This document discusses vertical integration of ultrafast semiconductor lasers for wafer-scale mass production. It outlines research on optically pumped vertical external cavity surface emitting lasers (VECSELs) and modelocked integrated external cavity surface emitting lasers (MIXSELs) for applications requiring compact ultrafast lasers. Key highlights include a 6.4 W modelocked MIXSEL chip operating at 960 nm, a 1 W femtosecond VECSEL at 960 nm, and a 2.62 W continuous wave VECSEL realized at 1550 nm. The goal is wafer-scale integration of ultrafast semiconductor lasers for applications such as telecommunications, microprocessing, and biophotonics.
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Vertical integration of ultrafast semiconductor lasers for wafer-scale mass production
1. Vertical integration of
ultrafast semiconductor lasers
for wafer-scale mass production
Prof. Eli Kapon & Dr. Alexei Sirbu
Institut de Photonique et d‘Electronique Quantiques, EPFL, Lausanne
Prof. Bernd Witzigmann
Computational Electronics and Photonics, University of Kassel
(previously ETH Zurich)
Prof. Pierre Thomann
Institut de Physique, Université de Neuchâtel
Prof. Ursula Keller & Dr. Thomas Südmeyer
Jan. 17, 2011 Laser
Ultrafast Physics Department, ETH Zurich ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
2. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
3. Compact ultrafast lasers for “real world application”
Telecom & Datacom Interconnects Optical Clocking
Multi-photon imaging
Frequency comb
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
4. The first VECSELs conference at Photonics West
Jan. 24 - 25, 2011
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
5. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
6. CW Optically-Pumped VECSELs
OP-VECSEL = Optically Pumped Vertical-External-Cavity
Surface-Emitting Semiconductor Laser
M. Kuznetsov et al., IEEE Photon. Technol. Lett. 9, 1063 (1997)
• Semiconductor gain
structure with reduced
pump output
coupler
thickness
laser
IEEE JQE 38, 1268 (2002)
gain structure
• Pump: high power diode bar
heat sink • External cavity
Ultrafast Laser
for diffraction-limited output
ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
7. VECSEL gain structure
heat gain structure
sink
pump output
coupler pump energy
laser
gain structure
heat sink ETH Zurich
Ultrafast Laser
Physics
nano-tera.ch Annual Meeting 12. 5. 11
8. Optically pumped semiconductor laser?
• Maybe a bad idea coming from semiconductor diode lasers?
• But for sure a good idea coming from diode-pumped solid-state
lasers:
- more flexibility in operation wavelengths
- broad tunability
- efficient mode conversion from low-beam-quality high-power diode
lasers
- modelocking possible with SESAMs
- waferscale integration - cheaper ultrafast lasers in the GHz pulse
repetition rate regime
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
9. Semiconductor materials: bandgap engineering
Wavelength of interest 960 nm, 1.3 µm, and 1.5 µm
1.5 µm
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
10. VECSELs: cw spectral coverage (Jennifer Hastie)
• 2‐2.8 μm – GaInAsSb / AlGaAsSb
• 1.5 μm – InGaAs / InGaAsP
• 1.2‐1.5 μm – AlGaInAs / InP (fused)
• 1.2‐1.3 μm – GaInNAs / GaAs
• 1‐1.3 μm – InAs QDs
• 0.9‐1.18 μm – InGaAs / GaAs
• 850‐870 nm – GaAs / AlGaAs
• 700‐750 nm – InP QDs
• 640‐690 nm – InGaP / AlGaInP
• Frequency‐doubled VECSELs have
been reported throughout the visible
and into the UV
Infrared review: N. Schulz et al., Laser & Photonics Reviews 2, 160 (2008)
Visible and UV review: S. Calvez et al., Laser & Photonics Reviews ETH Zurich
Ultrafast Laser 3, 407 (2009)
Physics
updated by Jennifer Hastie, University of Strathclyde, group of Prof. Martin Dawson
nano-tera.ch Annual Meeting 12. 5. 11
11. Ultrafast VECSELs: Modelocking with SESAMs
cw
laser
SESAM modelocked
Semiconductor laser
Saturable
Absorber Mirror
output
pump coupler
SESAM
gain structure
heat sink
Review articleUltrafast Laser
for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006
ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
12. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
13. Motivation for semiconductor lasers: Wafer scale integration
D. Lorenser et al., Appl. Phys. B 79, 927, 2004
Passively modelocked VECSEL
vertical external cavity surface emitting laser
