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« Control of pattern formation in a single feedback system by photonic bandgap structures »

« Control of pattern formation in a single feedback system by photonic bandgap structures ». Nicolas Marsal , Germano Montemezzani, Delphine Wolfersberger, Marc Sciamanna Lab. Matériaux Optiques, Photonique et Systèmes (CNRS - UMR 7132) Université Paul Verlaine - Metz and SUPELEC France

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« Control of pattern formation in a single feedback system by photonic bandgap structures »

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  1. « Control of pattern formation in a single feedback system by photonic bandgap structures » Nicolas Marsal, Germano Montemezzani, Delphine Wolfersberger, Marc Sciamanna Lab. Matériaux Optiques, Photonique et Systèmes (CNRS - UMR 7132) Université Paul Verlaine - Metz and SUPELEC France Dragomir Neshev Nonlinear Physics Centre, Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australia

  2. Outline • Introduction to pattern and photonic lattice • 2. Our experimental setup • 3. Results • 4. Conclusions

  3. Pattern Nonlinear medium Free propagation Photorefractive crystal, Kerr… 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions Mirror Single feedback Liquid-crystal light valves (LCLV),Photorefractive crystal, Na vapors… Active medium Linear cavity Lasers…

  4. Pattern : properties • Light structures spatially modulated and correlated • Generated thanks to noise and modulation instability • Disordered or ordered geometry 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions Goal Control of pattern

  5. E External illumination Fourier Filter • Pattern : control C. Denz, Ann. Phys. (Leipzig) 13, 391 (2004) 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions C. Denz, Phys. Rev. Let. 81, 1614 (1998) A.V. Mamaev, M. Saffman, Europhys. Lett. 34, 669 (1996) And with a photonic lattice … ? R. Neubecker and A. Zimmermann, Phys. Rev. E 65, 035205 (2002)

  6. n1 n0 real space 1st and 2nd BZ w = kc / n Constant refractive index • Photonic lattice Periodic illumination ( lattices or light interferences ) Periodic variation of the refractive index inside the medium Light sensitive medium ( photorefractive crystal ) Properties 2π / a 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions k space photonic crystal a Light induced photonic crystal Bandgap effect Periodic refractive index

  7. Experimental setup Pattern control by a photonic lattice Goal Photorefractive BaTiO3 crystal Mirror 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions Far field (k space) External periodic illumination

  8. Experimental setup Horizontal polarization M : Mirror λ = 532 M BS : Beam Splitter LASER HWP : Half Wave Plate HWP BSP BSP : Polarizing Beam Splitter BS L : Lens SF : Spatial Filter LA : Linear Atenuator PC : Photorefractive Crystal 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions Vertical polarization VM : Virtual Mirror : Pattern beam : Lattice beam : Feedback loop 4f system L2 SF L1 Lattice f2 f f L3 f2 VM L4 PC 2f 2f LA Far Field CAM

  9. Lattice Bragg plane Lattice k vector k space Pattern k vector = • Results 1D Lattice Beam Photorefractive crystal Mirror Pattern Beam 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions +

  10. Results 1. Pattern beam intensity above thresholdand fixed lattice periodicity ( kL = 2 kP ) Bragg / bandgap effect ? 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions 2. Pattern beam intensity below threshold with fixed lattice intensity (arbitrary lattice periodicity) Forcing ? 1D lattice 2D lattice

  11. Results Pattern formation with and without lattice (lattice intensity fixed) Ihex 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions kL = 2 kP Bragg effect Hexagonal pattern formation without lattice Hexagonal pattern formation with 1D lattice Forcing Iin Hexagonal pattern threshold

  12. Conclusions • We have provided a rapid survey of different concepts • Pattern • Photonic lattice • We have experimentallystudied the possibility to control a pattern by an optically induced photonic lattice 1. Patterns / photonic lattice 2. Setup 3. Results 4. Conclusions • Photorefractive BaTiO3 in single feedback configuration • External periodic illumination to create a virtual photonic crystal inside the BaTiO3 • We have observed 2 different behaviors which may be due to : • Bandgap effect • Forcing

  13. Thank you for your attention !

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