平面金属等离激元超材料对光学Tamm态及相关激射行为的增强作用

Optical Tamm state and related lasing effect enhanced by planar plasmonic metamaterials

本文对具有类EIR色散特性的平面金属等离激元超材料(planar plasmonic metamaterials,PPM)对光学Tamm态及相关激射行为的增强作用进行了研究.我们首先运用传输矩阵方法分析了利用PPM结构的色散来增强光学Tamm态对应模式电磁局域密度的可能性.其次,我们将具有类EIR特性的PPM与一维光子晶体(photonic crystal,PC)合在一起设计了一种平面等离激元超材料-光子晶体(PPM-PC)异质结构.研究发现,通过在电磁局域密度最高的PPM结构中(或附近)加入增益介质,可观察到比通常光学Tamm态更强的激射增强效应及更明显的单色性响应.这些特性使得这种PPM-PC结构有望被应用于低阈值激光器、荧光增强等方面.

Optical Tamm state （OTS） refers to a kind of interface state between the metal layer and the photonic crystal （PC） reflectors. Given the matching conditions being satisfied, the electromagnetic waves tend to tunnel through the metal-PC hetero-structure e？ciently. Quite different from the conventional surface plasmon polaritons （SPPs） on metal surface, OTSs can be excited directly by normally incident propagating waves for both TE and TM polarizations to occur. In the meantime, strong electromagnetic （EM） localization around the interface can be achieved, leading to potential applications such as polariton lasers, enhancement of Faraday rotation, various nonlinear effects, and so on. To further enhance the EM localization around the interface, some well designed artificial structures are patterned on the thin metal layer. For instance, confined Tamm plasmon modes with the aid of metallic microdisks are proposed by Gazzano et al. to control the spontaneous optical emission. Moreover, in 2013 it was also demonstrated that planar plasmonic metamaterials （PPM） with electromagnetically-induced-reflection-like （EIR-like） dispersion can boost the Q-factor of OTS tunneling mode, as well as the EM localization around the interface between planar plasmonic metamaterials and PC. Both these methods can be understood in the same scheme： the structure-induced dispersion provides exotic power of modulating the propagation of OTS. In this paper, the enhancement of optical Tamm state and related lasing effect is investigated by introducing planar plasmonic metamaterials with EIR-like dispersion. The planar plasmonic metamaterials are achieved by periodic patterning some plasmonic units on the planar metal layer. Through fine tuning each unit cell, EIR-like dispersion can be achieved, making the properties of hetero-structure more tunable. One-dimensional photonic crystals composed of TiO2/SiO2 are also designed properly to support the optical Tamm state in PPM-PC hetero-structure. First, to analyze the possibility of enhancing local electromagnetic field density of optical Tamm state, a transfer matrix method is performed when EIR-like dispersion of PPM structure is hired. Next, full wave simulations based on FDTD method are also carried out to verify a hetero-structure composed of PPM and one-dimensional photonic crystal embbed with gain media. By introducing gain medium into （or near） the PPM structure, where the maximum local electromagnetic field density exists, the lasing effect is found obviously enhanced. Better emitting e？ciency and monochromic response can be observed compared to the common metal-PC hetero-structure. These features make our structure promising to reduce the lasing threshold, enhance the fluorescence, and so on.