Abstract
The ridge waveguide integrated grating couplers (GCs) in lithium niobate on insulator (LiNbO 3 , LNOI) were designed, fabricated and characterized. Two ends of the gratings structures were connected through the middle photonic rib-waveguide of a sub-micrometric-diameter, which was nanostructured with the geometry of side-wall corrugated subwavelength gratings structure. A high coupling efficiency of -5.1 dB for the best thin film LiNbO 3 (TFLN) grating coupler was measured at the telecommunication wavelength of 1561 nm for quasi-transverse-electric (TE) polarized signals, with a broad 3-dB optical bandwidth of wider than 95 nm. All the devices structure patterns for the integrated LNOI GCs could be simultaneously defined by one step of electron-beam lithography, and then easily fabricated by the dry-etching processes. This compact component exhibited magnificent performance, and might show the potential functionalities for the TFLN-based integrated optical waveguide devices.
Highly-Efficient thin Film LiNbO3 Surface Couplers Connected by Ridge-Waveguide Subwavelength Gratings