Research On Silicon-based Two-dimensional Grating Mode Coupler

Due to the high integration,simple technology and low cost,silicon-based platform,the important platform for photonic integrated circuits,has aroused extensive attention.With the rapid development of silicon photonics,different kinds of optics components have been very mature.However,as an indirect band gap material,silicon cannot meet the luminous efficiency and the chips need to introduce external sources.Because of high coupling efficiency,polarization independence,simple process and flexible location,the two-dimensional grating coupler has become an important bridge between external light sources and on-chip structures,and plays an important role in silicon-based integration.This paper will carry out a series of researches around the two-dimensional grating coupler.The main contents are as follows:(1)The basic principle,important performance indicators and numerical analysis methods of two-dimensional grating coupler are introduced.Through numerical simulation,the effects of two-dimensional grating structural parameters,coupling angle,thickness of Si O2 layer and waveguide inclination angle on the performance of two-dimensional grating couplers are discussed,and the optimal structural parameters of traditional gratings are obtained.(2)By analyzing the source of polarization-dependent loss,a new etching pattern with ellipse-like etching holes,which can compensate the spectral drift,is proposed.With the ellipse-like structure,an ultra-low polarization-dependent loss of the two-dimensional grating coupler is realized.Furthermore,comparative analysis of multiple groups of two-dimensional gratings explores the tolerance of the structural parameters and the difficulty of the process.Finally,it is proved experimentally that the ellipse-like etching hole can reduce the polarization-dependent loss from 2.6d B to 0.2d B without reducing the coupling efficiency.(3)In order to implement the coupling between few-mode fiber and silicon-based chip,a multi-mode coupler based on two-dimensional grating is proposed.By optimizing the etching depth,hole radius,horizontal grating period and vertical grating period of the two-dimensional grating coupler,the theoretically efficient coupling of the LP₀₁ mode and the LP_11a mode is achieved.The coupling efficiency of the LP₀₁ mode and the LP_11a mode is 41%and 42.5%respectively,and the mode crosstalk is less than 5%.According to the simulation design,the layout design and device fabrication of related chips are completed,and the corresponding test scheme is developed.