Abstract:
A ferrule has a cylindrical body constructed from a single piece of material and having an outer circumferential surface. A first insertion hole of the cylindrical body is bounded by a first inner surface of the cylindrical body and is configured to receive therein a first preselected portion of an optical fiber so that the first preselected portion of the optical fiber is in direct contact with the first inner surface of the cylindrical body. A second insertion hole of the cylindrical body is disposed in communication with the first insertion hole. The second insertion hole is bounded by a second inner surface of the cylindrical body and is configured to receive therein a second preselected portion of the optical fiber enclosed in a buffer coating so that the second preselected portion of the optical fiber is in direct contact with the second inner surface of the cylindrical body. A flange member separate and independent from the cylindrical body is connected directly to the outer circumferential surface of the cylindrical body.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a ferrule as one portion of a plug side constituting an optical connector for making an optical connection. 
   2. Background Information 
   In the optical connector used in the optical connection of an optical fiber used in communication, etc., the optical fiber is inserted and fixed into the ferrule processed with respect to inside and outside diameters with high accuracy. Thereafter, the end face of a connecting portion of the optical fiber is polished in a convex spherical surface shape, and the optical connection is made by making the optical fibers come in physical contact with each other. 
   In the ferrule for inserting and holding such an optical fiber, there is a structure constructed by a cylindrical member, a cylindrical body for the ferrule arranged within the cylindrical member, and a flange member fixed to only the outer circumferential face of the cylindrical member. 
   Here, the conventional ferrule for inserting and holding the optical fiber will be explained in detail.  FIG. 12  is a sectional view of the ferrule in the prior art. 
   As shown in  FIG. 12(   a ), the ferrule  100  has a cylindrical member  110  having a through hole  101  extending therethrough in the axial direction, a cylindrical body  120  for the ferrule fitted to the side of a tip portion of the through hole  101  arranged in the cylindrical member  110  and inserting and holding the optical fiber, and a flange member  130  fixed to only the outer circumferential face of the cylindrical member  110 . 
   For example, the cylindrical member  110  is formed by a metal such as stainless steel, etc., and the through hole  101  is formed in the cylindrical member  110  over the axial direction. 
   An insertion hole  102  of the cylindrical body for the ferrule for inserting and fixing the cylindrical body  120  for the ferrule by press fitting is formed on the tip portion side of this through hole  101 . An optical buffered fiber insertion hole  103  for inserting and holding an optical buffered fiber formed by coating the outer circumference of the optical fiber is formed on the side of a rear end portion of the through hole  101 . 
   The cylindrical body  120  for the ferrule fixed into the through hole  101  of the cylindrical member  110  is formed by hard ceramic and glass such as zirconia, etc. An optical fiber insertion hole  121  for inserting and holding the optical fiber is formed in the cylindrical body  120  for the ferrule over the axial direction. A taper portion  122  having an inside diameter gradually increased is arranged on the rear end portion side of this optical fiber insertion hole  121 . No tip of the optical fiber inserted from the side of the optical buffered fiber insertion hole  103  abuts on the rear end face of the cylindrical body  120  for the ferrule, etc. by the taper portion  122  so that this tip is easily inserted into the optical fiber insertion hole  121 . 
   The cylindrical member  110  is constructed by a large diameter portion  111  having a large outside diameter on the tip side, and a small diameter portion  112  having an outside diameter smaller than that of the large diameter portion  111  and arranged on the rear end side. A projecting portion  113  is projected in the small diameter portion  112  so as to have an outside diameter approximately equal to that of the large diameter portion  111  over the circumferential direction of the outer circumferential face. 
   The flange member  130  having a ring shape and fixed to only the outer circumferential face is arranged in this small diameter portion  112 . For example, this flange member  130  is formed by a metal such as stainless steel, etc. 
   A through hole  131  is extended through this flange member  130  over the axial direction. A large diameter through hole  131   a  having an inside diameter slightly larger than the outside diameter of the projecting portion  113  is arranged on one end portion side of the through hole  131 . A small diameter through hole  131   b  having an inside diameter slightly larger than the small diameter portion  112  of the cylindrical member  110  and slightly larger than the outside diameter of the projecting portion  113  is arranged on the other end portion side of the through hole  131 . Namely, a step difference portion  131   c  is formed within the through hole  131  of the flange member  130  by the inside diameter difference between the large diameter through hole  131   a  and the small diameter through hole  131   b.    
   The flange member  130  is inserted from the large diameter through hole  131   a  side to the small diameter portion  112  side of the cylindrical member  110 . The movement of the flange member  130  onto the large diameter portion  111  side with respect to the cylindrical member  110  is regulated by abutting the step difference portion  131   c  of the flange member  130  on the projecting portion  113  of the cylindrical member  110 . 
   Thus, the movement of the flange member  130  onto the tip side with respect to the cylindrical member  110  is regulated. Accordingly, for example, when ferrules  100  are used in the optical connector, the tip faces of the ferrules  100  area butted on each other at a predetermined pressure by biasing the flange member  130  of each of the ferrules  100  optically connected by abutting their tip faces on each other on the tip face side. Therefore, it is possible to prevent the flange member  130  from being moved onto the tip face side with respect to the cylindrical member  110 . 
