Abstract:
An optical fiber insertion unit includes a ferrule; a lens sleeve having a lens at a front end portion thereof and a ferrule insertion opening portion at a rear end portion thereof for inserting the ferrule; and a refractive index matching portion disposed between the ferrule and the lens sleeve. The refractive index matching portion is filled with a refractive index matching material so that the refractive index adjusting agent contacts with at least the lens.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
       [0001]    The present invention relates to an optical connector, and a method of connecting an optical fiber to the optical connector on-site such as a site of optical fiber-lying work. 
         [0002]    Generally speaking, at a factory of producing an optical fiber cable having an optical connector at an end part thereof, first, the optical fiber is cut into a standard length in advance. Afterward, in order to reduce a connection loss due to roughness of an end surface of the optical fiber, the end surface of the optical fiber is subjected to a polishing process. On the other hand, at an optical fiber-lying site, since the lengths of the optical fibers to be used may vary according to the optical fiber-lying site, each optical fiber is cut into a specific length each time, rather than using the optical fiber already cut in the standard length at the factory. In this case, it is difficult to apply the polishing process to the optical fiber when the optical fiber is cut in the specific length at the fiber-lying site without equipment furnished in the factory. 
         [0003]    According to a conventional technique, for example, as described in Japanese Patent Application Publication No. 2012-68672 (Patent Reference 1), in a step of abutting and connecting end surfaces of optical fibers, a refractive index matching material is used instead of a process of treating an end surface of the optical fiber. Accordingly, it is possible to reduce the connection loss due to reflected light or scattered light without polishing the end surfaces of the optical fibers. 
         [0004]    It should be noted that Japanese Patent Application Publication No. 2004-61671 (Patent Reference 2) and Japanese Patent Application Publication No. 05-113519 (Patent Reference 3) have also described the conventional technique for preventing the reflection and the connection loss using the refractive index matching material. 
         [0005]    In addition, as described in Japanese Patent Application Publication No. 2012-68672 (Patent Reference 1), according to the conventional onsite wire-connecting method for the optical fibers, a ferrule having an optical fiber therein is used. Accordingly, a rear end surface of the optical fiber provided in the ferrule is abutted and connected to another external optical fiber via a refractive index matching material.
   Patent Reference 1: Japanese Patent Application Publication No. 2012-68672   Patent Reference 2: Japanese Patent Application Publication No. 2004-61671   Patent Reference 3: Japanese Patent Application Publication No. 05-113519   
 
         [0009]    In the conventional onsite wire-connecting method for the optical fibers, however, when the ferrule is produced, it is necessary to enclose the optical fiber therein in advance, thereby increasing the manufacturing cost. In addition, the optical fiber is already enclosed in the ferrule. Accordingly, it is necessary to carefully handle the ferrule at the optical fiber-lying site. Furthermore, it is difficult to apply the refractive index matching material on an end surface of the ferrule. Accordingly, when the ferrule is produced, it also is necessary to polish an end surface of the optical fiber on the front end side thereof, thereby increasing the manufacturing cost. 
         [0010]    In order to solve the problems of the conventional technique described above, an object of the present invention is to provide an optical connector having an optical fiber insertion unit having a structure that does not require having an optical fiber in a ferrule in advance. Further, another object of the present invention is to provide a method of onsite wire-connecting method using the optical connector. More specifically, according to the invention, an object of the present invention is to provide an optical connector having an optical fiber insertion unit composed of a ferrule and a lens sleeve suitable for onsite wire connection of the optical fiber. Further, another object of the present invention is to provide an onsite wire-connecting method of connecting the optical fiber using the optical connector without applying a polishing process to an end surface of the optical fiber. 
         [0011]    Further objects and advantages of the present invention will be apparent from the following description of the present invention. 
