arXiv subjects

M. Lakshmanan

Publications and source records attributed to M. Lakshmanan.

At least 73 records · Page 4Linked to original sources

arXiv2021

Modulation instability induced supercontinuum generation in liquid core suspended photonic crystal fiber with cubic-quintic nonlinearities

In this paper, we propose a liquid core suspended photonic crystal fiber (LCSPCF) as a potential waveguide structure for nonlinear applications. We emphasize the dramatic improvement of the nonlinear properties of the PCF through the infiltration of liquid and highlight the effect of suspension in the further enhancement of nonlinearity. To demonstrate the capability of LCSPCF, we perform a modulation instability (MI) study and illustrate the MI enhancement in the LCSPCF against conventional PCF. As the LCSPCF possesses high nonlinearity, it is important to consider the effects of higher-order nonlinearities. We observe that the quintic nonlinearity (QN) increases the MI for cooperating nonlinearities while it suppresses the MI for competing nonlinearities. We have also importantly studied the effect of QN on the MI induced supercontinuum generation (SCG) for silica and CS2 liquid core PCF. Thus, we propose the LCSPCF as a platform for nonlinear applications such as SCG, pulse compression, etc., owing to the presence of high and controllable nonlinear coefficients.

physics.optics↗

arXiv2021

Large Amplitude Spin-Hall Oscillations due to Field-like Torque

Large amplitude spin-Hall oscillations are identified in a ferromagnetic layer with two perpendicular in-plane easy axis in the presence of field-like torque without any polarizer and external field. The analytical study confirms the possibility of oscillations in the presence of field-like torque. The investigation shows that the oscillation frequency can be tuned from 2 GHz to 80 GHz by current and enhanced by field-like torque. Further, the enhancement of frequency along with the Q-factor by current and field-like torque is also observed.

nlin.AO↗

arXiv2021

Multihumped nondegenerate fundamental bright solitons in $N$-coupled nonlinear Schrödinger system

In this letter we report the existence of nondegenerate fundamental bright soliton solution for coupled multi-component nonlinear Schrödinger equations of Manakov type. To derive this class of nondegenerate vector soliton solutions, we adopt the Hirota bilinear method with appopriate general class of seed solutions. Very interestingly the obtained nondegenerate fundamental soliton solution of the $N$-coupled nonlinear Schrödinger (CNLS) system admits multi-hump natured intensity profiles. We explicitly demonstrate this specific property by considering the nondegenerate soliton solutions for $3$ and $4$-CNLS systems. We also point out the existence of a special class of partially nondegenerate soliton solutions by imposing appropriate restrictions on the wavenumbers in the already obtained completely nondegenerate soliton solution. Such class of soliton solutions can also exhibit multi-hump profile structures. Finally, we present the stability analysis of nondegenerate fundamental soliton of the $3$-CNLS system as an example. The numerical results confirm the stability of triple-humped profile nature against perturbations of 5\% and 10\% white noise. The multi-hump nature of nondegenerate fundamental soliton solution will be usefull in multi-level optical communication applications with enhanced flow of data in multi-mode fibers.

nlin.PS↗

arXiv2021

Stable Bloch oscillations and Landau-Zener tunneling in a non-Hermitian $\cal{PT}$-symmetric flat band lattice

This article aims to study the existence of stable Bloch oscillations and Landau-Zener tunneling in a non-Hermitian system when exposed to external fields. We investigate a non-Hermitian $\cal{PT}$-symmetric diamond chain network and its transport dynamics in two different situations, namely in a flat band case and a non-flat band case. The considered system does not support unbroken-$\cal{PT}$ phase or completely real eigenspectra in any of the parametric regions in both the flat and non-flat band cases. In the flat band case, up to a critical value of the gain-loss parameter, the bands are found to be gapless or inseparable, and for other values the bands are isolated. Considering the non-flat band case, all the bands are found to be complex dispersive and are also isolated. In the case of completely broken $\cal{PT}$ phase, we look upon the possibility to have stable dynamics or Bloch oscillations upon the application of external fields like synthetic electric field. In particular, when the complex bands are isolated, we point out that the Landau-Zener tunneling induced by the synthetic electric field can enable Bloch oscillations. The amplitude of these Bloch oscillations is large and persists for a long propagation distance which reveals that super Bloch oscillations can be observed in the broken $\cal{PT}$ phase of the system. We also report the amplified Bloch oscillations which pave the way towards controlling transport phenomena in non-Hermitian systems.