   For example, four key grooves  132  of a concave shape are arranged on the outer circumferential face of the flange member  130 , and regulate the movement in the rotating direction when the ferrule  100  is assembled into an unillustrated optical connector, etc. by the key grooves  132 . 
   Such a ferrule  100  can be formed by fixing the cylindrical body  120  for the ferrule to the cylindrical member  110  by pressing fitting and adhesion, and then center-grinding and processing an assembly body constructed by this cylindrical member  110  and the cylindrical body  120  for the ferrule, and further performing centerless finishing and then fixing the flange member  130  by the press fitting and adhesion. 
   However, a problem exists in that the number of parts is large and cost is high in such a ferrule  100 . 
   A problem also exists in that the ferrule  100  is heavy in weight since the cylindrical member  110  and the flange member  130  almost occupying the ferrule  100  are formed by a metal such as stainless steel, etc. 
   Further, a problem exists in that the grinding amount is large and a long working time is taken to perform the finishing operation with high accuracy since the center grinding work and the centerless finishing are performed after the cylindrical body  120  for the ferrule and the cylindrical member  110  are assembled. 
   Therefore, a ferrule constructed by the cylindrical body for the ferrule and the flange member fitted to the rear end portion of this cylindrical body for the ferrule without arranging the cylindrical member  110  is proposed. 
   As shown in  FIG. 12(   b ), this ferrule  100 A has a cylindrical body  120 A for the ferrule having an optical fiber insertion hole  121 A for inserting and holding an optical fiber and extending through the cylindrical body  120 A for the ferrule over the axial direction, and a flange member  130 A fitted to the rear end portion of the cylindrical body  120 A for the ferrule. 
   For example, the cylindrical body  120 A for the ferrule is constructed by ceramic such as zirconia, etc., and a taper portion  122 A having an inside diameter gradually increased is formed in the rear end portion of the optical fiber insertion hole  121 A extended and formed in the axial direction. 
   The flange member  130 A is constructed by a metal such as stainless steel, etc., and an optical buffered fiber insertion hole  103 A is formed so as to extend through the flange member  130 A in the axial direction and be communicated with the optical fiber insertion hole  121 A of the cylindrical body  120 A for the ferrule. 
   A flange portion  133  projected in the circumferential direction is integrally arranged in the outer circumference of the flange member  130 A, and a key groove  132 A is arranged in this flange portion  133 . 
   Such a ferrule  100 A can be fixed and formed by fitting and adhering the flange member  130 A to the rear end portion of the cylindrical body  120 A for the ferrule by press fitting after the center grinding work and the centerless work are made with respect to the cylindrical body  120 A for the ferrule. 
   The ferrule  100 A can be made light in weight and reduced in cost by constructing the ferrule  100 A by the cylindrical body  120 A for the ferrule and the flange member  130 A in this way. 
   Further, a time required to grind the cylindrical body  120 A for the ferrule can be shortened by grinding the cylindrical body  120 A for the ferrule constructed by a single member. 
   Since the cylindrical body for the ferrule constructed by such zirconia ceramic is formed by extrusion molding, the optical fiber insertion hole formed in the cylindrical body for the ferrule can be formed over the axial direction approximately at only the uniform inside diameter. However, in recent years, a method for forming the cylindrical body for the ferrule by the extrusion molding of a zirconia compound is established, and the degree of freedom of the shape formation of the optical fiber insertion hole formed in the cylindrical body for the ferrule is increased. Accordingly, the cylindrical body for the ferrule having the inside diameter of a so-called precise nozzle shape can be manufactured. 
   However, a problem exists in that manufacture cost is high in the ferrule formed by press-fitting and fixing the flange member to the rear end portion of the above cylindrical body for the ferrule since the flange member is formed by cutting a metal such as stainless steel, etc. 
   A problem also exists in that the ferrule is heavy in weight since the flange member is formed by the metal such as stainless steel, etc. 
   In consideration of such a situation, an object of the present invention is to provide a ferrule made light in weight and reduced in manufacture cost. 
   SUMMARY OF THE INVENTION 
   To solve the above problem, a first mode of the present invention resides in a ferrule comprising a cylindrical body for the ferrule which is constructed by ceramic and has an optical fiber insertion hole for inserting an optical fiber thereinto and also has an optical buffered fiber insertion hole communicated with the optical fiber insertion hole and inserting and holding an optical buffered fiber formed by coating the optical fiber; and a flange member fixed to only the outer circumferential face of the cylindrical body for the ferrule. 
   A second mode of the present invention resides in the ferrule in which said flange member is fixed to the outer circumferential face of said cylindrical body for the ferrule by press fitting in the first mode. 
   A third mode of the present invention resides in the ferrule in which said flange member is fixed to the outer circumferential face of said cylindrical body for the ferrule by forming said flange member by molding in the first mode. 
