Classifications

• • 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
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/11—Glass compositions containing silica with 40% to 90% silica, by weight containing halogen or nitrogen
  • C03C3/112—Glass compositions containing silica with 40% to 90% silica, by weight containing halogen or nitrogen containing fluorine
  • C03C3/115—Glass compositions containing silica with 40% to 90% silica, by weight containing halogen or nitrogen containing fluorine containing boron
  • C03C3/118—Glass compositions containing silica with 40% to 90% silica, by weight containing halogen or nitrogen containing fluorine containing boron containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/02—Other methods of shaping glass by casting molten glass, e.g. injection moulding
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B32/00—Thermal after-treatment of glass products not provided for in groups C03B19/00, C03B25/00 - C03B31/00 or C03B37/00, e.g. crystallisation, eliminating gas inclusions or other impurities; Hot-pressing vitrified, non-porous, shaped glass products
• • 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
  • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
  • C03C17/34—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions
  • C03C17/3411—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions with at least two coatings of inorganic materials
• • 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
  • C03C23/002—Other surface treatment of glass not in the form of fibres or filaments by irradiation by ultraviolet light
• • 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
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/062—Glass compositions containing silica with less than 40% silica by weight
  • C03C3/064—Glass compositions containing silica with less than 40% silica by weight containing boron
• • 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
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
• • 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
  • C03C4/00—Compositions for glass with special properties
  • C03C4/0085—Compositions for glass with special properties for UV-transmitting glass
• • 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
  • C03C4/00—Compositions for glass with special properties
  • C03C4/04—Compositions for glass with special properties for photosensitive glass
• • 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
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
• • 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
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/122—Basic optical elements, e.g. light-guiding paths
  • G02B6/124—Geodesic lenses or integrated gratings
• • 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
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/122—Basic optical elements, e.g. light-guiding paths
  • G02B6/125—Bends, branchings or intersections
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
  • C03B2201/21—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with molecular hydrogen
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/31—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with germanium
• • 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
  • C03C2201/00—Glass compositions
  • C03C2201/06—Doped silica-based glasses
  • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
  • C03C2201/21—Doped silica-based glasses containing non-metals other than boron or halide containing molecular hydrogen
• • 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
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B2006/12133—Functions
  • G02B2006/12147—Coupler
• • 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
  • G02B6/02114—Refractive index modulation gratings, e.g. Bragg gratings characterised by enhanced photosensitivity characteristics of the fibre, e.g. hydrogen loading, heat treatment

Definitions

• the present invention relates generally to UV (ultraviolet) photosensitive bulk glass, and particularly to batch meltable alkali boro-alumino-silicate glasses.
• the photosensitive bulk glass of the invention exhibits photosensitivity to UV wavelengths below 250 nm.
• the photosensitivity of the alkali boro-alumino-silicate bulk glass to UV wavelengths below 250 nm provides for the making of refractive index patterns in the glass.
• a radiation source below 250 nm such as a laser, refractive index patterns are formed in the glass.
• the inventive photosensitive optical refractive index pattern forming bulk glass allows for the formation of patterns in glass and devices which utilize such patterned glass.
• the photosensitivity of the inventive bulk glass is utilized to make Bragg gratings in the glass.
• the inventive photosensitive bulk glass is particularly suited for the maldng of photonic devices utilized in optical telecommunications.
• the invention includes a photosensitive glass.
• the starting glass is a photosensitizable alkali boro-alumino-silicate glass that can be loaded with hydrogen to make it photosensitive.
• the glass is a below 250 nm photosensitive glass which has a composition of 40-80 mole % SiO , 2-15 mole % GeO 2 , 10-36 mole % B 2 O 3 , 1-6 mole % Al 2 O 3 and 2-10 mole % R 2 O where R is chosen from the alkali elements with the glass exhibiting photosensitivity to below 250 nm wavelengths.
• the invention further includes a molecular hydrogen loadable photosensitive bulk glass.
• the photosensitive bulk glass is an alkali boro-alumino silicate glass with a melting temperature no greater than 1650°C.
