Optical fibre connector

Abstract: A fibre-optic connection system comprises three interfitting plastic parts (12,18,24). A two-piece cable terminal (10) includes a cable receiving body (12) and a terminal body (18). The terminal body has two spaced projections (20,22) which mount the fibre ends (116,118) and has a pair of converging cable guide walls (76,78). The cable receiving body (12) has walls (96,98) with gripper teeth (102) complementary to the guide walls (76,78). When two cable strands (116,118) are introduced and the bodies (12,18) are interconnected to form the terminal connector (10), the walls (76-98) trap the cables (116,118). The fibre ends are finished by hot plate melting. The terminal connector (10) is inserted into a header (24) having pockets (140) to mount electro-optical devices (26). The pockets (140) have integral spring rails (158) to force the devices (26) into contact with the projections (20,22) containing the fibre ends upon assembly. A series of integral lock tangs (46,48,84,86,162) and shoulders (34,36,112,114) retain the component parts interconnected to prevent inadvertent disassembly.

Description: This invention relates to an optical fibre connector terminal, a connector header for connecting an optical fibre to a device, and to a method of fitting an optical fibre to a connector terminal. Optical fibres used for data transmission are most often supplied in cable form in which the cable comprises a pair of jacketed fibres carried within a protective sheath. Each jacketed fibre comprises a plastic fibre core, a thin cladding, and a protective jacket which can include strain relief fibres. Connecting the fibre optic cable to electro-optical devices or other cable requires the provision of a terminal on the cable end. The fitting of the cable to a terminal is often performed as a field operation, such as when installing data transmission systems, such as computer LANs (Local Area Networks). To provide a durable and optically efficient interface between a fibre end and an electro-optical device, it is preferable to mount the fibre end in a suitable terminal connector in a manner that will provide good signal transmission. It is also necessary to align and engage properly and reliably the fibre ends with the electro-optical devices so as to enable effective data transmission across the interface. Many different connection systems have been developed to connect optical fibre ends with electro-optical devices. One such system is shown in U.S. Patent No. 4,678,264, in which a cable containing both electrical and optical fibres is provided with a terminal in which the fibres are adhesively mounted. This connector is then inserted into a header mounted on a circuit board and latched by connector lock tabs which engage mating header slots. This arrangement has several shortcomings. There is no provision to bias the terminal ends into engagement with the devices to assure a good optical interface. The adhesive mounting of the fibre end in the terminal must be carefully performed to prevent fouling of the fibre end with adhesive and is not suitable for field use. The disclosed arrangement is unduly complex and, therefore, expensive. Another connection assembly is illustrated in U.S. Patent No. 4,875,755 in which a cable is inserted through a flexible boot which fits in a housing. The cable is stripped and the two fibre ends are inserted into and cemented in ferrules that are retained in spaced cavities. Electro-optical devices are mounted in a cover plate which is screwed onto the housing. Compression springs in the cavities bias the ferrules into contact with the electro-optical devices. While this arrangement provides for biasing the fibre ferrule ends into contact with the electro-optical devices, it requires the provision of two discrete compression springs. It again requires the use of adhesive. It is also an expensive and complex assembly. An improved connection system is disclosed in U.S. Patent No. 4,993,803 in which a ferrule is clamped to a fibre jacket and the fibre end is processed. The ferrule is slidable in a two-part terminal body. The terminal is inserted into a header housing an electro-optical device and latched. A compression spring biases the ferrule to contact the fibre end with the device. The terminal and header also carry electrical contacts. A separate spring is required for each fibre ferrule. A more simple connection system is shown in U.S. Patent No. 4,479,696. Here a single fibre is mated to a single electro-optical device mounted in a pocket of a header. The