System and method for limiting protrusion of a fiber-optic cable from a mounting structure

A system for minimizing a protrusion of a fiber-optic cable from a mounting structure comprises a fiber-optic connector, an adapter for a fiber-optic connector, and a standoff The standoff positions the adapter and the connector at a fixed distance from a front surface of the mounting structure. A fiber-optic cable is routed from the connector through a penetration extending between the front and the rear surfaces of the mounting structure. The standoff has a minimum length that ensures that the connector does not protrude from the rear surface of the mounting structure. This arrangement allows a curvature to be imposed on the cable as it exits the rear surface. By imposing a curvature equal to the minimum bending radius of the cable, and extending this curvature through an arc of 90 degrees, a protrusion of the cable in a direction normal to the rear surface can be limited to the minimum bending radius of the cable.

BACKGROUND OF THE INVENTION
 Minimal external dimensions are considered a desirable characteristic in
 many contemporary electronic devices. One commonly-used approach to
 achieving such minimization involves increasing the density in which the
 internal components of the device are packaged, i.e., placing the internal
 components in closer proximity to adjacent components and structures
 within the device.
 Increases in component-packaging density typically necessitate a
 corresponding reduction in the area occupied by the wiring or cabling that
 interconnects the components. Such reductions are particularly difficult
 to achieve with fiber-optic cabling. These difficulties arise from the
 need to avoid any sharp bends in fiber-optic cables. More specifically, a
 fiber-optic cable cannot be routed in a manner that imposes a curvature
 which exceeds the minimum bending radius of the cable. Violation of this
 limit may impair the integrity of the signal transmission, and can damage
 the cable.
 Fiber-optic cables are often joined through the use of adapters. More
 particularly, adapters are used to support and couple two or more
 fiber-optic connectors, thereby forming a junction between the cables
 attached to the connectors. The adapter is frequently disposed on some
 type of mounting structure, e.g., a backplane. Adapters that are disposed
 in this manner are commonly known as "backplane adapters." Backplane
 adapters are typically mounted in a manner that causes the adapter (and
 the corresponding connectors) to protrude from both sides of the mounting
 structure.
 FIG. 1 illustrates a backplane adapter 10 installed on a backplane 11 in
 the above-noted manner. A first connector 12 and second connector 13 are
 disposed within the adapter 12. A fiber-optic cable 14 and a fiber-optic
 cable 15 are attached to the connectors 12 and 13, respectively. The cable
 14 has a minimum bending radius 16 and the connector 12 has a length 17.
 The adapter 10 straddles the backplane 11, thereby causing the connector
 12 and the cable 14 to protrude from a rear surface 11a of the backplane
 11. More specifically, the connector 12 and the cable 14 protrude in a
 direction normal to the surface 11a by a distance 18.
 A curvature is imposed on the cable 14 as it exits the connector 12. The
 curvature equals the minimum bending radius 16, and extends through an arc
 of about 90 degrees. Hence, the protrusion distance 18 is equal to the
 connector length 17 plus the minimum bending radius 16. Reducing the
 protrusion distance 18, without decreasing the connector length 17, would
 require imposing a curvature on the cable 14 that exceeds the minimum
 bending radius 16. Hence, the noted value represents the lowest level to
 which the protrusion distance 18 can be reduced using this particular
 mounting configuration.
 The cable 14 is shown in FIG. 1 as being routed between the backplane
 surface 11a and an adjacent structure 19, e.g., a panel of the electronic
 device in which the backplane 11 resides, or another circuit substrate. As
 is evident from the figure, the protrusion distance 18 represents the
 minimum required clearance between the backplane 11 and the structure 19.
 Hence, any reduction in the protrusion distance 18 will allow the
 backplane 11 to be positioned closer to other components such as the
 exemplary structure 19. Reducing the spacing requirements for the
 backplane 11 will facilitate increased component-packaging densities in
 electronic devices in which the backplane 11 is utilized. The present
 invention seeks to achieve this goal.
