Fast thermo-optical excitability in semiconductor 2D photonic crystals

Transcription

1 Fast thermo-optical excitability in semiconductor 2D photonic crystals Alejandro M. Yacomotti Laboratoire de Photonique et de Nanostructures (LPN) Marcoussis (south of Paris) - France With (LPN): P. Monnier, F. Raineri, R. Raj, et A. Levenson. Collaborators (LEOM- Lyon): B. Ben Bakir, Ch. Seassal.

2 Outline I. Introduction: - Excitability - Photonic Crystals II. Ingredients for Thermo-optical Excitability in a PhC: 1. Bistability 2. Thermal dissipation in PhC membranes - Thermo-optical mechanism of excitability III. Experimental Results: - Excitability Test - All optical delay using excitability Conclusions.

3 Introduction & Definitions

4 Excitability: definition Property coming from biology, applied to optics Excitable system: a non-linear dynamical system presenting 1 stable state, and reacts to external perturbation with "all-or-none" responses physical pendulum with dissipation and torque 2π -turn excitable pulse History: Hudgkin & Huxley (1952) excitability in neurons Calibrated response High saturation robustness High sensitivity

5 Excitability in non-linear optics Excitable response calibrated optical response Class I Excitability: transition to oscillations with zero frequency Lasers with optical injection/feedback M. Giudici et al., Phys. Rev. E 55, 6414 (1997) Class II Excitability: transition to oscillations with nonzero frequency (Hopf Bifurcation) S. Barland et al., Phys. Rev. E 68, (2003) THERMO-OPTICAL dynamics in lasers, amplifiers Ingredients: Optical bistability + thermal effects Two time scale dynamics: fast (electronic) and slow (thermal)

6 The context of micro and nanophotonics Main challenge for micro and nano photonics: LIGHT CONTROL Space (confinement, propagation) Time (memories, optical delay) Excitability allows: Propagation without deformation All-optical delay lines Excitable waves Critical slowing down

7 Photonic crystals: definition Periodic structuration of the refraction index in the wavelength scale 1D Superposition of GaAs/AlOx layers Examples: 2D Holes lattice etched in GaAs 3D Sedimentation of Si nanoparticules (Opals) Air/GaAs 250 nm 1 μm High refraction index contrast!!

8 THRESHOLD REDUCTIONS Interferences Index confinement Photonic crystals: the importance for microphotonics INTEGRATION 250 nm T. Tanabe et al, Opt. Lett. 30, 2575 (2005) (Notomi' s group) Index contrast + interferences Light confinement in resonators: Low losses (high Q) Small volumes High I inside (~Q/V) Decreases thresholds for active functions Architecture of defects in a PhC slab integrating photonic devices H. Nakamura et al, Opt. Express 12, 6606 (2004) (Asakawa' s group) Concerning excitability: PhCs allow the realisation of arrays of coupled microcavities

9 Light confinement in Photonic Crystals Dispersion relation: k = k(ω, q) States inside the band-gap= band-gap confinement Defect-like μ-cavities State-of-the-art: Q~10 6 See, e.g., B. S. Song et al., Nat. Mater. 4, 207 (2005); E. Kuramochi et al., APL (2006) Band-edge resonators 2D PhC-slab v g =dω/dk=0 Slow Bloch mode= lateral confinement based on low group velocity E See, e.g., S. Fan, PRB (2002)

10 SEM image QWs Our nonlinear high-q resonator: active band-edge Bloch mode E in E out InP SiO 2 Bragg Si/SiO 2 Si a/λ λ a A k 0 Γ Μ Κ Γ A Physical variables and time scales Photon in the resonator: τp ~ 3 ps Electrons in the Qw: τr ~200 ps Temperature in the slab: τth ~1 µs reflectivity Electronic n=n 0 +n 2 I p Thermal wavelength (nm) A. M. Yacomotti et al., AP B 81, 333 (2005) F. Raineri et el, APL 85, 1880 (2004)

11 II. Ingredients for Thermo-Optical Excitability in a Photonic Crystal

12 1. Optical Bistability Coexistence of two stable states for the same input parameters Optical resonator Band-edge Bloch mode resonator Nonlinear medium n=n(i) e - Carrier induced nonlinear refractive index in III-V QWs Resonant optical injection The nonlinear effect depends on the light intensity inside the resonator P ref CW injection P in Preflected (arb. units) λ inj = nm Power threshold: ~ Vol / Q 2 ~800 µw Pin (mw) A. M. Yacomotti, et al. Appl. Phys. Lett. 88, (2006).

