WO2004008211A1

WO2004008211A1 - Optical fibre connector

Info

Publication number: WO2004008211A1
Application number: PCT/GB2003/002659
Authority: WO
Inventors: Jan Watte; Thomas T. De Boer; Aad Middeldorp; Jacco Elenbaas
Original assignee: Tyco Electronics Raychem Nv; Tyco Electronics Uk Ltd
Priority date: 2002-07-16
Filing date: 2003-06-20
Publication date: 2004-01-22
Also published as: GB0216435D0; TW200403458A; AU2003240130A1

Abstract

An optical fibre connector (19), comprising a ferrule (1) to be fixed to an optical fibre such that the fibre extends through the ferrule along an axis thereof, and a connector body in which the ferrule is arranged to be received, wherein the ferrule may be received in the connector body only in a pre-set orientation about the axis of the ferrule, with respect to the connector body.

Description

Optical Fibre Connector

The present invention relates to optical fibre connectors, and in particular relates to connectors for forming mechanical splices between optical fibres.

Conventionally, mechanical splices between optical fibres are formed by producing a polished end face of each fibre in a plane perpendicular to the longitudinal axis of the fibre, and mechanically securing the two fibres with their end faces together and in alignment with each other. Index-matching gel may also be used in order to reduce the optical losses caused by the splice.

It is also known to form fusion splices between optical fibres (i.e. in which the fibres are fused together by heat), by providing an end face of each fibre at an angle that is not perpendicular to the longitudinal axis of the fibre. Such a non-perpendicular end face of the fibre has the advantage that the proportion of light leaving or entering the fibre which is reflected by the end face is not directed back towards the source of the light thereby causing problems such as an increase in the optical noise level and/or disturbing the operation of optical devices in the circuit. Instead, if the end face of the optical fibre is non- perpendicular to the axis of the fibre, back reflected light is directed away from the incident light beam, thereby avoiding such problems.

According to a first aspect, the present invention provides an optical fibre connector, comprising a ferrule to be fixed to an optical fibre such that the fibre extends through the ferrule along an axis thereof, and a connector body in which the ferrule is arranged to be received, wherein the ferrule may be received in the connector body only in a pre-set orientation about the axis of the ferrule, with respect to the connector body.

Preferably the ferrule may be received in the connector body only in a single pre-set orientation about the axis of the ferrule, with respect to the connector body.

The invention has the advantage that because the ferrule may be received in the connector body only in a pre-set orientation, by fixing the ferrule to an optical fibre before the ferrule is received in the connector body the optical fibre is automatically arranged in a pre-set orientation (about its axis) with respect to the connector body upon insertion of the ferrule in the connector body. This means, for example, that an optical fibre with an end face which is not perpendicular to the axis of the fibre (referred to herein as a "non-perpendicular end face") will have its end face automatically oriented in a pre-set orientation with respect to the connector body upon insertion of the ferrule in the connector body, if the relative orientations of the fibre and the ferrule are determined and fixed in advance. In this way, for example, if the connector is arranged to interconnect a pair of optical fibres having

• identically angled non-perpendicular end faces, the two end faces may be brought together \ such that they are in intimate contact with each other over substantially their entire surfaces simply by inserting their respective ferrules into the connector body.

By the "axis" of the ferrule is preferably meant a generally central axis of the ferrule. However, at least in the broadest aspects of the invention, the axis of the ferrule need not correspond with the centre of the ferrule or with an axis of symmetry of some or all of the ferrule; the axis may be off-centre.

Preferably the ferrule and the connector body have corresponding surfaces which cause the ferrule to be receivable in the connector body in only a single pre-set orientation (or alternatively in only one orientation at a time, of a plurality of discrete pre-set orientations). More preferably at least part of the axial length of an external surface of the ferrule and an internal surface of the connector body have such corresponding surfaces. Most preferably the corresponding surfaces of the ferrule and the connector body prevent rotation of the ferrule relative to the connector body when the ferrule is received within the connector body.

