J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
High-power fiber lasers /sources / amplifiers
[email protected]/hpfl.html
Johan NilssonOptoelectronics Research Centre
University of Southampton, England
KTH Winter SchoolRomme, Feb 5 2016
Questions welcome
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Tekn. Dr., fysik (optik), 1994Institutionen for Fysik II, KTH
Lindstedtsvägen 24
2
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 3
Southampton, England
• 100 km southwest of Heathrow• 100 km west of Gatwick• Please visit if you have a chance!
Heathrow
Gatwick
Southampton
London
J. Nilsson, “Fiber lasers at ORC”, Sandia, Jan 20 2012
The Optoelectronics Research CentreThe Optoelectronics Research Centre
170 staff and research studentsResearch in photonics & optoelectronics
Interaction between light and matterFabrication, materials, and applications focusedPhysics, Optics, Quantum Electronics, Chemistry and Materials Science, Nanotechnology, Mathematics, Biology...Lasers, fibers, glass, planar, telecom, bio, meta-materials, plasmonics...
www.orc.soton.ac.uk
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
New fabrication facilities
• 150 million pound investment• 944 m2 Class 100-1K
Cleanrooms• 564 m2 Class 1000
Cleanrooms• 4 fiber draw towers/3 lathes• New PECVD/FHD/PLD
systems• New activities/facilities:
– Silicon photonics– Metamaterials– Nanophotonics– Biophotonics
• 30 new photonics laboratories• Fully functional early 2010
• The Zepler Institute
Award from Royal Institute of British Architects!
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Fiber fabrication at ORC
• Silica lathes• Glass deposition
– MCVD, OVD
• Draw towers• Micro-structuring• Soft glass • RE-doping• Etc.
6
Drawtower
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Hollow core fibres
Transmission loss < 0.01 dB/m
MFD tailorable to any solid fibre direct splicing possible
Low bend loss even at 100 µm MFD
Power in glass < 0.01% γ ~ 0.001 W-1km-1
Can be made single moded spatial filtering
Polarisation maintaining design possible
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 9
multi -modepump fibre
multi -modepump fibre
GTWave fibre
single -modesignal fibre
9/125 µm100 W
Size for power!
40/650 µm> 1 kW
Air clad
Hi-bi
Multi core
Ribbon
Micro-structured “holey” fiber
Fibers for high-power lasers
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
10
9 / 125 µµµµm100 W
40 / 650 µµµµm, > 1 kW
• Large core to facilitate:
– power handling
– minimization of nonlinear
effects
– high energy storage for
pulsed application
– efficient pump absorption &
reduced device length
• Large inner cladding for launch
of high-power pump beams
• Silica-based
– Superb power-handling
– Excellent control of
parameters
Size matters!Silica matters, too!
Large size is the most important design feature of a high-power fibre laser
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
11
Schematic rare-earth-doped fibre laser
Rare-earth doped fibre
Pump diodePump diode
Laser output
Cavity mirror for external feedback
Cavity feedback from perpendicular fibre cleave
(4% Fresnel reflection)
Dichroic mirror for pump / signal combination
Lens
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 12
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 13
1.4 kW single-mode (ORC)
0.4 kW SF, SM, SP Yb MOPA
1996 1997 1998 1999 2000 2001 2002 2003 2004 20050.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
Lase
r po
wer
[kW
]
Year
30W, Nd10W, Yb, SF
110, Yb, SM (SDL)150W, Nd/Yb
135W, Yb, SM272W, Yb (ORC)
352W, Yb, SM (ORC)
485W, Nd/Yb, SM
1 kW, Nd, MM
2 kW, Yb, MM
10 kW, Yb, MM
20W, Yb, SF
120W, Yb, SF
87 W, Er/Yb, SFMOPA (ORC)
1.2mJ, 380fs, Yb7.7mJ, 10W, Yb (ORC)
2.8mJ, 50/100W, Yb
8.4mJ, 120W, Yb
1.2 kW single-mode (ORC)
366 W JAC Yb (ORC)280 W, JAC Yb PCF
1 kW, Yb, MM (ORC)
0.8 kW, Yb, SM(Dual-end output)
610W, Yb SM (ORC)
Different wavelengthsPulsed (fs – ns)Single frequency…
1.3 kW, M2 < 3 (Jena)MM
1.5 kW (Jena)
2 kW single-mode (IPG)
Pump power limited in many cases!
0.6 kW, SM, polarized (ORC)
160 W Er/Yb
80 W Tm. 2 µm
150 W SF, SM, Er:Yb MOPA
0.32 kW, 20 ps, Yb MOPA
264 W SF, SM, SP Yb MOPA
100 kW, Yb, MM
Fiber power!Many regimes!
0.3 kW EYDFL
3 – 20 kW SM (IPG)
0.1 kW 980 nm YDFL& Ramanlasers
0.3 kW, fs, Yb MOPA
0.4 kW SF, SM, SP Yb MOPA
0.8 kW TDFL
0.6 kW SM, SF TDFA
1 kW TDFL
1.7 kW quasi-SM, quasi-SF(ORC)
0.83 kW, Yb, fs
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 14
Energy levels in rare-earth ions• High-power fiber lasers are
generally doped with rare earths
• Lots of energy levels and transitions in RE ions
• In silica, only four meta-stable levels can be pumped with high-power laser diodes
• Six transitions have been used for high-power cladding-pumped silica fiber lasers
• Nd, Er, Tm, Yb, Ho
Figure from P. C. Becker, N. A. Olsson, and J. R. Simpson, Erbium-doped fiber amplifiers: fundamentals and technology (Academic Press 1999)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 15
Simplicity of Yb3+-ions makes YDFLs exceptionally efficient
• Only two energy levels No upconversion or cross-relaxation High concentrations can be usedVery low quantum defect (can be below 10%)
• Pump at ~915 nm – 975 nm• Emit at ~ 1060 nm
Figure from P. C. Becker, N. A. Olsson, and J. R. Simpson, Erbium-doped fiber amplifiers: fundamentals and technology (Academic Press 1999)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Yb-doped fiber sources
16
M. N. Zervas & C. A. Codemard, “High Power Fiber Lasers: A Review”, IEEE J. Sel. Top. Quantum Electron. 20, 1-23 (2014)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Some record resultsWhat Characteristics Who Comments
Highest-power fiber laser (MM)
100 kW IPGYb-doped, 10xx nm, cw. Large number of (SM) fiber lasers bundled together so no inherent limitation.
