Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
  • G02B1/045—Light guides
  • G02B1/046—Light guides characterised by the core material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
  • C08G65/002—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from unsaturated compounds
  • C08G65/005—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from unsaturated compounds containing halogens
  • C08G65/007—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from unsaturated compounds containing halogens containing fluorine
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
  • C08G65/02—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from cyclic ethers by opening of the heterocyclic ring
  • C08G65/32—Polymers modified by chemical after-treatment
  • C08G65/329—Polymers modified by chemical after-treatment with organic compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
  • C08G65/02—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from cyclic ethers by opening of the heterocyclic ring
  • C08G65/32—Polymers modified by chemical after-treatment
  • C08G65/329—Polymers modified by chemical after-treatment with organic compounds
  • C08G65/331—Polymers modified by chemical after-treatment with organic compounds containing oxygen
  • C08G65/332—Polymers modified by chemical after-treatment with organic compounds containing oxygen containing carboxyl groups, or halides, or esters thereof
  • C08G65/3322—Polymers modified by chemical after-treatment with organic compounds containing oxygen containing carboxyl groups, or halides, or esters thereof acyclic
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
  • C08G65/02—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from cyclic ethers by opening of the heterocyclic ring
  • C08G65/32—Polymers modified by chemical after-treatment
  • C08G65/329—Polymers modified by chemical after-treatment with organic compounds
  • C08G65/334—Polymers modified by chemical after-treatment with organic compounds containing sulfur
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
  • C08G65/02—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from cyclic ethers by opening of the heterocyclic ring
  • C08G65/32—Polymers modified by chemical after-treatment
  • C08G65/329—Polymers modified by chemical after-treatment with organic compounds
  • C08G65/335—Polymers modified by chemical after-treatment with organic compounds containing phosphorus
  • C08G65/3356—Polymers modified by chemical after-treatment with organic compounds containing phosphorus having nitrogen in addition to phosphorus
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G2650/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
  • C08G2650/02—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule characterized by the type of post-polymerisation functionalisation
  • C08G2650/20—Cross-linking
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G2650/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
  • C08G2650/28—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule characterised by the polymer type
  • C08G2650/46—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule characterised by the polymer type containing halogen
  • C08G2650/48—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule characterised by the polymer type containing halogen containing fluorine, e.g. perfluropolyethers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2312/00—Crosslinking

Definitions

• the present invention relates generally to polymeric materials, and more specifically to halogenated polymeric materials useful in the construction of devices for telecommunications.
• One preferred device for routing or guiding waves of optical frequencies from one point to another is an optical waveguide.
• the operation of an optical waveguide is based on the fact that when a light-transmissive medium is surrounded or otherwise bounded by an outer medium having a lower refractive index, light introduced along the axis ofthe inner medium substantially parallel to the boundary with the outer medium is highly reflected at the boundary, trapping the light in the light transmissive medium and thus producing a guiding effect along the longitudinal axis ofthe inner medium.
• a wide variety of optical devices can be made which incorporate such light guiding structures as the light transmissive elements.
• optical waveguides may support a single optical mode or multiple modes, depending on the dimensions ofthe inner light guiding region and the difference in refractive index between the inner medium and the surrounding outer medium.
• Optical waveguide devices and other optical interconnect devices may be constructed from organic polymeric materials. While optical devices built from planar waveguides made of glass are relatively unaffected by temperature, devices made from organic polymers may show a significant variation of properties with temperature.
• thermo-optic coefficient dn/dT
• thermally tunable or controllable devices incorporating light transmissive elements made from organic polymers.
• a thermally tunable device is a 1x2 switching element activated by the thermo-optic effect.
• light from an input waveguide may be switched between two output waveguides by the application of a thermal gradient induced by a resistive heater.
• the heating/cooling processes occur over the span of one to several milliseconds.
• the processes by which these waveguides have typically been made includes the use of a reactive ion etching process, which is cumbersome and can cause high waveguide loss due to scattering.
• deuteration is not an effective means of reducing loss in the 1550 nm wavelength range.
• Fluorinated polyimides and deuterated or fluorinated polymethacrylates have higher losses in the telecommunications window near 1550 nm, typically on the order of 0.6 dB/cm.
• O-H and N-H bonds also contribute strongly to loss at wavelengths near 1310 nm and 1550 nm. Consequently, compositions are sought in which the concentrations of O-H and N-H bonds are minimal.
• Photopolymers have been of particular interest for optical interconnect applications because they can be patterned using standard photolithographic techniques.
• Photolithography involves the selective polymerization of a layer ofthe photopolymer by exposure ofthe material to a pattern of actinic radiation. Material that is exposed to the actinic radiation is polymerized, whereas material that is not exposed remains unpolymerized.
• the patterned layer is developed, for example, by removal ofthe unexposed, unpolymerized material by an appropriate solvent.
• One aspect ofthe present invention relates to an energy curable composition including a compound having an aromatic or heteroaromatic moiety; at least two fluorinated alkylene, arylene or polyether moieties, each fluorinated alkylene, arylene or polyether moiety being linked to the aromatic or heteroaromatic moiety through an -O- or -S- linkage; and at least one ethylenically unsaturated moiety, each ethylenically unsaturated moiety being linked to one ofthe fluorinated alkylene, arylene or polyether moieties.
• Another aspect ofthe present invention relates to an energy curable composition
• a compound having an isocyanurate moiety including three fluorinated alkylene, arylene, or polyether moieties linked to the isocyanurate moiety at the nitrogens ofthe isocyanurate; and at least one ethylenically unsaturated moiety linked to one ofthe fluorinated alkylene, arylene, or polyether moieties.
• Another aspect ofthe present invention relates to a polymeric material, the polymeric material including a polymer or copolymer of an energy curable compound, the energy curable compound having an aromatic or heteroaromatic moiety; at least two fluorinated alkylene, arylene or polyether moieties, each fluorinated alkylene, arylene or polyether moiety being linked to the aromatic or heteroaromatic moiety through an -O- or -S- linkage; and at least one ethylenically unsaturated moiety, each ethylenically unsaturated moiety being linked to one ofthe fluorinated alkylene, arylene or polyether moieties.
