Abstract:
An optical connector comprising a ferrule including an optical fiber, wherein a hollow portion for optical fiber protrusion is formed on a front end face of the ferrule, the optical fiber is inserted into an optical fiber positioning hole extended from an optical fiber protrusion port provided on a bottom face of the hollow portion toward an inside of the ferrule, and a tip face of the optical fiber is drawn in the hollow portion. This makes it possible to provide an optical connector which can shorten a time for assembly and can be assembled easily and inexpensively.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an optical connector, and more particularly to an optical connector for mutually connecting optical fibers.  
           [0003]    2. Related Background Art  
           [0004]    Conventionally, in the case in which an optical connector is to be assembled at a job site, an adhesive is poured into an optical fiber inserting hole provided in a ferrule, the optical fiber is inserted therein and is fixed with the adhesive in the ferrule and the connecting end face of the optical connector is then polished. Consequently, the connecting end face of the optical connector is on the level with the tip face of the optical fiber so that the ferrules can be reliably coupled to each other. Such an example includes Japanese Patent Application Laid-Open No. 61-156207.  
         SUMMARY OF THE INVENTION  
         [0005]    However, the conventional optical connector, which has the above-mentioned structure, has been the following problem. More specifically, such an optical connector requires a precise end face polishing step due to the fact that the adhesive sticks to the tip face at an adhesive assembling step to be carried out at the site. Consequently, it takes a long time to assemble the optical connector. In addition, expensive equipment is required for the precise polishing.  
           [0006]    The present invention has been made to solve the above-mentioned problem and has an object to provide an optical connector which can shorten a time required for assembly and can be assembled easily and inexpensively.  
           [0007]    The present invention provides an optical connector comprising a ferrule including an optical fiber, wherein a hollow portion for optical fiber protrusion is formed on a front end face of the ferrule, the optical fiber is inserted into an optical fiber positioning hole extended from an optical fiber protrusion port provided on a bottom face of the hollow portion toward an inside of the ferrule, and a tip face of the optical fiber is drawn in the hollow portion.  
           [0008]    According to the optical connector of the present invention, the tip face of the optical fiber is not protruded from (or on the level with) the front end face of the ferrule but is drawn in the hollow portion formed on the front end face of the ferrule. In the hollow portion, accordingly, a free space exists in the vicinity of the tip face of the optical fiber. Consequently, in the case in which refuse or the like sticks to the tip face of the optical fiber, a wiping work can be considerably simplified and optical characteristics can be maintained easily and reliably. For example, the wiping work can be carried out with an applicator containing a cleaning solution. Even if the finishing precision of the tip face of the optical fiber is not increased, optical connection having a low loss can be implemented and the conventional precise polishing step can be simplified. Consequently, a time required for treating the end face can be shortened and a time required for assembling the optical connector can be reduced.  
           [0009]    Preferably, the hollow portion has a rectangular opening window. As a consequence, a cleaning member such as an applicator can be easily inserted in the hollow portion because of the rectangular opening window.  
           [0010]    Preferably, the hollow portion has a slit-shaped opening window. As a consequence, a cleaning member such as an applicator can be easily moved greatly along the hollow portion because of the slit-shaped opening window.  
           [0011]    Preferably, the hollow portion has a depth of 20 μm or more. As a consequence, a distance between the front end face of the ferrule and the tip face of the optical fiber (the lead-in amount of the optical fiber) can be maintained easily.  
           [0012]    Preferably, the tip face of the optical fiber is subjected to an edge removal treatment by an electron discharge machining. As a consequence, the optical fiber can be inserted into the optical fiber positioning hole of the ferrule with the tip of the optical fiber electrically rounded. Accordingly, the optical fiber can be inserted easily. In addition, it is possible to properly prevent the tip face of the optical fiber from being chipped and to rapidly carry out the work.  
           [0013]    Preferably, the tip face of the optical fiber is subjected to an edge removal treatment by a polishing. As a consequence, the optical fiber can be inserted easily with the tip of the optical fiber mechanically rounded. In addition, it is possible to properly prevent the tip face of the optical fiber from being chipped and to rapidly carry out the work.  
