Birefringent rugate filters

The design and fabrication of a birefringent rugate filter (birugate) is discussed. Zirconium oxide was deposited onto a slowly oscillating substrate to produce an optical medium with a sinusoidally modulated columnar microstructure. The modulated medium is inhomogeneous and biaxial, but normally incident beams of p and s polarised light propagate without cross-coupling. The birugate has displaced p and s transmittance peaks, and has potential uses in optical communications