About Omics Group
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Transcript of About Omics Group
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About Omics Group
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About Omics Group conferences
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308.09.14 / Alfredo Bismuto
High performance, low dissipation QCL across the Mid-IR range.
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Outline
Introduction
Single mode sources
Mid-IR spectral range: applicationsAlpes Lasers SA overview
Fabrication processQCLs for mass production (device length impact)Impact of front reflective coating on short devicesDFB sources below 1W between 4.5-9.3 µmHigh power DFBs
Conclusion and next steps
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Mid-IR range (2-20µm)
H2O abosorption
Strong molecular absorptions(orders of magnitude biggerthan in the NIR-range)
NO2, CO,CO2, CH4, NH3,CH2CO, O3, N2OHF, HCl
Isotopicallysensitive
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•Biochemical and Clinical diagnostics●Breath analysis (NO, CO, CH4, S)●Glucose level control (in-vivo)
•Enviromental gas monitoring●Atmospheric chemistry●Volcanic emissions
•Urban and Industrial emission control●Industrial plants●Automobile and Aircraft emissions
•Rural emission measurements
●Combustion process control
Applications
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•Laser sources●Low efficiency (~10%) compared to diode lasers (~50%)●High electrical dissipation (Wel>1W)
•Photonics●Difficult to do photonic integration
Limitation and challenges
●Nb of lasers per wafers still low (long lasers & small wafers)
●High electrical dissipation (Wel>1W)
●Detectors less sensitive and more expensive
●Optical elements expensive (lenses/windows/fibers)
●Fabrication is still expensive
A killer application is still missing...why?
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Things are changing....
Horizon
See also : http://www.flir.com/flirone/explore/
FLIR introduced the FLIRONE projecta IR camera compatible with the Iphone
The cameras should cost less than 350 $
Many big company are trying to developproducts in the IR
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Alpes Lasers● founded in 1998
● 21 employees (11PhD, 5 eng.)
● New product design team growing
● Fabless component manufacturer
● Widening products portafolio
● 2400+ sold lasers
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Our company
DFB technology
● Gratings written by standard lithography from 4-12 µm● Many different wavelengths can be fabricated at once● Efficient device mounting● Full 2''- wafer process● Polyvalent production process 08.09.2014Alfredo Bismuto 10
Proprietary design toolDFB grating during fabrication
UV-lithography
QCL subsystems
TO3-LHHL-L
TO3-W
LLH
Used only in the initial testing phase
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QCL subsystems
TO3-LHHL-L
TO3-W
LLH
Used only in the initial testing phase
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low consumption packages beingvalidated (TO5, etc.)
Outline
Introduction
Single mode sources
Impact of front reflective coating on short devicesHigh power DFBs
DFB sources below 1W between 4.5-8 µm
Mid-IR spectral range: applicationsAlpes Lasers SA overview
Fabrication processQCLs for mass production (device length impact)
Conclusion and next steps
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●Most of QCLs have 5-15 W of electrical dissipation●Up to 100 W are needed to control the temperature●Optical power levels of few mW sufficient for many applications
Thermal budget in QCLs
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●Most of QCLs have 5-15 W of electrical dissipation●Up to 100 W are needed to control the temperature●Optical power levels of few mW sufficient for many applications
Thermal budget in QCLs
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Research goal:●Low dissipation devices●Short chips●Still enough optical power for spectroscopy●
●Low dissipation (Easy cw bar testing)
●More devices per wafer
Advantages of short devices
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●Low dissipation (Easy cw bar testing)
●More devices per wafer
●Probability of defect (λ) follows a Poissonian law
●Failure rate sensibly reduced with shorter lasers
Advantages of short devices
𝑃=∑𝑘
λ𝑘𝑒− λ
𝑘 !
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Probabilityof major defectin the laser wg
Number of defects
Advantages of short devices
𝑃=∑𝑘
λ𝑘𝑒− λ
𝑘 !
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●Defect density estimated on the AL-Stock data (preliminary)
Probabilityof major defectin the laser wg
Number of defects
35%
8%
●Optical power levels of few mW sufficient for many applications●Low consumption●More devices per wafer●Probability of defect (λ) follows a Poissonian law
Advantages of short devices
𝑃=∑𝑘
λ𝑘𝑒− λ
𝑘 !
