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Applications of Cavity Solitons

Applications of Cavity Solitons. T. Ackemann. SUPA and Department of Physics , University of Strathclyde Glasgow, Scotland, UK. Email: t horsten .ackemann@ strath.ac.uk. What is special about CS? Some remarks:. all-optical processing all-optical network. bistable. para l lelism.

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Applications of Cavity Solitons

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  1. Applications of Cavity Solitons T. Ackemann SUPA and Department of Physics, University of Strathclyde Glasgow, Scotland, UK Email: thorsten.ackemann@strath.ac.uk Spring School ‚Solitons in Optical Cavities‘

  2. What is special about CS? Some remarks: all-optical processing all-optical network • bistable • parallelism optical interconnects • motion „plasticity“ novel ingredient some early processing schemes: Rosanov 1990s 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

  3. + input from: • B. Schäpers, W. Lange (WWU Münster) • 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) Outline • 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 Gütlich et al.)

  4. interactions: minimum and discrete distances • not all configurations of clusters are stable Can you really write arbitrary configurations? 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)

  5. 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, 046606(2002) Gomila and Firth (2005) Memories and arbitrary configurations appearance of states with N peaks hom. state wins fully decomposable  memory (questioned by Champneys and Firth) destruction of states with N peaks pattern wins appearance of states with N holes Pomeau front destruction of states with N holes Coullet et al., PRL 84, 3069 (2000); Chaos 14, 193 (2004)

  6. “Arbitrary” ensembles of spots !? For a memory you should be able to create arbitrary arrangements of CS 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, 013812 (2002)

  7. 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 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 plasticity Maggipinto et al., Phys. Rev. E 62, 8726, 2000; McSloy et al. PRE 66, 046606(2002)

  8. Noise in a homogeneous system: white noise  diffusive motion  CS will perform random walk amplifier model, time between frames 7440/k 90 ns but actually in reality this is not a problem ... Spinelli et al., PRA58,2542(1998)

  9. Inhomogeneities 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 won‘t diffuse in real structure • bad news: CS can‘t be positioned arbitrarily and this is essentially uncontrolled Hachair et al., INLN, Nice; similar to X. Hachair et al., PRA69(2004)043817

  10. addressing beam on addressing beam on addressing beam on adressing beam Na AOM holding beam B (Radial) Gradients what happens typically in single-mirror feedback system • 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 symmetrybut rotational symmetry  ring(or center) Schäpers et al., WWU Münster; similar: PRL 85, 748 (2000); IEEE QE 39, 227(2003)

  11. Solution:Pinningof positions of LS by intentional small-amplitude modulations • defined positions • diffusive movement due to noise suppressed • accuracy requirements for aiming relaxed Firth + Scroggie, PRL 76 1623 (1996); saturable absorber model; see also Rosanov 1990 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

  12. Simulations: Pixel array semiconductor amplifier model trap CS at lattice sites Spinelli et al., PRA58,2542(1998)

  13. Experiment: Pixel array experiment: single-mirror feedback system insert square aperture, slightly truncating input beam (diffractive ripples) input beam 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) Schaepers et al., Proc. SPIE 4271, 130 (2001)

  14. CS-based optical memory ? • so it seems that a CS-based optical memory will work • but: CS are „large“ - some micrometers medium Gbit/inch2 bit/mm2 CD 0.7 GB 0.05 0.1 DVD 4.7 GB 0.35 0.5 blu-ray 25 GB 1.9 2.9 blu-ray 100 GB 7.5 11.6 holografic storage 515 800 very best hard discs 300 470 • simple memories won‘t 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. this is cycling speed ! Hau et al., Nature397, 594(1999) „Slow light“ Boyd et al., OPN17(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., OPN17(4)18(2006)

  18. read out at other side all-optical delay line buffer register • time delayed version of input train • note: won‘t work for non-solitons / diffractive beams movie All-optical delay line parameter gradient inject train of solitons here • for free: serial to parallel conversion and beam fanning Harkness et al., CNQO, U Strathclyde (1998)

  19. adressing beam Na AOM tilt of mirror  soliton drifts holding beam B t = 0 ms t = 16 ms t = 32 ms t = 48 ms t = 64 ms t = 80 ms ignition of soliton by addressing beam proof of principle, quite slow, but in a semiconductor microresonator this is different ! Experimental realization sodium vapor driven in vicinity of D1-line with single feedback mirror Schäpers et. al., Proc. SPIE 4271, 130 (2001)

  20. First experiments in semiconductors spatio-temporal detection system: 6 local detectors + synchronized digital oscilloscopes BW about 300 MHz VCSEL (UP) 200 µm diameter quite homogeneous cavity resonance pumped above transparency but below threshold  amplifier F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished

  21. Experimental results • proof for drifting structures was found • triggering by optical address pulse possible • demonstration of embryonic all-optical delay line • however, data need more analysis before released to public in a written form • apologies for that F. Pedaci, S. Barland, M. Giudici, J. Tredicce, INLN, Nice, unpublished

  22. A theoretical analog !? 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 J. McSloy, PhD thesis, 2002; cf. also Scroggie, PRE66, 036607(2002); Tissoni, Opt. Exp. 10_1009(2002).