Highest-power SM fiber laser
15 - 20 kW IPGYb-doped, 10xx nm, cw, tandem-pumped with 1018 nm YDFLs (?)
Highest-power diode-pumped SM fiber laser
2 - 3 kWIPG, Jena, ORC,
CorningYb-doped, 10xx nm, cw
Highest-power Tm-doped 1 kW Q-Peak / Nufern 2000 nm, SM, cw
Highest-power Er-doped 0.3 kW ORC 1570 nm, cw, M2 = 3.9
Highest-power 980 nm 0.1 kW Jena, BordeauxCw, nearly diffraction-limited,air:silica micro-structured fiber
Highest-power 9xx Nd-doped fiber laser
10 – 20 WLightwave
Electronics, Uni. Caen
SM, pulsed (ns). Shortest-wavelength band demonstrated for cladding-pumped fiber lasers.
Highest-power Bi-doped laser
~ 20 W (?)FORC, General Physics Institute
~ 1150 nm, cw, SM, core-pumped by 10xx nm YDFL
17
These records may have been superseded in some cases. Many apologies for any left-out results.
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Some record resultsNarrow linewidth
What Characteristics Who Comments
Highest-power narrow-line 1.7 kW ORCYb-doped, 10xx nm, quasi-SM, cw, sub-GHz linewidth. Also highest-power high-gain MOPA.
Highest-power narrow-linepolarization-maintaining
1.1 kW ORCYb-doped, 10xx nm, quasi-SM, cw, 100-MHz-level linewidth.
Highest-power narrow-line “eye-safe”
0.6 kWNorthropGrumman
Tm-doped, 2 µm, SM, cw, single-frequency
Highest-power narrow-line Er-doped
0.15 kW ORC1550 nm, SM, cw, single-frequency, tunable
18
These records may have been superseded in some cases. Many apologies for any left-out results.
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Some record resultsWavelength-converted
19
These records may have been superseded in some cases. Many apologies for any left-out results.
What Characteristics Who Comments
Highest-power fiber Raman laser
1.3 kW SIOM
1120 nm, core-pumped by 1080 nm YDFL. Also highest-power core-pumped fiber laser of any description.
Highest-power cladding-pumped fiber Raman laser.
100 W ORC1120 nm, quasi-SM, cw, cladding-pumped by 1060 nm YDFL.
Highest-energy cladding-pumped fiber Raman laser
0.2 mJ ORC1120 nm, quasi-SM, cladding-pumped by 1060 nm YDFL.
Highest-powersupercontinuum source
50 WImperial College
CW, core-pumped by 1070 nm YDFL. SC-generation in air:silica micro-structured fiber
Highest-power frequency-doubled fiber laser
80 W (530 nm) ORC530 nm, SM, pulsed (ps), frequency-doubled polarized Yb-doped fiber MOPA
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Some record resultsPulsed
What Characteristics Who Comments
Highest-energy 82 - 113 mJMichigan U,
Tsinghua U
0.2 mm core diameter, Yb-doped, 10xx nmMichigan 82 mJ, M2 = 6.5, Tsinghua: 113 mJ, M2 = ?
Highest-energy (quasi-) single-mode
22 mJ Jena
Yb-doped, 10xx nm. “9-mJ pulse energy Q-switched large-pitch fiber laser system with excellent beam quality”, Paper 8237-31. 22 mJ reported at ASSP.
Highest-power fs.Also highest average power pulsed.
830 W JenaYb-doped fiber MOPA, CPA, SM, polarized, 120 MHz, 640 fs, 12 MW (compressed).
Highest-power mode-locked fiber laser
65 W JenaYb-doped, 10xx nm, 850 nJ. Compressed peak power 6 MW.
Highest in-fiber peak power
5 MW AculightYb-doped, 10xx nm, SM, 4.3 mJ, 1 ns. Air:silica micro-structured (“rod-type”) laser.
20
These records may have been superseded in some cases. Many apologies for any left-out results.
Also some of the record results on earlier slides were pulsed!
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 21
Optical fibres provide several fundamental advantages for lasers and amplifiers
• Confinement of pump and signal beams– High gain efficiency
• Long interaction length– RE-concentrations at quench-free level– Low heating per unit length– Simplified heatsinking
• Control of the propagation properties by the waveguide– Beam profile / single-mode output
• High gain• High power• High nonlinearities
– Sometimes good, often bad– High gain & high nonlinearities “interesting physics”
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 22
Interaction length: Bulk laser vs. fibre laser
Bulk: Not possible to maintain tight focusing over adequate length High threshold, high thermal load Pump
beam Laser crystal
Pump beam
Fibre
Tight beam confinement and maximum intensity over arbitrary length.
Low threshold High gain efficiency Even three-level low-concentration systems lase (EDFA) Low thermal load per unit length
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 23
An engineerable gain medium!
