Negative refraction of photonic and polaritonic waves in periodic structures

Negative refraction can be achieved in photonic crystals. We briefly summarize recent studies in this field, and show that such effects are also possible in polaritonic and plasmonic structures, such as the dipole crystal. We propose a practical realization of this crystal, a periodic lattice of dielectric spheres. We study its mode structure, and preliminary results demonstrate the negative refraction on a polaritonic band.