Abstract:
A novel panel-mountable fiber optic cable feedthrough is described that has two main body parts that can be brought together around single or multiple fiber optic cables and secured in place to prevent slippage of the cable(s). Use of two such main body parts that split along a plane that passes through the axis of the fiber optic cable(s) allows joining the two main parts at any position along the cable(s) without the need to thread the cable(s) through a one or more pre-formed cylindrical cavities in the body of the feedthrough. The main parts for this fiber optic feedthrough can be made by plastic injection molding suitably shaped to relieve bending strain in the glass optical fiber(s) within the cable(s). The foot-print for mounting such a feedthrough can be made compatible with that of a number of popular fiber optic connector mounts, including the SC-connector.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Non-Provisional patent application Ser. No. 14/929,703 filed Nov. 2, 2015, titled PANEL-MOUNTABLE FIBER OPTIC CABLE FEEDTHROUGH, the contents of which are hereby incorporated by reference herein. 
     
    
     TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION 
       [0002]    This invention relates to a novel panel-mountable fiber optic cable feedthrough that has two main body parts that can be brought together around a single or multiple fiber optic cables and secured in place to prevent slippage of the cable(s). 
       BACKGROUND OF THE INVENTION 
       [0003]    Terrestrial communications throughout the world has grown to rely heavily on optical fiber communications technology. And there is an increasing flow of signaling information that requires use of multiple optical fibers in communication links from one point to another. The various origination, termination, and relay points for optical fiber distribution systems form huge matrices—much more complicated than, say, a map of the railroads or the electrical power grid infrastructures in the United States and abroad. In fact, some optical fiber links do run along power lines and railroad right-of-ways. But, they also run under seas, across farmers&#39; fields, down city streets, into campuses and within buildings and homes. 
         [0004]    Management of complex fiber optic communication systems requires many different types of specialized optical and electronic equipment to ensure that correct signals are continuously being sent and received with minimum interruptions and that any failures are detected and quickly rectified. 
         [0005]    At a very basic level, it is necessary to use an optical tap to extract a portion of the optical signal in each fiber within a transmission cable so that its functionality can be monitored. In some cases, monitoring the total optical power level is sufficient [see U.S. patent application Ser. No. 14/203,566 dated Mar. 11, 2014 by G. Miller et al titled MULTI-PURPOSE APPARATUS FOR SWITCHING, AMPLIFYING, REPLICATING, AND MONITORING OPTICAL SIGNALS ON A MULTIPLICITY OF OPTICAL FIBERS]. In other cases where multiple optical channels are simultaneously transmitted on a single fiber using wavelength division multiplexing (WDM), it is often necessary to use arrayed waveguide gratings (AWGs) to separate the individual optical channels before they are directed to monitoring equipment [see U.S. patent application Ser. No. 14/205,368 dated Mar. 12, 2014 by G. Miller et al titled APPARATUS FOR SELECTIVE FIBER OPTICAL CHANNEL MONITORING AND CHANNEL REPLICATION OF WAVELENGTH DIVISION MULTIPLEXED (WDM) SIGNALS]. In other cases, optical splitters and optical switches are also employed for monitoring purposes. Due to the large number of optical fibers used in modern optical communication systems, many optical taps, AWGs, splitters and switches are employed. A multiplicity of these components is typically located inside of an equipment enclosure and these enclosures are mounted in racks that fill equipment bays often with a multiplicity of interconnecting fiber optic patch-cord cables [see U.S. patent application Ser. No. 14/072,528 dated Nov. 5, 2013 by G. Miller et al titled HIGH DENSITY ENCLOSURE FOR OPTICAL MODULES]. 
         [0006]    Clearly, it is desirable to reduce both the time and expense associated with interconnecting the various pieces of communication equipment within equipment bays and to minimize the optical attenuation associated with these interconnections. And this has been an ongoing evolutionary process for all types of equipment, enclosures and patch-cord cables used in modern fiber optical communication systems. 
