Abstract:
An optical connector has a ferrule comprises of a cylindrical body for supporting an optical fiber, and a flange member having an end portion connected to a first end of the cylindrical body and a flange part projecting from the end portion. A holding member supports the ferrule and has an engaging part. A rotation positioning part is formed in the flange part of the flange member for positioning the flange part relative to the holding member to provide a first clearance between the rotation positioning part and the engaging part of the holding member for restricting rotation of the ferrule about the fiber optical axis relative to the holding member. A rotation allowing part is formed in the flange part of the flange member and spaced from the engaging part of the holding member to provide a second clearance therebetween greater than the first clearance for allowing rotational movement of the ferrule so as to permit the ferrule to incline in a direction transverse to an axis of the optical connector.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an optical connector, such as an Angle-Pc connector, for connecting the slanted, polished surfaces of optical fibers together. 
   2. Description of the Related Art 
   As an optical connector, for use in optical communications or the like, a conventional Angle-Pc (Physical Contact) connector is used for the purpose of reducing connection loss and reflection return light at the connection of connectors, which has an optical fiber held in the ferrule and polished, at its end face together with an end face of the ferrule end face, oblique relative to a plane vertical to the axis of the optical fiber and into a convex spherical surface. 
   Herein, the ferrule to be used in the conventional Angle-PC connector is explained. 
     FIGS. 16A-16C  perspective and plan views of a ferrule according to the related art. 
   As shown in  FIGS. 16A-16C , a ferrule  160  used in an Angle-PC connector comprises a ferrule cylindrical body  140  having a tip face having a circular cylinder form provided as a convex surface form slanted relative to a plane orthogonal to the axis, and a flange member  150  fit in a rear end of the ferrule cylindrical body  140 . The flange member  150  has a flange part  153  radially projecting and circumferentially extending on the outer periphery thereof close to the ferrule cylinder  140 . The flange part  153  is provided with a key groove  154  which, when held in a not-shown plug frame of the Angle-PC connector, is to be engaged with the engaging projection axially provided in the same engaging width in the plug frame. The key grooves  154  are axially provided equal in width, in four locations at an interval of 90 degrees with respect to a circumferential direction of the flange part. 
   Such ferrules, held in plug frames, are to be optically connected at a low insertion loss and high return loss through an optical connector adapter or the like, by making an opposed connection with the end surfaces of the ferrules  160  placed in abutment against each other. 
   However, in the Angle-PC connector, there is a problem that, in case the ferrule has a great movement in rotational direction about the axis, the convex spherical surface is increased in eccentric center of curvature, thus making impossible to realize a low insertion loss and high return loss. 
   In this manner, in order to realize a low insertion loss and high return loss, there is a need to provide an eccentric center of curvature of 50 μm or less to the spherical surface provided at the tip surface of the ferrule cylindrical body. This requires to suppress the rotation angle of the ferrule in rotational direction about axis to ±2 degrees or less, preferably ±3 degrees or less. 
   For this reason, by providing 0.01-0.1 mm to a clearance between the flange-part key groove of the flange member and the engaging projection provided in the plug frame, the rotation chatter of the ferrule about the axis can be suppressed low to provide an eccentric center of curvature of 50 μm or less thereby providing a low insertion loss and high return loss. 
   However, conventionally, in case to provide a clearance 0.01-0.1 mm to between the key groove of the flange member and the engaging projection in order to suppress the rotation chatter of the ferrule about the axis, the optical connector plug when attached/detached to/from the optical connector adapter is restricted in the radial movement of the ferrule, resulting a problem of poor attaching/detaching stability. 
   Meanwhile, as compared to the optical connector plug using a ferrule cylindrical body having an outer diameter of 2.5 mm, the optical connector plug in which the ferrule cylindrical body uses a 1.25-mm ferrule cylindrical body has a necessity to reduce generally to a half the clearance between the flange-part key groove and the engaging projection in suppressing low the eccentric center of curvature. This, however, involves a problem that accurate working is required, thus making not feasible substantially. 
   SUMMARY OF THE INVENTION 
   It is an aspect of the present invention to provide an Angle-PC connector which can be stably attached/detached by eliminating stress during attachment/detachment. 
   A first form of the preset invention, for solving the foregoing problem, is in an Angle-PC connector having a ferrule made with a ferrule cylindrical body holding an optical fiber and having a tip face formed in a convex surface form slanting relative to a plane orthogonal to an optical fiber axis and a flange member to be fit to a rear end of the ferrule cylindrical body, and a holding member for restricting the ferrule from moving in an rotational direction about the optical fiber axis and urgingly holding the ferrule toward the axis, an Angle-PC connector comprising: a flange part provided in a polygonal or disk form circumferentially projecting on the flange member at a tip side thereof; an engaging part formed axially of the optical fiber and in a predetermined engaging width, in the holding member; the flange part having a predetermined clearance to the engaging part at an axial tip side thereof; a rotation positioning part restricting a movement in rotational direction of the flange part, and a rotation allowing part for forming, on a rear-end side of the rotation positioning part, a clearance greater than the clearance of between the rotation positioning part and the engaging part. 
