J. Nilsson, “High-power fiber lasers” KTH Winter School, Romme, Feb 5 2016 High-power fiber lasers /sources / amplifiers [email protected]www.orc.soton.ac.uk/hpfl.html Johan Nilsson Optoelectronics Research Centre University of Southampton, England KTH Winter School Romme, Feb 5 2016 Questions welcome
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J. Nilsson, “High-power fiber lasers”KTH Winter School, Romme, Feb 5 2016
– 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
• 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
34
• 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
35
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
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
46
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?
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
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
• 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 &
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
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
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)
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