Design of a Multichannel Biosensor Based on Directional Couplers

Photonic Integrated Circuits (PICs) have emerged as a highly promising technology for biomedical sensing applications. They offer interesting characteristics such as cost-effectiveness, rapid response, high sensitivity, and label-free detection. Typically, their operating principle relies on detecting variations in the refractive index at the device's surface upon interaction with a biological sample. PIC-based biosensors have become one of the most appropriate technology for lab-on-chip (LOC) due to their real-time diagnosis, extreme sensitivity, robustness, reliability, and their potential for multiplexing and low-cost mass production. These applications are redefining the boundaries of diagnostics and research since they distinguish themselves by their capability to detect multiple interactions within a single sample simultaneously. The multimode interferometers (MMI) are fundamental devices, as they can combine or split the optical power between different input and output channels, which can provide reference channels and enables parallel sensing of multiple biomarkers. This work presents a new sensor design for a multichannel refractive index sensor based on photoresist polymer waveguides fabricated on a SiO2 substrate, enabling a straightforward fabrication process using spin coating. The proposed architecture consists of a 1×2 MMI splitter followed by a three-waveguide directional coupler. We demonstrate using numerical simulations that the output power of the waveguides is sensitive to changes in the surface refractive index, providing the foundation for an effective sensing mechanism.