In this paper, we propose techniques to design and fabricate polymer micro-cantilevers for attachment onto the end of standard single mode fibers using laser machining. The polymer cantilever is fabricated by laser micro-machining a sheet of polymer into the required shape and then bonded onto the top of a ceramic ferrule by photo resist as a flat supporting and bonding layer. The dimension of resulting cantilever is ~1.2 mm long, ~300 μm wide, and 25 μm thick. In this work we describe the fabrication of single sensors, however the process could be scaled to offer a route towards mass production. Cantilever vibration caused by vibration signal are monitored by a DFB laser based phase interrogation system. Proof-of-concept experiments show that the sensor is capable of detecting vibration signal with a frequency range of 0-800Hz. By using thinner polymer sheet and machining longer cantilever, the frequency response range can be extended up to a few kHz.
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.
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.