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

Abstract 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 μm 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.