Design and analysis of broadband diffractive optical element for achromatic focusing

The achromatic diffractive optical element (DOE) was numerically studied. The light intensity distribution in the focal plane was studied by the vectorial diffraction theory, then the radially symmetric DOE to enable broadband achromatic focusing with low sidelobe intensity ratios and uniform central intensities were optimized by the simulated annealing (SA) algorithm. The plane wave with wavelength of 486nm, 588nm, and 656nm were used in our optimization and numerical research. Three DOEs with 60, 80, and 100 transition points were obtained. Numerical results shown that the sidelobe intensity suppression ratios of focal spots of these wavelengths are all less than 0.12, the principal peaks' intensities differences and spots' sizes differences of these focal spots are all less than 5% and 10%, respectively. The designed DOEs were polarization insensitive.