CONNECTOR FOR OPTICAL FIBER CABLE

Abstract: In a hermaphroditic biconic connector (20), an optical fiber cable (24) extends through a cap (46) into a tapered passageway of a flanged bushing. Optical fibers extend from the cable through a bore in a wedge (65) having a truncated conical shape and being received in the bushing. Portions of a strength member system (28) of the cable in the form of non-metallic filamentary strand material are captured between a wall which defines the tapered passageway and an outer surface of the wedge. The surfaces between which the strength members become locked are substantially smooth to avoid damage to the strength members. Forces applied to the cable and hence to the strength members cause the wedge to be seated further in the bushing. Also, the included angle between diametrically opposite lines on the surface of the wedge that lie in a plane that passes through the longitudinal axis of the wedge enhances the locking features of the connector. The fibers also extend through a retention nut (70) which is turned threadably over a threaded portion of the bushing and each fiber is connected to a truncated, conically shaped plug (94). The plugs are mounted adjacent to an end of the connector with one plug being received in an alignment sleeve (130). A sleeve retainer (140) is disposed over the sleeve and the other plug and includes alignment posts (145-145) so that when another connector is assembled thereto, a plug of the other connector is received in the unused end of the sleeve and a sleeve extending from another plug of the other connector receives the other plug of this connector.

Description: This invention relates to a connector for optical fiber cable, which includes at least one optical fiber and filamentary strength members. It is very important to prevent the transmittal of tensile forces to the optical fibers of an optical fiber cable. If this is not done, the fibers may be broken or microbending losses in the fiber may occur and degrade the quality of transmission. In order to avoid such breakage and losses at a connector terminating the cable, the strength members of the cable must be coupled to a housing portion of the connector so that tensile forces are transferred to the housing before the forces reach the optical fiber. In one prior art connector, polymeric yarn, which serves as the strength members of the cable, is held between cooperating surfaces of internal and external sleeves of the connector. The internal sleeve includes a bore through which the optical fibers extend and the external sleeve includes a conically shaped bore for receiving the internal sleeve. The polymeric yarn strands are passed through the bore of the internal sleeve and retroflexed about a peripheral end portion of the internal sleeve whereafter the external sleeve is caused to be disposed over the internal sleeve. This arrangement can lead to abrasion of the polymeric yarn where it engages the peripheral end portion of the internal sleeve. Also, the application of tensile forces to the cable may cause dislocation and an undoing of the terminations of the strength members. Seemingly, the prior art is devoid of a connector in which non-metallic filamentary strength members are secured to a housing of the connector and maintained as such during the application of forces to the cable while not compromising the integrity of the strength members. Desirably, connection of the strength members to the connector is accomplished in a manner which causes the secured terminations to be enhanced when the cable is subjected to tensile forces. Also, the connector should be one which facilitates alignment of plugs of connectors in sleeves and which prevents the ingress of moisture. GB-A-2030 723 discloses force transfer means including two conformable conically shaped surfaces which are adapted to be held in mating relationship with each other with portions of a strength system therebetween. US-A-4 185 586 discloses a hermaphroditic connector, which forms part of the prior art. According to the present invention, there is provided a cable as defined in claim 1. The foregoing problems have been solved by the optical fiber connector of an embodiment of this invention. The optical fiber connector is effective to terminate an optical fiber cable which includes at least one optical fiber and a non-metallic, filamentary strength system. Included in the connector are a housing having a longitudinal axis and force transfer means disposed adjacent to a cable entrance end of the housing and through which the optical fiber extends. The force transfer means is effective to clamp the non-metallic strength system of the cable to transfer forces from the cable to the housing. Also, the force-transfer