All -Paid US200 8, Jan 7 -Japan Winter School New Functionalities in Glass on

PPhotonichotonic GGlasslass ControllingControlling LightLight withwith NonlinearNonlinear OpticalOptical

GlassesGlasses andand TakumiTakumi FUJIWARAFUJIWARAPlasmonicPlasmonic TohokuTohoku UniversityUniversity GlassesGlasses DepartmentDepartment ofof AppliedApplied PhysicsPhysics OpticalOptical MaterialsMaterials andand SciencesSciences Lab.Lab. OOutlineutline

1)1) BackgroundBackground && MotivationMotivation 2)2) 22nd--orderorder opticaloptical nonlinearitynonlinearity inin glassglass -Controlling light with change of refractive index 3)3) TowardToward realreal applicationapplication ofof electroelectro-- opticoptic glassglass devices;devices; -“UV-poling” and Permanent χ(2) 4)4) RecentRecent topicstopics ofof ourour researchresearch worksworks -New EO glasses and fiber-type devices -“Plasmonic Glass”, light localization/propagation MMotivationotivation

Novel nonlinear “glass materials” for photonic applications

Glass key material

- High and wide range of transparency - Good connectivity to glass fiber - High environmental durability - Easy shaping to fiber and films

…… butbut notnot applicableapplicable forfor signalsignal processingprocessing suchsuch asas opticaloptical switchingswitching andand modulationmodulation etc.etc. AAdvanceddvanced PPhotonichotonic CCommunicationommunication

Functional Photonic Devices/Components with excellent connectivity to the fiber E/O-Switch, Modulator, Converter, etc drived by Second-Order Optical Nonlinearity SSecondecond--OrderOrder OpticalOptical NonlinearityNonlinearity inin GlassGlass

2nd-order optical nonlinearity (1) (2) (3) … P = ε0 (χ E + χ EE + χ EEE + )

P : polarization, ε0: dielectric constant, E: electric field of light 22ndnd--orderorder nonlinearitynonlinearity isis inin glassesglasses withPermanentPermanent inversion connectionconnection toto LiNbO3 crystal with inversion 3 glassglassNOTNOT allowedallowed --fibersfibers --symmetrysymmetry glass-crystal PhotonicPhotonic GlassGlass nonlinearitynonlinearity connection GlassGlass withwith 22nd--orderorder AlternativeAlternative DescriptionDescription ofof ΔΔnn EO effect (Pockels effect) Electric field of angular frequency：Ｅ（ω） Applied electric field：Ｅ（０） Nonlinear susceptibility：χ(2)

If E(0) > E(ω), at E=E(0) P(2) = ΔχE(ω) EO effect where Δχ=2χ(2)E(0) represents an increase in the susceptibility proportional to the electric field E(0). The corresponding incremental change of the refractive index is obtained by the relation n2=1+χ, to obtain 2nΔn=Δχ, from which Δn = (χ(2)/n)E(0) Δn= -rn3E/2 is defined in the Pockels effect, thus, EO coefficient r is described by SHG r = - 2χ(2) /n4 FermatFermat’’ss PrinciplePrinciple：： BoundaryBoundary RefractionRefraction

SpeedSpeed ofof lightlight：： small n (fast V ) VV＝＝CC0／／ｎｎ velocity in the medium： V free space velocity： C0 refractive index： ｎｎ

large ｎ →V：slow small ｎ →V：fast large n (slow V )

Light rays travel along the path of least time by

refraction in this case （Snell’ Law: sinθ/sinφ=nL/nS） ControllingControlling LightLight withwith EOEO EffectEffect

ChangeChange ofof refractiverefractive indexindex ((ΔΔnn))

AngleAngle ofof refractionrefraction changedchanged byby EEappl

Light Optical Fiber EO medium

Cotrolling light with EO devices through 2nd order optical nonlinearity ElectroElectro--OpticOptic DevicesDevices

Directional Coupler

2x2 Optical Switch

optical waveguides

electrodes

optical waveguides

Coupled-mode theory : “Optical waves in crystals” NLO substrates A. Yariv and P. Yeh AdvantagesAdvantages ofof ““PhotonicPhotonic GlassGlass

Photonic glass* is the best solution for glass-”” fiber networks. Ｘ *Second-Order Optical Nonlinearity

-Long-term stability -Low excess loss -Easy to connect HHowow toto induceinduce χχ(2) ??

