High peak power singlefrequency. applications

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1 High peak power singlefrequency MOPFA for lidar applications L. Lombard, G. Canat, A. Durécu, J. Le Gouët, A. Dolfi- Bouteyre, M. Valla, B. Augère, D Goular, C. Besson.

Applications of wind lidars Wake vortices monitoring

(CREDOS, FIDELIO EU projects) Turbulence & windshear

true air speed (AIM2 EU project) Windfarm optimization

feed-forward turbine control (Leosphere) Onera

developing the wind lidar - by developing the laser

2 Applications of wind lidars Wake vortices monitoring Lidar developments and tests on international airports (CREDOS, FIDELIO EU projects) Turbulence & windshear monitoring Turbulence & Wind mapping algorithms (UFO EU project) Courtesy from S. Wolf, IFALPA Airborne sensors Lidar developments for true air speed (AIM2 EU project) Windfarm optimization Use lidar information for wind mills optimization, feed-forward turbine control (Leosphere) Onera investigates most of those lidar applications - by developing the wind lidar - by developing the laser source Courtesy from Leosphere CLRC, High peak power single-frequency MOPFA for lidar applications

3 Wind lidar principle LASER ν Δν ν + Δν AOM Amplifier V r V air λ = 1,55 µm 5/5 Coupler telescope ν + Δν + ν Doppler Local Oscillator ν detector ν + Δν + ν Doppler cos(δν + ν Doppler ) ν Doppler = 2.V r /λ = V r. 1.3 MHz/(ms -1 Signal processing Δν + ν Doppler =>Vr Pulse launch Detected beat signal Δν + ν Doppler Time distance CLRC, High peak power single-frequency MOPFA for lidar applications

4 Wind lidar principle LASER λ = 1,55 µm ν Δν ν + Δν AOM Amplifier 5/5 Coupler Typical architecture ν + Δν MOPFA + ν Doppler Master oscillator power fiber amplifier telescope V r V air Local Oscillator ν detector Signal processing Δν + ν Doppler =>Vr ν + Δν + ν Doppler cos(δν + ν Doppler ) MO Why fiber lasers? High efficiency laser/amplifier sources, Compact lasers and amplifiers, No optical alignment for all-fiber systems, Low cost. +1MHz ν Doppler = 2.V r /λ AOM = V r. 1.3 MHz/(ms -1 Pulse shape Fiber amplifier(s) control MOPFA allows versatile pulsed sources: single-mode, singlefrequency, long-pulse (1ns 1µs) BUT: peak power limited by SBS for narrow linewidth CLRC, High peak power single-frequency MOPFA for lidar applications

PRF 1 + M 2 2 Source requirements: Narrow linewidth: Δv < 1 MHz High beam quality: M 2 < 1.

5 Wind lidar requirements => laser source requirements Example application Wind field monitoring around airport 1 km range; refresh rate: 1 mn for 36 CNR 2 E. PRF 1 + M 2 2 Source requirements: Narrow linewidth: Δv < 1 MHz High beam quality: M 2 < 1.3 Pulse duration: t pulse =.5 to 1 µs Maximum PRF = 1-15 khz Pulse energy E = 1 s µj => P peak = 1-1kW CLRC, High peak power single-frequency MOPFA for lidar applications

6 Power (a.u.) Wind lidar requirements => laser source requirements Typical architecture MOPFA Master oscillator power fiber amplifier +1MHz Pump wave at n p MO AOM Pulse shape control Fiber amplifier(s) Stokes wave at n s =n p -n B Acoustic wave at n B Catastrophic when: P peak >P th Typical Brillouin gain spectrum at 155nm pump wave + Stokes wave acoustic wave Stokes wave pulse Stokes (SBS) Time (µs) P th Dn B ~ 3MHz n s g B ~ m/w n B ~11GHz n p P th = 21 A eff g B L eff Aeff: effective core area Leff: effective fiber length gb: Brillouin gain CLRC, High peak power single-frequency MOPFA for lidar applications

