Patent Publication Number: US-7899288-B2

Title: Optical fiber structure

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical fiber structure in which a plurality of optical fiber arrays, each including a plurality of multimode optical fibers, are placed one on another. 
     2. Description of the Related Art 
     Conventionally, laser light has been used in the fields of printing and processing. For example, in production of printing blocks as described in U.S. Pat. No. 6,857,365, the laser light is used to process materials to produce print blocks. In recent years, high-output semiconductor lasers have been developed. Further, optical fiber structures that transmit high-output laser light, which is output from the high-output semiconductor lasers, through fibers and output the transmitted light are known. Further, in the field of optical fiber structures that are used in processing as described above, multicore-type optical fiber structures in which a plurality of optical fibers are fixed in such a manner that one-side ends thereof are arranged in line form or in block form are being developed to improve the processing efficiency. 
     When the laser light is used to process the print blocks as described in U.S. Pat. No. 6,857,365, there are cases in which laser light that has a small beam diameter is desirable and cases in which laser light that has a large beam diameter is desirable, depending on processing conditions. For example, when a highly-precise process should be carried out, the laser light that has a small diameter is desirable. In contrast, when a so-called solid processing should be performed, in other words, when the entire area of a certain area should be processed uniformly, the laser light that has a large diameter is desirable. However, in the conventional multicore-type optical fiber structure, there is a problem that it is impossible to change the beam diameter based on the processing conditions, because the multicore-type optical fiber structure includes a plurality of same optical fibers, which output beams having the same beam diameter. Meanwhile, there is an apparatus that changes the beam diameter of laser light by a special optical system provided in a later stage. However, there is a problem that such an optical system tends to be complex. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing circumstances, it is an object of the present invention to provide an optical fiber structure that has simple structure, but that can output light beams having different beam diameters from each other. 
     An optical fiber structure according to the present invention is an optical fiber structure comprising: 
     a first optical fiber array including a plurality of optical fibers, the output ends of which are linearly arranged; and 
     a second optical fiber array including a plurality of optical fibers, the output ends of which are linearly arranged, wherein the first optical fiber array and the second optical fiber array are placed one on the other, and wherein the optical fibers in the first optical fiber array and the second optical fiber array include at least one first optical fiber, the core diameter of which at the output end thereof is a first core diameter, and at least one second optical fiber, the core diameter of which at the output end thereof is a second core diameter, and wherein the first core diameter is different from the second core diameter, and wherein at least one of the first optical fiber and the second optical fiber has a taper portion, the core diameter of which decreases or increases along an optical axis. 
     The expression “the optical fibers in the first optical fiber array and the second optical fiber array include at least one first optical fiber, the core diameter of which at the output end thereof is a first core diameter” means that at least one of the optical fibers is the first optical fiber. Further, the expression “the optical fibers in the first optical fiber array and the second optical fiber array include . . . at least one second optical fiber, the core diameter of which at the output end thereof is a second core diameter, and wherein the first core diameter is different from the second core diameter” means that at least one of the optical fibers is a second optical fiber. 
     Further, when the first optical fiber array includes a plurality of first optical fibers arranged therein, the second optical fiber array may include a plurality of second optical fibers arranged therein. 
     Alternatively, each of the first optical fiber array and the second optical fiber array may include at least one first optical fiber and at least one second optical fiber arranged therein. Further, each of the first optical fibers and the second optical fibers may be arranged in such a manner that the arrangement in the second optical fiber array is in reverse order to the order of arrangement in the first optical fiber array. 
     The expression “the arrangement in the second optical fiber array is in reverse order to the order of arrangement in the first optical fiber array” means that when the second optical fiber array is placed upside down, the arrangement of the optical fibers in the second optical fiber becomes the same as the arrangement of the optical fibers in the first optical fiber array. 
     When the first optical fiber array includes the at least one first optical fiber arranged in a half of the first optical fiber array and the at least one second optical fiber arranged in the other half of the first optical fiber array, the second optical fiber array may include the at least one second optical fiber arranged in a half of the second optical fiber array and the at least one first optical fiber arranged in the other half of the second optical fiber array. 
     When the at least one first optical fiber and the at least one second optical fiber in the first optical fiber array are alternately arranged one by one, the at least one second optical fiber and the at least one first optical fiber in the second optical fiber array may be alternately arranged one by one. 
