Miniature circulator array devices and methods for making the same Number:6,785,431 from the United States Patent and Trademark Office (PTO) owispatent

Title: Miniature circulator array devices and methods for making the same

Abstract: Miniature optical devices, including circulator array devices, are fabricated using thin film coating technology. A typical optical device according to the present invention includes a spatial walkoff plate (SWP) coupled on opposite ends to first and second polarization orientation elements. First and second polarization beam splitter (PBS) elements are coupled to the first and second polarization orientation elements, respectively. The PBS elements are formed using thin film coating techniques and each includes an array of port coupling regions for coupling to an array of input/output fiber port assemblies. The SWP may be formed using thin film coating techniques or cut from a birefringent single crystal. Each polarization orientation element includes a Faraday rotator element, and in some embodiments, each also includes a wave plate formed using thin film coating techniques. The Faraday rotator elements are periodically poled in some embodiments using selective poling techniques to create oppositely oriented (bi-directional) magnetic domains so that polarization rotations of 45.degree. in both clockwise and counter-clockwise directions can be simultaneously achieved on the same magnetic garnet. Periodically etched half-wave plates are used in some embodiments. Depending on the orientation of the optical axes of the SWP and the first and second PBS elements, the constituents of each polarization orientation element are designed and oriented so that the circulator device achieves a circulating operation with optical signals at an input port, i, coupled to one PBS element being passed to an output port, i+1, coupled to the other PBS element in a non-reciprocal manner.

Patent Number: 6,785,431 Issued on 08/31/2004 to Pan,   et al.

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Inventors:	Pan; Jing-Jong (Milpitas, CA), Zhou; Ming (San Jose, CA), Zhang; Hong-Xi (San Jose, CA), Zhou; Feng-Qing (San Jose, CA)
Assignee:	Lightwaves 2020, Inc. (Milpitas, CA)
Appl. No.:	10/068,794
Filed:	February 6, 2002

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Current U.S. Class:	385/11 ; 359/280; 359/282; 359/483; 359/484; 359/494; 359/495; 359/497; 372/703; 385/15; 385/6
Field of Search:	385/6,11,15 359/280,282,483,484,494,495,497 372/703

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References Cited [Referenced By]

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U.S. Patent Documents

	5471340		November 1995		Cheng et al.
	5574596		November 1996		Cheng
	5872878		February 1999		Bergmann
	5936768		August 1999		Oguma
	6097869		August 2000		Chang et al.
	6212008		April 2001		Xie et al.
	6396629		May 2002		Cao
	6404549		June 2002		Huang et al.
	6441961		August 2002		Hou et al.
	2003/0058536		March 2003		Huang et al.

Primary Examiner: Ullah; Akm Enayet
Assistant Examiner: Petkovsek; Daniel
Attorney, Agent or Firm: Ritter, Lang & Kaplan LLP

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Parent Case Text

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CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. 10/068,796, filed concurrently herewith, entitled "MINIATURE CIRCULATOR DEVICES AND METHODS FOR MAKING THE SAME" (Attorney Docket No. 020858-001700), the disclosure of which is hereby incorporated by reference in its entirety.

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Claims

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What is claimed is:

1. An optical device for coupling arrays of optical fiber ports, the device comprising: a birefringent element arranged so that light traveling parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis; first and second polarization orientation elements coupled to opposite ends of the birefringent element; and first and second polarization beam splitting (PBS) films deposited on said first and second polarization orientation elements, respectively, wherein the end face of each of the first and second PBS films opposite the polarization orientation elements defines an array of two or more port coupling regions for coupling light signals from an array of two or more optical fiber ports, with one PBS film defining even numbered ports and the other defining odd numbered ports, wherein the first and second PBS films are dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light; wherein the first polarization orientation element is arranged with respect to the birefringent element and the first PBS film so as to orient the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region on the first PBS film parallel to the first linear polarization orientation so that both beams simultaneously pass through the birefringent element parallel to the propagation axis, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other, and wherein the first polarization orientation element refracts the light deflected by the birefringent element parallel to the propagation axis; and wherein the second polarization orientation element is arranged with respect to the birefringent element and the second PBS film so as to orient the polarization of both of the parallel light beams of a second optical signal propagating along a forward direction from a second port coupling region on the second PBS film parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are mutually perpendicular; whereby the first optical signal passes from the first port coupling region to the second port coupling region, and the second optical signal passes from the second port coupling region to a third port coupling region.

2. The device of claim 1, wherein the birefringent element is a spatial walk-off polarizer (SWP) cut from a birefringent crystal.

3. The device of claim 2, wherein the SWP crystal is selected from the group consisting of rutile, YVO.sub.4, calcite, and LiNbO.sub.3.

4. The device of claim 2, wherein the thickness of the SWP crystal along the propagation axis is between about 1.0 mm and about 3.0 mm.

