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Brillouin Optical Time Domain Analysis (BOTDA)

BOTDA refers to Brillouin Optical Time Domain Analysis. It is a double ended access to the light source and detection system for long sensing lengths combined with high strain and temperature resolution for up to 31 miles (50 km) without signal regeneration.

The BOTDA sensor system utilizes the backward stimulated Brillouin scattering (SBS) of an optical fiber. The pumping pulse light is launched at one end of the fiber and propagates in the fiber, while the CW light is launched at the opposite end of the fiber and propagates in the opposite direction. In this configuration, the pump pulse generates backward Brillouin gain in a single-mode fiber. When the CW light frequency is different from the pump pulse light as same as the Brillouin frequency of the optical fiber, then the CW light is amplified through Brillouin interaction with the pump pulse. Also, the Brillouin frequency of a fiber is changed by the strain or temperature applied on the fiber. Therefore, the Brillouin frequency shift can give the temperature or strain information as the following equation.

v(ε,T)= v(0,0)+C1*ε+ C2*T

where ε and T are strain and temperature, respectively; C1 and C2 are the strain and temperature coefficients, respectively, which are known to be about 0.05 MHz/micronstrain and 1.2 MHz/°C for conventional single mode optical fibers used at the 1500nm wavelength range of optical communication.


Figure. Working principle of fiber optic BOTDA technology


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