Gas sensors have broad applications for either industrial process control or biological detection. We developed a versatile and compact optical hybrid coupler gas sensor composed of a polymethyl methacrylate microwire and a silica microfiber. The light propagating in the microfiber interacts with the polymer microwire. When the hybrid coupler is exposed to different concentrations of ethanol vapor, the refractive indices of the polymer and the surroundings are changed, resulting in shifts in the resonant wavelength. The experimental sensitivity for ethanol vapor is 0.65 pm/ppm.
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