WO2011033387A1

WO2011033387A1 - Optical-fibre connector and method of assembly thereof

Info

Publication number: WO2011033387A1
Application number: PCT/IB2010/002521
Authority: WO
Inventors: John Hannigan; Sean Mcfadden; Joseph Fahey; Michael Nolan
Original assignee: Volex Europe Ltd.
Priority date: 2009-09-21
Filing date: 2010-09-20
Publication date: 2011-03-24
Also published as: GB0916569D0; GB2473818A

Abstract

The invention provides an optical-fibre connector for connecting an optical - fibre cable (108) to a mating connector or other optical device. The cable may (108) comprise one or more optical fibres (6) contained within a protective outer sheath (18), or tube. The connector comprises a connector main body (14), a connector back end (16) and an assembly nut (13) for securing the connector back end (16) to the connector main body (14). The main body (14) is for supporting an end of the optical fibre or fibres (16) in position for connection. The protective outer sheath (18) is securable to the connector back end (16) and the connector back end 816) is non- rotatably engageable with the connector main body (14).

Description

OPTICAL - FIBRE CONNECTOR AND METHOD OF AS SEMBLY THEREOF

The invention relates to an optical-fibre connector and to a method for connecting optical fibres.

In a conventional optical-fibre connector, the ends of two fibres to be connected are secured within cylindrical ceramic ferrules, and the end faces of the ferrules and the fibres are polished. The ferrules are then butted together within an alignment sleeve, usually in the form of a longitudinally-split ceramic sleeve of slightly smaller internal diameter than the external diameter of the ferrules, so that the sleeve is elastically deformed as the ferrules are inserted. The elastically deformed sleeve should then hold the ferrules in alignment in order to achieve a good optical connection. In a typical pair of connectors, a connector (or plug) engages with a mating connector (or socket). The alignment sleeve for each fibre connection is housed within one of the connectors, typically the plug, and the ferrules are supported in at least one of the connectors such that they are springloaded in an axial direction towards the alignment sleeve. Thus, when the connectors mate, the ends of the ferrules butt against each other within the alignment sleeve, urged together by the springloading within one or both connectors.

A problem can arise in such connectors due to misalignment or non-axial loading of the ferrules. Such misalignment, either in the form of lateral displacement between the ferrules or angular displacement between the axes of the ferrules, or non-axial loading such as due to lateral forces applied to a ferrule, can dramatically damage the optical performance of the connection between the optical fibres. This may be because the elastic deformation of the alignment sleeve is used to hold the ferrules in accurate alignment and if any lateral or tilting forces or loads are applied to either of the ferrules, such loads may overcome the force applied by the elastic deformation of the alignment sleeve and misalign the ferrule ends.

It is an object of the invention to solve this problem. Summary of Invention

The invention provides an optical-fibre connector and a method for connecting optical fibres as defined in the appended independent claims. Preferred or advantageous features of the invention are set out in dependent sub-claims.

In a conventional connector (and mating connector), optical fibres are terminated with ferrules which are slidably receivable in an alignment sleeve, as described above. The ferrules are supported by a connector main body in position for connection, to ensure that as the connector slides into engagement with the mating connector, the ferrules and the alignment sleeve remain in alignment and the ferrules can slide into the alignment sleeve.

However, the inventors in the present application have recognised a problem in the conventional connector structure, namely that any torque applied to the fibres even behind the connector main body may surprisingly damage the optical performance of a connector. This is surprising because conventional connectors are typically designed so that the connector main body supports the ferrules and the fibre leading into the ferrules, and it is believed that this should be sufficient to prevent misalignment of the ferrules and the alignment sleeve when connectors are engaged.

By contrast, the inventors have appreciated that it is important for a connector even to maintain alignment between the optical fibre(s) terminated by the connector and the protective outer sheath of an optical-fibre cable, even though the fibres usually fit loosely within the sheath, such that misalignment of the sheath would not be expected to affect the fibres.

In a first aspect, the invention may therefore provide an optical-fibre connector for connecting an optical-fibre cable to a mating connector or other optical device. The cable may comprise one or more optical fibres contained within a protective outer sheath, or tube. The connector comprises a connector main body, a connector back end and an assembly nut for securing the connector back end to the connector main body. The main body is for supporting an end of the optical fibre or fibres in position for connection. The protective outer sheath is securable to the connector back end and the connector back end is non-rotatably engageable with the connector main body.

