Refractive index sensing performance of stepped-mTFBG fabricated by flexibly-regulating wet etching process

In this paper, an interesting method was proposed to flexibly prepare the micron titled fiber Bragg grating (mTFBG) by using a quartz capillary. The etching region of mTFBG can be precisely controlled by inserting in and moving it out from the protection of the quartz capillary. In this way, the mTFBG with stepped diameter has been fabricated and demonstrated with its refractive index sensing performance. Compared with the uniformly-etched mTFBG, the refractive index sensitivity of stepped-mTFBG has been significantly-improved from 5.785 nm/RIU to 17.077 nm/RIU. Although this sensitivity is much lower than other types of refractive index optical fiber sensors, it provides the new method for the flexible design of FBG structures. Furthermore, it reveals that the transmission spectrum of mTFBG can be modulated continuously during the etching process, which suggests a new way to adjust the transmission spectra of optical fibers. © 2022 Elsevier B.V.