Metasurface enabled on-chip double-beam scheme for SERF atomic magnetometer

Double-beam atomic magnetometer (AM) working in spin-exchange relaxation-free (SERF) regime is drawing growing attention due to high sensitivity (femtotesla-level) and non-intrusion characteristics. Nowadays, chip integration of AMs in pursuit of dramatical reduction in volume has become a major trend as it is especially favorable for future high-spatial-resolution biomagnetism imaging. While micro-fabricated vapor cell with only two transparent windows (due to planar nano fabrication processes) has become the major obstacle to achieve double-beam scheme on chip. In this study, an ultra-compact on-chip double-beam scheme based on emerging metasurface is proposed for SERF atomic magnetometer application. With in-surface incident both pump light and probe light, this planar device enables optical-path manipulation of linearly-polarized probe beam to precise intersect with pump beam. Our method supports angle manipulation of probe light up to 45 degrees with efficiencies reaching 70%. The device is designed with silicon nitride with thickness of 0.6 um, which can be directly fabricated on the transparent window of vapor cell through basic CMOS compatible processes. In addition, there are more advantages of this method including dramatic volume reduction and potential low-cost mass fabrication, which is promising for future applications including high-resolution biomagnetism imaging and portable atomic devices.