     Further, the first optical fiber arranged in the first optical fiber array and the second optical fiber arranged in the second optical fiber array may face each other, and the second optical fiber arranged in the first optical fiber array and the first optical fiber arranged in the second optical fiber array may face each other. 
     The expression “the first optical fiber arranged in the first optical fiber array and the second optical fiber arranged in the second optical fiber array face each other, and the second optical fiber arranged in the first optical fiber array and the first optical fiber arranged in the second optical fiber array face each other” means that the first optical fiber arranged in the first optical fiber array and the second optical fiber arranged in the second optical fiber array are linearly aligned in a direction that is substantially perpendicular to the arrangement direction (extending direction) of the optical fiber arrays and that the second optical fiber arranged in the first optical fiber array and the first optical fiber arranged in the second optical fiber array are linearly aligned in a direction that is substantially perpendicular to the arrangement direction of the optical fiber arrays. The first optical fibers and the second optical fibers may be in direct contact with each other. Alternatively, a pressure plate or the like may be inserted between the first optical fiber and the second optical fiber. 
     In the optical fiber structure according to the present invention, a transparent member for protecting the end surfaces of the optical fibers may be attached to the surfaces of the output ends of the optical fibers by optical contact. 
     Further, an anti-reflection coating may be provided on the output side of the transparent member for protecting the end surfaces of the optical fibers. 
     Further, the power of light that is output from each of the optical fibers may be greater than or equal to 1 W. 
     The optical fiber structure according to the present invention is an optical fiber structure comprising: 
     a first optical fiber array including a plurality of optical fibers, the output ends of which are linearly arranged; and 
     a second optical fiber array including a plurality of optical fibers, the output ends of which are linearly arranged, wherein the first optical fiber array and the second optical fiber array are placed one on the other, and wherein the optical fibers in the first optical fiber array and the second optical fiber array include at least one first optical fiber, the core diameter of which at the output end thereof is a first core diameter, and at least one second optical fiber, the core diameter of which at the output end thereof is a second core diameter, and wherein the first core diameter is different from the second core diameter, and wherein at least one of the first optical fiber and the second optical fiber has a taper portion, the core diameter of which decreases or increases along an optical axis. Therefore, the core diameter of the first optical fiber at the output end thereof or the core diameter of the second optical fiber at the output end thereof can be easily changed to a desirable core diameter. Further, it is possible to output light beams that have different beam diameters from each other from a single optical fiber structure that has simple structure without providing a complicated optical system, which was necessary in conventional techniques. Further, since the optical fiber has the taper portion, the core diameter of which decreases or increases along an optical axis, it is possible to easily change the core diameter at the output end to a desirable core diameter. Hence, it is possible to obtain an optical fiber structure that can output a light beam having an arbitrary beam diameter. 
     Further, when the first optical fiber array includes a plurality of first optical fibers arranged therein and the second optical fiber array includes a plurality of second optical fibers arranged therein, if a user wants to use a light beam output from the first optical fiber, he/she can use the first optical fiber array. Alternatively, if the user wants to use a light beam output from the second optical fiber, he/she can use the second optical fiber array. Therefore, the convenience of the optical fiber structure is improved. 
     When each of the first optical fiber array and the second optical fiber array includes at least one first optical fiber and at least one second optical fiber arranged therein, and each of the first optical fibers and the second optical fibers is arranged in such a manner that the arrangement in the second optical fiber array is in reverse order to the order of arrangement in the first optical fiber array, two fiber arrays in which the optical fibers are arranged in the same manner may be produced. Then, one of the two fiber arrays may be placed in an ordinary direction, and the other fiber array may be placed upside down. Further, the two fiber arrays may be placed one on the other to produce the optical fiber structure. Hence, simple and low-cost production of the optical fiber structure becomes possible. 