       SUMMARY OF THE PRESENT INVENTION 
       [0012]    In order to attain the objects described above, according to a first aspect of the present invention, an optical fiber insertion unit includes a ferrule and a lens sleeve, which has a lens at a front end part thereof and a ferrule insertion opening for inserting the ferrule on a rear part thereof, in which there is provided a refractive index matching material on a front end part of the ferrule, and the ferrule is inserted to the lens sleeve from the ferrule insertion opening till the refractive index matching material contacts with at least the lens. 
         [0013]    According to a second aspect of the present invention, in the optical fiber insertion unit, the ferrule and the lens sleeve may be formed of different materials having different coefficients of linear expansion and the refractive index matching material attached on the front end part of the ferrule has fluidity. 
         [0014]    According to a third aspect of the present invention, an optical connector may include the optical fiber insertion unit; a shell having at least one unit insertion hole for inserting the optical fiber insertion unit and having a split sleeve within the unit insertion hole for securing the lens sleeve of the optical fiber insertion unit; a pressing plate having a passing hole that connects to the optical fiber insertion hole of the ferrule of the optical fiber insertion unit; and a connector sleeve. 
         [0015]    According to a fourth aspect of the present invention, the optical connector may include an elastic body for pressing the optical fiber insertion unit inserted in the unit insertion hole into the unit insertion hole by an elastic force between the flange of the optical fiber insertion unit and the pressing plate. 
         [0016]    According to a fifth aspect of the present invention, the optical connector may be used to form a plug connected with the optical fiber at an optical fiber-lying site. A onsite wire-connecting method of forming a plug that includes the optical connector of the present invention, a cord collar, and a fastening hardware includes a step of putting an optical fiber cable through inside the fastening hardware and the cord collar; a step of inserting a fiber core wire of the optical fiber cable in the ferrule of the optical fiber insertion unit through the optical fiber insertion hole of the passing hole of the pressing plate and the ferrule; and a step for connecting the cord collar to the optical connector and securing the cord tube and the optical fiber cable with the fastening hardware. 
         [0017]    According to a sixth aspect of the present invention, in the onsite wire-connecting method for forming the plug, in the step of inserting the fiber core wire, the bare fiber exposed for the certain length from the fiber core wire is inserted so as to contact with the refractive index matching material at a front end of the ferrule, and in the step of securing the optical fiber cable, the fiber core wire is secured inside of the ferrule with an adhesive applied on a surface of the fiber core wire. 
         [0018]    According to the present invention, the optical fiber insertion unit has a simple configuration that is composed of the ferrule and the lens sleeve, and it is not necessary to have the optical fiber in the ferrule in advance as in the conventional technique. Further, it is not necessary to perform the step of polishing an end surface of the optical fiber, so that it is possible to reduce the manufacturing cost of the optical fiber. 
         [0019]    Furthermore, according to the present invention, the refractive index matching material applied at the front end of the ferrule enters a gap formed between the ferrule and the lens sleeve. Accordingly, it is possible to prevent the connection loss between the end of the optical fiber and the lens. Moreover, the ferrule and the lens sleeve are formed of the different materials. Accordingly, even when heat is applied on the optical fiber, and the gap between the end portion of the optical fiber and the lens is widened due to the difference in the coefficients of linear expansion of the different materials, the refractive index matching material enters the widened gap, so that the optical fiber insertion unit of the present invention can also deal with the widening of the gap possibly occur later. 
         [0020]    In addition, according to the present invention, the optical connector having the optical fiber insertion unit does not include the optical fiber to be connected. Accordingly, there is no risk of accidentally damaging the optical fiber to be connected. 
