Unidirectional flow of symbiotic solitons and nonlinear modes of the Schrödinger equation with an external potential

The dynamics of bright–bright symbiotic solitons by a reflectionless double potential barrier in the framework of coupled nonlinear Schrödinger equations (i.e. the Manakov system) is investigated. The main objective is to achieve unidirectional flow, which can be used in the design of optical diodes. In particular, we consider the case of symbiotic solitons, where inter-component interaction is attractive, while intra-component one is repulsive. We consider the dynamics of such solitons passing through an asymmetric Pöschl–Teller (PT) double potential well to achieve unidirectional flow. Polarity reversal is also observed with attractive local and nonlocal interaction. In this scenario, the diode polarity is reversed. We provide an alternative explanation of the phenomenon, where we show that after a soliton interacts with the potential, an internal mode is excited. The mode emanates from the allowed band of the system and is unstable in its entire existence region, which explains the fact that there is almost no soliton trapping in the system.