Abstract:
An optical connector includes an optical fiber, and a ferrule configured to hold the optical fiber, wherein the ferrule has a front part, a rear part, a deformable mechanism to connect between the front part and the rear part, and an opening to allow the optical fiber to bend along with displacement of the deformable mechanism, and wherein the deformable mechanism has a restrictor to restrict the displacement or deformation of the deformable mechanism, the restrictor being provided at least between the deformable mechanism and the front part or between the deformable mechanism and the rear part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2013-121049 filed on Jun. 7, 2013, which is incorporated, herein by references in its entirety. 
       FIELD 
       [0002]    The embodiments discussed herein relate to an optical connector. 
       BACKGROUND 
       [0003]    In recent years and continuing, optical interconnections likely to provide wideband inter-chip communications at low power-consumption have been attracting attention in the technologies of supercomputers or servers. 
         [0004]    In supercomputers or servers, multiple boards are connected to a backplane board and a large-scale integration (LSI) chip is mounted on each board to carry out computation. With optical interconnections, electrical signals generated by the LSI chip are converted into optical signals by an electrical-to-optical converter on the board. The optical signals are transmitted to another board and converted into electrical signals before they are input to the LSI chip. Optical transmission paths are arranged on or inside the backplane board. Optical transmission paths are also arranged on each board, extending from the board edge to the optical-to-electrical converter and the electrical-to-optical converter. The boards are each connected to the backplane board using optical connectors. 
         [0005]    Optical connectors for use in connection with the backplane board are generally placed at the board edges. In general, multifiber optical connectors are used and an attachable and detachable structure is employed from the viewpoint of the system configuration and system maintenance. In an optical connector, an optical transmission line is held by a ferrule with a high degree of accuracy and housed in a connector housing. The ferrule is mated with a counterpart ferrule in the connector housing, 
         [0006]    For optical connectors, cost redaction, as well as quality improvement, is desired. To reduce manufacturing cost, unpolished fibers with their tips unpolished have promise. A connector structure enabling to achieve accurate optical connection between unpolished fibers is known. See, for example, Japanese Laid-open Patent Publication No. 2012-194481. This connector structure makes use of deformation of the ferrule and bending or buckling of optical fibers, and achieves low-loss connection between multifiber connectors, each having uneven fiber lengths. 
         [0007]    However, with the conventional structure making use of ferrule deformation and fiber buckling, undesirable external forces such as shaking or impingement may be applied to the bending optical fibers during connection of the ferrules inside the connector housing. If an external force acts in the direction of the ferrule insertion (parallel to the light propagation axis of an optical fiber), buckling exceeding a specified level occurs at the optical fibers. If an external force acts in the direction of the fiber alignment (orthogonal to the light propagation axis of the optical fiber), the bending fibers are subjected to excessive stress and optical fibers may be damaged. 
         [0008]    It is desired for an optical connector to prevent an excessive amount of buckling or stress from being generated in optical fibers over a specified level to avoid damage to the optical fibers. 
       SUMMARY 
       [0009]    According to an aspect of the embodiments, an optical connector includes an optical fiber and a ferrule configured to hold the optical fiber, wherein the ferrule has a front part, a rear part, a deformable mechanism to connect between the front part and the rear part, and an opening to allow the optical fiber to bend along with displacement of the deformable mechanism, and wherein the deformable mechanism has a restrictor to restrict displacement or deformation of the deformable mechanism, the restrictor being provided at least between the deformable mechanism and the front part or between the deformable mechanism and the rear part. 
