Electrospun TiO2/Polyimide Nanofibers Functionalized Tilted Fiber Bragg Grating for Enhanced CO2 Detection

Reliable and cost-effective detection of percent-level carbon dioxide (CO₂) is important for industrial process control, confined-space safety, agricultural storage, and leakage warning, where elevated CO₂ levels may pose risks to operational safety and human health. Here, we demonstrate a tilted fiber Bragg grating (TFBG) CO₂ sensor integrated with electrospun titanium dioxide/polyimide (TiO₂/PI) composite nanofibers. The porous reticular nanofibrous film provides abundant CO₂ adsorption sites and continuous gas diffusion channels, while enabling efficient coupling between gases induced material variations and the evanescent field of TFBG cladding modes. CO₂ adsorption alters the dielectric properties and effective refractive index of the TiO₂/PI coating, thereby perturbing the cladding-mode field and modulating the resonance intensity in the transmission spectrum. After optimization of the TiO₂ nanoparticle concentration and electrospun time, the sensor exhibited an intensity sensitivity of 0.050 dB/% within a CO₂ concentration range of 0–20%. The enhanced performance arises from the synergy between the CO₂ affinity of PI, the active TiO₂ sites, the porous nanofibrous coating, and the surface field sensitivity of the TFBG. Benefiting from its simple fabrication process, low material cost, good repeatability, and stable optical response, the proposed TiO₂/PI nanofibers integrated TFBG provides a promising optical platform for real-time CO₂ monitoring, especially in distributed and low-cost sensing applications.