Abstract:
An end face polishing method that can improve polishing accuracy of an end face of a ferrule and increase return loss in opposite connection is to be provided. In the end face polishing method in which the end face of a rod shape member is polished by pressing the rod shape member attached to a jig board to an abrasive member on a polishing board which is supported by a main body of an apparatus to be rotated and oscillated, by using the plurality of abrasive members whose hardnesses are higher than the rod shape member and different from the rod shape member, the end face of the rod shape member is polished with the abrasive members in a manner that the abrasive member is exchanged in the order from that of higher hardness to that of lower hardness.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an end face polishing method for polishing an end face of a rod shape member such as a fiber for optical communication or a ferrule in which the fiber for optical communication is held.  
           [0003]    2. Description of the Related ART  
           [0004]    The fiber for optical communication is used by polishing simultaneously and smoothly the end face of the ferrule and the end face of the fiber to be a mirror surface after the fiber is fixedly adhered to an inside of a center hole of the ferrule which is a main member of a connector. When polished surfaces of the polishing finished ferrule and fiber are not perpendicular to a central axis of the ferrule or there is a flaw on the polished surface, accuracy of facing position is deteriorated and loss is increased in the optical connector in which the ferrules are oppositely connected each other. Therefore, the polishing finish of the high accuracy is required for the polished surface of the ferrule including the optical fiber.  
           [0005]    For example, in JA-A-3-26456, there is disclosed an optical fiber end face polishing apparatus of the related art for polishing the end face of the ferrule including the optical fiber. The optical fiber end face polishing apparatus disclosed in the publication has an eccentric board which rotates on a concentric circle of a rotation disk and a planetary gear which transmits a rotation of a motor for a revolution to the eccentric board, connects them with a polishing board to rotate and revolve the polishing board, and polishes the end faces of a number of ferrules which are held to a jig board by a support portion provided in a main body of the apparatus while the end faces of the ferrules are pressed to an abrasive member fixed to the polishing board.  
           [0006]    In case that the end face of the ferrule is polished by using the above-described optical fiber end face polishing apparatus, generally, there is employed an optical fiber end face polishing method in which, in order, a rough polishing process is carried out by using the abrasive member having given hardness, an intermediate polishing process is carried out by using the abrasive member having the hardness higher than the abrasive member used for the rough polishing process, and then a final polishing process is carried out by using the abrasive member having the hardness higher than the abrasive member used for the intermediate polishing process.  
           [0007]    In the optical fiber end face polishing method, since the end face of the ferrule is polished by the abrasive member which is fixed to the rotated or revolved polishing board, for example, by rough-polishing the end face of the ferrule in the rough polishing process, a peripheral portion of a radial outside in the end face of the ferrule is gradually rough-polished and the end face of the ferrule is formed to be a convex sphere.  
           [0008]    After the rough polishing process, the intermediate polishing process and the final polishing process are carried out in order, and in these cases, the polishing is carried out in a manner that the abrasive member used in the immediately previous polishing process is changed for the abrasive member having the hardness higher than the abrasive member used in the immediately previous polishing process. That is to say, the end face of the ferrule is polished in a manner that the final polishing process is carried out with the abrasive member having the hardness higher than the abrasive member used for the intermediate polishing process after the intermediate polishing process is carried out with the abrasive member having the hardness higher than the abrasive member used for the rough polishing process. This allowed the mirror surface finish to be carried out in such a manner that, in a neighborhood of the end face of the optical fiber in the end face of the ferrule, the end face of the ferrule in the shape of the convex sphere is gradually polished to be smooth.  
           [0009]    However, in the above-described optical fiber end face polishing apparatus, since the end face of the ferrule is polished under pressure to the abrasive member with a given load while the abrasive members are changed in the order from those of the lower hardness to those of the higher hardness in each of the polishing processes, in the intermediate and final polishing processes after a nearly central portion of the end face of the ferrule is formed to be the convex in the first rough polishing process, polishing pressure against the end face of the ferrule is gradually decreased in a radially outward direction. That is to say, in the intermediate and final polishing processes, when the end face of the ferrule is polished under pressure, a change in an elastic deformation of the abrasive member is decreased compared with the rough polishing process, an area where the end face of the ferrule abuts on the abrasive member is gradually decreased toward the direction of the end face of the optical fiber. Therefore, there is a problem that the polishing pressure applied to the neighborhood of the end face of the optical fiber in the end face of the ferrule is increased, the peripheral portion of the radial outside in the end face of the ferrule is not polished in the intermediate and final polishing processes, consequently, a polishing residue of the rough polishing process is generated.  
