Abstract:
The present disclosure relates to a fiber optic device including a connector housing including a front housing piece, an intermediate housing piece, and a rear housing piece that is non-unitarily connected to the intermediate housing piece. The rear housing piece and the intermediate housing piece define passages that are in general alignment with one another. The fiber optic device also includes a hub positioned within the connector housing. The hub includes a passage that aligns generally with the passage of the intermediate housing piece. The hub is spring biased toward a front end of the connector housing. The fiber optic device further includes a ferrule connected to the hub, and a fiber optic cable. The ferrule defines a passage that extends in general axial alignment with the passage of the hub. A fiber portion of the fiber optic cable is adhesively bonded within the passage of the ferrule. A buffered portion of the fiber optic cable extends through the passage of the rear housing piece. An outer casing and a reinforcing portion of the fiber optic cable are crimped to the exterior of the rear housing piece.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fiber optic connectors for use in optical fiber signal transmission systems, and to methods for assembling such fiber optic connectors. 
     BACKGROUND OF THE INVENTION 
     Fiber optic cables are used in the telecommunications industry to transmit light signals in high speed data and communication systems. A standard fiber optic cable includes an inner light transmitting fiber surrounded by a coating layer of a polymeric material such as nylon. The coating layer is surrounded by a reinforcing or strength layer (e.g., Kevlar) that is covered by an outer casing or jacket made of a polymeric material such as polyvinyl chloride (PVC). 
     Fiber optic connectors are frequently used to non-permanently connect and disconnect optical elements in a fiber optic transmission system. There are many different fiber optic connector types. The most prevalent optic connectors are FC and SC connectors. Other common types of connectors include ST and D4-type connectors. 
     A typical fiber optic connector includes a housing having a front end positioned opposite from a rear end. The front end of the housing is commonly configured to be inserted within an adapter. A fiber optic cable is usually inserted into the connector through a passage (commonly referred to as a capillary) defined by the rear end of the housing. The connector typically includes a ferrule that is mounted adjacent the front end of the housing. The ferrule is axially moveable relative to the housing, and is spring biased toward the front of the connector. The fiber optic cable has an end that is stripped. The stripped end includes a bare fiber that extends through the ferrule, and a buffered portion that extends through the remainder of the connector. Adhesive (e.g., epoxy) is used to secure the fiber within the ferrule. The adhesive is often applied by a needle inserted through the passage defined by the rear end of the housing. A reinforcement layer of the fiber optic cable is frequently crimped to the rear end of the housing. 
     When a connector such as the connector described above is used to provide a fiber optic connection, the ferrule is typically forced to slide rearwardly within the housing. In concert with the movement of the ferrule, the buffered portion of the cable also slides relative to the housing. It is important for the buffered portion to be capable of sliding relative to the housing because, absent such capability, the fiber may break when the ferrule is moved. Misapplied adhesive within the connector housing has been known to cause the buffered portion to “lock-up” within the housing (i.e., the buffered portion becomes adhesively bonded to the housing) such that the buffered portion is prevented from sliding relative to the housing. Thus, in assembling a fiber optic connector, it is desirable to have safeguards for ensuring that the buffered portion is free to slide relative to the housing. Safeguards are particularly important when assembling connectors for small diameter fiber optic cables because such connectors have small inner diameters creating a situation where adhesive can inadvertently be misapplied to the small inner diameters. This is problematic because when cables are subsequently inserted in the connectors, the misapplied adhesive can cause the buffered portions of the cables to “lock up.” It is also desirable for fiber optic connectors to be capable of receiving fiber optic cables having different diameters. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention relates to a fiber optic device including a fiber optic connector and fiber optic cable secured to the connector. The fiber optic connector includes a first housing piece that extends along a longitudinal axis. The first housing piece includes a front end positioned opposite from a rear end. The first housing piece also defines an inner chamber. A hub is positioned within the inner chamber of the first housing piece. The hub includes a passage that extends along the longitudinal axis of the first housing piece. The hub is slidable along the longitudinal axis relative to the first housing piece. A ferrule is connected to the hub. The ferrule extends along the longitudinal axis from the hub toward the front end of the first housing piece. The ferrule defines a passage that extends in general axial alignment with the passage of the hub. A second housing piece is positioned at the rear end of the first housing piece. The second housing piece defines a passage that is in general alignment with the passage of the hub. A spring is captured between the hub and the second housing piece for biasing the hub toward the front end of the first housing piece. The connector further includes a third housing piece that is non-unitarily connected to the second housing piece. The third housing piece defines a passage that is in general axial alignment with the passage of the second housing piece. The third housing piece includes an outer crimp region against which a portion of the fiber optic cable is crimped. The fiber optic cable includes a fiber that extends through: (1) the passage of the ferrule; (2) the passage of the hub; (3) the passage of the second housing piece; and (4) the passage of the third housing piece. 
