Negative Refraction in Gyrotropic Media by Polaritons

We discuss the negative refraction in isotropic gyrotropic (chiral) Materials (having natural optical activity) from the point of view of crystal optics with account of a spatial dispersion, i.e. the linear dependence of the dielectric tensor $\varepsilon (\omega $,k) on the k-vector. We show that in the media with high enough rotatory power, (such as polylactic acid),negative refraction can be observed at optical frequencies for additional waves. We make computer modeling of lensing effect in naturally gyrotropic rectangular lenses and compare our results of spatial dispersion, polaritonic approach with those, demonstrated recently by J.B. Pendry (Science,v.306, p.1353) for a negative refraction near electrical dipole resonance.