Refractive index of fluoride crystals doped with rare earth ions with low concentration

Abstract

Abstract Refractive indices of SrF2 crystals doped with low concentrations of holmium, erbium, and thulium ions are investigated. These crystals are attractive as active laser media for developing planar waveguides for near and mid-IR spectral regions. It is shown that, by varying the concentration of impurity rare-earth ions in SrF2 crystals, it is possible to increase and control the refractive index of the medium. This allows one to develop planar waveguides with the core and shell of the same fluoride and control theirs numerical aperture and the number of excited modes. The design of single mode planar waveguide is calculated and proposed for the wavelength of 2 um.