APPARATUS FOR CONNECTING AN OPTICAL FIBRE TO AN OPTICAL DEVICE

Abstract: An optical fibre (3) is connected to an optical device (1) having a substrate (1) with locating means, such as a V-groove (7), forlocating the fibre (3) on the substrate (1). Attachment means (6) secure the optical fibre (3) at a position remote from the locating means (7) so that the fibre (3) is held in a state of elastic deformation to assist in holding the fibre (3) in contact with the locating means (7) without it being secured thereto.

Description: AP p ΛRATUS FOR CONNECTING AN OPTICAL FIBRE TQ AN OPTICAL DEVICE TECHNICAL ^'ELD This invention -elates to apparatus for connecting an optical fipre to an optical device BACKGROUND ART It is known to connect an ootical fibre to an optical device by mounting the end of the fiore in a V-groove provided in the face of an optical chip in orαer to align the ootical fiore with a waveguide on the chip The fibre is conventionally secured ,n :re V-groove ov acnes. ve cr solder wnicn can cause misalignment if too mucn cr tco little aches ve cr soider is used Such apparatus also suffers from disadvantages aπsirc : rcm solidification of the adhesive or solder or material creec < 'he aches, y y soider which can ooth cause movement of the fibre ana so disturb the alignment of the fiore with the waveguide The presert nvention SΘΘKS * o overcome or avoid such problems DISCLOSURE OF THE INVENTION According :c a τ' 'rst aspect of the invention there is provided apparatus for connecting an ootical fibre to an optical device comprising a substrate having locating means for locating a - ' ibre on the substrate and attacnment means for securing the ootical fibre at a position remote from the locating means such that when the fibre is secured to the attacnment means the fibre is neid in a state of elastic deformation so as to assist ,n holding the fibre in contact with said locating means without it being secured thereto Other features of the invention will be apparent from the following description and from the subsidiary claims of the specification BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further descπoed merely by way of example with reference to the accompanying drawings in which Figure 1 is a perspective view of the apparatus according to one embodiment of the invention Figure 2 is a side view of the apparatus snown in Figure 1 Figures 3A and 3B are schematic diagrams showing enlarged plan and side views of the apparatus according to the invention The curvature of the fibre snown in Figure 3B has been exaggerated to illustrate better a feature of the invention Figure 4 is a schematic cross-sectional side view of the aparatus shown in Figures 1 and 2 and Figure 5 is a perspective view of the apparatus according to a second embodiment of the invention BEST MODE OF CARRYING OUT THE INVENTION Figures 1 and 2 show a substrate in the form of an optical chip 1 mounted on a base 2 e g of aluminium oxide or aluminium nitride and an optical fibre 3 for transmitting signals received on an optical fibre cable 4 to an optical device on the chip 1 or vice versa A fibre jacket tie off 5 is provided on the base 2 for securing the jacket or other external coating of the fibre cable 4 to the base 2 or to a casing attached thereto so that external forces applied to the cable 4 are not transmitted to the chip 1 The tie off 5 is arranged so that it rigidly holds the external coating of the fibre cable 4 The fibre itself is not, however rigidly held by the tie-off 5 due to the provision of resilient plastics material around the fibre which permits the fibre itself to move to some extent relative to the tie off 5 Figures 1 and 2 also show a fibre attach pad 6 for securing the optical fibre 3 at a position remote from the chip 1 As more clearly shown in Figures 3A and 3B the end of the fibre 3 is located in a V-groove 7 provided in the surface of the optical chip 1 The Figures also show an optical waveguide 8 on the chip 1 with which the fibre 3 is to be aligned The V-groove serves to locate the lateral position of the fibre i e in a direction perpendicular to the optical axis of the waveguide 8 and the fibre 3 in this case the position of the fibre in a direction perpendicular to the plane of the chip 1 and its position in both directions perpendicular to the said optical axis within the plane of the chip 1 As snown in Figure 3B the fibre 3 is secured to the fibre attach pad 6 which is located remote from the V-groove 7 and the fiore is held by the pad 6 at a position further from the case 2 than the V-groove 7 so that the fibre 3 is held in a state of elastic deformation between the pad 5 and the V-groove 7 Thus the fibre 3 adopts a curved snaoe as shown (somewhat exaggerated) in Figure 3B This elastic deformation of the fibre 3 assists in nolding the eno of the fibre 3 in the V-groove as the elastic deformation urges the end of the fibre 3 in a direction towards the bottom of the V-groove and resists movement of the fibre out of the V-groove in a direction perpendicular to the plane of the chip 1 The end of the fibre 3 is thus held within the V-groove without the need for adhesive or soiαer in the V-groove The pad 6 is typically located between 2 and 10 mm from the V-groove