• the glass has a batch composition comprising no greater than 85 mole % SiO 2 , no less than 10 mole % B O 3 , no less than 2 mole % GeO 2 , and a combined alkali and alumina content no greater than 20 mole % Al O 3 +Alkali with the glass having a molecular hydrogen loadable level of at least 10 18 H 2 molecules/cm 3 .
• the invention further includes a method of making a refractive index pattern.
• the invention includes providing a photosensitive bulk glass having a 250 nm absorption less than 20 dB/cm, providing a radiation source below 250 nm, forming a pattern with the below 250 nm radiation, and exposing the photosensitive bulk glass to the pattern to form a modulated refractive index pattern in the bulk glass.
• the invention further includes a method of making a molecular hydrogen loadable photosensitive glass optical device preform.
• the method comprises making a refractive index pattern preform out of melted glass.
• the method includes providing a germania silica glass powder batch with a transition metal contamination level ⁇ 1 ppm by weight for transition metals and a heavy metal contamination level ⁇ 1 ppm by weight for heavy metals.
• the method includes melting the silica glass powder batch to form a homogeneous glass melt, cooling the glass melt into a UV transmitting bulk glass having a 250 nm absorption less than 20 dB/cm and forming the bulk glass into an optical device preform in which refractive index patterns can be made.
• the invention further includes a photosensitive glass optical refractive index pattern preform for use with UV light in the formation of refractive index patterns.
• the preform is comprised of an Alkali boro-alumino-silicate glass with a 250 nm absorption less than 20 dB/cm.
• the preform glass has a UV wavelength inducable modulated refractive index ⁇ n level >10 "5 with a molecular hydrogen level of at least 10 18 H 2 molecules/cm 3 .
• FIG. 1 is a plot of absorbance/nm versus UV wavelength (nm) (200-300 nm) in accordance with the invention.
• FIG. 2a is a plot of induced modulated refractive index [ ⁇ n (x 10 "4 )] versus UV exposure time (minutes) in accordance with the invention.
• FIG. 2b is a plot of induced modulated refractive index [ ⁇ n (x 10 "4 )] versus UV exposure fluence [mJ/cm 2 ] in accordance with the invention.
• FIG. 3 is a photosensitivity thermal stability plot of diffraction efficiency of induced refractive index changes in the bulk glass versus Houvs heated at 400 C in accordance with the invention.
• FIG. 4 is a plot induced refractive index [ ⁇ n] versus OH concentration in accordance with the invention.
• FIG. 4 inset is a plot of absorbance versus wave numbers (cm "1 ) showing OH stretching vibrations and absorbance before (dashed line) and after (solid line) a 90 minute UV exposure of 20 mJ/cm 2 /pulse.
• FIG. 5 is a plot of absorbance versus UV wavelength (nm) before (dashed line) and after (solid line) the 90 minute UV exposure of 20 mJ/cm 2 /pulse of FIG. 4.
• FIG. 6 is a plot of intensity (dBm) versus wavelength (1545 nm - 1559 nm) of refractive index pattern grating formed in the bulk glass in accordance with the invention.
• FIG. 6 inset show the geometry of the UV exposure and the reflectivity and transmission measurements of the plot.
• FIG. 7 illustrates the refractive index pattern grating of FIG. 6.
• FIG; 7a is a cross- section showing the refractive index pattern grating in the bulk glass.
• FIG. 8 illustrates a method in accordance with the invention.
• FIG. 9 illustrates a method in accordance with the invention.
• the invention comprises a below 250nm UV light photosensitizable glass with 40-
• the glass comprises 42-73 mole % SiO 2 , 2-15% mole % GeO 2 , 25-36 mole % B 2 O 3 , 2-6 mole % Al 2 O3, and 2-6 mole % R 2 O. More preferably the glass comprises 42-67 mole % SiO 2 , 2- 15 mole % GeO 2 , 25-36 mole % B 2 O 3?
• R 2 O is at least one Alkali oxide chosen from the group of Na, Li, and K.
• R is Na.
• R is Li.
• R is K.
