Assembly tolerant design of multi-cell laser power converters for wafer-level photonic packaging

Power over fiber is an attractive alternative for powering remote sensors in electromagnetically sensitive environments. Compared to energy harvesting, it can deliver uninterrupted energy to sufficiently supply elaborate sensing, computation or even actuation along with a continuous communication requirement in distributed sensor networks, as for example in structural health monitoring. For the photonic packaging the passive fiber-chip-coupling is one of the biggest challenges. Due to non-uniform illumination of the individual sub-cells and their technological mismatch in electrical characteristics the assembly tolerances are comparatively tight and therefore the manufacturing costs are respectively high. Hence, an assembly tolerant design of the laser-power-conversion (LPC) chip has to be developed to relax the photonic packaging demands. The paper will aggregate comprehensive real characterization results of existing multi-cell laser power converters and real-life fiber light sources into a dedicated design tool. In order to decrease the tolerance requirements and to adjust the LPC to a specific output power at an optimized efficiency, various LPC designs with different cell numbers and arrangements are numerically optimized and reviewed in comparison. The model initially calculates the overlap integral with an ideal uniform illumination. Then, the model can be enhanced by using real power distributions of typically used multimode fibers. The results presented in this paper are well suited to fabricate both efficient LPCs and validate their passive alignment for wafer-level packaging.