Terahertz characteristics of Mg-doped CuCrO₂ and its application to 2π phase modulators with high tunable capability

We have conducted a detailed characterization of the optical properties of Mg-doped CuCrO₂ (CuCrO₂: Mg) in the terahertz (THz) frequency range. By utilizing CuCrO₂: Mg as transparent electrodes, we have demonstrated the approach for developing high-transmittance and low-operative-voltage THz phase shifters by electrically tuning liquid crystals (LCs). Unlike traditional indium-tin-oxide thin films, we have applied 600 nm-thick CuCrO₂: Mg thin films as transparent electrodes, and our results show that this material has great potential for THz photonics. Specifically, the transparent electrode with THz transmission of ∼92 % reveals the feasibility of CuCrO₂: Mg as a suitable material for THz photonics applications. The phase shifter scheme, which employs a ∼2.2 mm-thick cell, achieves a THz transmittance ∼70 %, a phase shift of more than 2π at 1.0 THz can be achieved even for low driving voltages of 14 V(rms). By considering the figure of merit (FOM) of LCs phase modulators defined in this work, the device based on CuCrO₂: Mg thin film shows an FOM value of 17.99; much higher than previously reported values. These results suggest that functional electrodes based on CuCrO₂: Mg thin films are promising components of THz and 6 G devices.