Patent Publication Number: US-2020285005-A1

Title: Optical connection structure

Description:
TECHNICAL FIELD 
     The present invention relates to an optical connection structure. The present application claims priority based on Japanese Patent Application No. 2016-169166 filed on Aug. 31, 2016, and the entire description thereof is incorporated herein by reference. 
     BACKGROUND ART 
     Patent Literature 1 discloses a backplane connector that comprehensively connects a plurality of optical connectors using a backplane. In the backplane connector, a backplane housing attached to the backplane, and a printed board housing attached to a printed board provided for the backplane in a manner capable of advancing to and retracting from the backplane are each provided with a plurality of connector holes. The optical connectors are inserted into the respective connector holes. The printed board housing and the backplane housing are fitted to each other, thereby comprehensively connecting the optical connectors. 
     Patent Literature 2 discloses a backplane connector having a structure for accurately and comprehensively connecting optical connectors to each other by using the backplane. As to the backplane connector, latches for fixing optical connectors inside are provided on inner surfaces of connector holes of a backplane housing. The optical connectors are provided with respective latch engagement sections. When the optical connectors are inserted into backplane housing, the latches are engaged with the respective latch engagement sections, thereby fixing the optical connectors to the backplane housing. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2001-318274 
     Patent Literature 2: Japanese Unexamined Patent Publication No. 2001-154062 
     SUMMARY OF INVENTION 
     An optical connection structure of this disclosure includes: a plurality of optical connectors arranged along a first direction; and a housing having a connector hole, the plurality of optical connectors being inserted into the connector hole along a second direction intersecting with the first direction, the connector hole comprehensively holding the optical connectors. Each optical connector includes a first end surface disposed on one side along a third direction intersecting with the first and second directions, and a second end surface disposed on another side along the third direction. The connector hole includes first and second inner wall surfaces facing each other in the third direction. The first end surface includes a first guide rail extending along the second direction. The second end surface includes a second guide rail extending along the second direction or a latch. The first inner wall surface includes a plurality of first guide rail fitting sections provided corresponding to the respective optical connectors, the first guide rail fitting sections being slidably fitted to the first guide rails along the second direction. The second inner wall surface includes a plurality of second guide rail fitting sections provided corresponding to the respective optical connectors and being slidably fitted to the second guide rails along the second direction, or a plurality of latch engagement sections provided corresponding to the respective optical connectors, the latches being engaged with the latch engagement sections. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing an appearance of a backplane connector as an optical connection structure according to one embodiment. 
         FIG. 2  is an enlarged partial view of the backplane connector shown in  FIG. 1 . 
         FIG. 3  is a perspective view of typifying and showing one of a plurality of plug connectors, and shows an appearance of the plug connector when being viewed from an obliquely downward side. 
         FIG. 4  is a perspective view showing a guide rail fitting section and therearound in an enlarged manner. 
         FIG. 5  is a perspective view showing a configuration of a backplane connector according to one variation example. 
         FIG. 6  is a perspective view showing an appearance of a plug connector according to one variation example. 
         FIG. 7  is a perspective view showing a guide rail fitting section and therearound in an enlarged manner. 
         FIG. 8  is a perspective view showing a configuration of a backplane connector according to another variation example. 
         FIG. 9  is a perspective view showing a configuration of a typical backplane connector. 
         FIG. 10  is an enlarged partial view of the backplane connector shown in  FIG. 9 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Technical Problem Solved by Disclosure 
     A backplane connector is used to connect a plurality of optical connectors accommodated in a backplane housing, comprehensively to a back panel. It is desirable that at the backplane connector, the orientation of each optical connector be accurately held along a connection direction. For example, in a case where the plurality of optical connectors including MT ferrules are comprehensively connected to the back panel, the ferrules of the optical connectors on the backplane connector are required to be accurately positioned to ferrules of the optical connectors on the back panel by inserting guide pins into guide holes provided for the ferrules. However, in case the orientations of the optical connectors are not accurately held along the connection direction, the guide pins are not inserted into the guide holes and there is a possibility that the guide pints interfere with the ferrule end surfaces to damage the ferrule end surfaces. 
