Plasmonics

{{main|Surface plasmon|surface plasmon polariton|localized surface plasmon}}

Plasmonics typically utilizes surface plasmon polaritons (SPPs),{{cite journal|last1=Maier|first1=S. A.|last2=Brongersma|first2=M. L.|last3=Kik|first3=P. G.|last4=Meltzer|first4=S.|last5=Requicha|first5=A. A. G.|last6=Atwater|first6=H. A.|title=Plasmonics-A Route to Nanoscale Optical Devices|journal=Advanced Materials|volume=13|issue=19|year=2001|pages=1501–1505|doi=10.1002/1521-4095(200110)13:19<1501::AID-ADMA1501>3.0.CO;2-Z|bibcode=2001AdM....13.1501M }} that are coherent electron oscillations travelling together with an electromagnetic wave along the interface between a dielectric (e.g. glass, air) and a metal (e.g. silver, gold). The SPP modes are strongly confined to their supporting interface, giving rise to strong light-matter interactions. In particular, the electron gas in the metal oscillates with the electro-magnetic wave. Because the moving electrons are scattered, ohmic losses in plasmonic signals are generally large, which limits the signal transfer distances to the sub-centimeter range,{{cite journal | last=Barnes | first=William L | title=Surface plasmon–polariton length scales: a route to sub-wavelength optics | journal=Journal of Optics A| volume=8 | issue=4 | date=2006-03-21 | doi=10.1088/1464-4258/8/4/s06 | pages=S87–S93}} unless hybrid optoplasmonic light guiding networks,{{cite journal | last1=Boriskina | first1=S. V. | last2=Reinhard | first2=B. M. | title=Spectrally and spatially configurable superlenses for optoplasmonic nanocircuits | journal=Proceedings of the National Academy of Sciences| volume=108 | issue=8 | date=2011-02-07 | doi=10.1073/pnas.1016181108 | pages=3147–3151| pmid=21300898 | pmc=3044402 | arxiv=1110.6822 | bibcode=2011PNAS..108.3147B |doi-access=free}}{{cite journal | last1=Ahn | first1=Wonmi | last2=Hong | first2=Yan | last3=Boriskina | first3=Svetlana V. | last4=Reinhard | first4=Björn M. | title=Demonstration of Efficient On-Chip Photon Transfer in Self-Assembled Optoplasmonic Networks | journal=ACS Nano| volume=7 | issue=5 | date=2013-04-25 | doi=10.1021/nn401062b | pages=4470–4478| pmid=23600526 }}{{cite journal | last1=Santiago-Cordoba | first1=Miguel A. | last2=Boriskina | first2=Svetlana V. | last3=Vollmer | first3=Frank | last4=Demirel | first4=Melik C. | title=Nanoparticle-based protein detection by optical shift of a resonant microcavity | journal=Applied Physics Letters| volume=99 | issue=7 | date=2011-08-15 | doi=10.1063/1.3599706 | page=073701| arxiv=1108.2337 | bibcode=2011ApPhL..99g3701S | s2cid=54703911 }} or plasmon gain amplification{{cite journal | last1=Grandidier | first1=Jonathan | last2=des Francs | first2=Gérard Colas | last3=Massenot | first3=Sébastien | last4=Bouhelier | first4=Alexandre | last5=Markey | first5=Laurent | last6=Weeber | first6=Jean-Claude | last7=Finot | first7=Christophe | last8=Dereux | first8=Alain | title=Gain-Assisted Propagation in a Plasmonic Waveguide at Telecom Wavelength | journal=Nano Letters| volume=9 | issue=8 | date=2009-08-12 | doi=10.1021/nl901314u | pages=2935–2939| pmid=19719111 | bibcode=2009NanoL...9.2935G }} are used. Besides SPPs, localized surface plasmon modes supported by metal nanoparticles are referred to as plasmonics modes. Both modes are characterized by large momentum values, which enable strong resonant enhancement of the local density of photon states,S.V. Boriskina, H. Ghasemi, and G. Chen, Materials Today, vol. 16, pp. 379-390, 2013 and can be utilized to enhance weak optical effects of opto-electronic devices.

