Chip-scale optically pumped magnetometry enabled by metasurface polarization beam splitter with high transmission efficiency and extinction ratio

Abstract

Chip-scale optically pumped magnetometers (OPMs) hold great potential for high-resolution biomagnetic imaging, but their further miniaturization is constrained by the bulky macroscopic optical components conventionally used for polarization detection. However, existing nanophotonic devices designed to replace these bulk optics often exhibit degraded deflection efficiency and inadequate extinction ratios due to inherent cross-polarization coupling and phase discretization errors. In this study, an ultra-compact, inverse-designed dielectric metasurface polarization beam splitter operating at the Rb D1 line (795 nm) is proposed to enable highly integrated chip-scale OPMs. The metasurface design is driven by a multi-objective Bayesian optimization (MOBO) algorithm rather than conventional phase-mapping approaches. Through direct exploration of the geometric parameter space of amorphous silicon nanopillars, the optical performance is optimized while maintaining a maximum aspect ratio of 5.04 for practical CMOS-compatible nanofabrication. The results demonstrate that the optimized metasurface efficiently decouples orthogonally polarized components into spatially distinct ±30° diffraction channels. Specifically, the device achieves polarization deflection efficiencies of 83.39% and 82.61% for x- and y-polarized light, respectively. Moreover, it yields high polarization extinction ratios of 24.75 dB and 17.52 dB, satisfying the common-mode noise suppression requirements of OPMs. Finally, this metasurface-integrated approach establishes a technological foundation for constructing integrated vapor cells interfaced with planar optics, advancing the development of miniaturized quantum sensors.