 SUMMARY OF THE INVENTION
 The present invention is used in conjunction with a fiber-optic cable being
 routed from a mounting structure. The invention provides a system and a
 method for minimizing a protrusion of the cable from the mounting
 structure. More particularly, the invention allows the cable protrusion
 distance to be approximately, or less than, the minimum bending radius of
 the cable. This relatively short cable protrusion distance is achieved
 without compromising the structural and functional integrity of the cable.
 The invention can be used to minimize the required spacing between the
 mounting structure and another structure located adjacent to the mounting
 structure.
 The system comprises a fiber-optic connector, an adapter for a fiber-optic
 connector, and a standoff. The connector is supported and retained by the
 adapter. The adapter is coupled to an end of the standoff. An opposite end
 of the standoff is coupled to a mounting surface on the mounting
 structure. The standoff thus positions the adapter and the connector at a
 fixed distance from the mounting surface. In the exemplary embodiment, the
 standoff comprises two column-like supports and the mounting surface is a
 front surface of a backplane. A fiber-optic cable is fixed to the
 connector. The cable is routed from the connector through a penetration
 that extends between the front and rear surfaces of the backplane. The
 cable thus protrudes from the rear surface of the backplane. The system
 mates with a second fiber-optic connector for transmitting signals
 therebetween.
 The length of the standoff determines the positions of the adapter and the
 connector in relation to the rear surface of the backplane. The standoff
 could have a length chosen so as to ensure that the connector does not
 protrude from the backplane rear surface. A curvature can thus be imposed
 on the cable as it exits the rear surface. By imposing a curvature equal
 to the minimum bending radius of the cable, and extending this curvature
 through an arc of 90 degrees, the protrusion of the cable in a direction
 normal to the rear surface can be minimized. Specifically, the protrusion
 distance can be approximately, or less than, the minimum bending radius of
 the cable. This value represents the lowest level to which the cable
 protrusion can be reduced without compromising the structural and
 functional integrity of the cable. Minimizing the cable protrusion in this
 manner minimizes the required clearance between the backplane rear surface
 and an adjacent structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 A preferred embodiment of the invention is illustrated in FIGS. 2 through
 4. The embodiment comprises a mounting system 20. The system 20 comprises
 a standoff 21 and an adapter for a fiber-optic connector. The standoff 21
 is coupled to and supported by a mounting structure. In the described
 embodiment, the mounting structure is a backplane 22 and the adapter is a
 backplane adapter 23. The adapter 23 retains and couples a first
 fiberoptic connector 24 and a second fiber-optic connector 25.
 The adapter 23 is coupled to the standoff 21 using, for example, a suitable
 fastener. Alternatively, the adapter 23 and the standoff 21 may
 incorporate latches that secure the adapter 23 to the standoff 21. In
 another alternative embodiment, the adapter 23 and the standoff 21 can be
 unitarily formed. The standoff 21 suspends the adapter 23 at a fixed
 distance from a front surface 22a of the backplane 22. The standoff 21
 could comprise a first support 26 and a second support 27. The supports 26
 and 27 are substantially identical. The first support 26 and the second
 support 27 define a longitudinal axis 26a and a longitudinal axis 27a,
 respectively.
 The first support 26 comprises a first abutment surface 28 and a second
 abutment surface 29. The abutment surfaces 28 and 29 are substantially
 planar, and are disposed at opposite ends of the support 26. Furthermore,
 the surfaces 28 and 29 lie substantially perpendicular to the longitudinal
 axis 26a (hence, the surfaces 28 and 29 are substantially parallel in
 relation to each other). The second support 27 likewise comprises a first
 abutment surface 30 and a second abutment surface 31. The surfaces 30 and
 31 are substantially planar. The surfaces 30 and 31 are disposed at
 opposite ends of the support 27, and lie substantially perpendicular to
 the longitudinal axis 27a. The surfaces 28 and 30 are each coupled to the
 front surface 22a of the backplane 22. Thus, the longitudinal axes 26a and
 27a are substantially perpendicular to the surface 22a of the backplane
 22.
 The supports 26 and 27 preferably have a substantially rectangular
 cross-section. In the exemplary embodiment, the outer
 longitudinally-oriented edges of the supports 26 and 27 are tapered to
 conform to the shape of the adapter 23. This feature is evident in FIG. 2.