     As for the backplane connectors described in Patent Literatures 1 and 2, the optical connectors are isolated by the inner walls of the backplane housings. In this case, the dimensions of the backplane housing are increased by the thickness of the inner wall. Increase in the dimensions of the backplane housing obstructs ventilation to the back panel. Consequently, the back panel is not sufficiently heat-released, which may serve as causes of malfunctions. 
     Advantageous Effects of Disclosure 
     According to this disclosure, reduction in size of the optical connection structure can be facilitated while the optical connectors are comprehensively connected in a state where the orientations are stabilized. 
     DESCRIPTION OF EMBODIMENTS OF INVENTION OF THIS APPLICATION 
     First, the contents of embodiments of the present invention are listed and described. An optical connection structure according to one embodiment includes: a plurality of optical connectors arranged along a first direction; and a housing having a connector hole into which the respective optical connectors are inserted along a second direction intersecting with the first direction and which comprehensively holds the optical connectors. Each optical connector includes a first end surface disposed on one side along a third direction intersecting with the first and second directions, and a second end surface disposed on another side along the third direction. The connector hole includes first and second inner walls facing each other in the third direction. The first end surface includes a first guide rail extending along the second direction. The second end surface includes a second guide rail extending along the second direction or a latch. The first inner wall surfaces include a plurality of first guide rail fitting sections provided corresponding to the respective optical connectors, the first guide rail fitting sections being slidably fitted to the first guide rails along the second direction. The second inner wall surfaces include a plurality of second guide rail fitting sections provided corresponding to the respective optical connectors and being slidably fitted to the second guide rails along the second direction, or a plurality of latch engagement sections provided corresponding to the respective optical connectors, the latches being engaged with the latch engagement sections. 
     In the optical connection structure described above, the connector holes of the housing comprehensively hold the optical connectors. Accordingly, the optical connectors are held without being separated from each other by the inner walls. Consequently, the intervals between adjacent optical connectors can be reduced, and the width of the housing in the first direction can be reduced. That is, the housing can be reduced in size. In addition, when the optical connectors are inserted into the connector holes of the housing, the first guide rails provided for the respective optical connectors are slidably fitted to the first guide rail fitting sections provided on the first inner wall surfaces of the connector hole of the housing. The second guide rails (or latches) provided for the respective optical connectors are slidably fitted to the second guide rail fitting sections (or latch engagement sections) provided on the second inner wall surfaces of the connector hole of the housing. Accordingly, the orientations of the optical connectors are accurately held along the second direction (i.e., the connection direction). Consequently, according to the optical connection structure described above, the optical connectors can be comprehensively connected in a state where the orientations are stabilized. 
     In the optical connection structure described above, the first guide rail fitting section may be a groove denoted in the third direction, and include a flare section whose width in the first direction increases toward a first end in the second direction. In this case, the first guide rail may be inserted from the first end of the first guide rail fitting section. The first guide rail may be a projection projecting in the third direction, include a taper section whose width in the first direction decreases toward a second end in the second direction, and be inserted from the second end into the first guide rail fitting section. The narrower the gap in the first direction between the first guide rail and the first guide rail fitting section is, the more difficult the insertion of the first guide rail into the first guide rail fitting section becomes. Accordingly, as described above, the flare section or the taper section may be provided at an end of the first guide rail fitting section in the second direction, or an end of the first guide rail in the second direction. In this case, the first guide rail is guided by the taper section and is inserted into the first guide rail fitting section. Accordingly, the first guide rail can be easily inserted into the first guide rail fitting section. The gap in the first direction between the first guide rail and the first guide rail fitting section can be reduced, and the orientations of the optical connectors can be more accurately held. 
     In the optical connection structure described above, the first guide rail fitting section may be a projection projecting in the third direction, and the first guide rail may be a groove recessed in the third direction. 
