Abstract:
To provide a ferrule tubular body and a ferrule which is free from a fear that the end face of the ferrule may be roughened, which can eliminate an eccentric adjustment process performed after an optical fiber is fixed, and which can attain the optical connection less in insertion loss. An indicator section  1   d   , 3   a   , 1   e  or  3   b  making it possible to observe an eccentric direction of a though-hole to which an exposed optical fiber end portion is inserted to be held is provided on the outer surface of a ferrule tubular body  1 A,  1 B,  1 C,  1 D and/or the outer surface of a flanged member  3 A,  3 B,  3 C,  3 D securely fixed to the rear end of the ferrule tubular body  1 A,  1 B,  1 C,  1 D.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a ferrule that is a plug side member included in an optical connector for optical connection, and to a ferrule tubular body that is a member included in the ferrule. 
     To optically connect the end portions of optical fibers to each other, an optical connector is used, which includes a plug for fixing the end portions of the optical fibers and an adaptor fitted to the plug from respective opposite sides. The aforementioned optical connector is classified into various types such as SC type, MU type and so on, and employs an eccentric adjustment in order to eliminate an insertion loss (a loss of optical signals) in optical connection as much as possible. 
     The eccentric adjustment method which has been employed conventionally will be described with reference to FIGS. 6 and 7. First, as shown in FIG. 6, a flanged member  82 , which is formed with key grooves  82   a  at angular intervals of 90 degrees, is securely fixed to the rear end portion of a ferrule tubular body  81 , and an optical fiber F 1  that appears by removing a sheath of one end of an optical cord F by a predetermined length is inserted into and securely fixed to a through-hole  81   a , so that the optical cord F having a required length is set to be connected to the ferrule  8 . 
     A measurement device  9  as shown in FIG. 7 will be described briefly. The measurement device  9  includes a light source section  91 , an adjust plug  93  connected to the light source section  91  through an adjust cord  92  so as to make an optical axis eccentric in a predetermined direction, an adaptor  94  for facing and engaging the adjust plug  93  and the ferrule  8  with each other, and optical power-meter  95  for measuring the luminous energy. On the ferrule side of the adaptor  94 , one key (not-shown) for engagement with the key groove  7   a  is provided in order to indicate the eccentric direction of the adjust plug  93 . 
     The measuring device  9  thus constructed is set such that the ferrule  8  is engaged with the adaptor  94  with the key groove  82   a  matched with the key as well as the open end portion of the optical cord F is connected to the optical power-meter  95 . Then, the light is turned on, and a value indicated by the optical power-meter  95  is read. Next, the ferrule  8  is removed from the adaptor  94 , rotated by 90 degrees, and again engaged with the adaptor  94 , so that a value indicated by the optical power-meter  95  is read. 
     Further, this procedure is repeated twice, and a mark is applied to a key groove  82   a  that causes the value of the optical power-meter  95  to be maximum (the luminous energy to be maximum). Thereafter, the assembly is carried out to a housing of a desired external appearance, such as the SC type, MU type or the like, which is provided with a key indicating the eccentric direction, so that the marked key groove  82   a  is aligned with the key. 
     As explained above, in the conventional art, the eccentric adjustment is performed such that the optical connection is established actually in a state in which the optical cord F having a required length is connected to the ferrule  8 . Through the aforementioned process, plugs which are lower in insertion loss with respect to the adjust plug  93  whose optical axis is eccentric at a predetermined amount are mass-produced. By using these plugs, an optical connection always stabilized in insertion loss can be realized. 
     The eccentric adjustment in accordance with this system is preferable in view of the fact that an optical connection always stabilized in insertion loss can be realized. However, the adjustment needs the insertion and removal of the ferrule into and out of the adaptor, and thus it has been pointed out that the end face of the ferrule may roughened, which causes a problem in the process. 
     Further, it is impossible to realize an optical connection in which the insertion loss is further reduced by the adjustment of this system in which, as mentioned above, the luminous energy is measured at intervals of every 90 degrees (four-equi-angular-interval distribution) using the key engagement with respect to the adjust plug whose optical axis is made eccentric at the predetermined amount and the direction (the key groove) at which the insertion loss is the smallest among them is regarded as the eccentric direction. 
     Accordingly, it is an object of the present invention to provide a ferrule tubular body and a ferrule which is free from the fear that the end face of the ferrule may be roughened, which can eliminate the eccentric adjustment process performed after the optical fiber is fixed, and which can attain an optical connection in which the insertion loss is further reduced. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention for solving the aforementioned problems is embodied in a ferrule tubular body having a through-hole to which an end portion of an optical fiber is inserted to be held, the ferrule tubular body being characterized by including an indicator section for indicating an eccentric direction of the through-hole with respect to a center of an outer circumference of the body. 
