WO2001023923A1 - Densification profonde induite de maniere interne par un laser uv dans des verres de silice - Google Patents

Densification profonde induite de maniere interne par un laser uv dans des verres de silice Download PDF

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Publication number
WO2001023923A1
WO2001023923A1 PCT/US2000/026939 US0026939W WO0123923A1 WO 2001023923 A1 WO2001023923 A1 WO 2001023923A1 US 0026939 W US0026939 W US 0026939W WO 0123923 A1 WO0123923 A1 WO 0123923A1
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Prior art keywords
glass
silica
refractive index
core
laser
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PCT/US2000/026939
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English (en)
Inventor
Nicholas F. Borrelli
Douglas C. Allan
Charlene M. Smith
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Corning Incorporated
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Priority to AU79893/00A priority Critical patent/AU7989300A/en
Priority to KR1020027004133A priority patent/KR20020038786A/ko
Priority to JP2001527251A priority patent/JP2003510656A/ja
Priority to EP00970526A priority patent/EP1266249A4/fr
Publication of WO2001023923A1 publication Critical patent/WO2001023923A1/fr

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    • 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
    • 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
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • 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
    • G02B2006/12083—Constructional arrangements
    • G02B2006/121—Channel; buried or the like
    • 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
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12107—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
    • G02B6/10—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
    • G02B6/10—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
    • G02B2006/12159—Interferometer

