The Research Of Optical Filter And Polarization Properties Through Sub-wavelength Structured Metal Film

The filtering and polarization properties of sub-wavelength structured metal films have been studied. In recent years, metal films with sub-wavelength periodic structures have been well investigated and key elements such as color filters and polarizers for display applications have been designed based on these structures. The energy utilization of the current Liquid Crystal Display (LCD) system is less than 5%, which is mainly caused by the absorption of traditional color filters and polarizers, up to 87% of the light energy is lost here. Reducing this part of energy loss is very important for improving the energy utilization.A polarizing color filter based on one-dimensional metal gratings is proposed. The transmission peak wavelength of TM-polarized light depends on the surface plasmon resonance wavelength, which was chosen by tuning the period of the metal grating and parameters of the metal adjacent media. Polarization properties were optimized by utilizing the waveguide and cavity mode resonances, which can occur for both TE-polarized and TM-polarized incident light. FDTD algorithm is used to simulate and analyze the designed structures numerically. Two types of polarizing color filters were realized with peak transmittance of 80% and 72% , and full width at half maximum (FWHM) of 80nm and 110nm, respectively. Their extinction ratios are both above 1000:1 within the FWHM range of the filtering peaks, with TE-polarized light strongly reflected.Compare to the current color filters and polarizers used in LCDs, our structures have the following advantages: (1) Smaller bandwidth due to purer color display; (2) Extinction ratio is about 1 times higher so the display contrast can be improved; (3) The reflected TE-polarized light can be recycled by the backlight to improve the utilization of the total light energy. The peak transmission of TM-polarized light can be increased by about20% , and the display brightness is enhanced. Gratings with periods of 270nm and 340nm have been achieved by using the ultra-violet wavelength immersion interference lithography method. And the influences of experimental parameters were also discussed.