Efficiency improvement of THz overmoded surface wave oscillator by circular spoof surface plasmon polaritons coupler

Abstract

The terahertz surface wave oscillator (SWO) faces the problem of the low energy conversion efficiency due to the fact that working mode is the surface wave but the output mode is the volume wave, and it is very difficult to extract the terahertz wave efficiently. In the meantime, the possibility of the RF breakdown increases as a result of the intense electric field on the surface of slow wave structures (SWSs). To overcome these problems, the field distribution in the SWSs of the 0.147 THz relativistic SWO is analyzed in this paper, and the results indicate that the electric field distribution in the SWSs is similar to that in spoof surface plasmon polaritons (SSPPs). In order to improve the energy conversion efficiency of the SWO, we propose to adopt the circular SSPP coupler with tapered gratings at the end of the uniform SWSs, which is implemented to smoothly bridge the surface wave and guided wave. Second, the SWO with the coupler is simulated using particle-in-cell code UNIPIC. The simulation results indicate that the output terahertz power enhances 52% after the SSPP coupler is used. More importantly, the numerical results demonstrate that the intensity of the electric field decreases 25% on the corrugation surface of the SWSs, so the RF breakdown can be avoided in the terahertz relativistic SWO.