         [0021]    Furthermore, according to the present invention, in the onsite wire-connecting method using the optical connector, at the optical fiber lying site, it is not necessary to polish the end surface of the front end part (i.e., a bare fiber) of the optical fiber core wire exposed from the optical fiber cable that is cut into a suitable length. Rather, the optical fiber core wire is simply inserted into the optical fiber insertion unit within the optical connector. Accordingly, it is possible to easily connect the optical fiber cable to the optical connector. Accordingly, it is possible to significantly reduce the onsite work steps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIGS. 1(   a ) and  1 ( b ) are views showing an optical fiber insertion unit according to an embodiment of the present invention, wherein  FIG. 1  ( a ) is a side view showing the optical fiber insertion unit, and  FIG. 1  ( b ) is a side sectional view showing the optical fiber insertion unit taken along a line A-A in  FIG. 1(   a ); 
           [0023]      FIGS. 2(   a ) to  2 ( d ) are sectional views showing a ferrule and a lens sleeve of the optical fiber insertion unit according to the embodiment of the present invention; 
           [0024]      FIG. 3  is a sectional view showing an optical connector equipped with the optical fiber insertion unit therein according to the embodiment of the present invention; 
           [0025]      FIG. 4  shows an optical fiber before the optical fiber is connected to the optical connector according to the embodiment of the present invention; 
           [0026]      FIGS. 5(   a ) and  5 ( b ) are views showing the optical connector in a state that a tip of a fiber core wire is inserted in the ferrule provided inside the optical connector according to the embodiment of the present invention, wherein  FIG. 5  ( a ) is a side sectional view showing the optical connector and the optical fiber, and  FIG. 5  ( b ) is a side view showing the optical connector and the optical fiber; 
           [0027]      FIG. 6  is a perspective view showing a plug including the optical connector and a receptacle according to the embodiment of the present invention; and 
           [0028]      FIG. 7  is a sectional view showing the optical connector in a state that the optical connector contained in the plug is connected to the receptacle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    Hereunder, an embodiment of the present invention will be described with reference to the accompanying drawings. Here, in any of those drawings for describing embodiment of the present invention, the same reference numerals are basically used for the same members and repetitive explanation is omitted. 
         [0030]      FIGS. 1(   a ) and  1 ( b ) show an optical fiber insertion unit  100  according to an embodiment of the present invention. As shown in  FIG. 1(   a ), the optical fiber insertion unit  100  is composed of a ferrule  200  and a lens sleeve  300 .  FIG. 1(   b ) is a sectional view of the optical fiber insertion unit  100  taken along the line A-A in  FIG. 1(   a ). 
         [0031]    As shown in  FIGS. 1(   a ) and  1 ( b ), the ferrule  200  has a cylindrical shape. Further, the ferrule  200  has a flange  202  in a center part on an outer side thereof, and an optical fiber insertion hole  204  in an inner side thereof for inserting an optical fiber in the ferrule  200 . Further, the ferrule  200  has an optical fiber guide surface  206  having a tapered shape (e.g., conical shape) for guiding a tip (bare fiber) of the optical fiber to an end part of the ferrule  200 , and a bare fiber insertion hole  208  for inserting a bare fiber therein. At an end of the ferrule  200 , a refractive index matching material  210  is attached in order to prevent connection loss of the optical fiber. The lens sleeve  300  has a cylindrical shape, and includes a lens  302 . 
         [0032]      FIGS. 2(   a ) to  2 ( d ) are sectional views of the ferrule  200  and the lens sleeve  300  that compose the optical fiber insertion unit  100  according to the embodiment of the present invention, and show how to assemble the optical fiber insertion unit  100  using the ferrule  200  and the lens sleeve  300 . Here, the ferrule  200  and the lens sleeve  300  are made of different materials having different coefficients of linear expansion. According to one embodiment, the ferrule  200  is formed from metal such as zirconium, whereas the lens sleeve  300  is formed from another metal such as stainless steel. 
         [0033]      FIG. 2(   a ) is a sectional view of the lens sleeve  300 , and has a light passing hole  304  at an end thereof and a ferrule insertion opening  306  at an end on the other side thereof. An inner-side end portion of the lens sleeve  300  has a smaller diameter than that of the ferrule insertion opening  306 , and as shown in  FIG. 2(   b ), into the end portion, fitted is a lens  302 . Upon fitting the lens  302  therein, with a lens locking section  308  formed at an edge of the light passing hole  304 , the lens  302  is positioned and secured. 