5. The device of claim 1, wherein the birefringent element is a spatial walk-off polarizer (SWP) made by thin film deposition with a tilted substrate assembly.

6. The device of claim 5, wherein the thickness of the SWP film along the propagation axis is between about 0.5 mm and about 1.0 mm.

7. The device of claim 1, wherein the first and second polarization orientation elements each consists of a periodically poled Faraday rotator element having periodically reversed magnetic domains arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions.

8. The device of claim 7, wherein the birefringent element is oriented so that deflected light having the second linear polarization orientation has a deflection component along a deflection axis perpendicular to the propagation axis, and wherein the first and second PBS films are arranged such that the optic axis of each points in a direction that is approximately 45.degree. relative to the propagation axis and approximately 45.degree. relative to a third axis that is perpendicular to both the propagation and deflection axes.

9. The device of claim 1, wherein the first and second polarization orientation elements each includes a Faraday rotator element and a bi-layer waveplate film deposited thereon.

10. The device of claim 9, wherein the first and second PBS films are deposited on the first and second Faraday rotator elements, respectively, such that the first and second waveplate films are coupled to the birefringent element.

11. The device of claim 9, wherein the first and second PBS films are deposited on the first and second waveplate films, respectively, such that the first and second Faraday rotators are coupled to the birefringent element.

12. The device of claim 9, wherein each of the first and second Faraday rotator elements has periodically reversed magnetic domains and is arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions.

13. The device of claim 9, wherein each of the first and second Faraday rotator elements is uniformly poled such that the states of polarization of the two parallel light beams of an optical signal are rotated in the same direction, wherein one or more portions of each of the first and second waveplate films has been removed, and wherein each waveplate film is arranged and dimensioned such that the state of polarization of only one of the two parallel light beams of an optical signal is rotated.

14. The device of claim 9, wherein the birefringent element is a spatial walk-off polarizer (SWP) cut from a birefringent crystal, and wherein the SWP includes a diagonal cut, such that movement of the two pieces along the diagonal cut alters the dimension of the SWP along the propagation axis.

15. The device of claim 12 or 14, wherein the birefringent element is oriented so that deflected light having the second linear polarization orientation has a deflection component along a deflection axis perpendicular to the propagation axis, and wherein the first and second PBS films are arranged such that the optic axis of each points in a direction that is approximately 45.degree. relative to the propagation axis and parallel to the plane defined by both the propagation and deflection axes.

16. The device of claim 12 or 13, wherein the birefringent element is oriented so that deflected light having the second linear polarization orientation has a deflection component along a deflection axis perpendicular to the propagation axis, and wherein the first and second PBS films are arranged such that the optic axis of each points in a direction that is approximately 45.degree. relative to the propagation axis and in the plane defined by the propagation axis and a third axis perpendicular to both the propagation and deflection axes.

17. The device of claim 13 or 14, wherein the birefringent element is oriented so that deflected light having the second linear polarization orientation has a deflection component along a deflection axis perpendicular to the propagation axis, wherein the first PBS film is arranged such the optic axis points in a direction that is approximately 45.degree. relative to the propagation axis and approximately 45.degree. relative to a third axis that is perpendicular to both the propagation and deflection axes, and wherein the second PBS film is arranged such the optic axis points in a direction that is approximately 45.degree. relative to the propagation axis and approximately 135.degree. relative to the third axis.

18. The device of claim 1, wherein the elements of the optical device are dimensioned so as to allow for coupling of an N.times.M array of optical fiber ports on each of the first and second PBS films.

19. The device of claim 1, wherein the elements of the device are dimensioned such that the center-to-center spacing of port coupling regions on each of the first and second PBS films is between about 100 .mu.m and about 400 .mu.m.

20. The device of claim 19, wherein the elements of the device are dimensioned such that the center-to-center spacing of port coupling regions on each of the first and second PBS films is approximately 250 .mu.m.

21. The device of claim 1, wherein each of the first and second PBS films is deposited using a source material selected from the group consisting of Silicon (Si) and Ge.

22. The device of claim 1, wherein each of the first and second polarization orientation elements includes a Faraday rotator element formed in part by depositing a magnetic garnet film on a non-magnetic substrate.

23. The device of claim 22, wherein the garnet film is deposited using liquid phase epitaxy (LPE).

24. The device of claim 22, wherein the garnet film is grown in the form: RE1.sub.a RE2.sub.b Bi.sub.3-a-b Fe.sub.5-c-d M1.sub.c M2.sub.d O.sub.12, where RE1 and RE2 are each selected from the group consisting of La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu, and wherein M1 and M2 are each selected from the group consisting of Ga and Al.

25. The device of claim 22, wherein each of the first and second Faraday rotator elements have periodically reversed magnetic domains arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions.

