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Non-Hermitian systems based on anti-parity-time (PT) symmetry reveal rich physics beyond the Hermitian regime. Here, the anti-PT-symmetric photonic lattice is effectively achieved in a four-level inverted Y-type 85Rb atomic vapor. Such instantaneously reconfigurable anti-PT-symmetric photonic lattice possessing susceptibility of χ(x)=−χ∗(−x), is established by a one-dimensional standing-wave coupling field under the assist of a standing-wave driving field. The input probe beam experiences a periodic refractive index modulation when traveling through the photonic lattice, the evolution of output diffraction patterns with symmetric, asymmetric, and lopsided intensity distribution is obtained by adjusting the relevant parameters of constructed non-Hermitian system. Moreover, the anti-PT symmetry in two-dimensional case of both square and hexagonal lattices are correspondingly realized. Our work promotes the development of non-Hermitian devices, and also has some important applications in quantum simulation.

We investigate the realization and manipulation of a two-dimension (2D), asymmetric, electromagnetically induced grating (EIG) in a sample of Rydberg atoms exhibiting the van der Waals ( v d W ) interactions. The scheme relies on the application of a strong control field and a weak probe field, with the former periodically modulated in a 2D plane and the latter incident perpendicular to the 2D plane. We find that the probe field can be diffracted into an asymmetric intensity distribution depending on the relevant modulation parameters of the control field, as well as the density and length of the atomic sample. In particular, higher-order diffraction intensities can be enhanced in different ways as the v d W interaction, modulation strength, or sample length is increased. It is also of interest that the asymmetric diffraction distribution can be shifted to different quadrants by choosing appropriate modulation phases of the control field. These results may be used to develop new photonic devices with asymmetric diffraction properties required in future all-optical networks. [ABSTRACT FROM AUTHOR]

Non-Hermitian systems based on anti-parity-time (PT) symmetry reveal rich physics beyond the Hermitian regime. Here, the anti-PT-symmetric photonic lattice is effectively achieved in a four-level inverted Y-type 85Rb atomic vapor. Such instantaneously reconfigurable anti-PT-symmetric photonic lattice possessing susceptibility of χ (x) = − χ ∗ (− x) , is established by a one-dimensional standing-wave coupling field under the assist of a standing-wave driving field. The input probe beam experiences a periodic refractive index modulation when traveling through the photonic lattice, the evolution of output diffraction patterns with symmetric, asymmetric, and lopsided intensity distribution is obtained by adjusting the relevant parameters of constructed non-Hermitian system. Moreover, the anti-PT symmetry in two-dimensional case of both square and hexagonal lattices are correspondingly realized. Our work promotes the development of non-Hermitian devices, and also has some important applications in quantum simulation. • Providing a theoretical scheme with a four-level inverted Y-type 85Rb atomic vapor for the study of optical anti-PT symmetry. • The transition process from symmetric to lopsided diffractions in nontrivial photonic lattice, especially the asymmetric diffraction process, is theoretically explored. • The lopsided diffraction in this nontrivial photonic lattice highlights the significant role of the standing-wave driving field in transforming a trivial lattice into a nontrivial one. • The anti-PT symmetry are also theoretically obtained in two-dimensional case. [ABSTRACT FROM AUTHOR]

X‐ray third‐order nonlinear asymmetrical diffraction has three independent parameters: the asymmetry angle, the incident wave intensity and the deviation from the exact Bragg orientation. In contrast to the linear case, in the nonlinear case the total reflection region does not exist for all intensity values and asymmetry angles. Theoretical consideration leads to analytical conditions of the total reflection region, and the analysis can be carried out by a graphical method. An exact solution in the total reflection region is found. The numerical solutions of the third‐order nonlinear diffraction allow one to find the reflection curves for a fixed asymmetry angle or for a fixed intensity. For very large or very small asymmetry factors the third‐order nonlinear effects can be observed for beams with very low intensities. [ABSTRACT FROM AUTHOR]

A two-dimensional multi-element phase grating has been designed in terms of the offset refractive index to exhibit the spatially odd symmetry ( antisymmetry ) along one transparent diagonal line with an even number of rectangular elements while leaving other elements in a unit cell opaque. This grating can be engineered to attain a few intriguing phenomena of asymmetric diffraction, including the elimination of equally spaced oblique diffraction lines, the elimination of alternately crossed oblique diffraction lines, and the selection of equally spaced oblique diffraction lines. These phenomena of engineered asymmetric diffraction are well explained via destructive interference between transmitted field amplitudes from paired, dual-paired, and successive elements along the transparent diagonal line.

