Silicon grating coupler on a lithium niobate thin film waveguide

A silicon (Si) grating coupler on a Si-strip-loaded lithium niobate (LN) thin film waveguide was proposed and realized. The optimized coupling efficiency (CE) by simulation was −5 dB at a wavelength of 1550 nm by the two-dimensional finite-different time-domain method (2D-FDTD), while the measured CE was about −18 dB. The coupler was etched by the focused ion beam etching method (FIB) in the Si strip thin film which was deposited by magnetron sputtering technology, patterned by photolithography and a lift-off process. The realization of the Si grating coupler and tapered waveguide could benefit the research of more advanced and complicated integrated optical devices.