Design and Numerical Simulation of a Bandpass Filter Nano-film

Abstract

A bandpass filtering nano-film based on high refractive index materials is designed in this paper, it shows high transmittance for red light and high reflectance for visible light. The structure of the nano-filtration membrane is simple, which is composed of three nano-films with the overall thickness no more than 100 nm. At normal incidence, the red light (620-760nm) transmittance of the filter film is above 0.6, and the reflectance is below 0.05. At oblique incidence from 0 to 45 degree, the red light transmittance of the filter film under both TM and TE wave mode are all above 0.5, which achieve the transmission of red light in a wide range of incident angles. The light transmittance of the nano-filtration membrane was calculated by transfer matrix method (TMM), it is verified by finite-difference frequency-domain (FDFD) method, and the field distribution of the typical wavelength in the film was calculated. The thickness variation of each layer effects the transmittance of light wave in nano-film was studied. The passband of this filter is easy to be modulated, the bandwidth and waveband of the transmitted light can be modulated as long as changing the thickness of the film, which can be applied to medical or scientific research fields that requires specific light waveband.