Terahertz liquid crystal phase shifter controlled by graphene transparent electrode

Graphene films are characterized by high electrical conductivity and high optical transmittance. In this paper, we mixed graphene solution and polyvinyl alcohol (PVA) solution to make different concentrations of graphene solution. The electrical conductivity, optical transmittance, and phase shift of multilayer graphene films were measured in the THz range by coating graphene solution on the substrate. According to experimental results, the following conclusions are drawn: the film with a larger proportion of graphene has a smaller square resistance, that is, a better conductivity, a smaller transmittance, and a phase shift in the terahertz range under the same thickness. Subsequently, the solution made of 1:1.75 PVA and graphene solution was coated on the outside of the glass sheets containing E7 and HTD liquid crystals, respectively. The distance between the two glass sheets was 800um, which was the thickness of the liquid crystals. Then, a magnetic field is added along one side of the glass sheet (defined as the X direction). Through experiments, it is found that when the voltage is added to 100V (130V), the orientation of E7 (or HTD) liquid crystal can completely change the direction of the electric field. And in the case of the only magnetic field, E7 (or HTD) liquid crystal produces 0.5π phase difference corresponding frequency is 0.8THz (0.6THz), π phase difference corresponding frequency is 1.4THz (1.0THz).