  23. saturation speed limit  1.5 µm/ns Velocity • experiment suggests velocity of about 2 µm / ns = 2000 m / s = 7200 km / h > supersonic jet ! • theoretical expectationhere amplifier model(‚standard‘ parameters) • perturbative regime sorry, again analysis ongoing • semi-quantitative agreement fortutious (at present stage) Tissoni et al., unpublished; see also Kheramand et al., Opt. Exp. 11, 3612(2003)

  24. even this makes sense with experiment Bandwidth and bit rate • velocity: 2 µm / ns • CS diameter typically 10 µm  a local detector would see a signal of length 10 µm/(2 µm/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  d-response some ns 10 µm / 3 ns = 3.3 µm /ns  origin of numerically observed saturation behaviour

  25. „Slow media“: Non-instantaneous Kerr cavity g 0.01  semiconductor • velocity determined by response time • saturation for instantaneous medium  • faster medium will speed up response ! log (velocity / gradient) slope 1 • 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 log (g) A. Scroggie, Strathclyde, unpublished (1D, perturbation analysis)

  26. „Conventional“ approaches to slow light • modification of group velocity in vicinity of a resonance • two-level atom • electro-magnetically induced transparency • cavity resonance • .... • large effect needs steep slope, narrow resonance • bandwidth limited by • absorption • high-order dispersion Hau et al., Nature397, 594(1999)

  27. 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 1Tucker et al., Electron. Lett. 41, 208 (2005); 2Dahan, OptExp13, 6234(2005); 3GonsalezHerraez, APL87081113(2005); 4ChangHasnainProcIEE 911884(2003); 5Ku et al., OptLett29, 2291(2004); 5Hau et al., Nature 397, 594 (1999)

  28. Résumé: CS-based delay line other: wavelength-conversion by FOPA + dispersive fiber + back-conversion • drifting CS are a quite different approach to slow light pros and contras should be assessed • potentially very large delays • lot‘s of things to do • theory: saturation behaviour patterning effectst N = - A N – B N2 – C N3 +... • 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) McSloy, Strathclyde

  29. 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., PRL96, 033905, 2006) • characterize homogeneity of cavity resonance of a microcavity (INLN, Nice)

  30. with injection • left-right asymmetry • gradient in detuning • gradient in cavity resonance Broad-area microcavity laser 150 µm diameter VCSEL free-running this gradient was mapped out by other (tedious) experiments to be 400 GHz/150 µm Another clever way? Barland et al., Nature419, 699(2002)

  31. 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, APB83, 2303(2003)

  32. Quantitative linear relation  351 GHz / 150 µm Barland et al, APB83, 2303(2003)

  33. Soliton force microscope map relative – possibly absolute – gradients in transverse plane by measuring the displacement between CS and a (small-amplitude) steering beam W. J. Firth, Strathclyde Local probing • 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? Hachair et al., INLN, Nice; similar to X. Hachair et al., PRA69(2004)043817

  34. blow up add focused steering beam (addressing beam) CS moves to new equilibrium Idea of soliton force microscopy CS in a trap • measure displacement  infer relative local curvature (for fixed amplitude) • changing amplitude + calibrations  „absolute“ local curvature • „inverse“ problem: disentangle phase- and amplitude contributionsidentify origin of inhomogeneity

  35. 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-lockedCSL • array of self-pulsing laser sources  carrier pulse trains with highrepetition rate in a large number of output channels • all-optical control  „high-frequency carrier pulse train on demand“ e.g. Stubkjaer, IEEESel. Top. QE6,1428(2000)

  36. Anticipated scheme control beams • de-multiplexing • optical regeneration • routing • timescales  packet manipulation • advanced schemes might use plasticity ofCLB  processing, direct routing self-pulsing CSL pulse train time

  37. utilize plasticity • continuous Summary: Cavity solitons versus „pixels“ broad-area laser with CS array of micro-fabricated bistable elements • bistable • memory • switch • optical processing • discrete • 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

  38. cavity soliton laser Desirable Features and Systems • compact • integration • fast • robust (monolithic) semiconductor microcavity • moderate power requirements • cascadable active system amplifier or laser self-sustained laser incoherent switching of CS (or propagation in amplifier) • robust (phase-insensitive)

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