Advantageously, in preferred embodiments the ferrule may be received in the connector body only by substantially axial insertion of the ferrule into the connector body through an open end of the connector body. Preferably a said corresponding surface of the ferrule extends from a front end of the ferrule that is arranged to be the first part of the ferrule to be inserted into the connector body.

According to a second aspect, the invention provides a method of interconnecting two optical fibres by means of an optical fibre connector according to the first aspect of the invention, comprising fixing a respective said ferrule to each optical fibre such that an end portion of the fibre extends from a front end of the ferrule, and inserting the ferrules into the connector body such that the fibres form an in-line butt splice connection with each other.

Other preferred and optional features of the invention are described below and in the dependent claims.

The invention will now be described, by way of example, with reference to the accompanying drawings, of which:

Figure 1 shows a cross-sectional view of an embodiment of a ferrule of a connector according to the invention;

Figure 2 shows schematic top and side views of embodiments of ferrules of a connector according to the invention, illustrating an external profile of the ferrules intended to ensure that the ferrules may be received in a connector body of the connector in only a pre-set orientation about the axis of the ferrule; Figure 3 shows various component parts of an embodiment of a connector body of a connector according to the invention;

Figure 4 shows the component parts of a holder/ferrule assembly according to the invention;

Figure 5 shows how a holder/ferrule assembly is attached to the connector body: Figure 6 shows two views of an assembled embodiment of a connector according to the invention; and

Figure 7 shows a further view of the connector shown in Figure 4.

Figure 1 shows an axial cross-sectional view of an embodiment of a ferrule 1 of a connector according to the invention. The ferrule, which is formed from a deformable material, preferably metal, more preferably a metal alloy, for example phosphor bronze (preferably nickel plated to prevent corrosion), is generally cylindrical and has an axial bore 3 extending throughout its entire length. (The axis of the ferrule is indicated by the line A- A.) The bore 3 has a relatively wide diameter section 3' (e.g. of 1mm diameter) for example for accommodating the buffer jacket of an optical fibre, and a relatively narrow diameter section 3" (e.g. of 0.3 mm diameter) for example for forming a snug fit around an end section of the optical fibre from which the buffer jacket has been stripped. Between the sections 3' and 3" is a frusto-conical transition section 4 of the bore. The narrow diameter section 3" of the axial bore extends from a front end 5 of the ferrule 1, and the wide diameter section 3' extends from a rear end 7 of the ferrule 1.

At the rear end 7 of the ferrule the circumferential external surface 8 of the ferrule includes a pair of diametrically-opposed projections 9, the purpose of which will be explained below. Towards the front end 5 of the ferrule the circumferential external surface includes a circumferential N-groove 11 which may be used, for example, in an optical fibre

\ cleaving tool for positioning the ferrule with respect to a cleaving mechanism when the ferrule is fixed to an optical fibre extending through the ferrule.

Figure 1 does not show the most important aspect of the ferrule 1, namely a part of the circumferential external surface of the ferrule which causes the ferrule to be receivable in a connector body of a connector according to the invention in only a single pre-set orientation about the axis of the ferrule. However, this feature is shown in Figure 4, and comprises a cut-away flat surface part 15 of the circumferential external surface 8 extending from the front end 5 of the ferrule. Figure 2 shows schematic top and side views of two ferrules 1 according to the invention having optical fibres 13 extending therethrough. It can be seen that both ferrules 1 (which are identical to each other) have such a cut-away flat surface part 15 of their circumferential external surface 8 which is at a fixed orientation with respect to a cleaved non-perpendicular end face 17 of the respective optical fibre 13 extending through the ferrule. This was achieved as follows.

