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Active graphene metasurfaces for optoelectronic applications

Nima DabidianGennady Shvets group

University of Texas at Austin

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Switching of Mid-IR light Interferometric measurement of

phase modulation

High collection-efficiency photo-detector

Sub-diffraction low threshold nano-lasers

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The goal:

• Ultra-fast devices for modulation of light intensity, phase , polarization state

• Ultra-fast detection of light intensity. Polarization state.

• Thin device

• Efficient

• Active material: mechanical tunability vs electrical

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Mid-infrared optical properties of graphene

• Broadband response • Small losses

𝜎 (𝜔 )=𝜎 𝑟 (𝜔 )+𝑖𝜎 𝑖 (𝜔 )

𝜎 𝑟 : Resistive

: Inductive 𝝈𝒊/𝝈

𝒓

S. H. Mousavi, e al, Nano Lett. 2013,13,1111-1117

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How to switch light

• A mode with narrow linewidth (high quality factor)

• Large spectral shift (large field enhancement)

• Zero reflectivity at the minimum

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Double-Fano plasmonic metasurface

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Enhanced near-fields due to second Fano

Monopole mode Dipole mode

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Graphene interacts with tangential fields only

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Graphene optical conductivity

𝜎 (𝜔 )=𝜎 𝑟 (𝜔 )+𝜎 𝑖 (𝜔 ) 𝜎 0=𝑒2

4ℏ

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Large modulation depth

Relative reflectivity:

Modulation depth: 80 %

Gap=70nm

Increasing doping

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Higher modulation depth: 90 %

Gap=100nm

Dipole : 80%

Monopole:

23 %

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Triple-Lorenzian fit gives spectral position and life time of the resonances

fitted to Exp. Reflectivity

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QF enhancement near the phonon resonance

QF:

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QF enhancement near the phonon resonance

𝜀𝑒𝑓𝑓=𝜕𝜀𝑟𝑒𝜕𝜔 𝜔+𝜀𝑟𝑒

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Optimizing the optical responseof the resonances

𝜀𝑒𝑓𝑓=𝜕𝜀𝑟𝑒𝜕𝜔 𝜔+𝜀𝑟𝑒

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Collisional time (derivation from the optical conductivity

Electrical transport measurement

𝜏=18 𝑓𝑠 (293𝑐𝑚− 1)

𝜏=14 𝑓𝑠

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Interferometric measurement of phase modulation

• Conventional phase modulator : bulk • Metasurfaces cause abrupt phase shift• Applications in

-Phased array antennas : beam steering -Holograms -Tunable lenses-Tunable retarders

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The experimental setup

Laser

BS

Graphene metasurface

Detector𝐴𝑠𝑖𝑛(𝜔𝑡+Φ1 (𝑥 )+Φ1 ( 0 ))

𝐵(𝑣)𝑠𝑖𝑛(𝜔𝑡+Φ2(𝑉 ))

𝐶 (𝑥 ,𝑣 , 𝑡)𝑥𝑃1

𝑃2

Mirror on a motorized stage

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Beamsplitter

Mirror 1

Mirror 2

polarizer

lens

QCL

MCT detector

pinhole1

pinhole2

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Interference

• -

: Mirror position

(v)

intensity measurement (dots) fitted to the function:

|𝐶(𝑥

,𝑉)|2

𝑐 (𝑣 )=Φ1 (0 ) −Φ2 (𝑉 )

b

,

d (v )=|A|2

2+|B(v)|2

2

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Phase change derivation

Step size of closed loop actuator=63.5 nmΔΦ=Φ (𝑉 1 )− Φ (𝑉=0 )❑

=-c(0)

𝑉=0

𝑉=𝑉 1

𝑉=0

𝑉=0

𝑏𝑎𝑣𝑒𝑟𝑎𝑔𝑒≅ (𝑏¿¿1+𝑏2)/2¿

(

=

Fitted curves

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Y-Pol X-Pol

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Phase shift at

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Comparison between Sim. & Exp.

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Application example: Tunable retarder

𝐸𝑖𝑛𝑐=45°

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Phase shift at

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Application in ultra-fast motion detection

, Fitting parameter : x

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Conclusion

• Dynamic modulation of amplitude, phase , polarization state of Mid-IR light is made possible by integration of graphene to Fano-resonance plasmonic metasurfaces

• Electrically connected metasurface provide the opportunities for independent gating across metasurface and could be potentially used in holographic application.

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Acknowledgements

Collaborators:Prof. Rod Ruoff (UT)

Iskandar Khomanov A. Khanikaev,Kaya Tatar,Simeon Trendafilov, S. Hossein Mousavi, Carl Magnuson,

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Thank you !