         [0034]    In the embodiment, when light signals are sent from the optical fiber, the lens  302  converts the lights from the optical fiber with one fourth of sinusoidal wave, so that it is possible to widen the light emitted from the light passing hole  304 . The widened light is collected with a lens at a connecting section of an optical connector (receptacle), which is a receiving side, so that it is possible to reduce the connection loss due to axial displacement of end surfaces among optical fibers and to achieve high coupling efficiency. In addition, refractive index of the lens  302  is similar to that of glass, and for example, it is 1.45 to 1.46. 
         [0035]    As shown in  FIG. 2(   c ), with the refractive index matching material  210  is applied at the end of the ferrule  200 , the ferrule  200  is inserted from the ferrule insertion opening  306  to inside of the lens sleeve  300 . The refractive index matching material  210  has similar refractive index to that of the optical fiber and the lens  302 . 
         [0036]    For example, the refractive index of the refractive index matching material  210  is 1.4 to 1.5. In addition, the refractive index matching material  210  is a material having silicone-like or paraffin-like fluidity. According to one embodiment, the refractive index matching material  210  is an oil compound having high transparency that is close to that of quartz glass, and has consistency of 300 to 400 (worked penetration at 25° C. by JIS K 2220 Test Method). 
         [0037]    As shown in  FIG. 2(   d ), when the ferrule  200  is inserted in the lens sleeve  300 , the flange  202  touches an edge of the ferrule insertion opening  306 . At this point, the refractive index matching material  210  applied on the end of the ferrule  200  contacts with the lens  302 , presses thereon, and then fills the gap between the end of the ferrule  200  and the lens  302 . With the refractive index matching material  210  that fills the gap in this way, it is possible to reduce the connection loss of the optical fiber. 
         [0038]    In addition, when the ferrule  200  and the lens sleeve  300  are formed from different material having different coefficients of linear expansion, if the optical fiber insertion unit  100  composed of the ferrule  200  and the lens sleeve  300  is heated, there is a problem of widening of the gap between the end of the optical fiber (i.e., the bare fiber) and the lens  302  in comparison with the usual state thereof due to the difference in the coefficients of linear expansion of different materials. However, since the refractive index matching material  210  around the end of the ferrule  200  has fluidity, the refractive index matching material  210  enters the widened gap, so that it fills even the gap that could be formed later. In other words, even when the optical fiber insertion unit  100  is heated, there is always the refractive index matching material  210  between the bare fiber and the lens  302 , so that it is possible to prevent the connection loss of the optical fiber due to influence of heat. 
         [0039]    Here, there may be influence from expansion by heat between the ferrule  200  and the bare fiber inserted in the bare fiber insertion hole  208  in the ferrule  200 . However, generally speaking, the ferrule  200  and the bare fiber are made from the same material (e.g., zirconium), so that they have generally the same coefficient of linear expansion. Therefore, there is no adverse influence from the thermal stress between the ferrule  200  and the bare fiber. 
         [0040]      FIG. 3  shows an optical connector  400  according to an embodiment of the present invention, and is a sectional view of the optical connector  400  including two optical fiber insertion units  100 . The optical connector  400  includes a shell  402  and a pressing plate  404 . On the shell  402 , there is provided a unit insertion hole  406  for inserting the optical fiber insertion unit  100 . Inside the unit insertion hole  406 , there is provided a split sleeve  408  for securing the position of the end (i.e., lens sleeve  300 ) of the optical fiber insertion unit  100 . 
         [0041]    According to the embodiment illustrated in  FIG. 3 , into the two unit insertion holes, the two optical fiber insertion units  100  are inserted and secured therein with the pressing plate  404 . On the pressing plate  404 , there are provided passing holes  410  that connect to the optical fiber insertion hole  204  and are used for putting the optical fibers therethrough. Each optical fiber is inserted in the optical fiber insertion unit  100  in the optical connector  400  via the passing hole  410  and the optical fiber insertion hole  204 , and is tightly secured with a cord collar and a fastening hardware so as not to come off. 