The fibre 3 is secured to the fibre attach pad by adhesive e g a light-cured or heat-cured resin or solder e g a glass solder or may be secured thereto by mechanical means (not shown ) e g a clamp The top surface of the pad 6 is preferably inclined to the plane of the chip 1 by an angle θ so that the fibre 3 is held in an inclined position thereon The angle θ may typically be in the range 1 - 5 degrees and preferably in the range 2 5 to 3 5 degrees The angle selected will depend upon the geometry of the arrangement i e the height of the pad 6 its distance from the V-groove 7 etc and by the elastic properties of the fibre 3 The larger the angle the more securely the end of the fibre 3 is held in the V-groove 7 but if the angle is too large tensile strain induced on the fibre may lead to failure of the fibre due to static fatigue Preferably the angle is selected so as to introduce a maximum strain of 0 3 - 0 4% on the outer curved surface of the fibre However in some cases depending on the geometry of the arrangement and the strength of the fibre the maximum strain cue to the curvature of the fiore may be as low as 0 1 % and in other cases it may oe higner e g up to 1 % or 2% The arrangement snould also be designed so the elastic deformation holds the fibre in the V-groove with sufficient force to resist forces due to shock and vioration causing the fibre to move out of contact with the V-groove This αepenos on the application in cases where the apparatus is unlikely to be suoject to any extremes of motion the arrangement may be designed so as to resist movement of the fiore out of the V-groove when subject to an acceleration of uo to 40g In other cases it may be desirable to ensure the fibre remains neid in the V-groove by the forces caused by its elastic deformation when subject to accelerations of several thousand g In addition to avoiding misalignment problems associated with the use of adhesive or solder in the V-groove 7 the apparatus described also helps avoid long term stress corrosion problems with the fibre as it is only rigidly fixed at one point i e to the attach pad 6 In a conventional arrangement the fibre is secured by adhesive or solder in the V-groove 7 and also rigidly secured at the fibre jacket tie off 5 The length of fibre between these two fixed points is subject to differential thermal expansion with the case 2 which induces stresses and strains in the fibre wnich can lead to its failure In the arrangement descπoed herein the length of the ore etween the pad 6 and V-groove 7 is only secured at one end i e to the pad 6 so the end of the fibre on the chip 1 is free to move along its length as it expands and contracts without stresses or strains being induced therein This helps increase the long term reliability of the apparatus A similar proolem does not arise in the length of fibre between the pad 6 and the tie-off 5 as the latter only holds the fibre jacket and the optical fibre is still able to move due to the resilient nature of the plastics materials between the fibre and the tie-off 5 Figure 4 is a schematic cross-sectionai view througn the apparatus viewed from the side Figure 4 shows the fibre caoie Δ. secured to the tie-off 5 and the optical fibre 3 extending the r efrom to an optical device 1 Between the tie-off 5 and the device 1 the fiore 3 is attacned to the fiore attach pad 6 by means of epoxy resin 1 0 Preferaoly the fibre 3 is in contact with the inclined upper surface of the attach pad 6 with no eσoxy resin therebetween The fiore cable 4 comprises the ootical ficre 3 an inner sleeve or coating 1 1 and an outer coating or jacket 12 Both of the coatings 1 1 and 12 are formed of plastics material the inner coating 1 may for instance be formed of a U-V cured acrylate and the outer coating 12 may be polypropylene or another plastics material having similar properties As snown in Figure 4 both coatings 1 1 and 12 are rigidly secured to the tie-off 5 by means of an adhesive 1 3 such as an epoxy resin The fibre 3 itself is not however secured directly to the tie- off 5 and is thus free to move to some extent ,n an axial direction by virtue of the resilience of the coatings 1 1 and 12 ano/or by sliding within the inner coating 1 1 Such movement enables thermal expansion of the fibre 3 to be accommodated without inducing strain in the fibre In assembly of the apparatus the end of the fibre 3 is typically first located in the V-groove 7 and its axial position then adjusted to leave a gap of around 10 microns between the end of the fibre and the end of the waveguide 8 If desired stops ( not shown ) may be provided in the V-groove to prevent the fibre 3 being slid into contact with the waveguide 8 and potentially damaging the end of the waveguide 8 Furthermore as the adhesive fixing to the pad 6 is remote from the chip 1 there is greater freedom in the cnoice of adhesive or clamping technology used to secure the fibre as the effect of the technology on the chip 1 is not of such concern The waveguide 8 illustrated in Figure 3B is shown overhanging the eno of the V-groove 7 (which has an inclined end-wall) This form of connection is suitable for a rib waveguide formed on a silicon-on-insulator chip but it will be appreciated that other arrangements