Polarization Engineering through Nanoengineered Morphology Akhlesh Lakhtakia Department of...

Polarization Engineering throughNanoengineered Morphology

Akhlesh Lakhtakia

Department of Engineering Science and Mechanics

The Pennsylvania State University

March 11, 2008Faculty of EngineeringMultimedia UniversityCyberjaya, SelangorMalaysia

Optics Practice

Control of– Intensity– Operating frequency band– Polarization state

Optics Practice

Long History– Intensity– Operating frequency band

Short History– Polarization state

Optics Practice

Polarization – Discovered in 1809

Etienne-Louis Malus 1775 - 1812

Optics PracticePolarization – Discovered in 1809

– “Do not disturb” designs

Etienne-Louis Malus 1775 - 1812

Polarization Engineering

– Anisotropic materials– Uniaxial and biaxial crystals– Piezoelectric materials

– Bianisotropic materials– Chiral materials– Magnetoelectric materials


– Anisotropic materials– Bianisotropic materials

SPIE Press (2003)


– Sculptured Thin Films

SPIE Press (2005)

Students & Collaborators

• Joseph Sherwin, Sean Pursel, Benjamin Ross, Fei Wang (Penn State)

• Mark Horn, Jian Xu (Penn State)• Ian Hodgkinson (Otago)• John Polo (Edinboro)• Juan Adrian Reyes (UNAM, Mexico)

Outline

• Introduction• Optical Modeling• Examples of Polarization Engineering• More Examples• Electrical Control

INTRODUCTION

Sculptured Thin Films

Assemblies of Parallel Curved Nanowires/Submicronwires

Controllable Nanowire Shape

2-D - nematic3-D - helicoidal

combination morphologies

Sculptured Thin Films

Assemblies of Parallel Curved Nanowires/Submicronwires



combination morphologiesvertical sectioning

Sculptured Thin FilmsAssemblies of Parallel Curved Nanowires/Submicronwires



combination morphologiesvertical sectioning

Nanoengineered Materials (1-3 nm clusters)

Controllable Porosity (10-90 %)

Sculptured Thin FilmsAntecedents:

(i) Young and Kowal - 1959

(ii) Niuewenhuizen & Haanstra - 1966

(iii) Motohiro & Taga - 1989

Conceptualized by Lakhtakia & Messier (1992-1995)

Optical applications (1992- )

Biological applications (2003- )

Physical Vapor Deposition (Columnar Thin Films)

Physical Vapor Deposition (Sculptured Thin Films)

Rotate abouty axis fornematicmorphology

Rotate aboutz axis forhelicoidalmorphology

Mix and matchrotations forcomplexmorphologies

Physical Vapor Deposition(Serial Bideposition)

ξ (axis 2)

χv (axis 1)

SnO2

Adapted for STFs by Hodgkinson

Sculptured Thin FilmsOptical Devices: Polarization Filters

Bragg FiltersUltranarrowband FiltersFluid Concentration SensorsBacterial Sensors (Penn State)Light Sources (Penn State)

Biomedical Applications: Tissue Scaffolds (Penn State)Stents (Penn State)Bone Repair (Penn State)

Other Applications: Photocatalysis (Toyota)Thermal Barriers (Alberta)Energy Harvesting (Penn State, Toledo)

Toledo)

OPTICAL MODELING

Optical Modeling of STFs

LinearBianisotropic Materials

SPIE Press (2003)

Optical Modeling of STFsDielectric Materials

Optical Modeling of STFsLocally Orthorhombic Materials

Optical Modeling of STFsHomogenize a collectionofparallel ellipsoidsto get

Sherwin and Lakhtakia (2001-2003): Bruggeman formalism

Mathematica Program

Optical Modeling of STFsWave Propagation

Mathematica Program

EXAMPLES OF POLARIZATION ENGINEERING

Chiral Sculptured Thin Films

Chiral STFs: Circular Bragg Phenomenon

A simple explanation (Coupled-Wave Theory):

