MEASUREMENT METHOD OF THE BRILLOUIN SCATTERING FREQUENCY SHIFT ON THE OPTICAL FIBER LENGTH Russian patent published in 2017 - IPC G01N21/63 G01M11/00 

FIELD: measuring equipment.

SUBSTANCE: when implementing the measuring method of the Brillouin scattering frequency shift on the optical fiber length, the continuous optical radiation of the master laser is divided into two parts. The first part is modulated by the impulse chain, then amplified and injected into the test optical fiber. The supporting optical signal of one polarization is formed from the second part, which is fed to one balanced photodetector input, and the backscattering signal from the tested optical fiber is fed to the other balanced photodetector input. The low-frequency component of the signal is extracted at the output of the balanced photodetector by means of the filter, which is fed to the control and processing unit input. Change the frequency of the supporting optical signal with the steps not less than 100 MHz and repeat the measurements for each step at each frequency value, then change the polarization state of the supporting optical signal one polarization into the orthogonal and repeat the measurements. The Brillouin scattering frequency shift distribution is obtained at the length of the optical fiber. To form the supporting optical signal, the second part of the continuous optical radiation of the master laser is input into the supporting optical fiber, from the backscattering signal coming from the supporting optical fiber by means of the optical filter, the Brillouin backscattering signal is extracted, amplified, and then modulated with one side band by radio frequency signal, which is changed with the given step in the range up to several hundred megahertz. Further the component with one from two setting by the switchable polarizer of polarization orthogonal states is extracted, and the Brillouin scattering frequency shift is defined as the sum of the Brillouin scattering frequency shift in the optical fiber in the absence of temperature and mechanical influences and the frequency of the modulating radio frequency signal, at which the amplitudes sum value of the beat signals at the control and processing unit input, measured with two orthogonal states of the supporting signal, exceeds the specified threshold value.

EFFECT: application field expansion.

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