Optical solitons in media with focusing and defocusing saturable nonlinearity and a parity-time-symmetric external potential

TL;DR

This paper explores the existence and stability of various optical solitons in PT-symmetric waveguides with saturable nonlinearity, demonstrating how increased saturation can suppress instabilities.

Contribution

It introduces a model for solitons in PT-symmetric waveguides with saturable nonlinearity and analyzes their stability, including the effects of nonlinearity saturation strength.

Findings

Fundamental and multipole solitons are found in PT-symmetric waveguides.

Stability of solitons improves with higher nonlinearity saturation S.

Instability can be mitigated or suppressed by increasing S.

Abstract

We report results for solitons in models of waveguides with focusing or defocusing saturable nonlinearity and a parity-time(PT )-symmetric complex-valued external potential of the Scarf-II type. The model applies to the nonlinear wave propagation in graded-index optical waveguides with balanced gain and loss. We find both fundamental and multipole solitons for both focusing and defocusing signs of the saturable nonlinearity in such PT -symmetric waveguides. The dependence of the propagation constant on the soliton's power is presented for different strengths of the nonlinearity saturation, S. The stability of fundamental, dipole, tripole, and quadrupole solitons is investigated by means of the linear-stability analysis and direct numerical simulations of the corresponding (1+1)-dimensional nonlinear Schrodinger-type equation. The results show that the instability of the stationary solutions can be mitigated or completely suppressed, increasing the value of S.