my first two works

1. Active graphene metasurfaces for
optoelectronic applications
Nima Dabidian
Gennady Shvets group
University of Texas at Austin
1

2. Switching of Mid-IR light
Interferometric measurement of
phase modulation
High collection-efficiency
photo-detector
Sub-diffraction low threshold
nano-lasers
2

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
3

4. Mid-infrared optical properties of graphene
• Broadband response
• Small losses
𝜎 𝜔 = 𝜎𝑟 𝜔 + 𝑖 𝜎𝑖 𝜔
𝜎𝑟 ∶ Resistive
𝜎𝑖 : Inductive 𝝈𝒊/𝝈𝒓
S. H. Mousavi, e al, Nano Lett. 2013,
13,1111-1117 4

5. How to switch light
• A mode with narrow linewidth
(high quality factor)
• Large spectral shift (large field
enhancement)
• Zero reflectivity at the minimum
5

6. Double-Fano plasmonic metasurface
6

7. Enhanced near-fields due to second Fano
Monopole mode Dipole mode
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8. Graphene interacts with tangential fields only
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9. Graphene optical conductivity
𝜎 𝜔 = 𝜎𝑟 𝜔 + 𝜎𝑖 𝜔 𝜎0 =
𝑒2
4ℏ
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10. Large modulation depth
Relative reflectivity:
Modulation depth: 80 %
Gap=70nm
Increasing doping
10

11. Higher modulation depth: 90 %
Gap=100nm
Dipole : ∆𝜔 𝑑 Γ𝑑 ≈ 80%
Monopole: ∆𝜔 𝑚 Γ 𝑚 ≈ 23 %
11

12. Triple-Lorenzian fit gives spectral position and life
time of the resonances
𝑟(𝜔)
2
fitted to
Exp. Reflectivity
12

13. QF enhancement near the phonon resonance
QF:
13

14. QF enhancement near the phonon resonance
𝜀 𝑒𝑓𝑓 =
𝜕𝜀 𝑟𝑒
𝜕𝜔
𝜔 + 𝜀 𝑟𝑒
14

15. Optimizing the optical response
of the resonances
𝜀 𝑒𝑓𝑓 =
𝜕𝜀 𝑟𝑒
𝜕𝜔
𝜔 + 𝜀 𝑟𝑒
15

16. Collisional time (𝝉) derivation from
the optical conductivity
Electrical transport measurement
𝜎 ∶ 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦
𝜏 = 18 𝑓𝑠 (293 𝑐𝑚−1)
𝜏 = 14 𝑓𝑠
16

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
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18. The experimental setup
Laser
BS
Graphene metasurface
Detector
𝐴𝑠𝑖𝑛(𝜔𝑡 + Φ1 𝑥 + Φ1 0 )
𝐵(𝑣)𝑠𝑖𝑛(𝜔𝑡 + Φ2(𝑉))
𝐶(𝑥, 𝑣, 𝑡)
Type equation here.
𝑥
𝑃1
18
𝑃2
Mirror on a
motorized stage

19. Beam
splitter
Mirror 1
Mirror 2
polarizer
lens
QCL
MCT
detector
pinhole1
pinhole2
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20. Interference
• 𝐶 𝑡 = 𝐴𝑠𝑖𝑛 𝜔𝑡 + Φ1 𝑥 + Φ1 0 + 𝐵𝑠𝑖𝑛 𝜔𝑡 + Φ2 𝑉
• 𝐶(𝑥, 𝑉) 2
=
𝐴 2
2
+
𝐵 2
2
+ 𝐴𝐵𝑐𝑜𝑠(Φ1 𝑥 -Φ2 𝑉 + Φ1 0 )
𝑥: Mirror position
𝑉: 𝐺𝑟𝑎𝑝ℎ𝑒𝑛𝑒 𝑣𝑜𝑙𝑡𝑎𝑔𝑒
𝐶 𝑥, 𝑉 2 = a(v)cos 𝑏𝑥 + 𝑐(𝑣) + 𝑑(v)
intensity measurement (dots) fitted
to the function:
𝐶(𝑥,𝑉)2
𝑐(𝑣) = Φ1 0 − Φ2 𝑉
b= Φ1 𝑥
20
a(v) = AB(v),
d(v) =
A 2
2
+
B(v) 2
2

21. Phase change derivation
Step size of closed
loop actuator=63.5 nmΔΦ = Φ 𝑉1 − Φ 𝑉 = 0
= 𝑐(𝑉1) -c(0)
𝑉 = 0
𝑉 = 𝑉1
𝑉 = 0
𝑉 = 0
𝑏 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 ≅ (𝑏1+𝑏2)/2
21
𝑓𝑖𝑡 𝑡𝑜 𝑐𝑜𝑠(𝑏 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑥 + 𝑐)
𝐼 𝑛𝑜𝑟𝑚 𝑥, 𝑣 =
C x,v 2−d(v)
a(v)
=

22. Fitted curves

23. Y-Pol X-Pol
23

24. Phase shift at 𝝀 = 𝟕. 𝟔𝟗𝝁𝒎
24

25. Comparison between Sim. & Exp.
25

26. Application example: Tunable retarder
𝐸𝑖𝑛𝑐 = 45°
26

27. Phase shift at 𝝀 = 𝟕. 𝟔𝟗𝝁𝒎
27

28. Application in ultra-fast motion detection
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cos c v + b 𝑎𝑣𝑒x , 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.
29

30. Acknowledgements
Collaborators:
Prof. Rod Ruoff (UT)
Iskandar Khomanov
A. Khanikaev,
Kaya Tatar,
Simeon Trendafilov,
S. Hossein Mousavi,
Carl Magnuson,
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31. Thank you !
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