Optical Performance of Bragg Gratings Fabricated in Ti:LiNbO$_3$ Waveguides by Focused Ion Beam Milling

In this paper we propose an efficient technique for micromachining lithium niobate that is used in Ti-diffused waveguides. The use of Focused Ion Beam (FIB) etching allows obtaining homogeneous periodic microstructures. Bragg gratings with a period of 1.05 μm and an aspect ratio of 6:1 (depth-to-half period ratio) have been achieved. A reflectivity greater than 95 % associated with a bandwidth at half maximum of about 100 nm within a window centered at 1550 nm, is demonstrated for a Bragg grating of period Λ = 1.8 μm and a length of 144 μm, in good agreement with theoretical predictions.