Generation of Subwavelength Plasmonic Nanovortices via Helically Corrugated Metallic Nanowires.

Changming Huang,Abiola O. Oladipo,Fangwei Ye,Nicolae C. Panoiu,Xianfeng Chen

doi:10.1038/srep13089

Changming Huang, Abiola O. Oladipo + Show 3 more

Open Access

https://doi.org/10.1038/srep13089

Copy DOI

Abstract

We demonstrate that plasmonic helical gratings consisting of metallic nanowires imprinted with helical grooves or ridges can be used efficiently to generate plasmonic vortices with radius much smaller than the operating wavelength. In our proposed approach, these helical surface gratings are designed so that plasmon modes with different azimuthal quantum numbers (topological charge) are phase-matched, thus allowing one to generate optical plasmonic vortices with arbitrary topological charge. The general principles for designing plasmonic helical gratings that facilitate efficient generation of such plasmonic vortices are derived and their applicability to the conversion of plasmonic vortices with zero angular momentum into plasmonic vortices with arbitrary angular momentum is illustrated in several particular cases. Our analysis, based both on the exact solutions for the electromagnetic field propagating in the helical plasmonic grating and a coupled-mode theory, suggests that even in the presence of metal losses the fundamental mode with topological charge m = 0 can be converted to plasmon vortex modes with topological charge m = 1 and m = 2 with a conversion efficiency as large as 60%. The plasmonic nanovortices introduced in this study open new avenues for exciting applications of orbital angular momentum in the nanoworld.

Highlights

Is that the diffraction limited propagation of the vortical beams generated by these methods leads to spatially delocalized optical beams with size significantly larger than the operating wavelength
As an effective solution to this problem, in this report we demonstrate that one can generate subwavelength optical vortices by first confining the optical field to subwavelength scale using a metallic nanowire, the highly localized optical mode being converted into an optical vortex by means of a helical grating imprinted on the surface of the nanowire
The generation of subwavelength optical beams with zero angular momentum by using metallic nanowires has been investigated both theoretically[24,25] and experimentally[26], whereas the optical modes of helical gratings made of perfect conductors have been studied in a recent theoretical work[27]

Summary

Helically Corrugated Metallic Nanowires

Changming Huang[1,2], Xianfeng Chen[1,2], Abiola O. The general principles for designing plasmonic helical gratings that facilitate efficient generation of such plasmonic vortices are derived and their applicability to the conversion of plasmonic vortices with zero angular momentum into plasmonic vortices with arbitrary angular momentum is illustrated in several particular cases Our analysis, based both on the exact solutions for the electromagnetic field propagating in the helical plasmonic grating and a coupled-mode theory, suggests that even in the presence of metal losses the fundamental mode with topological charge m = 0 can be converted to plasmon vortex modes with topological charge m = 1 and m = 2 with a conversion efficiency as large as 60%. Our theoretical and computational study presented in this paper suggests that these ideas can be extended to the generation of subwavelength optical vortices, namely one can employ plasmonic helical gratings to convert the fundamental plasmonic mode of a uniform metallic nanowire to an optical beam carrying OAM, the conversion efficiency being as large as 60% even in the presence of optical losses in the metal

Results

Conclusions

Additional Information