• the R Alkali content of the glass includes mixtures of Na, Li, and K,
• the glass has an alkali-alumina ratio in the range of 1 ⁇ 0.5.
• the glass is essentially free of non-bridging oxygen ions and such are minimized and inhibited by the glass components.
• the photosensitizable glass has a loadable hydrogen content >10 18 H 2 molecules/cm 3 and preferably is loaded with at least 10 18 H 2 molecules. More preferably the glass has a loadable hydrogen content >10 19 H 2 molecules/cm 3 and preferably is loaded with at least 10 19 H 2 molecules for improved photosensitivity. More preferably the glass is loadable and loaded with at least 2 x 10 19 , and more preferred at least 3 x 10 19 hydrogen molecules per cm 3 .
• Such hydrogen load levels are preferably achieved with a hydrogen loading temperature no greater than 200°C with the molecular hydrogen entering the glass as molecular hydrogen (H ) and remaining as molecular hydrogen in the glass in that the hydrogen molecules contained in the glass do not disassociate and react with the glass until irradiated.
• the photosensitizable glass has a transition metal contaminant level ⁇ lppm by weight for transition metal contaminants.
• the glass also has a heavy metal contaminant level ⁇ lppm by weight for heavy metal contaminants.
• the glass has a Fe content ⁇ lppm by weight Fe, and more preferably lppm by weight Fe.
• the glass has a Ti content ⁇ lppm by weight Ti, and more preferably ⁇ . lppm by weight Ti.
• the photosensitizable glass has a 250nm absorption less than 30 dB/cm, preferably less than 20 dB/cm, and more preferably less than 15 dB/cm. Even more preferred the 250nm absorption is ⁇ 10 dB/cm and most preferably ⁇ 5 dB/cm.
• the photosensitizable glass is a melted glass, and most preferably a non- sintered glass.
• the glass has a melting temperature ⁇ 1650°C, and preferably ⁇ 1600°C which provides for formation by melting a mixed batch of glass feedstock powders to form a homogeneous glass melt which can be cooled into the glass.
• the glass has a melting temperature ⁇ 1550°C, and more preferably ⁇ 1500°C.
• the glass has a softening temperature ⁇ 700°C.
• Such glass forming temperatures allow for efficient and economic manufacturing of the glass and avoid the complications of sintering and sintered glass compositions.
• the glass has a below 250nm wavelength induced modulated refractive index ⁇ n >10 "5 where the exposure wavelength is no greater than 250nm and the glass is loaded with a molecular hydrogen content >10 18 H 2 molecules/cm 3 .
• the inventive glass exhibits photosensitivity as a consequence of exposure to light of no greater than 250nm wavelength, preferably with a below 250nm wavelength induced modulated refractive index ⁇ n >10 "4 when loaded with a molecular hydrogen content >10 19 H 2 molecules/cm 3 .
• the glass has a modulated refractive index ⁇ n >2 x 10 "4 when hydrogen loaded.
• the invention further includes a molecular hydrogen loadable photosensitive bulk glass comprised of an alkali boro-alumino-silicate glass with a melting temperature ⁇ 1650°C.
• a molecular hydrogen loadable photosensitive bulk glass comprised of an alkali boro-alumino-silicate glass with a melting temperature ⁇ 1650°C.
• the alkali boro-alumino-silicate glass has a batch composition of ⁇ 85 mole % SiO 2 , >10 mole % B 2 O 3 , >2 mole % GeO 2 , and a combined Alkali and alumina content ⁇ 20 mole % Al 2 O 3 + Alkali.
• the glass has a molecular hydrogen loadable level of at least 10 1S H 2 molecules/cm 3 , and more preferably at least 10 19 H 2 molecules/cm 3 .
• the molecular hydrogen loadable level >2 x 10 19 H 2 molecules/cm 3 , and most preferred >3 x 10 19 H 2 molecules/cm 3 .
• the batch composition is ⁇ 80 mole % SiO 2 and >20 mole % B 2 O 3 . More preferably the batch composition has ⁇ 70 mole % SiO 2 and >25 mole % B 2 O 3 .