• Another aspect ofthe present invention relates to a polymeric material, the polymeric material including a polymer or copolymer of an energy curable compound, the energy curable compound having an isocyanurate moiety; three fluorinated alkylene, arylene, or polyether moieties linked to the isocyanurate moiety at the nitrogens ofthe isocyanurate; and at least one ethylenically unsaturated moiety linked to one ofthe fluorinated alkylene, arylene, or polyether moieties.
• an optical element including a polymeric core, the polymeric core including a polymer or copolymer of an energy curable compound having an aromatic or heteroaromatic moiety; at least two fluorinated alkylene, arylene or polyether moieties, each fluorinated alkylene, arylene or polyether moiety being linked to the aromatic or heteroaromatic moiety through an -O- or -S- linkage; and at least one ethylenically unsaturated moiety, each ethylenically unsaturated moiety being linked to one ofthe fluorinated alkylene, arylene or polyether moieties.
• an optical element including a polymeric core, the polymeric core including a polymer or copolymer of an energy curable compound having an isocyanurate moiety, three fluorinated alkylene, arylene, or polyether moieties linked to the isocyanurate moiety at the nitrogens ofthe isocyanurate, and at least one ethylenically unsaturated moiety linked to one ofthe fluorinated alkylene, arylene, or polyether moieties.
• compositions and devices ofthe present invention result in a number of advantages over prior art compositions and devices.
• the compositions of the present invention have a very low optical loss at telecommunications wavelengths, making them suitable for the fabrication of planar waveguides and other optical devices.
• the compositions ofthe present invention can have a higher refractive index than analogous compositions not including aromatic or heteroaromatic moieties, making them useful in the tuning ofthe refractive indices ofthe different layers of an optical device.
• the compositions ofthe present invention may also have higher hydrolytic stability than analogous carboxylate ester-based compositions.
• FIG. 1 is a schematic diagram of a planar waveguide optical element ofthe present invention.
• an energy curable composition that may be cured to yield a polymeric material with a low optical loss at communications wavelengths.
• an energy curable composition is a composition which may be cured by at least one of heat and actinic radiation.
• an energy curable composition includes a compound having an aromatic or heteroaromatic moiety; two fluorinated alkylene, arylene or polyether moieties each linked to the aromatic or heteroaromatic moiety through an -O- or -S- linkage; and at least one ethylenically unsaturated moiety linked to one ofthe fluorinated alkylene, arylene or polyether moieties, h especially suitable compounds for use in the compositions ofthe present invention, the -O- or -S- linkages are bound directly to an aromatic atom ofthe aromatic or heteroaromatic moiety.
• Desirable compounds for use in the compositions ofthe present invention have an ethylenically unsaturated moiety linked to each ofthe fluorinated alkylene, arylene, or polyether moieties. Linkage directly to an aromatic atom is preferable to linkage through intervening methylene groups, as it allows for compounds having lower losses at telecommunications wavelengths. Preferably, the -O- or -S- linkage is not part of a carboxylate ester.
• the energy curable compositions ofthe current invention may include a compound having formula (I):
• R-(Y-CH 2 -Rf-CH 2 -O-E) n (I) wherein R is an aromatic or heteroaromatic moiety; Y is O or S; Rf includes a fluorinated alkylene moiety, a fluorinated arylene moiety, or a fluorinated polyether moiety; E is an ethylenically unsaturated moiety; and n is an integer between about 2 and about 10.
• -O- linked acrylates ofthe present invention may be synthesized in two steps from the corresponding aromatic or heteroaromatic halide and fluorinated alkylene or polyether diol according to the reaction scheme:
• the aromatic or heteroaromatic halide is reacted with the fluorinated alkylene or polyether diol and n equivalents of base to yield an -O- linlced alcohol.
• the -O- linlced alcohol is then capped with acrylate to give the -O- linked acrylate ofthe present invention.
• the -O- linlced alcohol may be capped with other ethylenically unsaturated moieties using methods familiar to the skilled artisan.
• the fluorinated alkylene, arylene or polyether diol is converted to a bis(tetrafluorobutanesulfonate), which is reacted with the alkali salt of a polyfunctional aromatic or heteroaromatic polythiol.
• the resulting -S- linked tetrafluorobutanesulfonate is saponified to give a -S- linked alcohol, which is capped with acrylate to give the -S- linked acrylate ofthe present invention.
• the -S- linked alcohol may be capped with other ethylenically unsaturated moieties using methods familiar to the skilled artisan.
• the aromatic or heteroaromatic moiety (R) may be any desired aromatic or heteroaromatic moiety.
• Desirable aromatic or heteroaromatic moieties for use in the present invention have a minimal number of hydrogen atoms.
• Especially desirable aromatic or heteroaromatic moieties have no hydrogen atoms at all.
• suitable aromatic moieties for use in the present invention include
• Suitable heteroaromatic moieties include
• each X is individually selected from the group consisting of H, D, F, CI, Br, alkyl, aryl, heteroaryl, alkoxy and aryloxy.
• a cyclotriphosphazene moiety is a cyclotriphosphazene moiety.
• -O- linlced cyclotriphosphazene compounds may be made, for example, by reacting hexachlorocyclotriphosphazene with a suitable diol and sodium hydride, as shown in the reaction scheme below.
• -S- linked cyclotriphosphazene compounds may be made, for example, by reacting hexachlorocyclotriphosphazene with a suitable dithiol and metallic sodium, as shown in the reaction scheme below.
• the -O- linked and -S- linlced alcohols can be capped with ethylenically unsaturated moieties using methods familiar to the skilled artisan.
• the aromatic or heteroaromatic moieties R are incorporated into the compounds ofthe present invention through their corresponding halides or sulfide salts.
• the aromatic moiety octafluorobiphenylene may be incorporated using decafluorobiphenyl.
• the heteroaromatic 1,3,5-triazine moiety may be incorporated using cyanuric chloride.
