Design and Optimization of Refractive Index-based Spiral Shape Twin-core Photonic Crystal Fiber Sensor for Detection of Blood Components.

In this article, we have proposed a sensor capable of sensing and detecting various blood constituents within the terahertz frequency range. Our model has been constructed using COMSOL Multiphysics software, and we have analyzed the optical properties using the full vectorial finite-element method (FV-FEM). A solid core is chosen for the proposed sensor due to its unique ability to transmit light across a wide range of wavelengths. Since blood is a critical fluid in the human body, the identification of its components holds significant importance. Our innovative design features a spiral-shaped twin-core photonic crystal fiber (SSTC-PCF) sensor that targets key blood components having different refractive indices (RI), including water, plasma, white blood cells (WBCs), hemoglobin, and red blood cells (RBCs). The cladding in spiral geometry enhances the modal confinement and offers enhanced birefringence to our structure. In the proposed PCF design, different blood components are introduced into the small central elliptical hole serving as the sensing channel. Further, the sensing capabilities have been assessed by evaluating the coupling length and analyzing the transmission power spectrum, which has been calculated using the effective mode indices of the coupling modes. The presented model is simulated in the terahertz range (0.7-0.8 THz) to calculate optical properties. The proposed sensor is designed to work within a refractive index range of 1.33-1.40, allowing for effective detection of key blood components. The proposed SSTC-PCF sensor exhibits the highest sensitivity achieved at 5,75,511 nm/RIU with less coupling length and better than published previous works, which is the main feature of the proposed sensor. Additionally, maximum birefringence values for x-polarization are 3.27 × 10, 3.67 × 10, 3.90 × 10, 4.44 × 10 and 5.14 × 10 for water, plasma, WBC, Hemoglobin, and RBC, respectively, and the highest coupling length values for x-polarization are 0.09 m for water, 0.08 m for plasma, 0.08 m for WBCs, 0.07 m for hemoglobin, and 0.06 m for RBC. This sensor design offers high sensitivity and a short coupling length, making it suitable for various applications in the biomedical field.