Chip-scale reflective optically pumped SERF magnetometer with distributed Bragg reflector

Emerging miniaturized optically pumped magnetometers (OPMs) are attracting widespread attention due to enormous potential in biomagnetic imaging. However, construction of ultrasensitive reflective OPMs within small footprint remains long-standing challenge. In this study, a novel chip-scale femtotesla-level atomic magnetometer is developed with distributed Bragg reflector (DBR) directly integrated onto a microfabricated vapor cell to realize a self-aligned double-pass pumping configuration. The all-dielectric DBR achieves a peak reflectivity of 95% at 795 nm (the Rb D1 line), while maintaining reflectivity above 93% for incident angles up to ± 10°. We integrated the DBR onto the microfabricated vapor cell and performed proof-of-concept experiments in the SERF regime, which show that the double-pass configuration enhances the average electron polarization by 21.92% compared with the single-pass configuration. The DBR-integrated magnetometer achieves a long-term average sensitivity of 10.59 fT/Hz^1/2 over 800 s and best instantaneous sensitivity of 6.75 fT/Hz^1/2. In comparison, the mirror-based double-pass configuration achieves 10.72 fT/Hz^1/2 and 8.54 fT/Hz^1/2, respectively, while the corresponding values for the single-pass configuration are 12.24 fT/Hz^1/2 and 8.97 fT/Hz^1/2. The slightly improved performance of the DBR-integrated configuration over the mirror-based double-pass configuration is attributed to its higher robustness, which eliminates complex external alignment and reduces parasitic reflections. This work presents a scalable, cost-effective approach to high-performance miniaturized OPMs, which further pave the way for future wearable, high-spatial-resolution biomagnetic imaging applications.