다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

This paper presents a literature review on recent applications and design aspects of the intelligent reflecting surface (IRS) in the future wireless networks. Conventionally, the network optimization has been limited to transmission control at two endpoints, i.e., end users and network controller. The fading wireless channel is uncontrollable and becomes one of the main limiting factors for performance improvement. The IRS is composed of a large array of scattering elements, which can be individually configured to generate additional phase shifts to the signal reflections. Hence, it can actively control the signal propagation properties in favor of signal reception, and thus realize the notion of a smart radio environment. As such, the IRS’s phase control, combined with the conventional transmission control, can potentially bring performance gain compared to wireless networks without IRS. In this survey, we first introduce basic concepts of the IRS and the realizations of its reconfigurability. Then, we focus on applications of the IRS in wireless communications. We overview different performance metrics and analytical approaches to characterize the performance improvement of IRS-assisted wireless networks. To exploit the performance gain, we discuss the joint optimization of the IRS’s phase control and the transceivers’ transmission control in different network design problems, e.g., rate maximization and power minimization problems. Furthermore, we extend the discussion of IRS-assisted wireless networks to some emerging use cases. Finally, we highlight important practical challenges and future research directions for realizing IRS-assisted wireless networks in beyond 5G communications.

Toward Smart Wireless Communications via Intelligent Reflecting Surfaces: A Contemporary Survey

Near-field coupled plasmonic systems generally achieve plasmonically induced transparency (PIT) using only one-way bright–dark mode coupling. However, it is challenging to realize such well-designed devices, mainly because they depend significantly on the polarization direction. We exploit surface plasmons supported by two crossed layers of graphene nanoribbons (GNRs) to achieve dynamically tunable PIT, where each GNR operates as both the bright and dark modes simultaneously. The proposed PIT can result from either one-way bright–dark mode interactions or bidirectional bright–bright and bright–dark mode hybridized coupling when the polarization is perpendicular/parallel or at an angle to the GNRs, respectively. Additionally, identical ribbon widths yield polarization-insensitive single-window PIT, whereas different ribbon widths produce polarization-dependent double-window PIT. We examine the proposed technique using plasmon wave functions and the transfer matrix method; analytical and numerical results show excellent agreement. This study can provide physical insight into the PIT coupling mechanisms and advance the applicability and versatility of PIT-based sensing platforms and other active devices.

Plasmonically induced transparency in double-layered graphene nanoribbons

To achieve plasmonically induced transparency (PIT), general near-field plasmonic systems based on couplings between localized plasmon resonances of nanostructures rely heavily on the well-designed interantenna separations. However, the implementation of such devices and techniques encounters great difficulties mainly to due to very small sized dimensions of the nanostructures and gaps between them. Here, we propose and numerically demonstrate that PIT can be achieved by using two graphene layers that are composed of a upper sinusoidally curved layer and a lower planar layer, avoiding any pattern of the graphene sheets. Both the analytical fitting and the Akaike Information Criterion (AIC) method are employed efficiently to distinguish the induced window, which is found to be more likely caused by Autler-Townes splitting (ATS) instead of electromagnetically induced transparency (EIT). Besides, our results show that the resonant modes cannot only be tuned dramatically by geometrically changing the grating amplitude and the interlayer spacing, but also by dynamically varying the Fermi energy of the graphene sheets. Potential applications of the proposed system could be expected on various photonic functional devices, including optical switches, plasmonic sensors.

Dynamically tunable plasmonically induced transparency in sinusoidally curved and planar graphene layers

We demonstrate a nonequilibrium phase transition in a dilute thermal atomic gas. The phase transition, between states of low and high Rydberg occupancy, is induced by resonant dipole-dipole interactions between Rydberg atoms. The gas can be considered as dilute as the atoms are separated by distances much greater than the wavelength of the optical transitions used to excite them. In the frequency domain, we observe a mean-field shift of the Rydberg state which results in intrinsic optical bistability above a critical Rydberg number density. In the time domain, we observe critical slowing down where the recovery time to system perturbations diverges with critical exponent α=-0.53±0.10. The atomic emission spectrum of the phase with high Rydberg occupancy provides evidence for a superradiant cascade.

Nonequilibrium Phase Transition in a Dilute Rydberg Ensemble

The well-known EIT-based storage and retrieval of optical pulses can be applied to nonlinear, solitonic pulses which have minimal dispersion.