means includes two conformable, substantially smooth conically shaped surfaces which are held in mating relationship with each other with portions of the strength member system therebetween. Each surface diverges in a direction from the cable entrance end of the housing toward another end such that an included angle between diametrically opposed lines on each of the surfaces which are disposed in a plane passing through the axis of revolution of each surfaces does not exceed a predetermined value. Plugs which terminate the optical fibers are disposed adjacent to the other end of the housing with a plug associated with one of the fibers being disposed in an alignment sleeve which in an opposite end thereof is adapted to receive a plug which terminates an optical fiber of another connector to be assembled to this connector. Retaining facilities are disposed at an entrance to the other end of the housing to retain the sleeve in the housing and to guide a sleeve of another connector to cause another plug of this connector to be received in one end of the sleeve of the other connector. In a preferred embodiment, the force transfer portion of the connector comprises a bushing which includes a flange and a hub connected to the flange. The hub has threads formed externally thereon and has a passageway therethrough which is tapered to cause a small diameter portion to be adjacent to the flange. The passageway through the bushing is defined by a wall having a substantially smooth surface. A wedge having a truncated conical shape is adapted to conform to the wall which defines the tapered passageway of the bushing to capture non-metallic, filamentary strength members of the optical fiber cable between the wedge and the bushing when the optical fibers of the cable extend through the wedge. The outer surface of the wedge which mates with the wall of the bushing also is substantially smooth. As a result of this arrangement, tensile loads applied to the cable are transferred to the bushing to prevent damage to the optical fibers which are to be connected to other optical fibers. A fastener turned onto the hub holds the wedge within the bushing. Brief Description of the Drawing FIG. 1 is an elevational view partially in section of a hermaphroditic biconic connector for optical fiber cables which includes an alignment sleeve and two plugs each of which terminates an optical fiber; FIG. 2 is a partially exploded perspective view of the connector of FIG. 1 at an end portion thereof where an optical fiber cable enters the connector; FIG. 3 is an exploded elevational view in section of a force transfer portion of the connector of FIG. 1; FIG. 4 is a side elevational view in section of the force transfer portion of FIG. 3 after it has been assembled with non-metallic filamentary strength members disposed between portions thereof; FIG. 5 is an exploded view of a plug end of the connector of FIG. 1; FIG. 6 is an end view of the plug end of the connector of FIG. 1; and FIG. 7 is an elevational view partially in section which shows the assembly of two of the connectors of FIG. 1. Referring now to FIG. 1, there is shown a hermaphroditic connector which is designated generally by the numeral 20 and which is used to terminate optical fibers 22-22 of an optical fiber cable 24. Each of the optical fibers 22-22 may include a buffer cover 26 which is made of a plastic material. The optical fibers 22-22 are enclosed with a strength member system 28 (see also FIG. 2) which may be a polymeric yarn material and preferably a KEVLAR® yarn, for example. A jacket 29 which may be made of a plastic material encloses the yarn. In the preferred embodiment, the cable 24 includes two optical fibers. The connector 20, which may be referred to as a first connector, is adapted to cause the optical fibers terminated therein to become connected to optical fibers which are terminated in a second connector, which is identical to the first connector. The cable 24 extends through a strain relief portion 30 (see FIGS. 1 and 2) which is disposed at a cable entrance end 34 of the connector and which includes a somewhat conically shaped bend limiter 31. Also, the cable 24 extends through a cable seal 33, which may be made of neoprene, for example, and which is held in tight enagement with the cable 24 by a cable seal wedge 35. A portion 37 of the bend limiter 31 is disposed between the cable 24 and a metallic insert 39 about which has been molded the bend limiter 31. The cable 24 extends through the strain relief portion 30 and into a main portion 40 of the connector 20. Interposed between the cable seal wedge 35 and the metallic insert of the strain relief portion is depending portion 44 of an end cap 46. The depending portion 44 of the end cap is threaded