An Integrated High-Sensitivity VCSEL-Based Spin-Exchange Relaxation-Free Magnetometer With Optical Rotation Detection

In the integrated design of spin-exchange relaxation-free (SERF) magnetometers, vertical cavity surface emitting laser (VCSEL) is a promising candidate as a light source. However, VCSEL often has high frequency and amplitude noise, thereby hindering the development of high-sensitivity SERF magnetometers. In the previous VCSEL-based SERF magnetometer with optical absorption detection, a laser control loop in magnetometer electronic system is used to address this issue, but it is a challenging task to design the loop due to the strong resonance absorption. In this paper, we propose a different approach by using optical rotation detection instead of the absorption detection to develop an integrated high-sensitivity VCSEL-based SERF magnetometer. It can be implemented easily, just by switching the circularly polarized light to the elliptically polarized light in magnetometer optical system. The elliptically polarized light used in here is not only to implement a single-beam configuration as in the previous fiber-coupled SERF magnetometer with a stable distributed feedback laser, but more importantly to accomplish the optical rotation detection and hence to strongly suppress the VCSEL noise. Thus the challenging electronic control problem can be avoided, and meanwhile a simplified optical arrangement is maintained. The difficulty of the integration of VCSEL-based SERF magnetometer can then be significantly reduced. Eventually, an integrated VCSEL-based SERF magnetometer is implemented and achieves a sensitivity of approximately 35 fT/Hz ^1/2 . Using the integrated magnetometer, magnetocardiography signals are recorded.