CMOS-Compatible Vertical Grating Coupler With Quasi Mach–Zehnder Characteristics

A vertical grating coupler on silicon-on-insulator substrates has been designed and demonstrated. The light from a vertical fiber can be coupled in and split equally into two arms with the fiber placed in the grating center. An optical combiner is used to collect the transmission from the two arms. The measured peak coupling efficiency is 37%. Our device can also function like a Mach-Zehnder interferometer. In a device with an arm difference of 30 μm, the normalized transmission spectra of 20-nm free spectral range and more than 12-dB extinction ratio at 1567 nm are obtained.