Abstract:
A connector includes a pair of connector members for simultaneously contacting a first plurality of optical fibers with a second plurality of optical fibers. A cup for fixing the ferrule-tipped ends of mating optical fibers is wholly contained within each of a plurality of channels through the members. The cup is capable of axial movement within a channel through a body element of a connector member. A spring member is located in the channel between a back plate and the cup to act upon the base of the cup. Aligned dowel channels are provided for receiving a thick external dowel that resides within the aligned dowel channels of the body member of one of the connector members and the holder of the other. An internal dowel is press fit within the body element and holder dowel channels of the other connector member to enhance the ruggedness and durability of the device.

Description:
The invention herein claimed was made under contract number N66604-95-C-0004 with the United States Navy. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a connector for use with a fiber optic sensor array system. More particularly, this invention pertains to a connector for simultaneously completing a plurality of reliable low-loss optical interconnections between the upstream on-board elements (e.g. source and photodetector) and downstream elements such as an optical cable or a towed array of hydrophones. 
     2. Description of the Prior Art 
     U.S. Pat. No. 5,590,229 of Goldman et al. covering “Multichannel Fiber optic Connector” addresses problems posed, for example, by hydrophone arrays that require maintenance of multiple reliable optical contacts within the operational environment. Optical fiber connections, unlike electrical connections, require precise alignments of mating fibers and are subject to significant degradation by environmentally-related factors. The failure to obtain precise alignment of fiber terminations can contribute significantly to optical signal loss. 
     The device disclosed in the patent includes a two-part connector, each half accommodating a plurality of optical fibers for simultaneously completing optical-quality connections between paired fibers. One fiber is accommodated in one half of the connector and the other held in the other half. The connector provides an interface for coupling optical signals from the hydrophones of either a towed or planar array to upstream shipboard elements including, for example, a laser source, a photodetector and processing electronics. Should a grouping of seven (7) hydrophones be employed, for example, a total of fifteen (15) fiber couplings must be accomplished by the connector. 
     The device of the referenced patent is designed for extremely high performance applications characterized by very high return loss in operation. This results in a rather complex and difficult-to-manufacture structure that is necessarily quite costly. In the device of the patent, multiple optical fibers with ferrule terminations are spring-loaded within a plurality of internal channels of each of the connector halves. The stringent return loss requirements demand that not only axial, but also rotational, alignment be maintained between the faces of contacting fibers. As a consequence, the faces of the ferrules are angularly-inclined, necessitating a rotational alignment structure for assuring that mating angular alignments are simultaneously obtained among the plurality of pairs of fibers housed in the two connector halves. 
     The structures required for rotational alignment include the keyed ends of the cups into which the ferrules are inserted, in combination with the slotted rear faces of body elements of the male and female connector halves. The fabrication of each of such elements is complex and requires precision machining, reducing yield while increasing cost and complexity. 
     In contrast to the types of optical interconnections and associated connectors required to maintain rotational, as well as axial, alignment precision in the most demanding applications, there exist many useful applications that do not require rotational alignment between mating optical fibers for satisfactory performance. FIGS.  1 ( a ) and  1 ( b ) are side sectional views illustrating a ferrule  10  having a symmetrical face (as opposed to one that is angularly-inclined for rotational alignment). Such a ferrule  10  is suitable for optical interconnections in numerous, primarily non-military, applications. 
     The ferrule  10  comprises a generally cylindrical elongated body with an outer shell  12 , preferably of tungsten carbide, that encloses a filler material  14  (preferably a relatively soft silver/nickel alloy). The filler material  14  encircles an optical fiber  16 , substantially encapsulating it within a shaped fitting  18  of EPOXY or like adhesive. A brass element  20  stiffens the fiber  16 . An outer plastic coating  22  is stripped from the fiber  16 . 
