High peak power Erbium-Ytterbium MOPFA for coherent Lidar anemometry

Transcription

1 High peak power Erbium-Ytterbium MOPFA for coherent Lidar anemometry G. Canat, L. Lombard, A. Dolfi-Bouteyre, C. Planchat, A. Durecu, M. Valla ONERA, France S. Jetschke, S. Unger, J. Kirchhof, IPHT Jena, Germany

2 Outline 1.5µm laser technologies for compact coherent detection lidar Erbium-Ytterbium LMA master oscillator power fiber amplifiers Multifilament core fibers 2

3 Monolithic compact lasers for coherent lidar anemometry Required properties: Good atmospheric transmission (1.5 µm or 2 µm) Eyesafe wavelength Compact, simple, cheap laser Solutions at 1.5µm: Semiconductor MOPA (CW regime) Pure Erbium MOPFA (CW/pulsed) Erbium-Ytterbium MOPFA (CW/pulsed) 3

4 All semi-conductor MOPA for coherent lidar (1/2) P=0.9 W υ<100 khz M 2 fast=1.16 / M 2 slow=1.43 Limited to CW regime Single frequency regime Broad band phase noise? René Skov Hansen and Christian Pedersen, «All semiconductor laser Doppler anemometer at 1.55 μm», Opt. Express 16, (2008) 4

5 All semi-conductor MOPA for coherent lidar (2/2) Peter John Rodrigo and Christian Pedersen, «Doppler wind lidar using a MOPA semiconductor laser at stable single-frequency operation», Technical University of Denmark, CLEO Europe 2009 Measurement on rotating diffusing target for 5 days 5

6 MOPFA with LMA fibers Injection: CW low power laser with very good spectral and spatial qualities Modulation: arbitrary shape and arbitrary high repetition rate (> 10 khz) Amplification: monolithic fiber medium with high gain Acousto-optic modulator Preamplifier Power amplifier 1.5 µm => Erbium doping 6

7 Stimulated Brillouin Scattering in optical fibers Stokes wave Diffusion Signal wave ωp ωs = ωp-ωb Acoustic wave Ω B Acoustic wave Signal wave Stokes wave Electrostriction P 21 seuil g A B eff L eff Singlemode 1.5 µm P th L=880 W.m without gain. P th =80 W for an amplifying fiber of a few meters. 7

8 Erbium-Ytterbium fibers Ytterbium Erbium 2 F 5/2 4 I 11/2 975 nm 2 F 7/2 4 I 13/ nm 4 I 15/2 Quantum defect ~ 33% 8

9 High peak power amplification in Er-Yb fibers High peak power amplification requires: Large core diameter Low NA (otherwise multimode) LMA Er/Yb Diam. 30µm / ON 0.10 Index difference (x 1000) Phosphorous Alumina Er, Yb Radial position (µm) ErYb doped fibers: problem of refractive index dip Bad fundamental mode shape, Bad mode discrimination ErYb doped LMA fibers limited to ~25µm 9

10 Resonant pumping of pure Erbium doped fibers 4 I 11/2 4 I 13/ nm 1560 nm 4 I 15/2 Quantum defect ~ 3% only! M. Dubinskii, J. Zhang, and I. Kudryashov, Appl. Phys. Lett. 93, (2008). ARL Global efficency still low, long fiber length required, low non-linear threshold 10

11 Outline 1.5µm laser technologies for compact coherent detection lidar Erbium-Ytterbium LMA master oscillator power fiber amplifiers Multifilament core fibers 11

12 A high energy amplifier multistage MOPFA for the FIDELIO project SM/PM Er doped SM/PM DC/ErYb doped LMA PM DC/ErYb doped DC/LMA ErYb doped PM IPHT DFB Laser Diode λ=1545 nm Acousto-optic modulator 4 µj 30 µj ~250 µj ~1000 µj PRF=4 khz Pulse duration 1 µs Pedestal fiber Multifilament core fiber 12

13 Principle of pedestal fibers Reduced NA Doped Core Pedestal Inner clad Outer clad 13

14 MOPFA detailed architecture 300 2,6 1, ,4 0,9 0,8 Pulse Energy (µj) ,2 2,0 1,8 1,6 1, , Repetition frequency (khz) Average Power (W) Amplitude (A.U.) 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0, Time (µs) 14

