Source: http://www.google.com/patents/US6888987?dq=6721967
Timestamp: 2014-09-19 03:58:34
Document Index: 286857464

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'application No. 60', 'application No. 60', 'application No. 60']

Patent US6888987 - Cylindrical processing of optical media - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsA method for cylindrical processing of an optical medium, including optical fiber and optical materials of substantially cylindrical form. The method of the preferred embodiments includes the steps of rotating an optical medium about a longitudinal relative rotation axis thereof relative to a processing...http://www.google.com/patents/US6888987?utm_source=gb-gplus-sharePatent US6888987 - Cylindrical processing of optical mediaAdvanced Patent SearchPublication numberUS6888987 B2Publication typeGrantApplication numberUS 09/788,303Publication dateMay 3, 2005Filing dateFeb 16, 2001Priority dateFeb 17, 2000Fee statusPaidAlso published asUS6865317, US6891996, US6891997, US20020037132, US20020041730, US20020044739, US20040197051, WO2001061394A1, WO2001061395A1, WO2001061870A2, WO2001061870A3, WO2001065701A2, WO2001065701A3Publication number09788303, 788303, US 6888987 B2, US 6888987B2, US-B2-6888987, US6888987 B2, US6888987B2InventorsPeter C. Sercel, Kerry J. Vahala, David W. Vernooy, Guido HunzikerOriginal AssigneeXponent Photonics IncExport CitationBiBTeX, EndNote, RefManPatent Citations (17), Non-Patent Citations (25), Referenced by (22), Classifications (48), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetCylindrical processing of optical mediaUS 6888987 B2Abstract A method for cylindrical processing of an optical medium, including optical fiber and optical materials of substantially cylindrical form. The method of the preferred embodiments includes the steps of rotating an optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; spatially selectively applying the processing tool to a portion of a surface of the optical medium in operative cooperation with relative rotation of the optical medium and the processing tool, thereby producing a patterned (i.e., spatially selective) structural alteration of the optical medium, the pattern including altered, differentially-altered and unaltered portions of the optical medium. Specialized techniques for spatially selectively generating the structural alteration may include masking/etching, masking/deposition, machining or patterning with lasers or beams, combinations thereof, and/or functional equivalents thereof.
1. A method for cylindrical processing of an optical medium, comprising the steps of:
a. rotating an optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and b. spatially selectively applying the processing tool to a portion of a surface of an optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool, thereby producing spatially selective alterations in the optical medium, wherein the optical medium comprises a silica-based optical fiber including a core and a cladding layer, and the alterations include at least one ring. 2. A method for cylindrical processing of an optical medium, comprising the steps of:
a. rotating an optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and b. spatially selectively applying the processing tool to a portion of a surface of an optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool, thereby producing spatially selective alterations in the optical medium, wherein the optical medium comprises a silica-based optical fiber including a core and a cladding layer, and the alteration includes a spatially selective surface mask. 3. A method for cylindrical processing of an optical medium, comprising the steps of:
a. rotating an optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and b. spatially selectively applying the processing tool to a portion of a surface of an optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool, thereby producing spatially selective alterations in the optical medium, wherein the optical medium comprises a silica-based optical fiber including a core and a cladding layer, and the optical medium includes a hermetic carbon outer coating and the alteration includes the step of spatially selectively removing the hermetic carbon coating. 4. The cylindrical processing method of claim 2, wherein the processing-tool-applying step includes the step of forming a surface mask by spatially selective deposition of mask material on portions of the optical medium.
5. A method for fabricating a fiber-ring resonator comprising the steps of:
a. rotating a resonator optical fiber about a longitudinal relative rotation axis thereof relative to a processing tool; and b. spatially selectively applying the processing tool to a portion of the optical resonator fiber, in operative cooperation with the relative rotation of the resonator fiber to the processing tool, thereby producing a resonator segment in the resonator fiber, the resonator segment having a circumferential optical path length differing from the circumferential optical path length of the resonator fiber adjacent to the resonator segment. 6. The fabricating method of claim 5, wherein the processing tool deposits material on the resonator fiber.
7. The fabricating method of claim 5, wherein the processing tool removes material from the surface of the resonator fiber adjacent to the resonator segment.
8. The fabricating method of claim 5, further including the step of providing an alignment member on the outer circumference of the resonator segment of the resonator fiber.
9. The fabricating method of claim 5, further including the step of altering the circumferential optical path length of the resonator segment, thereby altering a resonant frequency of a resonator optical mode supported by the resonator segment.
10. A method of fabricating an alignment member by cylindrical processing of an optical fiber, comprising the steps of:
a. rotating an optical fiber about a longitudinal relative rotation axis thereof relative to a processing tool; and b. spatially selectively applying the processing tool to a portion of the optical fiber and the processing tool, thereby producing alterations of the optical fiber including a radially-projecting portion or a radially-recessed portion. 11. A method for producing a spatially selective alteration on a substantially cylindrical optical medium, the method comprising the steps of:
rotating the optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to a portion of the surface of the optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool thereby spatially selectively altering the optical medium to produce the spatially selective alteration thereon, wherein the optical medium comprises an optical fiber, and the optical fiber includes a hermetic carbon outer coating layer. 12. A method for producing a spatially selective alteration on a substantially cylindrical optical medium, the method comprising the steps of:
rotating the optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to a portion of the surface of the optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool thereby spatially selectively altering the optical medium to produce the spatially selective alteration thereon, wherein the optical medium comprises an optical fiber, and the optical fiber comprises a hollow-core optical fiber. 13. A method for producing a spatially selective alteration on a substantially cylindrical optical medium, the method comprising the steps of:
rotating the optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to a portion of the surface of the optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool thereby spatially selectively altering the optical medium to produce the spatially selective alteration thereon, wherein the optical medium comprises an optical fiber, and the optical fiber comprises a hollow-core optical fiber and the hollow core contains an optically scattering material or an optically absorbing material. 14. A method for producing a spatially selective alteration on a substantially cylindrical optical medium, the method comprising the steps of:
rotating the optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to a portion of the surface of the optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool thereby spatially selectively altering the optical medium to produce the spatially selective alteration thereon, wherein the optical medium comprises an optical fiber, and the spatially selective alteration includes at least one ring between first and second segments of the optical fiber. 15. The method of claim 14, wherein the spatially selective alteration includes at least one full ring.
16. The method of claim 14, wherein the spatially selective alteration includes at least one partial ring.
17. A method for producing a spatially selective alteration on a substantially cylindrical optical medium, the method comprising the steps of:
rotating the optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to a portion of the surface of the optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool thereby spatially selectively altering the optical medium to produce the spatially selective alteration thereon, wherein: the optical medium comprises an optical fiber; the spatially selective alteration includes spatially selectively removal of optical material from the optical medium; the processing-tool-applying step includes surface-masked wet etching; the optical medium is a silica-based optical fiber including a hermetic carbon outer fiber coating; a surface mask for the optical fiber includes at least a portion of the hermetic carbon outer fiber coating; and surface-masked wet etching is performed with an aqueous hydrofluoric-acid-based etchant. 18. A method for producing a spatially selective alteration on a substantially cylindrical optical medium, the method comprising the steps of:
rotating the optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to a portion of the surface of the optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool thereby spatially selectively altering the optical medium to produce the spatially selective alteration thereon, wherein: the optical medium comprises an optical fiber; the spatially selective alteration includes spatially selective alteration of a refractive index of the optical medium; the refractive index is increased by spatially selective optical-irradiation-induced densification of the optical medium; and the optical fiber is a germano-silica optical fiber. 19. The method of claim 18, wherein the germano-silica optical fiber is a pre-etched germano-silica-core multi-mode optical fiber.