     Another aspect of the present invention relates to a method for assembling a fiber optic device. The method includes providing a connector including a housing having a first end positioned opposite from a second end. The connector also includes a ferrule that is spring biased toward the first end of the housing. The ferrule defines a longitudinal ferrule passage. The second end of the housing defines an access opening. Adhesive is provided to the ferrule passage by inserting an adhesive delivering tool through the access opening. After the adhesive has been provided to the passage of the ferrule, an extension piece is connected to the second end of the housing. Also after the adhesive has been provided, a fiber of a fiber optic cable is inserted within the ferrule passage. The method further includes inserting at least a portion of the fiber optic cable through the extension passage and the access opening, and securing at least a portion of the fiber optic cable to an exterior of the extension piece. 
     A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate several aspects of the invention and together with the description, serve to explain the principles of the invention. A brief description of the drawings is as follows: 
     FIG. 1 is a respective view of an SC-type connector constructed in accordance with the principles of the present invention; 
     FIG. 2 illustrates the connector of FIG. 1 with a rear extension removed; 
     FIG. 3 is a cross-sectional view taken longitudinally through the connector of FIG. 1; 
     FIG. 4 is a cross-sectional view taken longitudinally through the connector of FIG. 2; 
     FIG. 5 illustrates adhesive being applied to the connector of FIG. 4; 
     FIG. 6 illustrates the connector of FIG. 5 with a fiber optic cable inserted therein and the rear extension mounted on the housing; 
     FIG. 7 illustrates the connector of FIG. 6 with the fiber optic cable crimped on the rear extension, with a boot positioned over the rear extension, and with a conventional grip mounted at the front of the connector; 
     FIG. 8 illustrates a perspective view of another connector constructed in accordance with the principles of the present invention; 
     FIG. 9 illustrates the connector of FIG. 8 with a rear extension piece removed; and 
     FIG. 10 is a cross-sectional view taken longitudinally through the connector of FIG.  8 . 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary aspects of the present invention that are illustrated in the accompanying drawings. Where ever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. A similar part in different embodiments will be assigned that same reference number with the addition of an apostrophe differentiate the embodiments. 
     FIG. 1 illustrates an SC-type connector  20  constructed in accordance with the principles of the present invention. The connector includes a housing  22  having a front housing piece  24  connected to a rear housing piece  26 . A rear extension piece  28  is connected to the rear housing piece  26  by a non-unitary connection. The phrase “non-unitary connection” is intended to mean that the rear housing piece  26  and the rear extension piece  28  are not formed as a single, unitary, seamless piece. For example, FIG. 2 shows the rear extension piece  28  is formed as a separate piece from the rear housing piece  26 . Exemplary types of non-unitary connections that can be used between the rear housing piece  26  and the rear extension piece  28  include, among other things, press fit connections, adhesive connections, and threaded connections. 
     For clarity, no fiber optic cable has been provided in FIG.  3 . Also for clarity, a number of other elements conventionally found in SC-type connectors (e.g., a hood or boot mounted at the rear of the connector and a slidable outer grip located at the front of the housing) have not been shown in FIG.  3 . However, as will be described later in the specification, such elements are shown mounted on the connector  20  in FIG.  7 . 
