Abstract:
A method to assemble an optical assembly is disclosed. The method includes steps of rough and fine alignment between the sleeve member and the J-sleeve, and the alignment of the J-sleeve with the optical device. The rough alignment slides the sleeve member on the J-sleeve as tracing closed loops concentric to each other by alternating a direction of the slide in clockwise and counter clockwise in respective loops.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a process to manufacture an optical assembly to transmit an optical signal or to receiving an optical signal, in particular, the invention relates to a process to align a sleeve member with an optical device. 
       BACKGROUND ART 
       [0002]    An optical assembly applicable to the optical communication system generally includes, as shown in  FIG. 4 , a sleeve member  2 , an optical device, and a joint sleeve (hereafter denoted as J-sleeve) . The sleeve member guides an optical ferrule attached in a tip end of an external optical fiber to couple the external optical fiber with the optical device. The optical device  3 , which converts signals between an electrical form and an optical form, is inserted into the J-sleeve  4  to couple with the external fiber. The J-sleeve  4  makes the optical device  3  optically coupling with the sleeve member  2 . 
         [0003]    The optical alignment of the optical assembly  1  shown in  FIG. 4  may be carried out by s steps, one of which is the alignment along the optical axis Z and the other is the alignment within the plane perpendicular to the optical axis Z. The former alignment, which is often called as the Z-alignment, is performed by adjusting an insertion depth of the optical device  3  within a bore  4   c  of the J-sleeve  4 . Because the outer diameter of the optical device in the cap  3   a  thereof is slightly smaller than a diameter of the bore  4   c,  the adjustment of the optical device  3  within the bore  4   c  along the optical axis Z may be easily carried out. 
         [0004]    The latter alignment, which is often called as the XY-alignment, may be performed by sliding the sleeve member  2  on the flat end  4   b  of the J-sleeve  4 . Because the stub  2   b  in the center of the sleeve  2   a  and the holder  2   c  that press-fits the stub  2   b  therein and is press-fit within the gap between the cover  2   d  and the sleeve  2   a;  the lateral movement of the sleeve member  2  on the flat end  4   b  of the J-sleeve  4  is equivalent to move the sleeve  2   a  and the stub  2   b  with respect to the longitudinal axis of the optical device. Thus, the XY-alignment between the sleeve  2   a  and the optical device  3  may be performed. 
         [0005]    The XY-alignment described above is often carried out by two procedures, one of which is the rough alignment and the other is fine alignment. The rough alignment moves the sleeve member  2  widely in a region on the flat end  4   b  to estimate a position where a maximum optical coupling efficiency between the sleeve member  2  and the optical device is obtained; then, a fine alignment is performed to slide the sleeve member  2  finely from the position above to find the optimum point at which the optical coupling efficient between two members,  2  and  3 , becomes maximum. Because the Z-alignment shows a larger tolerance compared to the XY-alignment, the Z-alignment is generally performed after the XY-alignment and two members,  2  and  3 , are permanently fixed by, for instance, the YAG laser welding. The optical device  2  is fixed to the J-sleeve  4  by the laser welding or the like. 
         [0006]    The rough alignment between two processes generally takes a dominant tact time. That is, the rough alignment often adopts, what is called, the spiral alignment as shown in  FIG. 5  where a starting point P 0  where a substantial coupling is available is empirically selected first; then the sleeve member  2  is spirally moved in counter clockwise as tracing concentric squares to find the position where a maximum coupling is obtained. 
         [0007]    However, the spiral alignment above described often causes a rotation of the J-sleeve  4  with respect to the optical device  3 . When the optical assembly  1  implements the optical isolator  5 , especially in a case where the optical isolator is assembled in the J-sleeve  4 , the rotation of the J-sleeve  4  during the rough alignment misaligns the optical isolator  5  with the polarization direction of the LD  3   c.  The LD  3   c  has the polarization direction of the light emitted therefrom in parallel to the stacking direction of the semiconductor layers when it has a type of the edge-emitting arrangement. Thus, the un-intentional rotation of the isolator around the optical axis Z may lower the optical coupling efficiency between the optical device  3  and the external optical fiber set in the optical sleeve  2   a.  The present invention is to provide a method to align the J-sleeve  4  with the optical device  3  without inducing the rotation thereof. 
       SUMMARY OF INVENTION 
       [0008]    The invention of the present application relates to a method to manufacture an optical assembly. The optical assembly includes a sleeve member, a J-sleeve, and an optical device. The manufacturing method includes steps of: (1) roughly aligning the sleeve member with the J-sleeve; (2) finely aligning the sleeve member with the J-sleeve; and (3) aligning the J-sleeve with the optical device. A feature of the method is that the rough alignment of the sleeve member with the J-sleeve includes a step to slide the sleeve member on the J-sleeve as tracing closed loops concentric to each other by alternating the direction of the slide in clockwise and counter clockwise in respective closed loops. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    Non-limiting and non-exhaustive embodiments of the present invention will be described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
           [0010]      FIG. 1  is a side view of an optical assembly according to an embodiment of the present invention; 
           [0011]      FIG. 2  shows a process to align the sleeve member supported by the upper chuck with the optical device supported by the lower chuck; 
           [0012]      FIG. 3  shows a trace of the sleeve member in the rough alignment according to an embodiment of the present invention; 
           [0013]      FIG. 4  is a cross section of a conventional optical assembly; and 
