Abstract:
A receptacle module capable of suppressing deterioration of characteristics of optical signals transmitted in optical fiber cables even when an external force is applied in a direction orthogonal to a longitudinal direction in a state where an optical fiber connector is attached in a receptacle. The reception module is provided with a receptacle having a first sleeve for holding in a detachable manner an optical fiber connector provided at end of an optical fiber cable, a second sleeve, and a window communicating the first and second sleeves and with an optical module held and fixed in the second sleeve. A projection of the optical module passes over the window to be positioned in the first sleeve and moves a ferrule a bit to press a spring when the connector is inserted in the first sleeve. The ferrule is moved to the right against the pushing force of the spring  21   a . The abutting force increases the connection load between the optical fiber cables.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a receptacle module for connecting optical fiber cables.  
           [0003]    Specifically, the present invention relates to a receptacle module into which an optical module provided with a light emitting element and/or a light receiving element is fixed by insertion and to a receptacle module into which an optical fiber connector is inserted to optically connect an optical fiber cable of an optical module and an optical fiber cable of the optical fiber connector.  
           [0004]    2. Description of the Related Art  
           [0005]    Known in the art is an optical fiber connection assembly obtained by positioning two optical fiber connectors to face each other and causing the end faces of the optical fiber cables to come into facial contact.  
           [0006]    An example of such an optical fiber connection assembly will be explained with reference to FIG. 1. The optical fiber connection assembly illustrated in FIG. 1 is comprised of an adapter  2  and optical fiber connectors la and lb as examples of MT-RJ connectors. The optical fiber connectors  1   a  and  1   b  are engaged by using the adapter  2  to bring the end faces of optical fiber cables  30   a  and  30   b  passing through these optical fiber connector  1   a  and  1   b  into facial contact with each other and thereby optically connect the optical fiber cables  30   a  and  30   b.    
           [0007]    The optical fiber cable  30   a , as illustrated in FIG. 3B, is provided with a plurality of, for example, four, optical fibers. FIG. 1 illustrates only one optical fiber among them.  
           [0008]    The adapter  2  has a first (left side) sleeve  10   a  for receiving the optical fiber connector  1   a  and a second (right side) sleeve  10   b  for receiving the optical fiber connector  1   b . The first sleeve  10   a  and the second sleeve  10   b  are formed integrally. The adapter  2  is formed is with a window  10   c  with an opening for communicating the two sleeves  10   a  and  10   b . A right front end of a left side ferrule  22   a  explained later and a left front end of a right side ferrule  22   b  are inserted into the opening of the window  10   c  so as to achieve stable positioning of the end faces of the optical fiber cables exposed at the end faces of these ferrules  22   a  and  22   b  at the position of this window  10   c.    
           [0009]    An engagement use opening  10   a   1  extending from the inside to the outside of the sleeve  10   a  is formed in the wall of the sleeve  10   a . When a latch  20   a   1  of a housing  20   a  is inserted in the engagement use opening  10   a   1 , the optical fiber connector  1   a  held in the sleeve  10   a  is fixed in place.  
           [0010]    The optical fiber connector  1   a  partially inserted in the inside space of the first sleeve  10   a  has the housing  20   a , a spring  21   a , and the ferrule  22   a.    
           [0011]    The housing  20   a  is shaped as a hollow cylinder with a bottom. The spring  21   a  and part of the ferrule  22   a  are contained in the hollow cylinder of the housing  20   a . The latch  20   a   1  and a guard shaped pressing portion  20   a   2  are provided on the outer wall of the housing  20   a  along an axial direction.  
           [0012]    The ferrule  22   a  is comprised of a middle large area part and small area parts on its two sides. The left small area part and the middle large area part are contained in the hollow cylinder of the housing  20   a , but the right small area part is passes through the opening of the housing  20   a  and is inserted into the opening of the window  10   c.    
           [0013]    The ferrule  22   a  is pressed to the right side by the spring  21   a  contained in the inside space of the housing  20   a , but the middle large area part abuts against the opening of the housing  20   a  and stops it there. Conversely, when a leftward pressing force is added to the right small area part, the ferrule  22   a  moves to the left side, but stops at a position balanced with the force of the spring  21   a.    
           [0014]    The optical fiber cable  30   a  passes through the inside of the housing  20   a  and is exposed at the end face of the right small area part of the ferrule  22   a . The other optical fiber cable  30   b  also posses through the inside of the housing  20   b  and is exposed at the end face of the left small area part of the ferrule  22   b.    
           [0015]    The optical fiber connector  1   b  is structured the same as the optical fiber connector  1   a.    
           [0016]    The end face of the right small area part of the ferrule  22   a  of the optical fiber connector  1   a  and the end face of the left small area part of the ferrule  22   b  of the optical fiber connector  1   b  are polished to a fiber protrusion so that they may be accurately physical connected. For example, a diameter of the mode field of the single mode optical fiber is about 10 μm. Therefore, it is necessary to very precisely process these end faces so as to prevent deterioration in the resistance to insertion loss and other various characteristics when connecting these optical fiber cables.  
           [0017]    When the housing  20   a  is pushed into the sleeve  10   a  until the guard shape pressing portion  20   a   2  abuts against the front end of the sleeve  10   a  and the latch  20   a   1  is fits in the engagement use opening  10   a   1  of the sleeve  10   a , the optical fiber connector  1   a  is inserted in the sleeve  10   a.    
           [0018]    The optical fiber connector  1   b  is similarly inserted in the sleeve  10   b.    
           [0019]    At this time, the right end face of the ferrule  22   a  and the left end face of the ferrule  22   b  abut against each other at an optical reference plane  40  at the substantial center of the window  10   c . Due to this connection, the spring  21   a  contained in the inside space of the housing  20   a  and the spring  21   b  contained in the inside space of the housing  20   b  are compressed. The spring  21   a  and the spring  21   b  are manufactured to substantially same characteristics and uniformly press against the end faces of the ferrule  22   a  and the ferrule  22   b  which they abut against so as to maintain the connection of the right end face of the ferrule  22   a  and the left end face of the ferrule  22   b.    
           [0020]    The right end face of the ferrule  22   a  and the front end of the optical fiber cable  30   a  exposed there are polished to a fiber protrusion. Similarly, the left end face of the ferrule  22   b  and the front end of the optical fiber cable  30   b  exposed there are polished to a fiber protrusion. Therefore, when the right end face of the ferrule  22   a  and the left end face of the ferrule  22   b  are connected, the end face of the optical fiber cable  30   a  and the end face of the optical fiber cable  30   b  directly contact each other and therefore the optical fiber cable  30   a  and the optical fiber cable  30   b  are optically connected.  
           [0021]    The connection load (stress) of the connecting part of the optical fiber cables  30   a  and  30   b  is defined by certain standards, for example, the Japan Industrial Standard (JIS standard). For example, in the case of a fiber transmission system optical fiber connector (FC) and a single fiber coupling connector (SC), it is prescribed that the load be 7.8 to 11.8 N, while in the case of a multiple fiber push on connector (MPO), it is prescribed that the load be 6.8 to 11.8 N.  
           [0022]    In addition to optical fiber connection assemblies connecting optical fiber connectors la and lb explained with reference to FIG. 1, direct connection of the optical module fixed in the receptacle and the optical fiber connector has been demanded. The principle is basically the same as the optical fiber connection assembly explained with reference to FIG. 1.  
           [0023]    The combination of a receptacle and optical module is referred to as a “receptacle module” in the present specification.  
           [0024]    A novel structure of a receptacle module enabling stable optical connection of the optical fiber cable of an optical fiber connector and the optical fiber cable of an optical module is being sought. The connection load for connection with an optical fiber cable in an optical module when inserting an MT-RJ connector in a receptacle module has not yet been stipulated, but a connection load of 7.8 to 11.8 N is being considered.  
         SUMMARY OF THE INVENTION  
         [0025]    An object of the present invention is to provide a receptacle module of a novel structure enabling stable optical connection between an optical fiber cable of an optical fiber connector and an optical fiber cable of an optical module.  