An end section of an optical fibre 13 had its buffer jacket stripped to expose the primary coating, and the end of the fibre was threaded through the axial bore 3 of a ferrule 1 from the rear end 7 until the buffer jacket of the fibre abutted the transition section 4 of the bore. A sufficient length of the buffer jacket of the optical fibre 13 was stripped to ensure that a significant length of the stripped fibre extended from the front end 5 of the ferrule 1. The ferrule 1 (containing the fibre 13) was then inserted into a crimping and cleaving tool which is the subject of a co-pending UK patent application of the present applicant. The tool was used firstly to crimp a rear section for the ferrule 1 (i.e. a section through which the relatively wide portion 3' of the axial bore extends) around the optical fibre 13 so that the ferrule was fixed in place on the fibre. Then the tool was used to cleave a portion of the optical fibre extending from the front end 5 of the ferrule, such that a non-perpendicular end face 17 of the fibre was produced. The cut-way flat surface part 15 of the ferrule 1 was used in the tool to orient the ferrule (about its axis) with respect to the cleaving mechanism of the tool, such that the non-perpendicular cleaved end face 17 of the fibre has a pre-set orientation with respect to the flat surface part 15 of the ferrule 1. Because the ferrule is firmly crimped in place on the fibre, this pre-set orientation is a fixed orientation.

Figure 3 shows the various component parts of an embodiment of a connector body 19 of a connector according to the invention. The connector body 19 has a hollow, generally cylindrical shape and preferably is formed from polymer and/or metal, preferably PPS (polyp henylene sulphide) containing a glass filler. The connector body 19 has an elongate aperture 21 extending axially throughout its entire length between opposite open ends 23 and 25. Each open end 23, 25 is arranged to receive a respective ferrule 1 in a single pre-set orientation about the axis of the ferrule, with respect to the connector body.

This is achieved by each of two opposite end sections of the aperture which are intended to receive respective ferrules 1 having a cross-sectional shape corresponding to the external circumferential shape of a front portion of a ferrule 1, with a flat surface part (not shown) corresponding to the flat surface part 15 of the ferrule and arranged at a position (around the axis of the connector body 19) so as to achieve a desired orientation of its respective ferrule 1. Preferably, the two ferrules 1 received by the connector body 19 are substantially identical to each other, and therefore the flat surface parts of the aperture 21 preferably are situated on diametrically opposite sides of the aperture 1 from each other, in order to provide a relative orientation between the two ferrules as shown in the "Top view" of Figure 2. That is, the two opposing ferrules 1, when received in the aperture 21 of the connector body 19 preferably are arranged such that their front ends 5 face each other and their orientations about their axes (which are coaxial with the aperture 21) are diametrically opposed. In this way, if the non-perpendicular cleaved end faces 17 of the optical fibres (to which the ferrules 1 are fixed) have been formed in an identical way, such that their orientations relative to their respective ferrules are identical, then mere insertion of the two ferrules in the connector body 19 results in a correct opposing orientation of the two end faces 17 (as shown in Figure 2), so that an intimate contact between the two end faces over substantially their entire surfaces is possible.

At a central region 27 of the connector body 19 (i.e. central along the axis of the connector body between the two open ends 23 and 25 of the aperture 21) the aperture 21 narrows at frusto-conical transition regions 29 to provide a narrow central region of the aperture 21. This narrow region of the aperture 21 is arranged to accommodate the end sections of the optical fibres 13 extending from the front ends 5 of the ferrules, and in particular is arranged to accommodate and provide support for the intimate contact between the end faces 17 of the two optical fibres. Preferably this narrow region of the aperture 21 is sufficiently narrow to prevent any significant buckling of the fibres in this region.

For formation of a fibre splice, the connector body 19 is openable to expose the narrow central region of the aperture 21 so that the end faces 17 of the optical fibres being spliced together may be observed as the ferrules 1 are inserted into the connector body (to ensure that the splicing operation is successful and the fibres are not damaged). The connector body 19 is openable in this region by means of a removable part 2 of the connector body. The connector body 19 may subsequently be permanently closed by fitting the part 2 to the main part of the connector body and sliding closure sleeves 31 over the exterior of the connector body from respective opposite ends 23, 25 of the connector body until the two sleeves 31 overlap the part 2 and are permanently retained in place between a central projection 6 on the exterior of the part 2 and respective projections 35 on the exterior of the main part of the connector body 19. The sleeves 31 slide into place along the main part of the connector body 19 with inwardly directed lips 33 sliding within a longitudinal channel 37 provided on the exterior of the connector body.