• a 1,5-thiadiazoyl moiety may be incorporated using dipotassium 1,5-dimercaptothiadiazole.
• energy curable compositions include a compound having an isocyanurate moiety, three fluorinated alkylene, arylene or polyether moieties linked to the isocyanurate moiety at the nitrogens ofthe isocyanurate, and at least one ethylenically unsaturated moiety linlced to one ofthe fluorinated alkylene, arylene or polyether moieties.
• Especially desirable compounds for use in the compositions ofthe present invention have ethylenically unsaturated moieties linked to each fluorinated alkylene, arylene, or polyether moiety.
• an energy curable composition ofthe present invention may include a compound having formula (II):
• Rf includes a fluorinated alkylene, arylene or polyether moiety and E is an ethylenically unsaturated moiety.
• isocyanurate alcohols may be synthesized from cyanuric acid and a fluorinated alkylene or polyether diol according to the reaction:
• the fluorinated moieties (Rf) may be any desired fluorinated alkylene or arylene moiety.
• Rf has the formula -(CF 2 ) X -, where x is between 1 and about 10.
• the fluorinated alkylene moiety is incorporated into the compounds of formulae (I) and (II) through the corresponding diol.
• 2,2,3,3,4,4,5,5- octafluorohexane-l,6-diol may be used to incorporate the fluorinated alkylene moiety - (CF ) 4 -.
• 2,2,3, 3,4,4,5,5,6,6,7,7-dodecafluorooctane-l,8-diol maybe used to incorporate the fluorinated alkylene moiety -(CF 2 ) 6 ⁇ .
• Rf has the formula -(C 6 F ) X -, where x is between 1 and about 10.
• 2,3,5, 6-tetrafluoroxylene- ⁇ , ⁇ '-diol maybe used to incorporate the fluorinated arylene moiety -(C 6 F 4 )- into the compounds of formula (I) and (II).
• other fluorinated diols may be used to provide different fluorinated alkylene or arylene moieties Rf.
• the fluorinated moieties ofthe compositions ofthe present invention may also be fluorinated polyethers.
• suitable fluorinated polyether Rf moieties for use in the present invention include:
• fluorinated polyethers are incorporated into the compounds of formula (I) of through the corresponding diol.
• fluorinated polyether diols ofthe formula HOCH 2 CF 2 O-[(CF 2 CF 2 O) m (CF 2 O) n ]-CF 2 CH 2 OH are available from Ausimont U.S.A. of Thorofare, NJ under the trade name FLUOROLINK.
• FLUOROLINK D has a molecular weight of about 2000 g/mol
• FLUOROLINK D10 has a molecular weight of about 1000 g/mol.
• Fluorinated polyether diols ofthe formula HOCH 2 CF 2 O- (CF 2 CF 2 ⁇ ) m -CF 2 CH 2 ⁇ H may also be used to provide the fluorinated polyether moiety ofthe compounds of formula (I).
• Fluorinated poly(tetramethylene glycol) having the formula HOCH 2 CF 2 CF 2 CF 2 O- (CF 2 CF 2 CF 2 CF 2 O) h -CF 2 CF 2 CF 2 CH 2 ⁇ H, with an average value of h of about 1.2 is available from Exfluor Research Corp.
• fluorinated polyether moieties e.g. a perfluorinated poly(propylene glycol)
• samples ofthe polyethers used in the present invention may have a distribution of molecular weights, and therefore non-integral average values ofthe h, i, j, k, m, n and p subscripts described above.
• the ethylenically unsaturated moieties of the present invention are not limited to the acrylates described in the Examples below.
• Alternative ethylenically unsaturated moieties such as methacrylate, haloacrylate, halomethacrylate, vinyl, allyl, and maleimide are contemplated for use in the present invention.
• Art-recognized methods for capping alcohols with alternative ethylenically unsaturated moieties may be used to form such compounds.
• the energy curable compositions may include compounds which are the oligomeric homologues of Formula (I).
• Oligomeric compounds ofthe present invention include an aromatic or heteroaromatic core, and fluorinated alkylene, arylene or polyether moieties bound to the core through an -O- or -S- linkage.
• fluorinated alkylene, arylene or polyether moieties bound to the core through an -O- or -S- linkage.
• One or more additional -R-Y-CH 2 -Rf-CH 2 -Y- moieties are bound to the fluorinated alkylene, arylene or polyether moieties through an -O- or -S- linkage.
• the terminal -CH 2 -Rf-CH 2 -O- moieties are capped with ethylenically unsaturated moieties.
• oligomeric compounds ofthe present invention may have the formula:
• each R is an aromatic or heteroaromatic moiety; each Y is O or S; each Rf includes a fluorinated alkylene moiety, a fluorinated arylene moiety, or a fluorinated polyether moiety; each E is an ethylenically unsaturated moiety; each j and m is 2, 3, or 4, and the sum ofthe n subscripts in each formula is 2, 3 or 4.
• the formulae above are intended only to be exemplary of oligomeric structures. Oligomers ofthe present invention may have a variety of alternative structures.
• the energy curable compositions may include compounds which are the oligomeric homologues of Formula (II).
• Oligomeric compounds ofthe present invention include an isocyanurate core, and fluorinated alkylene, arylene or polyether moieties bound to the isocyanurate through the nitrogens ofthe isocyanurate.
• One or more additional -isocyanurate-(CH 2 -Rf-CH 2 )- moieties are bound to the fluorinated alkylene, arylene or polyether moieties through a nitrogen ofthe isocyanurate.
• the terminal -CH 2 -Rf-CH 2 -O- moieties are capped with ethylenically unsaturated moieties.
• oligomeric compounds ofthe present invention may have the formula:
• C N 3 O 3 is the isocyanurate nucleus; each Rf includes a fluorinated alkylene moiety, a fluorinated arylene moiety, or a fluorinated polyether moiety; each E is an ethylenically unsaturated moiety; each n, nl, and n2 is 0, 1, 2 or 3; and the sum ofthe n subscripts in each formula is 3.