20. The method of claim 18, wherein the germano-silica optical fiber is hydrogen-loaded before irradiation.
21. The method of claim 18, wherein the germano-silica optical fiber is boron co-doped germano-silica optical fiber.
22. A method for producing a spatially selective alteration on a substantially cylindrical optical medium, the method comprising the steps of:
rotating the optical medium about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to a portion of the surface of the optical medium, in operative cooperation with relative rotation of the optical medium and the processing tool thereby spatially selectively altering the optical medium to produce the spatially selective alteration thereon; wherein: the optical medium comprises an optical fiber; the processing-tool-applying step includes the steps of i) controlling relative longitudinal motion of the optical medium and the processing tool, and ii) controlling relative radial motion of the optical medium and the processing tool; and application of the processing tool to the optical fiber is synchronous with relative rotation of the optical fiber and the processing tool thereby producing a partial ring. 23. The method of claim 22, wherein the processing tool comprises a processing beam, the processing beam being synchronously attenuated while the optical medium is rotated thereby producing a partial ring.
24. An apparatus for producing a spatially selective alteration on a substantially cylindrical optical medium, the apparatus comprising:
a processing tool; an optical medium rotator, the rotator being adapted for rotating the optical medium about a longitudinal relative rotation axis thereof relative to the processing tool; and a processing tool positioner, the positioner being adapted for spatially selectively applying the processing tool to a portion of the surface of the optical medium in operative cooperation with relative rotation of the optical medium and the processing tool thereby altering the optical medium to produce the spatially selective alteration thereon, wherein: the processing tool includes a processing beam source and a processing beam delivery assembly for spatially selectively delivering the processing beam to the optical medium; and the processing tool positioner includes a shadow-mask adapted for spatially-selectively applying the processing beam to the optical fiber. 25. A method for fabricating at least one fiber-ring resonator on a resonator optical fiber, the fiber-ring resonator comprising a transverse fiber-ring resonator segment integral with the resonator optical fiber between first and second segments of the resonator optical fiber, the resonator segment having a circumferential optical path length sufficiently different from a circumferential optical path length of an immediately adjacent portion of the first segment or the second segment of the resonator optical fiber so as to enable the resonator segment to support at least one resonant optical mode near an outer circumferential surface of the resonator segment, the method comprising the steps of:
rotating the resonator optical fiber about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to at least a portion of a surface of the resonator optical fiber thereby producing a difference between the circumferential optical path length of the resonator segment and the circumferential optical path length of the immediately adjacent portion of the first or the second segment of the resonator optical fiber. 26. The method of claim 25, wherein the resonator segment is greater than about 1 μm in width.
27. The method of claim 25, wherein the resonator segment is greater than about 2 μm in width.
28. The method of claim 25, wherein the resonator segment is less than about 10 μm in width.
29. The method of claim 25, wherein the resonator segment is less than about 4 μm in width.
30. The method of claim 25, wherein the resonator segment is greater than about 10 μm in diameter.
31. The method of claim 25, wherein the resonator segment is greater than about 20 μm in diameter.
32. The method of claim 25, wherein the resonator segment is greater than about 100 μm in diameter.
33. The method of claim 25, wherein the resonator segment is greater than about 400 μm in diameter.
34. The method of claim 25, wherein the resonator segment is greater than about 500 μm in diameter.
35. The method of claim 25, wherein the resonator segment is less than about 150 μm in diameter.
36. The method of claim 25, wherein the resonator segment is less than about 200 μm in diameter.
37. The method of claim 25, wherein the resonator segment is less than about 600 μm in diameter.
38. The method of claim 25, wherein the resonator segment is less than about 1000 μm in diameter.
39. The method of claim 25, wherein a spectral width of a resonance band of the fiber-ring optical resonator is smaller than an optical channel spacing of the optical WDM system.
40. The method of claim 25, wherein comprising wherein a spectral width of a resonance band of the fiber-ring optical resonator is substantially equal to an optical channel spacing of the optical WDM system.
41. The method of claim 25, wherein a spacing between spectrally-adjacent resonance bands of the fiber-ring optical resonator is greater than an optical channel spacing of the optical WDM system.
42. The method of claim 25, wherein spectrally-adjacent resonance bands of the fiber-ring optical resonator are spaced by about an integer times an optical channel spacing of the optical WDM system.
43. The method of claim 42, wherein the optical WDM system is an optical DWDM system having a channel spacing less than about 400 GHz.
44. The method of claim 42, wherein spectrally-adjacent resonance bands of the fiber-ring optical resonator are spaced by about twice the optical channel spacing of the optical WDM system.
45. The method of claim 25, wherein applying the processing tool to the resonator optical fiber includes removing material from the immediately adjacent portions of the first segment or the second segment of the resonator optical fiber so that a radius of the resonator segment is sufficiently larger than a radius of the immediately adjacent portion of the first segment or the second segment of the resonator fiber so as to enable the resonator segment to support at least one resonant optical mode near an outer circumferential surface of the resonator segment.
46. The method of claim 45, wherein the resonator segment of the resonator fiber is at least about 0.1 μm larger in radius than the immediately adjacent portion of the first segment or the second segment of the resonator fiber.
47. The method of claim 45, wherein the resonator segment of the resonator fiber is at least about 0.5 μm larger in radius than the immediately adjacent portion of the first segment or the second segment of the resonator fiber.
48. The method of claim 45, wherein the resonator segment of the resonator fiber is at most about 20 μm larger in radius than the immediately adjacent portion of the first segment or the second segment of the resonator fiber.
49. The method of claim 45, wherein the resonator segment of the resonator fiber is at most about 1.5 μm larger in radius than the immediately adjacent portion of the first segment or the second segment of the resonator fiber.
50. The method of claim 45, wherein material is removed from the resonator optical fiber by surface-masked wet etching of the resonator optical fiber.
51. The method of claim 50, further comprising the step of producing a surface mask on the resonator optical fiber, the surface mask including a primary masked ring substantially covering the resonator segment between unmasked rings on the first and second segments of the resonator optical fiber.
52. The method of claim 51, wherein the unmasked rings are produced by laser machining of a resonator optical fiber outer coating layer.
53. The method of claim 51, wherein the surface mask includes a secondary masked ring adjacent the primary masked ring with a secondary unmasked ring therebetween, the primary masked ring being wider than the secondary masked ring, the secondary masked ring being wider than the secondary unmasked ring, so that upon etching of the resonator fiber an axially-displaced fiber-taper positioning-and-support structure is produced on the resonator optical fiber adjacent the fiber-ring resonator, the positioning-and-support structure including a radially-extending radially-tapered transverse flange.
54. The method of claim 53, wherein the positioning-and-support structure extends completely around the resonator optical fiber.
55. The method of claim 53, wherein the positioning-and-support structure subtends an angle less than about 180�.
56. The method of claim 53, wherein the positioning-and-support structure subtends an angle greater than about 45�.
57. The method of claim 53, wherein the positioning-and-support structure is greater than about 10 μm in length.
58. The method of claim 53, wherein the positioning-and-support structure is greater than about 50 μm in length.
59. The method of claim 53, wherein the positioning-and-support structure is less than about 500 μm in length.
60. The method of claim 53, wherein the positioning-and-support structure is less than about 150 μm in length.
the resonator fiber is a silica-based optical fiber; the surface mask comprises portions of a hermetic carbon outer coating layer of the resonator optical fiber; and the etching employs an aqueous-hydro-fluoric-acid-based etchant. 62. The method of claim 50, further comprising the step of removing at least a portion of the surface mask from the resonator optical fiber after etching.
63. The method of claim 50, further comprising the step of leaving at least a portion of the surface mask remaining on the first segment or the second segment of the resonator optical fiber after etching, the remaining portion of the surface mask serving as an optical mode suppressor.
64. The method of claim 50, further comprising the step of a second surface-masked wet etch, wherein a second surface mask includes an unmasked ring on the resonator segment between masked rings on the resonator segment, so that upon etching of the resonator fiber a radially-displaced fiber-taper positioning-and-support structure is produced on a circumference of the fiber-ring resonator, the positioning-and-support structure including paired axially-juxtaposed radially-extending radially-tapered transverse flanges.
65. The method of claim 25, further comprising the step of adjusting an optical resonance frequency of the fiber-ring resonator after fabricating the fiber-ring resonator on the resonator optical fiber.
66. The method of claim 65, wherein the adjusting step includes irradiating the fiber-ring resonator with ultra-violet light thereby altering the resonance frequency by altering a refractive, index of the fiber-ring resonator.
67. The method of claim 65, wherein the adjusting step includes doping the fiber-ring resonator thereby altering the resonance frequency by altering a refractive index of the fiber-ring resonator.
