Optical switching device and image display device

• US 6,381,381 B1
• Filed: 11/23/1999
• Issued: 04/30/2002
• Est. Priority Date: 01/20/1998
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Yonekubo, Masatoshi, Kamijima, Shunji, Ito, Hirokazu, Takeda, Takashi
• Primary Examiner(s): Sanghavi, Hemang
• Assistant Examiner(s): ROJAS, OMAR R
• Application Number:
  US09/381,495
• Time in Patent Office: 889 Days
• Field of Search: 385/16-19, 385/30, 385/40, 385/41, 359/222, 359/223, 359/224
• US Class Current: 385/16
• CPC Class Codes: G02B 26/0816 by means of one or more reflecting elements
• CPC Class Codes: G09G 2300/06 Passive matrix structure, i.e. with direct application of both column and row voltages to the light emitting or modulating elements, other than LCD or OLED
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• 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

An optical switching device comprises: a light guide including a total reflection plane capable of totally reflecting light thereby transmitting the light; a switching part capable of, at a position where its extraction plane is in close contact with the total reflection plane, capturing evanescent light and reflecting the captured light thereby outputting it; and a driving part for driving the optical switching part. The light guide, the switching part, and the driving part are laminated in this order into a multilayer structure. The employment of the multilayer structure makes it possible to optimize the respective layers independently of one another. The extracted light does not pass through the driving part. This allows the driving part to be optimized so as to achieve an optical switching device capable of operating at a high speed with low power consumption. Thus, it is possible to provide a low-loss and high-contrast optical switching device using an evanescent wave, which can respond at a high speed.

Claims

1. An optical switching device comprising:

a light guide including a total reflection plane capable of totally reflecting light thereby transmitting the light;

a switching part including a light-transmissive extraction plane capable of extracting evanescent light leaking through said total reflection plane and reflecting the extracted light toward said light guide; and

driving means for moving said switching part to a first position at which said extraction plane is within an extraction range which allows an evanescent light to be extracted and a second position at which said extraction plane is out of said extraction range,

wherein said light guide, said switching part, and said driving means are disposed in this order in a direction in which light is output, and

wherein said driving means includes;

a supporting member for elastically supporting said switching part; and

electrostatic driving means for driving said switching part by an electrostatic force acting between at least one pair of electrodes, and

wherein when no electrostatic force is generated by said electrostatic driving means, said supporting member is capable of pressing said switching part at said first position toward said light guide.

2. An optical switching device according to claim 1, wherein said light guide, said switching part, and said driving means are placed one on another into the form of a multilayer structure.

3. An optical switching device according to claim 1, wherein said light guide is a member in the form of a flat panel including no structure on the total reflection plane.

4. An optical switching device according to claim 1, wherein said driving means is disposed on an integrated circuit substrate.

5. An optical switching device according to claim 1, wherein said switching part includes a microprism or a light-dispersive light outputting member for reflecting light extracted through said extraction plane.

6. An optical switching device according to claim 1, wherein said supporting member is a spring member adapted to have a residual deformation when said switching part is at said first position.

7. An optical switching device according to claim 1, wherein said switching part is supported by said supporting member via a spacer, said spacer serving to reduce the distance between said electrodes and provide a space in which said supporting member is allowed to be elastically deformed.

8. An optical switching device according to claim 7, wherein said supporting member is a spring member in the form of a plate one end of which is supported by a post disposed near a boundary of said switching part, and the other end of which is connected to said switching part, and wherein said spacer is T-shaped or inverted trapezoidal-shaped in cross section.

9. An optical switching device according to claim 8, wherein said spring member has a slit or an opening formed near said boundary.

10. An optical switching device according to claim 8, wherein said spring member is in the form of a plate having a small width and radially extending from said switching part, said one end of the spring member being connected to said post disposed near the boundary.

11. An optical switching device according to claim 8, wherein said spring member is in the form of a plate including a part extending in a spiral fashion along said boundary.

12. An optical switching device according to claim 8, wherein said spring member is in the form of a plate with a reduced thickness central part.

13. An optical switching device according to claim 8, further comprising an auxiliary supporting member for supporting said spring member from the side of said light guide,

wherein said spring member is in the form of a plate which allows the side where said switching part is disposed to be substantially hermetically enclosed, and wherein the side where said switching part is disposed has a lower pressure than the side where said driving means is disposed.

14. An optical switching device according to claim 8, wherein the inside of said optical switching device includes a hermetically enclosed space, said driving means being disposed in said hermetically enclosed space such that said driving means is capable of driving said switching part in an ambient with a low pressure.

15. An optical switching device according to claim 8, further comprising a plurality of posts disposed at regular intervals or at random near said boundary.

16. An optical switching device according to claim 8, wherein said spring member is an electrically conductive member and at least a part of said electrically conductive member also serves as an electrode of said electrostatic driving means.