externally and is turned into an internally threaded cup-shaped portion 48 of the insert 39. As may be viewed in FIG. 1, the right side portion of the end cap 46 is threaded internally so that the end cap can be turned onto an end portion 49 of a connector shell or housing 50. In a preferred embodiment, the connector shell 50 is made of a metallic material. The connector shell 50 is adapted to house devices for terminating the optical fibers and a strength member retention system or device 52 which is effective to prevent tensile pulls on the cable from being transferred to the optical fibers and to their being transferred to the optical fibers and to their terminations with bionic plug portions of the connector 20. Viewing now FIGS. 2 and 3-4, it can be seen that the device 52 includes a bushing 56 having a flange 58 and a hub 59. A passageway 61 is formed through the hub and the flange and is tapered through the hub and in the flange region with the small diameter portion oriented toward the bend limiter 31. The cable 24 extends to a location just within the flange whereafter the jacket 29 of the cable is removed to expose the strength member yarn and the optical fibers. The optical fibers 22-22 extend through a bore 63 of a wedge 65 which is disposed within the passageway 61 of the bushing 56. Seated between a hexagonal, recessed portion 66 (see FIGS. 1 and 2) of an end of the connector shell 50 and an inner end surface 68 of the end cap is the flange 58 of the bushing 56 of the strength member retention system. Desirably, an included angle, α between diametrically opposed lines on the inner surface of the tapered passageway 671 that appear in a sectional view when a plane is passed through the axis of revolution of that surface which generally is coincident with a longitudinal axis 67 (see FIG. 1) of the shell 50 does not exceed a predetermined value. It has been found that α should not exceed a value of about 6° and preferably is about 3° The strength member yarn is disposed between the tapered inner surface 61 of the bushing and a conformable tapered external surface of the wedge. As a result, portions of the strength member system 28 are held between these surfaces and any pull which is imparted to the cable 24 is transferred by the strength member system to the shell 50. The wedge 65 and the bushing 56 cooperate to provide a self-enhancing locking arrangement for the strength member system 28 of the cable 24. As pulling forces are applied to the cable 24 at the strain relief end, these forces are transferred to the portions of the strength member system 28 which causes the wedge 65 to move to the left as viewed in FIG. 4. As this occurs, the wedge 65 becomes seated further in the passageway 61 of the bushing thereby further locking the yarn and preventing any strain from being transferred to the optical fibers. In order to achieve a substantial locking action without damaging the non-metallic strength member system 28, the bushing 56 and the wedge 65 must be further characterized. The conformable surfaces of the wedge 65 and the bushing 56 must be substantially smooth. If not, portions of the non-metallic strength member system 28 conform to the surface roughness. As a result, non-uniform pressure as between portions of the roughened surfaces causes those portions of the strength member system to be crushed and non-effective in the transfer of forces from the cable 24 to the housing shell 50. Also, the includes angle α is important in reducing the angle which portions of the strength member system make as they exit the cable 24 and become disposed between the wedge 65 and the bushing 56. The greater the angle which the portions of the strength member system 28 make with the longitudinal axis 67 of the connector, the greater the probability for portions of the strength member system to break about the entrance to the annular conical space between the complimentary surfaces. Further, the intersection between the outer surface is formed with a radius to preclude damage to the non-metallic strength members. It should be observed that this arrangement is advantageous from several standpoints. First, a locking arrangement which is self-enhancing is provided. The greater the pull, the greater the locking of the portions of the strength member system 28 within the connector 20. Also, unlike prior art connectors, portions of the strength member system 28 need not be retroflexed about a peripheral edge surface of a portion of the connector to secure the portions within the connector. Instead, the force-transfer portions of the strength member system are disposed at a relatively gentle angle to the longitudinal axis 67 of the housing between two substantially smooth surfaces. The wedge 65 is further secured