EDITORIAL ADVISORY BOARD G.S. Agarwal Stillwater, USA T. Asakura Sapporo, Japan M.V. Berry Bristol, England C. Brosseau Brest, France A.T. Friberg Joensuu, Finland F. Gori Rome, Italy D.F.V. James Toronto, Canada P. Knight London, England G. Leuchs Erlangen, Germany P. Milonni Los Alamos, NM, USA J.B. Pendry London, England J. Peˇrina Olomouc, Czech Republic J. Pu Quanzhou, PR China W. Schleich Ulm, Germany T.D. Visser Amsterdam, The Netherlands VOLUME FIFTY EIGHT PROGRESS IN OPTICS Edited by E. WOLF University of Rochester, NY, USA Contributors Timothy Bunning, Iain F. Crowe, Luciano De Sio, Greg Gbur, Matthew P. Halsall, Hans Peter Herzig, Kishore T. Kapale, Myun-Sik Kim, Brian R. Kimball, Andrew P. Knights, Carsten Rockstuhl, Tyler Roschuk, Toralf Scharf, Nelson Tabiryan, Cesare Umeton Amsterdam • Boston • Heidelberg • London • New York • Oxford Paris • San Diego • San Francisco • Singapore • Sydney • Tokyo Elsevier The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands First edition 2013 Copyright © 2013, Elsevier B.V. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher. Permissions may be sought directly from Elseviers Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visit- ing the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material. Notices No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-444-62644-8 ISSN: 0079-6638 For information on all Elsevier publications visit our website at store.elsevier.com Printed and bound in Great Britain 13 14 15 16 17 11 10 9 8 7 6 5 4 3 2 1 CONTRIBUTORS Timothy Bunning Air Force Research Laboratory, Wright-Patterson Air Force Base, OH, USA Iain F. Crowe Photon Science Institute and School of Electrical and Electronic Engineering, University of Manchester, Manchester, United Kingdom Luciano De Sio Department of Physics and Centre of Excellence for the Study of Innovative Functional Materials CEMIF-CAL, University of Calabria, Institute for Chemical Physics Processes IPCF-CNR, UOS Cosenza, Italy Greg Gbur Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, NC, USA Matthew P. Halsall Photon Science Institute and School of Electrical and Electronic Engineering, University of Manchester, Manchester, United Kingdom Hans Peter Herzig Optics & Photonics Technology Laboratory, Ecole Polytechnique Fédérale de Lausanne, Neuchâtel, Switzerland Kishore T. Kapale Department of Physics, Western Illinois University, Macomb, IL, USA Myun-Sik Kim SUSS MicroOptics SA, Rouges-Terres 61, Hauterive, Switzerland Brian R. Kimball US Army Natick Soldier Research, Development & Engineering Center, Kansas Street, Natick, MA, USA Andrew P. Knights Department of Engineering Physics and the Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario, Canada Carsten Rockstuhl Institute of Condensed Matter Theory and Solid State Optics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Jena, Germany Tyler Roschuk The Blackett Laboratory, Imperial College London, Prince Consort Road, London, United Kingdom Toralf Scharf Optics & Photonics Technology Laboratory, Ecole Polytechnique Fédérale de Lausanne, Neuchâtel, Switzerland vv vi Contributors Nelson Tabiryan Beam Engineering for Advanced Measurements Company, Winter Park, FL, USA Cesare Umeton Department of Physics and Centre of Excellence for the Study of Innovative Functional Materials CEMIF-CAL, University of Calabria, Institute for Chemical Physics Processes IPCF-CNR, UOS Cosenza, Italy PREFACE The present volume contains review articles on the following subjects: Low-dimensional silicon structures for use in photonic circuits, phase anomalies in microoptics, invisibility physics, dynamic photonic materials based on liquid crystals, and subwavelength atom localization. Experimental, as well as, theoretical researches are reviewed. Emil Wolf Department of Physics and Astronomy and The Institute of Optics University of Rochester Rochester, NY 14627, USA March 2013 iixx