arXiv subjects

Dia'aaldin J. Bisharat

Publications and source records attributed to Dia'aaldin J. Bisharat.

8 recordsLinked to original sources

arXiv2022

Engineering Equifrequency Contours of Metasurfaces for Self-Collimated Surface Wave Steering

Metasurfaces provide unique capability in guiding surface waves and controlling their polarization and dispersion properties. One way to do that is by analyzing their equifrequency contours. Equifrequency contours are the 2D projection of the 3D dispersion diagram. Since they are a k-space map representation of the surface, many of the wave properties can be understood through the Equifrequency contours. In this paper, we investigate numerically and experimentally the engineering of equifrequency contours using C-shape metasurface design. We show the ability to provide high self-collimation as well as spin-dependent wave splitting for the same metasurface by tuning the frequency of operation. We also show the ability to steer the wave along a defined curved path by rotating the C-shape which results in rotating its equifrequency contours. This work demonstrates how engineering equifrequency contours can be used as a powerful tool for controlling the surface wave propagation properties.

physics.class-ph↗

arXiv2022

Topologically Protected Edge States in Triangular Lattices

We describe the possibility for topologically robust edge states existing on interfaces of triangular lattices which are supported by rotational symmetries that are sensitive to boundary conditions. Such states are trivial from the perspective of Berry curvature, but result instead from an interplay between crystalline symmetries and finite boundary effects. Regardless, we show such states are in a distinct topological phase, provided the gauge-dependent symmetries are maintained. Such a model describes a number of recent bosonic experimental demonstrations on triangular lattices, the physics for which has thus far eluded explanation.

cond-mat.mes-hall↗

arXiv2022

Designing Topological Defect Lines Protected by Gauge-dependent Symmetry Indicators

Symmetry indicators are a modern tool for characterizing topological phases that require only minimal computational expense but provide an elegant means of designing practical devices. This paper demonstrates how a rotational symmetry indicator can be used to construct and characterize a topologically robust waveguide, which is then verified experimentally on a printed circuit board (PCB) platform. The design takes advantage of the real-space gauge-dependency of the symmetry indicators and adopts a $C_6$ lattice with simple shifts, forming a defect line supporting topological edge modes. It is shown that the modes can realize the same features as previous topological waveguides, but in addition possesses a greater degree of reconfigurability and the unique ability to form a one-way termination. Moreover, the design illustrates the critical role real space information plays in determining the topological properties of photonic crystals, enabling a wider range of possible realizations.

physics.app-ph↗

arXiv2021

On-chip unidirectional waveguiding for surface acoustic waves along a defect line in a triangular lattice

The latest advances in topological physics have yielded a rich toolset to design highly robust wave transfer systems, for overcoming issues like beam steering and lateral diffraction in surface acoustic waves (SAWs). However, presently used designs for topologically protected SAWs have been largely limited to spin or valley-polarized phases, which rely on non-zero Berry curvature effects. Here we propose and experimentally demonstrate a highly robust SAW waveguide on lithium niobate (LiNbO3), based on a line defect within a true triangular phononic lattice, which instead employs an intrinsic chirality of phase vortices and maintains a zero Berry curvature. The guided SAW mode spans a wide bandwidth and shows confinement in the lateral direction with 3 dB attenuation within half of the unit-cell length. SAW routing around sharp bends has been demonstrated in such waveguide, with less than ~4% reflection per bend. The waveguide has also been found robust for defect lines with different configurations. The fully on-chip system permits unidirectional SAW modes that are tightly bound to the waveguide, which provides a compact footprint ideal for miniaturization of practical applications and offers insight into the possibility of manipulating highly focused SAW propagation.

physics.app-ph↗

arXiv2021

Chiral Surface Wave propagation with Anomalous Spin-momentum Locking

The ability to control the directionality of surface waves by manipulating its polarization has been of great significance for applications in spintronics and polarization-based optics. Surface waves with evanescent tails are found to possess an inherent in-plane transverse spin which is dependent on the propagation direction while an out-of-plane transverse spin does not naturally occur for surface waves and requires a specific surface design. Here, we introduce a new type of surface waves called chiral surface wave which has two transverse spins, an in-plane one that is inherent to any surface wave and an out-of-plane spin which is enforced by the design due to strong x-to-y coupling and broken rotational symmetry. The two transverse spins are locked to the momentum. Our study opens a new direction for metasurface designs with enhanced and controlled spin-orbit interaction by adding an extra degree of freedom to control the propagation direction as well as the transverse spin of surface waves.

physics.optics↗

arXiv2021

Photonic topological insulators a beginner's introduction

Control and manipulation of electromagnetic waves has reached a new level with the recent understanding of topological states of matter. These metamaterials have the potential to revolutionize many areas in traditional electromagnetic design, from highly robust cavities to small footprint waveguides. Much of the past literature has been on the cutting edge of condensed matter physics, but there is now ample opportunity to explore their usage for practical microwave and optical devices. To assist the beginner, in this Tutorial we give a basic introduction to the essential concepts of topological phenomena in electromagnetic systems, including geometric phases, topological invariants, pseudospin states, and the integer/valley/spin quantum Hall effects. Our focus is on engineered photonic topological insulators (PTIs) in two-dimensional systems. We highlight methods for characterizing such structures and how they result in unique wave-guiding properties. In addition, we provide recipes on how to realize PTIs using photonic crystals and metasurfaces, examine differences between different types of PTIs, and discuss limitations and advantages of some of the existing enabling platforms.

physics.optics↗

arXiv2021

Classical-to-Topological Transmission Line Couplers

Recent advances in topologically robust waveguiding for electromagnetic systems have presented opportunities for improving practical photonic and microwave devices. To bring this rich area of physics within the reach of application, it is critical for such systems to be interfaced with classical, continuous waveguiding and transmission line technology. This Letter presents a compact, highly efficient transition from a classical metallic transmission line to a topologically nontrivial line wave emulating the quantum spin Hall effect. A zero-gap antipodal slot line is used as the starting transmission line, which is then coupled to the topological metasurface via a field matching procedure. Additional modifications to the interface between the two structures to eliminate unwanted edge coupling improves transmission further. A simulated loss analysis isolates the effect of the transitions from the rest of the structure, showing a loss contribution of only 2.1% per classical-to-topological conversion. Using the transition, a quantitative characterization of the robustness of common topologically protected devices is presented. This design lays the foundation to integrate topologically robust metasurface transmission lines to traditional systems, opening the door to future uses of such structures in systems.

physics.app-ph↗

arXiv2017

Guiding waves along an infinitesimal line between impedance surfaces

We present a new electromagnetic mode that forms at the interface between two planar surfaces laid side by side in free space, effectively guiding energy along an infinitesimal, one-dimensional line. It is shown that this mode occurs when the boundaries have complementary surface impedances, and it is possible to control the mode confinement by altering their values correspondingly. The mode exhibits singular field enhancement, broad bandwidth, direction-dependent polarization, and robustness to certain defects. As a proof-of-concept, experimental results in the microwave regime are provided using patterned conducting sheets. Our proposed effective-medium-based approach is general, however, thus allowing for potential implementation up to optical frequencies. Our system is promising for applications including integrated photonics, sensing, switching, chiral quantum coupling, and reconfigurable waveguides.

cond-mat.mes-hall↗