MIXSEL - Nanotera Annual 2012-For Web

ETH Zurich Ultrafast Laser Physics

nano-tera.ch annual 2012

Vertical integration of ultrafast semiconductor lasers for wafer-scale mass production

Prof. Ursula Keller (PI) Physics Department, ETH Zurich

Prof. Eli Kapon, Dr. Alexei Sirbu Institut de Photonique et d‘Electronique Quantiques, EPFL, Lausanne

Prof. Thomas Südmeyer Institut de Physique, Université de Neuchâtel

Prof. Bernd Witzigmann Computational Electronics and Photonics, University of Kassel (previously ETH Zurich)

nano-tera.ch



Ultrafast lasers

… generate coherent light pulses with pico- or femtosecond duration

observe and use fast dynamics • understand chemical reaction dynamics • fast communication • …

interconnects optical clocking

access ultrashort time scales

1



Ultrafast lasers



concentrate in time and space achieve extremely high intensities • material processing • multi-photon biomedical imaging • …


R. Aviles-Espinosa, G. Filippidis, C. Hamilton, G. Malcolm, K. J. Weingarten, T. Südmeyer, Y. Barbarin, U. Keller, S. I. C. O Santos, D. Artigas and P. Loza-Alvarez, “Compact ultrafast semiconductor disk laser: targeting GFP based nonlinear applications in living organisms”, Biomedical Optics Express, vol. 2, No. 4, pp. 739-747, 2011



Ultrafast lasers



achieve extremely high intensities • material processing • multi-photon biomedical imaging • …

broad optical spectrum generate ultrastable frequency combs • high precision spectroscopy • optical clocks • …

concentrate in time and space


1



Ultrafast semiconductor lasers

1

• Currently, typical ultrafast lasers are bulky and complex

• Our approach: semiconductor laser with vertical integration

Modelocked Integrated External-Cavity Surface Emitting Laser

MIXSEL VECSEL Vertical External Cavity Surface Emitting Laser

Semiconductor Saturable Absorber Mirror

SESAM



Outline

Motivation and research targets

Introduction to VECSELs, SESAMs, and MIXSELs

Research targets

Highlights

- CW & modelocked VECSELs with wafer fusion (granted patent)

- 1-W femtosecond OP-VECSEL

- First QW-absorber based MIXSEL

- First modelocked VECSEL with multi-pass (new patent application)

- Generation of ultra-low-noise microwave for precision metrology

Summary and outlook



OP-VECSEL = Optically Pumped Vertical-External-Cavity Surface-Emitting Semiconductor Laser

M. Kuznetsov et al., IEEE Photon. Technol. Lett. 9, 1063 (1997)

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

pump

laser

heat sink

gain structure

output coupler

CW optically-pumped VECSELs



Bandgap engineering



SESAM for pulse formation

pump

laser

heat sink

gain structure

output coupler

cw-laser modelocked laser

pump

laser

gain structure

SESAM

heat sink

output coupler



MIXSEL

MIXSEL Modelocked Integrated External-Cavity Surface Emitting Laser

VECSEL Vertical External Cavity Surface Emitting Laser

SESAM Semiconductor Saturable Absorber Mirror

abso

rber

in

tegr

atio

n

A. R. Bellancourt et al., “Modelocked integrated external-cavity surface emitting laser” IET Optoelectronics, vol. 3, Iss. 2, pp. 61-72, 2009 (invited paper)



OP-VECSEL: potential for cost-efficient mass-production

Green laser: optically-pumped VECSEL (OSRAM)

Ulrich Steegmueller et al., “Progress in ultra-compact green frequency doubled optically pumped surface emitting lasers”, High-Power Diode Laser Technology and Applications VII, Proc. of SPIE Vol. 7198 719807, 2009

H. Lindberg et al., “Recent advances in VECSELs for laser projection applications”, Vertical External Cavity Surface Emitting Lasers (VECSELs), Proc. of SPIE Vol. 7919 79190D, 2011

less than 0.4cm3 >70 mW green



Outline



Research targets

Highlights






Summary and outlook



Research tasks Targets Better optically-pumped MIXSELs: higher power, shorter duration, new wavelengths

Better understanding and optimization of saturable absorbers

First electrically-pumped MIXSELs

Application studies: frequency combs and high precision metrology

Simulations of ultrafast VECSELs and MIXSELs

Optical testing

Semiconductor structures and characterization

Frequency comb generation and stabilization

Prof. Ursula Keller (PI) Physics Department, ETH Zurich

Prof. Eli Kapon, Dr. Alexei Sirbu Institut de Photonique et d‘Electronique Quantiques, EPFL, Lausanne

Prof. Thomas Südmeyer Institut de Physique, Université de Neuchâtel

Prof. Bernd Witzigmann Computational Electronics and Photonics, University of Kassel (previously ETH Zurich)

Partners



Outline



Research targets

Highlights






Summary and outlook



Novel wafer-fusion technology: patent granted

3 4 5 6 7 8 9 100

20

40

60

80

100

120

Out

put p

ower

(mW

)Input pump power (W)

5

10

15

20

25

30

Pul

se w

idth

(ps)

