Uniaxial optical phase change metamaterials

Abstract

Optical metamaterials are artificially engineered materials with exceptional electromagnetic properties that cannot be found in nature. Over the last 20 years, optical metamaterials have driven forward a plethora of fields from telecommunications to solar energy harvesting. They owe their unique optical properties to their carefully arranged subwavelength structural elements. By tuning the shape, geometry, and arrangement of these structures, unconventional optical properties like a negative refractive index can be achieved over a broadband wavelength range of operation. By incorporating optical phase change materials, materials with outstanding optical contrast upon a solid-state phase transition, more control over the optical modulative properties of metamaterials can be achieved. In this paper, Ge₂Sb₂Te₅ (GST) is chosen as a model phase change material due to its high reflectance contrast between states, fast switching speeds, and high metastability. Here, we theoretically investigate the reflectance and form birefringence of GST-based optical metamaterials. These optical properties are simulated on the basis of effective medium theory (EMT) and transfer matrix method (TMM). The findings in this paper demonstrate that broadband wavelength regions of high reflectance, high birefringence, and zero-crossing birefringence can be found and tuned as a function of material thickness and fill fraction in simulated GST-based optical metamaterials. These findings will be valuable for imminent nano and microfabrication in optical devices.