           [0014]    Preferably, plural optical fiber protrusion ports are provided on the bottom face of the hollow portion corresponding to the number of the optical fibers. As a consequence, it is possible to roughly cut the tip portion of the optical fiber in a slight misalignment state with a predetermined alignment error even if the tip face of the optical fiber is not cut to be aligned with high precision at the previous step of inserting each optical fiber into the ferrule. As a result, the cutting work can be carried out rapidly and a time required for assembling the optical connector can be shortened.  
           [0015]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.  
           [0016]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a perspective view showing a ferrule and an optical fiber which are to be utilized for an optical connector according to the present invention;  
         [0018]    [0018]FIG. 2 is a plan view showing the optical connector in a state in which the optical fiber is attached to the ferrule;  
         [0019]    [0019]FIG. 3 is a sectional view taken along the line III-III in FIG. 2;  
         [0020]    [0020]FIG. 4 is a perspective view showing an optical fiber press member to be utilized for assembling the optical connector according to the present invention;  
         [0021]    [0021]FIG. 5 is a plan view showing the optical fiber cut to have a predetermined length;  
         [0022]    [0022]FIG. 6 is an enlarged view showing the discharging state of the optical fiber;  
         [0023]    [0023]FIG. 7 is an enlarged view showing the polishing state of the optical fiber;  
         [0024]    [0024]FIG. 8 is a plan view showing the state in which the optical fiber press member has not been assembled into the ferrule;  
         [0025]    [0025]FIG. 9 is a plan view showing the state in which the optical fiber press member has been assembled into the ferrule;  
         [0026]    [0026]FIG. 10 is an enlarged sectional view showing a main part in the state in which the optical fiber is inserted in the ferrule;  
         [0027]    [0027]FIG. 11 is a plan view showing the state in which an alignment load is applied to the optical fiber;  
         [0028]    [0028]FIG. 12 is a sectional view showing the state in which the tip faces of the optical fibers are aligned;  
         [0029]    [0029]FIG. 13 is an enlarged sectional view showing an optical fiber alignment groove having a C-shaped section;  
         [0030]    [0030]FIG. 14 is a plan view showing the state in which the ferrule is filled with an adhesive;  
         [0031]    [0031]FIG. 15 is a plan view showing the optical connector in which the optical fiber has been completely attached to the ferrule;  
         [0032]    [0032]FIG. 16 is a sectional view showing an optical connector according to a second embodiment;  
         [0033]    [0033]FIG. 17 is an enlarged sectional view showing the state in which an optical fiber is provided in the optical fiber alignment groove of a ferrule and is pressed from above by means of a clamp member;  
         [0034]    [0034]FIG. 18 is a plan view showing the state in which the tip face of the optical fiber is drawn in the ferrule in a non-alignment state;  
         [0035]    [0035]FIG. 19 is a perspective view showing an optical connector according to a third embodiment; and  
         [0036]    [0036]FIG. 20 is a perspective view showing an optical connector according to a fourth embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]    The embodiments of the optical connector of the present invention will be described with reference to the accompanying drawings. Note that the same reference numerals denote the same parts throughout the drawings, and a repetitive description will be avoided. FIG. 1 is a perspective view showing a ferrule and an optical fiber which are applied to the optical connector according to the present invention. The ferrule  1  shown in FIG. 1 is made of a resin (or zirconia or glass) in the form of an almost rectangular parallelepiped, and is utilized as a part of the optical connector (for example, a MT connector). Moreover, the ferrule  1  is incorporated and utilized as a part of another connector or the like in some cases.  
         [0038]    As shown in FIGS.  1  to  3 , a hollow portion  50  for optical fiber protrusion having a width A (3 mm), a height B (1.5 mm) and a depth D (0.03 mm) is formed on the center of a front end face  1   a  of the ferrule  1 . The hollow portion  50  has a rectangular opening window  50   a . Four optical fiber positioning holes  4  are formed on a front part in the ferrule  4 . Each of the optical fiber positioning holes  4  serves to perform positioning by inserting four (four-core) optical fibers  3  exposed from the tip of a ribbon-shaped optical fiber  2  (which will be hereinafter referred to as a “optical fiber ribbon”) respectively and has a diameter of 126 μm to 127 μm for the optical fiber  3  having a diameter of 125 μm. Each optical fiber positioning hole  4  is extended from a bottom face  50   b  of the hollow portion  50  rectilinearly in parallel, and the front end opening of the optical fiber positioning hole  4  is formed as an optical fiber protrusion port  5 . Accordingly, the four optical fiber protrusion ports  5  are aligned on the bottom face  50   b  of the hollow portion  50 . An optical fiber inlet  6  for introducing the optical fiber  3  from the outside is provided in the rear portion of the ferrule  1 .  
