Fano-resonant hybrid Metasurface for Carbon Dioxide sensing at telecommunication wavelengths

The development of compact and selective carbon dioxide (CO₂) sensors is in significant demand due to the severe effect of CO₂ on global warming and human health. Introducing a functional smart material for CO₂ adsorption represents an excellent solution for miniaturized selective devices. However, most of these devices operate beyond the telecommunication wavelengths, limiting their applicability for photonic integrated circuits (PICs). In this work, we report a hybrid metasurface - polyhexamethylene biguanide (PHMB) design for a highly selective and sensitive optical sensor. We leverage the Fano-resonant metasurface of coupled nanodisk and nanobar resonators to be integrated with infiltrated polymer (PHMB) as a functional smart material for selective CO₂ adsorption. The design parameters are optimized at an operational wavelength of 1.55 μm to achieve an optimal trade-off between Q-factor and modulation depth. Our proposed design offers an outstanding sensitivity reaching an of 45 pm/ppm (212 nm/RIU) accompanied by an exceptional Q-factor of approximately 8[Formula: see text]. Furthermore, we demonstrate that increasing the polymer thickness remarkably enhances the sensitivity up to 312 nm/RIU, while the figure-of-merit (FOM) reaches 12,500. These results hold significant promise for the development of highly selective, sensitive and miniaturized sensors with ease of fabrication and low cost.