header contains a bifurcated extension that includes a receptacle for a fibre terminal fitting. The fitting has a peripheral frusto-conical rib which is engaged by mating surfaces on the header upon forcing of the terminal into the receptacle to a position adjacent the electro-optical device. The mating header surfaces are so positioned as to exert a wedging force on the rib. The axial component of this wedging force biases the terminal fitting into engagement with the device. How the fibre is mounted in the terminal is not disclosed. Although this arrangement eliminates springs, it presents a paradox. There is no positive latch. The only force maintaining the terminal in contact with the header is the axial component of the wedging force. If this force is to be substantial, so will be the force required to insert the terminal. Since the method of mounting the terminal on the fibre optic cable is not disclosed, the problem of dealing with the substantial axial stress inherent in inserting the terminal in the header is not addressed. EP-A-0,177,937 discloses an optical fibre connector formed of an internal member and a separate cover member. The internal member includes a block having a hole therein for receiving an end of an optical fibre and a pair of cantilevers which have facing toothed surfaces. When the cover member is slid over the internal member, the toothed surfaces are urged towards one another and engage the sheath of an optical fibre so as to hold the fibre in the connector. JP-A-1-169,416 discloses a connector for coupling an optical fibre to an optical device. The connector includes a bore having a saw tooth internal surface. The teeth are resilient and engage the sheath of an optical fibre in the bore when a withdrawing force is applied to the fibre, thereby preventing withdrawal of the fibre from the bore. The optical device is mounted on a sprung member which pushes the device towards the optical fibre thereby ensuring continued coupling of the device and fibre together on movement of the fibre due to engagement of the teeth. To enable the widespread use of fibre optics in data transmission, it is necessary to simplify the connection system and to provide one which is both economical and reliable. There is a distinct need for a simple and inexpensive connection system for mating the end of an optical fibre with an electro-optical device. There is also a need for a simple, inexpensive and effective terminal connector for a fibre optic cable. This invention seeks to provide an improved connector terminal for an optical fibre and connector header for use in connecting an optical fibre to a device. According to an aspect of the present invention, there is provided a connector terminal for an optical fibre as specified in claim 1. According to a further aspect of the present invention, there is provided a method of fitting an optical fibre to a connector terminal as specified in claim 13. In a preferred embodiment, a terminal connector for a fibre optic cable having a jacketed fibre comprises interconnecting first and second body members. The first body member includes a terminal projection having an exit aperture for receiving a fibre therethrough and a guide wall for a jacketed fibre extending rearwardly from the projection. The second body member includes an entrance aperture for a fibre optic cable, a second wall formed to complement the guide wall in spaced relation upon interconnection of the body members to define a guide channel for the jacketed fibre. A plurality of gripper teeth are formed on the surface of the second wall for engaging the jacketed fibre to trap it against the guide wall upon interconnection of the body members. In a practical embodiment, a terminal connector for a fibre optic cable having a pair of jacketed fibres, comprises interconnecting first and second body members. The first body member comprises a pair of spaced terminal projections, each including an exit aperture for receiving a fibre therethrough, and a pair of inner guide walls for jacketed fibres extending rearwardly and convergingly from each projection. The second body member comprises an entrance aperture for a fibre optic cable, spaced outer walls formed to complement the inner guide walls in spaced relation upon interconnection of the body members to define diverging guide channels for separated jacketed fibres, a plurality of gripper teeth formed on the inner surfaces of the outer walls for engaging the jacketed fibres to trap them against the inner walls upon interconnection of the body members. Another