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Investigations into the manner in which the brain incorporates prior knowledge to accelerate information processing in general and object recognition in particular: this research is performed in collaboration with biologists, cognitive psychologists, computational scientists and philosophers of perception. The most recent approach to these questions probes the extraordinary capabilities of autistic child artists.
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We give the first closed form exact expression for the dynamical evolution of nonstationary beams of arbitrary intensity and width propagating in a uniform nonlinear medium and in both two and three dimensions. This shows that periodic and quasi-periodic (non-radiating) beams can exist in a non-Kerr nonlinear medium. The Schrödinger equation is solved for Gaussian beams in a saturable medium. For one critical (initial) beam width, the Gaussian is a stable stationary soliton or bullet, independent of its intensity; otherwise, it breathes. New quasi periodic beams (mighty morphing solitons) and bullets (mighty morphs) of elliptical cross section also exist whose ellipticity changes with propagation.
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Using only intuitive physics, it is possible to `read' the stability and qualitative characteristics of all self guided (bounded) beams directly from the graph of refractive index vs intensity that characterizes any nonlinear medium. This approach predicts new soliton classes. It reveals important differences between solitons of one and two-transverse dimensions. It links the physical characteristics of solitons and their possible multistabilities directly with topological features of the material nonlinearity, n(I).
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Different types of dark solitons and their properties have been analysed. For the first time, the perturbation theory and Lagrangian formalism for dark solitons have been elaborated. Several important physical problems, including the effect of two-photon absorption on dark solitons and transverse instability of dark solitons (recently verified in the School's Laser Physics Centre (LPC) and ring dark solitons (recently discovered in Bulgaria), have been solved with the help of this approach.
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General criteria for the stability of dark solitons and multi-parameter vector solitons, have been obtained for the first time. This approach also helped to solve the problem of the temporal jitter on dark solitons in a system with periodical amplifiers, which seems to be an important step for understanding a possible use of dark solitons for long-distance communication systems recently achieved at NTT, Japan.
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Bright, dark, and gap optical solitons in a diffractive (or dispersive) medium with quadratic nonlinearities have been analyzed. The classification and stability of these solitons have been considered for the first time. Some of the results have already found experimental verification in the USA and Germany. These solitons can also be described from a linear perspective.
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Stable dark optical bullets in optical self trapping, and parametric solitons for wavelength division multiplexing information transmission, have been discovered. Delineation of the difference in polarisation instabilities of birefringent fibres between continuous waves and solitons, prediction of the onset of chaos in periodically mismatched nonlinear couplers, and derivation of stability criteria for black, grey and bright nonlinear guided waves in a thin film bounded by a self defocussing medium have recently been achieved.
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Novel planar optical devices, such as splitters, mode combiners, separators and transformers, multiport couplers, multilayered guides, grating-assisted devices and planar graded index lenses, are being devised for a broad range of applications, including optoelectronic lenses circuitry, telecommunications networks, optical sensing and confocal microscopy. The experimental work is being undertaken in collaboration with LPC, the Plasma Research Laboratory (PRL) and the Australian Photonics CRC.
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Practical application-specific fibres, such as multicore fibre devices and capillary and evanescent fields for optical sensing, as well as optimised fibre devices, including multicore connectors, grating-assisted wavelength demultiplexers and hybrid couplers for confocal microscopy applications have been developed.
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Colliding solitons can create an intricate distribution of refractive index through the nonlinear properties of the medium. For example, two solitons colliding at an angle will pass through each other and leave behind them two intersecting waveguides: an X-junction. This junction possesses the quality of being totally lossless. One can create a completely transparent junction where the light input in one arm stays in that arm when crossing the junction. Such a junction, and other types of similar devices may have application in integrated optics.
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Using the photosensitivity of germanium-doped silica, waveguiding structures can be optically written using ultra-violet light. It is conceivable that entire optical circuits could be written this way including the waveguides themselves alongside structures such as gratings, couplers, interferometers, etc.
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The theory of soliton evolution in optical systems with gain and loss based on the complex Ginzburg-Landau equation, including optical transmission lines as well as laser systems has been developed. New regimes of pulse propagation have been discovered. These results are important for high bit-rate optical telecommunication links and their components: sources for soliton generation, all-optical amplifiers, etc.
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The development of a method which leads to solutions of the linear Schrödinger equation with the potential given by the nonlinear Schrodinger equation: This method reveals new classes of time- and space-dependent, exactly solvable potentials for the Schrödinger equation. It also allows quantitative characterisation for light-guiding-light phenomena, and the exact calculation of transfer matrices for elements in integrated optics, and qualitative interpretation of the soliton theory.
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Professor and Head of Centre
A.W. Snyder, SM MIT, MS Harv, PhD DSc Lond, FAA, FTS, FRS
Professors
D.J. Mitchell, BSc Syd, PhD NSW
J.D. Love, MA Camb, MA DPhil DSc Oxf
(from 23 July)
Senior Fellows
N. Akhmediev, DSc USSR Acad Sci
J.D. Love, MA Camb, MA DPhil DSc Oxf
(until 22 July)
Yu. Kivshar, PhD USSR Acad Sci
ARC Senior Research Fellows
A. Ankiewicz, BSc BE UNSW, PhD
Y. Chen, BSc MS PhD Shang
Research Fellow
F. Ladouceur, BSc, MSc, Montréal, PhD
Postdoctoral Fellows
V. Afanasjev, PhD USSR Acad Sci (until August)
O. Bang, MSc PhD Tech U of Denmark
I. Gold, BA MA McGill, MSc Rutgers, PhD Princeton
P. Miller, BS Southern Methodist U, MS PhD Arizona
Visiting Fellows
W.M. Henry, BSc PhD
A. Hughes, MA Oxf, PhD DSc Edin
W.S. Jagger, BA Yale, PhD Phil
S.B. Poole, BSc Nott, PhD South'n
S.C. Rashleigh, BE PhD Qld
M.G. Sceats, BSc PhD Qld
R.S. Tucker, BE PhD Melb
Departmental Administrator
A.G. Robins