quant-ph↗

arXiv2020

Dispersion Managed Generation of Peregrine Solitons and Kuznetsov-Ma Breather in an Optical Fiber

Optical rogue waves and its variants have been studied quite extensively in the context of optical fiber in recent years. It has been realized that dispersion management in optical fiber is experimentally much more feasible compared to its nonlinear counterpart. In this work, we report Kuznetsov-Ma (KM)-like breathers from the first three orders of rational solutions of the nonlinear Schrödinger equation with periodic modulation of the dispersion coefficient along the fiber axis. The breather dynamics are then controlled by proper choice of modulating parameters. Additionally, the evolution of new one-peak and two-peak breather-like solutions has been displayed corresponding to the second-order rational solution. Direct numerical simulations based on modulational instability has also been executed which agree well with the analytical results, thereby making the proposed system more feasible for experimental realization.

physics.optics↗

arXiv2020

$N$-channel comb filtering and lasing in $\mathcal{PT}$-symmetric superstructures

A comb spectrum generating device based on Bragg grating superstructures with gain and loss is suggested in this paper. It includes a comprehensive analysis of the device formulation, generation and manipulation of the comb spectrum with a number of degrees of freedom such as duty cycle, sampling period and gain-loss parameter. For applications such as RF traversal filters and tunable multi-wavelength laser sources, the reflected intensities of the comb resulting from the superstructures should have uniform intensities, and this is guaranteed by optimizing the physical length of the device, gain and loss in the unbroken $\mathcal{PT}$-symmetric regime. Alternatively, it can be accomplished by reducing the duty cycle ratio of the superstructure to extremely small values in the broken $\mathcal{PT}$-symmetric regime. Such a customization will degrade the reflectivity of the conventional grating superstructures, while it gives rise to narrow spectral lines with high reflectivity in the proposed system. Remarkably, combs with an inverted envelope are generated for larger values of gain and loss.

physics.optics↗

arXiv2020

Dynamical modelling and analysis of COVID-19 in India

We consider the pandemic spreading of COVID-19 in India after the outbreak of the coronavirus in Wuhan city, China. We estimate the transmission rate of the initial infecting individuals of COVID-19 in India by using the officially reported data at the early stage of the epidemic with the help of Susceptible (S), Exposed (E), Infected (I), and Removed (R) population model, the so-called SEIR dynamical model. Numerical analysis and model verification are performed to calibrate the system parameters with official public information about the number of people infected, and then to evaluate several COVID -19 scenarios potentially applicable to India. Our findings provide an estimation of disease occurrence in the near future and also demonstrate the importance of governmental and individual efforts to control the effects and time of the pandemic-related critical situations. We also give special emphasis to individual reactions in the containment process.

q-bio.PE↗

arXiv2020

Modulational instability in non-Kerr photonic Lieb lattice with metamaterials

We present an analysis of modulational instability of diffractionless waves in a face-centered square lattice of waveguides featuring non-Kerr nonlinearity, which are constituted by a combination of positive and negative refractive indices. The unit cell of the lattice consists of three different waveguides with different optical properties. The dispersion curve of the lattice supports flat bands and thereby the base equations describing the model have particular solutions that correspond to the diffractionless waves propagating along the waveguides. We also observe a unique ramification of nonlinearities in controlling the flat bands optically. The diffractionless wave solutions are derived and the stability of these distributions are investigated in a nutshell by adopting the standard linear stability approach.

nlin.PS↗

arXiv2020

Reviving Modulational Instability with Third-Order Dispersion

It is well-known that third-order dispersion (TOD) never allows the continuous wave of any nonlinear Schroedinger (NLS) type system to experience modulational instability (MI). Remarkably, we demonstrate a new kind of MI induced by TOD with spatial dispersion accounting for Wannier exciton mass in a ZnCdSe/ZnSe semiconductor superlattice. We also numerically predict the existence of novel Akhmediev breathers and Peregrine solitons due to the nonlinear development of MI with TOD.

nlin.PS↗

arXiv2020

Self-diffusion Driven Pattern Formation in Prey-Predator System with Complex Habitat under Fear Effect

