Abstract:
An optical fiber connector assembly has a holding member and a housing having a cavity for receiving the holding member. The holding member has a first surface, a second surface, grooves formed in the first surface for holding respective ferrules each supporting an optical fiber element, and through-holes for respectively receiving therethrough the optical fiber elements and for communicating the grooves with the second surface. The housing has a base surface, through-holes extending through the base surface, and side surfaces defining with the base surface a cavity for receiving the holding member so that the through-holes of the holding member are communicated with the through-holes of the housing for receiving therethrough the optical fiber elements.

Description:
This application is a division of application Ser. No. 09/383,654, file Aug. 26, 1999. U.S. Pat. No. 6,224,270, which is a division of application Ser. No. 08/891,901, file Jul. 14, 1997. U.S. Pat. No. 6,151,432. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to universal optical fiber connectors and their basic plugs, wherein the optical fiber connectors have some common elements for their connector-functions to permit an installation of optical fiber into one of the different type connectors for establishing their connector to connector connection more easily and to facilitate a tuning operation with positioning key maintaining the same direction between eccentricity of the fiber core and the key. 
     For the sake of clarity, in general, the technical term “optical fiber connectors” means all of elements where each of them is terminated on an end portion of an optical fiber. Conceptually, the optical fiber connector may be of any shape, such as a plug with a tip formed as a male member, an adapter with a tip formed as a female member, a combination thereof, or the like. 
     2. Description of Related Art 
     Heretofore, an optical fiber connector has the configuration in which a ferrule is coupled to a plug flame after fixing an optical fiber into the center of the ferrule to establish a connection between different optical fibers in opposite directions. 
     A FC-type plug as an example of such conventional optical fiber connector is depicted in FIG.  24 . As shown in the figure, the FC-type plug comprises a ferrule  101 , a frame  102 , and a tightening member  103 , with an integrated configuration of coaxially arranging these elements around a bare optical fiber  99  as the center thereof. Furthermore, there is a key ring  104  oriented along a direction of a displacement of the center of the bare optical fiber  99  fixed in the ferrule  101 . 
     For coupling the plugs  100  together, it is necessary to provide an adapter  201  for connecting plugs to its ends, respectively. The adapter  201  is comprised of a flange portion  202  and a cylindrical portion  203  in a one-piece design. An outer peripheral surface of the cylindrical portion  203  has a male screw thread  204  and a depressed portion  205 . Also, a mating slot  206  is concentrically formed in the center of the cylindrical portion  203 . In an inner side of the mating slot  206 , there is a separate sleeve  207  on which the ferrule  101  of the plug  100  is fit and attached in a removable manner. 
     For coupling the plug  100  with the adapter  201 , a positioning key  104   a  is engaged into the depressed portion  205  in addition to fitting the ferrule  101  of the plug  100  into the separate sleeve  207  of the adapter  201  to adjust their positions so as to be in their right places in a circumferential direction. Then a female thread  105   a  of a coupling nut  105  is screwed to a male screw thread  204 , so that the plug  100  is coupled to the adapter  201  tightly and thus it prevents them from becoming detached. 
     Up to the present, optical fiber connectors of the FC SC, ST type and so on with various connection forms have been commercially used. In this case, the different type optical fiber connectors are grouped together so as to put them to proper use. Under certain circumstances such as the changing of a system configuration, the need for the mutual connection between the different types of optical fiber connectors comes about and thus a converting adopter is required. Therefore, there are several problems including that many different type of converting adapters should be prepared so as to be used in the mutual connection and a quality of signal to be transmitted is decreased as an optical loss in optical transmission path is increased. 
     Conventionally, furthermore, it is very difficult to detach the key ring when it should be shifted in the right place to adjust eccentricity of the fiber core after the completion of the connector assembly. Depending on the connector type, moreover, the position of the key ring cannot be re-adjusted. 
     There may be cases where the optical fiber connector is fitted to an end portion of an optical fiber cable or an optical fiber code in installing the necessary wiring in building, mechanical system, or the like. In this case, optical fiber connectors of the FC, SC, ST type, and so on with various connection forms should be selected and combined to proper use depending on their applications. 
     Under certain circumstances, such as the changing of a system configuration, the need for the mutual connection between the different types of optical fiber connectors comes about and thus a converting adapter required. Therefore, there are several problems including that many different types of converting adapters should be prepared so as to be used in the mutual connection and a quality of signal to be transmitted is decreased as an optical loss in optical transmission path is increased. 
     In general, an adapter to be provided as a coupling portion of the optical fiber connector has two end portions, one for fixing on a fixing member such as a panel and the other for receiving a plug to be fixed to an optical fiber cable or the like. 
     There may be cases where a ferrule&#39;s tip of the plug fixed through the adapter requires cleaning for preventing a loss in the optical transmission path. However, there is a problem that it is very difficult to clean the ferrule&#39;s tip of the plug in a state of being coupled with the adapter. 
     To solve those problems laid open, Japanese Patent Application No. 122570/1996 discloses a tightening mechanism of plug that allows removal of a an adapter from its fixing member. 
     According to the above document, there is a problem that the method is costly performed because it requires an intricate structure for laterally fixing a standard type plug on a fixing member such as a panel in a special shape. 
     For using the optical fiber connector in installing the necessary wiring in a building or a mechanical system, as described above, the optical fiber connector should have an excellent strength against bending stress. 
     For use in various environments, the optical fiber connector should long term stability. 
     SUMMARY OF THE INVENTION 
     Therefore, a first object of the present invention is to provide a basic plug to solve the above problems in the conventional related art and to easily establish connection with an optical fiber without depending on the type of connector to cope with much more sophisticated devices. 
     A second object of the present invention is to provide a universal optical fiber connector to solve the above problems in the conventional related art and to easily establish connection with an optical fiber without depending on the type of connector to cope with much more sophisticated devices. 
     A third object of the present invention is to provide a jack-housing to solve the above problems in the conventional related art and to easily establish connection with an optical fiber without depending on the type of connector to cope with much more sophisticated devices. 
     A fourth object of the present invention is to provide a universal optical fiber connector that enables the user to clean a ferrule&#39;s head in spite of being fixed on a panel or the like. 
     A fifth object of the present invention is to provide a universal optical fiber connector that enables its end portion connecting with an optical fiber or the like to generate an excellent strength against bending stress. 
     A sixth object of the present invention is to provide a ferrule-holding member and a universal connector to be manufactured at low cost with the properties of rust free and good environmental stability. 
     In the first aspect of the present invention, a basic plug for connecting separate optical fibers together through a housing member comprises: 
     a ferrule having at least one common dimensional structure for securing an optical fiber; 
     a spring element being held so as to exert force against said ferrule in an axial direction; and 
     a cylindrical tube having a function of securing an optical fiber cable in which said optical fiber is embedded and a function of holding said spring element by sandwiching said spring element between said cylindrical tube and said ferrule, wherein 
     said basic plug has a shape that enables to engage said housing member and to connect said optical fiber to another optical fiber through said housing. 
     Here, the basic plug may further comprise an engaging member that includes: 
     a mating portion having a flange on at least a part of a periphery thereof, in which the rear end portion of said ferrule is fitted; 
     a long-sized cylinder portion coaxially arranged on said rear end portion of said ferrule, on which said spring element is held; and 
     an engaging portion to be engaged to said cylindrical tube formed on the rear end portion of said long-sized cylinder portion, wherein 
     said spring is held between said flange of said mating portion and said cylindrical tube by engaging said engaging portion to said cylindrical tube in addition to hold said engaging portion on a periphery of said continuous cylinder portion. 