An effort is currently being made to integrate plasmonics with electric circuits, or in an electric circuit analog, to combine the size efficiency of electronics with the data capacity of photonic integrated circuits (PIC).{{cite journal|last1=Ebbesen|first1=Thomas W.|last2=Genet|first2=Cyriaque|last3=Bozhevolnyi|first3=Sergey I.|title=Surface-plasmon circuitry|journal=Physics Today|volume=61|issue=5|year=2008|pages=44–50|doi=10.1063/1.2930735|bibcode=2008PhT....61e..44E}} While gate lengths of CMOS nodes used for electrical circuits are ever decreasing, the size of conventional PICs is limited by diffraction, thus constituting a barrier for further integration. Plasmonics could bridge this size mismatch between electronic and photonic components. At the same time, photonics and plasmonics can complement each other, since, under the right conditions, optical signals can be converted to SPPs and vice versa.

One of the biggest issues in making plasmonic circuits a feasible reality is the short propagation length of surface plasmons. Typically, surface plasmons travel distances only on the scale of millimeters before damping diminishes the signal.Brongersma, Mark. "Are Plasmonics Circuitry Wave of Future?" Stanford School of Engineering. N.p., n.d. Web. 26 Nov. 2014. . This is largely due to ohmic losses, which become increasingly important the deeper the electric field penetrates into the metal. Researchers are attempting to reduce losses in surface plasmon propagation by examining a variety of materials, geometries, the frequency and their respective properties.{{cite journal | last=Ozbay | first=E. | title=Plasmonics: Merging Photonics and Electronics at Nanoscale Dimensions | journal=Science| volume=311 | issue=5758 | date=2006-01-13 | doi=10.1126/science.1114849 | pages=189–193| pmid=16410515 | bibcode=2006Sci...311..189O | hdl=11693/38263 | s2cid=2107839 | hdl-access=free }} New promising low-loss plasmonic materials include metal oxides and nitrides{{cite journal | last1=Naik | first1=Gururaj V. | last2=Kim | first2=Jongbum | last3=Boltasseva | first3=Alexandra | title=Oxides and nitrides as alternative plasmonic materials in the optical range [Invited] | journal=Optical Materials Express| volume=1 | issue=6 | date=2011-09-06 | pages=1090–1099 | doi=10.1364/ome.1.001090 | arxiv=1108.0993 | bibcode=2011OMExp...1.1090N | s2cid=13870978 }} as well as graphene.{{cite journal | last1=Vakil | first1=A. | last2=Engheta | first2=N. | title=Transformation Optics Using Graphene | journal=Science| volume=332 | issue=6035 | date=2011-06-09 | doi=10.1126/science.1202691 | pages=1291–1294| pmid=21659598 | bibcode=2011Sci...332.1291V | s2cid=29589317 }} Key to more design freedom are improved fabrication techniques that can further contribute to reduced losses by reduced surface roughness.

