Beyond 10 Km range wind-speed measurement...
Transcript of Beyond 10 Km range wind-speed measurement...
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Beyond 10 Km range wind-speed measurement witha 1.5 μm all-fiber laser source
A. Dolfi-Bouteyre, V. Brion, W. Renard, D. Goular, M. Valla, C. Planchat, B. Augère, J. Le Gouët, C. Besson and G. Canat
Overview on Research on Wake Vortices at ONERA
���� Lidar detection
���� Wake Vortex Dynamics
���� Radar detection
Cooperation : LEOSPHERE, THALESinvolved in Sesar, UFO projects
V. Brion ONERA
Research on Radar detection
Update on current research at ONERA on Clear Air response
b0
- Theoretical / Numerical approach to calculate RCS
- Analysis of Sources of WV RCS
radar
vortexpair
aircraft
- Clear air feasability remains in question
Scattering in clear air
Θ0
õ
y
z
radar
õ target to radar direction
V scattering volume
2
2
4i
s
E
ERRCS π=
V( )*rrε∆
R
definition
Ei
Scattering in clear air
Θ0
õ
y
z
radar
õ target to radar direction
V scattering volume
( ) 2*~.2*
4
2
2*
44
∆== ∫
−
V
ojkrr
i
s dVerk
E
ERRCS ε
ππ
V( )*rrε∆
scattering integral
R
definition
Ei
� Born hypothesis
� Farfield approximation� Cylindrical incident beam
Tvapor
vapordryr
ρρρε 48.3598446106 ++=×∆
Approach to calculate the RCS
Electromag.
scattering
Wake properties(circulation,separation,vorticity profile)
Flow solver(laminar)
RCS
radar setup(elevation and frequency)
atmosphere properties(stratification, humidity)
εr is the dielectric constant wrt vaccum
dry air water vapor temperature
1−=∆ rr εε
Flow solver
Modelling atmosphere & WVNormalized Brunt-Vaisala frequency
W0 descent speed of the initial vortex pair
N=1
vorticity field
t*=4.5t*=3t*=2t*=1t*=0
0
0
W
NbN =
vortex pair
secondary wake
b0 vortex separation
t* normalized time
Boussinesq
model
buyoancy
ρε2
Nr ∝∆Constant humidity ����
Calculated RCS
10 log10 RCSdry
RCSdry in [ -70 ; -130 ] dBm 2
� High wavenumber response ~ k4
scaled wavenumber
beam
ele
vatio
n
� Low wavenumber response
by flow scales kb0 ~ 1
� Agreement with past studies
Prospects : include turbulence and engine exhaust (warm and humid)
( ) 2*~.2*
4*
4
∆= ∫
−
V
ojkrr dVer
kRCS ε
π
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UFO project will deal with ultrafast wind and ambient air turbulence monitoring .
Technical Laser requirements for :
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Lidar development for UFO project
UltraF ast wind sensO rsfor wake ‐‐‐‐vortex hazards mitigation
ConfigurationRequirements
Measurement range
Pulse duration (ns)
Integration time (s)
PRF (kHz)
Needed Mean power
(W)
Volume Wind:
Long Range
Medium resolution
High measurement frequency
10-km 500 to 800 0,15 <15 kHz 4
Wake:
Medium range
High resolution
Very High measurement
frequency
2-km 150 to 250 0,02 <75 kHz 4
Wind profiling:
Low range
High resolution
Low measurement frequency
0,5-km 200 to 400 10 < 300 kHz
0,5
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Windmapping lidar : Fiber Laser requirements
Pulse duration: τp = 0.5 to 0,8 µsMaximum PRF: 15 kHzAverage power: 4 W
Narrow linewidth : ∆ν < 1 MHzHigh beam quality : M2 < 1.3� pulse energy > 300 µJ
� peak power > 400 W
10 km range, Refresh rate: 1 mn full PPI,
0,15 s integration time,
200 m spatial resolution
���� Design of high peak power coherent fiber laser
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Fiber lasers and peak power limitations
ModulationAmplification stages
Injection
� Peak power limited by SBS for narrow linewidth
Brillouin Scattering
Pump wave at νp
Acoustic wave at νB
Stokes wave at νs=νp-νB
Pump wave + stoke wave �acoustic wave reinforce through electrostriction effect � Stimulated Brillouinscattering regime (strong back reflection)
Why fiber lasers :
•High efficiency laser/amplifier sources,•Compact lasers and amplifiers,
•Good thermal management,
•No optical alignment for all-fiber systems,•Low cost.
Typical architecture (Master oscillator power ampli fier) :
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Typical Brillouin gain spectrum at 1550 nm
νννν0
ννννB ~11GHz
g B ~ 2 10-11m/W
∆ν∆ν∆ν∆νB ~30MHz
21=eff
outeffB
A
PLg
• Use of LMA fibers with mode-field-diameter >> 30 µmLimited by spatial quality (M² < 1,3)
• Control of dopants concentration profile (pedestal d oped fibers)Compatibility with complex compositions, high efficiency
• Use of highly doped short fibersLimited by crystalisation of rare-earth dopants into the fiber core
• Longitudinal variation of Brillouin frequencyusing temperature, fiber compositions, strain…
•CT~1.1 MHz/K
•Cε~400-600 MHz/%εCompatibility with other requirements (lifetime…)?
