Optical fiber sensing solutions

1、BOTDR - a self released solution for deep scattering

In BOTDR, the properties of optical fiber materials related to Brillouin scattering signal and Brillouin scattering light frequency are mainly affected by temperature and strain. Therefore, distributed temperature and strain measurement can be realized by measuring the frequency shift of back Brillouin scattering light of pulse light.

The continuous light from the narrow linewidth laser source is divided into two parts by the coupler. One part is modulated into pulse light by the electro-optic modulator (EOM), an incident on the sensing optical fiber. The other part enters the reference optical path as the local oscillator light. The backscattered light generated by the pulse light enters the photodetector for coherent detection with the local vibration light, takes out the difference frequency component. 
     The Brillouin frequency shift signal analyzes the Brillouin frequency spectrum to get the change of Brillouin parameters to get out the temperature and strain information. The time delay between the backscattered light and the pulse light provides the optical fiber position information's measurement.

BOTDA stimulated Brillouin scattering solution

Based on the microwave external modulation single laser ring BOTDA system, the light source is divided into two channels by the coupler or two fiber pairs according to the needs to achieve single end incidence, to simplify the equipment, reduce the measurement time and achieve high measurement accuracy.

The system uses a narrow linewidth laser with a 1550nm working wavelength and divides the light source into two channels through a 3dB coupler. One of the optical signals is modulated by the electro-optic modulator (eom1) to pulse light, amplified by EDFA, filtered by grating, and then entered the sensing fiber. Another optical signal of the coupler is modulated by an electro-optic modulator (eom2) to produce a frequency shift of about 11 GHz. The stimulated Brillouin scattering has the most substantial effect when the frequency difference of the two beams transmitted in the opposite direction is consistent with the fiber's Brillouin frequency shift. The probe light enters the photodetector through the circulator for detection. Then the high-speed data acquisition equipment (A / D) and the computer carry out the superposition average and spectrum fitting to determine the corresponding frequency difference when the Brillouin gain of each optical fiber section reaches the maximum. The frequency difference is equal to the Brillouin frequency shift on each optical fiber section, so the temperature and strain with the linear relationship with the Brillouin frequency shift can be determined To realize the distributed measurement of pressure or temperature.