         [0007]    The state-of-the-art for interconnecting various optical components like optical taps is to pack some manageable number of them into a modular container (also referred to as a cassette) that has optical connectors on one or more of its narrow sides. These modular containers are, in turn, closely packed side-by-side into an equipment enclosure that is mounted in an equipment rack such that most or all of the optical connectors on the modular containers face outward for convenient access. 
         [0008]    However, for various reasons, including the desirability of increasing the packing density of the cassettes within an equipment enclosure, the cassettes are sometimes located internal to an equipment enclosure well away from the front panel. [see U.S. patent application Ser. No. 14/072,528 referenced above] In such cases, the connection between an equipment cassette and the front panel of the equipment enclosure is typically made with an optical fiber or multi-fiber optic ribbon cable internal to the equipment enclosure that terminates with an optical connector mounted on the outer surface of the enclosure. Then optical patch-cord cables, also terminated with optical connectors, are used to interconnect equipment enclosures. 
         [0009]    While use of optical patch-cord cables in this manner is a broadly used installation practice within equipment bays, it is apparent that in some cases it might be desirable to eliminate one or more optical connectors mounted on the surface of equipment enclosures and simply feed the optical patch-cord cable directly through a hole in the enclosure&#39;s surface (panel) so that it may continue to an internal equipment cassette where it can be connected (terminated). This strategy would have several advantages: (1) it would eliminate both the cost and optical attenuation associated with an optical connection located on the surface of the equipment enclosure, (2) the patch-cord could possibly be terminated with an optical connector outside of the equipment enclosure, where access is not limited, and simply passed through a conveniently located hole in the outer surface of the equipment enclosure, (3) this strategy might be used at both ends of the fiber optic patch-cord cable for even greater savings of cost and installation time. However, at present there are no fiber optic cable feedthroughs that are inexpensive, easy to install, and capable of securing a pre-terminated (with optical connector) fiber optic cable patch-cords in place. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The purpose of this disclosure is to describe a novel panel-mountable fiber optic cable feedthrough that has all of the above mentioned characteristics: easy to install, capable of securing a pre-terminated fiber optic patch cord firmly in place and is inexpensive to produce. While the specific design of the panel-mountable fiber optic feedthrough discussed here is based on the dimensions of the popular SC fiber connector design first introduced by NTT (Nippon Telephone and Telegraph) in Japan that has now become an industry standard, the choice is one of convenience to provide a specific example rather than a necessity to limit the feedthrough design to only the SC fiber connector foot-print on a panel associated with an equipment enclosure. In fact, there is a quite a variety of fiber optic connectors including the LC, FC, MT and MTP, as discussed in “Fiber Optic Product Families” published by Molex and available on the Internet (www.molex.com/fiber) and many of them could also provide a suitable foot-print for a fiber optic feedthrough. In any case, it would be preferable, if practical, to select a feedthrough foot-print that manufacturers and users are familiar with and have existing tooling to make the necessary holes in metal or plastic panels. The choice of the SC foot-print satisfies this criteria but it is not essential to the design of the feedthrough. 
         [0011]    The essential design features for any panel mounted fiber optic patch-cord feedthrough include (1) one or more cylindrical cavities within the body of the feedthrough through which the patch-cord cable(s) can pass, (2) means for gripping and securing the patch-cord cable(s) in place relative to the feedthrough body, and (3) means for securing the feedthrough to the equipment panel. Additional desirable design features include (4) means for limiting the strain in the optical cable(s) where it exits the feedthrough (strain relief), and (5) elimination of the stress need to thread or pull an optical cable through a cylindrical cavity. 
         [0012]    The first three essential design features could be satisfied in a rather straightforward manner using a cylindrically symmetric feedthrough structure with a threaded outside diameter that is partially inserted in a circular hole in an equipment panel and that is secured in place with one or two screw-threaded retaining nuts (with two nuts, one on each side of the panel). But, there are some undesired complications using such a structure because it may not include the desirable feature (4) and will not include the desirable feature (5), mentioned above. 
