Most computer modeling methods for diffraction structures suffer from at least one of
the following problems:
 Excessive computational requirements
 Restrictions to certain geometrical configurations (such as rectangular shaped
structures)

The Surface Impedence Method, as described by Hessel and Oliner*, overcomes these
problems. By finding the wave impedence at the surface of the structure, Z_{s},
one has essentially solved the diffraction problem.

The problem is finding Zs for a particular periodic diffraction structure.


Using the circuit theory anology we find




The whole problem reduces to finding Z_{filter}, which may or may not be easy
to deduce.

* A. Hessel and A. A. Oliner, "A New Theory of Wood's Anomalies on
Optical Gratings", Applied Optics, 4, 12751298, October
1965. 

