Hollow and filled fiber bragg gratings in nano-bore optical fibers**Project supported by the Beijing Natural Science Foundation, China (Grant No. 4192047), the Fundamental Research Funds for the Central Universities, China (Grant Nos. 2018JBM070 and 2018JBM065), and the National Natural Science Foundation of China (Grant No. 61675019).

Abstract

To combine the technical functions and advantages of solid-core fiber Bragg gratings (FBGs) and hollow-core optical fibers (HCFs), the hollow and filled FBGs in nano-bore optical fibers (NBFs) with nano-bore in the GeO2-doped core are proposed. The fundamental mode field, effective mode index, and confinement loss of NBF with 50 nm–-diameter hollow and filled nano-bore are numerically investigated by the finite element method. The reflected spectra of FBGs in NBFs are obtained by the transmission matrix method. The hollow FBGs in NBFs can be acheived with (∼5% power fraction in the bore and the (∼0.9 reflectivity when bore diameter is less than . The filled FBGs can be realized with (∼1% power fraction and 0.98 reflectivity with different fillings including o-xylene, trichloroethylene, and chloroform for 800-nm bore diameter. The feasibility of the index sensing by our proposed NBF FBG is also analyzed and discussed. The experimental fabrication of hollow and filled FBGs are discussed and can be achieved by current techniques. The aim of this work is to establish a principle prototype for investigating the HCFs and solid-core FBGs-based fiber-optic platforms, which are useful for applications such as the simultaneous chemical and physical sensing at the same position.