Strain relief connector for optical fiber

Abstract: An optical fiber connector (10) for terminating and providing strain relief on an optical fiber cable (12) having an inner fiber (14), an outer jacket (18) and longitudinal strength material (22) therebetween. A housing (24) has a rear input end (38) into which the fiber, stripped of the outer jacket, extends, along with a front termination end. The rear input end of the housing is externally threaded and about which the longitudinal strength material (22) is positionable. An internally threaded strain relief member (26) is provided through which the cable (12) extends. The strain relief member (26) is threadable onto the externally threaded rear input end of the housing to clamp the longitudinal strength material directly between the threads (38) of the housing and the strain relief member. Grooves (44) span the threads of the housing to prevent at least some of the longitudinal strength material from spiralling with the threads when the strain relief member is threaded onto the housing.

Description: The invention relates to optical fiber connectors with the features of the preamble to claim 1. Low loss optical fibers are being used, at an ever increasing rate, in the communication industry for transmitting signals. The optical fibers have to be coupled and complementarily mateable connectors have been created for that purpose. When coupling optical fibers, it is essential to avoid pulling forces on the optical fibers in order not to degrade the quality of the transmission. Therefore, many optical fiber connectors include strain relief for the optical fiber cable. Such connectors usually. are of a very complicated design involving a plurality of parts which must be fabricated to considerable precision and, consequently, the myriad of parts themselves can degrade the quality of transmission between coupled optical fiber ends. An example of a connector for an optical fiber cable is shown in U.S. Patent No. 4,863,235 to Anderson et al., dated September 5, 1989. This patent shows a connector wherein non-metallic filamentary strength members, or yarn, are clamped by a wedge system which includes a plurality of components, including an interior wedge sleeve externally threaded to an internally threaded compression nut which biases the strength members against still a further truncated member about which the strength members are disposed. Like so many other similar connectors, all of these components must be fabricated individually, to precision, in addition to the other housing and related components of the connector which terminate the optical fiber to another fiber in a complementarily mateable connector. An optical fiber connector according to the preamble of claim 1 is known from GB-A 2 042 817. An extra strain relief device is provided to clamp the strength material between inner and outer sleeve members, which include threads along a conical surface. The optical fiber cable so provided with the strain relief is assembled with the connector housing which consists of two halves which are closed over the strain relief device. A further preknown optical fiber connector (US-A 4,795,229) includes four housing components, three thereof being used for the strain relief. The strength material is clamped onto serrations formed on a first retention member by means of a sleeve which is pressed on the first retention member by a second retention member screwed onto the first retention member. Another preknown optical fiber connector (EP-A 0 199 267) comprises housing components having serrations on conical surfaces for clamping the strength material therebetween. This is accomplished by sticking the parts together. This invention is directed to solving the problem of strain relief on optical fibers and satisfying the continuing need of a simplified system to combat losses in optical fibers due to pulling forces exerted on the optical fiber cable. An object, therefore, of the invention is to provide a new and improved optical fiber connector for providing strain relief on an optical fiber cable. Solutions to this problem can be found in the teachings of the dependent claims. In the exemplary embodiment of the invention, the optical fiber connector is designed for terminating and providing strain relief on an optical fiber cable which includes an inner or central optical fiber, an outer jacket or cladding and longitudinal strength material, such as polymeric yarn, disposed therebetween. The connector includes a housing having a rear input end into which the optical fiber, stripped of its outer jacket, extends. The housing has a front termination end which may include a plastic or ceramic ferrule for locating the terminating end of the fiber. The rear input end of the housing is externally threaded and about which the longitudinal strength material is positionable. An internally threaded strain relief member, through which the optical fiber cable extends, is threadable onto the externally threaded rear input end of the housing to clamp the longitudinal strength material directly between the threads. Therefore, no internal or extraneous components whatsoever are required to provide strain relief on the cable. A unique feature of the invention is the provision of interruption means between the housing and the strain relief member to prevent at least some of the longitudinal strength material from spiralling with the threads when the strain relief member is threaded onto the rear input end of the housing. As disclosed herein, the interruption means are provided in the form of groove means spanning the threads on at least one of the housing or strain relief member, the groove means extending longitudinally of the cable or generally parallel to the rotating axis of the two components. Other objects, features and advantages of the invention will be apparent form the following detailed description taken in connection with the accompanying drawings. Brief Description of the Drawings