Materials science

Surface finish

Wavelength

Surface roughness

Photonics

Laser

Physics

Nanotechnology

Optics

Lithium niobate

Thin film

Polishing

Composite material

Photolithography

Femtosecond

Optoelectronics

Nanometre

Insulator (electricity)

Photonic integrated circuit

Nanomaterials

In this paper, we develop a technique for realizing multi-centimeter-long lithium niobate on insulator (LNOI) waveguides with a propagation loss as low as 0.027 dB/cm. Our technique relies on patterning a chromium thin film coated on the top surface of LNOI into a hard mask with a femtosecond laser followed by chemo-mechanical polishing for structuring the LNOI into the waveguides. The surface roughness on the waveguides was determined with an atomic force microscope to be 0.452 nm. 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.

Long Low-Loss-Litium Niobate on Insulator Waveguides with Sub-Nanometer Surface Roughness