This paper proposes a novel detection scheme simultaneously to measure strain and temperature, based on a simple to construct device using a section of a specially designed few-mode fiber (FMF). The parameters and index profile of the FMF used as the key sensor element are such that the fiber supports only the LP01 and LP02 modes. The propagation constant difference between LP01 and LP02 modes Δβ has a maximum corresponding to the critical wavelength (CWL) in the fiber transmission spectrum. Because the two peaks located closest to the CWL from both sides, left peak 1 and right peak 1, shift in opposite directions, with different sensitivities under axial strain and temperature variations, the FMF device is capable of measuring the strain and temperature simultaneously. A theoretical analysis has been carried out as part of the design process and the experimental results obtained are found to agree well with the theoretical predictions. The characteristics of this sensor scheme are discussed in light of other competing approaches to simultaneous temperature and strain monitoring and are found to show advantages that suit several practical applications including compactness, ease of fabrication and implementation, relatively high sensitivities, and low cost.
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