13 2. Thermal effect Thermal dissipation in our sample: E in E in d=250 nm Thermal diffusion through the membrane τ diff =d 2 /D Si Thermal conduction to the substrate Heat diffusion is fast Good thermal conduction through the substrate, but can be still improved: for example Au/SiC (S. Barbay et al. in VCSELs) τ th =1µs

14 Thermo-optical mechanism of excitability Reflectivity spectrum Hysteresis cycle reflectivity (arb.units) wavelength (nm) P ref P in Experimental results: Noise-triggered excitable pulses OSC 0.02 P ref time (μs) CW-injection Pin time (μs)

15 III. Experimental Results

16 Excitability test: Short pulse (ps) perturbations OSC P ref ps-pulses CW-injection High sensitivity 80 KHz intensity (arb. units) 0.04 ps perturbation 0.02 Excitation energies ~ pj excitable response time (μs) Calibrated response High sensitivity (<1 pj)

17 Fast thermo-optical excitability Fast: increasing detuning, 80 KHz High repetition rate: 80 MHz >Excitation energies ~ 6pJ ps perturbation excitable response time (ns) intensity (arb. units) time (ns) Fast in pulse duration Fast in repetition rate Pulse duration can be much shorter than τ th Nonlinear resonator: you can kick it faster than its natural frequency without loosing contrast A. M. Yacomotti, P. Monnier, F. Raineri, B. B. Bakir, C. Seassal, R. Raj, and J. A. Levenson, Phys. Rev. Lett. 97, (2006).

18 Optical delay using excitability CRITICAL SLOWING DOWN threshold=slow flow region in phase space NONLINEAR DYNAMICAL CONTROL Example: all-optical delay Above threshold intensity (arb. units) On-threshold t(ns) INTEGRATION: Arrays of excitable microcavities Towards excitable delay lines Delay ~ pulse duration

19 Conclusions Excitability in photonic crystal: Thermo-optical dynamics can be useful: Thermal response is already fast (small τ th ), and can be still improved! Thermally-driven dynamics can be even faster than τ th (e.g., reduce duration by increasing the detuning). Small & Compact good stability & sensitivity How much can we reduce the threshold? Can we use excitable PCs as sensors? In general: Photonic Crystals provide an extreme versatility to control light in different ways: non linear-dynamical: taking benefit of the phase space structure critical slowing down to realize optical delay lines in photonic excitable µ-resonators

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21 I. Optical Bistability: definition Coexistence of two stable states for the same input parameters Optical resonator (Band-edge Bloch mode) Nonlinear medium (QWs) Resonant optical injection The nonlinear effect depends on the light intensity inside the resonator Power threshold: ~ Vol / Q 2 modulated injection

22 History & Applications In the past Predicted in 1969 by Szöke (MIT) Demonstrated by Gibbs (1976) in Na vapour Semiconductors: 1979 in GaAs and in InSb Semiconductor microcavity ~1985 And now...in PC s: State-of-the-Art: Advantages : Q et Vol (P th ~ Vol / Q 2 ) Integration towards integrated optical memories and logic gates Thermal Nonlinearity P. Barclay et al., Opt. Express 13, 801 (2005). M. Notomi et al., Opt. Express 13, 2678 (2005). Electronic nonlinearity T. Tanabe et al, Opt. Lett. 30, 2575 (2005) (Notomi' s group, NTT)

23 III. Results P in P out reflectivity Spectrum: P out Hysteresis cycle: 200ns 10 µs wavelength (nm) Injection waveform: Quasi-stationary modulation Minimize thermal effects Preflected (arb. units) Experimental Result: 0.4 λ inj = nm Pin (mw) P in

24 Hysteresis cycles Varying injection wavelength: Contrast~65% Preflected (arb. units) 0.4 λ inj = nm Pin (mw) Preflected (arb. units) λ inj = nm λ inj = nm A. M. Yacomotti et al., Appl. Phys. Lett. 88, (2006) reflectivity wavelength (nm) P th ~800μW Pin (mw) λ inj = nm λ inj = nm λ inj = nm

25 Conclusions First demonstration of ultrafast optical bistability in a bandedge Bloch mode of a 2D photonic crystal Electronic nonlinearity: <2 ns switch time Low threshold (800µW) High contrast 65% THIS GEOMETRY: Combines vertical approach (like VCSELs) with guided approach PERSPECTIVES: Active materials (InP) regenerate/amplify input signals Integrated logic gates High coupling efficiency

