Abstract:
A fiber optic connector with an epoxy preform is described that facilitates integration of an optical fiber with a connector body and a ferrule. In an illustrated embodiment, the epoxy preform is a cylindrical thermosetting epoxy element having a passage therethrough adapted to receive an optical fiber of a predetermined diameter. The passage through the preform is positively secured within a cavity within the connector body to precisely align the passage with an opening in an abutting ferrule.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fiber optic connectors, and more particularly to a fiber optic connector with a preloaded, thermosetting epoxy preform. 
     BACKGROUND OF THE INVENTION 
     Sealing materials, such as liquid epoxy, are commonly employed to mount the end of a glass or optical fiber in an assembly such as a fiber optic connector. One attribute of liquid epoxy is that is it difficult and time consuming to work with. Generally, two different compounds must be thoroughly mixed in a proper ratio for a predetermined time, then placed into a syringe which is used to apply the mixed compounds as desired. Each of these steps is technique dependant, requiring an attentive, experienced technician to achieve consistent results. Catalytic compounds have the distinct disadvantage of forcing a technician to rush to apply the mixed materials before they set or become difficult to apply. With respect to fiber optic connectors, a portion of the connector is generally filled with the epoxy and the fiber is passed therethrough. After passing the fiber through the liquid epoxy, the fiber must be threaded into a ferrule, a task made more difficult by the viscous liquid. Not infrequently, some of the liquid epoxy is inadvertently deposited on surfaces that must remain epoxy free, necessitating clean-up with an alcohol pad, for example. 
     An alternative to liquid epoxy is an epoxy preform. Epoxy preforms are solid shapes of one-part epoxy, stable at room temperatures. When exposed to elevated temperatures, they melt to form a rigid seal. Epoxy preforms can be configured in many shapes, such as rings or tubes, and are fabricated with dimensions having ±0.002&#34; or tighter tolerances depending upon a particular application. Advantages of epoxy preforms include ease of use and application, consistent quality and quantity, as well as minimal waste and spillage. 
     U.S. Pat. No. 4,984,865 to Lee et al., discloses a fiber optic connector that includes a thermoplastic slug disposed in a hollow of a connector body. The thermoplastic slug has a longitudinal opening through which an optical fiber is passed. Heat is applied to liquify the thermoplastic slug to cause it to bond to the optical fiber and the wall of the hollow. However, thermoplastic epoxies are disadvantageous in applications wherein the fiber optic connector is subjected to heat, as the epoxy can soften or even become displaced, thereby destroying the connection, rendering the fiber unstable and susceptible to breakage, and permitting contaminants to enter the connector body. 
     Further with respect to the connector disclosed by Lee, the thermoplastic slug is not positively retained within the hollow, allowing the slug to either be partially displaced, thereby placing the longitudinal opening through the slug, having a diameter not much greater than the fiber, out of alignment with an opening in a ferrule against which the slug abuts. Worse yet, the connector configuration in Lee can easily permit the slug to become completely dislodged, and possibly lost, if the opening in the connector through which the slug is introduced is not maintained in a substantially upright orientation. 
     A need exists for a fiber optic connector which facilitates rapid, yet precise connection of an optical fiber with a connector body, while providing a heat tolerant epoxy seal between the fiber, the connector body, and a ferrule. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages described above by providing a fiber optic connector with an adhesive preform having an outer diameter greater than of a bore through the fiber optic connector. The preform is positively secured within a cavity defined by a portion of the fiber optic connector to precisely align the passage with an opening in an abutting ferrule. 
     In an illustrative embodiment, the preform is a cylindrical thermosetting epoxy element having a passage adapted to receive an optical fiber of a predetermined diameter. The preform is positively secured within a cavity defined by the connector body by an annular seat and an abutting ferrule having a conical inlet to a longitudinal passage adapted to receive the optical fiber. The seat and the inlet maintain the passage in precise alignment to facilitate introduction of the fiber into the connector body, through the preform, and into the passage in the ferrule. 