   A fourth mode of the present invention resides in the ferrule in which a convexo-concave face for non-slip is formed on the outer circumferential face of said cylindrical body for the ferrule for fixing said flange member in any one of the first to third modes. 
   A fifth mode of the present invention resides in the ferrule in which said flange member is constructed by a plastic material in any one of the first to fourth modes. 
   A sixth mode of the present invention resides in the ferrule in which said cylindrical body for the ferrule is constructed by a single member in any one of the first to fifth modes. 
   In any one of the first to fifth modes of the present invention, a seventh mode of the present invention resides in the ferrule in which said cylindrical body for the ferrule is constructed by a cylindrical portion constructed by ceramic, and an adjusting portion arranged on at least one end side of the interior of the cylindrical portion and having a hardness lower than that of the cylindrical portion, and the core center of a tip face of said optical fiber is aligned with the center with the outer circumference of said cylindrical portion as a reference by deforming said adjusting portion. 
   An eighth mode of the present invention resides in the ferrule in which said cylindrical portion is constructed by ceramic, and said adjusting portion is constructed by a copper-nickel alloy in the seventh mode. 
   A ninth mode of the present invention resides in the ferrule in which said ceramic is zirconia in any one of the first to eighth modes. 
   In the present invention, the ferrule can be made light in weight and manufacture cost can be reduced by forming the ferrule by the cylindrical body for the ferrule and the flange member fixed to only the outer circumferential face of the cylindrical body for the ferrule. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is an exploded perspective view of a ferrule in accordance with an embodiment mode 1 of the present invention and  FIG. 1B  is a perspective view in which one portion of this ferrule is notched. 
       FIG. 2A  is an exploded perspective view and  FIG. 2B  is a sectional view of an optical connector plug in accordance with the embodiment mode 1 of the present invention. 
       FIG. 3  is a perspective view in which one portion of an adapter in accordance with the embodiment mode 1 of the present invention is notched. 
       FIG. 4A  is an exploded perspective view of a ferrule in accordance with an embodiment mode 2 of the present invention and  FIG. 4B  is a perspective view in which one portion of this ferrule is notched. 
       FIG. 5A  is an exploded perspective view of a ferrule in accordance with an embodiment mode 3 of the present invention and  FIG. 5B  is a perspective view in which one portion of this ferrule is notched. 
       FIG. 6  is a perspective view and a sectional view of a ferrule in accordance with an embodiment mode 4 of the present invention. 
       FIG. 7  is a plan view showing an assembly state of the ferrule in accordance with the embodiment mode 4 of the present invention. 
       FIG. 8A  is a perspective view of an optical connector in accordance with an embodiment mode 5 of the present invention, and  FIG. 8B  is a perspective view in which a main portion of the optical connector is notched. 
       FIG. 9A  is a plan view and  FIG. 9B  is a sectional view of the optical connector in accordance with the embodiment mode 5 of the present invention. 
       FIGS. 10A–10B  are exploded perspective views of a ferrule in accordance with another embodiment mode of the present invention. 
       FIG. 11  is an exploded perspective view of a ferrule in accordance with another embodiment mode of the present invention. 
       FIGS. 12A–12B  are sectional views of a ferrule in the prior art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will next be explained in detail on the basis of the embodiment modes. 
   (Embodiment Mode 1) 
     FIG. 1  is an exploded perspective view of a ferrule in accordance with an embodiment mode 1 and a perspective view in which one portion of this ferrule is notched. 
   As shown in  FIG. 1 , the ferrule  10  of this embodiment mode is a ferrule  10  for holding the tip of an optical fiber and used in an optical connector plug of an SC type, an FC type, etc. The ferrule  10  has a cylindrical body  20  for the ferrule having 2.5 mm in outside diameter and a flange member  30  fixed to only the outer circumferential face of the cylindrical body  20  for the ferrule. 
   A through hole  21  is extended through the cylindrical body  20  for the ferrule over the axial direction. An optical fiber insertion hole  22  for inserting and holding the optical fiber  1  is formed on the side of a tip portion of the through hole  21 . An optical buffered fiber insertion hole  23  for inserting and holding an optical buffered fiber  2  is formed on the side of a rear end portion of the through hole  21 . The outer circumference of the optical fiber  1  having a diameter larger than the optical fiber insertion hole  22  is coated in the optical buffered fiber  2 . 
   A taper portion  24  is arranged between the optical fiber insertion hole  22  and the optical buffered fiber insertion hole  23 , and has an inside diameter gradually increased toward the rear end portion side by the inside diameter difference. The optical fiber  1  inserted from the optical buffered fiber insertion hole  23  side is easily inserted into the optical fiber insertion hole  22  by the taper portion  24 . 
   For example, such a cylindrical body  20  for the ferrule is constructed by ceramics such as zirconia, etc. 
   For example, a flange member  30  fixed to only the outer circumferential face of such a cylindrical body  20  for the ferrule has a ring shape formed by a plastic material. An insertion hole  31  having an inside diameter approximately equal to the outside diameter of the cylindrical body  20  for the ferrule is formed in the flange member  30  over the axial direction. 