22ndnd--orderorder nonlinearitynonlinearity inducedinduced inin glassglass 1. Poling with UV/heating 2. Crystallization PolingPoling CrystallizationCrystallization χ(2) value ~10~10 pm/Vpm/V ~1~1 pm/Vpm/V patterning YesYes (UV)(UV) NoNo stability (no decay) NoNo YesYes

LiNbOLiNbO33 :: ~28~28 pm/Vpm/V PolingPoling inin Glass/FiberGlass/Fiber Breaking of inversion symmetry in glass

Poling in glass… electrodes + glass AppliedApplied electricelectric fieldfield --AtAt elevatedelevated temperaturetemperature --WithWith UVUV--laserlaser irradiationirradiation _

Field-Induced Microstructuring in Glass Materials UVUV--PolingPoling inin Glass/FiberGlass/Fiber

The Optical Fibre Technology Centre (OFTC) University of Sydney, Australia UV-Poling in Ge:SiO Fiber Thermal Poling 2

χ(2) was limited by -Larger χ(2) : ~10pm/V <1pm/V -Periodic structure: χ(2) gratings -Degradation mechanism?mechanism? (2) (2) EE EE χ χ E E (3) (3) χ χ

EE~ EE~ (2) (2) χ χ (2) (2) χ χ

agents agents

Orientation of Orientation of Possible Origin of Induced Possible Origin of Induced UVUV--PolingPoling inin Ge:SiOGe:SiO22 GlassGlass

UV-poling in bulk glass Maker-fringe SHG measurement

-VAD preforms: 15GeO2-85SiO2 -Quantitative evaluation of SHG -E -field: 0~3x105 V/cm d (χ) coefficients

-UV-laser: 193 nm -Values of d33, d31 -Refractive index: ne, no CreationCreation ofof χχ(2)(2) inin UVUV--PoledPoled GlassGlass

UV-poling electric field dependences in Ge-doped SiO2

d =(1/2)χ(2) DecayDecay BehaviorsBehaviors ofof InducedInduced χχ(2)(2)

--χχ(2) disappearancedisappearance --singlesingle--expo.expo. decay?decay? QuantitativeQuantitative AnalysisAnalysis ofof DecayDecay (1)(1)

Absorption Spectra and defects in Ge-doped SiO2 Glass QuantitativeQuantitative AnalysisAnalysis ofof DecayDecay (2)(2) Decay of Δα Deconvolution of Δα

χχ(2) decaydecay isis similarsimilar toto GeEGeE’’ !! DecayDecay TimeTime ConstantConstant ofof InducedInduced χχ(2)

Decay time constant of χ(2) induced in UV-poled glass

~280 days at RT MechanismMechanism ofof χχ(2)(2) DecayDecay

Comparison of ValuesValues ofof EEaa activation energies χ(2) decay and GeE’ ~0.4 eV

Dark conductivity ~0.4 eV IntroductionIntroduction ofof electronelectron scavengers?scavengers? ForFor longlong--termterm stabilitystability

HydrogenHydrogen dopingdoping AchievementAchievement ofof StableStable χχ(2)(2)

applicationapplication toto realreal fieldfield

ForFor 2020 years,years, >90%>90% performanceperformance OriginOrigin andand DecayDecay ofof χχ(2) inin UVUV--PoledPoled GlassGlass EffectiveEffective χχ(2) throughthrough thirdthird--orderorder nonlinearitynonlinearity (2) ~ (3) E χχ ~ χχ Escsc

χχ(3) susceptibility: increased Esc : space-charge field by crystallization caused by defect formation

PermanentPermanent χχ(2) ?? BaBa22TiGeTiGe22OO88 (BTG)(BTG) Fresnoite Crystalline Structure

Origin of Ps(spontaneous polarization)

c axis O

Ti

TiO5 unit

TiO5 unit NovelNovel CrystallizedCrystallized GlassGlass－－BTGBTG

Surface Crystallization and Orientation

×: Benitoite (002) phase

T =750 °C × HT

(001) (311) Benitoite phase c-axis

THT=730 °C BTG crystalline layer Intensity (arb. units) THT=710 °C 5 μm Glass THT=700 °C

10 20 30 40 50 Stoichiometric composition 2θ / deg. 2nd2nd--OrderOrder NonlinearityNonlinearity inin BTGBTG

BTG55BTG55:: 30BaO30BaO2--15TiO15TiO2--55GeO55GeO2

0.3 720°C, 3 h

0.2 d =25 pm/V YAG 532 nm λ=1064 nm 0.1 SH intensity (arb. unit) BTG crystallized glass 0 -40 -20 0 20 40 Appl. Phys. Lett., 81, 223(2002). Angle of incidence / deg.