     Further, when the first optical fiber arranged in the first optical fiber array and the second optical fiber arranged in the second optical fiber array face each other and the second optical fiber arranged in the first optical fiber array and the first optical fiber arranged in the second optical fiber array face each other, the first optical fiber and the second optical fiber can carry out processing with respect to the same pixel, for example, in print processing or the like. Hence, the usability and convenience of the optical fiber structure is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating the structure of an optical fiber structure according to a first embodiment of the present invention; 
         FIG. 2  is a schematic diagram illustrating the structure of an optical fiber; 
         FIG. 3  is a schematic diagram illustrating the structure of an optical fiber array; 
         FIG. 4  is a schematic diagram illustrating the structure of an optical fiber; 
         FIG. 5  is a schematic diagram illustrating the structure of an optical fiber array; 
         FIG. 6A  is a schematic diagram illustrating the structure of another optical fiber structure; 
         FIG. 6B  is a schematic diagram illustrating the structure of an optical fiber structure according to a second embodiment of the present invention; 
         FIG. 7  is a schematic diagram illustrating the structure of an optical fiber structure according to a third embodiment of the present invention; 
         FIG. 8  is a schematic diagram illustrating the structure of an optical fiber array; 
         FIG. 9A  is a schematic diagram illustrating the structure of another optical fiber structure; 
         FIG. 9B  is a schematic diagram illustrating the structure of an optical fiber structure according to a fourth embodiment of the present invention; 
         FIG. 10  is a schematic diagram illustrating the structure of an optical fiber structure according to a fifth embodiment of the present invention; 
         FIG. 11  is a schematic diagram illustrating the structure of an optical fiber array; and 
         FIG. 12  is a schematic diagram illustrating the structure of an optical fiber structure according to a sixth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An optical fiber structure according to a first embodiment of the present invention will be described with reference to the attached drawings.  FIG. 1  is a schematic diagram illustrating the structure of an optical fiber structure  100 . 
     As illustrated in  FIG. 1 , the optical fiber structure  100  includes a first fiber array (first optical fiber array)  110 , a second fiber array (second optical fiber array)  120  and a pressure plate  130 . The first fiber array  110  includes a substrate  111  having four V-shaped grooves  112  and four optical fibers  10 , the ends of which are fixed onto the substrate  111  having the four V-shaped grooves. The second fiber array  120  includes a substrate  121  having four V-shaped grooves  122  and four optical fibers  20 , the ends of which are fixed onto the substrate  121  having the four V-shaped grooves. The first fiber array  110  and the second fiber array  120  are placed one on the other with the pressure plate  130  therebetween in such a manner that the optical fibers  10  and the optical fibers  20  face each other, and the positions of the first fiber array  110  and the second fiber array  120  are fixed. 
     As illustrated in  FIG. 2 , the optical fiber  10  is a multimode fiber having a core  12  and a cladding (a clad or a cladding layer)  14 . The optical fiber  10  includes an ordinary portion  16  and a taper portion  18 . The core diameter of the ordinary portion  16  is 105 μm, and the outer diameter of the fiber at the ordinary portion  16  is 125 μm. The taper portion  18  is formed at the tip of the ordinary portion  16 . In the taper portion  18 , the core diameter and the outer diameter of the fiber decrease along an optical axis. Further, at the leading end of the taper portion  18 , in other words, at the output end  11   a  of the optical fiber  10 , the core diameter is 60 μm, and the outer diameter of the fiber is 80 μm. Further, a polished end surface  13   a  of the core is exposed at the output end  11   a  of the optical fiber  10 . When light beam B 1 , which has propagated through the optical fiber  10 , is output from the output end  11   a  of the optical fiber  10 , the beam diameter L 1  of the light beam B 1  at the output end  11   a  is the same as the core diameter, which is 60 μm. As illustrated in  FIG. 3 , the output ends  11   a  of four optical fibers  10  are fixed into the V-shaped grooves  112  in the substrate  111  having the V-shaped grooves  112 , respectively, in such a manner that the output ends  11   a  of the optical fibers  10  are linearly arranged at the ends of the V-shaped grooves  112  of the substrate  111  having the V-shaped grooves  112 . The optical fibers  10  are fixed into the V-shaped grooves  112  with an ultraviolet-setting resin (a UV-setting resin, a UV-curable resin or an ultraviolet-curable resin), a thermosetting adhesive resin (a thermosetting resin or a thermally curable resin) or the like. 
