terahertz metamaterials: a bulk approach

TERAHERTZ METAMATERIALS: A BULK APPROACH

Eric Lheurette 1, Frédéric Garet 2, Shenxiang Wang 1, Charles Croënne 1, Karine Blary 1,

Jean-Louis Coutaz 2 et Didier Lippens 1

1 IEMN - UMR CNRS 8520, Université de Lille 1, 59652 Vi lleneuve d'Ascq Cedex - France 2 IMEP LAHC - UMR CNRS 5130, Université de Savoie, 7337 6 Le Bourget du Lac Cedex - France

GDR THz - International Workshop, 29 March - 1 April 20 11, Tignes, France

Outline

• Negative Index Metamaterials (NIM)• Targeting the THz spectrum• Stacked subwavelength hole arrays

Design and fabrication

R & T measurements

Angular measurements

• ApplicationsEnvironment sensing

Polarization rotation

Focusing


Negative Index Metamaterials (NIM)

• Negative permittivityDiluted metal in order to decrease the plasma frequency

• Negative permeabilityResonating current loops

J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs, "Extremely LowFrequency Plasmons in Metallic Mesostructures," Physical Review Letters, vol. 76, pp. 4773, 1996.

J. B. Pendry, A. J. Holden, D. J. Robbins, and W. J. Stewart, "Magnetism fromconductors and enhanced nonlinear phenomena," Microwave Theory andTechniques, IEEE Transactions on, vol. 47, pp. 2075-2084, 1999

H

Ek

D. R. Smith and S. Schultz, UCSD

The combination of wire and current loopsarrays permits one to synthesize a Negative Index Metamaterial


Negative Index Metamaterials (NIM)

F. Zhang, D. P. Gaillot, C. Croenne, E. Lheurette, X. Melique, and D. Lippens, "Low-loss left-handed metamaterials at millimeter waves," Applied Physics Letters, vol. 93, pp. 083104, 2008.

Incident wave polarization requirement:

The substrates need to be stacked and illuminatedunder grazing incidence.


Targeting the THz spectrum

• Stacked subwavelength arrays

M. Navarro-Cia, M. Beruete, M. Sorolla, and I. Campillo, "Negative refraction in a prism made of stacked subwavelength hole arrays," Opt. Express, vol. 16, pp. 560-566, 2008.

• « Fishnet » approach

S. Zhang, W. Fan, K. J. Malloy, S. R. Brueck, N. C. Panoiu, and R. M. Osgood, "Near-infrared double negative metamaterials," Opt. Express, vol. 13, pp. 4922-4930, 2005.

J. Valentine, S. Zhang, T. Zentgraf, E. Ulin-Avila, D. A. Genov, G. Bartal, and X. Zhang, "Three-dimensional optical metamaterial with a negative refractive index," Nature, vol. 455, pp. 376-379, 2008

• « Nanorod » approach

V. M. Shalaev, W. Cai, U. K. Chettiar, H.-K. Yuan, A. K. Sarychev, V. P. Drachev, and A. V. Kildishev, "Negative index of refraction in optical metamaterials," Opt. Lett., vol. 30, pp. 3356-3358, 2005

B. Kante, S. N. Burokur, A. Sellier, A. d. Lustrac, and J. M. Lourtioz, "Controlling plasmonhybridization for negative refraction metamaterials," Physical Review B (Condensed Matterand Materials Physics), vol. 79, pp. 075121, 2009.


Stacked subwavelength hole arraysdesign and fabrication

Fullwavesimulations

Eigenmode

Scatteringparameters

Typical size of the unit cell

Diameter of the aperture 125 µm

Elliptical Aspect Ratio (EAR) 1,8

Metal thickness 0,4 µm

Periodicity along k 26 µm

Periodicity along E : ay 340 µm

Periodicity along H : ax 340 µm

BenzoCycloButhene (BCB) / gold stackLimited thickness due to to the stress in BCB interlayers



C. Croënne, F. Garet, K. Blary, É. Lheurette, J.-L. Coutaz and D. Lippens, Bulk metamaterials at terahertz frequencies : thesubwavelength hole stacked arrays approach, EuMC 2009, Roma

Impedance matching for EAR > 1,6The dispersion diagrams do not fit.



2,121,12

2,222,111,221,121,222,122,221,112

2,122

1,1212 ))(cosh(2

SS

SSSSSSSSSSll

−−+++=−γ

1,ijS : structure of length l1

2,ijS : structure of length l2 B. Bianco and M. Parodi, "Determination of the propagation constant of uniformmicrostrip line," Alta Frequenza, vol. 2, pp. 107, 1976.

Description of the dispersion from a7-3 unit cell differential analysis



• BCB coating (13 µm)Dow-Cyclotene 3022-63

• BCB polymerisation

• Optical lithographyAznLOF 2070

• Metal evaporating, lift-offCr : 200 Å / Au : 4000 Å / Cr : 200 Å

C. Croënne, F. Garet, É. Lheurette, J-L. Coutaz, and D. Lippens, "Left handed dispersion of a stack of subwavelength hole metal arrays at terahertz frequencies," Applied Physics Letters, vol. 94, pp. 133112, 2009.



