Liquid crystal flat panel color display with surface plasmon scattering

• US 5,451,980 A
• Filed: 10/19/1993
• Issued: 09/19/1995
• Est. Priority Date: 10/19/1993
• Status: Expired due to Fees

• Current Assignee: University of Toledo
• Original Assignee: University of Toledo
• Inventors: Wang, Yu, Simon, H. J.
• Primary Examiner(s): Weldon, Ulysses
• Assistant Examiner(s): Liang, Regina
• Application Number:
  US08/138,925
• Time in Patent Office: 700 Days
• Field of Search: 345/63, 345/32, 345/102, 345/88, 345/89, 345/72, 345/147, 345/87, 359/48, 359/49, 359/64, 359/40
• US Class Current: 345/88
• CPC Class Codes: G02F 1/195 by using frustrated reflection digital reflection using controlled total internal reflection G02F1/315
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127

Abstract

A flat panel color display is provided in which white collimated light incident on a light coupling means having a metal layer and a liquid crystal layer formed on a surface of the coupling means produces a colored spot of light at the interface of the metal layer and liquid crystal layer through the excitation of surface plasmons. The present invention utilizes the color selective scattering of incident white light by surface plasmons and includes a coupling device, such as a high index glass prism, with a metal film layer and a liquid crystal layer formed on the coupling device. Surface plasmon waves can be generated at a negative dielectric (metal layer)-positive dielectric (liquid crystal layer) interface when the dispersion relationship is satisfied. The incident white light includes photons which have frequencies approximately equal to the plasmon resonance, and such photons are strongly scattered. Photons having a frequency other than the plasmon resonance will be totally reflected. The dispersion relationship of the metal-liquid crystal interface depends on the dielectric constant of the metal, which is not typically variable, and the dielectric constant of the liquid crystal, which is variable. An external voltage control/modulator may be used to vary the dielectric constant of the liquid crystal, thereby controlling the plasmon resonance condition and the frequencies (color) of the scattered photons.

Claims

1. A display assembly comprising:

a) a source of polarized incident white light;

b) coupling means for matching a wave vector of incident light in said coupling means to a wave vector of a surface plasmon mode, said coupling means being positioned in a light coupling relationship to said source at an angle of incidence for excitation of the surface plasmon mode;

c) a layer of medium having a negative dielectric constant formed on a surface of said coupling means, said negative dielectric constant medium providing desired dispersion properties in the surface plasmon mode;

d) a layer of medium having a positive dielectric constant formed on said layer of negative dielectric medium, said layers of medium forming an interface capable of supporting the surface plasmon mode, the interface being positioned to receive incident light at the angle of excitation of the surface plasmon mode such that a portion of the incident light is selectively absorbed and scattered, and the balance of the incident light is reflected away from the interface;

e) an outer transparent panel positioned parallel to said layers of medium for display of the light scattered at the interface; and

f) control means for defining a matrix of variable color pixels on said positive dielectric medium, said control means including a controller for selectively controlling the dielectric constant of said positive dielectric medium at each pixel in the matrix by transmitting voltage signals to each pixel, which controls the wavelength of the incident light for excitation of the surface plasmon mode, including the color of the incident light that is reflected and the color of the incident light that is scattered from the interface at each pixel to said outer panel to form a color picture.

2. The display assembly defined in claim 1 wherein said layer of medium having a positive dielectric constant is a layer of liquid crystal material.

3. The display assembly defined in claim 1 wherein said layer of medium having a negative dielectric constant is a layer of metal material.

4. The display assembly defined in claim 2 wherein said means for controlling the dielectric constant includes a first planar array of parallel linear electrodes formed in said layer of negative dielectric medium on one side of said layer of liquid crystal material and a corresponding second array of parallel linear transparent electrodes on the opposite side of said layer of liquid crystal, the second array of transparent electrodes positioned in a parallel plane and perpendicular to the first array of electrodes, said first and second arrays of electrodes defining a matrix of pixels on said layer of liquid crystal, and a color controller for selectively transmitting voltage signals between corresponding electrodes of the first and second arrays for varying the dielectric constant of the layer of liquid crystal at each of the color pixels, which controls the wavelength of the incident light for excitation of the surface plasmon mode, including the color of the incident light that is reflected and the color of the incident light that is scattered from the interface at each color pixel.