           [0014]      FIG. 5  shows a trace of the sleeve member in the rough alignment generally used in a conventional alignment process. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0015]    Details of an optical assembly according to an embodiment of the present invention will be described as referring to  FIG. 1 . The optical assembly of the present embodiment has a feature in a method to align optical axis Z thereof. The optical assembly includes members similar to or same as those shown in  FIG. 4 . 
         [0016]    The optical assembly  1  illustrated in  FIG. 1  includes an optical device  3  that implements an LD  3   c,  which should be referred to  FIG. 4 , a sleeve assembly  2  to receive an external optical connecter, and a joint sleeve  4  (hereafter denoted as J-sleeve). The J-sleeve  4 , as illustrated in  FIG. 4 , includes a bore into which the optical device  3  is set and a flat end  4   b  to which the sleeve member  2  is fixed. Adjusting the insertion of the optical device  3  into the bore  4   c,  the optical alignment along the optical axis Z may be carried out, meanwhile, sliding the sleeve member  2  on the flat end  4   b  of the J-sleeve  4  may carry out the optical alignment between the sleeve member  2  and the optical device  3  in the plane perpendicular to the optical axis Z may be performed. 
         [0017]      FIG. 2  illustrates a process to align optically between the sleeve member  2  and the optical device  3 , specifically,  FIG. 2  is a side view of an alignment apparatus of the optical assembly  1 . The alignment apparatus includes a mount  11  on which the optical devices  3  is set, a lower chuck  12  to hold the optical device  3  on the mount, an upper chuck  14  to hold the sleeve member  2 , where the upper chuck  14  is movable in the plane perpendicular to the optical axis Z, and an external optical connector  14  with an optical fiber  14   a,  where an optical power meter, which is not shown in  FIG. 2 , is coupled with a far end of the optical fiber  14   a.    
         [0018]    The process to assemble the optical assembly  1  will be described. The process first holds the optical device  3  on the mount  11  by the lower chuck  12 , then the J-sleeve  4  covers the optical device  3  such that the tip of the optical device  3  is inserted into the bore  4   c  as rotating the J-sleeve around the optical axis Z to align the direction to the optical isolator  5  with respect to the optical device  3 . Specifically, when the LD  3   c  has a type of, what is called, the edge emitting arrangement, the polarization direction of light emitted from the LID  3   c  is in parallel to the extending direction of the semiconductor layers constituting the laser structure of the LD  3   c,  which is in parallel to the page of  FIG. 4 . Accordingly, the direction of the isolator  5  is necessary to align with the polarization direction of the LD  3   c  by rotating the J-sleeve  4  around the axis of the optical device  3 . 
         [0019]    The process next supports the sleeve member  2  by the upper chuck  13 , where the sleeve member is assembled with the optical connector  14  in advance to the support, and makes the sleeve member  2  close to the J-sleeve  4 . Because the sleeve member  2  in a primary portions thereof and the J-sleeve  4  are made of magnetic material, the J-sleeve  4  may be lifted up by the magnetic force applied to the upper chuck  13  when the upper chuck  13  makes close to the J-sleeve  4 , and the end surface  2   f  of the sleeve member  2  is in contact with the flat end  4   b  of the J-sleeve  4 . Thus, the upper chuck  13  is forced to be close to the J-sleeve  4  to realize such a positional relation between the sleeve member  2  and the J-sleeve. 
         [0020]    Next, the process may rough align between the sleeve member  2  and the J-sleeve  4  in the plane perpendicular to the optical axis Z. Specifically, first the process slides the sleeve member  2  on the flat end  4   b  of the J-sleeve  4  to draw a plurality of ringed traces with a center common to respective ringed traces. In this process, the upper chuck  13  is moved such that respective directions of ringed trace are alternately changed. Then, the process decides the start point of the fine alignment, where the maximum optical coupling between the optical device  3  and the external connecter is obtained. 
         [0021]      FIG. 3  specifically illustrates the process to move the upper chuck  13  described above. The chuck  13  first moves the sleeve member  2  on the J-sleeve  4  in counter clockwise from the start point P 0  on the square trace T 1  with a side length L 1 . Next, the upper chuck  13  moves the sleeve member  2  on another square trace T 2  with a side greater than the former side, namely, L 1 +2A, with the center common to the trace T 1  but the direction thereof in clockwise. Subsequently, the upper chuck  13  repeats the process to move the sleeve member  2  as increasing the side of the square trace but alternately switching the direction until the whole range of the rough alignment is covered. 
         [0022]    The alignment process may carry out the fine alignment in the plane perpendicular to the optical axis Z from the position where the maximum optical coupling between the optical device  3  and the sleeve member  2  is obtained. After the fine alignment, the process may fix the holder  2   c  with the flat end  4   b  of the J-sleeve  4  by, for instance, the YAG laser welding or the resistance welding. Finally, adjusting the insertion depth of the optical device  3  into the bore  4   c  of the J-sleeve  4 , the optical alignment along the optical axis Z may be performed. The optical device  3  may be fixed to the J-sleeve  4  by, for instance, the YAG laser welding and so on. Thus, the optical subassembly  1  may be completed. 
         [0023]    Thus, the alignment process, in particular, the rough alignment between the optical device  3  and the sleeve member  2  in the plane the perpendicular to the optical axis Z, slides the sleeve member  2  on the J-sleeve  4  such that the sleeve member  2  traces counter squares by switching the direction of the trace; accordingly, the process may effectively prevent the J-sleeve  4  from rotating with respect to the optical device  3 . A table below compares the conventional alignment process with that of the present embodiment. Devices under test,  1  to  5 , were obtained by the conventional alignment process where the process slid the sleeve member  2  to trace contour squares in a spiral mode with the constant direction, while, devices,  6  to  10 , were obtained by the process of the present embodiment. In the comparison, the pitch between contour squares was 20 μm and the whole range for the rough alignment had a side of 500 μm. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Comparison of twisted angle 
               
