Study of thin, achromatic diffractive structures to focus terahertz radiation on a detector

Thin and lightweight achromatic focusing elements with F-number close to 1 are desirable in many practical applications. We present the idea to use diffractive structures designed to work for the substantially increased THz frequency range. The paper analyses mono- and multi-focal lenses forming point-like foci as well as axicon and light sword optical elements focusing THz radiation into line segments located along the optical axis. We consider diffractive elements in a form of the first and the second order kinoforms having various thicknesses. Designed and fabricated elements were numerically and experimentally examined to verify their achromatic functioning. We present point spread functions (XY scans) and 2D energy maps (XZ scans) for different THz frequencies. Moreover, a diagram of chromatic aberration is created by registering energy distribution along the optical axis for different frequencies. The distance corresponding to the highest energy is chosen for each frequency. Therefore, we can compare broadband working of designed structures. The spherical lens coded as kinoform of the second order provides the best broadband functioning, however it is two times thicker than structures providing extended depth of focus (light sword and axicon) working with slightly smaller efficiency but being much thinner

Frequency Division Multiplexing of Terahertz Waves Realized by Diffractive Optical Elements

Recently, one of the most commonly discussed applications of terahertz radiation is wireless telecommunication. It is believed that the future 6G systems will utilize this frequency range. Although the exact technology of future telecommunication systems is not yet known, it is certain that methods for increasing their bandwidth should be investigated in advance. In this paper, we present the diffractive optical elements for the frequency division multiplexing of terahertz waves. The structures have been designed as a combination of a binary phase grating and a converging diffractive lens. The grating allows for differentiating the frequencies, while the lens assures separation and focusing at the finite distance. Designed structures have been manufactured from polyamide PA12 using the SLS 3D printer and verified experimentally. Simulations and experimental results are shown for different focal lengths. Moreover, parallel data transmission is shown for two channels of different carrier frequencies propagating in the same optical path. The designed structure allowed for detecting both signals independently without observable crosstalk. The proposed diffractive elements can work in a wide range of terahertz and sub-terahertz frequencies, depending on the design assumptions. Therefore, they can be considered as an appealing solution, regardless of the band finally used by the future telecommunication systems

Investing in Distributed Generation Technologies at Polish University Campuses during the Energy Transition Era

The functioning of universities during the energy transition can be quite a challenge for them. On one hand, it is necessary to pursue a sensible policy of sustainable development based on the growth of their own renewable energy sources and electricity storage facilities. The aim of such measures is to increase self-consumption and ensure partial energy self-reliance while reducing carbon dioxide emissions into the atmosphere. On the other hand, the current geopolitical situation has indicated significant problems in the energy sectors of European Union countries. From the point of view of decision-makers at universities, the main concern should be ensuring the continuity of the operation of such a facility, including ensuring the energy security of the sites under management. Thus, it is necessary to merge these two areas and consider the development of an energy management strategy on university campuses oriented towards the development of distributed generation resources. For this purpose, one of the methods of multi-criteria decision aiding the ELECTRE I was used. As a result of the analyses, an energy management strategy was established for the main campus of the Warsaw University of Technology, which simultaneously ensures energy security and sustainability efforts