7 How to mitigate SBS in optical fiber? Sample SBS threshold: P th ~1 W in singlemode fibers P th ~3 W in commercial large mode area (LMA) fibers P th ~2 kw demonstrated in specialty fibers 1,2 Use of LMA with MFD > 3 µm Compatibility with good beam quality? P th = 21 A eff g B L eff Longitudinal variation of Brillouin frequency using temperature, fiber compositions, strain Compatibility with other requirements (beam quality )? Use of highly doped short fibers High efficiency? CLRC, High peak power single-frequency MOPFA for lidar applications

8 Why is this not so simple to increase A eff? Fiber doping: Er and Er:Yb at 1,55µm Beam quality in large core fibers Increase A eff : 1. MFC fibers 2. PAS fibers: large core Alternative way: decrease L eff with strain Strain principle 3. Application on LMA fiber Coherent combining of 2 singlmode amplifiers of 7 cores of a multicore fibers CLRC, High peak power single-frequency MOPFA for lidar applications

9 Doping for 1.5µm laser amplification: Er vs Er:Yb erbium only (Er) erbium + ytterbium codoping (Er:Yb) 4I 9/2 4I 9/2 4I 11/2 4I 11/2 Er 3+ 4I 13/2 Yb 3+ Er 3+ 4I 13/2 4I 15/2 4I 15/2 Good beam quality direct pumping => no P doping, low core NA possible Low pump absorption Er doping <1 3 ppm => avoid inter-ions energy transfer Fiber/setup design/cost need for small cladding size and high brightness pump High pump absorption high Yb doping Parasitic emission at 1µm Power limited by Er-Yb back transfer + non participating Yb Challenging beam quality P doping => central dip in refractive index profile 9

10 Dn x Increase Aeff : Beam quality in large core fibers Standard step index profile LMA step index profile. Diam. 3µm / ON.1 Er:Yb doped fibers: large NA and central dip Singlemode fiber Multimode fiber Position (um) CLRC, High peak power single-frequency MOPFA for lidar applications

aluminosilicates Qualité spatiale difficile à contrôler 15 1 5 Aculight 25 NP Photonics 211 FORC 214 Shangai 213, MTBF?

11 Efficacité o-o (%) State of the art of narrow linewidth 1.5µm fiber sources 25 2 ONERA, 214 ONERA, 214 Fibertek, 211 Fibres phosphates (NP Photonics) Fibres phosphosilicates Fibres MFC Fibres aluminophosphosilicates Fibres aluminosilicates Qualité spatiale difficile à contrôler Aculight 25 NP Photonics 211 FORC 214 Shangai 213, MTBF? ONERA 212 ONERA 215 ONERA 158nm ONERA 29 ORC M 2 >2,1 NP Photonics Puissance crête (W) 1 Difficile à fabriquer a compromise has to be made between efficiency and peak power strategies are required to maximize efficiency and peak power CLRC, High peak power single-frequency MOPFA for lidar applications

Ytterbium large mode area fiber B-doped stress applying parts (for birefringence) F-doped Silica Er 3+ /Yb 3+ cores Mode field distribution Modeling

12 Peak power (kw) 1. maintain uniform core profile Silica Phosphorous fibers: quality difficult to maintain Microstructured core fiber (IPHT/ONERA collaboration) Erbium Ytterbium large mode area fiber B-doped stress applying parts (for birefringence) F-doped Silica Er 3+ /Yb 3+ cores Mode field distribution Modeling Measurements, G. Canat, et al., Opt. Lett., 33, pp (28),,2,4,6,8 1, Time (µs) 2,5 2, 1,5 1,,5 P pump =28 W P pump =26 W 95 ns SBS-induced dip M 2 ~ 1.3 A eff ~ 8 µm 2 P th = 2 kw G. Canat, et al. CLEO 9, paper JTuB3 (29) CLRC, High peak power single-frequency MOPFA for lidar applications