     The engaging portion may be continuously formed on said long-sized cylinder portion and is provided as an engaging protrusion that protrudes outward and is inwardly deformable in a radius direction, and said engaging protrusion and said long-sized cylinder portion are able to insert in said cylindrical tube where an engaging hole in which said engaging protrusion is able to engage. 
     The insert-restricting portion for restricting an amount of inserting said long-sized cylinder portion to said cylindrical tube may be mounted on an outer peripheral surface of said long-sized cylinder portion. 
     The insert-restricting portion may be a protrusion or short-sized cylindrical tube having an outside shape thereof which is a slightly larger than an inner diameter of said cylindrical tube. 
     In the second aspect of the present invention a universal optical fiber connector, comprises: 
     a basic plug of the first aspect of the present invention, and 
     a housing member to be fitted on said basic plug. 
     Here, the housing member may incorporate a sleeve to be fitted on said ferrule, and also said housing member has an engaging portion on its tip portion on a side thereof opposite to a side of said basic plug, where said engaging portion conforms to various kinds of connector forms. 
     The plug housing may comprise: a key member for an alignment in a diagonal direction around an axis of said ferrule; and a plurality of engaging holes, and 
     said cylindrical tube of said basic plug has at least one elastic engaging piece, wherein 
     said elastic engaging piece is able to engage in a predetermined engaging hole selected from said plurality of said engaging holes at a time of inserting said cylindrical tube into said plug housing. 
     The plug housing may connect to a plug that conforms to various kinds of connector forms through an adapter that conforms to various kinds of connector forms to allow an optical connection between an optical fiber fixed in said ferrule and an optical fiber fixed in a ferrule in said plug. 
     The housing member may be an adapter housing having an engaging portion on its tip portion on a side thereof opposite to a side of said basic plug, and 
     said engaging portion is for engaging to another basic plug that conforms to various kinds of connector forms, wherein 
     at a time of engaging another basic plug in said engaging portion of said adapter housing, a ferrule of another basic plug is fitted into said sleeve to allow an optical connection between an optical fiber in said ferrule and said optical fiber in said ferrule of said basic plug. 
     The adapter housing may comprise: a key member for an alignment in a diagonal direction around an axis of said ferrule; and a plurality of engaging holes, and 
     said cylindrical tube of said basic plug has at least one elastic engaging piece, wherein 
     said elastic engaging piece is able to engage in a predetermined engaging hole selected from said plurality of said engaging holes at a time of inserting said cylindrical tube into said adapter housing. 
     On a side of said tip portion of said adapter housing, there may be a key member for an alignment in a diagonal direction around an axis of said ferrule of another basic plug; and a plurality of engaging holes, and 
     a cylindrical tube of another basic plug has at least one elastic engaging piece, wherein 
     said elastic engaging piece is able to engage in a predetermined engaging hole selected from said plurality of said engaging holes at a time of inserting said cylindrical tube into said adapter housing. 
     The adapter housing may be able to engage to a plurality of said basic plugs, and 
     a tip portion of said adapter housing has a plurality of engaging portion to be engaged to another basic plug. 
     The housing member may be a jack housing having an engaging portion on its tip portion on a side thereof opposite to a side of said basic plug, and 
     said engaging portion is for engaging to a plug that conforms to various kinds of connector forms, where 
     at a time of engaging another basic plug in said engaging portion of said jack housing, a ferrule of another basic plug is fitted into said sleeve to allow an optical connection between an optical fiber in said ferrule and said optical fiber in said ferrule of said basic plug. 
     The jack housing may comprise: a key member for an alignment in a diagonal direction around an axis of said ferrule; and a plurality of engaging holes, and 
     said cylindrical tube of said basic plug has at least one elastic engaging piece, wherein 
     said elastic engaging piece is able to engage in a predetermined engaging hole selected from said plurality of said engaging holes at a time of inserting said cylindrical tube into said jack housing. 
     The plug may be a plug that conforms to an optical fiber connector in a type of one selected from a group of FC, SC, and ST. 
     In the third aspect of the present invention, a jack housing for a universal optical fiber connector to be used for fitting to a basic plug of the first aspect of the present invention to allow an connection between said basic plug and a plug that conforms to various kinds of connector forms, comprises: 
     an sleeve integrated therein to be fitted to said ferrule; 
     an engaging portion formed on one side thereof to be engaged to said basic plug; and 
     an engaging portion formed on the other side thereof to be engaged to said plug that conforms to various kinds of connector forms, wherein 
     a ferrule of said plug is fitted in said sleeve when said plug is engaged to said engaging portion, allowing an optical connection between an optical fiber of said ferrule and said optical fiber in said ferrule of said basic plug. 
     Here, jack housing may comprise: a key member for an alignment in a diagonal direction around an axis of said ferrule; and a plurality of engaging holes, and 
     said cylindrical tube of said basic plug has at least one elastic engaging piece, wherein 
     said elastic engaging piece is able to engage in a predetermined engaging hole selected from said plurality of said engaging holes at a time of inserting said cylindrical tube into said jack housing. 
     The plug may be a plug that conforms to an optical fiber connector in a type of one selected from a group of FC, SC, and ST. 
     The housing member may have one end portion provided as a plug housing that conforms to various kinds of connector forms, wherein 
     a flange portion is formed on at least one part of an outer peripheral portion of said plug housing, for fixing said plug housing on a fixing member. 
     The plug housing may comprise: a key member for an alignment in a diagonal direction around an axis of said ferrule; and a plurality of engaging holes, and 
     said cylindrical tube of said basic plug has at least one elastic engaging piece, wherein 
     said elastic engaging piece is able to engage in a predetermined engaging hole selected from said plurality of said engaging holes at a time of inserting said cylindrical tube into said plug housing. 
     The plug housing may connect to a plug that conforms to various kinds of connector forms through an adapter that conforms to various kinds of connector forms to allow an optical connection between an optical fiber fixed in said ferrule and an optical fiber fixed in a ferrule in said plug. 
     The flange portion of said plug housing may have a hole for tightening with a thread member. 
     In the fourth aspect of the present invention, a universal optical fiber connector, comprises: 
     a basic plug as claimed in claim  1 ; an engaging ring for connecting an optical code tensile strength body to an outer peripheral portion of said basic plug; a plug housing for covering said ferrule and said basic plug; a hood having a securing hole for securing an optical code, where said hood fits on an outer peripheral portion of said plug housing and covers a connected portion of said optical code tensile strength body, said optical fiber connector further comprising: 
     a reinforcing pipe having one end portion to be fitted on an outside of said plug housing and the other end portion surrounding said engaging ring. 
     Here, the reinforcing pipe may be:placed on an inner peripheral portion of said hood. 
     In the fifth aspect of the present invention, a universal optical fiber connector, comprises: 
     a ferrule having at least one common dimensional structure for securing an optical fiber; 
     a forcing element made of rubber or elastomer, being held so as to exert force against said ferrule in an axial direction; and 
     a securing member for securing said forcing member for sandwiching said forcing element between said securing member and said ferrule; and 
     a connecting member for incorporating said securing member and for connecting to a plug or adapter of various kinds of connector forms. 
     Here, the connecting member may be a plug housing which is able to connect to an adapter that conforms to various kinds of connector forms. 
     The connecting member may be an adapter housing which is able to connect to an adapter that conforms to various kinds of connector forms. 
     In the sixth aspect of the present invention, a ferrule holding member comprises: 
     a ferrule having at least one common dimensional structure for securing an optical fiber; 
     a forcing element made of rubber or elastomer, being held so as to exert force against said ferrule in an axial direction; and 
     a securing member for securing said forcing member for sandwiching said forcing element between said securing member and said ferrule. 