   A second form of the invention is an Angle-PC connector according to the first form, wherein the ferrule has an rotation angle in rotational direction about the axis of ±3 degrees or less with respect to the holding member that is to be allowed by the predetermined clearance between the rotation positioning part and the engaging part. 
   A third form of the invention is an Angle-PC connector according to the second form, wherein the ferrule has an rotation angle in rotational direction about the axis of ±2 degrees or less with respect to the holding member that is to be allowed by the predetermined clearance between the rotation positioning part and the engaging part. 
   A fourth form of the invention is an Angle-PC connector according to any of the first to third forms, wherein the ferrule has an inclination angle from the axis of ±5 degrees or greater with respect to the rotation positioning part as a start point. 
   A fifth form of the invention is an Angle-PC connector according to any of the first to fourth forms, wherein the rotation positioning part and rotation allowing part of the flange part is formed by key grooves axially provided in the flange part, the engaging part being engaging projections projecting in the key grooves. 
   A sixth form of the invention is an Angle-PC connector according to the fifth form, wherein the ferrule cylindrical body has an outer diameter of substantially 2.5 mm. 
   A seventh form of the invention is an Angle-PC connector according to the fifth or sixth form, wherein the key grooves constituting the rotation positioning part have an axial length of 0.3-0.5 mm. 
   An eighth form of the invention is an Angle-PC connector according to any of the fifth to seventh forms, wherein the holding member is to engage an SC-type connector adapter. 
   A ninth form of the invention is an Angle-PC connector according to any of the first to fourth forms, wherein the rotation positioning part and rotation allowing part of the flange part is structured by an outer peripheral surface of the flange part, the engaging part being an engaging hole. 
   A tenth form of the invention is an Angle-PC connector according to the ninth form, wherein the rotation allowing part is formed in a manner inclining toward the axis. 
   An eleventh form of the invention is an Angle-PC connector according to the tenth form, wherein the taper surface structuring the rotation allowing part is formed at an angle of 5 degrees with respect to the axis. 
   A twelve form of the invention is an Angle-PC connector according to the tenth form, wherein the rotation positioning part is structured with an outer peripheral surface in a disk form. 
   A thirteenth form of the invention is an Angle-PC connector according to any of the ninth to twelve forms, where in the ferrule cylindrical body has an outer diameter of substantially 1.25 mm. 
   A fourteenth form of the invention is an Angle-PC connector according to the thirteenth form, wherein the flange part constituting the rotation positioning part has an outer peripheral surface having an axial length of 0.4-0.6 mm. 
   A fifteenth form of the invention is an Angle-PC connector according to any of the ninth to fourteenth forms, wherein the holding member is to engage an MU-type or LC-type optical connector adapter. 
   The present invention thus configured, because the holding member of the ferrule is allowed in its rotation angle of rotational direction within a predetermined range by the rotation positioning part and to be inclined toward the radial direction within a predetermined range, can easily realize a low insertion loss and high return loss during optical connection and further can be relieved of the stress in a direction different from that in the axial direction during attachment/detachment to/from an optical connector adapter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of an Angle-PC connector according to embodiment 1 of the present invention; 
       FIGS. 2A and 2B  are an exploded plan view and assembly sectional view of the Angle-PC connector according to embodiment 1 of the invention; 
       FIGS. 3A-3C  are a perspective view, plan view and sectional view, respectively, of the ferrule according to embodiment 1 of the invention; 
       FIGS. 4A-4C  are cross-sectional views of the Angle-PC connector according to embodiment 1 of the invention; 
       FIGS. 5A-5C  are plan views showing an axial length of the rotation positioning part according to embodiment 1 of the invention; 
       FIG. 6  is an exploded perspective view of an Angle-PC connector according to embodiment 2 of the invention; 
       FIGS. 7A and 7B  are an exploded plan view and assembly sectional view of the Angle-PC connector according to embodiment 2 of the invention; 
       FIGS. 8A-8C  are a perspective view, plan view and sectional view, respectively, of the ferrule according to embodiment 2 of the invention; 
       FIGS. 9A-9C  are cross-sectional views of the Angle-Pc connector according to embodiment 2 of the invention; 
       FIGS. 10A-10C  are plan views showing an axial length of the rotation positioning part according to embodiment 2 of the invention; 
       FIG. 11  is an exploded perspective view of the Angle-PC connector showing another example of flange part according to embodiment 2 of the invention; 
       FIGS. 12A-12B  are an exploded perspective view and a cross-sectional view, respectively, of the Angle-Pc connector showing another example of flange part according to embodiment 2 of the invention; 
       FIGS. 13A-13C  are a perspective view, plan view and sectional view, respectively, showing another example of flange part according to embodiment 2 of the invention; 
       FIGS. 14A-14C  are cross-sectional views of the Angle-Pc connector showing another example of flange part according to embodiment 2 of the invention; 
       FIGS. 15A-5C  are a perspective view, plan view and sectional view, respectively, showing another example of rotation allowing part according to embodiment 2 of the invention; and 
       FIGS. 16A-16C  are perspective and plan views of a ferrule according to a related art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be explained in detail on the basis of the embodiments. 
