GB2047913A - Coupling of light guides and electro-optical devices - Google Patents

Abstract

An efficient and inexpensive method and assembly for optically coupling light conductors, such as polymeric or glass optical fibers, to electro-optical devices (EOD's) is critically needed in the field of fiber optics. The method and assembly of the present invention employ a single component actinic light, photocurable or photopolymerizable composition which cures in one minute or less. The coupled assembly (especially when it comprises an optical fiber and a light emitting diode) is optically stable, the coupling not being susceptable to degradation by thermal cycling. FIG. 2 is a schematic depiction of an operable assembly suitable for practicing the present invention. The present invention provides methods for optically coupling light conductors such as polymeric or glass optical fibers and various electro- optical devices such as light emitting diodes, laser diodes, and photodiodes. The maintaining of precise alignment between the conductor and the EOD for a relatively long (5 to 15 minute) curing period is no longer required. <IMAGE>

Description

SPECIFICATION Coupling of light guides and electro-optical devices This invention relates to methods of joining light conductors, e.g., optical fibers, and electrooptical devices, e.g., light emitting diodes.

In one aspect this invention relates to methods of joining light conductors and electro-optical devices by the use of actinic light or photocurable materials, especially those cured with ultraviolet light.

The recent technological advances in the area of fiber optics have generated a critical need for efficient, inexpensive, methods for optically coupling light conductors such as polymeric or glass optical fibers (sometimes referred to herein as "fibers") and various electro-optical devices (EOD's), such as light emitting diodes (LED's), laser diodes; and photodiodes. One conventional method for optically coupling (i.e., joining so that light may pass therebetween) optical fibers and electro-optical devices (which typically have emission or detection dimensions of 50 micrometers or less to 200 micrometers or more) requires the microscopic alignment of the fiber adjacent to the surface of the EOD (usually to position the fiber so that the axis thereof is essentially parallel to the direction of propagation of light passing between the fiber and the EOD).This provides optical alignment therebetween while maintaining between the fiber and the EOD a small quantity of a material which polymerizes or cures to form a coupling therebetween which maintains the previously established optical alignment. A second conventional method for optically coupling electro-optical devices and optical fibers comprises using a curable material to anchor the fiber in spaced-apart relationship with respect to the LED (i.e., to leave an air gap therebetween), the fiber usually being bonded to an independent or attached substrate rather than to the light emitting surface of the LED. Materials used in the above described conventional processes have generally included catalytically cured materials such as epoxy resins.The use of epoxy resins to join light conductors and EOD's has the objectionable feature that the precise alignment between the conductor and the EOD must be maintained during the relatively long time period (e.g., 5 to 1 5 min.) required for conventional epoxy resins to cure. The long time period during which a precise alignment must be maintained increases the chance that the alignment will be disturbed, thereby reducing the optimum coupling of the fiber to the EOD. Additionally, in order to obtain a properly compounded resin, it is generally required that the quantity of resin actually compounded be considerably in excess of the quantity that could be used to connect the fiber and the EOD, thus wasting the excess resin.

Actinic light curable or photocurable compositions have been suggested for use in joining (i.e., splicing) optical fibers. The actinic light curable compositions suggested in the art to join optical fibers have generally been ill suited to bonding optical fibers and LED's because they lack the requisite physical characteristics, e.g., viscosity, to be easily and efficiently utilized.

The present invention provides a method of optically coupling light conductors and electro-optical devices (this method sometimes being referred to as "pigtailing" when an optical fiber and an LED are employed) that overcomes the problems associated with the prior art.

