COUPLING OF OPTICAL FIBRES TO OPTICAL WAVEGUIDES

Abstract: In a method of effecting permanent end-to-end connections between a plurality of optical fibres 2,3,4..., e.g. the optical fibres of an optical fibre ribbon 1, and the optical waveguides 12,13,14... of an integrated optic device or chip 11, each optical fibre in turn is so arranged that its end 2′ to be connected protrudes beyond the ends of the other unconnected optical fibres with its end face spaced a short distance from the end face of the corresponding optical waveguide, accurate axial alignment of the core of the optical fibre and the corresponding waveguide is effected, curable adhesive is applied to the optical fibre and is permitted or caused to cure so that the optical fibre is permanently fixed with respect to the optical component, and these three steps are repeated for each immediately adjacent optical fibre and corresponding optical waveguide.

Description: This invention relates to the jointing of a plurality of optical fibres, such as the optical fibres of an optical fibre ribbon, to optical waveguides of an optical component of the kind comprising a substrate supporting a plurality of optical waveguides. The invention is especially, but not exclusively, concerned with the jointing of a plurality of optical fibres to the optical waveguides of an optical component of the aforesaid kind generally referred to as an integrated optic device or an integrated optic chip. In the specification of EP-A-0170457 there is described and illustrated a method of affixing a single mode optical fibre to a waveguide substrate in optical alignment with a waveguide thereon, which method comprises the steps of preparing an end of the fibre such as to have a planar end face substantially normal with respect to the fibre axis, mounting on the surface of the substrate in which the waveguide is embedded a support block which straddles the waveguide and which has an end face substantially co-planar with the termination of the waveguide, optically aligning the fibre core and the waveguide, and affixing the end face of the optical fibre with transparent adhesive to the waveguide substrate and block. This specification is silent on how the method described can be modified to affix a plurality of optical fibres, such as the optical fibres of an optical fibre ribbon, to waveguides embedded in a substrate although it indicates that the method described can be used for this purpose. In the paper entitled "Permanent Attachment of Single-Mode Fibre Arrays to Waveguides" by E.J. Murphy et al which appeared in the IEEE Journal of Light Technology, Vol. LT-3, No. 4 of August, 1985, a method of permanently attaching a plurality of optical fibres to waveguides embedded in a substrate is described. In this method, the optical fibres are secured by epoxy resin in a plurality of anisotropically etched silicon V-grooves which position the fibres such that their cores are precisely periodically spaced along a straight line. The end faces of the optical fibres are then polished and the plurality of fibres, secured in the V-grooves, is butt coupled to an array of straight waveguides embedded in a substrate, the fibres and waveguides being aligned by simultaneously maximising the throughput of two of the fibre-waveguide channels. Permanent attachment of the fibres to the waveguides is then effected using UV curable cement. This method has the disadvantage that it requires that the transverse spacing of the waveguides embedded in the substrate and the transverse spacing of the V-groove in which the optical fibres are secured are identical. It is an object of the present invention to provide an improved method of effecting permament end-to-end connections between a plurality of optical fibres and optical waveguides of an optical component of the aforesaid kind. According to the invention, the improved method comprises the steps of positioning the optical component to one side of a jointing station with end faces of the optical waveguides of the component exposed at the side face of the substrate nearer the jointing station; stripping any protective covering from an end portion of each length of optical fibre to provide exposed end portions of the optical fibres; preparing the end faces of the exposed end portions of the optical fibres so that the end face of each optical fibre is substantially smooth; arranging the exposed end portions of the optical fibres in approximately axial alignment with, but spaced from the end faces of, the optical waveguides; so clamping the exposed end portions of the optical fibres that the exposed end portion of each optical fibre can be caused to move lengthwise towards the substrate to a limited extent relative to the exposed end portions of the other of said optical fibres; arranging the exposed end portions of the optical fibres, over a part of their lengths between the position at which they are so clamped and the distal ends of the exposed end portions