arXiv subjects

Christophe Caloz

Publications and source records attributed to Christophe Caloz.

At least 127 records · Page 7Linked to original sources

arXiv2015

Synthesis of Electromagnetic Metasurfaces: Principles and Illustrations

The paper presents partial overview of the mathematical synthesis and the physical realization of metasurfaces, and related illustrative examples. The synthesis consists in determining the exact tensorial surface susceptibility functions of the metasurface, based on generalized sheet transition conditions, while the realization deals with both metallic and dielectric scattering particle structures. The examples demonstrate the capabilities of the synthesis and realization techniques, thereby showing the plethora of possible metasurface field transmission and subsequent applications. The first example is the design of two diffraction engineering birefringent metasurfaces performing polarization beam splitting and orbital angular momentum multiplexing, respectively. Next, we discuss the concept of the "transistor" metasurface, which is an electromagnetic linear switch based on destructive interferences. Then, we introduce a non-reciprocal non-gyrotropic metasurface using a pick-up circuit radiator (PCR) architecture. Finally, the implementation of all-dielectric metasurfaces for spatial dispersion engineering is discussed.

physics.optics↗

arXiv2015

Metasurface Spatial Processor for Electromagnetic Remote Control

We introduce the concept of metasurface spatial processor, whose transmission is remotely and coherently controlled by the superposition of an incident wave and a control wave through the metasurface. The conceptual operation of this device is analogous to both that of a transistor and a Mach-Zehnder interferometer, while offering much more diversity in terms of electromagnetic transformations. We demonstrate two metasurfaces, that perform the operation of electromagnetic switching and amplification.

physics.optics↗

arXiv2015

Loss-Gain Equalized Reconfigurable Phaser for Dynamic Radio Analog Signal Processing (R-ASP)

We present a loss-gain equalized reconfigurable phaser for dynamic radio analog signal processing (R-ASP). Such a phaser provides real-time tunable group delay response with all-pass transmission. We propose a lumped loss-gain implementation, where tuning and equalization are mostly easily achieved. A theoretical study derives the transfer function and the fundamental characteristics of the device. The phaser is finally experimentally demonstrated, first using a single loss-gain pair and finally a three cascaded loss-gain pair structure with full reconfigurability , where up-chirp and down-chirp group delays are shown for illustration. It is expected that this phaser will find wide applications in radio analog signal processing (R-ASP) systems requiring dynamic adaptability.

physics.optics↗

arXiv2015

Space-Time Cross-Mapping and Application to Wave Scattering

Causality creates an asymmetry between space and time, even though the wave equation treats them on equal footing. In this work, we leverage this asymmetry to construct a cross-mapping between space and time. This cross-mapping is applied to simplify scattering in space-varying media, by eliminating the infinite reflections between interfaces. The method is shown to transform the implicit transfer matrix method into an explicit method for the analysis of electromagnetic field scattering by a stratified medium.

physics.optics↗

arXiv2015

General Metasurface Synthesis Based on Susceptibility Tensors

A general method, based on susceptibility tensors, is proposed for the synthesis of metasurfaces transforming arbitrary incident waves into arbitrary reflected and transmitted waves. The proposed method exhibits two advantages: 1)it is inherently vectorial, and therefore better suited for full vectorial (beyond paraxial) electromagnetic problems, 2) it provides closed-form solutions, and is therefore extremely fast. Incidentally, the method reveals that a metasurface is fundamentally capable to transform up to four independent wave triplets (incident, reflected and refracted waves). In addition, the paper provides the closed-form expressions relating the synthesized susceptibilities and the scattering parameters simulated within periodic boundary conditions, which allows one to design the scattering particles realizing the desired susceptibilities. The versatility of the method is illustrated by examples of metasurfaces achieving the following transformations: generalized refraction, reciprocal and non-reciprocal polarization rotation, Bessel vortex beam generation, and orbital angular momentum multiplexing.

physics.optics↗

arXiv2015

Single-Step Tunable Group Delay Phaser for Real-Time Spectrum Sniffing

This paper presents a single-step tunable group delay phaser for spectrum sniffing. This device may be seen as a "time filter", where frequencies are suppressed by time separation rather than by spectral attenuation. Compared to its multiple-step counterpart, this phaser features higher processing resolution, greater simplicity, lower loss and better channel equalization, due to the smaller and channel-independent group delay swing. A three-channel example is provided for illustration.