Ultraslow optical solitons and their storage and retrieval in an ultracold ladder-type atomic system

Realizing single light bullets and vortices that are stable in high dimensions is a long-standing goal in the study of nonlinear optical physics. The storage and retrieval of such stable high-dimensional optical pulses may offer a variety of applications. Here, we present a scheme to generate such optical pulses in a cold Rydberg atomic gas. By virtue of electromagnetically induced transparency, strong, long-range atom–atom interaction in Rydberg states is mapped to light fields, resulting in a giant, fast-responding nonlocal Kerr nonlinearity and the formation of light bullets and vortices carrying orbital angular momenta, which have extremely low generation power and very slow propagation velocity, and can stably propagate, with the stability provided by the combination of local and nonlocal Kerr nonlinearities. We demonstrate that the light bullets and vortices obtained can be stored and retrieved in the system with high efficiency and fidelity. Our study provides a new route for manipulating high-dimensional nonlinear optical processes via controlled optical nonlinearities in cold Rydberg gases.

Stable single light bullets and vortices and their active control in cold Rydberg gases

We investigate the optical Kerr nonlinearities of an ensemble of cold Rydberg atoms under the condition of electromagnetically induced transparency (EIT). By using an approach beyond mean-field theory, we show that the system possesses not only enhanced third-order nonlinear optical susceptibility, but also giant fifth-order nonlinear optical susceptibility, which has a cubic dependence on atomic density. Our results demonstrate that both the third-order and the fifth-order nonlinear optical susceptibilities consist of two parts, contributed respectively by photon-atom interaction and Rydberg-Rydberg interaction. The Kerr nonlinearity induced by the Rydberg-Rydberg interaction plays a leading role at high atomic density. We find that the fifth-order nonlinear optical susceptibility in the Rydberg-EIT system may be five orders of magnitude larger than that obtained in traditional EIT systems. The results obtained may have promising applications in light and quantum information processing and transmission at weak-light level.

Enhanced third-order and fifth-order Kerr nonlinearities in a cold atomic system via Rydberg-Rydberg interaction

We propose a scheme to realize a giant Kerr nonlinearity and create stable high-dimensional nonlinear plasmon polaritons via plasmon-induced transparency (PIT) in a metamaterial, which is constructed by an array of unit cell consisting of a cut-wire and a pair of varactor-loaded split-ring resonators. We show that, due to the PIT effect and the nonlinearity contributed by the varactor, the system may possess very large second-order and third-order nonlinear susceptibilities. We further show that the system supports a resonant interaction between longwave and shortwave and hence effective third-order nonlinear susceptibility can be further enhanced one order of magnitude. Based on these peculiar properties, we derive Davey-Stewartson equations governing the evolution of longwave and shortwave envelope, and demonstrate that it possible to generate plasmon dromions [i.e., (2+1)-dimensional plasmon solitons with coupled longwave and shortwave components] with very low generation power. Our study raises the possibility for obtaining new, giant Kerr effect and stable high-dimensional nonlinear plasmon polaritons at very low radiation intensity by using nonlinear PIT metamaterials.

Plasmon dromions in a metamaterial via plasmon-induced transparency

Realizing single light bullets and vortices that are stable in high dimensions is a long-standing goal in the study of nonlinear optical physics. On the other hand, the storage and retrieval of such stable high dimensional optical pulses may offer a variety of applications. Here we present a scheme to generate such optical pulses in a cold Rydberg atomic gas. By virtue of electromagnetically induced transparency, strong, long-range atom-atom interaction in Rydberg states is mapped to light fields, resulting in a giant, fast-responding nonlocal Kerr nonlinearity and the formation of light bullets and vortices carrying orbital angular momenta, which have extremely low generation power, very slow propagation velocity, and can stably propagate, with the stability provided by the combination of local and the nonlocal Kerr nonlinearities. We demonstrate that the light bullets and vortices obtained can be stored and retrieved in the system with high efficiency and fidelity. Our study provides a new route for manipulating high-dimensional nonlinear optical processes via the controlled optical nonlinearities in cold Rydberg gases.

Zhengyang Bai

Papers

Ultraslow optical solitons and their storage and retrieval in an ultracold ladder-type atomic system

Stable single light bullets and vortices and their active control in cold Rydberg gases

Enhanced third-order and fifth-order Kerr nonlinearities in a cold atomic system via Rydberg-Rydberg interaction

Plasmon dromions in a metamaterial via plasmon-induced transparency

Stable single light bullets and vortices and their active control in cold Rydberg gases