Maker fringe measurement: TheThe largestlargest dd--valuevalue inin glassglass everever reportedreported OpticalOptical AbsorptionAbsorption andand MicrostructureMicrostructure ofof BTG55BTG55 andand BTG50BTG50

100 10 μm BTG55 BTG50 80

60 BTG50 40 10 μm BTG55

Transparency / % Transparency 20

0 300 400 500 600 700 800 Wavelength / nm

CrystallineCrystalline layerlayer ofof BTG55BTG55 isis moremore densedense andand homogeneoushomogeneous thanthan thosethose ofof BTG50.BTG50. PlasmonicsPlasmonics

Surface plasmon locallized in metal nano-particles

J. R. Krenn (2001) -electron beam lithography (EBL)

-ITO doped glass substrates with 200 nm electric conductivity for EBL -gold nano-particles with 100 nm diameter and 40 nm height for a Optical intensity image of Au nano- plasmon resonance wavelength particles ordering in glass substrate of about 630 nm J. of Microscopy, 202, (2001) 122 -plasmon coupling observed by photon scanning tunnelling microscope (PSTM) SurafaceSuraface PlasmonPlasmon (SP)(SP)

1. Excitation of SP by photon coupling

b)

a) Kretschmann configuration and b) ray tracing of an Attenuated Total Reflection (ATR) setup for coupling surface plasmons. In the case, the surface plasmon propagates along the metal/dielectric interface. SurafaceSuraface PlasmonPlasmon (SP)(SP)

2. Dispersion relationship for SP

ω light metal non-radiative

Dielectric (glass) plasmon

Wave number of SP： kx Dielectric constants (relative)：ε1 and ε2 for metal and dielectric, respectively.

ω ε1ε2 1/2 kx = c ()ε1+ ε2

c : speed of light, ω : frequency of the wave Since ε1 < 0 in metal, for the solution of Dispersion curve for surface plasmons. At low k, kx (plasmon), the surface plasmon curve (red) approaches the photon curve (blue). ε1(ω) < -ε2, below ωsp LaserLaser--InducedInduced StructureStructure OrderingOrdering

Tellurite-based glasses Periodic Structure with PM

・Nano-crystallization by laser heating XeCl excimer laser（λ=308nm） ・Selective crystallization of metal Te?

・Large nonlinearity: d ~ 30d (LiNbO3) χ(3) ~ 10χ(3) (Au) Phase Mask (PM) 0 ff TeO -200 2 K2O Bi -400 2O3 GeO -600 2 KNbO3-TeO2 BaO -800 MgO glass CaO -1000 SiO 2

-1200 TiO2 P O -1400 2 5 formation (kJ/mol) (kJ/mol) formation formation B2O3

-1600 Al2O3

Nb2O5

Standard Gibbs free energy o o energy energy free free Gibbs Gibbs Standard Standard -1800 KNbO -TeO glass Er O 3 2 2 3 -2000 200 400 600 800 1000 1200 Temperature (K) PhotoPhoto--InducedInduced NanoNano--CrystallizationCrystallization byby UVUV--LaserLaser IrradiationsIrradiations PeriodicPeriodic StructuresStructures ofof NanoNano--ParticlesParticles 22

Structure Ordering in Glass

AFM image (enlarged) SEM image

100 nm ordered structure of nano-particles TEMTEM ImagesImages ofof SurfaceSurface CrossCross--SectionSection UV-Irradiation -Creation of nano-particles with ~100 nm diameter -Laser intensity dependence of nano-particles density -Te metal confirmed by electron diffraction pattern Metallic Nano-Structures on Glass Surface PlasmonicPlasmonic GlassGlass

102 202

101 201

500 nm 100 PlasmonicPlasmonic GlassGlass forfor NanoNano--CircuitCircuit

Photo-Induced Nano-Particles Structure

・Metal nano-particles on glass ・Physics for formation ・Design and control of particles ・Nano-photonic circuits

“Active”-particle Incident photon Output photon

Ordered Nano-Particle Structure Nano-particles ChangeChange ofof EE--fieldfield IntensityIntensity （ＦＤＴＤ）（ＦＤＴＤ）

0.50 0.45 Ex (d = 30 nm) Ex (d = 100 nm) 0.40 Ex (d = 300 nm) B 0.35 0.30 A (arb. units) x

E 0.25 0.20 0.15

Normalized 0.10 0.05 E-field：A 0.00 Normalized Ex = 200 300 400 500 600 700 800 E-field：B Wavelength (nm)

LowLow DegradationDegradation ofof EE--fieldfield inin 100100 nmnm SUMMARYSUMMARY

Controlling Light with Nonlinear Optical Glasses and Plasmonic Glasses

・・DevelopmentsDevelopments ofof newnew nonlinearnonlinear opticaloptical glassesglasses forfor EOEO photonicphotonic devicesdevices FiberFiber for Signal Processing--TypeType DevicesDevices in Optical Communication

・・FormationFormation ofof UVUV--laserlaser inducedinduced metallicmetallic nanonano-- particleparticle structuresstructures onon glassglass surfacesurface PlasmonicPlasmonic for Propagation/Localization of Light GlassGlass