Transcript Title of presentation

Lasers operating at nanoscale
Impact of quantum effects on coherence and dynamics
PhD
R. Hostein (now Paris 6)
R. Braive (now LPN)
D. Elvira
A. Lebreton
B. Fain
Post-Doc
X. Hachair (now industry)
Permanent
I. Robert-Philip
I. Sagnes
I. Abram
A. Beveratos
S. Barbay
G. Beaudoin
L. Le Gratiet
JC Girard
Moores Law of laser size ?
Optical interconnects
Miniaturized lasers
P. 2
Joannopoulos Research Group at MIT
Physics of small lasers ?
RT operation ?
Telecoms operation ?
O. Painter et.al. Science 284, 1819 (1999)
Outline
P. 3
 Introduction
 Defining the laser threshold as change in the dynamics
 High-speed modulation
 Room temperature telecom nanolaser, coherence properties
 Conclusion
What size ?
P. 4
Nanotransistor
(CNRS/LPA)
Microprocesseur
Transistor
(Intel)
UltraViolet
0.1 nm
1 nm
10 nm
Visible
100 nm
Infra-Red
1 µm
Nano-world
Miniature laser
10 µm
100 µm
How to make such a laser
P. 5
Cavity
Gain
medium
What gain material
 Semiconductors

Quantum Wells

Quantum Dots

Bulk material
QD InAs/GaAs –
10
nm
G. Patriarche (CNRS-LPN)
Conduction
band
InP
Valence
band
InAsP
InP
-- -- -
Energy
3 – 50 nm
Aborption/Emission (un. arb.)
P. 6
 Dye molecules
Aborption
Emission
Wavelength (nm)
x,y,
z
What cavity
P. 7
Total internal reflexion
Propagation in a periodic medium
Guiding effects
Interferences
c
o Bragg Mirrors
o Photonic Crystals
What cavity
P. 8
Micropillier
Microdisques
Cristaux photoniques sur
membrane
5 µm
• Interferences in the
pillar direction
• Guided in plane
• Guiding
• Interferences in the
membrane plane
• Guiding effects in the
perpendicular direction
Nanostructured laser cavities
P. 9
Phys. Rev. Lett. 98, 043906 (2007)
Univ Würzburg...
Phys. Rev. Lett. 96, 127404 (2006)
Appl. Phys. Lett. 91 031108 (2007)
Opt. Lett. 35, 1154 (2010)
UCSB, Univ. Stanford, Caltech,
Univ. Tokyo, Univ. Yokohama,
CNRS-LPN...
Plasmonic nanolasers
P. 10
Nature 461, 604 (2009)
Optics Express 17, 11107 (2009)
Nature 460, 1110 (2009)
M. Noginov, Univ. Norfolk
Nature Photonics, (2010)
Y. Fainman,
Univ. San Diego
Nature 461, 629 (2009)
X. Zhang, Berkeley
Why so much fuss ?
 factor of spontaneous emission in the laser mode
P. 11
Other modes
Laser mode
β=
Spontaneous emission in the laser mode
Total spontaneous emission
In classical lasers < 10-5 and generally neglected
In nanolasers lasers > 10-2 cannot be neglected
In free space
(emission rate 0)
In a cavity
(emission rate )

3 Q

F

p
2
3

4



V

n
0
(Purcell factor)
When  → 1
Light-out (a.u.)
P. 12
Light-in (a.u.)
Yamamoto, Phys. Rev. A 50, 1675 (1992)
Towards a thresholdless laser
→ ie does it always lase ? (and what does it mean)
Outline
P. 13
 Introduction
 Defining the laser threshold as change in the dynamics
 High-speed modulation
 Room temperature telecom nanolaser, coherence properties
 Conclusion
Threshold as change in the dynamics
P. 14
Spontaneous
only photons are
emited from the
mode
and N(t) slow
Stimulated
All photons are emitted
from the laser mode
And N(t) evolves quickly
X. Hachair et al, submitted PRA
No threshold = no difference
between the 2 regimes in the number
of photons, but different in the
populations
1,0
0,47 Pthres
0,69 Pthres
0,9
1,42 Pthres
Pumping Laser
P. 15
Normalised intensity (u.a.)
Threshold as change in the dynamics
0,8
0,7
0,6
0,5
0,4
1,9 Pthres
4,76 Pthres
0,3
0,2
0,1
0
0
20
40
60
80
100
Time (ps)
120
140
160
180
<< Threshold
>> Threshold
A threshold can still
be defined even for
=1
X. Hachair et al, submitted
Threshold as change in the dynamics
P. 16
Gain material
Laser cavity
InAs/GaAs QD
Density ~ 1.5 x 1010 cm-2
Emission around 900 nm
T~4K
5 µm
R. Braive et al. Opt. Lett. 34, 554 (2009)
Threshold as change in the dynamics
P. 17
X. Hachair et al, submitted
InAs/GaAS QD laser at
4K
Outline
P. 18
 Introduction
 Defining the laser threshold as change in the dynamics
 High-speed modulation
 Room temperature telecom nanolaser, coherence properties
 Conclusion
High-speed modulation
In optical communications
P. 19
Tb
…011010010…
Transmitter
Receiver
Coldren & Corzine,
Diode Lasers and Photonic Integrated Circuits, Wiley Series
High-speed modulation only possible with an important number
of photons in the cavity
Why nanolasers should be fast : A simple model
It takes time to have >1 photon in the mode
P. 20
Rapid
Turn on
=10-5
>1 photon is obtained very rapidly
=10-1
In a cavity
(emission rate )