of the optical fibres so that each fibre follows a curved path whose centre of curvature lies on a line extending transversely of said optical fibres; causing the exposed end portion of an outermost optical fibre to straighten and, instead, follow a substantially rectilinear path so that, as a result, its end to be connected protrudes beyond the ends of the exposed end portions of the other unconnected optical fibres with its end face spaced from the end face of the corresponding optical waveguide of the optical component; effecting accurate axial alignment of the core of said optical fibre and the corresponding optical waveguide; applying curable adhesive to said optical fibre and permitting or causing the adhesive to cure so that said optical fibre is permanently fixed with respect to the optical component; and repeating the latter three steps for each immediately adjacent exposed end portion of optical fibre and corresponding optical waveguide until permanent end-to-end connections have been effected between all the optical fibres and corresponding optical waveguides of the optical component. In one preferred technique of applying curable adhesive to said optical fibre in such a way that the optical fibre is permanently fixed with respect to the optical component in axial alignment with the corresponding optical waveguide, the side face of the optical component in which the end faces of the optical waveguides are exposed has integral therewith or permanently connected a supporting body, the exposed end portion of each optical fibre is disposed above the supporting body and the end of the exposed portion of each optical fibre is so permanently connected to the supporting body by curable adhesive that each optical fibre is indirectly permanently connected to the optical component in axial alignment with the corresponding optical waveguide. In this case, in effecting accurate axial alignment of the core of said optical fibre and the corresponding optical waveguide, preferably after the exposed end portion of said optical fibre has been so straightened, the said optical fibre is fixed and the position of the optical component with respect to said fixed optical fibre is adjusted until the axes of the core of the fixed optical fibre and of the corresponding optical waveguide are in alignment. In this case, also, preferably index matching liquid and/or anti-reflective material is present or introduced between the spaced end faces of said optical fibre and the corresponding optical waveguide. In a second preferred technique of applying curable adhesive to said optical fibre in such a way that said optical fibre is permanently fixed to the optical component in axial alignment with the corresponding optical waveguide, a transparent curable adhesive is introduced between the spaced end faces of said optical fibre and of the substrate of the optical component and is permitted or caused to cure to effect the permanent connection. Preferably, in this case, the potential area of contact between the end face of said optical fibre and the end face of the substrate is increased by mounting on the uppermost surface of the substrate a supporting body which overlies the substrate and which has a side face that is substantially co-planar with the side face of the substrate in which the end faces of the optical waveguides are exposed, the transparent curable adhesive being introduced between the end face of said optical fibre and the end faces of the substrate and overlying supporting block. In using this technique, preferably in effecting accurate axial alignment of the core of the optical fibre and the corresponding optical waveguide, the optical component is so clamped that it is fixed and said optical fibre is moved with respect to the optical component until the axes of the core of the optical fibre and of the corresponding optical waveguide are in axial alignment. In all of the above techniques of applying curable adhesive in which a supporting body is employed, preferably the supporting body is of a material which is the same as or which is similar to the material of the substrate of the optical component. In all cases, also, preferably at a position spaced lenghwise from the jointing station at which permanent connections between the optical fibres and the corresponding optical waveguides have been made, the exposed portions of the optical fibres are permanently connected to a supporting substrate by means of a curable adhesive. The end faces of the exposed end portions of the optical fibres may be prepared so that the end face of each optical fibre is substantially smooth and flat and lies either in a plane radial to the fibre axis or in a plane inclined at an acute angle to said radial plane; alternatively, the end face of each optical fibre may be so prepared that it is substantially smooth and rounded. The improved method of the present invention is especially, but not exclusively, suitable for effecting permanent