Research

9 pages, 1376 KiB

Open AccessCommunication

Dispersion Analysis of Twist-Symmetric Dielectric Waveguides

by Pilar Castillo-Tapia, Kwinten Van Gassen, Qiao Chen, Francisco Mesa, Zvonimir Sipus and Oscar Quevedo-Teruel

Photonics 2021, 8(6), 206; https://doi.org/10.3390/photonics8060206 - 08 Jun 2021

Cited by 6 | Viewed by 2493

Abstract

We propose a circular twist-symmetric dielectric waveguide that is polarization-selective. In the practical implementation of optical fibers, a selective circular polarization is more convenient than its linearly polarized counterpart where previous knowledge of the emitted polarization from the transmitter is unknown. The analysis [...] Read more.

We propose a circular twist-symmetric dielectric waveguide that is polarization-selective. In the practical implementation of optical fibers, a selective circular polarization is more convenient than its linearly polarized counterpart where previous knowledge of the emitted polarization from the transmitter is unknown. The analysis of the waveguide was conducted with three methods: an eigenmode approach, simulation of a truncated structure, and the so-called multimodal transfer-matrix method (MMTMM). The presented simulations demonstrate that the operational band can be manipulated by tuning the parameters of the structure. Furthermore, the MMTMM allows for a direct and accurate calculation of the attenuation constant of the rejected circular polarization. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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15 pages, 2133 KiB

Open AccessArticle

Electromagnetic Wave Scattering from a Moving Medium with Stationary Interface across the Interluminal Regime

by Zoé-Lise Deck-Léger, Xuezhi Zheng and Christophe Caloz

Photonics 2021, 8(6), 202; https://doi.org/10.3390/photonics8060202 - 05 Jun 2021

Cited by 12 | Viewed by 2469

Abstract

This paper extends current knowledge on electromagnetic wave scattering from bounded moving media in several regards. First, it complements the usual dispersion relation of moving media,

ω (θ_{k})

(

θ_{k}

: phase velocity direction, associated with the wave vector, [...] Read more.

This paper extends current knowledge on electromagnetic wave scattering from bounded moving media in several regards. First, it complements the usual dispersion relation of moving media,

ω (θ_{k})

(

θ_{k}

: phase velocity direction, associated with the wave vector,

k

), with the equally important impedance relation,

η (θ_{S})

(

θ_{S}

: group velocity direction, associated with the Poynting vector,

S

). Second, it explains the interluminal-regime phenomenon of double-downstream wave transmission across a stationary interface between a regular medium and the moving medium, assuming motion perpendicular to the interface, and shows that the related waves are symmetric in terms of the energy refraction angle, while being asymmetric in terms of the phase refraction angle, with one of the waves subject to negative refraction, and shows that the wave impedances of the two transmitted waves are equal. Third, it generalizes the problem to the case where the medium moves obliquely with respect to the interface. Finally, it highlights the connection between this problem and a spacetime modulated medium. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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21 pages, 2018 KiB

Open AccessArticle

Fundamentals of Lossless, Reciprocal Bianisotropic Metasurface Design

by Luke Szymanski, Brian O. Raeker, Chun-Wen Lin and Anthony Grbic

Photonics 2021, 8(6), 197; https://doi.org/10.3390/photonics8060197 - 04 Jun 2021

Cited by 6 | Viewed by 3197

Abstract

Lossless, reciprocal bianisotropic metasurfaces have the ability to control the amplitude, phase, and polarization of electromagnetic wavefronts. However, producing the responses that are necessary for achieving this control with physically realizable surfaces is a challenging task. Here, several design approaches for bianisotropic metasurfaces [...] Read more.

Lossless, reciprocal bianisotropic metasurfaces have the ability to control the amplitude, phase, and polarization of electromagnetic wavefronts. However, producing the responses that are necessary for achieving this control with physically realizable surfaces is a challenging task. Here, several design approaches for bianisotropic metasurfaces are reviewed that produce physically realizable metasurfaces using cascaded impedance sheets. In practice, three or four impedance sheets are often used to realize bianisotropic responses, which can result in narrowband designs that require the unit cells to be optimized in order to improve the performance of the metasurface. The notion of a metasurface quality factor is introduced for three-sheet metasurfaces to address these issues in a systematic manner. It is shown that the quality factor can be used to predict the bandwidth of a homogeneous metasurface, and it can also be used to locate problematic unit cells when designing inhomogeneous metasurfaces. Several design examples are provided to demonstrate the utility of the quality factor, including an impedance matching layer with maximal bandwidth and a gradient metasurface for plane wave refraction. In addition to these examples, several metasurfaces for polarization control are also reported, including an isotropic polarization rotator and an asymmetric circular polarizer. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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23 pages, 4152 KiB

Open AccessArticle

Free-Space Nonreciprocal Transmission Based on Nonlinear Coupled Fano Metasurfaces

by Ahmed Mekawy, Dimitrios L. Sounas and Andrea Alù

Photonics 2021, 8(5), 139; https://doi.org/10.3390/photonics8050139 - 23 Apr 2021

Cited by 16 | Viewed by 4069

Abstract

Optical nonlinearities can enable unusual light–matter interactions, with functionalities that would be otherwise inaccessible relying only on linear phenomena. Recently, several studies have harnessed the role of optical nonlinearities to implement nonreciprocal optical devices that do not require an external bias breaking time-reversal [...] Read more.