In a preferred embodiment, in order to assemble the connector, an end portion of the protective outer sheath is cut away, to expose the ends of the fibre(s) for connection. The ends of the fibre(s) are passed through the assembly nut and through a bore in the connector back end. The end of the protective outer sheath is then secured to the connector back end, for example by means of a crimped sleeve. The ends of the fibres can then be coupled to or engaged with the connector main body in position for connection before the assembly nut is screwed onto a corresponding threaded portion of the connector main body. As it is screwed on, the assembly nut abuts an abutment surface of the connector back end, thus urging the connector back end towards and into engagement with the connector main body.

The connector back end advantageously engages non-rotatably with the connector main body, to prevent or limit any rotation of the connector back end relative to the connector main body as the assembly nut is screwed on to the connector main body. Typically the assembly nut may be formed with an internally-extending flange which abuts a corresponding abutment surface of the connector back end. As the assembly nut is turned, a torque may be applied by the nut to the connector back end through the contact between the nut and the abutment surface, which tends to rotate the connector back end relative to the connector main body. It is the object of the invention to avoid this and so to solve the prior art problem described above.

Thus, in the first aspect of the invention described above, the sheath is secured to the connector back end and then rotation of the connector back end and the sheath relative to the connector main body and the fibres is prevented or limited as the assembly nut is tightened to secure the connector back end to the connector main body.

Preferably, the connector back end is slidably but non-rotatably engageable with the connector main body. Preferably, the connector back end may be of substantially circular cross- section but comprises a flat surface engageable with a corresponding flat surface of the connector main body, to prevent or limit relative rotation.

Alternatively, the connector back end may comprise a key engageable with a keyway of the connector main body, or vice versa.

Although the invention may be applicable to a fibre-optic cable containing a single fibre, it is particularly beneficial for cables containing two or more fibres. In the latter case, one or more of the fibres supported by the connector main body are spaced radially from a longitudinal axis of the connector, and so application of torque to the cable protective sheath may have an increased effect on misalignment of the fibres and ferrules.

In a second aspect, the invention may advantageously provide a method for terminating an optical-fibre cable at a connector. In the method, an end of a protective outer sheath of the cable may be stripped back and the fibre or fibres passed through an assembly nut, a crimp sleeve, and a bore defined within a connector back end. The end of the sheath may then be secured to the connector back end by crimping the sleeve. The fibre or fibres, which may be terminated by ferrules in known manner, may then be supported by the connector main body for connection to a mating connector or other device. The connector back end may then be non-rotatably engaged with the connector main body and the assembly nut screwed onto a threaded portion of the connector main body to secure the connector back end to the connector main body.

Figure 11 shows a prior art connector comprising a connector back end 16 securable by means of an assembly nut 13 to a connector main body 14. The protective outer sheath 19 of an optical-fibre cable 108 is secured to the connector back end by means of a crimped sleeve 4. The cable contains two fibres 6 which are terminated by ferrules 5. Plastic clips 94 engageable with the connector main body are used to position the ferrule assemblies and fibres within the connector main body. A flange 96 extends outwardly from the connector back end and provides an abutment surface against which the assembly nut can bear to secure the connector back end to the connector main body when the assembly nut is screwed onto the connector main body to assemble the connector as shown at the upper left of figure 1 1.

In this prior art connector, the connector back end is rotationally symmetrical and rotation of the assembly nut as it is screwed onto the connector main body applies torque to the connector back end and causes it to rotate relative to the connector main body. It is the conventional wisdom in the art that such rotation will be limited by the securing of the cable outer sheath to the connector back end, and that rotation, or twisting, of the connector main body has no effect on the quality of connection of the optical fibres, but the inventors have

appreciated that this is not correct. As in the embodiments of the invention described herein, eliminating or limiting rotation of the connector back end and the cable outer sheath relative to the connector main body may advantageously reduce twisting or misalignment of the optical fibres and unexpectedly improve the optical performance of the connector. Specific Embodiments and Best Mode of the Invention

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

Figure 1 shows a connector and a mating connector, or socket, embodying the invention, in assembled form, both connected and disconnected, with a rubber grip in place around the connector;