     Here, securing member may be a cylindrical tube having a function of securing an optical fiber cable in which said optical fiber is integrated. 
     The forcing member may be shaped so as to hold a plurality of ferrules in parallel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     With the above and other objects in view that will better appear, the nature of the invention will be more clearly understood by the following detailed description, the appended claims and several views illustrated in the accompanying drawings. 
     In the drawings: 
     FIG. 1 is a perspective view of a universal optical fiber connector as a first embodiment of the present invention; 
     FIG. 2 is a cross sectional view of the universal optical fiber connector as the first embodiment of the present invention; 
     FIG. 3 is a cross sectional view of a hood used in the universal optical fiber connector in accordance with the present invention; 
     FIG. 4 is a perspective view of a universal optical fiber connector as a second embodiment of the present invention; 
     FIG. 5 is a perspective view of a universal optical fiber connector as a third embodiment of the present invention; 
     FIG. 6 is a perspective view that illustrates a system configuration of the optical fiber connector in accordance with the present invention; 
     FIG. 7 is a perspective view of a universal optical fiber connector as a fourth embodiment of the present invention; 
     FIG. 8 is a cross sectional view of a main part of the universal optical fiber connector as the fourth embodiment of the present invention; 
     FIG. 9 is a perspective view of a universal optical fiber connector as a fifth embodiment of the present invention; 
     FIG. 10 is a perspective view of a universal optical fiber connector as another example of the fifth embodiment of the present invention; 
     FIG. 11 is a perspective view of a universal optical fiber connector as a sixth embodiment of the present invention; 
     FIG. 12 is a perspective view of a universal optical fiber connector as a seventh embodiment of the present invention; 
     FIG. 13 is a cross sectional view of the universal optical fiber connector as the seventh embodiment of the present invention; 
     FIG. 14 is a perspective view of a universal optical fiber connector as another example of the seventh embodiment of the present invention; 
     FIG. 15 is a perspective view of a universal optical fiber connector as still another example of the seventh embodiment of the present invention; 
     FIG. 16 is a perspective view of a universal optical fiber connector as an eighth embodiment of the present invention; 
     FIG. 17 is a cross sectional view of the universal optical fiber connector as an eighth embodiment of the present invention; 
     FIG. 18 is a perspective view that illustrates an example using the optical fiber connector of the eighth embodiment of the present invention; 
     FIG. 19 is a cross sectional view of a universal optical fiber connector as a ninth embodiment of the present invention; 
     FIG. 20 is a perspective view of a universal optical fiber connector as a tenth embodiment of the present invention; 
     FIG. 21 is a cross sectional view of the universal optical fiber connector as the tenth embodiment of the present invention; 
     FIG. 22 is a perspective view of a universal optical fiber connector as an eleventh embodiment of the present invention; 
     FIG. 23 is a cross sectional view of the universal optical fiber connector as the eleventh embodiment of the present invention; and 
     FIG. 24 is a perspective view of a conventional optical fiber connector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, we will describe the embodiments of the present invention by way of example. 
     Embodiment 1 
     FIG. 1 is an exploded perspective view of a universal optical fiber connector as one of the embodiments of the present invention. FIG. 2 is a cross sectional plan view of the optical fiber connector shown in FIG. 1, where a plug housing and a basic plug are depicted as separated cross sections, respectively. 
     In FIGS. 1 and 2, the universal optical fiber connector  10  is in the type of FC and is comprised of a basic plug  20  in which an optical fiber cable  1  is being fitted and a FC plug housing  30  for accommodating the basic plug  20 . 
     The FC plug housing  20  comprises a thread-fastening member  32  fitted to a mating member  31  for receiving the basic plug  20  in a manner as described below. In addition, a key ring  33  (FIG. 1) is fixed on an outer peripheral surface of the mating member  31  by an appropriate means and is provided as an index key that has the function of adjusting direction of core eccentricity. The structure of fixing the key ring  33  on the mating member  31  is, for example a well-known conventional structure as shown in FIG.  24 . 
     The other end of a mating member  31 , which is on the side receiving the basic plug  20 , is formed as an insert end portion  34  in which a ferrule can be inserted. Furthermore, engaging slots  35  are formed in a peripheral surface of the insert end portion  34  at established intervals. In this embodiment, there are four engaging slots  35  allowing 90 degrees spacing. 
     The basic plug  20  comprises: a ferrule  21  in which the optical fiber  1  is being fixed; a tubular member  22  fixed on the rear end portion of the ferrule  21 , having brim portions  22 A and recess portions  22 B (i.e., the brim portion  22 A is an uppermost edge of the recess portion  22 B); and a cylindrical tube  24  which is fitted on the tubular member  22  and is able to slide thereon in the axial direction. Thus the basic plug  20  holds and fixes a terminal  1 A (FIG. 2) of the optical fiber cable  1  in the rear end of the cylindrical tube  24  by covering the rear end of the cylindrical tube  24  with a tensile-strength member  210  (FIG.  2 ), followed by bounding them together or cramping a tubular member  215  on the covered portion. It is noted that the ferrule  21  has at least one common dimensional structure for adapting to various kinds of connectors. 
     There is a spring coil  25  between the brim portion  22 A of the tubular member  22  and the cylindrical tube  24  to forcefully keep them separated by its spring tension. That is, the tubular member  22  and the ferrule  21  is constructed as a spring-floating structure in which they are spring-loaded toward a front end of the ferrule  21  with respect to the cylindrical tube  24 . 
     To be more specific in the present embodiment, a cylindrical portion  22 B is integrally formed on the rear end portion of the brim portion  22 A of the tubular member  22  and extended along the lengthwise direction of the cylindrical tube  24 . An outer peripheral surface of the rear end portion of the cylindrical portion  22 B has protrusions  22 C which are formed so as to be flexibly distorted inwardly along the diameter of the cylindrical portion  22 B. In the front end portion of the cylindrical tube  24 , there are formed square openings  213  into which the respective protrusions  22 C are inserted with a space enough to slide along the length width direction of the cylindrical tube  24 . If the tubular member  22  moves forward with respect to the cylindrical tube  24 , its movement is restricted by contact between the protrusion  22 C and a front side of the square opening  213 . 
     In a state of being free, the contact between the protrusion  22 C and the front side of the square opening  213  is maintained by pushing the tubular member  22  forward by an extending force of the spring coil  25 . If the tubular member  22  is forcefully pushed backward against the extending force of the spring coil  25 , the protrusion  22 C can slide along its axial direction in the opening  213  to shift the position of the ferrule  21  with respect to the cylindrical tube  24 . 
     In the present configuration, the movement of the ferrule  21  against the extending force of the spring coil  25  is limited by contacting the protrusion  22 C with the rear side of the square opening  213 . Alternatively, the restriction of an amount of the movement may be performed by forming an additional member around the cylindrical portion  22 B for restricting the movement and contacting the additional member with the opening&#39;s side portion of the cylindrical tube  24 . The additional member for restricting the movement may be, for example, selected from a protrusion formed around a peripheral surface of the cylindrical portion  22 B, a short cylinder formed between the long cylindrical portion  22 B and the spring coil  25 , and the like. 
     A spring-loaded engagement piece  27  is integrally formed on the other end (i.e., the rear end) portion of the cylindrical tube  24  and comprises a tongued strip  27 A provided by forming a U-shaped slit  26  in the peripheral surface of the cylindrical tube  24  and an engagement protrusion  27 B formed and extended on a free end of the tongued strip  27 A. Therefore, the engagement protrusion  27 B on that free end can be displaced in the outward or inward direction by an effect of elastic deformation of the tongued strip  27 A. In this embodiment, there are two tongued strips  27 A spaced apart 180 degrees in a circumferential direction of the cylindrical tube  24 . 