embodiment features a connection system for connecting a fibre optic cable to an electro-optical device, comprising a terminal connector for the cable having interconnecting first and second body members and a header. The first body member includes a terminal projection having an exit aperture for receiving a fibre therethrough and a guide wall for a jacketed fibre extending rearwardly from the projection. The second body member includes an entrance aperture for a fibre optic cable and a second wall formed to complement the guide wall in spaced relation upon interconnection of the body members to define a guide channel for the jacketed fibre. A plurality of gripper teeth are formed on the surface of the second wall for engaging the jacketed fibre to trap it against the guide wall upon interconnection of the body members. The header comprises a housing having a receptacle for receiving the terminal projection upon connection of the terminal connector to the header. First latch means are provided on the connector and the housing for connecting the terminal connector to the header to retain the projection within the receptacle. The header has a pocket for receiving the electro-optical device, second latch means for latching the device within the pocket, and a spring member carried by the housing for biasing the device into an operating position relative to the terminal projection. In a practical implementation, this last-mentioned embodiment features a connection system for connecting a fibre optic cable, having a pair of jacketed fibres, to a pair of electro-optical devices, comprising a terminal connector for the cable, having interconnecting first and second body members, and a header. The first body member includes a pair of spaced terminal projections, each having an exit aperture for receiving a fibre therethrough, and a pair of inner guide walls for jacketed fibres extending rearwardly and convergingly from each projection. The second body member includes an entrance aperture for a fibre optic cable and spaced outer walls formed to complement the inner guide walls in spaced relation upon interconnection of the body members to define diverging guide channels for separated jacketed fibres. A plurality of gripper teeth are formed on the inner surfaces of the outer walls for engaging the jacketed fibres to trap them against the inner walls upon interconnection of the body members. The header comprises a housing having a pair of spaced receptacles for receiving the terminal projections upon connection of the terminal connector to the header. First latch means are provided on the connector and the housing for connecting the terminal connector to the header to retain the projections within the receptacles. The header has spaced pockets for receiving the electro-optical devices, second latch means for latching the devices within the pockets, and spring members carried by the housing for biasing each of the devices into an operating position relative to a terminal projection. Another embodiment of this invention features a header connector for providing a data link between a fibre optic terminal and an electro-optical device. A header housing has a receptacle for receiving the terminal, first latch means for retaining the terminal within the receptacle upon insertion, a pocket for receiving the electro-optical device, and second latch means for latching the device within the pocket. A spring member is carried by the housing for biasing the device into an operating position relative to the terminal. As will be apparent to the skilled person, this last-mentioned embodiment could be modified so as to connect an optical fibre to any other suitable device, or even to another optical fibre. Another embodiment of this invention features a method of forming a connector terminal for a jacketed fibre optic cable which includes two jacketed fibres carried in a protective sheath. The method of this embodiment comprises the steps of forming a first body member with a pair of spaced terminal projections, each including an exit aperture for receiving a fibre therethrough, and a pair of inner guide walls for jacketed fibres extending rearwardly and convergingly from each projection. A second body member is formed with an entrance aperture for a fibre optic cable, spaced outer walls to complement the inner guide walls in spaced relation upon interconnection of the body members to define diverging guide channels for the jacketed fibres, and with a plurality of gripper teeth on the inner surfaces of the outer walls. A fibre