     In the optical connection structure described above, the minimum value of the interval between the optical connectors may be 0.5 mm or less. According to the optical connection structure described above, the minimum value of the interval between the optical connectors can be such a significantly small value. Consequently, the width of the housing in the first direction can be further reduced. The housing can comprehensively hold the optical connectors in the connector hole while the adjacent optical connectors are not separated by the inner wall. Also in this case, the width of the housing in the first direction can be further reduced. 
     In the optical connection structure described above, the lengths of the first guide rail and the first guide rail fitting section in the second direction may be longer than half the length of a portion of the optical connector embedded in the connector hole in the second direction. Accordingly, the orientations of the optical connectors can be held sufficiently accurately. Meanwhile, the lengths of the first guide rails and the first guide rail fitting sections in the second direction may be shorter than the entire lengths of the optical connectors in the second direction. 
     In the optical connection structure described above, each of the optical connectors may include a latch, and a latch lever for releasing the engagement of the latch in the connector hole in the second end surface. Each of the optical connectors may include the latch, and the connector hole may include a latch engagement section to be engaged with the latch. As such structures are provided, the optical connectors can be connected to the housing by simple means for latch engagement, and the engagement can be easily released. 
     In the optical connection structure described above, the housing may further include other connector hole into which other optical connectors are inserted along the second direction and which comprehensively hold the other optical connectors. Inner wall may be provided between the connector hole and the other connector hole. 
     The inner wall may be provided at a center portion of the housing in the second direction. The connector hole and the other connector hole may have a symmetrical structure with respect to the inner wall. In this case, the optical connectors may include at least four optical connectors, for example. 
     Details of Embodiments of Present Invention 
     Specific examples of the optical connection structure according to the embodiment of the present invention are hereinafter described with reference to the drawings. It is intended that the present invention is not limited to such examples, is represented by the scope of claims, and encompasses all modifications within the meanings equivalent to the scope of claims and the range of the scope of claims. According to the following description, in the description of the drawings, the same elements are assigned the same signs, and redundant description is omitted. 
       FIG. 1  is a perspective view showing an appearance of a backplane connector  1 A as an optical connection structure according to one embodiment.  FIG. 2  is an enlarged partial view of the backplane connector  1 A shown in  FIG. 1 . For facilitating understanding,  FIG. 1  shows only one plug connector  10 A, and  FIG. 2  shows a plurality of (four in this embodiment) plug connectors  10 A. In each diagram, an XYZ orthogonal coordinate system is represented, as required. The X direction is the first direction in this embodiment. The Z direction is the second direction in this embodiment. The Y direction is the third direction in this embodiment. That is, the second direction is orthogonal to the first direction, and the third direction is orthogonal to the first and second directions. The orthogonality may be intersection. Consequently, the second direction may intersect with the first direction, and the third direction may intersect with the first and second directions. 
     The backplane connector  1 A in this embodiment includes a plurality of plug connectors  10 A (optical connectors) as shown in  FIG. 2 . 
     The plug connectors  10 A are arranged along the X direction. Each plug connector  10 A includes a plug housing  11 A having a rectangular parallelepiped shape extending in the Z direction (front and rear direction). The plug housing  11 A may be made of resin, for example. A tape fiber  51  extends from the rear end of the plug housing  11 A. 
     The tape fiber  51  includes a plurality of optical fibers. The plug connector  10 A is a multi-core optical connector that comprehensively connects these optical fibers. The backplane connector  1 A integrally performs connection and separation of these plug connectors  10 A to and from the corresponding optical connectors  62  embedded on the back panel  61 . 
