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Articles 1 - 28 of 28
Full-Text Articles in Physics
Robustness And Mode Selectivity In Parity-Time (Pt) Symmetric Lasers, M. H. Teimourpour, M. Khajavikhan, Demetrios N. Christodoulides, Ramy El-Ganainy
Robustness And Mode Selectivity In Parity-Time (Pt) Symmetric Lasers, M. H. Teimourpour, M. Khajavikhan, Demetrios N. Christodoulides, Ramy El-Ganainy
Ramy El-Ganainy
We investigate two important aspects of PT symmetric photonic molecule lasers, namely the robustness of their single longitudinal mode operation against instabilities triggered by spectral hole burning effects, and the possibility of more versatile mode selectivity. Our results, supported by numerically integrating the nonlinear rate equations and performing linear stability analysis, reveals the following: (1) In principle a second threshold exists after which single mode operation becomes unstable, signaling multimode oscillatory dynamics, (2) For a wide range of design parameters, single mode operation of PT lasers having relatively large free spectral range (FSR) can be robust even at higher gain …
Non-Hermitian Matter-Wave Mixing In Bose-Einstein Condensates: Dissipation-Induced Amplification, S. Wuster, Ramy El-Ganainy
Non-Hermitian Matter-Wave Mixing In Bose-Einstein Condensates: Dissipation-Induced Amplification, S. Wuster, Ramy El-Ganainy
Ramy El-Ganainy
We investigate the nonlinear scattering dynamics in interacting atomic Bose-Einstein condensates under non-Hermitian dissipative conditions. We show that, by carefully engineering a momentum-dependent atomic loss profile, one can achieve matter-wave amplification through four-wave mixing in a quasi-one-dimensional nearly-free-space setup—a process that is forbidden in the counterpart Hermitian systems due to energy mismatch. Additionally, we show that similar effects lead to rich nonlinear dynamics in higher dimensions. Finally, we propose a physical realization for selectively tailoring the momentum-dependent atomic dissipation. Our strategy is based on a two-step process: (i) exciting atoms to narrow Rydberg or metastable excited states, and (ii) introducing …
Power-Law Scaling Of Extreme Dynamics Near Higher-Order Exceptional Points, Q. Zhong, Demetrios N. Christodoulides, M. Khajavikhan, K. G. Makris, Ramy El-Ganainy
Power-Law Scaling Of Extreme Dynamics Near Higher-Order Exceptional Points, Q. Zhong, Demetrios N. Christodoulides, M. Khajavikhan, K. G. Makris, Ramy El-Ganainy
Ramy El-Ganainy
We investigate the extreme dynamics of non-Hermitian systems near higher-order exceptional points in photonic networks constructed using the bosonic algebra method. We show that strong power oscillations for certain initial conditions can occur as a result of the peculiar eigenspace geometry and its dimensionality collapse near these singularities. By using complementary numerical and analytical approaches, we show that, in the parity-time (PT) phase near exceptional points, the logarithm of the maximum optical power amplification scales linearly with the order of the exceptional point. We focus in our discussion on photonic systems, but we note that our results apply to other …
Topological Hybrid Silicon Microlasers, Han Zhao, Pei Mao University Of Pennsylvania, Mohammad H. Teimourpour, Simon Malzard, Ramy El-Ganainy, Henning Schomerus, Liang Feng
Topological Hybrid Silicon Microlasers, Han Zhao, Pei Mao University Of Pennsylvania, Mohammad H. Teimourpour, Simon Malzard, Ramy El-Ganainy, Henning Schomerus, Liang Feng
Ramy El-Ganainy
Topological physics provides a robust framework for strategically controlling wave confinement and propagation dynamics. However, current implementations have been restricted to the limited design parameter space defined by passive topological structures. Active systems provide a more general framework where different fundamental symmetry paradigms, such as those arising from non-Hermiticity and nonlinear interaction, can generate a new landscape for topological physics and its applications. Here, we bridge this gap and present an experimental investigation of an active topological photonic system, demonstrating a topological hybrid silicon microlaser array respecting the charge-conjugation symmetry. The created new symmetry features favour the lasing of a …
Non-Hermitian Engineering Of Single Mode Two Dimensional Laser Arrays, M. H. Teimourpour, Li Ge, Demetrios N. Christodoulides, Ramy El-Ganainy
Non-Hermitian Engineering Of Single Mode Two Dimensional Laser Arrays, M. H. Teimourpour, Li Ge, Demetrios N. Christodoulides, Ramy El-Ganainy
Ramy El-Ganainy
A new scheme for building two dimensional laser arrays that operate in the single supermode regime is proposed. This is done by introducing an optical coupling between the laser array and lossy pseudo-isospectral chains of photonic resonators. The spectrum of this discrete reservoir is tailored to suppress all the supermodes of the main array except the fundamental one. This spectral engineering is facilitated by employing the Householder transformation in conjunction with discrete supersymmetry. The proposed scheme is general and can in principle be used in different platforms such as VCSEL arrays and photonic crystal laser arrays.
