All-Optical Faraday-Rotation-Modulated SERF Magnetometer With Enhanced Sensitivity

Miniaturized spin-exchange relaxation-free atomic magnetometers (SERF AMs) employing an all-optical orthogonal pump-probe configuration are widely recognized for their exceptional sensitivity. However, their low-frequency sensitivity is susceptible to degradation due to factors such as electrical noise and fluctuations in optical parameters. Existing solutions modulate the Faraday rotation signal transmitted through the vapor cell, primarily focusing on polarization direction or amplitude modulations. Polarization modulation faces integration challenges while amplitude modulation leads to signal attenuation. In this study, we propose an all-optical Faraday rotation modulation (FRM) scheme for miniaturized SERF AMs. Contrary to conventional methods, our approach all-optically modulates the Faraday rotation process itself by periodically switching the probe light’s frequency rather than the generated Faraday rotation signal. Consequently, low-frequency noise is effectively isolated using lock-in amplifier technology and the response signal can be enhanced. Specifically, we innovatively integrate fiberized optical switches, which are widely used in optical communication, into AMs to compactly implement the FRM mode. Finally, an impressive 85% enhancement compared to traditional methods in low-frequency sensitivity was demonstrated in a 3 × 3 × 3 mm ⁸⁷Rb vapor cell, achieving 7 fT·Hz^-1/2 (averaged at 1–10 Hz) and 3.5 fT·Hz^-1/2 (at 10–100 Hz). Our method offers a solution to enhance both the low-frequency performance and sensitivity of miniaturized SERF AMs, making a significant contribution to biomagnetism research applications.