High-performance binary blazed grating coupler with a mixed structure of germanium and zinc selenide

A high-performance binary blazed grating coupler with a mixed germanium and zinc selenide structure on a Ge-on-Si platform is proposed for a perfectly vertical coupling. To obtain high coupling efficiency, grating parameters are repeatedly and carefully optimized. For the perfectly vertical coupler with transverse-magnetic polarized incident light, the coupling efficiency is 49.5% at the wavelength of 8 mu m with a 1-dB bandwidth of 110 nm. Thus, the coupling efficiency-bandwidth product is beyond 54.5 nm. Furthermore, the manufacturing route of the grating is discussed, which adopts the combination of electron-beam lithography and three-dimensional nanoprinting.