         [0010]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive to the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  illustrates a ferrule used in an optical connector according to the first embodiment; 
           [0012]      FIG. 2A  is an enlarged view of the deformable mechanism of the ferrule; 
           [0013]      FIG. 2B  is a cross-sectional view taken along the A-A′ line of  FIG. 1 ; 
           [0014]      FIG. 2C  is a perspective view of the first restricting member used in the deformable mechanism; 
           [0015]      FIG. 3  illustrates an optical connector in which optical fibers are inserted in the ferrule; 
           [0016]      FIG. 4  illustrates in three views of the optical connector in the unconnected state; 
           [0017]      FIG. 5  illustrates in three views of the optical connector in the connected state; 
           [0018]      FIG. 6  illustrates two optical connectors mated with each other; 
           [0019]      FIG. 7  illustrates a modification of the ferrule of  FIG. 1 ; 
           [0020]      FIG. 8A  is a diagram to explain an advantageous effect of the modification of  FIG. 7 ; 
           [0021]      FIG. 8B  is a diagram to explain an advantageous effect of the modification of  FIG. 7 ; 
           [0022]      FIG. 9  illustrates a ferrule used in an optical connector according to the second embodiment; 
           [0023]      FIG. 10  is a cross-sectional view of the deformable mechanism of the ferrule taken along the A-A′ line of  FIG. 9 ; 
           [0024]      FIG. 11  illustrates a ferrule used in an optical connector according to the third embodiment; 
           [0025]      FIG. 12A  is a cross-sectional view of the deformable mechanism of the ferrule taken along the A-A′ line; 
           [0026]      FIG. 12B  illustrates in the same cross-section a modified structure of the deformable mechanism; and 
           [0027]      FIG. 13  is a schematic diagram of inter-board optical interconnection to which the optical connector of the embodiments are applied. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    The embodiments of the inventions are now described with reference to accompanying drawings. 
       First Embodiment 
       [0029]      FIG. 1  illustrated in orthogonal views a ferrule  10  used in an optical connector according to the first embodiment. In the figure, part (A) is a top view of the ferrule, part (B) is a side view, part (C) is a cross-sectional view taken along the B-B′ line of the part (A), and part (D) is a front view. 
         [0030]    The ferrule  10  has a front part  10   a  with a mating face  19 , a rear part  10   b,  an opening  10   c,  and a deformable mechanism  11  connecting the front part  10   a  and the rear pars  10   b.  In this example, two deformable mechanisms  11  are provided at symmetrical positions with respect to the ferrule insertion, axis (i.e., the Y axis). 
         [0031]    Fiber guide holes  18  are formed in the front part  10   a  and the rear part  10   b  of the ferrule  10 . The front part  10   a  has a step  10   d  for supporting the optical fibers  31  (see  FIG. 3 ) positioned in the opening  10   c.  The opening  10   c  allows the optical fibers  31  to buckle or bend during connection with the counterpart connector. The front part  10   a  has a guide pin receiving hole  17 , and the rear part  10   b  has a guide pin receiving hole  16  and an adhesive inlet  28 . 
         [0032]    The deformable mechanism  11  has restrictors  25   a  and  25   b  to restrict displacement and/or deformation of the deformable mechanism  11  over a certain level. The restrictor  25   a  is provided between the deformable mechanism  11  and the rear-part  10   b  of the ferrule  10 . The restrictor  25   b  is provided between the deformable mechanism  11  and the front part  10   a  of the ferrule  10 . When the ferrule  10  is mated with a counterpart ferrule (or connector), the restrictors  25   a  and  25   b  prevent too much buckling generated in the optical fibers  31  over a specified level and prevent an excessive amount of stress from being applied to the optical fibers  31  bending in the opening  10   c.    
         [0033]    The deferrable mechanism  11  includes a first restricting member  12  extending from the front part  10   a  to the rear part  10   b  of the ferrule  10 , a second restricting member  14  extending from the rear part  10   b  to the front part  10   a  of the ferrule  10 , and a beam  13  extending obliquely between the first restring member  12  and the second restricting member  14 . The deformable mechanism  11  of this example has an N-shaped or Z-shaped top view, and the restrictors  25   a  and  25   b  are arranged symmetrically with, respect to the Y-axis direction of the ferrule  10 . 
         [0034]      FIG. 2A  is an enlarged view of the deformable mechanism  11 ,  FIG. 2B  is a cross-sectional view taken along the A-A′ line of  FIG. 1 , and  FIG. 2C  is a perspective view of the first restricting member  12 . The restrictor  25   a  has a protrusion  12   a  formed on the end face of the first restricting member  12  and a recess  21  formed in the rear part  10   b  of the ferrule  10 . A clearance (or a gap) is provided between the first restricting member  12  and the rear part  10   b  of the ferrule  10 , The restrictor  25   b  has a protrusion  14   a  formed on the end face of the second restricting member  14  and a recess  22  formed in the front part  10   b  of the ferrule  10 . A clearance (or a gap) is provided between the second restricting member  14  and the front part  10   a  of the ferrule  10 . 