     Referring to FIG. 3, the front housing piece  24  of the connector  20  extends along a longitudinal axis  30  and includes a front end  32  positioned opposite from a rear end  34 . The front housing piece  24  also defines a front chamber  36  and a rear chamber  38 . A transverse wall  40  separates the front and rear chambers  36  and  38 . An opening  42  centered about the longitudinal axis  30  is defined by the transverse wall  40 . The front and rear ends  32  and  34  of the front housing piece  24  are open. 
     The connector  20  also includes a hub  44  positioned within the rear chamber  38  of the front housing piece  24 . The hub is mounted to slide longitudinally along the axis  30  relative to the front housing piece  24  and includes a longitudinal passage  46  that extends along the longitudinal axis  30 . 
     The primary purpose of the hub  44  is to provide a secure mount for holding a ferrule  48 . For example, as shown in FIG. 3, the ferrule  48  has a rear portion mounted within a front recess defined by the hub  44 . Preferably, a conventional fastening technique (e.g., an adhesive such as epoxy) is used to secure the ferrule  48  to the hub  44 . 
     The ferrule  48  extends along the longitudinal axis  30  from the hub  44  toward the front end  32  of the front housing piece  24 . As shown in FIG. 3, the ferrule  48  extends through the central opening  42  of the transverse wall  40  between the rear and front chambers  38  and  36  of the front housing piece  24 . A longitudinal passage  50  extends through the ferrule  48 . The passage  50  is coaxially aligned with the longitudinal passage  46  of the hub  44  and is sized to receive a bare fiber of a fiber optic cable. 
     Referring still to FIG. 3, the rear housing piece  26  of the connector  20  is mounted at the rear end  34  of the front housing piece  24 . The rear housing piece  26  defines an access passage  52  that is coaxially aligned with the passage  46  of the hub  44  and the passage  50  of the ferrule  48 . The access passage  52  is defined at least partially by a projection  54  that projects rearwardly outward from a main body of the rear housing piece  26 . 
     The connector  20  further includes a coil spring  56  mounted within the rear chamber  38 . The coil spring  56  surrounds a portion of the hub  44  and is captured between a forwardly facing shoulder  58  formed by the rear housing piece  26  and a rearwardly facing shoulder  60  formed by the hub  44 . The spring  56  functions to bias the hub toward the front end  32  of the front housing piece  24 . Because the ferrule  48  is connected to the hub  44 , the spring  56  also functions to bias the ferrule  48  in a forward direction. 
     The rear extension piece  28  of the connector has a front end  62  positioned opposite from a rear end  64 . The front end  62  is mounted over the rear projection  54  of the rear housing piece  26 . An extension passage  66  extends longitudinally through the rear extension piece  28 . The extension passage  66  is coaxially aligned with the hub passage  46 , the ferrule passage  50  and the access passage  52 . Adjacent the front end  62  of the rear extension piece  28 , the diameter of the extension passage  66  increases such that the rear projection  54  of the rear housing piece  26  can be received within the extension passage  66 . 
     The rear end  64  of the rear extension piece  28  is adapted for connection to a fiber optic cable. For example, directly at the rear end  64  is a reduced outer diameter portion  68  configured for allowing an outer jacket  84  and reinforcing layer  82  of a fiber optic cable  76  (shown in FIG. 6) to be placed over the rear extension piece  28 . The rear end  64  also includes a crimping region  70 . The crimping region  70  is positioned adjacent to the reduced outer diameter portion  68  and includes an exterior surface defining a plurality of radial ribs or projections  72 . Alternatively, any surface conducive for securing a crimp (e.g., a knurled surface, a roughened surface, a high friction surface, a threaded surface, etc.) could be used. A radial shoulder  74  separates the reduced outer diameter portion  68  from the crimping region  70 . When a fiber optic cable is secured to the rear extension piece  28 , the reinforcing layer  82  of the cable  78  can be crimped around the outer circumference of the rear extension piece  28  adjacent the crimping region  70 . 
     Still referring to FIG. 3, the extension passage  66  has a diameter D 1  that is smaller than a diameter D 2  of the access passage  52 . Preferably, the diameter D 2  of the access passage  52  is at least 25% larger than the diameter D 1  of the extension passage  66 . 