optic cable is inserted through the entrance aperture into the second body, the protective sheath is removed to expose the jacketed cables, and the ends of the cables are stripped to expose the fibres. The cables are trained along the guide walls of the first body member, with the fibre ends projecting out of the exit apertures, and the body members are interconnected to engage the gripper teeth with the fibre jackets to trap the cables against the inner walls within the housing. Finally, a smooth, flat end surface is formed on the fibre ends. An embodiment of the present invention is described below, by way of example only, with reference to the accompanyings drawings, in which:- Figure 1 is an exploded perspective view of the component parts of an embodiment of fibre optic connection system comprising a two-piece cable terminal and a header; Figure 2 is a lateral, longitudinal sectional view of the connection system of Figure 1, taken along line 2-2 of Figure 3 and illustrating all components of the system operatively interconnected; and Figure 3 is a vertical, longitudinal sectional view, taken along line 3-3 of Figure 2 and further illustrating details of the connection system of Figure 1. As illustrated in Figure 1, the fibre optic connection system comprises a fibre optic cable terminal connector 10 which includes a cable body member 12 for receiving a fibre optic cable containing two jacketed optical fibres 14, 16; and a terminal body member 18 which interconnects with cable body member 12 and which includes a pair of spaced, slightly tapered and flexible projections 20, 22 which contain the terminal ends of fibres 14, 16. A header 24 is provided to house a pair of identical electro-optical devices 26 and to receive projections 20, 22 into optical connection with the devices 26. Header 24 includes a pair of longitudinal side slots 30, 32 which terminate in shoulders 34, 36. The mouth 38 of header 24 for receiving the terminal body member 18 of terminal connector 10 is formed in a peripheral end wall 40. Terminal body member 18 includes a pair of spring arms 42, 44 having ramped locking tangs 46, 48 which engage end wall 40 upon insertion. This engagement forces spring arms 42, 44 inwardly to enable full insertion, whereupon tangs 46, 48 spring outwardly and engage shoulders 34, 36 to lock terminal connector 10 to header 24. The spring arms 42, 44 terminate in finger tabs 50, 52 which can be manually grasped to depress spring arms 42, 44 sufficiently to disengage tangs 46, 48 from shoulders 34, 36 and enable withdrawal of terminal connector 10 from header 24. Tabs 50, 52 can also be utilized to eliminate the resistance caused by the tangs 46, 48 engaging end wall 40 during insertion of terminal connector 10. Header 24 includes apertured mounting bosses 54 and 56 for mounting the assembled terminal connector 10 and header 24 on a printed circuit board (not shown), with the electrical leads 58 of devices 26 conventionally received within holes in the board. Referring now to Figures 2 and 3, terminal body portion 18 comprises an outer housing 60, which includes the spring arms 42, 44, and an inner receptor housing portion 62 that mounts and forms a rearward extension of projections 20, 22. In their interior, projections 20, 22 include fibre channels 64, 66 which extend rearwardly from exit apertures 68, 70. Rearwardly, fibre channels 64, 66 open into enlarged cable guide channels 72, 74 formed by the inside of inner housing portion 62 and inner cable guide walls 76, 78. These guide walls 76, 78 extend rearwardly to a point of convergence at 80, forming a substantially V-shaped guide. Inner housing 62 has a rearward opening 82 and a pair of side-mounted external ramped locking tangs 84, 86. Cable body member 12 has an elongated cable guard 88 (Figure 1) that includes a cable channel 90 extending from an entrance aperture 92 to a cable splitter chamber 94. The chamber 94 is formed by diverging outer walls 96, 98 and a bifurcated supporting top wall 100 (Figure 1). The outer walls 96, 98 have superficial serrations or gripper teeth 102 and are profiled to complement guide walls 76, 78 upon mating of bodies 12 and 18, as later described. As best seen in Figure 1, cable body member 12 includes upper and lower mounting flanges 104, 106 and side walls 108, 110 that include lock notches 112, 114. The fibre optic cable is fitted to the terminal connector 10 as follows. The cable sheath is stripped away, exposing the cable strands 14, 16, which comprise clad plastic fibres 116, 118 and protective jacketing 120, 