Integrated tunable fabry-perot filter and method of making same

• US 20010028503A1
• Filed: 03/01/2001
• Published: 10/11/2001
• Est. Priority Date: 03/03/2000
• Status: Active Grant

• Current Assignee: Axsun Technologies Incorporated
• Original Assignee: Axsun Technologies Incorporated
• Inventors: Flanders, Dale C., Miller, Michael F., Shanfield, Stanley R., Whitney, Peter S., Le, Minh Van
• Granted Patent: US 6,525,880 B2
• Time in Patent Office: Days
• US Class Current: 359/578
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G02B 26/00 Optical devices or arrangements for the control of light using movable or deformable optical elements control of light by modification of the optical properties of the media of the elements involved therein G02F1/00
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G02B 26/02 for controlling the intensity of light G02B26/004 takes precedence
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A tunable Fabry-Perot filter includes an optical cavity bounded by a stationary reflector and a deformable or movable membrane reflector. A second electrostatic cavity outside of the optical cavity includes a pair of electrodes, one of which is mechanically coupled to the movable membrane reflector. A voltage applied to the electrodes across the electrostatic cavity causes deflection of the membrane, thereby changing the length of the optical cavity and tuning the filter. The filter with the movable membrane can be formed by micro device photolithographic and fabrication processes from a semiconductor material in an integrated device structure. The membrane can include an inner movable membrane portion connected within an outer body portion by a pattern of tethers. The tether pattern can be such that straight or radial tethers connect the inner membrane with the outer body. Alternatively, a tether pattern with tethers arranged in a substantially spiral pattern can be used.

Claims

1. A tunable optical filter comprising:

a first mirror structure;

a second, concave mirror structure;

a spacer layer separating the first mirror structure and the second mirror structure, the first mirror structure and the second mirror structure defining a resonant optical cavity of the optical filter; and

an electrostatic cavity across which electric fields are generated to control a separation between the first mirror structure and the second mirror structure to thereby change a length of the optical cavity.

2. A tunable filter as claimed in

claim 1

, wherein the first mirror structure is substantially flat.

3. A tunable filter as claimed in

claim 1

, wherein the first mirror structure is disposed on a membrane that is deflected by the electric fields of the electrostatic cavity.

4. A tunable filter as claimed in

claim 3

, wherein the membrane is formed in a membrane layer that is patterned with an outer portion and tethers extending from the outward portion inward to the membrane.

5. A tunable filter as claimed in

claim 1

, wherein the first mirror structure comprises a suspended HR coating layer that functions as a deflectable membrane layer.

6. A tunable filter as claimed in

claim 5

, further comprising a metal electrode that has been deposited on the HR coating layer.

7. A tunable filter as claimed in

claim 1

, wherein the resonant optical cavity is between 15 and 25 micrometers long.

8. A tunable optical filter comprising:

a support substrate;

a membrane layer comprising a membrane structure, on which a first mirror has been deposited;

a release layer between the membrane layer and the support substrate;

a mirror structure that supports a second mirror that defines a filter cavity in combination with the first mirror

wherein at least one of the first mirror and the second mirror is curved.

9. A tunable filter as claimed in

claim 8

, further comprising a spacer that separates the mirror structure from the membrane layer.

10. A tunable filter as claimed in

claim 8

, wherein the membrane layer is manufactured from silicon wafer material.

11. A tunable filter as claimed in

claim 8

, wherein the release layer is silicon oxide.

12. A tunable filter as claimed in

claim 8

, wherein the release layer defines an electrostatic cavity between the membrane structure and the support substrate.

13. A tunable filter as claimed in

claim 8

, wherein the filter cavity is between 15 and 25 micrometers long.

14. A tunable filter as claimed in

claim 8

, further comprising an optical port through the support substrate to the membrane layer.

15. A tunable filter as claimed in

claim 8

, further comprising an antireflective coating on the membrane layer opposite the first mirror.

16. A tunable filter as claimed in

claim 8

, wherein the mirror structure is bonded to the membrane layer via an intervening spacer with solder.

17. A tunable filter as claimed in

claim 8

, wherein the mirror structure is bonded to the membrane layer via intervening silicon spacer.

18. A tunable filter as claimed in

claim 8

, further comprising a metal spacer that separates the mirror structure from the membrane layer.

19. A tunable filter as claimed in

claim 8

, further comprising a silicon wafer material spacer that separates the mirror structure from the membrane layer.

20. A method for fabricating a tunable filter, the method comprising:

selectively removing part of a release layer to create a membrane structure in a membrane layer;

connecting a mirror structure to the membrane layer;

depositing highly reflective coatings on the membrane layer and the mirror structure to provide a curved mirror/flat mirror optical cavity.

21. A method as claimed in

claim 20

, further comprising patterning the membrane layer to comprise an outer portion and tethers extending from the outward portion inward to a center optical membrane portion.

22. A method as claimed in

claim 20

, further comprising forming the mirror structure with a concave surface.

23. A method as claimed in

claim 20

, further comprising forming an electrostatic cavity having one end defined by the membrane layer.

24. A method as claimed in

claim 20

, further comprising forming an electrostatic cavity across a void formed during the step of selectively removing the release layer.

25. A method as claimed in

claim 20

, further comprising forming an electrostatic cavity by covering the membrane layer with a sacrificial layer and then forming a patterned conductive material structure on the sacrificial layer, and then removing the sacrificial layer to create an air bridge cavity.

26. A method as claimed in

claim 20

, wherein the step of depositing the highly reflective coatings comprises depositing dielectric mirror coatings.

27. A method as claimed in

claim 20

, further comprising locating a spacer between the mirror structure and the membrane layer to yield a resonant optical cavity between the highly reflective coatings on the membrane layer and the mirror structure that is between 15 and 25 micrometers long.

28. A method as claimed in

claim 20

, wherein the membrane layer is manufactured from silicon wafer material.

29. A method as claimed in

claim 28

, wherein the release layer is silicon oxide.

30. A method as claimed in

claim 20

, further comprising etching an optical port through a support substrate to the membrane layer.

31. A method as claimed in

claim 20

, further comprising coating a back-side of the membrane structure with an antireflective coating.

32. A method as claimed in

claim 20

, further comprising bonding the mirror structure to the membrane layer via an intervening spacer with solder.

33. A method for fabricating a tunable filter, the method comprising:

depositing an membrane layer, including an HR coating, on a support substrate;

etching an opening through the support substrate to the membrane layer to create a deflectable membrane; and

connecting a curved mirror structure to membrane layer create an optical cavity.

34. A method as claimed in

claim 33

, further comprising depositing a metal electrode on the membrane layer.

35. A method as claimed in

claim 33

, further comprising:

polishing the support substrate to function as a spacer; and

attaching the curved mirror structure to the support substrate after polishing.

36. A method as claimed in

claim 33

, further comprising:

coating at least part of the membrane layer with a sacrificial layer;

forming a mounting structure; and

removing the sacrificial layer to define an electrostatic cavity between the membrane layer and the mounting structure.