Surface-plasmon-wave-coupled tunable filter

• US 5,986,808 A
• Filed: 10/10/1997
• Issued: 11/16/1999
• Est. Priority Date: 10/11/1996
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Wang, Yu
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Curtis, Craig
• Application Number:
  US08/949,151
• Time in Patent Office: 767 Days
• Field of Search: 345/88, 348/744, 349/105, 349/106, 349/196, 359/578, 359/579, 359/585
• US Class Current: 359/585
• CPC Class Codes: G02B 27/288 Filters employing polarising elements, e.g. Lyot or Solc filters G02B5/3016 takes precedence

Abstract

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.

Claims

1. An optical filter, comprising:

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 support first and second surface plasmon modes, respectively, at said first and second metal-dielectric interfaces and said dielectric layer is configured to transfer a selected spectral component in a p-polarized input electromagnetic wave from said first side of said dielectric layer to said second side by coupling said first and second surface plasmon modes.

2. The optical filter as in claim 1, further comprising:

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 formed on said second metallic film and configured to couple the energy of said selected spectral component to an output electromagnetic wave.

3. The optical filter as in claim 2, 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.

4. The optical filter as in claim 2, wherein said first and second coupling elements comprise diffraction gratings.

5. The optical filter as in claim 1, wherein said first dielectric material of said dielectric layer includes an electro-optic material whose index of refraction is controllable in response to a voltage control signal to change the wavelength of said selected spectral component, thereby changing a wavelength of an output electromagnettc wave.

6. The optical filter as in claim 2, wherein said dielectric layer includes an air gap and further comprising at least one adjustable spacer disposed between said first and second coupling elements to change the wavelength of said selected spectral component, thereby changing a wavelength of an output electromagnetic wave.

7. The optical filter as in claim 1, wherein said first predetermined thickness of said dielectric layer is on the order of one wavelength of an input optical wave.

8. The optical filter as in claim 1, wherein said second predetermined thickness of said first and second metallic films is from 5 nm to 150 nm.

9. The optical filter as in claim 1, further comprising an angle adjustment device operable to change the incident angle of the input p-polarized electromagnetic wave with respect to said first metal-dielectric interface to tune the wavelength of said selected spectral component.

10. The optical filter as in claim 1, wherein said first dielectric constant is positive and said second dielectric constant is negative.

11. An optical filter, comprising:

a first coupling element having a first coupling surface and operable to couple a p-polarized input electromagnetic wave to have a propagation component parallel to said coupling surface;

a first metallic film formed on said first coupling surface and operable to produce free electron oscillations in response to excitation of said p-polarized input electromagnetic wave;

a second coupling element configured to have a second coupling surface and disposed relative to said first coupling element so that said second coupling surface opposes and is spaced from said first coupling surface, said second coupling element operable to couple an electromagnetic wave propagating along said second coupling surface into an output electromagnetic wave;

a second metallic film formed on said second coupling surface of said second coupling element and operable to produce free electron oscillations in response to excitation of said p-polarized input electromagnetic wave; and

a dielectric material disposed between said first and second metallic films to respectively form first and second metal-dielectric interfaces which are configured to respectively support first and second surface plasmon modes at said first and second metal-dielectric interfaces and to transfer a selected spectral component in said p-polarized input electromagnetic wave from said first coupling surface to said second coupling surface by coupling said first and second surface plasmon modes.

12. The optical filter as in claim 11, wherein said dielectric material is an electro-optic material and further comprising a voltage supply connected to said first and second metalltc films to apply a control voltage, wherein the index of refraction of said electro-optic material changes in response to said control voltage to change the wavelength of said selected spectral component.

13. The optical filter as in claim 11, wherein said dielectric material is a gaseous medium and the spacing between said first and second coupling surfaces is variable in order to change the wavelength of said selected spectral component.

14. The optical filter as in claim 12 or claim 13, wherein said first and second coupling elements each comprise a prism having an index of refraction larger than said dielectric material.

15. The optical filter as in claim 12 or claim 13, wherein said first and second coupling elements each comprise a dielectric plate that has an index of refraction larger than said dielectric material and has a plurality of micro-prisms.

16. The optical filter as in claim 12 or claim 13, wherein said first and second coupling elements each comprise a diffraction grating.

17. The optical filter as in claim 11, further comprising an image sensor array that has a plurality of photo sensing elements, said image sensor array disposed relative to said second coupling element to receive said output electromagnetic wave.

18. The optical filter as in claim 11, further comprising a Fabry-Perot filter that is disposed relative to said first coupling element to produce said p-polarized input electromagnetic wave to said first coupling surface.

19. The optical filter as in claim 11, further comprising:

a liquid crystal display panel disposed relative to said second coupling element to receive and modulate said output electromagnetic wave in order to imprint an image; and

a display control circuit connected to said liquid crystal display panel to control the modulation of said output electromagnetic wave from said second coupling element and configured to control the wavelength of said selected spectral component that is coupled from said first coupling surface to said second coupling surface, wherein said image imprinted on said output electromagnetic wave is in color.

20. A method for filtering light, comprising:

forming a first metal-dielectric interface which is configured to support a first surface plasmon mode and a second metal-dielectric interface which is configured to support a second surface plasmon mode;

providing a coupling mechanism to couple said first and second surface plasmon modes to transfer electromagnetic energy between said first and second metal-dielectric interfaces; and

coupling an input electromagnetic wave to said first and second metal-dielectric interfaces to select a specified spectral component in resonance with said first and second surface plasmon modes so that said spectral component is transferred from one side of said first and second metal-dielectric interfaces to the other side to produce a transmitted output electromagnetic wave at the wavelength of said specified spectral component.