| Grating as a kind of important optical element has been known in the long history of exploration.Since the 1950 s grating technology began to flourish,technology has very mature.With not only the development of information technology,the research of silicon photonics,silicon grating coupler for its simple process,easy alignment,alignment tolerance,without scribing,facilitate the advantage of integration has been widely concerned.In this paper,according to the principle of the guide of planar waveguide mode,the analysis of the grating coupling conditions of position vector and light polarization characteristics in the waveguide,on the basis of using the method of effective medium model and limited time domain finite difference calculation method,we research and design polarization independent grating couplers,independent grating beam splitter,grating coupler for ultraviolet light,and silicon-on-sapphire(SOS)grating couplers at wavelength of 2.7?m.A number of novel achievements were obtained through the study:(1)A novel and simple polarization independent grating couplers is designed and analyzed here,in which the transverse electric(TE)polarization and the transverse magnetic(TM)polarization light can be simultaneously coupled into a silicon waveguide along the same direction with high coupling efficiency.For the polarization-insensitive grating coupler,the coupling efficiencies of two orthogonal polarizations light are more than 60% at 1550 nm wavelength.For TE mode the maximum efficiency is ~72% with more than 30 nm 1d B bandwidth,simultaneously,for TM mode the maximum efficiency is 75.15% with 40 nm 1dB bandwidth.Their corresponding wavelength difference between two polarizations' coupling peaks is demonstrated to be 35 nm.In this article,we discuss TE0 of base model of TE wave and first-order TM1 of first-order TM wave,designed the structure more simple than others,and the effective is better.(2)We describe a novel beam splitter with advantages of a single-layer,compact and vertical coupling structure,which is based on Bragg diffraction conditions and phase match equation.FDTD method is used to optimize the design of beam splitter.The result of simulation shows that both polarizations incident light are separated into two beams of nearly equal power(near 43% split and 45% split,respectively),which are coupled into opposite directions in the waveguide.For TE mode,the coupling efficiency of the right direction and the left direction are 42.54% and 43.68,respectively.That of TM mode is 46.03% and 44.07%,respectively.The power difference for two polarizations of two output port is less than 1% and 2%,in addition,40 nm and 65 nm bandwidth is achieved.The grating splitter is periodic structure design,the minimum line width is 360 nm,it is all the simplest structure in the design of the same type(3)A novel effectively grating coupler was reported in this paper.The design can couple ultraviolet light that the range of wavelength at 300 nm from fiber to waveguide efficiently.We use FDTD method to simulate and design the grating operated under TM polarization.With our optimization design,the coupling efficiency can be largely increased and beyond 88.5% at center wavelength 296 nm and 5nm 1d B bandwidth.This kind grating will be used to study on lab-on-a-chip spectroscopy applications.(4)Couplers are important parts in integrated optical circuit and high efficiency compact couplers are in great demand.We report on high-efficiency silicon-on-sapphire(SOS)grating couplers at wavelength of 2.7?m.A 75% coupling efficiency and 50 nm etching depth bandwidth from a standard single-mode fiber to an SOS waveguide is obtained. |
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