         [0042]    Although it is not necessary for forming the optical connector  400 , it is also possible to provide an elastic body between the flange  202  of the ferrule  200  and the pressing plate  404  in order to energize the optical fiber insertion unit  100  towards the end thereof. According to the embodiment shown in  FIG. 3 , there are provided energizing springs  412  as such elastic body. With the energizing springs  412  energize the optical fiber insertion units  100  towards the end of the optical connector  400 , when the optical connector  400  is connected to a receptacle, it is possible to keep the state of the end part of each optical fiber insertion unit  100  (lens sleeve  300 ) being crimped on the connecting section of the receptacle. 
         [0043]    Furthermore, according to the embodiment of  FIG. 3 , there is provided a waterproof ring  414  on the outer side of the end section of the shell  402  for connecting to the receptacle. On the outer side of the shell  402 , there is provided a connector sleeve  416  for fitting to the receptacle. 
         [0044]      FIG. 4  shows an optical fiber  500  before it is connected to the optical connector  400 . According to the embodiment of the present invention, the optical fiber  500  includes a cable  502  covered with outer coating, a fiber core wire  504  exposed from the outer coating of the cable  502 , and a bare fiber  506  exposed from the outer coating of the fiber core wire  504 , respectively. The optical fiber  500  may be cut into suitable lengths at a wire-lying site. The outer coatings of each cable  502  and each fiber core wire  504  may be cut into certain lengths with special cutting tool and then removed. 
         [0045]      FIGS. 5(   a ) and  5 ( b ) shows the optical connector  400  in a state where the end portions of the fiber core wires  504  are inserted in the ferrules  200  provided in the optical connector  400 . 
         [0046]    According to the embodiment of the present invention, the end surface of each bare fiber  506  passes through the bare fiber insertion hole  208  and reaches the refractive index matching material  210  attached on the end portion of each ferrule  200  as shown in the sectional view of  FIG. 5(   a ). The end surface of each bare fiber  506  can suitably transmit light (light signals) from the optical fiber  500  to the lens  302 , by contacting with the refractive index matching material  210 , so that it is possible to achieve reduction of the connection loss. Therefore, at an optical fiber-lying site, it is possible to easily connect to the optical fiber  400  without polishing the end surfaces of the optical fibers  500  (i.e., end surfaces of the bare fibers  506 ). 
         [0047]    Here, at the wire-lying site, if the optical fiber  500  is cut into suitable lengths, generally, it is not possible to have polishing equipment in the site, so that the end surfaces of the bare fibers  506  would not be polished. However, when the optical connector  400  and the optical fiber  500  are connected at a factory that is well furnished with equipment, needless to say, it is possible to polish the end surface of the bare fiber  506 . 
         [0048]    In the onsite wire-connecting method for an optical connector according to the embodiment of the present invention, the optical fiber  500  is cut into suitable lengths, the fiber core wires  504  are exposed from the optical fiber cable  502 , and then the bare fibers  506  are exposed from the fiber core wires  504 . Then, as shown in  FIG. 6 , putting the optical fiber  500  into the fastening hardware  420  and the cord collar  418  as shown in  FIG. 6  in advance, the optical fiber  500  is inserted in the optical connector  400  via the passing holes  410  and the optical fiber insertion holes  204  as shown in  FIG. 5(   a ). 
         [0049]    As a result, the state is as shown in  FIG. 5(   b ). In order to protect the fiber core wires  504 , putting the cord collar  418 , which was mounted in advance, to the optical connector  400  so as to couple thereto, and further in order to keep the optical fiber  500  from not coming off, the fastening hardware  420  is put at the end of the cord color  418  to couple thereto, and secured by fastening the outer coating of the optical fiber cable  502 . As described above, with the simple steps, it is possible to make a plug  450  as shown in  FIG. 6  at wire-lying site. 