     The backplane connector  1 A in this embodiment further includes a backplane housing  3  as shown in  FIG. 1 . The backplane housing  3  includes a planar-shaped external frame  4  extending in the XY plane, and connector accommodating sections  5  surrounded by the external frame  4 . The connector accommodating section  5  is made of resin, for example, and has one or more (two in this embodiment) connector holes  6 . In the example shown in  FIG. 1 , one inner wall  9  is provided at a center portion of the backplane housing  3  in the X direction between the two connector holes  6 . The two connector holes  6  may have a line-symmetric structure with respect to the inner wall  9 . The plug connectors  10 A are inserted along the Z direction into each connector hole  6 . That is, a plurality of (four in this embodiment) plug connectors  10 A are inserted into each connector hole  6 , while the inner wall that separates the plug connectors  10 A is not provided at the gap between the plug connectors  10 A adjacent to each other. 
     Consequently, each connector hole  6  comprehensively holds the plug connectors  10 A. As the inner wall is not provided, the minimum value of the interval between the plug connectors  10 A is a significantly small value, such as 0.5 mm or less, for example. 
       FIG. 3  is a perspective view typifying and showing one of the plug connectors  10 A, and shows an appearance of the plug connector  10 A when being viewed from an obliquely downward side. As shown in  FIG. 3 , the plug connector  10 A includes a plug housing  11 A, a ferrule  12 , and guide pins  15 . The plug housing  11 A has a rectangular parallelepiped shape, as described above, and includes: a front end surface  11   a  and a rear end surface  11   b  that are opposite to each other in the Z direction; a pair of side surfaces  11   c  and  11   d  that are opposite to each other in the X direction; and an upper surface  11   e  and a lower surface  11   f  that are opposite to each other in the Y direction. The lower surface  11   f  is the first end surface in this embodiment, and the upper surface  11   e  is the second end surface in this embodiment. The pair of side surfaces  11   c  and  11   d  are formed substantially flat except a depression provided near to the rear end. 
     The front end surface  11   a  of the plug housing  11 A includes an opening  11   g  for exposing the ferrule  12 . The ferrule  12  projects from the opening  11   g  forward in the Z direction. The ferrule  12  in this embodiment is what is called an MT ferrule, and has a rectangular-parallelepiped appearance. One end surface thereof (front end surface) in the Z direction is a connection end surface  12   a  that faces the corresponding ferrule. From the connection end surface  12   a , end surfaces of a plurality of optical fibers separated from the tape fiber  51  (see  FIGS. 1 and 2 ) are exposed. These end surfaces are arranged one-dimensionally or two-dimensionally. On the connection end surface  12   a , a pair of guide holes  12   b  for allowing the pair of guide pins  15  to be inserted therein is formed. These guide holes  12   b  are formed on the opposite sides in the Y-axis direction with the end surfaces of the optical fibers intervening therebetween. In  FIG. 3 , an example where the guide pins  15  are preliminarily inserted into the guide holes  12   b  is shown. Alternatively, the guide pins  15  may be preliminarily inserted into the guide holes of the ferrule of the corresponding optical connector (on the back panel  61 ). 
     The lower surface  11   f  of the plug housing  11 A includes a guide rail (first guide rail)  21  extending in the Z direction. A guide rail  21  is formed to have a projection shape projecting in the Y direction. Specifically, the guide rail  21  includes a pair of side surfaces  21   a  and  21   b  intersecting with the lower surface  11   f  of the plug housing  11 A, and a bottom surface  21   c  that connects the pair of side surfaces  21   a  and  21   b . The pair of side surfaces  21   a  and  21   b  are formed perpendicular to the lower surface  11   f , are parallel to each other, and extend in the Z direction. The bottom surface  21   c  is formed parallel to the lower surface  11   f  (that is, such that the normal direction is along the Y direction), and extends along the Z direction. 
     The guide rail  21  includes the taper section  23 . The taper section  23  is provided at one end (second end)  21   d  of the guide rail  21  in the Z direction. At the taper section  23 , the width of the guide rail  21  in the X direction gradually decreases toward the end  21   d . At the taper section  23  in this embodiment, the opposite side surface s  21   a  and  21   b  of the guide rail  21  are surfaces curved with respect to the central axis line C 1  of the guide rail  21 . At the taper section  23 , the opposite side surfaces  21   a  and  21   b  of the guide rail  21  may be flat surfaces inclined in directions opposite to each other with respect to the central axis line C 1  of the guide rail  21 . When the plug connector  10 A is inserted into the backplane housing  3 , the guide rail  21  is inserted (fitted) into a guide rail fitting section  22  from the end  21   d.    