     FIG.  1 ( b ) is an enlarged and detailed view, taken at line  1 ( b ) of FIG.  1 ( a ), of the terminal end of the optical fiber  16  in optical contact with an optical fiber  16 ′ (shown in shadow outline). The fibers  16  and  16 ′ include polished termination end faces  24 ,  24 ′ that are continuations of, and substantially coextensive with, faces  26  and  26 ′ of the respective ferrules. It is to be noted that the end faces  24  and  24 ′ and the faces  26  and  26 ′ are symmetrically rounded about the cores of the optical fibers  16  and  16 ′. Thus, there exists a small region of mutual tangency between the fibers  16  and  16 ′, facilitating the transmission of optical signals therebetween. Also, oppositely-acting axial compression forces (introduced by springs) tend to flatten the rounded end faces slightly in the region of mutual tangency. The area of intimate contact between the aligned faces is thereby slightly enlarged and stabilized to enhance the quality of the optical interconnection in a manner that is entirely satisfactory for all but the most demanding optical communication criteria. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     It is therefore an object of the present invention to provide a multichannel optical connector that achieves economies over that disclosed in U.S. Pat. No. 5,590,229 for applications that do not require rotational alignment between contacting optical fibers. 
     The preceding object is addressed by the present invention that provides a fiber optic connector. The connector includes a pair of mateable connector members. Each member comprises a body element having at least one channel therethrough that is adapted to receive a ferrule-tipped optical fiber. A cap is provided for fixedly receiving the ferrule. Such cap is of substantially-cylindrical shape. 
     At least one body element dowel channel is provided in each of the body elements with the dowel channels of the body elements being aligned with one another when the connector members are coupled to one another. A first connector member includes a holder located flush against the body element. The holder has at least one holder dowel channel aligned with a body element dowel channel. An internal dowel is captured within the aligned body element and holder dowel channels of the first connector member. 
     The preceding and other features and advantages of the present invention will become further apparent from the detailed description that follows. Such description is accompanied by a set of drawing figures. Numerals of the drawing figures, corresponding to those of the written description, point to the features of the invention. Like numerals refer to like features throughout both the written description and the drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS.  1 ( a ) and  1 ( b ) are a side sectional view of a ferrule termination of a type suitable for incorporation into a multiple optical connector in accordance with the invention and a greatly enlarged and detailed view of a portion of the terminal end of the optical fiber within that ferrule and a mating optical fiber (shown in shadow outline), respectively; 
     FIGS.  2 ( a ) and  2 ( b ) are side sectional views of the multichannel fiber optic connector of the invention with mating connector members disengaged and engaged respectively; and 
     FIG. 3 is an exploded perspective view of assemblies associated with a representative ferrule and optical fiber that render the ferrule subject to precise and reliable axial alignment within a connector channel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS.  2 ( a ) and  2 ( b ) are side sectional views of the fiber optic connector  28  of the invention with mating connector members  30  and  32  disengaged and engaged respectively. The connector  28  of the invention provides a low cost, easy-to-manufacture version of that disclosed in U.S. Pat. No. 5,590,229 for “Multichannel Fiber Optic Connector”. The teachings and disclosure of that patent, property of the assignee herein, are hereby incorporated by reference. It should be kept in mind during the discussion that follows that, while the details of only a single fiber-to-fiber optical connection is visible, the connector  28  facilitates and enables the simultaneous completion of a plurality of independent fiber-to-fiber connections of good optical quality. The extension of the teachings herein to a large plurality of optical connections is illustrated and taught in U.S. Pat. No. 5,590,229. 
     Referring first to the connector member  30 , such member is contained within a male housing or plug  34 . The rear portion of the plug  34  includes an annular shoulder  36  for capturing the proximate end of a hose-like rubber casing  38  that encloses an aligned plurality of hydrophones (not shown) which constitutes the downstream or sensing portion of the sensing system. The connector member  32  is contained within a female housing or receptacle  40  which may comprise a portion of the hull penetrator  42  of a vessel. The rear portion of the connector member  32  extends within the vessel and accommodates optical fibers leading to the upstream or on-board elements of the sensing system, such as a laser source and a photodetector (not shown). The front portion of the plug  34  includes internal threading  44  while the receptacle  40  includes exterior threading  46  for securing the two members together as shown in FIG.  2 ( b ). 