         [0050]    In addition, it is also possible to apply adhesive on the outer coating of the fiber core wires  504 , and upon inserting the optical fiber  500  in the optical connector  400 , the outer coating of the fiber core wires  504  and inside of the ferrules  200  become adhered to each other with the adhesive, so that it is possible to prevent the optical fiber  500  from coming off during plug  450  making work. Moreover, providing a securing screw to prevent loosening at the coupling part of the cord collar  418  that is to be fitted and coupled in the optical connector  400 , and fastening the securing screw after coupling, it is possible to prevent loosening of the cord collar  418 . Similarly, it is also possible to provide a securing screw for prevent loosening in the fastening hardware  420  to be fitted coupled to an end of the cord collar  418 . 
         [0051]      FIG. 6  shows the plug  450  and the receptacle  600 , for connecting an optical fiber, according to the embodiment of the present invention. As described above, the plug  450  is made by connecting the optical connector  400  and the optical fiber  500  by an onsite wire-connecting method as described above, and composed of the optical connector  400 , the cord collar  418 , and the fastening hardware  420 . 
         [0052]    The receptacle  600  includes a shell  602  to put the shell  402  of the optical connector  400  therein; a flange  604  and mounting holes  606  for securing the receptacle  600  onto a wall or the like; a locking groove  608  for securing the connection by fastening the connector sleeve  416  upon connecting the optical connector  400 , which composes the plug  450 , to the receptacle  600 ; a fitting opening  610  for fitting to the optical connector  400 , and a connecting section  612  for abutting to the lens sleeve  300  within the optical connector  400  and connect thereto. Referring to the sectional view of the receptacle  600  shown in  FIG. 7 , the receptacle  600  further includes a waterproof ring  614 , energizing springs  616 , which are elastic bodies to energize the connecting sections  612  towards the end thereof, and a pressing plate  618  for pressing the energizing springs  616 . In addition, each connecting section  612  is equivalent to the lens sleeve  300 , and the whole structure including the connecting section  612  is similar to that of the optical fiber insertion unit  100 . 
         [0053]      FIG. 7  shows a state where the optical connector  400  that composes the plug  450  is connected to the receptacle  600 . By twisting the connector sleeve  416 , a tab provided on an inner side is fitted in the locking groove  608 , and thereby it is possible to secure the connection between the optical connector  400  of the plug  450  and the receptacle  600 . 
         [0054]    Upon connecting the optical connector  400  and the receptacle  600 , the connecting section  612  is inserted in the split sleeve  408  of the optical connector  400 , and its end comes to contact with ends of the lens sleeves  300  of the optical connector  400 . At this point, with the energizing springs  616  provided between the connecting sections  612  on a side of the receptacle  600  and the pressing plate  618 , the connecting section  612  is energized towards the end, and similarly with the energizing springs  412  provided between the lens sleeves  300  provided on a side of the plug  450  and the pressing plate  404 , the lens sleeves  300  are also energized towards the end thereof. 
         [0055]    As a result, the end of the connecting section  612  and the end of the lens sleeve  300  contact to each other and become crimped to each other. Therefore, since those ends are in state of being crimped, it is possible to prevent formation of a big gap, which would cause connection loss between the lenses provided at their respective ends. 
         [0056]    The optical connector of the present invention may be applicable upon making a plug by connecting an optical fiber. In addition, an onsite wire-connecting method for an optical connector according to the present invention is applicable in wire-connecting work to connect an optical fiber without polishing work of the end surface of the optical fiber, using the optical fiber of the present invention in an optical fiber-lying work site. 
         [0057]    The disclosure of Japanese Patent Applications No. 2013-045016, filed on Mar. 7, 2013, is incorporated in the application by reference. 
         [0058]    While the present invention has been explained with reference to the specific embodiments of the present invention, the explanation is illustrative and the present invention is limited only by the appended claims.