     The upper surface lie of the plug housing  11 A includes a latch  13  and a latch lever  14 . The latch  13  projects obliquely rearward from the upper surface lie of the plug housing  11 A near to the front, and the distal end thereof is elastically displaced in the Y direction. As shown in  FIGS. 1 and 2 , the distal end of the latch  13  is engaged with a latch engagement section  31  of the backplane housing  3 . Accordingly, the plug connector  10 A is prevented from being detached from the backplane housing  3 . The latch lever  14  projects obliquely frontward from the upper surface lie of the plug housing  11 A near to the rear, and the distal end thereof covers the distal end of the latch  13 . By an operator pressing the distal end of the latch lever  14  downward, engagement between the latch  13  and the latch engagement section  31  is cancelled. 
       FIG. 1  is referred to again. The connector hole  6  includes inner walls  7  and  8  facing each other in the Y direction. The inner wall surface  7  is the first inner wall surface in this embodiment, and the inner wall surface  8  is the second end surface in this embodiment. The inner wall surface  7  includes guide rail fitting sections  22  provided corresponding to the respective plug connectors  10 A. Each guide rail fitting section  22  is slidably fitted along the Z direction to the guide rail  21  of the corresponding plug connector  10 A. In other words, each guide rail fitting section  22  limits the movement of the corresponding plug connector  10 A in the X direction, and allows the movement in the Z direction. 
       FIG. 4  is a perspective view showing the guide rail fitting section  22  and therearound in an enlarged manner. As shown in  FIG. 4 , the guide rail fitting section  22  is a groove recessed in the Y direction. Specifically, the guide rail fitting section  22  has a rectangular section perpendicular to the Z direction, and includes a pair of side surfaces  22   a  and  22   b  and a bottom surface  22   c . The pair of side surfaces  22   a  and  22   b  are formed perpendicular to the inner wall surface  7 , and extend in the Z direction. The bottom surface  22   c  is formed parallel to the inner wall surface  7  (that is, such that the normal direction is along the Y direction), and extends along the Z direction. When the guide rail  21  is inserted into the guide rail fitting section  22 , the pair of side surfaces  21   a  and  21   b  of the guide rail  21  face the corresponding pair of side surfaces  22   a  and  22   b  of the guide rail fitting section  22 , and the bottom surface  21   c  of the guide rail  21  faces the bottom surface  22   c  of the guide rail fitting section  22 . In the state where the guide rail  21  is fitted to the guide rail fitting section  22 , the plug housing  11 A is moved frontward in the Z direction in the connector hole  6  of the backplane housing  3 . 
     The guide rail fitting section  22  includes the flare section  24 . The flare section  24  is provided at one end (first end)  22   d  of the guide rail fitting section  22  in the Z direction. At the flare section  24 , the width of the guide rail fitting section  22  in the X direction gradually increases toward the end  22   d . At the flare section  24  in this embodiment, the opposite side surfaces  22   a  and  22   b  of the guide rail fitting section  22  may be flat surfaces inclined in directions opposite to from each other with respect to the central axis line C 2  of the guide rail fitting section  22 . At the flare section  24 , the opposite side surfaces  22   a  and  22   b  of the guide rail fitting section  22  may be surfaces curved in directions away from the central axis line C 2  of the guide rail fitting section  22 . When the plug connector  10 A is inserted into the backplane housing  3 , the guide rail  21  is inserted (fitted) from the end  22   d  of the guide rail fitting section  22 . 
