Assembly tolerance requirements for photonics packaging of multi-cell laser power converters

Power over fiber or photonic power is an attractive alternative for powering remote sensors in electromagnetically sensitive environments. Compared to energy harvesting, it can deliver uninterrupted energy in larger amounts (up to few hundreds of milliwatts) to enable more elaborate sensing, computation or even actuation along with continuous communication requirements. From the photonic packaging perspective, the passive fiber chip coupling becomes a challenge, since non-uniform illumination causes changes in the series resistance of individual cells and varying current-voltage characteristics. The paper at hand characterizes multi-cell laser power converters in depth and describes the integral coupling efficiency from 3D spatial mapping of its maximum power point. Besides the scans for the series connected cells, individual contributions of the segments are studied by single cell characterization to discover intra-individual deviations of cell resistance and conversion efficiency, which might affect the optimal power distribution. Moreover, the spatial responsivity distribution of individual cells, depending on different finger electrode and bus bar configurations. The measurements ultimately yield an assembly tolerance analysis for passive photonic packaging of multi-cell laser power converters. The results are well suited to optimize the packaging process as well as predict the expected device performance.