arXiv subjects

Tsampikos Kottos

Publications and source records attributed to Tsampikos Kottos.

At least 73 records · Page 4Linked to original sources

arXiv2017

Self-Regulated Transport in Photonic Crystals with Phase-Changing Defects

Phase changing materials (PCM) are widely used for optical data recording, sensing, all-optical switching, and optical limiting. Our focus here is on the case when the change in the transmission characteristics of the optical material is caused by the input light itself. Specifically, the light-induced heating triggers the phase transition in the PCM. In this paper, using a numerical example, we demonstrate that incorporating the PCM in a photonic structure can lead to a dramatic modification of the effects of light-induced phase transition, as compared to a stand-alone sample of the same PCM. Our focus is on short pulses. We discuss some possible applications of such phase-changing photonic structures for optical sensing and limiting.

physics.optics↗

arXiv2017

Giant Non-reciprocity Near Exceptional Point Degeneracies

We show that gyrotropic structures with balanced gain and loss that respect anti-linear symmetries exhibit a giant non-reciprocity at the so-called exact phase where the eigenfrequencies of the isolated non-Hermitian set-up are real. The effect occurs in a parameter domain near an exceptional point (EP) degeneracy, where mode-orthogonality collapses. The theoretical predictions are confirmed numerically in the microwave domain, where a non-reciprocal transport above 90dB is demonstrated, and are further verified using lump-circuitry modeling. The analysis allows us to speculate the universal nature of the phenomenon for any wave system where EP and gyrotropy can co-exist.

physics.class-ph↗

arXiv2016

Half-period Aharonov-Bohm oscillations in disordered rotating optical ring cavities

There exists an analogy between Maxwell equations in a rotating frame and Schrödinger equation for a charged particle in the presence of a magnetic field. We exploit this analogy to point out that electromagnetic phenomena in the rotating frame, under appropriate conditions, can exhibit periodicity with respect to the angular velocity of rotation. In particular, in disordered ring cavities one finds the optical analog of the Al'tshuler-Aronov-Spivak effect well known in mesoscopic physics of disordered metals.

physics.optics↗

arXiv2016

Resistor-network anomalies in the heat transport of random harmonic chain

We consider thermal transport in low-dimensional disordered harmonic networks of coupled masses. Utilizing known results regarding Anderson localization, we derive the actual dependence of the thermal conductance $G$ on the length $L$ of the sample. This is required by nanotechnology implementations because for such networks Fourier's law $G \propto 1/L^α$ with $α=1$ is violated. In particular we consider "glassy" disorder in the coupling constants, and find an anomaly which is related by duality to the Lifshitz-tail regime in the standard Anderson model.

cond-mat.dis-nn↗

arXiv2016

Experimental Realization of a Reflective Optical Limiter

Optical limiters transmit low-intensity light, while blocking laser radiation with excessively high intensity or fluence. A typical passive optical limiter absorbs most of the high level radiation, which can cause irreversible damage. In this communication we report the first experimental realization of a reflective optical limiter, which does not absorb the high-level laser radiation, but rather reflects it back to space. The design is based on a periodic layered structure composed of alternating SiO2 and Si3N4 layers with a single GaAs defect layer in the middle. At low intensities, the layered structure displays a strong resonant transmission via the localized defect mode. At high intensities, the two-photon absorption in the GaAs layer suppresses the localized mode along with the resonant transmission, the entire layered structure turns highly reflective within a broad frequency range covering the entire photonic band gap of the periodic layered structure. By contrast, a stand-alone GaAs layer would absorb most of the high-level radiation, thus acting as a basic absorptive optical limiter. The proposed design can only perform at shortwave IR, where GaAs displays negligible linear absorption and very strong nonlinear two-photon absorption. With judicious choice of optical materials, the same principle can be replicated for any other frequency range.