           [0026]    Another object of the present invention is to provide a receptacle module substantially free of deviation of optical positions of optically connected optical fiber cables and with little deterioration of characteristics of optical signals transmitted through the optical fiber cables even when an external force, vibration, or the like is applied to the receptacle module in a direction orthogonal to the axial direction in a state where the optical fiber connector is attached in the receptacle of the receptacle module.  
           [0027]    According to a first aspect of the present invention, there is provided a receptacle module having a receptacle having first and second sleeves formed at positions facing each other in an axial direction by way of a window and an optical module provided with at least one of a light receiving element and/or a light emitting element and a first optical fiber and having a projection for insertion through the window and a body for insertion into the second sleeve, the first optical fiber being exposed at an end face of the projection, wherein a length of the projection is formed to be substantially at least a length of the window in the axial direction, the end face of the projection positioned at an end face of the window at the first sleeve side or is positioned inside the first sleeve when the body of the optical module is fully inserted into the second sleeve, and the first sleeve receives an optical fiber connector having an the end face at which is exposed a second optical fiber is exposed for optical connection with the first optical fiber.  
           [0028]    Preferably, the surface of the first optical fiber exposed at the end face of the projection of the optical module is polished so as to connect with the second optical fiber by physical contact.  
           [0029]    More preferably, a connection load of at least 1.09 times the standard value of the connection load when optically connect two optical fiber connectors is applied to a connecting part of the first optical fiber and the second optical fiber when the optical fiber connector is inserted in the first sleeve.  
           [0030]    Still more preferably, a connection load of at least 8.5 N is applied.  
           [0031]    Preferably, the optical fiber connector is one having a ferrule through which the second optical fiber passes and is exposed at its end face, a housing holding the ferrule to be able to move in the axial direction, and a spring for pushing the ferrule in the housing toward the inside of the first sleeve.  
           [0032]    More preferably, the optical fiber connector is selected from an MT-RJ, MPO, SC, FC and MPX connectors.  
           [0033]    Preferably, the ferrule of the optical fiber connector is moved at least 0.5 mm at the end face of the projection of the optical module when the optical fiber connector is inserted in the first sleeve.  
           [0034]    According to a second aspect of the present invention, there is provided an optical fiber connection assembly having a receptacle having first and second sleeves formed at positions facing each other in an axial direction by way of a window; an optical module provided with at least one of a light receiving element and/or a light emitting element and a first optical fiber and having a projection for insertion through the window and a body for insertion into the second sleeve, the first optical fiber being exposed at an end face of the projection; and an optical fiber connector having a ferrule through which a second optical fiber cable passes and is exposed at its end face, a housing holding the ferrule to be able to move in the axial direction, and a spring for pushing the ferrule in the housing toward the inside of the first sleeve; wherein a length of the projection is formed to be substantially at least a length of the window in the axial direction; the end face of the projection positioned at an end face of the window at the first sleeve side or is positioned inside the first sleeve when the body of the optical module is fully inserted into the second sleeve; and the end faces of the first optical fiber and the second optical fiber are optically connected by a connection load of at least 1.09 times the standard value of the connection load when optically connect two optical fiber connectors when the optical fiber connector is inserted in the first sleeve.  
           [0035]    According to a third aspect of the present invention, there is provided a receptacle module comprising a receptacle having first and second sleeves spatially connected with each other and an optical module provided with at least one of a light receiving element and a light emitting element and an optical fiber, the optical fiber being exposed at an end face of the optical module and the optical module being fixed in the first sleeve of the receptacle; wherein the second sleeve of the receptacle receiving an optical fiber connector, an optical fiber being exposed at an end face of the optical fiber connector; and the optical module and the optical fiber connector being fixed with a load of at least 8.5 N at their end faces.  
           [0036]    According to a fourth aspect of the present invention, there is provided a receptacle module comprising a receptacle having first and second sleeves spatially connected with each other and an optical module provided with at least one of a light receiving element and a light emitting element and an optical fiber, the optical fiber being exposed at an end face of the optical module and the optical module being fixed in the first sleeve of the receptacle; wherein the second sleeve of the receptacle receiving an optical fiber connector, an optical fiber cable being exposed at an end face of the optical fiber connector; and the optical module and the optical fiber connector being fixed with a load of at least 1.09 times the lower limit of the standard load for connection of two optical fiber connectors.  
           [0037]    According to a fifth aspect of the present invention, there is provided a method for selecting a connection load applied to a connecting part of an optical module and an optical fiber connector having optical connectors to connect each other by physical contact, comprising: the connection load is selected as a value of at least 1.09 times the standard minimum value of the connection load when optically connect two optical fiber connectors. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]    These and other objects and features of the present invention will be more apparent from the following description given with reference to the accompanying drawings, wherein:  
         [0039]    [0039]FIG. 1 is a schematic sectional view of an adapter in a longitudinal (axial) direction when using the adapter to connect two optical fiber connectors;  
         [0040]    [0040]FIG. 2 is a schematic sectional view of a receptacle module in a longitudinal (axial) direction when connecting an optical fiber cable of an optical fiber connector and an optical fiber cable of an optical module by a receptacle in a first embodiment of the present invention;  
         [0041]    [0041]FIG. 3A is a schematic perspective view of the state before an optical fiber connector provided at an end of an optical fiber cable is attached to a receptacle in the second embodiment of the present invention,  
         [0042]    [0042]FIG. 3B is a front view of an end face of a ferrule of the optical fiber connector, and  
         [0043]    [0043]FIG. 3C is a front view of the receptacle with the optical module fixed thereto seen from the direction of attachment of the optical fiber connector;  
         [0044]    [0044]FIG. 4A is a sectional view of the receptacle of the second embodiment of the present invention,  
         [0045]    [0045]FIG. 4B is a sectional view of the optical module of the second embodiment of the present invention,  
         [0046]    [0046]FIG. 4C is a view of the state with the optical module fixed by insertion into a first sleeve of the receptacle, and  
         [0047]    [0047]FIG. 4D is a sectional view of the optical fiber connector;  
         [0048]    [0048]FIG. 5 is a schematic sectional view of the optical module shown in FIG. 3A and FIG. 4B;  
         [0049]    [0049]FIG. 6 is a schematic sectional view of an optical fiber connection assembly comprised of the receptacle module illustrated in FIG. 4C with the optical fiber connector inserted in it seen along the longitudinal direction;  
         [0050]    [0050]FIG. 7A is a graph of the relationship between the amount of movement of the ferrule and connection load, while  
         [0051]    [0051]FIG. 7B is a graph of the relationship between the return loss and the connection load;  
         [0052]    [0052]FIGS. 8A and 8B are graphs of the insertion loss measured for a plurality of samples of optical fiber cables of the optical fiber connector and the optical module illustrated in FIGS. 4C to  4 D of the single mode optical fiber (SMF) type and the grated index fiber (GIF) type;  
         [0053]    [0053]FIGS. 9A and 9B are graphs of the return loss measured for a plurality of samples of optical fiber cables of the optical fiber connector and the optical module illustrated in FIGS. 4C to  4 D of the single mode optical fiber (SMF) type and the grated index fiber (GIF) type;  
         [0054]    [0054]FIGS. 10A and 10B are graphs of the change of the insertion loss in 4ch optical fibers when using optical fiber cables of the optical connector and optical module illustrated in FIGS. 4C to  4 D of the SMF and GIF type, setting the wavelength λ of the optical signal to be transmitted at 1.31 μm, and repeatedly connecting and disconnecting the optical fiber connector to and from the receptacle;  