• the glass has a batch composition with a combined Alkali and alumina content >16 mole % Al 2 O 3 + Alkali.
• the photosensitive bulk glass is essentially free of transition metals and with a 250nm absorption less than 30 dB/cm.
• the transition metal contaminant levels are below lppm by weight, with the iron content ⁇ lppm by weight and more preferably ⁇ 0.1 ppm by weight.
• the titanium content is ⁇ lppm by weight, and more preferably ⁇ 0.1ppm.
• the bulk glass has a 250nm absorption ⁇ 20 dB/cm, more preferably ⁇ 15 dB/cm, more preferably ⁇ 10 dB/cm, and most preferred ⁇ 5 dB/cm.
• the glass has a refractive index photosensitivity level modulated ⁇ n >10 "5 with a loaded molecular hydrogen content >10 18 H 2 molecules/cm 3 .
• the glass has a refractive index photosensitivity level ⁇ n >10 "4 with a loaded molecular hydrogen content >10 19 H 2 molecules/cm 3 .
• the bulk glass is loadable with molecular hydrogen to a molecular hydrogen loaded level of at least 10 19 H 2 molecules/cm 3 with a hydrogen loading temperature ⁇ 200°C.
• the glass has a molecular hydrogen content >10 19 H molecules/cm 3 and a below 250nm wavelength induced modulated refractive index ⁇ n >10 .
• the bulk glass Alkali boro-alumino-silicate glass batch composition has a SiO 2 content ⁇ 65 mole % SiO 2 , and more preferably ⁇ 60 mole % SiO 2 .
• the bulk glass batch composition has a GeO 2 content >10 mole % GeO 2 , more preferably >15 mole % GeO , and most preferred >20 mole % GeO 2 .
• the bulk glass batch composition has a combined Alkali and alumina content ⁇ 13 mole % Al 2 O 3 + Alkali, more preferably ⁇ 10 mole % Al 2 O 3 +Alkali, and most preferred ⁇ 5 mole % Al 2 O 3 +Alkali.
• the Alkali comprises Na. In a further embodiment the Alkali comprises Li. In another embodiment the Alkali includes K.
• the bulk glass composition has an Al 2 O 3 content ⁇ 6 mole % Al 2 O 3 .
• the bulk glass composition has a NaO 2 content ⁇ 6 mole % Na 2 O.
• the bulk glass has a B 2 O 3 content >30 mole % B 2 O 3 .
• the glass has an increased OH content (such as shown by OH streeching vibration spectra) when loaded with molecular hydrogen and exposed to UV radiation, preferably with the glass having an OH range of about 100 to 1000 OH ppm by weight.
• the glass has a chlorine content less than lOppm by weight and more preferred ⁇ 5ppm, and most preferred ⁇ lppm.
• the bulk glass is a non-sintered glass, and preferably has a melting temperature ⁇ 1600°C, and more preferred ⁇ 1550°C.
• the glass is a cooled fluid melt mixture formed from a fluid melt, preferably with the fluid melt formed by melting glass batch feedstock powders.
• the bulk glass is a homogeneous glass device preform body with a homogeneous composition with glass dopants evenly spread throughout the glass body.
• the preform body has a homogeneous index of refraction and is free of pre-radiated core and claddings regions with a homogeneous distribution of glass component elements.
• the invention includes a method of making a refractive index pattern.
• the method comprises making a refractive index pattern grating.
• the method of making a pattern includes providing a photosensitive bulk glass having a 250nm absorption less than 30 dB/cm, preferably less than 20 dB/cm.
• the method includes providing a below 250nm radiation source and producing below 250nm radiation.
• the method includes forming a pattern with the below 250nm radiation and exposing the photosensitive bulk glass to the pattern to form a modulated refractive index pattern in the bulk glass.
• the provided bulk glass has a ⁇ 15 dB/cm absorption at 250nm, more preferably ⁇ 10 dB/cm, and most preferably ⁇ 5 dB/cm.
• Forming the pattern preferably comprises forming a pattern and exposing the bulk glass to the pattern to form a modulated refractive index grating in the bulk glass.