   Further, four key grooves  32  of a concave shape are arranged on the outer circumferential face of the flange member  30  at an equal interval in the circumferential direction. 
   The ferrule  10  is formed by fixing such a flange member  30  to only the outer circumferential face of the cylindrical body  20  for the ferrule. 
   The flange member  30  may be fixed to the cylindrical body  20  for the ferrule by press fitting and adhesion, and may be also formed and fixed to the outer circumferential face of the cylindrical body  20  for the ferrule by outsert molding. 
   Thus, in the ferrule  10  of this embodiment mode, the cylindrical body  20  for the ferrule holds the optical fiber  1  and the optical buffered fiber  2 , and the flange member  30  is fixed to only the outer circumferential face of the cylindrical body  20  for the ferrule. Therefore, the flange member  30  can be made light in weight so that the ferrule  10  can be made light in weight and manufacture cost can be reduced. 
   The ferrule  10  can be further made light in weight and reduced in cost by forming the flange member  30  by a plastic material. 
   The ferrule  10  of this embodiment mode is a ferrule  10  used in the optical connector of an SC type, an FC type, etc. for holding the tip of the optical fiber  1  and making the optical connection, and using the cylindrical body  20  for the ferrule having 2.5 mm in outside diameter. 
   Here, the SC type optical connector will be explained as one example of the optical connector.  FIG. 2  is an exploded perspective view and a sectional view of an optical connector plug in accordance with the embodiment mode 1.  FIG. 3  is a perspective view in which one portion of an adapter is notched. 
   The optical connector shown in  FIGS. 2 and 3  is the SC type optical connector. This SC type optical connector is constructed by an SC type optical connector plug  40  having the above ferrule  10  described in the embodiment mode 1, and an adapter  50  for the SC type optical connector for fitting the SC type optical connector plug  40  from both opposite sides thereof. 
   As shown in  FIG. 2 , this SC type optical connector plug  40  has a plug housing  41  fitted to the adapter  50  for the SC type optical connector, and a plug frame  42  fitted into this plug housing  41 . The ferrule  10  constructed by the above cylindrical body  20  for the ferrule and the flange member  30 , a compression spring  46  mounted to an outer circumferential portion of the rear end of the cylindrical body  2  of or the ferrule, and a stopper  47  fitted to the rear end of the cylindrical body  20  for the ferrule through this compression spring  46  are arranged within this plug frame  42 . Namely, the compression spring  46  is nipped between the flange member  30  and the stopper  47 . 
   The ferrule  10  holding the optical fiber, and the compression spring  46  and the stopper  47  inserted into the optical buffered fiber  2  in advance are sequentially inserted into the plug frame  42 . An engaging claw  47   a  of the stopper  47  is engaged with an engaging hole  43  of the plug frame  42 . Thus, this stopper  47  is fixed to the plug frame  42 , and the ferrule  10  is biased and held within the plug frame  42  in the axial direction through the compression spring  46 . The rotation of the ferrule  10  held within the plug frame  42  is regulated by engaging the key grooves  32  formed in the flange member  30  with four engaging projecting portions  44  arranged in the plug frame  42 . 
   An engaging convex portion  45  engaged with the plug housing  41  is arranged in the outer circumference of the plug frame  42 . The plug frame  42  is held within the plug housing  41  by engaging the engaging convex portion  45  with an engaging concave portion  41   a  of the plug housing  41 . 
   On the other hand, as shown in  FIG. 3 , a sleeve  51  for the optical connection for optically connecting the optical fibers  1  to each other by oppositely aligning the ferrules  10  building the optical fibers  1  therein is built in the adapter  50  for the SC type optical connector. Further, the sleeve  51  for the optical connection is held by a sleeve holder  52  divided into two in the axial direction. This sleeve holder  52  is held by a housing  53  divided into two in the axial direction. 
   The optical connection can be made by inserting the SC type optical connector plug  40  having the above ferrule  10  from both opening portions  54  and  55  of such an adapter  50  for the SC type optical connector, and abutting the end faces of the ferrules  10  on each other within the sleeve  51  for the optical connection. 
   (Embodiment Mode 2) 
   In the above embodiment mode 1, the ferrule  10  used in the optical connector plug of the SC type, etc. having the cylindrical body  20  for the ferrule having 2.5 mm in outside diameter is illustrated. However, in the embodiment mode 2, a ferrule having the cylindrical body for the ferrule having 1.25 mm in outside diameter, particularly, the ferrule of an MU type optical connector plug is used. 
     FIG. 4  is an exploded perspective view of the ferrule in accordance with the embodiment mode 2 and a perspective view in which one portion of this ferrule is notched. 
   The ferrule  10 A shown in  FIG. 4  is a ferrule  10 A arranged in the MU type optical connector plug, and has a cylindrical body  20 A for the ferrule having 1.25 mm in outside diameter and constructed by zirconia, and a flange member  30 A fixed to only the outer circumferential face of this cylindrical body  20 A for the ferrule. 
