5. Appendix: extending the notion of binary 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 ).