First-principles studies of dopant and radiation defect effects on optical fiber sensors

Density functional theory-based calculations and ab-initio molecular dynamics have been performed in order to study the effects of dopants and radiation defects on the structures and optical properties of amorphous silica in comparison to sapphire - another high-temperature and radiation-resistant material. Out studies focused on oxygen deficient centers ODCs (a typical point defect due to radiation damage) and fluorine F dopants. Optical properties depend on dielectric function, calculated from the charge density of the material. With real- and imaginary-part dielectric functions, all the other optical properties, such as refractive index, energy loss function, and absorption coefficient, could be derived. Optical properties of amorphous silica and sapphire become anisotropic with either ODC or F dopants. They contribute characteristic peaks to the optical spectra and induce minor peaks in the low photon energy ranges. Static optical coefficients significantly increase with F dopants, but they might remain or slightly increase with ODC. Our results suggest that adding dopants can improve the optical properties of the materials and potentially inhabit the formation of high-temperature and radiation defects, resulting in an enhancement of the light signal in their transmitted spectra. Controlling dopant concentration also plays a crucial role, because a high dopant concentration could cause a structural distortion and degrade the optical performance of the material.