Multiresonant Nondispersive Infrared Gas Sensing: Breaking the Selectivity and Sensitivity Trade-Off

In applications such as atmospheric monitoring of greenhouse gases and pollutants, the detection and identification of trace concentrations of harmful gases is commonly achieved using nondispersive infrared (NDIR) sensors. These devices typically employ a broadband infrared emitter, thermopile detector, and spectrally selective bandpass filter tuned to the vibrational resonance of the target analyte. However, fabrication of these filters is costly and limited to a single frequency. This limitation introduces a fundamental trade-off, as broadening the optical passband width enhances sensitivity but compromises selectivity, whereas narrowing improves selectivity at the expense of sensitivity. In this work, we validate a filterless NDIR gas sensing approach utilizing a multipeak thermal emitter developed through an inverse design. This emitter enhances detection sensitivity by simultaneously targeting multiple absorption bands, demonstrated through the creation of a sensor designed for the C-H vibrational modes of propane (C₃H₈). Additionally, a second set of single-peak emitters was developed to showcase the capability of designing highly selective sensors operating within close spectral proximity. These emitters, targeting the stretching modes of carbon monoxide (CO) and carbon dioxide (CO₂), exhibit quality factors (Q-factors) above 50 and minimal crosstalk, enabling accurate detection of the target gas without interference from gases with spectrally adjacent absorption bands. This is enabled by aperiodic distributed Bragg reflectors (a-DBRs), which achieve higher Q-factors with fewer layers than periodic Bragg reflectors. Experimental results demonstrate that this approach breaks the trade-off between sensitivity and selectivity.