SOI asymmetrical directional coupler based photonic biosensor for 1550nm optical range

Abstract Point-of-care testing is essential for providing rapid and cost-effective medical diagnostics close to the patient. Current devices, however, often face limitations in sensitivity and practicality, motivating the development of advanced optical biosensors. This study presents the design and simulation of an asymmetrical directional coupler-based biosensor, analysed in both the frequency and time domains. The device employs a Silicon-on-Insulator substrate, comprising a straight optical waveguide positioned alongside a slotted waveguide. Detection is achieved via selective mode coupling and evanescent field sensing, which respond to changes in the surrounding refractive index. The sensor achieved a sensitivity of 624 nm/RIU, a Figure of merit of 31.6 RIU⁻¹, an estimated detection limit of 1.15 × 10^(-3) RIU and an effective quality factor of 108. These findings demonstrate the potential of the device for rapid, affordable refractive index sensing in healthcare environments. With further modifications, the sensor could support on-chip spectrometry, enhancing its versatility, portability, and suitability for POCT.