Optical nonlinearities can enable unusual light–matter interactions, with functionalities that would be otherwise inaccessible relying only on linear phenomena. Recently, several studies have harnessed the role of optical nonlinearities to implement nonreciprocal optical devices that do not require an external bias breaking time-reversal symmetry. In this work, we explore the design of a metasurface embedding Kerr nonlinearities to break reciprocity for free-space propagation, requiring limited power levels. After deriving the general design principles, we demonstrate an all-dielectric flat metasurface made of coupled nonlinear Fano silicon resonant layers realizing large asymmetry in optical transmission at telecommunication frequencies. We show that the metrics of our design can go beyond the fundamental limitations on nonreciprocity for nonlinear optical devices based on a single resonance, as dictated by time-reversal symmetry considerations. Our work may shed light on the design of flat subwavelength free-space nonreciprocal metasurface switches for pulsed operation which are easy to fabricate, fully passive, and require low operation power. Our simulated devices demonstrate a transmission ratio >50 dB for oppositely propagating waves, an operational bandwidth exceeding 600 GHz, and an insertion loss of <0.04 dB. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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24 pages, 6393 KiB

Open AccessFeature PaperArticle

Synthesis of Super-Oscillatory Point-Spread Functions with Taylor-Like Tapered Sidelobes for Advanced Optical Super-Resolution Imaging

by Haitang Yang and George V. Eleftheriades

Photonics 2021, 8(3), 64; https://doi.org/10.3390/photonics8030064 - 25 Feb 2021

Cited by 5 | Viewed by 2951

Abstract

Recently, the super-oscillation phenomenon has attracted attention because of its ability to super-resolve unlabelled objects in the far-field. Previous synthesis of super-oscillatory point-spread functions used the Chebyshev patterns where all sidelobes are equal. In this work, an approach is introduced to generate super-oscillatory [...] Read more.

Recently, the super-oscillation phenomenon has attracted attention because of its ability to super-resolve unlabelled objects in the far-field. Previous synthesis of super-oscillatory point-spread functions used the Chebyshev patterns where all sidelobes are equal. In this work, an approach is introduced to generate super-oscillatory Taylor-like point-spread functions that have tapered sidelobes. The proposed method is based on the Schelkunoff’s super-directive antenna theory. This approach enables the super-resolution, the first sidelobe level and the tapering rate of the sidelobes to be controlled. Finally, we present the design of several imaging experiments using a spatial light modulator as an advanced programmable grating to form the Taylor-like super-oscillatory point-spread functions and demonstrate their superiority over the Chebyshev ones in resolving the objects of two apertures and of a mask with the letter E. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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11 pages, 793 KiB

Open AccessArticle

Stability Constraints on Practical Implementation of Parity-Time-Symmetric Electromagnetic Systems

by Josip Lončar, Josip Vuković, Igor Krois and Silvio Hrabar

Photonics 2021, 8(2), 56; https://doi.org/10.3390/photonics8020056 - 18 Feb 2021

Cited by 6 | Viewed by 2492

Abstract

Recently, several applications leveraging unconventional manipulation of electromagnetic radiation based on parity-time symmetry have been proposed in the literature. Typical examples include systems with unidirectional invisibility and asymmetric refraction. Such applications assume an inherent system stability and no occurrence of unbounded signal growth [...] Read more.

Recently, several applications leveraging unconventional manipulation of electromagnetic radiation based on parity-time symmetry have been proposed in the literature. Typical examples include systems with unidirectional invisibility and asymmetric refraction. Such applications assume an inherent system stability and no occurrence of unbounded signal growth or unwanted self-oscillations. Here, a general instability issue of parity-time-symmetric systems is investigated, with particular emphasis on a recently proposed system based on resistive metasurfaces. Explicit closed-form stability criterion is derived, crosschecked and verified by both time-domain transient simulations and the measurements on an experimental demonstrator operating in a lower radiofrequency range. Results of this study lead to the conclusion that any parity-time-symmetric system is necessarily marginally stable. Finally, it is shown that such a marginally stable system may easily become unstable if not designed carefully. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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11 pages, 3519 KiB

Open AccessEditor’s ChoiceArticle

Electromagnetic Scattering Analysis of SHDB Objects Using Surface Integral Equation Method

by Beibei Kong, Pasi Ylä-Oijala and Ari Sihvola

Photonics 2020, 7(4), 134; https://doi.org/10.3390/photonics7040134 - 18 Dec 2020

Cited by 1 | Viewed by 2522

Abstract

A surface integral equation (SIE) method is applied in order to analyze electromagnetic scattering by bounded arbitrarily shaped three-dimensional objects with the SHDB boundary condition. SHDB is a generalization of SH (Soft-and-Hard) and DB boundary conditions (at the DB boundary, the normal components [...] Read more.

