Laser welding process: Characteristics and inite element method simulations

Expertise of packaging for optoelectronic components requires the solution of optical, mechanical and electrical problems in the same way. The purpose of this study is to present three-dimensional simulations using finite element method (FEM) of thermomechanical stresses and strains in transmitter Laser modules induced by Nd:YAG crystal Laser welds on main sub-assembly Laser submount. Non-linear FEM computations, taking into account of experimental σ(ε) measured curves, show that Laser welding process can induce high level of strains around the Laser welding zone, bearing the Laser diode, responsible of an optical axis shift and a gradual drop of the optical power in relation with relaxation of accumulated stresses in the sub-assembly (Sherry and al., 1996). Typical stresses are close to 160 MPa with drift about 5 MPa with the dispersion of energy level of laser Nd : YAG beam. The introduction of both material and process dispersion in order to evaluate their impact on product life time distribution has been taking into account. Thermal cycles (-40°C/+85°C VRT) are used to estimate the robustness of the technology assembly. Previous paper demonstrated that Laser submount near laser welding zones is the most sensitive part of optical system (Deshayes and al., 2003).The gradual changes of stresses distribution from the laser welding process and after thermal cycles are estimate using FEM. Experimental analyses were also conducted to correlate simulation results and monitor the output optical power of Laser modules after 500 thermal cycles. The development of high bandwidth single mode fibre optics communication technologies coupled with the availability of transmitter components for wavelength multiplexing has created a revolution in the transmission technology during the last fifteen years. These performances can be reached by packaging interface and control circuits with the optical chips leading to the concept of high reliable technically-advanced Laser modules. Reduced cost, low consumption, hermetical and highly efficient optical coupling between the Laser diode and the single-mode fibre associated to a mechanical stability are some of the key issues. Moreover, packaging of such systems requires the resolution of optical, thermomechanical and electrical problems. These problems are often highly interactive and the stability of optoelectronic devices is still an essential factor to ensure high bandwidth data transmission, acceptable bit-error rate and develop reliable solutions. In actual telecommunication applications, photonic systems involve a non direct mechanical alignment between the laser diode and the optical fibre 7