Another foreseeable barrier plasmonic circuits will have to overcome is heat; heat in a plasmonic circuit may or may not exceed the heat generated by complex electronic circuits. It has recently been proposed to reduce heating in plasmonic networks by designing them to support trapped optical vortices, which circulate light powerflow through the inter-particle gaps thus reducing absorption and Ohmic heating,{{cite journal | last1=Boriskina | first1=Svetlana V. | last2=Reinhard | first2=Björn M. | title=Molding the flow of light on the nanoscale: from vortex nanogears to phase-operated plasmonic machinery | journal=Nanoscale| volume=4 | issue=1 | year=2012 | doi=10.1039/c1nr11406a | pages=76–90| pmid=22127488 | pmc=3339274 }}{{cite journal | last1=Ahn | first1=Wonmi | last2=Boriskina | first2=Svetlana V. | last3=Hong | first3=Yan | last4=Reinhard | first4=Björn M. | title=Electromagnetic Field Enhancement and Spectrum Shaping through Plasmonically Integrated Optical Vortices | journal=Nano Letters| volume=12 | issue=1 | date=2011-12-21 | doi=10.1021/nl203365y | pages=219–227| pmid=22171957 | pmc=3383062 }}S.V. Boriskina "Plasmonics with a twist: taming optical tornadoes on the nanoscale," chapter 12 in: Plasmonics: Theory and applications (T.V. Shahbazyan and M.I. Stockman Eds.) Springer 2013 In addition to heat, it is also difficult to change the direction of a plasmonic signal in a circuit without significantly reducing its amplitude and propagation length. One clever solution to the issue of bending the direction of propagation is the use of Bragg mirrors to angle the signal in a particular direction, or even to function as splitters of the signal.{{cite journal | last1=Veronis | first1=Georgios | last2=Fan | first2=Shanhui | title=Bends and splitters in metal-dielectric-metal subwavelength plasmonic waveguides | journal=Applied Physics Letters| volume=87 | issue=13 | date=2005-09-26 | doi=10.1063/1.2056594 | page=131102| bibcode=2005ApPhL..87m1102V }} Finally, emerging applications of plasmonics for thermal emission manipulation {{cite journal | last1=Boriskina | first1=Svetlana | last2=Tong | first2=Jonathan | last3=Huang | first3=Yi | last4=Zhou | first4=Jiawei | last5=Chiloyan | first5=Vazrik | last6=Chen | first6=Gang | title=Enhancement and Tunability of Near-Field Radiative Heat Transfer Mediated by Surface Plasmon Polaritons in Thin Plasmonic Films | journal=Photonics| volume=2 | issue=2 | date=2015-06-18 | doi=10.3390/photonics2020659 | pages=659–683| bibcode=2015Photo...2..659B |doi-access=free| arxiv=1604.08130 }} and heat-assisted magnetic recording {{cite journal | last1=Challener | first1=W. A. | last2=Peng | first2=Chubing | last3=Itagi | first3=A. V. | last4=Karns | first4=D. | last5=Peng | first5=Wei | last6=Peng | first6=Yingguo | last7=Yang | first7=XiaoMin | last8=Zhu | first8=Xiaobin | last9=Gokemeijer | first9=N. J. | last10=Hsia | first10=Y.-T. | last11=Ju | first11=G. | last12=Rottmayer | first12=Robert E. | last13=Seigler | first13=Michael A. | last14=Gage | first14=E. C. |display-authors=5| title=Heat-assisted magnetic recording by a near-field transducer with efficient optical energy transfer | journal=Nature Photonics| volume=3 | issue=4 | date=2009-03-22 | doi=10.1038/nphoton.2009.26 | pages=220–224| bibcode=2009NaPho...3..220C }} leverage Ohmic losses in metals to obtain devices with new enhanced functionalities.

