Grating coupler on lithium niobate thin film waveguide with a metal bottom reflector

To improve the coupling efficiency between a single-mode fiber and the waveguide on lithium niobate thin film (LNOI), a fiber-to-chip grating coupler with a metal bottom reflector was designed, fabricated, and characterized. A maximum coupling efficiency of -9.1 dB and -6.9 dB for a grating coupler on LNOI without and with a metal bottom reflector was measured, respectively. Fabrication error sensitivity of etch depth was experimentally investigated and the discrepancy between the simulation and experiment was discussed. (C) 2017 Optical Society of America