A study of the bandwidth of anisotropic-slab LP to CP polarizers

In this paper, we investigate the frequency effect upon the anisotropic-slab LP to CP polarizer. The effect is represented graphically in the polarization state diagram. For the CP polarizer design, usually the perfect CP cannot be achieved at all frequencies in the desired band. We define a transformation bandwidth based on a specified axial ratio, e.g., 3 dB. It is shown that the polarization locus for a given axial ratio leads to two circles in the polarization state diagram. When combined with the graphical description concerning the change in the polarization state reported earlier, the transformation bandwidth from a given incident polarization to CP can be obtained easily. This method eliminates the lengthy derivation and gives deeper physical insight to the problem. One example of the biaxial slab is studied, and the results are discussed and illustrated.