“Hybrid electronic-photonic devices at THz
frequencies: antennas and circuit elements
teach new tricks to THz photonic devices
Raffaele Colombelli
Institut d’Electronique Fondamentale
Univ. Paris Sud - Orsay
France
Cortona – Scuola di Fotonica 2013
1
Acknowledgements
The QCL team at our Institute:
Collaborations:
Elodie Strupiechonski
A. Degiron
Extreme light confinement in THz QCLs
Univ. Paris Sud, France
Gangyi Xu
J.F. Lampin
THz Photonic Heterostructures
IEMN, Lille (France)
I. Sagnes, G. Beaudoin
Bruno Paulillo
LPN – CNRS, France
Antenna-based THz devices
E. H. Linfield, S. P. Khanna, L. Li
University of Leeds, UK
Adel Bousseksou
Plasmonics - Mid-IR QCLs
C. Sirtori, Y. Todorov
Univ. Paris 7, France
Daniel Chastanet
Plasmonics - Mid-IR QCLs
Y. De Wilde, L. Greusard
ESPCI, Paris - FR
Yacine Halioua
THz Photonic Crystals
S. Dhillon, P.Cavalié
ENS Paris, France
Jean-Michel Manceau
Intersubband Polaritonics in the THz
G. Strasser, M. Andrews, P. Klang
Wien Univ. Austria
Souad Moumdji
QCLs Performances - THz
Cortona – Scuola di Fotonica 2013
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Outline
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators
 Antennas or circuits?
 Context of THz research
 Sub-wavelength sized resonators: circuit vision
 Sub-wavelength sized resonators: antenna vision
Towards antenna
detectors
Conclusions and
Perspectives
 Towards antenna detectors: coupling into small volumes
 Conclusions and Perspectives:
towards a THz nanolaser, antenna-coupled detectors…
Cortona – Scuola di Fotonica 2013
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What is an antenna?
• Balanis/Webster dictionary:
“a usually metallic device (as a rod or wire) for
radiating or receiving radio waves.”
D << 
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What is an antenna?
• Balanis/Webster dictionary:
“a usually metallic device (as a rod or wire) for
radiating or receiving radio waves.”
• Electromagnetics: a transition device between
free space and a region where EM waves are
localized / guided
THIS IS A MUCH MORE GENERAL DEFINITION!
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Schematics
D
Resonator
or
Source
or
Detector
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It can have a familiar shape
• The horn antenna: Cortona – Scuola di Fotonica 2013
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It can have a familiar shape
• The horn antenna: D
Exactly the same concept!
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The natural questions to ask an antenna
• At which frequency do you operate? • Do you operate in all directions of space, or at a special angles?
• How much radiation you capture? (0.01%, 10%, 99%?)
• These are all very reasonable questions!
• Bandwidth, Directivity, Efficiency…
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A different (different?) object: the familiar LC circuit
Magnetic
Field
Lines
Localized
Electric
Field
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Let’s ask some questions…1
Magnetic
Field
Lines
Localized
Electric
Field
At which frequency do you operate?
Narrowband, since there is a resonance frequency:
1
f 
2 L  C
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Intermezzo... on D and 
Magnetic
Field
Lines
Localized
Electric
Field
Note that: D << =c/f, in general!
Question: what is mediating the energy exchange?
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Let’s ask some questions…2
B
k-light
Do you operate in all directions of space, or at a special angle?
Energy can be fed to the system via the inductance.
But the magnetic field must be correctly oriented
There is therefore directionality
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Let’s ask some questions…3
B
k-light
How much radiation you capture? (0.01%, 10%, 99%?)
It depends on many factors …
(how many coil number? Which material is sandwiched in the capacitor plates? What is the resonance frequency?)
However, it is a good question!
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This is not an “academic” question: split‐ring resonators and metamaterials
λ
These are all LC circuits…
…or antennas
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Do you know the “duck test”?
If it looks like a duck, swims like a duck, and quacks like a duck…
then it probably is a duck! This system has the same properties of an antenna system!
