Design of sub-wavelength grating structure for filter regardless of polarization

For isotropic dielectric thin films, polarization effect is an inherent character. As it will make the performance of optical-electric system go to bad, such polarization-dependent properties are often intolerable and should eliminate its effect in many applications. So the design of polarization insensitive filter is an indispensability work. In this paper, based on a four-part period grating, a filter regardless of polarization is gained by combing rigorous wave theory and multiobjective immune optimization algorithm. Its working wavelength is 1315 nm which is often used in laser system. The results of our design shows that TE and TM polarized wave have a reflection 0.482 and 0.485, respectively, at designed wavelength 1315 nm. And it denotes that two values all approach to the design objective good, and the polarization deviation is very little for their difference is 0.003. Therefore, the effect of polarization deviation at 1315 nm wavelength can be eliminated very well by the designed filter.