Design of diffractive phase elements that implement axial intensity modulations with conjugate gradient algorithm

摘要

We employ conjugate gradient algorithm for designing diffractive phase elements (DPEs) that implement the predefined axial-intensity modulations over a given region. We introduce an error function used for guiding the design of DPEs and appraising their performance. We derive the analytical expression for the gradient of the error function with respect to the phases of DPEs. To demonstrate effectiveness of the related algorithms, we carry out model designs of several DPEs that realize different axial- intensity modulations. For instance, we achieve the designs of the DPEs for focusing incident uniform wave into four foci with equal or unequal spacing between the consecutive foci along the optical axis, and the DPE for realizing sinusoid-like axial-intensity modulation over a given region. We also present the designs of the DPEs for generating pseudo-nondiffracting beams with multiple-segment character. The results show that the designed DPEs can satisfactorily fulfill the practical requirements.