   Embodiment 1 
     FIG. 1  is an exploded perspective view of an Angle-PC connector according to embodiment 1 of the invention,  FIGS. 2A-2B  are an exploded plan view and assembly sectional view of the Angle-PC connector,  FIGS. 3A-3C  are a perspective view, plan view and sectional view, respectively, of a ferrule, and  FIGS. 4A-4C  are sectional views of the Angle-PC connector. 
   As shown in the figures, the Angle-PC connector  10  of this embodiment has a holding member or plug housing  20  to fit to an SC-type optical connector adapter, a holding member or plug frame  30  to fit in the plug housing  20 , a ferrule  60  holding the optical fiber for optical connection and to be inserted to the rear of the plug frame  30 , a stop ring  70  having a tip to engage a rear end of the plug frame  30 , and an urge spring  80  held between the ferrule  60  and the stop ring  70  and urging the ferrule  60  toward an axially forward direction. 
   As shown in  FIGS. 3A-3C , the ferrule  60  is structured with a ferrule cylindrical body  40  formed with an outer diameter of 2.5 mm and a flange member  50  fit to one end of the ferrule cylindrical body  40 . 
   The ferrule cylindrical body  40 , generally in a circular cylindrical form, has therein an optical-fiber insertion hole  41  penetrating in the axial direction to insert and hold an optical fiber  1  therein. The optical-fiber insertion hole  41  has, at its rear end, a taper  42  having an inner diameter gradually increasing toward an opening thereof. By providing the taper  42 , when inserting the optical fiber  1  in the optical-fiber insertion hole  41 , the optical fiber  1  at its tip can be prevented from being broken or fractured by a contact with the end face of the ferrule cylindrical body  40 . 
   For the ferrule cylindrical body  40 , the applicable material includes a ceramic material such as zirconia, a plastic material, a glass material such as crystallized glass, borosilicate glass and quarts, and a metal material such as stainless steel, nickel or nickel alloys. 
   Meanwhile, the ferrule cylindrical body  40  has a tip formed in a surface slanted with respect to the plane orthogonal to the axis or in a convex surface form such as a convex spherical surface. In this embodiment, the tip of the ferrule cylindrical body  40  was formed in a convex spherical surface form having a deviated center of curvature with respect to the axis of the optical fiber  1 . 
   When the Angle-Pc connectors  10  are oppositely connected through an optical connector adapter, the ferrule cylindrical bodies  40  are connected together within a split sleeve in such a positional relationship that the center of curvature of the convex spherical surface of each ferrule cylindrical body  40  and the connection point between the optical fibers  1  are positions on one line. 
   In order to realize a specification of a low insertion loss of 0.2 dB or less and a ultrahigh return loss of 60 dB or higher during such opposed connection, there is a need to provide the convex spherical surface with an eccentric center of curvature of 50 μm or less, preferably 30 μm-40 μm with respect to a reference plane having an predetermined angle of inclination (e.g. 8 degrees) relative to the plane orthogonal to the axis. This requires to provide the convex spherical surface with a center of curvature of 6 mm-9 mm. 
   The ferrule cylindrical body  40 , when oppositely connected at the convex spherical surfaces, must be held in the plug frame  30  such that the ferrule cylindrical body  40  has a moving amount in rotating direction about the axis relative to the plug frame  30  of ±3 degree or less, preferably ±2 degree or less, in rotation angle. 
   On the other hand, the flange member  50  is structured with a fit hole  51  to fit there in one end of the ferrule cylindrical body  40 , an optical-fiber-core insertion hole  52  to insert and hold therein an optical fiber core  2  coated on the periphery of the optical fiber  1 , and a flange portion or part  53  radially projecting a predetermined amount to circumferentially extend at the side the fit hole  51  is opened. 