It feeds light into a small volume
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A third example: photonic structures
•
Photonic crystals (PCs): structures where the phase velocity of electromagnetic waves varies periodically in 1D, 2D or 3D
•
In the ‘70’s several optical PCs were created:
– 1D optical PCs  the DFB laser – A 2D PC  multi‐layered “Bragg” fiber.
• Late 1980’s: PCs are “discovered” and described in the current form
– 1987: E.Yablonovitch “photonic bandgaps” for spontaneous emission control – 1987: S. John Anderson localization of photons
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A third example: photonic structures
•
Photonic crystals (PCs): structures where the phase velocity of electromagnetic waves varies periodically in 1D, 2D or 3D
•
In the ‘70’s several optical PCs were created:
– 1D optical PCs  the DFB laser – A 2D PC  multi‐layered “Bragg” fiber.
• Late 1980’s: PCs are “discovered” and described in the current form
– 1987: E.Yablonovitch “photonic bandgaps” for spontaneous emission control – 1987: S. John Anderson localization of photons
• Current PC research involves many areas:
Devices  Lasers, emission enhancement…
High-index (phase-velocity) contrast  Slow light
High Q-factors/small active volumes  All-optical switching
Metallic photonic-crystals (THz)  Surface emission and
control
Cortona – systems
Scuola di Fotonica 2013
 And more! Opto-mechanical




20
Photonic structures as antennas
453 µm (=4.3 )
Lght
Emission
Laser core
Ti/Au layer
• It couples radiation from a small region into free space
• It has a coupling efficiency • It has a preferential direction (orthogonal to the surface)
• It can be considered as an “antenna” too!
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Homework 1
453 µm (=4.3 )
Lght
Emission
Laser core
Ti/Au layer
• Which term this antenna relies on?
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Message 1:
Antennas are essentially optical transducers
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Message 2: Circuit picture or antenna picture are two sides of the same coin
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The goals: using THz QC lasers and THz (QWIP) detectors in combination with antennas/circuits
- “Nano”lasers
- Frequency tunability
with a circuit
THz Detectors with low dark currents
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Why the THZ
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators
 Antennas or circuits?
 Context of THz research
 Sub-wavelength sized resonators: circuit vision
 Sub-wavelength sized resonators: antenna vision
Towards antenna
detectors
Conclusions and
Perspectives
 Towards antenna detectors: coupling into small volumes
 Critical coupling?
 Conclusions and Perspectives:
towards a THz nanolaser, antenna-coupled detectors…
Cortona – Scuola di Fotonica 2013
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Context : Why the THZ (I)
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators
Photonics/Lasers
Electronics/Oscillators
Diffraction limit  /2
Resonance given by L and C
e f fici e
n
c
y
…
THz gap
radiowaves
…e f f
ici
en
cy
UV
Towards antenna
detectors
Conclusions and
Perspectives
Cortona – Scuola di Fotonica 2013
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Context : Why the THZ (II)
Electronics/Oscillators
No lower-size limit
(RC circuit)
Photonics/Lasers
Lower-size limit = /2
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Context : Why the THZ (III)
Antennas or
circuits?
e f fici e
Hybrid electronic
photonic sub-
resonators
Conclusions and
Perspectives
Diffraction limit  /2
Resonance given by L and C
Context of THz
research
Towards antenna
detectors
Photonics/Lasers
Electronics/Oscillators
n
c
y
…
THz gap
…e f
fi
cie
nc
radiowaves
Highly-confining
High-contrast
Metal-metal Waveguides
UV
Devices active regions:
- Quantum Cascade lasers
- Quantum well detectors
Mostly
“diffractive” devices
Surface plasmon mode:
extreme confinement
Sub-wavelength-thick AR
Nearly perfect metal in THz: low
loss (15-20 cm-1)
 Inter-subband transition
 Cascade design: high power
 Wavelength: 3m – 200 m
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y
Photonic crystals and graded photonic heterostructure
THz QC lasers: surface‐emission
Wavelength (µm)
453 µm (=4.3 )
On chip tunability,
surface emission
110
105
100
95
Optical power
•
115
2.6
2.7
2.8
2.9
3.0
3.1
Frequency (THz)
•
Above LN2 operation:
•
Excellent far‐field emission patterns:
Y. Chassagneux et al., Nature 2009
Y.Chassagneux et al., APL 2010
G. Sevin et al., APL 2010,
Scuola di Fotonica 2013
Xu et al. Nature Comms. 3,Cortona
952– (2012)
30
COURTESY: F. Capasso / Harvard Univ. (USA)
Wavefront engineering – 2D Collimator
Cortona – Scuola di Fotonica 2013
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Motivations merging THz lasers
with oscillators
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators
Towards antenna
detectors
Conclusions and
Perspectives
Can we develop a class of (THz) resonators
with functionalities borrowed from
electronics?
 A fundamental question: a laser with
fundamentally no lower-size limit in 3D?
Capacité
Région active
Inductance
Capacité
(Walther et al., Science 2010)
Extreme mode confinement
 THz Detectors
 Light-matter strong coupling regime
 Nanolasers
Frequency tunability with an external electronic circuit
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Hybrid electronic photonic sub- resonators
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators
Towards antenna
detectors
Conclusions and
Perspectives
 Antennas or circuits?
 Context of THz research
 Sub-wavelength sized resonators: circuit vision
 Sub-wavelength sized resonators: antenna vision
 The antenna vision: coupling into small volumes
 Perspectives: towards a THz nanolaser, antennacoupled detectors…
Cortona – Scuola di Fotonica 2013
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Device miniaturization in the THz
“Photonic” and “Electronic” regions
Antennas or
circuits?
Light confinement in an optical device
Photonic devices region
Context of THz
research
10
Metallic disk
PhC Laser
Conclusions and
Perspectives
Vtot/(/2neff)3
Towards antenna
detectors
1
Bragg
0.1
PBG default mode
LC laser
Walther et al., PhD Thesis
Hybrid electronic
photonic sub-
resonators
LC Polariton
0.01
electrical pumping
optical pumping
Spaser
1E-3
0.1
1
10
100
Electronic devices region
Lmax/(/2neff)
Noginov et al., Nature 460 (2009)
Cortona – Scuola di Fotonica 2013
Walther et al, Science 327, 1495 (2010)
Geiser et al., PRL 108, 106402 (2012)
34
Photonic devices: At least one dimension
must be /2n
Feedback due to mirror reflectivities:
L
r1
r2
Phase condition : r1r2ei2kLe(γ-Γ)L = 1
kL = mπ
,
(k2 = nω2/c2)
L
Lmin = λ0/2n
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Electronic devices: almost no size limitation
(LC resonators)
• Laser cavity
resonator
C : Capacitance
I
R : Résistance
R*I
Q
Q/C
L*dI/dt
L : Inductance
..
.
L*Q + R*Q + Q/C = 0
ω20 = 1/LC
.
..
m*x + mΓ*x + k*x = 0
Γ = R/L
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A link between these two worlds
exists already: metamaterials
Antennas or
circuits?
Electronic devices: almost no size limitation (LC resonators)
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Towards antenna
detectors
• SRRs are /10!
• Maxwell’s local equation for an isolated element:
Conclusions and
Perspectives

   D
rot H  j 
t
Now we understand better why certain antennas
are „small“ and other ones are not !
Cortona – Scuola di Fotonica 2013
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Device miniaturization in the THz
Sub-diffraction-limit devices? (non-exhaustive list)
Light confinement in an optical device
Antennas or
circuits?
10
Metallic disk
PhC Laser
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Vtot/(/2neff)3
Lmax= 16 μm
λ = 77 μm
Towards antenna
detectors
Conclusions and
Perspectives
Lmax= 44 nm
λ = 525 nm
1
Bragg
0.1
PBG default mode
LC laser
Walther et al., PhD Thesis
Context of THz
research
Photonic devices region
Lmax= 30 μm
λ = 207 μm
LC Polariton
0.01
electrical pumping
optical pumping
Spaser
1E-3
0.1
1
10
100
Electronic devices region
Lmax/(/2neff)
Noginov et al., Nature 460 (2009)
Cortona – Scuola di Fotonica 2013
Walther et al, Science 327, 1495 (2010)
Geiser et al., PRL 108, 106402 (2012)
38
Is it possible to make « optical »devices
in the «electronic » region?
Light confinement in an optical device
Antennas or
circuits?
Photonic devices region
10
Context of THz
research
Metallic disk
PhC Laser
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Bragg
PBG default mode
Towards antenna
detectors
Conclusions and
Perspectives
Vtot/(/2neff)
3
1
LC laser
0.1
LC Polariton
0.01
Spaser
1E-3
0.1
electrical pumping
optical pumping
?
1
Electronic devices region
Noginov et al., Nature 460 (2009)
Cortona – Scuola di Fotonica 2013
Walther et al, Science 327, 1495 (2010)
Geiser et al., PRL 108, 106402 (2012)
10
100
Lmax/(/2neff)
39
Device miniaturization in the THz
The simple way: SRR-like cavity
• Idea : place the SC in the region
where E is confined in a SRR
(usually planar):
• 3D object…
not easy to fabricate
Use the symetry properties:
Charge image
current
SRR-like type resonator:
• Fundamental magnetic mode:
Dipolar electric moment // ez
Dipolar magnetic moment // ey
Semiconductor
Metal
E.
Strupiechonski
APL 100,
131113 (2012)
Cortona
– Scuola et
di al.,
Fotonica
2013
Sub-diffraction-limit resonators operating on the fundamental magnetic resonance
40
Sub-diffraction-limit in 3D
SRR-like cavity vs Patch cavity
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Magnetic resonator: SRR-like cavity
Optical resonator: patch cavity
current
Semiconductor
Semiconductor
Metal
Metal
Towards antenna
detectors
Conclusions and
Perspectives
Lmax = d
Lmax = d
λmagnetic>> 2neffd
Ez
0
Magnetic Dipole
λdipolar< 2neffd
Electric Dipole
Ez
max
0
min
– Scuola diet
Fotonica
2013
E. Cortona
Strupiechonski
al., APL
100, 131113 (2012)
min
41
Device fabrication and characterization
Antennas or
circuits?
Context of THz
research
• SC: 1 µm thick GaAs
• Diameter variation: 5 to 13 µm
• Reflectivity measurement for several diameters (FTIR)
• Control of incident angle, polarization and sample orientation
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Towards antenna
detectors
Conclusions and
Perspectives
Cortona – Scuola di Fotonica 2013
42
Device fabrication and characterization
Antennas or
circuits?
Context of THz
research
• SC: 1 µm thick GaAs
• Diameter variation: 5 to 13 µm
• Reflectivity measurement for several diameters (FTIR)
• Control of incident angle, polarization and sample orientation
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Towards antenna
detectors
B Eφ
Conclusions and
Perspectives
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43
Reflectivity measurements allow one to
identify the modes
Magnetic resonator: SRR-like resonator
Antennas or
circuits?
Context of THz
research
Optical resonator: patch cavity
Semiconductor
Semiconductor
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Metal
Metal
Dipolar
Dipolars (degeneracy removed)
Diameter:
5 µm
7 µm
9 µm
11 µm
13 µm
2
Réflectivité
ONSET of
a NEW mode:
The true,
fundamental
magnetic
resonance
Réflectivité
2
1
1
Setup: FTIR
Lower frenquencies  TDS
0
0
0
1
2
3
4
5
6
7
8
9
10
0
1
Fréquence (THz)
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2
3
4
5
6
7
8
9
10
Fréquence (THz)
44
Sub-wavelength confinement achieved: /6
450
Magnetic resonance
Dipolar resonance
400
Wavelength (µm)
350
λ eff
300
/6
250
200
150
λ eff / 2
100
resonators
photonic
rd
a
d
n
ta
limit
S
diffraction
Below the
50
0
4
5
6
7
8
9
10
11
12
13
14
Diameter (µm)
Cortona
Scuola
di Fotonica
2013
E. Strupiechonski et al.,
APL–100,
131113
(2012)
45
But…is it still an optical cavity?
