Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
  • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
  • G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C15/00—Surface treatment of glass, not in the form of fibres or filaments, by etching
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C23/00—Other surface treatment of glass not in the form of fibres or filaments
  • C03C23/0005—Other surface treatment of glass not in the form of fibres or filaments by irradiation
  • C03C23/0025—Other surface treatment of glass not in the form of fibres or filaments by irradiation by a laser beam
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C25/00—Surface treatment of fibres or filaments made from glass, minerals or slags
  • C03C25/002—Thermal treatment
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
  • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
  • G02B6/02209—Mounting means, e.g. adhesives, casings

Definitions

• the present invention relates generally to the production of fiber optic components. More specifically, the present invention relates to methods for forming a
• a periodic variation in refractive index of the waveguide along the long axis of the waveguide is commonly known as an optical waveguide grating.
• a fiber Bragg grating is an optical waveguide grating in a waveguide fiber which will selectively filter propagated light having a wavelength which is twice the period of the grating. Such a fiber Bragg grating is useful as a wavelength filter.
• Fiber Bragg gratings may be formed by a multiple step process which includes writing with actinic radiation, etching, or other mechanisms for making periodic perturbations.
• Side writing is a technique for forming a grating in an optical waveguide fiber wherein light, such as actinic radiation, is caused to form a periodic series of alternating light and dark fringes along the long axis of the waveguide.
• An example of such a periodic series is an interference pattern formed on the side of a waveguide fiber and along a portion of the long axis of a waveguiding fiber.
• the periodic light intensity pattern, produced by the light interference induces a periodic change in refractive index along a portion of the long axis of the waveguide fiber.
• the present invention provides an advantageous method for forming a grating in an optical waveguide.
• the method includes placing an optical waveguide within an enclosing structure, sealing the structure so that the waveguide is secured within the structure, and forming a grating within a portion of the waveguide.
• an embodiment of the invention may include the steps of photosensitizing the optical waveguide, testing the spectral performance of the grating, tuning the grating within the sealed structure, and annealing the grating and the structure.
• the optical waveguide may have many specific forms including that of, for example, a single mode or a multimode optical fiber, a multicore optical fiber, a channel waveguide, or a planar waveguide.
• Fig. 1 is a cross sectional view of a grating package in accordance with the present invention
• Fig. 2 is a flowchart of a method of forming a fiber grating in accordance with the present invention
• Fig. 3 is a graph of a reflectance curve of a fiber grating formed in accordance with the present invention
• Fig. 4 is a graph of a transmittance curve of a fiber grating formed in accordance with the present invention.
• Fig. 5 is a graph of a transmission spectrum of a fiber grating at multiple time intervals formed in accordance with the present invention.
• Fig. 1 shows a cross-sectional view of a grating package 10, formed by methods described below, in accordance with the present invention.
• the waveguide is an optical waveguiding fiber and the package is generally tube-shaped is shown and discussed.
• An optical fiber 12 is partially enclosed by a tube-shaped structure 14 formed of material that is transparent to actinic radiation, such as ultraviolet (UV) light. Boron-doped silica or other glass which is transparent to UV light are suitable materials for the structure 14.
• the tube-shaped structure 14 has an inner diameter "a” (e.g., 255- 1000 ⁇ m), an outer diameter "b” (e.g., 3.0 mm) and a length "c” (e.g., 70 mm).
• the optical fiber 12 including its coating 16 has an outer diameter "d” (e.g., 250 ⁇ m). The coating 16 has been stripped from a length of the optical fiber 12 which is contained within the hollow tube 14.
• the optical fiber 12 has written into it a fiber grating 18 along a portion of the length which has been stripped of the coating 16.
• seals 20, 21 disposed at each end 22, 23 of the hollow tube 14 tensionally maintain and support the region of the optical fiber 12 containing the fiber grating 18.
• the seals 20, 21 may be frits, which include copper glass or other suitable material.
• the package 10 also includes two plugs 24, 25 of epoxy or other suitable material, disposed at each end 22, 23 of the tube-shaped structure 14.
• the ends 22, 23 of the structure 14 are funnel-shaped at an angle of, for example, 45° to facilitate placement of the plugs 24, 25 and insertion of the optical fiber 12.
• the grating package 10 of the present invention may include a variety of materials and sizes, and should not be construed as limited to the embodiments or dimensions shown and described herein, which are exemplary. Further details of other grating packages and packaging methods suitable for use with the present invention are provided in U.S. Patent Application (Attorney Docket No.
