Progress on Rare-Earth Ions Doped Midinfrared Chalcogenide Optical Fibers and Their Sensing Application

Mid-infrared light sources have some important applications in military and national economy, such as national defense safety, food safety, spectral analysis and so on. Recent research work on rare-earth element ions doped chalcogenide glasses and optical fibers mainly focuses on improving the solubility of rare-earth element ions, reducing the local phonon energy of rare-earth element ions and co-doping of sensitized ions. The mid-infrared fluorescence of rare-earth element ions such as Dy³⁺, Pr³⁺, Dy³⁺, Tb³⁺, and Sm³⁺ can be obtained in glass and optical fiber. This broadband mid-infrared fluorescence is applied in the sensing field to realize the sensing of gases such as CO₂ and CH₄. This review represented recent research progress on rare-earth element ions doped mid-infrared chalcogenide glasses and optical fibers. Various factors affecting the mid-infrared luminescence of chalcogenide glass fibers were discussed, i.e., the solubility of rare-earth element ions, phonon energy around rare-earth element ions, energy transfer between sensitized ions and impurity loss. The research progress of broadband mid-infrared fluorescence in the field of gas sensing was summarized. There are five deficiencies in the research of rare-earth element ions doped sulfur fiber gas sensor. Obtaining the mid-infrared laser in rare-earth element ions doped glass fiber is still a challenge. In addition to seeking the solutions from the perspective of active fiber preparation (i.e., matrix selection, rare-earth ions co-doping, local structure regulation, preform glass purification, etc.), some aspects of optical fiber grating writing technology, pump laser power and wavelength tuning were also concerned. Rare-earth element ions doped mid-infrared chalcogenide fiber as a promising optical material has a great application potential due to its advantages of compactness, compactness and economy.