A novel inspection of fiber post-weld-shift in butterfly laser module packaging

Butterfly packaging technology with a fiber pigtail is widely used in packaging optical modules, and laser welding is used to join components in a butterfly package. During laser welding, the rapid solidification of the welded region and the associated shrinkage of material are expected cause relative movement between prealigned components. Such a post-weld-shift (PWS) might significantly reduce the efficiency of light coupling. The laser hammer technique can be used to realign fiber that shifts during laser welding, and it requires that the fiber shift be measured in three directions. Measuring the shift along the Y axis is difficult because space is limited. In this paper, a reflector placed near the fiber during laser welding was used to determine the shift along the Y-axis. The fiber images obtained using the charge-coupled device (CCD) camera were sometimes deformed, so digital image processing was used to calibrate the deformed images and calculate the fiber shift along three axes. The experimental results indicate that the fiber shift along the Y-axis, when captured using reflector inspection could be measured precisely, and more strongly influenced power coupling loss than shifts in the other two directions. The results are useful in implementing the realignment method after butterfly packaging.