Detailed view about the optical antenna and its features.

1. OPTICALANTENNA
PRESENTED BY
GAZALI BASHIR

2. CONTENTS
• INTRODUCTION
• OPERATION
• PLASMONICS
• COMPARISION WITH RF ANTENNA
• Fabrication Of Optical Antenna
• APPLICATIONS
• CONCULUSION

3. OPTICALANTENNA
• A device designed to efficiently convert free-
propagating optical radiation into localized
energy , and vice versa .

4. ANTENNAS: FROM RADIO
FREQUENCIES TO OPTICS
• At radio frequencies, antennas represent the fundamental tool
allowing the connection of subwavelength regions of space
where sources or receivers are located with far-field radiation.
• The classical laws of electromagnetism, as expressed by
Maxwell–Heaviside’s equations, are scale invariant, which
allows the translation of concepts and designs from a frequency
region of the electromagnetic spectrum to another one.

5. • Particularly relevant is the fact that good conductors are not
available in the optical regime.
• In fact, as we get closer to the plasma frequency of metals
(typically in the visible or ultraviolet range), the real part of
their permittivity becomes small and negative, which has
several important implications for their operation as conductors.

6. Properties of metals at optical
frequencies
• The optical response of metals is described by a
complex frequency-dependent dielectric function
ε(ω) = ε1(ω) + iε2(ω).
• Relating the electric field E(ω) and the induced
polarization density as P (ω) = ε0[ε(ω) −
1]E(ω).

7. PLASMON?
• Plasmon is the Quantum of collective oscillations of Metals free
electrons (Plasma) in response to the electric field component of
the EM wave excitation.
• At resonance ,the nanoparticle efficiently absorbs and scatters
light, acts like an antenna.

8. INPUT IMPEDANCEAND MATCHING OF
DIPOLE NANOANTENNAS
• Input optical impedance Zin can be defined as the ratio
of the local potential difference V = g E at the gap and
the induced displacement current ID= jw|D| on the
nanoantenna terminals.
• For nano antennas with a well-defined feeding gap, it
is useful to interpret the input impedance as the
parallel

9. 45
C
L
mm nm
Re[s]>0
Re[s]<0
Load 1
D h
g
l
Slit Slit
Broadcast
Region
Receiver
Region
1 µm
1 µm
20
15
10
5
0
–5
Impedance
(K)
MaximumScattered
Field(a.u.)
–10
650 700 800 850750
Wavelength (nm)
(d)
Zin
Zgap Zdip
Rin
Xin
Rdip
Xdip
3,000
2,500
2,000
1,500
1,000
500
0
600 650 700 750 800 850 900 950
Wavelength (nm)
(e)
1.76
dB
Air (s = 1)
MgF2 (s =2.5)
SiO2 (s =3.9)
GaAs (s = 12.5)
8z
n
x –10
(c)
(b)
(a)
.
• FIG 1
THE NANODIPOLE OPTICAL ANTENNA

10. • connection of the intrinsic dipole impedance
Zdip and the gap impedance Zap [Figure 1(d)].
While Zdip is assumed to be an inherent
property of the nanoantenna and the
surrounding environment ( Rrad).
• Zgap can be modified by loading the gap with
different elements [Figure 1(a)], such as
nanoparticles acting as lumped optical circuit
elements (nanoinductors, nanocapacitors,
nanodiodes, and so on).

11. TUNING OF DIPLOE ANTENNA
• As routinely done at microwaves this loading technique can be
conveniently used to tune the resonance frequency of the
nanoantenna [Figure 1(e)] and/ or to achieve impedance
matching with respect to a given feeding element or network,
e.g., a quantum dot, and molecules, or an optical waveguide.

12. •When the nanoantenna is operated in receiving mode
[the right antenna of Figure 1(b)], gap loading can be
used to gap loading can be used to control the
scattered and received power.
•The quasi-static polarizability of the loaded dipole
antenna, which relates the induced dipole moment p to the
local electric field,
• P = αeElocal where α e= 4Zd+Zl *L
2
/3jwZd
Zd+Zl

13. • By modifying the gap impedance, it is therefore
possible to control the polarizability of the Nano
antenna. assuming .
• Based on these ideas, we can maximize light
absorption at the nanoscale, of large interest for
photovoltaic and energy-harvesting applications.
• Nanophotonic waveguides, which may allow
realizing efficient optical wireless links at the
nanoscale as shown in Figure 1(b) and (c).

14. DIRECTIVE SUBWAVELENGTH
NANOANTENNAS
• The radiation directivity of conventional optical
nanoantennas is limited by their mostly dipolar nature,
which implies a directivity value of D =1.5
• More directive radiation patterns can be obtained by
considering higher order multipolar contributions
[quadrupolar, octupolar, and so forth, as seen in Figure
3(a)], as the directivity grows with the multipolar order
n, as D = (2n + 1) /2.