The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention together with its objects and the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which: FIGURE 1 is a longitudinal or axial section through the optical fiber connector of the invention, particularly a complete section through the strain relief member and a fragmented section through the housing of the connector, with the components of the optical fiber cable in position for termination prior to the strain relief member being threaded onto the housing; FIGURE 2 is an elevational view of the connector fully assembled with the strain relief member completely threaded onto the rear of the housing; and FIGURE 3 is a vertical section on an enlarged scale, taken aenerally along line 3-3 of Figure 1. Referring to the drawings in greater detail, and first to Figure 1, the invention is embodied in an optical fiber connector, generally designated 10, for terminating and providing strain relief on an optical fiber cable, generally designated 12. The optical fiber cable includes an inner or central optical fiber 14 surrounded by a buffer cover or inner jacket 16 of plastic or like material, an outer jacket or protective cladding 18, and a strength member system, generally designated 20. The strength member system is in the form of longitudinal strength material or strands 22, such as of polymeric yarn. Optical fiber connector 10 includes a housing, generally designated 24, and a strain relief member, generally designated 26. Housing 24 may be of a variety of configurations designed particularly at its forward end for mating with a complementarily mateable connector (not shown). Basically, the housing must include a passageway for optical fiber 14, stripped of outer jacket 18, to extend. In the design of the housing shown in the drawings, a forward enlarged passage portion 28 is provided for receiving a plastic or ceramic ferrule 30 which, itself, includes a central passageway 32 which locates fiber 14 for termination. The housing also includes a smaller passage portion 34 for receiving an end of buffer cover 16 of the cable. Passage portion 34 extends all the way to the rear input end of housing 24, the rear input end being located generally where strength material 22 bends, as at 36. In essence, the housing is provided with a rear input end 38 into which fiber 14 and buffer cover 16 , stripped of outer jacket 18, extend. The rear input end 38 has external threads 39 about which the longitudinal strength material 22 is positionable. Strain relief member 26 generally is in the form of a sleeve having a bore 40 with internal threads 41. The width of the bore 40 is such that the optical fiber cable 12 can extend therethrough. Internally threaded bore 40 of strain relief member 26 is complementary to externally threaded end 38 of housing 24. In operation, and referring to Figure 1 in conjunction with Figure 2, outer jacket or cladding 18 first is stripped from a given length of the end of optical fiber cable 12 to be terminated. The given length is slightly longer than the combined length of housing 24, including ferrule 30. Longitudinal strength material 22 then is cut to a length to cover a substantial portion if not the entire length of externally threaded portion 38 of housing 24. Buffer cover 16 also is severed to a length equal to the length of passage portion 34 through the housing, leaving a bared length of fiber 14 for extending through ferrule 30. As is conventional, the fiber may extend slightly beyond the outer distal end of ferrule 30 for polishing. Before proceeding, it should be commented that longitudinal strength material 22 is shown in the drawings with the strands somewhat exaggerated in cross-sectional size in order to facilitate the illustration. Actually, such strength material as polymeric yarn is extremely fine but very strong and flexible. Once the components of optical fiber cable 12 are cut and positioned relative to housing 24 as shown in Figure 1, strain relief member 26 is threaded onto externally threaded rear end 38 of housing 24 as shown in Figure 2. This tightly clamps the fine strength material 22 directly between the complementary threads 39/41 of the housing 24 and the strain relief member 26 to resist longitudinal forces on cable 12 and transmit those forces directly to the connector 10 itself in order to avoid strain on fiber 14 and prevent any resulting transmission losses. It can be seen that, except for the use of fiber centering ferrule 30, a complete connector with strain relief capabilities are provided by only the two components of housing 24 and strain relief member 26. Another feature of the invention is the provision of interruption means to prevent longitudinal strength material 22 from spiralling along with the threads 39/41 when strain relief member 26 is threaded onto externally threaded rear end 38 of housing 24. As contemplated herein, and referring to Figure 3 in conjunction with Figures 1 and 2, the interruption means are provided in the form of grooves 44 spanning the threads 39/41 of at least one of the housing or strain relief member. As seen, for ease of manufacture, the grooves 44 are cut longitudinally through the threads 39 of rear input end 38 of housing 24. As shown in Figure 3, the grooves 44 are cut substantially entirely to the base or root of the threads 39. During use, a considerable number of the very fine strands of strength material 22 are captured in these grooves to insure that at least some of the longitudinal strands or yarn extend lengthwise of the cable over at least a portion of the length or axial dimensions of the threaded portions 38/40 of the housing and strain relief member. Again, it must be kept in mind that the strands are extremely fine and will not interfere with the threading function of the strain relief member. It will be understood that the invention may be embodied in other specific forms without departing from the scope of the attached claims. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.

