This study presents a one-dimensional defective photonic crystal (1D-DPhC) for terahertz sensing applications. The sensor is composed of alternating periodic layers of SiO2 and Si. The central defect layer acts as a cavity embedded between the SiO2 layers, and it is infiltrated with aqueous polyethylene glycol at different concentrations. The transmittance of the structure is evaluated using the transfer matrix method (TMM). The resonant transmission is used to assess the sensing performance of the sensor. Based on the numerical results, we find that the 1D-DPhC sensor exhibits a maximum frequency sensitivity of 139.75 GHz/RIU, intensity sensitivity of 57.41%/RIU, figure of merit of 34.621 RIU− 1, Q-factor of 420.67, and the detection limit of 1.4442 \(\:\times\:{10}^{-3}\) RIU. To enhance the sensing performance of the 1D-DPhC sensor, we modify its periodic layers through parity-time (PT) symmetry. The 1D PT-DPhC comprises the periodic layers of gain, passive and loss. Here, the gain and loss layers are realised by using the complex refractive index profiles of SiO2. The 1D PT-DPhC sensor exhibits a maximum frequency sensitivity of 200.79 GHz/RIU, roughly 1.5 times that of the 1D-DPhC sensor. Besides, its exhibits enhanced intensity sensitivity and figure of merit, with values of 62.77%/RIU and 41.083 RIU− 1, respectively. However, the Q-factor of 1D PT-DPhC reduced to 355.67 because the full width at half maximum of the resonance peak increases. This is due to signal amplification and attenuation as it propagates through the periodic layers of gain and loss. Further, the detection limit is also low at 1.217 \(\:\times\:{10}^{-3}\) RIU, and hence it can detect smaller concentrations of an analyte. Overall, the proposed THz sensor based on 1D PT-DPhC offers enhanced detection performance. This work provides a quantitative analysis of how the integration of PT symmetry structure in 1D-DPhC enhances the sensor’s detection capabilities.