end-to-end connections between the optical fibres of an optical fibre ribbon and optical waveguides of an optical component of the aforesaid kind. Preferably, the limited lengths of the exposed end portions of the optical fibres are arranged so that each fibre follows a curved path whose centre of curvature lies on a line extending transversely of the optical fibres by introducing under said limited lengths of the exposed end portions of the optical fibres in a direction transversely of the optical fibres an elongate member which has a convexly curved surface over and at least partially around which the exposed end portions of the optical fibres pass and which can be moved incrementally in the direction of its length and tranversely of the optical fibres in such a way that each optical fibre in turn can be caused to drop off an end of the elongate member and adopt a substantially straight and rectilinear path so that its end to be permanently connected to a corresponding optical waveguide then protrudes beyond the ends of the exposed end portions of the other unconnected optical fibres. Incremental movement of the elongate member in the direction transverse of the optical fibres is preferably effected by a screw threaded arrangement. Clamping of the exposed end portions of the optical fibres preferably is effected by arranging for the exposed end portions to lie in a plurality of longitudinally extending substantially parallel grooves in the upper surface of the base plate of a material having a low coefficient of friction, e.g. silicon, and by retaining them thereon by a spring-loaded pressure pad, e.g. of a rubber-like material, having a surface which engages the optical fibres and which is of a material having a low coefficient of friction, e.g. polytetrafluorethylene. In this case, the elongate member having a convexly curved surface over which the exposed end portions of the optical fibres lie, preferably comprises a rod of circular cross section having in its surface a single helically extending groove within and partially around turns of which the exposed end portions of the optical fibres are arranged to lie. The turns of the groove in the rod will be in substantial alignment with the grooves in the base plate of the clamping means. The improved method of the present invention is suitable for use with optical components in which the optical waveguides are wholly or partially embedded in the substrate and for use with optical components in which the optical waveguides are carried on the upper surface of a substrate. The improved method of the present invention has the important advantages that it provides for effecting a plurality of permanent end-to-end connections between optical fibres and optical waveguides of an optical component of the aforesaid kind in a simple and rapid manner. Optimum axial alignment of all the optical fibres with their corresponding optical waveguides can be effected by sequential automatic micro positioning with optical monitoring to ascertain that accurate axial alignment has been obtained. The improved method is especially suitable for use with optical fibre ribbon comprising production quality optical fibres (with corresponding tolerances). This renders the improved method especially suitable for splicing of optical components of the aforesaid kind into systems. The improved method also provides for inexpensive and labour-efficient pigtailing of optical components. Where the optical fibres have thin buffer coatings, the spacing between the optical waveguides of the optical component may be relatively small and this is attractive from the point of view of the design of the optical component. The invention is further illustrated by a description, by way of example, of two preferred techniques for effecting permanent connection between one optical fibre of an optical fibre ribbon and a corresponding optical waveguide of an integrated optic device or chip, with reference to the accompanying drawings, in which:- Figures 1 and 2, respectively, are side and plan views of the preferred apparatus for effecting permanent connection between one optical fibre of an optical fibre ribbon and a corresponding optical waveguide of an integrated optic device or chip; Figure 3 is a diagrammatic side view of one preferred permanent connection between one optical fibre of an optical fibre ribbon and a corresponding optical waveguide of an integrated optic device or chip, effected using the apparatus shown in Figures 1 and 2, and Figure 4 is a diagrammatic side view of a second preferred permanent connection between one optical fibre of an optical fibre ribbon and a corresponding optical waveguide of an integrated optic device or chip, effected using the apparatus shown in Figures 1 and 2. Referring to Figures 1 to 3, the preferred apparatus includes a jointing station 20 at which the plurality of optical fibres of an optical fibre ribbon 1 can be permanently connected end-to-end to the optical