"(or etching depth) must be larger than mode size to avoid the interference of mode field by mirror edge, and mirror surface roughness should be less than one tenth of the light wavelength to be optically smooth. The mirror tilt from verticality must be less than 4 in order to have a loss of less than 3 dB . Though the dry-etching methods can produce a vertical sidewall , its surface quality and the etching depth are inadequate. "
[Show abstract][Hide abstract] ABSTRACT: This paper presents a novel wet etching method for LiNbO<sub>3</sub> 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 LiNbO<sub>3</sub> can be expertly manipulated. Because the proton-exchanged region can be removed by using a mixture of HF/HNO<sub>3</sub> acids, the proposed wet-etching method can effectively control the shape of the etched region in the LiNbO<sub>3</sub> 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 LiNbO<sub>3</sub> possible. By utilizing the proposed wet-etching method, optical integrated circuits with higher integration density can be fabricated in LiNbO<sub>3</sub>.
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