   The cylindrical body  20 A for the ferrule has an outside diameter smaller than that of the cylindrical body  20  for the ferrule in the above embodiment mode 1, and a through hole  21 A is extended through this cylindrical body  20 A for the ferrule over the axial direction. 
   An optical fiber insertion hole  22 A for inserting and holding the optical fiber  1  is formed on the side of a tip portion of this through hole  21 A. An optical buffered fiber insertion hole  23 A for inserting and holding an optical buffered fiber  2 A is formed on the side of a rear end portion of the through hole  21 A. The outer circumference of the optical fiber  1  is coated in the optical buffered fiber  2 A. 
   A taper portion  24 A is arranged between the optical fiber insertion hole  22 A and the optical buffered fiber insertion hole  23 A, and has an inside diameter gradually increased toward the rear end portion side by an inside diameter difference. The optical fiber  1  inserted from the optical buffered fiber insertion hole  23 A side is easily inserted into the optical fiber insertion hole  22 A by the taper portion  24 A. 
   With respect to the outside diameter of the optical buffered fiber  2 A, the optical buffered fiber  2 A has a different thickness in accordance with a coating material, etc. arranged in the outer circumference of the optical fiber  1 . However, in this embodiment mode, the optical buffered fiber  2 A coated at a predetermined outside diameter or less, e.g., the optical fiber  1  having 125 μm in outside diameter and the optical buffered fiber  2 A having 250 μm in outside diameter are used to insert and hold the optical buffered fiber  2 A by the optical buffered fiber insertion hole  23 A arranged in the rear end portion of the cylindrical body  20 A for the ferrule. Namely, the inside diameter of the optical buffered fiber insertion hole  23 A is set to an inside diameter such as 300 μm slightly larger than 250 μm. 
   For example, the flange member  30 A fixed to only the outer circumferential face of such a cylindrical body  20 A for the ferrule approximately has a rectangular shape in section formed by a plastic material. An insertion hole  31 A having an inside diameter approximately equal to the outside diameter of the cylindrical body  20 A for the ferrule is formed in the flange member  30 A over the axial direction. 
   Similar to the above embodiment mode 1, the flange member  30 A may be fixed to the cylindrical body  20 A for the ferrule by press fitting and adhesion, and may be also formed and fixed to the outer circumferential face of the cylindrical body  20 A for the ferrule by outsert molding. 
   The ferrule  10 A is inserted into the insertion hole approximately formed in the rectangular shape in section in an unillustrated plug frame in assembly into the MU type optical connector plug even when no key groove is formed in the flange member  30 A. Therefore, the movement of the ferrule  10 A in its rotating direction can be regulated by forming the flange member  30 A in an outer shape approximately set to the rectangular shape in section. 
   Thus, similar to the above embodiment mode 1, the cylindrical body  20 A for the ferrule holds the optical fiber  1  and the optical buffered fiber  2 A, and the flange member  30 A is fixed to only the outer circumferential face of the cylindrical body  20 A for the ferrule as the ferrule  10 A assembled into the MU type optical connector plug. Therefore, the flange member  30 A can be made light in weight so that the ferrule  10 A can be made light in weight and manufacture cost can be reduced. 
   (Embodiment Mode 3) 
   The above embodiment mode 2 illustrates the ferrule  10 A having the cylindrical body  20 A for the ferrule of 1.25 mm in outside diameter assembled into the MU type optical connector plug. However, in the embodiment mode 3, the ferrule for the LC type optical connector will be explained. Members similar to those in the above embodiment mode are designated by the same reference numerals and their overlapping explanations are omitted. 
     FIG. 5  is an exploded perspective view of the ferrule in accordance with the embodiment mode 3 and a perspective view in which one portion of this ferrule is notched. 
   The ferrule  10 B shown in  FIG. 5  is a ferrule  10 B assembled into an LC type optical connector plug, and has a cylindrical body  20 A for the ferrule having 1.25 mm in outside diameter and constructed by zirconia, and a flange member  30 B fixed to only the outer circumferential face of the cylindrical body  20 A for the ferrule. 
   A member similar to that in the embodiment mode 2 is used in the cylindrical body  20 A for the ferrule, and its overlapping explanation is therefore omitted. 
   For example, the flange member  30 B fixed to only the outer circumferential face of the cylindrical body  20 A for the ferrule approximately has a hexagonal shape in section formed by a plastic material. The side of a tip portion of the flange member  30 B is formed in a taper shape. 
   Two key grooves  32 B of a concave shape each engaged with an unillustrated tool for adjusting the position around the central axis of the ferrule  10 B every 60° are arranged on the tip face of the flange member  30 B when the ferrule  10 B is assembled into the LC type optical connector plug. 
   Even when no key groove is arranged in the flange member  30 A, the ferrule  10 A is inserted into an insertion hole arranged in an unillustrated plug frame and approximately having a hexagonal shape in section when the ferrule  10 A is assembled into the LC type optical connector plug. Therefore, the movement of the ferrule  10 A in its rotating direction can be regulated by forming the flange member  30 A in an outer shape approximately set to the hexagonal shape in section. 
