Plastic optical fiber alkane gas sensor with polyisoprene cladding and carbon black-doped polyisoprene layers

Alkane-containing fuel gases, like gasoline and city gas, are commonly used in residential environments, creating a demand for sensors that are both easy to use and highly resistant to explosions. This study proposes a plastic optical fiber (POF) alkane sensor with a two-layer polymer cladding that swells in the presence of alkanes. Polyisoprene (PIP) was used as the lower layer, and a carbon black-doped PIP (CB PIP layer) was used as the upper layer. This sensor operates on the principle that the POF operation transitions from a leaky mode to a waveguide mode because of the swelling of the cladding layer in the presence of alkanes and the decrease in refractive index. The addition of a CB PIP layer on the upper layer increased the difference in transmitted light intensity between leaky and waveguiding modes, thereby improving sensitivity. Thus, the sensitivity was improved by a factor of 10 or more when the alkane vapor concentration reached 7 mmol/L or higher.