         [0055]    [0055]FIG. 11 is a graph of the change of the insertion loss in 4ch optical fibers when using optical fiber cables of the optical fiber connector and optical module illustrated in FIGS. 4C to  4 D of the SMF type and GIF type, setting the wavelength λ of the optical signal to be transmitted at 1.31 μm, and repeatedly connecting and disconnecting the optical fiber connector to and from the receptacle;  
         [0056]    [0056]FIGS. 12A and 12B are graphs of the change of the insertion loss in 4ch optical fibers in a case of causing side pull stress from various directions in the optical fiber connector attached to the receptacle illustrated in FIGS. 4C to  4 D;  
         [0057]    [0057]FIGS. 13A and 13B are graphs of the change of the insertion loss and the return loss in 4ch optical fibers when using optical fiber cables of the optical fiber connector and the optical module illustrated in FIGS. 4C to  4 D of the SMF type, setting the wavelength λ of the optical signal to be transmitted at 1.31 μm, and cyclically giving a temperature change to the receptacle with the optical fiber connector  1   a  attached;  
         [0058]    [0058]FIG. 14A is a graph of the connecting and disconnecting characteristics relating to the optical output of the laser diode shown in FIG. 5, while  
         [0059]    [0059]FIG. 14B is a graph of the connecting and disconnecting characteristics relating to the optical input sensitivity of the photo-detector shown in FIG. 5;  
         [0060]    [0060]FIG. 15A is a sectional view of the receptacle of the third embodiment of the present invention,  
         [0061]    [0061]FIG. 15B is a sectional view of an optical module of the third embodiment of the present invention,  
         [0062]    [0062]FIG. 15C is a view of the state where the optical module is fixed by insertion into a first sleeve of the receptacle, and  
         [0063]    [0063]FIG. 15D is a sectional view of the optical fiber connector;  
         [0064]    [0064]FIG. 16 is a sectional view of an optical fiber connection assembly comprised of the receptacle module illustrated in FIG. 15C and the optical fiber connector inserted in it;  
         [0065]    [0065]FIG. 17A is a sectional view of the receptacle of the fourth embodiment of the present invention,  
         [0066]    [0066]FIG. 17B is a sectional view of an optical module of the fourth embodiment of the present invention,  
         [0067]    [0067]FIG. 17C is a view of the state where the optical module is fixed by insertion into a first sleeve of the receptacle, and  
         [0068]    [0068]FIG. 17D is a sectional view of the optical fiber connector; and  
         [0069]    [0069]FIG. 18 is a sectional view of an optical fiber connection assembly comprised of the receptacle module illustrated in FIG. 17C and the optical fiber connector inserted in it. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0070]    First Embodiment  
         [0071]    First, a receptacle module according to a first embodiment of the present invention and an optical fiber connection assembly will be explained by referring to FIG. 2.  
         [0072]    [0072]FIG. 2 is a sectional view of a receptacle module according to the first embodiment of the present invention.  
         [0073]    In the present invention, the combination of a receptacle and an optical module is referred to as a “receptacle module” while the combination of the receptacle module with optical fiber connectors connected to connect the optical fibers is referred to as an “optical fiber connection assembly”.  
         [0074]    The receptacle module of the first embodiment illustrated in FIG. 2 is a combination of a receptacle  60  and an optical module  50 . The receptacle module of the first embodiment is designed for insertion of an optical fiber connector  1   a  for optical connection of the optical fibers of the optical fiber connector and the optical module.  
         [0075]    The optical fiber connector  1   a  is substantially the same as that explained with reference to FIG. 1.  
         [0076]    The receptacle  60  has a first (left side) sleeve  60   a  for receiving the optical fiber connector  1   a  at a left side of the figure and a second (right side) sleeve  60   b  for receiving the optical module  50  in a fixed state. The first sleeve  60   a  and the second sleeve  60   b  are formed integrally. A window  60   c  is formed between them.  
         [0077]    The optical module  50  is comprised of a body  50   a  and a projection  50   b . The body  50   a  contains a laser diode or other light emitting element and/or a photo diode or other light receiving element and an amplification circuit and other electronic circuits. The projection  50   b  is inserted into the opening of the window  60   c . Its end face extends up to the end face of the window  60   c  at the first sleeve  60   a  side.  
         [0078]    In the first embodiment, the length (width) L 1  of the window  60   c  and the length L 2  of the projection  50   b  are equal. The lengths L 1  and L 2  are for example 0.5 mm. The end face of the projection  50   b  and the left side end face of the window  60   c  are in register. The part where they abut against the right end face of the ferrule  22   a  defines a reference plane  70 .  
         [0079]    Inside the projection  50   b  is inserted an optical fiber  220  extending up to the end face for optical connection to the optical fiber cable  30   a  of the optical fiber connector  1   a . The end face of the projection  50   b  and the optical fiber  220  exposed there are polished to a fiber protrusion.  
         [0080]    The body  50   a  of the optical module  50  is inserted into the second sleeve  60   b  until the surface of the body  50   a  where the projection  50   b  is formed abuts against the right end face of the window  60   c . The abutting of the surface where the projection  50   b  is formed with the right end face of the window  60   c  enables precise positioning of the front end of the projection  50   b  in the receptacle  60 .  
         [0081]    The receptacle  60  and the optical module  50  are normally used fixed to other members or portions.  
         [0082]    The first sleeve  60   a  of the receptacle  60  is formed with an engagement opening  60   a   1  communicating the inside with the outside.  
         [0083]    The method of insertion of the optical fiber connector  1   a  into the first sleeve  60   a  of the receptacle  60  is similar to the method of insertion of the optical fiber connector  1   a  into the first sleeve  10   a  explained with reference to FIG. 1.  
         [0084]    The optical module  50  is fixed by insertion to the second sleeve  60   b . The end face  50   a   1  of the projection  50   b  which is to be joined with the fiber protrusion polished right end face of the ferrule  22   a  of the optical fiber connector  1   a  is positioned at the end face of the window  60   c  at the optical fiber connector  1   a  side.  
         [0085]    The ferrule  22   a  is comprised of a middle large area part  22   a M, a left small area part  22   a L, and a right small area part  22   a R. The middle large area part  22   a M and the left small area part  22   a L move in the space (cylinder) inside a housing  20   a , so are referred to as “inside moving parts” in the present invention. The right small area part  22   a R moves outside the housing  20   a , so is referred to as an “outside moving part” in the present invention.  
         [0086]    The right outside moving part  22   a R of the ferrule  22   a  is pressed by the end face  50   a   1  of the projection  50   b  of the optical module  50 . The inside moving parts (middle large area part  22   a M and left small area part  22   a L) of the ferrule  22   a  are pressed to the right side by a spring  21   a  contained in the space inside the housing  20   a . The abutting faces of the end face of the right outside moving part  22   a R of the ferrule  22   a  and the end face  50   a   1  of the projection  50   b  of the optical module  50  is located on the optical reference plane  70 .  
         [0087]    The connection load due to the connection at the connecting part of the end face of the outside moving part  22   a R of the ferrule  22   a  pressed to the right side by the spring  21   a  and the end face  50   a   1  of the projection  50   b  of the optical module  50  is set to be the same as when connecting the ferrule  22   a  and ferrule  22   b  shown in FIG. 1. For example, in the case of FC and SC connectors, it is 7.8 to 11.8 N, while in the case of MPO connectors, it is 6.8 to 11.8 N. The standard value for an MT-RJ connector has not yet been determined, but here it is assumed to be the same as the case of an SC connector or a range of 7.8 to 11.8 N.  
         [0088]    The amount of movement of the receptacle module and optical fiber connection assembly of the first embodiment illustrated in FIG. 2 is about 0.22 mm shown by the point A in FIG. 7A. The connection load at that time is about 8 N or satisfying the standard.  
         [0089]    Next, an explanation will be given of a case of occurrence of so-called side pull stress and/or vibration (sideward tensile stress and/or vibration) resulting in external force being applied to the optical fiber connection assembly in a direction orthogonal to the axial direction, for example, the direction indicated by an arrow A in FIG. 2, in a state where the optical fiber connector is attached to the adapter illustrated in FIG. 1 or a state where the optical fiber connector is attached to the receptacle illustrated in FIG. 2.  