within the tapered bushing by a thrust nut 70. As can be seen in the drawings, the thrust nut 70 has an internally threaded wall 72 which defines a bore for receiving the hub 59 of the bushing 56 which is threaded externally. The thrust nut 70 also includes a centrally disposed opening 74 in an end portion 76 thereof to allow the optical fibers to extend therethrough. An external surface 78 of the thrust nut is juxtaposed with an inner surface of the shell 50. Forward of the device 52 is a connector cavity 80. In the connector cavity 80, excess lengths of the optical fibers 22-22 are looped and then terminated. Each of the optical fibers 22-22 of the cable 24 is terminated by a biconic connector assembly, designated generally by the numeral 90, in a plug end 91 of the connector 20. The biconic connector assembly 90 which is shown partially disassembled in FIG. 5 includes a retaining plate 92 which is held within the connector shell 50 for receiving two plug assemblies. Each plug assembly 90 includes a plug 94 which terminates one of the optical fibers 22-22 (see FIG. 1). As can be seen in FIGS. 1 and 5, each plug 94 includes a cylindrical portion 96, which includes a bore 98, and an end portion 100. The end portion 100, which is referred to as a primary pedestal, has a truncated conical shape and includes a passageway 102 that communicates with the bore 98. A coated single optical fiber 22 which has been provided with a buffer comprised of a plastic material such as polyvinyl chloride, for example, and then assembled together with another such optical fiber to form the cable 24 is terminated with the plug 94 (see again FIG. 1). The jacketing material and the coating are removed from an end portion of each buffered fiber. Then, the cable is inserted into the bore 98 until the bared end portion is received in the passageway 102 with an end portion of the fiber 22 extending into a secondary pedestal 106 (see FIG. 5). An end face of the end portion of the fiber 22 is coincident with the end face of the secondary pedestal 106. Each plug 94 is provided with a retaining ring and a washer adjacent to its end portion 100. As can be seen in FIG. 1, each of the plug assemblies 90-90 includes a retaining ring 100 which is fixedly located about the plug 94 and abuts a washer 117. A compression spring114 of the plug between the washer 117 and another washer 115 and the retaining plate 92. The plug 94 is positioned in a connector body 120 with the washer 115 in engagement with the retaining plate 92 to hold the plug within the shell. Another retaining ring 118 is positioned on the plug 94 on the opposite side of the retaining plate 92 to hold the plug therein. with this arrangement, the plugs 94-94 in the retainer plate 92 can be moved to the left as viewed in FIG. 1, compressing the springs 114-114 and disengaging each retaining ring 118 from the plate 92. The connector body 120 which is positioned within the shell (see FIGS. 1 and 5) of the connector 20 is adapted to receive two plugs 94-94. The connector body comprises a cylindrical housing 122 which includes two opposed cavities 121-121 each of which is adapted to receive the cylindrical portion of a plug. An O-ring seal 123 is disposed about the connector body 120 and engages an inner surface of the shell to prevent ingress of moisture into the connector cavity 80. The connector body is provided with a keyway 126 which is adapted to receive a key 127 of the connector shell to prevent turning of the connector body within the shell 50. Also, the connector body 120 is secured within the shell 50 by an externally threaded retainer member 131. A radial face of the connector body 120 is provided with an oval shaped recess 124 for receiving a bellows seal 125. The bellows seal 125 is oval-shaped and includes two spaced openings each provided with a funnel-shaped' collar 128. Advantageously, each collar 128 is fit snugly about a plug 94 and is capable of permitting longitudinal movement of the plug. The bellows seal which is made of an elastomeric material is adapted to be held in the recess in the connector body 120 by a seal retainer 129. As can be seen in FIGS. 1 and 5 of the drawings, each plug extends through the connector body and retainer with one adapted to be received in a cavity of an alignment sleeve 130. The alignment sleeve 130 comprises two opposed, conically shaped cavities 132-132 which meet at a common plane 136. Both the plug 94 and the sleeve 130 are made of a crushed silica-filled, transfer molding grade epoxy composition, for example. However, it should be understood that the plug and sleeve could be made of other materials, such as metallic materials, for example. The alignment sleeve 130 is such that when end portions 100-100 of plugs 94-94 