Design of multifunctional diffractive optical elements

Diffractive optics has traditionally been used to transform a parallel beam of light into a pattern with a desired phase and intensity distribution. One of the advantages of using diffractive optics is the fact that multiple functions can be integrated into one element. Although, in theory, several functions can be combined, the efficiency is reduced with each added function. Also, depending on the nature of each function, feature sizes could get finer. Optical lithography with its 1 mu m limit becomes inadequate for fabrication and sophisticated tools such as e-beam lithography and focused ion beam milling are required. Two different techniques, namely, a modulo-2 pi phase addition technique and an analog technique for design and fabrication of composite elements are studied. A comparison of the beams generated in both cases is presented. In order to be able to compare methods, specific functions of ring generation and focusing have been added in all cases. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)