Efficient transport and focusing of optical signal and energy via spiral conical plasmonic tip integrated with optical fiber

Plasmonic nanostructures can help to greatly enhance light-matter interaction that in involved in many energy transfer and transformation processes [1, 2]. Here we discuss design and fabrication of symmetry-broken plasmonic spiral conical tips that enable efficient transport and focusing of optical signal and energy input from optical fiber via surface plasmon polariton (SPP) [3, 4]. Metallic probes with spiral corrugations can be readily fabricated with a 3D direct-laser writing (DLW) method followed by a metal deposition process. With the broken structural symmetry induced by the spiral corrugations, plasmonic focusing into a deep subwavelength size spot is demonstrated under the excitation of linearly polarized light with different polarization directions. Moreover, apertures with various sizes can be flexibly introduced at the apex of the conical probe structures with direct fabrication, which enables the observation of waveguide modes, the cutoff of waveguide modes and scattered light from surface plasmons, respectively. More importantly, such a plasmonic spiral conical tip can be incorporated with a single-mode optical fiber, and this offers a very promising means to build a high-efficiency scanning near-field optical microscopy tip.