are received in the cavities 132-132, the ends of the secondary pedestals are in the vicinity of the common plane 136. Also, as a connection is made, the plug portions are moved through the openings defined by lips of the openings in the retainer plate 92 to move the retaining rings 118-118 out of engagement with the lips. The sleeve 130 extends into a sleeve retainer 140 (see FIGS. 1 and 5) which is supported at one end of the connector shell 50. The sleeve retainer 140 is made from an impact-resistant thermoplastic material. Also, the sleeve retainer 140 includes a boss 142 and an opening 143 diametrically opposed thereto (see also FIG. 6). Externally projecting plug-protecting posts 145-145 are disposed on opposite diametrical portions of the opening. The boss 142 is adapted to hold a biconic sleeve 130 in which is seated the truncated conically shaped end portion of one plug. An angled entrance portion 147 of the boss 142 causes the sleeve 130 to be retained in the boss and connector body 120. The opening 143 in the sleeve retainer is adapted to receive a boss of a second connector, that boss also having an alignment sleeve 130 therein. When the first connector 20 is asseembled with a second connector 20 and the sleeve 130 of the second connector is received in the opening 143, a plug end which is seated in the sleeve of the second connector is caused to become disposed adjacent to a plug of the first connector having an end portion which extends into the opening. At the same time, a plug of the second connector 20 which extends into the opening 143 of its sleeve retainer 140 extends into and becomes seated in the other end of the alignment sleeve 130 held in the first connector. As the second connector is moved to engage the first connector, its posts 145-145 encompass the boss 142 projecting from the first connector. As a result of this arrangement, the two connectors mate hermaphroditically. The spring 114 of each plug assembly causes the plug end portion 100 to be seated firmly in engagement with the wall of the alignment sleeve. As seen in FIGS. 1 and 7, a leading end portion 151 of the connector shell 50 is threaded externally. As such, it is adapted to be turned into an internally threaded portion of a coupling nut 153. The coupling nut 153 extends forwardly of the sleeve retainer 140 so that it is adapted to receive the sleeve retainer of a second connector. Each connector 20 is provided with a coupling nut 153 which includes a lip 155 that is adapted to engage an abutment 157 of an end portion of the connector shell. When two connectors 20-20 are assembled together, the coupling nut 153 of a first one of the connectors is withdrawn from the leading end of the connector shell 50. the coupling nut 153 of a second connector is moved forward so that its threaded end engages the externally threaded portion of the first connector to secure together the connectors 20-20. It should be observed from FIG. 1, that prior to the assembly of the connector 20 with another, the secondary pedestal 106 of each biconic plug extends beyond a mating surface 160 of the connector. Therefore, in order for the surfaces 160-160 of the connectors to engage each other, the secondary pedestals and hence the plugs must be capable of moving inwardly into the shell 50. This is accomplished through the hereinbefore-described spring mounting of each plug. Furthermore, in order to maximize the alignment of the biconic plugs and the axes of the optical fibers therein, it is desirable to minimize the contact of the biconic plugs with supporting surfaces. For example, to avoid bends in the sleeves, interference by the supporting structure is minimized. As can be seen best in FIG. 1, when another connector is assembled to the connector 20, the contact between end portions of the plugs causes each plug to be moved inwardly. This disengages the retaining rings 118-118 from the retaining plate 92 and the cone-shaped external portions of the sleeves from surface 147 of the boss 142. As a result, each plug tends to float within the connector 20. Also, it should be observed that, advantageously, the bellows seal 125 because of its configuration is able to maintain a seal about each plug notwithstanding longitudinal and/or radial movement of the plugs which extend therethrough. This effectively prevents the ingress of moisture along the plugs whereas the O-ring 123 prevents the ingress of moisture between the connector body 120 and the shell 50. Additional seals are provided to prevent the ingress of moisture. As can be seen in FIGS. 1 and 7, seals 156-156, which typically are made of rubber, are disposed on ends of the connector shells 50-50 and abut each other when two connectors are mated, thus blocking the ingress of moisture.