15. 49
n = 1 n = 2 n = 3 n = 4
Dipole Quadrupole Octupole Hexadecapole
x
z
z
m
p
Huygens
Source
Anti-Huygens
Source
Zero Zero
(Minimum)
–0.5 0 0.5 1.0 –1.0 –0.5 0 0.5 1.0
0
45
30
15
105 90 75
120 60
135
150
165180
–1.0
195
210
225
240 300
255 270 285
345
330
315
0
45
30
15
105 90 75
120 60
135
150
165180
195
210
225
240 300
255 270 285
315
345
330
–3
–1.5
0
1.5
3
1.5
x
(µm
)
x
(µm
)
3
PbTe
–3 –1.5 0
z(µm)
(dB)
12
10
8
6
4
2
0
–2
–3
–1.5
0
1.5
3
1.5
y (µm)
y
(µm
)
3
(dB)
12
108
6
4
2
0
–2
2
0
–2
–2 –4
4
0
z (µm)
2
0SiC
(a)
(b)
–3 –1.5 0
z (µm)
(c)
FIGURE3.Electrically small directive nanoantennas. (a) The radiation patterns of different multipolar orders, corresponding to spherical waves of increasing
angular momentum n.(b) The Huygens and anti-Huygens radiation patterns produced by orthogonal electric and magnetic dipole moments oscillating in
phase or 180° out of phase, respectively.If the nanoantenna operates in receiving mode,then the anti-Huygens scattering patternexhibits a minimum, rather
than a zero,in the forward direction, as discussed in the text.(c)An example of an electrically small Huygens nanoantenna operating at IR frequencies: a
layered nanoparticle with a leadtelluride (PbTe)core and a silicon carbide (SiC) shell (theformer is dielectric, while the latter is plasmonic at IR frequencies).The
plots show the electric field intensity distribution (colors) and the Poynting vector distribution (arrows and streamlines) around the Huygens nanoantenna,
illuminated by a plane wave.Thetwo principal planes as well as a three-dimensional (3-D) view are shown. From the flow of power, it is clear that backward
scattering is minimal, whereas the nanoantenna scatters significantly in the forward direction [58].

16. Fabrication of nanoantennas
• Since the resonances of optical antennas strongly
depend on the exact geometry and dimensions.
• Fabrication of nanoantennas requires reliable and
reproducible structuring techniques with a typical
resolution below 10 nm .

17. Electron-beam lithography
• One of the most popular techniques to fabricate nanoantennas on a
flat substrate is EBL . In the typical implementation of EBL (see
Fig. 16) a high-resolution electron-sensitive resist, e.g. PMMA, is
patterned by means of a focused electron beam .
• The patterns are then developed and selectively removed.A thin
layer of metal with the desired thickness is then evaporated
covering both the voids and the remaining resist.
• Finally, the sample is subjected to a solvent which removes the
remaining resist and leaves the metal structures in the voids
unaffected (lift-off).

18. CONTENTS 41
ITO
Substrate-
beam
development
Au evaporation
lift off
Resist ITO
Substrate
patterning
EBL patterning FIB patterning
e Au
deposition
patterning
Ga+
ions
Au
Figure 16. Sketch of the main steps for standard EBL and FIB nanostructuring of nanoantennas.

19. 2. Focused-ion beam milling
• Another efficient machining technique for the
realization of optical antennas is FIB milling.
• FIB structuring is based on the localized sputtering of
material using accelerated Ga ions extracted from a
liquid metal ion source
• The emitted ions are accelerated, focused into a beam
with a few nanometer spot, and scanned over a
conductive substrate to produce a desired pattern .
• Ion collisions generate a cascade inside the solid, with
atoms being knocked off their equilibrium position, giving
rise to local surface erosion (see the typical fabrication
steps in Fig. 16).

20. APPLICATIONS OF
NANOANTENNAS
• Antennas for Nanoscale Imaging and Spectroscopy.
• Antennas for Photovoltaics
• Antennas for Coherent Control

21. CONCLUSION
• An optical antenna is designed to increase the interaction area of
a local absorber or emitter with free radiation, thereby making
the light-matter interaction more efficient. New ideas and
developments are emerging at a rapid pace, and it is clear that
the optical antenna concept will provide new opportunities for
optoelectronic architectures and devices. Today, the building
blocks for optical antennas are palsmonic nanostructures. It is
also conceivable that future optical antenna designs will draw
inspiration from biological systems such as light harvesting
proteins in photosynthesis.

22. REFERENCES
[1] Francesco Monticone,Chirstos,Argyropoulos,and Andrea Alu “Optical
Antennas controlling electromagnetic scattering ,radiation, and emission at
nanoscale” IEEE ANTENNAS & WAVE PROPAGATION MAGZINE DEC
2017.
[2] A. Mario and A. Alù, Optical Antennas. Cambridge, U.K.: Cambridge
Univ. Press, 2013.
[3] P. Bharadwaj, B. Deutsch, and L. Novotny, “Optical antennas,” Adv. Opt.
Photon, vol. 1, no. 3, pp. 438–483, 2009.

23. THANK YOU