Highly sensitive coated long period grating sensor for CO2 detection at atmospheric pressure

• A gas sensor based on a coated long period grating (LPG) is presented.
• The sensor was able to distinguish between N2 and CO2 gases with high reproducibility.
• The coated LPG was tested with different concentrations of CO2.
• The sensitivity of the coated LPG is 1.23 ± 0.08 pm/%CO2 and sensor resolution is ±4.07%CO2.

A gas concentration sensor comprising a long period grating with a high refractive index coating is reported. The deposition of a high refractive index coating on the optical fiber allows a reorganization of the cladding modes which leads to a substantial increase in the sensitivity to the surrounding refractive index. To maximize the grating sensitivity in the vicinity of the refractive index of CO2, the grating was coated with a 365 nm layer of polystyrene. The results show that the sensor is able to distinguish between the CO2 and N2 gases with high reproducibility and reversibility. The sensitivity of the sensor is 1.23 pm/%CO2.