Nonreciprocal guided waves in presence of swift electron beams

TL;DR

This paper proposes a novel, broadband, magnet-free method to achieve nonreciprocal guided waves in waveguides using swift electron beams, enabling unidirectional electromagnetic propagation for advanced photonic and microwave applications.

Contribution

It introduces a theoretical approach to break electromagnetic reciprocity using electron beams with constant velocity, distinct from traditional electron devices, and analyzes the resulting nonreciprocal wave properties.

Findings

Demonstrates nonreciprocal guided waves in 2D and 3D waveguides due to electron beam interaction.

Shows the nonreciprocity strength depends on electron velocity and density.

Provides dispersion and field distribution analysis for the proposed method.

Abstract

Breaking the reciprocity of electromagnetic interactions is of paramount importance in photonic and microwave technologies, as it enables unidirectional power flows and other unique electromagnetic phenomena. Here we explore a method to break the reciprocity of electromagnetic guided waves utilizing an electron beam with a constant velocity. By introducing an effective dynamic conductivity for the beam, we theoretically demonstrate how nonreciprocal guided waves and a one-way propagating regime can be achieved through the interaction of swift electrons with electromagnetic waves in two-dimensional (2D) parallel-plate and three-dimensional (3D) circular-cylindrical waveguides. Unlike the conventional electron beam structures such as traveling wave tubes and electron accelerators, here the goal is neither to generate and/or amplify the wave nor to accelerate electrons. Instead, we study the salient features of nonreciprocity and unidirectionality of guided waves in such structures. The relevant electromagnetic properties such as the modal dispersion, the field distributions, the operating frequency range, and the nonreciprocity strength and its dependence on the electron velocity and number density are presented and discussed. Moreover, we compare the dispersion characteristics of waves in such structures with some electric-current-based scenarios in materials reported earlier. This broadband tunable magnet-free method offers a unique opportunity to have a switchable strong nonreciprocal response in optoelectronics, nanophotonics, and THz systems.