Optical waveguide display with voltage-modulated controlled movable actuators which cause light leakage in waveguide at each display element to provide gradation in a display image

• US 6,211,853 B1
• Filed: 12/15/1997
• Issued: 04/03/2001
• Est. Priority Date: 12/16/1996
• Status: Expired due to Fees

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Takeuchi, Yukihisa, Nanataki, Tsutomu, Akao, Takayoshi, Ohwada, Iwao
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): Bell, Paul A.
• Application Number:
  US08/991,589
• Time in Patent Office: 1,205 Days
• Field of Search: 345/84, 345/85, 345/102, 345/108, 345/147, 385/1-10, 385/25, 385/30, 385/40, 385/41, 385/42, 385/901, 385/129-133, 310/311, 310/328, 310/330, 310/331, 310/332, 359/290-297
• US Class Current: 345/108
• CPC Class Codes: G02B 26/08 for controlling the direction of light in light guides G02B6/35
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0858 the reflecting means being moved or deformed by piezoelectric means
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/2022 using sub-frames
• 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: G09G 3/3493 using light modulating elements actuated by a piezoelectric effect
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

Disclosed is a display device comprising an optical waveguide plate for introducing light radiated from a light source thereinto, in which the display gradation is controlled by changing the entering amount into an evanescent region existing around the back surface of the optical waveguide plate. In the present invention, an actuator element is provided, which makes bending displacement in a direction to make approach to the optical waveguide plate in accordance with voltage application to a pair of electrodes. A plate member of a displacement-transmitting section for determining the picture element area is provided on the actuator element. The entering amount of the plate member into the evanescent region is changed by controlling voltage application to the actuator element so that display gradation of the picture element corresponding to the actuator element is controlled. Accordingly, the time required to perform row scanning is drastically shortened, and it is possible to easily deal with high quality image display.

Claims

1. A display device comprising:

an optical waveguide plate for receiving light from a light source, said waveguide plate having first and second principal surfaces opposed to one another, the refractive index of said waveguide plate being selected to reflect internally substantially all of the light introduced therein, said waveguide plate having an evanescent region adjacent said first principal surface; and

a driving section comprising a plurality of actuators facing said first principal surface of said waveguide plate, each of a plurality of said actuators having at least two displacement positions within the evanescent region, said displacement positions determining the gradation of images displayed on said second principal surface of said waveguide plate.

2. The display device according to claim 1, wherein said actuator elements have a number corresponding to a large number of picture elements, wherein:

a picture image corresponding to an image signal is displayed on said optical waveguide plate, by controlling leakage light at a predetermined portion of said optical waveguide plate by controlling displacement action of each of said actuator elements in a direction to make contact or separation with respect to said optical waveguide plate in accordance with an attribute of said image signal to be inputted.

3. The display device according to claim 2, wherein:

each said actuator element comprises a shape-retaining layer, an operating section having at least a pair of electrodes formed on said shape-retaining layer, a vibrating section for supporting said operating section, and a fixed section for supporting said vibrating section in a vibrating manner;

said display device further comprising;

a displacement-transmitting section for transmitting said displacement action of said actuator element to said optical waveguide plate, said displacement action being generated by voltage application to said pair of electrodes.

4. The display device according to claim 1, further comprising:

a first driving circuit for selecting actuator elements at least in one row unit, a second driving circuit for outputting display information for a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein;

said signal control circuit controls said first and second driving circuits so that gradation is controlled at least by means of a voltage modulation system.

5. The display device according to claim 4, wherein said signal control circuit analog-controls a voltage which is applied by the aid of said second driving circuit depending on display gradation, upon selection for said actuator element.

6. The display device according to claim 4, wherein when a still image is displayed on said second principal surface of said optical waveguide plate, a refresh voltage, which is subjected to analog adjustment in accordance with a display image, is applied to each of said actuator elements by the aid of said second driving circuit upon completion of a minimum still image display period.

7. The display device according to claim 4, wherein upon selection for said actuator element, said signal control circuit changes a number of times of application of minute pulse signals applied by the aid of said second driving circuit in accordance with display gradation.

8. The display device according to claim 7, wherein a pulse width and/or an amplitude of said minute pulse signal is set while considering maximum display gradation.

9. The display device according to claim 7, wherein a pulse width and/or an amplitude of said minute pulse signal is set depending on a wavelength of said light introduced into said optical waveguide plate.

10. The display device according to claim 4, wherein an angle of incidence of said light with respect to said optical waveguide plate is set depending on a wavelength of said light introduced into said optical waveguide plate.

11. The display device according to claim 7, wherein when a still image is displayed on said second principal surface of said optical waveguide plate, a refresh pulse comprising at least one of said minute pulse signals is applied to each of said actuator elements by the aid of said second driving circuit upon completion of a minimum still image display period.

12. The display device according to claim 4, wherein when an animation image is displayed on said second principal surface of said optical waveguide plate, assuming that a period to display one image included in said animation image is one field, a reset voltage, which is sufficient to reset displacement of said actuator element, is applied by the aid of said second driving circuit upon completion of each field.

13. A display device comprising:

an optical waveguide plate for receiving light from a light source, said waveguide plate having first and second principal surfaces opposed to one another, the refractive index of said waveguide plate being selected to reflect internally substantially all of the light introduced therein, said waveguide plate having an evanescent region adjacent said first principal surface;

a plurality of actuators facing said first principal surface of said waveguide plate, each of a plurality of said actuators having at least two displacement positions within the evanescent region;

means for controlling each actuator to assume at least one of said two displacement positions to in turn control gradation of images displayed on said second principal surface of said waveguide plate.

14. The display device according to claim 13, further comprising:

a first driving circuit for selecting at least one actuator element at least in one row unit, a second driving circuit for outputting display information for a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein;

said signal control circuit controls said first and second driving circuits so that gradation is controlled at least by means of a voltage modulation system.

15. The display device according to claim 14, wherein said signal control circuit analog-controls a voltage which is applied by the aid of said second driving circuit depending on display gradation, upon selection for said of least one actuator element.

16. The display device according to claim 14, wherein when a still image is displayed on a display surface of said optical waveguide plate, a refresh voltage, which is subjected to analog adjustment in accordance with a display image, is applied to at least one said actuator element by the aid of said second driving circuit upon completion of a minimum still image display period.

17. The display device according to claim 14, wherein upon selection to said actuator element, said signal control circuit changes a number of times of application of minute pulse signals applied by the aid of said second driving circuit in accordance with display gradation.

18. The display device according to claim 17, wherein a pulse width and/or an amplitude of said minute pulse signal is set while considering maximum display gradation.

19. The display device according to claim 17, wherein a pulse width and/or an amplitude of said minute pulse signal is set depending on a wavelength of said light introduced into said optical waveguide plate.

20. The display device according to claim 14, wherein an angle of incidence of said light with respect to said optical waveguide plate is set depending on a wavelength of said light introduced into said optical waveguide plate.

21. The display device according to claim 17, wherein when a still image is displayed on a display surface of said optical waveguide plate, a refresh pulse comprising at least one of said minute pulse signals is applied to said at least one actuator element by the aid of said second driving circuit upon completion of a minimum still image display period.

22. The display device according to claim 14, wherein when an animation image is displayed on a display surface of said optical waveguide plate, assuming that a period to display one image included in said animation image is one field, a reset voltage, which is sufficient to reset displacement of said at least one actuator element, is applied by the aid of said second driving circuit upon completion of each field.