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Optimal plasmonic waveguide designs strive to maximize both the confinement and propagation length of surface plasmons within a plasmonic circuit. Surface plasmon polaritons are characterized by a complex wave vector, with components parallel and perpendicular to the metal-dielectric interface. The imaginary part of the wave vector component is inversely proportional to the SPP propagation length, while its real part defines the SPP confinement.{{cite journal | last1=Sorger | first1=Volker J. | last2=Oulton | first2=Rupert F. | last3=Ma | first3=Ren-Min | last4=Zhang | first4=Xiang | title=Toward integrated plasmonic circuits | journal=MRS Bulletin| volume=37 | issue=8 | year=2012 | doi=10.1557/mrs.2012.170 | pages=728–738| s2cid=15391453 }} The SPP dispersion characteristics depend on the dielectric constants of the materials comprising the waveguide. The propagation length and confinement of the surface plasmon polariton wave are inversely related. Therefore, stronger confinement of the mode typically results in shorter propagation lengths. The construction of a practical and usable surface plasmon circuit is heavily dependent on a compromise between propagation and confinement. Maximizing both confinement and propagation length helps mitigate the drawbacks of choosing propagation length over confinement and vice versa. Multiple types of waveguides have been created in pursuit of a plasmonic circuit with strong confinement and sufficient propagation length. Some of the most common types include insulator-metal-insulator (IMI),{{cite journal | last1=Verhagen | first1=Ewold | last2=Spasenović | first2=Marko | last3=Polman | first3=Albert | last4=Kuipers | first4=L. (Kobus) | title=Nanowire Plasmon Excitation by Adiabatic Mode Transformation | journal=Physical Review Letters| volume=102 | issue=20 | date=2009-05-19 | doi=10.1103/physrevlett.102.203904 | page=203904| pmid=19519030 | bibcode=2009PhRvL.102t3904V }} metal-insulator-metal (MIM),{{cite journal | last1=Dionne | first1=J. A. | last2=Lezec | first2=H. J. | last3=Atwater | first3=Harry A. | title=Highly Confined Photon Transport in Subwavelength Metallic Slot Waveguides | journal=Nano Letters| volume=6 | issue=9 | year=2006 | doi=10.1021/nl0610477 | pages=1928–1932| pmid=16968003 | bibcode=2006NanoL...6.1928D }} dielectric loaded surface plasmon polariton (DLSPP),{{cite journal | last1=Steinberger | first1=B. | last2=Hohenau | first2=A. | last3=Ditlbacher | first3=H. | last4=Stepanov | first4=A. L. | last5=Drezet | first5=A. | last6=Aussenegg | first6=F. R. | last7=Leitner | first7=A. | last8=Krenn | first8=J. R. | title=Dielectric stripes on gold as surface plasmon waveguides | journal=Applied Physics Letters| volume=88 | issue=9 | date=2006-02-27 | doi=10.1063/1.2180448 | page=094104| bibcode=2006ApPhL..88i4104S }}{{cite journal | last1=Krasavin | first1=Alexey V. | last2=Zayats | first2=Anatoly V. | title=Silicon-based plasmonic waveguides | journal=Optics Express| volume=18 | issue=11 | date=2010-05-19 | pages=11791–9 | doi=10.1364/oe.18.011791 | pmid=20589040 | bibcode=2010OExpr..1811791K |doi-access=free}} gap plasmon polariton (GPP),{{cite journal |first1=K.-Y.|last1=Jung| last2=Teixeira | first2=F.L. | last3=Reano | first3=R.M. | title=Surface Plasmon Coplanar Waveguides: Mode Characteristics and Mode Conversion Losses | journal=IEEE Photonics Technology Letters| volume=21 | issue=10 | year=2009 | doi=10.1109/lpt.2009.2015578 | pages=630–632|bibcode=2009IPTL...21..630J|s2cid=6788393}} channel plasmon polariton (CPP),{{cite journal | last1=Bozhevolnyi | first1=Sergey I. | last2=Volkov | first2=Valentyn S. | last3=Devaux | first3=Eloïse | last4=Laluet | first4=Jean-Yves | last5=Ebbesen | first5=Thomas W. | title=Channel plasmon subwavelength waveguide components including interferometers and ring resonators | journal=Nature| volume=440 | issue=7083 | year=2006 | doi=10.1038/nature04594 | pages=508–511| pmid=16554814 | bibcode=2006Natur.440..508B | doi-access=free }} wedge surface plasmon polariton (wedge),{{cite journal | last1=Pile | first1=D. F. P. | last2=Ogawa | first2=T. | last3=Gramotnev | first3=D. K. | last4=Okamoto | first4=T. | last5=Haraguchi | first5=M. | last6=Fukui | first6=M. | last7=Matsuo | first7=S. | title=Theoretical and experimental investigation of strongly localized plasmons on triangular metal wedges for subwavelength waveguiding | journal=Applied Physics Letters| volume=87 | issue=6 | date=2005-08-08 | doi=10.1063/1.1991990 | page=061106| bibcode=2005ApPhL..87f1106P }} and hybrid opto-plasmonic waveguides and networks.{{cite journal | last1=Boriskina | first1=S. V. | last2=Reinhard | first2=B. M. | title=Spectrally and spatially configurable superlenses for optoplasmonic nanocircuits | journal=Proceedings of the National Academy of Sciences| volume=108 | issue=8 | date=2011-02-07 | doi=10.1073/pnas.1016181108 | pages=3147–3151| pmid=21300898 | pmc=3044402 | arxiv=1110.6822 | bibcode=2011PNAS..108.3147B | doi-access=free }} Dissipation losses accompanying SPP propagation in metals can be mitigated by gain amplification or by combining them into hybrid networks with photonic elements such as fibers and coupled-resonator waveguides. This design can result in the previously mentioned hybrid plasmonic waveguide, which exhibits subwavelength mode on a scale of one-tenth of the diffraction limit of light, along with an acceptable propagation length.M. Z. Alam, J. Meier, J. S. Aitchison, and M. Mojahedi,

