Control of photonic package alignment with asynchronous laser spot welds

The precise alignment of an optical fiber to a laser diode for maximum optical coupling is often accomplished with synchronous laser spot welds in three symmetric locations. To improve precision and reduce operational complexity, the utility of single-beam spot welds made in an asynchronous manner has been investigated. Independent measurements of fiber tip post weld shift have been made using eddy current sensors and CCD camera imaging analysis. For the cylindrical radially aligned Kovar ferrules examined, post weld shift has been found to be independent of both the location and number of prior spot welds. Post weld shift direction has been shown to be relatively consistent and predictable when the fiber containing ferrule is properly restrained. It has been demonstrated that through the application of an axial restraining force on radially aligned ferrules, post weld shift can be reduced to less than 2 mu m. Analytical equations have been presented that predict the magnitude of the measured post weld shift and also serve to guide engineers in optimal design geometries and preferred welding conditions.