Abstract:
A fiber optic connector for terminating an optical fiber is disclosed. The connector comprises a housing having opposed first and second ends, and the housing receives the optical fiber at its first end. An elongated member is retainable in the housing, and the elongated member includes a crimpable portion. An insert is disposable within the crimpable portion. The crimpable portion of the elongated member is disposed within the housing, and the crimpable portion includes opposed first and second ends and a point between the first and second ends. The crimpable portion is tapered from the point toward one of the first and second ends.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a fiber optic connector for terminating an optical fiber and, more particularly, to a crimpable fiber optic connector for terminating an optical fiber. The connector includes a crimpable portion having a contoured crimp area. 
     Typically, fiber optic connectors include a crimpable portion having a straight profile crimp area that produces a constant load under the crimp area, as shown in FIG.  6 . However, a straight profile crimp area may have an abrupt discontinuity at the ends of the crimp boundary, where the uncrimped regions meets the crimped region. This discontinuity may create a sharp micro-bend that may increase the stub connector&#39;s attenuation. 
     It would be desirable to provide a contoured crimp area configured so that when the crimp die force is applied to the crimp area, there will be minimal compression force at the ends of the crimp boundary and maximum compression force near the midpoint of the crimp area. 
     It would also be desirable to provide a crimp area having a smooth load transition at the ends of the crimp boundary. 
     It would further be desirable to apply a substantially triangular load distribution to the fiber optic cable (field fiber) that reduces fiber micro-bending within the top and bottom inserts in the crimp area during the crimping process, and thus, results in less fiber attenuation. 
     SUMMARY OF THE INVENTION 
     The invention includes a fiber optic connector for terminating an optical fiber. In one form, the connector comprises a housing having opposed first and second ends, and the housing receives the optical fiber at its first end. An elongated member is retainable in the housing, and the elongated member includes a crimpable portion. An insert is disposable within the crimpable portion. The crimpable portion of the elongated member is disposed within the housing, and the crimpable portion includes opposed first and second ends and a point between the first and second ends. The crimpable portion is tapered from the point toward one of the first and second ends. Moreover, the crimpable portion may be tapered from the point toward the other of the first and second ends. 
     Preferably, the connector includes two inserts disposable within the crimpable portion of the elongated member. 
     Preferably, the stub fiber contacts the glass fiber core in the two inserts. Alternatively, the stub fiber may contact the glass fiber core in the ferrule. 
     Preferably, the crimpable portion is configured so that when a crimp die force is applied to the crimpable portion, the force is greater at the point between the first and second ends than at the first and second ends. 
     The invention also includes a crimpable fiber optic connector for terminating an optical fiber, wherein the connector is crimpable by a crimp tool having opposed crimp dies thereon. At least one of the crimp dies has opposed first and second ends and a point between the first and second ends. The crimp die is tapered from the point toward one of the first and second ends. Preferably, the other crimp die has opposed first and second ends and a point between the first and second ends. The other crimp die is tapered from the point toward one of the first and second ends. 
     The invention also includes a method for assembling a fiber optic connector. Preferably, the crimpable portion of the elongated member and the buffer crimp portion are crimped simultaneously. 
     The invention further includes a method for terminating a multiple layered field optical fiber having a glass fiber core with an optical fiber connector. 
    
    
     BRIEF DESCRIPTION OF FIGURES 
     FIG. 1 shows an exploded view of a completely assembled connector in accordance with a preferred embodiment of the invention; 
     FIG. 2 shows an exploded view of an assembled inner housing assembly of the connector of FIG. 1; 
     FIG. 3 shows a cross-sectional view of the connector of FIG. 1 in a crimping die prior to compression of the die; 
     FIG. 4 shows a partial cross-sectional view of the connector of FIG. 1 in a crimping die after compression of the die; 
     FIG. 5 shows a partial cross-sectional view of the connector of FIG. 1 in a crimping die after compression of the die, taken along the line  5 — 5  in FIG.  4  and looking in the direction of the arrows; 
     FIG. 6 shows a load distribution profile for a straight crimp area in accordance with the prior art; 
     FIG. 7 shows a load distribution profile for a contoured crimp area in accordance with a preferred embodiment of the invention; 
     FIG. 8 shows a partial cross-sectional view of a connector in a contoured crimp die prior to compression of the die, in accordance with another embodiment of the invention; and 
     FIG. 9 shows a partial cross-sectional view of the connector of FIG. 8 in a contoured crimp die, after compression of the die. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The illustrated embodiment of the invention is directed to an SC-style fiber optic connector for facilitating the connection of an optical fiber found in the field (field fiber) to an optical fiber predisposed in the connector (stub fiber), such that a fiber optic signal (light) may be passed from the field fiber to the stub fiber with minimal signal degradation occurring at the interface between the fibers. 
     The disclosure of application Ser. No. 10/014915, filed on Oct. 23, 2001, and commonly owned by the assignee of the present invention, is hereby incorporated by reference. 
     FIG. 1 shows an exploded view of a completely assembled SC-style fiber optic connector  10 . As can be seen therein, in a preferred embodiment, the connector  10  includes an outer housing  20 , an inner housing assembly  30 , a crimp sleeve  80 , and a boot  90 . The connector is applied to a fiber optic cable  100 , such as the one shown in cross section in FIG.  1 . As also seen in FIG. 2, the inner housing assembly  30  includes a plastic inner housing  32  encircling an elongated, metallic, and sectionally tubular backbone  36 , a helical spring  46 , a cylindrical, polished ceramic ferrule  48 , and top  54  and bottom  56  inserts. 