13 Refractive index difference (x1) Peak power (W) ASE fraction % Average signal power (W) 2. chose co-dopants (Al, P) Phospho-alumino-silicate (PAS) LMA 3µm (Er,Yb:AlP) DM PD/OSA BS DFB laser diode AOM EDFA 6+1->1 PM AWG 6x 1W 975nm PM coeur Δn~ ,5 4, 3,5 3, slope 26% ,5 2, 2 M 2 ~ ,5 1,, Radial position (A.U.) Launched pump power (W), Launched pump power (W) Brillouin threshold P peak ~ 77W at 65ns pulse duration and 1kHz PRF Slope efficiency 26% Brillouin threshold P peak ~ 112W at 18ns pulse duration and 5kHz PRF Slope efficiency 19% W. Renard, et al. CLEO CLRC, High peak power single-frequency MOPFA for lidar applications

14 Why is this not so simple to increase A eff? Fiber doping: Er and Er:Yb at 1,55µm Beam quality in large core fibers Increase A eff : 1. MFC fibers 2. PAS fibers: large core Alternative way: decrease L eff with strain Strain principle 3. Application on LMA fiber Coherent combining of 2 singlmode amplifiers of 7 cores of a multicore fibers CLRC, High peak power single-frequency MOPFA for lidar applications

15 Strain δ Strain δ Power Frequency (GHz) Strain: principle (1) Absence of strain, (z)= everywhere Unstrained fiber With strain distribution, (z) Unstrained fiber 1% Strain single peak Maximum Brillouin strength 1.5 Power 2 peaks in the spectrum, Brillouin threshold inscreases by x Position 1% % position % position To gain more: continuous distribution CLRC, High peak power single-frequency MOPFA for lidar applications

Strain δ Strain δ Power Frequency (GHz) Strain: principle (2) Absence of strain, (z)= everywhere Unstrained fiber With strain distribution, (z) Unstrained fiber 1% Strain 11.6 11.6 11.4 11.4 11.2 11.

16 Strain δ Strain δ Power Frequency (GHz) Strain: principle (2) Absence of strain, (z)= everywhere Unstrained fiber With strain distribution, (z) Unstrained fiber 1% Strain single peak Maximum Brillouin strength 1.5 Power 2 peaks in the spectrum, Brillouin threshold inscreases by x Position 1% % position % position CLRC, High peak power single-frequency MOPFA for lidar applications

3. Use of strain distribution to increase the SBS threshold Backscattered power (A.U.) Peak power (W) Experiment: 1579nm high peak power single frequency MOPFA Strain distribution

17 3. Use of strain distribution to increase the SBS threshold Backscattered power (A.U.) Peak power (W) Experiment: 1579nm high peak power single frequency MOPFA Strain distribution 1,,9,8,7,6,5,4,3,2,1, Spectral broadening unbstrained fiber strainde fiber 1,8 11, 11,2 11,4 11,6 Frequency (GHz) 4 MHz 225 MHz G.Canat et al., CLEO Europe 213, G. Canat et al, ICSO 214 SBS threshold increase SBS limit strainded amplifier 55W 1.7 kw 26µJ SBS limit standard amplifier 23% efficiency Launched pump power (mw) CLRC, High peak power single-frequency MOPFA for lidar applications

18 Why is this not so simple to increase A eff? Fiber doping: Er and Er:Yb at 1,55µm Beam quality in large core fibers Increase A eff : 1. MFC fibers 2. PAS fibers: large core Alternative way: decrease L eff with strain Strain principle 3. Application on LMA fiber Coherent combining of 2 singlmode amplifiers of 7 cores of a multicore fibers CLRC, High peak power single-frequency MOPFA for lidar applications

for phase variations Sum of power of N lasers with same spatial, spectral, temporal characteristics

19 Coherent combining principle 1 Master oscillator (pulsed or continuous, narrow linewidth) N amplifiers with brightness: B ampli = P/(M²)² (P power, M² beam quality) Phase controller compensates for phase variations Sum of power of N lasers with same spatial, spectral, temporal characteristics Final brightness B final = N*B ampli CLRC, High peak power single-frequency MOPFA for lidar applications

4. Peak power improvement by Pulse Coherent Combining Pulse energy (µj) 15 1 5 Controller disabled Controller enabled Amp1 and Amp2 amplify the

output ( maximize O 1 output) The setup is adapted to pulse operation using a leak between pulses.

