The planned in-ice radio array of IceCube-Gen2 at the South Pole will provide unprecedented sensitivity to ultra-high-energy (UHE) neutrinos in the EeV range. A good understanding and modeling of the propagation of radio waves through the ice are crucial for the interpretation of experimental data, in particular, for reconstructing the neutrino's energy, direction, and flavor from the detected radio flashes. The birefringent properties of the ice split up the radio pulse into two orthogonal polarization components with slightly different propagation speeds. This provides useful signatures to determine the neutrino energy and is potentially important to determine the neutrino direction to degree precision.
Here, we study birefringence in the ice by calculating its effect from first principles. We integrated the calculations into the NuRadioMC simulation code and compared our predictions to in-situ measurements from the ARA and ARIANNA detectors at the South Pole which showed good agreement within the experimental uncertainties. Furthermore, we present the results of a systematic MC study on how birefringence affects the sensitivity of in-ice radio detectors.