Phase-sensitive optical time-domain reflectometry (φ-OTDR) has been widely used in many situations. In order to simplify the system structure and reduce costs, a new phase demodulation method is developed for φ-OTDR based on coherent detection. It works by extracting the time domain signals at two points in the disturbance area, and that could construct a pair of IQ component containing the disturbance phase information. Compared with most commonly used digital quadrature demodulation, the digital coherent signal is not required. And the need for high speed sampling frequency is reduced. The PZT induced vibration is applied to a certain section of fiber, which is used to introduce phase disturbance. Experimental results show that the phase change caused by external disturbance can be successfully demodulated in a sensing fiber of 22km, and a simple system structure is realized. When the central frequency of the beat signal is 200 MHz, the need for sampling rate can be reduced to 156MSa/s or less. Amplitude modulated disturbance tests show a reasonable linear response of the system with the R-square of 0.963.
Optical fiber Bragg grating (FBG) displacement sensors play an important role in various areas due to the high
sensitivity to displacement. However, it becomes a serious problem of FBG cross-sensitivity of temperature and
displacement in applications with FBG displacement sensing. This paper presents a method of temperature insensitive
measurement of displacement via using an appropriate layout of the sensor. A displacement sensor is constructed with
two FBGs mounted on the opposite surface of a cantilever beam. The wavelengths of the FBGs shift with a horizontal
direction displacement acting on the cantilever beam. Displacement measurement can be achieved by demodulating the
wavelengths difference of the two FBGs. In this case, the difference of the two FBGs’ wavelengths can be taken in order
to compensate for the temperature effects. Four cantilever beams with different shapes are designed and the FBG strain
distribution is quite different from each other. The deformation and strain distribution of cantilever beams are simulated
by using finite element analysis, which is used to optimize the layout of the FBG displacement sensor. Experimental
results show that an obvious increase in the sensitivity of this change on the displacement is obtained while temperature
dependence greatly reduced. A change in the wavelength can be found with the increase of displacement from 0 to
10mm for a cantilever beam. The physical size of the FBG displacement sensor head can be adjusted to meet the need of
different applications, such as structure health monitoring, smart material sensing, aerospace, etc.
Spatial resolution determines the minimum space unit that a distributed temperature sensor system can distinguish along the fiber thus it is an important parameter to evaluate the performance of the distributed temperature sensor system. A typical distributed temperature sensor system with a spatial resolution of 5m is built and an algorithm of linear fitting correction is proposed to realize temperature measurement of fiber length shorter than 5m accurately. With the method of linear fitting correction, the spatial resolution of the distributed temperature sensor system has been improved from 5m to 1m. The measured temperature of the DTS system is well calibrated by using linear fitting correction algorithm with a fiber length of 4m, 3m, 2m and 1m respectively. The maximum error of the corrective temperature is 2℃ for long term measurement.
KEYWORDS: Temperature metrology, Calibration, Signal attenuation, Optical fibers, Raman spectroscopy, Temperature sensors, Optical calibration, Error analysis, Signal detection, Demodulation
The effect of optical fiber attenuation differences (AD) induced temperature error of Raman distributed temperature sensor (RDTS) is analyzed using the temperature demodulation algorithm. First of all, a novel method to address the effects caused by the AD between Stokes and anti-Stokes light is proposed. Furthermore, the temperature measurement error caused by additional AD of fiber temperature is also reduced by using a formula obtained by experimental data. The experimental results demonstrate that the RDTS system can measure different temperature zones more accurately.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.