3 Q

F
p 2
3

4



V

n
0
Return to empty
state, fast recovery
10 GHz gain switched operation
Long
(movable)
L
S
Sample
L S
P. 21

Short

L
S
(Fixed)
Toward
Streak camera
First pump pulse
Two pulses
Second pump pulse
0
Intensity (a.u.)
0 2 4 6 8 10 12 14
0
0
Intensity (a.u.)
0 2 4 6 8 10 12 14

200
200
200
400
Time (ps)
400
Time (ps)
400
Time (ps)
800
800
600
800
600
600
R. Braive et al. Opt. Lett. 34, 554 (2009)
Intensity (a.u.)
0 2 4 6 8 10 12 14
10 GHz gain switched operation
4
P. 22 10
15
10 GHz
12,5
10
10
GHz
19 dB
0
3 GHz
200
5
2,5
100
0
7,5
2nd excitation
102
10
1rst excitation
Intensity (u.a.)
Intensity (u.a.)
103
400
Time (ps)
600
800
0
100
200
Time (ps)
Modulation rate of at least 10 GHz with quantum dots
Build-up time of 50 ps, a maximum of 20 GHz rep rate expected
10 µJ/cm2 per excitation pulse
R. Braive et al. Opt. Lett. 34, 554 (2009)
300
400
10 GHz gain switched operation
0 ps
0,20
15
P. 23
0,15
12.5
0,10
Intensity (a.u.)
10
0,05
7.5
0,00
5
-0,05
-0,10
2.5
-0,15
0
-0,20
400 ps
0
100
200
Time (ps)
R. Braive et al. Opt. Lett. 34, 554 (2009)
300
400
10 GHz gain switched operation
0 ps
0,20
15
P. 24
0 ps
0,15
12.5
Intensity (a.u.)
0,10
10
0,05
7.5
0,00
5
-0,05
-0,10
2.5
-0,15
0
400 ps
0
100
200
Time (ps)
R. Braive et al. Opt. Lett. 34, 554 (2009)
300
-0,20
400
400 ps
10 GHz gain switched operation
0,15
12.5
0,10
Intensity (a.u.)
10
0,05
7.5
0,00
5
-0,05
-0,10
2.5
-0,15
0
Relative wavelength shift (nm)
P. 25
0 ps
0,20
15
-0,20
0
100
200
300
400
Time (ps)
Same chirp behaviour as for single pulse excitation, even at high modulation
 Recovery time faster than 100 ps
 Same compensation for every pulse → possible down-to 11ps
 100 Mhz/ps chirp → H=3.5 (let's discuss after)
R. Braive et al. Opt. Lett. 34, 554 (2009)
400 ps
10 GHz gain switched operation
QD lasing
QW lasing (100GHz)
P. 26
15
10 GHz
10
7,5
5
2nd excitation
1rst excitation
Intensity (u.a.)
12,5
19 dB
2,5
0
0
100
200
Time (ps)
300
400
QD lasing
QW lasing
High quantum yield
Low quantum yield
R. Braive et al. Opt. Lett. 34, 554 (2009)
H. Altug et al. Nature 2, 484 (2006)
Outline
P. 27




