Enhancing the SNR of BOTDR by Gain-Switched Modulation

A scheme utilizing gain-switched modulation to enhance the signal-to-noise ratio (SNR) of Brillouin optical time domain reflectometer (BOTDR) is proposed and evaluated. The modulation mechanism of the gain switch is analyzed and how it improves the SNR of BOTDR is revealed. The experimental results show that the gain switch can produce optical pulses with the extinction ratio of 51.26 dB, nearly 16 dB higher than that of a conventional electro-optical modulator (EOM). The root-mean-square error of the measured Brillouin frequency shift at 9.941 km of the sensing fiber decreases from 2.49 to 0.78 MHz, and the fluctuation range minishes from 7.84 to 2.76 MHz. Meanwhile, the measurement distance of BOTDR utilizing the gain-switched modulation can be extended from 10.75 to 27.5 km with the 1-m spacial resolution under the same measurement condition compared to the conventional EOM.