Optics of complex micro structures

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2 Optics of complex micro structures dielectric materials λ L disordered partially ordered ordered random multiple scattering liquid crystals quasi crystals (Fibonacci) photonic crystals

3 Assembly of photonic materials diffusive systems: white paint fog/clouds gypsum human bones crystalline systems: photonic crystals opals

4 Scattering of optical waves single scattering phase is maintained multiple scattering interference

5 Interference in multiple scattering Speckle pattern in transmitted light Disordered dielectric (nematic liquid crystal) Phys. Rev. Lett., 92, (2004)

6 Anderson localization Interference localizes light Nature 390, 671 (1997)

7 Analogies between light and electron transport Anderson localization of light Coherent backscattering (weak localization) Optical Bloch oscillations / Zener tunneling of light Universal conductance fluctuations Ohm s law

8 Applications of photonic nano and micro structures Photonic (quasi) crystals: fibers, photonic circuits, resonators Disordered systems: Medical diagnostics, imaging caries in teeth internal structure of skin optical mammography Diffusing Wave Spectroscopy (DWS) dynamics of colloidal systems Visibility through fog in air/road traffic Random laser (laser based on multiple scattering)

9 Random laser action powdered laser crystal laser dye solution + microsphere suspension Nature 406, 132 (2000)

10 Diffusive laser threshold gain volume } loss surface critical volume: gain > loss Nature 373, 203 (1995)

11 Tunable random laser Diffusive random laser at low temperature Threshold at 42 degrees Nature 414, 708 (2001)

12 electric field Polymer dispersed liquid crystal Liquid crystal droplets in polymer matrix n_o = 1.53, n_polymer = 1.52 n_e = 1.75 random orientation: multiple scattering alignment in z direction: transparent in z Phys. Rev. Lett. 93, (2004)

13 Coherent effects Emission spectra from ZnO particle suspension in laser dye Narrow emission peak > modes? Hypothesis coherent feedback: - boundary effects? - particle resonances? - Anderson localized modes?? Broad range of mean free path

14 Amplified extended modes Path length distribution: finite size -> noise Amplification of rare long paths Narrow emission modes Phys. Rev. Lett. 93, (2004)

15 Partially ordered systems liquid crystals quasi crystals ordered systems with disorder: micro cavities photonic crystals

16 Quasi-crystals 1 dimensional case A B A B crystal A B B A A quasi-crystal A, B, AB, BAB, ABBAB, BABABBAB, ABBABBABABBAB,... Fibonacci (Leonardo Pisano), Liber Abaci, 1202

17 Fibonacci quasi-crystal Transmission Wavelength (nm) Photonic bandgap / quasi-localized modes Infinite sample is Cantor set Spectra self similar

18 Porous Silicon multilayers Fibonacci quasi-crystal A B B A A Layer A: 157 nm, 69% porosity, n = 1.6 Layer B: 105 nm, 47% porosity, n = 2.2 Univ. of Trento, group Pavesi Univ. of Amsterdam, group Lagendijk Phys. Rev. Lett. 91, (2003)

19 Quasicrystals in higher dimensions Cut irrational 2D slice out of 5 dimensional cubic lattice Can obtain quasicrystal in any dimension as slice out of higher dimensional periodic structure

20 3 dimensions self-assembly of micro spheres Photonic crystals natural opals holographic techniques 2 dimensions micro lithography chemical etching inverse Si opal (C. Lopez, G. Ozin, S. John, ) 2D wave guide with holes

21 Wave guiding 90 degree bend (Hammer, Univ. Twente) ring cavity

22 Local infiltration Writing a waveguide in a 2D photonic crystal

23 Single pore infiltration Emission image Reflection image Horizontal profiles Vertical profiles Reflected Intensity Position (μm) PL Intensity Reflected Intensity Position (μm) PL Intensity

24 Confocal image + SNOM The CLSM monitors the SNOM scan It is possible to control the relative distance between the tip and the infiltrated pore Infiltrated pores y PL images 20x20 μm tip Topography 12x12 μm x

25 Controlled infiltration 2D Silicon photonic crystal locally infiltrated with laser dye Silicon photonic crystals by: Univ. Paderborn, Wehrspohn Univ. of Trento, group Pavesi Waveguide written by infiltration Enabling technology rewritable photonic circuits

26 Conclusions random systems photonic crystals Fundamental physics of transport processes: Interference effects: weak and strong localization, Bloch oscillations, Zener tunneling Partially ordered systems, microcavities, liquid crystals, quasi crystals, anomalous diffusion Light transport in amplifying random systems Applications: Photonic circuits: rewritable structures containing shaped waveguides, active elements, light sources, micro lasers Random lasers: lighting, 4Pi sources in surgery, active displays

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