Controlling the null photonic gap and zero refractive index in photonic superlattices with temperature-controllable-refractive-index materials

Temperature-adjustable optical properties of two types of one-dimensional photonic superlattices made from lithium niobate or liquid crystal are theoretically investigated. The control of band structures and density of states is achieved through the temperature with various values of refractive index, layer width, and propagation wavelength. It is presented that a null photonic gap appears at certain temperature points, which are decided by the ratio of layer width and the refractive index. It is shown that the spatial average of the wave vector (k) vanishes at a specific temperature as functions of the layer thickness and refractive index. The values of the temperature corresponding to zero-refractive-index (zero- (n)) are demonstrated to be suppressed when the refractive index or the ratio of the layer width is enhanced. Null photonic gap and zero-(n) can appear simultaneously at certain wavelengths in the range of visible light, which can be modulated by the temperature. This implies the importance of one-dimensional photonic superlattices made from temperature-controllable-refractive-index materials for many important practical applications. (C) 2020 Optical Society of America