     As illustrated in  FIG. 4 , the optical fiber  20  is a multimode fiber having a core  22  and a cladding (a clad or a cladding layer)  24 . The diameter of the core  22  is 105 μm, and the outer diameter of the fiber is 125 μm. Further, a polished end surface  23   a  of the core is exposed at the output end  21   a  of the optical fiber  20 . When light beam B 2 , which has propagated through the optical fiber  20 , is output from the output end  21   a  of the optical fiber  20 , the beam diameter L 2  of the light beam B 2  is the same as the core diameter, which is 105 μm. As illustrated in  FIG. 5 , the output ends  21   a  of the four optical fibers  20  are fixed into the V-shaped grooves  122  in the substrate  121  having the V-shaped grooves  122 , respectively, in such a manner that the output ends  21   a  of the optical fibers  20  are linearly arranged at the ends of the V-shaped grooves  122  of the substrate  121  having the V-shaped grooves  122 . The optical fibers  20  are fixed into the V-shaped grooves  122  with an ultraviolet-setting resin, a thermosetting adhesive resin or the like. 
     The optical fiber structure  100  may be used, for example, as an optical head for processing print block plates (or to engrave print patterns on plates) or the like with laser light. In such a case, a high-output semiconductor laser having output power of 10 W or the like, which is not illustrated, is connected to the input end of each of the optical fibers  10  and the optical fibers  20 , the input end being opposite to the output end thereof. Further, an optical system (not illustrated) for condensing the light beam output from the optical fiber structure  100  onto the plate for printing is arranged between the optical fiber structure  100  and the plate for printing. It is possible to process the plate for printing by outputting laser light from a high-output semiconductor laser that is connected to a desirable optical fiber, which a user wants to use for the processing, while shifting the optical fiber structure  100  and the plate for printing relative to each other in the vertical direction of  FIG. 1 . 
     As described above, the beam diameter L 1  of the light beam B 1  at the output end  11   a  of the optical fiber  10  is the same as the core diameter of the optical fiber  10 , which is 60 μm. Further, the beam diameter L 2  of the light beam B 2  at the output end  21   a  of the optical fiber  20  is the same as the core diameter of the optical fiber  20 , which is 105 μm. The optical fiber structure  100 , which has simple structure, can output light beams that have different beam diameters. For example, when it is desirable to use a light beam that has a small diameter to carry out highly precise processing or the like, the light beam output from the optical fiber  10  is used. In contrast, when it is desirable to use a light beam that has a large diameter to carry out a so-called solid process (processing the entire area of a certain portion uniformly so that no unprocessed area substantially remains after the processing) or the like, the light beam output from the optical fiber  20  is used. Further, since the optical fiber  10  has the taper portion  18 , the core diameter of which decreases along an optical axis, it is possible to easily change the core diameter at the output end  11   a  to a desirable core diameter. Further, when fibers that have small diameters are prepared, if at least one of the fibers is used as the optical fiber  20 , and at least one of the fibers is used as the optical fiber  10  by forming a taper portion, it is possible to use an optical beam that has a small diameter and an optical beam that has an even smaller diameter. 
     Further, since the optical fibers  10  and the optical fibers  20  are arranged so as to face each other, it is possible to output light beams that have different beam diameters from each other for the same single pixel, for example, in print processing or the like. Hence, the optical fiber structure  100  is used even more usefully. 
       FIG. 6A  illustrates an optical fiber structure  140 , which is a modified example of the present embodiment. When it is not necessary that the optical fibers  10  and the optical fibers  20  are aligned in a direction perpendicular to the arrangement direction of each of the optical fiber arrays, the optical fibers  10  and the optical fibers  20  may be arranged as in the optical fiber structure  140 . In the optical fiber structure  140 , the optical fibers  10  and the optical fibers  20  are arranged as closely as possible, thereby reducing the size of the optical fiber structure. 
     Next, an optical fiber structure according to a second embodiment of the present invention will be described.  FIG. 6B  is a schematic diagram illustrating the structure of an optical fiber structure  150 . The structure of the optical fiber structure  150  is similar to that of the optical fiber structure  100 , illustrated in  FIG. 1 , except that a transparent member  160  for protecting the end surface is provided at the output end surface in the optical fiber structure  150 . Therefore, the same reference numerals will be assigned to corresponding parts and elements, and the explanation thereof will be omitted. 
     As illustrated in  FIG. 6B , the optical fiber structure  150  includes the first fiber array  110 , the second fiber array  120 , the pressure plate  130  and the transparent member  160  for protecting the end surface. The first fiber array  110  includes a substrate  111  having V-shaped grooves and four optical fibers  10 , the ends of which are fixed onto the substrate  111 . The second fiber array  120  includes the substrate  121  having V-shaped grooves and four optical fibers  20 , the ends of which are fixed onto the substrate  121 . The transparent member  160  for protecting the end surface is attached to the output end  11   a  of each of the optical fibers  10  and the output end  21   a  of each of the optical fibers  20  by optical contact. 