26. The device of claim 22, wherein each of the first and second Faraday rotator elements have a substantially uniform magnetic profile such that the states of polarization of the two parallel light beams of an optical signal are rotated in the same direction.

27. The device of claim 22, wherein each of the first and second polarization orientation elements further includes a waveplate film formed by depositing a bi-layer film on the respective Faraday rotator element.

28. The device of claim 27, wherein the thickness of each waveplate film along the propagation axis is between about 5 .mu.m and about 20 .mu.m.

29. The device of claim 27, wherein one or more portions of each of the first and second waveplate films have been removed, and wherein each of the first and second waveplate films are arranged such that the state of polarization of only one of the two parallel light beams of an optical signal is rotated by each waveplate film.

30. The device of claim 1, wherein the thickness of each PBS film along the propagation axis is between about 0.25 mm and about 0.5 mm.

31. The device of claim 22, wherein each of the first and second polarization orientation elements further includes a waveplate film deposited on the respective Faraday rotator, wherein each of the first and second waveplate films has two or more oppositely oriented regions arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions.

32. An optical device for coupling an array of optical fiber ports, the device comprising: a birefringent element arranged so that light traveling parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis, and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis; first and second polarization orientation elements coupled to opposite ends of the birefringent element; a polarization beam splitting (PBS) film deposited on said first polarization orientation element, wherein the end face of the PBS film opposite the first polarization orientation element defines an array of two or more port coupling regions for coupling light signals from an array of two or more optical fiber ports, wherein the PBS film is dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light; and a reflection element coupled to the second polarization orientation element opposite the birefringent element, wherein the reflection element is arranged such that the beam components of a light signal propagating in the forward direction are reflected back in the reverse direction; wherein the first polarization orientation element is arranged with respect to the birefringent element and the PBS film so as to orient the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other; and wherein the second polarization orientation element refracts the light deflected by the birefringent element parallel to the propagation axis, rotates the polarization state of each of the parallel light beams of the first optical signal propagating along the forward direction by 45.degree. in one direction, and rotates, by 45.degree. in the same direction, the polarization state of both of the parallel light beams of the first optical signal propagating along the reverse direction after being reflected by the reflection element such that both beams are parallel to the first linear polarization orientation, and such that both beams simultaneously pass through the birefringent element parallel to the propagation axis in the reverse direction; whereby the first optical signal passes from the first port coupling region to a second port coupling region.

33. The device of claim 32, wherein the birefringent element is a spatial walk-off polarizer (SWP) crystal.

34. The device of claim 32, wherein the birefringent element is a spatial walk-off polarizer (SWP) made by thin film deposition with a tilted substrate assembly.

35. The device of claim 32, wherein the first polarization orientation element consists of a periodically poled Faraday rotator element having periodically reversed magnetic domains arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions.

36. The device of claim 35, wherein the birefringent element is oriented so that deflected light having the second linear polarization orientation has a deflection component along a deflection axis perpendicular to the propagation axis, and wherein the first PBS film is arranged such that the optic axis points in a direction that is approximately 45.degree. relative to the propagation axis and approximately 45.degree. relative to a third axis that is perpendicular to both the propagation and deflection axes.

37. The device of claim 32, wherein the first polarization orientation element includes a Faraday rotator element and a bi-layer waveplate film deposited thereon.

38. The device of claim 37, wherein the birefringent element is oriented so that deflected light having the second linear polarization orientation has a deflection component along a deflection axis perpendicular to the propagation axis, wherein the PBS film is arranged such the optic axis points in a direction that is approximately 45.degree. relative to the propagation axis and approximately 45.degree. relative to a third axis that is perpendicular to both the propagation and deflection axes.

39. The device of claim 37, wherein the first Faraday rotator elements has periodically reversed magnetic domains and is arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions.

40. The device of claim 39, wherein the birefringent element is oriented so that deflected light having the second linear polarization orientation has a deflection component along a deflection axis perpendicular to the propagation axis, and wherein the PBS film is arranged such that the optic axis points in a direction that is approximately 45.degree. relative to the propagation axis and parallel to the plane defined by both the propagation and deflection axes.

41. The device of claim 37, wherein the first Faraday rotator element is uniformly poled such that the states of polarization of the two parallel light beams of an optical signal are rotated in the same direction, wherein one or more portions of the first waveplate film has been removed, and wherein the first waveplate film is arranged and dimensioned such that the state of polarization of only one of the two parallel light beams of an optical signal is rotated.

42. The device of claim 32, wherein the birefringent element is a spatial walk-off polarizer (SWP), and wherein the SWP includes a diagonal cut, such that movement of the two pieces along the diagonal cut alters the dimension of the SWP along the propagation axis.