• the formulae above are intended only to be exemplary of oligomeric structures. Oligomers ofthe present invention may have a variety of alternative structures. [0034]
• the structures ofthe compounds ofthe present invention are chiefly determined by the mole ratios ofthe reactants used in forming the compounds.
• reaction of one mole of cyanuric chloride with three moles of fluorinated diol gives a simple cyanurate ester alcohol:
• Increasing the relative amount of aromatic or heteroaromatic compound will allow for chain extension.
• reaction of two moles of 1,4-dichlorobenzene with tliree moles of fluorinated diol yields an oligomeric -O- linked alcohol:
• Mixed monomers and oligomers may be formed by using mixtures of fluorinated diols or (hetero)aromatic compounds.
• the ethylenically unsaturated -O- linked, -S- linked, and isocyanurate compounds ofthe present invention typically have a molecular weight of from about 1,000 g/mol to about 10,000 g/mol. Desirable compounds have a molecular weight between about 2,000 g/mol and about 6,000 g/mol. Such compounds may be regarded as oligomers, macromers or macromolecular monomers. Compounds with molecular weights of above 1,000 g/mol are non- volatile, and are therefore desirable in processes used in the fabrication of optical elements such as planar waveguide devices.
• the macromers of this invention have a much higher viscosity than the monomers empolyed in conventional compositions used for preparing polymeric optical elements.
• the compositions ofthe present invention have a viscosity (as determined at 25 °C using a Gilmont falling ball viscometer in accordance with ASTM 1343-93) of at least 100 centiPoise, and up to several thousand centiPoise (e.g. 5,000 centiPoise). Viscosities of at least 100 centiPoise are especially desirable in the fabrication of planar waveguide devices from the compositions ofthe present invention.
• the energy curable compositions ofthe present invention may include a selected amount of a free radical initiator.
• the free radical initiator can be a photoinitiator, generating free radical species upon exposure to actinic radiation. Any photoinitiator known to initiate the polymerization of acrylates can be used.
• the photoinitiator is desirably thermally inactive at common ambient temperatures, and is preferably inactive below about 60 °C.
• Suitable free-radical type photoinitiators nonexclusively include quinoxaline compounds; the vicinal polyketaldonyl compounds; the alpha-carbonyls; the acyloin ethers; the triarylimidazolyl dimers; the alpha-hydrocarbon substituted aromatic acyloins; polynuclear quinones and 5-triazines.
• Suitable photoinitiators include aromatic ketones such as benzophenone, acrylated benzophenone, 2-ethylanthraquinone, phenanthraquinone, 2-tert- butylanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone, 2,3- dichloronaphthoquinone, benzyl dimethyl ketal and other aromatic ketones, e.g.
• benzoin benzoin, benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether and benzoin phenyl ether, methyl benzoin, ethyl benzoin and other benzoins.
• Typical photoinitiators are 1-hydroxycyclohexyl phenyl ketone (IRGACURE 184), benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzophenone, benzodimethyl ketal (IRGACURE 651), 2,2-diethoxyacetophenone, 2- hydroxy-2-methyl-l-phenylpropan-l-one (DAROCUR 1173), l-[4-(2- hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-propan-l-one (DAROCUR 2959), 2- methyl-l-[4-(methylthio)phenyl]-2-morpholinopropan-l-one (IRGACURE 907), 2- benzyl-2-dimethylamino-l-(4-morpholinophenyl)butan-l-one (IRGACURE 369), poly ⁇ l-[4-(l -methylvinyl)phenyl] -2-hydroxy-2-
• photoinitiators are those which tend not to yellow upon irradiation.
• photoinitiators include benzodimethyl ketal (IRGACURE 651), ethyl 2,4,6- trimethylbenzoylphenylphosphinate (LUCERTN TPO-L, available from BASF), 2- hydroxy-2-methyl-l-phenylpropan-l-one (DAROCUR 1173 available from Ciba Specialty Chemicals of Tarrytown, NY), 1-hydroxycyclohexyl phenyl ketone (IRGACURE 184), and l-[4-(2-hydroxyethoxy) ⁇ henyl]-2-hydroxy-2-methylpropan-l- one (DAROCUR 2959).
• a fluorinated photoinitiator such as 2-(lH, lH,2H,2H-heptadecafluoro- 1 -decoxy)-2 -methyl- 1 -phenylpropan- 1 -one, described in U.S. patent 5,391,587, which is incorporated herein by reference, may be required.
• Initiators for use in this invention may also include selected amounts of thermal initiators, generating free radical species upon exposure to heat.
• Suitable known thermal initiators include, but are not limited to, substituted or unsubstituted organic peroxides, azo compounds, pinacols, thiurams, and mixtures thereof.
• operable organic peroxides include, but are not limited to, benzoyl peroxide, p- chlorobenzoyl peroxide, methyl ethyl ketone peroxide, tert-butyl perbenzoate, cumene hydroperoxide, di-sec-butyl peroxide, and l,l,-di(tert-butylperoxy)-3,3,5- trimethylcyclohexane.
• Suitable azo compound initiators include, but are not limited to, 2,2 ' -azobisisobutyronitrile, (1 -phenylethyl)azodiphenylmethane, dimethyl-2,2 ' - azobis(l-cyclohexanecarbonitrile), and 2,2'-azobis(2-methylpropane). Additional examples of photo- and thermal initiators may be found in publications known to those skilled in the art.
• the free radical generating initiator may be present in the energy curable composition in a selected amount sufficient to effect polymerization of the composition upon exposure to sufficient energy of an appropriate type.
• a photoinitiator is present in an amount sufficient to effect polymerization upon exposure to sufficient actinic radiation.
• the initiator is generally present in an amount of from about 0.01 % to about 10 % by weight ofthe overall composition, or more usually from about 0.1 % to about 6 % and suitably from about 0.5 % to about 4 % by weight based on the total weight ofthe composition.
• the energy curable composition may not require a free-radical initiator, since said free-radicals may be generated in situ via the action ofthe electron beam radiation.