and other types of optical chip may be used The fibre attach pad 6 may oe formed of any suitable material and may typically be formed of ceramic to help minimise any thermal mismatch in the adhesive joint with the fibre The pad 6 is preferably a separate item mounted on the base 2 but in other arrangements (not shown) it may form part of the cnip 2 or be mounted on the chip 2 The pad 6 should of course hold the fibre 3 in approximate alignment yvith the V-groove 7 but accurate alignment to within a few microns is not necessary due to its distance from the V-groove (typically around 4 - 6 mm) and oecause the V-groove is able to hold the fibre in alignment with the waveguide 8 even if the fibre is also subject to some sideways displacement i e in a direction perpendicular to the optical axis and within the plane of the chip 1 Other forms of locating means may be provided on the chip in place of a V- groove e g a step or one or more pedestals against wnich the side of the fibre abuts The fibre 3 may also be flexed sideways i e in a direction parallel to the plane of the chip 1 instead of or in addition to the flexing in a direction perpendicular to the plane of the chip Although the description given above relates to the alignment of an optical fibre with a waveguide the fibre may also be arranged to connect with other forms of optical devices e g a light emitter or a light receiver Multiple fibres e g in the form of a fibre ribbon may be connected in a similar way F.gure 5 snows an embodiment in which a fibre riDbon 14 comprising a plurality of ootical fibres e g four or more is connected to an optical device As in the embodiment described above the ribbon 14 is held by a tie-off 5A and the fibre ribbon is secured to a fibre attacn pad 6A positioned remote from an optical chip 1 Each of the optical fibres in the ribbon 14 is located within a respective V-groove (not snown) or other form of locating means on the chip 1 As shown in the Figure a single attach pad 6A is used to secure a plurality of optical ficres and a single tie-off 5A is used to nold the fibre ribbon 14

Claims: CLAIMS Apparatus for connecting an optical fibre to an optical device comprising a substrate having locating means for locating a fibre on the substrate and attachment means for securing the optical fibre at a position remote from the locating means such that when the fibre is secured to the attachment means the fibre is held in a state of elastic deformation so as to assist in holding the fibre in contact with said locating means without it being secured thereto Apparatus as claimed in Claim 1 in which the attachment means comprises mounting means inclined relative to a major face of the substrate by an angle ιr the range 1 to 5 degrees and preferably in the range 2 5 to 3 5 degrees Apparatus as claimed in Claim 1 or 2 in wnich the attachment means is located at a position 2 to 10 mm from the locating means and preferably 4 to 6 mm therefrom Apparatus as claimed in Claim 1 2 or 3 in which the locating means comprises a groove formed in a major face of the substrate Apparatus as claimed in Claim 4 in which the groove is a V-groove Apparatus as claimed in any preceding claim in which the fibre is secured to the attacnment means oy adhesive Apparatus as claimed :n any preceding claim in which the fibre is secured to the attachment means by mechanical means Apparatus as claimed in any preceding claim in which the securement of the optical fibre to the attachment means is the only point at which the fibre is rigidly fixed Apparatus as claimed in any preceding claim in which the substrate comprises a chip mounted on a base and the attachment means is also mounted on the base Apparatus as claimed in Claim 9 in which the chip is a silicon-on-insulator Apparatus as claimed in Claim 9 or 10 in wnich the attachment means is formed of a ceramic Apparatus as claimed in any preceding claim in which the elastic deformation induces a maximum strain of 0 3 - 0 4% on the fibre Apparatus as claimed in any preceding claim in which the end of the fibre on the substrate is free to move along its length Apparatus as claimed in any preceding claim in which a part of the fibre which is to be external of the apparatus is provided with a coating and securement means are provided for securing the coating to the apparatus Apparatus as claimed in Claim 14 in which the substrate is mounted on a base and the securement means secures the said coating to the case or to a casing attached to the base Apparatus as claimed in any preceding claim in which the fibre is aligned with a waveguide provided on the substrate Apparatus for connecting an optical fibre to an optical device substantially as hereinbefore described with reference to the accompanying drawings Apparatus as claimed in any preceding claim for for connecting a plurality of optical fiores to an optical device the substrate having a plurality of locating means for receiving the respective fibres and the attachment means being arranged to secure each of the plurality of fibres at positions remote from the locating means such that when the fibres are secured to the attachment means each fibre is held in a state of elastic deformation so as to assist in holding the fibre