"Super mode propagation in low index medium", Paper ID: JThD112, CLEO/QELS 2007.{{cite journal | last1=Sorger | first1=Volker J. | last2=Ye | first2=Ziliang | last3=Oulton | first3=Rupert F. | last4=Wang | first4=Yuan | last5=Bartal | first5=Guy | last6=Yin | first6=Xiaobo | last7=Zhang | first7=Xiang | title=Experimental demonstration of low-loss optical waveguiding at deep sub-wavelength scales | journal=Nature Communications| volume=2 | issue=1 | date=2011-05-31 | doi=10.1038/ncomms1315 | page=331| bibcode=2011NatCo...2..331S |doi-access=free}}{{cite journal | last1=Oulton | first1=R. F. | last2=Sorger | first2=V. J. | last3=Genov | first3=D. A. | last4=Pile | first4=D. F. P. | last5=Zhang | first5=X. | title=A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation | journal=Nature Photonics| volume=2 | issue=8 | date=2008-07-11 | doi=10.1038/nphoton.2008.131 | pages=496–500| bibcode=2008NaPho...2.....O |doi-access=free| hdl=10044/1/19117 | hdl-access=free }}{{cite journal | last1=Alam | first1=Muhammad Z. | last2=Aitchison | first2=J. Stewart | last3=Mojahedi | first3=Mo | title=A marriage of convenience: Hybridization of surface plasmon and dielectric waveguide modes | journal=Laser & Photonics Reviews| volume=8 | issue=3 | date=2014-02-19 | doi=10.1002/lpor.201300168 | pages=394–408| bibcode=2014LPRv....8..394A | s2cid=54036931 }}

The input and output ports of a plasmonic circuit will receive and send optical signals, respectively. To do this, coupling and decoupling of the optical signal to the surface plasmon is necessary.{{cite journal | last1=Krenn | first1=J. R. | last2=Weeber | first2=J.-C. | editor-last=Richards | editor-first=David | editor-last2=Zayats | editor-first2=Anatoly | title=Surface plasmon polaritons in metal stripes and wires | journal=Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences| volume=362 | issue=1817 | date=2004-04-15 | doi=10.1098/rsta.2003.1344 | pages=739–756| pmid=15306491 | s2cid=6870662 }} The dispersion relation for the surface plasmon lies entirely below the dispersion relation for light, which means that for coupling to occur additional momentum should be provided by the input coupler to achieve the momentum conservation between incoming light and surface plasmon polariton waves launched in the plasmonic circuit. There are several solutions to this, including using dielectric prisms, gratings, or localized scattering elements on the surface of the metal to help induce coupling by matching the momenta of the incident light and the surface plasmons.{{cite journal | last1=González | first1=M. U. | last2=Weeber | first2=J.-C. | last3=Baudrion | first3=A.-L. | last4=Dereux | first4=A. | last5=Stepanov | first5=A. L. | last6=Krenn | first6=J. R. | last7=Devaux | first7=E. | last8=Ebbesen | first8=T. W. | title=Design, near-field characterization, and modeling of 45° surface-plasmon Bragg mirrors | journal=Physical Review B| volume=73 | issue=15 | date=2006-04-13 | doi=10.1103/physrevb.73.155416 | page=155416| bibcode=2006PhRvB..73o5416G }} After a surface plasmon has been created and sent to a destination, it can then be converted into an electrical signal. This can be achieved by using a photodetector in the metal plane, or decoupling the surface plasmon into freely propagating light that can then be converted into an electrical signal.

