Research On Signal Circuit Of Self-oscillating Optically-pumped Cesium Magnetic Sensor

The self-oscillating circuit is an important part of the signal extraction of the optically-pumped cesium magnetic sensor.According to its working characteristic,the self-oscillating circuit of the optically-pumped cesium magnetometer is divided into two parts.One part is the modulation of the incident light by the germanium atoms in the absorption chamber,which mainly produces the Larmor frequency signal.The other part is the weak signal detection of the modulated transmitted light,which mainly consists of the amplifier and the phase shifter.The phase shifter's adjustment directly affects the measurement accuracy of the external magnetic field of the optically pumped cesium magnetometers.Based on the research status of self-oscillating circuit at home and abroad,there are still a series of problems,such as the insufficient analysis of the characteristics of optical signals,the narrow working band and the low accuracy of the phase shifter and so on.In this paper,the characteristics of the signal generated in the absorption chamber in the self-excited oscillation circuit have been analyzed in detail and the weak signal detection has been designed.Among them,a wideband automatic phase shifter has been designed to make the different Larmor frequency signal shifted 90°.The main research is as follows:Firstly,according to the working principle of the external magnetic field measurement by the optically-pumped cesium magnetometer and the related knowledge of atomic physics,the cesium atoms in the absorption have been modeled.Analyzing the modulation effect of the incident light under the combined action of the external magnetic field and the radio frequency magnetic field,and the transfer function of the optical signal through the absorption chamber has been further deduced.Therefore,combined with the derived optical signal function expression through the absorption chamber,the phase relationship has been analyzed,and the phase change relationship is obtained.Secondly,based on the analysis of the characteristics of the optical signal passing through the absorbing chamber in the self-oscillating circuit,after clarifying the phase requirements,a reasonable optical signal detection circuit has been designed.It mainly includes the design of four parts,namely the design of the I-V conversion module,the design of the multi-stage amplifier circuit module,the design of the phase shifter circuit,and the design of the system power supply module.Since the optical signal transmitted through the absorption chamber has been advanced by 90°,it requires a strict 90° phase shift in the optical signal detection circuit.When the self-oscillating circuit oscillates at the Larmor frequency corresponding to the external magnetic field,the requirement of the zero degree phase shift is satisfied.A phase deviation of 1 degree will cause 1 Hz change of the resonant frequency,and affecting the measurement of external magnetic field.In this paper,a design scheme for a wideband and high-precision automatic phase shifter has been proposed.It satisfies the goal of stabilizing the phase shift by 90° in the Larmor frequency range of the Earth's corresponding geomagnetic field,and analyzes the feasibility of its precise phase shift in principle.According to the Larmor frequency range of the corresponding magnetic field of the cesium atom,the purpose of the stable phase shift can be 90°,and the feasibility of precise phase shifting has been analyzed in principle.Finally,through the actual production of optical signal detection circuit,the experimental results were measured,and the feasibility of the design scheme was verified.Among them,the key parameters of the automatic phase shifter has been measured and analyzed.The phase shift error is less than 0.1°,and the effect on the resonance frequency is less than 0.1 Hz.According to the magnetic rotation ratio of the cesium atom,the influence on the measurement accuracy of the external magnetic field is less than 0.03 nT.Its working band satisfies the requirement of the phase shifter in the self-oscillating circuit.At the same time,it provides a scheme and technical support for the further development of the optically-pumped cesium magnetometer.