Amarendra K. Sarma

Modulation instability in nonlinear metamaterials induced by cubic–quintic nonlinearities and higher order dispersive effects

Abstract We have investigated modulation instability (MI) in metamaterials (MM) with both cubic and quintic nonlinearities, based on a model appropriate for pulse propagation in MM with cubic–quintic nonlinearities and higher order dispersive effects. We have included loss into account in our analysis and found that loss distorts the sidebands of the MI gain spectrum. We found that the combined effect of cubic–quintic nonlinearity increases the MI gain. The role of higher order nonlinear dispersive effects on MI has also been discussed.

Femtosecond-Soliton Switching in a Three-Core Coupler

Soliton switching in a three-core Kerr-coupler is studied numerically by taking into account intermodal dispersion (IMD), third-order dispersion and higher-order nonlinear effects, like the Raman and self-steepening effects. It is shown that the weak coupling regime is the most suitable for the purpose. Also, it is shown that IMD has negligible influence on switching, while, out of the higher-order nonlinear effects, Raman intrapulse scattering has the dominant effect.

Modulation instability in nonlinear complex parity-time symmetric periodic structures

We carry out a modulation instability (MI) analysis in nonlinear complex parity-time (PT) symmetric periodic structures. All three regimes defined by the PT-symmetry breaking point or threshold, namely, below threshold, at threshold, and above threshold, are discussed. It is found that MI exists even beyond the PT-symmetry threshold, indicating the possible existence of solitons or solitary waves, in conformity with some recent reports. We find that MI does not exist at the PT-symmetry breaking point in the case of normal dispersion below a certain nonlinear threshold. However, in the case of the anomalous dispersion regime, MI does exist even at the PT-symmetry breaking point.

Solitary waves in parity-time (PT)–symmetric Bragg grating structure and the existence of optical rogue waves

In this work, we have studied the traveling wave solution in a nonlinear Bragg grating structure in which the core of the optical fiber is having parity-time (PT)–symmetric refractive index distribution. Below the PT-threshold, we have found a bright-solitary-wave solution for forward waves and a dark-solitary-wave solution for backward waves. The effects of increasing the traveling wave speed on the spatio-temporal evolutions of the analytical solutions have been shown and above the PT-threshold, emergence of the optical rogue waves (ORWs) has been explored based on the system parameters.

Controllable optical bistability in a hybrid optomechanical system

We investigate, theoretically, the effect of optical feedback from a cavity containing an ultracold two-level atomic ensemble, on the bistable behavior shown by a mean intracavity optical field in an optomechanical cavity resonator. It turns out that the optical bistability can be controlled by tuning the frequency and power of the driving laser and is largely affected by the presence of the atomic ensemble in the feedback cavity. In essence, our work emphasizes the possibility of realization of a controllable optical switch depending on the hybrid interaction, commanding lower threshold power than a single optomechanical cavity.

Parity–time-symmetric closed form optical quadrimer waveguides

A closed form parity–time symmetric quadrimer optical waveguide structure, reminiscent of the four-state quantum system found in quantum optics, was studied. The beam dynamics of the structure were studied numerically. The effect of inclusion of nonlinearity and dispersion was also briefly investigated and is discussed.

Modulation instability of ultrashort pulses in quadratic nonlinear media beyond the slowly varying envelope approximation

We report a modulational instability (MI) analysis of a mathematical model appropriate for ultrashort pulses in cascaded-quadratic-cubic nonlinear media beyond the so-called slowly varying envelope approximation. The study shows the possibility of controlling the generation of MI and formation of solitons in a cascaded-quadratic-cubic medium in the few-cycle regimes.

DYNAMICS OF SUPER-SECH SOLITONS IN OPTICAL FIBERS

This paper obtains the parameter dynamics of super-sech optical solitons propagating through optical fibers. The variational principle is applied to obtain these parameter dynamics. Both polarization preserving fibers as well as birefringent fibers are studied in this paper. The study is then finally extended to the case of DWDM systems. The adiabatic parameter dynamics of soliton parameters is then obtained in the presence of perturbation terms. The numerical simulations are also obtained to complete the analysis.

Plasmon induced transparency effect through alternately coupled resonators in terahertz metamaterial.

We analyze plasmon induced transparency (PIT) in a planar terahertz metamaterial comprising of two C-shaped resonators and a cut-wire. The two C-shaped resonators are placed alternately on both sides of the cut-wire such that it exhibits a PIT effect when coupled with the cut wire. We have further shown that the PIT window is modulated by displacing the C-shaped resonators w.r.t. the cut-wire. A lumped element equivalent circuit model is reported to explain the numerical observations for different coupling configurations. The PIT effect is further explored in a metamaterial comprising of a cross like structure and four C-shaped resonators. For this configuration, the PIT effect is studied for the incident light polarized in both x and y directions. It is observed that such a structure exhibits equally strong PIT effects for both the incident polarizations, indicating a polarization independent response to the incident terahertz radiation. Our study could be significant in the development of slow light devices and polarization independent sensing applications.

Phase-induced soliton switching in fiber nonlinear directional couplers

A numerical study of femtosecond soliton switching by the relative phase change of a weak control pulse is carried out for a Kerr coupler with the simultaneous presence of intermodal dispersion, cross-phase modulation, third-order dispersion, self-steepening, and intrapulse Raman scattering. It is shown (numerically) that cross-phase modulation, though it appears as a very tiny parameter, plays a positive role in this mode of soliton switching and that these perturbative effects may lead to useful soliton switching if the relative phase of the control pulse is monitored judiciously.