Figure 2 shows a reverse view of the connectors of figure 1 ready for connection, with rubber grip and large assembly nut omitted;

Figure 3 shows assembled and exploded views of the connector of figure 1 , with rubber grip omitted;

Figure 4 is an exploded view of the mating connector, or socket, of figure 1 ; Figure 5 shows longitudinal sections of the connector and mating connector of figure 1 before engagement, or connection;

Figure 6 shows longitudinal sections of the connector and mating connector of figure 1 engaged, or connected;

Figure 7 shows longitudinal sections of a fibre support engaging with an insert to be received in a connector main body of the connector or mating connector of figure 1 ;

Figure 8 shows longitudinal sections of an assembled connector as shown in figure 1 , with rubber sleeve omitted;

Figure 9 shows three-quarter and plan views of the connector main body of the connector of figure 1 ;

Figure 10 shows end and side views, and a three-quarter view, of the connector main body of the mating connector, or socket, of figure 1 ; Figure 11 shows assembled and exploded views of a connector and a mating connector according to a second embodiment of the invention;

Figure 12 shows an exploded view of the mating connector of figure 11 from a reverse direction; and

Figure 13 shows three-quarter views of a prior art connector, both assembled and exploded.

Figure 1 shows a connector 100 and a mating connector or socket 102 according to a first embodiment of the invention. The connectors are shown engaged, or connected, at the lower left corner of figure 1 and disengaged at the upper right comer. The socket 102 comprises a flanged main socket body 27 securable to a fixed surface such as a bulkhead in known manner. An externally-threaded sleeve 104 extends forwardly from the socket body for receiving a plug portion 106 of a main plug body of the connector 100. Two keys 28, 30 extend into the socket sleeve to engage keyways 31 formed in the plug portion. These structures are shown clearly in figures 9 and 10, which show enlarged views of the main bodies of the connector and the mating connector. The keys prevent rotation of the plug portion relative to the socket 5 body and are of different sizes, to ensure correct orientation of the plug portion and the socket body. A large assembly nut 15 encircles the plug portion and screws onto the externally-threaded sleeve of the socket to engage the connector and the socket. o In figure 1 , the connector 100 is shown in fully assembled form, contained

within a protective rubber grip 17. Figure 2 shows a reverse view of the connector and socket before engagement, with the rubber grip and the large assembly nut omitted. The connector and socket of figures 1 and 2 are for connecting an optical-fibre cable 108 containing two optical fibres. The plugs portion 106 of the connector houses two alignment sleeves as described below, and has two openings 110 at its front end for receiving ferrules mounted on the ends of fibres housed within the socket and for guiding them into the alignment sleeves. o Figure 3 shows assembled and exploded views of the connector of figure 1 , omitting the rubber grip 17. Figure 4 shows a corresponding exploded view of the mating connector, or socket, 102, which is of similar construction except that the alignment sleeves are housed in the connector 100 as described below. Where appropriate, the same reference numerals are used to indicate5 similar components in figures 3 and 4.

The connector and socket each comprise a connector, or plug, back end 16. This is a moulded plastic component in the form of a circular tube having a front end 80 engageable with the connector main body and a rear end 82. A centralo circular bore 84 is defined through the connector back end. As shown in

figure 3, and in section in figures 5, 6 and 8, the optical fibre cable 108 comprises a cable outer jacket 18 surrounding a Kevlar (RTM) cable sheath 19. The outer jacket is stripped back, exposing the end of the Kevlar sheath, which is placed around the rear end 82 of the plug back end 16 and crimped in place5 using a large crimp sleeve 4, shown crimped in position in the assembled connector at the upper left of figure 3. A flange 112 extends outwardly from the plug back end 16 near its front end 82. A groove for carrying a small O-ring 12 is defined around the circumference of the connector back end between the flange and the front end 82. A small assembly nut 13 encircles the plug back 5 end and can screw onto a rear end 50 of the main plug body 14, abutting the flange and compressing the O-ring against the main plug body to form a closed and sealed connector housing.

The flange 112 is formed with two flats 86 on opposite sides of the connectoro back end. When the connector is assembled, the circular front end 80 of the connector back end slides into a corresponding circular bore 88 in the rear end of the connector main body and the flats 86 engage with corresponding flats formed on tabs 90 extending rearwardly from the connector main body (see figures 9 and 10). The O-ring 12 seals against the inner surface of the circulars bore 88.