     The transparent member  160  is a rectangular plate made of quartz, and a surface  161   b  of the transparent member  160  is coated with an anti-reflection coating  162 . The surface  161   b  is opposite to a surface  161   a  of the transparent member  160 , the surface  161   a  being in contact with the output ends of the optical fibers. 
     As described above, the transparent member  160  for protecting the end surfaces is attached to the output end of each of the optical fibers by optical contact. Therefore, the light beam that has been output from the output end of each of the optical fibers is transmitted through the transparent member  160 , and output to the outside of the transparent member  160  from the surface  161   b  of the transparent member  160 . Since the output end of each of the optical fibers is covered with the transparent member, it is possible to prevent the output ends of the optical fibers from being damaged by burning due to adhesion of dust or the like thereto. 
     Further, when the light beam passes through the transparent member  160 , the diameter of the light beam increases. Therefore, the density of the light beam at the output position from the optical fiber structure  150  to air, which is the surface  161   b  in this embodiment, is lower than the density of the light beam output from the optical fiber structure in which the transparent member  160  is not provided. Therefore, the transparent member  160  can prevent burning at the surface  161   b  of the transparent member  160 . Further, the transparent member  160  can prevent the anti-reflection coating  162  that has been applied to the surface  161   b  of the transparent member  160  from being damaged. Further, the transparent member  160  can reduce light that returns from the output surface of the light beam. Therefore, it is possible to prevent the lasers connected to the input ends of the optical fibers from being damaged. 
     Further, the optical fiber structure  140 , illustrated in  FIG. 6A , may be modified in such a manner that a transparent member  160  is provided at the output ends of the optical fibers, which output light beams. 
     Next, an optical fiber structure according to a third embodiment of the present invention will be described.  FIG. 7  is a schematic diagram illustrating the structure of an optical fiber structure  200 . In  FIG. 7 , the same reference numerals will be assigned to parts and elements corresponding to those of the optical fiber structure  100 , illustrated in  FIG. 1 , and the explanation thereof will be omitted. 
     As illustrated in  FIG. 7 , the optical fiber structure  200  includes a first fiber array  210 , a second fiber array  220  and a pressure plate  230 . The first fiber array  210  includes a substrate  211  having four V-shaped grooves  212 , two optical fibers  10  and two optical fibers  20 , the ends of the two optical fibers  10  and the two optical fibers  20  being fixed onto the substrate  211  having the V-shaped grooves. The second fiber array  220  includes a substrate  221  having four V-shaped grooves  222 , two optical fibers  10  and two optical fibers  20 , the ends of the two optical fibers  10  and the two optical fibers  20  being fixed onto the substrate  221 . The first fiber array  210  and the second fiber array  220  are placed one on the other, with the pressure plate  230  therebetween, in such a manner that the optical fibers  10  and the optical fibers  20  face each other, and fixed. In the first fiber array  210 , the two optical fibers  10  are arranged from the left side of the first fiber array  210  illustrated in  FIG. 7 . Further, the two optical fibers  20  are arranged on the right side of the optical fibers  10 . Meanwhile, in the second fiber array  220 , the two optical fibers  20  are arranged from the left side of the second fiber array  220  illustrated in  FIG. 7 . Further, the two optical fibers  10  are arranged on the right side of the optical fibers  20 . Specifically, the arrangement of the optical fibers in the first fiber array  210  and that of the optical fibers in the second fiber array  220  are opposite to each other (in other words, in reveres order). 
     In the second fiber array  220 , two optical fibers  10  and two optical fibers  20  are arranged as illustrated in  FIG. 8 . The two optical fibers  10  and the two optical fibers  20  are fixed into V-shaped grooves  222  of the substrate  221  having the V-shaped grooves, respectively, using an ultraviolet setting resin, a thermosetting resin or the like. The two optical fibers  10  and the two optical fibers  20  are fixed in such a manner that the output ends of the two optical fibers  10  and the two optical fibers  20  are linearly arranged at the ends of the V-shaped grooves  222  of the substrate  221  having the V-shaped grooves. 
