High Power Dense Spectral Combination Using … · Available Lasers and VHGs Christophe Moser, CEO...
Transcript of High Power Dense Spectral Combination Using … · Available Lasers and VHGs Christophe Moser, CEO...
Ondax,Inc. Page 1 AHPSL conference Sept 17-19 2007
High Power Dense Spectral Combination Using Commercially
Available Lasers and VHGsChristophe Moser, CEO
Contributors:Gregory Steckman, Frank Havermeyer, Wenhai Liu: Ondax Inc.
Christian Wessling, Martin Traub, Dieter Hoffman Fraunhofer Institute for Laser Technology, Aachen, Germany
Stefan HeinemannFraunhofer USA Center for Laser Technology, Plymouth, MI, U.S.A
Ondax,Inc. Page 2 AHPSL conference Sept 17-19 2007
Content:
Introduction: Coarse vs. Dense Wavelength Multiplexing (DWM)
Volume Holographic Gratings for High Power Lasers DWM
DWM Architecture – 1kW Fiber Coupled Unit
Fabrication and Reliability of Volume Holographic Gratings
Applications
Conclusions
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Coarse vs. Dense λ Multiplexing
80X 91X 94X 97X
970
971
980DENSE λ
multiplexing
Commercially AvailableHigh Power Laser DiodeWavelengths
COARSE λmultiplexing
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Challenges for Dense λ Muxing
Broad Linewidth:2.5 – 4nm
High TemperatureDependence:~0.3nm/oC
MUXING GRID
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Requirement for Dense λ Muxing
Laser Diodes
Combiner
10 X improvement over state of the art laser diodesi.e ~ <0.03nm/oC
10 X improvement over state of the art laser diodesi.e ~ 0.2nm
Temperature Dependence
Linewidth
20 X improvementOver State of The Art dichroicsi.e < 0.5nm
Bandpass
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VHG-FAC for Laser Linewidth Reduction
Volume Holographic Gratings (VHGs) in glass are critical for
narrowing the spectral linewidth of High Power Laser Diodes
VHG-FACHPSL
1,00E+06
3,00E+06
5,00E+06
7,00E+06
9,00E+06
1,10E+07
1,30E+07
940 950 960 970 980 990 1000
l [nm]
Inte
nsity
[a.u
.]
I = 90AI = 90A locked P = 70,1 W („free running“* )
P = 67,4 W (locked)VBG with 90% efficiency
* without FAC lensVHGs in FAC lenses improve off-the-shelf diode lasers:
10 X in linewidth : 4nm 0.2nm30 X in temperature dependence: 0.3nm/oC 0.01nm/oC
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VHG-FAC Working Principle
Commercially AvailableVHG-FAC CombinesCollimationAnd Wavelength NarrowingInto One
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972 973 974 975 976 977 9780
2000
4000
6000
8000
10000
12000
14000
16000
15A 25A 35A 45A 55A
Inte
nsity
[a.u
.]
wavelength [nm]972 973 974 977 978
Wavelength [nm]975 976
960 965 970 975 980 985 9900
2000
4000
6000
8000
10000
12000
14000
16000
15A 25A 35A 45A 55A
Inte
nsity
[a.u
.]
wavelength [nm]
960 965 970 975 980 985 9900
2000
4000
6000
8000
10000
12000
14000
16000
15A 25A 35A 45A 55A
Inte
nsity
[a.u
.]
wavelength [nm]960 965 970 985 990975 980Wavelength [nm]
6nm30nm
Linewidth Reduction Results
Lineshape without VHG-FAC Lineshape with VHG-FAC
“Wavelength Stabilization of HPDL Array - Fast Axis Collimation Optic with Integrated VHG”:C. Schnitzler, S. Hambuecker, O. Ruebenach, V. Sinhoff, G. Steckman, L. West, C. Wessling, D. Hoffman,Ingeneric GmbH, Ondax, Inc., Fraunhofer ILT, Photonics West, Jan. 2007
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Effects of Bar Smile and VHG Alignment
972 973 974 975 976 977 9780
2000
4000
6000
8000
10000
12000
14000
Optimum 1° 2° 3°
int
wavelength [nm]
Linewidth narrowing independent of bar smile and up to 3o FAC misalignment
Rolling 1o
Rolling 3o 972 973 974 977 978Wavelength [nm]
975 976
1nm
Off-the-shelf High Power Laser Diodes are collimated andlinewidth-narrowed to 0.2nm and collimated with a single VHG-FAC. These sources meet the requirement for dense wavelength multiplexing.