• The materials properties (spectroscopy) can be engineered to a degree with all gain media
• Fibers in addition open up for engineering of the geometry– Glass host with unique fabrication procedure
• This makes fibers much more amenable to engineering and they can have a high level of functionality
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 24
Engineering of fiber properties• Spectral control
– Distributed waveguide filtering– Bragg gratings in photosensitive fibers– Concentration & distribution of rare earths & co-dopants
• Spatial control– Single-mode propagation in multimode core– Mode filtering– Mode conversion
• Dispersion tailoring (temporal control)• Nonlinearity
Altogether much greater control than with conventional non-waveguiding gain media– CO2, Nd:YAG, Ti:Al2O3 ...
Great advantage for sources in different regimesMake the most of this
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 25
Fibers provide many additional advantages
Not only performance advantages• Compact packaging & low weight
– Can be coiled with cm-scale radius• Compatibility with telecom technology
– Telecom & fiber technology very sophisticated; still low cost– By far the biggest market for optics
• Thermal & mechanical stability, robustness• Reliability and lifetime
– High reliability and lifetime of telecom laser diodes and telecom devices
• Integrability– Fiber Bragg gratings, dyes, liquids, gases, nonlinearities... can be
engineered into fiber– Fibers can be spliced together for added integration
• Wavelength-selective couplers• Tapered fiber bundles• Fiberized components (modulators, isolators...)
– Integration to complex systems with high functionality
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Two dominating active fiber devices with very different characteristics
• Er-doped fibre amplifier for telecom– High gain efficiency– Long interaction length low concentration for low quenching– Single-mode operation– Enabled the Internet– Laid the foundation for active fiber technology
• High-power Yb-doped fibre lasers and amplifiers– Low thermal load per unit length & simplified heat sinking– Single-mode operation
26
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Power-scaling
Important points: High power fiber sources are,• Cladding-pumped by multimode laser diodes• Doped with rare-earth laser ions, notably Yb• Silica-based
(with few exceptions)
• The fibre converts the relatively low-brightness beam from a diode source to a much brighter beam with somewhat lower power
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
28
Principles of operation (amplifier) • Optical fibre doped with rare earth in the core• The RE ions are optically pumped to an excited state by laser diode
The excited RE ions generate / amplify light via stimulated emission• Pump coupler combines signal and pump
Signal in
isolator fibreisolator
Pumpdiode
Signal out
Pump coupler
Double-clad RE-doped fibre
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
29
Example: Schematic end-pumped rare-earth-doped fibre laser
Rare-earth doped fibre
Pump diodePump diode
Laser output
Cavity mirror for external feedback
Cavity feedback from perpendicular fibre cleave
(4% Fresnel reflection)
Dichroic mirror for pump / signal combination
Lens
• In this example, fibre is really only the gain medium• Similar to conventional bulk laser such as Nd:YAG• Far from the ideal “all-fibre” laser without free-space paths• Still, the fibre & waveguiding can provide many advantages!
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
30
Example: Amplifiers in different pumping configurations
Rare-earth doped fibre
Pump diodePump diode
Signal out
Dichroic mirror Lens
Signal in
End-pumped
Side-pumped• Pump not in same mode
as signal• “Space multiplexing”
• “All-fibre”• Allows for continuous
fibre path• Robust
Signal out(fibre)
Signal in(fibre)
Pump couplers Splice
Pump diode
Pump diode
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
31
Diode stacks0.2 – 1 kW, 808, 915, 940, 980 nm
Alternatively, use LOTS of single-emitter diodes with combining network!
• Power up to ~ 10 W each
• Packages with several single-emitter diodescan provide > 100 W of fibre-coupled power
High-power pump diodes
JDSU
Laserline
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
32
High-power pump diodes (II)
• High power• Low cost (< $5/W)• High efficiency
– 80% reported– 50% – 60% standard pigtailed
• But, multimode = “low” brightness
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
33
Why not simply use the diodes directly?
• Power is not enough– 100 W enough for lots of processing, but... don’t try it with a light bulb
• Power must be “concentrated” and ideally controllable– Spatially– Spectrally– Temporally (pulsed)– Brightness
• Fibres are very good for this at high powers– Long– Waveguide
• Also excellent amplifiers– MOPA
It’s not a lightbulb!!!!!!!
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
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• Spatial brightness• Related to focusability (beam quality, M2) and intensity
222222222 )( NAw
P
M
P
w
P
A
PB
πλθπ===
Ω=
Ω== BIA
P
w2θ
P: PowerA: Area at focusΩ: Solid angleI: Intensity
Brightness: key property of lasers
MM diodes:High powerPoor beam quality Limited brightness
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
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Cladding-pumped fibre
Diode pump beam at λλλλp
Pump launch:End- or side-pumping
Outer cladding:Low-index polymer-coating or all-glass structure
Inner cladding:Multimode waveguide to capture pump radiationSilica glassCore:
RE-doped silica glassMay be single-mode
Laser signalat λλλλs
• Cladding-pumping always leads to spatial concentration of light, from multimode diode to (nearly) diffraction-limited fibre laser output
• Enhancement of (spatial) brightness
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
36
Five orders of magnitude brightness-enhancement possible with cladding-pumping
• Launch low-brightness high-power diode into inner cladding of fibre!• The converted output beam emerges from a much smaller core with
much smaller NA than the inner cladding– Area up to 1000 times smaller in Yb-doped fibre laser– NA (angles) up to 10 times smaller
Brightness enhancement of over 105 possible in Yb-doped fibre laser– Ideally M2
out = 1; M2pump > 300 possible
Core Inner-cladding
Outer-cladding
Output
Pump
Fibre laser
22
=
⋅
=
outcore
pumppump
outcore
pumppump
pump
out
pump
out
NAr
NAw
NAr
NAw
P
P
B
B η
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Brightness and power of Yb-doped fiber sources and diode sources
37
Bri
gh
tne
ss (
W/m
m2-s
r)
0.01
0.1
1
10
100
1000
10000
Output Power (kW)
SM
MM
DD
1 102 3 20 30
M. N. Zervas & C. A. Codemard, “High Power Fiber Lasers: A Review”, IEEE J. Sel. Top. Quantum Electron. 20, 1-23 (2014)
MM: MultimodeSM: Single-modeDD: Directly from diode
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Pump launch
End-pumpingSide-pumping
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
39
Pros and cons of end-pumping+ Simplest approach
+ Straightforward fibre fabrication, preparation and setup+ High efficiency+ Minimal pump brightness degradation– At most two pump launch points– Launch point becomes hot-spot – risk for failure
– Multiple launch points or distributed pump injection preferable– Pre-empts splicing & “all-fibre” devices (without free-space path)
Pumpbeam
Focusing lens
Outer cladding
Inner cladding
Rare-earth-doped core
End-pumping
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
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Side-pumping schemes(more correctly, space (or mode) division multiplexing)
Outer cladding
Inner cladding
Rare-earth-doped core
V-groove
Focusing lens
Pump beam
Tapered fibre bundleFrom C. Headley, OFSAlso Sifam, ITF...