43. The device of claim 32, wherein the elements of the optical device are dimensioned so as to allow for coupling of an N.times.M array of optical fiber ports on the PBS film.

44. The device of claim 32, wherein the elements of the device are dimensioned such that the center-to-center spacing of port coupling regions on the PBS film is between about 100 .mu.m and about 400 .mu.m.

45. The device of claim 32, wherein each of the first and second polarization orientation elements includes a Faraday rotator element formed in part by depositing a magnetic garnet film on a non-magnetic substrate.

46. The device of claim 45, wherein the first Faraday rotator element has periodically reversed magnetic domains arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions, and wherein the second Faraday rotator element has a substantially uniform magnetic profile such that the states of polarization of the two parallel light beams of an optical signal are rotated in the same direction.

47. The device of claim 45, wherein each of the first and second Faraday rotator elements have a substantially uniform magnetic profile such that the states of polarization of the two parallel light beams of an optical signal are rotated in the same direction.

48. The device of claim 45, wherein the first polarization orientation element further includes a waveplate film formed by depositing a bi-layer film on the first Faraday rotator element.

49. The device of claim 48, wherein one or more portions of the first waveplate film has been removed, and wherein the first waveplate film is arranged such that the state of polarization of only one of the two parallel light beams of an optical signal is rotated by the first waveplate film.

50. The device of claim 32, wherein the reflection element includes a thin metallic film layer deposited on the second polarization orientation element.

51. The device of claim 32, wherein the reflection element includes one or more dielectric layers deposited on the second polarization orientation element.

52. The device of claim 45, wherein the first polarization orientation element further includes a waveplate film deposited on the first Faraday rotator, wherein the waveplate film has two or more oppositely oriented regions arranged such that the states of polarization of the two parallel light beams of an optical signal are rotated in opposite directions.

53. A method of forming an optical device for coupling arrays of optical fiber ports, the method comprising: providing a birefringent element, wherein light traveling within the birefringent element parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis, and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis; and attaching first and second polarization beam splitting (PBS) modules on opposite ends of the birefringent element, wherein each module includes a PBS film deposited on a polarization orientation element, with said polarization orientation elements being attached to the opposite ends of the birefringent element; wherein the end face of each of the first and second PBS films opposite the polarization orientation elements defines an array of two or more port coupling regions for coupling light signals from an array of two or more optical fiber ports, with one PBS film defining even numbered ports and the other defining odd numbered ports; wherein the first and second PBS films are dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light; wherein the first PBS module is arranged with respect to the birefringent element such that the first polarization orientation element orients the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region on the first PBS film parallel to the first linear polarization orientation so that both beams simultaneously pass through the birefringent element parallel to the propagation axis, and such that the first polarization orientation element orients the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other, and wherein the first polarization orientation element refracts the light deflected by the birefringent element parallel to the propagation axis; and wherein the second PBS module is arranged with respect to the birefringent element such that the second polarization orientation element orients the polarization of both of the parallel light beams of a second optical signal propagating along a forward direction from a second port coupling region on the second PBS film parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and such that the second polarization orientation element orients the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are mutually perpendicular.

54. The method of claim 53, wherein the birefringent element is a spatial walk-off polarizer SWP.

55. The method of claim 54, further comprising cutting the SWP from a birefringent crystal.

56. The method of claim 55, wherein the birefringent crystal is selected from the group consisting of rutile, calcite, LiNbO.sub.3 and YVO.sub.4.

57. The method of claim 54, wherein the SWP is a SWP film, the method further comprising forming the SWP film by thin film deposition in a tilted substrate assembly apparatus.

58. The method of claim 57, wherein the thickness of the SWP film along the propagation axis is between about 0.5 mm and about 1.0 mm.

59. The method of claim 53, wherein each of the first and second polarization orientation element includes a Faraday rotator element.

60. The method of claim 59, further including forming at least one of the first and second Faraday rotator elements by: depositing a magnetic garnet film on a non-magnetic garnet substrate; applying a substantially uniform magnetic field to the garnet film; and removing the substrate, wherein the Faraday rotator element has a substantially uniform magnetic profile.

61. The method of claim 60, further comprising cutting the garnet film so as to form the first and second Faraday rotator elements, each having a substantially uniform magnetic profile.

62. The method of claim 60, further comprising periodically poling the uniformly magnetized garnet film so as to form a Faraday rotator element having periodically reversed magnetic domains.

63. The method of claim 62, further comprising cutting the garnet film so as to form the first and second Faraday rotator elements, each having periodically reversed magnetic domains.

64. The method of claim 60, further including forming at least one of the first and second PBS modules by depositing a PBS film on the Faraday rotator element.

