Figure 1 shows the device structure of a multilayer birefringent reflective polarizer consisting of dozens of alternative layers (materials 1 and 2). Material 1 is an isotropic polymer and material 2 is a positive birefringence uniaxial polymer. There is a large refractive index difference between the two materials in the x axis. The refractive indices in the y and z axes are substantially matched. In this example, z represents the light propagating direction perpendicular to the layers.
Meanwhile, the optical thickness of each layer is controlled to be a quarter of a center wavelength. Therefore, Bragg reflection could be established for the polarization component along the x axis. For polarization along the y axis, the light sees a thick slab with uniform refractive index and is transmitted with high efficiency.
High-reflectance polarizers can be easily modeled and optimized with the RSoft DiffractMOD RCWA tool. In this application note, we will outline an example of how to do this.
In the example model shown in Figure 2, NOA81 and BL038 are the two materials used for the multilayer polarizer. For convenience, we designated the isotropic material’s refractive index as N1 and the uniaxial material’s refractive index in x direction as N2. The refractive indices can be expressed with following equation: