## 3 Experimental Results
Figure 7: The displacement sensing curve of the notch wavelength shifting (blue line) and cross-correlation peak shifting (red line). linearly with the displacement. The displacement sensitivity is low at the loose state of the microfiber and high at the tension state. For the notch wavelength marking method, the displacement sensitivity was 2.55 nm/mm at the loose state and 36.5 nm/mm at the tension state. For the cross-correlation method, the displacement sensitivity was 2.37 nm/mm at the loose state and 32.1 nm/mm at the tension state. There was a slight sensitivity difference between the two methods. However, the demodulation efficiency of the cross-correlation method is much higher than the wavelength marking method. The cross-correlation steps also suggest that the Fabry-Perot interferometer has potential applications in the field of microwave signal generation. The measurement sensitivity of both the methods mentioned here is higher than the displacement sensitivity of 22.8 nm/mm mentioned in [3], and the bandwidth of the proposed F-P (0.15) is far less than that of [3] (20 nm). The sensing resolution of the proposed F-P is 0.004 mm, calculating from the ratio of the 3-dB bandwidth to the sensitivity. The displacement sensing can be converted into strain sensing after calculation, the strain sensitivity comparison between the proposed F-P interferometer and other interferometer-type sensors are shown in Table 1.  
We can see that the sensitivity of the proposed F-P interferometer is higher than the Mach-Zehnder (M-Z) structure, while the 3-dB bandwidth is much narrower. The sensitivity of the proposed F-P interferometer is less than that of the single mode-multimode-single mode (SMS) structure, but the 3-dB bandwidth of the proposed F-P interferometer is much less than that of the SMS structure. The ratio of the bandwidth to the sensitivity is a very important parameter, which is often used to represent the sensing resolution. The sensing resolution of the proposed F-P interferometer is higher than the two common interferometer-type sensors. We also measured the temperature sensitivity, as shown in Figure 8.  
We can see from the temperature curve that for both the cross-correlation method and the notch wavelength shift monitoring method, the sensitivity is changing with the temperature as a quadratic \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sensor** & **Sensitivity** & **3-dB Bandwidth** & **Ratio of Bandwidth to Sensitivity** \\ \hline The proposed F–P & 6.4 pm/\(\mu\epsilon\) & 0.15 nm & 23.4 \(\mu\epsilon\) \\ M-Z [1] & 1.19 pm/\(\mu\epsilon\) & 4.3 nm & 3613 \(\mu\epsilon\) \\ SMS structure [2] & 42.5 pm/\(\mu\epsilon\) & 7.3 nm & 171.8 \(\mu\epsilon\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparisons between the references based on their interferometer-type sensors and the proposed sensor. Figure 8: The temperature sensing curve of the notch wavelength shifting (blue line) and cross-correlation peak shifting (red line). function. The temperature sensitivity was about 0.04 nm/\({}^{\circ}\)C at room temperature (25 \({}^{\circ}\)C), which was even lower than the optical spectra analyzer (OSA) resolution. Thus, the temperature variations to the displacement sensing can be ignored.