Photonic crystal structures with ultrahigh aspect ratio in lithium niobate fabricated by focused ion beam milling

Abstract

Lithium niobate (LiNbO3, LN) is an important material which is widely applied in fabricating photonic and acoustic devices. However, it is difficult to either wet etch or dry etch LN due to the material’s properties. Here, the authors report novel pattern fabrication based on LN using focused ion beam (FIB) milling. When an array of small holes is etched, a severe tapering problem is observed as is common, but by replacing the nanocylindrical hole array with a nanoring structure, the authors obtain photonic crystals with an aspect ratio of up to 50:1 (2 μm total etching depth and 40 nm gap aperture). Dense nanorod arrays with sub-30-nm ultrasmall gaps and more than 2.5 μm etching depth are also achieved with FIB milling.