MEMS variable optical attenuator

• US 6,275,320 B1
• Filed: 09/27/1999
• Issued: 08/14/2001
• Est. Priority Date: 09/27/1999
• Status: Expired due to Fees

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Inventors: Wood, Robert L., Mahadevan, Ramaswamy, Hill, Edward A., Dhuler, Vijayakumar R., Walters, Mark David
• Primary Examiner(s): Ben, Loha
• Application Number:
  US09/405,789
• Time in Patent Office: 687 Days
• Field of Search: 359/237, 359/290, 359/291, 359/295, 359/298, 359/308, 359/871, 359/872, 359/321, 359/322, 359/245, 385/24, 385/140, 385/73, 310/306, 310/307
• US Class Current: 359/237
• CPC Class Codes: B81B 2201/038 Microengines and actuators not provided for in B81B2201/031 - B81B2201/037
• CPC Class Codes: B81B 2201/047 Optical MEMS not provided for in B81B2201/042 - B81B2201/045
• CPC Class Codes: B81B 3/0054 For holding or placing an element in a given position
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 6/266 the optical element being an attenuator

Abstract

A MEMS (Micro Electro Mechanical System) variable optical attenuator is provided that is capable of optical attenuation over a full range of optical power. The MEMS variable optical attenuator comprises a microelectronic substrate, a MEMS actuator and an optical shutter. The MEMS variable optical attenuator may also comprise a clamping element capable of locking the optical shutter at a desired attenuation position. The variable light attenuator is capable of attenuating optical beams that have their optical axis running parallel and perpendicular to the substrate. Additionally, the MEMS actuator of the present invention may comprise an array of MEMS actuators capable of supplying the optical shutter with greater displacement distances and, thus a fuller range of optical attenuation. In one embodiment of the invention, the MEMS actuator comprises a thermal arched beam actuator. Additionally, the variable optical attenuator of the present invention may be embodied in a thermal bimorph cantilever structure. This alternate embodiment includes a microelectronic substrate and a thermal bimorph cantilever structure having at least two materials of different thermal coefficient of expansion. The thermal bimorph is responsive to thermal activation and moves in the direction of the material having the lower thermal coefficient expansion. Upon activation, the thermal bimorph intercepts the path of the optical beam and provides for the desired level of optical attenuation. The invention also provides for a method of optical attenuation and a method for fabricating an optical attenuator in accordance with the described structures.

Claims

1. A MEMS device for optically attenuating an optical beam, comprising:

a microelectronic substrate having a generally planar surface;

a microelectronic actuator disposed on the generally planar surface of said microelectronic substrate; and

an optical shutter disposed on the generally planar surface of said microelectronic substrate, wherein said optical shutter is actuatable by said microelectronic actuator and is adapted to be held at any one of a plurality of positions, and wherein said optical shutter is configured to block a different percentage of optical power in each position such that said optical shutter can block any percentage of optical power within an optical power range.

2. A MEMS device according to claim 1, further comprising:

an electrostatic clamping element disposed on said substrate and operably connected to said optical shutter that allows for said optical shutter to be electrostatically clamped at a desired attenuation position;

an electrostatic contact on said substrate which is electrostatically coupled to said electrostatic clamping element; and

means for applying an electrostatic force between said electrostatic clamping element and said electrostatic contact.

3. A MEMS device according to claim 2 wherein said electrostatic clamping element is comprised of a metal.

4. A MEMS device according to claim 2 wherein said electrostatic clamping element is comprised of a semiconductor-metal composite.

5. A MEMS device according to claim 1, wherein said microelectronic actuator further comprises a thermal arched beam actuator.

6. A MEMS device according to claim 5, further comprising a means for applying heat to said arched beam actuator to cause further arching of the arched beam, thereby actuating said optical shutter.

7. A MEMS device according to claim 6, wherein said means for applying heat further comprises an external heater disposed proximate to said actuator.

