Waveguide subwavelength gratings bridged thin-film LiNbO3 ridge-waveguide grating couplers

For the traditional light-coupling methods, grating coupler (GC) has been effectively adopted to interface optical fiber light into/from photonic waveguides. To date, the reported GCs fabricated on thin-film lithium niobate on insulator (LNOI) either have low coupling efficiency (CE) or need additional cladding and reflector and with complicated fabrication process to attain a high CE [1] – [3] . Noted that there exist the transmission and dispersion relationships between frequency and wavenumber in short-period gratings structure, the characteristics of sub-wavelength gratings (SWG) waveguide had been widely investigated [4] , while the reports of LNOI optical components integrated with waveguide SWG have not been fully exploited neither in simulations nor experiments [5] , [6] , especially for the research of highly-efficient GCs in LNOI.