• Providing the photosensitive bulk glass preferably includes providing an alkali boro- alumino-silicate glass.
• the provided bulk glass body preferably is homogeneous in composition and refractive index and does not have separate core/cladding regions.
• Providing the photosensitive bulk glass includes providing a non-sintered glass, with the glass being a melted glass.
• the glass is a melted glass with a melting temperature ⁇ 1650°C. More preferably the melting temperature of the bulk glass ⁇ 1600°C, more preferred ⁇ 1550°C, and most preferred ⁇ 1500°C.
• Providing the photosensitive bulk glass includes providing an alkali boro-alumino-silicate glass batch and melting the glass batch to form an alkali boro-alumino-silicate glass melt.
• the method includes cooling the glass melt into the bulk glass.
• melting includes containing the glass melt in a heated glassy fluid state and forming the glass melt into a coolable body, such as delivering the glass melt through an orifice and to a cooling site.
• the provided bulk glass is a molecular hydrogen loadable bulk glass.
• the method includes providing a melted bulk glass and loading the bulk glass with at least 10 18 H 2 molecules/cm 3 .
• loading the bulk glass includes loading with at least 10 19 H 2 molecules/cm 3 , and more preferably at least 2 x 10 19 H molecules/cm 3 .
• Loading the bulk glass is performed with a molecular hydrogen loading temperature ⁇ 300°C.
• the hydrogen loading temperature ⁇ 250°C, more preferably ⁇ 200°C, and most preferably ⁇ 150°C.
• a hydrogen load atmosphere of at least 2 atmospheres of hydrogen are used, and most preferably at least 100 atmospheres of H 2 is utilized to dope the bulk glass.
• Such loading can be achieved in high temperature vessels that contain the H 2 gas and the bulk glass.
• the bulk glass body has a glass body physical size with glass volume and surface area to provide efficient loading of the hydrogen, preferably with the bulk glass body being a near net shape of the preform and optical device it is made into.
• the bulk glass is exposed to the H 2 gas pressurized atmosphere for a H loading time sufficient and effective such that the center of the bulk glass body has a molecular hydrogen concentration that is at least 90% of the ambient H loading atmosphere.
• Exposing the photosensitive bulk glass preferably includes exposing the glass to form a pattern by inducing a refractive index ⁇ n >10 "5 , and most preferably ⁇ n >10 "4 .
• the invention includes a method of making a molecular hydrogen loadable photosensitive glass optical device preform.
• the method of making the preform includes providing a germania silica glass batch with a transition metal contamination level ⁇ lppm by weight for transition metals and a heavy metal contamination level ⁇ lppm by weight for heavy metals.
• the method includes melting the silica glass batch to form a homogeneous glass melt, cooling the glass melt into a UV transmitting bulk glass having a 250nm absorption less than 20 dB/cm and forming the bulk glass into an optical device preform.
• Forming the bulk glass into an optical device preform preferably includes loading the bulk glass with molecular hydrogen to a level of at least 10 18 H molecules/cm 3 , and more preferably at least 10 19 H 2 molecules/cm 3 .
• Providing the germania silica glass batch includes providing an alkali boro-alumino- silicate glass batch and melting the glass batch at a melting temperature ⁇ l 650°C.
• melting comprises melting at ⁇ 1600°C, more preferably ⁇ 1550°C, and most preferably ⁇ 1500°C.
• the method of making preferably includes pouring the glass melt to form bulk glass bodies, and more preferably includes delivering the glass melt through a glass forming orifice.
• Making the bulk glass preforms preferably includes forming a preform glass body bulk with a smallest size dimension that is greater than 5 ⁇ m.
• the invention further includes a photosensitive glass optical refractive index pattern preform for use with UV light in the formation of refractive index patterns.
• the inventive preform is comprised of an alkali boro-alumino-silicate glass with a 250nm absorption less than 20 dB/cm.
• the preform has a below 250nm UV wavelength inducable modulated refractive index ⁇ n level >10 "5 with the bulk glass exhibiting photosensitivity as a consequence of exposure to light of 250nm or less with a molecular hydrogen level of at least 10 18 H 2 molecules/cm 3 .
