Tunable finesse infrared cavity thermal detectors

• US 20080035846A1
• Filed: 05/22/2007
• Published: 02/14/2008
• Est. Priority Date: 05/23/2006
• Status: Active Grant

• Current Assignee: Regents of The University of Minnesota (University of Minnesota)
• Original Assignee: Regents of The University of Minnesota (University of Minnesota)
• Inventors: Wang, Yuyan, Sutton, Michael, Talghader, Joseph
• Granted Patent: US 7,968,846 B2
• Time in Patent Office: Days
• US Class Current: 250/338.1
• CPC Class Codes: G01J 2005/583 Interferences, i.e. fringe variation with temperature
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G01J 5/0225 Shape of the cavity itself or of elements contained in or suspended over the cavity
• CPC Class Codes: G01J 5/023 Particular leg structure or construction or shape; Nanotubes
• CPC Class Codes: G01J 5/045 Sealings; Vacuum enclosures; Encapsulated packages; Wafer bonding structures; Getter arrangements getter arrangements per se H01L23/26 and H01L21/3221
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0808 Convex mirrors
• CPC Class Codes: G01J 5/084 Adjustable or slidable
• CPC Class Codes: G01J 5/0853 having infrared absorbers other than the usual absorber layers deposited on infrared detectors like bolometers, wherein the heat propagation between the absorber and the detecting element occurs within a solid
• CPC Class Codes: G01J 5/0893 Arrangements to attach devices to a pyrometer, i.e. attaching an optical interface; Spatial relative arrangement of optical elements, e.g. folded beam path G01J5/049 takes precedence
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: G01J 5/58 using absorption; using extinction effect
• CPC Class Codes: G01J 5/60 using determination of colour temperature
• CPC Class Codes: G02B 5/288 comprising at least one thin film resonant cavity, e.g. in bandpass filters

Abstract

A cavity thermal detector assembly is presented that allows both tunable narrowband and broadband operation. This allows for high light efficiency, low thermal time constant, and flexibility in designing the optical path. The thermal detector/filter layers are part of the top mirror or mirrors of a Gires-Tournois-type optical cavity and provide absorption and reflection that can be adjusted to the desired width and position of the detected band. Tuning, if desired, can be achieved by applying micromechanical methods. Broadband operation may be achieved by bringing the sensor close to the bottom mirror. In this mode, the sensor or its supports may or may not touch over a small area.

Claims

1. A thermal detector configured to detect infrared radiation, comprising:

a first mirror;

a second mirror, the first and second mirrors defining a cavity therebetween, the second mirror having a first side which is external to the cavity and a second side which is positioned closer to the cavity than the first said; and

a thermal sensor coupled to the second mirror wherein the sensor is at least partially absorbing to the infrared radiation and positioned within the cavity or second mirror.

2. The apparatus of claim 1 wherein a spacing between the first and second mirrors is controllable.

3. The apparatus of claim 2 including an actuator configured to provide relative movement between the first and second mirrors.

4. The apparatus of claim 1 wherein the cavity provides a resonant cavity for the infrared radiation wherein only one frequency band is coupled to the thermal sensor.

5. The apparatus of claim 1 wherein the thermal sensor comprises an absorbing element.

6. The apparatus of claim 1 wherein the first and second mirrors are moveable together to thereby substantially collapse the cavity whereby the thermal detector receives broadband radiation.

7. The apparatus of claim 6 wherein the first and second mirrors are configured to contact each other.

8. The apparatus of claim 7 including standoffs to reduce contact area between the first and second mirrors.

9. The apparatus of claim 7 wherein the thermal standoffs prevent thermal conduction based upon contact area and pressure to the substrate from becoming the dominant heat transfer mechanism.

10. The apparatus of claim 1 wherein the thermal sensor is patterned into a diffractive optical element.

11. The apparatus of claim 1 wherein at least one of the first and second mirrors is patterned into a diffractive optical element.

12. The apparatus of claim 1 wherein at least one of the first and second mirrors is patterned into a grating.

13. The apparatus of claim 1 wherein at least one of the first and second mirrors is patterned into a Fresnel lens.

14. The apparatus of claim 1 wherein the device is designed to detect polarization.

15. The apparatus of claim 1 wherein at least one of the first and second mirrors is curved to form a Gaussian cavity.

16. The apparatus of claim 3 wherein the actuator comprises uses electrostatic force to provide the relative movement.

17. The apparatus of claim 3 wherein the actuator comprises uses magnetism to provide the relative movement.

18. The apparatus of claim 1 including a support configured to support one of the first and second mirrors.

19. The apparatus of claim 18 wherein the support provides a connection to one of the first and second mirrors.

20. The apparatus of claim 1 including control circuitry electrically coupled to at least one of the first and second mirrors to control spacing between the first and second mirrors.

21. The apparatus of claim 20 including a substrate which carries the control circuitry, the substrate including at least one via through the substrate which provides an electrical connection to the control circuitry.

22. A thermal detector configured to detect infrared radiation, comprising:

a first mirror;

a second mirror;

a thermal sensor configured to sense infrared radiation; and

an actuation mechanism configured to provide relative movement between the first and second mirrors between a first position in which the cavity is tuned to a frequency and the thermal sensor receives the frequency and a second position in which the first and second mirrors are positioned proximate each other and the thermal sensor receives broadband infrared radiation.

23. The apparatus of claim 22 wherein the second mirror has a first side which is external to the cavity and a second side which is positioned closer to the cavity than the first said, and the thermal sensor is positioned within the cavity including coincident with the first side of the second mirror.

24. The apparatus of claim 22 wherein a spacing between the first and second mirrors is controllable.

25. The apparatus of claim 22 wherein the thermal sensor comprises an absorbing element.

26. The apparatus of claim 22 including standoffs to reduce contact area between the first and second mirrors.

27. The apparatus of claim 22 wherein the thermal sensor is patterned into a diffractive optical element.

28. The apparatus of claim 22 wherein at least one of the first and second mirrors is patterned into a diffractive optical element.

29. The apparatus of claim 22 wherein at least one of the first and second mirrors is curved to form a Gaussian cavity.

30. The apparatus of claim 22 wherein the actuation mechanism comprises uses electrostatic force to provide the relative movement.

31. The apparatus of claim 22 wherein the actuation mechanism comprises uses magnetism to provide the relative movement.

32. The apparatus of claim 22 including a support configured to support one of the first and second mirrors.

33. The apparatus of claim 22 wherein the support provides a connection to one of the first and second mirrors.

34. The apparatus of claim 22 including control circuitry electrically coupled to at least one of the first and second mirrors to control spacing between the first and second mirrors.

35. The apparatus of claim 34 including a substrate which carries the control circuitry, the substrate including at least one via through the substrate which provides an electrical connection to the control circuitry.