         [0035]    As illustrated in  FIG. 2C , the first restricting member  12  has a same height “h” as that of the ferrule  10  and a thickness “t.” in the X direction of  FIG. 1 . The protrusion  12   a  provided on the end face of the first restricting member  12  has a length “l” in the height “h” direction of the first restricting member  12 , a width “w” in the thickness “t” direction, and a protruding amount “p”. The recess  21  formed in the rear part  10   b  of the ferrule  10  is a groove for receiving the protrusion  12   a.  The same structures are employed for the protrusion  14   a  on the end face of the second restricting member and the recess  22  formed in the front part  10   a  of the ferrule  10 . 
         [0036]    The beam  13  extending obliquely between the first restricting member  12  and the second restricting member  14  has dimensions “a” in the ferrule inserting direction (Y direction) and “b” along the line of the fiber guide holes  18  (in the X direction) in the top view. 
         [0037]    In the disconnected state of the optical connector, a clearance with a distance “d” exists in each of the restrictors  25   a  and  25   b.    
         [0038]    During connection of the optical connector, the protrusion  12   a  is fit into the recess  21 , while the protrusion  14   a  is fit into the recess  22 , and there is no clearance. Without the clearance, the deformable mechanism  11  cannot move or deform any longer. In this state, the beam  13  undergoes deformation due to the stress. 
         [0039]    A guide pin receiving hole  15  is formed in the beam  13  ( FIG. 2B ). The diameter of the guide pin receiving hole  15  is the same as or less than that of the guide pin receiving hole  16  formed in the rear part  10   b  of the ferrule  10 . On the other hand, the diameter of the guide pin receiving hole  15  is set greater than that of the guide pin receiving hole  17  formed in the front part  10   a  of the ferrule  10  such that the guide pin is held at a proper position even if the beam  13  undergoes deformation. 
         [0040]      FIG. 3  illustrates in orthogonal views the optical connector  1  in which the optical fibers  31  are inserted in the ferrule  10 . Part (A) is a top view of the optical connector  1 , part (B) is a side view, part (C) is a cross-sectional view taken along the C-C′ line of part (A), and part (D) is a front view. 
         [0041]    The optical connector  1  is, for example, a multifiber connectors in which two or more optical fibers  31  are used. The optical fibers  31  arranged in a line are held collectively by a tape  32  except for the end portions and define an optical transmission line  33 . The optical transmission line  33  is secured by an adhesive  35 . Each of the optical fibers  31  of the non-taped, portion is inserted in the corresponding one of the fiber guide holes  18  ( FIG. 1 ), and supported on the step  10   d  of the front part  10   a  of the ferrule  10 . The optical fibers  31  are unpolished fibers and the end tips of the optical fibers  31  vary in the length. The variation in the length Is absorbed in the opening  10   c  of the ferrule  10  during connection of the optical connector  1 . 
         [0042]      FIG. 4  illustrates the optical connector  1  in the disconnected state, and  FIG. 5  illustrates in three views the optical connector  1  in the connected state. In each of  FIG. 4  and  FIG. 5 , part (A) is a top view, part (B) is a side view, and part (C) is a cross-sectional view taken along the D-D′ line of part (A). 
         [0043]    In the disconnected state illustrated in  FIG. 4 , a clearance with a distance “d” exists in each of the restrictors  25   a  and  25   b.  In this state, the optical fibers  31  projecting from the tape  32  of the transmission line  33  extend straight in the ferrule  10  as illustrated in part (C) of  FIG. 4 . 
         [0044]    In the connected state illustrated in  FIG. 5 , the protrusion  12   a  is fit into the recess  21  at the restrictor  25   a,  while the protrusion  14   a  is fit into the recess  22  at the restrictor  25   b  (see FIG.  2 A), and there is no clearance left. The tips of the optical fibers  31  come into contact with she optical fibers of the counterpart connector and physical-contact (PC) connection is achieved. Even with variation in the length of the optical fibers  31 , all the optical fibers  31  can be brought into physical-contact connection because the optical fibers  31  bend (or buckle) in the opening  10   c  of the ferrule  10 , as illustrated in part (C) of  FIG. 5 . 
         [0045]      FIG. 6  illustrates an optical connector  1 A and an optical connector  1 B mated with each other. The optical connector  1 A has a guide pin  41 . The guide pin  41  is held by pin keeper  42 . When the optical connector  1 A is connected to the optical connector  1 B, the leading end of the guide pin  41  is inserted into a guide pin receiving hole  17  of the optical connector  1 B. 