Introduction
Defining the laser threshold as change in the dynamics
High-speed modulation
Room temperature telecom nanolaser, coherence properties
 Conclusion
Going to 1.55µm. Everything must be re-designed
P. 28
Gain material
InAsP/InP QD
Density ~ 1.5 x 1010 cm-2
Emission around 1.55 µm
Inhomogeneous ~ 145 nm
T ~ 300 K
R. Hostein et al. Appl. Phys. Lett 94, 123101 (2009)
Laser cavity
Going to 1.55µm. Everything must be re-designed
Stransky-Krastanov growth of InAsP/InP quantum dots
P. 29
Lattice mismatch : 3 %
Wavelength emission : from 1.2 µm to 2.3 µm
Quantum dots density : from 7x107 to 3x1010 QDs/cm2
A. Michon et.al. J. Appl. Phys. 104, 043504 2008
D. Elvira et al. Appl. Phys. Lett 97, 131907 (2010 )
Going to 1.55µm. Everything must be re-designed
P. 30
Quality factor Q  50000
<=> Photon lifetime  30 ps
R. Hostein et al. Appl. Phys. Lett 94, 123101 (2009)
Demonstration of room temperature operation
P. 31
CW RT operation
R. Hostein et al. Opt. Lett. 35, 1154 (2010)
Pulsed RT operation
How to define the threshold now ?
Classical definition
Quantum definition
Gain = Loss
Mean number of photons
P. 32
Statistical definition
Second order coherence g(2)(0)
0.5
1.0
Light-In
St
emission
1.5
2.0
0.1
0.1
1
Light-In
Do these definitions always
coincide ?
10
1
0.1
1
Light-In
10
Fano Factor
F = <n>(g(2)(0)-1)+1
F
Light-Out
0.0
2
g(2)(0)
Sp
emission
10 8
10 7
10 6
10 5
10 4
10 3
10 2
10 1
10 0
10 -1
10 -2
<n>
Light-Out
In the laser mode <n>=1
1
Light-In
10
N.J. Van Druten et al,
Phys. Rev. A 62, 05308 (2000)
0.0
0.5
1.0
1.5
Light-In
2.0
How to define the threshold now ?
P. 33
Light-Out
g(2)(0) -1
Sp
emission
0.0
0.5
1.0
Light-In
St
emission
1.5
2.0
Class B
Class A
g(2)(0)
2
1
0.1
1
Light-In
10
N.J. Van Druten et al, Phys. Rev. A 62, 05308 (2000)
2ond order autocorrelation function
SNSPD
(stop)
P. 34
SNSPD (start)
Filter
N.A. 0,4; x20
Sample
R. Hostein et al. Opt. Lett. 35, 1154 (2010)
SSPD : Superconducting single photon detector
2ond order autocorrelation function
2.0
P. 35
100k
1.9
80k
1.8
1.7
60k
1.5
(n)
g (0)
1.6
40k
1.4
1.3
20k
1.2
1.1
1.0
0
100
200
300
Pump Power (µW)
g//=400 ps
c=30 ps
=0.012
400
0
500
2ond order autocorrelation function hand waving explanation
Spontaneous
emission
Long transition
Stimulated
emission
region
2.0
P. 36
100k
1.9
80k
1.8
1.7
60k
1.5
(n)
g (0)
1.6
40k
1.4
1.3
20k
1.2
1.1
1.0
0
100
200
300
Pump Power (µW)
400
0
500
2ond order autocorrelation function hand waving explanation
2.0
100k
1.9
80k
1.8
P. 37
1.7
60k
1.5
(n)
g (0)
1.6
1.4
40k
(net damping rate of the loaded cavity)
20k
gN=g// (1+  n0) atomic damping
1.3
1.2
gn=c/(n0+1) photonic damping
(net stabilisation of the inversion of the laser dynamics)
1.1
1.0
0
100
200
300
400
0
500
Pump Power (µW)
High- laser => lasing with a small number of photons
=> gn > gN
=> Non poissonian statistics even above threshold
=> Mesoscopic Laser
Van Druten et.al. PRA 62, 053808 (2000)
D. Elvira et.al. to be submitted
Conclusion
P. 38
Defining the laser threshold as change in the dynamics
15
7,5
5
2nd excitation
1rst excitation
10
Intensity (u.a.)
High-speed modulation
10 GHz
12,5
19 dB
2,5
0
0
100
300
200
Time (ps)
400
Room temperature telecom nanolaser,
Defining lasing as g(2)(0)=1
2.0
100k
1.9
80k
1.8
1.7
60k
1.5
(n)
g (0)
1.6
40k
1.4
1.3
20k
1.2
1.1
1.0
0
100
200
300
Pump Power (µW)
400
0
500
Quelle cavité?
 Ingénierie de la courbe de dispersion dans un cristal photonique bidimensionnel
P. 39
a1
a2
0.255
a/
0.245
Zone I
Zone I
Zone II
0.225
0.3
0.34 0.38
0.42
0.46
0.5
k
From Ph. Lalanne et al
Fréquence c/a2
0.235
M
II
Zone I
M
Confinement optique
Transmission
Gap
Espace réel
• Sur Si : S. Noda et al, Nat. Mater 4, 207 (2005); T. Asano et al, Opt. Express} 14 (2006) 1996…
• Sur GaAs : E. Weidner et al, Appl. Phys. Lett. 89 (2006) 221104; R. Herrmann et al, Opt. Lett. 31
(2006) 1229 ...