Optical polarizer/isolator based on a rectangular waveguide with helical   grooves
  A chirality-based approach to making a one-way waveguide that can be used as an optical isolator or a polarizer is described. The waveguide is rectangular, and chirality is introduced by making slanted rectangular grooves on the waveguide walls. Chirality of the waveguide manifests as a strong circular dichroism, and is responsible for transmitting one circular polarization of light and reflecting the other. Optical isolation of the propagating circular polarization is accomplished when the chiral waveguide is placed in front of a non-chiral optical device. Even the crudest implementations of chirality are shown to exhibit significant circular dichroism. 
Gennady Shvets