     The engagement protrusion  27 B has a wedge-shape and the thickness thereof is gradually increased toward an opposite end thereof, resulting in a substantial protrusion through the peripheral surface of the cylindrical tube  24 . If the basic plug  20  is gradually inserted into the plug housing  30  through the insert end portion  34 , the engagement protrusion  27 B contacts with an inner edge of the insert end portion  34  and is gradually pushed into the cylindrical tube  24  at the time of passing the engagement protrusion  27 B through the insert end portion  34 . Then the engagement protrusion  27 B is engaged into the engaging slot  35  by recovering its original state by the elasticity of the tongue piece  27 A when the engagement protrusion  27 B faces one of the engaging slot  35 . In this state, the basic plug  20  is coupled to the FC plug housing  30 . 
     In addition, a rectangular protruded region  211  is formed on an outer peripheral surface of the cylindrical tubular  24 , with 90 degrees deviation from the engagement protrusion  27 B along the circumferential direction of the cylindrical tube  24 , while a groove  214  to be matched with that protruded region  211  is formed in an inner surface of the FC plug housing  30 . As shown in the figure, there is a gradual decrease in thickness of a front end portion (i.e., formed as a tapered portion) of the protruded region  211  to smooth the path to engage with the groove  214 . Thus, inserting the basic plug  20  into the FC plug housing  30  leads to mate the groove  214  and the protruded region  211  together, resulting in restrictions on the relative turns of the basic plug  20  and the FC plug housing  30  in the directions of their circumferences, respectively. 
     For the step of inserting the basic plug  20  into the insert end portion  34  of the FC plug housing  30 , each structural element is designed to have predetermined dimensions so that the brim portion  22 A comes into contact with a flange  31 A (FIG. 2) in an inward direction of the mating member  31  prior to engagement of the engagement protrusion  27 B with the engaging slot  35 . Thus the spring coil  25  is being compressed when the engagement protrusion  27 B in engaged in any engaging slot  35 . If the mating member  31  and the cylindrical tube  24  are coupled together by engaging the engagement protrusion  27 B into the engaging slot  35 , an extending force of the spring coil  25  pushes the ferrule  21  against the flange  31 A, and subsequently the ferrule  21  is fixed into the flange  31 A and then housed therein. Namely, the FC plug housing and the basic plug  20  are in a state of established assembly. 
     For canceling the assembly state, the engaging protrusion  27 B is forcefully pushed down against an elastic force of the tongued strip  27 A that tends to push it up to release the engagement between the engagement protrusion  27 B and the engaging slot  35 , resulting that the cylindrical tube  24  is removed quickly from the mating member  31  by an extending force of the spring coil  25 , resulting in a release from the assembly state. 
     The process of adjusting the center of the key ring  33  and the direction of eccentricity of the fiber core so that they are in proper relative position can be attained by positioning the engagement protrusion  27 B relative to the mating member  31  in a circumferential direction. More specifically, for the alignment to lead them in the right place, a plurality of grooves  22 D are formed in an outer peripheral surface of the brim portion  22 A and also a plurality of keys  31 B (FIG. 2) to be fit into their respective grooves  22 D are protruded from an inner surface of the mating member  31 , configuring so-called directional coupling key elements. Therefore, the best relative position of the key ring  33  and the direction of core eccentricity can be adjusted by shifting a phase of fitting the key  31 B into the groove  22 B by turning them relatively in a circumferential direction. 
     The cylindrical tube  24  may be integrally formed by an injection molding press. For this process, it is preferable to use polyetherimide, glass-fiber reinforced plastic thereof, polybutyl terephthalate, or glass-fiber reinforced plastic thereof as a material in terms of its strength. 
     As described above, the universal optical fiber connector  10  shown in FIG. 1 is able to construct a FC-type optical fiber connector assembly designed to connect directly to the corresponding FC-type optical fiber connector assembly by fitting and holding the basic plug  20  in the FC plug housing  30 . As a matter of fact, the rear end of the assembled universal optical fiber connector  10  may be covered with a hood C as shown in FIG. 3 for protecting the connection from external forces including bending stress and twisting stress of the optical fiber cable. 
     Embodiment 2 
     FIG. 4 shows a cross sectional view of an optical fiber connector  10 ′ in the type of SC, where the basic plug  20  is the same one as that of shown in FIGS. 1 and 2, comprising a SC plug housing  40  for connecting the basic plug  20  to the SC-type optical fiber connector different from the type FC. 
     The SC plug housing  40  has a mating member  41  with the same configuration as that of the mating member  31  shown in FIG.  2 . Near a ferrule-insert end  42  of the mating member  41 , thereof are a plurality of engaging slots  43  spaced every 90 degrees along a circumferential direction of that end  42 . On an outer peripheral portion of the mating member  41 , a push and pull tightening member  44  for the FC-type optical fiber connector is installed. The push and pull tightening member  44  has windows  45  at their respective positions facing to engaging slots  43 , respectively. Therefore, it is possible to release the engagement between the engagement protrusions  27 B and the engaging slots  43  through the windows  45 . In the figure, furthermore, the reference numeral  41 A indicates a flange in an inward direction corresponding to the flange  31 A in an inward direction, and also the reference numeral  41 B indicates a key corresponding to the key  31 B. 
     Using the SC plug housing  40  instead of the FC plug housing  30 , consequently, the SC-type optical fiber connector  10 ′ can be constructed by simply inserting the basic plug  20  into the SC plug housing  40 . 
     Embodiment 3 
     Referring now to FIG. 5, there is shown a ST plug housing  50  in addition to the basic plug  20  having the same configuration as those of shown in FIGS. 2 and 4, combining the ST plug housing with the basic plug  20  to provide an optical fiber connector  10 ″ in the type of ST. 
     The ST plug housing  50  has a mating member  51  which is constructed as the same structure as that of the mating member  31  in FIG.  2 . In the proximity of a ferrule-inserting portion  52  of the mating member  51 , engaging slots  53  are formed with a 90 degrees spacing in a circumferential direction of the mating member  51 . A bayonet fastening member  54  for the ST type optical fiber connector is fitted on an outer peripheral surface of the mating member  51 . The bayonet fastening member  54  is slideably supported on the mating member  51  and pressed rightward in FIG. 5 by a spring  55  arranged between the bayonet fastening member  54  and the mating member  51 . 
     Using the ST plug  50  instead of the FC plug housing  30  in this way, the ST type optical fiber connector  10 ″ can be constructed only by fitting the basic plug  20  into the ST plug housing  50 . 
     Using the SC plug housing  40  or the ST plug housing, just as in the case of the FC plug housing  30 , the basic plug  20  may be easily fitted in place or detached with a single motion. 
     As can be seen from the above description, and also as described below with reference to FIG. 6, any desired optical fiber connector of the type of FC, SC, or ST can be easily assembled or easily replaced with the other type optical fiber connector by any combination of the basic plug  20  with one selected from the FC plug housing  30 , the SC plug housing  40 , and the ST plug housing  50  if these components are prepared in advance. As a consequence, a universal optical fiber connector is capable of coupling to another optical fiber connector of any type. 
     Simultaneously, it is easy to find an appropriate position of the key ring by adjusting its position in the direction of eccentricity of the fiber core. For this purpose, grooves are formed on both ends of the adapter to engage the positioning keys of both optical fiber connectors, respectively, so that the adjusted optical fiber connectors can be arranged face to face in a straight line at the time of lining them up by the engagement, resulting in a stable connection between them without causing their substantial axial deviations between the fiber cores in opposite directions. 