   The flange part  53  is formed with a predetermined clearance to an engaging projection  34  corresponding to an engaging portion or part of the plug frame  30 , hereinafter detailed, thus having a rotation positioning portion or part  54  allowing a movement of the flange part  53  in a rotational direction about the axis of the optical fiber within a predetermined range by the predetermined clearance, and a rotation allowing portion or part  55  for forming, at the rear-end side of the rotation positioning part  54 , a clearance greater than the clearance between the rotation positioning part  54  and the engaging projection  34 . 
   In this embodiment, the flange part  53  is provided with axial key grooves in four locations at an interval of 90 degrees with respect to the circumferential direction. Thus, the rotation positioning part  54  and the rotation allowing part  55  are constituted by the key grooves. Specifically, the key grooves at their tips are given generally the equal axial width to thereby provide a rotation positioning part  54  forming a predetermined clearance to the engaging projection  34 . By gradually increasing the width at the rear-end side toward the rear end, a rotation allowing part  55  is provided that forms a clearance greater than the clearance of between the rotation positioning part  54  and the engaging projection  34 . 
   In this manner, the ferrule  60  is made such that, by providing a rotation positioning part  54  on the flange part  53 , the movement of the ferrule  60  in rotational direction is allowed with in a predetermined clearance of rotation angle while, by a length of the rotation positioning part  54  in lengthwise direction, the ferrule  60  is allowed to incline a predetermined angle in a radial direction of the ferrule cylindrical body  40  with respect to the rotation positioning part  54  as a start point. 
   Meanwhile, at a rear-end side of the flange  50 , there is provided a spring guide  56  having an outer diameter smaller than the outer diameter of the flange part  53 . Over the outer periphery of the spring guide  56 , the urge spring  80 , such as a compression spring, is clamped by the stop ring  70  and the flange part  53 . 
   Herein, the plug frame  30  into which the ferrule  60  is to be inserted and held by is formed, for example, of plastic, and has a ferrule-insertion hole  31  penetrating in the lengthwise direction and generally having a rectangular outer shape in section, as shown in FIGS.  1  and  2 A- 2 B. The ferrule-insertion hole  31  has a flange part  33  formed with a projection hole  32  that has an inner diameter somewhat greater than an outer diameter of the ferrule cylindrical body  40  so that only the ferrule cylindrical body  40  is allowed to project. 
   Also, in the ferrule-insertion hole  31 , an engaging part is provided adjacent the flange part  33  for engagement with the key grooves formed by the rotation positioning part  54  and rotation allowing part  55  of the flange part  53 . 
   In this embodiment, because the rotation positioning part  54  and rotation allowing part  55  provided on the flange part  53  are formed by the key grooves, an engaging part is formed as two engaging projections  34  projecting toward the axis in opposite directions in the ferrule insertion hole  31 . 
   The engaging projection  34  is provided in a predetermined engagement width entirely in the axial direction, i.e. in a predetermined thickness entirely in the axial direction, to form a predetermined clearance to the rotation positioning part  54 . The rotation allowing part  55  forms a clearance greater than the rotation positioning part  54 . 
   Due to this, as shown in  FIGS. 4A-4C  the ferrule  60  held in the ferrule-insertion hole  31  is allowed by the rotation positioning part  54 , to rotationally move about the axis within a clearance of rotation angle and incline a predetermined amount in a widthwise direction A of the engaging projection  34  with respect to the engaging projection  34  as a start point. 
   Also, the engaging projection  34  is formed with a protrusion amount forming a predetermined clearance at between an end face  39  of the engaging projection  34  close to the flange part  53  and a bottom face  59  of the key groove formed by the rotation positioning part  54  and rotation allowing part  55 . Consequently, by the clearance between the engaging projection  34  and the key groove, the ferrule  60  is allowed to incline in an opposite direction B to the engaging projection  34  with respect to the engaging projection  34  as a start point, in a radial direction of the ferrule cylindrical body  40 . 
   Namely, the ferrule  60  is held to the plug frame  30  in a manner inclining a predetermined amount in two radial, orthogonal directions in a state allowed to move in rotational direction about the axis. Accordingly, when attaching/detaching the Angle-PC connector  10  to/from the optical connector adapter, the ferrule  60  inclines to thereby remove the stresses in the different direction from the axial direction, whereby the ferrule  60  or split sleeve in the optical connector adapter can be prevented against the occurrence of breakage, such as mars or deformations thereby enabling stable attaching/detaching. 
   Incidentally, for providing a ultrahigh return loss (60 dB or less) at a low insertion loss (0.2 dB or less) during opposed connection, the eccentric center of curvature of the ferrule  60  must be given 50 μm or smaller. For this, the rotation angle of the ferrule  60  in rotational direction about the axis with respect to the plug frame  30  must be suppressed to ±3 degree or less, preferably ±2 degree or less. 