In one aspect, the present invention provides a method for optically coupling a light conductor and an EOD which employs a single component actinic light, photocurable or photopolymerizable composition. More particularly, the present method includes the steps of: providing a light conductor such as a glass or polymeric optical fiber and an electro-optical device such as a light emitting diode which are to be optically coupled; placing on said light conductor or said electro-optical device or both actinic light curable composition in sufficient quantity and in such position to fix said light conductor with respect to said EOD so as to provide optical alignment therebetween when cured, the composition having a viscosity in the range of 1000 to 200,000 centipoise and comprising an oligomeric composition having:: a) 10 to 60 percent by weight actinic light addition polymerizable amorphous moieties; b) 10 to 50 percent by weight divalent organic connecting moieties; c) O to 50 percent by weight diluent monomer; d) sufficient polyfunctional cross linking moieties having a plurality of addition polymerizable groups to provide a calculated molecular weight per crosslink of 500 to 5,000 (preferably 1,000 to 3,000) when said composition is cured; e) sufficient actinic light activatable addition polymerization initiator to initiate cure of said composition (generally 0.01 to 10 gram-moles initiator per 100 grams composition) when said composition is exposed to actinic light:: said composition having, when actinic light cured, a shear modulus in the range of 1 x 1 o8 to 3 X 109 dynes/cm, a 90% transmission of radiation having a wavelength of 0.4 micrometer to 2.0 micrometers, and being actinic light curable in less than one minute; positioning said light conductor adjacent to said electro-optical device so as to be optically aligned therewith; maintaining said optical alignment and curing said composition by exposure to actinic light, thereby providing said optical coupling.

By "oligomeric composition" is meant a composition comprising a single molecule having the above moieties or a plurality of molecular species (e.g., an admixture) having the above moieties distributed among the molecular species therein.

In one practice of the above method a quantity of the photocurable material is placed on the end of an optical fiber and the optical fiber is positioned adjacent to the light emitting surface of the electro optical device (usually not touching), the photocurable composition enveloping the end of the fiber and the light emitting surface of the EOD. At this point the optical alignment of the fiber with respect to the EOD is determined, and once a desirable alignment is obtained, the composition is cured in a minute or less, generally in about 10 seconds, by exposing the composition to actinic light.

In a preferred practice of the above method, an optical fiber and the active surface of a light emitting diode (i.e., a surface from which light emits) are positioned so that the axis of the fiber is essentially parallel (i.e., within about + 5 degrees) to the direction of propagation of light passing between the fiber and the LED, and the optical alignment of the fiber and the LED is optimized while passing light from the LED through the fiber. The intensity of the light passing through the fiber is monitored and the curing step is completed when the optimum (generally maximum) coupling between the fiber and the LED is obtained. In another preferred practice of the above method, the actinic light curable composition is ultraviolet light polymerizable in less than one minute.

The coupled assemblies produced in the practice of the present invention comprise an electrooptical device and a light guide, the device and light guide being aligned so that light can pass therebetween (i.e., they are optically aligned) the alignment being maintained by various means, all of which minimally include material obtained by actinic light cure of a composition having a viscosity in the range of 1000 to 200,000 centipoises and comprising an oligomeric compositions having:: a) 10 to 60 percent by weight actinic light addition polymerizable amorphous moieties; b) 10 to 50 percent by weight divalent organic connecting moieties; c) 0 to 50 percent by weight diluent monomer; d) sufficient polyfunctional crosslinking moieties having a plurality of addition polymerizable groups to provide a calculated molecular weight per crosslink of 500 to 5,000 (preferably 1,000 to 3,000) when said composition is cured; .e) sufficient actinic light activatable polymerization initiator to initiate cure of said composition (generally 0.01 to 10 gram-moles initiator per 100 grams composition) when said composition is exposed to actinic light; said composition having, when actinic light cured, a shear modulus in the range of 108 to 3 X 109 dynes/cm, 90% transmission of radiation having a wavelength of 0.4 micrometer to 2.0 micrometers, said composition being radiation curable in less than one minute.

The optically coupled assemblies of the present invention, especially when prepared according to the preferred method, are very stable, their optical coupling not being significantly reduced by multiple thermal cycling between -200C and 700C.

The present invention is described in greater detail hereinafter with reference to the accompanying drawings wherein like reference characters refer to the same elements in the several views and in which: Figure 1 is a schematic depiction of an assembly suitable for practicing the present invention; and Figure 2 depicts the assembly of Figure 1 in operation.

Thus in FIGURE 1 there is schematically shown an assembly 1 0 for joining a light conductor such as an optical fiber 12 and an electro-optical device such as a light emitting diode 14. Optical fiber 12 is connected on one end to an optical power detector 26, the remaining connecting end 17 of fiber 12 being positionable by means of a micromanipulator which may comprise a control section 18 which directs an arm 1 9. The light emitting diode 14 is mounted on a chip 20 and is coupled by leads 22 to a circuit 24 comprising an electrical signal generator 25. Also shown in Figure 1 is a source of actinic light or photopolymerizing radiation 28, the source providing actinic radiation (such as untraviolet radiation) of sufficient intensity to rapidly cure a quantity 30 of the actinic light curable bonding material described hereinbelow.