waveguides of an integrated optic device or chip 11 of the kind comprising a substrate supporting a plurality of optical waveguides. Positioned on one side of the jointing station 20, is an optical fibre clamping device 23 comprising a base plate 24 of silicon having in its upper surface a plurality of longitudinally extending parallel grooves and, for retaining a plurality of optical fibres of the optical fibre ribbon 1 in the grooves, a spring-loaded pressure pad 25 of a rubber-like material having an undersurface of polytetrafluoroethylene which will engage the optical fibres. Positioned beyond the clamping device 23 remote from the jointing station 20 is a rod 27 of circular cross-section having in its surface a single helically extending groove 28 and, at one of its ends, a knurled operating knob 29. As will be seen, the rod 27 extends in a direction normal to the grooves in the upper surface of the base plate 24 of the clamping device 23 and, by appropriate rotation of the knurled knob 29, can be caused to move incrementally in either direction normal to the grooves. Positioned on the other side of the jointing station 20, is an adjustable clamping device 30 for supporting an integrated optic device or chip 11, the clamping device being adjustable with respect to the clamping device 23 in a direction lengthwise of and in two directions normal to the grooves of the clamping device 23 and rotationally about axes extending in said three directions. In using the preferred apparatus illustrated in Figures 1 and 2 to effect permanent end-to-end connections between the plurality of optical fibres of the optical fibre ribbon 1 and the optical waveguides of an integrated optic device or chip 11, an end portion of the length of optical fibre ribbon is stripped to provide exposed end portions 2, 3, 4... of the optical fibres and the end faces of the exposed end portions of the optical fibres are prepared so that the end face of each optical fibre is flat and lies in a plane radial to the fibre axis. A substantially rigid supporting body 18 is permanently connected to a lower part of the side face of the substrate of the integrated optic device or chip 11 in which the end faces of the optical waveguides 12,13,14... are exposed and the integrated optic device or chip is positioned in the clamp 30 with said side face of the substrate at which the end faces of the optical waveguides are exposed nearer the jointing station 20. The exposed end portions of the optical fibres 2, 3, 4... are spaced a short distance from and are arranged in approximately axial alignment with the optical waveguides 12, 13, 14.... at the jointing station 20 and the exposed end portions are arranged to lie in the longitudinally extending parallel grooves in the upper surface of the base plate 24 of the clamping device 23 and are clamped therein by the spring-loaded pressure pad 25. By virtue of the fact that the base plate 24 is made of silicon and the undersurface of the pressure pad 25 is make of polytetrafluoroethylene, the exposed end portion of each optical fibre 2,3,4... of the optical fibre ribbon 1 can move lengthwise to a limited extent relative to the exposed end portions of the other optical fibres of the length of optical fibre ribbon. In their passage from the cut-back end of the optical fibre ribbon 1 to the clamping device 23, the exposed end portions of the optical fibres 2,3,4... of the optical fibre ribbon lie in turns of the single helically extending groove 28 on the transversely movable rod 27 so that, between the cut-back end of the optical fibre ribbon and the clamping device 23, the exposed end portions of the optical fibres follow a curved path 10 whose centres of curvature lie on a line extending transversely of the length of optical fibre ribbon (see Figure 1). The helically grooved rod 27 is then unscrewed incrementally in such a direction that the exposed end portion of an outermost optical fibre 2 of the length of optical fibre ribbon 1 falls off the free end of the rod and adopts a straight and rectilinear path so that its end 2' to be connected to the corresponding waveguide 12 of the integrated optic device or chip 11 protrudes beyond the ends of the exposed end portions of the other optical fibres 3,4... of the optical fibre ribbon 1 and overlies the supporting body 18 connected to the substrate of the integrated optic device or chip 11 (see Figure 2). The position of the integrated optic device or chip 11 with respect to the clamping device 23 and hence to the fixed optical fibre 2 is adjusted until the axes of the core of the fixed optical fibre 2 and the corresponding optical waveguide 12 are in alignment and, if desired index-matching liquid and/or an anti-reflective coating (not shown) may be introduced or may be present between the spaced end faces of the optical fibre 2 and the corresponding optical waveguide 12. Curable adhesive 19 is then applied to the protruding end 2' of the optical fibre 2 to