           [0010]    For example, when the ferrule in which the polishing residue has been generated is oppositely connected to an optical connector adaptor, there is a problem that the peripheral portion of the end face of the ferrule contacts an inside surface of a sleeve, which causes the flaw to be generated in the inside surface of the sleeve.  
           [0011]    Since the polishing pressure applied to the nearly central portion of the end face of the ferrule is increased with proceeding from the rough polishing process to the subsequent polishing processes, there are a problems that the neighborhood of the end face of the optical fiber in the end face of the ferrule is concaved by being excessively polished or that a scratch is generated in the end face in case that some foreign matter enters between the end face of the ferrule and the polishing surface of the polishing member.  
           [0012]    Furthermore, though abrasive particles which polish the end face of the ferrule intervene on the polishing surface of the polishing member, when the polishing pressure applied to the neighborhood of the end face of the optical fiber in the end face of the ferrule is large, a damaged layer is generated in the end face of the ferrule by an influence of the abrasive particle. This causes a problem that return loss is decreased when the ferrules are oppositely connected each other.  
         SUMMARY OF THE INVENTION  
         [0013]    In view of the foregoing, it is an object of the invention to provide an end face polishing method in which polishing accuracy of the end face of the ferrule is improved and the return loss is increased in opposite connection.  
           [0014]    A first aspect of the invention for solving the above-described problems is an end face polishing method in which a rod shape member is polished by pressing the rod shape member attached to a jig board to an abrasive member on a polishing board which is supported by a main body of an apparatus to be rotated and oscillated, which is characterized in that the end face of the rod shape member is polished by using a plurality of abrasive members having different hardnesses, in a manner that the abrasive member is changed from that of higher hardness to that of the lower hardness.  
           [0015]    A second aspect of the invention is characterized in that, in the first aspect, the rod shape member is pressed with a constant load while the rod shape member is supported at a given position with respect to the abrasive member.  
           [0016]    A third aspect of the invention is characterized in that, in the first or second aspect, the plurality of the abrasive members comprise a rough abrasive member having given hardness, an intermediate abrasive member having the hardness lower than the rough abrasive member, and a final abrasive member having the hardness lower than the intermediate abrasive member.  
           [0017]    A fourth aspect of the invention is characterized in that, in any one of the first to third aspects, the abrasive member comprises an elastic member fixed on the polishing board and an abrasive sheet placed on an upper surface of the elastic member.  
           [0018]    A fifth aspect of the invention is characterized in that, in any one of the first to fourth aspects, the rod shape member is a ferrule in which an optical fiber is held or an optical connector holding the ferrule. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a partially sectional view of an end face polishing apparatus according to a first embodiment of the invention;  
         [0020]    [0020]FIG. 2 is a schematically sectional view illustrating a rough polishing process of an end face polishing method according to the first embodiment of the invention;  
         [0021]    [0021]FIG. 3 is a schematically sectional view illustrating an intermediate polishing process of the end face polishing method according to the first embodiment of the invention;  
         [0022]    [0022]FIG. 4 is a schematically sectional view illustrating a final polishing process of the end face polishing method according to the first embodiment of the invention;  
         [0023]    [0023]FIG. 5 is a distribution view showing a frequency of each concave quantity according to a first Test Example of the invention, FIG. 5A is an Example, and FIG. 5B is a Comparative Example; and  
         [0024]    [0024]FIG. 6 is a distribution view showing a frequency of each return loss according to a second Test Example of the invention, FIG. 6A is an Example, and FIG. 6B is a Comparative Example.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Embodiments of the invention will be described in detail referring to the accompanying drawings.  
         [0026]    (First Embodiment)  
         [0027]    [0027]FIG. 1 is a partially sectional view of an end face polishing apparatus according to a first embodiment of the invention.  
         [0028]    As shown in FIG. 1, an end face polishing apparatus  10  comprises a jig board  13  in which a ferrule  12  holding an optical fiber  11  is fixed at a plurality of places, a main body  14  of the apparatus to which the jig board  13  is fixed, and a polishing board  15  which is provided below the jig board  13  and in the main body  14  of the apparatus so as to be rotated and oscillated.  
         [0029]    The jig board  13  has a plurality of through holes  16  which the ferrule  12  can be inserted, and the jig board  13  is fixed to the main body  14  of the apparatus by a screw  17  for fastening the jig.  
