Plasmonic Chain waveguides

Plasmonic Chain waveguides

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  Plasmonic chain waveguides R.Gandhimathi
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  ▪A structure whichguides light wave by limiting it to travel along a desired path ▪Waveguide contains a region of increased refractive index(core), compared with the surrounding medium (cladding) ▪An electromagnetic energy to be carried by a waveguide is injected into one end of the waveguide ▪The electric and magnetic fields associated with the signal bounce off inside walls back and forth as it progresses down the waveguide Optical wave guide Guided waves Insulation CoreCladding Core Refractive index ncladding < ncore Light entering is trapped as long as cladding core n sin n  
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  ▪ Plasmonics dealswith coupling Light to Nanoscale via Surface Plasmons (SPs) ▪ SPs are identified as optical modes at metal/dielectric interface and are characterized in terms of dispersion and spatial profile ▪ Both surface plasmon polaritons and localized surface plasmon modes support low-loss light wave propagation at subwavelength size ▪ Surface plasmonic waveguides have the ability to confine light at sub-wavelength scale ▪ Plasmon Waveguide can squeeze the optical signal by shrinking its wavelength by a factor of 10 or more and have a large number of applications in the field of nanocircuits, nanophotonics devices, biological and chemical sensors, holography, and other applications Plasmonic Waveguide
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  Different plasmonic waveguidestructures ▪ Layered structures ▪ Metallic nanowires ▪ Metallic nanoparticle arrays ▪ Metallic nano particles chain ▪ Channel plasmon polariton waveguides ▪ Wedge plasmon-polariton waveguides Plasmonic waveguide structures Metallic nanowires and nano-grooves support guided plasmonic modes and can be used as subwavelength waveguides of optical signal.
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  ▪ Nanoscale plasmonicwaveguides composed of metallic nanoparticles are capable of guiding electromagnetic energy below the optical diffraction limit ▪ Linear chains of plasmonic (silver or gold) nanoparticles concentrate the optical beam in a narrow region of space, in large part filled by lossy metal ▪ Energy transfer via dipolar interactions between closely spaced metal nano particles supports localized surface plasmons (LSP) and leads to the formation of a waveguide ▪ The coupling among the guided modes may improve the guidance performance Plasmonic Chain Waveguide Coupled mode theory is used in order to study systems of interacting plasmonic spheres
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  Factors to beconsidered ▪ Dynamic interaction among the infinite number of nanoparticles composing the linear arrays ▪ Realistic presence of losses and the frequency dispersion of the involved plasmonic materials Advantages ▪ longer propagation lengths ▪ More confined beams ▪ Design flexibility ▪ Easy construction within current nanotechnology ▪ the realization of such ultracompact waveguides ▪ operating analogously to transmission-line segments at lower frequencies Disadvantages ▪ strong sensitivity to material and radiation losses
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  Field enhancementField enhancement ➢In assembled metal nanoparticles, plasmons on the particles interact with each other to give characteristic spatial distributions of the electric field. ➢ Interparticle coupling associated with a strong induced charge in the hotspot enhance the field in the gap many times and this enhancement is much larger than the field enhancement close to a single nanoparticle. Nano particle dimer
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  • If thesize of nanoparticles is much smaller than the wavelength of the incident electromagnetic radiation, particles will behave as point dipoles • The excitations in nano particle dimer are recognized using dipole approximations. I.e. transverse and longitudinal modes • Depending on the polarization direction of the exciting light, it leads to a blue-shift of the plasmon resonance for the excitation of transverse modes, and a red-shift for longitudinal modes Dipole moments perpendicular to x-axis Transverse modes Dipole moments along the x-axis. longitudinal modes
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  E12 -Field generatedby the dipole 2 at the point dipole 1 E21 -Field generated by the dipole 1 at the point dipole 2 1, 2-Polarizability of the two nanoparticles 1 1 2 2 2 1 ( ) ( ) T T P g P P g P     = = 3 0 1 4 Tg a = −Coupling constant gT -Inverse cube of distance between the dipoles 1 1 12 2 2 21 ( ) ( ) P E P E     = = Induced Dipole moment 21 1TE g P= 12 2TE g P=&Where ➢Particle size and the distance between the particles are less than incident light wavelength ➢Dipoles interaction with each other and the incident field, giving rise dipole polarizations ➢All Scattering quantities can be obtained from these polarizations Interaction of dipole moments
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  T+ P1=P2 - symmetric Highfrequency Mode Low frequency Mode T+ T− Eigen frequencies of the modes & P1= -P2-antisymmetric modes T− 0 01T Tg   =  The eigen states or polarization states 3 0 3T R g a  = 3 0 3 1T R a   =  3 0 3 2 L R g a  = 3 0 3 2 1L R a   =  gL=2gT Dipole moments in same direction Opposite direction Transverse modes Longitudinal mode Frequency vs distance between he two metal nanoparticles Longer the distance between the particles, then weaker coupling gL –two times the transverse field
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  , 1 ,1 1 10 12 , 1 1 , 1 1 1 1 ( )( ) 1 ( )( ) ( ) ( ) n n n n n n n T n n n T n n T n n P E E n P E E E g P E g P P g P P       − + − − + + − + = + = = + = = = + Nanoparticle chain ➢ Each metal nanoparticle acts a dipole ➢ Only nearest neighbor interaction is considered . i.e., ➢ Particle n interacts with (n+1) and (n-1) particles only two particles ➢ The dipole moment of nth particle is defined by the fields generated by (n+1) & (n-1) particles n-1 n n+1 Guided wave propagation along linear arrays of plasmonic nanoparticles
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  ➢ When metalnanoparticles are assembled, interaction between plasmons on each one of the particles, through the electromagnetic field, becomes prominent. ➢ Interference between the plasmon-induced electric field also occurs. ➢ As a result, the assembled system shows totally different optical characteristics from isolated nanoparticles. ➢ Direct imaging of the electric-field distribution in such assembled nano particles gives the understanding of behavior of plasmons and a guiding principle to design and control plasmonic systems
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  Volker J Sorger,Rupert F Oulton, Ren-Min Ma, Xiang Zhang, Toward integrated plasmonic circuits, July 2012, DOI: 10.1557/mrs.2012.170 Weijia Wang, Mohammad Ramezani , AaroI. Väkeväinen , Päivi Törmä , Jaime Gómez Rivas, Teri W. Odom, “The rich photonic world of plasmonic nanoparticle arrays”, Materials Today d Volume 21, Number 3 d April 2018 M. Fevrier* P. Gogol, A. Aassime, R. Mégy, P. Beauvillain, J. M. Lourtioz, and B. Dagens*, “Integration of short gold nanoparticles chain on SOI waveguide”. Mohammed Alsawafta,MamounWahbeh, and Vo-Van Truong, “PlasmonicModes and Optical Properties of Gold and Silver Ellipsoidal Nanoparticles by the Discrete Dipole Approximation”, Journal of Nanomaterials, Volume 2012, doi:10.1155/2012/457968 Andrea Alù1,*, Pavel A. Belov2,3, and Nader Engheta, “Coupling and Guided Propagation along Parallel Chains of Plasmonic Nanoparticles”. References
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  Thnk you