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VHG for Dense λ Muxing (1)
Volume Holographic Gratings (VHGs) in glass provide a solution fornarrow wavelength combiners:
High PowerLaser λ1
High PowerLaser λ2
λ2 – λ1 <1nm
Spectral combining of high power linewidth-reduced laser diodes
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Properties of VHG Combiners
BC
• VHG combiners work in reflection• VHG combiners have sub-nanometer reflection bandwidth• Diffraction efficiency depends strongly on angle of incidence
for >90% combining efficiency, use FAC with less than 2 mrad rest divergence and 15 degree angle of incidence
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Summary: Dense Wavelength MultiplexingOff-the-shelfHigh Power Laser Diodes
VHG-FAC
Transform off-the-shelf High Power Laser Diodes intosuitable sources for DWM
VHG Combiner~90% Efficiency
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Architecture with DWM
GeometricalStacking Polarization
MultiplexingBeam
Transformation
λ1
DWM
λn
Fiber Coupling
Repeat DWM with 80Xnm, 90Xnm, 94Xnm, 97Xnmand combine with coarse dichroic filters
CoarseWM
Dense WavelengthMultiplexing (DWM)
Modules
λ1
DWM
λn
λ1
DWM
λn
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978nm
975nm
GeometricalStacking
DWM
DWM
DWM
978nm
975nm
978nm
975nm
PolarizationMultiplexing
Beam Transformation
911nm
908nm
GeometricalStacking
DWM
DWM
DWM
911nm
908nm
911nm
908nm
PolarizationMultiplexing
Beam Transformation
Coa
rse
wav
elen
gth
Mul
tiple
xing 952 Watts
Fiber Coupled
D=600umNA=0.175
1kW Fiber Coupled with DWM70W bars
80W bars
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Geometry of the Laser Diode Bars
1kW Fiber Coupled with DWM
0.5% AR Coated Front FacetExtended Locking Range (20nm)
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1kW Fiber Coupled with DWM
VHGCombiner
2 Wavelength Combiner Block
High Power Laserwith VHG
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1kW Fiber Coupled with DWM
Average combining efficiency for 6 units 908/911: 89.5%
Average combining efficiency for 6 units 975/978: 79.7%
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1kW Fiber Coupled with DWM
Facility Unit (Water Cooling, Current Drivers): 1000 x 600 x 1200mm3 (LxWxH)
DWM Laser Diodes
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2 4 6 8 10 12 14 16 18 200
102030405060708090
100Goal
ηtransmission98.5% ηdiffraction 90% η
λ locking 95%
Based on performance for 1kW demo
ηtransmission97% ηdiffraction 85% η
λ locking 93%
Cum
ulat
ive
com
bini
ng e
ffici
ency
[%]
Number of beam sources
Outlook Multi-kW with DWM
By multiplexing more wavelengths, the power in the fiber can be increased without increasing the fiber core or its numerical aperture.
With the same performance VHGs used in the 1kW demo, up to 10 sources canbe densely multiplexed with a cumulative efficiency of 70%.
Multi-kW fiber coupledpower can thus be achievedfrom a 600 µm coreand 0.175 N.A. fiber
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VHG Fabrication and TestWafer Fabrication – and Automated 100% Wafer Testing
Example of a wafer measurement from the database.All optical parameters of VHG measured at high spatial resolution.
45mm
35mm
150 µmspatial
resolution
efficiency
Efficiency [%]
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VHG Damage Threshold
• Pulsed 1064nm • 20Hz Rep. Rate• 20ns Pulse Width• 0.5mm Spot Size
High Damage Threshold : 3.85 J/cm2 or 175 MW/cm2
Samples tested with AR coating meeting MIL-C-675
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VHG Environmental Reliability
VHGs Kept at 150oC Show No Measurable Degradation Over Time
0 2000 4000 6000 8000 10000 120001.48640
1.48642
1.48644
1.48646
1.48648
1.48650
1.48652
1.48654
1.48656
1.48658
1.48660
Ref
ract
ive
Inde
x
Time (hrs)0 2000 4000 6000 8000 10000 12000
3.10
3.20
3.30
3.40
∆n (1
0-4)
Time (hrs)
Grating strength (∆n)Index variation
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Applications of Kilowatt Laser Diode Systems
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
0.1 1 10 100 1000 10000 100000Power (W)
BPF
ADADAD
Printing
Thermal Marking
Soldering
PlasticsWelding
Deep PenetrationWelding
Metal Sheet Cutting
SelectiveLaser PowderRemelting
CleaningMelting
Hardening
Brazing
CO2
Diode Laser
DPSSL
BPF: Beam Parameter FactorBPF: Beam Parameter FactorEfficiency * Beam Quality Efficiency * Beam Quality
Ondax,Inc. Page 25 AHPSL conference Sept 17-19 2007
Summary
Volume holographic gratings (VHG) are enabling Dense Wavelength Multiplexing withHigh Power Lasers Diodes by:
narrowing the emission spectra of commercially availablehigh power laser diodes and combining them
Commercially available VHGs are wafer produced and 100% tested.
FAC-VHGs incorporate collimation and line narrowing to reduce packaging costs.
952 W coupled in 600µm, NA:0.175 fiber with DWM by Fraunhofer Institute, Aachen:
Power loss due to wavelength narrowing: 5-10%
Combining efficiency at 908/911: 90%
Combining efficiency at 975/978: 80% cause by mismatch of theslow axis divergence (90% achievable)
Multi-kW fiber coupled power by adding Dense and Coarse wavelength combining