Optical Metamaterials: Fundamentals and Applications

206 Pages·2010·7.439 MB·English

by  Wenshan Cai, Vladimir Shalaev (auth.)

Optical Metamaterials
Wenshan Cai Vladimir Shalaev
•
Optical Metamaterials
Fundamentals and Applications
123
Dr.W.Cai Prof.V.Shalaev
StanfordUniversity PurdueUniversity
Stanford,CA WestLafayette,IN
USA USA
[email protected] [email protected]
ISBN978-1-4419-1150-6 e-ISBN978-1-4419-1151-3
DOI10.1007/978-1-4419-1151-3
SpringerNewYorkDordrechtHeidelbergLondon
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(cid:176)c SpringerScience+BusinessMedia,LLC2010
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TomysonSheling,mywifeYunTai,andto
thememoryofmymother,ShuxinWang
(1943–2008).
–WenshanCai
Tomyfamilyandclosefriends,whokeep
supportingmethroughmylifeandcareer.
–VladimirM.Shalaev
Preface
This book deals with optical metamaterials – artificially structured materials with
nanoscaleinclusionsandstrikinglyunconventionalpropertiesatopticalfrequencies.
Thesematerialscanbetreatedasmacroscopicallyhomogeneousmediaandcanex-
hibitavarietyofunusualandexcitingresponsestolight.Man-madematerialswith
subwavelengthinclusionshavebeenpurposelyutilizedbyartistsandcraftsmenfor
centuries, as indicated by a number of glass vessels ranging from the late Roman
eratotheRenaissanceperiod.However,opticalmetamaterialshaveflourishedonly
in the present century thanks to combined advances in nanofabrication, numerical
modeling,andcharacterizationtools.Inonlyafewyears,thefieldofopticalmeta-
materialshasemergedasoneofthemostexcitingtopicsinthescienceoflight,with
stunningandunexpectedoutcomesthathaverepeatedlyfascinatedresearchers,sci-
entists,andeventhegeneralpublic.
The philosophy behind the area of optical metamaterials is distinct from most
other branches of optical studies in that it does not emphasize the explanation,
implementation, or utilization of known phenomena, but rather it focuses on the
creation of entirely new stories and new events that no one has even considered.
ThisphilosophyisbestillustratedbyasimplequotationfromBacktoMethuselah
byGeorgeBernardShaw,oneofthefinestplaywrightsofthetwentiethcentury.The
quotebecamewidespreadafteritsadoptionbyRobertKennedyduringhispresiden-
tialcampaign:
“Somemenseethingsastheyareandsay‘Why?’Idreamthingsthatneverwereandsay,
‘Whynot?”’
Indeed,thepersistenceofasking“why”hasbeenfascinatingscientiststhroughout
the history of optics. From ancient scholars like Euclid, Ptolemy and Alhazen to
themoderngiantswhoshapedtoday’sknowledgeofoptics,thepursuitofanswers
toobservedphenomenahasledtomajordiscoveriesthathavemadeitpossiblefor
us to understand the realities of optics. By combing the knowledge derived from
asking“why”andtheimplementationofavailablematerials,numerousopticalcom-
ponents,devicesandsystemshavebeendevelopedthathaveradicallyalteredboth
theeverydaylifeofpeoplearoundtheglobeandthescopeofmodernscience.
Withalltheadvances inoptics throughout theages, now is perhaps the timeto
focus more on the theme of “why not.” It is time to rethink the limits of optics,
vii
viii Preface
andreconsiderthelong-establishedguidelineswithinwhichopticalscientistsoften
work. With this in mind, we choose to be bold and adventurous, rethinking the
answerstoquestionssuchas,“Whynotrefractlighttheotherway?”Ormaybewe
shouldask,“WhynotbuildamicroscopetoseeaDNAstrandwiththenakedeye?”
Wecanevenpondermoremysteriousandmythicalquestions,including,“Whynot
createacloakthatmakesanobjectinvisible?”Theseconceptsarenotstrictlypro-
hibited by any fundamental physical laws, nor are many other equally fascinating
possibilities. Perhaps, then, it is indeed time to explore many truly amazing ideas
thatmaybetemporarilybeyondourvision,butnotinherentlybeyondourreach.
Allthequestionsabove,nowopenforreconsiderationbyasking“whynot,”are
the pursuits of optical metamaterials. In this research field, the control of light is
notlimitedbythepropertiesofopticalmaterialsthatarereadilyavailable.Instead,
we choose to create materials that never were, by tailoring the elements of arti-
ficial structures down to the deeply subwavelength scale. This aspect of optical
metamaterialsisboundtorevolutionarilyalterthedesignstrategiesandimplementa-
tionphilosophiesthatpeopleuseinbuildingopticaldevicesandsystems.Thenew
research field of optical metamaterials opens a whole new world of fundamental
studiesandpracticalapplicationsthatwerequiteundreamtofintherealmofcon-
ventionaloptics.Stillinitsinfancy,theopticalmetamaterialshavealreadyoffered
hopetotheseeminglycrazydreamsmentionedabove,andtheyhavedemonstrated
potential benefits in various applications including optical sensing, novel waveg-
uides and antennas, sub-diffraction-limited imaging, nanoscale photolithography,
photonicnanocircuits,andmanymore.