Define the question…
… or apply the “DUCK” test!
 Let’s perform c-QED (cavity quantumelectrodynamics) with it
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Proof of principle of c-QED: ISB polaritons
Antennas or
circuits?
Optical cavity
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Towards antenna
detectors
Cavity mode
ISB transition
In the strong coupling regime:
Conclusions and
Perspectives
ωupper
ωISB
ωcav
ωlower
New eigen states:
Coherent superposition of
-the ISB excitations of the 2D electron gas
-the cavity photons
Rabi splitting:
2Rabi=ωupper - ωlower
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Proof of principle of c-QED: ISB polaritons
Antennas or
circuits?
Optical cavity
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Towards antenna
detectors
Cavity mode
ISB transition
In the strong coupling regime:
Conclusions and
Perspectives
ωupper
ωISB
ωcav
ωlower
New eigen states:
Coherent superposition of
-the ISB excitations of the 2D electron gas
-the cavity photons
Rabi splitting:
2Rabi=ωupper - ωlower
Room T:
Bare cavity resonance
Low T:
Cavity mode
coupled
with the ISB
fundamental transition
Y. Todorov et al., PRL 105, 196402 (2010)
Cortona – Scuola di Fotonica 2013
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Proof of principle of c-QED: ISB polaritons
Antennas or
circuits?
Optical cavity
SRR-like cavity
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Towards antenna
detectors
Cavity mode
ISB transition
In the strong coupling regime:
Conclusions and
Perspectives
ωupper
ωISB
?
ωcav
ωlower
New eigen states:
Coherent superposition of
-the ISB excitations of the 2D electron gas
-the cavity photons
Rabi splitting:
2Rabi=ωupper - ωlower
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Device miniaturization in the THz
Application to ISB polaritons
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Towards antenna
detectors
Conclusions and
Perspectives
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The concept is validated
with SRR-like cavities!
• Experimental data:
7% splitting increase!
Antennas or
circuits?
Context of THz
research
2.0
R (a.u.)
Hybrid electronic
photonic sub-
resonators:
The circuit vision
1.5
Towards antenna
detectors
1.0
Conclusions and
Perspectives
0.5
150 K
100 K
80 K
50 K
30 K
20 K
10 K
5K
1.51 THz
2
3
4
5
6
Frequency (THz)
7
8
- Extremely small effective volume: Veff=0.002·(/2·n)3
- Increased splitting due to slighly better overlap factor (etched
resonator)
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First conclusion: hybrid resonators CAN
operate in the electronic region!
Antennas or
circuits?
Photonic devices region
10
Context of THz
research
Metallic disk
PhC Laser
Hybrid electronic
photonic sub-
resonators:
The circuit vision
Bragg
1
PBG default mode
Towards antenna
detectors
Conclusions and
Perspectives
Vtot/(/2neff)
3
Electric dipolar modes
LC laser
0.1
LC Polariton
0.01
electrical pumping
optical pumping
Spaser
One Loop - GaAs 1um
One Loop - polariton
1E-3
Magnetic
mode
0.1
1
Electronic devices region
10
100
Lmax/(/2neff)
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Homework 2: where is the J (the current)
in the “spaser”?
Photonic devices region
10
Metallic disk
PhC Laser
Lmax= 44 nm
λ = 525 nm
Bragg
0.1
PBG default mode
LC laser
Walther et al., PhD Thesis
Vtot/(/2neff)3
1
LC Polariton
0.01
electrical pumping
optical pumping
Spaser
1E-3
0.1
1
10
100
Electronic devices region
Lmax/(/2neff)
Cortona – Scuola di Fotonica 2013
53
Outline
Antennas or
circuits?
Context of THz
research
 Antennas or circuits?
 Context of THz research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
 Sub-wavelength sized resonators: circuit vision
 Sub-wavelength sized resonators: antenna vision
Towards antenna
detectors
 The antenna vision: coupling into small volumes
 Critical coupling?
