In this work, we first designed a large-area binary blazed grating coupler with a high coupling efficiency and a wide bandwidth.
The proposed binary blazed grating structure is shown in Figure 2.
As shown in Figure 4, [H.sub.1] is the height of the common blazed grating, [h.sub.i] (i = 1,2, 3,4) is the height of each discrete multilevel grating, H denotes the height of the binary subwavelength blazed grating, and [n.sup.TE.sub.eff(i)] is the effective refractive indices of the binary grating:
where [H.sub.1] is the height of the common blazed grating, H denotes the height of the binary subwavelength blazed grating, and [n.sub.2] and [n.sub.1] are the refractive index of Si and BCB, respectively.
Schematic of the proposed binary blazed grating coupler is shown in Figure 6.