AAWSAP DIRD, Metamaterials for Aerospace Applications, April 2010

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UNCLASSIFIED/ (FOR OFEICI0k YSE 8Htt
,----------2
A=l ­ cos0-.Jt:YY I A , -sin. 20/(µxxA z>
(4)
cos0 + J£ YY Iµ,, - sin 2 0 l(µx.<µ ,,)
where we've assumed that, for normal incidence, this metamaterial is impedance­
matched: £ YY = 1-'zz = - 1+ i. Equation 4 can be simplified under the assumption
oflcS')'.)'I >> l,µ"" = 1: A :=:d - tan4(0/2), implying that A~ 0.97 even for 0 = n /6. The
challenge, if course, is to design a true impedance-matched optical metamaterial.
Success has been achieved in designing such a metamaterial (Reference 20).
The recently published design is shown in Figure 19. The unit cell consists of two layers
of plasmonic antennas; the cut-wire antenna that imparts magnetic (as well as some
electric) response to this metamaterial, and the continuous-wire antennas that impart a
purely electric response. It is found that the wide-angle capability could be very
important for several applications. Wide-angle power absorption efficiency is desirable
for miniaturizing photodetectors or microbolometers down to the wavelength size.
Continuous Silver
20
nm
80
nm
I
I
wires
control
µ eff
1450
1500
1550
1600
1650
1700
Wavelength [nm]
Figure 20. Specific Design of a Wide-Angle Plasmonic Absorber Based on Negative Index Metamaterial
Operating at A= 1550 nm. Left panel: Schematic of the silver-based plamonic structure. Right panel: Extracted
permittivity and permeability for the normal incidence demonstrate impedance matching: £ YY =µ,, =-1 + i.
(Reference 20)
For example, to focus light on a wavelength-sized photodetector or micro-bolometer
requires high-NA optics (a NA=0.5 or higher). Therefore, a photodetector should be
able to absorb light incident at 30 degree angle. For advanced aerospace platforms it is
easy to envision a scenario where an airborne platform is powered by a high-power
infrared laser source located on Earth. If the wavelength falls inside the transparency
window of the atmosphere (between 3 and 4 µm, and also around 10 µm), then such a
22
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3
2
_1
-2
-3
Impedance
- Matching , ..
, .
,'
-. lit -
..
I
,. ,.. • -
-
Re e
""'" Im E
■ •• Reµ
Im.ti
-4~----~-~ --~-~