         [0090]    In an optical fiber connection assembly using the adapter  2  shown in FIG. 1, the optical fiber connectors are not completely fixed with respect to the receptacle and are pressed by springs, so when one of the optical fiber connectors side pull stress and/or vibration, the other can move slightly to maintain the connection between the optical fibers. Since springs  21   a  and  21   b  are inserted into both of the optical fiber connectors  1   a  and  1   b  and the two springs press against each other, the connection load is load and therefore the connecting faces seldom shift from each other and communication of optical signals is not hindered.  
         [0091]    However, when connecting an optical fiber connector  1   a  to a receptacle module of the first embodiment shown in FIG. 2 where the optical module  50  and the receptacle  60  are positioned and fixed at predetermined locations, if the external force and/or vibration or the like is applied to the optical fiber connector  1   a  in the direction A orthogonal to the longitudinal direction, only the optical fiber connector  1   a  will move or vibrate in the direction in which the external force and/or vibration or the like is applied. The optical module will not move. Further, a spring  21   a  is only inserted in the optical fiber connector  1   a . Even when the optical module  50  is connected with the receptacle by for example a spring mechanism, the two move as one part in the connected state. As a result, if the elastic force of the spring  21   a  contained in the housing  20   a  of the optical fiber connector  1   a  is not sufficiently strong or if a spring  21   a  having a performance near the lower limit of the standard for the optical fiber cable  1   a  is used, due to the weakness of the connecting force, positional deviation or a clearance will occur at the connecting parts of the end face of the outside moving part  22   a R of the ferrule  22   a  and the end face  50   a   1  of the projection  50   b  of the optical module  50 .  
         [0092]    When considering such a side pull stress, a minimum load when using an MT-RJ connector of about 1.09 times the minimum 7.8 N of an SC connector, that is, about 8.5 N, is believed necessary. As shown by the point A of FIG. 7, the connection load of the receptacle module of FIG. 2 is about 8 N. This cannot be the to be a sufficient connection load for return loss.  
         [0093]    Second Embodiment  
         [0094]    A receptacle module according to a second embodiment of the present invention overcoming the problem of the first embodiment and an optical fiber connection assembly using the same will be explained next by referring to FIG. 3 to FIG. 6.  
         [0095]    [0095]FIG. 3A is a schematic perspective view of the state before an optical fiber connector  1   a  provided at an end of an optical fiber cable  30  is attached to a receptacle  160  in the second embodiment of the present invention, FIG. 3B is a front view of an outside moving part (right small area portion)  22   a   3  of the ferrule  22   a  of the optical fiber connector  1   a , and FIG. 3C is a front view of the receptacle  160  with the optical module  150  fixed thereto seen from the direction of attachment of the optical fiber connector  1   a.    
         [0096]    [0096]FIG. 4A is a sectional view of the receptacle  160 , FIG. 4B is a sectional view of the optical module  150 , FIG. 4C is a view of the state with the optical module  150  fixed by insertion into a first sleeve  160   b  of the receptacle  160 , and FIG. 4D is a sectional view of the optical fiber connector  1   a.    
         [0097]    [0097]FIG. 5 is a schematic sectional view of the optical module shown in FIG. 3A and FIG. 4B.  
         [0098]    [0098]FIG. 6 is a schematic sectional view of an optical fiber connection assembly comprised of the receptacle module illustrated in FIG. 4C with the optical fiber connector  1   a  inserted in it seen along the longitudinal direction.  
         [0099]    As illustrated in FIG. 3A and FIG. 4C, the receptacle module of the second embodiment is comprised of the receptacle  160  and the optical module  150  fixed by insertion into the receptacle  160 .  
         [0100]    The optical fiber connection assembly of the second embodiment, as illustrated in FIG. 6, is comprised of the receptacle module and the optical fiber connector  1   a  inserted into it.  
         [0101]    The receptacle  160  exhibits a rectangular cross section as illustrated in FIG. 3A and, as shown in FIG. 4A, has a first sleeve  160   a  for receiving the optical fiber connector  1   a  and a second sleeve  160   b  receiving and fixing the optical module  150 . The first sleeve  160   a  and the second sleeve  160   b  are formed integrally. A window  160   c  is formed between the sleeves  160   a  and  160   b  along the axial line direction. An engagement use opening  160   a   1  is formed in the wall above the sleeve  160   a.    
         [0102]    The axial line in the present specification means the line along the center axial line of the optical fiber cable  30   a  inserted into the optical fiber connector  1   a.    
         [0103]    The optical module  150 , as illustrated in FIG. 4B, has a body  150   a  and a projection  150   b  projecting out from the body  150   a  in the axial direction.  
         [0104]    As illustrated in FIG. 3C, the end face of the projection  150   b  is rectangular in shape and has a cross-section of the same size as the outside moving part (small area part)  22   a R of the ferrule  22   a  illustrated in FIG. 4D. The body  150   a  also has a rectangular cross-section.  
         [0105]    As illustrated in FIG. 3C, the end face  220  of the projection  150   b  has two guide pin holes  230  at the both sides of the optical fiber  220  at positions matching with the positions of two guide pin holes  22   h  formed at the both sides of the optical fiber  30   a  at the end face of the outside moving part  22   a R of the ferrule  32   a  illustrated in FIG. 3B.  
         [0106]    The optical fiber connector  1   a  illustrated in FIG. 4D is an MT-RJ connector having a housing  20   a , a spring  21   a , and a ferrule  22   a.    
         [0107]    The housing  20   a  has a rectangular cross section as illustrated in FIG. 3A and, as illustrated in FIG. 4D, has a rectangular space formed with an opening  20   a O at one end. The portion of the opening  20   a ) of the inside space of the housing  20   a  is formed smaller than the size of the middle large area part  22   a M of the ferrule  22   a.    
         [0108]    The inside space of the housing  20   a  contains the spring  21   a  and the inside moving parts (left small area part  22   a L and middle large area part  22   a M) of the ferrule  22   a.    
         [0109]    The outside wall of the housing  20   a  is provided along the axial direction with a latch  20   a   1  and a guard shaped pressing part  20   a   2 . The latch  20   a   1  is gently inclined in the direction of advance (right side of the figure) so as not to hinder the insertion when inserting the optical fiber connector  1   a  into the sleeve  160   a  of the receptacle  160  and has a face in the reverse direction to the direction of advance (left side of the figure) forming a right angle or sharp incline so that the optical fiber connector  1   a  becomes hard to detach from the sleeve  160   a  when the latch  20   a   1  is inserted engaged with the engagement use opening  160   a   1  of the sleeve  160   a . The guard shaped pressing part  20   a   2  is used when connecting and disconnecting the optical fiber connector  1   a  to and from the receptacle  160 .  
         [0110]    The optical fiber cable  30   a  penetrates through the inside of the housing  20   a . The optical fiber cable  30   a , as shown in FIG. 3B, is provided with a plurality of, for example, four, optical fibers. FIG. 4D illustrates only one optical fiber among them.  
         [0111]    The ferrule  22   a  having the rectangular cross-section is comprised of “inside moving parts” consisting of a middle large area part  22   a M and a left small area part  22   a L inserted in the space inside the housing  20   a  and moving in the inside space and a “outside moving part”  22   a R consisting of a right small area part  22   a R passing through the opening  20   a  of the housing  20   a  to project out from the opening  20   a O and moving outside of the housing  20   a.    
         [0112]    In the example shown in FIG. 4D, the left small area part  22   a L has a sectional area smaller than the middle large area part  22   a M, but the shape (sectional area) of the left small area part  22   a L may also be made the same shape (sectional area) as the middle large area part  22   a M.  
         [0113]    The left small area part  22   a L of the ferrule  22   a  is pressed by the spring  21   a , but the right side of the middle large area part  22   a M abuts against the edges of the opening  20   a O to stop there. Conversely, when the outside moving part  22   a R is pressed by the projection  150   b ′ of the optical module  150 A, the ferrule  22   a  moves to the left side, but stops at the position balanced with the force of the spring  21   a . In this way, the middle large area part  22   a M of the ferrule  22   a  is inserted in the inside space of the housing  20   a  movably in the axial direction.  
