Micromechanical optical switch

• US 6,407,851 B1
• Filed: 08/01/2000
• Issued: 06/18/2002
• Est. Priority Date: 08/01/2000
• Status: Expired due to Term

• Current Assignee: Cheetah Omni LLC
• Original Assignee: Cheetah Omni LLC
• Inventors: Islam, Mohammed N., Kuditcher, Amos
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Spector, David N.
• Application Number:
  US09/631,276
• Time in Patent Office: 686 Days
• Field of Search: 359/139, 359/290, 359/291, 359/578, 359/583, 359/589, 359/579, 385/16, 385/37, 385/39, 385/47
• US Class Current: 359/291
• 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 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 6/3516 the reflective optical element moving along the beam path, e.g. controllable diffractive effects using multiple micromirrors within the beam
• CPC Class Codes: G02B 6/3518 the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device MEMS devices in general B81B; manufacture of MEM devices in general B81C; micromechanical devices controlling the direction of light G02B26/0833
• CPC Class Codes: G02B 6/3546 NxM switch, i.e. a regular array of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/357 Electrostatic force electrostatic forces controlling reflecting elements in general G02B26/0841
• CPC Class Codes: G02B 6/3584 constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching MEMS per se B81B, B81C
• CPC Class Codes: G02B 6/3594 Characterised by additional functional means, e.g. means for variably attenuating or branching or means for switching differently polarized beams

Abstract

An optical switch element is described, which includes a fixed layer disposed outwardly from a substrate and a movable mirror assembly disposed outwardly from the fixed layer. The moveable mirror assembly is operable to move relative to the fixed layer responsive to a voltage applied to the movable mirror assembly. In a particular embodiment, the movable mirror assembly includes an inner strip spaced apart from the fixed layer by a first distance and an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance. The optical transmission of the optical switch element changes depending on the position of the movable mirror assembly.

Claims

1. An optical switch element comprising:

a fixed layer disposed outwardly from a substrate; and

a movable mirror assembly disposed outwardly from the fixed layer and operable to move relative to the fixed layer responsive to a voltage applied to the movable mirror assembly, the movable mirror assembly comprising;

an inner strip spaced apart from the fixed layer by a first distance; and

an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance, wherein the optical transmission of the optical switch element changes depending on the position of the movable mirror assembly.

2. The optical switch element of claim 1, wherein the optical switch element is substantially transmissive of an optical signal when no voltage is applied to the moveable mirror assembly, and less transmissive of the optical signal when a voltage is applied to the movable mirror assembly.

3. The optical switch element of claim 1, wherein the moveable mirror assembly comprises a unitary assembly wherein the inner and outer strips move substantially in unison.

4. The optical switch element of claim 1, wherein the first distance comprises approximately one half wavelength or an integer multiple of one half of a wavelength of an optical signal received by the switch element, and wherein the moveable mirror assembly is operable to move approximately one quarter wavelength of the optical signal relative to the fixed layer in response to the applied voltage.

5. The optical switch element of claim 1, wherein the fixed layer comprises a fixed mirror layer, which defines with the moveable mirror assembly a Fabry Perot interference cavity.

6. The optical switch element of claim 1, wherein the fixed layer comprises a layer of polysilicon having an optical thickness of approximately one quarter wavelength of an optical signal received at the optical switch element.

7. The optical switch element of claim 1, wherein the fixed layer comprises a polysilicon layer that has been doped sufficiently to render the polysilicon at least substantially conductive.

8. The optical switch element of claim 1, wherein the fixed layer comprises a layer of metal that is reflective of an optical signal received.

9. The optical switch element of claim 1, wherein the fixed layer comprises a fixed layer stack including:

an inner fixed layer disposed outwardly from the substrate;

a interstitial fixed layer disposed outwardly from the inner fixed layer; and

an outer fixed layer disposed outwardly from the interstitial fixed layer.

10. The optical switch element of claim 1, wherein each of the inner and outer mirror strips comprises a polysilicon layer having an optical thickness of approximately one quarter wavelength of an optical signal received at the optical switch element.