physics.optics↗

arXiv2016

Low-Temperature Linear Thermal Rectifiers Based on Coriolis forces

We demonstrate that a three-terminal harmonic symmetric chain in the presence of a Coriolis force, produced by a rotating platform which is used to place the chain, can produce thermal rectification. The direction of heat flow is reconfigurable and controlled by the angular velocity $Ω$ of the rotating platform. A simple three terminal triangular lattice is used to demonstrate the proposed principle.

cond-mat.mes-hall↗

arXiv2015

Hypersensitive Transport in Photonic Crystals with Accidental Spatial Degeneracies

A localized defect mode in a photonic-layered structure develops nodal points. Placing a thin metallic layer at such a nodal point results in the phenomenon of induced transparency. We demonstrate that if this nodal point is not a point of symmetry, then even a tiny alteration of the permittivity in the vicinity of the defect suppresses the localized mode along with the resonant transmission; the layered structure becomes highly reflective within a broad frequency range. Applications of this hypersensitive transport for optical limiting and switching are discussed.

physics.optics↗

arXiv2015

Interference of sound waves in a moving fluid

We investigate sound propagation in a moving fluid confined in a randomly corrugated tube. For weak randomness and small fluid velocities $v^{(0)}$, the localization length $ξ$ shows extreme sensitivity to the variation of $v^{(0)}$. In the opposite limit of large fluid velocities, $ξ$ acquires a constant value which is independent of the frequency of the incident sound wave, the degree of randomness and $v^{(0)}$ itself. Finally, we find that the standard deviation $σ_{\ln T}$ of the logarithm of transmittance $\ln(T)$ is a universal function of the ensemble average $\langle \ln T\rangle $, which is not affected by the fluid velocity.

cond-mat.dis-nn↗

arXiv2015

Engineering wavefront caustics trajectories in ${\cal PT}$-symmetric lattices

We utilize caustic theory in ${\cal PT}-$symmetric lattices to design focusing and curved beam dynamics. We show that the gain and loss parameter in these systems provides an addition degree of freedom which allows for the design of the same caustics trajectories with different intensity distribution in the individual waveguides. Moreover we can create aberration-free focal points at any paraxial distance $z_f$, with anomalously large focal intensity.

physics.optics↗

arXiv2014

Reflective Optical Limiter Based on Resonant Transmission

Optical limiters transmit low-level radiation while blocking electromagnetic pulses with excessively high energy (energy limiters) or with excessively high peak intensity (power limiters). A typical optical limiter absorbs most of the high-level radiation which can cause its destruction via overheating. Here we introduce the novel concept of a reflective energy limiter which blocks electromagnetic pulses with excessively high total energy by reflecting them back to space, rather than absorbing them. The idea is to use a defect layer with temperature dependent loss tangent embedded in a low-loss photonic structure. The low energy pulses with central frequency close to that of the localized defect mode will pass through. But if the cumulative energy carried by the pulse exceeds certain level, the entire photonic structure reflects the incident light (and does not absorb it!) for a broad frequency window. The underlying physical mechanism is based on self-regulated impedance mismatch which increases dramatically with the cumulative energy carried by the pulse.

physics.optics↗

arXiv2014

Thermal Transport in Phononic Cayley Tree Networks

We analytically investigate the heat current $I$ and its thermal fluctuations $Δ$ in a branching network without loops (Cayley tree). The network consists of two type of harmonic masses: vertex masses $M$ placed at the branching points where phononic scattering occurs and masses $m$ at the bonds between branching points where phonon propagation take place. The network is coupled to thermal reservoirs consisting of one-dimensional harmonic chains of coupled masses $m$. Due to impedance missmatching phenomena, both ${\cal I}$ and $Δ$, are non-monotonic functions of the mass ratio $μ=M/m$. In particular, there are cases where they are strictly zero below some critical value $μ^*$.

cond-mat.stat-mech↗

arXiv2014

A Concept of Linear Thermal Circulator Based on Coriolis forces

We show that the presence of a Coriolis force in a rotating linear lattice imposes a non-reciprocal propagation of the phononic heat carriers. Using this effect we propose the concept of Coriolis linear thermal circulator which can control the circulation of a heat current. A simple model of three coupled harmonic masses on a rotating platform allow us to demonstrate giant circulating rectification effects for moderate values of the angular velocities of the platform.