• additives may also be added to the energy curable compositions depending on the purpose and the end use ofthe compositions.
• these include solvents, antioxidants, photostabilizers, volume expanders, fillers such as for example silica, titania, glass spheres and the like (especially when in the nanoscale regime, particle size less than about 100 nm), dyes, free radical scavengers, contrast enhancers, nitrones and UN absorbers.
• Antioxidants include such compounds as phenols and particularly hindered phenols including IRGA ⁇ OX 1010 from Ciba Specialty Chemicals of Tarrytown, New York; sulfides; organoboron compounds; organophosphorous compounds; N, N'-hexamethylenebis(3,5-di-tert-butyl-4- hydroxyhydrocinnamamide) available from Ciba Specialty Chemicals under the tradename IRGANOX 1098.
• Photostabilizers and more particularly hindered amine light stabilizers include but are not limited to poly[(6-morpholino-s-triazine-2,4- diyl)[(2,2,6,6,-tetramethyl-4-piperidyl)imino]-hexamethylene [(2,2,6,6,-tetramethyl-4- piperidyl)imino]] available from Cytec Industries of Wilmington, Delaware under the trade name CYASORB UV-3346. Volume expanding compounds include such materials as the spiral monomers known as Bailey's monomer. Examples of dyes include methylene green, methylene blue, and the like.
• Suitable free radical scavengers include oxygen, hindered amine light stabilizers, hindered phenols, 2,2,6,6-tetramethyl- 1-piperidinyloxy free radical (TEMPO), and the like.
• Suitable contrast enhancers include other free radical scavengers such as nitrones.
• UN absorbers include benzotriazole, hydroxybenzophenone, and the like. Each of these additives may be included in quantities up to about 6%, based upon the total weight ofthe composition, and usually from about 0.1% to about 1%.
• the energy curable compositions ofthe present invention may include monomers other than the -O- linlced, -S- linked and isocyanurate compounds described herein.
• the compositions may include other low-loss halogenated monomers, such as the fluorinated acrylates described in U.S. Patent No. 6,306,563.
• the compositions may also include non-halogenated monomers, such as ethoxylated bisphenol A diacrylate.
• identities and amounts ofthe monomers and oligomers described herein and other monomers may be adjusted to lend desirable properties to the energy curable composition and the polymeric material made therefrom.
• the use of alternative monomers is limited strictly by their compatibility with the cured polymeric materials ofthe present invention.
• all components ofthe energy curable composition are in admixture with one another, and most desirably are in a substantially uniform admixture.
• the energy curable compositions ofthe present invention preferably include at least about 10% by weight ofthe (hetero)aromatic -O- linlced, (hetero)aromatic -S- linked, or isocyanurate compounds described herein.
• the energy curable compositions ofthe present invention may include substantially more than 10% by weight of these compounds (e.g. 25%, 50%, 75%, 99.5%).
• the present invention also includes polymeric materials which are polymers or copolymers ofthe compounds ofthe -O- linked, -S- linked and isocyanurate compounds described herein.
• the energy curable compositions ofthe invention may be polymerized by exposure to a suitable type and amount of energy.
• compositions formulated with a thermal initiator may be polymerized by the application of heat. Initiation temperatures depend on the thermal initiator and usually range from about 60 °C to about 200 °C, with temperatures between 70 °C and 100 °C being preferred. Thermal polymerization times may vary from several seconds to several hours, depending on the temperature and initiator used.
• compositions formulated with a photoinitiator may be polymerized by exposure to actinic radiation, defined as light in the visible, ultraviolet, or infrared regions ofthe electromagnetic spectrum, as well as electron beam, ion or beam, or X- ray radiation.
• Actinic radiation may be in the form of incoherent light or coherent light, for example, from a laser. Sources of actinic radiation and exposure procedures, times, wavelengths and intensities may vary widely depending on the desired degree of polymerization, the index of refraction ofthe material, and other factors known to those of ordinary skill in the art. Such conventional photopolymerization processes and their operational parameters are well known in the art.
• Sources of actinic radiation and the wavelength ofthe radiation may vary widely, and any conventional wavelength and source can be used. It is preferable that the photoinitiator require that photochemical excitation be carried out with relatively short wavelength (high energy) radiation, so that exposure to radiation normally encountered before processing (e.g. room lights) will not prematurely polymerize the energy curable composition. Thus, exposure to ultraviolet light or deep ultraviolet light are useful.
• Convenient sources include high pressure xenon or mercury-xenon arc lamps filled with appropriate optical filters to select the desired wavelengths for processing. Also, short wavelength coherent radiation is useful for the practice of this invention.
• An argon ion laser operating in the UN mode at several wavelengths near 350 nm is desirable.
• a frequency-doubled argon ion laser with an output near 257 nm wavelength is highly desirable.
• Electron beam or ion beam excitation may also be used.
• the processing can utilize a multiphoton process initiated by a high intensity source of actinic radiation such as a laser. Typical exposure times vary from a few tenths of seconds to about several minutes depending on the actinic source. When partial curing is desired, curing levels between about 50% and 90% are generally preferred. Photopolymerization temperatures usually range from about 10 °C to about 60 °C; however, room temperature is preferred.
• C H molar concentration of hydrogen
• Mw molecular weight ofthe compound
• p density ofthe material
• the C H for a formulated energy curable composition may be calculated as a weighted average ofthe C H values of each individual constituent. While an exact relationship between C H and the absorption loss of a particular material or fabricated device is unlikely, this relation gives an initial indication of which materials may be useful in lowering optical loss values.
• Suitable energy curable compositions and polymeric materials ofthe present invention have a C H of below about 55 M. Desirable energy curable compositions and polymeric materials have a C H of below about 30 M. Especially desirable energy curable compositions and polymeric materials have a C H of below about 20 M. For waveguide applications, the most desirable compositions and polymeric materials have a C H of below about 20 M, or even below about 10 M.
• C H may be controlled by judicious selection ofthe Rf and R moieties ofthe -O- linked, -S- linked and isocyanurate compounds described herein, as well as judicious selection of other monomers or oligomers in the energy curable composition.