         [0114]    The optical fiber cable  30   a  passing through the housing  20   a  passes through the spring  21   a  and the inside of the ferrule  22   a  and be exposed at the end face of the outside moving part  22   a R. The optical fiber cable  30   a  can therefore be optically connected with the front end of an optical fiber  220  exposed at the end face of the projection  150   b  to be connected with.  
         [0115]    As illustrated in FIG. 3B, the end face of the outside moving part  22   a R of the ferrule  22   a  is formed with two guide pin holes  22   h  at the both sides of the optical fiber  30   a  at positions matching with the positions of the guide pin holes  230  formed in the end face of the projection  150   b  illustrated in FIG. 3C.  
         [0116]    When guide pins are inserted into the guide pin holes  230  formed in the end face of the projection  150   b  and the guide pin holes  22   h  formed in the end face of the outside moving part  22   a R of the ferrule  22   a  of the optical fiber connector  1   a  is inserted into the first sleeve  160   a  of the receptacle  160 , the plurality of optical fibers  30   a  exposed at the end face of the outside moving part  22   a R of the ferrule  22   a  and the plurality of optical fibers  220  exposed at the end face of the projection  150   b  of the optical module  150  match connect.  
         [0117]    Further, a structure for obtaining precision of optical connection of the optical fibers in connection of the receptacle and housing and/or ferrule may of course also be applied.  
         [0118]    As illustrated in FIG. 5, the body  150   a  of the optical module  150  has two packages  207  and  208 . The two packages  207  and  208  carry a laser diode  204  as a light transmitting element, a photo-detector  205  as a light receiving element, and other optical elements. The package  208  is provided with various internal electronic circuits including the laser diode  204  and the photo-detector  205  and lead frame  210  for supplying power and signals to the internal electronic circuits. The lead frame  210  are connected to not illustrated external electronic circuits by not illustrated wiring.  
         [0119]    The left front edge of the package  207  is formed with the projection  150   b  having the same sectional shape as the outside moving part (right small area part)  22   a   3  of the ferrule  22   a.    
         [0120]    The projection  150   b  is formed with an optical fiber hole  207   k   2  extending from the end face  207   k   1  to the right end of a carrying part  202  and holding the optical fiber  220 .  
         [0121]    As illustrated in FIG. 4C, when the optical module  150 A is inserted into the second sleeve  160   b  of the receptacle  160  and the projection  150   b  is inserted in the opening of the window  160   c  and further the end face  207   a  of the package  207  on the projection  150   b  side abuts against the step face at the right side of the window  160   c  to come into facial contact, the insertion of the optical module  150  into the second sleeve  160   b  is stopped. The optical module  150  may be fixed to the receptacle  160  by adhesion or the optical module  160  may be fixed detachably to the receptacle  160  by engagement or another mechanical structure.  
         [0122]    A length L 2  (FIG. 5) of the projection  150   b  of the optical module  150  is longer than the length L 1  of the window  60   c  illustrated in FIG. 6 (L 2   a &gt;L 1 ), so the end face  207   k   1  of the projection  150   b  projects out from the window  160   c  to the inside of the sleeve  160   a . That is, the end face  207   k   1  of the projection  150   b  projects out to the inside of the sleeve  160   a  by exactly (L 2   a −L 1 ). For example, when the length L 1  of the window  160   c  is 0.5 mm and the length L 2   a  of the projection  150   b  is 0.8 mm in the illustrated example, the front end of the projection  150   b  projects out into the sleeve  160   a  by exactly 0.3 mm.  
         [0123]    Note that the length L 2  of the projection  50   b  of the optical module  50  illustrated in FIG. 2 is substantially the same length as the length L 1  of the window  60   c . For example, L 1 =L 2 =0.5 mm. Therefore, the projection  50   b  does not pass through the opening of the window  60   c  to project out into the sleeve  10   a.    
         [0124]    In the second embodiment, the explanation is given of the case where the length L 1  of the window  60   c  at the receptacle  60  illustrated in FIG. 2 and the length L 1  of the window  160   c  of the receptacle  160  illustrated in FIG. 4A are substantially the same.  
         [0125]    As illustrated in FIG. 4C, the optical module  150  is fixed in the receptacle  160  in the state where the projection  150   b  of the optical module  150  passes through the opening of the window  160   c  of the receptacle  160  and the front end of the projection  150   b  enters the sleeve  160   a . The optical module  150  and the receptacle  160  are fixed at predetermined positions (locations) when the optical module  150  is fixed inside the receptacle  160  in this way.  
         [0126]    Next, the attachment of the optical fiber connector  1   a  will be explained.  
         [0127]    Guide pins are inserted into the guide pin holes  230  illustrated in FIG. 3C. The housing  20   a  of the optical fiber connector  1   a  is then inserted into the first sleeve  160   a  so that the guide pins inserted in the guide pin holes  230  are inserted into the guide pin holes  22   h  of the outside moving part  22   a R of the ferrule  22   a.    
         [0128]    When the optical fiber connector  1   a  is deeply inserted into the first sleeve  160   a , as illustrated in FIG. 6, the end face of the outside moving part  22   a R of the ferrule  22   a  abuts against the end face  207   k   1  of the projection  150   b  of the optical module  150 .  
         [0129]    As illustrated in FIG. 6, when the housing  20   a  is pushed into the first sleeve  160   a  until the guard is shaped pressing part  20   a   2  of the housing  20   a  abuts against the front end of the first sleeve  160   a , the latch  20   a   1  enters the engagement use opening  160   a   1  of the sleeve  160   a  and the optical fiber connector  1   a  fixed in the sleeve  160   a.    
         [0130]    Note that when the optical fiber connector  1   a  is attached to the sleeve  160   a , a predetermined gap is required as a margin of safety between the front end of the housing  20   d  and the left side of the window  160   c . Without this margin, if the housing  20   d  also abuts against the left side of the window  160   c  when the projection  150   b  and the ferrule  22   a  abut, the elastic force of the spring  21   a  will not be able to be properly exhibited. The preferable value for this gap is for example 0.9 mm or so.  
         [0131]    In the second embodiment, the end face  207   k   1  of the projection  150   b  is positioned projecting out from the window  160   c  of the receptacle  160  into the first sleeve  160   a  along the axial direction by for example exactly (L 2   a −L 1 )=0.3 mm. Accordingly, the abutting position of the end face of the right small area part  22   a R of the ferrule  22   a  and the end face  207   k   1  of the projection  150   b  of the optical module  150  is located shifted into the first sleeve  160   a  by exactly 0.3 mm in comparison with the optical reference plane  70  illustrated in FIG. 2.  
         [0132]    At this time, the ferrule  22   a  is pressed by the projection  150   b , therefore the ferrule  22   a  presses against the spring  21   a  to compress it from the state of FIG. 4D to the state of FIG. 6. On the other hand, the ferrule  22   a  is pushed to the right side by the elastic force of the spring  21   a  and presses against the projection  150   b . In this way, the end face of the outside moving part  22   a R of the ferrule  22   a  and the end face  207   k   1  of the projection  150   b  come into facial contact.  
         [0133]    As illustrated in FIG. 3B and FIG. 4D, the front end of the optical fiber  30   a  protrude up to the end face of the outside moving part  23   a R of the ferrule  22   a . The front end of the optical fiber  30   a  of the outside having parts  22   a R are polished to a fiber protrusion for physical contact. Similarly, as illustrated in FIG. 3C, FIG. 4B, and FIG. 5, the front end of the optical fiber cable  220  protrude up to the end face of the projection  150   b . The front end of the optical fiber cable  30   a  of the end face of the outside moving part  22   a R are polished to a fiber protrusion for physical contact. Accordingly, when the end face of the outside moving part  22   a R of the ferrule  22   a  and the end face  207   k   1  of the projection  150   b  come into facial contact, the optical fibers  30   a  and the optical fibers  220  are physical connected by the elastic force of the spring  21   a.    