20 4. Peak power improvement by Pulse Coherent Combining Pulse energy (µj) Controller disabled Controller enabled Amp1 and Amp2 amplify the common MO Amp1 and Amp2 outputs overlap and interfere on a 5/5 beam splitter A CW multi-dithering phase controller is used (LOCSET) to minimize O 2 output ( maximize O 1 output) The setup is adapted to pulse operation using a leak between pulses Time (s) No beam degradation Overall beam combining efficiency: 95% Lombard et al., Opt. Lett. 36, (211) CLRC, High peak power single-frequency MOPFA for lidar applications

Pulse Coherent Combining in a Wind Lidar 3 Configurations to check CBC impact on instrument: - Single pulse amplifier (3W) - Coherently combined pulse amplifiers (3W) - Coherently combined pulse

21 Pulse Coherent Combining in a Wind Lidar 3 Configurations to check CBC impact on instrument: - Single pulse amplifier (3W) - Coherently combined pulse amplifiers (3W) - Coherently combined pulse amplifiers (96W) Amp 1 Amp 2 Output CBC A 49 W 29.5 W OFF B 18.5 W 1.6 W 29 W ON C 49 W 51 W 96 W ON Procedure: 1 min in each configuration Comparison of measurements: - Carrier to Noise Ratio (CNR) (quality of the signal) - Estimated frequency (wind speed) - Instrument noise floor CLRC, High peak power single-frequency MOPFA for lidar applications

22 Lidar performance comparison CNR and estimated frequency Results: CNR is equivalent for CBC ON and CBC OFF 96W is +5dB compared to 29W (expected 5.2dB) conf. A (1 lasers, 29.5W) 1 min conf. B (2 lasers, 29W) 1 point = 1 shots.1s conf. C (2 lasers, 96W) Noise floor is equivalent for CBC ON and CBC OFF.21 m/s.19 m/s.8 m/s First demonstration of wind lidar based on coherent combining! CLRC, High peak power single-frequency MOPFA for lidar applications Lombard et al., Opt. Lett. 4, (215)

modulator per channel Common pump and phase modulator Common

23 5. Coherent combination of a multicore fiber Several Fibers Multicore Fiber Easily increase the number of channel One pump and one phase modulator per channel Common pump and phase modulator Common environment CLRC, High peak power single-frequency MOPFA for lidar applications

24 4. Coherent Beam Combining : some experimental results 3.7 meters Residual phase fluctuations ~ λ/27 DOE zero order Combining efficiency 63% CLRC, High peak power single-frequency MOPFA for lidar applications

Sum up Onera has investigated various strategies to mitigate SBS Generating uniform core by microstructuration Adjusting fiber composition in PAS fibers Applying strain on the fiber Coherent

25 Sum up Onera has investigated various strategies to mitigate SBS Generating uniform core by microstructuration Adjusting fiber composition in PAS fibers Applying strain on the fiber Coherent combining Based on new specialty fibers and new architecture, high peak power single frequency MOPFA are available at 1.55 µm for wind lidar applications CLRC, High peak power single-frequency MOPFA for lidar applications

26 Long range wind speed measurements Horizontal measurement on a typical day. Wind speed ~ 4 km/h Horizontal measurement during «Hermann» storm. Wind speed up to 11 km/h 26

Progress on High Power Single Frequency Fiber Amplifiers at 1mm, 1.5mm and 2mm

Nufern, East Granby, CT, USA Progress on High Power Single Frequency Fiber Amplifiers at 1mm, 1.5mm and 2mm www.nufern.com Examples of Single Frequency Platforms at 1mm and 1.5mm and Applications 2 Back-reflection