In the present work, we explore the influence of habitat complexity on the activities of prey and predator of a spatio-temporal system by incorporating self diffusion. First we modify the Rosenzweig-MacArthur predator-prey model by incorporating the effects of habitat complexity on the carrying capacity and fear effect of prey and predator functional response. We establish conditions for the existence and stability of all feasible equilibrium points of the non-spatial model and later we prove the existence of Hopf and transcritical bifurcations in different parametric phase-planes analytically and numerically. The stability of the spatial system is studied and we discuss the conditions for Turing instability. Selecting suitable control parameter from the Turing space, the existence conditions for stable patterns are derived using the amplitude equations. Results obtained from theoretical analysis of the amplitude equations are justified by numerical simulation results near the critical parameter value. Further, from numerical simulation, we illustrate the effect of diffusion of the dynamical system in the spatial domain by different pattern formations. Thus our model clearly shows that the fear effect of prey and predator's functional response make an anti-predator behaviour including habitat complexity which helps the prey to survive in the spatio-temporal domain through diffusive process.

nlin.PS↗

arXiv2020

Nondegenerate Solitons and their Collisions in Manakov System

Recently, we have shown that the Manakov equation can admit a more general class of nondegenerate vector solitons, which can undergo collision without any intensity redistribution in general among the modes, associated with distinct wave numbers, besides the already known energy exchanging solitons corresponding to identical wave numbers. In the present comprehensive paper, we discuss in detail the various special features of the reported nondegenerate vector solitons. To bring out these details, we derive the exact forms of such vector one-, two- and three-soliton solutions through Hirota bilinear method and they are rewritten in more compact forms using Gram determinants. The presence of distinct wave numbers allows the nondegenerate fundamental soliton to admit various profiles such as double-hump, flat-top and single-hump structures. We explain the formation of double-hump structure in the fundamental soliton when the relative velocity of the two modes tends to zero. More critical analysis shows that the nondegenerate fundamental solitons can undergo shape preserving as well as shape altering collisions under appropriate conditions. The shape changing collision occurs between the modes of nondegenerate solitons when the parameters are fixed suitably. Then we observe the coexistence of degenerate and nondegenerate solitons when the wave numbers are restricted appropriately in the obtained two-soliton solution. In such a situation we find the degenerate soliton induces shape changing behavior of nondegenerate soliton during the collision process. By performing suitable asymptotic analysis we analyze the consequences that occur in each of the collision scenario. Finally we point out that the previously known class of energy exchanging vector bright solitons, with identical wave numbers, turns out to be a special case of the newly derived nondegenerate solitons.

nlin.PS↗

arXiv2020

Route to logical strange nonchaotic attractors with single periodic force and noise

Strange nonchaotic attractors (SNAs) have been identified and studied in the literature exclusively in quasiperiodically driven nonlinear dynamical systems. It is an interesting question to ask whether they can be identified with other types of forcings as well, which still remains as an open problem. Here, we show that robust SNAs can be created by a small amount of noise in periodically driven nonlinear dynamical systems by a single force. The robustness of these attractors is tested by perturbing the system with logical signals leading to the emulation of different logical elements in the SNA regions.

nlin.AO↗

arXiv2020

Impact of higher-order effects on dissipative soliton in metamaterials

We study the influence of higher-order effects such as third order dispersion (TOD), fourth order dispersion (FOD), quintic nonlinearity (QN), self steepening (SS) and second order nonlinear dispersion (SOND) on the dynamics of dissipative soliton (DS) in metamaterials. Considering each higher-order effect as a perturbation to the system and following Lagrangian variational method, we demonstrate stable dynamics of DS as a result of the interplay between different higher-order effects. We also perform numerical analysis to confirm the analytical results.

