Ultrabroad bandwidth and high-coupling-efficiency compact coupler using multilevel grating structure

A compact multilevel grating coupler based on SOI material structure is proposed to realize coupling between waveguide and waveguid, which has the ultrabroad bandwidth and extremely compact dimension ( with the grating length of 3 mu m). The incident wave is TE polarization and designed as normal incidence. The influences of the grating coupler characteristics, for instance, grating period, grating height and grating length, as well as the thickness of SiO2 layer on the coupling efficiency have been discussed. The simulation results indicate that the 3dB bandwidth of 160nm from 1390nm to 1550nm can be obtained, accompanied by the coupling efficiency of approximately 50% around 1550nm. Simultaneously, the sufficient high coupling efficiency of 67.5% at the wavelength of 1460nm has also been observed.