High-Sensitivity Fiber-Optic Fabry–Perot Interferometer Temperature Sensor

A Highly Sensitive Fiber-Optic Fabry–Perot Interferometer Based on Internal Reflection Mirrors for Refractive Index Measurement

“…Thus, a new formula is proposed in this work based on the linear thermal expansion coefficient of optical fiber, and is given by: where C is the linear thermal expansion coefficient of silica, T is the measurement temperature, T 0 is the initial temperature, and l is the initial length of the micro-cavity. Research results of our team and others have confirmed that, at various temperatures, the length change of the micro-cavity can be computed based on l ∙ [1 + C ∙ ( T − T 0 )]; thus, the effects resulting from the temperature change can be eliminated [ 25 , 26 , 35 , 36 ]. Therefore, the RI can be measured accurately using Equation (5) at different ambient temperatures.…”

“…Equation (4) is used to calculate the RI of the measuring medium, assuming that l is kept constant during the measurement. In practice, because the linear thermal expansion coefficient of pure silica is about 4.0 × 10 −7 /°C at room temperature [ 25 , 26 ], the length of the micro-cavity increases as the temperature rises. For instance, Figure 3 shows the effect of a temperature change on the position of interference spectra at a temperature difference of 500 °C, where n = 1.0 and l = 100 µm at the initial temperature.…”

“…Therefore, FFPI sensors have been widely used for measurement of a variety of parameters such as RI, temperature, strain, etc . [ 23 , 24 , 25 , 26 ]. Our team proposed an FFPI sensor based on the difference in the thermal expansion coefficient between fused silica and metallic materials, which has a high temperature sensitivity with 70 pm/°C [ 25 , 26 ].…”

“…[ 23 , 24 , 25 , 26 ]. Our team proposed an FFPI sensor based on the difference in the thermal expansion coefficient between fused silica and metallic materials, which has a high temperature sensitivity with 70 pm/°C [ 25 , 26 ]. Again, notice that the optical length of the micro-cavity is easier to change by the RI of the filling medium.…”

Sensing with ultra-short Fabry-Perot cavities written into optical micro-fibers

“…Examples include femtosecond laser micro-machining [17,25,26], ultraviolet laser ablation [16], the use of wet etching and fusion splicing of single mode fibers [7,8], splicing etched single mode fiber to form a micro-gap [15], and splicing single-mode fiber to either capillary tubing [9,18], C-shaped fiber [19], or photonic crystal fiber [27]. A technique that can provide high surface quality and can be easily tailored for different cavity geometries is to use a focused-ion beam microscope to mill micro-cavities [10][11][12][13][14][28][29][30][31]. Milling the entire fiber cross section is possible, but is a highly time consuming process [10,29].…”