nest cnr-infm and scuola normale superiore, pisa · 2009. 1. 29. · ultra fast signal processing...
TRANSCRIPT
Vertically emitting microdisklasers
Lukas MahlerNEST CNR-INFM and Scuola Normale Superiore,
Pisa
Presented at the COMSOL Conference 2008 Hannover
People involvedAlessandro Tredicucci, Fabio Beltram
NEST CNR-INFM and Scuola Normale Superiore, Pisa
Christoph Walther, Maria Amanti, Jérôme FaistInstitute for Quantum Electronics, ETH Zürich
Bernd WitzigmannIntegrated Systems Laboratory, ETH Zürich
Harvey Beere, David RitchieCavendish Laboratory, University of Cambridge
The THz gap!
1µ
10µ
100µ
1m
10m
100m
1
10
100Electronics
1000100101.1.01
Photonics
Impatt
Gunn
III-V's
Lead salts
Output P
ower ( W
atts )
SLED
Frequency ( Terahertz )
Photo-mixer
RTD array
RTD
HGQC Laser
THz QCs!
Technology applications
Information Ultra fast signal processingMassive data transmissionWireless communications
Space ScienceCosmology Planetary, cometary Cosmochemistry
Environment Atmospheric sensing
MedicineImaging of biological tissue
Security Controls
Defense Chemical agent detectionDigital radar Imaging radar Covert communication Space-space
Short range battle field Transportation
Collision avoidance Material processing
Tomography
⇒Unknown applications created by new technology
The unipolar semiconductor laser
layer thickness
CB
material
CB
VB
diodelaser:
Quantum Cascadelaser:
“materials by design”: band structure engineering and molecular beam epitaxy (MBE)population inversion, matrix elements, scattering times, and transport are designed for optimum performance
1971: amplification from intersubband transitions is first postulated by R. F. Kazarinov and R. A. Suris Sov. Phys. Semicond. 5, 207 (Ioffe)
1994: QC-laser is first experimentally demonstrated by J. Faist et al. Science 264, 553 (Bell Labs)
2002: THz QC-lasers Nature 417, 156 (INFM Pisa-Cavendish Lab)
Distributed feedback resonator for THz QCL
• Double metal waveguide• Periodic slits in the top metallization
Very big coupling constant
Linear gratings
Radiative mode
M. Schubert et al. JQE 42, 257 (2006)
Non-radiative mode
Ey
Hx
zx
y
Device
0.0
0.2
0.4
0.6
0.8
1.0
3.0 3.1 3.2 3.30
20
40
60
80
100
120
Rad
iativ
e ef
ficie
ncy
Qua
lity
fact
or
Frequency (THz)
-30 -20 -10 0 10 20 300.0
0.2
0.4
0.6
0.8
1.0
Inte
nsity
(a.u
.)
Angle (deg)
Slab mode analysis
0.0 0.2 0.4 0.6 0.8 1.0Intensity (a.u.)
neff = 3.60-0.011i
Vertically emitting disks
• Full 3D simulation• Gold layers approximated with perfect electric
conductors
• Coupling mechanism for whispering galleries
• “infinite” grating
Simulation
0.0
0.2
0.4
0.6
0.8
1.0
3.00 3.05 3.10 3.15 3.20 3.25 3.300
20
40
60
80
100
120
140
Rad
iativ
e ef
ficie
ncy
Qua
lity
fact
or
Frequency (THz)
• Good quality factor• Reasonable outcouplingefficiency
Fabrication
• Etch the top contact layer in the slit region• Dry etched mesa
Measurement
102 104 106 108 110 112 114
170 μm
174 μm
178 μm
Inte
nsity
(a.u
.)
Frequency (1/cm)
182 μm
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.200
2
4
6
8
10
12
14
Inte
nsity
(a.u
.)
Current (A)
• Mode shifts perfectly
• High slope efficiency
• Pumping ok?
Which modes are lasing?
0.0
0.2
0.4
0.6
0.8
1.0
3.05 3.10 3.15 3.20 3.25 3.300
20
40
60
80
100
120
140
Rad
iativ
e ef
ficie
ncy
Qua
lity
fact
or
Frequency (THz)
• Try prime symmetry
• Pump only the circumference
Prime symmetry
3.05 3.10 3.15 3.20 3.25 3.30 3.350
20
40
60
80
100
120
140
Inte
nsity
(a.u
.)
Qua
lity
Fact
orFrequency (THz)
• 17 periods on the circumference• Remove the top contact layer in the center
0 20 40 60 80 100 120 140 160 1800
50
100
150
200
250 17-period grating 16-period grating
Pow
er (μ
W)
Current (mA)
Light-Current
0 20 40 60 80 100 120 140 160 180 2000
10
20
30
40
50
60
70
80
90
Pow
er (μ
W)
Current (mA)
NearfieldMagnetic field
In the device
Above the device
Farfield
-40 -20 0 20 40
-40
-20
0
20
40
Ang
le(d
eg)
Angle(deg)
16-fold symmetryradial mode
17-fold symmetrywhispering gallery mode
Computed farfield of a whispering gallery mode
-90 -60 -30 0 30 60 90
Inte
nsity
(a.u
.)
Angle (deg)
From microdisk to milliring
The farfield is determined by λ/d
-20 -10 0 10 20
-20
-10
0
10
20
Ang
le (d
eg)
Angle (deg)
-20 -10 0 10 20
-20
-10
0
10
20
Ang
le(d
eg)
Angle(deg)
1 mm diameter1.5 THz
Conclusions• Accurate prediction of spectral
emission properties is possible• A good understanding of the
coupling mechanism and spatial emission properties is obtained
Spherical farfield plot of a ring