A surface integral equation (SIE) method is applied in order to analyze electromagnetic scattering by bounded arbitrarily shaped three-dimensional objects with the SHDB boundary condition. SHDB is a generalization of SH (Soft-and-Hard) and DB boundary conditions (at the DB boundary, the normal components of the D and B flux densities vanish). The SHDB boundary condition is a general linear boundary condition that contains two scalar equations that involve both the tangential and normal components of the electromagnetic fields. The multiplication of these scalar equations with two orthogonal vectors transforms them into a vector form that can be combined with the tangential field integral equations. The resulting equations are discretized and converted to a matrix equation with standard method of moments (MoM). As an example of use of the method, we investigate scattering by an SHDB circular disk and demonstrate that the SHDB boundary allows for an efficient way to control the polarization of the wave that is reflected from the surface. We also discuss perspectives into different levels of materialization and realization of SHDB boundaries. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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22 pages, 1693 KiB

Open AccessEditor’s ChoiceArticle

A Metamaterial-Inspired Approach to Mitigating Radio Frequency Blackout When a Plasma Forms Around a Reentry Vehicle

by Bruce A. Webb and Richard W. Ziolkowski

Photonics 2020, 7(4), 88; https://doi.org/10.3390/photonics7040088 - 06 Oct 2020

Cited by 8 | Viewed by 3062

Abstract

Radio frequency (RF) blackout and attenuation have been observed during atmospheric reentry since the advent of space exploration. The effects range from severe attenuation to complete loss of communications and can last from 90 s to 10 min depending on the vehicle’s trajectory. [...] Read more.

Radio frequency (RF) blackout and attenuation have been observed during atmospheric reentry since the advent of space exploration. The effects range from severe attenuation to complete loss of communications and can last from 90 s to 10 min depending on the vehicle’s trajectory. This paper examines a way of using a metasurface to improve the performance of communications during reentry. The technique is viable at low plasma densities and matches a split-ring resonator (SRR)-based mu-negative (MNG) sheet to the epsilon-negative (ENG) plasma region. Considering the MNG metasurface as a window to the exterior of a reentry vehicle, its matched design yields high transmission of an electromagnetic plane wave through the resulting MNG-ENG metastructure into the region beyond it. A varactor-based SRR design facilitates tuning the MNG layer to ENG layers with different plasma densities. Both simple and Huygens dipole antennas beneath a matched metastructure are then employed to demonstrate the consequent realization of significant signal transmission through it into free space beyond the exterior ENG plasma layer. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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24 pages, 3696 KiB

Open AccessArticle

Optical Forces Acting on a Double DNA-Like Helix, Its Unwinding and Strands Rupture

by Igor V. Semchenko, Ivan S. Mikhalka, Ihar A. Faniayeu, Sergei A. Khakhomov, Aliaksei P. Balmakou and Sergei A. Tretyakov

Photonics 2020, 7(4), 83; https://doi.org/10.3390/photonics7040083 - 27 Sep 2020

Cited by 4 | Viewed by 2959

Abstract

In this paper we study electromagnetic forces induced on DNA and DNA-like helices by external electromagnetic waves. We consider simultaneously occurring forces and torques, interconnected and acting along the double helix axis. Since the DNA molecule has an absorption band in the ultraviolet [...] Read more.

In this paper we study electromagnetic forces induced on DNA and DNA-like helices by external electromagnetic waves. We consider simultaneously occurring forces and torques, interconnected and acting along the double helix axis. Since the DNA molecule has an absorption band in the ultraviolet and visible range near wavelengths

λ_{1 r e s} = 280

nm and

λ_{2 r e s} = 500

nm, we expect that it may be possible to selectively apply engineered forces to DNA molecules using appropriate illumination by light in these frequency ranges. The optical forces are simulated for DNA fragments consisting of 20 and 35 turns. Fragments of this length are convenient for direct sequencing and subsequent use in experiments and in practice. It is shown that repulsion forces can arise between the strands of the double DNA-like helix in the field of external electromagnetic waves. Such forces are characteristic of a DNA-like helix with its specific pitch angle and are not inherent in double helices with more straightened or more compressed turns. These repulsion forces, acting along the entire helix, both for electric charges and for electric currents, can lead to damage and rupture of the strands in the double helix. In addition, there can also exist forces and moments of forces directed along the helix axis, which simultaneously stretch and unwind a double helix. The double helix equilibrium under the action of optical forces is also of interest from another point of view, i.e., for optimizing the structure of artificial magnetics and bianisotropic metamaterials for applications in all frequency ranges. Full article

(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)

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