the coupling surface, the coupling mesa array being located in correspondence with the light tap array to define the coupling proximity between each light tap and the light storage plate.

47. the optical display of claim 43 wherein each light tap comprises at least one coupling mesa located on the light tap in correspondence with the light storage plate coupling surface for defining the coupling proximity between the light tap and the light storage plate.

48. The optical display of claim 43 further comprising a viewing plate disposed adjacent to the light tap array, and wherein the scattering surface of each light tap comprises a forward scattering surface for scattering light that is coupled into a given light tap through the viewing plate into a viewing volume adjacent to the viewing plate.

49. The optical display of claim 43 wherein the light source is configured adjacent to an edge of the light storage plate such that light injected into the light storage plate undergoes total internal reflection.

50. The optical display of claim 49 further comprising a second light source disposed at an edge of the light storage plate.

51. The optical display of claim 43 further comprising a second light source disposed at a location on the back surface of the light storage plate.

52. The optical display of claim 49 wherein the light source comprises means for producing at least two different colors of light.

53. The optical display of claim 48 wherein each light tap in the light tap array comprises a conducting electrode, and wherein the viewing plate comprises an array of electrodes disposed on the viewing plate in correspondence with the array of light tap electrodes for producing an electrostatic force.

54. The optical display of claim 53 wherein the control circuitry comprises line and column electrode drive circuits and a controller for applying an electric field between selected one or more light tap and viewing plate electrodes in the array.

55. The optical display of claim 43 wherein the array of light taps forms an array of pixels, each pixel designated by a set of n light taps corresponding to a number n of pixel bits, each of the n light taps in a given pixel being controlled by the control circuitry to together produce for a given pixel one of a number 2ⁿ of possible optical intensities.

56. An optical display comprising:

a plastic light storage plate having a coupling surface, the light storage plate being characterized by a refractive index such that light injected into the plate is internally reflected;

an array of light taps formed of a plastic layer disposed in a selected spaced relationship with the light storage plate coupling surface for coupling internally reflected light out of the light storage plate into one or more of the light taps in the array, each light tap in the array free to individually move into coupling proximity with the light storage plate, each light tap including scattering means configured to enable coupled light to penetrate the light tap for scattering light that is coupled into the light tap, each light tap further including actuation means responsive to an applied electric field for causing the light tap to move to positions toward and away from the light storage plate coupling surface, and each light tap being configured with a stress condition that is selected to constrain movement of the tap in response to an applied electric field to only designated stable positions;

a light source disposed at an edge of the light storage plate for injecting light into the plate; and

control circuitry connected to the plastic sheet for applying an electric field to selected one or more of the light taps in the array.

57. The optical display of claim 56 further comprising a plastic viewing plate disposed adjacent to the light tap array plastic sheet.

58. The optical display of claim 57 wherein the plastic viewing plate comprises scattering means for scattering light emerging through the viewing plate into a viewing volume.

59. The optical display of claim 56 wherein the array of light taps comprises an array of conducting column electrodes disposed on the plastic sheet.

60. The optical display of claim 59 wherein the plastic viewing plate comprises an array of conducting line electrodes disposed on the viewing plate in correspondence with the column electrodes on the plastic sheet for producing an electrostatic force.

61. The optical display of claim 59 wherein the plastic sheet comprises an array of slots bordering the column electrodes.

62. The optical display of claim 56 wherein the plastic light storage plate comprises plastic spacer protrusions for holding the plastic sheet separated from the light storage plate.

63. The optical display of claim 57 wherein the plastic viewing plate comprises plastic support protrusions for holding the plastic sheet separated from the viewing plate.