Dual-channel linear-to-circular polarization conversion based on a photonic time crystal

The manipulation of electromagnetic (EM) waves in the time dimension provides a higher degree of freedom in controlling these waves, which has led to significant research in the field of time-varying media. Previous studies on polarization conversion in time-varying media have achieved line-to-line polarization conversion, altering the direction of EM wave vibration. This paper proposes a dual-channel linear-to-circular polarization conversion (DLCPC) that transforms linear polarization waves into circular polarization waves in both the forward and backward directions. Additionally, it is shown that DLCPC can be achieved within the bandgaps of both s-waves and p-waves, enabling a controlled wave amplification effect. The theoretical results, calculated using the transmission matrix method, are compared with numerical verifications based on the finite-difference time-domain method, confirming the validity of the findings. This study expands the research scope in the field of photonic time crystals (PTCs), demonstrating the use of PTCs for DLCPC, and establishes a relationship between this conversion and the wave amplification effect of the PTCs. The controlled wave amplification effect is achieved without impacting the DLCPC.