Analysis of X-cut lithium niobate electrooptic modulators with backside slots

A detailed microwave analysis of X-cut LiNbO₃ (LN) electrooptical (EO) modulators is presented in this paper by using the finite element method (FEM). The two-step back-slot structure considered here satisfies the velocity matching condition and eliminates the necessity of buffer layer of silicon dioxide (SiO₂) which is necessary for the ridge type Z-cut LiNbO₃ modulators. The optical 3-dB bandwidth and the effect of microwave loss on the bandwidth are shown in this paper. It has been shown that, an optical 3-dB bandwidth of more than 140 GHz can be achieved with X-cut LiNbO₃ substrate, when back side slots are incorporated in the structure.