physics.optics↗

arXiv2015

Electromagnetic Fields Radiated by a Circular Loop with Arbitrary Current

We present a rigorous approach to compute the electromagnetic fields radiated by a thin circular loop with arbitrary current. We employ a polar transmission representation along with a Kontorovich-Lebedev transform to derive integral representations of the field in the interior and exterior regions of a sphere circumscribing the loop. The convergence of the obtained expressions is discussed and comparisons with full-wave simulation and other methods are shown.

physics.class-ph↗

arXiv2014

Spatio-TemporalMetasurface for Real-time 2-D Spectrum Analysis

A spatio-temporal metasurface is proposed to decompose in real time the temporal frequencies of electromagnetic waves into spatial frequencies onto a two-dimensional plane. The metasurface is analyzed and demonstrated using Fourier analysis. The required transmittance function is derived from an equivalent free-space optical system consisting of the cascade combination of a wedge, a diffraction grating and a focusing lens. The metasurface must exhibit both multi-resonance over a broad bandwidth and 1-D grating-type scanning to achieve the specified 2-D frequency scanning in space. Compared to state-of-the art related systems, the proposed metasurface system is more compact as it requires only one dispersive structure, while maintaining the high frequency resolution that characterizes 2-D spatial-temporal mapping systems.

physics.optics↗

arXiv2014

Enhancement of Time Reversal Sub-wavelength Wireless Transmission Using Pulse Shaping Technique (submit/1139227)

A novel time-reversal subwavelength transmission technique, based on pulse shaping circuits (PSCs), is proposed. This technique removes the need for complex or electrically large electromagnetic structures by generating channel diversity via pulse shaping instead of angular spectrum transformation. It is shown that, compared to our previous time-reversal system based on chirped delay lines, the PSC approach offers greater flexibility and larger possible numbers of channels, i.e. ultimately higher transmission throughput. The PSC based time-reversal system is also demonstrated experimentally.

physics.optics↗

arXiv2014

Manipulating light at distance by a metasurface using momentum transformation

A momentum conservation approach is introduced to manipulate light at distance using metasurfaces. Given a specified field existing on one side of the metasurface and specified desired field transmitted from the opposite side, a general momentum boundary condition is established, which determines the amplitude, phase and polarization transformation to be induced by the metasurface. This approach, named momentum transformation, enables a systematic way to synthesize metasurfaces with complete control over the reflected and transmitted fields. Several synthesis illustrative examples are provided: a vortex hypergeometric-Gaussian beam and a "delayed-start" accelerated beam for Fresnel region manipulation, and a pencil beam radiator and a holographic repeater for Frauenhofer region manipulation.

physics.optics↗

arXiv2014

Compact Reflection-Type Phaser Using Quarter-Wavelength Transmission Line Resonators

A compact reflection-type phaser composed of quarter-wavelength transmission line resonators interconnected by alternating K- and J-inverters is proposed. A design method is also presented. To validate this method, a 4th-order example is designed and fabricated. The proposed phaser is shown to exhibit the benefits of smaller size, easier fabrication and suppressed even-order harmonics compared with previously reported half-wavelength phasers.

physics.class-ph↗

arXiv2014

Coupling Matrix Synthesis of Nonreciprocal Lossless Two-Port Networks using Gyrators and Inverters

A coupling matrix technique is presented for the synthesis of nonreciprocal lossless two-port networks. This technique introduces complex inverters to build the nonreciprocal transversal network corresponding to the nonreciprocal coupling matrix. It subsequently transforms this matrix into canonical topologies through complex similarity transformations. The complex inverters in the final topology are transformed into real inverters and gyrators for implementation simplicity. A second-order example is then given to illustrate the proposed technique. Possible implementations of the gyrators involved in the final design are also discussed.

physics.optics↗

arXiv2014

Enhancement of Time-Reversal Subwavelength Wireless Transmission Using Pulse Shaping