     In particular, as probably best seen in exploded FIG. 2, the backbone  36  has the helical spring  46  preferably disposed about a body portion  43  thereof, top and bottom inserts  54  and  56  respectively, are cooperatively inserted through the ferrule holding end  38  of the backbone  36  and into the glass fiber crimp section  42  thereof. The ceramic ferrule  48  is then inserted at least partly into the ferrule holding end  38  where it is maintained by interference fit friction, thereby securing the inserts  54  and  56  within the glass fiber crimp section  42 . Alternatively, the ferrule  48  could be held in the ferrule holding end  38  by an adhesive. The assemblage of backbone, inserts, ferrule, and spring is then inserted into the inner housing  32 , after which the front portion  68  of a corrugated endcap  66  is inserted into the rear of the inner housing  32  against the bias of the spring  46  until it snaps into place, thereby keeping the backbone  36  pressed as far forward as the projecting ring  40  thereof will permit it to travel until it comes flush with an interior portion of the inner housing  32 . The endcap  66  fits over primarily the body portion  43  of the backbone  36  so that the buffer crimp portion  44  extends through the rear portion  70  of the endcap  66 . Although the illustrated embodiment shows the backbone  36  and the component sections thereof being circular/cylindrical, they, and any later-described cooperating structure alternatively could be square/prismatic or otherwise shaped. 
     Top insert  54  and bottom insert  56 , as seen in perspective in FIG.  2  and in cross-section in FIGS. 3,  4 ,  8  and  9 , include tapered lead-ins  58  at the rear ends thereof to facilitate the field fiber  100  being inserted therebetween from the rear. As shown in FIG. 5, one or both of the inserts include groove portions  60  along the respective engagement surfaces thereof,  62  and  64 , to permit the glass fiber  102  to pass therebetween along the longitudinal length of the inserts and to align with the rear entry to the aperture  50  of the ceramic ferrule  48 . The ceramic ferrule  48  may also preferably include a tapered lead-in portion  52  at the rear end thereof to facilitate entry of the glass fiber  102 . Such a lead-in  52  may take the form of a generally conical cut-away portion of the ferrule. 
     In the field, prior to insertion into the connector, the field fiber  100  is prepared by appropriately stripping the insulative layer(s) and any stiffening layer(s) off the end of the field fiber. As can be seen in FIG. 1, the layers may typically include, for example, a jacket  104 , such as insulative rubber or plastic, and a buffer  106  made of insulative rubber or plastic. An intermediate strengthening layer (not shown), such as Kevlar®, may preferably circumferentially reside between the buffer  106  and jacket  104 . A portion of the jacket  104  and a portion of the buffer  106  are stripped off. The now exposed glass fiber  102  is precision cleaved to an appropriate length. 
     Once the inner housing assembly  30  is fully assembled, it is placed onto a lower glass fiber crimping die  120  of a crimping tool (not shown). At this point, the crimping tool may be closed with very light pressure to simply hold the assembly  30  in place on the die  120 . When the tool closes, the upper glass fiber crimping die  122  penetrates a crimp window  34  in the upper portion of the inner housing  32  to secure the assembly in place on the die. 
     After the inner housing assembly  30  is fully assembled and properly disposed on the crimping tool, the cleaved end of the field fiber  100  is then inserted through the buffer crimp portion  44  of the backbone  36 . The cleaved end travels through the backbone  36 , between the top and bottom inserts  54  and  56 , respectively, therein, before entering the rear of the ferrule  48  and coming into aligned contact with the suitably precision cleaned and/or polished stub fiber  110  within the narrow axial aperture  50  of the ferrule  48 . 
     Once the field fiber  100  is fully inserted into the inner housing assembly  30  so that it comes flush with the stub fiber  110  within the ceramic ferrule  48 , the crimping tool is then compressed more forcibly so that the preferably complementary upper glass fiber crimping die  122  of the tool compresses the glass fiber crimp section  42  of the backbone  36  about the top and bottom inserts,  54  and  56 , respectively, carried therein (shown in FIGS.  3  and  4 ). 
     The contoured crimp section  42  is shaped so that when the crimping tool applies force to the crimp dies  120  and  122  and, thus, the crimp section  42 , there is minimal compression force at the ends of the crimp section  42  and maximum compression force near the midpoint of the crimp section  42 . The contoured crimp section  42  applies the load to the field fiber  100  through the top and bottom inserts  54  and  56 , with a substantially triangular distribution profile, as shown in FIG.  7 . This provides a smooth load transition between the crimped and uncrimped regions of the top and bottom inserts. Thus, a micro-bend is not created because the load distribution profile is tapered without any abrupt transitions. 
     In another preferred embodiment of the invention, and as can be seen in FIGS. 8 and 9, lower and upper crimp dies,  130  and  132 , may have contoured surfaces, similar in shape to the contoured crimp section  42  disclosed in the embodiment shown in FIGS. 1-7. Contoured crimp dies  130  and  132  may be utilized with a straight profile crimp section to provide the substantially triangular load distribution profile shown in FIG.  7 . 
     The disclosed invention provides an improved fiber optic connector. It should be noted that the above-described and illustrated embodiments and preferred embodiments of the invention are not an exhaustive listing of the forms such a connector in accordance with the invention might take; rather, they serve as exemplary and illustrative of embodiments of the invention as presently understood. By way of example, and without limitation, a non-SC-style fiber optic connector, such as an FJ or ST-style connector, is contemplated to be within the scope of the invention. Similarly, though the illustrated embodiment is directed toward a multimode cable connection, a single mode connection is also contemplated by the invention. Many other forms of the invention are believed to exist.