10 Surface plasmon dispersion for thin films Drude modelε1(ω)=1-(ωp/ω) 2Two modes appearThinner film:Shorter SPwavelengthPropagationlengths: cm !!!(infrared)Example:HeNe = 633 nmSP = 60 nmL-L-(symm)L+(asymm)
11 Cylindrical metal waveguides kEzrEFundamentalSPP modeon cylinder:Can this adiabatic coupling scheme be realized in practice?Now when we let a small nanowire extend from this tip, the taper can serve as a coupling element to excite a wave propagating on the nanowire. This design is difficult to fabricate and integrate, however, so instead we will consider a structure that can be fabricated with standard planar lithography techniques, namely a laterally tapered metal stripe waveguide. To understand how to realize a similar adiabatic coupling in this geometry, we need to find the mode in the metal stripe that transforms to the nanowire mode as the stripe narrows.taper theory first demonstrated byStockman, PRL 93, (2004)
12 Delivering light to the nanoscale +1 µm|E|nanoscaleconfinementField symmetry at tip similar to SPP mode in conical waveguidekExzOptics Express 16, 45 (2008)Ewold Verhagen, Kobus Kuipers
13 Concentration of light in a plasmon taper: experiment AuErAl2O3λ = 1.5 μmEwold Verhagen, Kobus Kuipers
14 Concentration of light in a plasmon taper: experiment 60 nm apex diam.(1490 nm)Er3+ energy levelstransmission1 µm10 µmPL Intensity (counts/s)lexc = 1490 nmNano Lett. 7, 334 (2007)Ewold Verhagen, Kobus Kuipers
15 Concentration of light in a plasmon taper: experiment Detecting upconversion luminescence from the air side of the film (excitation of SPPs at substrate side)550 nm660 nmkExzPlasmonic hot-spotTheory: Stockman, PRL 93, (2004)Optics Express 16, 45 (2008)Ewold Verhagen, Kobus Kuipers
16 FDTD Simulation: nanofocussing to < 100 nm symasymEt, H|E|2z = -35 nm1 µm+En1 = 11 µmn2 = 1.74starttipNanofocusing predicted: 100 x |E|2 at 10 nm from tip3D subwavelength confinement: 1.5 µm light focused to 92 nm (/16)limited by taper apex (r=30 nm)Saturating scaleThe structure is excited by a SP mode at the substrate side of the film, just like in the experiment. When we look at the resulting field intensity in the plane of the Er ions, we see that SPs are indeed concentrated at the tip, to a dimension much smaller than the wavelength The width of this spot is 92 nm, and this number is limited by the rounding radius that we used to reflect the finite sharpness of the tip in the experiment. At a depth of 10 nm below the tip, the intensity is enhanced by a factor 100, which is btw not visible in this saturated color scale.Optics Express 16, 45 (2008)Ewold Verhagen, Kobus Kuipers
18 FIB milling of coaxial waveguides <w>=100 nm, L=485 nm<w>=50 nm, L=485 nm100 nm100 nmSilica substrates with nm thick AgRing width: nmTwo-step milling process~7° taper angleNano Lett. 9, in press (2009)René de Waele, Stanley Burgos18
19 Narrow channels show negative index Excitation above resonance, w>wsp25 nm-wide channel in Ag filled with GaPSimulation shows negative phase velocity with respect to power flowNegative refractive index of -2René de Waele, Stanley Burgos
20 Positive and negative index modes René de Waele, Stanley Burgos
21 Plasmonic toolbox: , (), d - Engineer () Plasmonic integrated circuitsPlasmonic multiplexerPlasmonic concentratorPlasmonic lensthin sectionAnd much more …..
22 Conclusions: surface plasmon polariton Surface plasmon: bound EM wave at metal-dielectric interfaceDispersion: (k) diverges near the plasma resonance: large k, small Control dispersion: control (k), losses, concentrationManipulate light at length scalesbelow the diffraction limit
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