Alternatively, the signal can be out-coupled into a propagating mode of an optical fiber or waveguide.{{citation needed|date=January 2025}}

The progress made in surface plasmons over the last 50 years has led to the development in various types of devices, both active and passive. A few of the most prominent areas of active devices are optical, thermo-optical, and electro-optical. All-optical devices have shown the capacity to become a viable source for information processing, communication, and data storage when used as a modulator. In one instance, the interaction of two light beams of different wavelengths was demonstrated by converting them into co-propagating surface plasmons via cadmium selenide quantum dots.{{cite journal | last1=Pacifici | first1=Domenico | last2=Lezec | first2=Henri J. | last3=Atwater | first3=Harry A. | title=All-optical modulation by plasmonic excitation of CdSe quantum dots | journal=Nature Photonics| volume=1 | issue=7 | year=2007 | doi=10.1038/nphoton.2007.95 | pages=402–406| bibcode=2007NaPho...1..402P }} Electro-optical devices have combined aspects of both optical and electrical devices in the form of a modulator as well. Specifically, electro-optic modulators have been designed using evanescently coupled resonant metal gratings and nanowires that rely on long-range surface plasmons (LRSP).{{cite journal | last1=Wu | first1=Zhi | last2=Nelson | first2=Robert L. | last3=Haus | first3=Joseph W. | last4=Zhan | first4=Qiwen | title=Plasmonic electro-optic modulator design using a resonant metal grating | journal=Optics Letters| volume=33 | issue=6 | date=2008-03-05 | pages=551–3 | doi=10.1364/ol.33.000551 | pmid=18347706 | bibcode=2008OptL...33..551W }} Likewise, thermo-optic devices, which contain a dielectric material whose refractive index changes with variation in temperature, have also been used as interferometric modulators of SPP signals in addition to directional-coupler switches. Some thermo-optic devices have been shown to utilize LRSP waveguiding along gold stripes that are embedded in a polymer and heated by electrical signals as a means for modulation and directional-coupler switches.{{cite journal | last1=Nikolajsen | first1=Thomas | last2=Leosson | first2=Kristjan | last3=Bozhevolnyi | first3=Sergey I. | title=Surface plasmon polariton based modulators and switches operating at telecom wavelengths | journal=Applied Physics Letters| volume=85 | issue=24 | date=2004-12-13 | doi=10.1063/1.1835997 | pages=5833–5835| bibcode=2004ApPhL..85.5833N }} Another potential field lies in the use of spasers in areas such as nanoscale lithography, probing, and microscopy.{{cite journal | last=Stockman | first=Mark I. | title=Spasers explained | journal=Nature Photonics| volume=2 | issue=6 | year=2008 | doi=10.1038/nphoton.2008.85 | pages=327–329| bibcode=2008NaPho...2..327S |author-link=Mark Stockman}}

Although active components play an important role in the use of plasmonic circuitry, passive circuits are just as integral and, surprisingly, not trivial to make. Many passive elements such as prisms, lenses, and beam splitters can be implemented in a plasmonic circuit, however fabrication at the nano scale has proven difficult and has adverse effects. Significant losses can occur due to decoupling in situations where a refractive element with a different refractive index is used. However, some steps have been taken to minimize losses and maximize compactness of the photonic components. One such step relies on the use of Bragg reflectors, or mirrors composed of a succession of planes to steer a surface plasmon beam. When optimized, Bragg reflectors can reflect nearly 100% of the incoming power. Another method used to create compact photonic components relies on CPP waveguides as they have displayed strong confinement with acceptable losses less than 3 dB within telecommunication wavelengths.{{cite journal | last1=Volkov | first1=Valentyn S. | last2=Bozhevolnyi | first2=Sergey I. | last3=Devaux | first3=Eloïse | last4=Ebbesen | first4=Thomas W. | title=Compact gradual bends for channel plasmon polaritons | journal=Optics Express| volume=14 | issue=10 | year=2006 | pages=4494–503 | doi=10.1364/oe.14.004494 | pmid=19516603 | bibcode=2006OExpr..14.4494V |doi-access=free}}

Maximizing loss and compactness with regards to the use of passive devices, as well as active devices, creates more potential for the use of plasmonic circuits.{{citation needed|date=March 2025}}

• Nanophotonics
• Metamaterials
• Spoof surface plasmon

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Category:Photonics

Category:Nanoelectronics

Category:Metamaterials

Category:Nanotechnology