connect the optical fibre permanently to the supporting body 18 and the adhesive is cured so that the optical fibre is permanently fixed with respect to the integrated optic device or chip 11. This sequence of steps is then repeated for each immediately adjacent optical fibre 3, 4... and the corresponding optical waveguide 13, 14... in turn until all the optical fibres of the optical fibre ribbon 1 have been permanently connected to the optical waveguides of the integrated optic device or chip 11. In the second preferred technique for effecting permanent connection between an optical fibre of an optical fibre ribbon and a corresponding optical waveguide of an integrated optic device or chip as shown in Figure 4, the potential area of contact between the end face of the optical fibre 32 and the end face of the substrate of the integrated optic device or chip 41 is increased by mounting on the uppermost surface of the substrate a supporting body 48 which overlies the substrate and which has a side face that is substantially co-planar with the side face of the substrate in which the end faces of the optical waveguides 42,43,44... (of which only waveguide 42 is shown) are exposed. In effecting the permanent connection between an optical fibre 32 and the corresponding optical waveguide 42, transparent curable adhesive 49 is introduced between the end face of the optical fibre and the end faces of the substrate and overlying supporting block 48. The apparatus illustrated in Figures 1 and 2 is used to effect permanent connections between the optical fibres 32,33,34... of an optical fibre ribbon, (of which only optical fibre 32 is shown) and the optical waveguides 42,43,44... of an integrated optic device or chip 41 using the technique illustrated in Figure 4 but, in this case, in effecting accurate axial alignment of the core of each optical fibre in turn and the corresponding optical waveguide, the integrated optic device or chip 41 is so clamped by the clamp 30 that it is fixed and the clamping device 23 is moved with respect to the integrated optic device or chip until the axes of the core of the optical fibre and the corresponding optical waveguide are in axial alignment. The improved method of the present invention has the very important advantage that it provides for sequential permanent connection of the optical fibres of a length of optical fibre ribbon with the optical waveguides of an integrated optic device or chip in such a way that each optical fibre of the ribbon is free to move lengthwise to a limited extent with respect to the other optical fibres of the ribbon and that, during permanent connection of any optical fibre with an optical waveguide, the risk that any other optical fibre of the ribbon will be prematurely partially permanently connected to the integrated optic device or chip during such permanent connection of said optical fibre and optical waveguide is substantially reduced.

Claims: A method of effecting permanent end-to-end connections between a plurality of optical fibres (2,3,4...) and optical waveguides (12,13,14...) of an optical component (11) of the kind comprising a substrate supporting a plurality of optical waveguides, which method comprises the steps of positioning the optical component (11) to one side of a jointing station (20) with end faces of the optical waveguides (12,13,14...) of the component exposed at the side face of the substrate nearer the jointing station; stripping any protective covering from an end portion of each length of optical fibre (2,3,4...) to provide exposed end portions of the optical fibres; preparing the end faces of the exposed end portions of the optical fibres so that the end face of each optical fibre is substantially smooth; arranging the exposed end portions of the optical fibres in approximately axial alignment with, but spaced from the end faces of, the optical waveguides; so clamping the exposed end portions of the optical fibres that the exposed end portion of each optical fibre can be caused to move lengthwise towards the substrate to a limited extent relative to the exposed end portions of the other of said optical fibres; arranging the exposed end portions of the optical fibres, over a part of their lengths between the position at which they are so clamped and the distal ends of the exposed end portions the optical fibres so that each fibre follows a curved path (10) whose centre of curvature lies on a line extending transversely of said optical fibres; causing the exposed end portion of an outermost optical fibre to straighten and, instead, follow a substantially rectilinear path so that, as a result, its end (2') to be connected protrudes beyond the ends of the exposed end portions of the other unconnected optical fibres with its end face spaced from the end face of the corresponding optical waveguide (12) of the optical component; effecting accurate axial alignment of the core of said optical fibre and the corresponding optical