Adaptive Wireless Power Transfer via Resonant Laser Beam Over Large Dynamic Range

Wireless power transfer (WPT) via resonant laser beam from a spatially distributed laser resonator not only benefits the instinct safety but also has important potential of adaptive operation without positioning and aiming when retroreflectors are used to enable the alignment-free operation of the laser. Despite the intense theoretical modeling and experimental efforts with different laser schemes, the adaptive resonant beam WPT across large dynamic range, including both working distance and Field of View (FoV), has never been demonstrated, due to the absence of true alignment-free laser. In this work, we summarized the requirements on the dynamic range and discussed the optimization criteria of dynamic range and laser safety, including the telescope in the laser resonator, the resonator stability, coupled-resonator scheme, and influences of the optical aberrations. The analysis indicated that loss induced by optical aberrations is the main issue limits the dynamic range. In the experiment, alignment-free laser with large dynamic range for WPT application was demonstrated with improved resonator design and optical design to compensate the aberrations. Efficient multiwatt optical output was obtained across a working distance of 1–5 m, a receiver FoV of ±30°, and a transmitter FoV of 4.6°; and over 1.3-W electrical output was obtained via an InGaAs photovoltaic cell, with dc–dc WPT efficiency being 4%. Our work proved the feasibility of large-dynamic-range alignment-free laser with distributed resonator, which paves the way for practical resonant beam charging and communication applications based on it for the Internet of Things devices.