nlin.PS↗

arXiv2020

Phase shifted $\mathcal{PT}$-symmetric periodic structures

We report the spectral features of a phase-shifted parity and time ($\mathcal{PT}$)-symmetric fiber Bragg grating (PPTFBG) and demonstrate its functionality as a demultiplexer in the unbroken $\mathcal{PT}$-symmetric regime. The length of the proposed system is of the order of millimeters and the lasing spectra in the broken $\mathcal{PT}$-symmetric regime can be easily tuned in terms of intensity, bandwidth and wavelength by varying the magnitude of the phase shift in the middle of the structure. Surprisingly, the multi-modal lasing spectra are suppressed by virtue of judiciously selected phase and the gain-loss value. Also, it is possible to obtain sidelobe-less spectra in the broken $\mathcal{PT}$-symmetric regime, without a need for an apodization profile, which is a traditional way to tame the unwanted sidelobes. The system is found to show narrow band single-mode lasing behavior for a wide range of phase shift values for given values of gain and loss. Moreover, we report the intensity tunable reflection and transmission characteristics in the unbroken regime via variation in gain and loss. At the exceptional point, the system shows unidirectional wave transport phenomenon independent of the presence of phase shift in the middle of the grating. For the right light incidence direction, the system exhibits zero reflection wavelengths within the stopband at the exceptional point. We also investigate the role of multiple phase shifts placed at fixed locations along the length of the FBG and the variations in the spectra when the phase shift and gain-loss values are tuned. In the broken $\mathcal{PT}$-symmetric regime, the presence of multiple phase shifts aids in controlling the number of reflectivity peaks besides controlling their magnitude.

physics.optics↗

arXiv2020

Influence of field-like torque in synchronization of spin torque oscillators

The magnetization dynamics of two parallelly coupled spin torque oscillators, destabilization of steady states and removal of multistability, are investigated by taking into account the influence of field-like torque. It is shown that the existence of such torque can cancel the effect of damping and can, therefore, cause the oscillators to exhibit synchronized oscillations in response to direct current. Further, our results show that the presence of field-like torque enhances the power and Q-factor of the synchronized oscillations. The validity of the above results is confirmed by numerical and analytical studies based on the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation.

nlin.AO↗

arXiv2020

Sliding Bifurcations in the Memristive Murali-Lakshmanan-Chua Circuit and the Memristive Driven Chua Oscillator

In this paper we report the occurrence of sliding bifurcations admitted by the memristive Murali-Lakshmanan-Chua circuit \cite{icha13} and the memristive driven Chua oscillator \citep{icha11}. Both of these circuits have a flux-controlled active memristor designed by the authors in 2011, as their non-linear element. The three segment piecewise-linear characteristic of this memristor bestows on the circuits two discontinuity boundaries, dividing their phase spaces into three sub-regions. For proper choice of parameters, these circuits take on a degree of smoothness equal to one at each of their two discontinuities, thereby causing them to behave as \textit{Filippov} systems. Sliding bifurcations, which are characteristic of Filippov systems, arise when the periodic orbits in each of the sub-regions, interact with the discontinuity boundaries, giving rise to many interesting dynamical phenomena. The numerical simulations are carried out after incorporating proper zero time discontinuity mapping (ZDM) corrections. These are found to agree well with the experimental observations which we report here appropriately.

nlin.AO↗

arXiv2020

Self-trapped dynamics of a hollow Gaussian beam in metamaterials

We present a systematic investigation on the dynamics of a hollow Gaussian beam (HGB) in metamaterials. We predict self-trapped propagation of HGBs and evolution of the beam is highly influenced by dimensionless dispersion coefficient (k), which determines the strength of dispersion over diffraction. The evolutions of HGBs such as disappearance of single ringed intensity pattern and appearance of patterns with a central bright spot are achievable with less propagation distance in metamaterials with higher values of k. On the other hand, metamaterials with low values of k can preserve single ring intensity distribution over a long propagation distance without focusing. When the strength of dispersion over diffraction increases, it significantly influences the evolution of the beam and may lead to the formation of tightly focussed beam with high peak intensity at the center. The phenomenon of tight focussing is found to have some applications in trapping of nanosized particles.

nlin.PS↗

arXiv2020

Frequency enhancement and power tunability in tilted polarizer spin-torque nano oscillator

In the absence of an applied magnetic field, a spin-torque nano oscillator(STNO) with a tilted polarizer is studied using numerical simulation of the associated Landau-Lifshitz-Gilbert-Slonczewski equation. We find considerable enhancement of frequency by tilting the polarizer out-of-plane appropriately. Also, we observe improved tunability of frequency of oscillations from 15 GHz to 75 GHz and increment in the power spectral density by current and tilt angle. In addition, our findings and insights pave a simple way for nanoscale level microwave generators to be implemented.

cond-mat.mes-hall↗