Highly sensitive carbon dioxide sensor based on guanidine derivative polymer functionalized Fabry-Perot interferometer

A highly sensitive carbon dioxide (CO 2 ) sensor based on a fiber Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The sensor is fabricated by splicing a hollow core capillary (HCC) at the end of a single mode fiber (SMF), coated by a CO 2 gas-sensitive film polyhexamethylene biguanide (PHMB). The FPI cavity is formed between the splicing point and the PHMB film, and the reflected light of the two surfaces interferes resulting in an interference peak in the reflection spectrum.