Simultaneous optical fibre distributed strain and temperature
measurements have been obtained, by measuring the spontaneous Brillouin
intensity and frequency shift, using the technique of microwave heterodyne
detection. The enhanced stability from using a single coherent source combined
with optical preamplification results in a highly accurate sensor. Using this
sensor, distributed temperature sensing at 57 km and simultaneous distributed
strain and temperature sensing at 30 km were achieved, the longest reported
sensing lengths to date for these measurements. As a simultaneous strain and
temperature sensor, a strain resolution of 100 µε and
temperature resolution of 4 °C were achieved.
We demonstrate a low-loss, long-range, single-ended distributed optical fiber sensor to measure both temperature and strain simultaneously and unambiguously. By using the Landau¿Placzek ratio and cascaded Mach¿Zehnder interferometric filters, we measure both the intensity and the frequency changes in the Brillouin backscattered signal. Strain and temperature measurements can then be independently resolved. A temperature resolution of 4 degrees C, a strain resolution of 290 muepsilon, and a spatial resolution of 10 m have been achieved for a sensing length of 15 km.
We present a novel technique for performing single-ended distributed fiber temperature measurements by use of microwave heterodyne detection of spontaneous Brillouin scattering. Brillouin frequency-shift measurements were obtained for a sensing length of 57 km, with a spatial resolution of 20 m. The rms error in frequency measurements at the far end of the sensing fiber was less than 3 MHz, and the overall frequency dependence on temperature was 1.07+/-0.06 MHz/K.
The authors report the operation of a single-frequency, diode-pumped laser in CW operation with a linewidth of 10kHz, which provides a prelase for a narrow linewidth Qswitched laser. This was achieved by incorporating an unpumped low Er 3+ -doped fibre. In Q-switched operation, a linewidth of less than 60MHz is reported for pulses of 1µs at a repetition rate of 960 Hz.
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