         [0046]    The optical connector  1 A and the optical connector  1 B are pressed against each other, and the beam  13  of the deformable mechanism  11  of each of the optical connectors  1 A and  1 B warps. Because the diameter of the guide pin receiving hole  16  of the rear part  10   b  of the ferrule  10  and the diameter of the guide pin receiving hole  15  of the beam  13  are set greater than that of the guide pin  41 , the optical connectors  1 A and  1 B are positioned correctly with respect to each other by the guide pin  41 . 
         [0047]    The optical fibers  31  of the optical connector  1 A and the optical fibers  31  of the optical connector  1 B are brought into physical contact, while bending in the height direction of the ferrule  10 . Even if an unexpected force is applied externally to the bending optical fibers  31 , excessive buckling over a tolerable level can be prevented because farther displacement of the deformable mechanism  11  is restricted by the restrictors  25   a  and  25   b.    
         [0048]    In the connected state illustrated in  FIG. 6 , the internal stress spreads over the entire part of the beam  13  and the restricting members  12  and  14 , and breakdown or breakage is prevented in relation to the material characteristics. Because of the interlock between the protrusion  12   a  and the recess  21  and between the protrusion  14   a  and the recess  22 , the ferrules  10  are held stably even if an external force is applied in the direction parallel to the alignment of the optical fibers  31 . 
         [0049]    The above-described arrangements can prevent excessive force from being applied to the optical fiber  31  bending inside the ferrule  10  during connection and protect the optical fibers  31  from breakage. 
       Example 1 
       [0050]    An actual example of fabricating the optical connector  1  with the above-described structure. The external dimensions of the optical connector  1  are the same as those of a mechanically transferable (MT) connector which is a standardized multifiber optical connector. 
         [0051]    Referring to  FIG. 2A  to  FIG. 2C , the height “h” of the first restricting member  12  of the restrictor  25   a  and the second restricting member  14  of the restrictor  25   b  is 2.5 mm, and the thickness “t” is 400 μm. 
         [0052]    The distance “d” of the clearance between the first, restricting member  12  and the rear part  10   b  and between the second restricting member  14  and the front part  10   a  of the ferrule  10  is 100 μm. 
         [0053]    The projection amount “p” of the protrusion  12   a  of the first restricting member  12  and the protrusion  14   a  of the second restricting member  14  is 50 μm. The length “l” of the protrusions  12   a  and  14   a  in the vertical direction of the drawing is 1 mm, and the width “w” is 200 μm. The depth of the recesses  21  and  22  is 50 μm, and the length and the width thereof are 1.01 mm and 201 μm, respectively. 
         [0054]    The size “a” of the top face of the beam  13  in the ferrule inserting direction (along the Y axis in  FIG. 1 ) is 1 mm, and the sire “b” of the beam  13  along the line of the fiber guide holes  18  (along the X axis in  FIG. 1 ) is 700 μm. The height of the beam  13  in the height direction of the ferrule  10  is 1.5 mm. The angle of the beams  13  with respect to the first restricting member  12  and the second restricting member  14  is 45 degrees. 
         [0055]    The diameter of the guide pin receiving hole  17  varies in the front part  10   a  of the ferrule  10 . From the mating face  19  ( FIG. 1 ) to 2 to 4 mm inside, the diameter is 701 μm which sire is almost the same as that of the guide pin receiving hole of an MT connector. The diameter of the guide pin receiving hole  17  becomes 800 μm deeper inside the front part  10   a  of the ferrule  10 . The diameter of the guide pin receiving hole  16  of the rear part  10   b  of the ferrule  10  and the diameter of the guide pin receiving hole  15  of the beam  13  are also 800 μm. 