 Although this particular configuration is preferred, other geometric
 cross-sections, e.g., circular, square, etc., are within the contemplated
 scope of the invention. An optimal length, i.e., longitudinal dimension,
 for the supports 26 and 27 is discussed below.
 The support 26 has a through hole 32 (shown in phantom in FIG. 2). The
 through hole 32 extends between the abutment surfaces 28 and 29, and
 parallels the longitudinal axis 26a. The support 27 likewise has a through
 hole 33 (also shown in phantom in FIG. 2). The through hole 33 extends
 between the abutment surfaces 30 and 31, and parallels the longitudinal
 axis 27a. The through holes 32 and 33 preferably have a circular
 cross-section. The significance of the through holes 32 and 33 is
 discussed below.
 Details concerning one type of adapter 23 usable with the present invention
 follow. An exemplary adapter 23 is a backplane adapter for a fiber-optic
 connector. A suitable adapter may be obtained, for example, from FCI--Berg
 Electronics, Inc. as part no. 74809-001. The adapter 23 comprises a body
 34, a first mounting wing 35, and a second mounting wing 36. The adapter
 23 defines a longitudinal axis 23a that passes through the geometric
 center of the body 34, as shown in the figures.
 The body 34 comprises a first housing 34a and a second housing 34b. The
 housings 34a and 34b are substantially identical. Preferably, the housings
 34a and 34b are unitarily formed. The connectors 24 and 25 are partially
 disposed within the first and the second housings 34a and 34b,
 respectively, as shown in FIG. 3. The inner dimensions of the housings 34a
 and 34b are approximately equal to the outer dimensions of the connectors
 24 and 25. Insertion of the connectors 24 and 25 into the housings 34a and
 34b thus fixes the positions of the connectors 24 and 25. More
 particularly, the housings 34a and 34b guide a mating surface 24a on the
 connector 24 into contact with a mating surface 25a on the connector 25.
 Furthermore, the housings 34a and 34b cause the optical axes of the
 connectors 24 and 25 to substantially align, thereby establishing a
 fiber-optic connection.
 The housings 34a and 34b define a polarizing slot 35a and a polarizing slot
 35b, respectively. The connectors 24 and 25 comprise a tab 24b and a tab
 25b, respectively. The tabs 24b and 25b are disposed along a side of the
 connectors 24 and 25, as shown in the figures. The tab 24b slidably
 engages the slot 35a as the connector 24 is inserted into the housing 34a.
 The tab 25b likewise engages the slot 35b as the connector 25 is inserted
 into the housing 34b. The protrusion of the tab 24b from the connector 24
 prevents the connector 24 from being inserted when the tab 24b is not
 aligned with the corresponding slot 35a. The tab 25b similarly prevents
 the insertion of the connector 25 when the tab 25b and the slot 35a are
 not aligned. This arrangement ensures that the connectors 24 and 25 are
 correctly polarized i.e., that the multiple fiber-optic strands within the
 connectors 24 and 25 are properly oriented.
 The housings 34a and 35a also perform the function of retaining the
 connectors 24 and 25 in pre-determined positions. The retaining function
 is accomplished by a pair of beam latches 36a and a pair of beam latches
 36b disposed within the housings 34a and 34b, respectively. Insertion of
 the connectors 24 and 25 into the housings 34a and 34b forces the beam
 latches 36a and 36b to deflect outward, i.e., toward the side of the
 housings 34a and 34b. A pair of detents 24c and a pair of detents 25c are
 disposed along the sides of the connectors 24 and 25, respectively. The
 detents 24c and 25c are positioned such that the latches 36a and 36b
 resiliently engage the detents 24c and 25c, respectively, when the
 connectors 24 and 25 have been fully inserted into the housings 34a and
 34b. Engagement of the passive latches 36a and 36b and the detents 24c and
 25c prevents movement of the connectors 24 and 25 in a direction opposite
 the direction of insertion, thereby retaining the connectors 24 and 25 in
 place.
