1. INTRODUCTION With the due course of the properties of light, an optimal amount of the guided light energy is in the form of evanescent waves which are very sensitive to changes occurring in the external environment, forms a multilayer structural photonic band gap propagating waves electromagnetic waves of certain wavelengths. Electromagnetic (EM) waves with frequencies that fall within photonic band gaps (PBGs) [1, 2] cannot propagate through the structure. Localized states can be created in PBGs by introducing defects into periodic structures. PCs have recently been the subject of in-depth studies thanks to their ability to control the propagation of light and the possibility of creating many new optical devices. If PBG can reflect incident EM waves at any angle with any polarization, then an omnidirectional band gap (OBG) can be achieved with negligible loss within a specific frequency range [3-6]. He found that one-dimensional PCs (1DPC) can have OBG, and the general conditions for obtaining OBG in 1DPC are presented in NUMERICAL METHOD and has potential applications [7, 8], such as terahertz omnidirectional mirrors [9], controllable switching [10], tunable polarizer [11], narrowband filters [12], and refractometric optical detection [13], etc. One-dimensional ternary photonic crystals (1DTPC) are also proposed to obtain the extended OBGs [11, 14-19]. 1DTPC consist of three material layers in a lattice period. The wavelength range of OBGs can be increased by 108 nm when the structure was modified by inserting a thin layer of ZrO2 between every two layers, as demonstrated by Awasthi et al [16]. When the sandwich layer was CeF3, the increase in the gap was 120 nm. OBGs can be significant in the middle of paper measurements. The use of one-dimensional ternary PBG structure is not limited to enhanced refractive index sensing, but can be further extended to enhanced temperature sensing by filtering the third layer of liquid crystal material, in which changes in refractive index can be thermally induced.5. TIPS FOR THE FUTURE: The refractometric optical sensor can be used as an index sensor to detect adulteration of different materials, as well as liquids or gases. It has been observed that a slight change in the refractive index in the layers of the material causes the perception of the change in the refractive index of the medium through which it is possible to easily differentiate the layers that are changed due to their different peaks of transmission or transmittance . The sensitivity and fabrication of different compounds can be improved and monitored by applying this detection method.