Fig. 1: Design of LN photonic-crystal EOM.
From: Lithium niobate photonic-crystal electro-optic modulator
a Schematic of the LN photonic-crystal EOM. b The structure of the unit cell (top: top view; bottom: cross-sectional view). The LN photonic-crystal nanobeam has a width of w = 1200 nm, layer thickness of t = 300 nm, and a partially etched wing layer with a thickness of 150 nm. The elliptical hole has dimensions of hx = 270 nm and hy = 490 nm, and a fully etched depth of 300 nm. a is the lattice constant. The full cross-section is shown in d. c Dispersion property of the partially etched LN photonic-crystal nanobeam, simulated by the finite element method (FEM). The blue open circles show the dielectric and air bands. The red solid and open circles denote the fundamental and second-order TE-like cavity modes shown in f and g. Our simulations show that there exhibits another mode with eigenfrequency within the band gap (gray open circles). This mode, however, has only negligible perturbation to the dielectric mode due to distinctive spatial symmetry, thus not affecting the quality of the defect cavity mode. d Cross-sectional schematic of the EOM structure, where the arrow profile shows the radio frequency (RF) electric field distribution and the color profile shows the optical cavity mode field distribution, both simulated by the FEM method. e Lattice constant a as a function of position, which is optimized for low insertion loss together with high radiation-limited optical Q. f Top view of the FEM-simulated optical mode field profile of the fundamental TE-like cavity mode \({\mathrm{{TE}}}_{01}^{0}\). The left inset shows the orientation of the LN crystal where the optical axis is along the z direction. g Simulated optical mode field profile of the second-order TE-like cavity mode \({\mathrm{{TE}}}_{01}^{1}\). The scale bar on the left represents the strength of normalized electrical field (Enorm) for d, f, g.