   Thus, similar to the above embodiment modes 1 and 2, the cylindrical body  20 A for the ferrule holds the optical fiber  1  and the optical buffered fiber  2 A and the flange member  30 B is fixed to only the outer circumferential face of the cylindrical body  20 A for the ferrule as the ferrule  10 B assembled into the LC type optical connector plug. Therefore, the flange member  30 B can be made light in weight so that the ferrule  10 B can be made light in weight and manufacture cost can be reduced. 
   (Embodiment Mode 4) 
     FIG. 6  is a perspective view and a sectional view of a ferrule in accordance with an embodiment mode 4 of the present invention.  FIG. 7  is a perspective view and a plan view of a main portion showing an assembly state of the ferrule. The same members as the above embodiment modes 1 to 3 are designated by the same reference numerals and their overlapping explanations are omitted. 
   As shown in these figures, the ferrule  10 C of this embodiment mode has a cylindrical body  20 B for the ferrule, and a flange member  30  fixed to only the outer circumferential face of the cylindrical body  20 B for the ferrule. 
   Here, the cylindrical body  20 B for the ferrule is constructed by a cylindrical portion  60  constructed by ceramic such as zirconia, etc., and an adjusting portion  70  held within the cylindrical portion  60  and formed by a member having a hardness lower than that of the cylindrical portion  60 . Thus, the ferrule  20 B having the cylindrical portion  60  constructed by ceramic is also a ferrule constructed by ceramic in the present invention. 
   A holding hole  61  approximately having the same outside diameter over the axial direction is extended through the cylindrical portion  60  over the axial direction. 
   A first optical buffered fiber insertion hole  62  for inserting and holding the optical buffered fiber  2  formed by coating the outer circumference of the optical fiber  1  is formed on the side of one end portion of this holding hole  61 . A large diameter portion  63  having an inside diameter larger than that of the first optical buffered fiber insertion hole  62  is formed on the other end portion side of the holding hole  61 . 
   For example, the cylindrical portion  60  can be set to 2.499 mm and 1.249 mm in outside diameter. With respect to about the same outside diameter of such a cylindrical portion  60  in its axial direction, an error in the outside diameter is preferably set to ±0.5 μm or less over the axial direction when the optical fiber  1  is e.g., a single mode optical fiber. Further, for example, when the optical fiber  1  is a multimode optical fiber, the error in the outside diameter is preferably set to 2.0 μm or less over the axial direction. 
   Further, the adjusting portion  70  having a hardness lower than that of the cylindrical portion  60  is arranged within the large diameter portion  63  of the holding hole  61  of the cylindrical portion  60 . 
   The adjusting portion  70  is continuously arranged over an opening edge portion of the large diameter portion  63  on the tip face of the cylindrical portion  60  from the interior of the large diameter portion  63  of the cylindrical portion  60 . A through hole  21  is extended through the adjusting portion  70  over the axial direction. 
   This through hole  21  is constructed by a second optical buffered fiber insertion hole  23  arranged on the first optical buffered fiber insertion hole  62  side and having an inside diameter approximately equal to the inside diameter of the first optical buffered fiber insertion hole  62 , and an optical fiber insertion hole  22  arranged on the tip face side and inserting and holding the optical fiber  1 . 
   Namely, the optical fiber  1  is inserted and held by the optical fiber insertion hole  22  of the adjusting portion  70 , and the optical buffered fiber  2  is inserted and held by the second optical buffered fiber insertion hole  23  of the adjusting portion  70  and the first optical buffered fiber insertion hole  62  of the cylindrical portion  60 . Thus, the optical fiber  1  and the optical buffered fiber  2  are held by the cylindrical body  20 B for the ferrule. 
   Such an adjusting portion  70  is not particularly limited if the adjusting portion  70  is formed by a material having a hardness lower than that of the cylindrical portion  60  constructed by ceramic such as zirconia, etc. For example, a copper-nickel alloy is used in the adjusting portion  70  in this embodiment mode. 
   Thus, the cylindrical body  20 B for the ferrule holding the optical fiber  1  presses against the tip face near the optical fiber insertion hole  22  of the adjusting portion  70  by e.g., an unillustrated aligning jig, and a V-groove  71  is formed on the tip face of the adjusting portion  70  in one portion of the periphery of the optical fiber insertion hole  22 . Thus, as shown in  FIG. 7 , the core position of the tip face of the optical fiber  1  can be positioned by deforming the adjusting portion  70  at the center with the outer circumference of the cylindrical portion  60  as a reference. 
   Thus, when the tip faces of the sleeve-shaped bodies  20 B for the ferrule are abutted and are optically connected to each other, the positioning is performed with the outer circumference of the cylindrical body  20 B for the ferrule as a reference. Therefore, the core of the optical fiber  1  held by each of the sleeve-shaped bodies  20 B for the ferrule abutted on each other can be positioned so that insertion loss can be reduced and the optical connection of high efficiency can be made. 