GTWave® SPI lasers
V-groove side-pumpingKeopsys
Silicone rubberCoating
Fused part
Pump fibre
Doped Fibre
Side splice
C. Renaud, thesis,U. Southampton 2001IPG??
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Tapered fiber bundle
41
Fiber bundleTapered bundle
Outer-cladding
Inner-cladding
Buffer
SpliceCore
or
6 pump fibers & 1
signal fiber into
1 active fiber7 pump fibers
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 201642
End-pumping Tapered fiber
bundle V-groove side-
pumping GTWave Side-splicing
End user ease of use and reconfigurability
Yes Yes No No Yes
Ruggedness Limited Good Medium Good Good
Type of active fiber Any Any Any Special
(polymer-coated) Polymer-coated
(strippable)
Signal launch efficiency Poor (free-space
launch) Good Best (continuous
fiber path) Best (continuous
fiber path) Best (continuous
fiber path)
Active fiber size Arbitrary 125 – 500 µm? Arbitrary (> 200 µm?)
100 – 200 µm? Arbitrary (> 125
µm?) Size of pump fiber / emitter
Arbitrary (same as active fiber) 125 – 200 µm
Arbitrary (same as active fiber) 100 – 200 µm? 100 µm??
Pump launch efficiency Best Excellent (?) Good Good Good (?) Pump power handling Good (> 3 kW) Best (>10 kW?) Medium Good (> 1 kW) Medium/good (??) Brightness preservation Best Good Poor Good Medium (?)
Pump launch points 2 2 – 18 Arbitrary Distributed
(Typically 4 ports) Arbitrary
Pump hot-spots? Yes Yes Yes (?) No No (?)
See also C. Headley III, et al., “Tapered fiber bundles for combining laser pumps”, in Fiber lasers II: technology, systems, and applications, L. N. Durvasula, A. J. W. Brown, and J. Nilsson, Eds., Proc. SPIE vol. 5709, pp. 263-272 (2005)
Notes: These are estimates. Published data are scarce.Pump power handling of a single launch point is very good with end-pumping, but the number of launch points is limited to two.
Pumping schemes pros and cons
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 43
Pump absorption:avoid circular symmetry
Wavelength [nm]850 900 950 1000 1050
Abs
orpt
ion
[dB
]
0
5
10
15
Pump absorption in 1 m long Er:Yb co-doped fiber with and without suppression of helical rays
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 44
(b) (c) (d)
(e) (f) (g)
M. N. Zervas & C. A. Codemard, “High Power Fiber Lasers: A Review”, IEEE J. Sel. Top. Quantum Electron. 20, 1-23 (2014)
But no need for pump absorption > 20 dB (?)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
45
Multi-kilowatt single-mode Yb-doped fibre laser
Diode stack@975 nm, 1.2 kW
ORC
2 × Diode stack@978 nm, 2×1.1 kW
SPI
M-HR-S
M-HR-S
M-HR-P
M-HR-P
M-HR-P M-HR-SLen-1
Len-2
Double-clad Yb-doped fibre
Power supply &Diode controller
Power supply &Diode controller
> 2 kW of output power!Spatial beam combination
M-HR-P
M-HR-P Signal output
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
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Multi-kilowatt single-mode Yb-doped fibre laser (II)
Output spectrum
• Maximum output (> 2.1 kW) was limited by available pump power– Not limited by thermal effects!
• Diffraction limited beam quality: M2 = 1.2– Five orders of magnitude brightness enhancement
• Excellent power handling indicates higher power possible– 10 kW?
1000 1020 1040 1060 1080 1100 1120 1140-80
-70
-60
-50
-40
-30
-20
Pow
er [d
B]
Wavelength [nm]
T0120L30087Output @2.1 kW
2.2 kW pump
1.2 kW pump
0 500 1000 1500 2000 2500 30000
500
1000
1500
2000
2500
Fibre: T0120L30087Core D/ Cladding D: 50 µm / 850 µmCore NA: 0.06L: 20 mAbsorption: 1 dB/m @976 nmPump: 978 nm + 975 nmSignal: 1095 nmSlope efficiency: 74%M2: 1.2
Lase
r po
wer
[W]
Launched pump power [W]
June 2007
JTO Contract No. FA9451-06-D-0014
Output power
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
2 kW YDFL / MOPA IPG, 2005
“2 kW CW ytterbium fiber laser with record diffraction-limited brightness”, V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, V. Fomin, A. Mashkin, M. Abramov, S. Ferin, CLEO-E 2005, CJ-1-1-THU
YDF: 10 m, 10.6 µm MFD
Grating Pumpcoupler
LD LD LD LD
20 W x 36 976 nmLDs in total
490 W @ 1090 nm
YDF: 6 m, 12 µm MFD
Splice
LD LD LD LD
20 W x 36 976 nm LDs in total
1040 W
YDF: 9 m, 14 µm MFD
LD LD LD LD
20 W x 72 976 nm LDs in total
1960 W
Not really laser, but cascade of low-gain amplifiers (7 dB)Total pumping 144 x 975 nm LDs with 20 W of power into 100 µm pigtail
-- Total pump power ~ 2880 W for 2 kW output power
SPI Lasers uses similar configuration
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
48
Ytterbium-doping isbest for power-scaling
• Highest fibre power (multi-kW)• Highest efficiency (> 80% slope efficiency)
– Reduces heat load• Simple spectroscopy• Emission wavelength 1 – 1.1 µm• Pump wavelength 0.9 – 1 µm
• Yb can be incorporated inhigh concentrations
– Fiber lengths 1 – 10 m rather than 10 – 100 m!
