Low loss ridge-waveguide grating couplers in lithium niobate on insulator

Abstract

The conventional ridge waveguides and grating-couplers in x-cut single-crystal lithium niobate on insulator (LNOI), have been designed, fabricated and characterized. All the device structures patterned on the sample were monolithically defined by one step of the electron-beam lithography process, followed by dry-etching. A low insertion loss (IL) of −6.3 dB/coupler for transverse-electric (TE) polarization inputs at the wavelength of 1543 nm was measured in the fabricated best device with the tapered structures, and exhibited a broad 3-dB optical bandwidth of more than 90 nm. This work may pave the way towards the future research of high-efficiency photonic waveguide components in thin-film LNOI.