Claims: An optical cable (24) which is terminated with a hermaphroditic connector (20) that includes provisions for transferring forces from nonmetallic filamentary strength members (28-28) of the cable to the connector, the terminated cable including two optical fibers (22-22) and nonmetallic, filamentary strength members, and a housing (50) having a cable input end into which the cable extends and a termination end; the terminated cable further including a bushing (56) which is disposed in said housing and which includes a tapered passageway (61) having a smooth surface; a truncated conically shaped wedging member (65) which is received in said passageway (61) of said bushing (56), said bushing and said wedging member cooperating to receive an end of the cable in a small diameter portion of said passageway with the nonmetallic strength members being disposed between the inner surface of said passageway and said outer surface of said wedging member, said wedging member having a longitudinally extending bore (63) through which optical fibers of the cable extend, said wedging member having a smooth outer surface conformable to said inner surface of the tapered passageway of said bushing; said bushing and said wedging member cooperating to transfer forces imparted to the cable to the housing to avoid the transmittal of the forces to the connection of the fibers; fastening means disposed within said housing and secured to said bushing to hold said wedging member (65) in said bushing (56); termination means being held in said housing adjacent to said termination end and terminating the optical fibers and comprising a first plug, an alignment sleeve (130) for receiving a leading portion of the first plug and a plug of a corresponding hermaphroditic connector which terminates an optical fiber of another cable and a second plug, which is adapted to be received in a sleeve of the other connector; characterized in that the passageway in said bushing and the outer surface of said wedging member diverge in a direction from the cable input of said housing toward the termination end of said housing, that the intersection between an end surface of said wedging member and an outer tapered surface of said wedging member are formed with a rounded surface to prevent damage to the strength members which are pressed therearound; that the first and second plug haveing truncated conically shaped end portions; and that the alignment sleeve (130) provided on the first plug had a biconical inner surface for receiving a leading portion of the first plug and a plug of a corresponding hermaphroditic connector which terminates an optical fiber the other cable. The terminated cable of claim 1, CHARACTERIZED IN THAT said fastening means includes a thrust nut (70) turned threadably onto an externally threaded portion of said bushing. The terminated cable of claim 1, CHARACTERIZED IN THAT the cable also includes an end cap (46) that encloses said bushing and said wedging member. The terminated cable of claim 1, CHARACTERIZED IN THAT a line disposed on the surface of the wedging member and disposed in a plane that passes through the longitudinal axis of the wedging member making an angle of about 1.5 degrees with the longitudinal axis of the wedging member. The terminated cable of claim 1, CHARACTERIZED IN THAT said bushing includes a Range (58) and a hub (59) connected to said Range, said hub having threads formed externally thereon and having a passageway (61) therethrough which is tapered to cause a small diameter portion to be adjacent to said flange, said passageway being defined by a wall having a substantially smooth surface; and said wedging member (65) having a truncated conical shape which conforms to the tapered passageway of said bushing to capture the non-metallic, filamentary strength members of the optical fiber cable between the wedging member and the bushing with the optical fibers of the cable extended through the wedging member to cause tensile loads applied to the cable to be transferred to the bushing to prevent damage to the optical fibers which are terminated by said termination means. The terminated cable of claim 5, CHARACTERIZED IN THAT each of said plugs (94-94) extends through are retaining plate (110) and a connector body (120) which are secured within said housing, said connector body includes a recess provided in an externally facing surface thereof and a bellows seal (125) which is received in said recess, said seal including two spaced openings in each of which is received a plug and said seal further including a protruding entrance portion which grips a plug which extends therethrough to allow longitudinal and transverse movement of said plug while preventing the ingress of moisture. The terminated cable of claim 3, CHARACTERIZED IN THAT the cable also includes a seal (33) which is disposed about the cable adjacent to said end cap, said seal being held in compressed engagement with the cable by a wedge which is held in engagement with said seal by a metallic insert having an internally threaded cavity which is in threaded engagement with threads formed about an outer wall of said end cap, the insert being enclosed by a bend limiter which has been assembled to the cable. The terminated cable of claim 1, CHARACTERIZED IN THAT the cable also includes a sleeve retainer (140) which includes a boss that is disposed over said alignment sleeve to facilitate entry of a plug of another connector and to hold said alignment sleeve in said housing and an opening aligned with said second plug for receiving an alignment sleeve of the other connector, said sleeve retainer also including two posts (145-145) which are disposed adjacent to said opening to guide a boss of the other connector over said second plug with posts of the other connector becoming disposed about the boss of said connector, each of said posts including an arcuate surface which conforms to and is adapted to become juxtaposed to an external surface of an boss of another connector with which said connector is to be assembled.

Inventors: ANDERSON, JERRY MAX, CANNON, THOMAS CALVIN, JR., DARDEN, BRUCE VAIDEN
Applicants: AMERICAN TELEPHONE AND TELEGRAPH COMPANY
Application year: 1987
Main classification: G02B6
IPC codes: G02B6