Silicon-Compatible Surface Plasmon Optical Elements

• US 20090052827A1
• Filed: 10/09/2007
• Published: 02/26/2009
• Est. Priority Date: 10/09/2006
• Status: Active Grant

• Current Assignee: Colorado School of Mines
• Original Assignee: Colorado School of Mines
• Inventors: Furtak, Thomas E., Durfee, Charles G., Collins, Reuben T.
• Granted Patent: US 7,949,210 B2
• Time in Patent Office: Days
• US Class Current: 385/2
• CPC Class Codes: G02F 1/035 in an optical waveguide structure
• CPC Class Codes: G02F 2203/10 plasmon

Abstract

This invention provides fundamental science and novel device architectures for surface plasmon (SP)-based, complementary metal oxide semiconductor (CMOS)-compatible, optical elements such as modulators, couplers, and switches. The primary focus of the work is on waveguides based on an ultra-long-range surface plasmon (ULRSP) waveguide mode recently discovered by our team. This mode exists at the metal-dielectric interfaces in a silicon-oxide-metal-silicon layer structure. While initial work focuses on noble metals to support the ULRSP, our analysis shows Si processing-compatible metals such as Cu and Al can also be used. Our modeling has also shown that variation in the thickness of the oxide layer can be used to give unprecedented propagation lengths in such structures. Electrically-induced free carrier modulation of the dielectric constant in the Si adjacent to the oxide can modulate the waveguide properties allowing novel Si-compatible electro-optic devices to be created. These waveguides function as the “wiring” in new classes of optical chips. This invention also provides integration of ULRSP waveguides and switches with other optical elements to create entirely new classes of hybrid optoelectronic technologies for defense applications. These range from chip-based chemical agent detection to extremely high performance processors and even all-optical computations.

Claims

1. A modulator for varying an optical signal by varying an electrical signal or varying an electrical signal by varying an optical signal, comprising:

an ultra-long-range surface plasmon (ULRSP) waveguide;

an optical waveguide coupled to said ULRSP waveguide.

2. The modulator of claim 1 wherein said ULRSP waveguide comprises:

a metal layer;

a first dielectric layer adjacent to one side of said metal layer;

an insulating layer adjacent to the other side of said metal layer; and

a second dielectric layer adjacent to said insulating layer.

3. The modulator of claim 1 wherein said ULRSP waveguide comprises:

a first dielectric layer having a high refractive index;

an insulating second dielectric layer having a low refractive index adjacent to said first dielectric layer;

a metal layer adjacent to said second insulating dielectric layer;

an insulating third dielectric layer having a low refractive index adjacent to said metal layer;

a fourth dielectric layer having a high refractive index adjacent to said insulating third dielectric layer.

4. The modulator of claim 2 wherein said ULRSP waveguide is a metal-oxide semiconductor (MOS) capacitor.

5. The modulator of claim 2 wherein said insulating layer is an oxide layer.

6. The modulator of claim 2 wherein said insulating layer is sufficiently thin to allow surface plasmon propagation.

7. The modulator of claim 1 wherein said optical waveguide is a visible-light optical waveguide.

8. The modulator of claim 1 wherein said optical waveguide is an infrared-light waveguide.

9. The modulator of claim 8 wherein said infrared-light waveguide is a portion of a MOS capacitor.

10. The modulator of claim 9 in combination with means for inducing a selected voltage across said capacitor, whereby light in said optical waveguide is modulated by changes in the voltage across said capacitor.

11. The modulator of claim 1 wherein the difference in the indices of refraction on either side of the metal layer is no more than about 0.1.

12. The modulator of claim 1 wherein said metal layer comprises a metal selected from the group consisting of silver, gold, copper, and aluminum.

13. The modulator of claim 1 wherein said optical waveguide is a dielectric waveguide and said ULRSP waveguide shares a semiconductor layer therewith.

14. The modulator of claim 13 wherein said ULRSP waveguide shares a dielectric silicon semiconductor layer with said optical waveguide.

15. The modulator of claim 1 comprising a silicon-compatible optical waveguide with an embedded ULRSP waveguide contained in a linear Fabry-Perot resonator with Bragg mirrors.

16. The modulator of claim 1 incorporated into a chemical detector.

17. The modulator of claim 1 incorporated into a computer processor.

18. The modulator of claim 2 wherein the low-index dielectric insulating layer changes refractive index, thereby modulating the effective index of the guided surface plasmon mode.