This work reports a simple optical fiber Surface Plasmon Resonance (SPR) sensor with ultra-high sensitivity for simultaneous measurement of the dual-parameter. The sensor is based on a D-shaped fiber with a nanolayer coating of Silver (Ag) and Hematite (α−Fe ₂ O ₃ ). The Ag/α− Fe ₂ O ₃ layer is deposited on the longitudinal surface of residual cladding, and a Fiber Bragg Grating (FBG) is inscribed on the single-mode fiber (SMF) for temperature compensation. The α− Fe ₂ O ₃ layer protects the Ag layer from oxidation and effectively enhances the surface plasmon wave while interacting with free electrons. Finite Element Method (FEM) modeling is employed to investigate the refractive index (RI) and temperature response of the SPR sensor. The SPR sensor exhibits an ultra-high RI sensitivity of 8,518 nm/RIU (refractive index unit) in the RI range of 1.33 to 1.40, and a temperature sensitivity of -52 pm/°C in the temperature range of 20°C to 60°C. The SPR performance suggests that it is a potential candidate for various applications of dual-parameter sensing.

Highly sensitive cascaded FPI based strain sensor with Vernier Effect is proposed and experimentally demonstrated. This FPI structure is fabricated by simple and cost-effective techniques such as, cleaving, splicing and tapering. Experimental results show that the proposed structure can provide a high strain sensitivity of 37.3 pm/μE, that is 13.3 times higher than the sensitivity of the single sensing FPI, which is 2.8 pm/μ. Proposed sensor also exhibits very low temperature cross sensitivity of 0.7 pm/°.This design can provide simple fabrication, stable and linear output response over a large range of applied strain and brings numerous prospects for sensing applications.

A hybrid interferometer for simultaneous measurement of strain and temperature is proposed and investigated experimentally. This hybrid design is composed of Fabry-Perot interferometer (FPI) and Michelson Interferometer (MI) cascaded with each other. It is developed by fusion splicing a single mode fiber (SMF), a multimode fiber (MMF), a dual side hole fiber (DSHF), a hollow core fiber (HCF) and a tapered-SMF. The tapered SMF was inserted into the HCF to form a reflection mirror for the FPI. The maximum temperature and strain sensitivity of the hybrid interferometer achieved through experiments is 11.6 pm/°C and 6.8 pm/με, respectively. The different sensitivities of FPI and MI to temperature and strain enable us to achieve simultaneous measurement. The proposed hybrid interferometer sensor has many attractive features such as, novel design, low cost, easy fabrication, compact size, and good sensitivity. Therefore, the proposed hybrid sensor could be widely deployed in plenty of applications, for instance, structural health monitoring, civil engineering, food manufacturing, chemical and medical fields.

A highly sensitive strain sensor based on tunable cascaded Fabry-Perot interferometers (FPIs) is proposed and experimentally demonstrated. Cascaded FPIs consist of a sensing FPI and a reference FPI which effectively generate the Vernier Effect (VE). The sensing FPI comprises a hollow core fiber (HCF) segment sandwiched between single-mode fibers (SMFs), and the reference FPI consists of a tunable air reflector, which is constituted by a computer programable fiber holding block to adjust the desired cavity length. Simulation results predict the dispersion characteristics of modes carried by HCF. The sensor’s parameters are designed corresponding to a narrow bandwidth range, i.e., 1530 nm to 1610 nm. Experimental results demonstrate that the proposed sensor exhibits optimum strain sensitivity of 23.9 pm/με in the range of 0 to 3000 με which is 13.73 times higher than the single sensing FPI strain sensitivity of 1.74 pm/με. The strain sensitivity of the sensor can be further enhanced by extending the source bandwidth. The proposed sensor exhibits ultra-low temperature sensitivity of 0.49 pm/°C in the wider temperature range of 25 °C to 135 °C, providing good isolation for eliminating cross-talk between strain and temperature. The sensor is very robust, cost-effective, easy to manufacture, repeatable, and shows a highly linear and stable response in the wider range of axial strain. Based on the sensor’s performance, it may suit plenty of practical applications in the real sensing world