A novel time-reversal subwavelength transmission technique, based on pulse shaping circuits (PSCs), is proposed. Compared to previously reported approaches, this technique removes the need for complex or electrically large electromagnetic structures by generating channel diversity via pulse shaping instead of angular spectrum transformation. Moreover, the pulse shaping circuits (PSCs) are based on Radio Analog Signal Processing (R-ASP), and therefore do not suffer from the well-known issues of digital signal processing in ultrafast regimes. The proposed PSC time-reversal systems is mathematically shown to offer high channel discrimination under appropriate PSC design conditions, and is experimentally demonstrated for the case of two receivers.

physics.optics↗

arXiv2014

A High-Resolution Transmission-Type (TT) Phaser Based on Reflection-Type (RT) Units for Radio Analog Signal Processing (R-ASP)

A high Radio Analog Signal Processing (R-ASP) resolution transmission-type (TT) phaser based on reflection-type (RT) phaser units is introduced, theoretically studied and experimentally demonstrated. It is first shown that RT phasers inherently exhibit higher R-ASP resolution than their TT counterparts because their group delay swing is proportional to the reflection coefficient associated with a resonator coupling mechanism (admittance inverter), easy to maximize towards unity, rather than to a coupled-line coupling coefficient, typically restricted to values will inferior to unity, as in the RT case. Moreover, a detailed sensitivity analysis reveals that the proposed phaser is simultaneously features high R-ASP resolution and low sensitivity to fabrication tolerance, which makes it an ideal solution for R-ASP. The proposed phaser exhibits a 5 ns group delay swing over a fractional bandwidth of about 50% around 4 GHz.

physics.optics↗

arXiv2014

Planar Reflective Phaser and Synthesis for Radio Analog Signal Processing (R-ASP)

A planar reflective phaser based on an open-ended edge-coupled-line structure is proposed. This phaser is the first reported phaser that combines the benefits of high resolution, inherent to cross-coupled resonator reflective phasers, and of compactness, inherent to planar circuits. A 4-ns swing 4.9-5.5 GHz quadratic phase (linear group delay) 4th-order microstrip phaser is synthesized and experimentally demonstrated. Given its advantages, this phaser may find vast applications in Radio Analog Signal Processing (R-ASP) systems.

physics.optics↗

arXiv2014

Circular Polarization of Periodic Leaky-Wave Antennas with Axial Asymmetry: Theoretical Proof and Experimental Demonstration

The paper includes two contributions. First, it proves that the series and shunt radiation components, corresponding to longitudinal and transversal electric fields, respectively, are always in phase quadrature in axially asymmetric periodic leaky-wave antennas (LWAs), so that these antennas are inherently elliptically polarized. This fact is theoretically proven and experimentally illustrated by two case-study examples, a composite right/left-handed (CRLH) LWA and a series-fed patch (SFP) LWA. Second, it shows (for the case of the SFP LWA) that the axial ratio is controlled and minimized by the degree of axial asymmetry.

physics.class-ph↗

arXiv2014

Enhanced-SNR Impulse Radio Transceiver based on Phasers

The concept of SNR enhancement in impulse radio transceivers based on phasers of opposite chirping slopes is introduced. It is shown that signal to-noise radio (SNR) enhancements by factors M2 and M are achieved for burst noise and Gaussian noise, respectively, where M is the stretching factor of the phasers. An experimental demonstration is presented, using stripline cascaded C-section phasers, where SNR enhancements in agreement with theory are obtained. The proposed radio analog signal processing transceiver system is simple, low-cost and frequency scalable, and may therefore be suitable for broadband impulse radio ranging and communication applications.

physics.optics↗

arXiv2014

Magneto-Electric Dipole Antenna Arrays

A planar magneto-electric (ME) dipole antenna array is proposed and demonstrated by both full-wave analysis and experiments. The proposed structure leverages the infinite wavelength propagation characteristic of composite right/left-handed (CRLH) transmission lines to form high-gain magnetic radiators combined with radial conventional electric radiators, where the overall structure is excited by a single differential feed. The traveling-wave type nature of the proposed ME-dipole antenna enables the formation of directive arrays with high-gain characteristics and scanning capability. Peak gains of 10.84 dB and 5.73 dB are demonstrated for the electric dipole and magnetic-dipole radiation components, respectively.

physics.optics↗