Abstract:
The present invention relates to a method and apparatus for measuring the position of a ferrule of a laser module. The apparatus comprises an XYZ stage, a base, a receiving portion and a laser displacement meter (LDM). The XYZ stage is used for moving in three-dimensional directions. The base has a first slot by which the base is detachably connected to the XYZ stage. The receiving portion is fixed to the base and has a second slot. The laser displacement meter is used for measuring the distance between the ferrule and the laser displacement meter. The laser displacement meter is detachably connected to the receiving portion in the second slot. Whereby, the quantitative measurement and correction to the effect of the postweld-shift (PWS) on the fiber alignment shifts in laser-welded laser module packaging is achieved. Therefore, the reliable laser modules with high yield and high performance used in low-cost lightwave transmission systems may be developed and fabricated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a method and apparatus for measuring the position of a ferrule of a laser module, particularly to a method and apparatus for measuring the position of a ferrule of a laser module for compensating the shift of the ferrule after the laser module is welded.  
         [0003]     2. Description of the Related Art  
         [0004]     There are many types of laser module packaging, and the co-axial type and the box type are broadly used. The greatest challenge for the co-axial type of laser module packaging is to use a reliable and accurate jointing process. During the welding process, the rapid solidification of the welded region and the associated material shrinkage often cause a postweld shift (PWS) between the welded components. For a typical single-mode-fiber application, if the PWS-induced fiber alignment shift by the laser-welding-jointing process is even only a few micrometers, up to 50% or greater loss in the couple power may occur. During the solidification, shrinkage causes many different levels of shift, and there are many factors affecting the shift, such as the input welding energy, the joint geometric design and material&#39;s conditions. Since the solidification- shrinkage-induced PWS is a nonlinear behavior, it is a difficult task to analyze the PWS.  
         [0005]     For the present laser module packaging, there is still not a quantitative measurement or a compensation principle for welded shift. In a conventional skill, it is measured by using hands to estimate the direction and level of the PWS. However, the sensitivity of the PWS for a coupled efficiency is smaller than 1 μm, and thus the measurement by using hands is not a quantitative measurement and is not accurately estimated, so that the additional welding process is inefficient, and the efficiency and yield of laser module packaging cannot be effectively improved.  
         [0006]     Consequently, there is an existing need for a method and apparatus for measuring the position of a ferrule of a laser module.  
       SUMMARY OF THE INVENTION  
       [0007]     One objective of the present invention is to provide a method and apparatus for measuring the position of a ferrule of a laser module. By utilizing the method and apparatus of the invention, the quantitative measurement and correction to the effect of the postweld-shift (PWS) on the fiber alignment shifts in laser-welded laser module packaging is achieved. Therefore, the reliable laser modules with high yield and high performance used in low-cost lightwave transmission systems may be developed and fabricated.  
         [0008]     Another objective of the present invention is to provide a measuring apparatus for measuring the position of a ferrule of a laser module. The measuring apparatus comprises an XYZ stage, a base, a receiving portion and a laser displacement meter (LDM). The base has a first slot, and the base is connected to the XYZ stage by a first fixing device and the first slot. The first slot extends along a vertical direction. Whereby, the base can be fixed in different positions of the XYZ stage. The receiving portion is connected to the base and has a second slot. The laser displacement meter is used for measuring the distance between the ferrule and the laser displacement meter. The laser displacement meter is connected to the receiving portion by a second fixing device and the second slot. The second slot extends along a horizontal direction. Whereby, the laser displacement meter can be fixed in different positions of the receiving portion.  
         [0009]     Still another objective of the present invention is to provide a method for measuring the position of a ferrule of a laser module. The method of the invention comprises the steps of: 
        (a) providing a laser module having a ferrule;     (b) measuring the distance between the ferrule and the laser displacement meter by utilizing a laser displacement meter;     (c) rotating the ferrule by a plurality of times and measuring the distance between the ferrule and the laser displacement meter of different angles respectively;     (d) changing the corresponding height between the ferrule and the laser displacement meter;     (e) measuring the distance between the ferrule and the laser displacement meter by utilizing the laser displacement meter;     (f) rotating the ferrule by a plurality of times and measuring the distance between the ferrule and the laser displacement meter of different angles respectively; and     (g) obtaining the position of the center of the ferrule according to the above measurements.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  shows a measuring apparatus for measuring the position of a ferrule of a laser module according to the present invention;  
