Polarization Angle Detection Method of High Stability Light Based on Faraday Modulation

Faraday modulation detection method uses magneto-optical rotation effect to modulate the polarization direction of linearly polarized light. Due to the fact that high-frequency modulation can suppress low frequency noise, this method is widely used in ultra-high sensitive inertial measurement or magnetic field. However, the instability of modulation amplitude and the small fluctuation of incident light intensity affect the measurement accuracy of the atomic sensors. In this paper, the first and second harmonic signals are demodulated by lock-in amplifier, and the real-time intensity signal of Faraday modulator is used to deal with the problem. Finally, polarization rotation angle is not affected by modulation amplitude and intensity fluctuation, which can significantly improve the long-term stability and measurement accuracy of the system.