Differential Cross Spectrum Technique for Improving the Spatial Resolution of BOTDR Sensor

We propose a technique in BOTDR fiber sensor to generate a pair of pulsed probes via intensity modulation scheme for measuring distributed strain at high spatial resolution. The first probe consists of a long-and short duration of pulses separated by a short interval. The second probe only has the long pulse of the first probe. Introducing FFT in correlating the backscattered signals sampled by wide and narrow window functions for each probe gives narrow Brillouin spectrum width. The subtraction of the correlated signals obtained by the two probes results in high spatial resolution measurement. The intensity modulation makes it easier to generate the pair of pulsed probes having the same waveform of the long pulse and to obtain the results according to the measurement principle. We have achieved 0.2 m spatial resolution and 3.2 MHz Brillouin frequency accuracy in measuring a 350 m fiber.