CHAPTERONE Dynamic Photonic Materials Based on Liquid Crystals LucianoDeSio*,NelsonTabiryan†,TimothyBunning‡, BrianR.Kimball§, and CesareUmeton* *DepartmentofPhysicsandCentreofExcellencefortheStudyofInnovativeFunctionalMaterials CEMIF-CAL,UniversityofCalabria,InstituteforChemicalPhysicsProcessesIPCF-CNR,UOSCosenza, 87036ArcavacatadiRende,Italy †BeamEngineeringforAdvancedMeasurementsCompany,WinterPark,FL32789,USA ‡AirForceResearchLaboratory,Wright-PattersonAirForceBase,OH45433-7707,USA §USArmyNatickSoldierResearch,Development&EngineeringCenter,KansasStreet, Natick,MA01760-5020,USA Contents 1. Introduction 2 2. PhotonicDevicesBasedonCholestericLiquidCrystals 3 2.1 Electro-ResponsiveCLCs 3 2.2 AzobenzeneLCs 12 2.3 PhototunableCLCs 15 3. HolographicPolymerDispersedinLiquidCrystals 17 4. POLICRYPSStructures 27 4.1 RealizationandTheoreticalModel 27 4.1.1 FabricationRecipes 28 4.1.2 TheoreticalModelforCompositeStructuresFormation 29 4.2 ApplicationsofNLC-BasedPOLICRYPS 32 4.2.1 SwitchableHolographicGrating 32 4.2.2 SwitchableBeam-Splitter 33 4.2.3 SwitchableWaveplate 34 4.2.4 TunableBraggFilter 37 4.3 ApplicationsPOLICRYPSBasedonCLCandFLC 40 4.3.1 MicrolaserArray 40 4.3.2 CLCinULHConfiguration 42 4.3.3 SSFLCSwitching 43 5. TunableDiffractiveWaveplates 45 5.1 TheNewGenerationofOptics 45 5.2 LightModulationConceptsBasedonDWs 47 6. LiquidCrystalsActivePlasmonicNanomaterials 49 6.1 GeneralOverview 49 6.2 PeriodicStructuresHostingPlasmonicCLCs 50 ProgressinOptics,Volume58 ©2013ElsevierB.V. ISSN0079-6638,http://dx.doi.org/10.1016/B978-0-444-62644-8.00001-7 Allrightsreserved. 1 2 LucianoDeSioetal. 6.3 RandomDistributionofGNPsLayeredwithNLC 54 7. Conclusions 59 Acknowledgments 59 References 59 1. INTRODUCTION Opticsandphotonicsinvolvematerialsciencesanddevicetechnology, at the basis of displays, computing devices, optical fibers, precision man- ufacturing,enhanced defense capabilities,and a plethora of medical diag- nostics tools. Opportunities arising from optics and photonics offer the potential for an even greater social impact in the next few decades,related to solar power generation,efficient lighting,and faster internet. Continu- ouslyincreasingdatacapacityrequirementsintelecommunicationsandinthe next-generation of dynamically reconfigurable networks increases demand for highly compact,non-mechanical,and high speed optical devices. New materials exhibiting enhanced optical properties are key to these develop- ments.Inparticular,liquidcrystals(LCs)haveattractedagreatdealofatten- tioninthelastthreedecades.Thisisduetotheircapabilitybothtobehaveas smartanisotropicmaterials,exhibitingself-organizingpropertiesalongwith fluidity,and to fulfill conditionsimposed from outside,due to their respon- sivenesstoawidevarietyofexternalperturbations,likeAC,DC,andoptical fields(Gennes&Prost,1995).Indeed,thelargebirefringence(∼0.5)ofLCs allowsfortherealizationoftunablephotonicdevicesforbothopticalcom- municationsandopticalsensingsystems.LCsandpolymershavebecomean excitingfieldofresearchwithpracticalapplicationsinflatpaneldisplaysand active optical devices.Thanks to achievements obtained in the micro/nano fabrication processes,such as Intensity and Polarization Holography,Elec- tron Beam (E-Beam) Lithography,Focused Ion Beam (FIB),and Dip-Pen nanolithography,severalcompositephotonicstructuresexploitingLCsprop- erties have been realized. Liquid Crystals are currently playing a significant roleinnanoscienceandnanotechnology,too.Theycanbeutilizedasbridge between“hardmatter”and“softmatter,”duetothefactthatnano-structured materials do not induce significant distortions of LC phases.Various nano- materials have been dispersed and studied in LCs to enhance their physical properties.Furthermore,alignmentandself-assemblyofnanoparticlesthem- selvescanbeachievedinsidetheLC,sinceitactsasatunablesolventforthe dispersionofnanomaterials.Asananisotropicmedium,itprovidesasupport