High Efficiency Binary Blazed Grating Waveguide Couplers

Blazed grating features result in a modification to the Bragg which yields only a single output radiation mode (either substrate or cladding). [1]. Since blazing requires a triangular grating line shape, fabrication can be difficult. As a simplification, a discrete step approximation is often used to approximate a blazed structure. However, the discrete approximation requires multiple exposure steps making the fabrication process complex. The fabrication process can greatly simplified by approximating the blazed grating line shape by a periodic rectangular grating with a varying duty cycle [2]. Thus, the process used to fabricate periodic rectangular gratings can be used to fabricate the binary approximation of a blazed grating. Dividing the blazed grating structure into several (I), substructures, results in a substructure (i), each having a different discrete refractive index based on their location along the slope as shown in Figure 1.