Impact on Polarization Extinction Ratio by Stresses in a Polarization Maintaining Fiber Soldered Into a Ferrule

The thermally induced stresses in an optical fiber soldered into a ferrule can affect the bi-refringence of polarization maintaining (PM) fibers, which results in a change to the polarization extinction ratio (PER) of the linear polarized light coupled into the slow axis of PM fibers. Stresses are induced by differences in thermal expansion between the fiber, the solder and the ferrule during the solder solidification process. In this work, the thermally induced stresses in the fiber, the solder, and the ferrule are modeled numerically, and the changes in PER of different fiber-solder-ferrule (FSF) assemblies are studied experimentally. The smallest degradation in PER is observed in FSF assemblies with a Kovar ferrule and glass solder. The results agree with the lowest thermally induced stresses predicted by the three-dimensional finite element analysis (3-D FEA). This demonstrated that the degradation in PER can be decreased by reducing thermally induced stresses through the proper selection of materials for the solder and ferrule for polarization sensitive applications, such as semiconductor pump lasers.