Analysis of Plasmon-polariton band structures of T-shaped plasmonicgratings

摘要

We study plasmon-polariton band structures theoretically for T-shaped plasmonic gratings. We analyze the structure using Fourier expansion and perform numerical simulation using Rigorous Coupled Wave Analysis (RCWA). A detailed derivation of equations which can be used to control the momentum gap behaviour using Fourier transform is given. A structure gap is introduced in the post of the T-shaped plasmonic grating and it is found that the size of this gap plays an important role in controlling the plasmon-polariton band gap and group velocities. We have found that the plasmon mode can be decupled with light when the upper post is displaced by half a period. Thus, such a structure can be used as plasmonic decupler. Furthermore, by displacing the T-shaped post we can tune the plasmon-polariton band gap and group velocity in a non-monotonic manner. We obtain energy band gaps ranging from 0.4eV to OeV by changing the size of the structure gap from 0 to 330 nm and from 0.115eV to 0.068eV by displacing the post of the T-shaped structure from 0 to 500 nm. We also obtain tunable group velocities ranging from one to several orders of magnitude smaller than the speed of light in the vacuum. This asymmetric T-shaped plasmonic grating is expected to have applications in surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for applications requiring large photonic band gap.