赝局域有效介质理论

Pseudo-local effect medium theory

有效介质理论在利用人工微结构材料拓展光学参数方面具有重要意义.本文对电介质光子晶体等具有非局域性质的人工微结构材料发展了一种新的赝局域有效介质理论,通过局域的有效介电常数■εp(ω)、局域的有效磁导率■μp(ω)、以及额外的波矢ka来描述其光学性质.研究发现,该赝局域有效介质兼具局域和非局域介质的性质,在与ka垂直的晶面上表现出局域介质的光学性质,而在与ka平行的晶面则表现出非局域介质的光学性质,如负折射、全反射等.进一步研究表明,对于所有入射角的光波在穿过拥有奇数层结构单元的赝局域有效介质时,都会出现额外的相位差,基于此设计了一种全角度相位光栅.相对于传统的光学材料,赝局域介质具有更加丰富有趣的光学性质,有望在未来应用到更多的新型光学器件设计之中.

Effective medium theory is of great importance for using the artificial microstructure materials to extend the optical parameters.In this article,we develop a new kind of effective medium theory for artificial microstructures with nonlocal effects,like photonic crystals,which we name the pseudo-local effective medium theory.The optical properties of the pseudo-local effective medium are described by effective local permittivity■εp(ω)and permeability■μp(ω)together with an additional wave vector ka,We find that the pseudo-local medium exhibits a unique blend of local and nonlocal characteristics.On the surface normal to ka,the pseudolocalmedium is optically equivalent to its local medium counterpart. While on the surface parallel to ka,theabnormal wave phenomena induced by inherent nonlocality, such as negative refraction and total reflection,may occur. Furthermore, it is found that a π phase shift is added to transmission wave through the pseudolocalmedium composed of odd number of unit cells under all incident angles. Based on this unique feature, anall-angle phase grating is proposed. Our work opens a route towards the advanced optical devices based on thepseudo-local effective media.