Multifunctional device for circular-to-linear polarization conversion and sensing

In this work, a multifunctional metastructure (MS) that combines the functions of a circular-to-linear polarization conversion (PC) and sensing is presented. The device uses a 2 × 2 array of three layers of media as the unit structure to modulate an incident circularly polarized wave into a linearly polarized one by reflection in the terahertz (THz) band. Its output linear polarized wave axial ratio (AR) is larger than 20 dB in the 1.61–2.638 THz range, with a relative bandwidth of 48% and an insertion loss below 4%. In addition, filling the device with liquids of different refractive indices shifts the frequency of the sharp AR peak generated by its output linear polarized wave. Utilizing this property, the device can also be used a refractive index sensor. When the thickness of the liquid to be measured is 2 μm, the device has a frequency sensitivity of 178 GHz/RIU (refractive index unit) and a figure of merit (FOM) of 12.7. Parameters and angles are also discussed and the principle is analyzed through current density plots. The given design can be applied in satellite communication systems, signal modulation, and sensing.