Tunable broadband polarization converters based on coded graphene metasurfaces

Ali Khajeh,Ali Farmani,Alireza Yahaghi,Zahra Hamzavi-Zarghani

doi:10.1038/s41598-020-80493-w

Ali Khajeh, Ali Farmani + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-80493-w

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Abstract

In this paper, two optimization algorithms (randomly initialized hill climbing and genetic algorithms) are considered to design broadband polarization converters based on coded metasurfaces. A pixeled graphene patch with an elliptic structure is proposed for the initial solution. Each pixel can be 1 and 0 which represents the presence and absence of the graphene. The initial guess tends to the optimum configuration after several optimization processes. Four broadband polarization converters are designed utilizing the optimization algorithms. By changing the chemical potential of graphene, the operation frequency of the polarization converters can be adjusted. Furthermore, the effects of relaxation time of graphene and incident angle on the polarization conversion bandwidth of the four designed structures are investigated.

Highlights

IntroductionTwo optimization algorithms (randomly initialized hill climbing and genetic algorithms) are considered to design broadband polarization converters based on coded metasurfaces
In this paper, two optimization algorithms are considered to design broadband polarization converters based on coded metasurfaces
The structures have been optimized by randomly initialized hill climbing and genetic algorithms to obtain broad bandwidth polarization conversion

Summary

Introduction

Two optimization algorithms (randomly initialized hill climbing and genetic algorithms) are considered to design broadband polarization converters based on coded metasurfaces. Polarization state is an important feature of the waves, many researches have been done to design polarization converters based on optical gratings, dichroic crystals and birefringence e ffect[4]. These conventional methods are realized by bulky structures because long distance is needed for phase accumulation. Four coded metasurfaces to rotate the linear polarization of the reflected wave are proposed relying on randomly initialized hill climbing and genetic optimization algorithms. The frequency range is considered between 20 and 40 THz for our four structures and the periodicity in both x and y directions is fixed to 200 nm

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