122. The cable strands 14, 16 are inserted into entrance aperture 92, through cable channel 90 and into splitter chamber 94. Jacketing 120, 122 is stripped sufficiently to extend fibres 116, 118 through fibre channels 64, 66 and out of exit apertures 68, 70. The strands are passed along guide walls 76, 78 and fibres 116, 118 are then inserted through channels 64, 66 so that the fibre ends project through exit apertures 68, 70 out of projections 20, 22. Cable body member 12 is then mated with terminal body member 18 to form terminal connector 10 as follows. Body member 12 is pushed into member 18, with its bifurcated projection 96, 98, 100 entering housing opening 82 and side walls 108, 110 embracing the sides of inner housing 62 and ramping over lock tangs 84, 86. The teeth 102 will gradually grip the jacketing 120, 122 until mating is completed, when lock tangs 84, 86 engage lock slots 112, 114 in side walls 108, 110. The fibre optic strands 14, 16 are now trapped by teeth 102 between the respective pairs of complementary walls 76 and 96, and 78 and 98. Several features of this terminal connector 10 are important. The dimensions of gripper teeth 102 are chosen so that the teeth grip jacketing 120, 122 firmly enough to effect retention without so distorting fibres 116, 118 to cause light signal degradation. The profile of the complementary wall pairs 76, 96 and 78, 98 are chosen to provide a large enough curvature to prevent boundary light leakage. The fitting of the optical fibres 116, 118 to the connector 10 is then completed by finishing the ends of fibres 116, 118. The fibre ends are cut a predetermined distance beyond the exit apertures 68, 70 in projections 20, 22. The fibre ends are then given a flat, smooth finish by a hot plate melting process. The terminal 10 is now complete and ready for mating with header 24. This finishing may be carried out in the manner described in our co-pending European patent application No. 0 484 994 (RJ/3564). As shown in Figures 2 and 3, header 24 includes a pair of interior spaced receptacles 130, 132 having slightly tapered interior surfaces 134, 136 to complement the shape of projections 20, 22. Receptacles 130, 132 are mounted on a base portion 138 which houses a pair of identical spaced pockets 140. Each of the pockets 140 is formed by a top wall 142, and spaced end walls 144, 146, and side walls 148, 150, which provide a bottom opening 152 for receiving the electro-optical devices 26. Side walls 150 include apertures 154 opening into the interior of receptacles 130 and 132 and are spaced from walls 148 a distance greater than the thickness of devices 26. As best seen in Figure 1, the rear walls 148 form a common wall and include pairs of spaced slits 156 which form rails 158 centrally of the wall and opposite apertures 154. In the interior of the pockets 140, the rails 158 each have a rib 160 which protrudes into its respective pocket 140. A lock tang 162 extends from the bottom of each rib 160. The connection system is assembled as follows. Electro-optical devices 26 are inserted through bottom openings 152 into pockets 140. To complete insertion, the devices 140 are forced over lock tangs 162, which snap over the bottom edges of the devices to retain them in the pockets against inadvertent removal. The rails 158 will force the devices against front walls 150, with the window 164 of each device in registry with apertures 154. The terminal connector 10 is then mated with header 24 by inserting housing 60 through mouth 38 until projections 20, 22 enter receptacles 130, 132. Tangs 46, 48 will engage the sides of end wall 40, urging spring arms 42, 44 inwardly until insertion is complete, when lock tangs 46, 46 will snap out to engage shoulders 34 to lock the terminal connector 10 to header 24. In this assembled state, the ends of projections 20, 22 extend through the apertures 154 to engage device windows 164. The header 24 and the terminal connector 10 are designed such that the projections 20, 22 must displace the devices 26 rearwardly of the pockets into engagement with the rear walls before the lock tangs 46, 48 can spring outwardly to engage the header locking shoulders 34, 36. As a result of the protruding ribs 160, this action stresses rails 158 to provide sufficient bias to maintain engagement of the fibre ends carried by projections 20, 22 and the device windows 154. This three-part plastic connection system is maintained assembled by lock tangs 84, 86 and 46, 48, while the electro-optical devices are retained by tangs 162. No additional springs are required.

