Linear-to-circular cross-polarization differential detection for atomic co-magnetometers based on polarization-multiplexed metasurfaces

Atomic co-magnetometers, serving as high-precision magnetic field sensors, find broad applications in autonomous navigation for unmanned systems and fundamental physics. However, their conventional optical detection modules relying on bulky components suffer from limited miniaturization and integration. Metasurfaces offer a promising route toward optical path miniaturization. Nevertheless, most existing metasurface designs focus on homogeneous polarization beam splitting, such as separating linear polarization states, which can introduce additional optical noise and energy loss. To overcome this limitation, we propose a linear-to-circular polarization differential detection scheme utilizing a polarization-multiplexed metasurface. Through phase-encoded amorphous silicon meta-atoms fabricated on fused silica, this device integrates dual functional zones: a polarization-retaining deflector (PRD) and a polarization-converting deflector (PCD), enabling simultaneous beam splitting and independent manipulation of linearly polarized (LP) and circularly polarized (CP) light. At the operational wavelength of 795 nm, the meta-atoms exhibit over 80% transmittance. The PRD and PCD zones achieve deflection angles of +24.1° and -23.8°, respectively, with deviations below 1.5% from theoretical predictions. Experimental characterization demonstrates an optical rotation sensitivity of 5.9184 × 10^-6 rad at 70 kHz, while the micron-scale thickness significantly enhances integration capability. This work establishes a novel paradigm for chip-scale atomic co-magnetometers and advances the convergence of nanophotonics with atomic sensing technologies.