Efficient color display using low-absorption in-pixel color filters

• US 6,097,456 A
• Filed: 08/12/1998
• Issued: 08/01/2000
• Est. Priority Date: 08/12/1998
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Wang, Yu
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGO, HUYEN LE
• Application Number:
  US09/133,281
• Time in Patent Office: 720 Days
• Field of Search: 349/105, 349/114, 349/71, 349/8, 349/62, 345/88, 348/744, 359/263, 356/445, 436/525
• US Class Current: 349/105
• CPC Class Codes: G02B 5/1809 with pitch less than or comparable to the wavelength
• CPC Class Codes: G02F 1/1335 Structural association of cells with optical devices, e.g. polarisers or reflectors
• CPC Class Codes: G02F 1/133521 Interference filters
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence

Abstract

A display system having a non-absorbing and reflective color filtering array and a reflector to improve light utilization efficiency. One implementation of the color filtering array uses a surface plasmon filter having two symmetric metal-dielectric interfaces coupled with each other to produce a transmission optical wave at a surface plasmon resonance wavelength at one interface from a p-polarized input beam on the other interface. Another implementation of the color filtering array uses a metal-film interference filter having two dielectric layers and three metallic films.

Claims

1. An image display system, comprising:

a display array having light-modulating pixels, each configured to modulate an intensity of light illuminating said display array to produce a spatial pattern indicative of an image to be displayed;

a light filtering array of optical filters formed over said display array, each optical filter configured to receive and transmit at least one selected spectral component of an input light beam to a respective light-modulating pixel in said display array and reflect other spectral components that are different from said at least one spectral component in said input light beam; and

an optical reflector disposed relative to said light filtering array and configured to reflect said other spectral components back to said light filtering array so that said light filtering array receives and filters said other spectral components to further illuminate said display array.

2. The system as in claim 1, wherein said display array is a liquid crystal display array and each of said light-modulating pixels includes a liquid crystal material.

3. The system as in claim 1, wherein each of said optical filters in said light filtering array comprises:

a dielectric layer having a first side and an opposite second side and comprising a first dielectric material with a first dielectric constant and a first predetermined thickness; and

first and second metallic films each having a second dielectric constant and a second predetermined thickness, said metallic films respectively formed on the opposite sides of said dielectric layer to form first and second metal-dielectric interfaces which are substantially symmetric with respect to said dielectric layer,

wherein said dielectric layer, said first and second metallic films are configured to respectively support surface plasmon waves at said first and second metal-dielectric interfaces and said dielectric layer is operable to transfer said selected spectral component in a p-polarized input electromagnetic wave from said first side of said dielectric layer to said second side.

4. The system as in claim 3, wherein each of said optical filters in said light filtering array further comprises:

a first coupling element, formed on said first metallic film and configured to couple the p-polarized input electromagnetic wave into said first surface plasmon mode at said fist metal-dielectric interface; and

a second coupling element substantially identical to said first light coupling element and formed on said second metallic film and configured to couple the energy of said selected spectral component to an output electromagnetic wave.

5. The system as in claim 4, wherein said first and second coupling elements comprise prisms which are made of a dielectric material having a dielectric constant higher than said first dielectric constant of said dielectric layer.

6. The system as in claim 4, wherein said first and second coupling elements comprise diffraction gratings.

7. The system as in claim 3, wherein an optical thickness of said dielectric layer is set at a value in a relation with respect to a wavelength of said selected spectral component.

8. The system as in claim 1, wherein each of said optical filters in said light filtering array comprises:

a first metallic layer configured to be optically transparent to said input light beam;

a first dielectric layer formed on said first metallic layer; and

a second metallic layer formed on said first dielectric layer and configured to be optically transparent to said input light beam.

9. The system as in claim 8, wherein said first and second metallic layers are formed of gold or silver.

10. The system as in claim 8, wherein each of said optical filters in said light filtering array further comprises:

a second dielectric layer formed on said second metallic layer; and

a third metallic layer formed on said second dielectric layer and configured to be optically transparent to said input light beam,

wherein said first and second dielectric layers are configured to allow for transmission of said selected spectral component.

11. The system as in claim 10, wherein said first, second and third metallic layers are less than about 40 nm thick and greater than zero.

12. The system as in claim 10, wherein said first and second dielectric layers are formed of a photoresist.

13. The system as in claim 10, wherein said first and second dielectric layers are formed of MgF₂, SiO₂, NaF, or LiF.

14. The system as in claim 1, wherein each of said optical filters in said light filtering array comprises an interference filter having a plurality of dielectric layers.

15. A system as in claim 1, wherein said optical reflector is spaced from said light filtering array and said display array by an optical path that allows a reflected beam from each optical filter to diverge and to fill the entirety of said light filtering array upon a single reflection by said optical reflector.

