Analysis and suppression of cross-axis modulation coupling errors in optically pumped magnetometers

We propose a method based on sensitive-axis high-frequency modulation (SHFM) method combined with PI closed-loop feedback to suppress the cross-axis modulation coupling error (CMCE) of the optically pumped magnetometer (OPM). Cross-axis modulation is a prevalent approach for three-axis measurement of OPM, but this scheme will introduce CMCE. These errors have the potential to pose undetected hazards in applications of multi-axis magnetic field measurement such as magnetoencephalography (MEG). The SHFM method suppressed the CMCE from 18.50% to 2.10% on average compared to the traditional method. Based on the static situation we also introduce PI closed-loop feedback, which suppressed the CMCE from 22.07% in open-loop mode to 2.10% in closed-loop mode. This approach is both straightforward and efficacious, offering seamless integration into an arrayed OPM-based system. Furthermore, SHFM has the potential to mitigate the challenges associated with MEG localization accuracy and other measurement errors introduced by CMCE, and further unleash the potential of applications of OPM–MEG system.