Study On Grating Coupler Based On Integrated Photonic Chip

In recent decades,with the rapid development of integrated circuit technology,the degree of integration has been improved and the performance has been enhanced.However,limited by its physical properties,the speed,delay and power consumption of integrated circuits have gradually become problems that can not be ignored.Compared with integrated circuits,silicon-based integrated photonic chip has great advantages in these aspects,so it has become a research hotspot in recent years,and various high-performance silicon-based devices have been successfully realized.However,in order to realize the practical application of integrated photonic chip,in addition to high-performance devices,high-performance couplers are also needed to realize the coupling between chip and fiber.Grating coupler has become an ideal coupling scheme because of its simple fabrication,large alignment tolerance and convenient layout.In this paper,the grating coupler between fiber and integrated photonic chip is studied,and a double-layer grating coupler structure is proposed,which has important practical significance for promoting the development of efficient coupling technology between fiber and integrated photonic chip.The main contents of this paper are as follows:(1)Based on the Bragg diffraction condition,the coupling principle of the grating coupler is analyzed qualitatively.The coupling conditions and coupling types of the grating coupler are analyzed.The modes in the fiber and the silicon waveguide are analyzed,and the calculation formula of the coupling efficiency is derived.(2)The model of single-layer grating coupler is established,and the influence of structure parameters of grating coupler on coupling efficiency is analyzed.By optimizing the structure parameters,a single-layer grating coupler with coupling angle of 12.5° is designed,and the influence of process error on coupling efficiency is analyzed.(3)The source of coupling loss of single-layer grating coupler is analyzed.Through numerical calculation,it is found that the loss mainly comes from the reflection and downward diffraction loss of grating.The theoretical model of the double-layer grating coupler is established,and the coupling loss of the grating coupler is reduced by interference.By optimizing the structure parameters,a near vertical coupling double-layer grating coupler with a coupling angle of 9° is designed.The coupling efficiency at 1550 nm is 81%,and the3 d B bandwidth is 90 nm.For the proposed near vertical coupling double-layer grating coupler,a feasible manufacturing process is proposed,and the process tolerance is analyzed.