Omnidirectional mirror based on the aperiodic and hybrid-order aperiodic-periodic chirped multilayers

Abstract

We propose an innovative design of highly reflective omnidirectional mirror based on chirped-type aperiodic and hybrid-order aperiodic-periodic multilayered structures in the spectral range from 400 nm to 3000 nm that contains a larger part of solar radiation. The aperiodic sequences considered are Fibonacci (FIB) and Thue-Morse (ThMo), while a power law function has been adopted to tune the thickness of layers. The chirping functions parameters were optimized to obtain maximum averaged reflectivity over the entire angular range. The numerical calculations were performed by a recursive formula via the scattering matrix method. For all the structures, the chirping effect improved the omnidirectional properties of multilayers in terms of average reflectivity and quasi omnidirectional spectral width (q-ODW). In detail, it was revealed that the ThMo based structures provide the best performance in terms of both averaged reflectivity and q-ODW. For ThMo chirped multilayer the q-ODW reached the value of 1605 nm with incident angular span 0-60°. On the other hand, the hybrid-order structure based on ThMo shows an q-ODW up to 2500 nm. Finally, for all the investigated structures the average reflectivity reaches a value larger than 0.93 using nearly 100 layers.