GB2058392A

GB2058392A - Optical Fibre Connections

Info

Publication number: GB2058392A
Application number: GB8027150A
Authority: GB
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1979-08-20
Filing date: 1980-08-20
Publication date: 1981-04-08

Abstract

A detachable fibre optic connector in which the ends of the fibres 5 to be joined are held in respective ferrules 3, the ferrules being an interference fit in a common sleeve 1. The respective ferrules are held in abutment by respective disc springs 4. A multi way fibre optic detachable plug and socket connector is also described. <IMAGE>

Description

SPECIFICATION Optical Fibre Connectors This invention relates to optical fibre connectors and in particular but not exclusively to such connectors used for detachably connecting together pairs of single optical fibres.

Increasing use is being made of optical fibre cables as a transmission medium for data transfer for example. A major problem associated with this use is that of providing joints in such cables without introducing high insertion losses. This problem becomes more apparent when single optical fibres, as opposed to bundles of optical fibres carrying the same signal in parallel, are used as the transmission medium. When such single fibres are used any connection within the transmission path requires that the fibre ends be accurately aligned and particularly in the case of fibre to fibre connections that the respective fibre ends should abut or be embedded in an index matching resin.

Among the many solutions to the problem of fibre to fibre connection is that of welding the respective ends of the fibres together. Such welding is a highly skilled and time-consuming operation which, whilst producing a good quality joint, is not readily carried out away from a factory or laboratory bench.

A further problem associated with the welding technique is that the connection once made is of a permanent nature. Thus if for example a section of fibre fails a considerable amount of time is spent in removing the faulty section and welding in a new section. Also, if the connection is to a piece of apparatus, maintenance of the apparatus must be carried out "in situ", it being necessary to break or cut the fibre if the apparatus is to be removed for repair.

It is therefore preferable for connections between fibres or between a fibre and apparatus to be detachable. Many detachable and pseudodetachable connectors for optical fibres are known but to overcome the stated problems of alignment and abutment such connectors require that a plurality of components be manufactured to close tolerances and/or sophisticated adjustment techniques must be used when the connection is made.

If manufacture to close tolerances is required it is difficult to employ modern "mass production" methods and the component parts of the connectors are costly, and in fact the connectors may be the major part of the cost of an optical fibre transmission system.

If sophisticated adjustment techniques are required on connection then skilled personnel and in some cases complicated test equipment must be used. This may also become a major part of the cost of an optical fibre transmission system and makes "in the field" connections difficult.

Accordingly optical fibre connectors have been developed in which an optical fibre termination is arranged to surround and hold an optical fibre, and is adapted to be fitted to a further optical fibre termination by means of a common sleeve. An optical fibre termination of this kind may also be used to connect an optical fibre to apparatus by means of a suitable adaptor or socket. Such optical fibre terminations are referred to hereinafter as optical fibre terminations of the kind specified.

According to one aspect of the present invention an optical fibre termination of the kind specified comprises a casing, a ferrule which is arranged to surround and hold an end of an optical fibre and which is located at least partially within the casing, and spring means interposed between the ferrule and the casing, said spring means being arranged to urge the ferrule in a direction which would tend to tension a fitted optical fibre.

Preferably the ferrule includes a capillary at one end, the capillary being adapted to be a close fit with an end of an optical fibre such that the fibre when fitted is held by interference forces.

The termination may include means for fixing it to a sleeve or socket, the fixing means being for example, a screw thread arranged to mate with a corresponding screw thread on the sleeve or socket.

The spring means may comprise at least one disc spring.

According to another aspect of the present invention in an optical fibre connector for detachably connecting optical fibres in an end to end relationship, said connector including a pair of optical fibre terminations and a common sleeve to which the terminations are held, at least one of the fibre terminations is a fibre termination in accordance with the first aspect of the present invention.

Preferably the respective casings of the terminations are arranged to screw onto the common sleeve and may include respective internal flanges arranged to act upon respective flanges of their respective ferrules to facilitate withdrawal of the ferrules from the sleeve when a respective casing is unscrewed from said sleeve.