65. The method of claim 60, wherein the thickness of the PBS film is between about 0.25 mm and about 0.5 mm.

66. The method of claim 60, wherein the thickness of the garnet film is between about 0.5 mm and about 0.7 mm.

67. The method of claim 59, wherein each polarization orientation element also includes a waveplate film, the method further comprising forming at least one of the first and second polarization orientation elements by: depositing a magnetic garnet film on a non-magnetic garnet substrate; applying a substantially uniform magnetic field to the garnet film so as to form a Faraday rotator element having a substantially uniform magnetic profile; and depositing a bi-layer waveplate film on the magnetized garnet film so as to form a polarization orientation element; and removing the substrate.

68. The method of claim 67, further comprising cutting the formed polarization orientation element so as to form both the first and second polarization orientation elements.

69. The method of claim 67, wherein removing the substrate is performed prior to depositing the waveplate film.

70. The method of claim 67, wherein removing the substrate is performed prior to applying the magnetic field to the garnet film.

71. The method of claim 67, further including forming at least one of the first and second PBS modules by depositing a PBS film on the polarization orientation element.

72. The method of claim 71, wherein the PBS film is deposited on the waveplate film opposite the Faraday rotator element.

73. The method of claim 71, wherein the PBS film is deposited on the Faraday rotator element opposite the waveplate film.

74. The method of claim 71, wherein the thickness of the PBS film is between about 0.25 mm and about 0.5 mm.

75. The method of claim 71, wherein the thickness of the PBS film is between about 5 .mu.m and about 20 .mu.m.

76. The method of claim 67, further comprising removing one or more portions of the waveplate film.

77. A method of forming an optical device for coupling an array of three or more optical fiber ports, the method comprising: providing a birefringent element, wherein light traveling within the birefringent element parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis, and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis; and attaching a polarization beam splitting (PBS) module on one end of the birefringent element, wherein the PBS module includes a PBS film deposited on a polarization orientation element, wherein the end face of the PBS film opposite the polarization orientation element defines an array of three or more port coupling regions for coupling light signals from an array of three or more optical fiber ports, and wherein the PBS film is dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light; and attaching a reflection module on the other end of the birefringent element opposite the PBS module, wherein the reflection module includes a reflection element coupled to a Faraday rotator element; wherein the PBS module is arranged with respect to the birefringent element such that the polarization orientation element orients the polarization of both of the parallel light beams of an optical signal propagating along a forward direction from a first port coupling region on the PBS film parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and such that the polarization orientation element orients the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other; and wherein the reflection module is arranged with respect to the birefringent element such that the Faraday rotator element rotates the polarization of both of the parallel light beams of the optical signal propagating along the forward direction by 45.degree. in one direction and rotates, by 45.degree. in the same direction, the polarization state of both of the parallel light beams of the optical signal propagating along the reverse direction after reflection by the reflection element such that both beams are parallel to the first linear polarization orientation, and such that both beams simultaneously pass through the birefringent element parallel to the propagation axis in the reverse direction.

78. The method of claim 77, wherein the birefringent element is one of a spatial walk-off polarizer (SWP)cut from a birefringent crystal and a SWP film.

79. The method of claim 77, wherein the polarization orientation element includes a Faraday rotator element formed by: depositing a magnetic garnet film on a non-magnetic garnet substrate; applying a substantially uniform magnetic field to the garnet film; and removing the substrate, wherein the Faraday rotator element has a substantially uniform magnetic profile.

80. The method of claim 79, further comprising periodically poling the uniformly magnetized garnet film so as to form a Faraday rotator element having two or more periodically reversed magnetic domains.

81. The method of claim 79, further comprising depositing a PBS film on the magnetized garnet film so as to form the PBS module.

82. The method of claim 77, wherein the polarization orientation element also includes a Faraday rotator element and a waveplate film, the method further comprising forming the polarization orientation element by: depositing a magnetic garnet film on a non-magnetic garnet substrate; applying a substantially uniform magnetic field to the garnet film so as to form a Faraday rotator element having a substantially uniform magnetic profile; and depositing a bi-layer waveplate film on the magnetized garnet film so as to form a polarization orientation element; and removing the substrate.

83. The method of claim 82, wherein removing the substrate is performed prior to applying the magnetic field to the garnet.

84. The method of claim 82, wherein removing the substrate is performed prior to depositing the waveplate film.

85. The method of claim 82, further comprising forming the PBS module by depositing a PBS film on the Faraday rotator element opposite the waveplate film.

86. The method of claim 82, further comprising forming the PBS module by depositing a PBS film on the waveplate film opposite the Faraday rotator element.

87. The method of claim 77, wherein the reflection element includes one or more dielectric layers deposited on the Faraday rotator element.

88. The method of claim 77, wherein the reflection element includes a thin metallic film deposited on the Faraday rotator element.

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Description

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BACKGROUND OF THE INVENTION

The present invention relates in general to optical devices such as optical circulators and optical isolators, and more particularly to optical devices that can be configured as an optical circulator having three, four or any number of optical ports, or as an optical isolator having two optical ports.