         [0134]    Next, the connection load (pressing force) at this time will be compared with that of the optical fiber connection assembly illustrated in FIG. 2. In the optical fiber connection assembly of this embodiment, the length of the projection  150   b  of the optical module  150  is longer than the length of the projection  50   b  of the optical module  50  illustrated in FIG. 2 and the ferrule  22   a  pushes the spring further to the left side to compress it, so when using a spring  21   a  having the same characteristics, the repulsion force of the spring  21   a  becomes large. Accordingly, the connection load (connecting force) at the end faces of the optical fiber  30   a  and the optical fiber  220  in the optical fiber connection assembly of the present embodiment becomes that much higher.  
         [0135]    The engagement of the latch  20   a   1  and the engagement use opening  160   a   1  may be released by pulling out the optical fiber connector  1   a  from the receptacle  160  in the state when pressing down the guard shaped pressing part  20   a   2  by the finger etc. to deform the pressing part  20   a   2 .  
         [0136]    Evaluation of Characteristics  
         [0137]    An optical fiber connection assembly using the receptacle module of the second embodiment explained with reference to FIG. 3 to FIG. 6 was evaluated for its characteristics. The results will be explained next.  
         [0138]    The optical fiber connection assembly evaluated was comprised of parts of the following specifications.  
         [0139]    1. Receptacle  160   
         [0140]    Material: PPS (polyphenyl sulfide)  
         [0141]    Total length: 23 mm  
         [0142]    First sleeve  160   a    
         [0143]    Inside width: 7.24 mm  
         [0144]    Inside height: 4.74 mm  
         [0145]    Length: 14 mm  
         [0146]    Opening of window  160   c    
         [0147]    Inside width: 4.51 mm  
         [0148]    Inside height: 2.56 mm  
         [0149]    Length L 1 : 0.5 mm  
         [0150]    2. Optical module  150   
         [0151]    Material: Epoxy resin  
         [0152]    Projection  150   b    
         [0153]    Width: 4.4 mm  
         [0154]    Height: 2.5 mm  
         [0155]    Length L 2 : 0.8 mm  
         [0156]    Optical fibers: Commercially available SiO 2  based fibers, quartz  
         [0157]    3. Optical fiber connector  1   a    
         [0158]    Housing  20   a    
         [0159]    Material: Polycarbonate  
         [0160]    Outer shape  
         [0161]    Width: 7.15 mm  
         [0162]    Height: 4.65 mm  
         [0163]    Length: 20.5 mm  
         [0164]    Inside shape  
         [0165]    Width: 5.6 mm  
         [0166]    Height: 3.3 mm  
         [0167]    Length: 15.3 mm  
         [0168]    Opening  
         [0169]    Width: 4.6 mm  
         [0170]    Height: 2.65 mm  
         [0171]    Length of inside space: 12.65 mm  
         [0172]    Ferrule  22   a    
         [0173]    Material: PPS (polyphenyl sulfide)  
         [0174]    Total length: 8.0 mm  
         [0175]    Middle large area part  22   a M  
         [0176]    Width: 5.0 mm  
         [0177]    Height: 3.05 mm  
         [0178]    Length: 2.0 mm  
         [0179]    Left small area part  22   a R  
         [0180]    Width: 5.0 mm  
         [0181]    Height: 3.05 mm  
         [0182]    Length: 2.0 mm  
         [0183]    Right small area part  22   a R  
         [0184]    Width: 4.4 mm  
         [0185]    Height: 2.5 mm  
         [0186]    Length: 6 mm  
         [0187]    Optical fibers: Commercially available SiO 2  based fibers, quartz  
         [0188]    [0188] 4 . Spring  21   a    
         [0189]    Material: SUS  304   
         [0190]    Diameter: 3.5 mm  
         [0191]    Length in natural state: 13.4 mm  
         [0192]    Spring coefficient (Young&#39;s modulus): 1.82 N/mm  
         [0193]    Relationship Between Amount of Movement of Ferrule and Connection Load  
         [0194]    [0194]FIG. 7A is a graph of the relationship between the amount of movement of the ferrule  22   a  (ordinate) and connection load (abscissa). FIG. 7B is a graph of the relationship between the return loss (ordinate) and the connection load (abscissa).  
         [0195]    From these graphs, in a configuration where an MT-RJ connector  1   a  illustrated in FIG. 4D is inserted into a receptacle module illustrated in FIG. 4C, when considering the side pull stress or vibration, a minimum connection load of about 8.5 N is required for reducing the return loss. That is, at least 1.09 times the minimum connection load of 7.8 N when connecting optical fiber connectors illustrated in FIG. 1 is considered required.  
         [0196]    In the first embodiment illustrated in FIG. 2, as shown by the point A, the ferrule  22   a  is pushed 0.2 mm to the left side. The connection load at this time is about 8 N. This connection load does not reach the minimum connection load of 8.5 N when considering the above side pull stress or vibration.  
         [0197]    As opposed to this, in the second embodiment illustrated in FIG. 3 to FIG. 6, the amount of movement of the ferrule  22   a  in the receptacle module illustrated in FIG. 2 was 0.3 mm greater. That is, in the above example, the ferrule  22   a  of the second embodiment moves about 0.5 mm. As shown by the point B of FIG. 7A, the connection load when the ferrule  22   a  is pushed 0.5 mm to the left is about 8.8 N. This is greater than the minimum connection load of 8.5 N when considering the above side pull stress or vibration.  
         [0198]    With such a connection load, even when an external force is applied to the optical fiber connector  1   a  and the receptacle  160  in a direction orthogonal to the axial direction, that is, the direction of the arrow A of FIG. 6, it is possible to suppress deviation or a gap between the optical fiber cable  30   a  and the optical fiber cable  220 .  
         [0199]    Therefore, according to the receptacle module (optical fiber connection assembly) of the second embodiment, a reduction of the characteristics of the optical signals input and output to and from the optical module  150  through the optical fiber cables  30   a  and  220  can be avoided.  
         [0200]    Insertion Loss  
         [0201]    [0201]FIG. 8A is a graph of the insertion loss measured for  144  samples of optical fiber cables  30   a  and  220  of the single mode optical fiber (SMF) type. The abscissa indicates the insertion loss (dB), while the ordinate indicates the number of samples.  
         [0202]    Note that, “insertion loss” means, as illustrated in FIG. 6, the insertion loss of an optical signal at a connecting part when inserting an optical fiber connector  1   a  holding an optical fiber  30   a , illustrated in FIG. 6, and a projection  150   b  of an optical module  150  holding an optical fiber  220  into a receptacle  160  so as to optically connect the right end face of the optical fiber cable held in the optical fiber connector  1   a  and the left end face of the optical fiber cable held in the projection  150   b . As the wavelength of the optical signal, for example, 1.31 μm was used.  
         [0203]    [0203]FIG. 8B is a graph of the insertion loss measured for  112  samples of optical fiber  30   a  and  220  of the grated index optical fiber (GIF) type. The abscissa indicates the insertion loss (dB), while the ordinate indicates the number of samples.  
         [0204]    As shown in FIG. 8A, when using the SMF type, the insertion loss was within a range of 0.1 to 0.5 dB centered about 0.1 and 0.2 dB and the average was 0.23 dB.  
         [0205]    As shown in FIG. 8B, when using the GIF type, the insertion loss was within a range of substantially 0.1 and 0.2 dB in all of the  112  samples and the average was 0.08 dB.  
         [0206]    In this way, according to the receptacle module (optical fiber connection assembly) of the second embodiment, the insertion loss can be made sufficiently small.  
         [0207]    Return Loss  
         [0208]    [0208]FIG. 9A is a graph of the return loss measured for  174  samples of the optical fiber  30   a  and  220  of the SMF type, while FIG. 9B is a graph of the return loss measured for  96  samples of optical fiber  30   a  and  220  of the GIF type. In FIGS. 9A and 9B, the abscissa indicates the return loss (dB) in units of 2 dB, and the ordinate indicates the number of samples.  