             
          
           
               
                   
                   
                 twisted angle 
                   
               
               
                   
                 DUT 
                 (degree) 
                 Process 
               
               
                   
                   
               
             
          
           
               
                   
                 1 
                 13.60 
                 Conventional 
               
               
                   
                 2 
                 11.03 
               
               
                   
                 3 
                 11.93 
               
               
                   
                 4 
                 13.29 
               
               
                   
                 5 
                 11.87 
               
               
                   
                 6 
                 −1.38 
                 Invented 
               
               
                   
                 7 
                 1.56 
               
               
                   
                 8 
                 −1.25 
               
               
                   
                 9 
                 −0.61 
               
               
                   
                 10 
                 −1.35 
               
               
                   
                   
               
             
          
         
       
     
         [0024]    As the table above clearly indicates, the conventional alignment process causes the twisted angle around 12° for the J-sleeve  4  to the optical device  3 , while, the process according to the embodiment described above shows the twisted angle only less than 2°. The former twisted angle is fatal, or causes an extreme degradation of the optical coupling between the optical device  3  and the sleeve member  2  due to the misdirection between the optical isolator and the polarization direction of the LD  3   c.  The process according to the present invention may effectively prevent the J-sleeve  4  from misdirecting. 
         [0025]    In the foregoing detailed description, the method of the present invention has been described with reference to specific exemplary embodiments thereof. However, it will be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present invention. For instance, the embodiment described above concentrates on the optical device installing the LD  3   c,  but the invention may be applicable to an optical device installing a photodiode. Moreover, the process to slide the sleeve member  2  on the flat end  4   b  of the J-sleeve  4  traces the concentric squares; however, the sleeve member  2  may trace concentric circles or concentric rectangles. Therefore, the present specification and figures are accordingly to be regarded as illustrative rather than restrictive.