Advanced diffractive optical elements implementing multiple-input spatial multiplexing of terahertz radiation

Abstract

Listen

Translate article

In recent years, there has been growing interest in the utilization of terahertz (THz) technologies in telecommunications applications. In such systems, radiation multiplexing is required. In one of the solutions, multiplexing can be achieved through the application of appropriate passive optical components. In this study, three different designs of passive diffractive optical elements (DOEs) that meet the functionality of spatial multiplexing of THz radiation are presented. The functionality was achieved by combining two spatially separated optical channels into a single optical path with an addition of the focusing effect, creating multiple-input single-output (MISO) system performance. Two structures were designed as various combinations of off-axis segmentation of kinoform focusing lenses with particular shifts. However, the distribution of the third structure was created with the interactive algorithm. The performance of all structures was verified with numerical simulations using propagation based on the modified convolution method, giving promising results. In this study, the novel, specially dedicated method of 3D modeling was applied. MISO structures were manufactured using fused deposition modeling (FDM) 3D printing technology from styrene-butadiene copolymer (SBC) material, which is remarkably transparent for the THz radiation range (its absorption coefficient value is less than 1 cm−1 in the range up to 750 GHz). The manufactured structures were examined in the experimental setup. All three MISO structures demonstrated proper functionality by redirecting and focusing radiation from two spatially separated radiation sources into the single focal spot located on the main optical axis. However, the structure designed with the iterative algorithm significantly surpassed the performance of the other structures. This structure redirected over two times higher intensity in the desired manner and exhibited approximately 68.12% higher relative efficiency compared to the others. The structure designed with an iterative method is recommended for further investigation and future application in 6G telecommunication systems.