Nonlinear suppression of time-reversals in PT-symmetric optical couplers

TL;DR

This paper explores how nonlinear effects in PT-symmetric optical couplers influence time-reversal phenomena, showing that nonlinearity suppresses time-reversals above a certain intensity threshold, leading to symmetry breaking and beam switching.

Contribution

It demonstrates the nonlinear suppression of time-reversal effects in PT-symmetric optical systems and reveals the invariance of threshold intensity under input exchange.

Findings

Below threshold, amplitudes oscillate with periodic time-reversals.

Above threshold, nonlinearity causes symmetry breaking and beam switching.

Threshold intensity remains unchanged when exchanging input intensities at gain and loss waveguides.

Abstract

We reveal a generic connection between the effect of time-reversals and nonlinear wave dynamics in systems with parity-time (PT) symmetry, considering a symmetric optical coupler with balanced gain and loss where these effects can be readily observed experimentally. We show that for intensities below a threshold level, the amplitudes oscillate between the waveguides, and the effects of gain and loss are exactly compensated after each period due to {periodic time-reversals}. For intensities above a threshold level, nonlinearity suppresses periodic time-reversals leading to the symmetry breaking and a sharp beam switching to the waveguide with gain. Another nontrivial consequence of linear PT-symmetry is that the threshold intensity remains the same when the input intensities at waveguides with loss and gain are exchanged.