68. The method of claim 65, wherein the adjusting step includes etching the fiber-ring resonator thereby altering the resonance frequency by altering a diameter of the fiber-ring resonator.
69. The method of claim 65, wherein the adjusting step includes depositing optical material on the fiber-ring resonator thereby altering the resonance frequency by altering a diameter of the fiber-ring resonator.
70. The method of claim 25, further comprising the step of providing a radially-extending transverse flange on the first segment or the second segment of the resonator optical fiber, the flange being adapted for engaging a corresponding groove in an alignment housing.
71. The method of claim 25, further comprising the step of providing a circumferential groove on the first segment or the second segment of the resonator optical fiber, the groove being adapted for engaging a corresponding flange in an alignment housing.
72. A method for fabricating multiple fiber-ring resonators on a resonator optical fiber, the fiber-ring resonators each comprising a transverse fiber-ring resonator segment integral with the resonator optical fiber and separated from each adjacent resonator fiber segment by an intervening fiber segment, the multiple fiber-ring resonators being positioned between first and second segments of the resonator optical fiber, the resonator segments each having a circumferential optical path length sufficiently different from a circumferential optical path length of at least one adjacent intervening segment of the resonator optical fiber so as to enable the multiple resonator segments to support at least one resonant optical mode of a resulting coupled-optical-resonator system near an outer circumferential surface of the resonator segments, the method comprising the steps of:
rotating the resonator optical fiber about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to at least a portion of a surface of the resonator optical fiber thereby producing a difference between the circumferential optical path length of the resonator segments and the circumferential optical path length of the intervening segments of the resonator optical fiber. 73. The method of claim 72, wherein applying the processing tool includes removing material from intervening segments of the resonator optical fiber so that the radii of the resonator segments are sufficiently larger than the radii of the intervening segments of the resonator fiber so as to enable the multiple resonator segments to support at least one resonant optical mode of a resulting coupled-optical-resonator system near an outer circumferential surface of the resonator segments.
74. The method of claim 73, wherein material is removed from the resonator optical fiber by surface masked wet etching of the resonator optical fiber.
75. The method of claim 74, further comprising the step of producing a surface mask on the resonator optical fiber, the surface mask including multiple masked rings substantially covering the multiple resonator segments between multiple unmasked rings on the intervening segments of the resonator optical fiber.
76. The method of claim 72, wherein the multiple fiber-ring resonators include at least four fiber-ring resonators.
77. The method of claim 72, wherein a spectral width of a resonance band of the coupled-optical-resonator system is smaller than an optical channel spacing of the optical WDM system.
78. The method of claim 72, wherein comprising wherein a spectral width of a resonance band of the coupled-optical-resonator system is substantially equal to an optical channel spacing of the optical WDM system.
79. The method of claim 72, wherein a spacing between spectrally-adjacent resonance bands of the coupled-optical-resonator system is greater than an optical channel spacing of the optical WDM system.
80. The method of claim 72, wherein spectrally-adjacent resonance bands of the coupled-optical-resonator system are spaced by about an integer times an optical channel spacing of the optical WDM system.
81. The method of claim 80, wherein the optical WDM system is an optical DWDM system having a channel spacing less than about 400 GHz.
82. The method of claim 80, wherein spectrally-adjacent resonance bands of the coupled-optical-resonator system are spaced by about twice the optical channel spacing of the optical WDM system.
each of the multiple fiber-ring resonators has substantially the same width, substantially the same diameter, and substantially the same de-coupled resonance frequency; and each intervening segment has substantially the same width and substantially the same diameter. 84. The method of claim 83, wherein the intervening segments are greater than about 1 μm in width.
85. The method of claim 83, wherein the intervening segments are less than about 20 μm in width.
the intervening segments are between about 5 μm and about 15 μm in width; and the intervening segments are less than about 0.7 μm smaller in radius than the resonator segments. 87. The method of claim 83, wherein:
the intervening segments are between about 1 μm and about 5 μm in width; and the intervening segments are greater than about 1 μm smaller in radius than the resonator segments. 88. A method for fabricating a fiber-taper alignment-and-support structure on a fiber-taper support fiber, the fiber-taper alignment-and-support structure comprising a taper-support segment integral with the fiber-taper support fiber between first and second segments of the fiber-taper support fiber, the taper-support segment being adapted for substantially reproducibly and substantially stably positioning a fiber-taper engaged therewith, the method comprising the steps of:
rotating the taper-support optical fiber about a longitudinal relative rotation axis thereof relative to a processing tool; and spatially selectively applying the processing tool to at least a portion of a surface of the taper-support optical fiber thereby producing the fiber-taper alignment-and-support structure on the taper-support segment of the taper-support optical fiber. 89. The method of claim 88, wherein the positioning-and-support structure extends completely around the taper-support optical fiber.
90. The method of claim 88, wherein the positioning-and-support structure subtends an angle less than about 180�.
91. The method of claim 88, wherein the positioning-and-support structure subtends an angle greater than about 45�.
92. The method of claim 88, wherein the positioning-and-support structure is greater than about 10 μm in length.
93. The method of claim 88, wherein the positioning-and-support structure is greater than about 50 μm in length.
94. The method of claim 88, wherein the positioning-and-support structure is less than about 500 μm in length.
95. The method of claim 88, wherein the positioning-and-support structure is less than about 150 μm in length.
96. The method of claim 88, wherein applying the processing tool to the taper-support optical fiber includes removing material from the immediately adjacent portions the first segment or the second segment of the taper-support optical fiber so that a radially-extending transverse flange results.
97. The method of claim 96, wherein material is removed from the taper-support optical fiber by surface-masked wet etching of the taper-support optical fiber.
98. The method of claim 97, further comprising the step of producing a surface mask on the taper-support optical fiber, the surface mask including a primary masked ring on the taper-support segment between unmasked rings on the first and second segments of the taper-support optical fiber.
99. The method of claim 98, wherein the unmasked rings are produced by laser machining of a taper-support optical fiber outer coating layer.
100. The method of claim 98, wherein the surface mask further includes an unmasked ring on the taper-support segment between masked rings on the taper-support segment, so that upon etching of the taper-support fiber a fiber-taper positioning-and-support structure is produced on the taper-support fiber, the positioning-and-support structure including paired axially-juxtaposed radially-extending radially-tapered transverse flanges.
101. The method of claim 97, wherein:
the taper-support fiber is a silica-based optical fiber; the surface mask comprises portions of a hermetic carbon outer coating layer of the taper-support optical fiber; and the etching employs an aqueous-hydro-fluoric-acid-based etchant. 102. The method of claim 97, further comprising the step of removing at least a portion of the surface mask from the taper-support optical fiber after etching.
103. The method of claim 97, further comprising the step of leaving at least a portion of the surface mask remaining on the first segment or the second segment of the taper-support optical fiber after etching, the remaining portion of the surface mask serving as an optical mode suppressor.
104. The method of claim 88, wherein applying the processing tool to the taper-support optical fiber includes removing material from the taper-support segment of the taper-support optical fiber so that a circumferential groove results.
105. The method of claim 104, wherein material is removed from the taper-support optical fiber by surface-masked wet etching of the taper-support optical fiber.
106. The method of claim 105, further comprising the step of producing a surface mask on the taper-support optical fiber, the surface mask including a primary unmasked ring on the taper-support segment between masked rings on the first and second segments of the taper-support optical fiber.
the taper-support fiber is a silica-based optical fiber; the surface mask comprises portions of a hermetic carbon outer coating layer of the taper-support optical fiber; and the etching employs an aqueous-hydro-fluoric-acid-based etchant. 108. The method of claim 105, further comprising the step of leaving at least a portion of the surface mask remaining on the first segment or the second segment of the taper-support optical fiber after etching, the remaining portion of the surface mask serving as an optical mode suppressor.
109. The method of claim 88, further comprising the step of providing a radially-extending transverse flange on the taper-support optical fiber, the flange being adapted for engaging a corresponding groove in an alignment housing.
110. The method of claim 88, further comprising the step of providing a circumferential groove on the taper-support optical fiber, the groove being adapted for engaging a corresponding flange in an alignment housing.