Conclusions and
Perspectives
 Perspectives: towards a THz nanolaser, antennacoupled detectors…
Cortona – Scuola di Fotonica 2013
54
Hybrid resonators: the complete vision
It is an antenna problem
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Towards antenna
detectors
HYBRID
RESONATOR
CLOSED-LOOP
ANTENNA
PATCH
1 µm
+
GaAs
/2
=
<<
This is the capacitive
section.
This is the inductive
section
Sets the losses
Sets essentially the
radiation coupling
Active
Core
< /2
Conclusions and
Perspectives
Qmaterial
or
Rmaterial
Qohmic + Qradiative
or
Rohmic+ Rradiative
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Q-factors vs Resistances:
two versions of the same thing!!
C : Capacitance
I
R : Résistance
R*I
..
.
L*Q + R*Q + Q/C = 0
Q
Q/C
L*dI/dt
L : Inductance
.
..
m*x + mΓ*x + k*x = 0
 This is a damped oscillator: we can talk about Q-factors: Q = ·
 The ohmic resistance damps the oscillator  low Qohm  high Rohmic
But we loose energy also via emission of electromagnetic waves!
 Then it is natural to define  Qrad and Rrad  low Qrad  high Rrad
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56
There is only one truth of course…. 
Personal opinion: choose the formalism which allows to best highlight the fundamental physical phenomena!
(F. Capasso’s lecture)
Example: envelope function vs tight binding
Could you calculate a QC lasers with tight binding?
Could you CONCEIVE a QC laser with tight binding?
Cortona – Scuola di Fotonica 2013
57
Hybrid resonators: the complete vision
It is an antenna problem
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Towards antenna
detectors
HYBRID
RESONATOR
CLOSED-LOOP
ANTENNA
PATCH
1 µm
+
GaAs
/2
=
<<
This is the capacitive
section.
This is the inductive
section
Sets the losses
Sets essentially the
radiation coupling
Active
Core
< /2
Conclusions and
Perspectives
Qmaterial
or
Rmaterial
Qohmic + Qradiative
or
Rohmic+ Rradiative
Cortona – Scuola di Fotonica 2013
58
Hybrid resonators: disentangling capacitive
and inductive elements
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
HYBRID
RESONATOR
CLOSED-LOOP
ANTENNA
PATCH
1 µm
GaAs
/2
+
=
Active
Core
< /2
<<
Towards antenna
detectors
Conclusions and
Perspectives
 Rload 
Cortona – Scuola di Fotonica 2013
1
i Cload
 Rohmic  Rrad  i Lant
59
The impedance formalism is very powerful…
 Impedance match: put a 50 Ohm cable into a 50 Ohm cable to avoid
reflections…
 The fundamental antenna equation:
Z antenna  Z
Cortona – Scuola di Fotonica 2013
*
Load
60
The result:
Rload
 The
1

 Rohmic  Rrad  i Lantenna
i Cload
imaginary part yields the frequency…
1
 i Lantenna
i Cload
f 
1
2 Cload Lantenna
 The
real part yields the radiative efficiency
(complex topic critical coupling)
Rload  Rohmic  Rrad
Cortona – Scuola di Fotonica 2013
61
Hybrid resonators: disentangling capacitive
and inductive elements
Antennas or
circuits?
HYBRID
RESONATOR
CLOSED-LOOP
ANTENNA
Context of THz
research
PATCH
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
1 µm
GaAs
+
/2
=
<<
Active
Core
< /2
Towards antenna
detectors
Conclusions and
Perspectives
“BAD” Antenna (high-Q):
- Nanolasers
- Phased-arrays
- Mechanically-tunable lasers
(MEMS?)
Cortona – Scuola di Fotonica 2013
62
“Very” small antennas are bad
<<
Radiation resistance for
small loop antennas
(taken from Balanis book).
It drops with dimensions
(see J. Faist’s Lecture)
Cortona – Scuola di Fotonica 2013
63
Hybrid resonators: disentangling capacitive
and inductive elements
Antennas or
circuits?
