GB2150705A

GB2150705A - Connector for optical fibres

Info

Publication number: GB2150705A
Application number: GB08427090A
Authority: GB
Inventors: Enrico Dotti
Original assignee: Pirelli Cavi SpA; Cavi Pirelli SpA
Current assignee: Pirelli and C SpA
Priority date: 1983-11-30
Filing date: 1984-10-26
Publication date: 1985-07-03
Also published as: IT1169146B; GB2150705B; FR2555763A1; GB8427090D0; AU3410384A; BR8405585A; IT8323933A0

Abstract

A connector for connecting two optical fibres 1, 1' end-to-end in abutting relationship comprising two cylindrical bodies 10, 10' provided with axial bores for housing terminal portions of the two fibres 1, 1'. A cylindrical sleeve 20 receives abutting end portions of said bodies 10. A respective ring-nut 11 is screw threaded on each end of the sleeve 20 and tightenable thereon for causing the end faces 30 of the body end portions to be urged axially together. A cylindrical plastics bushing 21 is interposed between said sleeve 20 and said end portions of said bodies 10. The bush 21 extends over at least a substantial length of said sleeve 20 and is provided with internal relief means 29 comprising internal recesses to assist deformation thereof. <IMAGE>

Description

SPECIFICATION Connector for optical fibres The present invention relates to connecting two optical fibres end-to-end in abutting relationship.

When making non-permanent connections between the optical fibres, the two terminal surfaces of the optical fibres to be linked should be accurately aligned since any misalignment, even though modest, causes unacceptable losses with regard to the signal transmitted, which, of course, are cumulative when the signal is transmitted through a series of connections.

Connectors for optical fibres are known where precise alignment of the two ends is achieved with devices for adjusting the axes of the fibres, after the fibres have been brought together in abutting relationship. Although connectors of this type are precise, they are not appropriate for general use.

Other known connectors which do not utilise adjustment devices do not provide a very precise coupling, or else, give rise to structural and assembling complications.

An aim of the present invention is to enable a connector for optical fibres to be provided which without the need for any external adjustments provides for more precise alignment of the fibres than hereto provided by such connectors.

According to the invention, there is provided a connector for connecting two optical fibres end-to-end in abutting relationship, said connector comprising two cylindrical bodies provided with axial bores for housing terminal portions of two fibres to be connected end-toend in abutting relationship, a cylindrical sleeve for receiving abutting end portions of said bodies, a respective ring nut adapted to be screw threaded on each end of said sleeve and tightenable thereon for causing the end faces of the body end portions to be urged axially together, and a cylindrical plastics bushing adapted to be interposed between said sleeve and said end portions of said bodies, said bush extending over at least a substantial length of said sleeve and being provided with relief means to assist deformation thereof.

The relief means may be provided on the inner side of the bush and may comprise circumferential grooves.

Preferably the relief means is present in portions of the bush axially intermediate a central portion thereof, in which the end faces of the body end portions are located in use, and respective end portions of the bush.

The cylindrical bodies are preferably each provided with a radially outwardly-extending, non-circular flange for engagement with corresponding non-circular internal recesses located at each end of the sleeve to prevent relative rotation of the sleeve and bodies.

In order that the invention may be better understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the accompanying drawing in which the single figure shows a fragmentary longitudinal cross-section of a connection of two optical fibres utilizing a connector embodying the invention, the top and bottom halves of the Figure showing different conditions of the connector.

In the figure, the illustrated connector is shown connecting two optical fibres 1, 1' end-to-end in abutting relationship. Each fibre is provided with a first covering 2, reinforcing fibres 3 of for example KELVAR (trade name), a thermoplastics sheath 4 and an outermost covering 5. Only the left hand end of the connector is fully illustrated and it is to be understood that the right hand end of the connector is a mirror image of the left hand end, the connector being symmetric about the radical plane containing the abutting end faces of the fibres 1, 1'. In view of the symmetry of the arrangement reference herein will be made primarily to the illustrated left hand end of the connector.