• Co-handed wave: Scalar Bragg grating

• Cross-handed wave: Homogeneous bulk medium

Chiral STF as CP Filter

Chiral STF as CP FilterEngineering of Bragg Regime and CP State

Chiral STF as CP Filter

Rotational Speed: Controls

Rotational Sense: Controls

Vapor Incidence Angle: Controls

Engineering of Bragg Regime and CP State

Chiral STF as CP FilterPost-Deposition Engineering of Bragg Regime

Annealing before after

Chiral STF as CP FilterPost-Deposition Engineering of Bragg Regime

Annealing

Blue-shift factors:(i) Decreases pitch(ii) Thins nanowires

Red-shift factors:(i) Increases permittivity

Blue-shifton annealing

Spectral Hole Filter

Central Phase Defect in a Chiral STF

- Homogeneous-layer defect- Isotropic- Anisotropic

- Twist defect

- Structurally-chiral-layer defect


Defect-free


Defect-free

With defect

Thin Chiral STF Thick Chiral STFReflection Hole Transmission HoleCo-handed Cross-handedTheory/Experiment Theory only

Spectral Hole FilterIsotropic-layer defect

Spectral Hole FilterTwist defect

Spectral Hole FilterPost-Deposition Engineering

Chemical Etching

Blue-shift

Pursel, Lakhtakia, and Horn, Opt. Eng. 45 (2007), 040507

Spectral Hole FilterPost-Deposition Engineering

Chemical Etching Columnar Thinning Blue Shift

Pursel, Lakhtakia, and Horn, Opt. Eng. 45 (2007), 040507

Fluid Concentration Sensor

MOREEXAMPLES OF POLARIZATION ENGINEERING

Tilt-Modulated Chiral STF

Tilt-Modulated Chiral STFOrdinary Dielectric Mirror

Advantages:

(1) Single material

(2) Bragg FWHM governed by tilt-modulation amplitude

Ambichiral STFReusch 1869

Ambichiral STF

All layers ofequal thickness.

2 Bragg regimes

Different CP statesreflected

Bragg L

Bragg R

Left-handed structure

Ambichiral STF

Layers ofunequal thickness.

1 Bragg regime

Ambichiral STF

Layers ofunequal thickness.

1 Bragg regime

EP states (and ) reflected

Better for CP and nearly CP states

ELECTRICALCONTROL

ofCIRCULAR BRAGG

PHENOMENON

ELECTRICALLY CONTROLLED CBP


DC voltage across the thickness


Normal incidence


Without dc voltage With dc voltage


Without dc voltage

Pseudo-IsotropicPoint



Pseudo-IsotropicPoint

Further Studies

Electrically Controlled CBP

DC voltage can enhance local linear birefringence Thinner CP filters

Normal incidence


Oblique incidence

Electrically Controlled Narrowband CP Filters: Reflection Holes

Incorporate a Central 90-deg-twist defect

Without dc voltage

L = 30

AmmoniumDihydrogenPhosphate

Normal incidence

Lakhtakia, Asian J. Phys. 15 (2006) 275-282

Electrically Controlled Narrowband CP Filters: Reflection Holes


With dc voltage

L = 16


Normal incidence


Electrically Controlled Ultranarrowband CP Filters: Transmission Holes


Without dc voltage

L = 180


Normal incidence


Electrically Controlled Ultranarrowband CP Filters: Transmission Holes


With dc voltage

L = 58


Normal incidence


Electrically Controlled CBP: Ambichiral Structure

Continuous spiral replaced by stepped spiral60-deg (or less) steps!


RCP rejection LCP rejection

Without dc voltage


Normal incidence


With dc voltage

Normal incidence

RCP rejection LCP rejection


More General Studies


(Local) point group symmetries:

Isotropic 2 classes

Uniaxial 13 classes

Biaxial 5 classes


Oblique incidence

Electrically Controlled CBPIsotropic (zinc telluride)

Without dc voltage

Withdc voltage

Electrically Controlled CBPUniaxial (lithium niobate)

Without dc voltage

Withdc voltage

Electrically Controlled CBPBiaxial (potassium niobate)

Without dc voltage

Withdc voltage

Tunable UltranarrowbandCP Filters: Transmission Holes


Uniaxial (lithium niobate)

Central 90-deg-twist defect


Biaxial (potassium niobate)

Central 90-deg-twist defect

Electrically Controllable CBP

Electrically Controllable CBP

Towards a nano-to-continuum control model

Thesis

Morphology can be nanoengineered

to obtain

desired polarization&

operating frequency band

ThankYou

Polarization Engineering through Nanoengineered Morphology Akhlesh Lakhtakia Department of...

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