Non-Hermitian multimode interference

Abstract

Multi-mode interference (MMI) and self-imaging are important phenomena of diffractive wave optics with major applications in optical signal processing, beam shaping and optical sensing. Such phenomena generally arise from interference of normal modes in lossless dielectric guiding structures, however the impact of spatially-inhomogeneous optical gain and loss, which break mode orthogonality and symmetries, has been overlooked. Here we consider MMI in non-Hermitian optical systems, either graded index or coupled optical waveguide structures with optical gain and loss, and reveal distinctive features, such as the absence of mirror images and strong-sensitivity of self-imaging to perturbations, making MMI in non-Hermitian waveguides of interest in optical sensing.

Data Center Four-Channel Multimode Interference Multiplexer Using Silicon Nitride Technology

“…The MMI phenomenon is rooted in the self-imaging principle. This principle involves multiple modes of light propagating within a multimode waveguide and undergoing constructive interference at periodic intervals, thereby reproducing the input light pattern at the output [ 18 ]. In the context of wavelength division multiplexing (WDM) systems, this capability is indispensable.…”

Sensitivity of topological edge states in a non-Hermitian dimer chain

“…EPs provide a new way to design new highly sensitive sensors beyond the linear response, and performance can be optimized as the order of the EPs increases [35][36][37][38][39][40][41][42][43][44][45]. Non-Hermitian topological structures contain new physical phenomena not usually found in normal Hermitian topological structures [46][47][48][49][50][51][52][53][54][55][56]. To date, the unique topological order [48,51], phase transition [46,53,54,56], and edge state [47,48,50,52] of the non-Hermitian 1D dimer chain have been studied.…”

“…Non-Hermitian topological structures contain new physical phenomena not usually found in normal Hermitian topological structures [46][47][48][49][50][51][52][53][54][55][56]. To date, the unique topological order [48,51], phase transition [46,53,54,56], and edge state [47,48,50,52] of the non-Hermitian 1D dimer chain have been studied. For example, the non-Bloch winding number as the topological invariant has been theoretically proposed [49], and topological protection of the edge states has been demonstrated experimentally [48].…”