5. A display assembly comprising:

a) a source of polarized incident white light;

b) coupling means for matching a wave vector of incident light in said coupling means to a wave vector of a surface plasmon mode, said coupling means being positioned in a light coupling relationship to said source at an angle of incidence for excitation of the surface plasmon mode;

c) a layer of metal formed on a surface of said coupling means, said layer of metal providing desired dispersion properties in the surface plasmon mode;

d) a layer of liquid crystal formed on said layer of metal, said layer of metal and said layer of liquid crystal forming an interface capable of supporting a surface plasmon mode, the interface being positioned to receive incident light at the angle of excitation of the surface plasmon mode such that a portion of the incident light is selectively absorbed and scattered, and the balance of the incident light is reflected away from the interface;

e) an outer transparent panel positioned parallel to said layer of metal and said layer of liquid crystal for display of the light scattered at the interface; and

t) control means for defining a matrix of variable color pixels on said positive dielectric medium, said control means including a controller for selectively controlling the dielectric constant of said layer of liquid crystal at each pixel in the matrix by transmitting voltage signals to each pixel to control the wavelength of the incident light for excitation of the surface plasmon mode, including the color of the incident light that is reflected and the color of the incident light that is scattered from the interface at each pixel to said display means to form a color picture.

6. The display assembly defined in claim 5 wherein said coupling means includes a prism, said layer of metal and said layer of liquid crystal being formed on the hypotenuse of said prism.

7. The display assembly defined in claim 5 wherein said coupling means includes a diffraction grating.

8. The display assembly defined in claim 5 wherein said coupling means includes a wave guide structure.

9. The display assembly defined in claim 5 wherein said layer of metal includes a layer of silver.

10. The display assembly defined in claim 5 wherein said layer of metal includes a layer of aluminum.

11. The display assembly defined in claim 5 wherein said layer of metal includes a combination of linear silver conductors and linear aluminum conductors to form electrodes positioned in a specified pattern of pixels, the silver segments designed to control the scattering of red and green light, and the aluminum segments designed to control the scattering of blue light.

12. The display assembly defined in claim 5 wherein said outer panel includes a glass substrate having a tinted coating.

13. The display assembly defined in claim 5 wherein said means for controlling the dielectric constant includes a first array of parallel linear electrodes formed in said layer of metal adjacent one side of said layer of liquid crystal, and a corresponding second array of parallel linear transparent electrodes adjacent the opposite side of said layer of liquid crystal, the second array of linear transparent electrodes positioned in a parallel plane and perpendicular to the first array of linear electrodes, said first and second arrays of electrodes defining a matrix of pixels on said layer of liquid crystal, and said means for controlling including a controller for selectively transmitting voltage signals between corresponding electrodes of the first and second arrays through a selected position on said layer of liquid crystal material whereby the voltage signals to the electrodes determines the color of light scattered through each of the pixels to said outer panel.

14. The display assembly defined in claim 13 wherein said controller utilizes modulation pulses to control the color of the light scattered through each of the pixels.

15. The display assembly defined in claim 13 wherein said controller transmits three separate voltage signals for red, green, and blue color to a single pixel whereby a single pixel may represent any color in a color light spectrum.

16. The display assembly defined in claim 13 wherein the pixels defined on said layer of liquid crystal are arranged in an array of red, green, and blue pixels, each pixel receiving a separate voltage signal from the controller, whereby a color picture is formed by the combination of red, green, and blue pixels.

17. The display assembly defined in claim 11 wherein said means for controlling the dielectric constant includes an array of transparent electrodes positioned between said layer of liquid crystal and said display means, the array of electrodes, the silver conductors, and the aluminum conductors defining a matrix of pixels on said layer of liquid crystal, and a controller for selectively transmitting voltage signals through the layer of liquid crystal material whereby the color of light scattered at each of the pixels is determined by said metal conductors and the voltage signals to the electrodes.