Definitions

  • the present invention relates to methods for efficiently forming optical devices in glass utilizing deep UV light ( ⁇ 300nm). Specifically, the invention relates to direct- write methods of forming light guiding structures in glass compositions through light- induced refractive index changes. The invention also relates to the optical devices made by the direct-write methods. The invention also relates to bulk glass substrate bodies in which densifled waveguides can be directly and efficiently written. Optical devices such as optical waveguides and Bragg diffraction gratings are widely known in the telecommunications field. In an optical waveguide, a higher refractive index core surrounded by a lower refractive index cladding guides light and can transmit a large amount of optical information over long distances with little signal attenuation.
  • the optical waveguide fiber is the prototype device of this type.
  • the fiber is produced by a method that, by virtue of its fabrication from different material core glasses and different material cladding glass with high and low refractive indexes, gives the proper waveguiding structure.
  • a Bragg grating is another type of an optical device that can be used to filter and isolate a narrow band of wavelengths from a broader signal.
  • the most common materials used commercially in telecommunications applications of light guiding devices are doped silica-based compositions such as germania doped silica core and pure dry hydroxyl-free silica clad.
  • laser sources can be used to effect both index changes and to produce physical damage in glass.
  • the use of a pulsed UV radiation laser source for writing Bragg gratings in germania doped silica core fibers is known.
  • a "direct- write" laser method of forming optical waveguides within a glass volume that is transparent to the wavelength of a femtosecond laser has been disclosed.
  • a 120 fs ⁇ pulsed 810-nm laser is focused within a polished piece of silica as the glass is translated perpendicular to the incident beam through the focus.
  • Increases in refractive index on the order of 10 " were reported for a specific condition in which the focus was scanned ten times over the exposed area.
  • Another problem in direct write methods of making optical structures relates to the trade-off between the dimensional stability of the writing device, e.g.. the laser, and the energy necessary to induce the desired refractive index change in the substrate material.
  • Silica-germania is often used as a material whose index can be altered with light.
  • H 2 -loading is typically employed as a method to increase the response of the glass.
  • the mechanism of index increase is by color center formation mechanism, through the Kramer-Kronig relationship.
  • the use of H 2 -loading introduces logistical issues, including time required to load with H 2 . for bulk materials, in particular, the time to impregnate H 2 at a temperature low enough that the H 2 does not react with the material, becomes prohibitively long. For example, a 3-mm thick piece of a silicate glass takes 36 days to load at 150°C. Once having gotten the H into the material, the storage of pieces containing H 2 becomes an issue, although for bulk material this is less of an issue.
  • the inventive utilization of the densification mechanism yields a feature that needs no thermal treatment for "fixing” and is generally more thermally robust in that features remain in the piece even at several hundred degrees, while providing writing deep into the interior of glass bodies that have depths from their surface that can be greater than 2 cm.
  • a focussed deep UV ( ⁇ 300 nm) laser beam is translated through the interior of a large dimension glass body to form densified glass waveguiding core structures through the glass interior with the densified glass waveguiding core structures able to traverse the glass body in three dimensions in multiple directions, through multiple planes and to multiple exterior surfaces of the glass body.
  • the inventive method includes internal direct write densification formation of waveguide cores within large glass bodies that have depths from the glass surface to the glass body interior of at least 1 cm, preferably at least 2 cm, preferably at least 3 cm, and most preferably at least 4 cm.
  • the invention includes making optical waveguide devices in three dimensional glass bodies with direct written densified waveguide cores with interior non-surface corepath parts that are at least 1 cm, preferably at least 2 cm, preferably at least 3 cm, and most preferably at least 4 cm away from the exterior surfaces of the glass body.
  • soft silica-based materials exhibit increased sensitivity to laser writing of optical structures in the bulk.
  • a method is provided to directly write light guiding structures in glass using lasers with substantially no physical damage of the glass.
  • a method is provided to write three dimensional optical structures in silica-based bulk glass.
  • the invention provides for translating the refractive index-increasing focus of a laser through a silica-based substrate in the x, y, and z-dimensions.