The connector comprises two cylindrical bodies 10, 10' for housing the terminal portions of the two fibres 1, 1'. The bodies 10, 10' are received in abutting relationship in a cylindrical sleeve 20 and a cylindrical plastics bushing 21 is interposed between the sleeve and the abutting end portions of the bodies 10, 10'.

The body 10, and of course the body 10', is provided with an axial bore 24 into which the end of the optical fibre is introduced and fixed, in such a way that the transmissive end surface of the fibre perpendicular to the axis A-A, is flush with the body's contacting end surface 30which is destined to abut with the corresponding surface of the other body.

The bore 24 has a diameter considerably greater than the diameter of the fibre 1 and of the covering 2 over the majority of its length but in the proximity of the surface 30, it becomes narrowed through a tapered-cone 25 to a bore 26 with diameter equal to only that of the optical fibre 1, into which the latter is introduced till it reaches the contacting surface 30.

The covering 2 of the fibre is removed at the end thereof over a very short distance B for the purpose of reducing as much as possible any axial misalignment originating from the phenomena of fibre-bending when the connection is made, and the fibre is secured inside the bore 24 with any suitable means, preferably through an adhesive agent 27, as shown.

The cable containing the fibres is fixed at the entry-end of the cylindrical body 1 0, through a plastics tube 9 which is inserted under the outermost covering 5. The tube 9 is forced on the end of the body 10, with the reinforcing fibres 3 interposed between the two so that the connection is able to resist axial tensile forces.

The cylindrical sleeve 20 joins and aligns the two cylindrical bodies 1 0. The sleeve 20 is mounted on the two cylindrical bodies and a respective ring-nut 11 provided with internal threading 1 9 is screw-threaded on a threading 1 8 at each end of the sleeve. The sleeve ends are provided with respective polygonal internal recesses for engaging with respective polygonal projections 1 6 extending around and radially outwardly of the cylindrical bodies 10, 10' to prevent relative rotation of the sleeve and bodies. It will be appreciated that to this end the polygonal formations used may be replaced by any other non-circular formation.

The ring-nut has an inner diameter which is greater than the outer diameter of the cylindrical body and, in the annular space that is thus formed, there is disposed a heiicoidal spring 7, which extends between two elastic rings 8, one of which abuts against the shoulder formed by the polygonal projection 1 6 of the cylindrical body and the other of which is retained against movement axially outwardly of the ring-nut by a cir-clip.

In the upper hålf of the figure, the ring-nut 11 is shown in its unscrewed position, whereas in the Idwer half of the same figure, there is shown the condition of the connector when the ring-nut is fully screwed onto the sleeve. In this condition the spring 7 is in a compressed state and, together with the spring of the unillustrated right hand end of the connector, exerts a calibrated axial pressure urging the two end surfaces 30 of the bodies 10, 10' one against the other.

The sleeve 20 is not in direct contact with the two abutting cylindrical bodies, in view of the bush 21 interposed between the outer surfaces of the bodies and the inner surface of the sleeve. The bush is a force-fit on the cylindrical bodies and is further compressed when the ring-nuts 11 are tightened upon the sleeve 20.

The cylindrical bush has a considerable length with respect to the sleeve and extends over at least a substantial length of the sleeve, a length approximate to, or equal to that of the said sleeve, being preferred. Moreover, the bush has circumferentially disposed internal relief means 29 that confer to it a certain deformability in the radial direction. This allows for aligning the cylindrical bodies over a greater distansc without having to exercise any excessive stresses for positioning the bush.As illustrated, the bush relief means are constituted by inner circumferential grooves or slots, or cuts of other forms resulting from material being removed from the inner surface of the bush and are present in portions of the bush axially intermediate a central portion thereof, in which the end faces 30 of the bodies are located and respective end portions of the bush. Thus, they are not provided at the bush ends, nor in the central portion adjacent to the contact zone of the cylindrical bodies, so that the bush maintains its rigidity at its ends and over its central portion. The bush is preferably formed from a relatively rigid plastics material-such as, for example, an acetal-resin.