Review: Physics Reports 429, 67-120, 2006
SESAM
MIXSEL
modelocked integrated external-cavity surface emitting laser
Ultrafast Laser D. J. H. C. Maas et al., Appl. Phys.ETH88, 493, 2007
B Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
14. MIXSEL wafer scale integration
A. R. Bellancourt et al., “Modelocked integrated external-cavity surface emitting laser” ETH Zurich
Ultrafast Laser
IET Optoelectronics, vol. 3, Iss. 2, pp. 61-72, 2009 (invited paper)
Physics
nano-tera.ch Annual Meeting 12. 5. 11
15. Comparison of Ultrafast GHz Lasers
Review articleUltrafast Laser
for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006
ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
16. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
17. Optically pumped ultrafast VECSELs / MIXSELs
B. Rudin, V. J. Wittwer, D. J. H. C. Maas, M. Hoffmann, O. D. Sieber, Y. Barbarin, M. Golling, T. Südmeyer, U. Keller,
Opt. Express 18, 27582, 2010
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
18. Resonant vs. antiresonant MIXSEL design
Initial MIXSEL demonstration had a resonant design:
D. J. H. C. Maas et al., Appl. Phys. B 88, 493, 2007
• sensitive to growth errors
• high GDD - long pulses
growth error simulation:
layer thickness variations < 1%
Here: MIXSEL demonstration • tolerant to growth errors
with Ultrafast Laser
antiresonant design • low GDD - short pulses
ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
19. MIXSEL: improved thermal management
heat thermal estimated pump/ temp. rise heat sink output
sink conductivity heating power laser (FE sim.) temperature power
material (W m-1K-1) (pump power) mode
radius
GaAs 45 1.5 W (1.7 W) 80 µm 149 K -15 °C 41.5 mW
copper 400 3.2 W (4.3 W) 80 µm 98 K +10 °C 660 mW
diamond 1800 26.6 W (36.7 W) 215 µm 100 K -15 °C 6400 mW
• exchange the copper with
CVD diamond
reasonable temperatures
• leads to highest output power
from a ultrafast
Finite Element (FE) temperature simulations
Ultrafast Laser semiconductorZurich
ETH laser
Physics
nano-tera.ch Annual Meeting 12. 5. 11
20. High power MIXSEL
• Optical pumping 36.7 W at 808 nm • Cavity length: 60.8 mm 2.47 GHz
• Pump / laser spot radius: ~215 m • Output coupling: 0.7%
• Efficiency (opt-opt): 17.4 % • TBP: 1.35 (4.2 times sech2)
B. Rudin, V. J. Wittwer,Laser H. C. Maas, M. Hoffmann, O. D. Sieber, Y. Barbarin, M. Golling, T. Südmeyer, U. Keller,
Ultrafast D. J. ETH Zurich
18, 27582, 2010
Opt. Express Physics
nano-tera.ch Annual Meeting 12. 5. 11
21. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
22. Optically pumped ultrafast VECSELs / MIXSELs
M. Hoffmann, O. D. Sieber, V. J. Wittwer, I. L. Kestnikov, D. A. Livshits, T. Südmeyer, U. Keller,
Ultrafast Laser
Opt. Express 19, 8108, 2011 ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
23. Femtosecond all Quantum Dot VECSEL
modelocked Separate pump mirror
laser DBR separation tuning for maximum
pump absorption
higher efficiency
Active region
chirped QD-layer positions
output • each layer stack resonant for
coupler QD-SESAM different laser wavelength
• according to absorption intensity
broader gain
QD-gain AR section
CVD-diamond hybrid semiconductor / fused silica
structure
reduction of the GDD
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
24. Femtosecond QD-VECSEL
modelocked
laser
heat sink: thinned QD gain structure on CVD substrate pump
output coupler: 100 mm
output coupler transmission: 2.5%
output
laser mode radius on QD-VECSEL: 115 µm coupler QD-SESAM
laser mode radius on QD-SESAM: 115 µm
heat sink temperature: -20°C CVD-diamond QD-gain
structure
pulse duration: 784 fs repetition rate: 5.4 GHz
output power: 1.05 W TBP: 1.3 sech2
center wavelength: 970 nm peak power: 219 W
Ultrafast Laser ETH Zurich
M. Hoffmann, O. D. Sieber, V. J. Wittwer, I. L. Kestnikov, D. A. Livshits, T. Südmeyer, U. Keller, Opt. Express 19, 8108, 2011
Physics
nano-tera.ch Annual Meeting 12. 5. 11
25. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
26. 2.62 W wafer fused VECSEL at 1550 nm
• Combine advantages of InP-based active
medium with GaAs/AlGaAs reflector
• Intra-cavity diamond for good heat dissipation
2.62 W cw
Ultrafast 21881-21886 (2008)
Opt. Express 16, Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
27. First wafer-fused modelocked VECSEL at 1550 nm
• First wafer-fused passively modelocked VECSEL at 1550 nm!