BOW-TIE ANTENNA
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
PATCH
1 µm
GaAs
/2
+
=
/2
Towards antenna
detectors
Conclusions and
Perspectives
“GOOD” Antenna (low-Q):
- THz quantum detectors
(dark current)
- Polaritonic emitters
(out-coupling from a small volume)
Cortona – Scuola di Fotonica 2013
64
Independent variation of L and/or C:
proof of principle
Antennas or
circuits?
HYBRID
RESONATOR
CLOSED-LOOP
ANTENNA
Context of THz
research
PATCH
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
1 µm
GaAs
+
/2
Towards antenna
detectors
=
< /2
<<
Decrease
of C
Increase
of L
Conclusions and
Perspectives
Active
Core
Two
Two Loops
Loops
Two Loops
One Loop
1 µm
GaAs
1 µm
3
3 um
µm
GaAs
E. Strupiechonski
al., submitted
Cortona
– Scuola dietFotonica
2013 paper
Hybrid electronic-photonic resonator cavities for THz applications
GaAs
65
The cavity height sets C,
The loop sets L
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Towards antenna
detectors
Conclusions and
Perspectives
Cortona – Scuola di Fotonica 2013
66
Device Fabrication and testing
Cortona – Scuola di Fotonica 2013
67
This new architecture leads to /9
confinement in ALL three directions of space
Two Loops
Antennas or
circuits?
Context of THz
research
Two Loops
One Loop
1 µm
3 µm
1 µm
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
450
λ
400
eff
e
nc
a
t
uc ase
d
In cre
in
/9
Conclusions and
Perspectives
Wavelength (µm)
350
Towards antenna
detectors
300
λ
eff
ce
Capacitan
decrease
/6
250
200
150
λ eff / 2
100
resonators
photonic
rd
a
d
n
ta
limit
S
diffraction
Below the
50
0
4
5
6
7
8
9
10
Cortona – Scuola di Fotonica 2013
Diameter (µm)
11
12
13
14
68
A very simple LC model provides
a qualitative understanding
Two-loop
Antennas or
circuits?
25
GaAs 1 m, One-loop
One-loop
GaAs 1 m, Two-loop
GaAs 3 m, Two-loop
20
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Inductance (pH)
Context of THz
research
Increase
of L
10
One Loop
5
GaAs
  c  2 LC
0
350
350
300
300
4
250
250
6
7
8
9
10
Diameter (m)
11
12
13
14
15
14
15
GaAs 1 m, One-loop
9
GaAs 1 m, Two-loop
GaAs 3 m, Two-loop
8
200
200
C   r 0
Capacitance (fF)
7
150
150
GaAs 1 m, One-loop
GaAs 1 m, Two-loop
One-loop,
m thick
GaAs
3 m,1 Two-loop
100
100
Two-loop,
m thick data
GaAs
1 m,1 One-loop
Two-loop,
m thick data
GaAs
1 m,3 Two-loop
50
50
0
5
10
Wavelength ( m)
Wavelength ( m)
Conclusions and
Perspectives
Two Loops
i
GaAs
450
450
400
400
Towards antenna
detectors
L   Li
15
6
Two Loops
S
g
GaAs
5
Decrease
of C
4
Two Loops
3
GaAs 3 m, Two-loop data
0 4
4
5
5
6
6
7
7
8
8
9
10
9
10
Diameter (m)
Diameter (m)
11
11
12
12
13
13
14
14
15
15
2
0
Cortona – Scuola di Fotonica 2013
GaAs
1
4
5
6
7
8
9
10
Diameter (m)
11
12
13
69 69
For accurate numbers: numerical modeling
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70
Hybrid resonators can populate
the “electronic”region…
Photonic devices region
Antennas or
circuits?
10
Metallic disk
Context of THz
research
PBG default mode
3
One Loop
1 um
Towards antenna
detectors
Conclusions and
Perspectives
Bragg
1
Vtot/(/2neff)
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
PhC Laser
LC laser
0.1
LC Polariton
0.01
electrical pumping
optical pumping
Spaser
One Loop - GaAs 1um
One Loop - polariton
Two Loops
1 um
Two Loops - GaAs 1um
Two Loops - GaAs 3 um
1E-3
Two Loops
3 um
0.1
1
10
100
Electronic devices region Lmax/(/2neff)
Cortona – Scuola di Fotonica 2013
71
Question:
Can we make a laser with this?
