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 μm 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