11. The optical switch element of claim 1, wherein each of the inner and outer mirror strips comprises a polysilicon layer that has been doped sufficiently to render the polysilicon at least substantially conductive.

12. The optical switch element of claim 1, wherein at least one of the inner and outer mirror strips comprises a stack of polysilicon layers, each separated by an interstitial layer.

13. The optical switch element of claim 1, wherein the inner mirror strip has a thickness that is different than the thickness of the outer mirror strip.

14. The optical switch element of claim 1, further comprising an antireflective layer disposed between the substrate and the fixed layer, wherein the antireflective layer comprises an index of refraction approximately equal to the square root of an index of refraction of the substrate.

15. The optical switch element of claim 1, wherein the voltage is applied between the moveable mirror assembly and the fixed layer, and wherein the moveable mirror assembly is operable to move toward the fixed layer in response to the applied voltage.

16. The optical switch element of claim 1, further comprising an outer conductive layer disposed outwardly from the moveable mirror assembly, wherein the voltage is applied between the moveable mirror assembly and the outer conductive layer, and wherein the moveable mirror assembly is operable to move away from the fixed layer in response to a voltage applied between the moveable mirror assembly and the outer conductive layer.

17. The optical switch element of claim 16, wherein the switch element is operable to be switched between a substantially transmissive state and a less transmissive state by alternating application of voltage between the moveable mirror assembly and the fixed layer, and between the moveable mirror assembly and the outer conductive layer.

62. An optical switch comprising:

a pair of collimating lens each having a central axis and each coupled to a fiber so that the axis of each collimating lens is at least partially offset from the axis of the fiber;

the optical switch element of claim 1 disposed between the collimating lenses along the central axis of the fiber and spaced from each of the lenses by approximately a focal length of the respective lens, wherein the optical switch element is operable to receive optical signals from one collimating lens and to either transmits those signals to the other collimating lens or to reflect those signals depending on the position of a moveable mirror assembly relative to a fixed layer within the switch element.

63. An optical switch, comprising:

a first optical switch element operable to receive an optical signal; and

a second optical switch element comprising the optical switch element of claim 1 operable to receive an optical signal, the second optical switch element coupled to the first optical switch element over a first mode, the first and second optical switch elements coupled to a single mode fiber wherein the first mode at least partially overlaps the mode of the single mode fiber so that optical signals from the first and second switch element couple to the fiber only when the first and second switch elements are substantially in phase with one another.

74. A fault tolerant network, comprising:

an ingress access node operable to receive an optical signal from a network element external to the fault tolerant network; and

a fault tolerant node operable to receive the optical signal from the ingress access node and to perform a switching operation on the optical signal depending on a voltage applied to an optical switch element within the fault tolerant node, wherein the fault tolerant node allows transmission of the optical signal when no voltage is applied to the switching element and wherein the optical switch element comprises the optical switch element of claim 1.

18. An optical switch element, comprising:

a fixed mirror layer disposed outwardly from a substrate; and

a movable mirror assembly comprising an inner mirror strip and an outer mirror strip disposed approximately adjacent to and outwardly from the inner mirror strip;

wherein the fixed mirror layer and the movable mirror assembly define a Fabry-Perot interference cavity, the movable mirror assembly operable to move with respect to the fixed mirror layer to change the reflective or transmissive qualities of the switch element.

19. The optical switch element of claim 18, wherein the movable mirror assembly comprises an air gap between the inner mirror strip and the outer mirror strip, the air gap operable to control air damping when the movable mirror assembly moves.

20. The optical switch element of claim 18, wherein the optical switch element is substantially transmissive of an optical signal when no voltage is applied between the moveable mirror assembly and the fixed mirror assembly, and less transmissive of the optical signal when a voltage is applied between the fixed mirror layer and the movable mirror assembly.

21. The optical switch element of claim 18, wherein the fixed mirror layer comprises a polysilicon layer that has been doped sufficiently to render the polysilicon at least substantially conductive.

22. The optical switch element of claim 18, wherein the fixed mirror layer comprises a layer of metal that is reflective of an optical signal received.