• the refractive index pattern preform has a UV wavelength inducable modulated refractive index ⁇ n level >10 "4 with a molecular hydrogen level of at least 10 19 H 2 molecules/cm 3 .
• the bulk glass preform has a 250nm absorption less than 15 dB/cm, more preferably less than 10 dB/cm, and most preferred less than 5 dB/cm.
• the alkali boro-alumino-silicate glass preform is a non-sintered glass body formed by a melting process to result in a melted glass.
• the invention includes a large UV-induced refractive index change in a melted alkali- alumino-boro-germano-silicate composition that has been loaded with molecular hydrogen.
• the UV exposures utilized include CW 244-nm light and a pulsed KrF excimer laser at 248- nm.
• a modulated refractive index of the order of 2-3 x 10 "4 has been measured in the bulk glass. It is believed that the ability to load with molecular hydrogen, and the photoreaction, depends on the composition of the glass.
• the UV spectroscopy of the bulk glass before and after exposure, as well as the magnitude of the induced refractive index correlates well with the growth of the OH absorption as measured in the IR (OH stretching vibrations).
• a Bragg grating was made in a bulk glass sample (Glass 5g, Glass Composition Table) by exposing through a phase mask from the top face, with a measured transmission and reflectivity as shown.
• the invention utilizes various constituents to make the glass softer and lower the melting temperature. This includes using constituents like ' alkali, alumina and boron to lower the melting temperature and to decrease the viscosity.
• the glass batch melting temperature is lowered by using a sufficient amount of a fluoride of the glass components to lower the melting temperature.
• a fluoride of the glass components For example with Glass 4b (Glass Composition Table) aluminum fluoride is utilized with a F batch composition of about 3.3 wt. %.
• the batch composition melting temperature is lowered with a batch composition incorporating of fluorine at a batch wt. % of ⁇ 4 wt. % F. The lowering of the melting temperature is done in such a way as not to move the fundamental absorption beyond 248-nm (5-eV).
• the fundamental absorption edge of pure silica is determined by the transition from the band consisting of the overlapping 2p oxygen orbitals (valence band) to the band made up from the sp 3 non-bonding orbitals of the silicon (conduction band).
• valence band the band consisting of the overlapping 2p oxygen orbitals
• conduction band the band made up from the sp 3 non-bonding orbitals of the silicon
• alkali introduces another set of levels associated with the non-bridging oxygen. When the concentration is high enough, a new band appears above that of the original valence band, thus moving the fundamental absorption edge to longer wavelengths.
• the addition of the network substitution ions such as boron, aluminum, and germanium has much less influence on the absorption edge.
• Impurities such as the transition metal ions or heavy metal ions that are inadvertently incorporated into the glass, either from the batch materials, the containment crucible, the furnace or forming, must be kept to the ⁇ lppm level. These ions, even in small amounts have a dramatic adverse effect on the UV-absorption edge.
• the invention includes making a SiO 2 -GeO 2 bulk glass that can be melted and formed in a conventional batch way by limiting the additional constituents sufficiently so as to maintain high transparency at 248-nm, and yet achieve melting at a reasonable temperature (1500°C) and a softening temperature of approximately of 600°C (softening temperature below 700°C preferred).
• Glasses were made from pure starting materials, in particular low iron content sand. They were melted in clean platinum crucibles at 1550°C for 16 hours. In the initial sampling procedure, the glass was poured into patties and annealed. Subsequently, the quality of the glass was improved in terms of (striae) defects and cords by using semi-continuous melting where the glass is not poured from a melt crucible which is the source of much of the striae, but delivered through an orifice.
• the hydrogen loading was done in a Parr tm pressurized reactor using 150°C loading temperature at 100 atm pressure.
• the IR spectroscopy was done with aNicolet tm FTIR spectrometer.