         [0056]    The guide pin receiving hole  15  formed in 
         [0057]    the beam  13  is slightly offset toward the inner side of the ferrule  10  (or closer to the opening  10   c ) as illustrated in  FIG. 2B . When using the deformable mechanism with an N-shaped or Z-shaped top view ( FIG. 1 ), the guide pin receiving hole  15  deforms toward the outer side of the ferrule  10  as the first restricting member  12  and the second restricting member  14  deform along with the displacement of the deformable mechanism  11 , If the guide pin  41  makes contact with the ferrule  10 , a frictional resistance is generated and the body of the ferrule  10  will not indicate a desired spring constant. To avoid this, the diameter of the guide pin receiving hole  16  of the rear part  10   b  of the ferrule and the diameter of the guide pin receiving hole  15  of the beam  13  are set about 100 μm greater than the diameter of the guide pin  41 . On the other hand, the diameter of the guide pin receiving hole  17  of the front part  10   a  of the ferrule  10  is set only 1 μm greater than the diameter of the guide pin  41  due to requirement for positioning accuracy with respect to the optical fibers of the counterpart connector. 
         [0058]    The ferrule  10  can be fabricated by mold injection. For the molding material, an olefin resin group may be used as an example of engineering plastic. The material of the ferrule  10  is not limited to this example, and many other materials such as polyamide (PA), polycarbonate (PC), polyasetal (polyoxymethylene: POM), modified polyphenylene ether (m-PPE), polybutylene terephthalate (PBT), amorphous polyarilate (PAR), polyether sulphon (PES), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyimide (PI), and polyetherimide (PEI) may be used. The ferrule  10  may be designed according to the mechanical characteristics of the material to be used. 
         [0059]    Twelve optical fibers  31  are inserted in the ferrule  10 . A 12-core fiber ribbon  33  is used as the transmission line  33 . The tape  32  of the leading end portion of the fiber ribbon  33  is removed to expose individual optical fibers  31 . Each of the optical fibers  31  is inserted independently into corresponding one of the fiber guide holes  18 . The base portions of the independent optical fibers  31  are secured by adhesive  35 . 
         [0060]    The optical fiber  31  is, for example, a single-mode 125-micron fiber or a multi-mode fiber. The optical fiber  31  is not limited to this example, and other types of fibers such as small-diameter optical fibers, large-diameter optical fibers, hard plastic clad fibers (HPCF), or plastic optical fibers (POF) may be used. 
         [0061]    As in the ordinary MT ferrule, the optical fibers  31  do not interfere with, any parts of the ferrule  10 . The tips of the optical fibers  31  are cut by a fiber cutter, laser machining, arcing or any suitable means and left unpolished. In spite of the unpolished tips, the optical fibers  31  can be connected to the counterpart optical fibers of ordinary MT connectors or thin-film optical waveguides held in MPT connectors. 
         [0062]    In the disconnected state of the optical connector  1 , the tips of the optical fibers  31  slightly go backward inside the fiber guide holes  18  from the mating face  19  of the front part  10   a  of the ferrule  10 . The variation in the length of the optical fibers  31  and the retracted position from the mating face  19  are within 100 μm (corresponding to the distance “d” of the clearance) which range is the deformable and deformable range of the deformable mechanism  11 . 
         [0063]    During connection of the optical connector  1 , the optical fibers  31  slightly project from the fiber guide holes  18  and come into physical contact with the optical fibers of a counterpart connector. As described in the foregoing, the restrictors  25   a  and  25   b  of the deformable mechanism  11  prevent an excessive amount of buckling from being generated in the optical fibers  31  in the optical axis direction. Even if an external force is applied in the direction of alignment of the optical fibers  31 , the bending optical fibers  31  are held stably in the ferrule  10 . 
       [Modification 1] 
       [0064]      FIG. 7  illustrates in four orthogonal views a ferrule  40  which is a modification of the ferrule  10  illustrated in  FIG. 1 . Part (A) is a top view, part (B) is a side view, part (C) is a cross-sectional view taken along the B-B′ line of part (A), and part (D) is a front view. The basic structure of the ferrule  40 , including the design of the deformable mechanism  11 , is the same as that of the ferrule  10 , and redundant explanation for those elements denoted by the same numerical symbols will be omitted. Although not depicted, the cross-sectional structure taken along the A-A′ line of part (A) is also the same as that illustrated in  FIG. 2A  to  FIG. 2C . 
         [0065]    The different part in the ferrule  40  is recesses  40   e  formed in the front part  40   a  of the ferrule  40  at positions from which fiber guide holes  18  are extending. If a slight amount of offset (or a manufacturing error) exists in the guide pin receiving hole  17  or fiber guide holes  18 , neither optical fiber  31 A nor optical fiber  31 B can project from the mating face  49 , as illustrated in  FIG. 8A , during connection between optical connectors  1 A and  1 B. In this case, the optical fiber  31 A and the optical fiber  31 B may not come into physical contact due to gap “G” in spite of the fact that the angles of the end faces of the optical fibers  31 A and  31 B are within the acceptable range for physical-contact (PC) connection under a buckling load. 
