Automated algorithms for multilayer thin film filter design using metamaterials
T M Threadgold, J W Bowen, G J Hawkins
Nanostructures for Optics and Photonics, NATO Science for Peace and Security Series B: Physics and Biophysics, Springer, ISBN 978-94-017-9142-7 (2013)
Currently, infrared filters for astronomical telescopes and satellite radiometers are based on multilayer thin film stacks of alternating high and low refractive index materials. However, the choice of suitable layer materials is limited and this places limitations on the filter performance that can be achieved. The ability to design materials with arbitrary refractive index allows for filter performance to be greatly increased but also increases the complexity of design. Here a differential algorithm was used as a method for optimised design of filters with arbitrary refractive indices, and then materials are designed to these specifications as mono-materials with sub wavelength structures using Bruggeman’s effective material approximation (EMA).