     Referring to FIGS.  2 ( a ) and  2 ( b ) in combination, the member  30  includes a back plate  48  which abuts and is in direct contact with a body element  50 , being secured thereto by means of a screw  52 . The body element  50 , having opposed planar faces  54  and  56 , lies in a flush, abutting relationship against both the back plate  48  and an adjacent holder  58 . A screw  60  is countersunk into the planar front surface  62  of the holder  58  for securing the holder  58  to the body element  50 . 
     The representative optical fiber  22  enters the member  30  through an aperture  64  within the back plate  48 . The aperture  64  is aligned with an internal channel of the member  30 . Such channel comprises an enlarged diameter portion  66  aligned with and connected to a smaller diameter portion  68  within the member  30 . The adjacent holder  58  includes an internal channel  70  which is in substantial axial alignment with the aforesaid channel that passes through the body element  50 . 
     A cup  72  lies completely within the enlarged diameter portion  66  of the channel of the body element  50 . This is in contrast to the type of cup employed in the device of U.S. Pat. No. 5,590,229 whose keyed end is captured outside the body element  50  by one of a plurality of grooves within the back plate of the connector. It will be shown below that the design of the cup  72  is simplified when compared to that of the referenced United States patent. The simplification of the cup  72  is accompanied by simplification of the design of the back plate  48  in view of the suitability of ferrules (and associated fibers) having symmetrically-rounded tips for numerous commercial applications. Generally, the suitability of ferrules having symmetrically-rounded (as opposed to angularly-inclined) faces reflects the absence of any necessity for rotational alignment between contacting fibers. In the prior art patent, the need for rotational alignment led to complex, difficult-to-machine cup and back plate structures. 
     The face  74  of the cup  72  abuts an internal annular ridge  76  defined by the transition between the enlarged diameter portion  66  and the smaller diameter portion  68  of the channel through the body element  50 . The ferrule  10  is fixed to the cup  72  and extends through the face  74  and into the channel  70  that passes through the holder  58 . A spring  78  is seated within the enlarged diameter portion  66  of the channel. As compressed, it exerts a force to urge the cup  72  away from the back plate  48 . One side of the spring  78  acts against the front planar surface of the back plate  48  (in the region adjacent the aperture  64 ) while the other end of the spring  78  acts against the rear base  80  of the cup  72 . The channel  70  terminates at an aperture  82  within the front face  74 . 
     The above-described structures pertaining to the spring-loaded mechanism for urging an individual optical fiber  22  into contact with an abutting fiber (discussed below) are illustrated in FIG. 3, an enlarged perspective view of assemblies associated with a representative ferrule  10  and optical fiber  22  that render the fiber  22  subject to precise and reliable axial alignment within a connector channel. As may be seen, the cup  72 , which is suitable for positioning a ferrule  10  having a symmetrically rounded face, is of simplified and relatively easy-to-manufacture design as opposed to that of U.S. Pat. No. 5,590,229. Unlike the cup of the referenced patent, the cup  72  is shorter to allow the spring  78  to abut the rear base  80  and requires no difficult-to-machine key or tab for engaging a slotted back plate. 
     Returning to FIGS.  2 ( a ) and  2 ( b ) and referring to the connector member  32 , such member is seen to differ from the member  30  principally insofar as it does not include and element corresponding to the holder  58 . The member  32  does, however, include both a body element  84  and an end plate  86  that are substantially identical to the corresponding elements of the member  30 . The structures of the member  32  are held within the receptacle housing  40  by means of an annular ring  88  that is received within an interior annular groove  90  of the housing  40 . 