Non-Hermitian Engineering Of Synthetic Saturable Absorbers For Applications In Photonics, M. H. Teimourpour, A. Rahman, K. Srinivasan, Ramy El-Ganainy
Non-Hermitian Engineering Of Synthetic Saturable Absorbers For Applications In Photonics, M. H. Teimourpour, A. Rahman, K. Srinivasan, Ramy El-Ganainy
Ramy El-Ganainy
We explore a type of synthetic saturable absorber based on quantum-inspired photonic arrays. We demonstrate that the interplay between optical Kerr nonlinearity, interference effects, and non-Hermiticity through radiation loss leads to a nonlinear optical filtering response with two distinct regimes of small and large optical transmissions. More interestingly, we show that the boundary between these two regimes can be very sharp. The threshold optical intensity that marks this abrupt “phase transition” and its steepness can be engineered by varying the number of the guiding elements. The practical feasibility of these structures as well as their potential applications in laser systems …
Supersymetric Laser Arrays, Ramy El-Ganainy, Li Ge, M. Khajavikhan, Demetrios N. Christodoulides
Supersymetric Laser Arrays, Ramy El-Ganainy, Li Ge, M. Khajavikhan, Demetrios N. Christodoulides
Ramy El-Ganainy
We introduce the concept of supersymmetric laser arrays that consist of a main optical lattice and its superpartner structure, and we investigate the onset of their lasing oscillations. Due to the coupling of the two constituent lattices, their degenerate optical modes form doublets, while the extra mode associated with unbroken supersymmetry forms a singlet state. Singlet lasing can be achieved for a wide range of design parameters, either by introducing stronger loss in the partner lattice or by pumping only the main array. Our findings suggest the possibility of building single-mode, high-power laser arrays and are also important for understanding …
Topological Tight-Binding Models From Nontrivial Square Roots, J. Arkinstall, M. H. Teimourpour, L. Feng, Ramy El-Ganainy, H. Schomerus
Topological Tight-Binding Models From Nontrivial Square Roots, J. Arkinstall, M. H. Teimourpour, L. Feng, Ramy El-Ganainy, H. Schomerus
Ramy El-Ganainy
We describe a versatile mechanism that provides tight-binding models with an enriched, topologically nontrivial band structure. The mechanism is algebraic in nature, and leads to tight-binding models that can be interpreted as a nontrivial square root of a parent lattice Hamiltonian—in analogy to the passage from a Klein-Gordon equation to a Dirac equation. In the tight-binding setting, the square-root operation admits to induce spectral symmetries at the expense of broken crystal symmetries. As we illustrate in detail for a simple one-dimensional example, the emergent and inherited spectral symmetries equip the energy gaps with independent topological quantum numbers that control the …
Accelerating Diffraction-Free Beams In Photonic Lattices, K. Makris, I. Kaminer, Ramy El-Ganainy, N. Efremidis, Zhigang Chen, M. Segev, Demetrios Christodoulides
Accelerating Diffraction-Free Beams In Photonic Lattices, K. Makris, I. Kaminer, Ramy El-Ganainy, N. Efremidis, Zhigang Chen, M. Segev, Demetrios Christodoulides
Ramy El-Ganainy
We study nondiffracting accelerating paraxial optical beams in periodic potentials, in both the linear and the nonlinear domains. In particular, we show that only a unique class of z-dependent lattices can support a true accelerating diffractionless beam. Accelerating lattice solitons, autofocusing beams and accelerating bullets in optical lattices are systematically examined.
