An ameliorative technique for distributed Brillouin-based fiber optics sensing

Abstract

ABSTRACT This paper reports an ameliorative technique for distributed fiber optics sensing based on Brillouin optical time-domain reflectometry (BOTDR) and Brillouin optical-fiber time-domain analysis (BOTDA). Because the electro-optic modulator in BOTDR system has a finite extinction ratio, the pulsed laser always contains a CW component, which is hereafter called leakage. The frequency of the leakage is v p which is the same as that of the pulse, and the frequency of the Stokes wave is v s . The frequency of the acoustic wave v b at each point along the fiber matches the beat frequency of the leakage and the Stokes wave . As a result, when given an appropriate extinction ratio, the leakage will have a biggish effect on the Stokes wave, which is the same as the function between the continuous wave and the Stokes in BOTDA system. The Stokes componen t in spontaneous Brillouin scattering (SPBS) is amplified by the leakage along the distance when it backs to the laser end, which is the well known stimulated Brillouin scattering (SBS) phenomena. So long as the distance from the point where the SPBS engender to the laser end is long, the intensity of the SBS signal is relatively large owing to the longer amplified interval. In BOTDR system, when setting the extinction ratio at 20dB, using the SBS si gnal we can achieve a SNR which is appr oximately 5 dB greater than that of traditional system and the dynamic range performance 3 dB greater. Utilizing this new technique in BOTDR system it also has an ascendency compared with BOTDA system in resp ect that it access to only one end of the fiber with probe pulse light. Keywords: BOTDR, BOTDA, Electro-optic modulator, Extinction ratio, CW, SBS, simulation system performance, application