Figure 4 shows the component parts of a holder/ferrule assembly 40 which is used to insert a ferrule 1 into the connector body 19 and to retain the ferrule in place in the connector body throughout the working lifetime of the optical fibre connector. The assembly 40 comprises a ferrule 1, a spring 41 (which performs the function of a resiliently compressible member) and a holder 39. In order to begin assembling the optical fibre connector and to form the mechanical splice, a ferrule 1 which has been fixed onto an optical fibre 13 (and the fibre subsequently cleaved as described above) is inserted into a holder 39 such that the optical fibre 13 extends completely through the holder 39, with the fibre 13 extending through the helical spring 41, and the spring 41 located between the rear end 7 of the ferrule and a rear retaining wall 44 of the holder (see figure 6). The ferrule 1 is received in the holder 39 via an open front end 45 of the holder in such a way that the pair of diametrically opposed projections 9 at the rear end 7 of the ferrule extend into respective side openings 46 of the holder 39. The rear end 47 of the holder 39 includes a plurality of external elongate members 49 by which the holder 39, and consequently the entire assembly 40, is arranged to be held and manipulated by an assembly tool 48, as shown in Figure 5. Figure 5(a) shows the connector body 19 held by a support 50, which itself is arranged to be retained in a splice tray (or the like) by means of retaining lugs 52. As illustrated in Figure 5(a), one holder/ferrule assembly 40 has already been attached to one end of the connector body 19, and a second holder/ferrule assembly is to be attached to the opposite end of the connector body such that the ferrule 1 is received in the connector body.

Views (a) and (b) of Figure 5 illustrate the process of attachment of the second holder/ferrule assembly to the connector body by means of the assembly tool 48. The tool 48 comprises a handle 51 from which a central elongate shank and a surrounding protective elongate sleeve 53 extend. The end of the central shank of the tool 48 (not shown in detail) opposite to the end attached to the handle 51 has elongate holding members which are arranged to interlock (via an axial sliding fit) with the elongate members 48 of the holder 39 of the assembly 40, so that the assembly 40 may be held and manipulated by means of the tool. The elongate protective sleeve 53 has an open slot 54 extending along at least part of

- its length from a flared open end 55 of the sleeve, in order to allow the optical fibre 13 extending from the rear end 47 of the holder 39 to extend out of the sleeve 53, as shown in views (b) and (c) of Figure 5. The protective sleeve 53 is retractable with respect to the central shank of the tool, in a direction towards the handle 51. Between the handle 51 and the sleeve 53 is a helical spring 56 which, in its relaxed state, causes the sleeve to adopt an extended position away from the handle 51 such that it surrounds and extends beyond the ferrule/holder assembly 40 held by the shank of the tool. In particular, the tool is arranged such that when the sleeve 53 is in its fully extended position the sleeve extends beyond, and therefore protects, the exposed cleaved optical fibre 13 extending from the front end 5 of the ferrule 1 of the assembly 40. In this way, the cleaved optical fibre end section is protected from damage during manipulation of the assembly prior to its insertion in the connector body 19.

The flared (female) open end 55 of the protective sleeve 53 of the tool 48 is arranged to form a mating fit with a corresponding (male) frusto-conical part 57 of the support 50, the part 57 partially surrounding an open end of the connector body 19 located on the support. This mating fit is illustrated in view (b) of Figure 5. View (c) shows the subsequent operation whereby the handle 51 of the tool 48 is pushed forwards towards the connector body 19 as indicated by arrow A. This motion of the handle causes the central shank of the tool, and hence the ferrule/holder assembly 40 held by the shank, to move towards the connector body 19 within the protective sleeve 53. The protective sleeve 53 of the tool remains motionless relative to the connector body 19 and the support 50, but it is retracted (by compression of the helical spring 56) relative to the shank and the handle 51 of the tool, as indicated by arrow B. Consequently the ferrule 1 and the cleaved end 17 of the optical fibre 13 to which the ferrule is fixed are inserted in a controlled and protected manner into the connector b o dy 19.

