We propose a task-specific method for calculating cascaded phase diffractive optical elements (DOEs) for focusing Q incident beams with different wavelengths to Q given points. Due to the utilization of a special optimization criterion, the proposed method makes it possible to calculate the elements of the cascaded DOE in a sequential way. In addition, the calculation of the diffractive microrelief of each DOE in the cascade is reduced to solving a set of independent and computationally simple “pointwise” optimization problems. Using the proposed method, cascades of two DOEs were designed to focus radiation of 11 different wavelengths to 11 different points. The presented numerical simulation results demonstrate good performance of the method. The chosen operating wavelengths correspond to a set of widely used vegetation indices enabling monitoring the vegetation status conditions and tracking the environmental stresses. This makes the obtained results promising for the application in remote sensing and smart agriculture.
