High efficiency compact grating coupler for integrated optical circuits

The area of integrated optical circuits has been undergoing rapid development and will have huge potential in the future due to the important applications of fiber communication systems and optical interconnects. A significant challenge of optical circuits lies in increasing circuit density while miniaturizing the devices. Couplers are important parts in integrated optical circuit and high efficiency compact couplers are in great demand. We report here the binary blazed grating coupler that can commendably solve these problems. The binary blazed grating is composed of subwavelength pillars with uniform height, which can be easily fabricated by only one etching step. It is found that this element substantially outperforms standard grating. Because of its high coupling efficiency and compact structure, the binary blazed grating coupler exhibits excellent performance in fiber-to-waveguide/waveguide-to-fiber coupling, waveguide-to-waveguide coupling, chip-to-chip vertical coupling, etc. In this paper, a basic design principle of the binary blazed grating coupler is presented, and some improved structures to enhance the coupling efficiency are proposed and estimated. The FDTD method is utilized to simulate and design the binary blazed grating operated under TE polarization for 1.55μm. With our optimization design, the coupling efficiency can be largely increased.