THALES Research & Technology - Institut d'Optique ELSA Remise en forme de faisceau après un amplificateur à fibre multimode L. Lombard, A. Brignon, J.P. Huignard, E. Lallier TRT (Thales Research and Technology) G. Lucas-Leclin, P. Georges, G. Pauliat, G. Roosen Laboratoire Charles Fabry de lInstitut dOptique

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA AMPLI A FIBRE Pompe Signal Fibre Pourquoi une fibre pour les lasers de puissance? Bon rendement Optique-Optique (bon recouvrement pompe et signal) Pas de problème thermique (ils sont répartis sur la longueur) Très hautes puissances accessibles (dans les fibres à grand cœur) Technologie performante: double cœur dopage Yb disponibilité des diodes de pompe haute puissance MOPA Pompe Fibre Laser à fibre Cœur signal dopé Cœur pompe non dopé

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Puissance : Augmenter la taille du cœur! Fibres LMA (Large Mode Area) quasi monomodes: Cœur 20µm / ON 0.06 Cœur 30µm / ON 0.06 Air-clad LMA (Tunnermann) 400µm 55µm Signal core Pump core Fibres Multimodes: Cœur 55µm / ON 0.2 (M²=10) Fibres Multicœurs, mise en phase spontanée Multi-Fibres!

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Multimode Fiber Amplifier Amplifier characteristics: Input Pump : 940 nm Signal : 1064 nm Output Amplified Signal : ~ 18 W, highly MultiMode (M² ~ 10) 400µm 55µm Signal core Pump core Pump Oscillator MMFA MM Fiber characteristics: Signal Core Diameter 55 µm, NA 0.19 Doping 6500 ppm (mol) Yb 2 O 3 Pump Core Diameter 340x400 µm, NA 0.39 D-shape for pumping efficiency

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Recovering Beam Quality How to recover the beam quality of a Multimode Fiber Amplifier ? 2 approaches : Pump Oscillator MMFA SM MM MMFA Pump Oscillator MM SM Beam Cleanup Phase Conjugation

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA How to recover Beam Quality ? 1. Beam cleanup (two wave mixing in a photorefractive crystal) Pump Oscillator MMFA SingleMode MultiMode Rh:BaTiO 3 Photorefractive crystal S R Ampl. R R and S interfere in the crystal and write a /2-shifted volume hologram. S energy (not its phase) is transferred to R

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA 2 W M : Coupled wave equations : Rh:BaTiO 3 : = 1.06 µm, large > 20 cm -1, low absorption = 0.1 cm -1 Reference Aberrated signal Amplified clean beam PR crystal Phororefractive Beam Cleanup

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Rh:BaTiO3 gain versus Signal / Reference power ratio Signal / Reference power ratio Gain (2WM) Rh:BaTiO 3 crystal 12.2 x 9.5 x 3.1 mm (W x H x D) cut at 45° from the crystal c-axis (to access large photorefractive gains) roof shape design to prevent any parasitic oscillation Rh:BaTiO 3 : an infrared sensitive (1.06 µm) photorefractive crystal Maximum gain : 2000 (= exp[( )L]) Photorefractive gain : 24.6 cm -1 (= ) absorption : 0.1 cm -1 (= )

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Experimental Setup 1 /2 MMFA Yb-doped 0.6 m Rh:BaTiO 3 Reference beam Laser 920 nm Nd:YAG 1064 nm Residual pump Camera PZT Phase stabilization R S Output Signal beam Vertical polarization

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Self referencing Two Wave Mixing Setup /2 MMFA Yb-doped 4 m Rh:BaTiO 3 MM Laser 940 nm Nd:YAG 1064 nm R S Output SM Vertical polarization PBS Dot Mirror Horizontal polarization Unpolarized beam SF MM Polarization recycling Self referencing Two Wave Mixing Polarization recycling: Insensitive to MM Fiber Amplifier depolarization Building Reference beam (Dot mirror + Spatial filter)

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Building Reference beam: Dot mirror and spatial filter MM DM SF Building Reference beam (Dot mirror + Spatial filter) MM SM To spatial filter to make it SM Reference (almost SM) Signal Aberrated (MM)

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Experimental results : Power S = 8.3 W S // = 6.6 W (Total 15W) R = 110 mW (SM) (SM) Ampl. R = 11.6 W 2.7 W Crystal efficiency = 78% Total Conversion efficiency = 63% Output Power vs time Time (s) Rise time : 2-3s

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Experimental results : Beam Quality Reference Amplified Reference Signals S and S // M² = 7.4 Depolarized M² = 1.2 Linearly Polarized M² = 1.0 Linearly polarized