• Energy curable compositions and polymeric materials ofthe present invention suitable for optical applications have an absorption loss of below about 0.5 dB/cm at a wavelength of 1550 nm. Desirable energy curable compositions and polymeric materials have an absorption loss of below about 0.3 dB/cm at a wavelength of 1550 nm. Especially desirable energy curable compositions and polymeric materials have an absorption loss of below about 0.2 dB/cm.
• Energy curable compositions and polymeric materials with absorption losses below about 0.15 dB/cm, or even below 0.1 dB/cm are very desirable. Absorption losses for representative energy curable compositions and polymeric materials ofthe present invention are given in the Examples, below.
• the compounds, energy curable compositions, and polymeric materials ofthe present invention provide a number of advantages over conventional compounds, compositions and polymeric materials. For example, the compositions ofthe present invention have a very low C H , and therefore very low optical loss at telecommunications wavelengths, making them suitable for the fabrication of planar waveguides and other optical devices.
• compositions ofthe present invention can have a higher refractive index than analogous compositions not including aromatic or heteroaromatic moieties, making them useful in the tuning ofthe refractive indices of the different layers of an optical device.
• the compositions ofthe present invention also provide macromers having more than two ethylenically unsaturated moieties, providing a cured polymeric material with a high degree of crosslinking.
• the compositions ofthe present invention may also have higher hydrolytic stability than analogous carboxylate ester-based compositions.
• compositions and polymers ofthe present invention are especially useful in the fabrication of optical elements such as planar optical waveguides.
• a method for the fabrication of polymeric waveguides is disclosed in commonly held and copending U.S. Patent application serial number 09/846,697.
• An example of a waveguide structure appears in FIG. 1.
• a suitable substrate 2 is rigorously chemically cleaned, for example with concentrated aqueous sodium hydroxide.
• the substrate 2 may then be primed with acrylate-, thiol-, amino-, or isocyanato-functionalized chloro- or alkoxysilane compounds. For example, it may be treated with (3-acryloxypropyl)trichlorosilane.
• a photosensitive adhesion promoting tie layer composition is optionally followed by application, via spin coating, of a photosensitive adhesion promoting tie layer composition.
• the edge bead formed in the spinning process may be removed by methods known by the skilled artisan (e.g. rinsing the circumference ofthe wafer with a suitable solvent during the final seconds ofthe spin).
• the tie layer is preferably highly crosslinlcable and contains either ethylenically unsaturated moieties, thiol moieties, or both. If used, the tie layer composition is exposed to sufficient actinic radiation to cure the tie layer to at least a level above its gel point.
• suitable tie layers may comprise other polymers such as epoxies, polyacrylates, or poly(vinyl ethers).
• a layer 4 of photosensitive buffer composition is applied by spin coating.
• the buffer composition is formulated in accordance with this invention, and is formulated, as described above, to have a refractive index when cured of about 1% to about 3% lower than that of a core material.
• the buffer composition is exposed to sufficient actinic radiation to partially cure it to a level below full cure and above its gel point.
• a photosensitive clad composition 6 is applied to the surface 5 ofthe polymeric buffer layer by spin coating.
• the clad composition is formulated in accordance with this invention, and is formulated, as described above, to have a refractive index when cured of about 0.3% to about 1.5% lower than that ofthe core material.
• the laminate so constructed is exposed to sufficient actinic radiation to partially cure the clad composition to a level below full cure and above its gel point.
• a layer ofthe photosensitive, polymerizable core composition formulated in accordance with this invention, is applied to the surface 7 ofthe polymeric clad layer by spin coating.
• the core composition is then imagewise exposed to sufficient actinic radiation to effect the at least partial polymerization of an imaged portion and to form at least one non-imaged portion ofthe core composition.
• a photomask may be used, hi this process, the photomask is lowered to a predetermined level above the core composition layer, usually less than about 20 ⁇ m above the core composition layer, and more usually from about 5 ⁇ m to about 20 ⁇ m above the core composition layer.
• the distance ofthe mask to the surface ofthe core composition layer may be controlled by, for example, using spacers such as thin wires ofthe desired thickness. Exposure through the photomask with sufficient actinic radiation to partially cure the core composition to a level below full cure and above its gel point yields areas of exposed, partially polymerized core, and unexposed liquid core composition.
• the core composition may be imaged by writing with a well- defined beam of actinic radiation such as that generated by a laser. Regardless ofthe method of exposure, the unexposed core composition may be developed by rinsing with a suitable solvent, leaving an exposed, partially polymerized patterned core 8.
• the patterned core may define, for example, waveguide structures with a rectangular or square cross-section.
• a photosensitive overclad composition 10 is applied to the surface 9 ofthe core by spin coating. The overclad composition coats the top and sides ofthe patterned core features.
• the overclad composition is formulated in accordance with this invention, and is formulated, as described above, to have a refractive index when cured of about 0.3% to about 1.5% lower than that ofthe core material.
• the structure is exposed to sufficient actinic radiation to completely cure the film. Finally, the structure may thermally annealed to ensure complete polymerization of all layers and remove any residual volatile substances.
• FIG. 3 A cross-sectional view of an example of a waveguide structure in accordance with the present invention appears in FIG. 3.
• the structure includes a polymeric patterned core 8 including a polymeric material which is a polymer or copolymer ofthe compound of formula (I).
• the polymeric patterned core is contiguous on at least one side with a polymeric clad layer 6, and contiguous on at least one side with a polymeric overclad layer 10.
• the clad layer is disposed above a substrate 2.
• the clad layer either rests directly on the substrate, or rests upon a buffer layer 4 that rests upon the substrate.
• Waveguide structures ofthe present invention have propagation losses of less than 0.5 dB/cm, 0.3 dB/cm, 0.2 dB/cm, 0.15 dB/cm, and even 0.1 dB/cm.
• the thicknesses and refractive indices ofthe layers are critical to waveguide device performance.
