Design and theoretical study of rectangular photonic crystal fiber based sensor for chemical sensing in terahertz regime

Abstract

This paper presents the design and theoretical analysis of a photonic crystal fiber (PCF) based chemical sensor model. To evaluate the efficiency of this model, various optical parameters are analysed using finite element method based COMSOL Multiphysics Software. Different analytes namely methanol (1.317), water (1.330), ethanol (1.354) and benzene (1.366) have been considered for the sensing purpose in this study. The core region is infiltrated with different analytes separately. The model is simulated in THz regime (0.5–1.5 THz) to evaluate optical properties. The proposed structure design exhibits a high relative sensitivity of 96.85%, 97.32%, 97.99% and 98.33% for methanol, water, ethanol, and benzene, respectively at an operating frequency of 1.3 THz. The proposed model demonstrates exceptionally low confinement loss values which are 2.22 × 10^–12 dB/m for methanol, 1.16 × 10^–11 dB/m for water, 1.34 × 10^–11 dB/m for ethanol and is 1.30 × 10^–12 dB/m for benzene. Additionally, the effective material loss for the designed PCF also comes out to be very low for all the analytes, 0.0044 cm⁻¹ for methanol, 0.0040 cm⁻¹ water, 0.0034 cm⁻¹ for ethanol and 0.0032 cm⁻¹, for benzene. Furthermore, the PCF shows large effective mode area and numerical aperture (NA) within the mentioned range, at 1.3 THz. The NA values obtained at 1.3 THz are 0.32 for methanol, 0.40 for water, 0.32 for ethanol, and 0.32 for benzene. The obtained Effective mode Area (EMA) values are 1.46 × 10⁵ μm² for methanol, 1.45 × 10⁵ μm² for water, 1.44 × 10⁵ μm² for ethanol and 1.43 × 10⁵ μm², for benzene. Subsequently, the optimal profile provides birefringence values of 0.0009 for methanol, 0.0010 for water, and 0.0011 for both ethanol and benzene. The practical implementation of the proposed PCF structure is possible using subsisting modern fabrication techniques. Consequently, the proposed PCF design should be helpful in industrial areas for chemical research, food and biomedical sensing.