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Power handling capability of Rh:BaTiO 3 Rh:BaTiO 3 Crystal depoling Depoling effect appears after several 100 hours of use. It reduces the conversion efficiency. The effect is temporary suppressed by illumination for several hours with 200mW, 532nm laser High power handling Low-absorption crystals: photorefractive crystals with low absorption are more indicated. Co:BaTiO 3 crystal is promising. Large aperture crystals

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Presentation dun nouveau concept et validation experimentale à 15W : ØUn oscillateur monomode est amplifié dans une fibre multimode. ØLa qualité de faisceau est ramenée à la limite de diffraction par un Convertisseur Spatial de faisceau photorefractif entrée: faisceau dépolarisé multimode cohérent sortie: faisceau monomode linéairement polarisé CONCLUSION

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Recovering Beam Quality How to recover the beam quality of a Multimode Fiber Amplifier ? 2 approaches : Pump Oscillator MMFA SM MM MMFA Pump Oscillator MM SM Beam Cleanup Phase Conjugation

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA How to recover Beam Quality ? 2. Conjugaison de phase MMFA Pump Oscillator MM SM Miroir à conjugaison de phase Miroir conventionnel Miroir à conjugaison de phase

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Manip actuelle Conjugaison de phase par effet Brillouin fibre multimode dopée 3m Pump Oscillator MM SM Fibre multimode non dopée 1km Miroir à conjugaison de phase par effet Brillouin

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Effet Brillouin dans une fibre monomode fibre monomode 13.6 km Diode laser monofréquence Onde acoustique (réseau de Bragg) Onde pompe Onde Stokes (réfléchie sur le réseau) Diffusion Brillouin Stimulée (Stimulated Brillouin Scattering, SBS) Photon bruit

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA SBS comme Miroir à conjugaison de phase Milieux non guidants Nécessite des kW crête! Onde pompe Onde Stokes Onde acoustique « cellule SBS » (CS 2 ) Bruit

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA SBS comme Miroir à conjugaison de phase Démarre sur du bruit… Mais sort conjugué en phase!

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA SBS comme Miroir à conjugaison de phase Gain local Stokes Gain global Stokes Puissances globales Pompe, Stokes Pour une aberration gausienne, lintensité du Speckle volumique sécrit Speckle Stokes aléatoire C=1 non conjugué en phase Speckle Stokes superposé au Speckle Pompe C=2; doublement du gain conjugué en phase Non CP CP

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA SBS dans une fibre multimode! Fibre Multimode Longueur 1km Cœur à saut dindice Diamètre 50µm, ON 0.22

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Schéma idéal Conjugaison de phase par effet Brillouin fibre multimode dopée 3m Pump Oscillator MM SM Fibre multimode non dopée 1km Miroir à conjugaison de phase par effet Brillouin « cellule SBS» (CS 2 ) kW crête!

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Phase conjugation by SBS : preliminary experiment Laser multimode fiber 0.07 m pulsed laser 20ns, 50Hz, single-frequency Brillouin (depolarized) Multimode fiber 0.46 m With a spherical mirror M²=3.6 (polarized) With a phase-conjugating mirror (0.46m fiber) M²=1.1

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Simulation dans une fibre multimode à Saut dindice Fibre multimode SI long. 0.5 m, diamètre 14µm, ON 0.22 Pompe (entrée) Stokes (retour) 1mm entrée 0.2m 0.5m Fidélité de la CP 90%. Pompe Stokes

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Pour une fibre un peu plus longue… Pompe (entrée) Stokes (retour) 1mm entrée 0.2m 0.5m 1m 2m 5m Pompe Stokes Fibre multimode SI long. 2 m, diamètre 14µm, ON 0.22 Fidélité de la CP 20%. Aberrations chromatiques pour les fibres SI > qq. m Le conjugué en phase nest plus favorisé.

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA Conjugaison de phase par diffusion brillouin stimulée: Amplification exponentielle du bruit Gain Double pour le conjugué en phase ( facteur ~10 4 ) Contrainte sur le milieu: Suffisamment long pour quil y ait sélectivité (plusieurs grains de Speckle Suffisamment court pour quil ny ait pas aberration chromatique (grains de Speckle décalés) CONCLUSION

This document and any data included are the property of THALES. They cannot be reproduced, disclosed or used without THALES' prior written approval. ©THALES Template trtco V JNOG 2004 THALES Research & Technology - Institut d'Optique ELSA CONCLUSION Solutions Impulsionnel ou très fortes réflectivités pour réduit la longueur dinteraction Utilisation dune fibre à gradient dindice, automatiquement corrigée des aberrations chromatiques Utilisation du phénomène de « Beam Cleanup » sur grande longueur de fibre: un seul mode en retour, dépend du couplage. Stokes Pompe