     In this embodiment, the connection between one single fiber and the other single fiber (i.e., between single ferrules) is described but not limited to such connection. It is also possible to apply to other connector forms with the same effects, such as a multiple optical fiber connector assembly in which a plurality of single optical fiber connectors are connected face to face as a single unit. 
     In this embodiment, furthermore, the description has been made on the cases of applying on the optical fiber connector in the type of FC, SC, ST, or the like, but is not limited thereto. Without relying on already-existing optical fiber connectors, it is also possible to use an adapter housing newly prepared for the basic plug of the present embodiment, resulting that the connection between the optical fiber cables can be easily performed without restraint. Hereinafter, therefore, we will describe other embodiments of the present invention without depending on already-existing optical fiber connectors. 
     Embodiment 4 
     FIG. 7 is a schematic perspective view showing an optical fiber connector as one of the embodiments of the present invention and FIG. 8 is a longitudinal cross section of a main part of the optical fiber connector shown in FIG.  7 . 
     The present embodiment is designed to directly connect the basic plug  20  to the adapter housing without using any plug housing. In this embodiment, the basic plug  20  is the same one as that of FIG.  2 . As shown in FIGS. 7 and 8, the adapter  60  is responsible for holding the coaxially-opposed basic plugs  20  on both sides thereof to connect optical fibers  1  in these plugs  20 . For that purpose, the adapter housing  60  comprises a pair of mating members  61  being constructed as the same structure as that of the mating member  31  shown in FIG. 2, and a sleeve  65  such as a separate sleeve on which a ferrule  21  can be fixed is embedded in the center portion between the mating members  61 . 
     At one end of the mating member  61  facing to the basic plug  20 , there is a ferrule-inserting portion  62  where four engaging slots  63  are spaced 90 degrees in its circumferential direction. On the other side of the mating member  61 , there are a flange  61 A and a key  61 B which correspond to the flange  31 A in an inward direction and the key  31 B, respectively, in FIG.  2 . As shown in the figure, a casing  64  coaxially holds the opposed mating members  61 , and also it coaxially holds the sleeve  65  between the mating members  61 . 
     Therefore, an optical connection between the bare optical fiber  99  can be completed by inserting the basic plugs  20  that hold the optical fiber cables  1  into their respective mating members  61  of adapter housing  60  to engage the engagement protrusion  27 B and the engage slot  63  and to fit a tip of the ferrule  21  into the sleeve  65  in the right place. 
     According to the present embodiment, a configuration of the connection is more simple than those of using optical fiber connectors in the types of FC, SC, ST, and so on, so that the number of elements to be required can be reduced and its manufacturing cost can be also reduced. 
     Using the basic plug  20 , therefore, it is possible to cope with a wide variety of available optical fiber connectors or the like by using members appropriate for the available members including FC plug housing  30 , SC plug housing  40 , and ST plug housing  50  and to make a simple connector structure by reducing the number of structural elements. 
     Embodiment 5 
     In the above embodiment shown in FIGS. 7 and 8, the optical connection between two single optical fibers is described in detail. However, the optical connection using the basic plug  20  is not limited to such arrangement. As a matter of course, the present invention may be applied on a multiple optical connection among a plurality of connectors in which they are oppositely coupled together to obtain the same effects. 
     FIG. 9 is a perspective view showing a duplex optical fiber connector for connecting four optical fiber cables at the same time to make two pairs of connected optical fibers. As shown in the figure, a duplex adapter housing  70  comprises two pairs of mating members  71 , so that two mating members  71  are arranged on one side of the duplex adapter housing  70 . Thus the basic plugs  20  can be fixed into the mating members  71  from both ends of the duplex adapter housing  70 , resulting in two pairs of connected optical fiber cables through the respective pairs of the mating members  71 . In addition, FIG. 10 is a perspective view showing an octuplex optical fiber connector for connecting sixteen optical fiber cables at the same time to make eight pairs of connected optical fibers. As shown in the figure, an octuplex adapter housing  80  comprises eight pairs of mating members  71 , so that eight mating members  81  are arranged on one side of the octuplex adapter housing  80 . Thus the basic plugs  20  can be fixed into the mating members  81  from both ends of the octuplex adapter housing  80 , resulting in eight pairs of connected optical fiber cables through the respective pairs of the mating members  81 . Consequently, a connection structure can be simplified by using the basic plug  20 , allowing reduction in the number of elements and the assembly at low cost. 
     Embodiment 6 
     Furthermore, FIG. 11 is a perspective view showing another embodiment of the present invention. As shown in the figure, an adapter housing  90  comprises two separate members, namely a male adapter housing  91  for basic plugs and a female adapter housing  92  for basic plugs to be mated together in a removable manner, in which each member has eight mating members  93  for receiving the basic plugs  20 . According to the present embodiment, for example, the male adapter housing  91  may be fixed on a panel, so that eight optical fiber cables arranged in the female adapter housing may be simultaneously connected to eight optical fiber cables arranged in the male adapter housing  91  with plug-in ease of use. 
     While the optical fiber connectors have been described in Embodiments 1-6 with reference to the drawings, such descriptions are for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the attached claims. 
     According to Embodiments 1-6 of the present invention, as described above, the form of optical fiber connector can be easily changed by a simple operation. Therefore, it is possible to connect any optical fibers by changing a plug housing while maintaining the basic plug as is, resulting in high utility in the optical connections. In addition, it is less expensive than using a converting adapter, and also there are no drawbacks such as a transmission loss. Furthermore, it is possible to optimally adjust the position of the key ring, so that the optical fiber connector can be much more sophisticated. 
     Furthermore, the basic plug of the present invention can be used as is. In this case, therefore, the connection structure can be simplified by using an adapter, so that the number of elements to be required can be reduced and its manufacturing cost can be also reduced. 
     Embodiment 7 
     FIG. 12 is an exploded perspective view of a universal optical fiber connector as one of the embodiments of the present invention, while FIG. 13 is a cross-sectional view of FIG.  12 . 
     A universal optical fiber connector  300  shown in FIGS. 12 and 13 is in the type of FC. The optical fiber connector  300  comprises a basic plug  20  and a FC jack housing  230  for holding the basic plug  20  as the same construction shown in FIG.  1 . 
     The jack housing  230  comprise having cylindrical-shaped casing  231 , a mating member  232  which is coaxially fixed in one end portion of the casing  231 , and sleeve  233  such as a separate sleeve for fitting to a ferrule  21 , which is coaxially fixed in the other end portion of the casing  231 . Thus, the jack housing  230  is responsible for fitting a basic plug  20  into a ferrule-inserting portion  234  and fitting a FC plug into a opposite end portion to make an optical connection by coaxially holding a bare fiber  99  of the basic plug  20  and an optical fiber of the FC plug in an opposite manner. 
     Furthermore, there are four engaging slots  235  formed in proximity to the ferrule-inserting portion  234  of the mating member  232  and spaced every 90 degrees along a circumferential direction thereof. In addition, an inner surface of an engaging slot region of the ferrule-inserting portion has grooves  239  in which protrusions  211  of the basic plug  20  are engaged. If the basic plug  20  is inserted into the FC jack housing  230 , protrusions  211  are fitted in the grooves  239  (FIG. 3) to limit the relative rotation between the basic plug  20  and the FC jack housing  230  in a circumferential direction. 