         [0018]      FIG. 2  shows a flowchart of the process of a method for measuring the position of a ferrule of a laser module according to the present invention;  
         [0019]      FIG. 3  shows a ferrule of the present invention;  
         [0020]      FIG. 4  shows the ferrule in three-dimensional coordinates of the present invention;  
         [0021]      FIG. 5  shows a flowchart of the process of compensating the shift of the ferrule after the laser module is welded according to the present invention; and  
         [0022]      FIG. 6  shows the ferrule after welding of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Referring to  FIG. 1 , it shows a measuring apparatus for measuring the position of a ferrule of a laser module according to the present invention. The measuring apparatus  1  of the present invention comprises an XYZ stage  11 , a base  12 , a receiving portion  13 , two sidewalls  14  and a laser displacement meter (LDM)  15 . The base  12  is connected to the XYZ stage  11 , and the base  12  can move in three-dimensional directions (x-direction, y-direction and z-direction) on the XYZ stage  11 .  
         [0024]     The base  12  has a first slot  121 , and the base  12  is detachably connected to the XYZ stage  11  by a first fixing device (for example a screw) (not shown in the  FIG. 1 ) and the first slot  121 . The first slot  121  extends along the vertical direction (i.e. z-direction), and the length of the first slot  121  is about 0.1 cm to 10 cm. Whereby, the base  12  can be fixed in different positions of the XYZ stage  11 , i.e., the base  12  can be adjusted to a predetermined position after the first fixing device is loosened, and then the base  12  is fixed on the XYZ stage  11  by using the first fixing device through the first slot  121 . Since the XYZ stage  11  can just move by a limited shift, by utilizing the first slot  121  of the base  12 , the shift of the laser displacement meter  15  in the vertical direction increases. In the embodiment, the base  12  is plate-shaped and extends along the vertical direction.  
         [0025]     The laser displacement meter  15  is used for measuring the distance between the ferrule and the laser displacement meter  15 . The laser displacement meter  15  is a conventional structure. In the embodiment, the laser displacement meter  15  is product of KEYENCE Company, and its type number is LC2430. The advantage of the laser displacement meter  15  is of a resolution of 20 nm and of immediate measurement.  
         [0026]     The receiving portion  13  is connected to the base  12  and is used to carry the laser displacement meter  15 . The receiving portion  13  has a second slot  131 . The second slot  131  extends along the y-direction, and the length of the second slot  131  is about 0.1 cm to 10 cm. In the embodiment, the receiving portion  13  is plate-shaped and extends along the horizontal direction (y-direction), and the receiving portion  13  is perpendicular to the base  12 . The laser displacement meter  15  is detachably connected to the receiving portion  13  by a second fixing device (for example a screw  132 ) through the second slot  131 . Whereby, the laser displacement meter  15  can be fixed in different positions of the receiving portion  13 , i.e., the laser displacement meter  15  can be adjusted to a designated position after the second fixing device  132  is loosened, and then the laser displacement meter  15  is fixed on the receiving portion  13  by using the second fixing device  132  through the second slot  131 . Since the XYZ stage  11  can only move by a limited shift, by utilizing the second slot  131  of the receiving portion  13 , the shift of the laser displacement meter  15  in the horizontal direction (y-direction) increases.  
         [0027]     The sidewalls  14  are located at two sides of the receiving portion  13  respectively and extend upwards. Each sidewall  14  has a third slot  141 , and the sidewalls  14  extend along the y-direction by about 0.1 cm to 10 cm. In the embodiment, the sidewalls  14  are plate-shaped and are perpendicular to the receiving portion  13 . A third fixing device (for example a screw  142  of which the length is longer than the distance between the third slots  141  and a nut  143 ) (not shown in  FIG. 1 ) is used for enhancing the connection between the third slots  141  to prevent the laser displacement meter  15  from rotating. The width of the laser displacement meter  15  is equal to the distance between the sidewalls  14  so that the sidewalls  14  can hold the laser displacement meter  15  securely. The laser displacement meter  15  contacts with the screw  142  and is fixed by the screw  142 .  