         [0013]    One complication with such a simple feedthrough design described above is that the fiber optic cable must be carefully threaded or pulled through a rather tight fitting cylindrical cavity in the feedthrough body and subsequently secured in place, possibly using a bonding agent or, perhaps, a compression ring that grips the fiber cable when the retaining nut(s) is tightened. Use of a bonding agent makes disassembly of such a feedthrough difficult while use of a compression ring becomes a substantial design and production complication which increases expense. Further, the required tight fit of the cable through the cylindrical cavity in the feedthrough would make it impractical to pass a pre-terminated fiber optic patch-cord cable due to the larger size of the optical connector relative to the cable diameter. In addition, incorporation of some form of strain relief would be substantially more complex for a circularly symmetric designed feedthrough because its outside diameter would have to be further enlarged to accommodate a strain relief mechanism. This in-turn would require a larger size retaining nut that would take up more valuable surface area on the panel that could be better used to support additional optical connectors and feedthroughs. Increasing connector and feedthrough packing density on equipment panels is already recognized as a desirable design objective. 
         [0014]    The complications noted above have been eliminated with several novel designs employing feedthroughs that all split open into two mating parts that can be closed around a single or multiple optical cable(s) at any desired location without the need for threading or pulling the cable(s) through one or more tight fit cylindrical cavities in the feedthrough&#39;s body. Each of the two main body parts that make up the feedthrough in such an axial-split design includes half of one or more cylindrical cavities. Simple provisions have been included to allow the two split body parts to first be loosely fit to surround the optical cable(s) and subsequently secured tightly together around the cable with minimum effort. 
         [0015]    Strain relief for the fiber optic cable can also be incorporated into this feedthrough design in a simple manner and without increasing the feedthrough&#39;s outside dimensions or adding additional parts. In addition, a series of ribs can be formed on the inside diameter(s) of the cylindrical cavities during injection molding to ensure a very tight grip on the fiber optic patch-cord cable(s) when the two main body parts are secured together. 
         [0016]    The novel design features of this type of panel-mountable fiber optic feedthrough will become more evident in the following discussion by referring to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1A  shows a cross sectional view of a panel-mounted fiber optic cable feedthrough secured in a panel with a pair or screws and matching nuts and having a fiber optic cable passing through it. 
           [0018]      FIG. 1B  is an isometric view of the same panel-mounted fiber optic cable feedthrough shown in  FIG. 1A . 
           [0019]      FIG. 1  C shows the shape and dimensions of a rectangular hole and two smaller circular holes in a panel that would be required to secure a fiber optic feedthrough in place, such as the one shown in FIG.  1 A, that is designed to match the standard dimensions of an SC fiber optic connector mount. 
           [0020]      FIG. 2A  is a hinged version of a fiber optic cable feedthrough that is made of two main body parts that are joined together with a hinge.  FIG. 2A  shows this feedthrough in an open position. 
           [0021]      FIG. 2B  shows the same hinged feedthrough parts as in  FIG. 2A  in a fully closed position. 
           [0022]      FIG. 3A  shows a snap-together version of a fiber optic cable feedthrough that is separated into two parts. 
           [0023]      FIG. 3B  shows the same snap-together feedthrough parts as in  FIG. 3A  that are snapped together in a fully closed position. 
           [0024]      FIG. 4A  is a screw adapter version of a fiber optic cable feedthrough that is also made with two principal body parts that can be joined together by two screws.  FIG. 4A  shows the feedthrough body parts in an open position. 
           [0025]      FIG. 4B  shows the same screw adapter version of the feedthrough body parts as in  FIG. 4A  in a fully closed position. 
