Optical‐to‐Terahertz Conversion Efficiency Enhancement in Plasmonic Photoconductive Antennas Using a Branch‐opening Split Ring Resonator

Abstract This study demonstrates that a plasmonic triangular nanoarray could significantly enhance the optical absorption and carrier generation rate in photoconductive antennas (PCAs), achieving a photoelectric conversion efficiency of 0.62%, which is 2.82 times that of the traditional designs. However, equivalent circuit analysis reveals a critical drawback: the plasmonic structure drastically reduces the source impedance, leading to a severe impedance mismatch with the dipole antenna and ultimately limiting the overall optical‐to‐terahertz conversion. To overcome this limitation, frequency‐dependent impedance of various split‐ring resonators was systematically investigated via finite element simulation. The results identified the split‐ring resonator structures could achieve higher impedance matching efficiency. Consequently, a new branch‐opening split‐ring resonator (BSRR) antenna was developed. Integration of the BSRR with the plasmonic triangular nanoarray elevated the impedance matching efficiency from 30.13% to 71.44%. Furthermore, the BSRR‐based PCA exhibits a high radiation efficiency of 94.32%, as verified by the simulated radiation gain and directivity. The final integrated device achieves an optical‐to‐terahertz conversion efficiency of 0.42%, which is 2.96 times greater than that of the plasmonic PCA without a split‐ring resonator. This work provides a viable strategy for developing high‐performance terahertz photoconductive sources, with considerable theoretical and practical implications.