The Generation Of 1550 Nm Vacuum Squeezed State And Quantum Enhanced Measurement Of Low Frequency Phase Signal

In the optical measurement,the measurement accuracy is limited by the quantum noise that caused by vacuum fluctuation,and there is a standard quantum limit,which is the maximum measurement accuracy that can be achieved by precise measurement using classical light sources.This characteristic reflects that the sensitivity of interferometer is limited by the quantum noise when it is used to measure the change of the small physical quantities.The continuous variable squeezed state can be used for quantum precision measurement to break through the standard quantum limit due to its characteristic that the noise fluctuation of the orthogonal component can be lower than that of the shot noise limit.In practical measurement,most of the measurements,such as displacement change and tension sensing,are concentrated in the low frequency range(below k Hz).Therefore,in order to achieve the quantum precision measurement of these physical quantities,it is necessary to prepare the squeezed state with stable output in the low frequency band and realize the quantum precision measurement in the low frequency band which breaks through the standard quantum limit.Laser interferometer can be used to measure small changes in refractive index,rotation or surface displacement,such as mechanical vibration.They convert the change of phase difference between two beams of light into the change of visibility of interference fringes at the output end and detect it by photodetector.Quantum enhanced low frequency signal measurement can be realized by injecting low frequency squeezed light into the vacuum channel of laser interferometer.Based on the experimental preparation of the vacuum squeezed state in the low frequency band of optical communication,this paper injects it into the vacuum channel of optical fiber Mach-Zehnder interferometer to measure the phase signal which breaks through the standard quantum limit.The main contents of this paper are as follows:1.Degenerate optical parametric oscillator(DOPO)is used to generateoptical communication waveband continuous variable 1550 nm low frequency vacuum squeezed state.DOPO is a half-block structure cavity composed of periodically polarized KTP crystal and concave mirror based on class I phase matching.Two acousto-optic modulators(AOM)are used to generate 25 MHz frequency-shift modulated coherent light into DOPO.The quadrature phase vacuum squeezed light is prepared by locking the squeezing angle of the vacuum squeezed state with coherent control technology.In the frequency range of 10-500 k Hz,the noise power spectrum of the vacuum squeezed light field is measured,and the Squeezing of squeezed state is 3 d B.2.Quantum-enhanced FMZI is realized by injecting the orthogonal phase vacuum squeezed state of DOPO output in 1550 nm optical communication band into the fiber Mach-Zehnder interferometer(FMZI)to fill the dark channel of the interferometer.The relative phase of FMZI arms is locked in π/2,and the phase modulation signal of 500 k Hz is loaded on one arm of the interferometer.When the vacuum squeezed state is injected,the quantum-enhanced FMZI is observed to achieve low-frequency phase signal measurement that breaks through the standard quantum limit.The signal-to-noise ratio of the interferometer is increased by 2 d B compared with that of the conventional interferometer.