Laser weldability analysis of high-speed optical transmission device packaging

A 2.5 Gb/s distributed feedback laser diode (DFB-LD) module was used as a test package to develop laser welding techniques. Various package weld joint geometries, such as lap, fillet, butt, and fillet-lap, were designed and welded to investigate the optimal package configuration that leads to the maximum coupling efficiency and minimum weld shift. Furthermore, the welded joints at a given set of laser parameters were cross-sectioned for metallurgical analysis, such as weld penetration and microcracks, for verification of the weld joint integrity. Through such analysis, some important laser welding parameters, such as depth-of-penetration (DOP), heat-affected zone (HAZ), shear-strength, and solidification formation of the weld pool were analyzed. Also, as the result of investigating 56 laser welded DFB-LD submodules, optimal laser parameters, and the suitable joint geometry for this package could be determined with the average weld shift less than 0.19 dB, which translates to less than 1.0 /spl mu/m in radial displacement. These laser welded packages exhibited an excellent tracking stability during environmental testing, which consequently resulted in obtaining a desirable bit-error rate (BER) during the data transmission performance analysis.