arXiv subjects

Christophe Caloz

Publications and source records attributed to Christophe Caloz.

At least 91 records · Page 5Linked to original sources

arXiv2018

Nonreciprocal Electromagnetic Scattering from a Periodically Space-Time Modulated Slab and Application to a Quasisonic Isolator

Scattering of obliquely incident electromagnetic waves from periodically space-time modulated slabs is investigated. It is shown that such structures operate as nonreciprocal harmonic generators and spatial-frequency filters. For oblique incidences, low-frequency harmonics are filtered out in the form of surface waves, while high-frequency harmonics are transmitted as space waves. In the quasisonic regime, where the velocity of the space-time modulation is close to the velocity of the electromagnetic waves in the background medium, the incident wave is strongly coupled to space-time harmonics in the forward direction, while in the backward direction it exhibits low coupling to other harmonics. This nonreciprocity is leveraged for the realization of an electromagnetic isolator in the quasisonic regime and is experimentally demonstrated at microwave frequencies.

physics.class-ph↗

arXiv2017

Synthesis of Spherical Metasurfaces based on Susceptibility Tensor GSTCs

The bianisotropic susceptibility Generalized Sheet Transition Conditions (GSTCs) synthesis method is extended from planar to spherical metasurfaces. Properties specific to the non-zero intrinsic curvature of the spherical shape are highlighted and different types of corresponding transformations are described. Finally, the susceptibility-GSTC method and exotic properties of spherical metasurfaces are validated and illustrated with three examples: illusion transformation, ring focusing and birefringence.

physics.app-ph↗

arXiv2017

Design, Concepts and Applications of Electromagnetic Metasurfaces

The paper overviews our recent work on the synthesis of metasurfaces and related concepts and applications. The synthesis is based on generalized sheet transition conditions (GSTCs) with a bianisotropic surface susceptibility tensor model of the metasurface structure. We first place metasurfaces in a proper historical context and describe the GSTC technique with some fundamental susceptibility tensor considerations. Upon this basis, we next provide an in-depth development of our susceptibility-GSTC synthesis technique. Finally, we present five recent metasurface concepts and applications, which cover the topics of birefringent transformations, bianisotropic refraction, light emission enhancement, remote spatial processing and nonlinear second-harmonic generation.

physics.optics↗

arXiv2017

Inverse Prism based on Temporal Discontinuity and Spatial Dispersion

We introduce the concept of the inverse prism as the dual of the conventional prism and deduce from this duality an implementation of it based on temporal discontinuity and spatial dispersion provided by anisotropy. Moreover, we show that this inverse prism exhibits the following three unique properties: chromatic refraction birefringence, ordinary-monochromatic and extraordinary- polychromatic temporal refraction, and linear-to-Lissajous polarization transformation.

physics.optics↗

arXiv2017

Computational Analysis of Metasurfaces

Metasurfaces represent one of the most vibrant fields of modern science and technology. A metasurface is a complex electromagnetic structure, that is typically deeply subwavelength in thickness, electrically large in transverse size and composed of subwavelength scattering particles with extremely small features; it may generally be bianisotropic, spacevarying and time-varying, nonlinear, curved and multiphysics. With such complexity, the design of a metasurface requires a holistic approach, involving synergistic synthesis and analysis operations, based on a solid model. The Generalized Sheet Transition Conditions (GSTCs), combined with bianisotropic surface susceptibility functions, provide such a model, and allow now for the design of sophisticated metasurfaces, which still represented a major challenge a couple of years ago. This paper presents this problematic, focusing on the computational analysis of metasurfaces via the GSTC-susceptibility approach. It shows that this analysis plays a crucial role in the holistic design of metasurfaces, and overviews recently reported related frequency-domain (FDFD, SD-IE, FEM) and time-domain (FDTD) computational techniques.

physics.optics↗

arXiv2017

Flexible-Resolution, Arbitrary-Input and Tunable Rotman Lens Spectrum Decomposer (RL-SD)