• the refractive indices ofthe layers may be defined by judicious formulation ofthe energy curable compositions ofthe present invention.
• the -O- linked, -S- linlced and isocyanurate compounds ofthe present invention tend to have higher refractive indices than do the analogous diol acrylates.
• the skilled artisan can formulate energy curable compositions with selected refractive indices by using different relative amounts of compounds of formulae (I) and (II) and other energy curable monomers.
• the refractive index ofthe core is in the range of from about 1.30 to about 1.7.
• the refractive indices ofthe buffer, clad, and overclad layers should be lower than that ofthe core, as described above. Thicknesses ofthe layers are determined in the spin coating step by spin speed and duration and by the viscosity ofthe energy curable composition.
• the height ofthe waveguides ofthe core layer is defined by the spin coating step, while the width ofthe waveguides is determined by the dimensions ofthe features ofthe photomask.
• a single mode waveguide has core cross-sectional dimensions of about 7 ⁇ m by 7 ⁇ m, core refractive index at 1550 nm of about 1.323, underclad thickness of about 2 ⁇ m, underclad refractive index at 1550 nm of about 1.316, buffer thickness of about 10 ⁇ m, buffer refractive index at 1550 nm of about 1.308, overclad thickness of about 15 ⁇ m, and overclad refractive index at 1550 nm of about 1.316.
• reaction mixture was again cooled with ice, and 25 mL acryoyl chloride (0.31 mol) was added dropwise. The temperature ofthe reaction mixture was maintained below 30 °C during the addition. The reaction mixture was stirred at room temperature for three hours.
• Rf -CF 2 0(CF 2 CF 2 0) m (CF 2 0) n CF 2 -
• This compound had a liquid loss of 0.10 dB/cm at a wavelength of 1550 nm.
• This compound had a C H of about 11 M.
• ⁇ , ⁇ -diethoxyacetophenone (1 wt%) was added to a small sample ofthe compound.
• the resulting energy curable composition was cured for 300 seconds with UV light while being purged with nitrogen.
• the refractive index ofthe cured sample was 1.323 at a wavelength of 1550 nm.
• Rf -CF 2 0(CF 2 CF 2 0) 2 CF 2 -
• This compound had a liquid loss of 0.27 dB/cm at a wavelength of 1550 nm.
• This compound had a C H of about 24 M.
• ⁇ , ⁇ -diethoxyacetophenone (1 wt%) was added to a small sample ofthe compound.
• the resulting energy curable composition was cured for 300 seconds with UN light while being purged with nitrogen.
• the refractive index ofthe cured sample was 1.368 at a wavelength of 1550 nm.
• Rf -CF 2 0(CF 2 CF 2 0) m (CF 2 0) n CF 2 -
• Rf -CF 2 0(CF 2 CF 2 0) m (CF 2 0) n CF 2 -
• This compound had a liquid loss of 0.15 dB/cm at a wavelength of 1550 nm.
• This compound had a C H of about 10 M.
• ⁇ , -diethoxyacetophenone (1 wt%) was added to a small sample ofthe compound.
• the resulting energy curable composition was cured for 300 seconds with UN light while being purged with nitrogen.
• the refractive index ofthe cured sample was 1.344 at a wavelength of 1550 nm.
• Rf -CF 2 0(CF 2 CF 2 0) m (CF 2 0) n CF 2 -
• This compound had a liquid loss of 0.10 dB/cm at a wavelength of 1550 nm.
• This compound had a C H of about 10 M.
• ⁇ , ⁇ -diethoxyacetophenone (1 wt%) was added to a small sample ofthe compound.
• the resulting energy curable composition was cured for 300 seconds with UV light while being purged with nitrogen.
• the refractive index ofthe cured sample was 1.340 at a wavelength of 1550 nm.
• the temperature ofthe reaction mixture was maintained below 30 °C during the addition.
• the reaction mixture was stirred at room temperature for one hour, washed three times with methanol, concentrated by rotary evaporation, and passed through a 0.2 ⁇ m filter. NMR has confirmed that the resultant colorless liquid is about 40% FLUOROLINK D10 diacrylate and about 60%
• Rf -CF 2 0(CF 2 CF 2 0) m (CF 2 0) n CF 2 - [0066]
• This composition had a liquid loss of 0.25 dB/cm at a wavelength of 1550 nm.
• the -S- linked compound had a C H of about 11 M.
• FLUOROLINK D10 diacrylate had a C ⁇ of about 14 M.
• the overall composition has a C H of about 12.3 M.
• ⁇ , ⁇ - diethoxyacetophenone (1 wt%) was added to a small sample ofthe compound, and the resulting energy curable composition was cured for 300 seconds with UV light while being purged with nitrogen.
• the refractive index ofthe cured sample was 1.336 at a wavelength of 1550 nm.
• the mixture was cooled to room temperature, washed three times with deionized water, and concentrated by rotary evaporation at 70 °C for an hour under vacuum to remove solvent.
• the resultant liquid is believed to be the -O- linlced alcohol having the structure
• Rf -CF 2 0(CF 2 CF 2 0) 2 CF 2 -
• the substantially solvent-free mixture was dissolved in 200 mL HFE7200, a fluorinated solvent available from 3M, and filtered using a 0.2 micron filter.
• To the filtered mixture was added 40 mL acryloyl chloride (0.47 mol).
• Triethylamine 64 mL, 0.46 mol was added dropwise with mechanical stirring, while a temperature of between 40 °C and 50 °C was maintained using an ice bath. A white precipitate formed upon addition ofthe triethylamine.
• the mixture was stirred mechanically for 4 hours, filtered using a 0.2 micron filter, then washed three times with an equal volume of water.
• the mixture was concentrated using rotary evaporation at 70 C for an hour under vacuum, yielding the diacrylate corresponding to the -O- linked alcohol given above.
• This compound had a liquid loss of 0.21 dB/cm at a wavelength of 1550 nm, and had a viscosity of about 55 cP.
• ⁇ , ⁇ -diethoxyacetophenone (1 wt%) was added to a small sample ofthe compound.