17. An optical switching device according to claim 1, further comprising driving control means for applying to said electrostatic driving means a driving voltage for driving said switching part and a fixed bias voltage which is equal in polarity to said driving voltage and which provides a holding force capable of stably holding said switching part at least at said first position by means of electrostatic force or elastic force.

18. An optical switching device according to claim 17, further comprising a stopper for assuring a minimum gap between said electrodes at one of said first and second positions at which the holding force is provided by said driving voltage,

wherein said driving control means applies said bias voltage which produces a force smaller than the elastic force of said supporting member at the position of said stopper.

19. An optical switching device according to claim 17, wherein said driving control means periodically applies said bias voltage which produces an electrostatic force smaller than the elastic force provided, at said first or second position, by said supporting member.

20. An optical switching device according to claim 19, further comprising a stopper for assuring a minimum gap between said electrodes at one of said first and second positions at which the holding force is provided by electrostatic force generated by said electrostatic driving means, and

wherein said driving control means periodically applies said bias voltage which produces a force smaller than the elastic force of said supporting member at the position of said stopper.

21. An optical switching device according to claim 17, wherein said switching part is moved by said supporting member from the second position to the first position and held at the first position by the elastic force of said supporting member,

and wherein said driving control means applies a driving voltage to said electrostatic driving means when said switching part is moved from said first position to said second position, said driving voltage resulting in no equilibrium only in the range between said first and second positions.

22. An optical switching device according to claim 17, wherein:

said supporting member is capable of supporting said switching part at a substantially central position between said first and second positions when no electrostatic force is exerted on said switching part;

said electrostatic driving means includes a first pair of electrodes for holding said switching part at said first position and a second pair of electrodes for holding said switching part at said second position; and

said driving control means alternately applies a driving voltage to said first and second pairs of electrodes.

24. An optical switching device according to claim 1, wherein:

said supporting member is capable of supporting said switching part at a substantially central position between said first and second positions when no electrostatic force is exerted on said switching part;

said electrostatic driving means includes a first pair of electrodes for holding said switching part at said first position and a second pair of electrodes for holding said switching part at said second position; and

said optical switching device includes driving control means for alternately applying a driving voltage to said first and second pairs of electrodes.

23. An optical switching device comprising:

a light guide including a total reflection plane capable of totally reflecting light thereby transmitting the light;

a switching part including a light-transmissive extraction plane capable of extracting evanescent light leaking through said total reflection plane and reflecting the extracted light toward said light guide; and

driving means for moving said switching part to a first position at which said extraction plane is within an extraction range which allows an evanescent light to be extracted and a second position at which said extraction plane is out of said extraction range,

wherein said light guide, said switching part, and said driving means are disposed in this order in a direction in which light is output, and

wherein said driving means includes;

a supporting member for elastically supporting said switching part; and

electrostatic driving means for driving said switching part by an electrostatic force acting between at least one pair of electrodes, and

wherein said supporting member is capable of moving said switching part from said second position to said first position by means of elastic force and holding said switching part at said first position,

and wherein said optical switching device further comprises driving control means for applying a driving voltage to said electrostatic driving means when said switching part is moved from said first position to said second position, said driving voltage resulting in no equilibrium only in the range between said first and second positions.

25. An optical switching device comprising:

a light guide including a total reflection plane capable of totally reflecting light thereby transmitting the light;

a switching part including a light-transmissive extraction plane capable of extracting evanescent light leaking through said total reflection plane and reflecting the extracted light toward said light guide; and

driving means for moving said switching part to a first position at which said extraction plane is within an extraction range which allows an evanescent light to be extracted and a second position at which said extraction plane is out of said extraction range,

wherein said light guide, said switching part, and said driving means are disposed in this order in a direction in which light is output, and

wherein in an early, intermediate, or final stage of the moving process, said driving means tilts the orientation of the extraction plane of said switching part with respect to a first direction in which said extraction plane faces when said switching part is at said first position.

26. An optical switching device according to claim 25, wherein said driving means is capable of applying a driving force with a distribution asymmetric about the center of gravitation of said switching part upon said switching part.

27. An optical switching device according to claim 26, wherein the center of gravitation of said switching part is located at a point shifted from the geometric center of said switching part.

28. An optical switching device according to claim 26, wherein said driving means includes a supporting means for elastically supporting said switching part, said supporting means including a part which is asymmetric about the center of gravitation of said switching part in terms of the distribution of the elastic modulus.

29. An optical switching device according to claim 26, wherein said driving means includes a first electrode disposed on said switching part and a second electrode disposed at a location opposing said first electrode, and wherein said driving means includes a part which is asymmetric about the center of gravitation of said switching part in terms of the shape of said first electrode, the shape of said second electrode, or the distance between said first and second electrodes.