– Allows for tandem-pumping for “ultra-low” thermal load
Wavelength [nm]
850 900 950 1000 1050 1100 1150
Cro
ss-s
ectio
n [m
2 ]
0
5e-25
1e-24
2e-24
2e-24
3e-24
3e-24
AluminosilicatePhosphosilicateBoro-aluminosilicate
Absorption Emission
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
49
MOPAs bring out the best of high power rare earth doped fibres
Cladding-pumped RE-doped fibres offer unique combination of high power high efficiency high gain broad bandwidth
MOPAs (master oscillator – power amplifiers) allow forcontrol, sophistication and high power at the same timeVersatile & rapidly reconfigurable
Seed Amp Amp Amp High power output with characteristics determined by seedHigh control High power
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
hνLhνp
N2
N1
∆E = hνP - hνL → Quantum defect heating
Excited-state absorptionAdditional heating from nonradiative loss (e.g., cross-relaxation, impurities)
Pump power
Heating Laseroutput
Heat removalHeat Heat removal
Temperature increase → Damage due to melting
or burning
Temperature gradient → Thermal lensing/guiding→ Thermally-induced stress
Why fibers for high-power, high brightness lasers?
for high power, high brightness lasersThermal effects enemy #1
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
ROD SLAB
THIN DISC
CLADDING PUMPED FIBRE
Heat
Heat
Heat
Heat
Pump
Pump Pump
Laser
Laser
Laser
Fiber geometry unsurpassed for heatsinking
Heat
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
52
Disadvantages
• High nonlinearities– Sometimes good, often bad– High gain & high nonlinearities “interesting physics”
• Low energy storage– The flip side of high gain efficiency (& tight confinement)
• Already a small stored energy creates a high gain, which leads to instabilities and large power losses to amplified spontaneous emission
• Low damage threshold– Especially in pulsed regime
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Optical damage
• Large core• (New materials? Air-guided??)
All operating regimes
Nonlinear degradation• Raman• FWM• SPM
• Large core• Short fiber
– Higher RE-concentration / new materials– Higher pump brightness
• Spectral filter
Primarily pulsed and narrow linewidth regimes
SBS • Linewidth broadening of signal– SBS negligible for > 10 GHz linewidth– No SBS for pulses shorter than ~5 ns
• Linewidth broadening of gain– Temperature, stress, compositional variations
Very narrow linewidth
Large core & short fiber helps, too!
Energy storage
• Large core High energy pulses
Thermal degradationIncl. TMI
• Longer fibers• Better coatings• Improved heatsinking• Tandem-pumping• Smaller core?
53
Limitations of fibersLong with tight beam confinement: Many advantages but some trade-offs
Optical damage
• Large core• (New materials? Air-guided??)
All operating regimes
Nonlinear degradation• Raman• FWM• SPM
• Large core• Short fiber
– Higher RE-concentration / new materials– Higher pump brightness
• Spectral filter
Primarily pulsed and narrow linewidth regimes
SBS • Linewidth broadening of signal– SBS negligible for > 10 GHz linewidth– No SBS for pulses shorter than ~5 ns
• Linewidth broadening of gain– Temperature, stress, compositional variations
Very narrow linewidth
Large core & short fiber helps, too!
Energy storage
• Large core High energy pulses
Thermal degradationIncl. TMI
• Longer fibers• Better coatings• Improved heatsinking• Tandem-pumping• Smaller core?
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
54
9 / 125 µµµµm100 W
40 / 650 µµµµm, > 1 kW
• Large core to facilitate:
– power handling
– minimization of nonlinear
effects
– high energy storage for
pulsed application
– efficient pump absorption &
reduced device length
• Large inner cladding for launch
of high-power pump beams
• Silica-based
– Superb power-handling
– Excellent control of
parameters
Size matters!Silica matters, too!
Large core is the most important design feature of a high-power fibre laser
Typically a few hundred square microns
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
55
Research on core area scalingSingle-mode operation of large cores
• Rod fibre• Straight, rigid, low NA• Crystal fibre, Jena,
Bordeaux, Aculight...
• Leakage channel fibre• High leakage loss for
higher order modes– “Modal sieve”
• U. Bath, IMRA
• Chirally coupled core• High resonant coupling loss
for higher order modes• U. Michigan
• Higher order mode fibre• Claim: Higher order mode more
robust than the fundamental mode• OFS
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
56
Diffraction-limited large-core fibre lasers Control of refractive index profile is essential
• More accurate RIP allows for diffraction-limited fundamental mode
• Precise control in large structures real challenge
Central dipM2 value ~ 3.2
Conventional process Improved processIn large cores, the beam follows the index profile. The fundamental mode is NOT diffraction-limited with ring-shaped large cores.
