Space-Time Medium Functions as a Perfect Antenna-Mixer-Amplifier Transceiver

We show that a space-time-varying medium can function as a front-end transceiver, i.e., an antenna-mixer-amplifier. Such a unique functionality is endowed by space-time surface waves associated with complex space-time wave vectors in a subluminal space-time medium. The proposed structure introduces pure frequency up- and down-conversions and with very weak undesired time harmonics. In contrast to other recently proposed space-time mixers, a large frequency up-/down conversion ratio, associated with gain is achievable. Furthermore, as the structure does not operate based on progressive energy transition between the space-time modulation and the incident wave, it possesses a subwavelength thickness (metasurface). Such a multi-functional, highly efficient and compact medium is expected to find various applications in modern wireless telecommunication systems

Offsetting self-phase modulation in optical fibre by sinusoidally time-varying phase

We report on our recent experimental and theoretical results on the use of a sinusoidally time-varying phase to suppress undesirable self-phase modulation of optical pulses propagating in fibre-optic systems

Parasitic Element Time-Modulation for Enhanced Effective Inter-Antenna Coupling: Utilization for Improved Gain-Bandwidth

Time variation has been recently introduced as an additional degree of freedom for wave engineering, that enables going beyond the performances that are expected by linear time-invariant (LTI) systems. In this paper, we introduce the concept of indirect time-modulation of antennas using an add-on time-varying scatterer (parasitic element) that gives rise to an inherent feedback mechanism via the airborne wave system. As opposed to a direct modulated system where a time-dependent element is in contact with the other elements, in an indirect time modulation scheme \emph{no} direct physical contact between the original LTI network and the time-varying add-on scatterer is needed, thus leading to additional flexibility in the design. Using indirect time modulation we demonstrate enhanced effective coupling between remote antenna elements, and the possibility to outperform the gain-bandwidth achieved for the same antenna structure but without time-modulation.Comment: 11 pages 5 figure

Universality of modulation length (and time) exponents

We study systems with a crossover parameter lambda, such as the temperature T, which has a threshold value lambda* across which the correlation function changes from exhibiting fixed wavelength (or time period) modulations to continuously varying modulation lengths (or times). We report on a new exponent, nuL, characterizing the universal nature of this crossover. These exponents, similar to standard correlation length exponents, are obtained from motion of the poles of the momentum (or frequency) space correlation functions in the complex k-plane (or omega-plane) as the parameter lambda is varied. Near the crossover, the characteristic modulation wave-vector KR on the variable modulation length "phase" is related to that on the fixed modulation length side, q via |KR-q|\propto|T-T*|^{nuL}. We find, in general, that nuL=1/2. In some special instances, nuL may attain other rational values. We extend this result to general problems in which the eigenvalue of an operator or a pole characterizing general response functions may attain a constant real (or imaginary) part beyond a particular threshold value, lambda*. We discuss extensions of this result to multiple other arenas. These include the ANNNI model. By extending our considerations, we comment on relations pertaining not only to the modulation lengths (or times) but also to the standard correlation lengths (or times). We introduce the notion of a Josephson timescale. We comment on the presence of "chaotic" modulations in "soft-spin" and other systems. These relate to glass type features. We discuss applications to Fermi systems - with particular application to metal to band insulator transitions, change of Fermi surface topology, divergent effective masses, Dirac systems, and topological insulators. Both regular periodic and glassy (and spatially chaotic behavior) may be found in strongly correlated electronic systems.Comment: 22 pages, 15 figure

Floquet–Mie Theory for Time‐Varying Dispersive Spheres

Exploring the interaction of light with time-varying media is an intellectual challenge that, in addition to fundamental aspects, provides a pathway to multiple promising applications. Time modulation constitutes here a fundamental handle to control light on entirely different grounds. That holds particularly for complex systems simultaneously structured in space and time. However, a realistic description of time-varying materials requires considering their material dispersion. The combination thereof has barely been considered but is crucial since dispersion accompanies materials suitable for dynamic modulation. As a canonical scattering problem from which many general insights can be obtained, a self-consistent analytical theory of light scattering by a sphere made from a time-varying material exemplarily assumed to have a Lorentzian dispersion is developed and applied. The eigensolutions of Maxwell\u27s equations in the bulk are discussed and a dedicated Mie theory is presented. The proposed theory is verified with full-wave simulations. Peculiar effects are disclosed, such as energy transfer from the time-modulation subsystem to the electromagnetic field, amplifying carefully structured incident fields. Since many phenomena can be studied on analytical grounds with the proposed formalism, it represents an indispensable tool that enables exploration of electromagnetic phenomena in time-varying and spatially structured finite objects of other geometries