Demonstration of Computational THz Diffractive Optical Elements Enabled by a Modified Direct Binary Search Technique

Computational diffractive optics is a powerful tool for designing THz optical elements. Furthermore, an optimization based modified search algorithm can enable us to find optimal solutions much faster than what is possible by employing search algorithms. In view of this, the proposed gradient descent optimization based modified binary search algorithm cannot just enable a faster convergence (up to l0-l00X), but also allows us to increase the dimension of the search space, thus the number of degrees of freedom on the problem, which can lead to much better design performance. Using this approach, we demonstrate a series of ultra-thin (1.5-3λ0), error-tolerant and efficient THz optical elements including (i) large N.A. 1D and 2D lenses for aberration-rectified narrow and broadband focusing and (ii) the THz equivalent of an optical spectrometer, i.e. a structure focusing different THz frequencies at different points in space. We present experimental results performed using 3D printed structures, which are backed by full wave simulations.