   Consequently, by providing 0.01 mm-0.10 mm to the widthwise clearance between the engaging projection  34  and the rotation positioning part  54 , the rotation angle of the ferrule  60  in rotational direction about the axis with respect to the plug frame  30  can be suppressed to ±2 degree or less. 
   Herein, in the case that, as shown in  FIG. 5A  for example, the engaging projection  34  is given a width 1.30 mm and a key groove  54  (rotation positioning part  54  in the key groove) having a width 1.35 mm is axially provided in the conventional flange part  53  such that a rotation angle of the ferrule in rotation direction about the axis with respect to the plug frame is ±2 degrees or less, i.e. in the case that the clearance is 0.05 mm, the flange part  53  inclines 1.8 degrees in a widthwise direction with respect to the engaging projection  34  as a start point as shown in FIG.  5 B. In this manner, with a slight inclination of 1.8 degrees, when the Angle-PC connector is attached/detached to/from the optical connector adapter, the unwanted stress in the direction different from the axial direction cannot be removed. Breakage such as mar or deformation is possibly caused in the optical connector adapter and Angle-PC connector. 
   In this manner, when there occurred a stress in the direction different from the axial direction, in case the inclination angle for releasing the stress is given 5 degrees or more, the axial length of a rotation positioning part  54  to be provided in the flange part  53  is 0.51 mm as shown in FIG.  5 C. 
   In this manner, the axial length of the rotation positioning part  54  is optimally 0.3 mm-0.5 mm depending upon working accuracy. 
   Meanwhile, the rotation allowing part  55  of the flange part  53  satisfactorily has a width increasing in a degree not abutted against the engaging projection  34  when inclined radially of the ferrule cylindrical body  40  with respect to the rotation positioning part  54  as a start point. For example, the inclination of the side surface of the rotation allowing part  55  forming the gradually increasing width may be approximately 5 degrees relative to the axial direction. 
   Meanwhile, the rotation allowing part  55  is not limited in shape, e.g. may be formed in a width greater than the width of the rotation positioning part  54  having a step to the rotation positioning part  54 . 
   Meanwhile, as shown in FIGS.  1  and  2 A- 2 B, the plug frame  30  is formed with two engaging holes  35  communicating with the ferrule-insertion hole  31  and opened in the outer periphery. The engaging hole  35  is adapted to engage the engaging part  75  provided at the tip of the hereinafter-referred stop ring  70 . 
   Also, the stop ring  70  is of a metal, such as stainless steel or brass, plastic or the like, formed in a circular cylindrical form having a penetration hole  71  axially penetrated to be inserted by the spring guide  56  of the flange member  50 . 
   The penetration hole  71  is structured with a large-diameter part  72  at the front side for insertion of the urge spring  80  and a small-diameter part  73  at the rear side for insertion of the spring guide  56  of the flange member  50 . The urge spring  80  at its one end is allowed to contact with a step  74  provided by the internal-diameter difference between the large-diameter part  72  and the small-diameter part  73 . 
   Incidentally, the urge spring  80  at its other end is in contact with the rear-end face of the flange part  53  so that the flange part  50  is urged axially frontward relative to the stop ring  70 . 
   Also, the stop ring  70  on its front outer periphery is provided with an engaging part  75  for the stop ring to project into the engaging hole  35  when inserted in the ferrule-insertion hole  31  of the plug frame  30 . The engaging part  75  is made in a taper form having a projection amount gradually decreasing as directed toward the tip. The engaging part  75  is made to be moved in the engaging hole  35  while spreading the rear end of the plug frame, into engagement with the engaging hole  35 . 
   In order to hold the ferrule  60  in the plug frame  30  thus constructed, the ferrule  60  holding an optical fiber  1  is inserted in the ferrule-insertion hole  31  of the plug frame  30  such that the rotation positioning part  54  and rotation allowing part  55  structured by key grooves of the flange part  53  is put into engagement with the engaging projection  34 . By sequentially inserting the urge spring  80  and stop ring  70  previously inserted over the optical fiber core  2 , the engaging part  75  of the stop ring  70  is engaged by the engaging hole  35  of the plug frame  30 . This fixes the stop ring  70  on the plug frame  30 . At this time, the front side face of the flange part  53  of the ferrule  60  abuts against the flange part  33  of the plug frame  30 . Due to this, the ferrule  60  is projected a predetermined amount at the projection hole  32  of the flange part  33  in a state restricted in movement toward the front, and held urged toward the axial forward. 
   Meanwhile, the ferrule  60  thus held is allowed to move in rotational direction about the axis with respect to the plug frame  30  within a predetermined range by the rotation positioning part  54 , and the radial inclination amount is placed in an allowed state within a predetermined range by the lengthwise length of the rotation positioning part  54 . 