As described above, each holder 39 includes a resiliently compressible member (as shown, a spring 41) situated between the respective ferrule 1, and the rear retaining wall of the holder. When a ferrule 1 is inserted into the connector body 19, its holder 39 is pushed onto the connector body initially without twisting the holder 39 relative to the connector body. The first of the two ferrule/holder assemblies 40 to be pushed onto the connector body 19 (i.e. the assembly 40 already attached to the connector body, as shown in Figure 5) is immediately secured to the connector body 19 by twisting the tool 48 (and hence the holder 39 of the assembly 40) with respect to the connector body 19 so that slots 43 of the holder 39 interlock with lugs 42 in a bayonet-style attachment. When the holder 39 is twisted with respect to the connector body 19 it is also twisted with respect to the ferrule 1 which it holds, because the ferrule has been inserted into the connector body and is unable to rotate due to its keyed orientation in the connector body (i.e. due to the corresponding flat surface parts of he ferrule 1 and the connector body 19). This twisting motion of the holder 39 with respect to its ferrule 1 causes the projections 9 at the rear end of the ferrule to dig into the material of the holder 39 (which preferably is formed from a plastics material, more preferably PBT, i.e. polybutylene teraphthalate) so that the ferrule is locked in position axially with respect to the holder.

Because the length of cleaved optical fibre 13 extending beyond the front end 5 of its respective ferrule 1 will vary slightly from fibre to fibre (due to cleavage tolerances) the distances by which the ferrules must extend into the connector body in order to form a non- stressed splice between contacting cleaved end faces of the optical fibres will vary from splice to splice. Consequently, when the second of the two ferrule/holder assemblies is attached to the connector body (i.e. after the first ferrule/holder assembly has already been secured to the connector body by a bayonet -style attachment), before the second assembly is twisted with respect to the connector body to secure the bayonet attachment, the resiliently compressible spring member 41 of the assembly will accommodate any so-called "fibre repel" between the fibres to be spliced. Fibre repel may occur due to cleavage tolerances, and results from the combined length of exposed fibre between the two ferrules being too

'great This is accommodated by the resiliently compressible spring member 41 of the

\ second assembly 40 compressing to allow the ferrule 1 of the second assembly to move rearwardly away from the opposite ferrule, so that a good splicing contact between the two optical fibres may be achieved. The resilience of the spring member 41 ensures, however, that there is a good contact between the cleaved end faces of the fibres.

Once a good splicing contact between the fibres, without significant buckling of the fibres, has been achieved, the second holder is twisted relative to the connector body 19 to secure a bayonet-style attachment between the holder and the connector body by means of slots 43 and lugs 42. The connector body is then closed by means of the part 2 and the closure sleeves 31 as described above, and the splicing of the fibres is complete.

Figure 6 shows cross-sectional and exterior plan views of the connector body 19 of Figures 3 and 5 with two ferrules 1 received therein, but with the central region 27 still exposed. Each ferrule 1 is retained in place within the connector body 19 by means of a respective holder 39 that is attached to the respective open end 23,25 of the connector body behind the ferrule 1. As described above, each holder 39 is attached to the connector body 19 by means of a bayonet-style attachment, with lugs 42 on the connector body 19 received in corresponding slots 43 of the holder. A completed, fully closed, connector according to the invention is illustrated in Figure 7.

Claims

1. An optical fibre connector, comprising a ferrule to be fixed to an optical fibre such that the fibre extends through the ferrule along an axis thereof, and a connector body in which the ferrule is arranged to be received, wherein the ferrule may be received in the connector body only in a pre-set orientation about the axis of the ferrule, with respect to the connector body.

2. A connector according to Claim 1, in which the ferrule may be received in the connector body only in a single pre-set orientation about the axis of the ferrule, with respect to the connector body.

3. A connector according to Claim 1 or Claim 2, in which the ferrule may be received in the connector body only by substantially axial insertion of the ferrule into the connector body through an open end of the connector body.

4. A connector according to any preceding claim, in which the ferrule and the connector body have corresponding surfaces which cause the ferrule to be receivable in the connector only in the pre-set orientation.

5. A connector according to Claim 4, in which at least part of an axial length of an external surface of the ferrule and an internal surface of the connector body have said corresponding surfaces.

6. A connector according to Claim 4 or Claim 5, when dependent upon Claim 3, in which said corresponding surface of the ferrule extends from a front end of the ferrule that is arranged to be the first part of the ferrule to be inserted into the connector body.

7. A connector according to Claim 4 or any claim dependent thereon, in which the corresponding surfaces of the ferrule and the connector body prevent rotation of the ferrule relative to the connector body when the ferrule is received within the connector body.

8. A connector according to any one of claims 4 to 7, in which said corresponding surfaces comprise substantially flat surface parts of the ferrule and the connector body.

9. A connector according to any preceding claim, in which the ferrule is fixed to the optical fibre before it is received in the connector body.

10. A connector according to any preceding claim, in which the ferrule has been fixed to the optical fibre, and the fibre extends through the ferrule along its axis.

11. A connector according to Claim 10, in which a portion of the optical fibre extending from a front end of the ferrule, and arranged to be received in, and connected by, the connector, has an end face which is not perpendicular to the axis of the fibre.

12. A connector according to Claim 11, when dependent upon any one of claims 4 to 8, in which the non-perpendicular end face of the fibre is fixed at a pre-set orientation with respect to said corresponding surface of the ferrule.

13. A connector according to any preceding claim, comprising said connector body and two said ferrules, the connector being arranged to interconnect two optical fibres, and each ferrule to be fixed to a respective fibre such that the fibre extends through the ferrule along an axis thereof.

14. A connector according to Claim 13, in which the ferrules are arranged to be received coaxially within the connector body, thereby to form an in-line butt splice between the optical fibres.

15. A connector according to Claim 14 when dependent upon Claim 12, in which each ferrule has been fixed to a respective optical fibre, and said non-perpendicular end face of each fibre is fixed at a pre-set orientation with respect to said corresponding surface of its respective ferrule, the ferrules and the connector body being arranged such that an intimate contact between the two fibre end faces over substantially their entire surfaces is possible merely by insertion of the ferrules in the connector body.

16. A connector according to Claim 15 when dependent upon any one of claims 4 to 8, in which the corresponding surfaces of the ferrules and the connector body are arranged such that when the ferrules are received in the connector body their orientations about their axes are diametrically opposed to each other.

17. A connector according to any preceding claim, further comprising at least one holder which is attachable to the exterior of the connector body to retain a said ferrule in place in the connector body.

18. A connector according to Claim 17, further comprising a resiliently compressible member arranged to be positioned between a said holder and its respective ferrule, thereby to urge the ferrule in a direction further into the connector body, at least upon initial insertion of the ferrule into the connector body.

19. A connector according to any preceding claim, in which the (or each) ferrule is fixed to its respective optical fibre by crimping.

20. A method of interconnecting two optical fibres by means of an optical fibre connector according to any preceding claim, comprising fixing a respective said ferrule to each optical fibre such that an end portion of the fibre extends from a front end of the ferrule, and inserting the ferrules into the connector body such that the fibres form an in-line butt splice connection with each other.

21. A method according to Claim 20, in which the end portion of each fibre extending from the front end of its respective ferrule is cleaved prior to insertion of the ferrule into the connector body, such that each fibre has an end face by which the in-line butt splice connection is formed, which is not perpendicular to the axis of the fibre.

22. A method according to claim 21, when dependent upon any of claims 4 to 8, in which said non-perpendicular end face of each fibre is fixed at a pre-set orientation with respect to said corresponding surface of its respective ferrule, and the ferrules and the connector body are arranged such that an intimate contact between the two fibre end faces over substantially their entire surfaces is achieved automatically upon complete insertion of the two ferrules in the connector body.

23. A method according to Claim 22, in which, when the two ferrules are completely inserted into the connector body their orientations about their axes are diametrically opposed to each other.