Highly sensitive and quick response carbon dioxide sensor based on sol–gel film coated four-leaf clover fiber mode interferometer

•A CO2 fiber sensor based on four-leaf clover fiber mode interferometer is proposed.•The sensor presents high wavelength sensitivity of 445 pm/% and short response time of 24/28 s.•The has high research value in CCUS project. A highly sensitive and quick response gaseous carbon dioxide (CO2) fiber sensor based on sol–gel film coated four-leaf clover fiber (FLCF) mode interferometer (MI) is proposed. The MI is constructed by using porous polymer tube to connect two sections of multi-mode fiber (MMF) with FLCF. By depositing thymol blue sol–gel film on the cladding wall of the FLCF, interference spectrum caused by the core mode and cladding mode of the MI can be modulated by CO2 concentration through the reaction between sol–gel film and CO2. By observing the shift of peak wavelength at 1555.7 nm, 1552.9 nm and 1549.3 nm, it is found that the interference spectrum changes linearly with CO2 concentration. Experimental results show that the FLCF-MI CO2 sensor has high wavelength sensitivity of 445 pm/% and short response time of 24/28 s. Besides, the sensor exhibits good temperature, humidity stability, and well selectivity, which shows great prospect in detecting CO2 concentration in carbon capture, utilization and storage (CCUS) project.