  • a variety of optical devices are disclosed which incorporate optical structures made by the methods described herein.
  • the invention includes selectively densifying traced internal volume regions within a larger bulk volume of a soft (annealing point ⁇ 1350°K) silica glass with a ⁇ 300 nm deep UV laser beam focus to form densified optical waveguide core tunnels.
  • FIG. 1(A) and FIG. 1(B) show the positioning of the incident laser beam relative to the scan direction in the top-write and axial-write orientations, respectively.
  • FIG. 2(A) and FIG. 2(B) show the scanning beam profile and a waveguides cross-sectional shape in the top-write and axial orientations, respectively.
  • FIG. 3(A) and FIG. 3(B) are perspective views of the top-write arrangement of directly writing three dimensional optical devices in bulk glass.
  • FIG. 4 shows densification as a function of exposure for glasses exposed to laser radiation (y-axis DENSIFICATION) (x-axis DOSE)
  • FIG. 5 shows the vacuum UV transmittance vs. wavelength for glasses used in the invention.
  • FIG. 6 is a plot of the 193 nm excimer laser induced ⁇ P/P vs. DOSE for silica glasses in accordance with the invention.
  • FIG. 6A is an enlargement of part of FIG. 6.
  • FIG. 7 is a plot of densification (natural log of prefactor a) vs. softness of the glass (reciprocal of the annealing point).
  • FIG. 8 is a scheme for less than 300nm laser exposure.
  • FIG. 9(A)-(E) show optical devices made in accordance with the invention.
  • the direct- write method of forming light guiding structures in a soft silica glass bulk substrate includes the steps of selecting a substrate made from a silica-based material in which the light guiding structure is to the written, focusing a ⁇ 300 nm UV laser beam to a focus at an internal position within the substrate effective to densify the focused-on material and translating the substrate and focus with respect to one another to form a scanned path light guiding structure within the substrate along the densified glass scan path.
  • the ⁇ ⁇ 300 nm laser beam selectively densified scan path within the glass body has an increased refractive index that is cladded by the surrounding lower original refractive index of the un-densified glass that has not been focused-on.
  • the densifying of the glass is preferentially produced through two-photon absorption and is dependent on the square of the intensity of the focused laser beam.
  • Focusing of the laser beam significantly increases the peak intensity of the beam compared to an unfocused beam.
  • the high intensity of the focused beam densifies the glass and induces an increase in the refractive index of the glass along the densified glass path traced by the beam focus as it is translated through the silica glass sample.
  • the resulting path region of increased refractive index densified glass can guide light and therefore can function as an optical waveguide path cladded by its surrounding undensified neighbor glass.
  • top densification writing results from translating the sample in a direction 13 that is substantially perpendicular to the densifying incident beam, as shown in FIG. 1(A).
  • An “axial writing” method results from translating the sample in a scan direction 13 that is substantially parallel to the incident beam, as shown in FIG. 1(B).
  • top- writing may also be accomplished by translating the sample in just the x-direction, just the y-direction, or both the x-direction and y-direction simultaneously.
  • a generally ellipsoid a cross-section of the waveguide may be formed.
  • axially- written waveguides are generally preferred in order to produce waveguides having substantially circular cross-sections.
  • Top-writing may be desired in order to write continuous linear waveguides longer than the focal length of the focusing lens. The ability to write three-dimensional waveguides in a sample using the present direct-write method is described further with reference to FIG. 3(A) and 3(B).
  • the laser beam 2 can be focused by a lens 5 to a focus 3 positioned within glass sample 4.
  • x and yi may be the same as x 2 and y 2 , respectively, yi and zi may be the same as y 2 and z , respectively, or xj and zi may be the same as x 2 and z 2 , respectively.
  • the laser can be any device capable of generating an appropriate powerful UV ⁇ 300-nm laser beam. Examples of useful lasers are described in the examples that follow.
  • the UV ⁇ ⁇ 300 nm laser beam is characterized by several beam parameters.
  • an excimer laser is used.
  • the laser used preferably has a pulse duration greater than 5 nanoseconds.
  • Excimer lasers are pulsed sources with pulse duration between 15 and 60 nsec.
  • the unfocused pulse energy per pulse fluences of the excimer laser for the application can be in the range of 2 to 100 mJ/cm with this pulse fluence increased by focusing of the laser beam.
  • an excimer laser with a wavelength less than 300 nm is utilized such as a KrF or ArF excimer laser.
  • the densifying laser can be non-excimer lasers which produce below 300 nm wavelength and appropriate intensities.
  • excimer laser sources include solid state lasers, such as Nd YAG and YLF, Ti sapphire based solid state lasers.