     In one embodiment, the end  21   d  of the guide rail  21  is positioned rearward than the front end surface  11   a  of the plug housing  11 A. An end  22   e  of the guide rail fitting section  22  opposite to the end  22   d  is disposed rearward than the most inner part of the connector hole  6  (on a nearer side in  FIG. 4 ). The Z-direction length of the guide rail  21  is shorter than the Z-direction length of the plug housing  11 A. Meanwhile, the Z-direction length of the guide rail  21  is longer than half the Z-direction length of a portion of the optical connector  10 A embedded in the connector hole  6 . More preferably, this length is longer than ¾ of the Z-direction length of the embedded portion. Likewise, the Z-direction length of the guide rail fitting section  22  is longer than half the Z-direction length of the embedded portion of the optical connector  10 A. More preferably, this length is longer than ¾ of the Z-direction length of the embedded portion. Meanwhile, the Z-direction length of the guide rail fitting section  22  is shorter than the Z-direction length of the plug housing  11 A. 
       FIG. 1  is referred to again. The inner wall surface  8  of the connector hole  6  includes a plurality of latch engagement sections  31 . The latch engagement sections  31  are provided corresponding to the respective plug connectors  10 A, and are engaged with the latches  13  provided on the upper surface  11   e  of the plug housing  11 A. 
     Specifically, each latch engagement section  31  has a shape, such as of a recessed groove being recessed in the Y direction with respect to the inner wall surface  8 , and extends in the Z direction. When the plug connector  10 A is inserted into the backplane housing  3 , the latch  13  of each plug connector  10 A is slidably fit to the corresponding latch engagement section  31  and is finally engaged with the latch engagement section  31 . Each latch engagement section  31  limits the movement of the corresponding plug connector  10 A in the X direction, and allows the movement in the Z direction. 
     Note that the upper surface lie of the plug housing  11 A may include a guide rail (second guide rail)  16  extending in the Z direction instead of the latch  13  (see  FIG. 8 ). In this case, the inner wall surfaces  8  of the backplane connector  1 C may include a plurality of guide rail fitting sections  32  instead of the plurality of the latch engagement sections  31 ; the guide rail fitting sections  32  are provided corresponding to the respective plug connectors  10 C, and are slidably fitted to the guide rails  16  along the Z direction. The specific configurations of these guide rails  16  and guide rail fitting sections  32  are analogous to those of the guide rails  21  and guide rail fitting sections  22  described above. 
     Advantageous effects obtained by the backplane connector  1 A according to this embodiment described above are described. As described above, the backplane connector  1 A is used to connect the plurality of optical connectors  10 A accommodated in the backplane housing  3 , comprehensively to the back panel  61 . It is desirable that at the backplane connector  1 A, the orientation of each optical connector  10 A be accurately held along the connection direction (Z direction). For example, in a case where the plurality of plug connectors  10 A including the MT ferrules  12  are comprehensively connected to the back panel  61 , the guide pins  15  are inserted into the guide holes  12   b  of the ferrules  12  (or the guide holes of the ferrules on the back panel  61 ), thereby accurately positioning the ferrules  12  of the plug connectors  10 A on the backplane connector  1 A and the ferrules of the plug connectors on the back panel  61  with respect to each other. However, in case the orientations of the plug connectors  10 A are not accurately held along the connection direction, there is a possibility that the guide pins  15  are not inserted into the guide holes  12   b  of the ferrules  12  (or the guide holes of the ferrules on the back panel  61 ), and the guide pins  15  interfere with the connection end surfaces  12   a  of the ferrules  12  (or the ferrule end surfaces on the back panel  61 ) to damage the connection end surfaces  12   a  (or the ferrule end surfaces on the back panel  61 ). 
     In a typical backplane connector, plug connectors are isolated by the inner walls of a backplane housing (for example, see Patent Literatures 1 and 2).  FIG. 9  is a perspective view showing a configuration of such a backplane connector  100 .  FIG. 10  is an enlarged partial view of the backplane connector  100  shown in  FIG. 9 . In the backplane connector  100 , plug connectors  110  are isolated by inner walls  105  of a backplane housing  103 . In this case, the dimension of the backplane housing  103  in the X direction is increased by the thickness of the inner walls  105 . Increase in the dimensions of the backplane housing  103  obstructs ventilation to the back panel  61 . Consequently, the back panel  61  is not sufficiently heat-released, which may serve as causes of malfunctions. 