           [0026]      FIG. 5A  is a clip adapter version of a fiber optic cable feedthrough that is also made with two principal body parts that can be joined together by a “U” shaped spring clip.  FIG. 5A  shows the feedthrough parts in an open (exploded) position. 
           [0027]      FIG. 5B  shows the same parts as in  FIG. 5A  fully assembled in a closed position. 
           [0028]      FIG. 6A  is a peg adapter version of a fiber optic cable feedthrough that is also made with two principal body parts that can be joined together by two cylindrical pegs.  FIG. 6A  shows the feedthrough parts in an open (exploded) position, and 
           [0029]      FIG. 6B  shows the same parts as in  FIG. 6A  fully assembled in a closed position. 
           [0030]      FIG. 7A  is a peg adapter version of a dual fiber optic cable feedthrough that is also made with two principal body parts that can be joined together by two cylindrical shaped pegs.  FIG. 7A  shows the feedthrough parts in an open (exploded) position, and 
           [0031]      FIG. 7B  shows the same parts as in  FIG. 7A  fully assembled in a closed position. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    With reference to the attached drawings, embodiments of the present invention will be described in the following: 
         [0033]      FIG. 1A  shows a cross-sectional view of the basic construction and installation details of a typical panel-mounted fiber optic cable feedthrough  100 . This feedthrough  100  has a lower flange  105   a  and an upper flange  105   b  each with a circular hole  106   a  and  106   b,  respectively, to accommodate two identical machine screws  3   a  and  3   b.  When the feedthrough  100  is installed in the panel  1 , the machine screws  3   a  and  3   b  pass through holes  106   a  and  106   b  in the flanges  105   a  and  105   b  and then through the two holes  11  in the panel  1 . The screws  3   a  and  3   b  are then secured in place by tightening matching nuts  4   a  and  4   b  or simply by rotating the screws  3   a  and  3   b  into pre-threaded holes in panel  1 . This action fastens the feedthrough  100  to the panel  1 . To be compatible with the standard SC mounting parts, the screws  3   a  and  3   b  should have a diameter of 2 mm and the holes  106   a,    106   b  and  11  (if nuts are used) through which these screws pass should have a nominal diameter of 2.4 mm to provide adequate clearance for these screws. The fiber optic cable  5  passes entirely through a cylindrical cavity  103  in the feedthrough  100  that has a trumpet-bell shaped flare  6  on one or both ends of the feedthrough  100 . Such a feedthrough can be made with various sized cylindrical cavities  103  to accommodate fiber optic cables  5  of varying diameters, including the industry standard diameters of 3.0 mm, 2.0 mm, and 1.6 mm. The fit of the fiber optic cable outside diameter to the diameter of the cylindrical cavity in the feedthrough should be snug with a minimum or zero clearance gap between the two diameters. This is to ensure a firm grip on the cable and to minimize any pathway for leakage of liquids that might be spilled on the equipment enclosure. 
         [0034]      FIG. 1B  is an isometric view of the same feedthrough  100  as shown in  FIG. 1A  as it would be seen on the outside of a panel  1 . 
         [0035]      FIG. 1C  shows the dimensions of a rectangular hole  10  and two smaller circular holes  11  that must be made in the panel  1 , to accommodate the installation of a feedthrough  100  as shown in  FIG. 1A  and  FIG. 1B  that would be compatible with a standard SC fiber optic connector mounting design details. The two holes  11  should both have a nominal diameter of 2.4 mm to provide adequate clearance for the 2.0 mm diameter attachments screws  3   a  and  3   b  shown in  FIG. 1A . 