  • the UV ⁇ ⁇ 300 nm laser beam intensity and profile preferably provides by focusing (preferably with a lens) a glass densifying focus with focused intensity > 10 mJ/cir ⁇ when measured at a 10 micron beam diameter.
  • the glass densifying focus has an intensity > 50 mJ/cm 2 and most preferably > 100 mJ/cm 2 at a measured 10 micron beam diameter.
  • An appropriate UV ⁇ ⁇ 300 nm laser used to internally densify the soft silica glass material has a focusable laser beam output with a densifying fluence which is focusable to a glass densifying focus with a large dimensions of about 10 microns (10 ⁇ 5 microns) and an intensity in the range from 10 mJ to 150 mJ/cm 2 .
  • a ⁇ ⁇ 300 nm glass densifying focus is utilized to internally densify write areas in the glass with the bulk glass having an internal transmission at the below 300 nm ⁇ that is > 70%/cm, preferably > 90%/cm, preferably > 95%/cm and most preferably > 98%/cm.
  • the focussed deep UV laser beam wavelengths are above 220nm. and preferably in the range of about 220nm to 250nm.
  • germania- free silica is the soft silica bulk glass substrate (undoped high purity fused silica or doped with nongermania softening dopants) written in with the focus
  • the focussed deep UV laser beam wavelengths are above 180nm, and preferably in the range of about 180nm to 220nm.
  • the glass densifying focus has an intensity which efficiently densifies the glass but is not so intense that voids are formed in the focus exposed glass. Such a densifying focus less than a high intensity micro-channeling avoids physical damage to the glass and inhibits laser induced break down of the glass such as evidenced by void formation.
  • the glass densifying laser focus could be moved relative to a fixed sample, or both the densifying laser focus and sample could be moved simultaneously with respect to a fixed reference point to achieve the desired relative translation speed between the sample and the pattern forming focus.
  • Preferably translating the focus relative to the substrate along a scan path at a scan speed effective to induce an increase in the density of the material along the scan path relative to that of the unexposed material while incurring substantially no laser induced breakdown of the material along the scan path includes using a scan speed in the range of about 1 micron to 1 mm per second.
  • the invention is not limited to such regular solid substrate geometries. Rather, the invention can be used to direct-write optical waveguides in virtually any regular-or irregular-shaped three-dimensional sample. It is preferred, however, that the sample be positioned relative to the incident laser beam such that the beam is substantially perpendicular to the surface of the sample through which the incident beam passes.
  • the substrate is a three-dimensional shape compared to a thin film layer.
  • the substrate has a thickness that is several times thicker than the path thickness, preferably at least hundred times, more preferably at least five hundred times , and most preferably at least 1,000 times.
  • composition of the substrates in which the light guiding structures may be written by the invention are silica-based materials, including undoped fused silica and doped binary and ternary silica systems.
  • Silica-based materials are preferred in light of their various desirable optical properties as well as their widespread use in telecommunication device applications.
  • Binary and ternary silica systems are often preferred for use in the present invention.
  • Binary and ternary silica based materials are preferred because of their enhanced sensitivity to densification.
  • silica-based materials glass compositions that include silica and which are essentially free of alkali, alkaline earth, and transition metal elements, as well as other impurities which would cause absorption in the 1300 - 1600 nm range. If present at all, such impurities will typically not be found in the silica-based materials used in this invention at levels higher than 10 ppb (parts per billion).
  • waveguides can be written more easily in bulk substrates made from soft silica-based compositions than in hard silica-based materials without sacrificing the magnitude of the induced index change.
  • Soft silica-based compositions appear to be more sensitive to direct writing of light guiding structures using excimer lasers than hard silica-based composition glasses.
  • "soft" silica-based materials are defined as doped or undoped silica-based materials having an annealing point less than that of a germania doped glass composition of 5 mol.% Ge0 2 - 95 mol.% SiO , i.e., and preferably the silica-based materials have an annealing point less than about 1380°K.
  • the preferred silica-based glasses are undoped and doped binary or ternary silica-based materials having an annealing point less than about 1380°K, more preferably less than about 1350°K, and most preferably within the range of about 900°K to about 1325°K.
  • the annealing point is defined as the temperature at which the viscosity of the material is 10 13 6 poise.