     On the other end of the casing  231 , a FC plug inserting portion  236  is formed to engage the conventional FC plug  100  as shown in FIG.  24 . The FC plug inserting portion  236  has a male thread portion  237  on its outer peripheral surface and is shaped so as to be able to receive the FC plug. Therefore, if the FC plug  100  is inserted into the FC plug inserting portion  236 , the male thread portion  237  formed on the outer peripheral surface of the casing  231  and the female thread formed in an inner peripheral surface of the a tightening member  103  of the FC plug are tightened together, following by inserting a tip of the ferrule  101  of the FC plug  100  into the sleeve  233  and contacting it to the ferrule  21  of the basic plug  20  to make an optical connection between the optical fibers. 
     For fixing the casing  231  on a fixing member such as a panel, a flange portion  238  is provided on an outer peripheral surface of the casing  231  at a region near the center of the casing  231  in its axial direction. 
     According to the present embodiment, it is possible to connect the basic plug  20  on one side of the jack housing  230  and to connect the FC-typed plug on the other side thereof. Thus, the optical connection can be performed without preparing any one of the various conventional adapters. In addition, for example, if jack housings that support the conventional plugs in the types of FC, SC, ST, and so on, respectively, there is no need to prepare various kind of conversion adapters, realizing the connection structures with various optical fiber connectors. Therefore, the number of the structural elements and the manufacturing costs can be attained. 
     As shown in FIG. 14, for example, a plug-coupling member  241  may be provided to connect the SC plug to the plug-inserting side of the jack housing  240 . As shown in FIG. 15, furthermore, a ST coupling member  251  may be provided to the plug-inserting side of the jack housing  250  for connecting the ST plug. In this embodiment, each of these jack housings  240  and  250  has the same structure as those shown in FIGS. 12 and 13 on its side of connecting the basic plugs. In the present embodiment, in addition, FC, SC, and ST type plugs are exemplified but is not limited thereto. It is also possible to adapt to another type such as a MU type optical fiber connector. 
     In all of the embodiments, it is understood that the flange portion is provided on the jack housing, but not limited thereto. The jack housing maybe constructed without any flange portion. 
     In the present embodiment, the optical connection described above using any optical fiber connector is in the type of connecting two single optical fibers or single ferrules. However, it is not limited thereto. The present embodiment may be applied on a multiple connector assembly in which a plurality of single connectors are provided as a set of oppositely coupled single connectors, resulting in the same effects as that of the connection between two single optical fibers. 
     According to Embodiment 7 of the present invention, as described above, various connection structures can be obtained very easily, as the optical fiber connector comprising an adapter has one end for directly connecting a common basic plug and the other end for connecting various connector types of plug. In addition, the present embodiment has the effect of enabling a change of types of various optical fiber connectors by a very simple configuration. For example, a combination of different optical fiber connectors can be included in the optical connection assembly that enables a connection between any optical fibers by just replacing the jack housings while using the basic plug as it is, so that it is less expensive as compared with the case of using a converting adapter, and also it does not cause any drawbacks such as a transmission loss. 
     Using the optical fiber connector of the present invention, furthermore, the basic plug of the present invention can be used just as it is. In this case, therefore, the connection structure can be applied on various conventional plugs, so that there is no need to replace the structural elements and its manufacturing cost can be also reduced. 
     Embodiment 8 
     FIG. 16 is an exploded perspective view of a universal optical fiber connector as one of the embodiments of the present invention, while FIG. 17 is a cross-sectional view of FIG.  16 . 
     A universal optical fiber connector  400  shown in FIG. 16 is in the type of SC. The optical fiber connector  400  comprises a basic plug  20  having the same construction as that shown in FIG. 1 and a SC plug housing  330  for holding the basic plug  20 . 
     The SC plug housing  330  comprises a mating member  331  and a push and pull tightening member  332 . Near a ferrule-insert end  335  (FIG. 17) of the mating member  331 , there are a plurality of engaging slots  332  spaced every 90 degrees along a circumferential direction of ferrule-insert and  335 . 
     On an outer peripheral portion of the mating member  331 , a push and pull tightening member  332  for the SC type optical fiber connector is installed. They are fixed together by means of adhesive or the like. The push and pull tightening member  332  has windows  334  at their respective positions facing engaging slots  333 , respectively. 
     Therefore, the basic plug  20  and the SC plug housing  330  can be coupled under the following condition. That is, as a basic plug  20  is inserted through the ferrule-insert end  335  of the SC plug housing  330 , the engagement protrusion  27 B is contacted to an inner edge of the ferrule-insert end  335  of the engagement and forced into an inner side of the mating member  331  at the time of passing the engagement through the ferrule-insert end  335 . On the other hand, the engagement protrusion  27 B is engaged in the engaging slot  333  by returning to its original states by means of elasticity of the tongued strip  27 A at the time of facing the engaging protrusion  27 B to one of the engaging slots  333 . 
     In addition, an inner peripheral surface of a region where the engaging slots  333  of the ferrule-inserting end  335  of the SC plug housing  330  are formed has grooves  337  for engaging with the protrusions  211  (FIG.  16 ). If the basic plug  20  is inserted into the SC plug housing  330 , protrusions  211  are fitted in the grooves  337  to limit the relative rotation between the basic plug  20  and the SC plug housing  330  in a circumferential direction. 
     In this embodiment, furthermore, the optical fiber connector has a predetermined dimension for contacting a brim portion  22 A of a tubular member  22  with an inward flange  331 A of the mating member  331  (FIG. 17) prior to engaging the engaging protrusion  27 B into the engaging slot  333  at the time of inserting the basic plug  20  through the ferrule-inserting end  335  of the SC plug housing  330 . During the period of engaging the engaging protrusion  27 B into any engaging slot  333 , a spring coil  25  is kept in the contracted state. Therefore, when the mating member  331  and the cylindrical tube  24  are coupled together by engaging the engaging protrusion  27 B into the engaging slot  333 , the ferrule  21  is press-contacted to the inward flange  331 A by a spring tension of the spring coil  25 , and then fixed and held therein, resulting in a specified assembly of the SC plug housing  330  and the basic plug  20 . 
     For canceling the assembly state, the engaging protrusion  27 B is forcefully pushed down against an elastic force of the tongued strip  27 A that tends to push it up to release the engagement between the engagement protrusion  27 B and the engagement slot  27 B, resulting that the cylindrical tube  24  is removed quickly from the mating member  331  by an extending force of the spring coil  25 , resulting in a release from the assembly state. 
     The process of adjusting the center of the key ring  336  and the direction of the fiber core eccentricity so that they are in proper relative position can be attained by positioning the engagement protrusion  27 B relative to the mating member  331  in a circumferential direction. More specifically, for the alignment to lead them in the right place, a plurality of grooves  22 D (FIG. 16) are formed in an outer peripheral surface of the brim portion  22 A and also a plurality of keys  31 B (FIG. 17) to be fit into their respective grooves  22 D are protruded from an inner surface of the mating member  331 , configuring so-called directional coupling key elements. Therefore, the best relative position of the key ring  336  and the direction of core eccentricity can be adjusted by shifting a phase of fitting the key  331 B into the groove  22 D by turning them relatively in a circumferential direction. 
     An end of the push and pull tightening member  332  has two flange portions  337  formed on its end on the side of ferrule insertion. A through hole  338  is formed through a region near the center of each flange portion  337 . The through hole  338  is responsible for the tightening using a screw. The flange  337  is responsible for fixing the SC plug housing  330  on a fixing member  350  such as a panel, and thus the plug can be fixed under the state of releasing an end face of the ferrule  21 . Therefore, it is possible to clean the end surface of the ferrule  21 . In addition, as shown in FIG. 18, it is possible to mount a plurality of the SC plug housing  330  on the fixing member  350 . In this case, it is also possible to clean the end surface of the ferrule  21 . Consequently, it brings efficiency to the operation of optical connection. 