     Further,  FIG. 8  may be viewed as a diagram in which the first fiber array  210 , illustrated in  FIG. 7 , is placed upside down. In  FIG. 8 , two optical fibers  10  and two optical fibers  20  are fixed into the V-shaped grooves  212  of the substrate  211  having the V-shaped grooves, respectively, using an ultraviolet setting resin, a thermosetting resin or the like. The two optical fibers  10  and the two optical fibers  20  are fixed in such a manner that the output ends of the two optical fibers  10  and the two optical fibers  20  are linearly arranged at the ends of the V-shaped grooves  212  of the substrate  211  having the V-shaped grooves. Specifically, the structure of the first fiber array  210  and that of the second fiber array  220  are the same. 
     The optical fiber structure  200  may be used, for example, as an optical head for processing plates for printing with a laser beam in a manner similar to the optical fiber structure  100 . The optical fiber structure  200  has advantageous effects similar to those of the optical fiber structure  100 . Further, the optical fiber structure  200  can be obtained by producing two fiber arrays that have the same structure and by placing the two fiber arrays one on the other. Therefore, the optical fiber structure  200  can be produced easily and at low cost. Further, the outer diameter of the optical fiber  10  and that of the optical fiber  20  are different from each other. Therefore, the heights of the optical fibers  10  and the optical fibers  20  in the first fiber array  210 , the heights at positions opposite to the substrate  211  having the V-shaped grooves, and the heights of the optical fibers  10  and the optical fibers  20  in the second fiber array  220 , the heights at positions opposite to the substrate  221  having the V-shaped grooves, are opposite to each other. In other words, the heights of the optical fibers facing each other are opposite to each other (when the height of an optical fiber is high, the optical fiber facing the optical fiber is low, and vice versa). Therefore, when the first fiber array  210  and the second fiber array  220  are placed one on the other, positioning can be performed easily. 
     An optical fiber structure  240 , which is a modified example of the present embodiment, is illustrated in  FIG. 9A . When it is not necessary that the optical fibers  10  and the optical fibers  20  are aligned in a direction perpendicular to the arrangement direction of each of the optical fiber arrays, the optical fibers  10  and the optical fibers  20  may be placed as arranged in the optical fiber structure  240 . In the optical fiber structure  240 , the optical fibers  10  and the optical fibers  20  are arranged as closely as possible, thereby reducing the size of the optical fiber structure. 
     Next, an optical fiber structure  250  according to a fourth embodiment of the present invention will be described with reference to  FIG. 9B .  FIG. 9B  is a schematic diagram illustrating the structure of the optical fiber structure  250 . In the optical fiber structure  250 , the output end of the optical fiber structure  200 , illustrated in  FIG. 7 , is placed in optical contact with the transparent member  160  for protecting the end, illustrated in  FIG. 6B . The action and the advantageous effect of the transparent member  160  are substantially similar to those of the transparent member  160  in the optical fiber structure  150  illustrated in  FIG. 6B . Therefore, detailed description on the transparent member  160  will be omitted. 
     Next, an optical fiber structure according to a fifth embodiment of the present invention will be described.  FIG. 10  is a schematic diagram illustrating the structure of an optical fiber structure  300 . In  FIG. 10 , the same reference numerals as those assigned to the corresponding elements in the optical fiber structure  100 , illustrated in  FIG. 1 , will be assigned to the parts and elements of the optical fiber structure  300 , and detailed descriptions thereof will be omitted. 
     As illustrated in  FIG. 10 , the optical fiber structure  300  includes a first fiber array  310 , a second fiber array  320  and a pressure plate  330 . The first fiber array  310  includes a substrate  311  having four V-shaped grooves  312 , two optical fibers  10  and two optical fibers  20 . The two optical fibers  10  and the two optical fibers  20  are alternately arranged, and the output ends thereof are fixed to the substrate  311  having the V-shaped grooves. The second fiber array  320  includes a substrate  321  having four V-shaped grooves, two optical fibers  10  and two optical fibers  20 . The two optical fibers  10  and the two optical fibers  20  are alternately arranged, and the output ends thereof are fixed onto the substrate  321  having the V-shaped grooves. Further, the first fiber array  310  and the second fiber array  320  are placed one on the other, with the pressure plate  330  therebetween, in such a manner that the optical fibers  10  and the optical fibers  20  face each other, and fixed. In other words, the optical fiber  10  in the first fiber array  310  faces the optical fiber  20  in the second fiber array  320 , and the optical fiber  20  in the first fiber array  310  faces the optical fiber  10  in the second fiber array  320 . In the first fiber array  310 , the order of arrangement of the optical fibers is the optical fiber  10 , the optical fiber  20 , the optical fiber  10 , and the optical fiber  20  from the left side of  FIG. 10 . Meanwhile, in the second fiber array  320 , the order of arrangement of the optical fibers is the optical fiber  20 , the optical fiber  10 , the optical fiber  20 , and the optical fiber  10  from the left side of  FIG. 10 . In other words, the optical fibers in the first fiber array  310  are arranged in reverse order to the order of arrangement of the optical fibers in the second fiber array  320 . 