Theintensedevelopmentintheevolvingfieldofopticalmetamaterialshasstarted
attracting an increasing number of students and researchers. Although a large and
drasticallygrowingnumberofpublicationsareconstantlyaddedtotheliteratureof
thisfield,wefeelthereremainsalackofareader-friendlybookthathelpstomake
opticalmetamaterialsaccessibletoawideraudience.Inparticular,newparticipants
inahighlyinterdisciplinaryfieldofstudylikeopticalmetamaterialscaneasilyget
lost if they have to wade through many textbooks of different subjects simultane-
ously. To describe optical metamaterials in a simple, easy-to-understand way was
ourprimarymotivationforembarkingonthisbook.
Inwritingthebook,wesoughttoprovideanaccessibleentranceintothefasci-
natingworldofopticalmetamaterials.Inarelativelyslimvolume,wearetryingto
providestudentsandresearcherswiththebasicknowledgethatisrequiredtoenter
this research area, as well as providing the broad perspective that is now needed
to understand the latest breakthroughs. It should be stressed that this book is not
intended as a thorough treatise and up-to-date review of all research work avail-
able in this field. Instead, the book provides a comprehensive, self-contained but
digestibleintroductiontothebasicideasandmajortopicsinopticalmetamaterials.
We hope that it will be useful to the interested reader as a stepping stone towards
moreadvanced researchcurrentlyunderway inthefield.Wehavetriedtoproduce
a balanced text from which the reader willbe able to gain a perspective of optical
metamaterialsasawholeaswellasaflavorforwherethesubjectisgoing.
Preface ix
We now wouldliketotakeamoment toguide you through thecontents of this
book. The material in the book is presented in an order that aims to progressively
increase the reader’s comprehension of the subject. The book starts with a discus-
sion of the definition, emergence, motivation and scope of the research field of
optical metamaterials. Then in Chap. 2 we discuss the optical properties of met-
als, dielectrics and their composites. The delicate arrangement of these materials
formstheconstituentbuildingblocksforthemetamaterialswearetrulyinterested
in studying. Chapter 3 covers the fabrication techniques, characterization schemes
and data treatment methods for optical metamaterials. Once the basics have been
established, fromChap. 4–6 we present three major categories of optical metama-
terials,namelyelectricmetamaterials,magneticmetamaterials,andnegative-index
metamaterials.Theprinciples,advances,andexamplesforeachcategorywillbean-
alyzedindetail.Thelastthreechaptersdealwithexcitingnovelopportunitiesmade
possiblebyopticalmetamaterials.InChap.7wediscussnonlineareffectsinoptical
metamaterials, including the necessary mathematical descriptions. Chapter8 de-
scribes metamaterial-based imaging systems with subwavelength resolution. Most
notably,severalmilestoneexperimentsrelatedtosuper-resolutioninboththenear-
and far-field regimes are discussed. Finally, in Chap. 9 we provide the principles
and applications of transformation optics, which molds the flow of light in an un-
precedented manner by specifying the spatial distributions of anisotropic material
parameters.Inparticular,thischaptergivesadetaileddiscussionofthemostintrigu-
ingoutcomeoftransformationoptics–anelectromagneticcloakofinvisibility.
We have attempted to introduce most of the major subjects involved in optical
metamaterials while at the same time keeping the book within a relatively small
compass.Althoughthefrontierinthestudyofopticalmetamaterialsisdeveloping
rapidly, the basic knowledge and ways of thinking presented in this book are ex-
pectedtobewidelyadoptedinmanyofthenewtopicsofopticalmetamaterialsthat
areeitherongoingorabouttobreachthehorizon.Thebookcanbeusedasarefer-
encetextbypeopleworkinginmetamaterials,plasmonics,nanophotonics,andother
relatedfields.Itcanalsobeusedasacoursetextbookorabookforself-instruction
at the senior undergraduate or graduate level, as well as for a short course offered
byaprofessionalsociety.Assuch,thebookpresumesthatthereaderhasageneral
knowledgeofbasicelectrodynamicsattheundergraduatelevel.
Thisbookwouldnothavebeencompletedwithoutthehelpofmanypeople.In
particular,wearedeeplygratefultoMarkThoresonforhispainstakingreviewand
criticalproofreadingoftheentiremanuscript.Wearealsothankfulforthesupport
andhelpfulsuggestionsfromProfessorMarkBrongersmaatStanfordUniversity.
