Domestic developments of IR optical materials based on solid solutions of silver halogenides and monovalent thallium

A review of the current progress in fiber optics for the mid-infrared range of the spectrum (2.0–50.0 $\mu$m) is performed. The problem in development of infrared (IR) optical fibers with the extended working-wavelength range also having increased radiation resistance, is substantiated. The study of diagrams of AgBr–TlI and AgBr–TlBr$_{0.46}$I$_{0.54}$ quasi-binary section of the AgBr–AgI–TlBr–TlI four-component system was conducted. Areas of homogeneity of solid solutions were revealed. An experimental technique was developed for determining the refractive index depending on the wavelength by the spectroscopic method for crystals of new compositions. The resistance of the studied materials to ionizing radiation was revealed. The photonic crystal structures based on metal-halide systems under consideration were simulated and single-mode optical fibers of the modelled structure with an increased mode field were produced by extrusion. It was found that the working spectral range of AgBr–TlI optical fibers is from 4 to 25 $\mu$m. The options for using the obtained IR light guides are considered.