     A ferrule  92  extends outwardly from a channel  94  and through an aligned aperture  96  in the face  98  of the body element  100  of the connector member  32 . The apertures  82  and  96 , as well as the respective channels within the connector members  30  and  32  are axially aligned and in registry with respect to one another so that, when the connector members  30  and  32  are mutually engaged as shown in FIG.  2 ( b ), the ends of the ferrules  10  and  92  that extend beyond the channels within the body elements  50  and  100  respectively enter and make face-to-face contact within the channel  70  of the holder  58  of the member  30 . The contacting faces of the ferrules  10 ,  92  are mutually urged toward one another by the action of the springs  78  and  102 , providing a compressive force to form a solid optical path between the cores of the fibers  22  and  104  that are mounted within the ferrules  10  and  92  respectively. 
     The springs  78 ,  102  (as well as like springs similarly situated in the multichannel connector of the invention) take up ferrule tolerance and length variations from optically contacting ferrule pair-to-ferrule pair. As a result, compression forces, within tolerable limits, are experienced at each pair of contacting fiber faces in contrast to so-called “hard” connections. This is particularly important in view of the small areas and critical sensitivities associated with fiber-to-fiber couplings. 
     Aligned pairs of dowels assure the durability of the connector  28  during use and guard against decoupling of the members  30  and  32 . One such pair comprises dowels  104  and  106 . The internal dowel  104  fits tightly within the member  30  in a channel that spans the body member  50  and the holder  58 . The internal dowel  104  is press-fit within the large diameter portion  108  of a dowel channel that runs through the body element  50 , there also existing an aligned small diameter portion  110 . The fit between the internal dowel, the enlarged diameter channel  108  and an aligned channel  112  (of slightly larger diameter) that passes through the holder  58  is sufficiently tight to insure that the internal dowel  104  may only be removed through the application of substantial force. The mere coupling and uncoupling of the members  30  and  32  to one another will not normally provide sufficient force to remove the internal dowel  104  from the channel  108 . 
     A dowel channel  114  through the body element  100  of the member  32  is a mirror image of the dowel channel comprising the aligned portions  108 ,  110 . The external alignment dowel  106  is press-fit within the larger diameter portion of the channel  114 . Again, the external dowel  106  may typically be removed only by the application of considerable force exceeding that required to couple and uncouple the members  30  and  32 . 
     Upon coupling of the members  30  and  32 , that portion of the alignment dowel  106  extending outwardly beyond the face  98  of the body element  106  is received within the channel  112  of the holder  58 . As mentioned above, the diameter of the channel  112  is marginally larger than the wider diameter portions of the dowel channels within the body elements of the members  30  and  32 . While the fit of the external dowel  106  within the holder channel  112  is of very high tolerance, the dowel  106  is slidable therein with relative ease. In this way, the external dowel  106  offers no significant resistance to coupling and uncoupling actions. 
     The relatively substantial sizes (thicknesses) of the alignment dowels  104  and  106  add considerable strength to the connection between the members  30  and  32 . Thus, the dowels  104  and  106  not only facilitate the initial alignment process, but thereafter offer considerable structural integrity to the connection. The dowels  104 ,  106  are capable of absorbing substantial torque-force loads to thereby preserve and maintain the optimal connections between abutting ferrules during use. 
     The connector of the present invention is particularly adapted for installed hardware on submarines, and has been configured to accommodate a significant number of ferrules, and hence connections for transmission of light through a length of fiber optic material. The elimination of upstanding keys from the ends of ferrule-retaining cups allows the accommodation of significantly more channels per square inch. As many as fifty connections can now be placed within the connector as a result of the compactness of the ferrule and cup arrangement. 
     The alignment dowels of the present invention also play a significant role in increased connector efficiency. Since less space is required for a given number of connections within the connector, a more substantial alignment dowel and support can be provided. The dowels not only facilitate initial alignment but assure a much stronger connection enabling the connector to withstand significantly more shock and much higher torque forces. 
     While this invention has been described with reference to its presently-preferred embodiment, it is not limited thereto. Rather, this invention is limited only insofar as it is defined by the following set of patent claims an includes within its scope all equivalents thereof.