         [0036]      FIG. 2A  shows an example of a hinged version of a fiber optic cable feedthrough  200  that is made of two principal parts  21  and  22  that are interconnected with a hinge  23 .  FIG. 2A  shows the feedthrough in an open position while  FIG. 2B  shows the same parts fully closed. The entire feedthrough assembly  200  including parts  21  and  22  as well as the hinge  23  can all be injection molded from a plastic material, such as high density polyethylene (HDPE), nylon, poly-acrylate, polyurethane or other similar material, in a single step. Part  22  includes two latching arms  24   a  and  24   b  and a semi-circular cavity  201  while part  21  includes two channels  25   a  and  25   b  into which the latching arms  24   a  and  24   b  fit as well as a similar semicircular cavity  202 . When these two main body parts are rotated about the hinge  23  to a closed position, the latching arms  24   a  and  24   b  fit into the channels  25   a  and  25   b  causing parts  21  and  22  to snap shut, as shown in  FIG. 2B . There are also a series of ribs  204 , typically with a semi-circular cross section or some other shape with a similar physical extent in the axial directions of the semi-circular channels  201  and  202  located on the inner surfaces of these channels. Each of these ribs  204  is typically in the range of 0.1 to 0.2 mm high for various standard fiber optic cable sizes ranging from 1.6 to 3.0 mm in diameter. Specifically, the nominally rib heights are 0.1 mm for a 1.6 mm diameter fiber optic cable, 0.15 mm for a 2.0 mm diameter fiber optic cable and 0.2 mm for a 3.0 mm diameter fiber optic cable. These heights are only approximate and may vary somewhat when optimizing a feedthrough design for a specific fiber optical cable depending on the particular jacketing material used in the cable. The ribs  204  have a typical spacing of 3 mm and there are typically three or more such ribs  204  per feedthrough. Their function is to contact and then locally compress the outer plastic jacket on the fiber optic cable when the feedthrough is closed upon a fiber optic cable  5 . These ribs  204  in effect “bite down” on the fiber optic cable  5  to help ensure a very firm grip of the feedthrough on this fiber optic cable. The feedthrough  200  also has a flange  205   a  and another flange  205   b  in main body parts  21  and  22 , respectively, with similar holes  206   a  (not shown) and  206   b  penetrating through these flanges for the purpose of attaching the feedthrough  200  to an equipment panel  1  with screws and optional nuts as shown in  FIG. 1A  but not in  FIG. 2A . 
         [0037]      FIG. 2B  shows the same fiber optic feedthrough as in  FIG. 2A  when closed. In this configuration, parts  21  and  22  form a circular cavity  203  shown both in  FIG. 2B  and  FIG. 1A  that may have a trumpet-bell shaped flare  6  at one or both of its ends. The purpose of this flare  6  is to provide a physical lower limit on the bending radius of curvature that the fiber optic cable  5  (not shown) may assume as it passes out of the cylindrical cavity  203 . Limiting this radius of curvature in this fashion to be equal to or greater than 3 mm is one way to limit the strain in the glass optical fiber(s) contained within the fiber optic cable  5  (shown in  FIG. 1A  but not  FIG. 2A ). Such a limitation is prudent to avoid breakage of the glass fiber(s). 
         [0038]      FIG. 3A  shows a snap-together version of a fiber optic cable feedthrough  300  that is separated into two unconnected parts  31  and  32  shown in  FIG. 3A  that are designed to be snapped together as shown in  FIG. 3B . When closed, as in  FIG. 3B , the feedthrough  300  is held firmly together by latching arms  34   a  and  34   b  in part  32  and latching arms  35   a  and  35   b  in part  31 . These four latching arms fit into four channels, two channels  36   a  and  36   b  in part  31  and two more channels  37   a  and  37   b  (not shown) in part  32 . This feedthrough design can also accommodate ribs  304 , similar to those shown as  204  in  FIG. 2A  to secure the fiber optic cable in place within the cylindrical cavity  303 . 
