Sub-wavelength Metal Polarization Grating Used In Visible Polarization Imaging

Polarization imaging has been widely used in military and civil, such as diagnose the cancer in medicine, and distinguish the disguisable objective in military. The sub-wavelength metal polarization grating has the characteristic of small volume, compact structure, easy to integration and can substitute the traditional polarizer. Using the sub-wavelength metal polarization gratings array to implement the synchronization polarization imaging has been the research hot.According to the characteristic of sub-wavelength metal grating, the theory and experiments on fabrication sub-wavelength metal grating were investigated in this paper. The main contents are as follows:Firstly, the significance of the research of sub-wavelength metal grating and the progress abroad and home of the research on sub-wavelength metal grating are presented. The operational principle of sub-wavelength metal grating is theoretical analyzed. For TE polarized light, the real part and imaginary part of the metal layer's equivalent refractive index are both very large, so the Al layer is equivalent to Al film and the vast majority of TE is absorbed and reflect; For TM polarized light, the real of the equivalent refractive index is very large and the image is very small, so the Al Layer is equivalent to dielectric film which has faint absorbance and most TM polarized light can transmit while only a little is absorbed.For efficiency calculation, the Finite Difference Time Domain (FDTD) theory is introduced in detail and the transmission efficiency and extinction ratio of sub-wavelength grating is discussed by FDTD theory. The best parameters of the grating used in visible light are pointed out. The influence of the angle of incidence and the process error on the characteristics of grating is analysed.For Fabrication technique, the stamp which is used for nanoimprint lithography is fabricated by holography-ion beam etching technology. The period of the grating is 250nm, the height of the grating is 380nm, and the duty ratio is about 0.5. The stamp meet the requirement of nanoimprint lithography.A covered metal wire grid fabricated on the quartz grating was proposed. The best parameters of the grating are optimized on the foundation of the structure of the quartz grating. Than the slope evaporation coating technology is used to fabricate the grating. The transmission efficiency and extinction ratio of the grating is measured and the polarization feature of this kind of grating is proved.