We present an enhanced design -- in terms of resolution flexibility, input port position arbitrariness and frequency-range tunability -- of the planar Rotman lens spectrum decomposer (RL-SD). This enhancement is achieved by manipulating the output port locations through proper sampling of the frequency-position law of the RL-SD, inserting a calibration array compensating for frequency deviation induced by input modification and introducing port switching, respectively. A complete design procedure is provided and two enhanced RL-SD prototypes, with uniform port distribution and uniform frequency resolution, respectively, are numerically and experimentally demonstrated.

physics.optics↗

arXiv2017

Metasurface Solar Sail for flexible Radiation Pressure Control

We propose to use metasurfaces as a mean of controlling radiation pressure for increasing the range of motions of spacecraft solar sails. Specifically, we present a theoretical study of different electromagnetic field configurations, and corresponding metasurface structures, that allow one to achieve repulsive, attractive, lateral and rotational forces.

physics.optics↗

arXiv2017

New Electromagnetic Modes in Space-Time Modulated Dispersion-Engineered Media

We report on new electromagnetic modes in space-time modulated dispersion-engineered media. These modes exhibit unusual dispersion relation, field profile and scattering properties. They are generated by coupled codirectional space-time harmonic pairs, and occur in space-time periodic media whose constituent materials exhibit specific dispersion. Excitation of a slab of such a medium with subluminal modulation results in periodic transfer of energy between the incident frequency and a frequency shifted by a multiple of the modulation frequency, whereas superluminal modulation generates exponentially growing frequencies. These modes may find applications in optical mixers, terahertz sources and other optical devices.

physics.optics↗

arXiv2017

Time-Reversal Routing for Dispersion Code Multiple Access (DCMA) Communications

We present the modeling and characterization of a time-reversal routing dispersion code multiple access (TR-DCMA) system. We show that this system maintains the low complexity advantage of DCMA transceivers while offering dynamic adaptivity for practial communication scenarios. We first derive the mathematical model and explain operation principles of the system, and then characterize its interference, signal to interference ratio, and bit error probability characteristics.

eess.SP↗

arXiv2017

Frequency Vectoralization and Frequency Birefringence

In view of momentum continuity at a temporal slab, it is shown that instantaneous switching of an isotropic medium to an anisotropic medium offers the incident frequency a directional property- a counterintuitive process which is called frequency vectoralization. By expressing the dispersion diagrams before and after the temporal transition, a general analogy between spatial and temporal interfaces is given and the concept of frequency birefringence, i.e. double frequency jump, will be explained. Furthermore, it will be shown that an anisotropic temporal interface diffracts a monochromatic beam in both the spatial and spectral domains.

physics.optics↗

arXiv2017

Ultra-high and Tunable Sensitivity Leaky-Wave Scanning Using Gain-Loss C-section Phasers

A periodic leaky-wave antenna (LWA) with tuning capability and enhanced scanning sensitivity is introduced in this paper. This antenna leverages the concept of active Gain-Loss C-section pairs to tune the group delay of each antenna unit cell without affecting its magnitude response. This in turn changes the scanning angle versus frequency rate in the periodic LWA. The proposed concept is well-suited for the application to real-time spectrum analysis, where it allows the frequency resolution to be tuned or significantly enhanced even with a low-permittivity substrate.

physics.app-ph↗

arXiv2017

Refracting Metasurfaces without Spurious Diffraction

Refraction represents one of the most fundamental operations that may be performed by a metasurface. However, simple phasegradient metasurface designs suffer from restricted angular deflection due to spurious diffraction orders. It has been recently shown, using a circuit-based approach, that refraction without spurious diffraction, or diffraction-free, can fortunately be achieved by a transverse metasurface exhibiting either loss-gain or bianisotropy. Here, we rederive these conditions using a medium-based - and hence more insightfull - approach based on Generalized Sheet Transition Conditions (GSTCs) and surface susceptibility tensors, and experimentally demonstrate two diffraction-free refractive metasurfaces that are essentially lossless, passive, bianisotropic and reciprocal.

