Noise and stability characteristics of electrically controllable mid-infrared filters for high-sensitivity NDIR sensors

This study investigates the noise performance of a non-dispersive infrared (NDIR) gas sensor using multi-quantum wells (MQW) and photonic crystal (PC) structures. Noise levels were evaluated using the Allan variance method, and the limit of detection (LOD) was found to be 3.8×10 −3 abs. at a 10 ms integration time and 2.7×10 −4 abs. at a 3 s integration time, and long-term stability was also evaluated through filter stacking. To enhance the performance, the filter design was optimized through adjustments to the MQW absorption peak, PC resonance frequency, and doping concentration. Additionally, improvements in the optical system increased the modulated light intensity by approximately 8.5 times, reducing the LOD to 3.2×10 −5 abs. at a 3 s integration time. These advancements enable high-sensitivity gas detection suitable for industrial applications such as automotive exhaust gas measurement and environmental monitoring.