• Carberry 6 filed on September 16, 1999, entitled “Method And Apparatus For Packaging Long-Period Fiber Grating” which is incorporated by reference herein in its entirety.
• Fig. 2 shows a method 30 of forming a waveguide grating in a package (such as the grating package 10) in accordance with the present invention.
• a sensitizing step In a sensitizing step
• a waveguide such as, for example, an optical fiber is photosensitized.
• An example of an optical fiber suitable for use with the present invention is a high-delta, germanium doped, step-index fiber with an index delta of substantially 2%.
• index delta refers to the relative refractive index difference between the core and the cladding of the optical fiber and is expressed as a percentage.
• An example of a process suitable for photosensitizing the optical fiber includes exposing the optical fiber to a hydrogen atmosphere at 100 atmospheres of pressure for two weeks. A section of the optical fiber is then flood exposed to ultraviolet light. A UV laser operating at 248 nm pulsed at 15 Hz has been found suitable for this flood exposure.
• the exposure may be at a pulse fluence of 75 millijoules/cm2 for 30 minutes.
• the optical fiber is then annealed for 24 hours at 125° C.
• Another process suitable for photosensitizing for use with the present invention is described in U.S. Patent Application No. 09/252, 151, filed on February 18, 1999 entitled "Optical Waveguide Photosensitization” which is incorporated by reference herein in its entirety.
• a packaging step 34 the optical fiber is placed within a hollow tube (such as the hollow tube 14) and sealed to form a package.
• the package securely holds and protects the optical fiber from contamination during the process steps.
• a grating writing step 36 a grating is written onto the optical fiber. Any of a variety of side writing techniques may be used to write the grating into the optical fiber.
• an excimer-pumped, frequency-doubled dye laser system operating at substantially 240 nm (nanometers) is used as the source of the ultraviolet (UV) light.
• the 240 nm beam produced by the laser is first passed through silica slits.
• Suitable silica slits are described in greater detail in U.S. Patent Application Serial No. 09/081,912, filed on May 19, 1998, entitled "Spatial Filter For High Power Laser Beam” which is incorporated by reference herein in its entirety.
• the phase mask may be a transmission diffraction grating, a component whose structure and characteristics are known in the art.
• a phase mask may also be a substrate having a series of periodically spaced openings.
• the tube 14 in the illustrated embodiment is located approximately 4 millimeters from the phase mask.
• the pulsed exposure from the beam of the excimer laser is at a repetition rate of
• a first testing step 38 the spectral performance of the grating is tested.
• Spectral performance is adjusted, or tuned, in a first tuning step 40.
• the grating is flood exposed to UV light provided by, for example, an excimer laser system operating at substantially 248 nm for 5 minutes in order to meet the spectral target required for the grating.
• the laser fluence is approximately 75 millijoules/cm2 and the repetition rate is 15 Hz.
• Fig. 5 shows an exemplary transmission spectrum of the fiber grating at multiple time intervals during the flood exposure. During the exposure time, a total wavelength shift of approximately 0.15 nm occurs. As seen in Fig. 5, the transmission minimum increases as exposure time increases due to a decrease in the amplitude of the grating modulation.
• the decrease in grating modulation is the result of an increase of the refractive index in the previously light exposed troughs of the grating.
• this is followed by a first annealing step 42.
• the package is annealed for 24 hours at 125° C.
• this may be followed by further testing, tuning and annealing steps.
• a second testing step 44 the spectral performance of the grating is tested to see if the grating meets the spectral target. If the grating does not meet the spectral target, then in a second tuning step 46 the grating is flood exposed to UV light by an excimer laser system operating at substantially 248 nm in order to tune the grating. As illustrated, at the position of the optical fiber, the laser fluence is approximately 75 millijoules/cm and the repetition rate is 15 Hz. In a final annealing step 48, the package is annealed for 24 hours at 125°C.

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• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Physics & Mathematics (AREA)
• General Chemical & Material Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Thermal Sciences (AREA)
• Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Manufacturing & Machinery (AREA)
• Diffracting Gratings Or Hologram Optical Elements (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)

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• 2000
  • 2000-08-25 KR KR1020027003503A patent/KR20020038756A/ko not_active Application Discontinuation
  • 2000-08-25 JP JP2001524922A patent/JP2003509732A/ja active Pending
  • 2000-08-25 AU AU74711/00A patent/AU7471100A/en not_active Abandoned
  • 2000-08-25 CN CN00813003A patent/CN1374932A/zh active Pending
  • 2000-08-25 EP EP00963274A patent/EP1237823A1/en not_active Withdrawn
  • 2000-08-25 WO PCT/US2000/023501 patent/WO2001021538A1/en not_active Application Discontinuation
  • 2000-08-25 CA CA002388493A patent/CA2388493A1/en not_active Abandoned
  • 2000-09-17 TW TW089119172A patent/TW518436B/zh active

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