Asymmetric coupling and dispersion of surface-plasmon-polariton waves on   a periodically patterned anisotropic metal film
  The morphology of a columnar thin film (CTF) of silver renders it an effectively biaxially anisotropic continuum. CTFs of silver deposited on one-dimensional gratings of photoresist showed strong blazing action and asymmetrically coupled optical radiation to surface plasmon-polariton (SPP) waves propagating only along one direction supported by either the CTF/photoresist or the CTF/air interfaces. Homogenization of the CTFs using the Bruggeman formalism revealed them to display hyperbolic dispersion, and the dispersion of SPP waves was adequately described thereby. 
Jhuma Dutta, S. Anantha Ramakrishna, and Akhlesh Lakhtakia
physics.optics