Two Loops
450
λ ef
400
f
1 µm
/9
Wavelength (µm)
350
300
250
Two important issues to address:
200
1) Laser active region  thin!
150
100
2) Electrical injection
50
0
4
5
6
7
8
9
10
11
12
13
14
Diameter (µm)
Cortona – Scuola di Fotonica 2013
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Answer to 1: yes!
o Active region: QC laser

o Metal-metal waveguide:
 Metals are nearly perfect in THz
 ISB transitions, TM polarized photons
 Wide wavelength choice: 3 µm – 200µm
 TM mode  NO CUT-OFF in vertical direction
Cortona – Scuola di Fotonica 2013
73
Answer to 1: yes!

Confinement ( λ/nefftAR )
18
9
4
1.4
800
1.0
600
Intensity (a.u.)
0.8
400
200
0.6
0.4
0.2
3.0
3.5
Frequency (THz)
0
2
4
Jth / Jth,10um
Jth (A/cm²)
1.2
6
8
10
0.0
Thickness (µm)
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74
Answer to 2: work to be done…
LC oscillator
AND
antenna
Insulating
layers
THz gain medium
Cortona – Scuola di Fotonica 2013
75
The “receiver” end: QWIP detectors
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Towards antenna
detectors
Conclusions and
Perspectives
Cortona – Scuola di Fotonica 2013
76
Goals: small size, but capturing light
 THz QWIP detectors have very high dark-currents 
 it is necessary to make them VERY small!
 Diffractive techniques cannot do that
Detector core
Several s !
The problem of capturing light efficiently…
Cortona – Scuola di Fotonica 2013
77
There is only one truth…. 
Choose the formalism which allows to best highlight the fundamental physical phenomena!
Cortona – Scuola di Fotonica 2013
78
Designing a PhC with impedances ?
Not really….
Q ,up
Light
Emission
Q//
QM
Q//
Laser core
Ti/Au layer
1
1
1


Qtotal QMaterial Qcavity
720µm

Cortona – Scuola di Fotonica 2013
1
1
1


QM Q// Q ,up
1
,
J th 
Qtotal
Qtotal

Q ,up
79
Designing an antenna detector with impedances ? Possibly yes! 
Antennas or
circuits?
 Example: the resonant dipole antenna
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Towards antenna
detectors
Conclusions and
Perspectives
QWIP
Z=73 + i·42.5 
 We have ·Lantenna= 43.5 Ohm = 1/(·Cqwip)
This allows to easily set the dimensions of the active
core!
 At 3 THz, for instance, C approx. femtoFarad.
 Alternative: full electromagnetic simulations
Cortona – Scuola di Fotonica 2013
80
Additional useful example:
the planar bow‐tie
 And the coupling? It is essentially a critical coupling issue
(F. Capasso’s talk) 
Rload  Rohmic  Rrad
Cortona – Scuola di Fotonica 2013
81
Conclusions
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Towards antenna
detectors
Hybrid electronic-photonic devices at
THz frequencies (antennas- circuit) can
lead to devices with novel functionalities
Conclusions and
Perspectives
Cortona – Scuola di Fotonica 2013
82
Perspectives: THz Nanolasers / THZ Detectors
Antennas or
circuits?
Context of THz
research
Hybrid electronic
photonic sub-
resonators:
The antenna
vision
Towards antenna
detectors
Conclusions and
Perspectives
 A laser with fundamentally no lower-size limit in 3D?
Technology challenges:
• How to inject current?
• Q-factors?
 Tunability of the laser with an external circuit?
• Mechanical tunability (convergence with MEMS)
• Electrical tunability (convergence with frequencyagile [meta]-materials)
 Reversing the concept of hybrid resonator 
Extremely sub-wavelength THz QWIP detectors
• Low dark-currents, not achievable
with diffractive techniques
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83
Thank you for your attention!
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84