2-dimensional photonic-crystal polarization filter with dual-band and wide working wavelength range

A novel design of photonic-crystal polarization filter was demonstrated with dual-band and wide working wavelength range. The structure of the filter is a 2-dimensional wavy structure of multilayer thin films consisted with a number of alternate high and low refractive indices transparent dielectric layers deposited sequentially on a periodic structured substrate. The fabrication of the photonic-crystal polarization filter is based on an autocloning method which integrated the techniques of lithography and thin film deposition. Different from the traditional polarizing beam splitters, the photonic-crystal polarization filter is a flat type of polarizer with normal incident angle. The transmission and reflectance spectra were analyzed using finite-difference time-domain method (FDTD). From the analysis result, we found the photonic bandgap was happened at transverse electric (TE) mode and the passband at transverse magnetic (TM) mode. So, the photonic crystal polarization filter can separate TE mode and TM mode effectively as the field is incident normally. We design the working wavelength range of the photonic-crystal polarization filter at both visible and near infrared regions, and have wide polarization separated band at normal incident. Finally, the bandwidth is about 100 nm in visible region and 300 nm at near infrared region. The extension ratio is about 20 both in visible region and near infrared region.