• the effect on the absorption spectrum with change in GeO 2 content for alkali- alumino-borosilicate glass family of R 2 O (3-4 mole %), Al 2 O 3 (3-4 mole %), B 2 O 3 (25-35 mole %), GeO 2 (2.5-15 mole %), and SiO 2 (66.5-42 mole %) is shown in FIG. 1. In all cases we were able to maintain high transmittance at a below 250 nm wavelength of 248-nm which was to be the UV exposure excitation wavelength.
• UV-induced photosensitivity we hydrogen loaded 0.5-mm thick bulk glass samples. We then exposed them through a chrome absorption mask with a 1 O ⁇ m grating pitch.
• the UV exposure source was a KrF excimer laser operating at 248-nm.
• the peak fluence was from 20-60 mJ/cm 2 /pulse at 50Hz for periods of time running from 5- 120 min.
• the sample was illuminated by a spatially filtered He-Ne laser and the diffraction efficiency of the induced phase grating was measured from the ratio of the intensity of the 1 st to 0 th order. As long as the diffraction efficiency is relatively weak one can use the following simple formula for the efficiency.
• L is the grating index
• ⁇ is the period of the index pattern.
• the range of measured values of the induced refractive index after a fixed 248-nm UV exposure was from 1 x 10 "4 to 3 x 10 "4 for the inventive alkali-alumino-borosilicate glasses.
• the induced modulated refractive index as a function of the exposure time at fixed fluence is shown in FIG. 2a.
• FIG. 2b shows the measured induced index as a function of fluence at fixed time. The latter is well represented by using the square of the fluence.
• a set of glasses with fixed germania content was loaded with H 2 and UV exposed at 248-nm.
• the Glass Composition Table gives the composition, relative amounts of H 2 incorporated and the 248-nm excimer laser induced refractive index change for the set.
• the thermal stability of the induced refractive index change was investigated by heating a sample having a grating and re-measuring the grating efficiency with time at temperature. The change with time after heating to 400 degrees is shown in FIG. 3.
• FIG. 4 shows the relationship of the increase in hydroxyl concentration (measured from the OH stretching vibration; see inset) with the induced refractive index also as shown in FIG. 5. There is also a large change in UV absorption after exposure.
• FIG. 7 shows the refractive index pattern grating formed in the bulk glass preform glass block.
• FIG. 7a is a cross section showing the refractive index pattern grating in the bulk glass preform glass block.
• Glass 4b of the Composition Table is the preferred composition of the invention.
• the weight percent batch composition was 35.8 wt. % SiO 2 , 21.5 wt. % GeO 2 , 4.48 wt. %, Al 2 O 3 , 3.38 wt. % F, 1.31 wt. % Li 2 O, and 33.5 wt.% B 2 O 3 .
• the batch material powders were ball milled to provide a homogeneous batch mix.
• high purity silica sand powder such as IOTA-6 brand SiO 2 from the Unimin
• high purity aluminum oxide powder such as Gamma brand aluminum oxide 99.999% from Alfa Aesar, A Johnson Mathey Company, Ward Hill, Ma 01835, was utilized with the 99.999% purity.
• high purity aluminum fluoride was also used, such as Alufluor brand aluminum fluoride from LidoChem,
• Li 2 CO 3 brand from FMC Corporation, Lithium Div., Gastonia, NC 28054, with a 99% + purity, with a Fe 2 O 3 wt. ⁇ .004 and a Cl wt. % ⁇ .01.
• lithium nitrate crystal was used, such as available from VWR Scientific, Rochester, NY 14603.
• boric oxide was used, such as Hi purity brand
• Bulk glass bodies 110 were made with a general dimension of 1.5 x 4 x 4 inches (3.81 x 10.16 x 10.16 cm) and annealed at 414°C. The annealed bulk glass bodies 110 were cut, finished, and polished to provide smaller bulk glass bodies 120 having a rectangular block shape. Bulk glass bodies 120 had a dimension of 5x5x3 mm 3 . As shown in FIG. 9, bulk glass bodies 120 were loaded with molecular hydrogen (H 2 ) in a hydrogen pressure vessel 200 using a hydrogen atmosphere 210 of about 100 atmospheres to provide H 2 loaded bulk glass body preforms 120.
• H 2 molecular hydrogen

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