In a preferred practice of the invention, the micromanipulator (by means of arm 19) is employed to position optical fiber 1 2 so that the central axis of fiber 1 2 is parallel to the direction of propagation of light emanating from the face 32 of the LED, i.e., the fiber is essentially normal to the face 32 of LED 14.

Generally, manipulation of fiber 12 is accomplished while observing the relationship between the LED 14 and the optical fiber 1 2 under a light microscope. A quantity or drop 30 of radiation polymerizable material is placed on the connecting end 1 7 (which is preferably polished) of optical fiber 1 2 and the fiber and drop of material 30 are positioned onto the face 32 of LED 14. When the fiber is positioned onto the LED, it is preferred that the polished end of optical fiber 12 not be in contact with the face 32 of LED 1 4 but that they be in slightly spaced-apart relationship, e.g., separated by 10-25 micrometers, with the optical axis of fiber 1 2 being perpendicular to the planar face 32 of the LED. At this point, radiation source 28 is activated (this being indicated by radiation arrows) and focused upon the optical fiber-LED juncture and the actinic light curable composition thereat. The juncture is flooded with ultraviolet radiation, thereby initiating polymerization of the actinic light curable material. The incident radiation cures the photocurable composition described herein (to cured material 30) in as little as 5 minutes and preferably less than 1 minute to produce a cured composition that aggressively holds the optical fiber in slightly spaced apart relationship with respect to the LED while maintaining the optical alignment.

In a preferred practice of the present invention, the radiation curable composition is cured by actinic radiation such as ultraviolet light having a wavelength in the range of 320 to 380 nanometers. In this embodiment, radiation source 28 is a source of ultrviolet radiation such as a medium pressure mercury discharge lamp. Further, after the quantity 30 of radiation curable bonding composition is placed on the end of optical fiber 12, the optical fiber is positioned on the light-emitting face 32 of the LED and electrical signal source 25 and optical power detector 26 are activated.While monitoring the intensity of light transmitted through optical fiber 12 to the optical power detector 16, the polished end of fiber 12 is positioned with respect to LED 14 by means of a micromanipulator arm 1 9 until an optmum (e.g., maximum) optical power is reached, the bonding composition enveloping the face of the LED and fiber end 1 7. At this point, radiation source 28 is activated, flooding the fiber-LED juncture and curing the bonding composition within the time period noted above. In this manner, optimum generally maximum optical alignment between the LED and the optical fiber is attained.

An actinic light curable bonding composition suitable for optically coupling light conductors and electro-optical devices comprises an oligomeric composition of actinic light polymerizable amorphous moieties, polyfunctional moieties having a plurality of actinic light polymerizable groups, divalent organic connecting moieties and preferably sufficient actinic light polymerizable monomers sufficient to provide the curable composition with a desired viscosity generally in the range of 1 ,000 to 200,000 centipoises. By "connecting moiety" is meant any organic divalent moiety which is capable of connecting addition polymerizable functionalities and amorphous moieties.

"Crosslink density", or calculated molecular weight per crosslink, is determined by dividing the weight of oligomeric composition in grams by the gram equivalents of polymerizable groups in excess of one that are present in the polyfunctional moiety of the oligomeric composition. For example, 100 g of an oligomeric composition containing 0.05 mole of a moiety having 3 polymerizable groups has a calculated crosslink density of 1 or + = 100/o.i= /01= 1000.

The amorphous moieties of this bonding composition generally comprise polymeric segments such as polyesters, polysiloxanes, polyacrylates, polyethers or polyolefins. These segments derive from corresponding mono- or polyols and mono- or polyamines which are preferably diols or triols. By "amorphous moieties" is meant materials having a weight average molecular weight in the range of about 500 to 5,000, a glass transition temperature of less than about 2500K and a crystallinity as indicated by x-ray diffraction of less than about 5% by weight. In the contest of the invention "actinic light polymerizable" materials are those materials which have addition-polymerizable groups which polymerize when exposed to actinic, e.g., UV light in the presence of an actinic light activatable addition polymerization initiator.Suitable compounds generally contain one, two or three actinic light additionpolymerizable groups selected from acrylyl, methacrylyl, allyl or epoxy groups. Thus, actinic light addition-polymerizable amorphous moieties are compounds that have an amorphous segment and one to three actinic light polymerizable groups.