RELATED APPLICATIONS This application claims benefit of prior filed now abandoned provisional Application No. 60/183,499 entitled �Resonant optical power control devices and methods of fabrication thereof� filed Feb. 17, 2000 in the names of Peter C. Sercel and Kerry J. Vahala, said provisional application being hereby incorporated by reference as if fully set forth herein. This application claims benefit of prior filed now abandoned provisional Application No. 60/226,147 entitled �Fiber-optic waveguides for evanescent optical coupling and methods of fabrication and use thereof�, filed Aug. 18, 2000 in the names of Peter C. Sercel, Guido Hunziker, and Robert B. Lee, said provisional application being hereby incorporated by reference as if fully set forth herein.
A1) U.S. provisional Application No. 60/111,484 entitled �An all-fiber-optic modulator� filed Dec. 07, 1998 in the names of Kerry J. Vahala and Amnon Yariv, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein; A2) U.S. application Ser. No. 09/454,719 entitled �Resonant optical wave power control devices and methods� filed Dec. 07, 1999 in the names of Kerry J. Vahala and Amnon Yariv, said application being hereby incorporated by reference in its entirety as if fully set forth herein; A3) U.S. provisional Application No. 60/108,358 entitled �Dual tapered fiber-microsphere coupler� filed Nov. 13, 1998 in the names of Kerry J. Vahala and Ming Cai, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein; A4) U.S. application Ser. No. 09/440,311 entitled �Resonator fiber bi-directional coupler� filed Nov. 12, 1999 in the names of Kerry J. Vahala, Ming Cai, and Guido Hunziker, said application being hereby incorporated by reference in its entirety as if fully set forth herein; and A5) U.S. provisional Application No. 60/183,499 entitled �Resonant optical power control devices and methods of fabrication thereof� filed Feb. 17, 2000 in the names of Peter C. Sercel and Kerry J. Vahala, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein. A6) U.S. provisional application entitled �Fiber-optic waveguides for evanescent optical coupling and methods of fabrication and use thereof�, filed Aug. 18, 2000 in the names of Peter C. Sercel, Guido Hunziker, and Robert B. Lee, Application No. 60/226,147, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein. A7) U.S. provisional Application No. 60/257,248 entitled �Modulators for resonant optical power control devices and methods of fabrication and use thereof� filed Dec. 21, 2000 in the names of Oskar J. Painter, Peter C. Sercel, Kerry J. Vahala, and Guido Hunziker, said provisional application being hereby incorporated by reference as if fully set forth herein. A8) U.S. provisional application entitled �Waveguides and resonators for integrated optical devices and methods of fabrication and use thereof�, filed Dec. 21, 2000 in the name of Oskar J. Painter, Application No. 60/257,218, said provisional application being hereby incorporated by reference as if fully set forth herein. A10). U.S. utility patent application Ser. No. 09/788,331 entitled �Fiber-ring optical resonators� filed concurrently with the present application in the names of Peter C. Sercel, Kerry J. Vahala, David W. Vernooy, and Guido Hunziker, said application being hereby incorporated by reference as if fully set forth herein. A11). U.S. utility patent application Ser. No. 09/788,300 entitled �Resonant optical filter� filed concurrently with the present application in the names of Kerry J. Vahala, Peter C. Sercel, David W. Vernooy, Oskar J. Painter, and Guido Hunziker, and said application being hereby incorporated by reference as if fully set forth herein. A12). U.S. utility patent application Ser. No. 09/788,301 entitled �Resonant optical power control device assemblies� filed concurrently with the present application in the names of Peter C. Sercel, Kerry J. Vahala, David W. Vernooy, Guido Hunziker, Robert B. Lee, and Oskar J. Painter, said application being hereby incorporated by reference as if fully set forth herein. A13) U.S. provisional Application No. 60/170,074 entitled �Optical routing/switching based on control of waveguide-ring resonator coupling�, filed Dec. 09, 1999 in the name of Amnon Yariv, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein. A14) U.S. Pat. No. 6,052,495 entitled �Resonator modulators and wavelength routing switches� issued Apr. 18, 2000 in the names of Brent E. Little, James S. Foresi, and Hermann A. Haus, said patent being hereby incorporated by reference in its entirety as if fully set forth herein. A15) U. S. Pat. No. 6,101,300 entitled �High efficiency channel drop filter with absorption induced on/off switching and modulation� issued Aug. 08, 2000 in the names of Shanhui Fan, Pierre R. Villeneuve, John D. Joannopoulos, Brent E. Little, and Hermann A. Haus, said patent being hereby incorporated by reference in its entirety as if fully set forth herein.
P1) Ming Cai, Guido Hunziker, and Kerry Vahala, �Fiber-optic add-drop device based on a silica microsphere whispering gallery mode system�, IEEE Photonics Technology Letters Vol. 11 686 (1999); P2) J. C. Knight, G. Cheung, F. Jacques, and T. A. Birks, �Phased-matched excitation of whispering gallery-mode resonances by a fiber taper�, Optics Letters Vol. 22 1129 (1997); P3) Hiroshi Wada, Takeshi Kamijoh, and Yoh Ogawa, �Direct bonding of InP to different materials for optical devices�, Proceedings of the third international symposium on semiconductor wafer bonding: Physics and applications, Electrochemical Society Proceedings, Princeton NJ., Vol. 95-7, 579-591 (1995). P4) R. H. Horng, D. S. Wuu, S. C. Wei, M. F. Huang, K. H. Chang, P. H. Liu, and K. C. Lin, �AlGaInP/AuBe/glass light emitting diodes fabricated by wafer-bonding technology�, Appl. Phys. Letts. Vol. 75(2) 154 (1999). P5) Y. Shi, C. Zheng,H. Zhang, J. H. Bechtel, L. R. Dalton, B. B. Robinson, W. Steier, �Low (sub-1-volt) halfwave voltage polymeric electro-optic modulators achieved by controlling chromophore shape�, Science Vol. 288, 119 (2000). P6) E. L. Wooten, K. M. Kissa, and A. Yi-Yan, �A review of lithium niobate modulators for fiber-optic communications systems�, IEEE J. Selected Topics in Quantum Electronics, Vol. 6(1), 69 (2000). P7) D. L. Huffaker, H. Deng, Q. Deng, and D. G. Deppe, �Ring and stripe oxide-confined vertical-cavity surface-emitting lasers�, Appl. Phys. Lett., Vol. 69(23), 3477 (1996). P8) Serpenguzel, S. Arnold, and G. Griffel, �Excitation of resonances of microspheres on an optical fiber�, Opt. Lett. Vol. 20, 654 (1995); P9) F. Treussart, N. Dubreil, J. C. Knight, V. Sandoghar, J. Hare, V. Lefevre-Seguin, J. M. Raimond, and S. Haroche, �Microlasers based on silica microspheres�, Ann. Telecommun. Vol. 52, 557 (1997); and P10) M. L. Gorodetsky, A. A. Savchenkov, V. S. Ilchenko, �Ultimate Q of optical microsphere resonators�, Optics Letters, Vol. 21, 453 (1996). P11) Ming Cai, Oskar Painter, and Kerry J. Vahala, �Observation of critical coupling in a fiber taper to a silica-microsphere whispering-gallery mode system�, Physical Review Letters, Vol. 85(1) 74 (2000). P12) Andreas Othonos, �Fiber Bragg gratings�, Rev. Sci. Instrum. Vol. 68(12) 4309(1997). P13) B. A. Little, S. T. Chu, H. A. Haus, J. Foresi, and J.-P. Laine, �Microring channel dropping filters�, J. Lightwave Technology Vol. 15 998 (1997). P14) Giora Griffel, �Synthesis of optical filters using ring resonator arrays�, IEEE Photonics Technology Letts. Vol. 12 810 (2000). P15) G. Metz et al., <<Bragg grating formation and germanosilicate fiber photosensitivity�, SPPIE Vol 1516 Int. Workshop on Photoinduced Self-organization in Optical Fiber (1991). P16) T. Erdogan, V. Mizrahi, P. J. Lemaire, and D. Monroe, �Decay of UV-induced fiber Bragg gratings�, J. Appl. Phys. Vol. 76 73 (1994). P17) Wei Xu, Mank Janos, Danny Wong, Simon Fleming, �Thermal poling of boron-codoped germanosilicate�, IEICE Trans. Electron., Vol E82-C(8) 1549 (1999). Optical fiber and propagation of high-data-rate optical pulse trains therethrough has become the technology of choice for high speed telecommunications. Wavelength division multiplexing (WDM) techniques are now commonly used to independently transmit a plurality of signals over a single optical fiber, independent data streams being carried by optical fields propagating through the optical fiber at a slightly differing optical carrier wavelengths (i.e., signal channels). WDM techniques include dense wavelength division multiplexing (DWDM) schemes, wherein the frequency spacing between adjacent signal channels may range from a few hundred GHz down to a few GHz. A propagating mode of a particular wavelength must be modulated, independently of other propagating wavelengths, in order to carry a signal. A signal carried by a particular wavelength channel must be independently accessible for routing from a particular source to a particular destination. These requirements have previously required complex and difficult-to-manufacture modulating and switching devices requiring extensive active alignment procedures during fabrication/assembly, and as a result are quite expensive. Such devices may require conversion of the optical signals to electronic signals and/or vice versa, which is quite power consuming and inefficient. In the patent applications A1 through A14 cited above a new approach has been disclosed for controlling optical power transmitted through an optical fiber that relies on the use of resonant circumferential-mode optical resonators, or other optical resonators, for direct optical coupling to a propagating mode of an optical fiber resonant with the optical resonator, thereby enabling wavelength-specific modulation, switching, and routing of optical signals propagating through the optical fiber. A thorough discussion of the features and advantages of such optical power control devices and techniques, as well as methods of fabrication, may be found in these applications, already incorporated by reference herein.