         [0039]    Furthermore, an adhesive filling hollow portion  7  for accommodating an adhesive R is provided between the optical fiber inlet  6  and the optical fiber positioning hole  4 , and an adhesive filling window  8  forming a rectangular opening into which the adhesive is poured is formed on the top of the adhesive filling hollow portion  7 . Four optical fiber alignment grooves  9  extended along the overall length are formed on a bottom face  7   a  of the adhesive filling hollow portion  7 . Each optical fiber alignment groove  9  is positioned on the extension of each optical fiber positioning hole  4 , and is extended between the optical fiber positioning hole  4  and the optical fiber inlet  6 . Furthermore, each optical fiber alignment groove  9  is formed to have a C-shaped section and is extended to have the same diameter as the diameter of the optical fiber positioning hole  4  (see FIG. 13). A guide pin inserting hole  10  for inserting a guide pin (not shown) is formed on both sides of the hollow portion  50  over the front end face  1   a  of the ferrule  1 .  
         [0040]    The optical fiber  3  inserted from the optical fiber inlet  6  of the ferrule  1  is provided in the optical fiber positioning hole  4  along the optical fiber alignment groove  9 . In this case, while a tip face  3   a  of the optical fiber  3  is protruded from the optical fiber protrusion port  5 , it is led in with a retreat amount S of approximately 5 μm to 10 μm with respect to the front end face  1   a  of the ferrule  1  and is drawn in the hollow portion  50 . In consideration thereof, it is preferable that the depth of the hollow portion  50  should be set to 20 μm or more. Moreover, when the adhesive R is filled in the adhesive filling hollow portion  7 , the optical fiber  3  can be fixed to the optical fiber alignment groove  9  through the adhesive R. This implements the firmer fixation of the optical fiber  3  to the ferrule  1 . In this case, since a difference between the diameters of the optical fiber  3  and the optical fiber positioning hole  4  is very small, the adhesive R rarely flows from a rear end  4   a  side of the optical fiber positioning hole  4 .  
         [0041]    An optical connector C having such a structure does not depend on the shape of the tip face  3   a  of the optical fiber  3  and is readily applicable to the MT (Mechanically Transferable) connector which can perform high-speed switching for a CATS (Cable Transfer System) or the like. More specifically, it is not necessary to enhance the cutting precision or polishing precision of the tip face  3   a  of the optical fiber  3  and a time required for a work of attaching the optical fiber  3  to the ferrule  1  can be shortened greatly. Moreover, since the tip face  3   a  of the optical fiber  3  is not protruded from the front end face  1   a  of the ferrule  1 , an operator does not touch the tip end face  3   a  of the optical fiber  3  carelessly during handling.  
         [0042]    Furthermore, a step of precisely polishing the front end face  1   a  of the ferrule  1  is not required at the final stage of fixing the optical fiber  3  to the ferrule  1 . Consequently, the time required for working can be shortened greatly. In addition, it is possible to prevent the tip face  3   a  of the optical fiber  3  from being chipped during polishing. A retreat amount (withdrawal amount) S of the optical fiber  3  is set such that the tip face  3   a  of the optical fiber  3  is not protruded from the front end face  1   a  of the ferrule  1  even if a temperature is changed in consideration of a coefficient of linear expansion of a member forming the optical connector C. By inserting a boot  11  made of rubber which is fitted in the optical fiber  3  into the optical fiber inlet  6  of the ferrule  1 , the optical fiber  2  can be prevented from being bent.  
         [0043]    An example of a method for assembling the optical connector C having such a structure will be described below.  
