Fabrication of ridge optical waveguide in thin film lithium niobate by proton exchange and wet etching

In this paper, a low-loss ridge waveguide based on the thin film lithium niobate (TFLN) is successfully fabricated using a proton-exchanged wet etching (PEWE) technique, which can result in a much better vertical sidewall angle and improve the surface roughness to reduce the scattering loss. The average etching rate is obviously improved by the structural defects and phase transition induced by our modified PE process, and the finally optimized etching rate is as fast as 13.5 nm/min. The propagation loss of the fabricated straight ridge waveguide is measured to be 4.3 dB/cm by using an 850 nm single mode laser as the light source. Meanwhile, a Y-branch waveguide is also measured with a uniform light splitting ratio of nearly 1:1. Furthermore, this work offers the route for the manufacturing of low-cost and high-efficiency photonic integration platform.