Theoretical study of ferroelectric barium strontium titanate-based one-dimensional tunable photonic crystals

Tunable photonic crystals (PCs) have attracted much attention in the past decade because of their various applications such as ultra-fast optical filters and optical waveguides with add-drop functionalities. A common means of tuning PC is by changing the refractive indices of the constituent materials via the linear or quadratic electro-optic effect, which leads to a shift of the bandgap positions of the PC. The lead-free material, barium strontium titanate (BST), has a high quadratic electro-optic coefficient comparable to lanthanum-modified lead zirconate titanate (PLZT), and is a promising candidate as a lead-free tunable PC. Here we present a study on the feasibility of developing a one-dimensional tunable PC based on a BST and magnesium oxide (MgO) multilayer structure. The bandgap diagram of the PC structure is calculated using the plane-wave expansion (PWE) method. For a 1% change in the refractive index of BST, a 0.99% frequency shift in the bandgap can be achieved. It corresponds to a wavelength shift of 15.4 nm at a wavelength of 1550nm. Design of a tunable optical filter at a wavelength of 1550nm based on a BST/MgO 1D PC is suggested. The transmission property of the 1D PC is further verified by simulation, using the transfer matrix method (TMM).