26 Applications : our research towards all-optical information processing ΔR/R ps!!! F. Raineri et al,, Appl. Phys. Δt (ps) Lett. 86, (2005) F. Raineri et al., Appl. Phys. Lett. 86, (2005) Switch Amplification & μ-lasers optical reconfiguration (fast tuning) A. M. Yacomotti et al., Appl. Phys. B 81, 333 (2005) special issue on Photonic Crystals. F. Raineri et el, Appl. Phys. Lett. 85, 1880 (2004). Memories (bistable) F. Raineri et al, Opt. Lett. 30, 64 (2005). A. M. Yacomotti et al, Appl. Phjys. Lett., to appear

27 Applications : nos recherches dans l él équipe Traitement tout otique de l informationl ΔR/R ps!!! F. Raineri et al,, Appl. Phys. Δt (ps) Lett. 86, (2005) F. Raineri et al., Appl. Phys. Lett. 86, (2005) commutation (switch) Amplification & μ-lasers reconfiguration optique (accord rapide) A. M. Yacomotti et al., Appl. Phys. B 81, 333 (2005) special issue on Photonic Crystals. F. Raineri et el, Appl. Phys. Lett. 85, 1880 (2004). Mémoires (bi-stable) F. Raineri et al, Opt. Lett. 30, 64 (2005).

28 image SEM Notre résonateur à fort Q: mode de Bloch en bord de bande photonique E in E out E in E out InP QWs SiO 2 Bragg Si/SiO 2 Vol~5µm 3 FDTD- 3D Si image SEM reflectivity Q tr ~ wavelength (nm)

29 μ-cavités à défaut ponctuel Résonateurs Cristal Photonique en 2D Relation de dispersion: k = k(ω, q) Etat permis dans la bande interdite= confinement par interférence destructive Etat de l'art: Q~10 6 Résonateurs en bord de bande 2DPC-slab a/λ λ a A Vitesse de groupe: v g =dω/dk=0 0 Γ Μ Κ Γ k A Mode de Bloch lent= confinement latéral par faible vitesse de groupe E

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31 Effet non-lin linéaire dispersif (Kerr) dans la queue d Urbachd Pompe 100 nm non-linear shift (nm) Sonde 120 nm e - Luminescence des puits Dynamique de l effet NL delay (ps) reflectivity a/λ λ a A Mode photonique 0 Γ Μ Κ Γ n=n 0 +n 2 I p k wavelength (nm) A

32 In Photonic Crystals: State of the Art Experimental Demonstrations : Thermal Nonlinearity Electronic nonlinearity T. Tanabe et al, Opt. Lett. 30, 2575 (2005) (Notomi' s group, NTT)

33 A 2-dimensional 2 platform 1D Stack of layers of different materials 2D Example: air holes in a semiconductor slab 3D Sedimentation od Si nanoparticules (Opals) Air/GaAs AlOx/GaAs n sc /n air ~3 n sc /n AlOx ~2 1 μm High refraction index contrast!!

34 Our goal: understanding nonlinear dynamical processes From applications to new physical regimes in photonic crystals: II. Ulrafast dynamics of the EM field and charge carriers in a high-q μ-resonator femtosecond pump and probe dynamics III. Optical memories: bistability IV. Excitability photonic neurons nonlinear dynamics under CW injection

35 Photonic crystals: the importance of nonlinear optics Refraction index structuration in the wavelength scale Index contrast + interferences Light localization Good news for nonlinear optics In space: Vol 250 nm Small Vol High I In spectrum: Q λ Δλ Q= stored energy/ dissipated energy Large Q High stored energy

36 Active 2DPC: nonlinear effect in the Urbach tail of the QWs 100 fs pump nm non-linear shift (nm) fs probe nm e - QW Dynamique de l effet NL delay (ps) reflectivity a/λ λ a A Band-edge Bloch mode 0 Γ Μ Κ Γ n=n 0 +n 2 I p k wavelength (nm) A A. M. Yacomotti et al., AP B 81, 333 (2005) F. Raineri et el, APL 85, 1880 (2004)

37 Electromagneti c field dynamics NONADIABATIC DYNMICS A. M. Yacomotti et al., Phys. Rev. Lett. 96, (2006). Carrier lifetime photon liftime The Joannopoulos Research Group at MIT e - Carrier dynamics Thermal dynamics Thermal lifetime photon liftime