High energy fiber lasers limited by Stimulated Brillou in Scattering (SBS) – Reduction of SBS threshold
gB: Brillouin gain coefficientLeff: effective lengthPout: output peak powerAeff: fiber mode effective area
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Design of high peak power coherent fiber lasersfor lidar applications
Design and build of a MOFPAWith 3 amplification stages
Design and build of MOFPAWith 4 amplification stages
Based on special fiber developments
800 µJ, 1 kW peak, 4 kHz, ∆ν < 1 MHz, M² = 1,1
multifilaments core fiber
MOFPA laser(Master Oscillator Fiber Power Amplifier)
Incease in peak power by control of the Brillouin threshold
200 µJ commercial amplifier
with narrow linewidth
Spécificities:• high spectral & spatial quality• Modularity of beam characteristics
2005 2006 2007 2008100 µJ 240 µJ 600 µJ 800 µJ
M² = 1,8 M² = 1,4 M² = 2,2 M² = 1,1
tomorrow> 1 mJ
- special fibers- coherent combining
- other innovative techniques…
technology transfer
(Année de démonstration laboratoire)ModulationAmplification stages
Injection
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Strain distribution technique for MOFPA peak power inc rease (1/4)
Increase of the extractable peak power :by increasing the SBS threshold with adistributed strain on the fiber (Onera Patent)Applicable to various laser architectures designs• Results:
Fiber Ppic without Ppic with Gain
ErYb 7 28 W 186 W 8 dB
ErYb 12 L1 58 W 223 W 6 dB
ErYb 12 L2 106 W 420 W 6 dB
ErYb 25 300 W 600 W 3 dB
0 200 400 600 800 1000 12000
50
100
150
200
250
Po
wer
(W
)
Time (ns)
τeff
≈ 300 ns
• Conclusion :with standard (SM)ErYb fibre : Ppic ≈ 400W, +3dB / bestcommercialy available sources
With large coreErYb fibre : Ppic ≈ 600W, +5dB / best commercialy available sources
avec τpulse~1µs,Ep~0.6mJ
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Experimental set up
Master Oscillator1545 nm
Pump diodes
Acousto-Optic
modulator
Pre-Amplifier 15
µJ
Mode Field
Adaptation
PM Fiber ���� PM LMA
Pump Combine
r
PM LMA Er/Yb-doped
fiber
Output fiber
Experimental set up : 3 stages MOPFA
two first stages : commercial 15 µJ fiber laser.
third stage : polarization maintaining large mode area (LMA) Er/Yb fiber with SBS mitigation strategy (Onera’s Patent).
Strain distribution technique for MOFPA peak power inc rease (2/4)
Strain distribution
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Fiber laser source performances without strain mitigation strategy
0 2 4 6 8 10 12
0,0
0,5
1,0
1,5
2,0
Pump power (W)
Mea
n po
wer
(W
)
0
100
200
300
Pea
k po
wer
(W
)
Mean power and peak power after the lasthigh power fiber amplifier, SBS limits pulses
energy
Fiber laser source performances with our strainmitigation strategy
2 4 6 8 10 12 14 16 18 20 220,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
Pump power (W)
Mea
n po
wer
(W
)
100
150
200
250
300
350
400
450
500
Pea
k po
wer
(W
)
SBS Limit
Mean power and peak power after the last highpower fiber amplifier. SBS threshold is increased with
our mitigation system.
Strain distribution technique for MOFPA peak power inc rease (3/4)
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2 2.5 3 3.5 4 4.5 5
x 10-6
0
0.05
0.1
0.15
0.2
0.25
0.3
Time (s)
Pow
er (
u.a.
)
Output pulse shape, 850 ns duration
current achievement : • 4 W average power, • PRF = 10 kHz,
• 470 W peak power,
• PER > 17 dB• M² ~1.3 in both axis
• Reliability tests during 1 mounth before Lidar integration
Strain distribution technique for MOFPA peak power inc rease (4/4)
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Fiber laser integration in our Licorne doppler Lidar
Scanner
BoosterPBS
CW Laser
Det.
Booster
Telescope
High energy pulsed fiber laser
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Licorne Signal processing
Fourier transform
Temporal signal
Frequency spetra
spectrogram
Spe
ctra
lden
sity
Range (m)
Vel
ocity
(m/s
)
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2013-12-12 Licorne measurements
spectrograms
Rea
l tim
e
bary
cent
er
Real timevelocity
Vel
ocity
(m
/s)
Vel
ocity
(m
/s)
Time (a.u.) Time (a.u.)
Range (m)Range (m)
Ran
ge (
m)
Ran
ge (
m)
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2013-12-12 Licorne measurements
Range (m)
win
d sp
eed(
m/s
)
average time =0.1024 s
0 2000 4000 6000 8000 10000 12000 14000
-30
-20
-10
0
10
20
30
40
50
60
-1
0
1
2
3
4
5PSD(au)
0 2000 4000 6000 8000 10000 12000 14000-40
-35
-30
-25
-20
-15
-10
-5
0
Z = range (m)
CN
R (d
B)
CNR of lidar signalexp(-alpha*Z)/Z²
Fixed LOS
2013-12-12
CNR vs range fitted with theoretical curve
> 10 km range in 0.1 saverage time
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UFO Lidar integration
Photo lidar 400S normal
UFO transformation
Telescope
Door
Laser diodes
Onera’s highpower amplifier
Preamplifier15µJ
Sca
nner
rac
k
PC
and
opto
elec
rack
s
LD controller