my works slideshare hl

1

Active graphene metasurfaces for optoelectronic applications

Nima DabidianGennady Shvets group

University of Texas at Austin

2

Switching of Mid-IR light Interferometric measurement of

phase modulation

High collection-efficiency photo-detector

Sub-diffraction low threshold nano-lasers

3

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

4

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

5

How to switch light

• A mode with narrow linewidth (high quality factor)

• Large spectral shift (large field enhancement)

• Zero reflectivity at the minimum

6

Double-Fano plasmonic metasurface

7

Enhanced near-fields due to second Fano

Monopole mode Dipole mode

8

Graphene interacts with tangential fields only

9

Graphene optical conductivity

𝜎 (𝜔 )=𝜎 𝑟 (𝜔 )+𝜎 𝑖 (𝜔 ) 𝜎 0=𝑒2

4ℏ

10

Large modulation depth

Relative reflectivity:

Modulation depth: 80 %

Gap=70nm

Increasing doping

11

Higher modulation depth: 90 %

Gap=100nm

Dipole : 80%

Monopole:

23 %

12

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

fitted to Exp. Reflectivity

13

QF enhancement near the phonon resonance

QF:

14

QF enhancement near the phonon resonance

𝜀𝑒𝑓𝑓=𝜕𝜀𝑟𝑒𝜕𝜔 𝜔+𝜀𝑟𝑒

15

Optimizing the optical responseof the resonances

𝜀𝑒𝑓𝑓=𝜕𝜀𝑟𝑒𝜕𝜔 𝜔+𝜀𝑟𝑒

16

Collisional time (derivation from the optical conductivity

Electrical transport measurement

𝜏=18 𝑓𝑠 (293𝑐𝑚− 1)

𝜏=14 𝑓𝑠

17

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

18

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

19

Beamsplitter

Mirror 1

Mirror 2

polarizer

lens

QCL

MCT detector

pinhole1

pinhole2

20

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

21

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

23

Y-Pol X-Pol

24

Phase shift at

25

Comparison between Sim. & Exp.

26

Application example: Tunable retarder

𝐸𝑖𝑛𝑐=45°

27

Phase shift at

28

Application in ultra-fast motion detection

, Fitting parameter : x

29

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.

30

Acknowledgements

Collaborators:Prof. Rod Ruoff (UT)

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

31

Thank you !