   Furthermore, on the outer periphery of the plug frame  30  thus assembled, there are provided two of engaging convex parts  36  for engagement with the plug housing  20 . By engaging these engaging convex parts  36  with the engaging concave parts  21  of the plug housing  20 , the plug frame  30  is held movable within an axial predetermined range in the plug housing  20 , thus configuring an Angle-PC connector. 
   The Angle-PC connector  10  thus formed, when oppositely connected by a not-shown optical connector adapter, is to be held in a state the ferrule  60  is moved toward the stop ring  70  such that mutual abutment is under a predetermined pressure. 
   In this manner, when the Angle-PC connector  10  is attached/detached to/from the optical connector adapter, the ferrule  60  is exerted by an axial pressure. However, the ferrule  60  held in the plug frame  30  can radially incline in a predetermined range in a state that its movement in rotational direction about the axis is allowed within a predetermined angle range with respect to the plug frame  30  by the rotation positioning part  54  and rotation allowing part  55 . Consequently, the unwanted stress in a direction different from the axial direction can be removed. The optical connector adapter or Angle-PC connector  10  is prevented against the occurrence of breakage, such as mar or deformation, thereby improving attaching/detaching stability. 
   Incidentally, because the Angle-PC connector  10  can oppositely connect between the ferrules  60  in a state the movement in rotational direction of the ferrule  60  is allowed within a predetermined range, it is possible to easily realize an optical connection with a low insertion loss and high return loss. 
   Embodiment 2 
     FIG. 6  is an exploded perspective view of an Angle-PC connector according to embodiment 2 of the invention,  FIGS. 7A-7B  are an exploded plan view and assembly sectional view of the Angle-Pc connector,  FIGS. 8A-8C  are a perspective view, plan view and sectional view respectively, of a ferrule, and  FIGS. 9A-9C  are sectional views of the Angle-Pc connector. 
   Although the foregoing embodiment 1 was on the SC-type Angle-PC connector that the ferrule cylindrical body  40  had the outer diameter of 2.5 mm, embodiment 2 is on an example of an Angle-PC connector that a ferrule cylindrical body  40 A has an outer diameter of 1.25 mm. Incidentally, the corresponding parts to the foregoing embodiment 1 are attached with the same references to thereby omit the duplicated explanation. 
   As shown in the figure, the Angle-PC connector  10 A of this embodiment has a plug housing  20 A to fit to an optical connector adapter, a plug frame  30 A to fit in the plug housing  20 A, a ferrule  60 A holding an optical fiber  1  for optical connection and to be inserted to the rear of the plug frame  30 A, a stop ring  70 A having a tip to engage a rear end of the plug frame  30 A, and an urge spring  80 A held between the ferrule  60 A and the stop ring  70 A and urging the ferrule  60 A toward the axial forward. 
   As shown in  FIGS. 8A-8C , the ferrule  60 A is formed with an outer diameter of 1.25 mm, and structured with a ferrule cylindrical body  40 A formed of a ceramic material such as zirconia, a glass material, a metal material such as stainless steel, nickel, nickel alloy or the like, and a flange member  50 A fit to one end of the ferrule cylindrical body  40 A. 
   The flange member  50 A has a flange part  53 A radially projecting to circumferentially extend on an outer periphery opened with a fit hole  51 A to which the ferrule cylindrical body  40 A at one end is to be fit. 
   The flange part  53 A is formed generally rectangular in radial section, and has a rotation positioning part  54 A configured by four axially-parallel surfaces at a side close to the ferrule cylindrical body  40 A and a rotation allowing part  55 A configured by four taper surfaces slanted toward the axis in a direction toward the stop ring  70 A. 
   On the other hand, as shown in FIGS.  6  and  7 A- 7 B, the plug frame  30 A is provided with an engaging hole  34 A for engagement with the rotation positioning part  54 A and rotation allowing part  55 A, adjacently to the flange part  33 A having a projection hole  32 A provided in the ferrule-insertion hole  31 A. 
   In this embodiment, because the rotation positioning part  54 A and rotation allowing part  55 A is provided generally rectangular in radial section, the engaging part has a radial section generally in the same shape to the rotation positioning part  54 A and a section somewhat greater than the rotation positioning part  54 A made as a generally rectangular engaging hole  34 A. 
   The engaging hole  34 A is constantly provided with an engaging width in the axial direction, i.e. axially extending having vertical and horizontal opening width in a predetermined width. This forms a predetermined clearance at between the rotation positioning part  54 A and the engaging hole  34 A, and a clearance greater than the rotation positioning part  54 A at between the rotation allowing part  55 A and the engaging hole  34 A. 