 The mounting wings 35 and 36 of the adapter 23 are substantially identical,
 and are disposed on opposite sides of the adapter body 34. The mounting
 wing 35 comprises an abutment surface 37 and a second surface 38. The
 surfaces 37 and 38 are substantially planar. The surfaces 37 and 38 are
 disposed in a substantially perpendicular orientation in relation to the
 longitudinal axis 23a of the adapter 23. The abutment surface 37 is
 coupled to the second abutment surface 29 of the first support 26. The
 second surface 38 thus faces upward, i.e., away from the backplane 22. The
 mounting wing 35 has a through hole 39 extending between the surfaces 37
 and 38. The through hole 39 is substantially aligned with the through hole
 32 of the first support 26.
 The mounting wing 36 likewise comprises an abutment surface 40 and a second
 surface 41. The abutment surface 40 is coupled to the second abutment
 surface 31 of the second support 27. The surfaces 40 and 41 are
 substantially parallel, and lie substantially perpendicular to the
 longitudinal axis 23a. The mounting wing 36 has a through hole 42
 extending between the surfaces 40 and 41. The through hole 42 is
 substantially aligned with the through hole 33 in the second support 27.
 (The described mating configuration between the adapter 23 and the
 supports 26 and 27 is a preferred methodology. Other configurations, such
 as fixing the adapter 23 to a side of the supports 26 or 27, or forgoing
 the use of a second support, are within the contemplated scope of the
 invention.)
 The backplane 22 comprises a rear surface 22b. In the exemplary embodiment,
 the backplane 22 has a through hole 43 and a through hole 44. The
 backplane 22 also has a penetration 45. The through holes 43 and 44 and
 the penetration 45 each extend between the front surface 22a and the rear
 surface 22b of the backplane 22.
 In the past, the adapter 23 would rest within the aperture 45, and the
 holes 39 and 42 on the wings 35 and 36 would align with the through holes
 43 and 44 in the backplane 22. In the present invention, however, the
 through hole 43 is substantially aligned with the through hole 42 of the
 first support 26, and with the through hole 39 of the adapter 23. The
 through hole 44 is substantially aligned with the through hole 43 of the
 second support 27, and with the through hole 42 of the adapter 23. The
 penetration 45 is disposed between the through holes 43 and 44, and is
 substantially aligned with the connectors 24 and 25. As shown in FIG. 3,
 the connector 24 extends through the aperture 45 to engage the adapter 23.
 The adapter 23, supports 26 and 27, and backplane 22 are preferably coupled
 through the use of a first fastener 46 and a second fastener 47. The
 fasteners 46 and 47 are substantially identical. The first fastener 46 may
 be a nut and bolt, and may comprise a first retaining member 46a, a shaft
 46b, and a second retaining member 46c (member 46c is illustrated in
 phantom in FIG. 2). At least a portion of the shaft 46b is disposed within
 the through holes 32, 39, and 43. The first retaining member 46a is
 disposed on the top surface 38 of the adapter 23 and is fixedly attached
 to an end of the shaft 46b. The second retaining member 46c is disposed on
 the rear surface 22b of the backplane 22, and is fixedly attached to an
 opposite end the shaft 46b. Hence, the first fastener 46 fixedly couples
 the first mounting wing 35, the first support 26, and the backplane 22.
 The second fastener 47 likewise may be a nut and bolt, and may comprise a
 first retaining member 47a, a shaft 47b, and a second retaining member 47c
 (the member 47c is shown in phantom in FIG. 2). At least a portion of the
 shaft 47b is disposed within the through holes 33, 42, and 44. The first
 retaining member 47a is disposed on the top surface 41 of the adapter 23,
 and is fixedly attached to an end of the shaft 47b. The second retaining
 member 47c is disposed on the rear surface 22b of the backplane 22, and is
 fixedly attached to an opposite end the shaft 47b. Thus, the second
 fastener 47 thus fixedly couples the second mounting wing 36, the second
 support 27, and the backplane 22.
 Most preferably, the shafts 46b and 47b each comprise a threaded rod, the
 members 46a and 47a are four or six-sided heads fixed to the corresponding
 threaded rod, and the members 46c and 47c are bolts adapted to engage the
 threaded rods. (The use of the fasteners 46 and 47 to couple the supports
 26 and 27 to the backplane 22 is a preferred methodology. Other fastening
 means, e.g., mounting tabs, adhesive, soldering, etc., are also within the
 contemplated scope of the invention.)