• Combine advantages of InP-based active medium with GaAs/AlGaAs reflector
• Intracavity diamond for good heat dissipation
• Beam-spot diameters: 210 µm on gain chip; 50 µm on GaInNAs-based SESAM
• 600 mW in 16 ps pulses at 1.29 GHz with 10 W pump power
E. J. Saarinen, J. Puustinen, A. Sirbu, A. Mereuta, A. Caliman, E. Kapon, O. Okhotnikov,
Ultrafast Laser ETH Zurich
Optics Letters, 34, 3139 (2009)
Physics
nano-tera.ch Annual Meeting 12. 5. 11
28. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
29. Electrical vs. optical pumping
OP-VECSEL Output
EP-VECSEL
coupler
Pump laser
Top ring contact
Active
region ~ 50 μm
DBR
DBR
Heat spreader
Ultrafast Laser ETH Bottom
Zurich disk contact
Physics
nano-tera.ch Annual Meeting 12. 5. 11
30. ETH Zurich EP-VECSEL design
AR section
Suitable for modelocking
SiNx • Relatively low GDD: AR section
top contact
current spreading • Confined current injection for good beam profile
• 6 µm current spreading layer
layer
• bottom p-doped, top n-doping
n-DBR • small bottom disk p-contact
p-DBR
Power scalability
bottom contact • Wafer removal
active region
• Large apertures possible
SiNx Trade off between electrical and optical losses
CuW wafer • Optimized doping profile
• High doping → high free carrier absorption
SEM • Low doping → high resistivity
• Intermediate n-DBR for increased gain
Design guidelines:
P. Kreuter, B. Witzigmann, D.J.H.C. Maas,
Y. Barbarin, T. Südmeyer and U. Keller,
14 µm Appl. Phys. B, 91, 257, 2008
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nano-tera.ch Annual Meeting 12. 5. 11 11
31. First EP-VECSEL results
Growth, processing, and evaluation implemented
60 different EP-VECSEL lasing in cw
Output power up to 120 mW (cw) achieved
Good homogenous electroluminescence profiles measured for
devices up to 100 µm (excellent agreement with our simulations)
Ultrafast Laser ETH Zurich
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nano-tera.ch Annual Meeting 12. 5. 11
32. EP-VECSEL cw results
40 EP-VECSELs with different bottom contact diameters
Power scaling considerations
• Output power should scale with area (P α Ø2)
and current density (P α J )
• Ideal power scaling, ∆T independent of device size
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11 17
33. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
34. A key application: optical frequency combs
offer
- Phase stable link between optical (100s THz)
and microwave frequencies (GHz)
- Counting of arbitrary optical frequencies
practicable for the first time
impact
- Fundamental physics
- Optical clocks
- Satellite navigation
- Large bandwidth telecommunication
- Spectroscopy
- Medical applications, noninvasive
diagnostics
Ultrafast Laser
Physics
www.faszination-uhrwerk.de
ETH Zurich
nano-tera.ch Annual Meeting 12. 5. 11
36. Moving of the laser from ETH to Neuchatel
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
37. Noise performance of DPSSLs and VECSELs
DPSSLs
+ high-Q cavity, low nonlinearities
⇒ extremely low intrinsic noise
+ convenient and robust
Example excellent noise performance of DPSSLs: Optical ultra-stable microwave oscillator
Compare 75 MHz 1.5-µm Er:Yb glass DPSSL with commercial 1.5-µm Er-fiber laser
Relative frequency stability of the CEO frequency
measured with the same feedback loop
S.Schilt, M. C. Stumpf, L. Tombez, N.
Bucalovic, V. Dolgovskiy,
G. Di Domenico, D. Hofstetter,
S. Pekarek, A. E. H. Oehler,
T. Südmeyer, U. Keller, P. Thomann,
“Phase noise characterization of a
near-infrared solid-state laser
optical frequency comb for ultra-
stable microwave generation”,
Optical Clock Workshop, Torino, Italy,
December 1-3, 2010
(right scale: Ultrafast Laser
relative frequency stability with respect to the optical carrier) ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
38. VECSELs for Frequency Comb Generation
crucial for frequency comb stabilization:
detection of the carrier envelope offset frequency (fCEO)
fCEO detected with a DPSSL
targeted VECSEL
without pulse compression or amplification
278 fs p 200 fs
74 mW Pav 1W
75 MHz frep 1 GHz
3.1 kW Ppeak 4.4 kW
1550 nm λcenter 960 nm
Stumpf, Pekarek, Oehler, Südmeyer, Dudley, Keller,
Appl. Phys. B 99, 401 (2010)
Femtosecond VECSEL:
promising candidate for compact, low cost frequency comb generation
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11
39. Outline
Motivation and research targets
VECSELs and SESAMs
MIXSEL concept
Highlights
• 6.4 W modelocked OP-MIXSEL chip at 960 nm.
• 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm.
• 2.62 W cw average power from a 1550 nm OP-VECSEL realized
with wafer fusion. First Modelocking result at 1550 nm.
• 120 mW cw average power from an EP-VECSEL.
• Full stabilization of a frequency comb (CEO beat and laser repetition
rate) using a SESAM modelocked diode-pumped Er:Yb:glass
Summary and outlook
Ultrafast Laser ETH Zurich
Physics
nano-tera.ch Annual Meeting 12. 5. 11