Optimization of light-analyte interaction in Si3N4/polymer hybrid waveguide for sensitive sensing of pyridine vapor with ppb-level detection limit

Abstract

High-sensitivity and miniature volatile organic compound (VOC) sensor is considerably significant for environment monitoring. Herein we performed the theoretical and experimental optimization of waveguide sensor to realize the sensitive detection of volatile toxic pyridine vapor with ppb-level detection limit. The miniature sensor is based on the CMOS-compatible silicon nitride (Si3N4) Mach-Zehnder interferometer (MZI) waveguide with dipolar polycarbonate as sensitive cladding material. Theoretical optimization by varying the waveguide width and the thickness of sensitive cladding is carried out to tune the group refractive index and evanescent field. Experimentally, two MZIs with distinct waveguide widths and sensitive cladding thickness are fabricated to compare their performance in pyridine vapor sensing. The sensing results show that the thickness of sensitive layer plays a key role in sensing sensitivity and response time. The final obtained pyridine sensing sensitivity can reach 63 pm/ppm and the detection limit can be as low as 476 ppb. Our demonstration provide a simple and efficient strategy for sensitive sensing of hazardous chemical vapors, which may find application in biochemical sensing.