MIMO-type structures for terahertz band

Mateusz Kałuża

supervisor: Ryszard Piramidowicz, Agnieszka Siemion

In the twenty first century, the rapid development of terahertz (THz) technologies is evident and finds more and more applications in many fields of science and industry. Some of these applications will be used in future 6G telecommunication systems, where wireless THz MIMO (Multiple-Input Multiple-Output) systems will find their place.

The design of the MIMO-type structures is based on the diffractive solutions. The diffractive optical elements (DOEs) are designed using the algorithms typical for synthetic holograms and use an iterative algorithm (e.g., ping-pong algorithm). Selecting appropriate parameters and predefining desired results according to demultiplexing phenomenon is crucial for proper performance of the DOE. The solution allows to redirect the incident radiation illuminating DOE and focus it into three separated by 25 mm focal spots. The algorithm generated a phase map described by a grey-scale bitmap defining the phase level in the manufactured structure (Fig 1a). The performance of the designed 3in1 structure was verified in numerical simulations (Fig 1b). Subsequently, the 3D model of the structure was created and manufactured using the additive manufacturing technique FDM (Fused Deposition Modelling). The DOE was fabricated using dedicated algorithm to create STL files and examined in optical setup. Different configurations of SIMO (Single-Input Multiple-Output) structures were proposed and experimentally verified.

Fig. 1 Synthetic hologram generated by ping-pong algorithm used to redirect radiation into three focal spots,
a) grey-scale bitmap corresponding to the phase delay map introduced by the diffractive element,
b) simulation results illustrating the three focal spots in the focal plane,
c) the experimental results plotting the intensity distribution in the focal plane.