Development of terahertz two-dimensional phase gratings based on a high-accuracy phase retrieval algorithm

High efficiency and accuracy phase gratings are of crucial importance for large format heterodyne array receivers at terahertz frequencies. Here, by developing a design approach that can create gratings with arbitrary two-dimensional diffraction distributions, we have realized a reflective metallic phase grating that generates 2×2 diffraction beams at 0.85 THz. The measured total power efficiency of the diffraction beam pattern is 81.9%, which demonstrates at least 17% improvement in efficiency compared with the standard pseudo-2D Fourier phase grating. In addition, we report the realization of the so called the non-zero padding Gerchberg-Saxton (GS) algorithm, which can create phase gratings generating diffraction distributions with high intensity accuracy. By analyzing the modified algorithm with different padding values, the relation between total diffraction efficiency and intensity distribution accuracy is evaluated. For a 100-pixel two-dimensional phase grating, the non-zero padding GS algorithm outperforms the standard GS algorithm by one orders of magnitude in accuracy of the intensity profile. The results pave the way for the development of large-pixel terahertz multi-beam heterodyne receivers.