         [0066]    To avoid this, a recess  40   e  is provided to a corresponding one of the fiber guide holes  18 , at or near the mating face  49  of the ferrule  40 , as illustrated in  FIG. 8B . With the recesses  40   e,  the optical fiber  31 A and the counterpart optical fibers  31 B can be brought into physical contact even if a slight amount of offset is contained in the fiber guide holes  18 . 
       Second Embodiment 
       [0067]      FIG. 9  illustrates in four orthogonal views a ferrule  50  used in an optical connector according to the second embodiment. Part (A) is a too view, part (B) is a side view, part (C) is a cross-sectional view taken along the E-E′ line of part (A), and part (D) is a front view. 
         [0068]    The ferrule  50  has a deformable mechanism  51 . The deformable mechanism  51  has a pair of beams  53   a  and  53   b  extending obliquely between a first restricting member  12  and a second restricting member  14 . 
         [0069]    Unlike the beam  13  illustrated in  FIG. 2B , the beams  53   a  and  53   b  are separately positioned at a lower part and an upper part in the height “h” direction of the ferrule  50 . In the example of  FIG. 9 , the beam  53   a  is positioned at a lower part and the beam  53   b  is positioned at an upper part in the height direction of the ferrule  50 . A guide pin P depicted by the dashed line in the cross-sectional view of part (C) passes through the space between the upper beam  53   b  and the lower beam  53   a.  It is unnecessary to form a guide pin receiving hole in the beam  53   a  or the beam  53   b.    
         [0070]      FIG. 10  is a cross-sectional view of the beam  53   a  taken along the A-A′ line of part (A) of  FIG. 9 . The beam  53   a  is connected to the first restricting member  12  and the second restricting member  14  under the position of the guide pin P. The other beam  53   b  is connected to the first restricting member  12  and the second restricting member  14  above the position of the guide pin P as illustrated in part (B) and part (C) of  FIG. 9 . By inserting the guide pin between the beams  53   a  and  53   b,  the deformable mechanism  51  is easy to deform. 
         [0071]    The structures of the restrictors  25   a  and  25   b  are the same as those illustrated in  FIG. 2A . Although the deformable mechanism  51  is designed so as to be more deformable, the restrictors  25   a  and  25   b  prevent excessive amounts of buckling stress from being applied to the optical fibers  31 . Breakage of the optical fibers can be prevented advantageously as in the first embodiment. 
       Third Embodiment 
       [0072]      FIG. 11  illustrates in four orthogonal views a ferrule  60  used in an optical connector according to the third embodiment. Part (A) is a top view, part (B) is a side view, part (C) is a cross-sectional view taken along the F-F′ line of part (A), and part (D) is a front view of the ferrule  60 , 
         [0073]    The ferrule  60  has a front part  60   a  with a mating face  69 , a rear part  60   b,  and an opening  60   c . Fiber guide holes  18  and guide pin receiving holes  67  are formed in the front part  60   a.  Fiber guide holes  18  and guide pin receiving holes  66  are formed in the rear part  60   b  of the ferrule  60 . 
         [0074]    A deformable mechanism  61  is provided between the front part  50   a  and the rear part  60   b  of the ferrule  60 . Two deformable mechanisms  61  are positioned symmetrically with respect to the insertion axis (or the Y axis) of the ferrule  60 . The deformable mechanism  61  includes a first restricting member  62 , a second restricting member  64 , and a beam  63  obliquely extending between the first restricting member  62  and the second restricting member  64 . In this example, the first restricting member  62  is positioned at a lower part in the height “h” direction of the ferrule  60  and extends from the front part  60   a  to the rear part  60   b . The second restricting member  64  is positioned at an upper part in the height “h” direction of the ferrule  60  and extends from the rear part  60   b  to the front part  60   a.    