         [0039]      FIG. 3B  shows the fiber optic feedthrough parts in  FIG. 3A  in a fully closed position. The purpose or the optional trumpet-bell shaped flared end(s)  6  of the cylindrical cavity  303  is, as discussed in  FIG. 2B , above, for strain relief of the fiber optic cable. The feedthrough  300  also includes a flange  305   a  and another flange  305   b  in main body parts  21  and  22 , respectively, with similar holes  306   a  (not shown) and  306   b  penetrating through these flanges for the purpose of attaching the feedthrough  300  to an equipment panel  1  with screws and optional nuts as shown in  FIG. 1A  but not in  FIG. 3B . 
         [0040]      FIG. 4A  is a screw adapter version of a fiber optic cable feedthrough  400  that is also made with two principal body parts  41  and  42  that can be joined together by two identical screws  43 .  FIG. 4A  shows the feedthrough parts in an open (separated) position while  FIG. 4B  shows the same parts fully closed and secured by the two screws. It should be noted that in this design, the position of the holes  44   a  and  44   b  (not shown) to pass and secure the screws in parts  41  and  42  are off-set from the cylindrical cavity  403  so as not to interfere with the fiber optic cable that will be located within this cavity. Ribs  404  and the optional trumpet-bell shaped flared end(s)  6  of the cylindrical cavity  403  may also be included in this design and serve the same functions as discussed in the descriptions of  FIG. 2A  and  FIG. 3A . The feedthrough  400  also has a flange  405   a  and flange  405   b  in main body parts  21  and  22 , respectively, with similar holes  406   a  and  406   b  penetrating through these flanges for the purpose of attaching the feedthrough  400  to an equipment panel  1  as shown in  FIG. 1A  but not in  FIG. 4B . 
         [0041]      FIG. 4B  shows the same fiber optic feedthrough parts as in  FIG. 4A  assembled in a fully closed position. 
         [0042]      FIG. 5A  shows a clip adapter version of a fiber optic cable feedthrough  500  that is also made with two principal parts  51  and  52 , similar to the one shown in  FIG. 4 , but that can be joined together by a “U” shaped spring clip  53  rather than screws.  FIG. 5A  shows the feedthrough parts in an open position (exploded view) while  FIG. 5B  shows the same parts fully assembled in a closed position. Both ends of the spring clip  53  have detents  55   a  and  55   b  that secure in channel  56   a  in part  52  and channel  56   b  (no shown) in part  51  when the split parts of this feedthrough are closed and secured. Ribs  504  and the optional trumpet-bell shaped flared end(s)  6  of the cylindrical cavity  503  may also be included in this design and serve the same functions as discussed in the descriptions of  FIG. 2B  and  FIG. 3B . The feedthrough  500  also has a flange  505   a  and flange  505   b  in main body parts  51  and  52 , respectively, with similar holes  506   a  and  206   b  penetrating through these flanges for the purpose of attaching the feedthrough  500  to an equipment panel  1  as shown in  FIG. 1A  but not in  FIG. 5A . 
         [0043]      FIG. 5B  shows the same fiber optic feedthrough parts as in  FIG. 5A  assembled in a fully closed position. 
         [0044]      FIG. 6A  shows a peg adapter version of a fiber optic cable feedthrough  600  that is also made with two identical parts  61  and  62 , similar to the ones shown in  FIG. 4A , but that can be joined together by a press fit of two integral cylindrical pegs  63   a  and  63   b  into two hexagonal shaped holes  64   a  and  64   b.    FIG. 6A  shows the feedthrough parts in an open position (exploded view). Both identical pegs  63   a  and  63   b  (only  63   a  is shown in  FIG. 6A ) have rounded tops  65   a  and  65   b  to assist in their initial manual insertion into identical hexagonal shaped holes  64   a  and  64   b.  The base  66   a  or  66   b  of each peg has a male cylindrical bevel  67   a  or  67   b  that serves to center the peg into a corresponding female cylindrical bevel  68   a  or  68   b  located at the entrance of each hexagonal hole. 