The pollyfunctional moieties of the bonding composition are organic compounds having in one molecule two or more actinic light addition-polymerizable groups, preferably selected from acrylyl, methacrylyl, allyl and epoxy groups. Such compounds are preferably compounds which contain the amorphous moiety and two or more addition-polymerizable groups in one molecule. Other suitable compounds for providing the polyfunctional moieties of the bonding composition are di or tri -acrylyl, methacrylyl, -allyl or -epoxy compounds such as ethyleneglycol dimethacrylate, diethyleneglycoldiacrylate, diallylphthalate, and 4,5-epoxy-2-cyclohexylmethyl 2,4-epoxycyclohexanecarboxylate.

Where these compounds are used as the polyfunctional moiety, the bonding composition must contain the amorphous moiety in another molecule.

The preferred actinic light polymerizable compositions are urethane oligomeric compositions having amorphous segments connected to at least two addition-polymerizable groups in one molecule that have the structure:

wherein A is an amorphous segment as defined above that is the residue (after substitution for -OH) of an amorphous oligomeric polyol, A(OH)n; n is an integer from 2 to 6 inclusive; R is the residue of an organic diisocyanate, R(NCO)2; and P is a moiety having an addition-polymerizable group selected from acrylyl, methacrylyl, allyl and vic-epoxy groups.

The most preferred radiation polymerizable compositions herein are polymerizable urethane oligomers in accordance with Formula I wherein A is an amorphous polyalkylene ether segment having pendent fluorocarbon groups. Such oligomers have the general formula:

wherein: R is the residue or reaction product of a hydroxyl-containing material with an epoxy-containing material the hydroxyl-containing material having n hydroxyls:: n is an integer from 2 to 6 inclusive; W is a polyvalent connecting moiety; Rf is a monovalent highly fluorinated fluorocarbon radical; m is an integer from 1 to about 20; R' is a polyvalent residue or reaction product of an organic diisocyanate, R'(NCO)2 (preferably a cycloaliphatic or aromatic diisocyanate) and a hydroxyl-containing material; R2 is a divalent saturated aliphatic group having 2 to 6 carbon atoms and optionally one or two non-vicinal catenary oxygen atoms; and, R3 is hydrogen or methyl.

In II, Rf is a pendent, monovalent, highly flourinated, aliphatic, aryl, or alkaryl radical. "Pendent" as the term is used herein means not of the backbone carbon chain, ie., non-catenary. By "highly fluorinated" is meant that generally 35 to 85 weight percent, preferably 50-77 weight percent, of the fluorocarbon radical is fluorine with at least 75 percent of the non-catenary carbon valence bonds being attached to fluorine atoms. The weight percent of fluorine in the preferably saturated pendent fluorocarbon radical is found by dividing the total atomic weight of the radical into the total atomic weight of the fluorine atoms present in the radicals (e.g., -CF3 is 82.6 weight percent fluorine). Where R, contains a plurality of carbon atoms in a skeletal chain, such chain may be straight, branched or cyclic, but preferably is straight.The skeletal chain of carbon atoms can be interrupted by divalent oxygen or trivalent nitrogen heteroatoms, each of which is bonded only to carbon atoms, but where such hereoatoms are present, it is preferable that the skeletal chain contain not more than one said hereroatom for every two carbon atoms. An occasional carbon-bonded hydrogen atom, bromine atom, or chlorine atom may be present. Where such atoms are present, they are preferably present to the extent of not more than one such atom for every two carbon atoms in the chain. Thus, the non-skeletal valence bonds are preferably carbon-to-fluorine bonds, that is, Rf is preferably perfluorinated. The total number of carbon atoms of Rf can vary and can be, for example, 1 to 18, preferably 1 to 12.Where Rf is or contains a cyclic structure, such structure preferably has 5 or 6 ring member atoms, 1 to 2 of which can contain heteroatoms, e.g., oxygen and/or nitrogen. Where Rf is aryl, (i.e., having an aromatic structure) it has 1 or 2 rings. Where Rf is an aromatic structure, the aromatic structure may be substituted with lower alkyl radicals (i.e., alkyl radicals having 1 4 carbon atoms). Examples of such aryl radicals include perfluorophenyl