23. The optical switch element of claim 18, wherein each of the inner and outer mirror strips comprises a polysilicon layer that has been doped sufficiently to render the polysilicon at least substantially conductive.

24. The optical switch element of claim 18, wherein at least one of the inner and outer mirror strips comprises a stack of polysilicon layers, each separated by an interstitial layer.

25. The optical switch element of claim 18, wherein the inner mirror strip has a thickness that is different than the thickness of the outer mirror strip.

26. The optical switch element of claim 18, wherein the fixed mirror layer comprises a fixed mirror layer stack including:

an inner fixed mirror layer disposed outwardly from the substrate;

a interstitial fixed layer disposed outwardly from the inner fixed mirror layer; and

an outer fixed mirror layer disposed outwardly from the interstitial fixed layer.

27. The optical switch element of claim 18, wherein the inner mirror strip is spaced from the fixed mirror layer by one wavelength of an optical signal received by the switch element.

28. The optical switch element of claim 18, further comprising an antireflective layer disposed between the substrate and the fixed mirror layer, wherein the antireflective layer comprises an index of refraction approximately equal to the square root of an index of refraction of the substrate.

29. The optical switch element of claim 18, further comprising an outer conductive layer disposed outwardly from the moveable mirror assembly, wherein the moveable mirror assembly is operable to move away from the fixed mirror layer in response to a voltage applied between the moveable mirror assembly and the outer conductive layer.

30. The optical switch element of claim 29, wherein the switch element is operable to be switched between a substantially transmissive state and a less transmissive state by alternating application of voltage between the moveable mirror assembly and the fixed mirror layer, and between the moveable mirror assembly and the outer conductive layer.

31. An optical switch element, comprising:

a fixed layer disposed outwardly from a substrate; and

a unitary movable mirror assembly disposed outwardly from the fixed layer and forming with the fixed layer an optical cavity, the moveable mirror assembly operable to move relative to the fixed layer in response to a voltage applied to the moveable mirror assembly to affect a change in the transmissive characteristics of the optical cavity;

wherein the optical switch element is operable to switch between a substantially transmissive state and a less than substantially transmissive state at a rate optimized for a specified packet size.

32. The optical switch element of claim 31, wherein the moveable mirror assembly comprises:

an inner strip spaced apart from the fixed layer by a first distance; and

an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance.

33. The optical switch element of claim 31, wherein the fixed layer comprises a fixed mirror layer and wherein the optical cavity comprises a Fabry Perot cavity.

34. The optical switch element of claim 31, wherein the rate is faster than once every microsecond.

35. The optical switch element of claim 31, wherein the rate is faster than once every 10 microseconds.

36. The optical switch element of claim 31, wherein the rate is faster than once every 30 microseconds.

37. The optical switch element of claim 31, wherein the specified packet size comprises an average packet size of packets encountered by the switch element.

38. The optical switch element of claim 31, wherein the specified packet size comprises between 40 and 60 bytes and wherein the rate comprises between once each 300 nanoseconds and once each 100 nanoseconds.

39. A method of forming an optical switch element, the method comprising:

forming a fixed layer outwardly from a substrate;

forming a movable mirror assembly outwardly from the fixed layer, the movable mirror assembly comprising;

an inner strip disposed outwardly from the fixed layer by a first distance; and

an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance, wherein the optical transmission of the optical switch element changes depending on the position of the movable mirror assembly.

40. The method of claim 39, wherein forming the fixed layer comprises forming a layer of polysilicon having an optical thickness approximately equal to one quarter of one wavelength of an optical signal received by the optical switch element.

41. The method of claim 39, wherein forming the fixed layer comprises:

forming an inner polysilicon layer outwardly from the substrate;

forming an interstitial dielectric layer outwardly from the inner polysilicon layer; and

forming an outer polysilicon layer outwardly from the interstitial dielectric layer.

