Polarization-Splitting Grating Coupler on Lithium Niobate Thin Film

In this study, one-dimensional grating coupler on single-crystal lithium niobate thin film (lithium niobate on insulator, LNOI) that also served as a polarization splitter was designed. The coupler could separate both orthogonal polarization states into two opposite directions while coupled light from a standard single-mode fiber to a waveguide on LNOI at the same time. Using segmented and apodized designing, the peak coupling efficiencies (CEs) around telecommunication wavelength 1550 nm for fundamental TE and TM modes of -2.82 dB and -2.83 dB, respectively, were achieved. The CEs could be optimized to -1.97 dB and -1.8 dB when a metal layer was added below the silicon dioxide layer.