         [0044]    In order to carry out this method, an optical fiber press member  20  made of a resin in the form of an almost rectangular parallelepiped is prepared as shown in FIG. 4. The front face of the optical fiber press member  20  is provided with a flat ferrule connecting face  20   a  to abut on the front end face  1   a  of the ferrule  1 . The ferrule connecting face  20   a  is provided with a positioning protrusive portion  21  having the shape of a square pole to be inserted in the hollow portion  50  of the ferrule  1 , and the positioning protrusive portion  21  is formed to have such a size to be fitted in the hollow portion  50 . The tip of the positioning protrusive portion  21  is provided with a flat rectangular optical fiber press face  21   a . The optical fiber press face  21   a  is protruded from the ferrule connecting face  20   a  by approximately 5 to 10 μm. This corresponds to an amount in which the tip face  3   a  of the optical fiber  3  can retreat from the front end face  1   a  of the ferrule  1 . Moreover, a guide pin inserting hole  22  corresponding to each guide pin inserting hole  10  of the ferrule  1  is provided. The optical fiber press member  20  having such a structure is prepared before the work.  
         [0045]    As shown in FIG. 5, first of all, the optical fiber  2  is inserted into the boot  11  made of rubber, and a covering portion F having a predetermined length is removed from the tip portion of the optical fiber  2  by a heating type remover or the like, and a covering waste is wiped off with alcohol or the like with the four optical fibers  3  exposed. After the optical fibers  3  are cut to have a predetermined length by means of a cleaver or the like such that they are aligned, the tip face  3   a  of the optical fiber  3  is subjected to an edge removing treatment by the discharging work as shown in FIG. 6. This is intended for preventing the end face from being chipped by the contact of the optical fiber  3  with the ferrule  1  when the optical fiber  3  is to be inserted into the ferrule  1  and for rapidly carrying out the inserting work. For the same edge treatment, the tip face  3   a  of the optical fiber  3  may be mechanically treated by a polishing rotor  23  or a manual work as shown in FIG. 7.  
         [0046]    As shown in FIG. 8, next, a grease-like silicon based refractive index matching material K is applied onto the front end face  1   a  of the ferrule  1  such that it enters the hollow portion  50  of the front end face  1   a  of the ferrule  1 . Then, the exposed end side of the guide pin P is inserted in the guide pin inserting hole  10  of the ferrule  1  (see FIG. 1) with the guide pin P inserted in the guide pin inserting hole  22  of the optical fiber press member  20 . With the positioning protrusive portion  21  of the optical fiber press member  20  entering the hollow portion  50  of the ferrule  1  by the induction of the guide pin P, the ferrule connecting face  20   a  of the optical fiber press member  20  is pressed against the front end face  1   a  of the ferrule  1 . As a result, the optical fiber press face  21   a  enters the hollow portion  50  by approximately 5 to 10 μm with the index matching material K entering the hollow portion  50  (see FIG. 10). In order to maintain this state, the ferrule  1  and the optical fiber press member  20  may be interposed and fixed on both sides by means of a clip which is not shown.  
         [0047]    As shown in FIG. 9, then, the optical fibers  3  are inserted from the optical fiber inlet  6  of the ferrule  1 . Thus, the optical fibers  3  are inserted in the optical fiber positioning holes  4 , respectively. As shown in FIG. 10, the optical fiber  2  is advanced to such an extent that the tip face  3   a  of the optical fiber  3  abuts on the optical fiber press face  21   a  of the positioning protrusive portion  21 . As a result, the tip face  3   a  of the optical fiber  3  retreats to be led in by approximately 5 to 10 μm (corresponding to the amount of protrusion of the positioning protrusive portion  21 ) with respect to the front end face  1   a  of the ferrule  1 , and is drawn in the hollow portion  50 . Furthermore, the hollow portion  50  is filled with the silicon based refractive index matching material K, and the tip face  3   a  of the optical fiber  3  is completely drawn in the index matching material K.  
         [0048]    Furthermore, a misalignment of approximately several μm is generated on the tip face  3   a  of the optical fiber  3  during cutting. Therefore, it is necessary to align the tip faces  3   a  in order to eliminate an optical connection loss caused by the misalignment. As shown in FIG. 11, therefore, the ferrule  1  and the optical fiber positioning member  20  are fixed onto a base plate  24  and the covering portion F of the optical fiber  2  is held by means of a fiber holder  25  which can be slid over the base plate  24  in a longitudinal direction. In this state, pressure is applied forward to give such an alignment load that the tip faces  3   a  of all the optical fibers  3  abut on the optical fiber press face  21   a  of the positioning protrusive portion  21  (such a load as to give 0.2 kgf (about 1.96 N), for example, to the four optical fibers  3  forward).  