4-trifluoromethylphenyl, and perfluoronaphthyl. Rf is also preferably free of ethylenic or other carbonto-carbon unsaturation, that is, it is a saturated aliphatic or heterocyclic radical.Examples of useful Rf radicals are fluorinated alkyl, e.g., -CF3 or -C8F17, and alkoxyalkyl, e.g., CF30CF -' said radicals being preferably perfluorinated straight-chain alkyl radicals, CnF2n+1, where n is 1 to 12 W in the above formula is a polyvalent connecting moiety having a valence of at least 2 and is preferably selected from the group consisting of carbon-to-carbon single bonds,

The pendent group WRf is herein sometimes referred to as "the pendent fluorocarbon substituent", or the "highly fluorinated fluorocarbon substituent".

In reaction I above, catalysts may be employed such as Lewis acids, optionally modified with organotin compounds. Generally, the reaction may be run without solvent at a temperature of about 250C to 1 500C. It is important to note at this juncture that the fluorocarbon substituent of the epoxide (WRf in II) becomes the pendent fluorocarbon substituent of the novel polyetherurethaneacrylates of the invention. Hence, in this preparative route, the pendent fluorocarbon substituent of the end product is determined by the materials reacted in the first step.

The above-described compositions are the subject of assignee's copending application entitled "Curable Fluorocarbon Substituted Polyetherurethaneacrylates", S.N. 28,966, filed of even date herewith in the names of Richard G. Newell and Stephen F. Wolf, incorporated herein by reference.

The amorphous segments, and the moieties having two or more polymerizable groups can be present in different components of the bonding composition, e.g., a mixture of an amorphous polyester acrylate, a urethane acrylate, and a diacrylate such as ethyleneglycol diacrylate.

Representative actinic light curable oligomeric compositions useful in the present invention are generally prepared by nucleophilic condensation or addition reactions between species selected from amines, alcohols and thioles, and epoxides with acyl compounds, e.g., isocyanates, carboxylic acids, esters and anhydrides, and derivatives thereof such as esters, anhydrides and carbonyl halides. The above listed polymerizable groups may be present in either the amorphous or the polyfunctional moiety as long as sufficient actinic light polymerizable groups are present to initiate and propagate polymerization and crosslinking of the material.

Suitable addition-polymerizable urethane oligomers are known and include the preferred oligomeric urethane-acrylates such as the polyesterurethane acrylates, e.g., the polyesterurethane acrylates disclosed in U.S. Patent 3,641,199 and U.S. Patent 3,907,574, and the polylactoneurethane acrylates, e.g. the polycaprolactoneurethane acrylates disclosed in U.S. Patent 3,700,643. Other suitable polymerizable urethane oligomers are the poiy(alkylenether) urethane acrylates disclosed in U.S. Patents 3,448,171; 3,850,770; 3,907,865 and 3,954, 584, the poly(oxydihydrocarbylsilene) urethane acrylates disclosed in U.S. Patent 3,577,262, and the polyolefinurethane acrylates, e.g. the polybutadieneurethane acrylates of U.S.Patent 3,678,014, and polypentadieneurethane acrylates of U.S. Patent 3,886,111.

Example 1.

A light-emitting diode (LED) commercially available from the Fairchild Company under the trade designation "FPE-2000" was mounted by means of a conductive epoxy resin onto a ceramic support.

One end of a 250-micrometer acrylic core optical fiber (the cladding near to the end of the fiber having been removed), commercially available from the E.l. du Pont de Nemours and Company under the trade designation "Crofon", was mounted so that the light passing through said fiber would fall onto the face of a silicon photodiode optical power detector. The optical power detector utilized a lock-in amplifier to indicate the intensity of the light emerging from the fiber. By means of the holder arm of a micromanipulator, the other end of the optical fiber (previously polished) was positioned adjacent the light-emitting active surface of the LED. A small amount (about 50 milligrams) of an ultraviolet radiation curable bonding composition was placed onto the polished end of the optical fiber using a small dip stick.The bonding composition was prepared by diluting with 2-N-butylcarbamylethyl methacrylate to a viscosity at 200C of 8700 centipoises a polycaprolactone urethane methacrylate prepared in accordance with the teachings of U.S. Patent 3,700,643 and having essentially the structure:

Using the micromanipulator, the polished end of the optical fiber was brought into a position normal to the surface of the LED, the fiber end being separated from the LED surface by a distance of about 1 5 micrometers. By means of the signal generator interfaced with the LED, the signal generator and accordingly the LED were operated in a repetitive pulsed mode. Further, the optical power detector was activated to monitor the intensity of the optical signal which had passed through the optical fiber from the LED.The vertical and horizontal co-ordinates of the polished end of the optical fiber were adjusted by the micromanipulator until, as indicated by the optical power detector, maximum signal intensity was obtained. The optical fiber-LED junction (which was enveloped by the bonding composition) was irradiated with ultraviolet light having a wavelength of 350-380 nanometers, the ultraviolet light source being a "Spectronics B-i 00" 250-watt mercury vapour lamp. After 1 minute of exposure to the ultraviolet radiation, the bonding composition had been cured to a sufficient degree to preliminarily optically align the optical fiber and the LED. A further small quantity of the above bonding composition was placed over and around the fiber-LED juncture and irradiated 4 additional minutes.

This second quantity of radiation-curable composition was applied to increase the strength of the LEDfiber juncture. Lastly, the optical fiber was released from the arm of the micromanipulator. The resulting assembly comprised an optical fiber which was firmly bonded to the face of LED. This was evidenced by the fact that when a pulling force was applied to the fiber, the fiber broke before the fiber-LED junction separated. The "pig-tailed" LED was then cycled from -200C to 700C for 5 cycles at the rate of 32 cycles per 24 hours with no measurable change in the optical output from the fiber at the completion of the test.A film was made by casting a 6-mil film (150-micrometers) of the above composition onto glass and polymerizing it by exposing it to the ultraviolet light generated by a 400 watt mercury vapor ultraviolet light source (365 nanometers wavelength) for 1 minute at 4 inch separation. The optical transmission of the 1 50 micrometer film was 96.2% that of air at 0.82 micrometer and 95.8% that of air at 1.3 micrometers. The film had a tensile strength of 250 psi (1.72 x 107 dynes/cm2) when measured on "lnstron Universal Tester" using a microtensile dumbell specimen having 2 cm gage length at a strain rate of 100% per minute.

Example 2.

Example 1 was repeated with the exception that the bonding composition used was "Optical Adhesive 65" (commercially available from Norland Optical Co.). This above bonding composition is thought to be a polyether having acrylic and allylic functional groups and containing a photoinitiator such as benzophenone and diethoxyacetophenone. This bonding composition had a Brookfield viscosity at 200C of 1200 centipoises as measured. A film made by casting the composition at a thickness of 1 50 micrometers onto a glass plate and polymerizing the film by exposing it to ultraviolet, had an optical transmission of 95.9% of that of air at a wavelength of 0.82 micrometer and 95.3% at 1.3 micrometers. The film had a tensile strength of 1 500 psi (1.03 x 108 dynes/cm2) and an elongation at break of 80%.The intensity of the radiation passing through the pigtailed optical fiber which has been "pig-tailed" to the LED did not change upon being thermally cycled from -200C to 700C 32 times in a 24 hour period.

Example 3.

Example 2 was repeated using as bonding composition a mixture of a radiation curable oligomer having essentially the structure:

and, based on the bonding composition, 0.1 percent diethoxyacetophenone radical polymerization initiator. The composition had a viscosity of 39,000 centipoises and on polymerization of a coating provided a film having a tensile strength of 1220 psi (8.41 x 107 dynes/cm2), an elongation at break of 9.4%, and an optical transmission of 97.3% at 0.82 micrometer and 97.6% at 1.3 micrometers. The UV-cured film has a refractive index of 1.41. The "pigtailed" LED did not change in optical transmission upon thermal cycling.

Examples 4-6.

Several "pigtailed" LED's were prepared using as bonding compositions the various radiationcurable oligomeric compositions shown in Table I. Table I also indicates the physical characteristics of films made using the various bonding compositions.

The optical output of the pigtailed optical fiber was found to be relatively constant irrespective of thermal cycling.

