Novel automatic angular tracking method for fiber-optic alignment in butterfly laser module packaging

Butterfly packaging technology with a fiber pigtail is widely used in packaging optical modules. Fiber-optic alignment method is used to assure the receiving fiber rapidly capture the maximum optical power from the laser diode. Typically, there are six degrees of freedom that should be aligned synchronously: three linear axes (X, Y, Z) and three angular axes (pitch, yaw and roll). Currently, most fiber alignment algorithms are only suitable for linear axes, and for angular alignment, manual coupling is still widely used in product line. In recent years, engineers have tried to apply some automatic algorithms such as Hill-climbing algorithm to realize angular alignment, but since the pivot point is not always the end point of the fiber tip, an angular movement will cause an extra offset in linear axis. Consequently, the whole alignment process will cost much more time. In this paper, a novel automatic angular tracking method based on machine vision is presented. Two charge-coupled device (CCD) cameras are posited to capture the image of the fiber tip from two different directions. Particularly, digital image processing is used to calculate every extra offset in linear direction and correct the fiber tip back to its original position while angular alignment is beginning. Experiment results show that when using other algorithms to correct the extra linear offset, the total alignment time was more than 200 seconds while the automatic tracking method can reduce the total time less than 160 seconds. It is obviously that this automatic tracking method is rapidly improved the efficiency in butterfly packaging.