Frequency Division Multiplexing of Terahertz Waves Realized by Diffractive Optical Elements

Abstract

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.

Analysis and Experiment of Wireless Optical Communications in Applications Dedicated to Mobile Devices with Applicability in the Field of Road and Pedestrian Safety

“…Table 1 shows the OCC reference implementations with notable results, using smartphones, but also DSLR cameras, highlighting the problems or limitations they faced. The most relevant systems tested in the OCC direction based on OCC used combined modulation schemes and ON/OFF coding in the form of phase shift subsampling (UPSOOK), and the processing used multiplexing with a division into wavelengths (WDM) [48,49]. These aspects have reached quite decent distances near the communication area of 1.5-2 m, but the transfer rate is between 378 bps and 480 bps [50].…”

Segmentation of THz holograms for homogenous illumination

“…Additionally, high-order kinoforms allow one to obtain relatively thin solutions and, therefore, introduce fewer losses due to absorption in the material. Diffractive optical elements (DOEs) also provide a unique possibility of multiplexing 12 – 14 —especially dividing their surface into segments, each realizing different functions, such as drawing separate parts of a letter at the output plane 15 . Applying DOEs for uniform illumination was previously reported 16 .…”

Subwavelength Diffractive Optical Elements for Generation of Terahertz Coherent Beams with Pre-Given Polarization State

“…Structuring radiation from new sources in the terahertz range, including high-power ones, such as free-electron lasers (FELs) [ 41 ], requires optical elements designed with consideration of the features of such radiation, including wavelength and high-power density [ 42 , 43 , 44 , 45 ]. A good overview of the recently invented terahertz optical structures based on diffraction design is presented in [ 46 ].…”

“…A good overview of the recently invented terahertz optical structures based on diffraction design is presented in [ 46 ]. The fabricated diffractive optical elements (DOEs) were used to focus [ 42 , 43 , 47 , 48 , 49 ] and split [ 45 , 50 , 51 ] the terahertz laser beam, as well as to control the transverse-mode composition of the beam [ 52 , 53 , 54 ]. In particular, silicon binary elements were used to transform the illuminating beam of a high-power free-electron terahertz laser into the Hermite–Gaussian, Laguerre–Gaussian, and Bessel single-mode beams [ 52 , 54 ].…”