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Doublefold impact on the number of chips/wafer
Probabilityof major defectin the laser wg
Number of defects
Optimizing reflectivity for short devices
●Starting range 4.5 m and 5.5 m
●Optimize the grating coupling to obtain both
low consumption DFBs and high power
DFBs on the same wafer
●750 µm long devices, 3-4 µm wide
●Back-facet HR coating
●Partial front HR coating
λ = 4.5 µm
Front HR coating (dielectric)
Optical powerincreases withfront coating
Before frontcoating
750 µm long devices3 µm wide ridge
No-lasing before back-side coupling
Low consumption devices
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●Dissipation at threshold as low as 0.3W●Max consumption < 1.4W between 4.5m and 5.3m
Max dissipation
Thresholddissipation
Low consumption devices
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●Dissipation at threshold as low as 0.3W●Max consumption < 1.4W between 4.5m and 5.3m
Low-dissipation DFB devices at 4.5 m
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●very low threshold current : 29mA●Pel max ~1.2W●Single mode
Low-dissipation DFB devices at 4.5 m
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●opt power up to 48mW●Pel max ~1.4W●Single mode
Low-dissipation DFB devices at 4.90m
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Low dissipation devices
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●Gain starving (too low doped structure)
●Elctrical dissipation as low as 0.3 W
●No cooling needed
●Max dissipation 0.7 W
0.3 W
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0.7 W
Low consumption devices
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●Max consumption < 2.6W between 4.5m and 8.4m
2-nd atmopheric window
Low-dissipation DFB devices at 7.8m
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●Very low threshold current : 66 mA●Very low threshold power : 0.55 W●Pmax > 70 mW / huge dynamical range
Low-dissipation DFB devices at 8.4m
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●did not lase while uncoated/HR !●As for the 4.9 µm case the design is too little doped●low threshold power : 1.06W
Low consumption devices (9.3 µm)
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preliminary results at 9.3m (only HR on back facet)FF coating being developed
Low consumption devices
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Can we package this devices in low-dissipation packages?
DFB devices at 7.8m in TO3-L (dissipation level)
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●blue : uncoated device in a TO3-L
Device sold in TO-3 package(older generation device)
DFB devices at 7.8m in TO3-L
higher currents but CW operation in TO3-L
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DFB devices at 7.8m in TO3-L (dissipation level)
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●blue : uncoated device in a TO3-L
DFB devices at 7.8m in TO3-L (dissipation level)
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Smaller packages arebeing investigated
High power DFB devices
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●~ 80mW/facet at RT / still > 40mW/facet at 50C●Pel max < 6.4W●Single mode across the full range
High-power device at 4.56 µm
High power DFB devices
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●~ 200mW at RT / still >140mW at 50C●Pel max < 5.5W●Single mode across the full range
High-power device at 7.72 µm
Conclusion and next steps
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● Low-dissipation DFB lasers between 4.5 and 9.3 µm with Top up to >50C
● High-power DFB using the same fabrication process (140mW at 50C episide-up)
● Soon to be expanded from 3.3 µm to 14 µm● Genetic optimisation of the active region design to
increase the efficiency● Broad gain optimisation for cw operation● Cloud simulation capability
Conclusion and next steps
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● Low-dissipation DFB lasers between 4.5 and 9.3 µm with Top up to >50C
● High-power DFB using the same fabrication process (140mW at 50C episide-up)
● Soon to be expanded from 3.3 µm to 14 µm● Genetic optimisation of the active region
design to increase the efficiency● Broad gain optimisation for cw operation● Cloud simulation capability
Thank you for your attention
How to improve QCLs?
TechnologyGrowth and processing
DesignLocal optimization yields contradictory resultsTry and error very expensive
Better wallplug efficiency, higher powers, broader gain
Reliable simulation tool
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e-
e-
QCL design
Electron injection
Active region
Injector
Extraction barrier
Injection barrier
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Density matrix formalism
Able to predict opticalpower-current-voltage curves
1 H. Willenberg et al., Phys. Rev. B. 67, 085315 (2003)2 R. Terazzi et al., New J. Phys. 12, 033045 (2010)
Reliable in the whole Mid-IR range
Design tool
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Quantum cascade laser
The scattering mechanisms implemented in the computation
LO-PhononsInterface roughnessAlloy disorderIonized impurities (Dopants)
Missing interactions:
Electron-electronLA-Phonon
1 Unuma et al., J. Appl. Phys. 93, 1586 (2003)
Program input parameters
waveguide losseslaser length
laser width
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Examples
λ= 8.5 µm**
λ= 4.5 µm*
** A. Bismuto et al., Appl. Phys. Lett. 96, 141105 (2010)* A. Bismuto et al., Appl. Phys. Lett. 98, 091105 (2011)
Reliable across the whole Mid-IR range (4-10 µm )
In the 3-4 µm range intervalley scattering missing
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Toward genetic optimization
Merit function selectionUse of ETH Cluster (BRUTUS, 10000 cores)
Currently using Amazon cloud service
Wallplug efficiency
Too many parameters to control manually (~20 layers)
Simulation tool able to predict actual laser performance
QCL designerQCL designer
Now processing..