8. A MEMS device according to claim 5, further comprising an actuator member that is configured to be displaced by said thermal arched beam actuator and attaches said optical shutter to said thermal arched beam actuator.

9. A MEMS device according to claim 5, further comprising a temperature compensation element on said microelectronic substrate and adapted to prevent said actuator from actuating in response to changes in ambient temperature.

10. A MEMS device according to claim 9, wherein said temperature compensation element further comprises a rigid frame structure surrounding said thermal arched beam actuator, said rigid frame structure having at least one anchor point affixing said rigid frame structure to said substrate, the remainder of the frame suspended above said substrate and operably connected to said thermal arched beam actuator.

11. A MEMS device according to claim 1, further comprising a support structure for supporting said optical shutter on said substrate.

12. A MEMS device according to claim 11, wherein said support structure further comprises a folded beam suspension structure.

13. A MEMS device according to claim 1, wherein said microelectronic actuator further comprises an array of microelectronic actuators.

14. A MEMS device according to claim 13, wherein said array of microelectronic actuators further comprises an array of thermal arched beam actuators.

15. A MEMS device according to claim 14, further comprising means for applying heat to said array of thermal arched beam actuators to cause further arching of the arched beams, thereby actuating said optical shutter.

16. A MEMS device according to claim 15, wherein said means for applying heat further comprises at least one external heater disposed proximate to said array of microelectronic actuators.

17. A MEMS device according to claim 14, further comprising at least one temperature compensation element on said microelectronic substrate and adapted to prevent said actuators from actuating in response to changes in ambient temperature.

18. A MEMS device according to claim 17, wherein said at least one temperature compensation element further comprises at least one rigid frame structure surrounding said array of thermal arched beam actuators, said rigid frame structure having at least one anchor point affixing said rigid frame structure to said substrate, the remainder of the frame suspended above said substrate and operably connected to said array of thermal arched beam actuators.

19. A MEMS device according to claim 14, further comprising a central hub disposed on the microelectronic substrate having at least two hub spokes operably connected to at least one MEMS actuator within said array and at least one lever operably connected to said central hub and said optical shutter, wherein said MEMS actuators are configured to provide the force to move said at least two hub spokes, thereby imposing a rotational force upon said central hub that moves said at least one lever so as to cause said optical shutter to attenuate an optical beam.

20. A MEMS device according to claim 19, further comprising at least one lever operably connected to said central hub and a clamping element attached to said at least one lever wherein said MEMS actuators are configured to provide the force to move said at least two hub spokes, thereby imposing a rotational force upon said central hub that moves said at least one lever so as to cause said clamping element to reach a position where a clampdown voltage may be applied.

21. A MEMS device according to claim 20, wherein said microelectronic substrate defines at least one opening spaced proximate to said central hub, and wherein said optical shutter further comprises at least one optical shutter operably coupled to said central hub through at least one lever and adapted to at least partially affect attenuation of optical beams by moving across, respective, said at least one opening.

22. A MEMS device according to claim 14, further comprising an actuator member that is configured to be displaced by said array of thermal arched beam actuators and attaches said optical shutter to said array of thermal arched beam actuators.

23. A MEMS device according to claim 1, wherein said microelectronic actuator further comprises first and second microelectronic actuators and said optical shutter further comprises first and second optical shutters corresponding, respectively, to the first and second microelectronic actuators.

24. A MEMS device according to claim 23, wherein said first and second microelectronic actuators further comprise first and second thermal arched beam actuators.

25. A MEMS device according to claim 24, wherein said first and second thermal arched beam actuators actuate in generally the same plane and in generally opposite direction within the plane.

26. A MEMS device according to claim 25, wherein said first and second optical shutters are shaped to allow for an overlap upon actuation causing the first and second optical shutters to contact each other.

27. A MEMS device according to claim 1, wherein said optical shutter is of a predetermined shape that allows for complete attenuation of the optical beam.

28. A MEMS device according to claim 1, wherein said optical shutter is of a predetermined shape that allows for partial attenuation of the optical beam.

