Lab-on-Fiber Fabry–Perot Interferometer Integrated With Functionalized Polymer for Carbon Dioxide Sensing

To take full advantage of lab-on-fiber technologies for gas sensing, we propose a reflective Fabry-Perot interferometer (FPI) CO2 gas sensor composed of the functional material [polyhexamethylene biguanide (PHMB)] and a single-mode fiber (SMF)-hollow core capillary (HCC) structure. The theoretical analysis of the FPI cavity mode in the PHMB film is discussed. The experiment results show a maximum sensitivity of 286 pm/ppm in the low-concentration region of 0–1000-ppm detection range and a high sensitivity of 6.88 pm/ppm in the atmosphere CO2 concentration range (200–600 ppm). The response time of the CO2 sensor is about 10 min. Repeated experiments show that the sensor has good sensing stability and a high selectivity for CO2 gas. In addition, the sensitivity of our CO2 sensor is stable to temperature changes. Moreover, the results of monitoring the real in-door atmosphere verify the repeatability and desirable sensing performance of our sensor. This reflective lab-on-fiber CO2 sensor has a concise structure, low cost, and high sensitivity possessing more possibilities in various and complex applications.