On-Chip Multi 4-Port Optical Circulators, Ramy El-Ganainy, Miguel Levy
On-Chip Multi 4-Port Optical Circulators, Ramy El-Ganainy, Miguel Levy
Ramy El-Ganainy
We present a new geometry for on-chip optical circulators based on waveguide arrays. The optical array is engineered to mimic the Fock space representation of a noninteracting two-site Bose–Hubbard Hamiltonian. By introducing a carefully tailored magnetooptic nonreciprocity to these structures, the array operates in the perfect transfer and surface Bloch oscillation modes in the forward and backward propagation directions, respectively. We show that an array made of ð2N þ 1Þ waveguide channels can function as N 4-port optical circulators with very large isolation ratios and low forward losses. Numerical analysis using beam propagation method indicates a large bandwidth of operation.
Light Transport In Pt-Invariant Photonic Structures With Hidden Symmetries, M. H. Teimourpour, Ramy El-Ganainy, A. Eisfeld, A. Szameit, Demetrios N. Christodoulides
Light Transport In Pt-Invariant Photonic Structures With Hidden Symmetries, M. H. Teimourpour, Ramy El-Ganainy, A. Eisfeld, A. Szameit, Demetrios N. Christodoulides
Ramy El-Ganainy
We introduce a recursive bosonic quantization technique for generating classical PT photonic structures that possess hidden symmetries and higher order exceptional points. We study light transport in these geometries and we demonstrate that perfect state transfer is possible only for certain initial conditions. Moreover, we show that for the same propagation direction, left and right coherent transports are not symmetric with field amplitudes following two different trajectories. A general scheme for identifying the conservation laws in such PT-symmetric photonic networks is also presented.
Exceptional Points And Lasing Self-Termination In Photonic Molecules, Ramy El-Ganainy, M. Khajavikhan, Li Ge
Exceptional Points And Lasing Self-Termination In Photonic Molecules, Ramy El-Ganainy, M. Khajavikhan, Li Ge
Ramy El-Ganainy
We investigate the rich physics of photonic molecule lasers using a non-Hermitian dimer model.We show that several interesting features, predicted recently using a rigorous steady-state ab initio laser theory (SALT), can be captured by this toy model. In particular, we demonstrate the central role played by exceptional points (EPs) in both pump-selective lasing and laser self-termination phenomena. Due to its transparent mathematical structure, our model provides a lucid understanding for how different physical parameters (optical loss, modal coupling between microcavities, and pump profiles) affect the lasing action. Interestingly, our analysis also confirms that, for frequency mismatched cavities, operation in the …
On-Chip Non-Reciprocal Optical Devices Based On Quantum Inspired Photonic Lattices, Ramy El-Ganainy, A. Eisfeld, Miquel Levy, Demetrios N. Christodoulides
On-Chip Non-Reciprocal Optical Devices Based On Quantum Inspired Photonic Lattices, Ramy El-Ganainy, A. Eisfeld, Miquel Levy, Demetrios N. Christodoulides
Ramy El-Ganainy
We propose integrated optical structures that can be used as isolators and polarization splitters based on engineered photonic lattices. Starting from optical waveguide arrays that mimic Fock space (quantum state with a well-defined particle number) representation of a non-interacting two-site Bose Hubbard Hamiltonian, we show that introducing magneto-optic nonreciprocity to these structures leads to a superior optical isolation performance. In the forward propagation direction, an input TM polarized beam experiences a perfect state transfer between the input and output waveguide channels while surface Bloch oscillations block the backward transmission between the same ports. Our analysis indicates a large isolation ratio …
Supersymmetric Mode Converters, Matthias Heinrich, Mohammad-Ali Miri, Simon Stützer, Ramy El-Ganainy, Stefan Nolte, Alexander Szameit, Demetrios N. Christodoulides
Supersymmetric Mode Converters, Matthias Heinrich, Mohammad-Ali Miri, Simon Stützer, Ramy El-Ganainy, Stefan Nolte, Alexander Szameit, Demetrios N. Christodoulides
Ramy El-Ganainy
Originally developed in the context of quantum field theory, the concept of supersymmetry can be used to systematically design a new class of optical structures. In this work, we demonstrate how key features arising from optical supersymmetry can be exploited to control the flow of light for mode division multiplexing applications. Superpartner configurations are experimentally realized in coupled optical networks, and the corresponding light dynamics in such systems are directly observed. We show that supersymmetry can be judiciously utilized to remove the fundamental mode of a multimode optical structure, while establishing global phase matching conditions for the remaining set of …