  • Undoped silica-based materials include, for example, commercial grade fused silica, such as Corning Incorporated 's HPFS R type high purity fused silica 7980 glass, which can have an annealing point in the range of about 1261°K to about 1323°K.
  • the soft high purity fused silica glass utilized in the invention is a non-dry high purity fused silica with an OH content >50ppm by wt., more preferably >100ppm, more preferably >200ppm, and most preferably >500ppm.
  • the preferred dopants which may be used to soften silica include oxides of the elements boron, phosphorous, aluminum, and germanium, such as borate (B O 3 ), phosphate (P O 5 ), alumina (Al 2 O 3 ), and germania (GeO 2 ), respectively. Any desired concentration of dopant can be used.
  • the borate content may comprise up to 20 wt.% or more borate.
  • the binary glass system is in the composition range from 9 wt.% B 2 O 3 -91 wt.% SiO 2 to 20 wt.% B 2 O 3 -80 wt.% SiO 2 .
  • the annealing point of the 9 wt.% B 2 O 3 -9I wt.% SiO 2 composition is about 1073°K.
  • the annealing point of the 20 wt.% B 2 O 3 -80 wt.% SiO 2 composition is about 999°K.
  • the phosphate content may also comprise up to 20 wt.% or more phosphate, with a preferred range of about 7 to 20 wt. %.
  • the binary glass system is in the composition range from 10 wt.% P 2 O 5 -9O wt.% SiO 2 to 7 wt.% P 2 O 5 -93 wt.% SiO 2 .
  • the annealing point of the 7 wt.% P 2 O 5 -93 wt.% Si0 2 composition is about 1231°K.
  • the alumina content comprise up to 20 wt.% or more alumina, with a preferred range of about 10 to 20 wt. %.
  • the binary glass systems 10 wt.% Al 2 ⁇ 3 -90 wt.% SiO 2 may be used.
  • the germania content may comprise up to about 22 wt.% or more germania, with a preferred range of about 15 to 25 wt. %.
  • the binary glass systems are in the composition range from 20 wt.% GeO 2 -80 wt.%) SiO 2 to 22 wt.% Ge0 2 -78 wt.% SiO 2 may be used.
  • the annealing point of the 20 wt.% GeO 2 -80 wt.% SiO 2 composition is about 1323°K while that of the 22 wt.% Ge0 2 -78 wt.% SiO 2 composition is about 131 1°K.
  • An alternative range contains from 14% to 9% germania.
  • the binary composition range from 9% to 22% germania.
  • germanium doped glasses can be used, it is not necessary to use germanium.
  • the invention can be used in silica glass free of germanium.
  • the soft silica glass is substantially free of Ge.
  • Hard silica-based materials are defined as doped or undoped silica-based materials having an annealing point higher than that of the 5 mol.% GeO 2 - 95 mol.% SiO 2 glass system, i.e., higher than about 1380°K.
  • hard silica-based materials include dry fused silica which has an annealing point of about 1425°K.
  • dry fused silica has virtually no residual hydro xyl groups, while commercial grade fused silica such as Corning HPFS R silica may have higher levels, for example, >200 ppm by wt. hydroxyl groups, and >800 ppm.
  • the silica-based materials used in this invention are preferably made by a flame hydrolysis process.
  • silicon-containing gas molecules are reacted in a flame to form SiO 2 soot particles. These particles are deposited on the hot surface of a rotating body that consolidate into a very viscous fluid which is later cooled to the glassy (solid) state.
  • glass making procedures of this type are known as vapor phase hydrolysis/oxidation processes or simply as flame hydrolysis processes.
  • other known processes can be used.
  • the silica based materials are produced by a single step direct deposition and consolidation process. In an alternative the glass is made by deposition and later consolidation.
  • densification a density change
  • the glass Upon treatment with the laser, the glass is denser with a concomitant higher refractive index. Density change can be induced through exposure to, for example. 248 nm and 193 nm, excimer laser pulses.
  • the pulse duration can be 5 to 30 nanoseconds, preferably 20-30ns, while the un-focused pulse energy is at least 10-100 mJ/cm 2 .
  • the densification by a focused laser beam inside the glass substrate body is utilized to write patterns into the glass and form waveguiding paths.
  • Especially useful silica glasses to be exposed are those discussed above that maintain a high degree of transparency, especially in the deep uv. This is because, for excimer exposure, the sample should be substantially transparent at least 70% to
  • the preferred densification mechanism is a two photon process with the two photon absorption rate increasing with decreasing wavelength, the best soft silica glasses are those that transmit to the shortest wavelength.
  • Tg any other measure of the viscosity versus temperature behavior, such as the annealing or softening temperature, the more sensitive the glass is to induced changes as manifested by refractive index.
  • Polished silica glass substrate bulk samples were exposed to excimer laser radiation through an aperture, with the experimental arrangement described in D.C.
  • the laser used for the 193nm and 248 nm exposures was a Lumonics 600.
  • the energy through the aperture was monitored with a Molectron thermal detector.
  • the optical phase induced by the exposure was measured interferometrically using a ZYGO Mark-IV instrument. From the measured optical phase shift the "unconstrained" densification ⁇ p/p was obtained with the aid of a finite-element model.
