Research on Lithium Niobate-based Photonic Crystal with Wide Bandgap

Photonic crystal is a structure formed by arranging materials with different dielectric coefficients in space according to a certain period. Photonic crystal has a variety of applications, e.g., can be used to design photonic crystal fibers, cavity optomechanics, photonic crystal antennas, etc. Most of the raw materials for the photonic crystal are Si, SiN, GaAs, etc., and lithium niobate is a new type of photonic crystal material, because of its rich photoelectric effect, stable physical and chemical properties, and wide light transmission range. With the continuous development of lithium niobate single crystal thin film processing technology, it is now possible to provide single crystal thin film lithium niobate with a thickness of 300-900nm, making it possible to use lithium niobate for photonic crystal fabrications. Therefore, this paper investigates and simulates the wide bandgap characteristics of lithium niobate photonic crystals. By using finite difference time domain (FDTD) method, the simulations and investigations of the photonic bandgap in a hole-shaped lithium niobate on insulator silica is provided in this paper, through controlling the ratio among the lattice constant, the radius of the air hole layer and the thickness of lithium niobate layer. The results indicate that the radius of the air hole and the thickness of the lithium niobate photonic crystal will affect the center wavelength and bandwidth of the photonic crystal bandgap. And when the ratio of the radius to the lattice constant is about 0.35, by adjusting the thickness of the lithium niobate, a lithium niobate photonic crystal with a wide bandgap of 1387 nm-1726 nm is obtained. Based on this optimization results, the lithium niobate photonic crystal cavity with high Q factor, and also the lithium niobate photonic crystal optomechanical cavity can be achieved.