physics.class-ph↗

arXiv2017

Generalized Sheet Transition Condition FDTD Simulation of Metasurface

We propose an FDTD scheme based on Generalized Sheet Transition Conditions (GSTCs) for the simulation of polychromatic, nonlinear and space-time varying metasurfaces. This scheme consists in placing the metasurface at virtual nodal plane introduced between regular nodes of the staggered Yee grid and inserting fields determined by GSTCs in this plane in the standard FDTD algorithm. The resulting update equations are an elegant generalization of the standard FDTD equations. Indeed, in the limiting case of a null surface susceptibility ($χ_\text{surf}=0$), they reduce to the latter, while in the next limiting case of a time-invariant metasurface $[χ_\text{surf}\neqχ_\text{surf}(t)]$, they split in two terms, one corresponding to the standard equations for a one-cell ($Δx$) thick slab with volume susceptibility ($χ$), corresponding to a diluted approximation ($χ=χ_\text{surf}/(2Δx)$) of the zero-thickness target metasurface, and the other transforming this slab in a real (zero-thickness) metasurface. The proposed scheme is fully numerical and very easy to implement. Although it is explicitly derived for a monoisotropic metasurface, it may be straightforwardly extended to the bianisotropic case. Except for some particular case, it is not applicable to dispersive metasurfaces, for which an efficient Auxiliary Different Equation (ADE) extension of the scheme is currently being developed by the authors. The scheme is validated and illustrated by five representative examples.

physics.class-ph↗

arXiv2017

Perfectly Refractive Metasurface using Bianisotropy

A passive and reciprocal perfectly refractive metasurface is designed using a general susceptiblity synthesis method. The metasurface uses weak spatial dispersion in the form of bianisotropy to achieve perfect refraction. Its operation is validated using a full-wave simulation of the metasurface implemented with cascaded metallic layers separated by dielectric.

physics.class-ph↗

arXiv2017

Efficient Analysis of Metasurfaces in Terms of Spectral-Domain GSTC Integral Equations

We present a spectral-domain (SD) technique for the efficient analysis of metasurfaces. The metasurface is modeled by generalized sheet transition conditions (GSTCs) as a zero-thickness sheet creating a discontinuity in the electromagnetic field. The SD expression of these GSTCs for a specified incident field leads to a system of four surface integral equations for the reflected and transmitted fields, which are solved using the method of moments in the spectral domain. Compared to the finite-difference and finite-element techniques that require meshing the entire computational domain, the proposed technique reduces the problem to the surface of the metasurface, hence eliminating one dimension and providing substantial benefits in terms of memory and speed. A monochromatic generalized-refractive metasurface and a polychromatic focusing metasurface are presented as illustrative examples.

physics.optics↗

arXiv2017

Optical Isolation based on Space-time Engineered Asymmetric Photonic Bandgaps

Nonreciprocal electromagnetic devices play an important role in modern optical and microwave technologies. Conventional methods for realizing such systems are incompatible with integrated circuits. With recent advances in integrated photonics, the need for efficient on-chip magnetless nonreciprocal devices is more urgent than ever. This paper leverages space-time engineered asymmetric photonic bandgaps to generate optical isolation. It is shown that a properly designed space-time modulated slab is highly reflective/transparent for opposite directions of propagation. The proposed method requires a low modulation frequency, is magnetless and can achieve very high isolation levels. Experimental proof of concept at microwave frequencies is provided.

physics.optics↗

arXiv2017

Mathematical Synthesis and Analysis of Nonlinear Metasurfaces

We propose a discussion on the synthesis and scattering analysis of nonlinear metasurfaces. For simplicity, we investigate the case of a second-order nonlinear isotropic metasurface possessing both electric and magnetic linear and nonlinear susceptibility components. We next find the synthesis expressions relating the susceptibilities to the specified fields, which leads to the definition of the nonlinear metasurface conditions for no reflection, themselves revealing the nonreciprocal nature of such structures. Finally, we provide the approximate expressions of the scattered fields based on perturbation theory and compare the corresponding results to finite-difference time-domain simulations.

physics.optics↗

arXiv2017

Finite Element Modeling of Metasurfaces with Generalized Sheet Transition Conditions

A modeling of metasurfaces in the finite element method (FEM) based on generalized sheet transition conditions (GSTCs) is presented. The discontinuities in electromagnetic fields across a metasurface as represented by the GSTC are modeled by assigning nodes to both sides of the metasurface. The FEM-GSTC formulation in both 1D and 2D domains is derived and implemented. The method is extended to handle more general bianistroptic metasurfaces. The formulations are validated by several illustrative examples.

physics.class-ph↗