13/05/2006 Spring School Solitons in Optical Cavities1 Applications of Cavity Solitons T. Ackemann SUPA and Department of Physics, University of Strathclyde Glasgow, Scotland, UK 2 Agenda Paul: This is a school, not a workshop everything known now: not so well established, partially more like Science Fiction but like every good piece of Science Fiction, it is based on facts What is special about CS?Some remarks: parallelism optical interconnects motion plasticity novel ingredient bistable all-optical processing all-optical network some early processing schemes: Rosanov 1990s 3 Outline + input from: B. Schpers, W. Lange (WWU Mnster) F. Pedaci, S. Barland, M. Giudici, J. R. Tredicce + others (INLN, Nice) G. Tissoni, L. L. Lugiato, M. Brambilla + others (INFM, Como, Bari) A. Scroggie, W. J. Firth, G.-L. Oppo + others (U Strathclyde, Glasgow) optical memory all-optical delay line buffering information in telecom soliton forve microscope characterization of structures all-optical processing, routing telecommunications + apologies to people working on LCLV (e.g. poster of Gtlich et al.) 4 Writing information for optical memory an ideal homogeneous system has translational symmetry ability to choose position in plane at will all states are equally likely code arbitrary information memory Harkness et al., CNQO, U Strathclyde (1993) Can you really write arbitrary configurations? interactions: minimum and discrete distances not all configurations of clusters are stable 5 Memories and arbitrary configurations Coullet et al., PRL 84, 3069 (2000); Chaos 14, 193 (2004) hom. state wins pattern wins fully decomposable memory appearance of states with N peaks destruction of states with N peaks appearance of states with N holes Pomeau front destruction of states with N holes width of this region in general unknown and system dependent, but seems to be comfortable wide in worked out models memory is feasible !(?) McSloy et al. PRE 66, (2002) Gomila and Firth (2005) (questioned by Champneys and Firth) 6 Arbitrary ensembles of spots !? Firth + McSloy saturable absorber model (private communication) Logvin et al. sodium vapor + feedback PRE 61, 4622 (2000) Taranenko et al. exp.: driven SC microresonator PRA 65, (2002) For a memory you should be able to create arbitrary arrangements of CS 7 but rather unstable... in systems with translational symmetry translation is a neutral mode no energy is needed for translation any perturbation couples easily to neutral mode and induces motion neutral mode is derivate of soliton and odd any odd perturbation (gradient) will cause drift until you are in a local extremum (even) where CS at rest / trapped Maggipinto et al., Phys. Rev. E 62, 8726, 2000; McSloy et al. PRE 66, (2002) plasticity 8 Noise Spinelli et al., PRA 58, 2542 (1998) amplifier model, time between frames 7440/ 90 ns in a homogeneous system: white noise diffusive motion CS will perform random walk but actually in reality this is not a problem... 9 Inhomogeneities Hachair et al., INLN, Nice; similar to X. Hachair et al., PRA 69 (2004) semiconductor amplifier after addressing beam is switched off, CS moves to a position slightly away from ignition point interpretation: CS is moving and finally trapped in small-scale irregularities of wafer structure good news: CS wont diffuse in real structure bad news: CS cant be positioned arbitrarily and this is essentially uncontrolled 10 (Radial) Gradients addressing beam on addressing beam on addressing beam on CS/FS can exist at any locations equivalent by symmetry in a system with a circular pump beam of Gaussian shape this is not translational symmetry but rotational symmetry ring (or center) what happens typically in single-mirror feedback system Schpers et al., WWU Mnster; similar: PRL 85, 748 (2000); IEEE QE 39, 227(2003) B Na adressing beam holding beam AOM 11 Application: Pixel array a) code arbitrary information ability to choose position in plane at will system should be as homogeneous as possible b) robust against noise Solution: Pinning of positions of LS by intentional small-amplitude modulations Firth + Scroggie, PRL (1996); saturable absorber model; see also Rosanov 1990 defined positions diffusive movement due to noise suppressed accuracy requirements for aiming relaxed 12 Simulations: Pixel array Spinelli et al., PRA 58, 2542 (1998) semiconductor amplifier model trap CS at lattice sites 13 Experiment: Pixel array pinning of positions of LS by amplitude modulations defined positions, diffusive movement due to noise suppressed pixel array, however not all cells are bistable at the same time (residual inhomogeneities) input beam Schaepers et al., Proc. SPIE 4271, 130 (2001) experiment: single-mirror feedback system insert square aperture, slightly truncating input beam (diffractive ripples) 14 CS-based optical memory ? so it seems that a CS-based optical memory will work but: CS are large - some micrometers mediumGbit/inch 2 bit/ m 2 CD0.7 GB DVD4.7 GB blu-ray 25 GB blu-ray100 GB holografic storage very best hard discs simple memories wont compete with existing technology need to exploit other, unique (!?) features 15 Enhancing CS arrays combine with processing e.g. all-optical routing remember that it is light cavity soliton laser as self-luminescent