42. The method of claim 39, wherein forming a movable mirror assembly comprises:

forming an inner sacrificial layer outwardly from the fixed layer, the inner sacrificial layer associated with a first etch rate;

forming a median sacrificial layer outwardly from the inner sacrificial layer, the median sacrificial layer associated with a second etch rate that is faster than the first etch rate;

forming an outer sacrificial layer outwardly from the median sacrificial layer, the outer sacrificial layer associated with the first etch rate; and

performing a single step etch of portions of the inner, median, and outer sacrificial layers, wherein the single step etch results in an undercut region between the inner and outer sacrificial layers.

43. The method of claim 42, wherein forming the movable mirror assembly comprises forming a first polysilicon layer outwardly from the etched sacrificial layers, a portion of the first polysilicon layer residing on the inner sacrificial layer comprising the inner strip, a portion of the first polysilicon layer residing on the outer sacrificial layer comprising the outer strip.

44. The method of claim 42, further comprising:

forming a dielectric layer outwardly from the polysilicon layer; and

forming a second polysilicon layer outwardly from the dielectric layer.

45. The method of claim 42, wherein:

the inner sacrificial layer comprises a thickness approximately equal a desired air gap between the fixed layer and the inner strip; and

the median and outer sacrificial layers have a combined thickness equal to a desired air gap between the fixed layer and the outer strip.

46. The method of claim 39, wherein the inner strip of the movable mirror assembly is separated from the fixed layer by an air gap of one wavelength of an optical signal received by the optical switch element.

47. The method of claim 39, wherein the fixed layer comprises a fixed mirror layer that defines with the moveable mirror assembly a Fabry Perot interference cavity.

48. The method of claim 39, further comprising forming an outer conductive layer outwardly from the moveable mirror assembly, the outer conductive layer operable to receive a voltage applied between the moveable mirror assembly and the outer conductive layer causing the moveable mirror assembly to move away from the fixed layer.

49. A method of communicating optical signals, comprising:

receiving an optical signal at an optical switch element having a fixed layer and a moveable mirror assembly disposed outwardly from the fixed layer, the moveable mirror assembly comprising;

an inner strip spaced apart from the fixed layer by a first distance; and

an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance;

applying a voltage to the moveable mirror assembly to change its position relative to the fixed layer and cause a change in the optical transmission of the optical switch element.

50. The method of claim 49, wherein the optical switch element is substantially transmissive of an optical signal when no voltage is applied to the moveable mirror assembly, and less transmissive of the optical signal when a voltage is applied to the movable mirror assembly.

51. The method of claim 49, wherein the first distance comprises approximately one half wavelength or an integer multiple of one half of a wavelength of the optical signal, and wherein the moveable mirror assembly is operable to move approximately one quarter wavelength of the optical signal relative to the fixed layer in response to the applied voltage.

52. The method of claim 49, wherein the fixed layer comprises a fixed mirror layer, which defines with the moveable mirror assembly a Fabry Perot interference cavity.

53. The method of claim 49, wherein the fixed layer comprises a layer of metal that is reflective of an optical signal received.

54. The method of claim 49, wherein the fixed layer comprises a fixed layer stack including:

an inner fixed layer disposed outwardly from the substrate;

a interstitial fixed layer disposed outwardly from the inner fixed layer; and

an outer fixed layer disposed outwardly from the interstitial fixed layer.

55. The method of claim 49, wherein at least one of the inner and outer mirror strips comprises a stack of polysilicon layers, each separated by an interstitial layer.

56. The method of claim 49, wherein the inner mirror strip has a thickness that is different than the thickness of the outer mirror strip.

57. The method of claim 49, wherein applying a voltage to the moveable mirror assembly comprises applying a voltage between the moveable mirror assembly and the fixed layer, and wherein the moveable mirror assembly is operable to move toward the fixed layer in response to the applied voltage.

58. The method of claim 49, wherein the optical switch element further comprises an outer conductive layer disposed outwardly from the moveable mirror assembly, and wherein applying a voltage to the moveable mirror assembly comprises applying a voltage between the moveable mirror assembly and the outer conductive layer, and wherein the moveable mirror assembly is operable to move away from the fixed layer in response to the applied voltage.

