Single-step etched grating couplers for silicon nitride loaded lithium niobate on insulator platform

Dielectrically loaded thin-film lithium niobate (LiNbO3) on insulator (LNOI) platforms have enabled a range of photonic integrated circuit components, such as high-speed optical modulators, switches, and nonlinear devices, while avoiding the direct etching LiNbO3 thin film. Silicon nitride (Si3N4) is one most attractive dielectric loading materials it has similar refractive index transparency window to can be deposited patterned by mature fabrication processes. The patterning Si3N4 opens opportunity fabricate grating couplers in same step, providing efficient interfaces for wafer-scale testing. In this paper, we investigate demonstrate single-step etched Si3N4-LNOI (X-cut) platform. (straight curved) are designed fabricated TE-polarized modes along Y Z crystallographic directions, considering crystal’s birefringence. experimentally demonstrated coupling losses low 4.02 4.24 dB respectively. corresponding peak wavelengths 1609 1615 nm, measured 3-dB bandwidths wider than 70 nm both directions. We also numerically investigated influence variations fiber angle transmission. To best our knowledge, work first demonstration with different light propagation directions LNOI