cond-mat.stat-mech↗

arXiv2013

Non-Linear Localized Modes Give Rise to a Reflective Optical Limiter

Optical limiters are designed to transmit low intensity light, while blocking the light with excessively high intensity. A typical passive limiter absorbs excessive electromagnetic energy, which can cause its overheating and destruction. We propose the concept of a layered reflective limiter based on resonance transmission via a non-linear localized mode. Such a limiter does not absorb the high level radiation, but rather reflects it back to space. Importantly, the total reflection occurs within a broad frequency range and for an arbitrary direction of incidence. The same concept can be applied to infrared and microwave frequencies.

physics.optics↗

arXiv2013

Random Matrix Theory approach to Mesoscopic Fluctuations of Heat Current

We consider an ensemble of fully connected networks of N oscillators coupled harmonically with random springs and show, using Random Matrix Theory considerations, that both the average phonon heat current and its variance are scale-invariant and take universal values in the large N-limit. These anomalous mesoscopic uctuations is the hallmark of strong correlations between normal modes.

cond-mat.stat-mech↗

arXiv2013

Scaling Theory of Heat Transport in Quasi-1D Disordered Harmonic Chains

We introduce a variant of the Banded Random Matrix ensemble and show, using detailed numerical analysis and theoretical arguments, that the phonon heat current in disordered quasi-one-dimensional lattices obeys a one-parameter scaling law. The resulting beta-function indicates that an anomalous Fourier law is applicable in the diffusive regime, while in the localization regime the heat current decays exponentially with the sample size. Our approach opens a new way to investigate the effects of Anderson localization in heat conduction, based on the powerful ideas of scaling theory.

cond-mat.dis-nn↗

arXiv2012

PT-Symmetric Electronics

We show both theoretically and experimentally that a pair of inductively coupled active LRC circuits (dimer), one with amplification and another with an equivalent amount of attenuation, display all the features which characterize a wide class of non-Hermitian systems which commute with the joint parity-time PT operator: typical normal modes, temporal evolution, and scattering processes. Utilizing a Liouvilian formulation, we can define an underlying PT-symmetric Hamiltonian, which provides important insight for understanding the behavior of the system. When the PT-dimer is coupled to transmission lines, the resulting scattering signal reveals novel features which reflect the PT-symmetry of the scattering target. Specifically we show that the device can show two different behaviors simultaneously, an amplifier or an absorber, depending on the direction and phase relation of the interrogating waves. Having an exact theory, and due to its relative experimental simplicity, PT-symmetric electronics offers new insights into the properties of PT-symmetric systems which are at the forefront of the research in mathematical physics and related fields.

cond-mat.other↗

arXiv2012

PT-Symmetric Talbot Effects

We show that complex PT-symmetric photonic lattices can lead to a new class of self-imaging Talbot effects. For this to occur, we find that the input field pattern, has to respect specific periodicities which are dictated by the symmetries of the system. While at the spontaneous PT-symmetry breaking point, the image revivals occur at Talbot lengths governed by the characteristics of the passive lattice, at the exact phase it depends on the gain and loss parameter thus allowing one to control the imaging process.

physics.optics↗

arXiv2012

Bragg solitons in nonlinear PT-symmetric periodic potentials

It is shown that slow Bragg soliton solutions are possible in nonlinear complex parity-time (PT) symmetric periodic structures. Analysis indicates that the PT-symmetric component of the periodic optical refractive index can modify the grating band structure and hence the effective coupling between the forward and backward waves. Starting from a classical modified massive Thirring model, solitary wave solutions are obtained in closed form. The basic properties of these slow solitary waves and their dependence on their respective PT-symmetric gain/loss profile are then explored via numerical simulations.

physics.optics↗