         [0030]    An abrasive member  18  polishing the end face of the ferrule  12  is detachably mounted on an upper surface portion of the polishing board  15 . The abrasive member  18  includes an elastic member  19  fixed on the polishing board  15  and an abrasive sheet  20  placed on an upper surface of the elastic member  19 .  
         [0031]    The abrasive member  18 , though described in more detail below, comprises a rough polishing member having a rough polishing sheet of given polishing roughness on an elastic member for the rough polishing of given hardness, an intermediate polishing member having an intermediate polishing sheet of the polishing roughness larger than the rough polishing sheet on an elastic member for the intermediate polishing of the hardness lower than the elastic member for the rough polishing, and a final polishing member having a final polishing sheet of the polishing roughness larger than the intermediate polishing sheet on an elastic member for the final polishing of the hardness lower than the elastic member for the intermediate polishing.  
         [0032]    A material used for the elastic member  19  is not particularly limited, so long as the material can be properly adjusted to the given hardness, and rubber, elastomer, resin and the like are taken as an example.  
         [0033]    The abrasive sheet  20  comprises an abrasive grain (not shown) including, for example, diamond, silicon oxide, cerium oxide, silicon nitride or the like, and the abrasive sheet  20  is adhered to an upper surface of the elastic member  19 .  
         [0034]    The jig board  13  comprises a holding member  21  which presses the end face of the ferrule  12  to the polishing surface of the abrasive member  18  with a constant load, while an edge portion of the ferrule  12  is inserted into the through hole  16  and the end face of the ferrule  12  abuts an upper surface of the abrasive member  18 .  
         [0035]    The holding member  21  is provided with a holding hole  22  which holds the ferrule  12  and a through hole for inserting  23  which communicates with the holding hole  22  and allows the optical fiber  11  held by the ferrule  12  to insert through.  
         [0036]    An adjusting spring  24  for pressing the end face of the ferrule  12  to the polishing surface of the abrasive member  18  with the constant load and an adjusting spring  25  for adjusting the load are fitted inside the holding hole  22 .  
         [0037]    As described above, the end face of the ferrule  12  pressed to the upper surface of the abrasive member  18  with the constant load is polished by rotating or revolving the polishing board  15 , and at this point, the polishing is carried out in a manner that exchanges the abrasive member is changed in order from that of higher hardness to that of lower hardness in each of the rough polishing process, the intermediate polishing process, and the final polishing process.  
         [0038]    The end face polishing method of the embodiment will be described in detail referring to FIG. 2 to FIG. 4. FIG. 2 to FIG. 4 are schematically sectional views illustrating each polishing process of the end face polishing method according to the first. embodiment of the invention.  
         [0039]    As shown in FIG. 2A, in the rough polishing process, the end face of the ferrule  12  including the optical fiber is rough-polished while the end face of the ferrule  12  is pressed with the constant load to a surface of a rough polishing sheet  20   a  on an elastic member for the roughly polishing  19   a  of the given hardness, which is fixed on the polishing board  15 . At this point, by pressing the end face of the ferrule  12  with the constant load, a rough abrasive member  18 A is elastically deformed in a thickness direction and a portion where the end face of the ferrule  12  is pressed is concaved a given amount.  
         [0040]    And then, while the end face of the ferrule  12  is pressed to the upper surface of the rough abrasive member  18 A, the end face of the ferrule  12  is rough-polished by rotating or revolving the polishing board  15 . In this case, as shown in FIG. 2B, the polishing pressure applied to the end face of the ferrule  12  is gradually increased from the nearly central portion of the end face of the ferrule  12  toward the radial outside. Thus, as shown in FIG. 2C, the peripheral portion of the radial outside in the end face of the ferrule  12  is rough-polished, and the end face of the ferrule  12  is formed to be the convex sphere.  
         [0041]    As shown in FIG. 3A, in the intermediate polishing process, at first the elastic member for the rough polishing  19   a  used in the rough polishing process is changed for an elastic member for the intermediate polishing  19   b  of the hardness lower than the elastic member for the rough polishing  19   a , then, in the same way as the rough polishing process, the end face of the ferrule  12  which has been formed to be the convex sphere by the rough polishing is polished while the end face of the ferrule  12  is pressed with the constant load to a surface of an intermediate polishing sheet  20   b  adhered on the elastic member for the intermediate polishing  19   b . At this point, since the polishing is carried out with the constant load by changing the elastic member for the rough polishing  19   a  for the elastic member for the intermediate polishing  19   b  of the hardness lower than the elastic member for the rough polishing  19   a  in the intermediate polishing process, the amount of the elastic deformation of an intermediate abrasive member  18 B is increased compared with the rough polishing.  
