Abstract
The capability to focus electromagnetic energy at the nanoscale plays an important role in nanoscinece and nanotechnology. It allows enhancing light matter interactions at the nanoscale with applications related to nonlinear optics, light emission and light detection. It may also be used for enhancing resolution in microscopy, lithography and optical storage systems. Hereby we propose and experimentally demonstrate the nanoscale focusing of surface plasmons by constructing an integrated plasmonic/photonic on chip nanofocusing device in silicon platform. The device was tested directly by measuring the optical intensity along it using a near-field microscope. We found an order of magnitude enhancement of the intensity at the tip's apex. The spot size is estimated to be 50 nm. The demonstrated device may be used as a building block for "lab on a chip" systems and for enhancing light matter interactions at the apex of the tip.
Highlights
Localization of optical energy at the nanoscale by using surface plasmon polariton (SPP) modes has been proposed and investigated in various applications: nanosensing [1,2], microscopy [3,4] and quantum optics [5,6]
In the past ten years different geometries of SPP waveguide for light concentration were studied and demonstrated like thin films [7], channel and v-grove waveguides [8,9,10], metal-dielectric-metal (MDM) and dielectric-metal-dielectric (DMD) waveguides [11,12,13]
We designed, fabricated and empirically demonstrated the on-chip integration in silicon platform between a photonic waveguide and a plasmonic nanotip for the purposes of obtaining field enhancement and nanoscale spot size at the apex of the tip. Both the photonic waveguide and the plasmonic nanofocusing device are made of silicon, where the later is surrounded by a metallic cladding from its both sides
Summary
Localization of optical energy at the nanoscale by using surface plasmon polariton (SPP) modes has been proposed and investigated in various applications: nanosensing [1,2], microscopy [3,4] and quantum optics [5,6]. Further enhancement of electromagnetic energy density via nanoscale focusing of surface plasmon waves has been proposed and demonstrated by using different approaches such as metallic plasmonic lenses [14,15,16], tapered metallic probes [17,18,19,20,21,22], metallic coated dielectric tips [23,24] and other sub-wavelength structures [25,26,27]. In this paper we present the realization (design, simulation, optimization, fabrication and measurement) of an on-chip integrated approach by coupling light from the silicon photonic platform directly into the plasmonic nanoscale focusing device. The electromagnetic energy is first propagating in the dielectric waveguide, coupled into the MDM tip and is being concentrated at the apex of the tip. A schematic drawing of our device with the calculated electromagnetic intensity distribution is presented in Fig. 1a and Fig.1b
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