in contact with the respective locating means without it bemα secured thereto AMENDED CLAIMS [received by the International Bureau on 19 March 1999 (19.03.99); original claims 1,2 and 4-18 replaced by new claims 1,2 and 4-13 remaining claims unchanged (2 pages)] 1. Apparatus for connecting an optical fibre to an optical device on an optical chip, the optical fibre having at least one resilient coating, the apparatus comprising: a base; securement means for securing the optical fibre, via said at least one resilient coating, to the base; an optical chip mounted on the base and having the optical device thereon; locating means formed on the optical chip for locating the optical fibre on the chip relative to the optical device; and attachment means mounted on the base for securing the optical fibre at a position remote from the locating means, the optical fibre being rigidly secured to the attachment means such that the optical fibre is held in a state of elastic deformation so as to assist in holding the optical fibre in contact with the locating means without the optical fibre being secured thereto so that the securement. of the optical fibre to the attachment means is the only point at which the optical fibre is secured and the length of the fibre between the attachment means and the locating means is free to move along its length due to thermal expansion and contraction. 2. Apparatus as claimed in Claim 1 in which the attachment means comprises mounting means inclined relative to a major face of the optical chip by an angle in the range 1 to 5 degrees and preferably in the range 2.5 to 3.5 degrees. 3. Apparatus as claimed in Claim 1 or 2 in which the attachment means is located at a position 2 to 10 mm from the locating means and preferably 4 to 6 mm therefrom. 4. Apparatus as claimed in Claim 1 , 2 or 3 in which the locating means comprises a groove formed in a major face of the optical chip. 5. Apparatus as claimed in Claim 4 in which the groove is a V-groove. 6. Apparatus as claimed in any preceding claim in which the optical fibre is rigidly secured to the attachment means by adhesive. 7. Apparatus as claimed in any preceding claim in which the optical fibre is rigidly secured to the attachment means by mechanical means. 8. Apparatus as claimed in any preceding claim in which the optical chip is a silicon-on-insulator chip. 9. Apparatus as claimed in any preceding claim in which the attachment means is formed of a ceramic. 10. Apparatus as claimed in any preceding claim in which said elastic deformation induces a maximum strain of 0.3 - 0.4% on the fibre. 11. Apparatus as claimed in any preceding claim in which the optical fibre is aligned with a waveguide provided on the optical chip. 12. Apparatus for connecting an optical fibre to an optical device substantially as hereinbefore described with reference to the accompanying drawings. 13. Apparatus as claimed in any preceding claim for for connecting a plurality of optical fibres to one or more optical devices, the optical chip having a plurality of locating means formed thereon for receiving the respective optical fibres and the attachment means being arranged to secure each of the plurality of optical fibres at positions remote from the respective locating means such that when the optical fibres are rigidly secured to the attachment means each optical fibre is held in a state of elastic deformation so as to assist in holding the optical fibre in contact with the respective locating means without it being secured thereto. STATEMENT UNDER ARTICLE 19 The invention relates to a permanent connection between an optical fibre and an optical device on an optical chip Such a permanent connection requires a precise and carefully controlled flexing of the fibre to ensure stable location of the fibre but, at the same time, avoid introducing stress corrosion problems in the fibre The optical device is provided on an optical chip and locating means, eg a V- groove, provided on the chip The locating means can thus be accurately formed, eg by lithographic techniques, and automatically aligned with the optical device as their positions may be defined by the same lithographic step The attachment means provides a stable mounting for the fibre and should be of a material compatible with the technology used to secure the fibre thereto The attachment means is mounted on the base and can thus be formed ot a suitable material, eg a ceramic The properties of the locating means at the attachment means can therefore be selected independently of each other The optical fibre is secured to the apparatus via a resilient coating provided on the fibre, and the optical fibre itself is only rigidly secured at one point, le to the attachment means, which provides the required control over its elastic deformation The end of the fibre is not secure to the locating means, or anything else, so is free to expand and contract without stress corrosion arising therein Claim 1 has been amended to clarify the differences between the invention and the cited prior art

Inventors: YEANDLE JONATHAN CHARLES, YEANDLE, JONATHAN, CHARLES
Applicants: BOOKHAM TECHNOLOGY LTD, BOOKHAM TECHNOLOGY LIMITED
Application year: 1998
Main classification: G02B6
IPC codes: G02B6