By way of example, the length of the bush is at least five times that of the diameter of the cylindrical body 10, which itself, for instance, may be about 3 mm.

It will be appreciated that the presence of co-operating polygonal formations on the sleeve 20 and the cylindrical bodies prevents any torsional effects taking place during the tightening of the ring-nuts.

In order to make the illustrated connection, the optical fibre 1 is bared for a very short length B to reduce to a minimum any bending and is introduced into the cylindrical body 10, where the presence of the conical portion 25 facilitates the centering of the fibre and its insertion into the bore 26. Once centered and positioned, the fibre is fixed inside of the body by means of the adhesive 27, and the free end surface 30 is lapped to obtain the desired degree of surface smoothness. The fibre 1' is similarly located in the body 10' and the cylindrical bodies of the two terminations are inserted from opposite ends into the bush within the sleeve such that they are positioned in abutting relationship within the sleeve 20 with the centering-bush 21 forcibly interposed therebetween.The bush is a force fit on the bodies, as mentioned previously, and is also an interference fit within the sleeve. Additionally the ends of the bush abut the polygonal projections 1 6. The ring-nuts are threaded on to the sleeve and tightened to the position shown in the lower part of the figure so that the helicoidal spring 7, situated in the annular underlying space in each ring-nut is compressed to the maximum.

The employment of a centering bush-that is relative long and provided with relief means, allows for working with normal tolerances, for example in the order of about 1-2 hundredths of mm, instead of highly accurate machining-as would be necessary in the absence of the centering effect of the bush. In the embodiment it will be appreciated that the interior of the bush contacts throughout its circumferential extent the bodies 10, 10' immediately adjacent their contacting end surfaces 30 over its central portion and at respective portions of the bodies 10, 10' axially spaced from the contacting surfaces over its end portions. The support thus provided enables the bodies 10, 10' and, therefore, the fibres 1, 1' to be accurately aligned.

Claims

1. A connector for connecting two optical fibres end-to-end in abutting relationship, said connector comprising two cylindrical bodies provided with axial bores for housing terminal portions of two fibres to be connected end-toend in abutting relationship, a cylindrical sleeve for receiving abutting end portions of said bodies, a respective ring nut adapted to be screw threaded on each end of said sleeve and tightenable thereon for causing the end faces of the body end portions to be urged axially together, and a cylindrical plastics bushing adapted to be interposed between said sleeve and said end portions of said bodies, said bush extending over at least a substantial length of said sleeve and being provided with relief means to assist deformation thereof.

2. A connector as claimed in claim 1, wherein said relief means is provided on the inner side of the bush.

3. A connector as claimed in claim 1 or 2, wherein said relief means comprises circumferential grooves.

4. A connector as claimed in any one of the preceding claims, wherein said relief means is present in portions of the bush axially intermediate a central portion thereof, in which the end faces of the body end portions are located in use, and respective end portions of the bush.

5. A connector as claimed in any one of the preceding claims, wherein the plastics bushing is formed of acetal-resin.

6. A connector as claimed in any one of the preceding claims, wherein the cylindrical bodies are each provided with a radially outwardly extending, non-circular flange for engagement with corresponding non-circular internal recesses located at each end of the sleeve to prevent relative rotation of the sleeve and bodies.

7. A connector as claimed in claim 6, wherein each non-circular flange extends around the body and comprises a polygonal formation.

8. A connector for connecting two optical fibres in end-to-end abutting relationship, substantially as herein described with reference to the accompanying drawing.

9. A connection, comprising two optical fibres connected end-to-end in abutting relationship with a connector as claimed in any one of the preceding claims.