Efficient grating couplers on a thin film lithium niobate–silicon rich nitride hybrid platform

A grating coupler on a thin film x-cut lithium niobate–silicon rich nitride hybrid platform is proposed and demonstrated. An inverse taper is applied to suppress higher-order mode excitation. A coupling efficiency of −5.82dB and 3 dB bandwidth of 57 nm are obtained near the wavelength of 1550 nm between the standard single-mode fiber (SMF-28) and sub-micrometer waveguides.