     A second aspect of the present invention is based on the ferrule tubular body as set forth in the first mode, and is characterized in that the indicator section is a visual indication provided on an outer circumferential surface of the ferrule tubular body. 
     A third aspect of the present invention is based on the ferrule tubular body as set forth in the first mode, and is characterized in that the ferrule indicator section is a recess provided in an outer circumferential surface of the ferrule tubular body. 
     A fourth aspect of the present invention is based on the ferrule tubular body as set forth in the second or third mode, and is characterized in that the indicator section is provided on at least one of a leading end portion and a rear end portion of the ferrule tubular body. 
     A fifth aspect of the present invention is embodied in a ferrule including a ferrule tubular body having a through-hole to which an end portion of an optical fiber is inserted to be held, and a flanged member securely fixed to a rear end portion of the ferrule tubular body, the ferrule being characterized in that an indicator section indicating an eccentric direction of the through-hole with respect to a center of an outer circumference of the ferrule tubular body is provided on at least one of the ferrule tubular body and the flanged member. 
     A sixth aspect of the present invention is based the ferrule as set forth in the fifth mode, and is characterized in that the indicator section is an indication or a recess provided on a leading end of the ferrule. 
     A seventh aspect of the present invention is based on the ferrule as set forth in the fifth mode, and is characterized in that the indicator section is a visual indication or a recess provided on the flanged member. 
     As factors of this eccentricity hindering the optical connection, it can be pointed out the following; e.g. that an optical fiber is not held at the center of a through-hole of a ferrule, a core is not positioned at the center of the optical fiber, a through-hole is not opened at the center of the outer circumference of a ferrule tubular body, and so on. The eccentricities in the held position of optical fiber with respect to the through-hole of the ferrule and the position of the core within the optical fiber are minute and thus can be disregarded in contrast to the eccentricity in the position of the through-hole in the ferrule. Accordingly, since the present invention makes it possible to recognize the eccentric direction of the through-hole, the eccentric adjustment with high precision in comparison with the conventional eccentric adjustment can be realized. 
     In addition, it is not essential to provide the indicator sections noted above in the eccentric direction of the through-hole with respect to the center of the outer circumference of the ferrule tubular body. That is, it suffices that the eccentric direction of the through-hole can be observed relatively from the external side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view showing the leading end side of a ferrule tubular body in accordance with the present invention, 
     FIGS. 2A and 2B are perspective view showing the ferrule tubular bodies in accordance with the present invention, 
     FIGS. 3A,  3 B,  3 C and  3 D are perspective view showing ferrules in accordance with the present invention, 
     FIG. 4 is an exploded perspective view showing a plug using the ferrule in accordance with the present invention, 
     FIG. 5 shows a detector for detecting an eccentric direction of a through-hole opened through the ferrule tubular body or the ferrule in accordance with the present invention, 
     FIG. 6 is a plan view for explanation about the conventional art, showing the leading end side in a state where an exposed optical fiber is inserted into and securely fixed to a ferrule, and 
     FIG. 7 is aschematic view showing a measurement device for measuring the core eccentricity, which is used in the conventional art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Next, embodiments of a ferrule tubular body and a ferrule in accordance with the present invention will be described with reference to the drawings. 
     FIGS.  1  and  2 A- 2 B shows embodiments of a ferrule tubular body  1  in accordance with the present invention, FIGS. 3A-3D and  4  show embodiments of a ferrules  2 A- 2 D in accordance with the present invention, and FIG. 5 shows a detector  4  for detecting an eccentric position of the ferrule tubular body  1  or the ferrule  2 A- 2 D in accordance with the present invention. 
     First of all, the embodiments of the ferrule tubular body  1  in accordance with the present invention will be described. The ferrule tubular body  1  is a member having a cylindrical outer surface and is included in a ferrule that itself is a plug side member included in an optical connector for optical connection. As shown in FIG. 1, the ferrule tubular body  1  is a tubular member made of a ceramic, such as zirconia or the like, or stainless steel or the like, and provided at its substantially central portion with a through-hole  1   a  into which an optical fiber from which a sheath of a predetermined length is removed from one end of an optical cord is insertable. This through-hole  1   a  is essentially required to be opened at and aligned on the axis C of the ferrule tubular body  1 , but actually it is opened and provided at a slightly eccentric position E as illustrated in FIG.  1 . 
