Temperature-Compensated Multifunctional All-Fiber Sensors for Precise Strain/high-Pressure Measurement

We propose two types of temperature-compensated all-fiber sensors based on a novel laser-machined Fabry–Perot interferometer (FPI) whose sensitivity is adjusted by controlling the FPI gauge length and fiber material. The sensors are demonstrated to achieve precise multiparameter measurements under high temperatures. One sensor is an enhanced sensitivity FPI cascaded with a femtosecond laser inscribed fiber Bragg grating. We propose a modified calculation formula considering the temperature dependence of strain/pressure sensitivities to ensure measurement accuracies. The experiment shows that the cascaded sensor exhibits excellent sensing performance with the maximum strain and pressure sensitivities of 41.6 pm/ $\boldsymbol {\mu \varepsilon }$ and $-222$ pm/MPa, respectively, and in a stable environment, its strain–temperature and pressure–temperature crosstalk are 0.139 $\boldsymbol {\mu \varepsilon }$ / $^{\circ }$ C and 0.027 MPa/ $^{\circ }$ C, respectively. The other sensor is the FPI itself with a length-matched gutter. It achieves an ultralow average thermal drift of $\sim$ 0.1 pm/ $^{\circ }$ C over 16–400 °C. Experimental results show that it exhibits low temperature–pressure and temperature–strain cross sensitivities of $\sim$ $-$ 0.0017 MPa/ $^{\circ }$ C and $\sim$ 0.015 $\boldsymbol {\mu \varepsilon }$ / $^{\circ }$ C, respectively.