Abstract
Cross-sensitivity (crosstalk) to multiple parameters is a serious but common issue for most sensors and can significantly decrease the usefulness and detection accuracy of sensors. In this work, a high sensitivity temperature sensor based on a small air core (10 µm) hollow core fiber (SACHCF) structure is proposed. Co-excitation of both anti-resonant reflecting optical waveguide (ARROW) and Mach-Zehnder interferometer (MZI) guiding mechanisms in transmission are demonstrated. It is found that the strain sensitivity of the proposed SACHCF structure is decreased over one order of magnitude when a double phase condition (destructive condition of MZI and resonant condition of ARROW) is satisfied. In addition, due to its compact size and a symmetrical configuration, the SACHCF structure shows ultra-low sensitivity to curvature and twist. Experimentally, a high temperature sensitivity of 31.6 pm/°C, an ultra-low strain sensitivity of -0.01pm/µε, a curvature sensitivity of 18.25 pm/m-1, and a twist sensitivity of -22.55 pm/(rad/m) were demonstrated. The corresponding temperature cross sensitivities to strain, curvature and twist are calculated to be -0.00032 °C/µε, 0.58 °C/m-1 and 0.71 °C/(rad/m), respectively. The above cross sensitivities are one to two orders of magnitude lower than that of previously reported optical fiber temperature sensors. The proposed sensor shows a great potential to be used as a temperature sensor in practical applications where influence of multiple environmental parameters cannot be eliminated.
Highlights
Optical fiber sensors (OFSs) have attracted tremendous interest for the detection of changes in physical and bio-chemical parameters in a variety of applications due to their inherent advantages such as high sensitivity, compact size, fast response, good resistance to electromagnetic interference, and capability to work in harsh environments [1]
A few Mach-Zehnder interferometer (MZI) have been proposed for strain independent temperature measurement based on modified singlemode-multimode-singlemode (SMS) structures by using a seven-core fiber, a suspended-core fiber, a small core photosensitive fiber, multiple sections of singlemode and multimode fibers, and a photonic crystal fiber [3,4,5,6,7], but these fiber structures are demonstrated with high cross sensitivity to curvature [16,17,18,19]
Strong periodic dips with small variations in their central wavelengths are excited in air for both samples with a free spectral range (FSR) of circa 21 nm at 1570 nm. These strong dips are produced by the anti-resonant reflecting optical waveguide (ARROW) effect as the dip wavelengths are independent of the sensor length and the fact that the measured FSR is well matched with the theoretical value (20.3 nm) calculated by Eq (3)
Summary
Optical fiber sensors (OFSs) have attracted tremendous interest for the detection of changes in physical and bio-chemical parameters in a variety of applications due to their inherent advantages such as high sensitivity, compact size, fast response, good resistance to electromagnetic interference, and capability to work in harsh environments [1]. In many temperature measurement environments, there is the presence of unavoidable strain, curvature/bending and twist/torsion effects. A good example is a MZI which provides simple fabrication and high sensitivity when used as a temperature sensor, but it suffers from high cross sensitivities to strain, curvature/bending and twist/torsion. A few MZIs have been proposed for strain independent temperature measurement based on modified singlemode-multimode-singlemode (SMS) structures by using a seven-core fiber, a suspended-core fiber, a small core photosensitive fiber, multiple sections of singlemode and multimode fibers, and a photonic crystal fiber [3,4,5,6,7], but these fiber structures are demonstrated with high cross sensitivity to curvature [16,17,18,19]. There has been no temperature sensors proposed with a high resistance to all above three parameters (strain, curvature and twist)
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