Enhancing Optical Isolator Performance In Nonreciprocal Waveguide Arrays, Miguel Levy, Turhan Carroll, Ramy El-Ganainy
Enhancing Optical Isolator Performance In Nonreciprocal Waveguide Arrays, Miguel Levy, Turhan Carroll, Ramy El-Ganainy
Ramy El-Ganainy
We investigate the operation of optical isolators based on magneto-optics waveguide arrays beyond the coupled mode analysis. Semi-vectorial beam propagation simulations demonstrate that evanescent tail coupling and the effects of radiation are responsible for degrading the device’s performance. Our analysis suggests that these effects can be mitigated when the array size is scaled up. In addition, we propose the use of radiation blockers in order to offset some of these effects, and we show that they provide a dramatic improvement in performance. Finally, we also study the robustness of the system with respect to fabrication tolerances using the coupled mode …
Observation Of Accelerating Wannier-Stark Beams In Optically Induced Photonic Lattices, Xinyuan Qi, Konstantinos Makris, Ramy El-Ganainy, Peng Zhang, Jintao Bai, Demetrios Christodoulides, Zhigang Chen
Observation Of Accelerating Wannier-Stark Beams In Optically Induced Photonic Lattices, Xinyuan Qi, Konstantinos Makris, Ramy El-Ganainy, Peng Zhang, Jintao Bai, Demetrios Christodoulides, Zhigang Chen
Ramy El-Ganainy
We generate optical beams analogous to the Wannier–Stark states in semiconductor superlattices and observe that the two main lobes of the WS beams self-bend (accelerate) along two opposite trajectories in a uniform one-dimensional photonic lattice. Such self-accelerating features exist only in the presence of the lattice and are not observed in a homogenous medium. Under the action of nonlinearity, however, the beam structure and acceleration cannot be preserved. Our experimental observations are in qualitative agreement with theoretical predictions.
Resonant Dipole-Dipole Interaction In Confined And Strong-Coupling Dielectric Geometries., Ramy El-Ganainy, Sajeev John
Resonant Dipole-Dipole Interaction In Confined And Strong-Coupling Dielectric Geometries., Ramy El-Ganainy, Sajeev John
Ramy El-Ganainy
Using the electromagnetic response function of an electric dipole located within a dielectric geometry, we derive the mathematical equivalence between the classical response and quantum mechanical resonant dipole–dipole interaction between two quantum objects (atoms, quantum dots, etc). Cooperative spontaneous emission likewise emerges from this equivalence. We introduce a practical numerical technique using finite difference time domain for calculating both dipole–dipole interaction and collective spontaneous emission in confined dielectric structures, where strong light–matter coupling might arise. This method is capable of obtaining resonant dipole–dipole interaction over a wide range of frequencies in a single run. Our method recaptures the results of …
Supersymmetric Optical Structures, Mohammad-Ali Miri, Matthias Heinrich, Ramy El-Ganainy, Demetrios N. Christodoulides
Supersymmetric Optical Structures, Mohammad-Ali Miri, Matthias Heinrich, Ramy El-Ganainy, Demetrios N. Christodoulides
Ramy El-Ganainy
We show that supersymmetry can provide a versatile platform in synthesizing a new class of optical structures with desired properties and functionalities. By exploiting the intimate relationship between superpartners, one can systematically construct index potentials capable of exhibiting the same scattering and guided wave characteristics. In particular, in the Helmholtz regime, we demonstrate that one-dimensional supersymmetric pairs display identical reflectivities and transmittivities for any angle of incidence. Optical supersymmetry is then extended to two-dimensional systems where a link between specific azimuthal mode subsets is established. Finally, we explore supersymmetric photonic lattices where discreteness can be utilized to design lossless integrated …
Enhanced Optical Anderson Localization Effects In Modulated Bloch Lattices, Ramy El-Ganainy, Mohammad-Ali Miri, Demetrios N. Christodoulides
Enhanced Optical Anderson Localization Effects In Modulated Bloch Lattices, Ramy El-Ganainy, Mohammad-Ali Miri, Demetrios N. Christodoulides
Ramy El-Ganainy
We study Anderson localization dynamics in periodically modulated optical Bloch arrays. Using an effective model, we show that, in such arrangements, even a weak disorder may play an important role and can lead to enhanced Anderson localization effects.