  • the use of unconstrained densification as the metric for the densification process takes into account the sample geometry and the spatial aspects of the exposure beam. The nature of the model and its utilization is fully explained in Allan, et al., SPIE Vol. 3578, 16
  • the finite element model accounts for the elastic response of the glass when the exposed region shrinks under densification. and allows for integrating the photoelastic response of the exposed and unexposed regions.
  • the glasses in Table 1 were exposed to 193-nm excimer laser to induce densification.
  • Table 1 there is shown the unconstrained densification for an exposure of 1 OmJ/cm for 10 pulses with a pulse duration of 30ns. The value of the induced refractive index is obtained by multiplying the densification by roughly 0.4.
  • FIG. 4 The actual development of the densification as a function of exposure is shown in FIG. 4 for the three samples.
  • the x-axis is Dose and the y-axis densification.
  • the progression of increased refractive index change from undoped silica to silica-germania to silica-boron for the excimer laser-induced refractive index change strongly suggests the softness of the glass as a key parameter in the amount of index change that can be obtained.
  • the germania glass is considerably softer than the undoped silica, while the boron glass is considerably softer than the germania glass.
  • ⁇ is the viscosity
  • ⁇ is ⁇ n/n expressed as a percent.
  • ⁇ is 1%, so the silica-germania glass is considerably softer than silica.
  • boron the effect is even more dramatic.
  • a composition of 10mol% B 2 O 3 /SiO has a softening point about 300 degrees less than silica.
  • Other binary systems that would lead to softer glasses include the oxides of phosphorous and aluminum. For example, P 2 O 5 /Si ⁇ 2 . again at 10 mol% P O 5 would have a lower softening temperature by 500 degrees.
  • the glass preferably should include a softening component, such as boron.
  • the magnitude of the change is in proportion to the effect of the doped component on softening point.
  • the invention preferably includes softening a silica glass with softening dopants.
  • the glass and the waveguide fabrication method By proper choice of the exposure wavelength, the glass and the waveguide fabrication method, one can maximize the densification contribution to the induced refractive index, and provide a thermally stable waveguide structure.
  • the densification rate in silica glass obtained by using a 193nm excimer laser, instead of 248 nm, has been found to be much faster, perhaps by a factor of 5-10. For example, one could achieve an index change of 10 "4 at 193nm with 330mJ/cm "2 pulses at 100Hz in only 16 minutes.
  • the densification rate for all the glasses is also found to be a strong function of the excimer laser wavelength in the order 193nm>248nm.
  • the glasses below were obtained by flame hydrolysis. Corning HPFS ® silica is deposited directly from flame and concurrently consolidated with an SiO 2 direct soot one step deposition/consolidation.
  • HPFS ® high purity fused silica is denoted by HPFS.
  • the other glasses were prepared by a soot deposition then a subsequent consolidation into a glass body.
  • a porous soot blank is formed from the flame hydrolysis of a metal precursor.
  • the porous soot blank is then consolidated in a drying atmosphere. Formation of undoped fused silica by this two step process results in a much lower residual OH concentration than HPFS ® silica.
  • the lower OH content influences both the optical transmittance below 170-nm as well as the anneal point of the undoped fused silica.
  • the binary glasses were also prepared by the two-step process where precursors for the various metals (B, P, Ge) were hydrolyzed along with the silica precursor to form a doped porous soot blank which was then consolidated.
  • Vacuum UV transmittance spectra of the various silica-based glasses are shown in FIG. 5.
  • Unconstrained densification of the 193 nm exposed glasses is plotted against the dose, (F N/r ), in FIG. 6.
  • F is the fluence per pulse in mJ/cm
  • N is the number of pulses in millions
  • the power law fits used are shown in FIG. 6 for the 193nm laser induced densification.
  • the values of the prefactor a are listed in Table 3.
  • the rate of densification correlates with the "softness" of the glass. That is, the lower the viscosity of the glass at a given temperature, the faster the rate of ⁇ 300 nm laser-induced densification.
  • the measured anneal points of the glasses are found in Table 3.
  • the relationship between the laser-induced densification and the "softness" of the glass is shown in FIG. 7 where there is plotted ln(a) vs. the reciprocal of the anneal point.
  • Densification is represented by the value of the prefactor a in the equation with b fixed at 0.53.
  • the straight line fit suggests an activated process for the densification where the barrier to the structural rearrangement is 1.7 eV.
  • the actual mechanism of the structure rearrangement to give a more dense structure is not clear, however this result establishes that there is a kinetic factor in the densification mechanism.