J. Sahu, CLEO 2004
No central dipM2 value ~ 1.4
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
But, core area scaling doesn’t end all problems
• 36.6 kW maximum output power with assumed parameters– Diode pumped Yb-doped fibre
Pump launchThermal beam distortions
Stimulated Raman scattering
Maximum output power: contour lines in kW
From J. W. Dawson et al., "Analysis of the scalability of diffraction-limited fiber lasers and amplifiers to high average power," Opt. Express 16, 13240 (2008)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
For highest powers, we need to balance thermal effects and nonlinearities
• There are lots of different nonlinearities and thermal effects– Stimulated Raman scattering, self-phase modulation, stimulated
Brillouin scattering...– Thermal lensing, thermal mode instabilities, thermal damage...
• Nonlinearities mitigated by short fibers and large core area• Thermal effects mitigated by long fibers and small core area
• Possible to find optimum value of length / area– Compromise between SRS and thermal beam distortions– Maximum power a constant 36.6 kW on ridge
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Why fibre is better than bulk
• Optimum value of length / area ~1000 times larger than the value of length / area for laser rod– Fundamentals of beam propagation (diffraction-limited beam &
Gaussian optics) vs. materials constants (thermal conductivity, thermo-optic constants, nonlinear coefficients...)
Waveguiding helps! The fibre waveguide allows us to find best trade-off between nonlinearities and thermal distortions, as governed by fundamentally different materials parameters and physical aspects, whereas a rod laser doesn’t! Pump launch
Thermal beam distortions
Stimulated Raman scattering
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Applications
J. Nilsson, High power fibre sourcesShort course SC748, Photonics West, Jan 25 2009
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
61
Unique characteristics enable unique devices
• High-gain broadband amplifiers for telecom– Erbium-doped fibre amplifier in particular, also Raman amplifiers– High gain efficiency and low threshold– Single-mode operation and low polarization-dependence crucial fibre attributes
• High-power broadband ASE-sources– Require high gain
• Amplifiers for ultrashort pulses– Require broad bandwidth– The controllable dispersion provides additional advantages
• Efficient high-power Nd-doped fibre amplifiers at 900 nm (Ti:Al2O3 replacement?)– Requires suppression of dominating 1100 nm transition– Possible with distributed fibre filter– Also S-band EDFAs
• Distributed feedback fibre lasers -- with FBGs written into the fibre• High-power MOPAs with superb control of optical parameters
– Impossible to obtain directly in high-power lasers– Fibre amplifiers work very well in high-power MOPA systems
• And many more, including high-power tunable fibre lasers
And, of course... High efficiency and geometry of Yb-doped fibres ideal for high powers
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
62
Industrial Materials processing, welding, printing ….
Aerospace & defence Lidar, range-finding, directed energy, remote sensing...
Pump sources Lasers Nonlinear converters
UV (lithography, etc.), X-rays, visible, supercontinuum… Medical
Imaging, laser surgery, cosmetics… Scientific Telecoms (?)
Raman lasers, high-power multi-port EYDFA, free-space communications, ...
Displays (?) Requires visible sources
Application areas
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Materials processing most important application
63
cladding
hardening
steel - Al welding
deep penetration welding
brazingpolymer welding
soldering
non-metal cutting
marking
drilling
low-quality printing
1W 10W 100W 1kW 10kW
BP
P (
mm
-mra
d)
1
10
100
1,000
Optical Power (at the workpiece)
metal cutting
sintering, welding
100kW
sintering
flexography
0.1
CO2
Fiber (SM)
2ω0
2θ0f#4
(diffraction limit @1µm)
(diffraction limit
@10µm)
M. N. Zervas & C. A. Codemard, “High Power Fiber Lasers: A Review”, IEEE J. Sel. Top. Quantum Electron. 20, 1-23 (2014)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Tm-doped fiber lasers(high power)
• After Yb, Tm may be most important dopant for high-power fiber lasers• Emit at ~ 2000 nm• Can be pumped with high-power diodes at ~ 800 nm• Output power up to 1 kW
• Not nearly as good as Yb-doped fiber lasers, but potential may be greater
64
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 65
Tm3+-doped silica fiber lasers at 2 µm:Spectroscopy
900 1200 1500 18000
5
10
15
20
1670nm
1212nm796nm
Abs
orpt
ion
wavelength [nm]
3F23F33F4
3H5
3H4
3H6
Multi-phononrelaxation
Cross relaxation
Laser transitionat ~2000 nm
Tm3+
Pumpat ~800, 1200, or 1600 nm
Efficient high-power diodes are only available at ~ 800 nm, out of the possible pump wavelengths
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 66
Tm3+-doped silica fiber lasers at 2 µm
• 2 for 1 cross-relaxation process improves efficienc y beyond Stokes limit with 800 nm diode pumping
• Requires short distance between Tm-ions• Works better at high concentrations
• 70% slope efficiency reported• 170% quantum efficiency