Local Pt Invariance And Supersymmetric Parametric Oscillators, Ramy El-Ganainy, Konstantinos G. Makris, Demetrios N. Christodoulides
Local Pt Invariance And Supersymmetric Parametric Oscillators, Ramy El-Ganainy, Konstantinos G. Makris, Demetrios N. Christodoulides
Ramy El-Ganainy
We introduce the concept of local parity-time symmetric (PT) invariance in optical waveguides (or cavity) structures. Starting from a Lagrangian formalism, we establish the connection between light dynamics in these configurations and the seemingly different physics of “supersymmetric” parametric oscillators. Using this powerful tool, we present analytical solutions for optical beam propagation in local PT-invariant coupled systems and we show that the intensity tunneling between the two channels critically depends on the initial conditions. For unbalanced inputs, symmetric as well as asymmetric power evolution can be observed depending on the excitation channel. On the other hand, under certain physical conditions, …
Discrete Beam Acceleration In Uniform Waveguide Arrays, Ramy El-Ganainy, Konstantinos G. Makris, Mohammad-Ali Miri, Demetrios N. Christodoulides, Zhigang Chen
Discrete Beam Acceleration In Uniform Waveguide Arrays, Ramy El-Ganainy, Konstantinos G. Makris, Mohammad-Ali Miri, Demetrios N. Christodoulides, Zhigang Chen
Ramy El-Ganainy
Within the framework of the tight-binding model we demonstrate that Wannier-Stark states can freely accelerate in uniform optical lattices. As opposed to accelerating Airy wave packets in free space, our analysis reveals that in this case the beam main intensity features self-bend along two opposite hyperbolic trajectories. Two-dimensional geometries are also considered and an asymptotic connection between these Wannier-Stark ladders and Airy profiles is presented.
Unidirectional Nonlinear Pt-Symmetric Optical Structures, Hamidreza Ramezani, Tsampikos Kottos, Ramy El-Ganainy, Demetrios N. Christodoulides
Unidirectional Nonlinear Pt-Symmetric Optical Structures, Hamidreza Ramezani, Tsampikos Kottos, Ramy El-Ganainy, Demetrios N. Christodoulides
Ramy El-Ganainy
We show that nonlinear optical structures involving a balanced gain-loss profile can act as unidirectional optical valves. This is made possible by exploiting the interplay between the fundamental symmetries of parity (P) and time (T), with optical nonlinear effects. This unidirectional dynamics is specifically demonstrated for the case of an integrable PT -symmetric nonlinear system.
Pt-Symmetric Optical Lattices, Konstantinos G. Makris, Ramy El-Ganainy, Demetrios N. Christodoulides, Z. H. Musslimani
Pt-Symmetric Optical Lattices, Konstantinos G. Makris, Ramy El-Ganainy, Demetrios N. Christodoulides, Z. H. Musslimani
Ramy El-Ganainy
The basic properties of Floquet-Bloch (FB) modes in parity-time (PT )-symmetric optical lattices are examined in detail. Due to the parity-time symmetry of such complex periodic potentials, the corresponding FB modes are skewed (nonorthogonal) and nonreciprocal. The conjugate pairs of these FB modes are obtained by reflecting both the spatial coordinate and the Bloch momentum number itself. The orthogonality conditions are analytically derived for a single cell, for both a finite and an infinite lattice. Some of the peculiarities associated with the diffraction dynamics in PT lattices such as nonreciprocity, power oscillations, and phase dislocations, are also examined.
