title: Supersymmetry-inspired non-Hermitian optical couplers.
abstract: Supersymmetry has been shown to provide a systematic and effective framework for generating classes of isospectral optical structures featuring perfectly-phase-matched modes, with the exception of one (fundamental) mode which can be removed. More recently, this approach has been extended to non-Hermitian scenarios characterized by spatially-modulated distributions of optical loss and gain, in order to allow the removal of higher-order modes as well. In this paper, we apply this approach to the design of non-Hermitian optical couplers with higher-order mode-selection functionalities, with potential applications to mode-division multiplexing in optical links. In particular, we highlight the critical role of the coupling between non-Hermitian optical waveguides, which generally induces a phase transition to a complex eigenspectrum, thereby hindering the targeted mode-selection functionality. With the specific example of an optical coupler that selects the second-order mode of a given waveguide, we illustrate the aforementioned limitations and propose possible strategies to overcome them, bearing in mind the practical feasibility of the gain levels required.
authors.affiliation: 1] Waves Group, Department of Engineering, University of Sannio, I-82100, Benevento, Italy [2] Optoelectronic Division, Department of Engineering, University of Sannio, I-82100, Benevento, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Principe
authors.affiliation: Waves Group, Department of Engineering, University of Sannio, I-82100, Benevento, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Castaldi
authors.affiliation: Optoelectronic Division, Department of Engineering, University of Sannio, I-82100, Benevento, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Consales
authors.affiliation: Optoelectronic Division, Department of Engineering, University of Sannio, I-82100, Benevento, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cusano
authors.affiliation: Waves Group, Department of Engineering, University of Sannio, I-82100, Benevento, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Galdi