Generating terahertz multiple vortex beams using graphene metasurfaces

• Published in: Optical and quantum electronics 2024-05, Vol.56 (7), Article 1117
• Main Authors: Zainud-Deen, Anas S., Malhat, Hend A., Sebak, Abdel-Razik, Badawy, Mona M.
• Format: Article
• Language: English
• Subjects: Angular momentum; Characterization and Evaluation of Materials; Chemical potential; Computer Communication Networks; Directivity; Electrical Engineering; Electron beams; Graphene; Ground plane; Lasers; Linear polarization; Metasurfaces; Optical Devices; Optics; Photonics; Physics; Physics and Astronomy; Plane waves; Polysilicon; Reflectance; Relaxation time; Silicon dioxide; Silicon substrates; Terahertz frequencies; Unit cell; Wireless communications
• ISSN: 1572-817X; 0306-8919; 1572-817X
• DOI: 10.1007/s11082-024-06994-4

This paper investigates the generation of orbital angular momentum vortex beams using a graphene metasurface in the terahertz frequency band. The proposed design consists of 20 × 20 unit-cell elements to operate in 1.2 THz applications. Each element is a graphene ring patch printed on a silicon dioxide substrate backed with a polysilicon ground plane of size 75 × 75 × 25 µm 3 . The graphene reconfigurable surface conductivity is used to control the beam shape, direction, and directivity radiated from the metasurface, through the application of DC biasing voltages. A parametric study on the effect of graphene chemical potential, relaxation time and temperature on the unit-cell reflection properties is introduced. The reflection magnitude varies from − 2.1 dB to -0.8 dB with a 350-degree phase variation for µ c ranging from 0.25 eV to 1.6 eV at =5 ps, and T  = 300 K. The effect of graphene relaxation time from 0.3 ps to 10 ps on the reflection coefficient at µ c  = 0.7 eV, and T  = 300 K is investigated. The metasurface radiation characteristics are investigated under the illumination of two types of incidence sources, plane-wave, and focused-waves. A depiction of a single vortex beam in various orientations θ = 0, 30 o , 50 o , and 70 o , φ = 90 o for l  = 1 is presented. The purity of the OAM single beam shows that 94% of the power is concentrated in the designed mode. A graphene metasurface can to convert linearly polarized input into multiple beams exhibiting orthogonal modes. Two/four vortex beams in different directions are demonstrated. The capacity for wireless communication in the terahertz band can be enhanced by utilizing a graphene metasurface.