29. A MEMS device according to claim 1, wherein said optical shutter has openings to allow for optical beam passage.

30. A MEMS device according to claim 1, wherein said optical shutter is generally block shaped.

31. A MEMS device according to claim 30, wherein said optical shutter has a predetermined thickness along the faces of the generally block shaped optical shutter.

32. A MEMS device according to claim 1, wherein said optical shutter has a contoured surface.

33. A MEMS device according to claim 1, wherein said optical shutter comprises a metal.

34. A MEMS device according to claim 1, wherein said optical shutter comprises a semiconductor-metal composite.

35. A MEMS device according to claim 1, wherein said microelectronic substrate defines an opening therethrough, the opening allowing for the passage therethrough of the optical beam.

36. A MEMS device according to claim 35, wherein the optical beam has an optical axis generally perpendicular to the generally planar surface of said microelectronic substrate and said optical shutter lies in a plane generally parallel to the generally planar surface of said microelectronic substrate.

37. A MEMS device according to claim 1, wherein said microelectronic substrate further defines a transparent material that allows for an optical beam to be passed therethrough.

38. A MEMS device according to claim 1, wherein said microelectronic substrate defines a trench along the generally planar surface, the trench allowing for the passage therethrough of the optical beam.

39. A MEMS device according to claim 1, wherein the optical beam has an optical axis generally parallel to the generally planar surface of said microelectronic substrate and said optical shutter lies in a plane generally parallel to the generally planar surface of said microelectronic substrate.

40. A MEMS device according to claim 1, wherein said optical shutter is attached to said microelectronic actuator, lies in a plane generally parallel to the generally planar surface of said microelectronic substrate and is capable of being extended beyond an edge of said microelectronic substrate upon actuation, thereby allowing for the attenuation of an optical beam that passes along the edge of said microelectronic substrate.

41. A MEMS device according to claim 40, wherein the optical beam is in a plane generally parallel to the generally planar surface of said microelectronic substrate.

42. A MEMS device according to claim 40, wherein the optical beam is in a plane generally perpendicular to the planar surface of said microelectronic substrate.

43. A MEMS device according to claim 1, wherein said optical shutter lies in a plane generally perpendicular to the generally planar surface of said microelectronic substrate.

44. A MEMS device according to claim 43, wherein said optical shutter is a pop-up shutter released from said substrate during MEMS device fabrication.

45. A MEMS device according to claim 43, wherein said optical shutter is supported on said substrate by a hinged type structure.

46. A MEMS device according to claim 43, wherein said optical shutter is supported on said substrate by a flexible torsional support structure.

47. A MEMS device for optically attenuating an optical beam, comprising:

a microelectronic substrate having a generally planar surface; and

a moveable composite actuator disposed on the planar surface of said microelectronic substrate and adapted for thermal actuation so as to controllably move along a predetermined path and attenuate an optical beam lying in the path of actuation wherein said moveable composite actuator blocks a different percentage of optical power in each position along the path such that said moveable composite actuator can block any percentage of optical power within an optical power range.

48. A MEMS device according to claim 47 wherein said moveable composite actuator further comprises at least two layers which respond differently to thermal actuation, a fixed portion of said composite actuator attached to said microelectronic substrate and a distal portion of said composite actuator adapted to bend so as to controllably move along a predetermined path and attenuate an optical beam lying in the path of actuation.

49. A MEMS device according to claim 48, wherein the distal portion is adapted to move in response to thermal actuation in an upward direction and attenuate an optical beam having an optical path lying above the generally planar surface of said microelectronic substrate.

50. A MEMS device according to claim 48, wherein the distal portion is adapted to move in response to thermal actuation in a downward direction and attenuate an optical beam having an optical path lying below the generally planar surface of said microelectronic substrate.

51. A MEMS device according to claim 50, wherein said microelectronic substrate defines a trench through which the optical beam extends.

