Photonics Group (Prof. Dumitru Mihalache)

Group leader - Professor Dumitru Mihalache

Department of Theoretical Physics

The National Institute for Physics and Nuclear Engineering “Horia Hulubei”

In the course of the last decade, a new level of understanding has been achieved about conditions for the existence, stability and excitation of solitary waves in both conservative (Hamiltonian) and dissipative nonlinear optical media.
Novel results in the area of spatiotemporal optical solitons (light bullets) have been obtained in both phenomenological models and those obtained from the first principles (first of all, the one based on quadratic optical nonlinearities). Prof. Mihalache has published in J. Opt. B an overview of spatiotemporal optical solitons in collaboration with Prof. B. A. Malomed, Tel-Aviv University, Prof. F. Wise, Cornell University, and Prof. L. Torner, ICFO-Institute de Ciencies Fotoniques, Barcelona). Recently, in collaboration with Prof. H. Leblond, Angers University, France, an adequate description of few-cycle optical solitons beyond the slowly varying envelope approximation was given:

B. A. Malomed, D. Mihalache, F. Wise, and L. Torner, J. Opt. B Quantum Semiclassical Opt. 7, R53-R72 (2005).

H. Leblond and D. Mihalache, Phys. Rev. A 79, 063835 (2009).

H. Leblond, D. Kremer, and D. Mihalache, Phys. Rev. A 80, 053812 (2009).

Main results

We demonstrated the existence of stable vortex tori in the 3D cubic-quintic Ginzburg-Landau equation (in collaboration with Prof. B. A. Malomed, Tel Aviv University, Dr. L.-C. Crasovan, Dr. Y. V. Kartashov and Prof. L. Torner, ICFO-Institut de Ciencies Fotoniques, Barcelona, Spain, and Prof. F. Lederer, Jena University), see Phys. Rev. Lett. 97, 073904 (2006).

The study of existence and stability of three-dimensional solitons supported by cylindrical Bessel lattices in self-focusing media. The Hamiltonian versus soliton energy diagram features a "swallowtail" bifurcation pattern. The model applies to Bose-Einstein condensates and to optical media with saturable nonlinearity, suggesting new ways of making stable three-dimensional solitons and "light bullets" of an arbitrary size (in collaboration with Prof. B. A. Malomed, Tel Aviv University, Dr. L.-C. Crasovan, Dr. Y. V. Kartashov and Prof. L. Torner, ICFO-Institut de Ciencies Fotoniques, Barcelona, Spain, and Prof. F. Lederer, Jena University), see Phys. Rev. Lett. 95, 023902 (2005).

The concept of “walking solitons” in quadratically nonlinear optical media (in collaboration with Prof. L. Torner, ICFO-Institut de Ciencies Fotoniques, Universitat Politecnica de Catalunya, Barcelona, Spain), see Phys. Rev. Lett. 77, 2455-2458 (1996).

The stability of two-parameter families of “walking vector solitons”. We found that the soliton instability is characterized by the occurrence of complex eigenvalues of the Lyapunov operator, leading to “oscillatory instabilities”, see Phys. Rev. Lett. 81, 4353-4356 (1998).

The prediction of stable spinning three-dimensional solitons, which is the second (after Skyrmions) example of localized physical objects of that type known in physics (in collaboration with Prof. B. A. Malomed, Tel Aviv University, Prof. L. Torner, and Prof. F. Lederer, Jena University), see Phys. Rev. Lett. 88, 073902 (2002).

The prediction of robust propagation of quasistable two-color soliton clusters in media with competing quadratic and cubic self-defocusing nonlinearities (in collaboration with Dr. Ya. V. Kartashov, M. V. Lomonosov Moscow State University, Moscow, Russia, Dr. L.-C. Crasovan, and Prof. L. Torner), see Phys. Rev. Lett. 89, 273902 (2002).

The possibility of tailoring, or even arresting, the collapse of wave packets in nonlinear optical media, whose dynamics is governed by nonlocal two-dimensional nonlinear Schroedinger-like equations. The key ingredient of the proposed scheme is the self-generation of nonlocal optical nonlinearities mediated by wave rectification (in collaboration with Dr. L.-C. Crasovan, Dr. J. P. Torres, and Prof. L. Torner), see Phys. Rev. Lett. 91, 063904 (2003).

Main research directions

Spatiotemporal solitons

A new topic in both theoretical and experimental studies of optical solitons is provided by the possibility of existence of spatiotemporal optical solitons (sometimes called “light bullets” or “superspikes”), which are completely localized pulses of light. These fully localized spatiotemporal physical objects result from the simultaneous balance of diffraction and dispersion by nonlinear phase modulation.
They hold promise for potential applications in ultrafast all-optical processing devices, where each spatiotemporal soliton may represent an elementary bit of information, provided that stable solitons can be formed from pulses at reasonable energy levels in available optical materials.

Solitons in quadratic nonlinear media

The quadratic solitons in optical media are intrinsically multi-component (multi-color) localized states of light, which can exist in media without inversion symmetry. They may occur as spatial localized beams or temporal nondispersive pulses, or as spatiotemporal optical solitons (non-diffracting, non-dispersing self-trapped three-dimensional light signals). They might be the ultimate bits of information in future light processing devices.

Solitons in cubic and saturable nonlinear media

The main research interest is the study of temporal solitons in optical fibers, which are bell-shaped light pulses that under appropriate conditions can propagate without distortion for large distances. In optical fibers they typically form with short pulses (~20 ps) that keep in balance temporal broadening due to chromatic dispersion and spectral broadening due to self-phase modulation. Fiber solitons enjoy a truly remarkable stability against perturbations, including noise, periodic all-optical amplification and cross-talk.

Solitons in dissipative media

Dissipative solitons (or more properly dissipative solitary waves) are “nonlinear modes” of non-integrable non-Hamiltonian physical systems. Dissipative optical solitons occur as ultra-short pulses generated by laser systems, dispersion-managed solitons in all-optical transmission systems with gain and loss, spatial solitons in wide aperture lasers, cavity solitons, etc.
New kind of multidimensional non-spinning and spinning solitons (spiral waves) described by the cubic-quintic Ginzburg-Landau equation were studied.

Vortices in Bose-Einstein condensates

Vortices are ubiquitous physical entities that have been observed in almost all branches of physics. They appear as flows in hydrodynamics, persistent currents in superfluids, nested phase singularities in optical fields or vortex lines in Bose-Einstein condensates.
We investigate new stable families of topological excited collective states of condensed atoms (tightly confined non-rotating symmetric and asymmetric Bose-Einstein condensates).