Research On The Fabrication And Polarization Properties Of Micro/Nano Gratings

Polarization imaging provides us with new dimension information besides intensity(brightness) and frequency(color). Polarizer is an important component of a polarization detection system to achieve a particular polarization direction light filtering. With the development of nano-fabrication technology, sub-wavelength polarization gratings can be achieved. As a new type of polarizer, sub-wavelength metal gratings have the advantages of small size and high integration.In this report, we fabricated polarization gratings with 200 nm period using both electron beam lithography and interference lithography for Polarization imaging applications.Firstly, the equivalent medium theory was used to explain the polarization property of sub-wavelength grating. Then three-dimensional FDTD simulation was carried out to verify it. Secondly, an immersion interference lithography system was designed based on the principle of interference lithography. The geometry relationship between the incident angle of exposure and triangular liquid container was analyzed. Methods for precise control of the grating period in interference lithography were proposed. Thirdly, electron beam lithography and reactive ion beam etching were used to fabricate thin film polarizers of sub-wavelength aluminum gratings with four orientations. Gratings with the 200 nm period were successfully achieved. The etching time of reactive ion beam lithography was optimized with the observation by a confocal microscope. Finally, an optical system used to evaluate the optical performance of aluminum gratings was built. The extinction ratio was calculated and the result showed that the aluminum grating behaved as a polarizer.The micro-nano grating can be very thin, which allows light with large incident angles without affecting the performance of the extinction ratio. Micro-nano gratings can provide higher levels of integration and stability for polarization imaging and display applications.