Role of dielectric film in metal grating for improved polarized transmittance in 0.9–1.7 µm range

Abstract

It is found that the TM light transmittance and polarized extinction ratio in the near infrared range (0.9-1.7 µm) can be greatly increased by incorporating a dielectric layer between metal gratings (MGs) and high refractive index substrate (InP). The role of the dielectric layer and the physical mechanism of the polarized transmittance improvement are elucidated based on numerical simulation. Besides anti-reflection role as it is known to all, the incorporated dielectric layer is found eliminating energy losses from the Rayleigh anomalies and surface plasmon (SP)-cavity mode between adjacent metal grids. By optimizing the refractive index and thickness of the dielectric layer, it is demonstrated that the TM transmittance at the central wavelength (1.3 µm) can reach above 95% for Au MG with the period as large as 400 nm.