   The flange member  30  of this embodiment mode is the same as the above embodiment mode 1, and its overlapping explanation is therefore omitted. 
   (Embodiment Mode 5) 
   In the above embodiment mode 1, the optical connector plug using the ferrule  10  is explained as one example. However, no device using the ferrule of the present invention is particularly limited to this optical connector plug. 
   Here, other examples of the optical connector using the ferrule of the present invention will be explained.  FIG. 8  is a perspective view of an optical connector in accordance with an embodiment mode 5, and a perspective view in which one portion of this optical connector is notched.  FIG. 9  is a plan view and a sectional view of this optical connector. Members similar to those in the above embodiment modes are designated by the same reference numerals, and their overlapping explanations are omitted. 
   As shown in these figures, the optical connector  80  of this embodiment mode has a sleeve  81  for the optical connection for inserting a ferrule  10 D thereinto from both ends of this sleeve  81 , an adapter main body  82  for holding the sleeve  81  for the optical connection and fixed to a mounting substrate  91 , and a clamp  83  for abutting the tip faces of the ferrules  10 D on each other by a predetermined pressing force. 
   The ferrule  10 D is constructed by a cylindrical body  20  for the ferrule and a flange member  30 C fixed to only the outer circumferential face of this cylindrical body  20  for the ferrule. 
   The cylindrical body  20  for the ferrule has a shape similar to that in the above embodiment mode 1, and holds the optical fiber  1  and the optical buffered fiber  2 . 
   The flange member  30 C has a disk shape, and no key groove is formed on the outer circumferential face of the flange member  30 C. A small diameter disk portion  35  arranged on the tip face side of the cylindrical body  20  for the ferrule and having a small outside diameter, and a large diameter disk portion  36  arranged on the rear end portion side of the cylindrical body  20  for the ferrule and having a diameter larger than the outside diameter of the small diameter disk portion  35  are integrally formed in such a flange member  30 C. 
   Similar to the above embodiment mode 1, the flange member  30 C may be fixed to the cylindrical body  20  for the ferrule by press fitting and adhesion, and may be also formed and fixed to the outer circumferential face of the cylindrical body  20  for the ferrule by outsert molding. 
   On the other hand, the adapter main body  82  has holding portions  84  each having a U-shape and both ends bent oppositely to each other. 
   A ferrule holding hole  85  having an inside diameter slightly larger than the outside diameter of the cylindrical body  20  for the ferrule is coaxially arranged in each of these two holding portions  84 . 
   The sleeve  81  for the optical connection is nipped by the pair of holding portions  84  between the holding portions  84  of these ferrule holding holes  85 . 
   The sleeve  81  for the optical connection has a ferrule insertion hole  86  having a cylindrical shape and extending through this sleeve  81  over its axial direction, and a slit  87  of one stripe extending through the sleeve  81  over the axial direction on its side face. The ferrule insertion hole  86  is formed so as to have an inside diameter slightly smaller than the outside diameter of the cylindrical body  20  for the ferrule. 
   The cylindrical body  20  for the ferrule inserted into the ferrule holding hole  85  from each of both end sides of the ferrule insertion hole  86  is inserted into the sleeve  81  for the optical connection so that the optical fibers  1  are optically connected to each other. 
   At this time, the sleeve  81  for the optical connection is elastically deformed by the insertion of the cylindrical body  20  for the ferrule in a direction for widening the slit  87 . Therefore, the cylindrical body  20  for the ferrule can be closely attached to the inner circumferential face of the ferrule insertion hole  86 . 
   Thus, the sleeve-shaped bodies  20  for the ferrule inserted from both the ends of the ferrule insertion hole  86  can be aligned with each other along the inner circumferential face of the ferrule insertion hole  86  so that the optical fibers  1  can be reliably optically connected to each other without any axial shift, etc. Accordingly, when the optical fibers  1  are optically connected to each other, there is no fear that optical characteristics such as insertion loss, etc. are reduced. Namely, stable optical characteristics can be obtained. 
   For example, zirconia, phosphor bronze, stainless steel, plastic, etc. are used as a material for forming such a sleeve  81  for the optical connection. In this embodiment mode, zirconia is used as this material. 
   Such a sleeve  81  for the optical connection is arranged within the ferrule holding hole  85  and is abutted on a step difference portion  88  for the sleeve abutted on each of both the end faces of the sleeve  81  for the optical connection. Thus, the sleeve  81  for the optical connection is held in a state in which the movement of the sleeve  81  for the optical connection in the axial direction is regulated. 
   The adapter main body  82  is divided approximately at the center of the holding portion  84  so that the sleeve  81  for the optical connection can be nipped by the step difference portion  88  for the sleeve. 
   Further, the tip faces of the pair of ferrules  10 D inserted and held in the ferrule holding hole  85  of the adapter main body  82  and the ferrule insertion hole  86  of the sleeve  81  for the optical connection are abutted on each other by a clamp  83  at a predetermined pressure. 