80%..
Use of genetic algorithms (fully automized)
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Toward genetic optimization
Starting point: Bound to continuum design at 4.6 µm
Random variation of the reference design(less than 20%)
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Best designs used to create the newpopulation (Darwin’s law)
Q. Yang et Al., Appl. Phys. Lett. 93, 251110 (2008)
33000 individuals per population
32 designs selected to create the newgeneration
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Toward genetic optimization
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....
1st generation 2nd generation 3rd generation ....
optimizeddesign
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Merit function: Wallplug efficiency
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Unstable pathological structures were excluded(e.g. coherent transport of electrons over unphysical lengths)
Structure in the average position of the best generation selected
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Designs comparison
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Emission wavelength kept constant
Lower alignement voltage, higher gain
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Designs comparison
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Simulations Measurements
8.5 µm wide, 4.9 mm long laser
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Lower alignment voltageHigher powerSmaller threshold
Light-current-voltage
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Wallplug improvement
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growth optimization has to be performedalso on the optimized design
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The optimized design showshigher efficiency
14.07.2014A. Bismuto et al., APL 101, 021103 (2012)
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growth optimization has to be performedalso on the optimized design
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The optimized design showshigher efficiency
Wallplug improvement
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growth optimization as to be performedalso on the optimized design
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Wallplug improvement
The optimized design showshigher efficiency
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Quantum cascade laser
The scattering mechanisms implemented in the computation
LO-PhononsInterface roughnessAlloy disorderIonized impurities (Dopants)
1 Unuma et al., J. Appl. Phys. 93, 1586 (2003)
Interface roughness hasa major impact on laserperformance
How to improve the quality of the interfaces...
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Epitaxy: Interfaces
Cut across interfaces
Interfaces are- graded (over 3-4ML)- rough
P. Offerman et al., Appl. Phys. Lett. 83, 4131 (2003)
STM cross-section
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Interface roughness
Most relevant scattering mechanism in mid-IR quantum cascade lasers
average stepheight
correlationlength
●Historically, focused on the minimization of●the emission broadening
1 A.Bismuto et al., Appl. Phys. Lett. 96, 141105 (2010)2 Y. Yao et al., New J. Phys. 97, 081115 (2010)
●Recently high performance broad gain●lasers were presented 1,2
..Is emission broadening the right parameter?
3 Unuma et al., J. Appl. Phys. 93, 1586 (2003)
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How to modify the correlation length?
Growth temperature Correlation length (Λ)
Smaller effect temperature dependence of step height (Δ)
T=475 °CT=515 °CT=525 °C
Same processing4.6 µm
three wells design
Diagonal design more sensitive to the interface roughness14.07.2014Alfredo Bismuto 60
Growth conditions are modified to systematically vary interface roughness
Growth temperature Correlation length (Λ)
Smaller effect temperature dependence of step height (Δ)
T=475 °CT=515 °CT=525 °C
Same processing
How to modify the correlation length?
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Simulated performance
Threshold current density
Current at roll-over
Slope efficiency
FWHM luminescence
1 A.Bismuto et al., Appl. Phys. Lett. 98, 091105 (2011)62Alfredo Bismuto 14.07.2014
Simulated performance
Threshold current density
Current at roll-over
Slope efficiency
FWHM luminescence
1 A.Bismuto et al., Appl. Phys. Lett. 98, 091105 (2011)
Model fails to predict emission linewidths
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Simulated performance
Best laser performance for Λ ~ 90 A
Threshold current density
Current at roll-over
Slope efficiency
FWHM luminescence
1 A.Bismuto et al., Appl. Phys. Lett. 98, 091105 (2011)
Model fails to predict emission linewidths
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How to justify laser behavior ?
Population inversion
Lower lasing state shows a minimumcorrisponding to best laser performance
Population inversionshows a maximum
resonance corresponding to qΛ~1(q exchanged wavevector during intersubband transition)
(transition energy of 34 meV)
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Lifetimes
QC lasers and electronics
NSBare chips AlN submount (3x6mm)
TC3 Driver kits
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Low-dissipation DFB devices at 4.5 m
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●opt power up to 48mW●Pel max ~1.4W
Low-dissipation DFB devices at 5.25m
very low threshold power : 0.31W
Pel max < 0.75W
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Fabrication process
AR
InP
InP
InGaAsInsulating
InPInsulating
InP
Electroplated Au
Front facet Buried grating
●Most of QCLs have 5-15 W of electrical dissipation●Up to 100 W are needed to control the temperature
*Courtesy of B. Hinkov, ETHZ08.09.2014Alfredo Bismuto 70
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