15 3rd Stage: M 2 measurement M 2 ~1.2/ Diameter (µm) Position (cm) 15

16 Modes superposition a = 1 α ELP01 + α ELP 11 y e iψ Relative phase Relative power 4,0 3,5 3,0 ψ=0 ψ=0.1 π ψ=0.2 π ψ=0.6 π Pure LP 01 =>-M 2 always >1.7 M 2 M 2 2,5 2,0 -Instable 60 1,5 Pure LP Position Centroid position (% of beam diameter) M 2 M 2 X 1,0 0,0 0,2 0,4 0,6 0,8 1,0 α ,0 1,8 1,6 1,4 1,2 (b) (c) Index variation (10-3 ) 16

17 SWAN lidar set up for CREDOS campaign at Frankfurt (February March 2007) EDFA CL BP FM FL L2 QWP FM SWAN lidar characteristics : Fibered PM Laser 100µJ Real time signal processing Eye safe laser 1D scanning pattern 17

18 CREDOS vortex measurement campaign (2007) 18

19 Outline 1.5µm laser technologies for compact coherent detection lidar Erbium-Ytterbium LMA master oscillator power fiber amplifiers Multifilament core fibers 19

20 Multi Filament Core fibers Silica Er:Yb/Silica F/Silica Er:Yb/Silica Boron doped stress applying parts (for birefringence) Global core Core Diameter 24 µm by 32 µm Birefringence 10-4 Core Losses nm (mostly due to diffusion on filaments-silica interfaces) Pump Abs nm nm Filaments in the Core Fil. number 37 Fil. diameter 1.8 µm Fil. period 5.1 µm F/Silica Silica 20

21 Modeling: guided optical modes Index profile Only one guided mode (there is not 1 mode/filament but 1 global mode because of strong filament interaction) Expected M 2 = 1.5, A eff =1100 µm x-direction y-direction Guided mode intensity profile Intensity (a.u.) Distance (µm) «Multifilament-core fibers for high energy pulse amplification at 1.5 µm with excellent beam quality», Opt. Lett., 33 pp (2008) 21

22 Pulsed amplifier performances 1545nm DFB AOM 5-30kHz 800ns pulses Preamp 200µJ 250W peak power MFC fiber Angle cleaved 1550 nm 975 nm 38W 975nm pump Photodiode Camera Powermeter Polar. analyzer Energy (µj) Energy (µj) (a) 940 W peak power Pulse frequency (khz) pump PRF Launched pump power (W) Power (W) Peak power (W) 22

23 SBS threshold measurement in the MFC fiber 1545nm DFB 5-30kHz 800ns pulses 120ns AOM Preamp 120ns 200µJ 250W peak power MFC fiber Angle cleaved 1550 nm 975 nm 38W 975nm pump Photodiode Camera Powermeter Polar. analyzer Peak power (kw) P pump =28 W P pump =26 W P pump =25 W 95 ns Dip Time (µs) Input pulse duration 120ns >> phonon lifetime P th ~2 kw peak power C g B B = P th L eff CB A K eff 410 W m L eff and A eff are calculated by simulations and K=1 g B ~ m.w -1 23

24 Conclusion Intrinsic difficulties of Erbium-Ytterbium fibers due to homogeneities and large NA. With pedestal fibers beam quality can be kept good enough to extract 250 W peak power, 100 µj, make a Lidar for 400 m range vortex measurements New special fiber structure is the Multifilament Core Fibers: ~2 kw peak power M 2 ~1.5 single mode, 1 mj 24

25 ONERA lidar range increase Portée 1.5 µm des fiber lidars lidar fibrés range ONERA 2007 Range Portée (m) Laser Energie energy laser (mj) (mj) 25

26 We would like to acknowledge for fundings provided by Region Ile de France, European Union FP6 projects FIDELIO, CREDOS 26

27 See talk of C. Besson in Session 8 on Wednesday about FIDELIO project Pulsed 1.5 µm LIDAR for axial aircraft wake vortex detection 27