Study On Wide-spectrum, Wide Viewing Angle Polarization Characteristics Of Sub-wavelength Metal Gratings

Polarization beam splitter is one of the most important optical components in optical polarization system,and the traditional polarization beam splitter is unable to meet the requirements of high efficiency,easy integration,etc.Subwavelength metal grating has different diffraction effect for polarized light,and it's period is smaller than the wavelength of the incident.The polarization beam splitter which was made by subwavelength metal grating can achieve high efficiency,wide spectrum,wide angles.So,subwavelength metal grating is widely used optical storage,optical fiber communication and polarization imaging system,etc.Based on the rigorous coupled wave theory,the grating diffraction model of a single rectangle and multilayer grating have been designed,and the problem of numerical instability of multilayer grating is solved by using the enhanced transmission matrix method.This paper designed the three types of subwavelength metal Ag grating: multilayer metal grating of center wavelength of 1550 nm,sandwiched metal grating of center wavelength of 800 nm and embedded metal grating of center wavelength of 800 nm.And then we optimize the optimal structure parameters of three types of gratings by using rigorous coupled wave theory and genetic algorithm.By discussing the relationship between the polarization characteristics of three kinds of grating versus and the incident wavelength and incident angle,the wide spectrum and wide angle of grating are studied.Finally,we analysis manufacture tolerance of three metal gratings.Results show that the designed three kinds of subwavelength metal gratings meet requirements of wide spectrum,wide angle,high diffraction efficiency,high extinction ratios.The analysis of manufacture tolerance shows three gratings have good manufacture tolerance to period and groove depth and covering layer thickness.Three kinds of gratings own many good characteristics such as simple structure,low cost,and obvious polarization,providing a theoretical basis for making subwavelength metal grating with wide spectrum,wide angle,high diffraction efficiency,high extinction ratios.