FIG. 8A illustrates a method for fabricating a circumferential-mode resonator on an optical fiber according to the present invention. All views arc side cross-sectional views, and the density of the stippled shading indicates the relative refractive index, density, and/or dopant concentration.
FIGS. 22A and 22B schematically illustrate the spectral properties of a coupled optical resonator systems.
For purposes of the present written description and/or claims, �transmission fiber-optic waveguide� (equivalently, transmission waveguide, transmission fiber-optic, transmission optical fiber, TFOWG, TWG) shall denote an optical fiber (polarization-maintaining or otherwise) provided with a evanescent optical coupling segment where an evanescent portion of a propagating optical mode may extend beyond the fiber-optic waveguide and overlap a portion of some other optical mode, thereby enabling evanescent optical coupling between the transmission optical waveguide and another optical element. Such a transmission optical waveguide may comprise an optical fiber taper, a D-shaped optical fiber, an optical fiber with a saddle-shaped concavity in the cladding layer, an optical fiber with a side-polished flattened portion, and/or functional equivalents. Such transmission optical waveguides are described in further detail in earlier-cited applications Al through A6. Such transmission fiber-optic waveguides typically serve to facilitate insertion of optical power control devices according to the present invention into an optical power transmission system.
For purposes of the written description and/or claims, �evanescent optical coupling� shall generally denote those situations in which two optical elements, each capable of supporting a propagating and/or resonant optical mode and at least one having an evanescent portion extending beyond its respective optical element, are optically coupled by at least partial spatial overlap of the evanescent portion of one optical mode with at least a portion of the other optical mode. The amount, strength, level, or degree of optical power transfer from one optical element to the other through such evanescent optical coupling depends on the spatial extent of the overlap (both transverse and longitudinal), the spectral properties of the respective optical modes, and the relative spatial phase matching of the respective optical modes (also referred to as modal index matching). To transfer optical power most efficiently, the respective modal indices of the optical modes (equivalently, the respective modal propagation constants), each in its respective optical element, must be substantially equal. Mismatch between these modal indices decreases the amount of optical power transferred by evanescent coupling between the optical elements, since the coupled modes get further out of phase with each other as each propagates within its respective optical element and the direction of the optical power transfer eventually reverses itself. The propagation distance over which the modes interact (i.e., the effective interaction length) and the degree of index matching (or mismatching) together influence the overall flow of optical power between the coupled modes. Optical power transfer between the coupled modes oscillates with a characteristic amplitude and spatial period as the modes propagate, each in its respective optical element. Neglecting the effects of optical loss in the optical elements, an ideal system consisting of two coupled modes can be characterized by the following coupled system of equations: ∂ E 1 ∂ z = i ⁢ ⁢ β 1 ⁢ E 1 + i ⁢ ⁢ κ ⁢ ⁢ E 2 ∂ E 2 ∂ z = i ⁢ ⁢ β 2 ⁢ E 2 + i ⁢ ⁢ κ * ⁢ E 1 Where the following definitions apply:
E1,2 amplitudes of the coupled fields β1,2 propagation constants of the coupled fields κcoupling amplitude resulting from spatial overlap of the fields z propagation distance coordinate
For the purpose of illustration, assume that the coupling amplitude κ is constant over an interaction distance L. Then, an incident field of amplitude E1 that is spatially confined to the first optical element before interaction will couple to the other wave guide with a resultant field amplitude E2(L) at z=L (where we define z=0 as the start of the coupling region) given by the following expression,  E 2 ⁡ ( L )  2  E 1 ⁡ ( 0 )  2 =  κ  2 q 2 ⁢ sin 2 ⁡ ( q ⁢ ⁢ L ) q 2 =  κ  2 + 1 4 ⁢ Δ ⁢ ⁢ β 2 Consider the phase mismatch term (Δβ=β2−β 1) and the interaction length in this expression. As is well known, a condition of phase mismatch between the two spatial modes causes an oscillatory power transfer to occur between the waveguides as the interaction length is varied. The spatial period of this oscillation, a so-called �beat length�, can be defined as the distance over which power cycles back and forth between the guides. Greater amounts of phase mismatch will reduce the beat length. Also note that the absolute magnitude of power transfer will diminish with increasing phase mismatch. Finally, it is apparent that increased amounts of interaction length will introduce an increased spectral selectivity to the power coupling.
By controlling the phase mismatch and/or transverse spatial overlap between optical modes, these characteristics may be exploited for controlling optical power transfer between optical elements. For example, by altering the phase mismatch, a device may be switched from a first condition, in which a certain fraction of optical power is transferred from a first optical mode in a first optical element to a second optical mode in a second optical element (phase mismatch set so that the effective interaction length is about half of the characteristic spatial period described above), to a second condition in which little or no optical power is transferred (phase mismatch set so that the effective interaction length is about equal to the characteristic spatial period). Further discussion of optical coupling may be found in Fundamentals of Photonics by B. E. A. Saleh and M. C. Teich (Wiley, New York, 1991), hereby incorporated by reference in its entirety as if fully set forth herein. Particular attention is called to Chapters 7 and 18.
A preferred method for reducing the size of the adjacent portions relative to the resonator segment comprises the steps of: 1) providing the resonator segment with a mask; 2) spatially-selectively etching the adjacent portions, thereby reducing their diameters relative to the diameter of the resonator segment; and 3) removing the mask (FIG. 3). Many optical fibers are supplied with an outer coating comprising a polymer jacket (acrylate, polyimide, or the like), and this jacket may be used as a mask provided it adheres sufficiently to the optical fiber during etching. A preferred mask may comprise an outer fiber coating (shown as stippled shading in FIG. 3) comprising a carbon coating. Optical fiber having a hermetic carbon outer coating (with or without a polymer jacket over the hermetic carbon coating) may be obtained commercially (Hermeticoat optical fiber, sold by Spectran Specialty Optics) or may be fabricated by deposition of a carbon layer on the fiber cladding (see for example U.S. Pat. No. 5,281,247, said patent being hereby incorporated by reference in its entirety as if fully set forth herein). A carbon coating has been found to adhere very well to the optical fiber during etching of the optical fiber. A metal coating may also be employed, and whatever type of coating is used, it may first be deposited on the fiber.