         [0049]    Consequently, the tip face  3   a  of the optical fiber  3  is forcibly aligned as shown in FIG. 12. In this case, it is necessary to absorb an amount of the optical fiber  3  to be compressed. As shown in FIG. 13, therefore, it is preferable that the optical fiber alignment groove  9  should have a C-shaped section and a slit-shaped opening  9   a  having a smaller width than the diameter of the optical fiber  3  should be formed over the optical fiber alignment groove  9 . By providing such an opening  9   a , the optical fiber  3  can be prevented from jumping out so that the adhesive R can flow into the optical fiber alignment groove  9 .  
         [0050]    As shown in FIG. 14, then, the adhesive filling hollow portion  7  of the ferrule  1  is filled with an epoxy based thermosetting type adhesive R. In this state, the ferrule  1  is properly heated by a heater which is not shown so that the adhesive R is cured. At the final step, the ferrule  1  and the optical fiber  3  slightly change their dimensions by expansion and contraction (particularly, the ferrule  1  made of a resin is greatly expanded and contracted). However, the tip face  3   a  of the optical fiber  3  is previously led in. Therefore, the tip face  3   a  of the optical fiber  3  is not protruded from the front end face  1   a  of the ferrule  1 .  
         [0051]    As shown in FIG. 15, the optical fiber press member  20  is removed from the ferrule  1 . Consequently, the work for assembling the optical fiber  2  into the ferrule  1  is completed with the tip face  3   a  of the optical fiber  3  aligned reliably (see FIG. 12). The refractive index matching material K in the hollow portion  50  is cleaned and removed after the assembling work if necessary. Moreover, the expansion and contraction of the ferrule  1  and the optical fiber  3  can be prevented by using a ultraviolet curing adhesive or a room temperature curing adhesive for the adhesive R. In the case in which refuse or the like sticks to the tip face  3   a  of the optical fiber  3  protruded in the hollow portion  50 , it is preferable that the tip portion of the optical fiber  3  should be cleaned by inserting and turning a cleaning member such as an applicator in the hollow portion  50 . Thus, the hollow portion  50  also serves to easily clean the tip face  3   a  of the optical fiber  3 .  
         [0052]    Next, another optical connector C 1  according to the present invention will be described. The components, which are identical or similar to those of the optical connector C, have the same reference numerals. As shown in FIG. 16, a ferrule  30  to be applied to the optical connector C 1  is provided with a housing  32  for a fiber press fixing member for accommodating a block-shaped fiber press fixing member  31 , and the top of the housing  32  is formed as a rectangular opening  33  for inserting the fiber press fixing member  31  therein. Four optical fiber alignment grooves  34  extended over the whole length are formed on the bottom face of the housing  32 . When the fiber press fixing member  31  is inserted from the opening  33 , the four optical fibers  3  in the optical fiber alignment groove  34  can be pressed downward at one time by a lower face  31   a  of the fiber press fixing member  31  (see FIG. 17).  
         [0053]    The optical connector C 1  has a spring member  35  for energizing the fiber press fixing member  31  inserted into the housing  32 . The spring member  35  is constituted as a clamp member having a U-shaped section which is extended from the upper face of the ferrule  30  to the lower face thereof. The fiber press fixing member  31  is elastically held in the housing  32  by means of the clamp member  35 . Accordingly, each optical fiber  3  in each optical fiber alignment groove  34  can be firmly fixed to the ferrule  30  with a predetermined fixed load by utilizing the clamp member  35 .  
         [0054]    The material of the clamp member  35  is phosphorus bronze or stainless steel which has been subjected to cold working. Consequently, the clamp member  35  can have strong spring force and high durability. Thus, long-term reliability of clamp force can be ensured. Moreover, the clamp member  35  is formed to have a U-shape by an upper plate-shaped piece  35   a , a lower plate-shaped piece  35   b  and an intermediate piece for coupling them (which is not shown), thereby generating proper clamp force by the upper piece  35   a  of the clamp member  35 .  
         [0055]    Furthermore, the optical connector C 1  has a block-shaped covering portion press fixing member  39  for fixing a covering portion F of a optical fiber ribbon  2  to the ferrule  30  in addition to the fiber press fixing member  31  for fixing the optical fiber  3  to the ferrule  30 .  
