Numerical Study On The Negative Refractive Materials Based On Tuning Chiral Structure

Negative refractive material, also known as left-handed material, is a new hot spot in the international electromagnetics research in the21st Century. It has broad application prospects in the field of microwave, optics, electromagnetic stealth and communication. Traditional negative refractive materials are the left-handed materials of which permittivity and permeability are simultaneously negative. However, negative refractive characteristics of left-handed materials can also be achieved by designing the chiral structure, which is called the chiral structure materials or chiral negative refractive materials. Chirality refers to the object’s attribute of not completely overlapping its mirror after the operation of the translation, rotation, and any change in space, and its strength is mainly determined by the size of the micro-structure chiral parameters. Chiral negative refractive materials do not need negative permittivity and negative permeability simultaneously. The chiral structure negative refractive materials are not only in line with the characteristics of left-handed materials with negative refractive index, it can also produce other electromagnetic properties like optical rotation, etc. In recent years, the operating frequencies of a large number of left-handed materials are in the microwave band. More recently, researchers are trying to obtain frequency of terahertz wavelengths and optical band. Constructing chiral structure and improving the properties of negative refractive materials which has low-loss, more/broadband segment, are the focusing research in this area. In order to seek the chiral structure negative refractive materials with good performance, we put forward the multipass appliance design scheme of chiral structure negative refractive materials across the microwave, terahertz wave and lightwave band.In this paper, we study the chiral structure negative refractive materials in the following aspects:(1) The research progress and present situation of traditional negative refractive materials, the main research contents and development of the negative refractive materials are described; the basic concepts, research methods and the latest progress of chiral negative refractive materials are presented.(2) The electromagnetic theory foundation, the theory of chirality negative refraction and its inversion method are described. The electromagnetic parameters of negative refractive index materials that need to characterized are analyzed, including transmission spectrum of LCP/RCP wave, rotation angle, the elliptic partial degrees, circular dichroism, refractive index of LCP/RCP wave, traditional, chirality parameters, relative dielectric constant and relative magnetic permeability. The design method and principle of negative refractive index materials microstructure are discussed. (3) Based on the Babinet principle, the complementary "cross-shaped" chiral negative refractive materials in microwave band are designed. The numerical simulation by the inversion calculation of the structure are presented for circular dichroism, rotation angle, chirality parameters, relative permeability, relative dielectric constants and refractive index, etc. The results show that the structure has a strong optical activity and negative refractive index properties in the microwave band. By simulating the surface current and magnetic field distributions of the micro-structure, the negative refractive index characteristics and the optically active principle are examined. Then a new design of complementary cross-shaped chiral structure with multi-band negative refractive index properties and a large optical activity is proposed based on the principle aforementioned.(4) Complementary cross-type chiral negative refractive materials are designed in terahertz band, and the electromagnetic properties are examined through numerical simulation. Four key parameters, such as rotation angle, the thickness of the dielectric layer, the width and the length of the slit open seam, are optimized so that the structure has the stronger optical activity and negative refractive index characteristics in terahertz band.(5) A negative refractive index material with crossed fold-line chiral structure is designed in the infrared, its electromagnetic properties are analyzed by numerical simulation in the infrared. Furthermore, a complementary crossed fold-line chiral structure is designed for infrared bands of negative refractive index materials. The numerical results show that the complementary structure has higher LCP/RCP wave transmittance and optical activity as well as multi-band negative refraction characteristics. Further detailed discussion on the structure parameters (including tunable dielectric layer thickness, width, thickness of the metal layer) is presented fot the electromagnetic characteristics of the infrared band. This novel crossed fold-line chiral structure is expected to be applied in a compact and broadband optics.