The optical-fibre cable contains two fibres 6. Each fibre comprises a fibre 6 within a buffer 1 , contained within a tube comprising a Kevlar (RTM) sheath 11 within a plastic (PVC) inner jacket 2. The buffered fibre is contained looselyo within the tube and is therefore movable longitudinally within the tube.

Each fibre is terminated as follows. The plastic jacket 2 of the tube is stripped back, exposing a length of the Kevlar (RTM) 11. The buffered fibre is passed through a central bore 114 defined within a support 9, and the end of the Kevlar5 (RTM) is crimped onto a rear portion of the support 116, formed with

circumferential ridges, by means of a small crimp sleeve 3.

The end of each fibre emerging from the central bore of the support is secured to a ferrule assembly 52. A rear portion of the ferrule assembly comprises ao cylindrical piston 7, which fits loosely within the bore 114 of the support 9 (as shown in figure 7). A further bore 115 is defined within the piston, sized to receive the buffered fibre 1. A front portion of the ferrule assembly comprises a fibre-optic ferrule 5. A fibre-receiving bore is defined within the ferrule, sized to receive the fibre 6. The buffer layer is removed from an end portion of the fibre, which extends within and is secured within the ferrule 5, for example using an epoxy resin.

The ferrule assembly 52 comprises an outwardly-extending flange 54 between the ferrule 5 and the piston 7, against which a helical spring 22 can abut. The support 9 is formed with a corresponding abutment surface 56, for receiving the other end of the helical spring 22. When the ferrule assembly, the helical spring and the support are assembled, the helical spring acts as a compression spring urging the ferrule assembly away from the support.

In the assembled connector, the ferrule 5 for each fibre is urged by its spring 22 into an alignment sleeve 24 in the form of a split-sleeve coupling as shown in figure 3 and, in section, in figures 5 and 6. Each alignment sleeve is held within a bore 118 defined within the main plug body 14, retained by a retaining bush 20.

The support 9 for each fibre is retained within a sub-assembly insert 10 as shown most clearly in figure 7. The insert is moulded from a plastic material and has a generally-cylindrical outer surface 120, which is shaped to fit within a corresponding recess within the rear of the main plug body 14. A key 122 extending from the outer surface of the insert fits within a corresponding keyway in the main plug body to align and prevent rotation of the insert relative to the main plug body. The insert is formed with spring clips 124 which latch with corresponding recesses in the main plug body to hold the insert in place.

Figure 5 shows the connector in cross section, disengaged from the socket, and figure 6 shows the connector and socket engaged, or connected, in cross section. As seen most clearly in the enlarged Detail 2 in figure 6, when the connector and socket are engaged the ferrules 5 are butted together within each alignment sleeve 24. Each ferrule is urged into the alignment sleeve by its respective spring, and each spring is compressed by the abutment of the two ferrules. This can be seen by comparing Detail AE in figure 5, in which the flange 54 of the ferrule assembly of the connector is pressed by the spring 22 into contact with the alignment-sleeve-retaining bush 20, with Detail Z in figure 6, in which the flange 54 has moved away from the bush 20 to produce an axial clearance 136. A corresponding axial clearance 138 can be seen in the socket adjacent the flange 54 in Detail Z.

Figures 1 1 and 12 show a connector and a mating connector according to a second embodiment of the invention. The structure of these components is the same as in the first embodiment described above except that the connector back end comprises a key 92 engageable with a keyway 94 formed in the corresponding connector main body, rather than the flats of the first embodiment, in order to prevent or limit rotation of the back end relative to the main body.