S. D. Jackson, “Cross relaxation and energy transfer upconversion processes relevant to the functioning of 2 µm Tm3+-doped silica fibre lasers”, Opt. Comm. 230, 197-203 (2004)
3F4
3H5
3H4
3H6
Cross relaxation
Laser transitionat ~2000 nm
Tm3+
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Erbium:ytterbium co-doped fiber lasers for power-scaling in the 1.5 – 1.6 µm range
• The pump absorption of Er3+:silica has been too low for high-power direct-diode cladding-pumping of Er-doped fibers (without Yb)• Core absorption limited to ~ 50 dB/m
• Ytterbium co-doping (sensitization) increases the pump absorption and enables cladding-pumping of Er-doped fibers with high-power diodes
• Erbium is tremendously important for telecom and probably the 3rd most important dopant for high-power fiber lasers
• Ytterbium sensitization (co-doping) used for high-power lasers and to some degree for telecom amplifiers with ~ 1 W of output power
67
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 68
Principles of Er:Yb co-doped fiber lasers
• Energy transfer between ions concentrations need to be high• Yb-concentration 5 – 20 times higher than Er-concentration• Each Er-ion is
– Likely to have nearby Yb-ion– Unlikely to have nearby Er-ion (avoids Er concentration quenching)
• Each Yb-ion must be able to transfer energy to nearby Er-ion– Sufficient Er-concentration
• The high Yb-concentration also allows for adequate pump absorption
Yb3+ Er3+
2F5/2
2F7/24I15/2
pumping
4I13/2
4I11/2
up-conversion(Wup)
4I9/2
Energy transfer
M. Laroche, S. Girard, J. K. Sahu, W. A. Clarkson, and J. Nilsson, “Accurate efficiency calculation of energy transfer processes in phosphosilicate Er3+-Yb3+ codoped fibers”, J. Opt. Soc. Am. B, 23, 195 – 202 (2006)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 69
EYDFL experimental set-up
Diode stack@975 nm
Signal output@1563 nm
Double-clad Er/Yb-doped fiber
HT @975 nm, ~1.1 µmHR @~1.5 µm
HR @975 nm, ~1 µmHT @~1.5 µm
~1.1 µmHT @975 nmHR @~1.1 µm
HT @975 nm, ~1.1 µmHR @~1.5 µm
Un-absorbed pump& signal @~1.1 µm
HT: high transmission, HR: high reflection
Pump: 975 nm diode stack sourceLaunch coupling lens: f = 8 mmPump launch efficiency: > 80%Fiber ends: perpendicularly cleaved 4% - 4% feedback also at 1060 nm!
Fiber details:Core 30 µµµµm, NA 0.2Inner-cladding diameter 400 µµµµm, NA ~0.48L = 4 mPump absorption: 4.5 dB/m
J. K. Sahu, Y. Jeong, D. J. Richardson, and J. Nilsson, “Highly efficient high-power erbium-ytterbium co-doped large core fiber laser”, ASSP 2005, paper MB33
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 70
Launched pump power [W]
0 50 100 150 200 250 300 350
Lase
r po
wer
[W]
0
20
40
60
80
100
120
140
Output @ 1060 nm
Output @ 1567 nm
Slope efficiency = 40 %
M2 = 1.9
Er:Yb-doped DCFL – 120 W
Roll-off in output power due to parasitic Yb-lasing at ~ 1 µm.
Max power: 103 W
0 50 100 150 200 250 300 350 4000
20
40
60
80
100
120MeasuredFit
Slope efficiency: 33%
Output @1565 nmOutput @1064 nm
Lase
r po
wer
[W
]
Launched pump power [W]
Fiber Improvements:Optimised Yb/Er ratio and fiber core composition to suppress ~ 1 µm lasing
Yb-emission below 1.5 Wat highest pump power!
1520 1540 1560 1580 1600-80
-60
-40
-20
0
Pow
er [d
B]
Wavelength [nm]
Output spectrum
Res: 0.5 nm
J. K. Sahu et al., Opt. Commun., vol. 227, pp. 159-163, 2003
J. K. Sahu, Y. Jeong, D. J. Richardson, and J. Nilsson, “Highly efficient high-power erbium-ytterbium co-doped large core fiber laser”, ASSP 2005, paper MB33
120 W @ 1567 nmSlope efficiency: 40%Beam quality M 2 : 1.9Linewidth 3 nmRandomly polarized
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 71
Diode stack@975 nm, 1.2 kW
Double-clad Er:Yb fiber
HT @975 nm, ~1 µmHR @~1.5 µm
Signal output@1567 nm
HT @975 nm, ~1 µmHR @~1.5 µm
Emission@~1 µm
HT @975 nmHR @~1 µm
Unabsorbedpump
Emission@~1 µm
297 W
0.3 kW EYDFL @ 1567 nm
0 200 400 600 800 10000
50
100
150
200
250
300
350
Slope efficiency
21%
39%
Signal wavelength: 1567 nm
Sig
nal p
ower
[W]
Launched pump power [W]
Output spectrum
1500 1520 1540 1560 1580 1600-80
-70
-60
-50
-40
-30
-20
Pow
er [d
B]
Wavelength [nm]Y. Jeong et al., “Erbium:ytterbium co-doped large-core fiber laser with 297 W continuous-wave output power”, IEEE J. Sel. Top. Quantum Electron. 13, 573-579 (2007)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 72
High-power C-band & L-band tuning
All-fiber configuration utilizing a tunable FBG and tapered splicing technique
1520 1530 1540 1550 1560 1570 1580-80
-60
-40
-20
Rel
ativ
e po
wer
[dB
]
Wavelength [nm] Wavelength [nm]
1540 1560 1580 1600 1620
Pow
er [d
B]
-70
-60
-50
-40
-30
-20
-10
0
52 nm
C-band: Max. power > 40 WShort fiber
L-band: Max. power > 70 WLong fiber
C-band configuration
Y. Jeong et al., IEEE Photonics Technol. Lett. 16, 756 (2004) J. K. Sahu et al., CLEO 2004, paper CMK1
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Bismuth-doped silica fiber lasers
Relatively new and unproven dopant for fiber lasers
Potential for amplification in elusive 1300 nm telecoms window
Power-scalable (?)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 74
Bismuth-doped fiberbasics
• Bismuth-doped silica
• Silica host opens up for power scaling
• Bismuth is not a rare earth– “Poor metal”– Multiple oxidization states with
