MENP: An Open-Source MATLAB Implementation of Multipole Expansion for Applications in Nanophotonics

TL;DR

MENP is an open-source MATLAB tool that performs multipole expansion analysis of light scattering in nanophotonics, aiding the design and interpretation of metasurfaces and related phenomena.

Contribution

It provides an efficient, validated MATLAB implementation for multipole decomposition of scattering data, including electric, magnetic, and toroidal moments, for nanophotonic applications.

Findings

Validated against Mie theory for nanospheres

Demonstrated analysis of anapole states and toroidal dipoles

Enables detailed near- and far-field interaction insights

Abstract

In modern nanophotonics, multipolar interference plays an indispensable role to realize novel optical devices represented by metasurfaces with unprecedented functionalities. Not only to engineer sub-wavelength structures that constitute such devices but also to realize and interpret unnatural phenomena in nanophotonics, a program that efficiently carries out multipole expansion is highly demanded. MENP is a MATLAB program for computation of multipole contributions to light scattering from current density distributions induced in nanophotonic resonators. The main purpose of MENP is to carry out post-processing of a rigid multipole expansion for full-field simulations which in principle provide the information of all near- and far-field interactions (e.g. as a total scattering cross section). MENP decomposes total scattering cross sections into partial ones due to electric and magnetic dipoles and higher-order terms based on recently developed exact multipole expansion formulas. We validate the program by comparing results for ideal and realistic nanospheres with those obtained with the Mie theory. We also demonstrate the potential of MENP for analysis of anapole states by calculating the multipole expansion under the long-wavelength approximation which enables us to introduce toroidal dipole moments.