Subwavelength Mode Profile Customisation Using Functional Materials

TL;DR

This paper introduces a method to precisely customize the longitudinal mode profile in electromagnetic waveguides at sub-wavelength scales using tailored permittivity variations, enabling advanced control without active synthesis.

Contribution

It presents a novel approach for designing waveguide permittivity profiles to achieve specific mode shapes, including complex profiles inspired by Mathieu functions, without active modulation.

Findings

Achieved subwavelength control of mode profiles in waveguides.

Demonstrated shaping of field profiles for charged particle beam applications.

Showed that custom profiles can be designed directly from desired shapes.

Abstract

An ability to completely customise the mode profile in an electromagnetic waveguide would be a useful ability. Currently, the transverse mode profile in a waveguide might be varied, but this is usually a side effect of design constraints, or for control of dispersion. In contrast, here we show how to control the longitudinal (propagation direction) mode profile on a sub-wavelength scale, but without the need for active solutions such as synthesizing the shape by combining multiple Fourier harmonics. This is done by means of a customised permittivity variation that can be calculated either directly from the desired mode profile, or as inspired by e.g. the range of shapes generated by the Mathieu functions. For applications such as charged particle beam dynamics, requiring field profile shaping in free space, we show that it is possible to achieve this despite the need to cut a channel through the medium.