Claims: A connector terminal for an optical fibre with a jacket (120,122), said connector terminal comprising a terminal body member (18) which includes a terminal projection (20,22) comprising an exit aperture (68,70) through which an end portion of an optical fibre (116,118) to be inserted can extend, and a guide wall (76,78) located within the terminal body member (18) and arranged to guide the optical fibre towards the terminal projection; said connector terminal further comprising a cable body member (12) which includes an entrance aperture (92) through which the optical fibre to be inserted can pass, a second wall (96,98) facing the guide wall when said body members (18,12) are mounted together so as to form a guide channel for the optical fibre between the facing walls (76,78,96,98), and gripping means (102) provided on the second wall and adapted to engage the jacket (120,122) of the optical fibre when inserted so as to secure the optical fibre in the connector terminal between the guide wall (76,78) and the second wall (96,98) when the terminal body members (18) and the cable body members are mounted together. A connector terminal according to claim 1, wherein the gripping means comprises a plurality of gripper teeth (102) which, when the terminal and cable body members are connected together, are spaced from the guide wall by an amount so as to engage the jacket of the optical fibre and so as not to affect the passage of light through the optical fibre. A connector terminal according to claim 1 or 2, wherein the terminal is adapted to receive two or more optical fibres and includes a terminal projection (20,22), a guide wall (76,78), a second wall (96,98) and gripping means (102) for each optical fibre receivable in the terminal; the terminal projections (20,22) being spaced from one another. A connector terminal according to claim 3, wherein the connector is adapted to receive two optical fibres and comprises two guide walls (76,78) merging together at a location remote from the terminal projections. A connector terminal according to any preceding claim, wherein the or each guide channel has a curvature, which curvature is adapted not to affect the passage of light through the optical fibre. A connector terminal according to any preceding claim, including a header comprising a housing (24) including a receptacle within which the terminal body member (18) is receivable, first latch means (34,36,46,48) for securing the terminal body member (18) within the receptacle, a pocket (140) for receiving a device (26) to be connected to an optical fibre (116,118) of the terminal, second latch means (62) for securing the device within the pocket, and biasing means (160) for biasing the device into an operating position relative to the optical fibre. A connector terminal according to claim 6, wherein the biasing means comprises a sprung rib (160) formed integrally with the housing. A connector terminal according to claim 6 or 7, wherein the pocket (140) comprises a top wall (142), first and second end walls (144,146), a front wall (150) including an aperture (154) therein, and a rear wall (148); an entrance aperture (152) to the pocket being provided between the first and second end walls, the front wall and the rear wall; the biasing means (160) including a sprung rib (160) disposed between a pair of elongate openings (156) in the rear wall (148). A connector terminal according to claim 8, wherein the resilient rib (160) projects into the pocket and is deflectable by the device when the device is inserted into the pocket, thereby to provide a biasing force for use in urging the device into an operating position. A connector terminal according to any one of claims 6 to 9, wherein the second latch means (162) comprises a locking tang (162) carried by the biasing means and operative to engage a portion of the device upon insertion of the device into the pocket. A connector terminal according to any one of claims 6 to 10, wherein the first latch means (34,36,46,48) comprises a latch (46,48) on the terminal body member (18) which is operative to engage a corresponding portion (34,36) of the header housing so as to secure the terminal body member within the receptacle. A connector terminal according to any one of claims 6 to 11, wherein the header is operative to connect two or more devices to an optical fibre terminal body member (18) which includes two or more optical fibres, and comprises a pocket (140), second latch means (62) and biasing means (160) for each device connectable thereto. A method of fitting an optical fibre to a connector terminal according to any preceding claim, comprising the steps of inserting an optical fibre (14,16) through the or a respective entrance aperture of the cable body member (12); stripping a cover off the optical fibre to expose the optical fibre (116,118); passing the optical fibre along the or a respective guide wall (76,78) of the terminal body member (18) and through the or a respective exit aperture (68,70) such that an end of the optical fibre extends out of the exit aperture; connecting the terminal and cable body members together, thereby causing the gripping means (102) to move towards the guide wall to form the guide channel and thereby to engage a jacket (120,122) of the optical fibre so as to secure the optical fibre to the terminal between the guide wall and the facing second wall; and finishing the end of the optical fibre extending out of the exit aperture so as to give the optical fibre a smooth and substantially flat end surface. A method according to claim 13, wherein the end surface of the fibre is produced by cutting the fibre at a predetermined distance beyond the exit aperture, and hot-plate melting the fibre end so as to provide a smooth and substantially flat fibre end surface.

Inventors: COPE KENNETH PAUL, GLADD JOSEPH HOWARD, PLYLER ROBERT GILBERT, STEELE ROBERT EDWARD, YURTIN JOHN ALLAN, COPE, KENNETH PAUL, GLADD, JOSEPH HOWARD, PLYLER, ROBERT GILBERT, STEELE, ROBERT EDWARD, YURTIN, JOHN ALLAN
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1991
Main classification: G02B6
IPC codes: G02B6