Parts and Features Lists for Figures

PART# DESCRIPTION

1 Fibre Buffer

2 Fibre Inner Jacket

3 Small Crimp Sleeve

4 Large Crimp Sleeve

5 Fibre-Optic Ferrule

6 Optical Fibre

7 Ferrule Back (Piston)

8 Adhesive Heat Shrink (12mm)

9 Rear Support

10 Sub-Assembly Insert (SAI)

11 Synthetic Fibre

12 Small O-Ring

13 Small Assembly Nut

14 Main Plug Body

15 Large Assembly Nut

16 Plug Back End

17 Rubber Grip

18 Cable Outer Jacket

19 Synthetic Fibre

20 Retaining Bush

21 Rubber Washer 22 Spring

24 Alignment Sleeve

25 Socket Back End

26 Large O-Ring

27 Main Socket Body

28 Key Pin A

29 Tube Strain Relief

30 Key Pin B

50 Rear End of Main Plug Body

54 Flange of Ferrule Assembly

56 Support (9) Spring Abutment Surface

62 Insert (10) Front Wall

64 Insert (10) Resilient Clips

66 Insert (10) Snap-Fit Hooks

80 Front End of Connector Back End

82 Rear End of Connector Back End

84 Central Bore of Connector Back End

86 Torque Control Flats on Connector Back End

88 Inner Surface of Connector Main Body

90 Torque Control Flats of Connector Main Body

100 Connector

102 Mating Connector or Socket

104 Externally Threaded Socket Sleeve

106 Plug Portion of Connector

108 Optical-Fibre Cable

110 Openings in Front Surface of Plug Portion of Connector

114 Central Bore of Support (9)

115 Bore Within Ferrule Back (Piston) for Receiving Buffered Fibre

116 Rear Portion of Support (9)

117 Forward Portion of Support (9)

118 Bore in Rear Portion of Main Plug Body (14)

120 Insert Outer Surface

122 Key on Insert Outer Surface

124 Insert Spring Clips

128 Opening in Insert Front Wall (62) 130 Support (9) Groove

132 Support (9) Square Flange, or Shaped Flange

134 Surface of Resilient Arm Corresponding to Square Flange (132)

136 Clearance Between Ferrule-Assembly Flange and Bush in

Engaged Connector

138 Clearance Between Ferrule-Assembly Flange and Socket Body in Engaged Socket

Claims

1. An optical-fibre connector for terminating an optical-fibre cable in which an optical fibre is contained within a protective cable outer sheath, the connector comprising;

a main connector body for supporting an end of the optical fibre in position for connection;

a connector back end securable to an end of the cable outer sheath, such that the optical fibre can pass through a bore defined within the connector back end to reach the main connector body; and

an assembly nut encircling the connector back end and abutting an abutment surface of the connector back end, the assembly nut being threadably engageable with a rear portion of the main connector body to urge the connector back end towards the main connector body on assembling the connector;

in which the connector back end is non-rotatably engageable with the main connector body.

2. An optical-fibre connector according to claim 1 , in which the connector back end is non-rotatably engageable with the connector main body so as to prevent torque applied to the assembly nut on assembling the connector from causing rotation of the connector back end relative to the connector main body.

3. An optical-fibre connector as defined in claim 1 or 2, in which the connector back end is slidably engageable with the connector main body.

4. An optical-fibre connector as defined in claim 3, in which a front portion of the connector back end is slidably receivable within a bore defined within a rear portion of the connector main body.

5. An optical-fibre connector as defined in any preceding claim in which the connector back end is non-rotatably engageable with the connector main body by engagement of a key and a keyway.

6. An optical-fibre connector as defined in any preceding claim in which the connector back end is non-rotatably engageable with the connector main body by engagement of corresponding flats formed on the connector back end and the connector main body.

7. An optical-fibre connector according to any preceding claim, for terminating an optical-fibre cable containing two or more optical fibres.

8. A method for assembling a fibre-optic connector, for terminating an optical-fibre cable in which an optical fibre is contained within a protective outer sheath, comprising the steps of;

passing an end of the optical fibre through a bore defined within a connector back end;

securing an end of the protective outer sheath to the connector back end;

positioning the end of the optical fibre within a connector main body in position for connection;

non-rotatably engaging the connector back end with the connector main body; and

threading an assembly nut, which encircles the connector back end and abuts an abutment surface of the connector back end, on to a threaded rear portion of the connector main body.

9. A method according to claim 8, in which the step of non-rotatably engaging the connector back end with the connector main body includes engaging a key with a keyway.

10. A method according to claim 8 or 9, in which the step of non-rotatably engaging the connector back end with the connector main body includes engaging corresponding flats, or flat surfaces, of the connector main body and the connector back end.

11. A method according to claim 8, 9 or 10, in which the end of the protective outer sheath is secured to the connector back end by means of a crimped sleeve.