waveguide; applying curable adhesive (19,49) to said optical fibre and permitting or causing the adhesive to cure so that said optical fibre is permanently fixed with respect to the optical component; and repeating the latter three steps for each immediately adjacent exposed end portion of optical fibre and corresponding optical waveguide until permanent end-to-end connections have been effected between all the optical fibres and corresponding optical waveguides of the optical component. A method as claimed in Claim 1, wherein the side face of the optical component in which the end faces of the optical waveguides are exposed has integral therewith or permanently connected thereto a supporting body (18), the exposed end portion of each optical fibre is disposed above the supporting body and the end of the exposed portion of each optical fibre is so permanently connected to the supporting body by curable adhesive (19) that each optical fibre is indirectly permanently connected to the optical component (11) in axial alignment with the corresponding optical waveguide. A method as claimed in Claim 2, wherein, in effecting axial alignment of the core of said optical fibre and corresponding optical waveguide, after the exposed end portions of said optical fibre has been so straightened the said optical fibre is fixed and the position of the optical component with respect to said fixed optical fibre is adjusted until the axes of the core of the fixed optical fibre and of the corresponding optical waveguide are in alignment. A method as claimed in Claim 1, wherein a transparent curable adhesive (49) is introduced between the spaced end faces of said optical fibre and of the substrate of the optical component and is permitted or caused to cure to effect the permanent connection. A method as claimed in Claim 4, wherein the potential area of contact between the end face of said optical fibre and the end face of the substrate is increased by mounting on the uppermost surface of the substrate a supporting body (48) which overlies the substrate and which has a side face which is substantially co-planar with the side face of the substrate in which the end faces of the optical waveguides are exposed, the transparent curable adhesive being introduced between the end face of said optical fibre and the end faces of the substrate and overlying supporting block. A method as claimed in Claim 4 or 5, wherein, in effecting accurate axial alignment of the core of the optical fibre and the corresponding optical waveguide, the optical component is so clamped that it is fixed and said optical fibre is moved with respect to the optical component until the axes of the core of the optical fibre and of the corresponding optical waveguide are in axial alignment. A method as claimed in any one of the preceding Claims, wherein the limited lengths of the exposed end portions of the optical fibres are arranged so that each fibre follows a curved path (10) whose centre of curvature lies on a line extending transversely of the optical fibres by introducing under said limited lengths of the exposed end portions of the optical fibres in a direction transversely of the optical fibres an elongate member (27) which has a convexly curved surface over and at least partially around which the exposed end portions of the optical fibres (2,3,4...) pass and which can be moved incrementally in the direction of its length and transversely of the optical fibres in such a way that each optical fibre in turn can be caused to drop off an end of the elongate member and adopt a substantially straight and rectilinear path so that its end to be permanently connected to a corresponding optical waveguide then protrudes beyond the ends of the exposed end portions of the other unconnected optical fibres. A method as claimed in Claim 7, wherein incremental movement of the elongate member in the direction transverse of the optical fibres is effected by a screw threaded arrangement. A method as claimed in Claim 7 or 8, wherein clamping of the exposed end portions of the optical fibres is effected by arranging for the exposed end portions to lie in a plurality of longitudinally extending substantially parallel grooves in the uppersurface of a base plate (24) of a material having a low coefficient of friction and by retaining them thereon by a spring loaded pressure pad (25) having a surface which engages the optical fibres and which is of a material having a low coefficient of friction. A method as claimed in Claim 9, wherein the elongate member having a convexly curved surface over which the exposed end portions of the optical fibres lie comprises a rod of circular cross-section having in its surface a single helically extending groove (28) within and partially around turns of which the exposed end portions of the optical fibres are arranged to lie.

Inventors: KEENE, IAN WILLIAM
Applicants: BICC PUBLIC LIMITED COMPANY
Application year: 1987
Main classification: G02B6
IPC codes: G02B6