Claims: An optical fiber connector (10) for terminating and providing strain relief on an optical fiber cable (12) which has an inner fiber (14), an outer jacket (18) and longitudinal strength material (22) therebetween, which is exposed by a length of the outer jacket (18) being removed, the connector comprising: a housing having a rear input end (38) for the cable (12) and a front termination end (28) for the fiber (14), strain relief means including an inner member with external threads and an outer member with internal threads for clamping said strength material (22) between the threaded surfaces (39, 41), characterized in that the connector further comprises a fiber centering ferrule (30), wherein said housing (24) at its rear input end (38) is provided with said external threads (39) arranged on a cylindrical surface so as to form said inner member, and wherein said strain relief member (26) is generally in the form of a sleeve forming said outer member with internal threads (41) arranged along a cylindrical bore (40) and complementary to the external threads (39) of said housing (24), so that the strain relief is provided by only two components and wherein the threads (39, 41) on at least one of said housing (24) and strain relief member (26) are interrupted by interruption means (44) formed as grooves to prevent at least some of the longitudinal strength material (22) from spiralling with the threads (39, 41) when the strain relief member (26) is threaded onto the housing (24). The optical fiber connector of claim 1 wherein said interruption means comprise groove means (44) spanning the threads (39, 41) longitudinally of the cable (12). The optical fiber connector of claim 2 wherein the groove means (44) is of a depth at least to the bottom of the spanned threads (39, 41). The optical fiber connector according to any of claims 1-3 wherein said strain relief member (26) has a through bore through which said optical fiber cable (12) extends and which carries said internal threads (40). The optical fiber connector according to any of claims 1-4 wherein said housing (24) includes a first passage (34) for receiving said inner fiber (14) covered by a buffer (16), and a second passage (32) for receiving and locating said inner fiber (14), the diameter of said first passage (34) being larger than the diameter of said second passage (32). The optical fiber connector of claim 5 wherein said second passage (32) is part of a fiber centering ferrule (30) which is inserted (28) in said housing (24). An optical fiber termination system (10), comprising in combination: an optical fiber cable (12) having at least an inner fiber (14), an outer jacket (18) and a longitudinal strength material (22) therebetween; and an optical fiber connector (10) according to any of claims 1 through 6. A method of terminating and providing strain relief on an optical fiber cable (12) having an inner fiber (14), an outer jacket (18) and longitudinal strength material (22) therebetween, comprising the steps of: providing an optical fiber connector (10) comprising the features of any of claims 1 to 7; stripping a length of the jacket (18) from an end of the optical fiber cable (12) to expose the inner fiber (14/16) and the longitudinal strength material (22); positioning the fiber (14/16) through the connector housing (24) with the longitudinal strength material (22) about the external threads (39); and threading the strain relief member (26) onto the connector housing (24) to clamp the longitudinal strength material (22) directly between the respective threads (39, 41) wherein the clamping step includes collecting some of the strength material (22) in groove means (44) of the connector housing (24) to prevent the collected longitudinal strength material (22) from spiralling with the threads (39, 41) when the housing (24) and the strain relief member (26) are threaded together.

Inventors: GROIS IGOR, MARGOLIN MARK, GROIS, IGOR, MARGOLIN, MARK
Applicants: MOLEX INC, MOLEX INCORPORATED
Application year: 1991
Main classification: G02B6
IPC codes: G02B6