   Due to this, as shown in  FIGS. 9A-9C , the ferrule  60 A held in the ferrule-insertion hole  31 A is allowed, by the rotation positioning part  54 A, such that the movement in rotational direction about the axis is a predetermined clearance of rotation angle, and to incline a predetermined amount in opposite two directions of a plane forming the rotation positioning part  54 A with respect to the engaging hole  34 A as a start point. 
   Herein, in the case that, as shown in  FIG. 10A  for example, the engaging hole  34 A is given a width and height of 2.82 mm and a flange part  53 A having a width and height of 2.77 mm is axially provided in the conventional flange member such that a rotation angle of the ferrule in rotation direction about the axis with respect to the plug frame is 2 degrees or less, or 1.973 degrees in this embodiment, i.e. in the case that the clearance is 0.05 mm, the ferrule inclines 2 degrees with respect to the flange part  53 A as a start point as shown in FIG.  10 B. With such a slight inclination of 2 degrees, when the Angle-PC connector is attached/detached to/from the optical connector adapter, the unwanted stress in the direction different from the axial direction cannot be removed. Breakage such as mar or deformation is possibly caused in the optical connector adapter and Angle-PC connector. 
   In this manner, when there is a stress occurring in the direction different from the axial direction, in case the inclination angle for releasing the stress is assumably given 5 degrees or more, the axial length of a rotation positioning part  54 A to be provided in the flange part  53 A is 0.69 mm or smaller as shown in FIG.  10 C. 
   Such an axial length of the rotation positioning part  54 A is optimally 0.4 mm-0.6 mm in consideration of working accuracy. 
   Meanwhile, the rotation allowing part  55 A may be formed with a taper surface in such a degree as not abutted against the inner surface of the engaging hole  34 A when the ferrule  60 A is inclined radially relative to the plug frame  30 A with respect to the rotation positioning part  54 A as a start point. For example, the inclinations of the four taper surfaces configuring the rotation allowing part  55 A may be respectively given approximately 5 degrees with respect to the axial direction. 
   In this manner, by providing a rotation positioning part  54 A and rotation allowing part  55 A on the Angle-PC connector  10 A, the rotation of the ferrule  60 A in rotational direction about the axis relative to the plug frame  30 A is allowed to a predetermined rotation angle and a predetermined slant can be allowed in the radial direction. Accordingly, similarly to the foregoing embodiment 1, when attaching/detaching to/from the optical connector adapter, the unwanted stress in a direction different from the axial direction can be removed to prevent the optical connector adapter or Angle-PC connector  10 A against the occurrence of breakage, such as mar or deformation, thereby enabling optical connection with low insertion loss and high return loss. 
   Incidentally, because the engagement of plug frame  30 A and stop ring  70 A, the engagement of plug frame  30 A and plug housing  20 A and the like are similar to embodiment 1, the same parts such as engaging holes, engaging projections and the like to be used in engagement are attached by the corresponding references, to omit duplicated explanations. 
   Meanwhile, in this embodiment, although the flange part  53 A was made generally rectangular in radial section, this is not limited to, e.g. the flange may be made hexagonal in radial section. Such examples are explained in the below. 
     FIG. 11  is an exploded perspective view of an Angle-Pc connector showing another flange example,  FIGS. 12A-12B  are an exploded perspective view and assembly sectional view of the Angle-PC connector showing the other flange example,  FIGS. 13A-13C  are a perspective view, plan view and sectional view of a ferrule respectively, showing the other flange example, and  FIGS. 14A-14C  are sectional views showing the other flange example. 
   As shown in the figure, the Angle-PC connector  10 B has a plug housing  20 A, a plug frame  30 B to fit in the plug housing, a ferrule  60 B holding an optical fiber for optical connection and to be inserted to the rear of the plug frame  30 B, a stop ring  70 A having a tip to engage a rear end of the plug frame  30 B, and an urge spring  80 A held between the ferrule  60 B and the plug frame  30 B and urging the ferrule  60 B toward the axial forward. 
   The flange member  50 B, to be fit to the rear end of the ferrule cylindrical body  40 A of the ferrule  60 B, has a flange part  53 B projecting to circumferentially extend on an outer periphery of the fit part  51 A close to the opening and formed hexagonal in radial section. 
   The flange part  53 B is formed hexagonal in radial section, and has a rotation positioning part  54 B configured by six surfaces parallel with the axial direction at a side close to the ferrule cylindrical body  40 A and a rotation allowing part  55 B configured by six taper surfaces slanted in the axial direction toward a side close to the stop ring  70 A. 
   On the other hand, as shown in FIGS.  11  and  12 A- 12 B, the plug frame  30 B is provided with an engaging part  34 B for engagement with the rotation positioning part  54 B and rotation allowing part  55 B, adjacently to the flange part  33 A provided in the ferrule-insertion hole  31 A. 
