Beyond 10 Km range wind-speed measurement...

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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

Overview on Research on Wake Vortices at ONERA

���� Radar detection

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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Beyond 10 Km range wind-speed measurement witha 1.5 μm all-fiber laser source

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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 Lidar real time display

5A

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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

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Thank you for your attention.

Acknowledgements to :European commission UFO Project

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