Abstract
A useful method for eliminating the detrimental effect of laser frequency instability on Brillouin signals by employing the self-heterodyne detection of Rayleigh and Brillouin scattering is presented. From the analysis of Brillouin scattering spectra from fibers with different lengths measured by heterodyne detection, the maximum usable pulse width immune to laser frequency instability is obtained to be about 4 µs in a self-heterodyne detection Brillouin optical time domain reflectometer (BOTDR) system using a broad-band laser with low frequency stability. Applying the self-heterodyne detection of Rayleigh and Brillouin scattering in BOTDR system, we successfully demonstrate that the detrimental effect of laser frequency instability on Brillouin signals can be eliminated effectively. Employing the broad-band laser modulated by a 130-ns wide pulse driven electro-optic modulator, the observed maximum errors in temperatures measured by the local heterodyne and self-heterodyne detection BOTDR systems are 7.9 °C and 1.2 °C, respectively.
Highlights
Due to the merits, such as high brightness and directivity, good monochromaticity, and coherence, lasers with high frequency and power stability have been widely used in the research of biology, medicine, chemistry, coherent optical communication and optical fiber sensing, wind LiDAR, and high-resolution spectroscopy [1,2,3,4,5,6,7]
To signals experimentally by the self-heterodyne detection of Brillouin scattering, the signals experimentally by the self-heterodyne detection of Rayleigh and Brillouin scattering, the experimental setups based on local heterodyne detection and self-heterodyne detection experimental setups based on local heterodyne detection and self-heterodyne detection Brillouin optical time domain reflectometer (BOTDR)
The output lights of the narrow-band and broad-band lasers were divided into two beams, one beam was modulated to optical pulse with a width of 130 ns and a peak power of of 27.8
Summary
Due to the merits, such as high brightness and directivity, good monochromaticity, and coherence, lasers with high frequency and power stability have been widely used in the research of biology, medicine, chemistry, coherent optical communication and optical fiber sensing, wind LiDAR, and high-resolution spectroscopy [1,2,3,4,5,6,7] Among these studies, optical fiber sensors based on Brillouin scattering have attracted much attenuation due to their capability to measure the distribution of temperature and/or strain, vibration and moisture in large civil structures, power cables, geological disasters, and road embankments [8,9,10,11,12,13]. Modeling Analysis of Heterodyne Detection Brillouin Signals with Laser Frequency Instability
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