fortheself-assemblyofthosematerialsintolargeorganizedstructures,even DynamicPhotonicMaterialsBasedonLiquidCrystals 3 inmultipledimensions.Mostimportantly,inordertoexploitthedistinctive characteristics and capabilities of LC technologies, a variety of means for alignmentandconfinementofLCshavebeeninvestigatedandemployed.In this chapter,we review our achievements in the fabrication and characteri- zation of LC-based photonic devices,underlining,in particular,the“active way”we utilize to controltheir properties.Themostimportantaspects and novelties are highlighted in different sections of the paper.We begin with an overview of electro-responsive and light sensitive chiral nematic LCs. We continue by reporting on the optical and electro-optical properties of holographicstructurescontainingseveralkindsofLCphasesand,finally,we show how it is possible to exploit and control the plasmonic nanomaterial properties by means of LCs utilized as active host media. 2. PHOTONICDEVICESBASEDONCHOLESTERICLIQUID CRYSTALS 2.1 Electro-ResponsiveCLCs In Cholesteric Liquid Crystals (CLCs),also called chiral nematic LCs,the molecules are arranged in a helical structure such that in each plane of the system the directors are aligned (and lay in that plane) and the director orientation changes progressively along the direction perpendicular to the planes (such direction,h,constitutes the axis of the helix). If the helix axis is along z and n is the director orientation,the angle θ between n and a reference direction in the xy plane can be expressed as follows: θ = (2π/P)z, (1.1) where the parameter P is the pitch of the helix,that is the distance along h over which the orientation of the molecules rotates by 2π. In each xy plane (constant z) the system only has orientational order but no trans- lational order. Because of the periodicity in the director orientation in z, CLCsbehaveasone-dimensionalphotonicbandgapsystemandpropagation of light of certain wavelengths and polarizations states is forbidden (Blinov, 1983;Yeh & Gu, 1999). In particular, for a CLC system in a planar state (h (cid:3) z,perpendicular to the plane of the cell,xy) and at normal incidence (k (cid:3) e , where k is the propagation wavevector of the light beam), cir- z cularly polarized light of wavelength between n P and n P (n and n are o e o e the ordinary and extraordinary refractive indices of the material, respec- tively) with the same handedness as the helix is reflected by the CLC layer, whiletheoppositesenseofcircularpolarizationpropagatesthroughtheCLC 4 LucianoDeSioetal. Figure1 TransmissionspectrumofaCLCcell(80%E7,20%R811)atnormalincidence: sampleintheplanarhomogeneousstatewithλ0=825nm,nofieldapplied(blueline); sampleinafocalconicstateatE =1.5V/µm(greenline);sampleinthehomeotropic stateatE =5V/µm(redline).Allfieldsquarewavesat1kHz.(Forinterpretationofthe referencestocolorinthisfigurelegend,thereaderisreferredtothewebversionofthis book.) unaffected. For unpolarized light,an ideal sample reflects 50% of the light and transmits the remaining 50% in the wavelength range n P < λ < n P, o e whereasthesampleistransparentoutsidethisrange(Figure1,blueline).The center of the reflection band occurs at: λ = (cid:4)n(cid:5)P, (1.2) 0 where(cid:4)n(cid:5)istheaveragerefractiveindex,(cid:4)n(cid:5) = (n +n )/2andthebandwidth e o is given by: (cid:5)λ = (cid:5)nP = (n −n )P. (1.3) e o Becauseofthedielectricanisotropyofthematerial,thedirectororienta- tionoftheliquidcrystalscanchangeinthepresenceofanelectricfield,and thiseffecthasbeenusedtodesignvarioustypesofelectro-responsivedevices based on CLCs. For a CLC with a positive dielectric anisotropy ((cid:5)ε > 0), thehelicalstructureisnotstablewhenanelectricfieldisappliedparallelto thehelicalaxis(E (cid:3) h)(Blinov,1983).Whenanelectricfieldisfirstapplied toaplanaraligned(homogeneous)CLCcell,thesamplebecomesscattering at a field above a critical value.The axis of the helix becomes tilted (from