Whether the outer coating comprises a polymer jacket or a carbon film, the outer coating must be spatially patterned appropriately, thereby yielding a mask substantially covering the desired resonator segment upon etching. The mask may preferably be patterned by spatially selective laser machining of the outer coating, removing the outer coating from the adjacent portions and leaving the outer coating on the resonator segment. A polymer jacket outer coating may be laser machined using a UV-emitting excimer laser. A carbon film outer coating may be laser machined using a pulsed laser (presumably ablatively) or with a substantially continuous laser (presumably thermally). During laser machining to pattern the mask the optical fiber may preferably be rotated about its long axis to produce ring-like mask patterns on the fiber. This rotation should preferably be concentric (thereby substantially minimizing any �orbital� motion of the fiber cross-section about the rotation axis, also referred to as centration error). This may preferably be achieved by using a rotational guide such as a vacuum V-block for defining a fiber rotation axis. Sufficient negative pressure may be applied to maintain low centration error during rotation, but must be sufficiently low to allow smooth rotation at a sufficiently high speed (typically 100-300 rpm). Paired V-blocks may be employed, one on each side of the fiber length to be machined, to enhance the positioning stability of the rotating fiber. Alternatively, a capillary tube or fiber ferrule (singly or in pairs) may be used in any equivalent manner to align the fiber for rotation and laser machining. (Hereinafter, use of a capillary for fiber alignment as described herein shall be understood to equivalently encompass use of a fiber ferrule). A capillary tube should be chosen having an inner diameter closely matching the optical fiber diameter. For example, the carbon-coated fiber mentioned hereinabove has a nominal diameter of 125 μm. Capillary tubing is commercially available (0.4 lambda supplied by Drummond Scientific, Inc.) having an inner diameter of 126.4-0.3 μm, making it ideal for concentrically aligning and rotating the fiber during laser machining. This V-block, capillary or fiber ferrule alignment technique for substantially concentric rotation of the optical fiber may be employed during any other fabrication step requiring such rotation of the optical fiber, as set forth hereinbelow. Similar use of a capillary for substantially concentric rotation of an optical fiber during laser processing is described in a publication of Presby et al. (Applied Optics 29 2692 (1990)), said publication being hereby incorporated by reference in its entirety as if fully set forth herein. While remaining within the scope of inventive concepts disclosed and/or claimed herein, any suitable means may be employed for substantially concentric rotation of the optical fiber during laser machining, including but not limited to V-blocks, a capillary tube, a fiber ferrule, an alignment chuck, an alignment jig, an indexed fiber holder, and so forth, either singly or in pairs.
In a preferred method for precisely machining rings in a hermetic carbon mask material, the carbon coated fiber may be threaded through a first V-block, capillary tube or other rotation guide. A relatively long segment of the carbon coated fiber (as long as several inches or more) may extend from the first end of the capillary, and is coupled to a rotation device. The rotation device must produce controlled, substantially uniform rotary motion of the fiber with minimal thrust error. (The term �thrust error� refers to any unwanted longitudinal motion that may accompany the desired rotary motion. The thrust error that is synchronous with the rotation results in a tilt of the machined ring with respect to a plane perpendicular to the fiber axis, an effect which may be used to intentionally produce tilted rings. Provided that the thrust error is kept small, less than about 10% of the ring diameter, the ring tilt will not result in substantial undesirable radiative loss from the ring segment. Control of the tilt may be exploited to tune the resonant frequency of a ring fabricated from an optical fiber of a given diameter, since the perimeter path length, and hence the optical resonance frequencies, of the ring can be varied by varying the ring tilt angle by adjusting the thrust �error�). A prototype system (FIG. 4) has been successfully constructed using a precision drill press (Cameron Micro Drill), but a preferred embodiment, also successfully prototyped, comprises an air bearing spindle 400 (Professional Instruments 4B) belt-driven by a stepper motor/encoder system (not shown). An air-bearing spindle may be preferred as having the smallest achievable thrust error currently available commercially (as small as 25 nm; thrust error of about 1μm or less is generally sufficient for the present invention; thrust error as high as 10 μm may be tolerated under less demanding circumstances). Carbon coated fiber 402 may be secured substantially co-axially to the air bearing spindle (optionally cemented within a capillary tube 404 and the capillary tube secured to air bearing spindle 400). Without departing from inventive concepts disclosed and/or claimed herein, other devices may be equivalently employed to produce the desired rotary motion, including but not limited to rotation stages, stepper-motor-driven rotators, servo-motor-driven rotators, and the like. As the air-bearing spindle or other rotary device rotates the carbon-coated fiber, the fiber rotates within a vacuum V-block, capillary tube, or other rotation guide 408 with low centration error. As long as both fiber and the rotation guide are substantially uncontaminated, this rotation of the fiber within the capillary will not damage the carbon coating. If desired, it may be possible to drive air or other gas through a capillary around the rotating fiber to serve as an air-bearing. The alignment fiber is substantially rigidly mounted in a standard fiber chuck or other similar device 409, and a relatively short segment of the carbon-coated fiber 402 extends beyond the second end of the rotation guide 408. A second rotation guide may be employed on the far end of the fiber to further limit lateral motion during rotation. A microscope objective 410 (60X in the prototype; others may be used as appropriate) for delivering a laser beam for laser machining may be mounted on a precision 3-axis translator 412 for precise positioning relative to the carbon-coated fiber.
A laser beam 414 from an argon ion laser (typically multi-line visible output, mainly 488 nm and 514 nm, between about 10 mW and about 100 mW average power) or a continuous wave frequency-doubled YAG laser laser (visible output, at 532 nm nm, between about 10 mW and about 100 mW average power) is brought to a spot size between about 0.2 μm and about 3 μm, preferably about 0.5-1.0 μm, by the objective 410 onto the surface of the fiber 402 as it rotates, thereby removing the carbon coating from the fiber (presumably by a thermal mechanism). A beamsplitter 416 in the laser beam path allows back-scattered and/or back-reflected laser light from the fiber to be imaged at 418 in order to adjust the focus of the laser beam sufficiently precisely relative to the surface of the fiber. The laser beam need not necessarily be focused at the surface of the fiber (although it could be, if desired). Use of a microscope objective is important for several reasons. The highly convergent beam enables the machining of rings in the hermetic carbon coating as small as 0.5 to 3 μm wide with relatively sharp edges, which in turn reduces the roughness of the edges of the resonator segment produced by subsequent etching. A tight focus on the machined surface of the fiber also insures that the laser beam transmitted through the fiber will be sufficiently defocused when it reaches the opposite surface of the fiber so that none of the coating will be removed from the opposing surface, which would degrade the precision of the edges of the machined rings. The centration error of the carbon-coated fiber within the capillary tube is typically sub-micron, well within the depth-of-focus of the tightly focused laser beam (typically a few microns). It has also been observed that microscopic defects may occur in the portions of the carbon coating left behind after laser machining, resulting in unwanted etched spots and edge roughness in the resonator fiber segment and degradation of the performance of the resulting WGM resonator. This effect is believed to be due to excessive heating of the carbon-coated fiber during laser exposure, which causes damage to the carbon coating and/or the underlying silica adjacent to the carbon being exposed. In addition, exposure of the carbon-coated fiber at high power (greater than about 30 mW) causes texturing of the silica underlying the exposed carbon, presumably due to melting of the underlying silica. It has been observed that reducing the optical power of the exposing laser beam to 10-25 mW substantially eliminates the thermal damage problem as well as the surface texturing problem. It has also been observed that flowing gas (O2, N2, and ambient air have been used successfully, although O2 may be preferable) around the fiber as it is machined seems to mitigate the defect problem.