First wafer fused SESAM fabricated according to the new invention demonstrates average output power in excess of 100 mW and pulsewidth as low as 6 ps:J. Rautiainen, J. Lyytikäinen, L. Toikkanen, J.Nikkinen, A. Sirbu, A. Mereuta, A. Caliman, E. Kapon,

and O. Okhotnikov, IEEE Photon. Technol. Lett., v.22, pp. 748-750, 2010

A novel wafer-fusion process allowing to considerably reduce the defect formation in the active region: A. Sirbu, A. Mereuta, A.Caliman,

VERTICAL CAVITY SURFACE EMITTING DEVICES INCORPORATING WAFER FUSED REFLECTORS,

International Publication Number WO 2011/000568 A1

CL image of a wafer-fused structure with no dark-line defects in the active region



Outline



Research targets

Highlights






Summary and outlook



First Watt-level femtosecond VECSEL

pulse duration: 784 fs

output power: 1.05 W

repetition rate: 5.4 GHz

center wavelength: 970 nm

pump

modelocked laser

CVD-diamond QD-gain structure

output coupler QD-SESAM



Outline



Research targets

Highlights






Summary and outlook



Pulse duration of MIXSELs

• slow recombination of the of the QD-absorber in the previous MIXSEL

• compared to the QD-SESAM used in the 1 W femtosecond VECSEL

• novel QW absorber with fast recombination and low Fsat



shorter pulses higher repetition rates: 20 GHz

novel fast QW absorber with a low Fsat more than 3 times shorter pulses

First MIXSEL with QW-absorber

25

Next step: optimize dispersion & demonstrate fs-MIXSEL with >1 W



Outline



Research targets

Highlights






Summary and outlook



Biomedical imaging

Yb- hi rep

2-photon imaging FOM map of laser sources

Average power 0.1 mW 1 mW 10 mW 100 mW 1 W 10 W 100 W

100 kW

10 kW

1 kW

100 W

10 W

1 W

0.1 W

Ti:S, Er-fiber (at sample plane)

Peak

pow

er

Nanosurgery

Photodamage Er-fiber (full power)

Yb-fiber (full power)

Ti:S 2G

Ti:S (full power)

Melting/

Burning?

TargetZone

Cr:F 500M

Double rep rate, double average power, keep peak power constant

Er-SCG

shorten pulsewidth

Note: microscope systems have loss of 3-10X typical from input

to sample plane VECSEL 500M

at sample

in collaboration with Dr. Kurt Weingarten



Multi-pass for increased peak power (patent application)

Semiconductor gain: short gain lifetime (~1 ns)

⇒ limit in low-repetition rate operation, challenge for highest peak powers

Solution multipass-cavity: gain is passed every ns

⇒ 250 MHz operation achieved

⇒ new patent application



Outline



Research targets

Highlights






Summary and outlook



Low-noise frequency comb

• Coherent stabilized CEO peak with only 5 kHz feedback bandwidth

• One of the lowest residual integrated phase noise (0.72 rad rms in 0-100 kHz) for a 1.5-µm comb

Diode-pumped solid-state laser (DPSSL) frequency comb with excellent noise performance

• 10-8 relative instability (at 1 s integration time) on the 20-MHz CEO contributes only 10-15 to the optical carrier frequency instability

• 20-fold improvement compared to a commercial self-referenced fiber comb

S. Schilt, N. Bucalovic, V. Dolgovskiy, C. Schori, M. C. Stumpf, G. Di Domenico, S. Pekarek, A. E. H. Oehler, T. Südmeyer, U. Keller, P. Thomann, “Fully stabilized optical frequency comb with sub-radian CEO phase noise from a SESAM-modelocked 1.5-µm solid-state laser”, Optics Express, 2012



Generation of ultra-low-noise microwave



Generation of ultra-low-noise microwave

fCEO detected with a DPSSL without pulse compression or amplification

targeted VECSEL

crucial for frequency comb stabilization: detection of the carrier envelope offset frequency (fCEO)

278 fs

74 mW

75 MHz

3.1 kW 1550 nm

p Pav

frep

Ppeak

λcenter

200 fs

1 W

1 GHz

4.4 kW 960 nm

Femtosecond VECSEL: promising candidate for compact, low cost frequency comb generation

goals consistent with biomedical applications (two photon imaging FOM) – similar peak, but lower rep-rate (with lower average power)

Stumpf, Pekarek, Oehler, Südmeyer, Dudley, Keller, Appl. Phys. B 99, 401 (2010)



Outline



Research targets

Highlights






Summary and outlook



Prospects for year 4 • Demonstration of frequency comb with femtosecond OP-VECSELs and OP-MIXSELs

• Power scaling EP-VECSEL with modified designs (Simulations helped to identify key power limiting issues: heating, optical losses, electrical resistance in P-DBR ...)

• SESAM modelocked EP-VECSEL • First demonstration of wafer-fused SESAM modelocked femtosecond VECSELs at 1550 nm • Explore new collaborations: - several new industrial collaborations - inter nano-tera-project collaborations - international collaborations



Further information: poster session

Documents

MIXSEL - Nanotera Annual 2012-For Web