• the resulting energy curable composition was cured for 300 seconds with UV light while being purged with nitrogen.
• the refractive index ofthe cured sample was 1.440 at a wavelength of 1550 nm.
• the perfluorinated ether diacrylate has the structure
• This material may be made by acrylation of FLUOROLINK D, available from Ausimont USA, Red Bank, NJ.
• An unoxidized four inch silicon wafer was cleaned by immersion in 4M aqueous sodium hydroxide for one hour, followed by rinsing with deionized water for 12 minutes. The wafer was blown dry with nitrogen and further dried on a 120 °C hotplate for 10 minutes.
• the wafer was allowed to cool, and then treated with neat (3- acryloxypropyl)trichlorosilane using a cleanroom swab. Excess silane was removed from the wafer surface by ethanol washing followed by a gentle wipe with a cleanroom cloth to remove particulate matter. The wafer was rinsed with ethanol while spinning on a spin coater, then dried on a 120 °C hotplate for two minutes. [0073] The core, clad and buffer compositions were filtered through 0.1 ⁇ m TEFLON filters, and loaded into 10 mL pipettors. The wafer was centered on the chuck of a stainless steel spin coater (available from the Cost Effective Equipment division of Brewer Science, Inc., Rolla, MO).
• the spin program was 150 rpm for 30 sec; and ramp at 100 rpm/sec to 700 rpm for 20 sec. In the 700 rpm part ofthe program, a small nozzle dispensed acetone along the top edge and along the bottom edge ofthe wafer for edge bead removal.
• the wafer was then transferred to a leak-free vacuum-purge chamber with an internal volume of 3 liters was used.
• the chamber was constructed with aluminum walls, VITON o-rings and quartz window, and allowed for both evacuation of air and nitrogen purging. Clamps on the box lid and a check valve were used to ensure that a positive pressure of nitrogen could be established during purging. This also ensured that no air could leak in during the purge cycle. Likewise, air could easily be eliminated in the vacuum cycle by ensuring that the chamber was leak free.
• the chamber could be evacuated to 0.2 Torr or less with a standard rotary vein mechanical pump. For process consistency, a standard purge cycle was established. Vacuum was applied for 30 seconds until a level of 6 Ton was reached.
• the wafer was then illuminated for 37 seconds at approximately 10.9 W/cm 2 through a 3° diffuser using a Tamarack UN light source to partially polymerize the buffer layer.
• the wafer was recentered on the spin coater chuck, approximately 7 mL ofthe clad composition was applied, and the wafer was spun to yield a 2 ⁇ m thick layer ofthe clad composition.
• the spin program was 150 rpm for 30 sec; ramp at 100 rpm sec to 6000 rpm for 50 sec; and ramp at 100 rpm/sec to 700 rpm for 20 sec.
• a small nozzle dispensed acetone along the top edge and along the bottom edge ofthe wafer for edge bead removal.
• the wafer was then transfe ⁇ ed to the vacuum-purge chamber. Vacuum was applied for 30 seconds until a level of 6 Torr was reached. This was followed by 2 minutes of nitrogen purging at 9.9 L/min.
• the wafer was then illuminated for 40 seconds at approximately 10.9 W/cm 2 through a 3° diffuser using a Tamarack UV light source, partially polymerizing the clad layer.
• the wafer was recentered on the spin coater chuck, approximately 7 mL ofthe core composition was applied, and the wafer was spun to yield a 6 ⁇ m thick layer ofthe core composition.
• the spin program was 150 rpm for 30 sec; ramp at 100 rpm/sec to 4000 rpm for 50 sec; and ramp at 100 rpm/sec to 700 rpm for 20 sec.
• a small nozzle dispensed acetone along the top edge and along the bottom edge ofthe wafer for edge bead removal.
• GALDEN HT110 perfluorinated ether solvent (Ausimont USA) was used to rinse the core composition from the outer ⁇ 1 cm ofthe wafer.
• the wafer was then placed onto a vacuum chuck in the vacuum purge box.
• a harness fabricated from 25 mm thick plastic sheet with a 5 inch diameter hole in the center and with five small loops of 35 mm thick wire attached to it, was lowered onto the wafer, with the loops of wire resting on the 1 cm edge ofthe wafer that is free from core composition.
• a photomask was lowered into position over the wafer and rested on a retractable plastic wedge at an elevated angle off the wafer. The photomask has transparent areas defining the core of a waveguide.
• the box is closed, and vacuum was applied to the box for 30 seconds, or until the pressure falls to approximately 6 Ton. This was followed by 2 minutes of nitrogen purging at 9.9 L/min.
• the wedge was retracted, allowing the photomask to rest on the loops of 35 mm wire ofthe harness.
• the wafer was then exposed for 100 seconds at 10.9 W/cm 2 using a Tamarack UN light source without a diffuser. Areas ofthe core layer that were allowed by the photomask to be exposed were partially polymerized, while areas ofthe core layer that were not allowed to be exposed remained substantially unpolymerized.
• the wedge was replaced, lifting the photomask, and the wafer was removed from the box. [0078]
• the wafer was recentered on the spin coater chuck, and spun at 1300 rpm for 60 seconds. For the first 40 seconds of this spin cycle, the wafer was rinsed with v.
• the wafer was recentered on the spin coater chuck. About 7 mL of clad was applied to the surface ofthe wafer, and the wafer was spun to yield a 15 ⁇ m thick layer ofthe clad composition.
• the spin program was 150 rpm for 30 sec, and than ramp at 100 rpm/sec to 700 rpm for 30 sec. In the 700 rpm part ofthe program, a small nozzle dispensed acetone along only the bottom edge ofthe wafer for edge bead removal.
• the wafer was then transferred to the vacuum-purge chamber. Vacuum was applied for 30 seconds until a level of 6 Torr was reached. This was followed by 2 minutes of nitrogen purging at 9.9 L/min.
• the wafer was then illuminated for 500 seconds at approximately 10.9 W/cm 2 through a 3° diffuser using a Tamarack UV light source, partially polymerizing the clad layer.

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