# Femtosecond-Laser-Assisted Fabrication of Radiation-Resistant Fiber Bragg Grating Sensors
## 5 Conclusions  
In summary, we fabricated radiation-resistant F-doped FBG sensors for operation under heavy radiation conditions. Infrared femtosecond laser-assisted phase mask technology was used to fabricate the FBGs, having a Bragg resonance at 1542 nm, inside acrylate-coated F-doped silica fibers. Experimental results exemplify that fabrication parameters such as focal length, laser wavelength, laser power, laser exposure time, and grating length have a significant impact on the performance of the FBG sensors. The optimal values of the laser parameters to fabricate high-quality radiation-resistant FBG sensors were: a laser power of 350 mW, a laser exposure time of 15 s, and a FBG length of 15 mm. We compared the performance of our infrared femtosecond laser-fabricated F-doped FBG sensors with commercial Ge-doped FBG sensors fabricated by infrared and ultraviolet femtosecond lasers. The infrared femtosecond laser-fabricated FBG sensors showed better performance  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**Our**} & \multirow{2}{*}{**[PERSON] et al. [20]**} & \multirow{2}{*}{**[PERSON] et al. [22]**} & \multirow{2}{*}{**[PERSON] et al. [23]**} \\  & **Achievements** & & & \\ \hline Peak Received & & & & \\ Signal Power, dBm & 20.6 & \(-\)20.80 & N/A & \(-\)21 \\ (without radiation) & & & & \\ Peak Received & & & & \\ Signal Power, dBm & 0.7 & \(-\)21.12 & N/A & \(-\)27 \\ (with radiation) & & & & \\ Bragg Wavelength & & & & \\ Shift, pm & \(-\)5.5 & 120 & \(-\)32 & \(-\)2750 \\ (with radiation) & & & & \\ Highest & & & & \\ Temperature & 14.4 & 5.48 & 10.53 & 5.97 \\ Sensitivity, pm/\({}^{\circ}\)C & & & & \\ (with radiation) & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of our experimental results with other reported research works.  
as compared with the ultraviolet femtosecond laser-inscribed FBG sensors. Among all FBG sensors, our F-doped sensor showed the best radiation resistance under \(10^{5}\) Gy of Gamma radiation, where the wavelength shift was just \(-5.5\) pm. The highest reflected signal power of 0.7 dBm was detected in the F-doped FBG sensors with a maximum reflected signal power reduction of 0.45 dBm. In contrast, the infrared femtosecond laser-based F-doped FBG sensors showed excellent temperature sensitivity over the temperature range of 25-335 \({}^{\circ}\)C, where the highest temperature sensitivity of 14.4 pm/\({}^{\circ}\)C was noticed at 310 \({}^{\circ}\)C. The temperature sensitivity of the proposed infrared femtosecond laser-fabricated F-doped FBG sensor was the highest among all the studied radiation-resistant FBG sensors. We strongly believe that the proposed radiation-resistant F-doped FBG sensors will play significant role in dynamic application areas, including the atomic energy industry and space research.  
Conceptualization, H.-K.C. and I.-B.S.; methodology, H.-K.C., Y.-J.J., B.-A.Y. and J.-H.S.; validation, I.-B.S., J.-Y.K. and M.S.A.; formal analysis, H.-K.C., B.-A.Y. and J.-H.S.; investigation, H.-K.C., Y.-J.J. and J.-Y.K.; resources, I.-B.S. and J.-Y.K.; writing--original draft preparation, M.S.A.; writing--review and editing, H.-K.C. and I.-B.S.; visualization, H.-K.C. and M.S.A.; supervision, I.-B.S. and J.-Y.K.; project administration, I.-B.S.; funding acquisition, I.-B.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by a GIST Research Institute (GRI) grant funded by the GIST in 2022, the National Research Foundation of Korea (NRF), Republic of Korea (Research Grant No.: NRF-2017M2A8A4017221), and the High-Efficiency Laser Laboratory of the Agency for Defense Development, Republic of Korea (Research Grant No.: UD190015 ID). The APC was funded by the GIST Research Institute (GRI).  
Not applicable.  
The authors declare no conflict of interest.