different spectroscopic properties are likely
V. V. Dvoyrin, V. M. Mashinsky, L. I. Bulatov, I. A. Bufetov, A. V. Shubin, M. A. Melkumov, E. F. Kustov, E. M. Dianov, A. A. Umnikov, V. F. Khopin, M. V. Yashkov, and A. N. Guryanov, "Bismuth-doped-glass optical fibers—a new active medium for lasers and amplifiers," Opt. Lett. 31, 2966-2968 (2006)
http://www.laserfocusworld.com/articles/print/volume-51/issue-09/features/fiber-for-fiber-lasers-bismuth-doped-optical-fibers-advances-in-an-active-laser-media.html
http://www.nature.com/lsa/journal/v1/n5/full/lsa201212a.html
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 75
High power bismuth doped fiber laser
• 15 W output power• Emission wavelength ~ 1150 nm• Slope efficiency ~ 20%• Pumped by Yb-doped fiber laser
at around 1060 nm
• Low pump absorption (~ 0.3 dB/m)– Long fiber– Core pumping
Evgeny M. Dianov, Alexey V. Shubin, Mikhail A. Melkumov, Oleg I. Medvedkov, and Igor A. Bufetov, “High-power cw bismuth fiber lasers”, J. Opt. Soc. Am. B 24, 1749-1755 (2007)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Broad gain bandwidth in bismuth-doped phospho-germanosilicate fiber
Power still low, but several tens of watts now reported at 1.1 – 1.2 mm in aluminosilicate fibers.See also I. A. Bufetov and E. M. Dianov, “Bi-doped fiber lasers”, Laser Phys. Lett. 6, 487-504 (2009)
76
Arrows indicate pump wavelengths; laser and corresponding pump wavelengths are shown by lines
of the same type
E. M. Dianov, S. V. Firstov, O. I. Medvedkov, I. A. Bufetov, V.F. Khopin, and A.N. Guryanov, “Luminescence and laser generation in Bi-doped fibers in a spectral region of 1300-1520 nm”, OFC 2009, OWT3
From E. Dianov
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Power-scaling of fiber Raman lasers
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Stimulated Raman scattering in silica is wavelength-agile
78
Wavelength [ µµµµm]0.8 1.0 1.2 1.4 1.6 1.8 2.0
Background loss [dB
/km]
0
5
10
15
20
Yb
Nd NdNd
Er
Ho
Tm
Raman scattering
Flexibility in signal & pump wavelength
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
kW-level fiber Raman laser
• Core-pumped by YDFL at 1080 nm– No brightness-enhancement...
79
Lei Zhang, Chi Liu, Huawei Jiang, Yunfeng Qi, Bing He, Jun Zhou, Xijia Gu, and Yan Feng, "Kilowatt Ytterbium-Raman fiber laser," Opt. Express 22, 18483-18489 (2014)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Fiber Raman laser cladding-pumped directly by diodes
80
Pump @ 975 nmf= 6.84 mm
DCRF
f= 11 mm
HR
f= 20 mm
DM 1
VBG
DM 2
60% reflector
Diagnostics
920 970 1020 1070 1120-80
-70
-60
-50
-40
-30
-20
-10
Resolution: 2nm
Rel
ativ
e po
wer
(dB
m)
Wavelength (nm)
Results: • M2 = 1.9• Output power: 6 W• Slope efficiency 19%; Threshold: 33 W• Efficiency limited by high background loss of tested fiber• Order-of-magnitude brightness enhancement
T. Yao et al., “High-power continuous-wave directly-diode-pumped fiber Raman lasers” Appl. Sci. 5, 1323-1336 (2015)
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
81
Summary
• Thermal properties make fibres excellent for high-power, high-brightness operation– Low threshold helps, too
• Ytterbium-doped fibre lasers available at 10 – 20 kW• Fibres are engineerable• Beam combination (e.g., phased-array lasers) open up for multi-
element diffraction-limited power-scaling• MOPAs enable high control at kW level
– Temporal– Spatial– Spectral
It may be difficult to make a multi-kW fibre source with record-breaking performance but it is Very Easy to splice together a 10 W source that is very useful for your research!
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
Books on Rare Earth DopedFibre Amplifiers and Lasers
France, P. W., ed., Optical fibre lasers and amplifiers (Blackie 1991) -- Old and thin but quite good.
Bjarklev, Anders, Optical fiber amplifiers: design and system applications (Artech House, 1993) -- Provides good insight. Mostly EDFAs. Good introduction.
Digonnet, Michel J. F., ed., Rare earth doped fiber lasers and amplifiers, 2nd ed. (Marcel Dekker 2001) -- Best coverage of fibre lasers and physics.
Desurvire, Emmanuel, Erbium-doped fiber amplifiers: principles and applications (Wiley, 1994) --Lots on noise, lots of everything except WDM. In-depth and difficult at times. Exclusively EDFAs.
Desurvire, E., D. Bayart, B. Desthieux, S. Bigo, Erbium-doped fiber amplifiers – device and system developments (Wiley 2002) – Covers aspects such as WDM and other developments since Desurvire’s first book.
Sudo, Shoichi, Ed., Optical fiber amplifiers (Artech House, 1997) -- Lots on fabrication.Becker, P. C., N. A. Olsson, and J. R. Simpson, Erbium-doped fiber amplifiers: fundamentals
and technology (Academic Press 1999) – Less mathematical than Desurvire but still quite comprehensive. Lots on WDM. Exclusively EDFAs.
R. W. Berdine and R. A. Motes, Introduction to High Power Fiber Lasers (Directed Energy Professional Society; ISBN-10: 0979368731, 2009)
D. J. Richardson, J. Nilsson, and W. A. Clarkson, “High power fiber lasers: current status and future perspectives”, J. Opt. Soc. Am. B 27, B63-B92 (2010)Not book but 30 page review article
J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016 83
Submission deadline April 21