         [0056]    An optical fiber guide hole  40  extended rearward from the optical fiber alignment groove  34  is provided in the ferrule  30 , and a covering portion inserting member  36  is positioned therebehind. The covering portion inserting member  36  has at least such a width as to accommodate the covering portion F of the optical fiber ribbon  2 . A housing  37  for the covering portion press fixing member is formed as a notch on the rear end of the ferrule  30  in parallel with the housing  32  for the fiber press fixing member. The covering portion press fixing member  39  can be provided in the housing  37 . Moreover, the optical connector C 1  has a spring member  38  for energizing the covering portion press fixing member  39  in the housing  37 . The spring member  38  is constituted as a clamp member having a U-shaped section which is extended from the upper face of the ferrule  30  to the lower face thereof. The covering portion press fixing member  39  is elastically held in the housing  37  by means of the clamp member  38 .  
         [0057]    In the same manner as the optical connector C, a hollow portion  50  for optical fiber protrusion is provided on the center of a front end face  30   a  of the ferrule  30  and the tip face  3   a  of the optical fiber  3  is not protruded from the front end face  30   a  of the ferrule  30  but is drawn in the hollow portion  50 .  
         [0058]    An optical connector according to a further embodiment of the present invention will be described below. As shown in FIG. 18, tip faces  3   a  of four optical fibers  3  may not be aligned but be provided in a hollow portion  50 . More specifically, in the case in which the tip face  3   a  of each optical fiber  3  is drawn in the hollow portion  50 , the amount of the optical fiber  3  protruded from an optical fiber protrusion port  5  may be uneven. The reason is that independent optical connection is carried out in the respective optical fibers  3 . In other words, when four optical fibers  28   a  provided on a ferrule  28  of another optical connector  27  are to be optically connected to the optical fiber  3  of a ferrule  1 , the optical fiber  3  performs independent optical connection to the optical fiber  28   a.    
         [0059]    By drawing the tip face  3   a  of the optical fiber  3  in the hollow portion  50  of the ferrule  1 , the following advantages can further be obtained. More specifically, it is possible to roughly cut the tip portion of the optical fiber  3  in a slight misalignment state with an alignment error of several μm even if the tip face  3   a  of the optical fiber  3  is not cut to be aligned with high precision at the previous step of inserting the optical fiber  3  into the ferrule  1 . As a result, the cutting work can be carried out rapidly. In this case, even if the tip face of the optical fiber  3  is obliquely cut, the connection is affected with difficulty. Moreover, also after the optical fiber  3  in the misalignment state of the end face is incorporated in the ferrule  1 , it is not necessary to align and cut the tip portion of the optical fiber  3  again. Consequently, the work of assembling the optical fiber  3  can be carried out very rapidly. Furthermore, a change in the amount of protrusion of the optical fiber  3  caused by a coefficient of thermal expansion can also be permitted. When the tip face  3   a  of the optical fiber  3  is rounded by a discharging work at the previous step of inserting the optical fiber  3  into the ferrule  1 , the optical fiber  3  can easily be inserted into an optical fiber positioning hole  4  and so is the ferrule  30 .  
         [0060]    The optical connector according to the present invention is not restricted to various embodiments described above. For example, a hollow portion  61  having a slit-shaped opening window  61   a  may be provided on the center of a front end face  60   a  of a ferrule  60  in an optical connector C 2  as shown in FIG. 19. In this case, it is easy to greatly move a cleaning member such as an applicator along the hollow portion  61 . The opening window  61   a  may be formed slenderly in the transverse direction to include a guide pin inserting hole  10  on both sides over the front end face  60   a  of the ferrule  60 .  
         [0061]    As a matter of course, the coverage of the optical connector described above includes multi-fiber optical connectors of other types and single core optical connectors of SC and MU types in addition to an optical connector of an MT type. As shown in FIG. 20, for example, a hollow portion  71  having a slit-shaped opening window  71   a  may be provided on the center of a front end face  70   a  of a cylindrical ferrule  70  in a single core optical connector C 3 . In this case, an optical fiber  72  having a single core is utilized and a tip face  73   a  of an optical fiber  73  is drawn in the hollow portion  71 .  
         [0062]    From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.