The thin element approximation is widely used to predict the diffraction efficiency of thin periodic diffractive optical elements (DOEs). However, as the period-to-wavelength ratio is reduced, the approximation becomes inaccurate. A model based on a "shadow concept" can be used to predict the diffraction efficiency with high accuracy. Hereby we extend the model to include the effect of multi-level staircase structures and non-perpendicular incident angles. We also present an error map and define regions of validity for the thin element approximation (TEA) and the shadow model.
- Blazed gratings