Fig. 1. Transition from a saw-tooth blazed grating to a binary blazed grating with similar optical function （a） Saw-tooth groove shape, （b）pPhase change of normal incident light transmitting through （a）, （c） rectangular groove with continuously-changed refractive index, （d） phase change of （c）, （e） rectangular groove with discretely-changed refractive index, （f） phase change of （e）, （g） 1D binary groove shape, （h） phase change of （g）, （i） 2D binary groove shape, （j） Phase change of （i）

Fig. 2. Lateral view of sub-period in 1D binary blazed grating.

Fig. 3. Peak efficiencies of pure 1D binary blazed grating for different M

Fig. 4. Diffraction efficiency of the designed 1D binary blazed grating

Fig. 5. Top view of 2D binary blazed grating （a） Groove unit, （b） sub-period of grating groove

Fig. 6. Relationship between effective index of a 2D binary structure and its shape-factors, f_x and f_y, at a reference wavelength of 0.7 μm （a） n_eTE, （b） n_eTM

Fig. 7. Change of |n_eTE- n_eTM| relative to shape-factors. The zero-value area （curve） corresponds to suitable shape-factors for n_eTE= n_eTM, meaning non-birefringent for the 2D pillars with these shape-factors

Fig. 8. Dependence of diffraction efficiency at 0.7 μm with the groove depth h of the designed 2D binary blazed grating

Fig. 9. Groove structures of the designed 2D binary blazed grating

Fig. 10. Near field distributions of the designed 2D binary blazed grating under （a） TE-polarized, and （b） TM-polarized illuminations.

Fig. 11. Diffraction efficiency of the designed 2D binary blazed grating. The efficiencies of TE and TM polarizations over the wavelength range are both above 70%. The DOP is negligible at 0.7 μm and the maximum DOP is 2.6% at 0.8 μm

Fig. 12. Different locations of 2D pillars in sub-periods of a groove unit （a） at the top, （b） at the bottom, and （c） at random locations in each sub-period along y-axis and in the center along x-axis, （d） on the left side, （e） on the right side, and （f） at random locations in each sub-period along x-axis and in the center along y-axis

Fig. 13. Diffraction efficiencies and DOPs of the 2D binary blazed gratings with different pillar locations. The upper three curves refer to diffraction efficiencies of three gratings with different locations of 2D pillars along x-axis, and the lower three curves refer to their DOPs

Table 1. Fill-factor and effective index of each sub-period in the designed 1D binary blazed grating

Table 2. Shape-factor and effective index of each sub-period in the designed 2D binary blazed grating

Table 3. Main characteristics of six gratings with different pillar locations as shown in Fig. 12.