59. The method of claim 58, wherein applying a voltage to the moveable mirror assembly comprises alternating between applying a voltage between the moveable mirror assembly and the fixed layer to cause the moveable mirror assembly to move toward the fixed layer and applying a voltage between the moveable mirror assembly and the outer conductive layer to cause the moveable mirror assembly to move away from the fixed layer.

60. An array of optical switch elements operable to switch optical signals depending on a voltage applied to the switch element, at least one of the optical switch elements, comprising:

a fixed layer disposed outwardly from a substrate; and

a movable mirror assembly disposed outwardly from the fixed layer and operable to move relative to the fixed layer responsive to a voltage applied to the movable mirror assembly, the movable mirror assembly comprising;

an inner strip spaced apart from the fixed layer by a first distance; and

an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance, wherein the optical transmission of the optical switch element changes depending on the position of the movable mirror assembly.

61. An optical switch comprising a Mach-Zender interferometer comprising:

an optical switch element including;

a fixed layer disposed outwardly from a substrate; and

a movable mirror assembly disposed outwardly from the fixed layer and operable to move relative to the fixed layer responsive to a voltage applied to the movable mirror assembly, the movable mirror assembly comprising;

an inner strip spaced apart from the fixed layer by a first distance; and

an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance, wherein the optical transmission of the optical switch element changes depending on the position of the movable mirror assembly.

64. An electro-optic router operable to receive a plurality of optical signals and to switch the optical signals using an array of optical switch elements, at least one of the optical switch elements comprising:

a fixed layer disposed outwardly from a substrate; and

a movable mirror assembly disposed outwardly from the fixed layer and operable to move relative to the fixed layer responsive to a voltage applied to the movable mirror assembly, the movable mirror assembly comprising;

an inner strip spaced apart from the fixed layer by a first distance; and

an outer strip disposed approximately adjacent to the inner strip and spaced apart from the fixed layer by a second distance which is greater than the first distance, wherein the optical transmission of the optical switch element changes depending on the position of the movable mirror assembly.

65. The electro-optic router of claim 64, wherein the optical switch element is substantially transmissive of an optical signal when no voltage is applied to the moveable mirror assembly, and less transmissive of the optical signal when a voltage is applied to the movable mirror assembly.

66. The electro-optic router of claim 64, wherein the fixed layer comprises a fixed mirror layer, which defines with the moveable mirror assembly a Fabry Perot interference cavity.

67. The electro-optic router of claim 64, wherein the fixed layer comprises a fixed layer stack including:

an inner fixed layer disposed outwardly from the substrate;

a interstitial fixed layer disposed outwardly from the inner fixed layer; and

an outer fixed layer disposed outwardly from the interstitial fixed layer.

68. The electro-optic router of claim 64, wherein at least one of the inner and outer mirror strips comprises a stack of polysilicon layers, each separated by an interstitial layer.

69. The electro-optic router of claim 64, wherein the inner mirror strip has a thickness that is different than the thickness of the outer mirror strip.

70. The electro-optic router of claim 64, wherein the voltage is applied between the moveable mirror assembly and the fixed layer, and wherein the moveable mirror assembly is operable to move toward the fixed layer in response to the applied voltage.

71. The electro-optic router of claim 64, further comprising an outer conductive layer disposed outwardly from the moveable mirror assembly, wherein the voltage is applied between the moveable mirror assembly and the outer conductive layer, and wherein the moveable mirror assembly is operable to move away from the fixed layer in response to a voltage applied between the moveable mirror assembly and the outer conductive layer.

72. The electro-optic router of claim 64, wherein the switch element is operable to be switched between a substantially transmissive state and a less transmissive state by alternating application of voltage between the moveable mirror assembly and the fixed layer, and between the moveable mirror assembly and the outer conductive layer.

73. The electro-optic router of claim 64, further comprising:

a fiber optic tap operable to receive the optical signal and to separate a header portion of the optical signal from a payload portion of the optical signal;

a delay line operable to communicate the payload portion to the switching array after a delay period; and

an electronic processor operable to process the header portion and to communicate a processed header portion to the array.