Controlling Kerr Nonlinearity via Balanced Gain/Loss for Short Optical Pulse Propagation in a Non-Hermitian Directional Coupler Under Negligible Dispersion

Abstract

The impact of the concurrent presence of Kerr nonlinearity and balanced gain/loss on picosecond pulse propagation in twin-core AlGaAs waveguides is investigated under negligible dispersion using the Split-Step Fourier Method. This dual influence establishes a mechanism for controlling the longitudinal length at which the excited pulse breaks, termed the breaking length. For a fixed input power, a reduction in the balanced gain/loss transforms a breaking pulse with a broad, noisy spectrum into a normal pulse with a narrow spectrum through intermediate states of simultaneous splitting in both cores and splitting confined to one core. Conversely, increasing the coupling coefficient at constant gain/loss and input power also drives this transition. Therefore, balanced gain/loss serves as a control parameter to regulate nonlinear effects at a fixed wavelength, providing the basis for a sensing strategy in non-resonant non-Hermitian coupler structures. Furthermore, increasing the wavelength at constant gain/loss and input power decreases the effective nonlinearity, and consistent sensing performance can be maintained by precise power adjustment across a range of central wavelengths. Overall, this non-Hermitian control of nonlinear pulse dynamics opens new opportunities for device design with gain–loss and coupling regulation in integrated photonic platforms.