         [0045]    The purpose for the use of a cylindrical peg and a hexagonal hole is to limit the common contact surface area between the outer surface of the peg and the inner surface of the hole so that assembly and disassembly of the feedthrough parts  61  and  62  typically requires less force as compared with the use a cylindrical peg and a mating cylindrical hole. Although a hexagonal shaped hole as shown in  FIG. 6A  is preferred, other polygon shaped holes with rotational symmetry (including a circle in the limit of a polygon with an infinite number of sides) would also be satisfactory for use in this type of fiber optic feedthrough design. 
         [0046]    Ribs  604  and the optional trumpet-bell shaped flared end(s)  6  of the cylindrical cavity  603  may also be included in this design and serve the same functions as discussed in the descriptions of  FIG. 2A  and  FIG. 3A . The feedthrough  600  also has a flange  605   a  and flange  605   b  in main body parts  61  and  62 , respectively, with similar holes  606   a  and  606   b  penetrating through these flanges for the purpose of attaching the feedthrough  600  to an equipment panel  1  as shown in  FIG. 1A  but not in  FIG. 6A . 
         [0047]      FIG. 6B  shows the same parts as shown in  FIG. 6A  fully assembled in a closed position. 
         [0048]      FIG. 7A  shows a peg adapter version of a dual fiber optic cable feedthrough  700  that is made with two identical parts  71  and  22 , similar to the ones shown in  FIG. 6A , but with two cylindrical cavities  703   a  and  703   b  that can be joined together by a press fit of two integral tapered cylindrical pegs  73   a  and  73   b  into two hexagonal shaped holes  74   a  and  74   b.    FIG. 7A  shows the feedthrough parts in an open position (exploded view). Both identical pegs  73   a  and  73   b  (only  73   a  is shown in  FIG. 7A ) have rounded tops  75   a  or  75   b  to assist in their initial manual insertion into identical hexagonal shaped holes  74   a  and  74   b.  The base of each peg  73   a  or  73   b  has a male cylindrical bevel  77   a  or  77   b  that serves to center the peg into a corresponding female cylindrical bevel  78   a  or  78   b  at the entrance of each hexagonal hole  74   a  or  74   b.    
         [0049]    The purpose for the use of a cylindrical peg and a hexagonal hole is to limit the common contact surface area between the outer surface of the peg and the inner surface of the hole so that assembly and disassembly of the feedthrough parts  71  and  72  typically requires less force as compared with the use a cylindrical peg  73   a  or  73   b  and companion cylindrical hole  74   a  or  74   b  that have a constant cross-sectional areas throughout their depth. Although a hexagonal shaped hole is shown in  FIG. 7A  is preferred, other polygon shaped holes with rotational symmetry would also be satisfactory for use in this type of fiber optic feedthrough design (including a circle in the limit of a polygon with an infinite number of sides). 
         [0050]      FIG. 7B  shows the same parts as shown in  FIG. 7A  fully assembled in a closed position. 
         [0051]    The design of dual cavity fiber optic cable feedthrough shown in  FIG. 7A  and  FIG. 7B  is an example of a multi-fiber optic cable feedthrough having three or more parallel cavities. 
         [0052]    Ribs  704  and the optional trumpet-bell shaped flared end(s)  6  of the cylindrical cavities  703   a  and  703   b  may also be included in this design and serve the same functions as discussed in the descriptions of  FIG. 2A  and  FIG. 3A . The feedthrough  700  also has a flange  705   a  and flange  705   b  in main body parts  71  and  72 , respectively, with similar holes  706   a  and  706   b  penetrating through these flanges for the purpose of attaching the feedthrough  700  to an equipment panel  1  as shown in  FIG. 1A  but not in  FIG. 7A . 
         [0053]    While the above drawings provide representative examples of specific embodiments of the inventive panel-mounted fiber optic feedthroughs all with axial-split body designs, there are numerous variations in the shape and design details of these feedthroughs and the diameters of optical fiber cables (containing a varying number of optical fibers) that can be secured within them.