Preferably also said sleeve is arranged to be an interference fit with the end of said ferrule at or about the longitudinal centre of the sleeve. Said sleeve may be made of a plastics material polycarbonate for example and may have a groove formed in the outside of the sleeve to relieve the interference forces between said sleeve and the ferrules.

A further feature of the present invention is a device housing including a ferrule and a casing with spring means between said casing and said ferrule, the housing being arranged to hold optical transmitting or receiving means for example.

A plurality of common sleeves may be arranged to form a socket used with two plugs, each of said plugs comprising a plurality of ferrules arranged to be fitted to respective sleeves of the socket to form a connector for detachably connecting a plurality of pairs of single optical fibres. Such a connector may be used for detachably connecting a plurality of optical fibre inputs to optical transmitting or receiving devices mounted on a printed circuit board for example.

The socket may be formed as a one-piece moulding.

Optical fibre connectors in accordance with the present invention will now be described by way of example only with reference to the accompanying drawings of which: Figure 1 shows a cross sectional view of a connector, Figures 1 A and 1 B show sectional views of alternative parts for the connector of Figure 1, Figure 2 shows an enlarged cross sectional view of a part of the connector shown in Figure 1, Figure 2A shows a cross sectional view along the line A-A of Figure 2, Figure 3 shows a cross sectional view of a device connector, Figure 4 shows isornetrically a multiple sleeve socket, Figures 5 and 6 respectively show sectional plan and elevation views of a multiple plug for use with the socket shown in Figure 4, and Figure 7 shows a front view of the multiple plug.

Referring first to Figure 1 the connector comprises a sleeve 1 to which two fibre terminations may be fitted. Each of the terminations comprises a case 2 and a ferrule 3 arranged to surround and hold an optical fibre in axial alignment. At least one disc spring 4 is interposed between the case 2 and the ferrule 3, the disc spring being arranged to urge the ferrule away from the case.

The sleeve 1 is manufactured from a plastics material for example, polycarbonate and is arranged to have a slight interference fit with the ends of the ferrules 3, at or adjacent to the point at which the ends of the ferrules 3, meet The sleeve has external screw threads between each end and respective flanges 6, the cases 2 having corresponding internal screw threads from their respective ends to respective internal flanges 7.

The ferrule 3 is made of stainless steel brass or plastics material and has at its mating end a substantially flat face. This mating face has a concentric hole arranged to be a close fit with the end of an optical fibre 5. Any casing material surrounding the optical fibre end must be removed to leave sufficient bare fibre to enable the fibre end to be fitted into the hole in the mating face. The optical fibre 5 may be glued into the ferrule 3. To prevent damage to the face of the optical fibre by scratching for example the fibre end need not be inserted until it is flush with the mating face provided that sufficient fibre is passed into the hole to ensure axial alignment. If the fibre end is not inserted to be flush with the mating face then the end may be sealed with a suitable index matching resin.At the end of the ferrule 3 away from the mating face there is a flange 8 against which the disc spring 4 operates.

The case 2 is also made from stainless steel brass or plastics material and prior to assembly has the appearance of a tube with an internal thread at one end leading to the flange 7.

Fitting of the termination is simply carried out by threading the end of the fibre 5 through the disc spring 4, stripping the outer sheath from the end of the fibre and fitting the ferrule 3. The opposite end of the tube to that which has been threaded is passed over the ferrule 3 until the respective flanges 7 and 8 meet. The unthreaded end of the tube is then peened or foided over to hold the ferrule 3 and disc spring 4 to form the complete termination. The end of the case may be folded over until it grips the outer sheath of the optical fibre 5.

Referring also to Figures 1 A and 1 B alternative means of closing the end of the case 2 are shown.

Sealing may be effected by means of a plug 9 having an external thread which may be screwed into a corresponding internal thread of the case 2.

Alternatively sealing may be carried out by means of a cap 10 with an internal thread in which case the case 2 has a corresponding external thread.

