Adaptive Optics for Improved Mode - Coupling Efficiencies

Low insertion loss is a critical requirement for some newly emerging applications, such as optical quantum computing. We have demonstrated improved free-space to single-mode fiber coupling via wavefront correction using an adaptive-optic (AO) mirror. By introducing AO correction paired with a three-step optimization algorithm, we have obtained 97.3 ± 0.3% of the Fresnel-reflection-limited mode-coupling efficiency. Our optimization scheme utilizes wavefront sensing for close-loop correction of wavefront aberrations, followed by evolutionary and convex maximization of coupled power. We have further shown a 9-nm RMS wavefront flatness through close-loop correction, limited only by the AO mechanical tolerances, as well as similar flatness utilizing only coupled-power optimization.