     According to the backplane connector  1 A in this embodiment, the connector holes  6  of the backplane housing  3  comprehensively hold the plug connectors  10 A. Accordingly, the plug connectors  10 A are held without being separated from each other by the inner walls. Consequently, the intervals between adjacent plug connectors  10 A can be reduced, and the width of the backplane housing  3  in the X direction can be reduced. That is, the backplane housing  3  can be reduced in size. When the plug connectors  10 A are inserted into the connector holes  6 , the guide rails  21  provided for the respective plug connectors  10 A are slidably fitted to the guide rail fitting sections  22  provided on the inner wall surfaces  7  of the connector holes  6 . The latches  13  (or guide rails) provided for the respective plug connectors  10 A are slidably fitted to the latch engagement sections  31  (or guide rail fitting sections) provided on the inner wall surfaces  8  of the connector holes  6 . 
     Accordingly, the orientations of the plug connectors  10 A are accurately held along the Z direction (i.e., the connection direction). 
     Consequently, according to the backplane connector  1 A in this embodiment, the plug connectors  10 A can be comprehensively connected in a state where the orientations are stabilized. The advantageous effects obtained by the backplane connector  1 C are analogous to the advantageous effects obtained by the backplane connector  1 A that have been described above and are described below. 
     In the case where the guide rail fitting section  22  is a groove recessed in the Y direction as with this embodiment, the guide rail fitting section  22  may include the flare section  24  whose width increases in the X direction toward the end  22   d  in the Z direction. In the case where the guide rail  21  is the projection projecting in the Y direction, the guide rail  21  may include the taper section  23  whose width decreases in the X direction toward the end  21   d  in the Z direction. 
     The narrower the gap in the X direction between the guide rail  21  and the guide rail fitting section  22  is, the more difficult the insertion of the guide rail  21  into the guide rail fitting section  22  becomes. Accordingly, as described above, the taper and flare sections  23  and  24  may be provided at the one end  22   d  of the guide rail fitting section  22  in the Z direction and the one end  21   d  of the guide rail  21  in the Z direction. In this case, the guide rails  21  are guided by the taper and flare sections  23  and  24 , and are inserted into the guide rail fitting sections  22 . Accordingly, the guide rail  21  can be easily inserted into the guide rail fitting section  22 . The gap in the X direction between the guide rail  21  and the guide rail fitting section  22  can be reduced, and the orientations of the plug connectors  10 A can be more accurately held. In this embodiment, the guide rail  21  and the guide rail fitting section  22  include the taper and flare sections. Alternatively, only one of the guide rail  21  and the guide rail fitting section  22  may include the taper or flare section. 
     As with this embodiment, the minimum value of the interval between the plug connectors  10 A may be 0.5 mm or less. According to the backplane connector  1 A in this embodiment, the minimum value of the interval between the plug connectors  10 A can be such a significantly small value. Consequently, the width of the backplane housing  3  in the X direction can be further reduced. 
     As described in this embodiment, the Z-direction lengths of the guide rail  21  and the guide rail fitting section  22  may be longer than half the Z-direction length of the part of the plug connector  10 A inserted in the connector hole  6 . Accordingly, the orientations of the plug connectors  10 A can be held sufficiently accurately. 
     Variation Example 
       FIG. 5  is a perspective view showing a configuration of a backplane connector  1 B according to one variation example of this embodiment described above.  FIG. 6  is a perspective view showing an appearance of a plug connector  10 B according to this variation example. The difference between this variation example and the embodiment described above is the shapes of the guide rails and the guide rail fitting sections. That is, the guide rails  21  in the embodiment described above are the projections protruding in the Y direction, while guide rails  25  in this variation example are grooves recessed in the Y direction. The guide rail fitting sections  22  in the embodiment described above are the grooves recessed in the Y direction, while guide rail fitting sections  26  in this variation example are projections protruding in the Y direction. 
