The use of scalar diffraction theory is the basis of a fundamental part of diffractive optics. We prefer to call this part digital holography. The consideration of different parts of diffractive optics on the basis of the diffraction theory seems to be a useful criterion to discuss fundamental characteristics of diffractive elements. In digital holography a coding theory has been developed. The theory itself and its consequences are briefly described.
Frank Wyrowski, Frank Wyrowski,
"Digital holography: diffractive optics on the basis of scalar diffraction theory", Proc. SPIE 1718, Workshop on Digital Holography, (5 January 1993); doi: 10.1117/12.138567; https://doi.org/10.1117/12.138567