• BCB coating (26 µm)


• Optical lithography

• Metal evaporating, lift-off



• BCB coating (13 µm)




GaAs substrate wet etchingH2SO4 : 1 / H2O : 1 / H2O2 : 8


Stacked subwavelength hole arraysR & T measurements

transmission reflexion

• Pump-probe methodPhase information

• Transmission and reflection measurementsDefinition of the generalized Sij matrix

L. Duvillaret, F. Garet and J.L. Coutaz., « A reliable method for extraction of material parameters in THz Time-Domain Spectroscopy»IEEE Journal of Selected Topics in Quantum Electronics, 1996, Vol. 2, pp. 739 – 746.

-20

-10

0

10

20

30

40

50

0 12 24 36 48 60

sign

al (

a.u.

)

time (ps)

0.001

0.01

0.1

1

10

0 1 2 3 4 5 6

THz

field

(u.a

.)

frequency (THz)

IMEP-LAHC, Chambéry, University of Savoie



Transmission properties of a 3-cell structure

Bandgap between the left- and right-handed bands



Transmission properties of a 5-cell structure

Continuous evolution from the left- to the right-handed ba nds



S. Wang, F. Garet, K. Blary, C. Croënne, E. Lheurette, J.-L. Coutaz, and D. Lippens, "Composite left/right-handed stacked hole arrays at sub-millimeter wavelengths," Journal of Applied Physics 107, 074510 (2010)

Refractive index dispersion

3-cell structure 5-cell structure


Stacked subwavelength hole arraysAngular measurements

Radiation boundary

Wave port

Perfect electric boundary

5 step-prism

10 step-prism

Electric field mapping

Output plane refracted angle

FEM simulations conditions



FEM simulations: 5-step prism

f = 0.456 THz



f = 0.492 THz




f = 0.490 THz




f = 0.630 THz




THz – Time Domain Spectroscopy

Ti:Sa laser excitation (50 fs pulse duration for a repetition rate of 100 MHz )

Low temperature-grown GaAs substrates integratingdipole antennas

High resistivity silicon hyper hemispherical lenses

Characterization of 5 and10-step prisms



Experimental results: 5-step prism



Experimental results: 10-step prism

S. Wang, F. Garet, K. Blary, E. Lheurette, J.-L. Coutaz, and D. Lippens, "Experimental verification of negative refraction for a wedge-type negative index metamaterial operating at terahertz," Applied Physics Letters, vol. 97, pp. 181902, 2010


ApplicationsEnvironment sensing

ay 29 µm

ax ax = 2*ay

Metal thickness 0,4 µm

BCB thickness : az 13 µm

dy 170 µm

dx 170 µm


ApplicationsPolarization rotation

E-vector orientation for mode 1

E-vector orientation for mode 2

Cylindrical coefficients

)(

)(

TyxTxyiTyyTxxT

TyxTxyiTyyTxxT

−−+=−−++=+

T

T

−

+ Right-Handed CircularPolarization (RCP)

Left-Handed CircularPolarization (LCP)


ApplicationsPolarization rotation

[ ])arg()arg(2

1−+ −= TTθ

Rotary power ~ 1035 /λ

100 degrees rotation for a 3-layer structure


ApplicationsFocusing

1 THz focusing with gradient refractive index lens

Structure:Number of layes: 5ax=ay=170 µmaz=13 µmThickness of gold: 400 nmElliptical ratio: 2Diameter of short axis: ~59 µm 8.00x1011 9.00x1011 1.00x1012 1.10x1012 1.20x1012

-5

-4

-3

-2

-1

0

1

2

Rea

l (n)

Frequency (Hz)

n_53um n_54um n_55um n_56um n_57um n_58um n_59um n_60um n_61um n_62um n_63um

A. O. Pinchuk and G. C. Schatz, "Metamaterials with gradient negative index of refraction," J. Opt. Soc. Am. A, vol. 24, pp. A39-A44, 2007.


ApplicationsFocusing

1 THz focusing with gradient refractive index lens

Simulation of one lens (9 metallic stacked layers) @ 940 GHzDiameter decreases along the radius from 62 to 52 µm (parabolic function)(yellow arrow)

Hk

E

E field magnitude Real Poynting vector


Conclusions

• Stacked subwavelength hole arrays as THz NIMR & T measurements:

-3 dB @ 0.5 THz Zero index working capabilities

Angular measurementsNegative refraction with a significant level near the Zero angle

• ApplicationsEnvironment sensing

FOM > 500 by means of an asymmetric pattern (~1 THz)

Polarization rotationRotary power > 1000 / λ

FocusingDesign of a NIM GRIN lens for 1 THz operation


terahertz metamaterials: a bulk approach

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