   The clamp  83  is constructed by a member of a leaf spring shape having a tip portion  89  bent in a U-shape. A notch portion  90  is arranged in a bent tip portion  89 . A notch portion  90  for inserting a rear end portion of the ferrule  10 D, i.e., only the rear end portion of the cylindrical body  20  for the ferrule thereinto is arranged in the bent tip portion  89 . 
   This notch portion  90  is inserted into the rear end portion of the cylindrical body  20  for the ferrule, and is abutted on the rear end face of the flange member  30 C of the ferrule  10 D, i.e., the rear end face of the large diameter disk portion  36 . Thus, the pair of ferrules  10 D are held in a state in which the tip faces of these ferrules  10 D are abutted on each other at a predetermined pressure. 
   Such an optical connector  80  is mounted to the mounting substrate  91  by fixing the adapter main body  82  to the mounting substrate  91  by a fixing member  92  such as a screw, etc. 
   Thus, in this embodiment mode, the ferrule  10 D can be made compact and light in weight by using the optical connector  80  able to directly optically connect the ferrule  10 D holding the optical fiber  1  without using the optical connector plug of the above embodiment mode 1. Further, the optical connector  80  can be made compact and light in weight by using the above ferrule  10 D made compact and light in weight in the present invention in such an optical connector  80 . 
   (Other Embodiment Modes) 
   The embodiment modes 1 to 5 of the present invention is explained above, but the basic constructions of the ferrules  10  to  10 D are not limited to the above embodiment modes. 
   For example, non-slip portions may be arranged on the outer circumferential faces for fixing the flange members  30  to  30 C of the sleeve-shaped bodies  20 ,  20 A for the ferrule so as not to slip the flange members  30  to  30 C. 
   Each of  FIGS. 10 and 11  shows one example in which the non-slip portion is arranged in the ferrule  10  of the above embodiment mode 1.  FIGS. 10 and 11  are exploded perspective views of ferrules in accordance with other embodiment modes. 
   As shown in  FIG. 10(   a ), a non-slip portion  25  constructed by a V-shaped groove is formed over the axial direction on the rear end portion side of the outer circumferential face of the cylindrical body  20 C for the ferrule constituting the ferrule  10 E. 
   A projecting portion  33  engaged with the non-slip portion  25  constructed by the groove of the cylindrical body  20 C for the ferrule is arranged in a flange member  30 D over the axial direction on the inner circumferential face of an insertion hole  31 D. 
   Thus, the movements of the flange member  30 D in the rotating direction and on the axial tip portion side with respect to the cylindrical body  20 C for the ferrule are reliably regulated by arranging the non-slip portion  25  constructed by the groove on the outer circumferential face of the cylindrical body  20 C for the ferrule, and also arranging the projecting portion  33  engaged with the non-slip portion  25  on the inner circumferential face of the flange member  30 D. 
   Further, no non-slip portion is limited to this case. For example, as shown in  FIG. 10(   b ), a non-slip portion  26  constructed by the groove of a spiral shape is formed on the outer circumferential face of the cylindrical body  20 D for the ferrule constituting the ferrule  10 F. 
   A flange member  30 E is formed by outsert molding. The inner circumferential face of an insertion hole  31 E of the flange member  30 E is formed in a shape equal to that of the outer circumferential face of the cylindrical body  20 D for the ferrule. Namely, a projecting portion  34  of a spiral shape is arranged on the inner circumferential face of the insertion hole  31 E of the flange member  30 E. 
   Thus, the movements of the flange member  30 E in the rotating direction and the axial direction with respect to the cylindrical body  20 D for the ferrule are reliably regulated by arranging the non-slip portion  26  constructed by the groove on the outer circumferential face of the cylindrical body  20 D for the ferrule, and also arranging the projecting portion  34  engaged with the groove on the inner circumferential face of the flange member  30 E. 
   Further, no non-slip portion is limited to this case. For example, as shown in  FIG. 11 , a convexo-concave face  27  for the non-slip is formed on the outer circumferential face of the cylindrical body  20 E for the ferrule constituting the ferrule  10 G by surface coarse processing such as blast processing, etc. and injection molding, etc. 
   Thus, the movements of the flange member  30  in the rotating direction and the axial direction with respect to the cylindrical body  20 E for the ferrule are reliably regulated by arranging the convexo-concave face  27  on the outer circumferential face of the cylindrical body  20 E for the ferrule. 
   Thus, the non-slip portions  25  to  27  are not particularly limited in shape, size, etc. if the movements of the flange members  30 ,  30 D and  30 E in the rotating direction and the axial direction are reliably regulated. In  FIGS. 10 and 11 , the non-slip portion is arranged in the ferrule  10  of the embodiment mode 1 as an example, but the movements in the rotating direction and the axial direction are reliably regulated by arranging the non-slip portion in each of the ferrules  10 A,  10 B and  10 C of embodiment modes 2 to 4. 
   As explained above, in accordance with the ferrule of the present invention, since the ferrule is constructed by the cylindrical body for the ferrule and the flange member fixed to only the outer circumferential face of the cylindrical body for the ferrule, the flange member can be made light in weight and manufacture cost can be reduced.