   In this embodiment, because the rotation positioning part  54 B and rotation allowing part  55 B is formed hexagonal in radial section, the engaging part has a radial section generally in the same shape to the rotation positioning part  54 B and a section somewhat greater than the rotation positioning part  54 B made as a generally hexagonal engaging hole  34 B. 
   The engaging hole  34 B is provided equal in engaging width in the axial direction, i.e. constant in the distance between the opposed inner surfaces in the axial direction. This forms a predetermined clearance at between the rotation positioning part  54 B and the engaging hole  34 B, and a clearance greater than the rotation positioning part  54 B at between the rotation allowing part  55 B and the engaging hole  34 B. 
   Even in case the flange part  53 B and the engaging hole  34 B are made hexagonal in radial section, the ferrule  60 A held in the ferrule-insertion hole  31 A as shown in  FIGS. 14A-14C  is allowed, by the rotation positioning part  54 B, such that the movement in rotational direction about the axis is a predetermined clearance of rotation angle with respect to the plug frame  30 B, and to incline a predetermined amount in opposite three directions of a plane forming the rotation positioning part  34 A with respect to the engaging hole  34 B as a start point. The similar effect to the above embodiment is obtainable. 
   Meanwhile, such a ferrule  60 B having a flange part  53 B hexagonal in radial section is used, in many cases, in an LC-type Angle-PC connectors. 
   Of course, in also the FC-type, MU-type or LC-type Angle-PC connector, the similar effect to the above embodiment can be obtained by providing a rotation positioning part  54 B and rotation allowing part  55 B on the flange part  53 B as described above. 
   Incidentally, the shape of the rotation allowing part of the flange part is not especially limited unless abutting against an engaging projection at a predetermined angle or less and restricting the inclination when inclined to an inclination angle defined by the rotation positioning part, e.g. may be circular cylindrical as shown in  FIGS. 15A-15C . 
   In this manner, by configuring the ferrule  60 C with a ferrule cylindrical body  40 A and a flange member  50 C to be fit to the rear end of the ferrule cylindrical body  40 A and having a sectionally hexagonal rotation positioning part  54 B and circular cylindrical rotation allowing part  55 C, it is possible to easily work a fine flange part  53 C. 
   Meanwhile, in the case of making a flange having only a rotation positioning part without providing a rotation allowing part, there is a fear of weak strength and hence breakage upon urged by an urge spring. Because the urge spring abuts against the rear-end face of the rotation allowing part formed in a cylindrical form or by a taper surface in the outer periphery, it is possible to prevent the flange from being broken by an urge force of the urge spring. 
   Other Embodiments 
   Although embodiments 1 and 2 of the invention were explained above, the basic structure of Angle-PC connector is not limited to those described above. 
   For example, although the foregoing embodiment 1 had the rotation positioning part and rotation allowing part made by key grooves and the engaging part by engaging projections, this is not limited to, e.g. even in the case of an SC-type Angle-PC connector, it may be made with a flange generally rectangular or hexagonal in radial section and an engaging part by an engaging hole generally in the same form as the rotation positioning part, similarly to the embodiment 2. 
   Also, the embodiments 1 and 2 were by the rotation positioning part  54 ,  54 A and  54 B having a predetermined axial length, these are not limited to, e.g. the rotation allowing part  55 ,  55 A and  55 B may be provided axially of a flange part  53 ,  53 A,  53 B and  53 C. Namely, abutting a front corner of the rotation allowing part against an engaging part provides a rotation positioning part to restrict the movement in rotational direction to a predetermined range. Abutting a slant surface of the rotation allowing part against the engaging part restricts the movement in an inclination direction to a predetermined amount. Consequently, in the case of providing a rotation allowing part in the axial direction, the inclination angle to the axis of the rotation allowing part can be rendered as an inclination angle of the ferrule itself. 
   Furthermore, although the embodiments 1 and 2 exemplified the SC-type Angle-PC connector  10 ,  10 A,  10 B, these are not limited to. It is naturally possible to use the present invention for an FC-type and MU-type, LC-type or the like. 
   As explained above, according to the Angle-PC connector of the present invention, by providing a rotation positioning part and rotation allowing part in the flange part, the holding member of the ferrule can be allowed in its rotation angle of rotational direction within a predetermined range and can be inclined within a predetermined range toward the radial direction. A low insertion loss and high return loss can be easily realized during optical connection, and the stress in a different direction from the axial direction can be removed when attached/detached to/from an optical connector adapter. Breakage, such as mar or deformation, is prevented during attaching/detaching thereby enabling stable attaching/detaching.