16. A system as in claim 1, wherein said optical reflector is spaced from said light filtering array by D/2θ

, where D is the dimension of said light filtering array and θ

is a full divergence angle of a reflected beam from each optical filter.

17. An image display system, comprising:

a display array having liquid crystal pixels, each configured to modulate an intensity of light illuminating said display array to produce a spatial pattern indicative of an image to be displayed;

a light filtering array formed over said display array and configured to have thin-film optical filters, each comprised of a first metallic layer optically transparent to said light, a first dielectric layer formed on said first metallic layer, a second metallic layer formed on said first dielectric layer and configured to be optically transparent to said light, a second dielectric layer formed on said second metallic layer, and a third metallic layer formed on said second dielectric layer and configured to be optically transparent to said input light beam, wherein each thin-film optical filter is operable to receive and transmit at least one selected spectral component of said light beam to a respective light-modulating pixel and reflect other spectral components in said light; and

an optical reflector disposed relative to said light filtering array and configured to reflect said other spectral components back to said light filtering array so that said light filtering array receives and filters said other spectral components to further illuminate said display array.

18. A system as in claim 17, wherein said optical reflector is spaced from said light filtering array and said display array by an optical path that allows a reflected beam from each optical filter to diverge and to fill the entirety of said light filtering array upon a single reflection by said optical reflector.

19. An image display system, comprising:

a display array having liquid crystal pixels each configured to modulate an intensity of light illuminating said display array to produce a spatial pattern indicative of an image to be displayed;

a light filtering array formed over said display array and configured to have a plurality of optical filters respectively to transmit filtered light to said light-modulating pixels, each optical filter comprised of a dielectric layer having a first side and an opposite second side and comprising a first dielectric material with a first dielectric constant and a first predetermined thickness, and first and second metallic films each having a second dielectric constant and a second predetermined thickness, said metallic films respectively formed on opposite sides of said dielectric layer to form first and second metal-dielectric interfaces which are substantially symmetric with respect to said dielectric layer, wherein said dielectric layer, said first and second metallic films are configured to respectively support surface plasmon waves at said first and second metal-dielectric interfaces and said dielectric layer is operable to transmit a selected spectral component in a p-polarized input electromagnetic wave in said light from said first side of said dielectric layer to said second side and reflect other spectral components in said light; and

an optical reflector disposed relative to said light filtering array and configured to reflect said other spectral components back to said light filtering array so that said light filtering array receives and filters said other spectral components to further illuminate said display array.

20. A system as in claim 19, wherein said optical reflector is spaced from said light filtering array and said display array by an optical path that allows a reflected beam from each optical filter to diverge and to fill the entirety of said light filtering array upon a single reflection by said optical reflector.

21. A method for forming a color representation of an image, comprising:

(1) filtering an input beam to transmit at least a first selected spectral component of said input light beam and to reflect other spectral components;

(2) modulating an intensity of said first selected spectral component to imprint a first color component for one image pixel of an image thereon to be displayed;

(3) filtering other spectral components to transmit at least a second selected spectral component and to reflect remaining spectral components;

(4) modulating an intensity of said second selected spectral component to imprint a second color component for said one image pixel of said image; and

(5) repeating (1)-(4) to form at least said first and second color components for other image pixels of said color representation of said image.

22. A method as in claim 21, further comprising reflecting each reflected beam after said filtering step to allow each reflected beam to be filtered and modulated at least one more time to form a color component for at least another image pixel of said image.

23. A color display system, comprising:

a plurality of light-modulating pixels forming a display array, each pixel configured to modulate an intensity of light illuminating said display array to produce a spatial pattern indicative of an image to be displayed, wherein three adjacent light-modulating pixels respectively modulate beams of three different colors to form one color pixel for said image;

a light filtering array of optical filters formed over said display array, each optical filter configured to receive and transmit a selected spectral component of an input light beam to a respective light-modulating pixel in said display array and reflect other spectral components that are different from said at least one spectral component in said input light beam, wherein three adjacent optical filters belonging to one color pixel are configured to respectively to transmit three different colors; and

an optical reflector positioned to receive and reflect reflected beams from said light filtering array back to said light filtering array so that each reflected beam diverges to fill said light filtering array upon a single reflection.

24. A system as in claim 23, further includes an optical integrator between said optical reflector and said light filtering array.

25. A system as in claim 24, wherein said optical integrator include a transparent rod.

26. A system as in claim 24, wherein said optical integrator includes two lenslet arrays of a common focal length.

27. A system as in claim 24, wherein said optical integrator includes a fiber bundle.

28. A system as in claim 23, wherein said display array includes a LCD panel.