A novel wet-etching method using electric-field-assisted proton exchange in LiNbO3

This paper presents a novel wet etching method for LiNbO₃ using electric-field-assisted proton exchange. By applying voltage with appropriate polarity on designed electrodes placed on both sides of substrate, the induced electric-field distribution can effectively suppress or enhance proton diffusion in the lateral and depth directions. Thus, the proton-exchanged range in LiNbO₃ can be expertly manipulated. Because the proton-exchanged region can be removed by using a mixture of HF/HNO₃ acids, the proposed wet-etching method can effectively control the shape of the etched region in the LiNbO₃ substrate. Under appropriate electrode and proton-exchange parameters, a vertical sidewall with smooth surface is successfully produced, which makes fabricating reflection mirrors and T-junctions in LiNbO₃ possible. By utilizing the proposed wet-etching method, optical integrated circuits with higher integration density can be fabricated in LiNbO₃.