Bandwidth Extension Enabled by Modulated VCSEL Pumping for Quantum Sensing Application

Emerging quantum sensing devices, namely, atomic magnetometers, have become promising candidate for future biomagnetism imaging. However, the limitation of detection bandwidth is a major drawback for devices of this kind. Conventional approaches, including transverse magnetic field modulation and close-loop control, have seen challenging tradeoffs between size, resolution, and bandwidths. In this study, a wide bandwidth zero-field magnetometer with a miniaturized light source has been developed for alternating current (ac) magnetic field detection. A dual-beam spin-exchange relaxation-free (SERF) magnetometer using a 4 × 4 × 4 mm³ alkali metal vapor cell achieves a bandwidth of 188 Hz. This represents a threefold increase in bandwidth compared with nonmodulated mode. The sensitivity under modulated mode demonstrated a sensitivity of 55 fT/Hz ^1/2 within the frequency range of 10–188 Hz. Our results also demonstrated that the sensitivity is constrained by relaxation induced by the modulation of pumping source, so possible tradeoffs can be made based on various applications. The proposed method provides novel approach for bandwidth extension of atomic magnetometers which further pave the way for future applications including magnetoencephalography (MEG), particularly in reducing magnetic noise crosstalk and enhancing spatial resolution.