Investigation On Sandwich Wire Grid Polarizer With High Performances

Polarizers are essential optical elements and have significant applications in many systems such as optical display, optical switches, projection systems, optic-fiber networks, data storage, imaging systems. When optical devices and systems become smaller and smaller, integrated and inexpensive polarizers with high performances are expected. In the past a few years, several new kinds of polarizers based on metamaterials, graphene and single wall carbon nanotubes were proposed. However, in terms of the compatibility with the fabrication process of large scale integrated circuit and the possibility of commercial application, wire grid is the best candidate for making high-quality polarizer. As is well known, although single layer wire grid polarizer has high TM transmittance, its extinction ratio is not large because of the limitations of line width and aspect ratio of the polarizer. The extinction ratio of polarizer can be improved greatly by dual layer wire grid structure. Nevertheless, the TM transmittance of polarizer decreases dramatically. In this thesis, in order to overcome the shortcomings of both single layer and dual layer wire grid polarizers, a new kind of polarizer with both high TM transmittance and large extinction ratio is designed. The main work we have done includes:1. The diffraction behaviors of optical waves in both single layer and multi-layer sub-wavelength gratings were analyzed by rigorous coupled waves analysis (RCWA), providing theoretical evidence to the later numerical simulation.2. We designed a Metal/Dielectric/Metal sandwich polarizer. As is shown in numerical simulation based on RCWA, the sandwich polarizer possesses much better performances than the dual layer wire grid polarizer surprisingly. The field distribution of the polarizer reveals that these better performances with both high TM transmittance and large extinction ratio are due to the localized magnetic resonance in the sandwich polarizer.3. The influences of materials, periods, duty cycles and thicknesses of wire grids(including the total thickness and each layer thickness) on the performances of the sandwich polarizer were discussed. After the optimization, the best parameters of the sandwich polarizer were obtained. Considering the normal incidence, the TM transmittance and extinction ratio of the optimized sandwich polarizer reaches 85%-94% and 49-55 dB, respectively, at 1.3-2 μm telecommunication band. Especially, the TM transmittance of the polarizer achieves 94%and the extinction ratio exceeds 52 dB at X=1.55μm.4. We analyzed the incident angle dependent transmission spectra of the sandwich polarizer to evaluate its performances. It is found that, when the incident angle increases from 0° to 65°, the TM transmittance of the sandwich polarizer decreases less than 4% and extinction ratio increases gradually. Thus, the sandwich polarizer has fantastic incident angle tolerance.5. The influences of fabrication mismatching on the performances of the sandwich polarizer were also investigated. The numerical simulation results illustrate that the TM transmittance and extinction ratio of the sandwich polarizer change less than 1% and 0.5 dB, respectively, within ±10 nm fabrication mismatching, which6. means that the sandwich polarizer has an excellent fabrication tolerance.7. Feasible fabrication processes of the sandwich polarizer were proposed.8. We also suggested a performance test system for the sandwich polarizer. It can measure the performances of the sandwich polarizer effectively such as TM transmittance, extinction ratio, bandwidth, incident angle tolerance and so on.