The invention relates to a distributed
fiber vibration sensing system capable of eliminating declining noises and a
demodulation method of the
system. The
system comprises a
signal generation module, a narrow linewidth
laser source module, a frequency-sweeping light chopping pulse module, a
circulator, a sensing
fiber, a coherent reception module, a
photoelectric conversion module and a
digital signal processing module; a computer generates multiple digital band pass filters of different frequency ranges but not overlapped and combines
original data segments from
multiple frequency-sweeping detection light pulses to obtain a
reflectivity curve of the sensing
fiber; phase-shaft averaging is carried out on the
reflectivity curve to obtain multiple interference-free and polarization-declining integrated
reflectivity curves;
delay differential
processing is carried out on the integrated reflectivity curves to obtain phase differential curves; variances of the phase differential curves are solved to obtain a
phase variance curve; and a vibration point is determined according to variances in the
phase variance curve, and position and vibration waveform of the vibration point are obtained. According to the system and method of the invention, design is reasonable, the positioning accuracy is high, and
space resolution and long detection distance can be obtained at the same time.