Light-Induced Self-Synchronizing Flow Patterns, Elad Greenfield, Carmel Rotschild, Alexander Szameit, Jonathan Nemirovsky, Ramy El-Ganainy, Demetrios N. Christodoulides, Meirav Saraf, Efrat Lifshitz, Mordechai Segev
Light-Induced Self-Synchronizing Flow Patterns, Elad Greenfield, Carmel Rotschild, Alexander Szameit, Jonathan Nemirovsky, Ramy El-Ganainy, Demetrios N. Christodoulides, Meirav Saraf, Efrat Lifshitz, Mordechai Segev
Ramy El-Ganainy
In this paper, we present the observation of light-induced self-synchronizing flow patterns in a light–fluid system. A light beam induces local flow patterns in a fluid, which oscillate periodically or chaotically in time. The oscillations within different regions of the fluid interact with each other through heat- and surface-tension-induced fluid waves, and they become synchronized. We demonstrate optical control over the state of synchronization and over the temporal correlation between different parts of the flow field. Finally, we provide a model to elucidate these results and we suggest further ideas on light controlling flow and vice versa.
Optical Control Of Thermocapillary Effects In Complex Nanofluids, Yuval Lamhot, Assaf Barak, Carmel Rotschild, Mordechai Segev, Meirav Saraf, Efrat Lifshitz, Abraham Marmur, Ramy El-Ganainy, Demetrios N. Christodoulides
Optical Control Of Thermocapillary Effects In Complex Nanofluids, Yuval Lamhot, Assaf Barak, Carmel Rotschild, Mordechai Segev, Meirav Saraf, Efrat Lifshitz, Abraham Marmur, Ramy El-Ganainy, Demetrios N. Christodoulides
Ramy El-Ganainy
We study the strong coupling of light and nanoparticle suspensions and their surface tension effect in capillaries. We show experimentally and theoretically that increasing the intensity of a narrow laser beam passing through a capillary far away from the surface results in a significant decrease in the fluid level. The underlying mechanism relies on light-induced redistribution of nanoparticles in the bulk and the surface of the fluid, facilitating continuous optical control over the surface position. The experiments manifest optical control from afar over properties of fluid surfaces.
Nonlinear Optical Dynamics In Nonideal Gases Of Interacting Colloidal Nanoparticles, Ramy El-Ganainy, Demetrios N. Christodoulides, E. M. Wright, W. M. Lee, K. Dholakia
Nonlinear Optical Dynamics In Nonideal Gases Of Interacting Colloidal Nanoparticles, Ramy El-Ganainy, Demetrios N. Christodoulides, E. M. Wright, W. M. Lee, K. Dholakia
Ramy El-Ganainy
We show that many-body effects in stabilized nanocolloidal suspensions can have a profound effect on their optical nonlinearity. By considering the screened Coulomb repulsions between nanoparticles, we find that the nonlinear optical behavior of these colloids can range from polynomial to exponential depending on their composition and chemistry. The dynamics and stability properties of optical beams propagating in such nonideal gas environments of interacting colloidal particles are investigated. Our analysis provides a theoretical foundation for understanding the recently observed super-Kerr nonlinear optical response of such systems.
Beam Dynamics In Pt Symmetric Optical Lattices, Konstantinos Makris, Ramy El-Ganainy, Demetrios Christodoulides, Z. Musslimani
Beam Dynamics In Pt Symmetric Optical Lattices, Konstantinos Makris, Ramy El-Ganainy, Demetrios Christodoulides, Z. Musslimani
Ramy El-Ganainy
The possibility of parity-time (PT) symmetric periodic potentials is investigated within the context of optics. Beam dynamics in this new type of optical structures is examined in detail for both one- and two- dimensional lattice geometries. It is shown that PT periodic structures can exhibit unique characteristics stemming from the nonorthogonality of the associated Floquet-Bloch modes. Some of these features include double refraction, power oscillations, and eigenfunction unfolding as well as nonreciprocal diffraction patterns.
Optical Solitons In Pt Periodic Potentials, Z. H. Musslimani, Konstantinos G. Makris, Ramy El-Ganainy, Demetrios N. Christodoulides
Optical Solitons In Pt Periodic Potentials, Z. H. Musslimani, Konstantinos G. Makris, Ramy El-Ganainy, Demetrios N. Christodoulides
Ramy El-Ganainy
We investigate the effect of nonlinearity on beam dynamics in parity-time (PT) symmetric potentials. We show that a novel class of one- and two-dimensional nonlinear self-trapped modes can exist in optical PT synthetic lattices. These solitons are shown to be stable over a wide range of potential parameters. The transverse power flow within these complex solitons is also examined.