As generally known, in an optical isolator, a signal in the forward direction is passed from a first optical port to a second optical port. An optical circulator is a non-reciprocal optical device which allows the passage of light from a first optical port to a second one (as in an optical isolator), while a reverse signal into the second port is totally transmitted to a third port and so on for the remaining port(s) for a so-called circulating operation. Any two consecutive ports of an optical circulator are, in effect, an optical isolator since signals travel only one way.

Optical circulator devices play key roles in fiber optical networking systems and devices, for example, in fiberoptic amplifiers, dense wavelength division multiplexing (DWDM) systems and components and optical add-drop module (OADM) components. Several types of optical circulators have been developed. Examples of current optical circulator devices include those disclosed in U.S. Pat. Nos. 5,204,771; 5,471,340; 5,872,878; 6,002,512; 6,064,522 and 6,052,228. However, manufacturing such conventional circulator devices typically requires precise alignment of each optical element, leading to a low yield and high production costs. Furthermore, such conventional circulator devices tend to be bulky and expensive.

It is, therefore, desirable to provide a compact circulator array that is cost-effective and easily manufactured, and which is capable of routing any number of input signals within one integrated circulating module. It is also desirable that an optical circulator module have optimum performance, i.e., very high isolation, very low polarization dependent loss (PDL), very low polarization mode dispersion (PMD), low insertion loss, very low cross-talk, and high power handling capability. An optical circulator should also be designed for mass production with simple assembly processes.

The present invention avoids many of the problems above and substantially achieves an optical circulator or isolator which has a very high performance and which is easily manufactured. The present invention presents optical devices which are useful for long distance and high data rate communication systems.

SUMMARY OF THE INVENTION

The present invention provides optical isolator and circulator devices, and methods for making the same, having two optical ports in isolator embodiments and three, four or any number of optical ports in circulator embodiments.

According to embodiments of the present invention, miniature optical devices, including circulator array devices, are fabricated using thin film coating technology. A typical optical device according to the present invention includes a spatial walkoff plate (SWP), or other birefringent element, coupled on opposite ends to first and second polarization orientation elements. First and second polarization beam splitter (PBS) elements are coupled to the first and second polarization orientation elements, respectively. The PBS elements are formed using thin film coating techniques and each includes an array of port coupling regions for coupling to an array of input/output fiber port assemblies. The SWP may be formed using thin film coating techniques or cut from a birefringent single crystal. Each polarization orientation element includes a Faraday rotator element, and in some embodiments, each also includes a half-wave plate formed using thin film coating techniques. The Faraday rotator elements are periodically poled in some embodiments using selective poling techniques to create oppositely oriented (bi-directional) magnetic domains so that polarization rotations of 45.degree. in both clockwise and counter-clockwise directions can be simultaneously achieved on the same magnetic garnet. Periodically etched half-wave plates are used in some embodiments. Depending on the orientation of the optical axes of the SWP and the first and second PBS elements, the constituents of each polarization orientation element are designed and oriented so that the circulator device achieves a circulating operation with optical signals at an input port, i, coupled to one PBS element being passed to an output port, i+1, coupled to the other PBS element in a non-reciprocal manner. In some embodiments, a reflective element replaces one of the PBS elements so as to provide a circulator device having a reflective operation, with an optical signal at an input port, i, coupled to the PBS element being passed to the next consecutive port, i+1, coupled to the PBS element.

According to an aspect of the present invention, an optical device for coupling arrays of optical fiber ports is provided. The device typically comprises a birefringent element arranged so that light traveling parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis. the device also typically comprises first and second polarization orientation elements coupled to opposite ends of the birefringent element, and first and second polarization beam splitting (PBS) films deposited on said first and second polarization orientation elements, respectively, wherein the end face of each of the first and second PBS films opposite the polarization orientation elements defines an array of two or more port coupling regions for coupling light signals from an array of two or more optical fiber ports, with one PBS film defining even numbered ports and the other defining odd numbered ports, wherein the first and second PBS films are dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light. The first polarization orientation element is typically arranged with respect to the birefringent element and the first PBS film so as to orient the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region on the first PBS film parallel to the first linear polarization orientation so that both beams simultaneously pass through the birefringent element parallel to the propagation axis, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other. Additionally, the second polarization orientation element is typically arranged with respect to the birefringent element and the second PBS film so as to orient the polarization of both of the parallel light beams of a second optical signal propagating along a forward direction from a second port coupling region on the second PBS film parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are mutually perpendicular.

