We describe an alternative design for the 4-quadrant phase maskcoronagraph described recently by Rouan et al. (2000). Based onthe same principle, i.e. producing a very efficient nulling bymutually destructive interferences of the coherent light from themain source, our mask realises the π phase shift using someproperties of ZOGs (Zeroth Order Gratings) and according to anoriginal scheme respecting the 4-quadrant symmetry. When theperiod of the one-dimension grating structure is smaller than thewavelength of the incident light, the structure becomesbirefringent. The effective refractive indices depend on thewavelength. Using this feature, we can design a mask whose nullingefficiency is maintained within a wide wavelength range. Numericalsimulations were made according to the RCWA (Rigorous Coupled WaveAnalyses).