  • germanium-doped silica densification behavior is significantly different from the other binary glasses discussed above.
  • the densification process is believed to be a two- photon initiated mechanism since the silica and boron doped and phosphorous doped materials exhibit low absorption at these wavelengths.
  • the germanium-doped glass densifies faster than would be predicted based solely on anneal point. From the VUV spectrum FIG. 5 it is also clear that the absorption of this glass C (20% GeO 2 silica) material at 193-nm is higher than the other binaries studied, suggesting that under 193- nm irradiation, the absorption process is linear. The observed anomalously high densification could then be explained by more efficient coupling of light into the glass with the consequence of increased excitation events that eventually lead to densification.
  • one major effect of prolonged deep UV irradiation of fused silica is densification.
  • This densification produces a corresponding refractive index change.
  • the induced refractive index change can for example be 0.0001, and has been found as high as 0.001.
  • This densification-induced refractive index can be used to write patterns and to make, for example, Bragg gratings and waveguide scan paths.
  • the exposure system of the invention has sufficiently high numerical aperture, roughly (D/2)/f in FIG. 8, to keep the densification localized to a small enough diameter, d.
  • This latter number should be the order of about lO ⁇ m ( ⁇ 5 ⁇ m).
  • the exposure levels should be in the range of >100mJ/cm for the order of 10 6 pulses. This provides beneficial densification and induces measurable index changes.
  • a single mode waveguide can be written inside a bulk silica glass substrate.
  • a single mode waveguide with a 5 micron radius at a wavelength of 633 nm can be written with a refractive index difference of 0.001.
  • An appropriate densification and induced refractive index change of boron doped soft silica glass Sample D of Table 3 can be induced by a dose of 7500 [(mJ/cm (M pulses/s)].
  • a 1 mJ output of a 193 nm excimer laser through a circular 5 mm aperture can be focused by a 200 mm lens to a 10 micron large dimension diameter and provide such a dose with 220,000 pulses. At a 220 Hz repetition rate the exposure would be for about 1000 seconds.
  • FIG. 9 Optical devices of the invention are shown in FIG. 9.
  • a wide variety of optical devices in bulk glass can be made using the presently described materials and methods, for example, an Y-coupler device as shown in FIG. 9(d).
  • the present invention can also be used to make a star coupler having central guide 22 surrounded by a plurality of peripheral guides 23, as shown in FIG. 9(a).
  • the invention can also be used to make a passive Mach-Zehnder coupler including a pair of Mach-Zehnder guides 26, as shown in FIG. 9(b).
  • An active Mach-Zehnder coupler including Mach-Zehnder guides 26 and a thermal (electrically heated) or other type activator 24, as shown in FIG. 9(c), is preferably made using this invention.
  • the present invention can also be used to make Bragg or other types of diffraction gratings in bulk glass, as shown in FIG. 9(d).
  • Waveguide 16 leads to grating lines 25.
  • FIG. 9(e) shows an optical device produced by the inventive method with the glass body having a first exterior side and a second exterior side, said first exterior side lying in a first plane, said second exterior side lying in a second plane, said second plane non-parallel to said first plane, wherein a waveguiding core tunnels from an input at the first exterior side to an output at the second exterior side.
  • the devices of FIG. 9 are produced with the inventive densification method with glass body having a planar exterior base side, wherein waveguiding cores tunnel in planes non-parallel to the planar base side.
  • FIG. 9 are produced with the inventive densification method by forming a first raised refractive index waveguiding core tunnel path, a second raised refractive index waveguiding core tunnel path, and a third raised refractive index waveguiding core tunnel path, wherein the third tunnel path is in a plane separate from the first tunnel path and the second tunnel path.
  • Making of the FIG. 9 devices includes forming a first raised refractive index waveguiding core tunnel path and an adjacent second raised refractive index waveguiding core tunnel path wherein guided light is coupled from said first core tunnel path to said second core tunnel path.
  • 9 devices includes forming a wavelength division multiplexer for multiplexing a plurality of optical wavelength channels by forming a plurality of waveguiding core tunnel inputs for separately inputting the plurality of optical wavelength channels, forming a multiplexing coupling region for multiplexing the inputted channels, and forming an output waveguiding core tunnel for outputting the multiplexed inputted channels.
  • Line spacings of 0.5 ⁇ m are possible using this invention.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Optical Integrated Circuits (AREA)
  • Glass Compositions (AREA)