     Furthermore, the flange portion  337  may be shaped into the same form as that of a flange portion of the already-existing adapter to avoid additional machining operation or the like on the fixing member and to fix the universal optical fiber connector  400  on the already-existing fixing member. 
     In the present embodiment, the plug housing is in the type of adapting to the shape of SC connector but not limited to that shape. Another plug housing to be adapted to one selected from various connector shapes, such as FC or ST connector or the like, may be used. 
     According to the optical fiber connector of the present embodiment  8 , a tip of the ferrule can be positioned forward of the fixing member by means of the flange portion of the tightening member, so that a side face of the ferrule car, be easily cleaned. In addition, we can provide an easy-to-clean optical fiber connector at low cost by shaping it into the same form as that of a flange portion of the already-existing adapter. 
     Embodiment 9 
     FIG. 19 is a cross-sectional view of an assembled structure of an optical fiber connector as one of the preferred embodiments of the present invention. As shown in the figure, a basic configuration of an optical fiber connector of the present embodiment is a basic plug and a plug housing as shown in FIG.  1 . 
     In the present embodiment, a reinforcing cylindrical pipe  28  is placed on an inner peripheral surface of a hood C being attached to the rear end of assembled universal optical fiber connector  500 . The reinforcing cylindrical pipe  28  is made of a metal such as nickel-plated brass, stainless steel, or the like and is integrally formed by an insert molding simultaneously with the step of forming the hood C. 
     One end of the reinforcing cylindrical pipe  28  is fitted onto one end of the plug housing  30 , while the other end thereof surrounds a cylindrical member  215  that fixes a tensile strength body  210  on the other end of the basic plug  20 . 
     Accordingly, the optical fiber connector  500  of the present embodiment increases in strength by mounting the reinforce metal pipe on an inner peripheral surface of the hood C. If the hood C and its surrounding areas receive external stress, for example large bending stress through an optical fiber cable  1  or pressed beneath the feet, in a connected state, the reinforce pipe  28  transfers the stress to the plug housing  30 . 
     Therefore, the cylindrical member fixed on the other end of the basic plug  20  hardly receives stress, so that a fracture or distortion in the basic plug  20  may be prevented. 
     For the optical fiber connector  500  of the present embodiment described above, the reinforce cylindrical pipe  28  is arranged on an inner peripheral surface of the hood C. However, it is also possible to arrange the reinforce cylindrical pipe  28  on an outer peripheral surface of the hood C or in an inside of thereof. In addition, the reinforce pipe  28  may be shaped into a rectangle so as to fit to the shape of optical fiber connector. 
     Furthermore, the reinforce pipe  28  may be provided as a separate equipment to be attached to the hood C if required. It is essential only that the assembled optical fiber connector is configured so that one end portion of the reinforce pipe  28  is fitted to the outside of basic plug  20  which is inner of the one end portion thereof (by which the cylindrical member  215  is swaged) and the other end portion of the reinforce pipe  28  covers the cylindrical member  215  having a tensile strength body  210  being fixed on the end portion of the basic plug  20 . 
     Furthermore, a basic configuration of the optical fiber connector is not restricted by the present embodiment. It is also possible to prepare the optical fiber connector by means of resin molding in which a brim, a compression spring, and a stopper may be molded in one piece. 
     According to the optical fiber connector of Embodiment 9 of the present invention, a ferrule is connected to one end portion of the basic plug and is covered with a plug frame so as to receive the force from a press means at the time of connection. On the other hand, the other end portion of the basic plug has an engagement ring for fixing a tensile strength body on an outer peripheral surface of that portion. Then this fixed portion is covered with the hood to be fixed on an outer peripheral surface of the plug frame. Furthermore, the reinforce pipe is placed, for example, on an inner peripheral surface of the hood, so that the strength of the head and the optical fiber connector is improved. Therefore, any stress or force (such as bending stress, tensile force, or shearing force) applied on the hood is hardly transmitted to the basic plug, so that we can provide the optical fiber connector without causing any damage, such as stress cracking, in a quest to obtain greater durability. 
     Embodiment 10 
     FIG. 20 is an exploded perspective view of a universal optical fiber connector as one of the preferred embodiments of the present invention, while FIG. 21 is a cross-sectional view of FIG.  20 . 
     A universal optical fiber connector  600  shown in these figures is in the type for connecting to an adapter of a FC-type connector model. The optical fiber connector  600  comprises: a ferrule-holding member  420  in which a single optical fiber cable  1  is coaxially fixed; and a FC plug housing  430  for holding the ferrule-holding member  420  for connecting it to the FC-connector type adapter. 
     The ferrule-holding member  420  comprises: a ferrule  21  that holds the optical fiber cable  1 ; a tubular member  422  having a brim  422 A and coaxially fixed on the rear end of the ferrule  21 ; a ferrule-forcing member  425  that holds the rear end of the tubular member  422 ; and a cylindrical tube  424  to be coaxially fitted on the tubular member  422  in a slideable manner. Thus, the rear end of the cylindrical tube  424  secures a tip  1 A (FIG. 21) of the optical fiber by means of a tensile strength material  210  (FIG.  21 ). In this case, the tensile strength material  210  is placed over the rear end portion of the cylindrical tube  424 , followed by crimping or boding a cylindrical member  215 . The ferrule  21  has at least one common dimensional structure compatible with various connector models. 
     The ferrule-forcing member  425 , which is secured between the brim  422 A of the tubular member  422  and the cylindrical tube  424 , is made of rubber or elastomer and is installed so as to exert elastic deformation forces against them in opposite directions to keep them separated. That is, the tubular member  422  and the ferrule  21  are constructed as an elastic-floating structure in which they are elastomer-loaded toward a front end of the ferrule  21  with respect to the cylindrical tube  424 . 
     To be more specific in the present embodiment, a long-sized cylindrical portion  422 B passing through the ferrule-forcing member  425  is integrally formed on the rear end portion of the brim  422 A of the tubular member  422  and is extended along the lengthwise direction of the cylindrical tube  424 . An outer peripheral surface of the rear end portion of the cylindrical portion  422 B has protrusions  422 C which are formed so as to be flexibly distorted inwardly along the diameter of the cylindrical portion  422 B. In the front end portion of the cylindrical tube  424 , there are square openings  428  (FIG. 20) into which the respective protrusions  424 C are inserted with a space enough to slide along the length width direction of the cylindrical tube  424 . If the tubular member  424  moves forward with respect to the cylindrical tube  424 , its movement is restricted by contacting the protrusion  424 C with a front side of the square opening  428 . 
     In a state of being free, the contact between the protrusion  422 C and the front side of the square opening  428  is maintained by pushing the tubular member  422  forward by an extending force of the ferrule-forcing member  425 . If the tubular member  422  is forcefully pushed backward against the extending force of the ferrule-forcing member  425 , the protrusion  422 C can be slid along its axial direction in the square opening  428  to shift the positions of both of the ferrule  21  and the tubular member  422  with respect to the cylindrical tube  424 . The movement of the ferrule  21  against the elastic deformation force of the ferrule-forcing member  425  is limited by contacting the protrusion  22 C with the rear side of the square opening  213  or by the elastic limit of the ferrule-forcing member  425 . 
