Appendix: extending the notion of binary optics
Binary optics and their application to imagery Focusing optics

With the development of photolithography, the notion of binary optics can be extended, increasing the number of possible components. A binary component can therefore be considered as an optic that can be produced from a single photolithography mask, or even from a few masks.

Thus, a Fresnel lens can be approximated by a multi-level profile, 2 levels being the initial definition of binary optics; N photolithography steps produce a component composed of 2 ^N phase levels. The result is a discrete multi-level profile made up of N staircases (figure 13 ).