     On the leading end portion of the ferrule tubular body  1 , an indicator section  1   b  in the form of a desired character, mark or the like is provided as a permanent marking in the vicinity of the position at which an imaginary line passing from the axis C through the hole center E of this through hole  1   a  intersects the outer surface of the ferrule tubular body  1 , i.e. on the eccentric direction outer surface with respect to the axis C, so that the eccentric direction of the through-hole  1   a  can be observed. This indicator section  1   b  is not limited to one indicated by a marking, and as shown in FIG. 2B, it may be a recess (an indicator section)  1   c  formed as a consequence of notching the outer surface of the ferrule tubular body  1  into a recessed configuration. Further, it may be formed instead of or in addition to that illustrated on the rear end portion of the ferrule tubular body  1 . 
     These indicator sections  1   b  and  1   c  provided on the leading end portions are preferable since each of these can be observed after the flanged member has been securely fixed to the rear end portion. Since the marking such as a simple printing or the like may disappear, the one that is formed as a consequence of the notching as described above is further preferable. Moreover, the provision of the indicator section at the rear end portion does not cause any possible hinderance in optical connection, but there is a possibility that the indicator section cannot be observed after the flanged member is securely fixed. Therefore it is preferable that the flanged member formed preliminarily with an indicator section is securely fixed so as to be aligned with the indicator section formed on the rear end portion of the ferrule tubular body  1 . 
     Next, the embodiments of ferrules  2 A,  2 B,  2 C and  2 D in accordance with the present invention will be described with reference to FIGS. 3A-3D. The ferrules  2 A,  2 B,  2 C and  2 D in accordance with the present invention are constructed by securely fixing flanged members  3 A,  3 B,  3 C and  3 D to the rear end portions of ferrule tubular bodies  1 A,  1 B,  1 C and  1 D, respectively, and each of these ferrules is a plug side member that is used upon assembly into a housing of a desired outer appearance such as SC type, MU type or the like and that is included in an optical connector for optical connection. Indicator sections  1   d ,  3   a ,  1   e  and  3   b  of respective modes, as shown in the drawing, with which the eccentric directions of the through-holes  1   a  with respect to the axes C of the ferrule tubular bodies  1 A,  1 B,  1 C and  1 D can be observed, are provided on the ferrule tubular bodies  1 A,  1 B,  1 C and  1 D or the flanged members  3 A,  3 B,  3 C and  3 D of the ferrules  2 A,  2 B,  2 C and  2 D. 
     That is, the recess (the indicator section)  1   d  is formed by notching a part of the chamfered portion at the leading end outer surface of the ferrule tubular body  1 A as shown in FIG. 3A, the indicator section  3   a  is indicated by a dot-like marking on the outer surface of the flanged member  3 B as shown in FIG. 3B, the indicator section  1   e  is indicated by a marking on the leading end outer surface of the ferrule tubular body  1 C as shown in FIG. 3C, and the recess (the indicator section)  3   b  is formed by notching, into the substantially V-shaped form, the bottom portion located within the key groove  3   d  of the flanged member  3 D as shown in FIG.  3 D. In addition, these may be combined in arbitrary manner. 
     Further, these ferrules  2 A,  2 B,  2 C and  2 D may be provided such that the ferrule tubular bodies  1 A,  1 B,  1 C and  1 D on which eccentric directions are first detected are securely fixed to the flanged members  3 A,  3 B,  3 C and  3 D in a posterior process, and alternatively such that the ferrule tubular bodies  1 A,  1 B,  1 C and  1 D are securely fixed to the flanged members  3 A,  3 B,  3 C and  3 D preliminarily and then the eccentric directions are detected in the posterior process to provide the indicator sections  1   d ,  3   a ,  1   e  and  3   b.    
     Each of the ferrules  2 C and  2 D, in which four key grooves  3   d  are circumferentially provided on the flanged member  3 C or  3 D at the constant angular intervals, is used, for instance, as a member included in an SC plug  5  as shown in FIG. 4 (the ferrule  2 C exemplified by and shown in FIG. 3C is illustrated in FIG.  4 ), and it is engaged with and integrated to a plug frame  6  of the SC plug  5 , which has a key for engagement with the four key grooves  3   d  distributed at the constant angular intervals. 
     On the inner surface of this plug frame  6  there is formed the key (not shown) which is opposed to a chamfered upper surface  6   a  in the perpendicular direction. The plug frame  6  is engaged with a stop ring  7  under a condition that either of the key grooves  3   d  is fitted to this key. Since the plug frame  6  is designed so that its upper surface  6   a  side is aligned with the eccentric direction, the integration is performed such that the key groove  3   d  is engaged with the key of the plug frame  6  while the indicator section  1   e  indicating the eccentric direction is located at the upper surface  6   a  side. 
     Next, a detector  4  for detecting the eccentric direction of the through-hole  1   a  opened through the ferrule tubular body  1  will be described with reference to FIG.  5 . The detector  4  includes a mounting section  41 , an imaging section  42 , illumination section  43 , an image processing section  44  and a marking section  45 . The mounting section  44  is constructed by a V-block  411  for supporting the ferrule tubular body  1 , i.e. the subject to be detected, and a roller portion  412  contacted with the ferrule tubular body  1  thus supported to rotate the ferrule tubular body  1 . This roller portion  412  is electrically communicated with the later described image processing section  44  so that its rotation can be controlled by a control signal sent from the image processing section  44 . 
     The imaging section  42  is comprised of a CCD camera that is disposed in the vicinity of the mounting section  41  and directed toward the leading end face of the ferrule tubular body  1  so as to capture a partial image of and around the through-hole  1   a  within the leading end face of the ferrule tubular body  1  in a magnification manner. The image section is electrically communicated with the later described image processing section  44  so that a signal of the image thus captured can be transmitted to the image processing section  44 . In addition, the rate of this magnification of the subject to be imaged is such a degree that a boundary line between the through-hole  1   a  and a structural surface therearound, i.e. a part of peripheral edge portion is divided into two halves perpendicularly on a monitor that will be described later. 
     The illumination section  43  is disposed on the rear end face side of the ferrule tubular body  1 , and designed to illuminate the rear end face of the ferrule tubular body  1  so as to obtain an image contrast with which the through-hole  1   a  and the surface therearound can be recognized clearly. The image processing section  44  is comprised of a controller  441  in which a required control program is installed, and a monitor  442  electrically communicated with the controller  441 . A sequence of the operation thereof will be described later. 
     The marking section  45  is electrically communicated with the image processing section  44  so that in accordance with the command from the image processing section  44  a required mark is applied by marking of a laser marking type onto the outer surface of the ferrule tubular body  1  located in the eccentric direction and in the vicinity of the leading end portion. In the detector  4  thus constructed, the control program is executed to start rotating the ferrule tubular body  1  mounted on the V-block  411  and contacted at its side surface with the roller  412 , and concurrently the image processing section  42  captures images in the magnification manner so that a part of the peripheral edge portion of the through-hole  1   a  within the leading end surface of the ferrule tubular body  1  is divided into two halves perpendicularly on the monitor  442 . 
     In this operation, the signals of the images successively captured are transmitted to the control section  441 , and binarized using a predetermined threshold value, so that the binarized image (an image consisting of a white component ( 1 ) and a black component ( 0 )) is displayed on the monitor such that the boundary line is shifted laterally on a screen depending on the eccentricity. Concurrently, positional data obtained by sampling the boundary every predetermined rotational angles are stored successively in a frame memory provided within the controller  441  until the ferrule tubular body is rotated by one turn (360 degrees). After the sampling is complete, a rotational angle at which the most white components are contained is selected from the rotational angles at which the sampling has been carried out (in a case where the image indicating the through-hole  1   a  is set as the white component image), and the ferrule tubular body  1  is rotated to that rotational angle. Thereafter, a desired character, mark or the like is applied by the marking section to provide the indicator section  1   b  with which the eccentric direction of the through-hole  1   a  can be observed at a glance. 
     In addition, the detection by this detector can be made not only on the ferrule tubular body but also on the ferrule in which the flanged member  3  is securely fixed to the rear end portion of the ferrule tubular body  1 . Further, the detection process carried out using this detector is not limited to one that has been described above, and it may be carried out such that the eccentric direction is detected in a static manner without the rotation of the ferrule tubular body  1 . Further, it is not particularly limited to the use of this detector, as long as the eccentric direction can be detected in a non-contact manner. 
     The present invention thus constructed provides the following advantageous effects. By preliminarily providing the ferrule tubular body or the ferrule, in which the eccentric direction of the through-hole can be observed, it is possible to construct the plug the eccentric direction of which can be confirmed without the eccentric adjustment requiring the insertion and removal of the ferrule into and out of the adaptor at every rotations of 90 degrees (four-equi-angular-interval distribution) after the optical fiber has been already assembled to the adaptor. Further, since this eccentric adjustment per se is eliminated, the problem caused due to the insertion and removal of the ferrule into and the out of the adaptor, for instance, the roughening of the ferrule end face, can be eliminated, thereby making it possible to construct the high-quality plug. 
     Further, in contrast to the system in which the luminous energy is measured at every rotations of 90 degrees (four-equi-angular-interval distribution) and the direction at which the insertion loss is the smallest among them is regarded as the eccentric direction, the plug can be constructed using the actual eccentric direction. The use of the plugs including the ferrule tubular bodies or the ferrules obtained in this manner makes the optical connection less in the insertion loss.