Design and implementation of the automatic phase compensation in optically pumped magnetometer

As an important part of the self-excited optically pumped magnetometer detecting circuit, the stability and accuracy of the phase-shifting network directly affect the accurate measurement of the magnetic field. A phase deviation of 1 degree will cause 1 Hz change of the resonant frequency. In order to meet the continuous measurement of the geomagnetic field, an automatic phase-shifting network based on the all-pass filter has been designed. It can be used to precisely compensate for the phase of the detected signal in a wide range of frequencies from 30 kHz to 350 kHz. The scheme indicates that the phase compensation can be precisely controlled by tracking the frequency of the detected signal and a certain function relationship. Through the actual test and analysis, the phase compensation precision of the automatic phase-shifting network is less than 0.2 °, and the error of the magnetic field measurement is less than 0.06nT. It has been proved the feasibility of the automatic phase-shifting network applied to the self-excited cesium optically pumped magnetometer.