Dual Encryption of Terahertz Metasurface by Frequency-Temperature Co-Determination

In recent years, terahertz metasurfaces have becomepowerful tools for manipulating terahertz waves. The rapidadvancement of intelligence and information technology createsa growing demand for tunable and reconfigurable devices inengineering applications to adapt to various scenarios andconditions. Dynamic metasurfaces, with their tunable proper-ties, enable the creation of reconfigurable and programmableelectromagnetic devices, thus advancing the development ofsophisticated multifunctional systems. Apart from techniquesincluding optical pumping of semiconductor materials and micro-electromechanical systems, phase-change materials have alsoemerged as a promising approach for the dynamic modulationof terahertz metasurfaces. In this letter, vanadium dioxide withtwo different phase transition temperatures was integrated into asingle unit. By utilizing the effect of electromagnetically inducedtransparency and prearranging metasurface units according toa specific hologram, an image requiring encryption was encodedinto the metasurface, achieving optical encryption through tem-perature variation. When the temperature is below 60 degrees C,the transmitted light field appears as random spots, devoidof any useful information. However, when the temperaturerises to between 60 degrees C and 72 degrees C and terahertz waves at afrequency of 0.631 THz are incident, the encrypted letter "C"can be reconstructed. When the temperature exceeds 72 degrees C andterahertz waves at a frequency of 0.43 THz are incident, theencrypted letter "E" can be reconstructed. If the conditionsof temperature and frequency are not simultaneously satisfied,no useful information can be obtained. The proposed methodprovides a novel approach for the design of reconfigurableterahertz metasurfaces, with substantial potential for applicationsin optical encryption and anti-counterfeiting technologies.