As an alternative to the mask-and-etch procedure described hereinabove, the diameters of the adjacent portions may be reduced by direct laser machining of the fiber to remove optical fiber material (FIG. 5). Substantially concentric rotation may preferably be employed during laser machining using one or more vacuum V-blocks as described hereinabove. Laser machining may be performed without removing a fiber jacket (if present), in which case the fiber jacket is removed from the adjacent portions during laser machining and the portion of the jacket remaining on the resonator segments may be removed after laser machining by any appropriate method. Alternatively, the fiber jacket (if present) maybe removed from the resonator segment and the adjacent portions prior to laser machining. A fluorine excimer laser emitting at 157 nm may preferably be used for laser machining a silica or silicate-based optical fiber, although other appropriate laser sources (pulsed UV-emitting laser sources, amplified and/or modelocked titanium:sapphire lasers, pulsed CO2 lasers, and so forth) may be employed (particularly for other types of optical fiber) while remaining within the scope of inventive concepts disclosed and/or claimed herein. The earlier discussion of a low NA laser-beam-delivery optical assembly (if the fiber is substantially opaque at the laser-machining wavelength) versus a high NA laser-beam-delivery optical assembly (if the fiber is substantially transparent at the laser-machining wavelength) applies to direct machining of the optical fiber (a high NA assembly, i.e., a microscope objective, is shown in FIG. 5 and is exemplary only). Following laser machining the fiber, including the resonator segment and the adjacent portions, may be polished to reduce and/or eliminate laser-machining-induced irregularities on the circumferential-mode resonator. Such irregularities may act as light scattering centers, thereby degrading the performance (Q-factor, for example) of the circumferential-mode resonator. Suitable polishing techniques may include but are not limited to spatially non-selectively etching, thermal polishing with a flame or CO2 laser, polishing with an electrical arc or fusion splicer, and so forth. Once the adjacent portions have been reduced in diameter relative to the resonator segment, the diameter of the resonator segment may be reduced to achieve a desired circumferential-mode resonant frequency and/or a desired free spectral range between modes, while producing a diameter of the resonator segment 100 the desired amount larger than the diameter of the adjacent portions 200. The desired free spectral range will be determined by the wavelength spacing of channels in the particular WDM standard in use and the number of these channels desired to be modulated by an optical power control device employing circumferential-mode resonator according to the present invention. The circumferential-mode free spectral range divided by the channel spacing yields the approximate number of channels that may be simultaneously modulated by a single device or a series of devices on a single transmission optical fiber. Resonator segment diameters below about 10 μm may result in a circumferential-mode resonator Q-factor that is unacceptably low. The thickness of the resonator segment should preferably be between about 1 μm and about 10 μm, and most preferably between about 2 μm and about 4 μm. The diameter of the resonator segment may be reduced by spatially non-selective etching, employing aqueous HF (as described hereinabove) or other suitable etching agent (FIG. 6). This may also reduce the thickness of the resonator segment by etching the edges of the resonator segment, and the resulting edges may be slightly concave (as described earlier). Alternatively, the diameter of the resonator segment may be reduced by laser machining as described hereinabove and shown in FIG. 5 (and may preferably include use of a V-block, capillary tube, or fiber ferrule for substantially concentric rotation of the optical fiber during laser machining, as described hereinabove). Relatively fine-tuned selection of the circumferential-mode resonator diameter and/or thickness may be required to select a particular wavelength component from among the wavelength components present in a wavelength-division-multiplexed (WDM) optical signal. This process may be referred to a resonator trimming. For example, to fabricate a circumferential-mode resonator selectively resonant with a single channel (typically about 10 GHz wide, for example) from among the 50 GHz- or 100 GHz-spaced WDM channels present within the ca. 80 nm overall bandwidth of the erbium amplifier C and L bands (centered around 1550 nm), the diameter must controlled to within about �5 nm (�10 GHz for the resonator frequency), requiring control of the etch time on the order of about 1 second to about �10 seconds. Such precision of fabrication may be readily achieved using standard techniques of laser machining or other precision machining methods, or by careful control of etch conditions (etchant concentration and/or pH, temperature, and/or etching time). Appropriate dilution of the etchant may yield slower etch rates, thereby enabling enhanced precision for the final diameter of an etched resonator segment.
An alternative process may be employed to trim a fiber-ring resonator to a desired resonance frequency. It is well-know that germano-silicate optical fiber (including hydrogen loaded and boron-co-doped germano-silicate optical fiber) is photosensitive. This phenomena has been used to write Bragg gratings into an optical fiber, for example. Irradiation leads to an increase in the refractive index of the material. By exposing a fiber-ring resonator, fabricated with a photosensitive germano-silicate resonator fiber, to visible or UV irradiation, the resonance frequencies may be precisely adjusted. The irradiation may be done using a focused visible or UV source (such as an excimer laser, ion laser, or doubled, tripled, or quadrupled solid-state laser, or other visible or UV source), or may be done using surface or shadow mask techniques and an unfocused visible or UV source. It is desirable to monitor the resonance spectrum of the fiber-ring during trimming, and this may be done by monitoring the transmission spectrum of a fiber taper or other evanescent waveguide coupled to the fiber-ring resonator during trimming. A particularly elegant solution involves delivering the visible or UV illumination through the same fiber taper used to monitor the resonance frequency. The length of fiber that may be used in this way is limited, due to the relatively high loss of most optical fiber in the UV. This visible or UV trimming technique may be used on single fiber-ring resonators, or may be applied to a coupled system of fiber-ring resonators, either individually or as a group. To individually monitor one resonator from a coupled system, it is necessary to suppress the resonant modes of the other resonators in the system, for example, by contacting all other resonators except the one monitored with a loss probe. It has been observed that for long term stability of the trimming, thermal annealing of the fiber-ring is necessary. The refractive index (and therefore the resonance frequency) of the fiber-ring may shift slightly during the annealing process. Some experimentation is typically required to establish an exposure calibration that accounts for the frequency shift during annealing.
Alternatively, a desired circumferential-mode resonant frequency may be obtained by fabrication of a suitably tilted resonator segment as set forth hereinabove. The resonant frequency shift varies as sin2 θ, where θ is the angle between the tilted ring and a plane perpendicular to the longitudinal axis of the optical fiber. Controlled longitudinal motion of the fiber during rotation as the fiber is machined may be employed to impart the desired tilt angle on the resonator. It should be noted that controlled longitudinal motion of the fiber or laser focusing objective may be employed to produce sinusoidal rings, or rings having any desired curvilinear shape. This may be accomplished by including a longitudinal actuator in the fiber rotation assembly, or alternatively by utilizing the longitudinal positioner 412 of the objective lens 410.
A dielectric material may typically be preferred as the deposited material. Suitable materials may include, but are not limited to: silicate, rare-earth-doped glasses, semiconductor-doped glasses, amorphous semiconductors, chalcogenide glasses, amorphous silicon alloys, combinations thereof, and/or functional equivalents thereof. It may be preferred to use a material having substantially fixed optical properties (silica, for example), thereby yielding a circumferential-mode resonator having substantially fixed properties. Alternatively, it may be desirable to deposit material that enables subsequent modification and/or modulation of the circumferential-mode resonator properties. Such a material may comprise a pure material, a mixture of materials, a secondary material deposited as a thin film coating on a primary material, and/or a primary material having one or more secondary materials as dopants therein. Materials may be selected, designed, and/or formulated to enable controlled modulation of optical properties of the circumferential-mode resonator, including but not limited to: optical loss, optical gain, optical coupling to/from the circumferential-mode resonator, resonant frequencies, free spectral range, and so forth. The materials used may include, but are not limited to: dielectric materials, electro-optic materials, electro-absorptive materials, non-linear optical materials, semiconductor materials, metals, polymers, combinations thereof, and/or functional equivalents thereof Application of electronic, optical, and/or other control signals to the circumferential-mode resonator may be employed for modulation of one of more of the circumferential-mode optical properties.
In order to achieve and maintain reliable, reproducible, and stable evanescent optical coupling between a transmission optical waveguide, a circumferential-mode resonator, and an optical modulator (for a resonant optical modulator) or second optical waveguide (for a resonant optical filter) during and after manufacture of a resonant optical power control device according to the present invention, an alignment device may be employed, as illustrated by the exemplary assemblies of FIGS. 11-14. Such an alignment device may comprise a first alignment substrate 502 having a transmission-waveguide-alignment groove 506 thereon, and various embodiments are described in detail in earlier-cited applications A4, A5, and A7. Alignment substrate 502 may be further provided with a circumferential-mode-resonator-alignment groove 504, or groove 504 may be provided on a second alignment substrate 702. A method for fabricating a resonant optical power control device according to the present invention comprises the steps of: 1) positioning and securing a transmission fiber-optic waveguide within the transmission-waveguide-alignment groove 506; and 2) positioning and securing the circumferential-mode optical resonator within the resonator-alignment groove 504 (as shown, for example, in 11A-11C for the case when grooves 504 and 506 are both provided on substrate 502). The transmission fiber-optic- waveguide may comprise a fiber taper 600, an optical fiber with a saddle-shaped evanescent optical coupling segment, a D-shaped optical fiber, or any other functionally equivalent transmission optical waveguide having an evanescent coupling segment. The circumferential-mode resonator may comprise a fiber-ring 602 connected to adjacent portions 604, or any other functionally equivalent circumferential-mode resonator structure. Notwithstanding the exemplary combinations shown in the Figures, any suitable circumferential-mode resonator may be combined with any suitable transmission fiber-optic waveguide to yield a resonant optical power control device according to the present invention. The transmission-waveguide-alignment groove 506 may be positioned on the alignment substrate 502, and resonator-alignment groove 504 may be positioned on the alignment substrate 502 or 702, so that when positioned and secured therein (and substrates 502 and 702 are assembled, if groove 504 is provided on substrate 702), the transmission fiber-optic waveguide and the circumferential-mode resonator are in substantial tangential or circumferential engagement (preferably mechanical contact between a fiber-optic-taper segment and a taper-positioner provided for the fiber-ring resonator, as described above), thereby evanescently optically coupling the circumferential-mode resonator to the transmission fiber-optic waveguide.
