Strain sensor based on a pair of single-mode-multimode-single-mode fiber structures in a ratiometric power measurement scheme

The strain and temperature dependencies of a step-index single-mode-multimode-single-mode (SMS) fiber structure are investigated numerically and experimentally. For intensity-based strain measurement using a single SMS fiber structure, at a selected wavelength, it is found that there is a high strain dependence, but also a temperature dependence that will induce strain measurement error. To minimize the temperature-induced strain measurement error, two SMS fiber structures are proposed and demonstrated in a ratiometric power measurement scheme; one SMS structure acts as the strain sensor, and the other SMS structure acts as the temperature monitor. The extracted temperature information is used to determine a strain value based on a suitable calibration of strain responses with temperature variations. It is demonstrated that for strain measurement from 0 to 1000 μ∑ within the temperature range from 10°C to 40°C, the proposed configuration can provide a strain and temperature resolution of 0.34μ∑ and 0.14°C, respectively, with a temperature-induced strain measurement error as low as 0.39 μ∑.