         [0075]    The deformable mechanism  61  has restrictors  75   a  and  75   b.  The restrictor  75   a  has a protrusion  62   a  formed on the end face of the first restricting member  62  and a recess  81  formed in the rear part  60   b  of the ferrule  60 . The restrictor  75   b  has a protrusion  64   a  formed on the end face of the second restricting member  64  and a recess  82  formed in the front part  60   b  of the ferrule  60 . In the third embodiment, the protrusions  62   a  and  64   a  and the recesses  81  and  82  extend parallel to the line of the optical fibers or fiber guide holes  18 . 
         [0076]    The beam  63  connects obliquely between the first restricting member  62  positioned at or near the bottom and the second restricting member  64  positioned at or near the top of the ferrule  60 . A guide pin receiving hole  65  is formed in the beam  63 . 
         [0077]      FIG. 12A  is a cross-sectional view taken along the A-A′ line of part (A) of  FIG. 11 . The guide pin receiving hole  65  is formed in the beam  63  extending between the first restricting member  62  and the second restricting member  64 . The diameter of the guide pin receiving hole  65  is equal to or less than the diameter of the guide pin receiving hole  66  formed in the rear part  60   b,  and greater than the diameter of the guide pin receiving hole  67  of the front part  60   a  of the ferrule  60  (see  FIG. 11 ). 
         [0078]      FIG. 12B  illustrates a modification of the beam  63 . In the modification, a pair of beams  73   a  and  73   b  extend parallel to each other between the first restricting member  62  and the second restricting member  64 . The beam  73   a  and the beam  73   b  extend obliquely between the first restricting member  62  and the second restricting member  64  as illustrated in Part (C) of  FIG. 11 , while forming a space to receive a guide pin. 
         [0079]    The guide pin is inserted between the beam  73   a  and the beam  73   b  at the position P of the circle indicated by the dashed line. It is unnecessary for this arrangement to form guide pin receiving holes in the beams  73   a  and  73   b.  In this example, thin beams  73   a  and  73   b  are used and the deformable mechanism  61  is easy to move or deform, while excessive displacement or deformation is prevented by the restrictors  75   a  and  75   b.    
         [0080]      FIG. 13  is a schematic diagram illustrating optical interconnect  100  to which optical connectors of the embodiments (including the modifications) are applied. An optical transmission path  103  is formed on a backplane board  101 , and optical connectors  102  are arranged at designated positions. 
         [0081]    Multiple boards  110  are connected to the backplane board  101  in parallel to each other. On the board  110  are mounted electronic or optoelectronic devices such as an LSI chip  120 , a memory  115 , an optical-to-electric and electric-to-optical (abbreviated as “OE/EO”) converter module  117 . An optical connector  112  is provided at the edge of the board  110 . An optical transmission path  113  is provided between the optical connector  112  and the OE/EO converter module  117 , and electric interconnects  116  are provided between the OE/EO converter module  117  and the LSI chip  120  or the memory  115 . 
         [0082]    Each of the boards  110  is connected to the backplane board  101  in a disconnectable manner. When expanding the system or carrying out maintenance, the optical connector  112  is disconnected from the optical connector  102  and the board  110  is removed from the backplane board  101 . 
         [0083]    The connectors  102  and  112  may use any types of ferrules  10 ,  40 ,  50  and  60  described in the embodiments and modifications. Any types of the structures can prevent an excessive quantity of external force from being applied, to the optical fibers so as not to exceed a predefined deformation (e.g., 100 μm) even if too much load is applied in the ferrule inserting direction or the fiber aligning direction during connection or disconnection. The optical connectors of the embodiments may be connected to existing MT connectors or PMT connectors. 
         [0084]    The structures of the first embodiment through the third embodiment may be combined with each other. The recess ( FIG. 7 ) of the modification 1 may be applied to the ferrule of the second embodiment or the third embodiment. In the embodiment the restrictor  25   a  is provided between the deformable structure  11  and the rear part  10   b  of the ferrule  10  and the restrictor  25   b  is provided between the deformable structure  11  and the front part  10   a  of the ferrule  10 . However, only one restrictor may be used. From the viewpoint of preventing stress on the optical fibers  31  in the fiber aligning direction, it is desired to provide restrictors  25   a  and  25   b  on either side of the ferrule, Ferrule  10 ,  40 ,  50  or  60  may be housed in a connector housing (not illustrated) and mated with a counterpart ferrule inside the connector housing. 
         [0085]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization, of such examples in the specification relate to a showing of superiority or inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.