Low-loss Lithium Niobate on Insulator (LNOI) Waveguides of a 10 cm-length and a Sub-nanometer Surface Roughness

TL;DR

This paper presents a novel fabrication technique for ultra-low-loss lithium niobate on insulator waveguides, achieving sub-nanometer surface roughness and centimeters in length, suitable for scalable photonic circuits.

Contribution

A new chemo-mechanical polishing method combined with femtosecond laser patterning for creating long, low-loss LNOI waveguides with ultra-smooth surfaces.

Findings

Propagation loss as low as 0.027 dB/cm

Surface roughness of 0.452 nm

Compatible with high-throughput manufacturing

Abstract

We develop a technique for realizing lithium niobate on insulator (LNOI) waveguides of a multi-centimeter-length with a propagation loss as low as 0.027 dB/cm. Our technique relies on patterning a chromium (Cr) thin film coated on the top surface of LNOI into a hard mask with a femtosecond laser followed by the chemo-mechanical polishing for structuring the LNOI into the waveguides. The surface roughness on the waveguides is determined to be 0.452 nm with an atomic force microscope (AFM). The approach is compatible with other surface patterning technologies such as optical and electron beam lithographies or laser direct writing, enabling high-throughput manufacturing of large-scale LNOI-based photonic integrated circuits.