Fabrication and characterization of single mode annealed proton exchanged waveguides in -x-cut lithium niobate

• Waveguides were fabricated in -x-cut lithium niobate substrate.
• Proton exchange and annealing parameters were optimized to improve transmission.
• Polishing techniques and cleaning reduced surface residue and improved transmission.
• Waveguides demonstrated losses as low as 10 dB/cm insertion losses.

Lithium niobate is a key, well-known material in optical communication that maintains its importance due to its high speed in electro-optical modulators and other optical devices. Using a benzoic acid proton exchange method and annealing in wet O2, we have fabricated waveguides along the y-axis of -x-cut lithium niobate substrate. We have optimized proton exchange and annealing time to make waveguides with the highest transmission we observed to date. The optical transmission was measured in waveguides between 3 μm and 7 μm in width, and 10 mm in length. The near-field mode properties of the waveguides were also examined. In addition, we discovered that the transmission through waveguides is reduced by the surface residues which are underestimated in most fabrication processes. This paper outlines the full fabrication process as well as characterization methods in detail, including a supercontinuum laser source.