The present talk is devoted to the use of beams with orbital angular momentum (OAM)  for development THz multichannel systems based on the mode division multiplexing (MDM) approach. The work  shows the results of the feasibility study of organizing a multichannel terahertz (THz) communication system based on controlling the transverse-mode composition of a coherent beam of terahertz radiation. In [1,2], however, it was only a question of changing the transverse mode composition without changing the polarization state of the illuminating beam.
In the long run, the development of methods for simultaneous control of the transverse mode composition and polarization state of a terahertz beam will allow developing multichannel terahertz telecommunication systems with high information capacity. In the work , the authors designed, produced, and examined a subwavelength axicon for converting linearly polarized terahertz radiation into a cylindrically polarized beam. In the present talk perspectives of application of terahertz non-uniformly polarized beams for telecommunication are also considered.
This work was supported by the RF Ministry of Science and Higher Education under the government project of the FSRC “Crystallography and Photonics” and by the Russian Foundation for Basic Research (grant 19-07-00423). The experiments were performed at the Shared Research Center SSTRC based on the Novosibirsk FEL.
 Yu.Yu. Choporova, B.A. Knyazev, G.N. Kulipanov, V.S. Pavelyev, M.A. Scheglov, N.A. Vinokurov, B.O. Volodkin, V.N. Zhabin, “High-power Bessel beams with orbital angular momentum in the terahertz range”, Physical Review A, vol. 96(2), 023846, 2017.
 Y.Y. Choporova, B.A. Knyazev, N.D. Osintseva, V.S. Pavelyev, K.N. Tukmakov, “Two-channel terahertz communication based on spatial mode multiplexing, Proceedings of 44th International Conference on Infrared, Millimeter, and Terahertz Waves”, IRMMW-THz, 2019.
 S.N. Khonina, K.N. Tukmakov, S.A. Degtyarev, A.S. Reshetnikov, V.S. Pavelyev, B.A. Knyazev, Yu.Yu. Choporova, “Design, fabrication and investigation of a subwavelength axicon for terahertz beam polarization transforming”, Computer Optics, vol. 43(5), pp.756-764, 2019.