     FIGS. 4-7 illustrate various stages of a method for assembling the connector  20  of FIGS. 1-3. FIG. 4 shows the connector  20  before the rear extension piece  28  has been connected to the rear housing piece  26 . With the rear extension piece  28  separate from the rear housing piece  26 , the access passage  52  provides ready access to the rear chamber  38  of the front housing piece  24 . For example, the relatively large diameter of the access passage  52  along with its close proximity to the hub  44  assist in allowing an adhesive applying tool to be used to fill the ferrule passage  50  of the ferrule  48  with adhesive (e.g., epoxy). For example, as shown in FIG. 5, a needle  53  can easily be inserted through the access passage  52  and used to precisely inject adhesive into the hub passage  46  and the ferrule passage  50 . Because the needle  53  is not required to pass through the rear extension piece  28 , adhesive is prevented from being inadvertently applied to the interior of the rear extension piece  28 . 
     After the adhesive has been injected into the ferrule passage  50 , the rear extension piece  28  is connected to the rear housing piece  26 , and the fiber optic cable  76  is fed into the connector  20 . As shown in FIG. 6, the cable  76  includes a central fiber  78 , a polymeric coating  80  (e.g., PVC, nylon, etc.) covering the fiber  78 , the reinforcing material  82  (e.g., Kevlar) surrounding the coating  80 , and the outer jacket  84  (e.g., a PVC jacket) surrounding the reinforcing material  82 . To prepare the cable  76  for insertion into the connector  20 , the free end of the cable  76  is stripped to form a bare fiber portion  86 . Adjacent the bare fiber portion  86 , the fiber optic cable  76  is stripped down to the coating  80  to form a buffered portion  88 . Additionally, a portion  77  of the reinforcing material  82  is exposed for use in crimping the fiber optic cable  76  to the connector  20 . 
     To insert the fiber optic cable  76  into the connector  20 , the cable  76  is inserted through the coaxially aligned passages  66 ,  52 ,  46  and  50 . After insertion, the bare fiber portion  86  extends through the passage  50  of the ferrule  48 , and the buffered portion  88  extends through the hub passage  46 , the access passage  52 , and the extension passage  66 . An overlap portion  85  of the outer jacket  84  and the reinforcing layer  82  overlap the reduced outer diameter portion  68  of the rear extension piece  28 . Also, the exposed portion  77  of reinforcing material  82  overlaps the crimping region  70  of the rear extension piece  28 . 
     Preferably, the diameter D 1  of the extension passage  66  is selected to closely surround and support the buffered portion  88  of the fiber optic cable  76 . In one particular embodiment, a clearance less than 0.004 inches is provided between the buffered portion  88  and the wall defining the extension passage  66 . For example, in one non-limiting embodiment, the buffered portion has an outer diameter of about 0.035 inches and the diameter D 1  of the extension passage  66  is about 0.042 inches. The separate rear extension piece  28  allows the front portion of the connector  20  to accommodate fiber optic cables having varying diameters. For example, if a smaller diameter cable is required, a rear extension piece  28   a  (shown in FIG. 4) having a smaller diameter D 1a  is selected and used in concert with the front portion of the connector  20 . By contrast, if a larger diameter fiber optic cable is required, the rear extension piece  28  having the larger diameter D 1  is selected. Therefore, regardless of the size of fiber optic cable selected, a rear extension piece suitable for providing adequate support and guidance to the cable can be selected. 
     FIG. 7 shows the connector  20  as fully assembled. As shown in FIG. 7, the exposed portion  77  of the reinforcing material  82  is secured to the crimping region  70  by a circumferential crimping tube  90 . Also, a boot  92  (i.e., a hood) is shown attached to the rear extension piece  28 . Further, a conventional grip  93  is shown snap fit over the front housing piece  24 . 
     Still referring to FIG. 7, the connector  20  is shown in alignment with a conventional adapter  94 . When the front end  32  of the front housing piece  24  is inserted within the adapter  94 , transverse projections  96  formed on the front housing piece  24  move past resilient tabs  98  within the adapter  94  to provide a snap fit connection. To remove the connector  20  from the adapter  94 , the grip  93  is pulled rearwardly causing the tabs  98  to deflect outward such that the connector can be pulled from the adapter  94 . 