     The present invention further includes a method of providing a connection between a fiber optic cable and the fiber optic connector of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be more fully understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a sectional view of a fiber optic connector of the invention; and 
     FIG. 2 is an exploded sectional view of the fiber optic connector of FIG. 1, aligned with a fiber optic cable prepared for mating. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a sectional view of a fiber optic connector 10 of the invention. The connector 10 includes a connector body 12 having a bore or passage therethrough. The connector body 12 has a first end adapted to receive an adhesive preform 14, such as a dry epoxy. In the illustrated embodiment, the preform 14 is a thermosetting epoxy having a cylindrical shape with a central passage therethrough. The thermosetting epoxy preform 14 retains its manufactured configuration at normal room temperatures, allowing it to be conveniently available when ready for insertion into the connector. 
     An important characteristic of thermosetting plastic is that once subjected to a heating cycle wherein it becomes flowable, then allowed to cool and harden, it will not soften or become flowable again if subjected to another heating cycle. This provides a particular advantage in applications wherein the connector 10 is mated to heat producing equipment or is located in a thermally hostile environment, because a seal or mate provided by the thermosetting epoxy is assured. 
     Insertion depth of the preform 14 into the first end of the connector body 12 is limited by an engagement portion such as a shoulder or an annular seat 16. A ferrule 18 is positioned within the first end of the connector body 12 in an abutting relationship with the preform 14. The preform is thus held snugly in position and cannot become dislodged from the connector 10 unless the ferrule 18 is removed therefrom. In one embodiment, the end of the ferrule 18 abutting the preform 14 has a conical inlet 20 leading to a passage through the ferrule. The conical inlet 20 guides an optical fiber to be mated with the ferrule 18 into the passage. In this embodiment, the passage through the connector body 12 and the preform 14 leading to the ferrule 18 has a diameter at least as great as the diameter of the conical inlet 20 to further facilitate introduction of an optical fiber into the ferrule. 
     The connector body has a second end adapted to receive a fiber optic cable and includes an abutment surface 22 to limit an insertion distance of a portion of the fiber optic cable. In the illustrated embodiment, the abutment surface has a frustroconical shape that facilitates guiding an optical fiber into the passage through the connector body 12. The connector 10 further includes a spring 24, a nut 26, and a C-clip 28 used to secure the connector 10 to other equipment (not shown). 
     Advantageous features of the connector 10, as well as a method of providing a connection between a fiber optic cable and the fiber optic connector of the invention, are better appreciated by referring to FIG. 2 which is an exploded sectional view of the fiber optic connector of FIG. 1, aligned with a fiber optic cable 30 prepared for mating. The exemplary fiber optic cable 30 includes an optical fiber 32, a buffer 34, and Kevlar® fibers 36 encased in an outer jacket 38. A crimp sleeve 40 and boot 42 are disposed on the outer jacket 38. 
     In an exemplary embodiment, the fiber optic cable 30 is prepared for mating to the connector 10 by retracting the boot 42 from the crimp sleeve 40; and stripping from one end of the cable approximately 38 mm of the outer jacket 38, 32 mm of the fibers 36, and 25 mm of the buffer 34 to expose approximately 25 mm of the optical fiber 32. 
     Mating the prepared fiber optic cable 30 to the connector 10 is accomplished by the following steps. As a preliminary matter, the exposed fiber 32 is slightly bent to ensure that no nicks occurred during stripping. If the fiber was nicked, it will easily break. The exposed fiber 32 is then cleaned by drawing it through an alcohol pad. Next, the fiber is inserted into the second end of the connector body 12 while the fibers 36 surround the second end of the connector body 12. The crimp sleeve 40 is slid over the fibers and crimped with an appropriate crimp die to the second end. The boot 42 is then slid over the crimped connection. During the insertion process, the optical fiber 32 has traveled through the passage in the connector body 12, the preform 14, and the ferrule 18. 
     In embodiments wherein the preform 14 is a thermosetting epoxy, the connector 10 is subsequently heated to deform or cause the thermosetting epoxy preform 14 to flow, and then cure, thereby securing the optical fiber 32 within the connector 10. The cured thermosetting epoxy preform is then allowed to cool. In the exemplary embodiment, the connector is heated for 20-30 minutes at 150° C. to fully cure. 
     Normally, a portion of the optical fiber 32 extends beyond the free end of the ferrule 18. The extending portion is removed and the end of the ferrule 18 is prepared for optical connection using cutting and polishing techniques known in the art. 
     Many modifications of the presently disclosed invention will become apparent to those skilled in the art having benefitted from the instant disclosure.