Abstract

L'invention concerne un procédé d'écriture d'une structure (26) de guidage de lumière dans un substrat (4) en verre en vrac consistant à sélectionner un substrat (4) en verre en vrac obtenu à partir d'une matière molle à base de silice. Un faisceau laser à excimère (5) est focalisé à un point (3) de focalisation dans le substrat tandis que le foyer est déplacé par rapport au substrat le long du trajet de balayage. Le faisceau laser (5) est déplacé à une vitesse de balayage de manière à induire une augmentation de l'indice de réfraction de la matière le long du trajet par rapport à celui de la matière non exposée, alors qu'une quantité faible de laser provoque la décomposition de la matière le long du trajet de balayage. Différents dispositifs optiques, y compris les guides d'onde, peuvent être obtenus grâce à ce procédé.
PCT/US2000/026939 1999-09-30 2000-09-29 Densification profonde induite de maniere interne par un laser uv dans des verres de silice WO2001023923A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
AU79893/00A AU7989300A (en) 1999-09-30 2000-09-29 Deep uv laser internally induced densification in silica glasses
KR1020027004133A KR20020038786A (ko) 1999-09-30 2000-09-29 실리카 유리의 심층 ｕｖ 레이저 내부 유도 치밀화방법
JP2001527251A JP2003510656A (ja) 1999-09-30 2000-09-29 石英ガラスの深紫外レーザによる内部誘起緻密化
EP00970526A EP1266249A4 (fr) 1999-09-30 2000-09-29 Densification profonde induite de maniere interne par un laser uv dans des verres de silice

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US15673799P 1999-09-30 1999-09-30
US60/156,737 1999-09-30

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WO2001023923A1 true WO2001023923A1 (fr) 2001-04-05

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JP (1) JP2003510656A (fr)
KR (1) KR20020038786A (fr)
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AU (1) AU7989300A (fr)
TW (1) TW526342B (fr)
WO (1) WO2001023923A1 (fr)

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US6950591B2 (en) 2002-05-16 2005-09-27 Corning Incorporated Laser-written cladding for waveguide formations in glass
CN1321337C (zh) * 2002-04-25 2007-06-13 独立行政法人科学技术振兴机构 在玻璃内部形成分相区域的方法
US8547008B2 (en) 2006-01-12 2013-10-01 Ppg Industries Ohio, Inc. Material having laser induced light redirecting features
US8629610B2 (en) 2006-01-12 2014-01-14 Ppg Industries Ohio, Inc. Display panel

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US10992104B2 (en) 2015-12-17 2021-04-27 Ii-Vi Delaware, Inc. Dual layer grating coupler
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WO2019138821A1 (fr) * 2018-01-11 2019-07-18 住友電気工業株式会社 Dispositif optique et procédé de fabrication de dispositif optique
US10809456B2 (en) 2018-04-04 2020-10-20 Ii-Vi Delaware Inc. Adiabatically coupled photonic systems with fan-out interposer
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US11435522B2 (en) 2018-09-12 2022-09-06 Ii-Vi Delaware, Inc. Grating coupled laser for Si photonics
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CN113720443A (zh) * 2020-05-26 2021-11-30 深圳市大族数控科技股份有限公司 一种激光功率测试系统及测试方法

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CN1321337C (zh) * 2002-04-25 2007-06-13 独立行政法人科学技术振兴机构 在玻璃内部形成分相区域的方法
US6950591B2 (en) 2002-05-16 2005-09-27 Corning Incorporated Laser-written cladding for waveguide formations in glass
US8547008B2 (en) 2006-01-12 2013-10-01 Ppg Industries Ohio, Inc. Material having laser induced light redirecting features
US8629610B2 (en) 2006-01-12 2014-01-14 Ppg Industries Ohio, Inc. Display panel

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AU7989300A (en) 2001-04-30
CN1377470A (zh) 2002-10-30
JP2003510656A (ja) 2003-03-18
EP1266249A1 (fr) 2002-12-18
KR20020038786A (ko) 2002-05-23
TW526342B (en) 2003-04-01
EP1266249A4 (fr) 2003-07-16

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