According to another aspect of the present invention, an optical device for coupling an array of optical fiber ports is provided. The device typically comprises a birefringent element arranged so that light traveling parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis, and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis. The device also typically comprises first and second polarization orientation elements coupled to opposite ends of the birefringent element, and a polarization beam splitting (PBS) film deposited on said first polarization orientation element, wherein the end face of the PBS film opposite the first polarization orientation element defines an array of two or more port coupling regions for coupling light signals from an array of two or more optical fiber ports, wherein the PBS film is dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light. The device also typically comprises a reflection element coupled to the second polarization orientation element opposite the birefringent element, wherein the reflection element is arranged such that the beam components of a light signal propagating in the forward direction are reflected back in the reverse direction. The first polarization orientation element is typically arranged with respect to the birefringent element and the PBS film so as to orient the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other. The second polarization orientation element typically arranged so as to rotate the polarization state of each of the parallel light beams of the first optical signal propagating along the forward direction by 45.degree. in one direction, wherein the second polarization orientation element rotates, by 45.degree. in the same direction, the polarization state of both of the parallel light beams of the first optical signal propagating along the reverse direction after being reflected by the reflection element such that both beams are parallel to the first linear polarization orientation, and such that both beams simultaneously pass through the birefringent element parallel to the propagation axis in the reverse direction

According to yet another aspect of the present invention, a method is provided for forming an optical device for coupling arrays of optical fiber ports. The method typically comprises providing a birefringent element, wherein light traveling within the birefringent element parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis, and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis, and attaching first and second polarization beam splitting (PBS) modules on opposite ends of the birefringent element, wherein each module includes a PBS film deposited on a polarization orientation element, with said polarization orientation elements being attached to the opposite ends of the birefringent element. The end face of each of the first and second PBS films opposite the polarization orientation elements defines an array of two or more port coupling regions for coupling light signals from an array of two or more optical fiber ports, with one PBS film defining even numbered ports and the other defining odd numbered ports. The first and second PBS films are typically dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light. The first PBS module is typically arranged with respect to the birefringent element such that the first polarization orientation element orients the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region on the first PBS film parallel to the first linear polarization orientation so that both beams simultaneously pass through the birefringent element parallel to the propagation axis, and such that the first polarization orientation element orients the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other, and wherein the first polarization orientation element refracts the light deflected by the birefringent element parallel to the propagation axis. The second PBS module is typically arranged with respect to the birefringent element such that the second polarization orientation element orients the polarization of both of the parallel light beams of a second optical signal propagating along a forward direction from a second port coupling region on the second PBS film parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and such that the second polarization orientation element orients the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are mutually perpendicular.

According to yet a further aspect of the present invention, a method is provided for forming an optical device for coupling an array of three or more optical fiber ports. The method typically comprises providing a birefringent element, wherein light traveling within the birefringent element parallel to a propagation axis and having a first linear polarization orientation passes through parallel to the propagation axis, and light traveling parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is deflected at an angle relative to the propagation axis, and attaching a polarization beam splitting (PBS) module on one end of the birefringent element, wherein the PBS module includes a PBS film deposited on a polarization orientation element, wherein the end face of the PBS film opposite the polarization orientation element defines an array of three or more port coupling regions for coupling light signals from an array of three or more optical fiber ports, and wherein the PBS film is dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light. The method also typically includes attaching a reflection module on the other end of the birefringent element opposite the PBS module, wherein the reflection module includes a reflection element coupled to a Faraday rotator element. The PBS module is typically arranged with respect to the birefringent element such that the polarization orientation element orients the polarization of both of the parallel light beams of an optical signal propagating along a forward direction from a first port coupling region on the PBS film parallel to the second linear polarization orientation so that both beams are simultaneously deflected in the birefringent element, and such that the polarization orientation element orients the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other. The reflection module is typically arranged with respect to the birefringent element such that the Faraday rotator element rotates the polarization of both of the parallel light beams of the optical signal propagating along the forward direction by 45.degree. in one direction and rotates, by 45.degree. in the same direction, the polarization state of both of the parallel light beams of the optical signal propagating along the reverse direction after reflection by the reflection element such that both beams are parallel to the first linear polarization orientation, and such that both beams simultaneously pass through the birefringent element parallel to the propagation axis in the reverse direction.

Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an isometric view diagram showing the structure of a multiple-port circulator device according to an embodiment of the present invention; FIG. 1B is a top view showing the structure and operation of the multiple-port circulator device of FIG. 1A; FIG. 1C is a state diagram showing the polarization and position of beam(s) at different locations between two sets of consecutive ports of the multiple-port circulator device of FIGS. 1A and 1B; FIG. 1D illustrates the orientation of the optical axes and principal planes of the SWP and PBS elements of FIG. 1A relative to the light propagation direction (Z-axis) according to an embodiment of the present invention;

FIGS. 2A-2C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device according to an embodiment of the present invention;

FIGS. 3A-3D illustrate by way of an isometric view, a top view, a side view and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device according to an embodiment of the present invention;

FIGS. 4A-4C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device having an adjustable SWP according to an embodiment of the present invention;

FIGS. 5A-5C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device according to an embodiment of the present invention;

FIGS. 6A-6C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device according to an embodiment of the present invention;

FIGS. 7A-7C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device according to an embodiment of the present invention;

FIGS. 8A-8C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device having an adjustable SWP according to an embodiment of the present invention;

FIGS. 9A-9D illustrate by way of an isometric view, a top view, a side view, and a polarization state diagram, respectively, the structure and operation of another multiple-port circulator device having uniformly poled Faraday rotator elements according to an embodiment of the present invention;

FIGS. 10A-10C illustrate by way of an isometric view, a top view, and a side view, respectively, the structure and operation of a multi-tiered, multiple-port circulator device according to an embodiment of the present invention;

FIGS. 11A-11C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of a reflective-type multiple-port circulator device according to an embodiment of the present invention;

FIGS. 12A-12C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another reflective-type multiple-port circulator device according to an embodiment of the present invention;

FIGS. 13A-13C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of another reflective-type multiple-port circulator device according to an embodiment of the present invention;

FIG. 14 illustrates a fabrication process of a core structure of a multiple port circulator device similar to the circulator device of FIG. 1 according to an embodiment of the present invention;

FIG. 15 illustrates a magnetic processing methodology for obtaining the desired magnetic profile in a magnetic garnet according to an embodiment of the present invention.;

FIG. 16 illustrates a cold poling process arrangement according to an embodiment of the present invention;

FIG. 17 illustrates a waveplate created from bi-directionally obliquely deposited thin films according to an embodiment of the present invention;

FIG. 18 illustrates a flux collimating and limiting arrangement for creating PBS and SWP layers by depositing thin films using either e-beam evaporation or ion-beams;

FIG. 19 illustrates another fabrication process of a core structure of a multiple port circulator device similar to the circulator device of FIG. 8 according to an embodiment of the present invention;

FIG. 20 illustrates a circulator device attached to a fiber array according to an embodiment of the present invention;

FIGS. 21A-21C illustrate by way of an isometric view, a top view, and a polarization state diagram, respectively, the structure and operation of a multiple-port circulator device including half-wave plates having oppositely oriented regions according to an embodiment of the present invention; and

FIG. 22 illustrates a process of fabricating a half-wave plate having oppositely oriented regions according to an embodiment of the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Circulator Devices

FIGS. 1A-1C show the elements and operation of a multiple-port circulator device 100 according to an embodiment of the present invention. In FIG. 1A the multiple-port circulator device 100 includes polarization beam splitter (PBS) elements 110 and 170, periodically poled Faraday rotator elements 120 and 160 and half-wave plates 130 and 150 arranged on either side of a spatial walkoff plate (SWP) 140. Light signal pass to and from the circulator device 100 through port coupling regions 180 on the end face of PBS element 110 and on the end face of PBS element 170 (not shown). Each port coupling region 180 represents a coupling location for an optical port assembly. For example, as shown in the top view of FIG. 1B, ten optical port assemblies (ports) are arranged on the circulator device with consecutive ports on opposite sides of the circulator device 100. That is, ports 1, 3, 5, 7 and 9 are arranged on one side and ports 2, 4, 6, 8, and 10 are arranged on the opposite side. As explained below, light from port 1 passes to port 2, light from port 2 passes to port 3, light from port 3 passes to port 4, and so on, such that for an N-port circulator device, light from port N-1 passes to port N.

It should be appreciated that circulator device structures according to the present invention, including the circulator device 100, may be extended in size such that any number of optical port assemblies may be attached thereto. For example, practical circulator device embodiments including 40 or more, and even 100 or more optical port assemblies coupled thereto are readily produced and implemented using the teachings of the present invention. Further, it should be appreciated that the circulator device structures according to the present invention, including the circulator device 100, may be reduced in size such as to accommodate only three or four optical port assemblies, or only two in isolator embodiments.

Each optical port assembly is nearly identical to the others. In one embodiment, a multisection fiber collimator assembly is used to couple an array of fibers to the devices of the present invention. One example of such a multi-section collimator assembly is discussed in U.S. Pat. No. 6,014,486, the disclosure of which is hereby incorporated by reference in its entirety for all purposes. As shown in one embodiment therein, for example, a multisection collimator includes an array of multimode graded index fiber sections bonded to an array of silica (e.g., step index) fiber sections. An array of single mode fibers may be bonded to either or both of the silica and graded index sections.

Each of the PBS elements 110 and 170 divides a light beam having an arbitrary state of polarization received from each coupled port in the forward direction into two linearly polarized components with mutually perpendicular polarization states, and combines two mutually perpendicular polarized components in the reverse direction.