Identification of the Hermite-Gaussian and Bessel modes of a terahertz beam with diffractive optical elements

Subject of study. A technique for identifying Hermite-Gaussian and Bessel modes using diffractive optical elements is investigated in the terahertz range. The aim of the study is the development and testing of a method for identifying the mode composition of a terahertz radiation beam using binary phase diffractive optical elements for single- and multimode cases. Method. The proposed approach is based on the correlation filtering method. A beam with a high content of the mode under study was formed using the binary phase diffractive element, and then it illuminated the filter system consisting of a similar element and lens. If the forming and filtering elements were the same, a bright spot, the so-called positive response, was observed in the center of the image. Otherwise, radially symmetrically located petals with a dark spot in the center were observed, which corresponds to a negative response. Main results. The experimental results on the identification of Hermite-Gaussian modes [with numbers (1, 0) and (0, 1)] and Bessel modes (with topological charge modulus |l| = 1, 2, 3, 4) in the case of the single-mode beam are introduced. For the case of the multimode beam, a combination of Bessel beams with topological charges - 1 and - 2 was formed. Practical significance. Wireless data transmission at terahertz frequencies (the target frequency range of 6G communications) using multimode Bessel beams will allow a significant increase in the data rate up to the order of Tbits/s. The method described in the paper can be used to decode the signals transmitted in a multimode beam. (c) 2024 Optica Publishing Group