optically-addressable display exploit plasticity all-optical delay line unique feature best bang for the bug 16 Slow light this is cycling speed ! Hau et al., Nature 397, 594 (1999) Boyd et al., OPN 17(4) 18 (2006) 17 All-optical buffers and delay lines buffers can enhance performance of networks future high-performance photonic networks should be all-optical need for all-optical buffers with controllable delay Boyd et al., OPN 17(4) 18 (2006) 18 All-optical delay line inject train of solitons here read out at other side parameter gradient time delayed version of input train all-optical delay line buffer register for free: serial to parallel conversion and beam fanning Harkness et al., CNQO, U Strathclyde (1998) note: wont work for non-solitons / diffractive beams movie 19 Experimental realization B Na adressing beam holding beam AOM sodium vapor driven in vicinity of D 1 -line with single feedback mirror t = 0 st = 80 st = 64 st = 48 st = 32 st = 16 s ignition of soliton by addressing beam proof of principle, quite slow, but in a semiconductor microresonator this is different ! Schpers et. al., Proc. SPIE 4271, 130 (2001) tilt of mirror soliton drifts 20 First experiments in semiconductors F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished spatio-temporal detection system: 6 local detectors + synchronized digital oscilloscopes BW about 300 MHz VCSEL (UP) 200 m diameter quite homogeneous cavity resonance pumped above transparency but below threshold amplifier 21 Preparation of holding beam with 6 detectors you cannot investigate two- dimensional spatio-temporal structures create quasi-1D situation by introducing Mach-Zehnder interferometer stripes with modulation depth of 1 there is also a gradient along the stripes F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished 22 Results: Noise-driven events anti-phase oscillation possible interpretation: structure oscillating back and forth in a potential well F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished intentional (bang on table) or intrinsic perturbations trigger release of pulse 23 An animation strong indication of a drifting structure F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished 24 Reproducibility F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished noise triggered events appear at fairly random time intervals superposition of 50 events deterministic propagation compatible with interpretation of a noise triggered drifting CS 25 A theoretical analog !? J. McSloy, PhD thesis, 2002; cf. also Scroggie, PRE 66, (2002); Tissoni, Opt. Exp. 10_1009(2002). model: passive semiconductor microcavity + temperature dynamics self-propelled CS some oscillation followed by eruption of CS Caution: this is only to illustrate that similar things can happen in a model it is not claimed that this is the explanation 26 Optical addressing F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished gate addressing beam with an electro-optical modulator rise/fall times < 1 ns 100 s this is an embryonic all optical delay line ! optically addressed drifting structure delay 12 ns distance 25 m velocity 2.1 m/ns delay / width 2-4 27 Velocity experiment suggests velocity of about 2 m / ns = 2000 m / s = 7200 km / h > supersonic jet ! theoretical expectation here amplifier model (standard parameters) perturbative regime saturation speed limit 1.5 m/ns semi-quantitative agreement fortutious (at present stage) Tissoni et al., unpublished; see also Kheramand et al., Opt. Exp. 11, 3612(2003) 28 Bandwidth and bit rate velocity: 2 m / ns CS diameter typically 10 m a local detector would see a signal of length 10 m/(2 m/ns) = 5 ns bit rate 100 Mbit/s not great, but certainly a start limit: time constant of medium (carriers) typically assumed to be about 1 ns -response some ns 10 m / 3 ns = 3.3 m /ns origin of numerically observed saturation behaviour even this makes sense with experiment 29 Slow media: Non-instantaneous Kerr cavity A. Scroggie, Strathclyde, unpublished (1D, perturbation analysis) 0.01 semiconductor log (velocity / gradient) log ( ) slope 1 velocity determined by response time saturation for instantaneous medium faster medium will speed up response ! response time can be engineered by growers: low-temperature growth, ion implantation, QW close to surface, quantum dots need to pay for it by increase of power 30 Conventional approaches to slow light modification of group velocity in vicinity of a resonance two-level atom electro-magnetically induced transparency cavity resonance .... Hau et al., Nature 397, 594 (1999) bandwidth limited by absorption high-order dispersion large effect needs steep slope, narrow resonance 31 Comparison to other systems slow light in the vicinity of resonances: electro-magnetically induced transparency, linear cavities, photonic crystals interplay of useful bandwidth and achievable delay systemspeedlengthdelaybandwidthbandwidth delay product EIT in cold vapor m/s230 m~ 10 s300 kHz2.1 EIT in SC QD 1 4 (calc) m/s1 cm8 ns10 GHz81 SC QW (PO, calc) m/s0.2 m0.02 ns2 GHz0.04 SBS in fiber km/s2 m18.6 ns30-50 MHz> 1 Raman in fiber 2 2 km0.16 ns10 GHz > THz 2 (demonstr.) > 160 (pot.) CS (demonstrated)2000 m/s25 m12 ns300 MHz3.6 CS (optimize delay)2000 m/s200 m100 ns300 MHz30 CS (optimize BW)40000 m/s200 m5 ns6 GHz30 1 Tucker et al., Electron. Lett. 41, 208 (2005); 2 Dahan, OptExp 13, 6234(2005); 3 GonsalezHerraez, APL (2005); 4 ChangHasnain Proc IEE (2003); 5 Ku et al., Opt Lett 29, 2291(2004); 5 Hau et al., Nature 397, 594 (1999) 32 Rsum: CS-based delay line drifting CS are a quite different approach to slow light pros and contras should be assessed potentially very large delays lots of things to do theory: saturation behaviour patterning effects t N = - A N B N 2 C N fabrication:homogeneity experiment:control gradients, improve ignition, larger distances... in a cavity soliton laser there are (at least) two other twists relaxation oscillations are faster than carrier decay time and modulation frequency of modern SC lasers is certainly faster (at least 10 Gbit/s) possibility of fast spontaneous motion (Rosanov, since about 2002) other: wavelength-conversion by FOPA + dispersive fiber + back-conversion McSloy, Strathclyde 33 Material parameters from nonlinear dynamics nonlinear dynamics often depends sensitively on parameters old idea: use this to determine material parameters not many examples: e.g. ferro-fluids apparently not much done in optics (remarks welcome) relaxation and diffusion constant from below threshold patterns (Agez et al., PhD thesis, 2005, Lille; Opt. Commun. ?) defect characterization by looking at symmetry breaking of SHG conical emission (Chen et al., PRL 96, , 2006) characterize homogeneity of cavity resonance of a microcavity (INLN, Nice) 34 Broad-area microcavity laser Barland et al., Nature 419, 699 (2002) 150 m diameter VCSEL free-running with injection left-right asymmetry gradient in detuning gradient in cavity resonance this gradient was mapped out by other (tedious) experiments to be 400 GHz/150 m Another clever way? 35 Probing the gradient fine structure coarse structure wavenumber should scale as square root of detuning qualitative right but not suitable for quantitative analysis modulational instability threshold Barland et al, APB 83, 2303 (2003) 36 Quantitative linear relation 351 GHz / 150 m Barland et al, APB 83, 2303 (2003) 37 Local probing Hachair et al., INLN, Nice; similar to X. Hachair et al., PRA 69 (2004) the patterns allow only for large-scale and directed inhomogeneities What about local probing? the trapped CS indicate extrema of phase/amplitude Can we find depth of potential well? Soliton force microscope W. J. Firth, Strathclyde map relative possibly absolute gradients in transverse plane by measuring the displacement between CS and a (small-amplitude) steering beam 38 Idea of soliton force microscopy CS in a trap add focused steering beam (addressing beam) blow up CS moves to new equilibrium measure displacement infer relative local curvature (for fixed amplitude) changing amplitude + calibrations absolute local curvature inverse problem: disentangle phase- and amplitude contributions identify origin of inhomogeneity 39 All-optical processing pulse trains with a high repetition rate are needed in optical communications time-division multiplexing (TDM) demultiplexing regeneration routing self-pulsing CSL, ideally a mode-locked CSL array of self-pulsing laser sources carrier pulse trains with high repetition rate in a large number of output channels all-optical control high-frequency carrier pulse train on demand e.g. Stubkjaer, IEEE Sel. Top. QE 6, 1428 (2000) 40 Anticipated scheme de-multiplexing optical regeneration routing time scales packet manipulation advanced schemes might use plasticity of CLB processing, direct routing self-pulsing CSL control beams pulse train time 41 Summary: Cavity solitons versus pixels broad-area laser with CSarray of micro-fabricated bistable elements discrete bistable memory switch optical processing continuous utilize plasticity all-optical delay line (different access to slow light) soliton force microscope continue to think hard about combination of parallelism, all-optical switching/processing/routing and plasticity 42 Desirable Features and Systems compact integration fast robust (monolithic) semiconductor microcavity moderate power requirements cascadable active system amplifier or laser robust (phase-insensitive) self-sustained laser incoherent switching of CS (or propagation in amplifier) cavity soliton laser 43 Relevance of modulated backgrounds in general modulations of the pump or the refractive index can be used It is generally believed that cavity solitons get stuck at the maxima of the background modulation. a) advantageous improve accuracy and robustness of optical memories b) limiting provides pinning mechanism for drifting CS 44 Pinning of drift motion A. Scroggie, unpublished (USTRAT) motion of CS might be affected in extreme case pinned by modulations or localized inhomogenities study motion of CS on noisy backgrounds position along device dashed line: perturbation solid line: speed of CS soliton averages over scales < CS width 45 Transition between locking and drift example: single-mirror feedback system with Na as nonlinear medium locking of hexagonal patterns (not solitons !) at large-scale envelope produced by pump profile transition discontinous possibly we are close in semiconductors !? Seipenbusch et. al., PRA 56, R4401 (1997); AG Lange, WWU Mnster