30. An optical switching device according to claim 26, wherein said driving means includes a first electrode disposed on said switching part and a second electrode disposed at a location opposing said first electrode, and wherein said first or second electrode is divided into a first part and a second part which are asymmetric in shape to each other about the center of gravitation of said switching part,

and further wherein said optical switching device further comprises a driving control means power supply capable of supplying electric power to said first and second parts of the first or second electrode such that the timing of supplying the electric power is different between said first and second parts or such that voltages supplied to said first and second parts are different from each other.

31. An optical switching device according to claim 25, wherein the extraction plane of said switching part is tilted with respect to said first direction at said second position.

32. An optical switching device according to claim 31, wherein said driving means includes a supporting means for elastically supporting said switching part, said supporting means including a part which is asymmetric about the center of gravitation of said switching part in terms of the distribution of the elastic modulus.

33. An optical switching device according to claim 31, wherein said driving means includes a first electrode disposed on said switching part and a second electrode disposed at a location opposing said first electrode, said driving means including a part which is asymmetric about the center of gravitation of said switching part in terms of the distance between said first and second electrodes.

34. An optical switching device according to claim 31, further comprising a supporting post that said switching part is in contact with at said second position, said supporting post including a part which is asymmetric about the center of gravitation of said switching part in terms of the distance between said supporting post and said switching part.

35. An image display device comprising a plurality of optical switching devices, each of said plurality of optical switching devices comprising:

a light guide including a total reflection plane capable of totally reflecting light thereby transmitting the light;

a switching part including a light-transmissive extraction plane capable of extracting evanescent light leaking through said total reflection plane and reflecting the extracted light toward said light guide; and

driving means for moving said switching part to a first position at which said extraction plane is within an extraction range which allows an evanescent light to be extracted and a second position at which said extraction plane is out of said extraction range,

wherein said light guide, said switching part, and said driving means are disposed in this order in a direction in which light is output, and

wherein said driving means includes;

a supporting member for elastically supporting said switching part; and

electrostatic driving means for driving said switching part by an electrostatic force acting between at least one pair of electrodes, and

wherein when no electrostatic force is generated by said electrostatic driving means, said supporting member is capable of pressing said switching part at said first position toward said light guide, and

wherein said plurality of optical switching devices are two-dimensionally arranged wherein said light guide is connected such that said light guide can transmit white light or three-color light.

36. A method of controlling an optical switching device, said optical switching device comprising:

a light guide including a total reflection plane capable of totally reflecting input light thereby transmitting the light;

at least one switching part being in contact at a first position with the total reflection plane of said light guide, said switching part serving to extract evanescent light leaking through the total reflection plane, said switching part being capable of moving to a second position apart from said first position;

a supporting member for elastically supporting said switching part; and

electrostatic driving means including at least one pair of electrodes for driving said switching part, said method including;

a control step for applying to said electrostatic driving means a driving voltage for driving said switching part and a fixed bias voltage which is equal in polarity to said driving voltage and which provides a holding force capable of stably holding said switching part at least at said first position by means of electrostatic force or elastic force, and

wherein said switching part is adapted to be moved by said supporting member from said second position to said first position and held at said first position by the elastic force of said supporting member,

and wherein, in said control step, when said switching part is moved from said first position to said second position, said driving voltage is applied to said electrostatic driving means such that said driving voltage results in no equilibrium only in the range between said first and second positions.

37. A method of controlling the optical switching device, according to claim 36, wherein said optical switching device further comprises a stopper for assuring a minimum gap between said electrodes at one of said first and second positions at which the holding force is provided by said driving voltage,

and wherein, in said control step, said bias voltage is selected such that the electrostatic force generated by said bias voltage when said switching part is at the stopper position is smaller than the elastic force of said supporting member.

38. A method of controlling the optical switching device, according to claim 36, wherein, in said control step, said bias voltage is periodically applied such that the electrostatic force generated by said bias voltage becomes smaller than the elastic force of said supporting member when said switching part is at said first or second position.

39. A method of controlling the optical switching device, according to claim 36, wherein said optical switching device further comprises a stopper for assuring a minimum gap between said electrodes at one of said first and second positions at which the holding force is provided by electrostatic force generated by said electrostatic driving means,

and wherein, in said control step, said bias voltage is periodically applied such that the electrostatic force generated by said bias voltage becomes smaller than the elastic force of said supporting member when said switching part is at said stopper position.

40. A method of controlling the optical switching device, according to claim 36, wherein said supporting member supports said switching part at a substantially central position between said first and second positions when no electrostatic force is exerted on said switching part, and said electrostatic driving means includes a first pair of electrodes for holding said switching part at said first position and a second pair of electrodes for holding said switching part at said second position,

and wherein, in said control step, said driving voltage is alternately applied to said first and second pairs of electrodes.