Record-breaking conversion efficiency in a THz nonlinear diode chain using an asymmetric double-layer topology

Abstract The exploitation of radiation in the terahertz (THz) range hinges on the continued development of THz sources. Schottky barrier diode (SBD)--based frequency multiplier devices are one of the most attractive options, as they can produce high power in comparison to direct generation, and can be integrated into all-solid-state systems. Yet, the scaling of the output power of such devices is often limited by the power handling capacity of a single diode. This motivates the idea of forming a connected chain of SBD devices, accompanied by a power combining approach to achieve higher THz output power. While effective, the uneven field distribution among the diodes can pose a significant challenge as it leads to lower efficiency and premature breakdown. This phenomenon is rooted in the similarity between the THz wavelength and the physical dimensions of the diodes themselves. To address this issue, we propose an innovative solution based on an asymmetric double-layer C-type diode chain structure. This arrangement allows for the adjustment of local electromagnetic field distribution, and dramatically enhances the conversion efficiency of the diode chain. Our device achieves the highest frequency doubling efficiency recorded at 38%, with an output exceeding 300 mW at 170 GHz. This design paves the way for a new direction in the development of diode-based THz nonlinear devices.