A Polarization-Modulated Laser Frequency-Shifted Feedback System Reducing the Parasitic Noise Intensity by About Three Orders of Magnitude

Abstract

We propose a parasitic noise suppression laser frequency-shifted feedback system based on polarization modulation, which can reduce the parasitic noise intensity by about 30 dB without affecting the signal of interest by applying different polarization modulations to the parasitic noise and the signal to make them converted to system-insensitive and sensitive states, respectively. Therefore, the proposed system can still get correct information which is originally drowned in parasitic noise. Based on the proposed principle, the displacement of the aluminum block 2 m away from the system is successfully recovered. Furthermore, the vibration of an ordinary carton which is 80 m away from the system is demodulated, and the voice signal near the carton is restored according to the vibration information with much better performance than there is no parasitic noise suppression. During the vibration recovery process, the effective response energy as low as 5.5 photons is achieved in each feedback modulation cycle. The successful implementation of the proposed parasitic noise suppression laser frequency-shifted feedback system based on polarization modulation provides a practical anti-interference and sensitive coherent detection method in weak light signals detection.