A useful method for eliminating the detrimental effect of laser frequency instability on\nBrillouin signals by employing the self-heterodyne detection of Rayleigh and Brillouin scattering\nis presented. From the analysis of Brillouin scattering spectra from fibers with different lengths\nmeasured by heterodyne detection, the maximum usable pulse width immune to laser frequency\ninstability is obtained to be about 4 Ã?¼s in a self-heterodyne detection Brillouin optical time domain\nreflectometer (BOTDR) system using a broad-band laser with low frequency stability. Applying the\nself-heterodyne detection of Rayleigh and Brillouin scattering in BOTDR system, we successfully\ndemonstrate that the detrimental effect of laser frequency instability on Brillouin signals can be\neliminated effectively. Employing the broad-band laser modulated by a 130-ns wide pulse driven\nelectro-optic modulator, the observed maximum errors in temperatures measured by the local\nheterodyne and self-heterodyne detection BOTDR systems are 7.9 ââ??¦C and 1.2 ââ??¦C, respectively.
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