Inaddition,itisapleasuretoacknowledgeourdebtandgratitudetomanycol-
leagueswhoseexpertise,discussions,andcollaborationhavebenefitedusover the
years. These include Drs. A. V. Kildishev, A. K. Sarychev, V. P. Drachev, A. K.
Popov,U.K.Chettiar,H.-K.Yuan,I.R.Gabitov,S.A.Myslivets,N.M.Litchinitser,
E. E. Narimanov, A. E. Boltasseva, T. A. Klar, Sir J. B. Pendry, V. G. Veselago,
x Preface
X. Zhang, D. R. Smith, M. Wegener, N. Engheta, N. I. Zheludev, U. Leonhardt,
M. A. Noginov, V. A. Podolskiy, G. W. Milton, D. H. Werner, I. C. Khoo, A. I.
Maimistov,R.Z.Sagdeev,D.A.Genov,A.Boardman,andI.I.Smolyaninov.We
arealsogratefultoourfamiliesandclosefriendsfortheirsupport.
Stanford,CA WenshanCai
WestLafayette,IN VladimirM.Shalaev
Contents
1 Introduction.................................................................... 1
1.1 WhatareMetamaterials?................................................. 1
1.2 MacroscopicEffectiveParameters....................................... 5
References....................................................................... 8
2 OpticalPropertiesofMetal-DielectricComposites........................ 11
2.1 OpticalMaterialsandElectronicStructures............................. 11
2.2 OpticalPropertiesofDielectricMaterials............................... 13
2.3 OpticalPropertiesofMetals ............................................. 19
2.4 Metal-DielectricCompositesandMixingRules........................ 25
References....................................................................... 36
3 ExperimentalTechniquesandDataTreatment ............................ 39
3.1 FabricationofTwo-DimensionalOpticalMetamaterials............... 39
3.2 ApproachingtheThirdDimension ...................................... 43
3.3 CharacterizationofSpectralProperties.................................. 47
3.4 ExtractionofHomogenizedOpticalParameters........................ 51
References....................................................................... 56
4 ElectricMetamaterials........................................................ 59
4.1 ABriefOverviewofArtificialDielectrics .............................. 59
4.2 OpticalPropertiesofStratifiedMetal-DielectricComposites.......... 60
4.3 PeriodicArrayofMetallicWires ........................................ 64
4.4 SemicontinuousMetalFilms............................................. 71
References....................................................................... 74
5 MagneticMetamaterials...................................................... 77
5.1 NegligibleOpticalMagnetisminNature................................ 77
5.2 Split-RingResonators.................................................... 78
5.3 OpticalMagneticElements .............................................. 82
5.4 MagnetismintheVisibleSpectrum ..................................... 88
xi
xii Contents
5.5 AnalyticalModelofMagneticNanostrips .............................. 93
5.6 High-PermittivityRoutetoArtificialMagnetism....................... 96
References....................................................................... 98
6 Negative-IndexMetamaterials...............................................101
6.1 ABriefHistoricalReview................................................101
6.2 ReversedPhenomenainNegative-IndexMedia.........................103
6.3 NegativeRefractioninMicrowaveFrequencies ........................105
6.4 TheDebutofOpticalNegative-IndexMaterials ........................107
6.5 GeneralRecipeforConstruction.........................................112
6.6 AlternativeApproaches ..................................................116
References.......................................................................120
7 NonlinearOpticswithMetamaterials.......................................123
7.1 RecentAdvancesofNonlinearEffectsinMetamaterials...............123
7.2 Second-HarmonicGenerationandtheManley–Rowe
RelationsinNegative-IndexMaterials...................................126
7.3 OpticalParametricAmplificationsinNegative-indexMaterials .......131
References.......................................................................134
8 SuperResolutionwithMeta-Lenses.........................................137
8.1 PerfectLenswithSubwavelengthResolution...........................137
8.2 Near-FieldSuperlens.....................................................140
8.3 “Tunable”SuperlensUsingRandomComposites.......................142
8.4 PotentialApplicationsoftheCompositeLens..........................148
8.5 Far-FieldImagingwithSuper-Resolution...............................149
References.......................................................................155
9 TransformationOpticsandElectromagneticCloakofInvisibility.......159
9.1 InvisibilityandTransformationOptics:AnOverview..................159
9.2 CloakingbyCoordinateTransformation ................................162
9.3 TowardsExperimentalDemonstrations .................................167
9.4 Non-magneticOpticalCloak.............................................171
9.5 CloakingwithHigh-OrderTransformations ............................176
9.6 DesignsforHigh-OrderOpticalCloaking...............................180
9.7 AlternativeApproachesforOpticalCloaking...........................187
9.8 ConcludingRemarksonTransformationOptics........................191
References.......................................................................193
Index.................................................................................197