Manipulating surface-plasmon-polariton launching with quasi-cylindrical waves

Chengwei Sun,Qihuang Gong,Jianjun Chen,Hongyun Li,Wenjie Yao

doi:10.1038/srep11331

Abstract

Launching the free-space light to the surface plasmon polaritons (SPPs) in a broad bandwidth is of importance for the future plasmonic circuits. Based on the interference of the pure SPP component, the bandwidths of the unidirectional SPP launching is difficult to be further broadened. By greatly manipulating the SPP intensities with the quasi-cylindrical waves (Quasi-CWs), an ultra-broadband unidirectional SPP launcher is experimentally realized in a submicron asymmetric slit. In the nano-groove of the asymmetric slit, the excited Quasi-CWs are not totally damped, and they can be scattered into the SPPs along the metal surface. This brings additional interference and thus greatly manipulates the SPP launching. Consequently, a broadband unidirectional SPP launcher is realized in the asymmetric slit. More importantly, it is found that this principle can be extended to the three-dimensional subwavelength plasmonic waveguide, in which the excited Quasi-CWs in the aperture could be effectively converted to the tightly guided SPP mode along the subwavelength plasmonic waveguide. In the large wavelength range from about 600 nm to 1300 nm, the SPP mode mainly propagates to one direction along the plasmonic waveguide, revealing an ultra-broad (about 700 nm) operation bandwidth of the unidirectional SPP launching.

Highlights

Holes) and play an important role in nanoscale structures and devices[33,34,35,36,37]
The excited SPPs in the nano-groove can be reflected back and forth off the metal walls, and each round trip can contribute to the SPPs along the metal surface
The SPPs dominate the Quasi-CWs in the visible regime[29], the conversion efficiency of CW-to-SPP becomes large at short wavelengths[32], and the transmittance of the original SPPs in the 400-nm-deep groove to the SPPs along the front metal surface (SPP-to-SPP) becomes very small (10% at λ = 650 nm for the 400-nm-deep groove on the metal surface)

Summary

Introduction

Holes) and play an important role in nanoscale structures and devices[33,34,35,36,37]. By adjusting the slit width, the SPPs scattered from the Quasi-CWs will interfere destructively with that scattered from the SPPs in the nano-groove. This greatly manipulates the SPP intensity along the front metal surface. The propagation direction of the excited SPPs in the asymmetric nanoslit is altered, and broadband unidirectional SPP launching is realized theoretically and experimentally. This principle can be extended to 3D models, in which the Quasi-CWs near the aperture can be effective converted to the tightly guided SPP mode along the subwavelength plasmonic waveguide

Methods

Results

Conclusion