High-efficiency surface plasmon meta-couplers: concept and microwave-regime realizations

Abstract

Surface plasmon polaritons (SPPs) and their low-frequency counterparts (i.e., spoof SPPs on artificial surfaces) have recently found numerous applications in photonics, but traditional devices to excite them (such as gratings and prism couplers) all suffer from problems of inherent low efficiency because the generated SPPs can decouple, returning to free space, and reflections at the device surface can never be avoided. Here, we propose a new SPP excitation scheme based on a transparent gradient metasurface and numerically demonstrate that it exhibits inherently high efficiency (~94%) because the designed meta-coupler suppresses both decoupling and surface reflections. As a practical realization of this concept, we fabricated a meta-coupler for operation in the microwave regime and performed near-field and far-field experiments to demonstrate that the achieved excitation efficiency for spoof SPPs reaches ~73%, which is several times higher than that achieved by other available devices in this frequency domain. Our findings can motivate the design and fabrication of high-performance plasmonic devices to harvest light–matter interactions, particularly those related to spoof SPPs in the low-frequency domain. A meta-coupler in the microwave regime that has a high excitation efficiency for spoof surface plasmon polaritons (SPPs) has been made. Due to their local field enhancement and subwavelength confinement, SPPs are finding applications in many photonics applications, but conventional devices for producing them suffer from low excitation efficiencies. Now, a research team in China led by Lei Zhou has proposed a new scheme for generating SPPs that employs a transparent gradient metasurface. Numerical analysis predicts that the scheme will have a high generation efficiency of 94% since both decoupling and reflection are suppressed at the surface. The researchers demonstrated the concept experimentally by constructing a metacoupler in the microwave regime that had an excitation efficiency for spoof SPPs of about 73% – several times higher than those of other devices in this frequency region.