TABLE I Tensile Elongation Modulus of Oligomeric Viscosity, Optical Transmission strength at break, Elasticity composition cps UO psi (d/cm2) % psi 0.82 1.30 "a" 1675 94.8 95.3 1000 14 "b" 3650 97.2 97.2 1628 50 25,000 "c 350 95.9 95.1 3000 38 150,000 "a" is a mixture of 77.3 parts of 3, 4-epoxycyclohexyl-methyl-2, 4-epoxycyclohexane carboxylate, 9.7 parts of epoxysilane (commercially available from Union Carbide Corp. under the designation "Al 87", 9.7 parts polyoxytetramethylene glycol ("Terecol 1000", commercially available from E. I.

duPont de Nemours and Company), 2.9 parts of diphenyliodonium hexafluoro-phosphate and 0.4 part of 2-chlorothiaranthone.

"b" oligomer has essentially the structure:

"c" Norland Optical Adhesive 61, which appears to be essentially the same as Adhesive 65 described in Example 2 except that the only photoinitiator was benzophenone.

Claims (12)

CLAIMS:

1. A method for optically coupling a light conductor to an electro-optical device which includes the steps of: providing a light conductor and an electro-optical device which are to be optically coupled; placing on said light conductor or said electro-optical device a quantity of an actinic light curable composition in sufficient quantity and in such position to fix said light conductor with respect to said electro-optical device so as to provide optical alignment therebetween when cured, said oligomeric composition having a viscosity in the range of about 1000 to 200,000 centipoises and comprising:: a) 10 to 60 percent by weight actinic light addition polymerizable amorphous moieties; b) 10 to 50 percent by weight divalent organic connecting moieties; c) O to 50 per cent by weight diluent monomer; d) sufficient polyfunctional cross linking moieties having a plurality of addition polymerizable groups to provide a calculated molecular weight per crosslink of 500 to 5,000 when said composition is cured; e) sufficient actinic light activatable addition polymerization initiator to initiate cure of said composition when said composition is exposed to actinic light;; said composition having, when actinic light cured, a shear modulus in the range of 1 x 1 o8 to 3 x 109 dynes-cm, a 90% transmission of radiation having a wavelength of 0.4 micrometers to 2.0 micrometers, a tensile strength at break of greater than about 75 kg/cm and an elongation at break of at least 10%, said composition being radiation curable in less than about one minute; positioning said light conductor adjacent to said electro-optical so as to be optically aligned therewith; and curing said composition so as to maintain said optical alignment by exposing said composition to radiation having a wavelength which cures said composition in less than one minute.

2. A method according to claim 1 wherein the light conductor is an optical fiber.

3. A method according to claim 2 wherein the end of said fiber is positioned contigudus to the active portion of said electro-optical device.

4. A method according to claim 3 wherein said quantity of said composition envelopes the end of said fiber and the active portion of said electro-optical device.

5. A method according to claim 2 wherein there is an air space between said fiber and said device.

6. A method according to claim 2, said positioning step further includes aligning the optical axis of said light conductor normal to the active face of said device.

7. A method according to claim 1 wherein said positioning step further includes the optimization of the optical alignment of the light conductor and the eiectro-optical device by passing light from the electro-optical device through said conductor and monitoring the intensity of the light emerging therefrom.

8. A method according to claim 1 wherein said curing step is accomplished by passing radiation through said optical conductor.

9. An assembly comprising an electro-optical device and a light guide, the device and light guide being aligned so that light can pass therebetween, the alignment being maintained by means which including material obtained by actinic light cure of a composition having a viscosity in the range of 1000 to 200,000 centipoise and comprising an oligomer having:: a)

10 to 60 percent by weight actinic light addition polymerizable amorphous moieties; b) 10 to 50 percent by weight diva lent organic connecting moieties; c) O to 50 percent by weight diluent monomer; d) sufficient polyfunctional cross linking moieties having a plurality of addition polymerizable groups to provide a calculated molecular weight per crosslink of 500 to 5,000 (preferably 1,000 to 3,000) when said composition is cured; e) sufficient actinic light activatable addition polymerization initiator to initiate cure of said composition when said composition is exposed to actinic light; said composition being radiation curable in less than one minute; and optionally being admixed with actinic light polymerizable diluent monomers in sufficient quantity to provide desired viscosity.

1 0. An assembly according to claim 9 wherein said light guide is an optical fiber and said electrooptical device is a light emitting diode.

11. A method of optically coupling a light conductor to an electro-optical device substantially as described herein with reference to the accompanying drawings.

1 2. A method of optically coupling a light conductor to an electro-optical device substantially as described in any of the examples herein.

1 3. An assembly comprising an electro-optical device and a light guide connected by a method according to Claim 11 or Claim

12.