STO/PDMS composite film achieving continuously tunable terahertz phase modulation via mechanical and thermal regulation

Phase is the basic property of electromagnetic waves, and controlling the phase is one of the eternal research topics in the field of electromagnetic waves. Here, a broadband terahertz phase shifter made of polydimethylsiloxane (PDMS) and strontium titanate (STO) has been theoretically proposed and experimentally demonstrated. The mixed material design gives the phase shifter the dual properties of PDMS and STO. Therefore, the phase shifter can not only change the thickness through stretching but also change the effective refractive index through temperature changes. The thickness and refractive index changes directly cause the transmission phase of the phase shifter to move synchronously. Because the material does not have frequency selection characteristics, the phase shifter realizes customized phase control in a wide range of the terahertz band. In the experiment, any phase shift can be achieved by adjusting the doping ratio, stretching ratio, and temperature. The proposed broadband phase shifter is simple to fabricate and has various control methods, which provides a variety of modes of terahertz wave phase modulation.