         [0028]     Referring to  FIG. 2 , it shows a flowchart of the process of a method for measuring the position of a ferrule of a laser module according to the present invention. The operation method and measuring method of the measuring device  1  are described as follows. Referring to  FIG. 1  and  FIG. 2 , firstly, in step S 201 , a laser module  2  is provided. The laser module  2  comprises a ferrule  21 , a fiber  22  and a housing  23 . The ferrule  21  carries the fiber  22 , and the ferrule  21  is disposed on the housing  23 . The housing  23  is then disposed at a clip  31  of a welding machine  3 .  
         [0029]     Referring to  FIG. 3 , it shows the ferrule of the present invention. The principle of the present invention is described as follows. In the present invention, the position of the ferrule  21  is represented by the position vector  C 1 C 2   , wherein C 1  and C 2  are the centers of the high position Z 1  and the low position Z 2  respectively. Circles S 1  and S 2  are corresponding to Z 1  and Z 2  respectively. The circles S 1  and S 2  are obtained by rotating the welding machine  3  with an angle of 30 degrees, then by quantitatively measuring the distance between the laser displacement meter  15  and the ferrule  21 , and finally by matching with curves.  
         [0030]     Referring to  FIG. 4 , it shows the ferrule in three-dimensional coordinates of the present invention. Actually, it is impossible for the origin of the position vector  C 1 C 2    to be the same as that of the origin of the coordinates O 0 . As shown in  FIG. 4 , the origin of the position vector  C 1 C 2    moves from O 0  to O 1  on the X-Y plane. The shift of the origin is represented by the angle α between the horizontal axis r of the polar coordinates and the horizontal axis X of the coordinates. In addition, the ferrule  21  circuits round the Z′-axis with a rotating angle θ and circuits round the Y′-axis with an angle of inclination ψ. Therefore, the position vector  C 1 C 2    of the ferrule  21  can be described as a function of the above four parameters (r, α, θ and ψ), and the shift of the ferrule  21  after welding can be calculated by the position vectors before and after welding.  
         [0031]     Referring to  FIG. 1  and  FIG. 2  again, according to the above principle, after the housing  23  is mounted on the clip  31 , the laser displacement meter  15  is roughly adjusted to a suitable position by utilizing the first slot  121  and the first fixing device to cooperate with adjusting the vertical height of the base  12 . The detecting light spot of the laser displacement meter  15  focuses on 1500 μm high above the bottom of the ferrule  21 , and the position is defined as the low position Z 1 . Referring to step S 202 , the distance between the ferrule  21  and the laser displacement meter  15  is measured, and at the same time, the XYZ stage  11  must be finely tuned to make the distance between the laser displacement meter  15  and the ferrule  21  closest, and the distance is recorded.  
         [0032]     Referring to step S 203 , the clip  31  of the welding machine  3  is used to rotate the ferrule  21 , and the distance between the ferrule  21  and the laser displacement meter  15  of different angles are measured respectively and are recorded. The distances and the angles corresponding to the distances can be used to calculate the center C, of the ferrule  21  at the low position Z 1 . In the embodiment, the closest distance between the ferrule  21  and the laser displacement meter  15  is measured every 30 degrees.  
         [0033]     Referring to step S 204 , the corresponding height between the ferrule  21  and the laser displacement meter  15  is changed, and this can be achieved by vertically moving the ferrule  21 , the laser displacement meter  15  or both of the ferrule  21  and the laser displacement meter  15 . In the embodiment, the laser displacement meter  15  is moved upwards to make the detecting light spot of the laser displacement meter  15  focus on 3000 μm high above the bottom of the ferrule  21 , and the position is defined as the high position Z 2 . Referring to step S 205 , the distance between the ferrule  21  and the laser displacement meter  15  is measured, and at the same time, the XYZ stage  11  must be finely tuned to make the distance between the laser displacement meter  15  and the ferrule  21  closest, and the distance is recorded.  
         [0034]     Referring to step S 206 , the clip  31  of the welding machine  3  is used to rotate the ferrule  21 , and the closest distance between the ferrule  21  and the laser displacement meter  15  of different angles are measured respectively and are recorded. The distances and the angles corresponding to the distances can calculate the center C 2  of the ferrule  21  at the high position Z 2 . In the embodiment, the closest distance between the ferrule  21  and the laser displacement meter  15  is measured every 30 degrees.  
         [0035]     Finally, referring to step S 207 , by utilizing the above measurements, the four parameters (r, α, θ and ψ) for describing the center of the ferrule  21  can be calculated. Since the center of the fiber  22  is the same as the center of the ferrule  21 , the center of the fiber  22  is calculated.  
         [0036]     Referring to  FIG. 5 , it shows a flowchart of the process of compensating the shift of the ferrule after the laser module is welded according to the present invention. The steps S 301  to S 307  of the compensating method are the above steps S 201  to  207 , and the compensation method is used to calculate the center of the ferrule  21  before welding. The step S 308  shows the welding steps. The bottom surface of the ferrule is welded on the top surface of the housing by a plurality of welding spots  40  by utilizing the laser beam providing by the laser welding machine  3 , as shown in  FIG. 6 . Generally, the number of the welding spots  40  is three.  
