Optical filter fabrication method and apparatus, optical filter, fiber holder with spiral groove, and phase mask
First Claim
Patent Images
1. An optical filter, comprising:
- a fiber holder having a flat surface with a spiral groove; and
an optical fiber with a periodically modulated refractive index, held in said spiral groove.
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Abstract
An optical filter is manufactured by placing a photosensitive optical fiber in a spiral arrangement on a fiber holder, preferably having a spiral groove for holding the fiber, and exposing the fiber to ultraviolet light through a phase mask having a spiral diffraction grating, forming an in-fiber Bragg grating. The fiber can be conveniently scanned by an ultraviolet beam as the fiber holder and phase mask turn on a rotating stage. The fiber can be compactly packaged between the fiber holder and a cover. The fiber holder and cover can be formed by coating a substrate with layers of polymer material, the spiral groove being formed by photolithographic patterning of one of the layers.
34 Citations
34 Claims
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1. An optical filter, comprising:
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a fiber holder having a flat surface with a spiral groove; and
an optical fiber with a periodically modulated refractive index, held in said spiral groove. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
a flat substrate; and
a polymer layer covering said flat substrate except in a spiral region constituting said spiral groove.
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10. The optical filter of claim 9, further comprising a protective underlayer covering said flat substrate beneath said polymer layer and in said spiral groove.
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11. The optical filter of claim 10, wherein said protective underlayer comprises a polymer material.
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12. The optical filter of claim 9, further comprising an upper protective layer covering said polymer layer and said optical fiber.
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13. The optical filter of claim 12, wherein said upper protective layer comprises a polymer material.
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14. The optical filter of claim 1, wherein said fiber holder has an annular disc shape, said spiral groove extending from an outer perimeter of said fiber holder to an inner perimeter of said fiber holder.
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15. The optical filter of claim 1 wherein said optical fiber is photosensitive.
- 16. A fiber holder for holding a photosensitive optical fiber, comprising a flat plate having on one surface a spiral groove for receiving said photosensitive optical fiber.
- 20. A phase mask comprising a plate transparent to ultraviolet light, having a spiral pattern of periodic pits forming a spiral diffraction grating on one surface.
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23. An apparatus for manufacturing an optical filter by forming a Bragg grating in a photosensitive optical fiber, comprising:
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a fiber holder formed as a flat plate having an upper surface, with a spiral groove on said upper surface, said photosensitive optical fiber being held in said spiral groove;
a phase mask formed as a plate transparent to ultraviolet light, having a spiral pattern of periodic pits forming a spiral diffraction grating on one surface, said phase mask being disposed facing said fiber holder with said one surface parallel to the upper surface of said fiber holder, said spiral pattern being aligned with the spiral groove of said fiber holder;
a rotating stage supporting said fiber holder and said phase mask, rotating on an axis passing through a center of the spiral pattern of said phase mask, perpendicular to the upper surface of said fiber holder; and
an optical system for illuminating said photosensitive optical fiber with ultraviolet light through said phase mask. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
a light source for generating said ultraviolet light; and
a mirror for directing said ultraviolet light toward said phase mask.
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29. The apparatus of claim 28, further comprising a scanning controller for moving said mirror, thereby causing said ultraviolet light to scan across said phase mask in a radial direction of said spiral pattern.
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30. The apparatus of claim 29, wherein said scanning controller synchronizes movement of said mirror with rotation of said rotating stage.
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31. The apparatus of claim 23, further comprising an apodizing system for varying an amount of ultraviolet light to which said optical fiber is exposed according to position on the upper surface of said fiber holder.
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32. The apparatus of claim 31, wherein said optical system produces pulses of ultraviolet light, and said apodizing system controls a repetition rate of said pulses.
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33. The apparatus of claim 31, wherein said apodizing system comprises a variable optical attenuator for attenuating said ultraviolet light by varying amounts.
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34. The apparatus of claim 31, wherein said apodizing system controls the rotational speed of said rotating stage.
Specification