Efficient Demodulation of Brillouin Phase Spectra and Performance Enhancement in BOTDA Incorporating Phase Noise Elimination

A Brillouin phase spectra (BPS) demodulation approach in Brillouin optical time-domain analysis (BOTDA) based on phase to intensity conversion is proposed and demonstrated. By utilizing the cascaded modulation of the probe light and coherent detection in a symmetric double-sidebands BOTDA, the Brillouin phase shift is transferred into the signal intensity so that it can be recovered with a simple envelope detection. Moreover, the measurement accuracy is significantly improved by the reduction of phase noise caused by the fiber transmission. A 2-m spatial resolution over 39.1-km fiber and 0.7 °C temperature accuracy at the end of the fiber are achieved using the BPS measurement. Compared with the conventional IQ demodulation without phase noise elimination, the precision is improved ~6.3 dB and the maximum variation of the Brillouin frequency shift (BFS) is reduced from 13 MHz down to 2 MHz. Meanwhile, the comparison experiment with the Brillouin gain spectrum (BGS) detection is also implemented. The proposed method achieves smaller BFS uncertainty in comparison with the conventional BGS detection. At the end of the fiber, uncertainty is reduced from 1 MHz down to 0.7 MHz.