         [0042]    Consequently, as shown in FIG. 3B, a pressure distribution of the polishing pressure applied to the end face of the ferrule  12  can be concentrically and nearly uniformly dispersed to a whole area of the end face of the ferrule  12  without concentrating the pressure distribution of the polishing pressure on the neighborhood of the end face of the optical fiber  11 . As shown in FIG. 3C, therefore, while the neighborhood of the end face of the optical fiber  11  in the end face of the ferrule  12  is polished, the peripheral portion of the radial outside in the end face of the ferrule  12  can also be polished.  
         [0043]    As shown in FIG. 4A, in the final polishing process, at first the elastic member for the intermediate polishing  19   b  used in the intermediate polishing process is changed for an elastic member for the final polishing  19   c  of the hardness lower than the elastic member for the intermediate polishing  19   b , then, in the same way as in the rough and intermediate polishing processes, the end face of the ferrule  12  is polished while the end face of the ferrule  12  is pressed with the constant load to a surface of an final polishing sheet  20   c  adhered on the elastic member for the final polishing  19   c.    
         [0044]    At this point, since in the final polishing process, the polishing is carried out with the constant load by changing the elastic member for the intermediate polishing  19   b  for the elastic member for the final polishing  19   c  of the hardness lower than the elastic member for the intermediate polishing  19   b , an area where the end face of the ferrule  12  contacts a surface of a final abrasive member  18 C is increased compared with the intermediate polishing process. As shown in FIG. 4B, this allows the polishing pressure applied to the end face of the ferrule  12  to be more nearly uniformly dispersed, compared with the intermediate polishing process. Accordingly, as shown in FIG. 4C, the end face of the ferrule  12  including the optical fiber  11  can be final-polished to be smooth.  
         [0045]    As described above, according to the end face polishing method of the embodiment, by polishing the end face of the ferrule  12  while each of the abrasive member is changed in the order from that of the higher hardness  18 A to that of the lower hardness  18 C, the polishing pressure applied to the end face of the ferrule  12  can be gradually and uniformly dispersed to polish smoothly the end face of the ferrule  12 .  
         [0046]    In the rough abrasive member used for the rough polished process, it is proper that the hardness of the elastic member for the rough polishing is in the range from about 95 Hs to about 65 Hs, while in the intermediate abrasive member used for the intermediate polishing process, it is good that the hardness of the elastic member for the intermediate polishing is lower than that of the elastic member for the rough polishing, for example, about 55±10 Hs, in the final abrasive member used for the final polishing process, it is preferable that the hardness of the elastic member for the final polishing is lower than that of the elastic member for the intermediate polishing, for example, about 45±10 Hs.  
         [0047]    In the embodiment, there is described the method in which the abrasive member is changed in the order from that of higher hardness to that of lower hardness in each of the rough polishing process, the intermediate polishing process, and the final polishing process, however, the intermediate abrasive member used in the intermediate polishing process after the rough polishing process may be changed for the abrasive member having the hardness lower than the rough abrasive member, and then the final abrasive member used in the final polishing process after the intermediate polishing process may be as hard as the intermediate abrasive member or ±10 Hs, or harder than the intermediate abrasive member. In more detail, the elastic member for the intermediate polishing of the intermediate abrasive member, which is used for the intermediate polishing process after the rough polishing process, is changed for the elastic member having the hardness lower than the elastic member for the rough polishing, and then the elastic member for the polishing which is as hard as the elastic member for the intermediate polishing or has the hardness of a difference of about ±10 Hs from that, or the elastic member for the polishing having the hardness higher than the elastic member for the intermediate polishing is used as the elastic member for the final polishing of the final abrasive member, which is used for the final polishing process. Even if such constitution is adopted, the polishing pressure applied to the end face of the ferrule can be uniformly dispersed to polish the whole surface of the end face of the ferrule, and almost the same effect as the first embodiment can be obtained.  
         [0048]    By uniformly dispersing the polishing pressure applied to the end face of the ferrule  12 , generation of the damaged layer in the end face of the optical fiber  11 , which is caused by an influence of the abrasive grain on the surface of each of the abrasive sheets  20   a  to  20   b , can be prevented. Accordingly, when the ferrules  12  are oppositely connected, the return loss can be increased.  