         [0209]    “Return loss” indicates attenuation of the reflected light of an optical signal transmitted via the optical fiber  30   a  and  200  occurring at the connecting part of the end face of the right small area part  22   a R of the ferrule  22   a  of the optical connector  1   a  and the end face  207   k   1  of the projection  150   b  of the optical module  150 .  
         [0210]    As shown in FIG. 9A, when using the SMF type, the return loss was within a range of 36 to 54 dB and the average return loss was 44.4 dB.  
         [0211]    As shown in FIG. 9B, when using the GIF type, the return loss was within a range of 36 to 52 dB and the average return loss was 42.3 dB.  
         [0212]    In this way, according to the receptacle module (optical fiber connection assembly) of the second embodiment, the return loss can be made sufficiently small.  
         [0213]    Repeated Durability Characteristic  
         [0214]    [0214]FIG. 10A is a graph of the change of the insertion loss in the four parallel optical fibers illustrated in FIG. 3B and FIG. 3C using optical fiber  30   a  and  220  of the SMF type, setting the wavelength μ of the optical signal to be transmitted at 1.31 μm, and repeatedly connecting and disconnecting the optical fiber connector  1   a  to and from the first sleeve  160   a  of the receptacle  160  of the receptacle module 0 to 500 times.  
         [0215]    [0215]FIG. 10B is a graph of the change of the insertion loss in the four parallel optical fibers illustrated in FIG. 3B and FIG. 3C using optical fiber  30   a  and  220  of the GIF type, setting the wavelength λ of the optical signal to be transmitted at 1.31 μm, and repeatedly connecting and disconnecting the optical fiber connector  1   a  to and from the first sleeve  160   a  of the receptacle  160  of the receptacle module 0 to 500 times.  
         [0216]    In FIGS. 10A and 10B, the ordinate indicates the change of the insertion loss, and the abscissa indicates the number of times of attachment and detachment.  
         [0217]    As shown in FIG. 10A, when using the SMF type, for 0 to 500 cyclic connecting and disconnecting operations, the change of the insertion loss for all optical fibers of the optical fiber cables  30   a  and  220  was within a range of about 0.0 to about 0.3 dB.  
         [0218]    As shown in FIG. 10B, when using the GIF type, for 0 to 500 cyclic connecting and disconnecting operations, the change of the insertion loss for all optical fibers of the optical fiber cables  30   a  and  220  was within a range of about 0.0 to about 0.1 dB.  
         [0219]    [0219]FIG. 11 is a graph of the change of the insertion loss in the four parallel optical fibers illustrated in FIG. 3B and FIG. 3C using optical fiber  30   a  and  220  of the SMF type, setting the wavelength λ of the optical signal to be transmitted at 1.31 μm, and repeatedly connecting and disconnecting the optical fiber connector  1   a  to and from the first sleeve  160   a  of the receptacle  160  of the receptacle module 1500 to 2000 times.  
         [0220]    As shown in FIG. 11, when using the SMF type, for 1500 to 2000 cyclic connecting and disconnecting operations, the change of the insertion loss for all optical fibers of the optical fiber  30   a  and  220  was within a range of about 0.1 to about 0.15 dB.  
         [0221]    Side Pull Stress Characteristics  
         [0222]    [0222]FIG. 12B is a graph of the change of the insertion loss in the four parallel optical fibers of the optical fiber  30   a  and  220  illustrated in FIG. 3B and FIG. 3C in a case of causing side pull stress (sideward tensile stress, sideward tensile load) in the optical fiber connector  1   a  attached to the receptacle  160  in directions of 0°, 180°, 45°, 225°, 90°, 270°, 135°, and 315° as shown in FIG. 12A. In this case, use was made of optical fiber  30   a  and  220  of the SMF type, and the wavelength λ of the optical signal to be transmitted was set to 1.31 μm.  
         [0223]    In FIG. 12B, the abscissa indicates the angle (direction) of the side pull, the ordinate on the left side indicates the change of the insertion loss, and the ordinate on the right side indicates the return loss.  
         [0224]    As shown in FIG. 12B, the change of the insertion loss in this case (scale on the left side ordinate) becomes about −0.1 to about 0.05 dB, while the return loss (scale on the right side ordinate) becomes 40 to −50 dB.  
         [0225]    Note that, in the receptacle module of the first embodiment shown in FIG. 2, the change in the insertion loss was about 0.6 dB, and the change of the return loss was about −20 dB.  
         [0226]    In this way, according to the second embodiment, it is learned that in the state where side pull stress is applied, the change of the insertion loss was remarkably lowered and the change of the return loss was also improved.  
         [0227]    Temperature Characteristic  
         [0228]    [0228]FIG. 13A is a graph of the change of the insertion loss in the four parallel optical fibers illustrated in FIG. 3B and FIG. 3C when using optical fiber  30   a  and  220  of the SMF type, setting the wavelength λ of the optical signal to be transmitted at 1.31 μm, and cyclically giving a temperature change of a range of −40 to +85° C. to the receptacle  160  with the optical fiber connector  1   a  attached.  
         [0229]    [0229]FIG. 13B is a graph of the return loss in the four parallel optical fibers illustrated in FIG. 3B and FIG. 3C when using optical fiber  30   a  and  220  of the SMF type, setting the wavelength λ of the optical signal to be transmitted at 1.31 μm, and cyclically giving a temperature change of a range of −40 to +85° C. to the receptacle  160  with the optical fiber connector  1   a  attached.  
         [0230]    In FIG. 13A, the left side ordinate indicates the change of the insertion loss, the right side ordinate indicates the temperature, and the abscissa indicates the number of times of attachment and detachment per unit time (cycle).  
         [0231]    In FIG. 13B, the left side ordinate indicates the return loss, the right side ordinate indicates the temperature, and the abscissa indicates the number of times of attachment and detachment per unit time (cycle).  
         [0232]    As shown in FIG. 13A, the change of the insertion loss due to a cyclic change of the temperature in the range of −40 to +85° C. is within a range of about 0.02 to about 0.3 dB. Also, as shown in FIG. 13B, the return loss due to a cyclic change of the temperature in the range of −40 to +85° C. is within a range of about −46 to about −52 dB.  
         [0233]    Attachment and Detachment Characteristics of Laser Diode and Photo-detector  
         [0234]    [0234]FIG. 14A is a graph of the connecting and disconnecting characteristics relating to the optical output power change of the laser diode  204  shown in FIG. 5, in which the abscissa indicates the number of times of connecting and disconnecting, and the ordinate indicates the change in optical output.  
         [0235]    [0235]FIG. 14B is a graph of the connecting and disconnecting characteristics relating to the optical input sensitivity change of the photo-detector  205  shown in FIG. 5, in which the abscissa indicates the number of times of connecting and disconnecting, and the ordinate indicates the optical input sensitivity change.  
         [0236]    As shown in FIG. 14A, the change of the optical output of the laser diode  204  is within a range of about −0.1 to about 0 dB even with connecting and disconnecting 0 to 500 times.  
         [0237]    As shown in FIG. 14B, the change of the optical sensitivity of the photo-detector  205  is within a range of about −0.12 to about 0.05 dB even with connecting and disconnecting 0 to 500 times.  
         [0238]    As explained above, the characteristics of the receptacle module of the present embodiment are as good as when connecting the freely movable optical fiber connectors shown in FIG. 1. Particularly, the side pull stress characteristics are greatly improved compared with the receptacle module (optical fiber connection assembly) of the first embodiment shown in FIG. 2.  
         [0239]    Third Embodiment  
         [0240]    Next, an explanation will be given of a receptacle module according to a third embodiment of the present invention and an optical fiber connection assembly using the same with reference to FIGS. 15A to  15 D and FIG. 16.  