The embodiment of FIG. 15 suggests a method for even more reproducible and stable evanescent optical coupling between a fiber-optic-taper segment and a fiber-ring optical resonator. By wrapping the fiber-optic-taper segment partially around the fiber-ring resonator, an extended region for evanescent optical coupling is created. Furthermore, the level of evanescent optical coupling is adjustable, since the degree of coupling is directly related to the interaction length. When used in conjunction with the fiber-taper positioners described hereinabove, wrapping the taper around the fiber-ring optical resonator enables essentially full adjustment of the coupling condition of the fiber-optic taper and the fiber-ring resonator, from an under-coupled condition at first tangential contact, through critical coupling, to an over-coupled condition. In the absence of additional optical loss due to a modulator or other component, a preferred degree of coupling results in about 90% transmission through the taper on resonance, yielding linewidths commensurate with typical WDM or DWDM systems. The taper may be wrapped around the fiber-ring resonator to any desired degree, but wrapping angles between about 0� and about 180� are typical, and angles between about 45� and about 180� are preferred Generally, an interaction length on the order of 50 μm to about 150 μm result in a degree of coupling in the desired range.
For a resonant optical modulator, similar alignment substrates may be employed whether the optical modulator is a waveguide or resonator, and whether the optical modulator is loss-modulated, index-modulated, resonance-modulated, or interference-modulated. Exemplary assemblies include: slab modulator waveguide 132 shown in FIGS. 12A-12B (with groove 504 on substrate 502); 2D modulator waveguide 134 on substrate 136 shown in FIGS. 13A-133B (with groove 504 on substrate 502); and ridge modulator waveguide 2252 shown in FIGS. 14A-14B (with groove 504 on substrate 702).
The spectral spacing between adjacent resonance peaks or resonance bands maybe manipulated to produce a resonant optical filter with particular wavelength dependent routing characteristics, for either single- or multiple-resonator devices. A particularly useful device in WDM and DWDM systems are slicer/interleavers wherein every other optical signal channel is routed from one waveguide to the other. A preferred filter function for such a device would comprise a series of routing bands separated (�center-to-center�) by twice the channel wavelength spacing of the WDM or DWDM system and about equal to the channel spacing in width (such channel spacings may range from more than several hundred GHz down to tens of GHz, depending on the particular system). Other slicer/interleaver devices may be constructed wherein the routing peak/band spacing and width are chosen to route other combinations of optical signal channels. For example, the resonance spacing may preferably be chosen to be an integer multiple N of the channel spacing, while the resonance width might be chosen to be an integer multiple M of the channel spacing, with M<N. The resulting filter function would route M consecutive channels out of each successive group of N channels. Other filtering schemes may be implemented without departing from inventive concepts disclosed and/or claimed herein.
1) Switching the circumferential-mode optical resonator between an over-coupled condition (where the loss per round trip in the circumferential-mode optical resonator is small compared to the optical coupling between the fiber-optic waveguide and circumferential-mode optical resonator, and the transmission through the fiber-optic waveguide past the resonator is large) and the condition of critical coupling (at which the optical coupling of the fiber-optic waveguide and circumferential-mode optical resonator is substantially equal to the round trip loss of the circumferential-mode optical resonator, and substantially all of the optical power is dissipated by/from the circumferential-mode optical resonator resulting in near zero optical transmission through the fiber-optic waveguide past the circumferential-mode optical resonator); or
2) Switching states between the condition of critical coupling (near zero transmission through the fiber-optic waveguide) and a condition of under-coupling (where the loss per round trip in the circumferential-mode optical resonator is large compared to the optical coupling between the fiber-optic waveguide and circumferential-mode optical resonator, and the transmission through the fiber-optic waveguide past the circumferential-mode optical resonator is non-zero).
For all of these modes of operation, there are essentially two classes of mechanism by which one can introduce round trip loss to a circulating optical wave (i.e., resonant circumferential optical mode) in the circumferential-mode resonator. Either optical power of the circulating wave can be absorbed, or it can be gated out of the circumferential-mode optical resonator into a second optical element, such as a second waveguide or second resonator. The gating may preferably be achieved by control of the optical coupling between the circumferential-mode optical resonator and the second optical element and functions rather like a trapdoor. These two general possibilities are both disclosed in earlier-cited applications A1, A2, A5, and A6. The current disclosure describes such devices in greater detail, particularly optical loss transducers or elements provided as a separate element to control optical loss from a circumferential-mode resonator by either of these means (as distinguished from designs in which the loss control element is an integral part of the circumferential-mode optical resonator structure).
The application of a control signal to a modulator of a circumferential-mode resonator via a modulator control element enables controlled modulation of the optical power transmitted through the transmission optical fiber of the optical power control device. This may be accomplished in a variety of ways, depending on the nature of the modulator employed, and several specific examples follow. Modulating the optical loss of the circumferential-mode resonator between essentially zero loss and the so-called critical-coupling loss (wherein the circumferential-mode resonator loss roughly equals the coupling between the transmission fiber and the circumferential-mode resonator) enables modulation of an optical wave that is resonant with a whispering-gallery mode of the circumferential-mode resonator between about 0% (substantially unattenuated transmission) and about 100% (substantially blocked transmission). A similar result may be obtained by keeping the circumferential-mode optical loss constant while modulating the optical coupling between the transmission optical fiber and the circumferential-mode resonator. Alternatively, modulating a resonant frequency of a circumferential-mode having optical loss substantially equal to the critical-coupling loss may enable similar modulation of an optical wave as the circumferential-mode resonant frequency is moved out of and brought into resonance with, the optical wave. The foregoing are exemplary only, and many other transmission optical fiber modulation schemes may be devised by suitable modulation of circumferential-mode resonator optical properties while remaining within the scope of inventive concepts disclosed and/or claimed herein.
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B23K26/4075, B23K26/4065, G02B6/122, G02B6/29338, G02F1/0118, G02B6/12007, B23K26/407, B23K2201/40, G02F2203/15, B23K26/4095, G02B6/2934, B23K26/403, G02B6/02052, G02B6/2852, G02B6/29343, B23K26/408, B23K26/0823, G02F1/225European ClassificationB23K26/40B11B, B23K26/40B11B12, B23K26/40L, B23K26/40B7H, B23K26/40B11, G02B6/293D4L, B23K26/40B7, G02B6/293E4R, G02F1/225, G02B6/12M, B23K26/08D, G02B6/122, G02B6/02E, G02F1/01C5C, G02B6/293E4R2, G02B6/293E4R6Legal EventsDateCodeEventDescriptionNov 1, 2012FPAYFee paymentYear of fee payment: 8Oct 30, 2008FPAYFee paymentYear of fee payment: 4Nov 14, 2007ASAssignmentOwner name: HOYA CORPORATION USA, CALIFORNIAFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:XPONENT (ASSIGNMENT FOR THE BENEFIT OF CREDTORS), LLC;REEL/FRAME:020156/0485Effective date: 20071113Owner name: XPONENT (ASSIGNMENT FOR BENEFIT OF CREDITORS), LLCFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:XPONENT PHOTONICS INC.;REEL/FRAME:020156/0470Effective date: 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