Unique multistable states in periodic structures with saturable nonlinearity

TL;DR

This paper uncovers novel multistable behaviors in saturable periodic structures, including ramp-like and vortex-like states, and explores their dynamics within parity-time symmetry regimes, revealing new phenomena not seen in traditional nonlinear systems.

Contribution

It introduces the discovery of unique ramp-like and vortex-like multistable states in saturable nonlinear structures, especially within PT-symmetric regimes, expanding understanding of nonlinear optical dynamics.

Findings

Ramp-like optical bistability and multistability observed.

Vortex-like multistable states with increasing switch powers.

Revival of S-shaped states in unbroken PT-symmetry regime.

Abstract

We report that conventional saturable periodic structures, in sharp contrast to the conventional systems with different nonlinearities which exhibit the typical S- shaped optical bi- and multi-stable states, reveal some unusual and unique nonlinear dynamics. These include the onset of ramp-like optical bistability (OB) and optical multistability (OM) curves which further transit into mixed OM states combining both ramp-like states followed by the S-shaped multistable curves. We also extend this study to another domain of physics, namely parity-time ($\mathcal{PT}$)- symmetry, by including equal amount of gain and loss into the system which then establishes additional degree of freedom by enabling the investigation into additional two domains which are the unbroken and broken $\mathcal{PT}$- symmetric regimes. Although these bi- and multi-stable states are unusual and unique, when the frequency detuning is introduced, the revival of S-shaped stable states is possible but only in the presence of unbroken $\mathcal{PT}$- symmetry. Conversely, the broken $\mathcal{PT}$- symmetry which usually generates ramp-like multistable states, gives rise to the birth of novel multistable states with a vortex like envelope, (the curve that features simultaneous increase in the critical switch-up and switch-down powers with an increase in the input power) causing a novel structure which has not been reported in the existing literature of different physical systems manifesting multi-stable states.