     As illustrated in  FIG. 11 , in the second fiber array  320 , the two optical fibers  10  and the two optical fibers  20  are fixed in such a manner that the output ends of the two optical fibers  10  and the two optical fibers  20  are linearly arranged at the ends of the V-shaped grooves  322  of the substrate  321  having the V-shaped grooves. The optical fibers are fixed into the V-shaped grooves  322 , respectively, using an ultraviolet setting resin, a thermosetting resin or the like. 
     Further,  FIG. 11  may be viewed as a diagram in which the first fiber array  310 , illustrated in  FIG. 10 , is placed upside down. In  FIG. 11 , the two optical fibers  10  and the two optical fibers  20  are fixed into the V-shaped grooves  312  of the substrate  311  having the V-shaped grooves, respectively, using an ultraviolet setting resin, a thermosetting resin or the like. The two optical fibers  10  and the two optical fibers  20  are fixed in such a manner that the output ends of the two optical fibers  10  and the two optical fibers  20  are linearly arranged at the ends of the V-shaped grooves  312  of the substrate  311  having the V-shaped grooves. Specifically, the structure of the first fiber array  310  and that of the second fiber array  320  are the same. 
     The optical fiber structure  300  may be used, for example, as an optical head for processing plates for printing with a laser beam in a manner similar to the optical fiber structure  100 . The optical fiber structure  300  has advantageous effects similar to those of the optical fiber structure  100 . Further, the optical fiber structure  300  can be obtained by producing two fiber arrays that have the same structure and by placing the two fiber arrays one on the other. Therefore, the optical fiber structure  300  can be produced easily. Further, the outer diameter of the optical fiber  10  and that of the optical fiber  20  are different from each other. Therefore, the projections/depressions of the first fiber array  310 , the projections/depressions positioned opposite to the substrate  311  having the V-shaped grooves, and the projections/depressions of the second fiber array  320 , the projections/depressions positioned opposite to the substrate  321  having the V-shaped grooves, are opposite to each other (a projection faces a depression, and vice versa). Therefore, when the first fiber array  310  and the second fiber array  320  are placed one on the other, positioning can be performed easily. Further, for example, when so-called solid processing is performed, in other words, when the entire area of a certain portion is processed uniformly using a multiplicity of light beams having large diameters, since a contact area between the optical fibers is small, it is possible to prevent the ends of the optical fibers from being damaged by heat. 
     Further, in the optical fiber structure  300 , when it is not necessary that the optical fibers  10  and the optical fibers  20  are aligned in a direction perpendicular to the arrangement direction of each of the optical fiber arrays, the optical fiber structure  300  may be modified in such a manner that the optical fibers  10  and the optical fibers  20  are placed as closely as possible. Further, in the modified example, the transparent member  160  may be attached to the output ends of the light beams. 
     In the above example, the optical fibers are alternately arranged one by one. Alternatively, when a large number of optical fibers should be arranged, the optical fibers may be alternately arranged two by two (in twos), or three by three (in threes). 
     In each of the aforementioned embodiments, four optical fibers are arranged in each of the optical fiber arrays. However, the number of the optical fibers is not limited to four. For example, 16, 32 or 64 optical fibers may be arranged in each of the optical fiber arrays. 
     In each of the aforementioned embodiments, an optical fiber having a taper portion, the core diameter of which decreases along an optical axis, is used as the optical fiber  10 . Alternatively, for example, an ordinary optical fiber may be used as the optical fiber  10  and an optical fiber having a taper portion, the core diameter of which increases along an optical axis, may be used as the optical fiber  20 . Alternatively, an optical fiber having a taper portion, the core diameter of which decreases along an optical axis, may be used as the optical fiber  10  and an optical fiber having a taper portion, the core diameter of which increases along an optical axis, may be used as the optical fiber  20 .