     When the connector  20  is inserted in the adapter  94 , a polished end face  100  of the ferrule  48  of the connector  20  is pressed against a corresponding ferrule end face of an opposing connector (not shown) mounted in the adapter  94 . As the ferrule  48  engages the ferrule of the opposing connector (not shown), the ferrule  48  slides rearwardly within the front housing piece  24 . When the ferrule  48  slides in a rearward direction relative to the front housing piece  24 , the buffered portion  88  of the fiber optic cable  76  also slides relative to the housing  22 . The relative sliding motion between the buffered portion  88  and the housing  22  is important to reduce the risk of breaking or otherwise damaging the fiber  78 . In this regard, the manufacturing method described above is advantageous because, since the needle  53  (shown in FIG. 5) is not required to be inserted through the rear extension piece  28 , adhesive is inhibited from being inadvertently applied to the interior of the rear extension piece  28 . 
     It will be appreciated that the aspects of the present invention are particularly applicable to fiber optic connectors for use with small diameter fiber optic cables (i.e., fiber optic cables having a outer jacket diameters less than  2  millimeters). One particular non-limiting application relates to connectors for fibers having outer jacket diameters of about 1.7 millimeters. 
     To accommodate a small diameter fiber optic cable, it is desirable for the outer diameter of the rear extension  28  (e.g., at the crimping region  70 ) to be relatively small (e.g., less than 2 millimeters). This is desirable because small cables have relatively little reinforcing material (e.g., Kevlar) due to their small diameters. To equally distribute tensile load relief, the reinforcing material should be evenly distributed about the crimp region. If the reinforcing material is not evenly distributed, the fiber of the cable may break when a tensile load is applied to the cable. The use of a small outer diameter at the crimp region  70  facilitates uniformly distributing the reinforcing material. 
     Since the outer diameter of the rear extension is preferably relatively small, the extension passage  66  of the connector also has a relatively small diameter. If the rear extension  28  were formed as a single piece with the rear housing piece  26 , adhesive would need to be applied to the ferrule passage  50  by inserting the needle  53  through the extension passage  66 . Since the diameter of the extension passage  66  is small, at least some adhesive would likely be coated within the extension passage  66  when the needle  53  is withdrawn. In view of the small clearance between the buffered portion  88  and the extension passage  66 , any adhesive present in the extension passage  66  could cause the buffered portion  88  to bind or otherwise lock up relative to the housing  22  thereby increasing the likelihood of fiber breakage. The various aspects of the present invention eliminate this problem by making the rear extension  28  a separate piece. 
     FIGS. 8-10 illustrate an FC-type connector  20 ′ constructed in accordance with the principles of the present invention. The connector  20 ′ includes a front housing piece  24 ′ (shown in FIG. 10) and rear housing piece  26 ′. The rear housing piece  26 ′ is threaded within the front housing piece  24 ′. A nut  102  for securing the connector  20 ′ to an adapter is rotatably mounted about the front housing piece  24 ′. A spring biased ferrule  48 ′ is slidably mounted within the front housing piece  24 ′. Similar to the embodiment of FIGS. 1-7, a rear extension piece  28 ′ is non-unitarily connected to the rear housing piece  26 ′. In FIG. 9, the rear extension piece  28 ′ has been removed from the remainder of the rear housing piece  26 ′. 
     It will be appreciated that the connector  20 ′ can be assembled in a manner similar to the connector  20  described in FIGS. 1-7. It will also be appreciated that for the purpose of clarity, a fiber optic cable has not been shown positioned within the connector  20 ′. 
     With regard to the foregoing description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size and arrangement of the parts without the scope of the present invention. For example, while FC and SC-type connectors have been shown in this specification, it will be appreciated that the principles of the present invention are application to any number of other different types of connectors. It is intended that the specification and depicted aspects be considered exemplary only, with a true scope and spirit of the invention being indicated by the broad meaning of the following claims.