Experimental Evaluation of the Polarization Crosstalk When Soldering a Polarization-Maintaining Fiber Into a V-Grooved Substrate

The influence of stress on the polarization extinction ratio (PER) when solderjet-bumping a bow-tie polarization-maintaining fiber (PMF) to a V-grooved ceramic substrate is experimentally evaluated. Throughout this paper, the linear polarization of the coupling laser beam is kept perpendicular to the V-grooved substrate plane while the fiber is rotated by a high-precision fiber gripper such that one of the fiber's main axes is aligned with the incoming polarization. On-axis alignment is conducted by positioning a small aspheric coupling lens with a high-precision multiaxis actuator. After alignment, the fiber is soldered to the substrate by a lead-free solder alloy. For each fiber sample, the PER is evaluated before and after soldering. Statistically relevant sample sets are evaluated in similar conditions and both fiber axes are considered for coupling. For the sake of comparison, this paper is also carried out while using UV-curing adhesive bonding as a fixing method. Under the experimental conditions, the decrease in PER when using solderjet bumping is evaluated to be about 7% of the initial value, showing that the technique could be suitable for mass-production PMF-based-devices microassembly.