52. A MEMS device for optically attenuating an optical beam, comprising:

a microelectronic substrate having a generally planar surface;

a microelectronic actuator disposed on the generally planar surface of said microelectronic substrate;

an optical shutter disposed on the generally planar surface of said microelectronic substrate, wherein said optical shutter is actuatable by said microelectronic actuator and is adapted to attenuate any percentage of optical power within an optical power range;

an electrostatic clamping element operably connected to said optical shutter that allows for said optical shutter to be electrostatically clamped at a desired attenuation position;

an electrostatic contact on said substrate which is electrostatically coupled to said electrostatic clamping element; and

means for applying an electrostatic force between said electrostatic clamping element and said electrostatic contact.

53. A system for variable optical attenuation, the system comprising:

a MEMS variable optical attenuator having a microelectronic substrate having a generally planar surface, a microelectronic actuator disposed on the generally planar surface of said microelectronic substrate, an optical shutter disposed on the generally planar surface of said microelectronic substrate, an electrostatic clamping element operably connected to said optical shutter that allows for said optical shutter to be electrostatically clamped at a desired attenuation position;

an electrostatic contact on said substrate which is electrostatically coupled to said electrostatic clamping element; and

a voltage source for applying an electrostatic force between said electrostatic clamping element and said electrostatic contact.

54. A method for optical attenuation using a MEMS variable optical attenuator having a microelectronic substrate having a generally planar surface, a microelectronic actuator disposed on the generally planar surface of said microelectronic substrate, an optical shutter disposed on the generally planar surface of said microelectronic substrate, an electrostatic clamping element disposed on said substrate, the method comprising the steps of:

activating the microelectronic actuator;

actuating the optical shutter by way of the microelectronic actuator so that the optical shutter is placed in a prescribed attenuation position so as to intersect at least a portion of a plane through which an optical beam passes;

activating electrostatically the clamping element thereby locking the optical shutter at the prescribed attenuation position; and

deactivating the microelectronic actuator while the optical shutter is locked at the prescribed attenuation position.

55. A method of fabricating a MEMS variable optical attenuator comprising:

forming an oxide layer on a generally first planar surface of a microelectronic substrate;

forming a silicon layer on the oxide layer;

defining a mechanical structure of the attenuator in the silicon layer, the mechanical structure defining a thermal arched beam actuator, an actuator member and an optical shutter;

releasing a portion of the silicon layer from the substrate by etching away the oxide layer underlying the arched beams of the thermal arched beam actuator and the actuator member;

doping at least a portion of the silicon layer to provide a predetermined conductivity; and

etching a second surface of the microelectronic substrate, opposite the first surface, and etching the oxide layer underlying the optical shutter to release the optical shutter from the substrate.

56. The method of claim 55, wherein said defining step further defines the mechanical structure as including a clamping element and said releasing step further includes the etching away of the oxide layer underlying the clamping element.

57. The method of claim 56 further comprising the steps of:

oxidizing the underside of the clamping element following said releasing step to provide a dielectric between the substrate and the clamping element; and

defining a metal electrode on the first surface of said substrate to provide an electrical connection for the clamping element.

58. The method of claim 56 wherein said defining step further comprises defining the mechanical structure to include etch holes in the clamping element and the actuator member so as to facilitate later release from the substrate.

59. The method of claim 55, wherein said defining a mechanical structure step further comprises the substeps of:

patterning a mask defining the mechanical structure on the silicon layer; and

etching away the silicon layer in accordance with patterned mask to define the mechanical structure.

60. The method of claim 55 wherein said forming the silicon layer step further comprises using an epitaxial process to grow single crystal silicon on the substrate.

61. The method of claim 55 wherein said forming the silicon layer step further comprises fusion bonding a single crystal silicon layer to the substrate and oxide construct.

62. The method of claim 55 further comprising the step of metalizing the optical shutter following said defining the mechanical structure step to provide non-optically transmitting surfaces.

63. The method of claim 55 wherein said defining step further comprises defining the mechanical structure to include etch holes in the optical shutter and the actuator member.