Flat broadband birefringent retardation of the zero-order quarter-wave plates made from multi-birefringent materials

We present a theoretical model in order for flat broadband birefringent phase retardation (BPR) of the zero-order quarter-wave plates made from multi-birefringent materials by eliminating high-order wavelength-dependent BPRs. The BPR dispersions of the plates decrease monotonously when the wavelength moves close to a selected wavelength, so the plates are very suitable for controlling the polarization of the broadband light pulses which gather most of the light energy around the central. The criterion to choose material and the flexibility of the model are discussed.