Referring to Figures 2 and 2A the sleeve 1 is shown in greater detail. A groove 11 is formed in the outer circumference of the sleeve and positioned so that it extends longitudinally beyond the ends of a thickened interference section 12. The groove 11 allows the sleeve 1 to flex slightly at the time of initial insertion of the ferrules 3, and reduces the interference forces between the sleeve and the ferrules once a connection has been made.

When a connection is to be made one of the ferrules, say 3, is inserted into the sleeve 1 and the case 2 is screwed onto the sleeve 1. The flange 6 prevents the case 2 from being advanced too far thus ensuring that the interfering end of the ferrule is positioned within the interference section of the sleeve 1. The other ferrule 3 is not introduced to the free end of the sleeve 1 and its case 2 is screwed on to the sleeve 1. The disc springs 4 act between their respective cases 2 and ferrules 3, against the interference between the sleeve 1 and the ends of the ferrules 3, and against each other to urge the mating faces of the ferrules 3 into abutment.

Since the optical fibres 5 are held substantially concentrically in the mating faces they are thus connected in axial alignment with their end faces or respective index matching seals in abutment.

Referring now to Figure 3 a device termination is shown including a device housing 13. Typically an optical transmitter (not shown) or receiver (not shown) is mounted in space 14 within the housing and an optical fibre 1 5 which is integral with the optical device passes via a tube at the front of the housing 1 3 and is sealed in the ferrule 3 as previously described. The ferrule 3 may then be attached to the housing 13 by adhesive for example. The ferrule 3 is adjustable along the length of the front of the housing 13 prior to the fixing operation so that optical devices with various lengths of integral optical fibres may be accommodated without requiring accurate cutting of the fibres. The termination functions in the same way as the terminations previously described and corresponding parts are designated accordingly.

Referring now to Figures 4, 5, 6 and 7 a multiway optical fibre connector for detachably connecting a plurality of single optical fibres to a printed wiring board for example comprises a multiple-sleeved socket as shown in Figure 4 and two multiple-termination plugs as shown in Figures 5, 6 and 7.

The socket comprises say eight sleeves 20 held between a pair of end plates 21, the sleeves being approximately aligned with holes 24 in thickened sections 23 of the end plates 21. The end plates 21 and the sleeves 20 may be made from a plastics material, polycarbonate for example.

Each multi-way plug comprises say eight ferrules 3 with respective disc springs 4, the ferrules holding respective optical fibres 5. The ferrules 3 are fitted through a holding piece 31, a front plate 30 holding the plug together by means of a wedge shaped cutaway in the front plate being keyed with a similarly shaped thickening in the holding piece 31.

When a plug is fitted to one end of the socket, spring clips 22 attached to the socket are clamped over the edges of the frontplate 30 of the plug to hold the plug to the socket. Cutaways 32 are provided at the corners of the frontplate 30 to allow the spring clips 22 to pass over.

When plugs are fitted to both ends of the socket the disc springs 4 act between respective ferrules 3 and each frontplate 30 to urge the ends of their respective ferrules 3 against the interference of respective sleeves 20 and into abutment with the ends of the corresponding ferrules 3 in the opposed plug.

The multiway connector system may also be made with for example respective single rows of sleeves and ferrules which may be advantageous where space is limited for example for connections made to printed circuit boards housed side by side on a shelf.

The design of connector may advantageously be made of a small size when compared with currently available optical fibre connectors a typical 4x2 way multiple connector being approximately 25 mm long by 20 mm wide and 12 mm deep.

It will be readily realised that the form of multiway socket hereinbefore defined need not be manufactured in a plurality of parts and is suitable for forming in one piece by use of a plastics vacuum forming process for example.

Claims

1. An optical fibre termination of the kind specified comprising a casing, a ferrule which is arranged to surround and hold an end of an optical fibre and which is located at least partially within the casing, and spring means interposed between the ferrule and the casing, said spring means being arranged to urge the ferrule in a direction which would tend to tension a fitted optical fibre.

2. An optical fibre termination as claimed in Claim 1 in which the ferrule includes a capillary at one end, the capillary being adpated to be a close fit with an end of an optical fibre such that the fibre when fitted is held by interference forces.