We investigate the realization and manipulation of a two-dimension (2D), asymmetric, electromagnetically induced grating (EIG) in a sample of Rydberg atoms exhibiting the van der Waals (vdW) interactions. The scheme relies on the application of a strong control field and a weak probe field, with the former periodically modulated in a 2D plane and the latter incident perpendicular to the 2D plane. We find that the probe field can be diffracted into an asymmetric intensity distribution depending on the relevant modulation parameters of the control field, as well as the density and length of the atomic sample. In particular, higher-order diffraction intensities can be enhanced in different ways as the vdW interaction, modulation strength, or sample length is increased. It is also of interest that the asymmetric diffraction distribution can be shifted to different quadrants by choosing appropriate modulation phases of the control field. These results may be used to develop new photonic devices with asymmetric diffraction properties required in future all-optical networks.

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3D asymmetric structure could induce asymmetric diffraction with spatial coupling behavior for various optical applications, but the study still faces challenges due to the complicated local-field coupling mechanism within structures. In this study, the spatial asymmetry based on inclined all-dielectric structure was theoretically modeled. The normal reflection of the 2D array shows that the increasing structural inclination selectively enhances the Fano resonance between different polarization directions which is mainly due to the oriented spatial coupling effect by increasing structural asymmetry, proved with the near-field distribution. The angular-resolved reflection shows the selected enhancement of first-order diffraction even over that of zero order by combining the structural asymmetry and oblique incidence. Our study provides a new insight for exploring asymmetric photonic structures and relative devices in practical applications. [ABSTRACT FROM AUTHOR]

Diffraction is a fundamental phenomenon that reveals the wave nature of light. When a plane wave is transmitted or reflected from a grating or other periodic structures, diffracted light waves propagate at several angles that are specified by the period of the given structure. When the optical period is shorter than the wavelength, constructive interference of diffracted light rays from the subwavelength-scale grating forms a uniform plane wave. Many studies have shown that through the appropriate design of meta-atom geometry, metasurfaces can be used to control light properties. However, most semitransparent metasurfaces are designed to perform symmetric operation with regard to diffraction, meaning that light diffraction occurs identically for front- and back-side illumination. We propose a simple single-layer plasmonic metasurface that achieves asymmetric diffraction by optimizing the transmission phase from two types of nanoslits with I- and T-shaped structures. As the proposed structure is designed to have a different effective period for each observation side, it is either diffractive or nondiffractive depending on the direction of observation. The designed structure exhibits a diffraction angle of 54°, which can be further tuned by applying different period conditions. We expect the proposed asymmetric diffraction meta-grating to have great potential for the miniaturized optical diffraction control systems in the infrared band and compact optical diffraction filters for integrated optics.

An algorithm is developed based on the dynamical theory of X-ray diffraction for calculating the profiles of the diffracted beam, i.e. the diagrams of the intensity distribution versus 2θ when a crystal is fixed at an angle of its maximum diffracted intensity. Similar to Fraunhofer (far-field) diffraction for a single-slit case, in the proposed algorithm the diffracted beam from one atomic layer excited by X-rays is described by the composition of ( N + 1) coherent point oscillators in the crystal. The amplitude and the initial phase of the electric field for each oscillator can be calculated based on the dynamical theory with given boundary conditions. This algorithm not only gives diffraction profiles but also provides the contribution of the excitation of modes when extremely asymmetric diffraction is involved in the diffraction process. Examples such as extremely asymmetric two-beam surface diffraction and three-beam surface diffraction are presented and discussed in detail. [ABSTRACT FROM AUTHOR]

Diffraction is a fundamental phenomenon that reveals the wave nature of light. When a plane wave is transmitted or reflected from a grating or other periodic structures, diffracted light waves propagate at several angles that are specified by the period of the given structure. When the optical period is shorter than the wavelength, constructive interference of diffracted light rays from the subwavelength-scale grating forms a uniform plane wave. Many studies have shown that through the appropriate design of meta-atom geometry, metasurfaces can be used to control light properties. However, most semitransparent metasurfaces are designed to perform symmetric operation with regard to diffraction, meaning that light diffraction occurs identically for front- and back-side illumination. We propose a simple single-layer plasmonic metasurface that achieves asymmetric diffraction by optimizing the transmission phase from two types of nanoslits with I- and T-shaped structures. As the proposed structure is designed to have a different effective period for each observation side, it is either diffractive or nondiffractive depending on the direction of observation. The designed structure exhibits a diffraction angle of 54°, which can be further tuned by applying different period conditions. We expect the proposed asymmetric diffraction meta-grating to have great potential for the miniaturized optical diffraction control systems in the infrared band and compact optical diffraction filters for integrated optics. [ABSTRACT FROM AUTHOR]