         [0241]    [0241]FIG. 15A is a sectional view of the receptacle of the third embodiment of the present invention, FIG. 15B is a sectional view of an optical module of the third embodiment of the present invention, FIG. 15C is a view of the state where the optical module is fixed by insertion into a first sleeve of the receptacle, and FIG. 15D is a sectional view of the optical fiber connector.  
         [0242]    [0242]FIG. 16 is a sectional view of an optical fiber connection assembly comprised of the receptacle module illustrated in FIG. 15C and the optical fiber connector inserted in it.  
         [0243]    The third embodiment relates to an improvement of the receptacle module and optical fiber connection assembly of the first embodiment explained with reference to FIG. 2.  
         [0244]    The receptacle  160 A of the third embodiment, as shown in FIG. 15A, is formed with the position of the engagement use opening  160   a   1 ′ of the first sleeve  160   a ′ shifted to the right by exactly the distance of (L 2   a −L 1 ) in the second embodiment, for example, exactly 0.3 mm.  
         [0245]    The optical module  50  illustrated in FIG. 15B is similar to that of the first embodiment. That is, the length L 2  of the projection  50   b  of the optical module  50  is the same as the length (width) L 1  of the window  160 C or for example 0.5 mm. Therefore, when attaching the optical module  50  to the second sleeve  160   b  of the receptacle  60 A, as illustrated in FIG. 15C, the end face of the projection  50   b  registers with the left side face of the window  160   c . That position becomes the optical reference plane  70 . The positional relationship is the same as the state illustrated in FIG. 2.  
         [0246]    In the third embodiment, however, the position of the engagement use opening  160   a   1 ′ formed in the first sleeve  160   a   1  of the receptacle  160  is shifted to the right by for example exactly 0.3 mm, so when the optical fiber connector  1   a  the same as in the first and second embodiment illustrated in FIG. 15D is fully inserted into the first sleeve  60   a ′ and the latch  20   a   1  engages with the engagement use opening  60   a   1 ′, the ferrule  22   a  is pushed by the end face of the projection  50   b  by exactly 0.3 mm more than in the first embodiment.  
         [0247]    In this way, the amount of movement of the ferrule  22   a  due to being abutted against and pushed by the projection  50   b  becomes similar to that of the second embodiment explained with reference to FIG. 3 to FIG. 6.  
         [0248]    Therefore, the characteristics of the receptacle module of the third embodiment become the same as those explained with reference to FIG. 7 to FIG. 14.  
         [0249]    In the optical fiber connection assembly of the third embodiment, the gap between the left side face of the window  60   c  and the housing  20   a  becomes shorter than those of the first and second embodiments. The gaps in FIG. 2 and FIG. 6 were for example 0.9 mm, but the gap in FIG. 16 becomes shorter by exactly the length by which the engagement use opening  60   a   1 ′ is shifted to the right, for example, by exactly 0.3 mm, or becomes 0.6 mm.  
         [0250]    Fourth Embodiment  
         [0251]    Next, an explanation will be given of a receptacle module of a fourth embodiment of the present invention and an optical fiber connection assembly using the same with reference to FIGS. 17A to  17 D and FIG. 18.  
         [0252]    [0252]FIG. 17A is a sectional view of the receptacle of the fourth embodiment of the present invention, FIG. 17B is a sectional view of an optical module of the fourth embodiment of the present invention, FIG. 17C is a view of the state where the optical module is fixed by insertion into a first sleeve of the receptacle, and FIG. 17D is a sectional view of the optical fiber connector.  
         [0253]    [0253]FIG. 18 is a sectional view of an optical fiber connection assembly comprised of the receptacle module illustrated in FIG. 17C and the optical fiber connector inserted in it.  
         [0254]    The third embodiment relates to a modification of the receptacle module and the optical fiber connection assembly of the second embodiment explained with reference to FIG. 3 to FIG. 6. That is, the receptacle module and the optical fiber connection assembly of the fourth embodiment are configured resembling the receptacle module and the optical fiber connection assembly of the second embodiment explained with reference to FIGS. 4A to  4 D to FIG. 6.  
         [0255]    The receptacle  160 A of the fourth embodiment, as illustrated in FIG. 7A, has a length (width) L 1   a  of the window  160   c ′ changed from the for example L 1 =0.5 mm of the first and third embodiments to a length substantially equal to length L 2   a , for example, L 2   a= 0.8 mm, of the projection  150   b  of the optical module  150  illustrated in FIG. 17B, that is, a length L 1   a  of 0.8 mm. With the exception of the shortening of the depth of the first sleeve  160   a ′ by the increase in the length (width) L 1   a  of the window  160   c ′ (or the shortening of the depth of the second sleeve  160   b ), the configuration is the same as that of the receptacle module (optical fiber connection assembly) of the second embodiment.  
         [0256]    As illustrated in FIG. 17C, when attaching the optical module  150  in the second sleeve  160   b  of the receptacle  160 A, the front end face  207   k  of the projection  150   b  of the optical module  150  and the left side face of the window  160   c ′ come into register.  
         [0257]    The optical fiber connector  1   a  illustrated in FIG. 17D is the same as that illustrated in FIG. 4D.  
         [0258]    [0258]FIG. 18 is a sectional view of the state of attachment of the optical fiber connector  1   a  to the first sleeve  160   a ′ of the receptacle module illustrated in FIG. 17C.  
         [0259]    The position where the end face of the outside moving part  22   a  of the ferrule  22   a  abuts against the end face  207   k  of the projection  150   b  when the optical fiber connector  1   a  is inserted in the first sleeve  160   a ′ is the same as that in the second embodiment explained with reference to FIG. 3 to FIG. 6, so the connection load at the end faces of the optical fiber cable  30   a  of the optical fiber connector  1   a  and the optical fiber  220  of the projection  150   b  becomes the same as in the second embodiment. Therefore, the characteristics of the receptacle module of the fourth embodiment become the same as those explained with reference to FIG. 7 to FIG. 14.  
         [0260]    In the optical fiber connection assembly of the fourth embodiment, the left side face of the window  160   c ′ has a shorter gap with the housing  20   a . The gap in FIG. 6 was for example 0.9 mm, but the gap in FIG. 18 becomes shorter or 0.6 mm by exactly the amount of increase of length L 1   a  of the window  160   c   1 , for example, 0.3 mm.  
         [0261]    The above numerical values, for example, the dimensions of the optical fiber connection assembly, the materials of the optical fiber connection assembly, etc. were all illustrations. The present invention is not limited to these values or materials when being worked.  
         [0262]    The first to fourth embodiments of the present invention explained above illustrated various means of making the connection load between optical fibers for example more than 1.09 times that of the case of connecting optical fiber connectors together so as maintain the connection between optical fibers even in the face of side pull stress and lateral vibration and to prevent a reduction in the characteristics illustrated in FIG. 7 to FIG. 14 when optically connecting an optical fiber cable  30   a  in an MT-RJ connector, for example, various optical fiber connectors  1   a  with dimensions illustrated in FIG. 4A within standard limits, to the optical fiber  220  of the optical module.  
         [0263]    While the invention has been described with reference to specific embodiment chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.  
         [0264]    For example, in the above embodiments, as illustrated in FIGS. 3B and 3C, the explanation was given with reference to the case of using optical fiber  30   a  and  200  containing four optical fibers, but the present invention can also be applied to a case of using optical fiber cables containing a single optical fiber or two, three, or more than four optical fibers.  
         [0265]    Summarizing the effects of the present invention, as explained above, according to the receptacle module of the present invention and the optical fiber connection assembly using the same, even when the spring strength of the optical fiber connector is low, the connection between the optical fiber connector and the optical module in the receptacle can be made strong and even when external force is applied to a direction orthogonal to the longitudinal (axial) direction, deviation or a gap at the connecting part can be suppressed. As a result, the reduction of the characteristics of optical signals transmitted through the related connecting part can be prevented.  
         [0266]    The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-111933, filed on Apr. 7, 2000, the disclosure of which is expressly incorporated herein by reference in its entirety.