Three-dimensional FEM simulations of thermomechanical stresses in 1.55 μm Laser modules

The purpose of this study is to present three-dimensional simulations using finite element method (FEM) of thermomechanical stresses and strains in 1550 nm Laser modules induced by Nd:YAG crystal Laser welds and thermal cycles on two main sub-assemblies: Laser submount and pigtail. Non-linear FEM computations, taking into account of experimental σ() measured curves, show that Laser welding process can induce high level of strains in columns of the Laser platform, 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. In the case of thermal cycles, stresses can occur on elements sensitive to coefficient of thermal expansion mismatches such as solder joint between the Laser platform and thermoelectric cooler and as fiber glued into the pigtail leading to crack propagation with sudden drop of optical power. The main objective of the paper is to evaluate thermomechanical sensitivity and critical zones of the Laser module in order to improve mechanical stability after Laser weld and reach qualification standards requirements without failures. Experimental analyses were also conducted to correlate simulation results and monitor the output optical power of Laser modules after 500 thermal cycles (−40 °C/+85 °C VRT).