Integrated subwavelength gratings on a lithium niobate on insulator platform for mode and polarization manipulation

Abstract

Lithium niobate on insulator (LNOI) has emerged as a promising platform for photonic integrated circuits, with a fast-growing toolbox of components. In this paper, we propose, design and experimentally demonstrate compact subwavelength grating (SWG) waveguides on a LNOI platform for on-chip mode and polarization manipulation. To overcome the limitation of waveguide fabrication, the SWGs are designed and formed on a silicon nitride thin film deposited onto the surface of LNOI chip. As proof-of-concept devices, the SWG-based spatial mode filters and a TM-pass polarizer are fabricated successfully on the same chip, with the device lengths of only ~50 μm. The measured insertion losses for the devices are lower than 3.1 dB, with high extinction ratio larger than 30 dB, at a wavelength of 1550 nm. The proposed and demonstrated SWGs can serve as important building blocks in a series of mode and polarization handling devices for LNOI integrated photonics.