         [0049]    Examples of the above-described end face polishing method of the invention will be described, however, the invention is not limited to them.  
       EXAMPLE  
       [0050]    In an Example, the hardness of the elastic member for the rough polishing was set to 65 Hs in the rough abrasive member used for the rough polishing process, the hardness of the elastic member for the intermediate polishing was set to 55 Hs in the intermediate abrasive member used for the intermediate polishing process, the hardness of the elastic member for the final polishing was set to 45 Hs in the final abrasive member used for the final polishing process, and the end face of the ferrule including the optical fiber was polished. The load which the end face of the ferrule was pressed against the abrasive sheet on the abrasive member used for each process was set to 2.0N. The silicon oxide (SiO 2 ) was used as the abrasive sheet.  
       COMPARATIVE EXAMPLE  
       [0051]    For purposes of comparison, the end face of the ferrule including the optical fiber was polished by using reverse processes of the Example. The polishing conditions of each polishing process were set to be the same as the Example.  
       FIRST TEST EXAMPLE  
       [0052]    The plurality of ferrules which were polished in the Example and the Comparative Example were prepared, the concave quantity (μm) which the end face of the ferrule was concave in the axis direction was measured with respect to these ferrules of the Example and the Comparative Example. FIG. 5 is a distribution view showing a frequency of each concave quantity, FIG. 5A is the Example, and FIG. 5B is the Comparative Example. In the concave quantity, the quantity which is concave in the axial direction of the optical fiber is indicated by a numerical value with a sign of (−).  
         [0053]    Comparing FIG. 5A and FIG. 5B, since the frequency of generation of the concave in the face of the optical fiber is lower in the Example compared with the Comparative Example, it is found that the end face of the optical fiber has been able to be smoothly polished.  
       SECOND TEST EXAMPLE  
       [0054]    In the same way as the first Test Example, the plurality of ferrules which were polished in the Example and the Comparative Example were prepared, the return loss (dB) in case that the ferrules polished in the Example were oppositely connected and the return loss (dB) in case that the ferrules polished in the Comparative Example were oppositely connected were measured respectively. The result is shown in FIG. 6. FIG. 6 is a distribution view showing a frequency of each return loss, FIG. 6A is the Example, and FIG. 6B is the Comparative Example.  
         [0055]    Comparing FIG. 6A and FIG. 6B, it was found that the larger return loss in the Example can be obtained compared with the Comparative Example. Particularly, in the case that the ferrules polished in the Example were oppositely connected, the opposite connection can frequently be carried out with the return loss not lower than 60 dB.  
         [0056]    (Other Embodiments)  
         [0057]    Though the first embodiment of the invention has been described, a basic constitution of the end face polishing method is not limited to the above-described one.  
         [0058]    In the first embodiment, the abrasive sheet is adhered to the upper surface of the elastic member, however, it is not limited to this but the elastic member and the abrasive sheet may be integrally formed.  
         [0059]    Though the end face of the ferrule including the optical fiber is polished by the abrasive sheet, it is not limited to this but, for example, polishing liquid in which the abrasive particle polishing the end face of the ferrule and the optical fiber is uniformly dispersed may be applied on the abrasive sheet to polish the end face of the ferrule including the optical fiber by the abrasive particle in the polishing liquid.  
         [0060]    In this case, as described above, since the polishing pressure applied to the end face of the ferrule can be uniformly dispersed, the damaged layer in neighborhood of the end face of the optical fiber in the end face of the ferrule, which may be caused by an influence of the abrasive grain in the polishing liquid, is not formed. Accordingly, even if the polishing liquid is intervened between the end face of the ferrule and the surface of the abrasive sheet, the end face of the ferrule can be smoothly polished by the abrasive particle, and the return loss can be increased in the opposite connection.  
         [0061]    Furthermore, in the first embodiment, though the polishing of the end face of the ferrule including the optical fiber was described, it is not limited to this but, for example, the end face of the rod shape member such as the optical connector holding the ferrule may be polished.  
         [0062]    As described above, according to the end face polishing method of the invention, by polishing the end face of the ferrule while the abrasive member is changed in the order from that of higher hardness to that of lower hardness, the polishing pressure applied to the end face of the ferrule can be gradually and uniformly dispersed to polish smoothly the end face of the ferrule, and the return loss in the opposite connection can be increased.