Study On Dual-band Unidirectional Reflectionless Properties In Metamaterials

Metamaterial is an artificially designed composite material that break through the limitations of some natural law by the orderly design of physical structure.It exhibited the extraordinary physical properties that natural materials do not possess,such as negative refraction,invisible,perfect absorption and unidirectional reflectionlessness,and so on.The unidirectional reflectionless is a phenomenon in which the reflectivity of one port is higher and the reflectivity of the other port is close to zero when the incident wave is driven from both sides of the structure.It will potential applications in the integrated nanophotonic devices,such as optical filters,sensors,optical diodes,and so on.In this thesis,based on numerical simulation and analytical calculation,we studied the dual-band unidirectional redlectionlessness and unidirectional absorption phenomenon in metamaterial.The main research contents are as follows:First of all,we propose a metamaterial structure consisting of two gold hole resonators of different radii.Based on far-field coupling between two gold hole res-onators,the dual-band unidirectional reflectionlessness and unidirectional absorp-tion are realized at two exceptional points.Furthermore,by simply manipulating the angle of incident wave and distance between two resonators,we found that the dual-band unidirectional reflectionlessness and unidirectional absorption can be re-alized in a wide ranges of incident angle(O°?50°)and distance(255 nm-355 nm).Moreover,the absorptions are close to 0.90 and 0.86 in the-z and+z directions at 262 THz and 276.24 THz and the quality factors are close to 20,respectively.Furthermore,our scheme is insensitive to polarization of incident wave due to the circular-hole structure.In addition,we propose a metamaterial structure consisting of three gold bars of the same width and height but different lengths.The dual-band unidirectional reflectionlessness and unidirectional absorption are realized by near-field coupling between a single resonator and the resonant modes of two resonators showing an electromagnetically induced-transparency-like(EIT-like)effect at two exceptional points.We found that the dual-band unidirectional reflectionlessness and unidirec-tional absorption can be achieved in a narrow range of distance(25 nm?58 nm)by changing the distance between a single resonator and two resonators.Moreover,the absorption are close to 0.94 and 0.87 in the+z and-z directions at 231.5 THz and 251 THz,and the quality factors are close to 28.75 and 41.83,respectively.Further-more,numerical simulation and analytical calculation have good consistency in our scheme.