Investigation Of Optimization Methods And Fabrication Of Tilted Multi-focus Fresnel Binary Optical Elements

Binary optical technology has been applied in many fields such as storage, recording and processing of optical information, optical interconnection, multi-channel optical information processing systems and multi-object reconition systems,which need binary optical elements of large depth of focus and multi-focus.Based on the application backgrounds,we investigate optimization methods and fabrication of tilted multi-focus Fresnel binary optical elements.Based on the scalar diffraction theory,physics meaning of Fresnel diffraction is analysed, and tilted multi-focus Fresnel diffractive formula is presented in detail. According to the theory, tilted multi-focus Fresnel binary optical elements are fabricated. The general optimization methods,namely the iterative Fourier transform algorithm and the simulated annealing algorithm,have been discussed and modified to design and fabricate tilted multi-focus Fresnel binary optical elements.Comparison on one-step and multi-step circle algorithm of optimizing multi-focus binary optical element shows both the faster speed and the higher diffraction efficiency can be achieved for the one-step algorithm. We fabricate the tilted multi-focus Fresnel binary optical elements of two phase levels and four phase levels using square-shaped spot photolithographic systems. The experimental results are given.It is very useful for designing multi-focus Fresnel diffraction elements with the presented optimization methods. Both the higher diffraction efficiency and the faster speed can be obtained by our optimization methods, which is proved accurately by our experiments.