         [0037]     The step S 309  repeats steps S 302  to S 306  to calculate the center of the ferrule  21  after welding. Referring to step S 310 , the level and direction of the shift of the center of the ferrule  21  is calculated by comparing the center of the ferrule before welding in step S 307  and the center of the ferrule after welding in step S 309 .  
         [0038]     Finally, referring to step S 311 , an additional welding spot is welded for compensating the shift according to the level and direction of the shift. In the embodiment, the additional welding spot is welded in the direction against the lateral of the ferrule  21 , so that the ferrule  21  has a after-welding shift with a direction against the direction of the antecedent after-welding shift. Those shifts in opposite directions countervail each other so that the final shift becomes smaller.  
         [0039]     Referring to list  1 , it shows the measurements of the four parameters (r, α, θ and ψ) by using the compensation method. There are eight modules in the list  1 , wherein the second column is for the before-welding position of the ferrule  21 ; the third column is for the after-welding (not compensated) position of the ferrule  21 ; and the fourth column is for the after-compensating position of the ferrule  21 . The level and direction of the after-welding can be calculated by comparing the second column and the third column. By comparing the second column and the fourth column, the after-compensating position of the ferrule  21  is closer to the original position (the second column) than the uncompensated (the third column) position of the ferrule  21 , i.e., welding an additional welding spot effectively reduces the after-welding shift and reduces the power loss.  
         [0040]     While the embodiments have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention may not be limited to the particular forms as illustrated, and that all modifications that maintain the spirit and scope of the present invention are within the scope as defined in the appended claims.  
                                                                                                                                                             List 1: Measurements of the four parameters (r, α, θ and ψ) before       welding, after welding and after compensating            Module   Before welding (μW)   After welding (μW)   After compensating (μW)            number   r(μm)   α(°)   ψ(°)   θ(°)   r(μm)   α(°)   ψ(°)   θ(°)   r(μm)   α(°)   ψ(°)   θ(°)                    1   2.93   81.78   0.12   −34.11   3.82   59.67   −0.84   −29.91   3.37   66.73   −0.54   34.25       2   2.96   13.01   0.23   3.64   4.20   −7.18   0.10   −1.20   3.58   −15.22   0.13   5.17       3   1.90   −55.66   0.01   19.21   2.12   −74.30   0.08   30.16   2.01   −64.93   0.02   24.73       4   3.28   209.35   0.06   7.23   3.38   192.16   0.02   2.79   3.33   181.77   0.09   −1.36       5   2.15   36.42   0.07   193.56   2.23   13.46   0.04   188.17   2.19   21.83   −0.01   176.94       6   2.09   355.94   −0.14   17.54   2.51   345.53   −0.02   15.22   2.30   337.29   0.06   20.64       7   1.54   310.72   0.07   −56.32   1.98   288.23   −0.17   −69.13   1.76   274.15   0.11   74.36       8   3.55   77.69   −0.13   −6.47   5.08   50.50   −0.06   −3.57   4.31   59.23   0.16   −7.82                  
 
         [0041]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
               
               
                 List 2: Power before welding, after welding and after compensating 
               
             
          
           
               
                   
                 Coupled 
                 Coupled 
                   
               
               
                 Module 
                 power before 
                 power after 
                 Coupled power after 
               
               
                 number 
                 welding (μW) 
                 welding (μW) 
                 compensating (μW) 
               
               
                   
               
             
          
           
               
                 1 
                 524 
                 416 
                 467 
               
               
                 2 
                 741 
                 506 
                 597 
               
               
                 3 
                 892 
                 759 
                 798 
               
               
                 4 
                 912 
                 864 
                 880 
               
               
                 5 
                 934 
                 856 
                 875 
               
               
                 6 
                 1026 
                 730 
                 802 
               
               
                 7 
                 1103 
                 796 
                 897 
               
               
                 8 
                 1198 
                 812 
                 1002