     An elastomer-loaded engagement piece  427  is integrally formed on the other end (i.e., the rear end) portion of the cylindrical tube  424  and comprises a tongued strip  427 A provided by forming a U-shaped slit  426  in the peripheral surface of the cylindrical tube  24  and an engagement protrusion  427 B formed and extended on a free end of the tongued strip  427 A. Therefore, the engagement protrusion  427 B on that, free end can be displaced in the outward or inward direction by an effect of elastic deformation of the tongued strip  427 A. In this embodiment, there are two tongued strips  427 A spaced apart 180 degrees in a circumferential direction of the cylindrical tubule  424 . The engagement protrusion  427 B has wedge-shape where the thickness thereof is gradually increased from a boundary of the tongued strip  427 A and the engagement protrusion  427 B to an opposite end of the latter, resulting in a substantial protrusion through the peripheral surface of the cylindrical tube  424 . In addition, a rectangular protruded region  429  is formed on an outer peripheral surface of the cylindrical tube  424 , with 90 degrees deviation from the engagement protrusion  427 B along the circumferential direction of the cylindrical tube  424 . As shown in the figure, there is a gradual decrease in thickness of a front end portion (i.e., formed as a tapered portion) of the protruded region  429  to smooth the path to engage with a groove  436  described below. 
     The ferrule-forcing member  425  may be selected from, for example, the group of silicon rubber, acrylonitrile-butadiene rubber (NBR), natural rubber, isopropylene rubber, chloroprene rubber, fluorine rubber, polyurethane elastomer, and polyester elastomer, molded in a cylindrical shape. 
     The FC plug housing  430  comprises a thread-fastening member  432  fitted to a mating member  431  for receiving the ferrule-holding member  420 . In addition, a key ring  433  is fixed on an outer peripheral surface of the mating member  431  by an appropriate means and is provided as an index key that has the function of adjusting the direction of core eccentricity to make sure the mating member  431  is in the right place. The structure of fixing the key ring  433  on the mating member  431  is, for example a well-known conventional structure as shown in FIG.  24 . 
     The other end of the mating member  431 , which is on the side of receiving the ferrule-holding member  420 , is formed as a ferrule-inserting end portion  434 . Furthermore, engaging slots  435  are formed in a peripheral surface of the ferrule-inserting end portion  434  at established intervals. In this embodiment, there are four engaging slots  435  allowing 90 degrees spacing. A groove  436  to be matched with that protruded region  429  is formed in an inner surface of the FC plug housing  430 . 
     When the ferrule-holding member  420  is gradually inserted into the FC plug housing  430  through the insert end portion  434 , the engagement protrusion  427 B contacts with an inner edge of the insert end portion  434  and is gradually pushed into the cylindrical tube  424  at the time of passing the engagement protrusion  427 B through the insert end portion  434 . Then the engagement protrusion  427 B is engaged into the engaging slot  435  by recovering its original state by the elasticity of the tongue piece  427 A when the engagement protrusion  427 B faces one of the engaging slot  435 . In this state, the ferrule-holding member  420  is coupled to the FC plug housing  430 . 
     Thus, inserting the ferrule-holding member  420  into the FC plug housing  430  leads to mate the groove  436  and the protruded region  429  together, resulting in restrictions on the relative turns of the ferrule-holding member  420  and the FC plug housing  430  in the directions of their circumferences, respectively. 
     For the step of inserting the ferrule-holding member  420  into the insert end portion  434  of the FC plug housing  430 , each structural element is designed to predetermined dimensions so that the brim portion  422 A comes into contact with a flange  431 A (FIG. 21) in an inward direction of the mating member  431  prior to engaging the engagement protrusion  427 B into the engaging slot  435 . Thus the ferrule-forcing member  425  is being compressed when the engagement protrusion  427 B in engaged in any engaging slot  435 . If the mating member  431  and the cylindrical tube  424  are coupled together by engaging the engagement protrusion  427 B into the engaging slot  435 , an extending force of the ferrule-forcing member  425  pushes the ferrule  21  against the flange  431 A, and subsequently the ferrule  21  is fixed into the flange  431 A and then housed therein. Namely, the FC plug housing  430  and the basic plug  420  are in a state of established assembly. 
     For canceling the assembly state, the engaging protrusion  427 B is forcefully pushed down against an elastic force of the tongued strip  427 A that tends to push it up to release the engagement between the engagement protrusion  427 B and the engaging slot  427 B, resulting that the cylindrical tube  424  is removed quickly from the mating member  431  by an extending force of the ferrule-forcing member  425 , resulting in a release from the assembly state. 
     The process of adjusting the center of the key ring  433  and the direction of the core eccentricity so that they are in proper relative position can be attained by positioning the engagement protrusion  427 B relative to the mating member  431  in a circumferential direction. More specifically, for the alignment to lead them in the right place, a plurality of grooves  422 D are formed in an outer peripheral surface of the brim portion  422 A and also a plurality of keys  431 B (FIG. 21) to be fit into their respective grooves  422 D are protruded from an inner surface of the mating member  431 , configuring so-called directional coupling key elements. Therefore, the best relative position of the key ring  433  and the direction of core eccentricity can be adjusted by shifting a phase of fitting the key  431 B into the groove  422 B by turning them relatively in a circumferential direction. 
     Embodiment 11 
     FIG. 22 is a perspective view in schematic form depicting a multiple optical fiber connector assembly as another preferred embodiment of the present invention, and FIG. 23 is a cross-sectional view of the optical fiber connector assembly shown in FIG.  22 . 
     A multiple optical fiber connector assembly comprises a plurality of ferrules in parallel. As shown in FIGS. 22 and 23, a multiple ferrule-holding structure  700  of the optical fiber connector assembly according to the present embodiment comprises a plurality of ferrules (four ferrules in this embodiment), a holding member or ferrule-forcing member  562  made of rubber or elastomer, and a housing  563  for holding the ferrule-forcing member  562 . 
     The ferrule  561  has a collar portion  565  on its rear end, while the core of an optical fiber comes into the middle of the ferrule  561  and is fixed therein. A ferrule-forcing member  562  is coupled to the collar portion  565  to exert a press force to the ferrules  561 . The ferrule-forcing member  562  is provided as a rectangular-shaped rubber or elastomer with portions for mounting a plurality of ferrules  561  and collar portions  565 . Namely, the portions includes a plurality of grooves  567  in which the collar portions  565  are fitted and a plurality of through-holes into which the nylon jacked optical fibers are inserted. The ferrule-forcing member  562  may be formed as two separated components for sandwiching a plurality of ferrules  563  between them. In addition, the housing  561  has a cavity or pit portion  569  in which the ferrule-forcing member  562  can be fitted and through-holes  570  drilled through the bottom of the pit portion  591 . Each nylon jacketed optical fiber passes through the through-hole  570  from the outside of the housing. 
     Therefore, each ferrule  561  is held in the housing  563  in a manner that the ferrule  561  is able to move in an axial direction thereof by an effect of elastic deformation of the ferrule-forcing member  562 . Thus the ferrule  561  can be optically connected to another connector or the like. That is, the optical connection with any one of various optical fiber connectors can be attained by assembling the multiple ferrule-holding structure into a casing compatible with the multiple optical fiber connectors of various specifications. 
     In this embodiment, a plurality of the ferrules is held in one ferrule-forcing member but not limited to this configuration. For example, ferrules may be held in their respective tubular or rectangular ferrule-forcing components in one housing. 
     In a quest to give the optical fiber connector greater durability, it is easy to keep each of the optical fiber connectors of Embodiments 10 and 11 rust free if the elastic member for applying a press force to the ferrule is made of a rubber or elastomer material as described above. In a quest to attain cost-reduction, it is easy to reduce the number of components in the optical fiber connector because of the configuration described above. Furthermore, it is easy to be compatible with connectors of various forms because the elastic member can be formed in any shape.