       FIG. 7  is a perspective view showing the guide rail fitting section  26  and therearound in an enlarged manner. As shown in  FIG. 7 , the guide rail fitting sections  26  includes a pair of side surfaces  26   a  and  26   b  intersecting with the inner wall surface  7  of the connector hole  6 , and a bottom surface  26   c  that connects the pair of side surfaces  26   a  and  26   b . The pair of side surfaces  26   a  and  26   b  are formed perpendicular to the inner wall surface  7 , and extend in the Z direction. The bottom surface  26   c  is formed parallel to the inner wall surface  7  (that is, such that the normal direction is along the Y direction), and extends along the Z direction. 
     As shown in  FIG. 6 , the guide rail  25  has a rectangular section perpendicular to the Z direction, and includes a pair of side surfaces  25   a  and  25   b  and a bottom surface  25   c . When the guide rail  25  is inserted into the guide rail fitting section  26 , the pair of side surfaces  26   a  and  26   b  of the guide rail fitting section  26  face the corresponding pair of side surfaces  25   a  and  25   b  of the guide rail  25 , and the bottom surface  26   c  of the guide rail fitting section  26  faces the bottom surface  25   c  of the guide rail  25 . In the state where the guide rail fitting section  26  is fitted to the guide rail  25 , the plug housing  11 B is moved frontward in the Z direction in the connector hole  6  of the backplane housing  3 . 
     Also in the mode as in this variation example, the orientations of the plug connectors  10 B are accurately held along the Z direction (i.e., the connection direction) in a manner analogous to that of the embodiment described above. Consequently, according to the backplane connector  1 B in this variation example, the plug connectors  10 B can be comprehensively connected in a state where the orientations are stabilized. 
     The optical connection structure according to the present invention is not limited to the embodiment described above. Other various modifications can be made. For example, the embodiment and variation example described above may be combined with each other in conformity with required objects and advantageous effects. In the embodiment described above, the configuration of the present invention is applied to the backplane connector. Alternatively, the configuration of the present invention may be applied to the connectors on the back panel. For example, at least one of the guide rail and the guide rail fitting section of the backplane connector according to the variation example may have a taper or flare section as in the embodiment described above. In the embodiment described above, the case where each optical connector is the multi-core optical connector has been exemplified. Alternatively, each optical connector may be a single-core optical connector. 
     REFERENCE SIGNS LIST 
       1 A,  1 B,  1 C . . . backplane connector,  3  . . . backplane housing,  4  . . . external frame,  5  . . . connector accommodating section,  6  . . . connector hole,  7 ,  8  . . . inner wall surface,  9  . . . inner wall,  10 A,  10 B . . . plug connector,  11 A,  11 B . . . plug housing,  11   a  . . . front end surface,  11   b  rear end surface,  11   c ,  11   d  . . . side surface,  11   e  . . . upper surface,  11   f  lower surface,  11   g  . . . opening,  12  . . . ferrule,  12   a  . . . connection end surface,  12   b  . . . guide hole,  13  . . . latch,  14  . . . latch lever,  15  . . . guide pin,  16 ,  21 ,  25  . . . guide rail,  21   a ,  21   b ,  25   a ,  25   b  . . . side surface,  21   c ,  25   c  . . . bottom surface,  21   d  . . . end,  22 ,  26 ,  32  . . . guide rail fitting section,  22   a ,  22   b ,  26   a ,  26   b  . . . side surface,  22   c ,  26   c  . . . bottom surface,  22   d  . . . end,  23 ,  24  . . . flare and taper sections,  31  . . . latch engagement section,  51  . . . tape fiber,  61  . . . back panel,  62  . . . optical connector,  100  . . . backplane connector,  103  . . . backplane housing,  105  . . . inner wall,  110  . . . plug connector, C 1 , C 2  . . . central axis line.