3. An optical fibre termination as claimed in Claim 1 or Claim 2 including means to detachably connect the termination to a sleeve or socket.

4. An optical fibre termination as claimed in Claim 3 in which the fixing means is a screw thread cut in the casing said screw thread being arranged to mate with a corresponding screw thread on the sleeve or socket.

5. An optical fibre termination as claimed in any preceding Claim in which the spring means is at least one disc spring.

6. An optical fibre termination as claimed in any preceding claim in which the casing is a tubular sleeve having an inwardly extending flange arranged to limit the forward movement of the ferrule.

7. An optical fibre termination as claimed in Claim 6 in which the spring means and ferrule are enclosed between a back face of the casing and the flange.

8. An optical fibre termination as claimed in Claim 7 in which the back face is formed by deforming an end of the tubular sleeve.

9. An optical fibre termination as claimed in Claim 7 in which the back face of the casing is formed by an end face of a plug or a cap fitted to the end of the tubular sleeve.

10. An optical fibre termination as claimed in Claim 9 in which the plug or the cap has a screw thread arranged to mate with a corresponding screw thread of the tubular sleeve.

11. An optical fibre connector for detachably connecting two optical fibres in an end to end relationship said connector comprising a pair of optical fibre terminations and a sleeve to which the terminations are arranged to be fitted, one of said terminations being an optical fibre termination in accordance with any one of Claims 1 to 10.

12. An optical fibre connector as claimed in Claim 11 in which each of the terminations is an optical fibre termination in accordance with any one of Claims 1 to 10.

13. An optical fibre connector as claimed in Claim 11 or Claim 12 in which the sleeve is arranged to be a close or interference fit with each of the ferrules at or substantially equidistantly about the longitudinal centre of the sleeve.

14. An optical fibre connector as claimed in any one of Claims 11-13 in which a longitudinal groove or slit is formed substantially equidistantly about the longitudinal centre of the sleeve said groove or slit being arranged to relieve the interference forces between the ferrules and the sleeve.

1 5. A device housing comprising an at least partially enclosed cavity within which a transmitting or receiving device may be mounted, a projecting tube having a capillary through which an optical fibre may pass, a ferrule which surrounds the tube and which is arranged to surround and hold an end of a fitted optical fibre, the ferrule being located at least partially with a casing, and spring means interposed between the ferrule and the casing, said spring means being arranged to urge the ferrule in the direction which tends to tension the fitted optical fibre, the ferrule, casing and spring means being an optical fibre termination in accordance with any one of Claims 1 to 10.

1 6. A plug for terminating a plurality of optical fibres said plug comprising a casing, a plurality of ferrules each of which are arranged to surround and hold a respective optical fibre, and respective spring means interposed between each ferrule and the casing, said spring means being arranged to urge the respective ferrules in a direction which tends to tension respective fitted optical fibres.

1 7. A plug as claimed in Claim 1 6 in which each of the ferrules includes a respective capillary at one end, each of the ferrules being arranged to surround and hold its respective optical fibre and each of the capillaries being a close fit with an end of its respective optical fibre such that the respective fibre when fitted is held by interfere forces.

18. A plug as claimed in Claim 16 or Claim 17 in which each of the spring means is at least one respective disc spring.

19. A connector for connecting a plurality of pairs of optical fibres in an end-to-end relationship comprising a socket having a plurality of sleeves, and two plugs at least one of which is a plug as claimed in any one of Claims 16, 1 7 or 18.

20. A connector as claimed in Claim 1 9 in which each of the plurality of sleeves has a respective longitudinal groove or slit formed substantially equi-distantly about its respective longitudinal centre the grooves or slits being arranged to relieve intererence forces between their respective sleeves and respective pairs of ferrules of the two plugs fitted to the socket.

21. An optical fibre termination substantially as herein before described with reference to Figure 1 of the accompanying drawings.

22. An optical fibre connector substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

23. A device housing substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

24. A plug for terminating a plurality of optical fibres substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.

25. A connector for connecting a plurality of optical fibres substantially as hereinbefore described with reference to Figures 4, 5, 6 and 7 of the accompanying drawings.