 Fiber-optic cables 48 and 49 are attached to the connectors 24 and 25,
 respectively. One end of the cable 48 is disposed along the mating surface
 24a of the connector 24, as shown in phantom in FIG. 4. One end of the
 cable 49 is likewise disposed along the mating surface 25a of the
 connector 25. The cable 48 has a minimum bending radius 48a. The minimum
 bending radius 48a typically has a value equal to approximately ten times
 the diameter of the optical fiber of the cable 48. In the particular
 embodiment herein described, the cable 48 is routed through the
 penetration 45 in the backplane 22. The cable 48 thus protrudes from the
 backplane 22. More particularly, the cable 48 protrudes in a direction
 normal to the backplane rear surface 22b by a distance 50.
 An adjacent structure 51 is shown in FIG. 3 for illustrative purposes. The
 cable 48 is routed between the backplane 22 and the structure 51 in this
 exemplary layout. The structure 51 can be virtually any type of structure
 which is capable of being placed in relatively close proximity to the
 backplane 22. For example, the structure 51 may be a door of a cabinet in
 which the backplane 22 is mounted. As another example, the structure 51
 may be a printed circuit board which is housed within an electronic device
 along with the backplane 22. As is evident from FIG. 3, the minimum
 required clearance between the structure 51 and the backplane 22
 corresponds to the cable-protrusion distance 50.
 The length of the supports 26 and 27 can be tailored for a suitable cable
 protrusion distance 50, which could be approximately, or even less than,
 the minimum bending radius of the cable 48. Specifically, the length of
 the supports 26 and 27 determines the positions of the adapter 23 and the
 connectors 24 and 25 in relation to the backplane 22. Preferably, the
 length of the supports 26 and 27 is sufficient to place the entirety of
 the connector 24 on the same side of the rear surface 22b as the adapter
 23 and the connector 25. This arrangement will exist when the mating
 surface 24a of the connector 24 is located at a specific minimum distance
 or greater from the rear surface 22b. This minimum distance could
 correspond to a length 24d of the connector 24.
 FIG. 3 illustrates the relative positions of the connector 24, the cable
 48, and the backplane 22 when the mating surface 24a and the rear surface
 22b are separated by a distance equal to at least the connector length
 24d. Separating the mating surface 24a and the rear surface 22b by at
 least the connector length 24d eliminates any protrusion of the connector
 24 from the rear surface 22b. Hence, a curvature can be imposed on the
 cable 48 as it exits the rear surface 22b, as shown in FIG. 3. The cable
 protrusion 50 can be minimized by imposing a curvature equal to the
 minimum bending radius 48a, and extending this curvature through an arc of
 at least 90 degrees. In such an arrangement, the protrusion 50 will thus
 equal approximately the minimum bending radius 48a of the cable 48.
 Increasing the length of the standoff 21 could decrease the protrusion
 distance 50 to less than the minimum bending radius 48a. Such a small
 protrusion distance 50 occurs without imposing a curvature greater than
 the minimum bending radius 48a.
 The invention thus minimizes the amount of space required to route the
 cable 48 from the backplane 22. In the exemplary layout, the invention
 allows the backplane 22 and the adjacent structure 51 to be placed in
 closer proximity than would otherwise be possible, i.e., the minimum
 required clearance between the backplane 22 and the adjacent structure 51
 is reduced through the use of the invention. Such a reduction can
 facilitate higher component-packaging densities within electronic devices
 in which the invention is utilized. Such increases, as noted previously,
 are highly valued due to the strict spacial constraints imposed on
 contemporary electronic devices. Furthermore, the invention achieves this
 advantage without compromising the structural or functional integrity of
 the cable 48.
 It is to be understood that even though numerous characteristics and
 advantages of the present invention have been set forth in the foregoing
 description, together with details of the structure and function of the
 invention, the disclosure is illustrative only, and changes may be made in
 detail, especially in matters of shape, size, and arrangement of the
 parts, within the principles of the invention to the full extent indicated
 by the broad general meaning of the terms in which the appended claims are
 expressed.